Yixiang Deng, Dimitrios P. Papageorgiou, Xuejin Li, Nikolaos Perakakis, Christos S. Mantzoros, Ming Dao, George Em Karniadakis
Fibrinogen is regarded as the main glycoprotein in the aggregation of red blood cells (RBCs), a normally occurring phenomenon that has a major impact on blood rheology and hemodynamics, especially under pathological conditions, including type 2 diabetes mellitus (T2DM). In this study, we investigate the fibrinogen-dependent aggregation dynamics of T2DM RBCs through patient-specific predictive computational simulations that invoke key parameters derived from microfluidic experiments. We first calibrate our model parameters at the doublet (a rouleau consisting of two aggregated RBCs) level for healthy blood samples by matching the detaching force required to fully separate RBC doublets with measurements using atomic force microscopy and optical tweezers. Using results from companion microfluidic experiments that also provide in vitro quantitative information on cell-cell adhesive dynamics, we then quantify the rouleau dissociation dynamics at the doublet and multiplet (a rouleau consisting of three or more aggregated RBCs) levels for obese patients with or without T2DM. Specifically, we examine the rouleau breakup rate when it passes through microgates at doublet level and investigate the effect of rouleau alignment in altering its breakup pattern at multiplet level. This study seamlessly integrates in vitro experiments and simulations and consequently enhances our understanding of the complex cell-cell interaction, highlighting the importance of the aggregation and disaggregation dynamics of RBCs in patients at increased risk of microvascular complications.
DOI
Wednesday, October 7, 2020
Displacement Detection Decoupling in Counter-Propagating Dual-Beams Optical Tweezers with Large-Sized Particle
Xunmin Zhu, Nan Li, Jianyu Yang, Xingfan Chen and Huizhu Hu
As a kind of ultra-sensitive acceleration sensing platform, optical tweezers show a minimum measurable value inversely proportional to the square of the diameter of the levitated spherical particle. However, with increasing diameter, the coupling of the displacement measurement between the axes becomes noticeable. This paper analyzes the source of coupling in a forward-scattering far-field detection regime and proposes a novel method of suppression. We theoretically and experimentally demonstrated that when three variable irises are added into the detection optics without changing other parts of optical structures, the decoupling of triaxial displacement signals mixed with each other show significant improvement. A coupling detection ratio reduction of 49.1 dB and 22.9 dB was realized in radial and axial directions, respectively, which is principally in accord with the simulations. This low-cost and robust approach makes it possible to accurately measure three-dimensional mechanical quantities simultaneously and may be helpful to actively cool the particle motion in optical tweezers even to the quantum ground state in the future.
DOI
As a kind of ultra-sensitive acceleration sensing platform, optical tweezers show a minimum measurable value inversely proportional to the square of the diameter of the levitated spherical particle. However, with increasing diameter, the coupling of the displacement measurement between the axes becomes noticeable. This paper analyzes the source of coupling in a forward-scattering far-field detection regime and proposes a novel method of suppression. We theoretically and experimentally demonstrated that when three variable irises are added into the detection optics without changing other parts of optical structures, the decoupling of triaxial displacement signals mixed with each other show significant improvement. A coupling detection ratio reduction of 49.1 dB and 22.9 dB was realized in radial and axial directions, respectively, which is principally in accord with the simulations. This low-cost and robust approach makes it possible to accurately measure three-dimensional mechanical quantities simultaneously and may be helpful to actively cool the particle motion in optical tweezers even to the quantum ground state in the future.
DOI
Experimental Realization of Diffusion with Stochastic Resetting
Ofir Tal-Friedman, Arnab Pal, Amandeep Sekhon, Shlomi Reuveni, and Yael Roichman
Stochastic resetting is prevalent in natural and man-made systems, giving rise to a long series of nonequilibrium phenomena. Diffusion with stochastic resetting serves as a paradigmatic model to study these phenomena, but the lack of a well-controlled platform by which this process can be studied experimentally has been a major impediment to research in the field. Here, we report the experimental realization of colloidal particle diffusion and resetting via holographic optical tweezers. We provide the first experimental corroboration of central theoretical results and go on to measure the energetic cost of resetting in steady-state and first-passage scenarios. In both cases, we show that this cost cannot be made arbitrarily small because of fundamental constraints on realistic resetting protocols. The methods developed herein open the door to future experimental study of resetting phenomena beyond diffusion.
DOI
Stochastic resetting is prevalent in natural and man-made systems, giving rise to a long series of nonequilibrium phenomena. Diffusion with stochastic resetting serves as a paradigmatic model to study these phenomena, but the lack of a well-controlled platform by which this process can be studied experimentally has been a major impediment to research in the field. Here, we report the experimental realization of colloidal particle diffusion and resetting via holographic optical tweezers. We provide the first experimental corroboration of central theoretical results and go on to measure the energetic cost of resetting in steady-state and first-passage scenarios. In both cases, we show that this cost cannot be made arbitrarily small because of fundamental constraints on realistic resetting protocols. The methods developed herein open the door to future experimental study of resetting phenomena beyond diffusion.
DOI
Plasmonic tweezers for optical manipulation and biomedical applications
Hongtao Tan, Huiqian Hu, Lin Huang and Kun Qian
Plasmonic tweezers are an emerging research topic because of their breakthrough in the conventional diffraction limit and precise manipulation at the nanoscale. Notably, their compatibility with analytical techniques (e.g. fluorescence, surface-enhanced Raman scattering (SERS), and laser desorption/ionization mass spectrometry (LDI MS)) opens up opportunities in optical manipulation and biomedical applications. Herein, we first introduce the structures and trapping forces, followed by a summary of the properties of plasmonic tweezers. The optical trapping of biosamples by plasmonic tweezers are then reviewed, including microorganisms and biomolecules. Finally, we highlight the integration of plasmonic tweezers with analytical techniques towards bioanalytical applications. We conclude with perspectives on the future directions for this topic. We foresee the upcoming era of biological detection by plasmonic tweezing in both academy and industry, which calls for the interest and efforts of scientists from diverse fields.
DOI
Plasmonic tweezers are an emerging research topic because of their breakthrough in the conventional diffraction limit and precise manipulation at the nanoscale. Notably, their compatibility with analytical techniques (e.g. fluorescence, surface-enhanced Raman scattering (SERS), and laser desorption/ionization mass spectrometry (LDI MS)) opens up opportunities in optical manipulation and biomedical applications. Herein, we first introduce the structures and trapping forces, followed by a summary of the properties of plasmonic tweezers. The optical trapping of biosamples by plasmonic tweezers are then reviewed, including microorganisms and biomolecules. Finally, we highlight the integration of plasmonic tweezers with analytical techniques towards bioanalytical applications. We conclude with perspectives on the future directions for this topic. We foresee the upcoming era of biological detection by plasmonic tweezing in both academy and industry, which calls for the interest and efforts of scientists from diverse fields.
DOI
Angular Trapping of Spherical Janus Particles
Xiaoqing Gao Yali Wang Xuehao He Mengjun Xu Jintao Zhu Xiaodong Hu Xiaotang Hu Hongbin Li Chunguang Hu
Developing angular trapping methods, which enable optical tweezers to rotate a micronsized bead, is of great importance for studies of biomacromolecules in a wide range of torque‐generation processes. Here a novel controlled angular trapping method based on model composite Janus particles is reported, which consist of two hemispheres made of polystyrene and poly(methyl methacrylate). Through computational and experimental studies, the feasibility to control the rotation of a Janus particle in a linearly polarized laser trap is demonstrated. The results show that the Janus particle aligned its two hemispheres interface parallel to the laser propagation direction and polarization direction. The rotational state of the particle can be directly visualized by using a camera. The rotation of the Janus particle in the laser trap can be fully controlled in real time by controlling the laser polarization direction. The newly developed angular trapping technique has the great advantage of easy implementation and real‐time controllability. Considering the easy chemical preparation of Janus particles and implementation of the angular trapping, this novel method has the potential of becoming a general angular trapping method. It is anticipated that this new method will significantly broaden the availability of angular trapping in the biophysics community.
DOI
Developing angular trapping methods, which enable optical tweezers to rotate a micronsized bead, is of great importance for studies of biomacromolecules in a wide range of torque‐generation processes. Here a novel controlled angular trapping method based on model composite Janus particles is reported, which consist of two hemispheres made of polystyrene and poly(methyl methacrylate). Through computational and experimental studies, the feasibility to control the rotation of a Janus particle in a linearly polarized laser trap is demonstrated. The results show that the Janus particle aligned its two hemispheres interface parallel to the laser propagation direction and polarization direction. The rotational state of the particle can be directly visualized by using a camera. The rotation of the Janus particle in the laser trap can be fully controlled in real time by controlling the laser polarization direction. The newly developed angular trapping technique has the great advantage of easy implementation and real‐time controllability. Considering the easy chemical preparation of Janus particles and implementation of the angular trapping, this novel method has the potential of becoming a general angular trapping method. It is anticipated that this new method will significantly broaden the availability of angular trapping in the biophysics community.
DOI
Tuesday, October 6, 2020
Paraxial and tightly focused behaviour of the double ring perfect optical vortex
Carolina Rickenstorff, Luz del Carmen Gómez-Pavón, Citlalli Teresa Sosa-Sánchez, and Gilberto Silva-Ortigoza
In this paper we compare the intensity distributions in the paraxial and tightly focused regimes corresponding to a double ring perfect optical vortex (DR-POV). Using the scalar diffraction theory and the Richards-Wolf formalism, the fields in the back focal plane of a low and high (tight focusing) NA lens are calculated. In the paraxial case we experimentally observed a DR-POV whose rings enclose a dark zone thanks to the destructive interference introduced by a π phase shift. In the tightly focused regime, however, the numerical simulations showed that the intensity near the focus is influenced by the input field polarization and it is not intuitive. In both cases we found that the dark region subtended between the rings has a minimal width that is inversely proportional to the pupil radius of the system, reaching 0.42λ for the radially polarized DR-POV. For the tightly focused case, we calculated the optical forces in the transversal and longitudinal coordinates exerted on a metallic particle. As a result, it is theoretically demonstrated that the circularly polarized DR-POV can trap Au metallic particles in 3D using a light wavelength close to its resonance.
DOI
In this paper we compare the intensity distributions in the paraxial and tightly focused regimes corresponding to a double ring perfect optical vortex (DR-POV). Using the scalar diffraction theory and the Richards-Wolf formalism, the fields in the back focal plane of a low and high (tight focusing) NA lens are calculated. In the paraxial case we experimentally observed a DR-POV whose rings enclose a dark zone thanks to the destructive interference introduced by a π phase shift. In the tightly focused regime, however, the numerical simulations showed that the intensity near the focus is influenced by the input field polarization and it is not intuitive. In both cases we found that the dark region subtended between the rings has a minimal width that is inversely proportional to the pupil radius of the system, reaching 0.42λ for the radially polarized DR-POV. For the tightly focused case, we calculated the optical forces in the transversal and longitudinal coordinates exerted on a metallic particle. As a result, it is theoretically demonstrated that the circularly polarized DR-POV can trap Au metallic particles in 3D using a light wavelength close to its resonance.
DOI
Surface plasmon resonance effect on laser trapping and swarming of gold nanoparticles at an interface
Chih-Hao Huang, Tetsuhiro Kudo, Roger Bresolí-Obach, Johan Hofkens, Teruki Sugiyama, and Hiroshi Masuhara
Laser trapping at an interface is a unique platform for aligning and assembling nanomaterials outside the focal spot. In our previous studies, Au nanoparticles form a dynamically evolved assembly outside the focus, leading to the formation of an antenna-like structure with their fluctuating swarms. Herein, we unravel the role of surface plasmon resonance on the swarming phenomena by tuning the trapping laser wavelength concerning the dipole mode for Au nanoparticles of different sizes. We clearly show that the swarm is formed when the laser wavelength is near to the resonance peak of the dipole mode together with an increase in the swarming area. The interpretation is well supported by the scattering spectra and the spatial light scattering profiles from single nanoparticle simulations. These findings indicate that whether the first trapped particle is resonant with trapping laser or not essentially determines the evolution of the swarming.
DOI
Laser trapping at an interface is a unique platform for aligning and assembling nanomaterials outside the focal spot. In our previous studies, Au nanoparticles form a dynamically evolved assembly outside the focus, leading to the formation of an antenna-like structure with their fluctuating swarms. Herein, we unravel the role of surface plasmon resonance on the swarming phenomena by tuning the trapping laser wavelength concerning the dipole mode for Au nanoparticles of different sizes. We clearly show that the swarm is formed when the laser wavelength is near to the resonance peak of the dipole mode together with an increase in the swarming area. The interpretation is well supported by the scattering spectra and the spatial light scattering profiles from single nanoparticle simulations. These findings indicate that whether the first trapped particle is resonant with trapping laser or not essentially determines the evolution of the swarming.
DOI
Particle size measurement using a fibre-trap-based interference approach
Zhihai Liu, Lu Wang, Yu Zhang, Yaxun Zhang, Xiaoyun Tang, Chunyu Sha, Jianzhong Zhang, Jun Yang, Libo Yuan
We propose and demonstrate the measurement of the particle size using an all-fibre interference approach via a single fibre tweezer with a coaxial core fibre. The coaxial core fibre has an external annular core and a centre core. The external annular core is used to trap the microparticle and the centre core sends and receives interference signals for size measurement. The reflected lights from the fibre end face and the trapped particle surface will cause interference and the particle size is obtained from the FSR of the interference spectrum. Using this interference approach, we conduct a label-free, non-contact, and real-time particle size measurement. The proposed measurement approach can be further applied in biology, medical science, and lab-on-fibre technology research.
DOI
We propose and demonstrate the measurement of the particle size using an all-fibre interference approach via a single fibre tweezer with a coaxial core fibre. The coaxial core fibre has an external annular core and a centre core. The external annular core is used to trap the microparticle and the centre core sends and receives interference signals for size measurement. The reflected lights from the fibre end face and the trapped particle surface will cause interference and the particle size is obtained from the FSR of the interference spectrum. Using this interference approach, we conduct a label-free, non-contact, and real-time particle size measurement. The proposed measurement approach can be further applied in biology, medical science, and lab-on-fibre technology research.
DOI
Optically trapped particle dynamic responses under varying frequency sinusoidal stimulus
Tan Xu, Qingchuan Zhang, Shangquan Wu, Zhaoxiang Jiang, Xiaoping Wu
Optical tweezers have become indispensable and powerful micro-manipulation tools and acute force probes in biomedical fields. Therefore, calibrating the optical trap is essential for precise force measurements in biomolecular interactions. Currently, however, mainstream calibration methods mainly focus on analyzing nanometer level Brownian motions of trapped particles. There is thus an urgent need to investigate trapped particle dynamic processes in slightly large range to address practical situations for the biological application of optical tweezers. This paper proposes a varying frequency sinusoidal excitation method to probe trapped particle responses and develops a mathematical model to extract trap stiffness. Experimental results revealed that the proposed method achieved significantly lower relative error ( < 5%) even when particle size or laser power varied, and that the excitation frequency didn’t have much impact on trap stiffness. Thanks to its simplicity, effectiveness and robustness, our method provides an ideal candidate for further picoNewton force measurement studies for dynamic interactions in biomedical applications.
DOI
Optical tweezers have become indispensable and powerful micro-manipulation tools and acute force probes in biomedical fields. Therefore, calibrating the optical trap is essential for precise force measurements in biomolecular interactions. Currently, however, mainstream calibration methods mainly focus on analyzing nanometer level Brownian motions of trapped particles. There is thus an urgent need to investigate trapped particle dynamic processes in slightly large range to address practical situations for the biological application of optical tweezers. This paper proposes a varying frequency sinusoidal excitation method to probe trapped particle responses and develops a mathematical model to extract trap stiffness. Experimental results revealed that the proposed method achieved significantly lower relative error ( < 5%) even when particle size or laser power varied, and that the excitation frequency didn’t have much impact on trap stiffness. Thanks to its simplicity, effectiveness and robustness, our method provides an ideal candidate for further picoNewton force measurement studies for dynamic interactions in biomedical applications.
DOI
Axial displacement calibration and tracking of optically trapped beads
Guoteng Ma, Chunguang Hu, Shuai Li, Xiaoqin Gao, Hongbin Li, Xiaotang Hu
High-precision axial displacement tracking of trapped beads is an indispensable feature of optical tweezers in advanced single-molecule studies. Here, we demonstrate an alternative method that enables axial calibration and tracking to be carried out on the same sample to avoid unnecessary errors. This method works by applying a dynamic force balance on a bead trapped between a piezoelectrically driven glass slide and an optical trap; in this configuration, the bead can be stopped precisely in different positions and imaged by a camera. A simple gradient algorithm is used to process the images into calibration data. After optimization of the calibration method and samples, our method exhibited better than 5 nm experimental axial resolution, with a measurement range of +/-500 nm around the objective focus at video speed. Moreover, for the first time, the deviation of the focusing plane in dual-trap optical tweezers was measured. We confirmed the axial deviation between two optical traps in our setup to be ~10 nm, corresponding to a force spectroscopy gage error of ~1 pN. This approach offers a favorable solution for in-use setup updating, as it can be seamlessly integrated into any optical tweezers system without requiring new hardware updates.
DOI
High-precision axial displacement tracking of trapped beads is an indispensable feature of optical tweezers in advanced single-molecule studies. Here, we demonstrate an alternative method that enables axial calibration and tracking to be carried out on the same sample to avoid unnecessary errors. This method works by applying a dynamic force balance on a bead trapped between a piezoelectrically driven glass slide and an optical trap; in this configuration, the bead can be stopped precisely in different positions and imaged by a camera. A simple gradient algorithm is used to process the images into calibration data. After optimization of the calibration method and samples, our method exhibited better than 5 nm experimental axial resolution, with a measurement range of +/-500 nm around the objective focus at video speed. Moreover, for the first time, the deviation of the focusing plane in dual-trap optical tweezers was measured. We confirmed the axial deviation between two optical traps in our setup to be ~10 nm, corresponding to a force spectroscopy gage error of ~1 pN. This approach offers a favorable solution for in-use setup updating, as it can be seamlessly integrated into any optical tweezers system without requiring new hardware updates.
DOI
Monday, October 5, 2020
Real-time measurement of three-dimensional morphology of blood cells in batches by non-orthogonal phase imaging
Hao Han, Yuanyuan Xu, Jingrong Liao, Shuangshuang Xue, Yawei Wang
In order to overcome the shortcoming of traditional tomography requires the vast amount of data and the limitation of intersection angle between two beams existed in a microscope objective to realize the real-time detection of three-dimensional (3D) morphological distribution of blood cells in batches, a method of reconstructing cell substructure with only two non-orthogonal phases is proposed in this paper. In this work, an optimized maximum entropy tomography (MET) algorithm is used for rapid 3D reconstruction which requires less phase information from non-orthogonal directions. Moreover, two phase images can be obtained simultaneously by the phase imaging system combined with flow cytometry and optical tweezers (OT). We perform simulations of two types of cell models and experiments of red blood cell (RBC), thrombocyte and lymphocyte. Results demonstrate this method is of great significance for 3D morphological analysis of blood cells in the field of clinical diagnosis or even life sciences.
DOI
In order to overcome the shortcoming of traditional tomography requires the vast amount of data and the limitation of intersection angle between two beams existed in a microscope objective to realize the real-time detection of three-dimensional (3D) morphological distribution of blood cells in batches, a method of reconstructing cell substructure with only two non-orthogonal phases is proposed in this paper. In this work, an optimized maximum entropy tomography (MET) algorithm is used for rapid 3D reconstruction which requires less phase information from non-orthogonal directions. Moreover, two phase images can be obtained simultaneously by the phase imaging system combined with flow cytometry and optical tweezers (OT). We perform simulations of two types of cell models and experiments of red blood cell (RBC), thrombocyte and lymphocyte. Results demonstrate this method is of great significance for 3D morphological analysis of blood cells in the field of clinical diagnosis or even life sciences.
DOI
A concise review of microfluidic particle manipulation methods
Shuaizhong Zhang, Ye Wang, Patrick Onck & Jaap den Toonder
Particle manipulation is often required in many applications such as bioanalysis, disease diagnostics, drug delivery and self-cleaning surfaces. The fast progress in micro- and nano-engineering has contributed to the rapid development of a variety of technologies to manipulate particles including more established methods based on microfluidics, as well as recently proposed innovative methods that still are in the initial phases of development, based on self-driven microbots and artificial cilia. Here, we review these techniques with respect to their operation principles and main applications. We summarize the shortcomings and give perspectives on the future development of particle manipulation techniques. Rather than offering an in-depth, detailed, and complete account of all the methods, this review aims to provide a broad but concise overview that helps to understand the overall progress and current status of the diverse particle manipulation methods. The two novel developments, self-driven microbots and artificial cilia-based manipulation, are highlighted in more detail.
DOI
Particle manipulation is often required in many applications such as bioanalysis, disease diagnostics, drug delivery and self-cleaning surfaces. The fast progress in micro- and nano-engineering has contributed to the rapid development of a variety of technologies to manipulate particles including more established methods based on microfluidics, as well as recently proposed innovative methods that still are in the initial phases of development, based on self-driven microbots and artificial cilia. Here, we review these techniques with respect to their operation principles and main applications. We summarize the shortcomings and give perspectives on the future development of particle manipulation techniques. Rather than offering an in-depth, detailed, and complete account of all the methods, this review aims to provide a broad but concise overview that helps to understand the overall progress and current status of the diverse particle manipulation methods. The two novel developments, self-driven microbots and artificial cilia-based manipulation, are highlighted in more detail.
DOI
Strong optical force of a molecule enabled by the plasmonic nanogap hot spot in a tip-enhanced Raman spectroscopy system
Li Long, Jianfeng Chen, Huakang Yu, and Zhi-Yuan Li
Tip-enhanced Raman spectroscopy (TERS) offers a powerful means to enhance the Raman scattering signal of a molecule as the localized surface plasmonic resonance will induce a significant local electric field enhancement in the nanoscale hot spot located within the nanogap of the TERS system. In this work, we theoretically show that this nanoscale hot spot can also serve as powerful optical tweezers to tightly trap a molecule. We calculate and analyze the local electric field and field gradient distribution of this nanogap plasmon hot spot. Due to the highly localized electric field, a three-dimensional optical trap can form at the hot spot. Moreover, the optical energy density and optical force acting on a molecule can be greatly enhanced to a level far exceeding the conventional single laser beam optical tweezers. Calculations show that for a single H2TBPP organic molecule, which is modeled as a spherical molecule with a radius of 𝑟𝑚=1 nm, a dielectric coefficient 𝜀=3, and a polarizability 𝛼=4.5×10−38 C·m2/V, the stiffness of the hot-spot trap can reach a high value of about 2 pN/[(W/cm2)·m] and 40 pN/[(W/cm2)·m] in the direction perpendicular and parallel to the TERS tip axis, which is far larger than the stiffness of single-beam tweezers, ∼0.4 pN/[(W/cm2)·m]. This hard-stiffness will enable the molecules to be stably captured in the plasmon hot spot. Our results indicate that TERS can become a promising tool of optical tweezers for trapping a microscopic object like molecules while implementing Raman spectroscopic imaging and analysis at the same time.
DOI
Tip-enhanced Raman spectroscopy (TERS) offers a powerful means to enhance the Raman scattering signal of a molecule as the localized surface plasmonic resonance will induce a significant local electric field enhancement in the nanoscale hot spot located within the nanogap of the TERS system. In this work, we theoretically show that this nanoscale hot spot can also serve as powerful optical tweezers to tightly trap a molecule. We calculate and analyze the local electric field and field gradient distribution of this nanogap plasmon hot spot. Due to the highly localized electric field, a three-dimensional optical trap can form at the hot spot. Moreover, the optical energy density and optical force acting on a molecule can be greatly enhanced to a level far exceeding the conventional single laser beam optical tweezers. Calculations show that for a single H2TBPP organic molecule, which is modeled as a spherical molecule with a radius of 𝑟𝑚=1 nm, a dielectric coefficient 𝜀=3, and a polarizability 𝛼=4.5×10−38 C·m2/V, the stiffness of the hot-spot trap can reach a high value of about 2 pN/[(W/cm2)·m] and 40 pN/[(W/cm2)·m] in the direction perpendicular and parallel to the TERS tip axis, which is far larger than the stiffness of single-beam tweezers, ∼0.4 pN/[(W/cm2)·m]. This hard-stiffness will enable the molecules to be stably captured in the plasmon hot spot. Our results indicate that TERS can become a promising tool of optical tweezers for trapping a microscopic object like molecules while implementing Raman spectroscopic imaging and analysis at the same time.
DOI
Stand-off trapping and manipulation of sub-10 nm objects and biomolecules using opto-thermo-electrohydrodynamic tweezers
Chuchuan Hong, Sen Yang & Justus C. Ndukaife
Optical tweezers have emerged as a powerful tool for the non-invasive trapping and manipulation of colloidal particles and biological cells1,2. However, the diffraction limit precludes the low-power trapping of nanometre-scale objects. Substantially increasing the laser power can provide enough trapping potential depth to trap nanoscale objects. Unfortunately, the substantial optical intensity required causes photo-toxicity and thermal stress in the trapped biological specimens3. Low-power near-field nano-optical tweezers comprising plasmonic nanoantennas and photonic crystal cavities have been explored for stable nanoscale object trapping4,5,6,7,8,9,10,11,12,13. However, the demonstrated approaches still require that the object is trapped at the high-light-intensity region. We report a new kind of optically controlled nanotweezers, called opto-thermo-electrohydrodynamic tweezers, that enable the trapping and dynamic manipulation of nanometre-scale objects at locations that are several micrometres away from the high-intensity laser focus. At the trapping locations, the nanoscale objects experience both negligible photothermal heating and light intensity. Opto-thermo-electrohydrodynamic tweezers employ a finite array of plasmonic nanoholes illuminated with light and an applied a.c. electric field to create the spatially varying electrohydrodynamic potential that can rapidly trap sub-10 nm biomolecules at femtomolar concentrations on demand. This non-invasive optical nanotweezing approach is expected to open new opportunities in nanoscience and life science by offering an unprecedented level of control of nano-sized objects, including photo-sensitive biological molecules.
DOI
Optical tweezers have emerged as a powerful tool for the non-invasive trapping and manipulation of colloidal particles and biological cells1,2. However, the diffraction limit precludes the low-power trapping of nanometre-scale objects. Substantially increasing the laser power can provide enough trapping potential depth to trap nanoscale objects. Unfortunately, the substantial optical intensity required causes photo-toxicity and thermal stress in the trapped biological specimens3. Low-power near-field nano-optical tweezers comprising plasmonic nanoantennas and photonic crystal cavities have been explored for stable nanoscale object trapping4,5,6,7,8,9,10,11,12,13. However, the demonstrated approaches still require that the object is trapped at the high-light-intensity region. We report a new kind of optically controlled nanotweezers, called opto-thermo-electrohydrodynamic tweezers, that enable the trapping and dynamic manipulation of nanometre-scale objects at locations that are several micrometres away from the high-intensity laser focus. At the trapping locations, the nanoscale objects experience both negligible photothermal heating and light intensity. Opto-thermo-electrohydrodynamic tweezers employ a finite array of plasmonic nanoholes illuminated with light and an applied a.c. electric field to create the spatially varying electrohydrodynamic potential that can rapidly trap sub-10 nm biomolecules at femtomolar concentrations on demand. This non-invasive optical nanotweezing approach is expected to open new opportunities in nanoscience and life science by offering an unprecedented level of control of nano-sized objects, including photo-sensitive biological molecules.
DOI
RNA Nanoparticles as Rubber for Compelling Vessel Extravasation to Enhance Tumor Targeting and for Fast Renal Excretion to Reduce Toxicity
Chiran Ghimire, Hongzhi Wang, Hui Li, Mario Vieweger, Congcong Xu, and Peixuan Guo
Rubber is a fascinating material in both industry and daily life. The development of elastomeric material in nanotechnology is imperative due to its economic and technological potential. By virtue of their distinctive physicochemical properties, nucleic acids have been extensively explored in material science. The Phi29 DNA packaging motor contains a 3WJ with three angles of 97°, 125°, and 138°. Here, the rubber-like property of RNA architectures was investigated using optical tweezers and in vivo imaging technologies. The 3WJ 97° interior angle was contracted or stretched to 60°, 90°, and 108° at will to build elegant RNA triangles, squares, pentagons, cubes, tetrahedrons, dendrimers, and prisms. RNA nanoarchitecture was stretchable and shrinkable by optical tweezer with multiple extension and relaxation repeats like a rubber. Comparing to gold and iron nanoparticles with the same size, RNA nanoparticles display stronger cancer-targeting outcomes, while less accumulation in healthy organs. Generally, the upper limit of renal excretion is 5.5 nm; however, the 5, 10, and 20 nm RNA nanoparticles passed the renal filtration and resumed their original structure identified in urine. These findings solve two previous mysteries: (1) Why RNA nanoparticles have an unusually high tumor targeting efficiency since their rubber or amoeba-like deformation property enables them to squeeze out of the leaky vasculature to improve the EPR effect; and (2) why RNA nanoparticles remain non-toxic since they can be rapidly cleared from the body via renal excretion into urine with little accumulation in the body. Considering its controllable shape and size plus its rubber-like property, RNA holds great promises for industrial and biomedical applications especially in cancer therapeutics delivery.
DOI
Rubber is a fascinating material in both industry and daily life. The development of elastomeric material in nanotechnology is imperative due to its economic and technological potential. By virtue of their distinctive physicochemical properties, nucleic acids have been extensively explored in material science. The Phi29 DNA packaging motor contains a 3WJ with three angles of 97°, 125°, and 138°. Here, the rubber-like property of RNA architectures was investigated using optical tweezers and in vivo imaging technologies. The 3WJ 97° interior angle was contracted or stretched to 60°, 90°, and 108° at will to build elegant RNA triangles, squares, pentagons, cubes, tetrahedrons, dendrimers, and prisms. RNA nanoarchitecture was stretchable and shrinkable by optical tweezer with multiple extension and relaxation repeats like a rubber. Comparing to gold and iron nanoparticles with the same size, RNA nanoparticles display stronger cancer-targeting outcomes, while less accumulation in healthy organs. Generally, the upper limit of renal excretion is 5.5 nm; however, the 5, 10, and 20 nm RNA nanoparticles passed the renal filtration and resumed their original structure identified in urine. These findings solve two previous mysteries: (1) Why RNA nanoparticles have an unusually high tumor targeting efficiency since their rubber or amoeba-like deformation property enables them to squeeze out of the leaky vasculature to improve the EPR effect; and (2) why RNA nanoparticles remain non-toxic since they can be rapidly cleared from the body via renal excretion into urine with little accumulation in the body. Considering its controllable shape and size plus its rubber-like property, RNA holds great promises for industrial and biomedical applications especially in cancer therapeutics delivery.
DOI
Saturday, October 3, 2020
Statistics of work performed by optical tweezers with general time-variation of their stiffness
Petr Chvosta, Dominik Lips, Viktor Holubec, Artem Ryabov and Philipp Maass
We derive an exact expression for the probability density of work done on a particle that diffuses in a parabolic potential with a stiffness varying by an arbitrary piecewise constant protocol. Based on this result, the work distribution for time-continuous protocols of the stiffness can be determined up to any degree of accuracy. This is achieved by replacing the continuous driving by a piecewise constant one with a number n of positive or negative steps of increasing or decreasing stiffness. With increasing n, the work distributions for the piecewise protocols approach that for the continuous protocol. The moment generating function of the work is given by the inverse square root of a polynomial of degree n, whose coefficients are efficiently calculated from a recurrence relation. The roots of the polynomials are real and positive (negative) steps of the protocol are associated with negative (positive) roots. Using these properties the inverse Laplace transform of the moment generating function is carried out explicitly. Fluctuation theorems are used to derive further properties of the polynomials and their roots.
DOI
We derive an exact expression for the probability density of work done on a particle that diffuses in a parabolic potential with a stiffness varying by an arbitrary piecewise constant protocol. Based on this result, the work distribution for time-continuous protocols of the stiffness can be determined up to any degree of accuracy. This is achieved by replacing the continuous driving by a piecewise constant one with a number n of positive or negative steps of increasing or decreasing stiffness. With increasing n, the work distributions for the piecewise protocols approach that for the continuous protocol. The moment generating function of the work is given by the inverse square root of a polynomial of degree n, whose coefficients are efficiently calculated from a recurrence relation. The roots of the polynomials are real and positive (negative) steps of the protocol are associated with negative (positive) roots. Using these properties the inverse Laplace transform of the moment generating function is carried out explicitly. Fluctuation theorems are used to derive further properties of the polynomials and their roots.
DOI
Enantioselective manipulation of single chiral nanoparticles using optical tweezers
Rfaqat Ali, Felipe A. Pinheiro, Rafael S. Dutra, Felipe S. S. Rosa and Paulo A. Maia Neto
We put forward an enantioselective method for chiral nanoparticles using optical tweezers. We demonstrate that the optical trapping force in a typical, realistic optical tweezing setup with circularly-polarized trapping beams is sensitive to the chirality of core–shell nanoparticles, allowing for efficient enantioselection. It turns out that the handedness of the trapped particles can be selected by choosing the appropriate circular polarization of the trapping beam. The chirality of each individual trapped nanoparticle can be characterized by measuring the rotation of the equilibrium position under the effect of a transverse Stokes drag force. We show that the chirality of the shell gives rise to an additional twist, leading to a strong enhancement of the optical torque driving the rotation. Both methods are shown to be robust against variations of size and material parameters, demonstrating that they are particularly useful in (but not restricted to) several situations of practical interest in chiral plasmonics, where enantioselection and characterization of single chiral nanoparticles, each and every one with its unique handedness and optical properties, are in order. In particular, our method could be employed to unveil the chiral response arising from disorder in individual plasmonic raspberries, synthesized by close-packing a large number of metallic nanospheres around a dielectric core.
DOI
We put forward an enantioselective method for chiral nanoparticles using optical tweezers. We demonstrate that the optical trapping force in a typical, realistic optical tweezing setup with circularly-polarized trapping beams is sensitive to the chirality of core–shell nanoparticles, allowing for efficient enantioselection. It turns out that the handedness of the trapped particles can be selected by choosing the appropriate circular polarization of the trapping beam. The chirality of each individual trapped nanoparticle can be characterized by measuring the rotation of the equilibrium position under the effect of a transverse Stokes drag force. We show that the chirality of the shell gives rise to an additional twist, leading to a strong enhancement of the optical torque driving the rotation. Both methods are shown to be robust against variations of size and material parameters, demonstrating that they are particularly useful in (but not restricted to) several situations of practical interest in chiral plasmonics, where enantioselection and characterization of single chiral nanoparticles, each and every one with its unique handedness and optical properties, are in order. In particular, our method could be employed to unveil the chiral response arising from disorder in individual plasmonic raspberries, synthesized by close-packing a large number of metallic nanospheres around a dielectric core.
DOI
Laser-triggered dynamical plasmonic optical trapping targets advanced Raman detection sensitivity
Yan Kang, Feng Yang, Ting Wu, Siqian Lu, Yiping Du and Haifeng Yang
A novel method of laser-triggered Ag nanoparticles-based plasmonic optical trapping targets is developed. Such dynamically optimized Raman enhanced protocol exhibits superior detection sensitivity for Serratia marcescens and tetrabromobisphenol A with the LODs of 5×105 CFU mL-1 and 6×10-7 M, respectively.
DOI
A novel method of laser-triggered Ag nanoparticles-based plasmonic optical trapping targets is developed. Such dynamically optimized Raman enhanced protocol exhibits superior detection sensitivity for Serratia marcescens and tetrabromobisphenol A with the LODs of 5×105 CFU mL-1 and 6×10-7 M, respectively.
DOI
Wednesday, September 30, 2020
Laser Trapping of Circular Rydberg Atoms
R. G. Cortiñas, M. Favier, B. Ravon, P. Méhaignerie, Y. Machu, J. M. Raimond, C. Sayrin, and M. Brune
Rydberg atoms are remarkable tools for quantum simulation and computation. They are the focus of an intense experimental activity, mainly based on low-angular-momentum Rydberg states. Unfortunately, atomic motion and levels lifetime limit the experimental timescale to about 100 μs. Here, we demonstrate two-dimensional laser trapping of long-lived circular Rydberg states for up to 10 ms. Our method is very general and opens many opportunities for quantum technologies with Rydberg atoms. The 10 ms trapping time corresponds to thousands of interaction cycles in a circular-state-based quantum simulator. It is also promising for quantum metrology and quantum information with Rydberg atoms, by bringing atom-field interaction times into unprecedented regimes.
DOI
Rydberg atoms are remarkable tools for quantum simulation and computation. They are the focus of an intense experimental activity, mainly based on low-angular-momentum Rydberg states. Unfortunately, atomic motion and levels lifetime limit the experimental timescale to about 100 μs. Here, we demonstrate two-dimensional laser trapping of long-lived circular Rydberg states for up to 10 ms. Our method is very general and opens many opportunities for quantum technologies with Rydberg atoms. The 10 ms trapping time corresponds to thousands of interaction cycles in a circular-state-based quantum simulator. It is also promising for quantum metrology and quantum information with Rydberg atoms, by bringing atom-field interaction times into unprecedented regimes.
DOI
Optical Transport and Sorting of Fluorescent Nanodiamonds inside a Tapered Glass Capillary: Optical Sorting of Nanomaterials at the Femtonewton Scale
Christophe Pin, Ryohei Otsuka, and Keiji Sasaki
Nanoparticles from biological, environmental, or industrial sources always show some dispersion in size, shape, composition, and related physical or chemical properties. Sorting nanoparticles according to well-defined criteria is often a crucial but challenging task. While optical forces may be used to target some specific properties such as the size, shape, absorption wavelength, and chirality of nanoparticles, optical sorting techniques usually suffer from the fast diffusion of nanoparticles in comparison to the relative weakness of the optical forces acting on dielectric nanomaterials in liquid dispersion. To achieve high-efficiency optical sorting of an ensemble of nanoparticles in colloidal dispersion, all the nanoparticles to be sorted should be gathered and kept in the light path for a sufficient time. For this purpose, we investigate the use of tapered glass capillaries as optofluidic platforms for optical manipulation and optical sorting applications. While the transparent pipe-like structure of the capillary serves as an optical waveguide that focuses the laser light over a few-millimeter-long distance, the inner part of the capillary forms a microfluidic channel that is filled with a water dispersion of 100 nm fluorescent nanodiamonds (NDs). We first demonstrate power-dependent optical transport of NDs inside few-micrometer-large capillaries. It is observed that NDs located inside the waist of the tapered capillary can be optically propelled at velocities reaching few tens of micrometer per second. We then show how a liquid flow inside the channel enables efficient, size-dependent sorting of a large ensemble of NDs. An analytical model is used to evaluate the influence of the NDs’ size on the optical and hydrodynamic drag forces acting on the nanoparticles, both being in the femtonewton range.
DOI
Nanoparticles from biological, environmental, or industrial sources always show some dispersion in size, shape, composition, and related physical or chemical properties. Sorting nanoparticles according to well-defined criteria is often a crucial but challenging task. While optical forces may be used to target some specific properties such as the size, shape, absorption wavelength, and chirality of nanoparticles, optical sorting techniques usually suffer from the fast diffusion of nanoparticles in comparison to the relative weakness of the optical forces acting on dielectric nanomaterials in liquid dispersion. To achieve high-efficiency optical sorting of an ensemble of nanoparticles in colloidal dispersion, all the nanoparticles to be sorted should be gathered and kept in the light path for a sufficient time. For this purpose, we investigate the use of tapered glass capillaries as optofluidic platforms for optical manipulation and optical sorting applications. While the transparent pipe-like structure of the capillary serves as an optical waveguide that focuses the laser light over a few-millimeter-long distance, the inner part of the capillary forms a microfluidic channel that is filled with a water dispersion of 100 nm fluorescent nanodiamonds (NDs). We first demonstrate power-dependent optical transport of NDs inside few-micrometer-large capillaries. It is observed that NDs located inside the waist of the tapered capillary can be optically propelled at velocities reaching few tens of micrometer per second. We then show how a liquid flow inside the channel enables efficient, size-dependent sorting of a large ensemble of NDs. An analytical model is used to evaluate the influence of the NDs’ size on the optical and hydrodynamic drag forces acting on the nanoparticles, both being in the femtonewton range.
DOI
Probing optical mode hybridization in an integrated graphene nano-optomechanical system
Aneesh Dash, S. K. Selvaraja, and A. K. Naik
We propose a scheme for sensitive local monitoring of mode hybridization in vertically asymmetric waveguides with a nano-optomechanical probe based on graphene. Extracting local information about mode hybridization is challenging using intensity measurements at the output or scanning optical probes over the waveguide. Transferring the information about the guided field profiles into the mechanical mode of graphene (with ultra-low-force sensitivity) using the optical gradient force allows for sensitive probing of the mode hybridization. In our proposed scheme, we estimate that a 100% change in the TE fraction of the fundamental quasi-TM waveguide mode would cause a change in the vibration amplitude of graphene on the order of 1000 pm. The limit of detection of the TE fraction is approximately 0.001. The change in the TE fraction due to index perturbations in the core and cladding can also be used for index sensing with responsivity on the order of 1000 pm change in vibration amplitude per refractive index unit and a limit of detection of 2×10−4 refractive index units. This work provides novel methods for applications in optomechanical modulation and sensing.
DOI
We propose a scheme for sensitive local monitoring of mode hybridization in vertically asymmetric waveguides with a nano-optomechanical probe based on graphene. Extracting local information about mode hybridization is challenging using intensity measurements at the output or scanning optical probes over the waveguide. Transferring the information about the guided field profiles into the mechanical mode of graphene (with ultra-low-force sensitivity) using the optical gradient force allows for sensitive probing of the mode hybridization. In our proposed scheme, we estimate that a 100% change in the TE fraction of the fundamental quasi-TM waveguide mode would cause a change in the vibration amplitude of graphene on the order of 1000 pm. The limit of detection of the TE fraction is approximately 0.001. The change in the TE fraction due to index perturbations in the core and cladding can also be used for index sensing with responsivity on the order of 1000 pm change in vibration amplitude per refractive index unit and a limit of detection of 2×10−4 refractive index units. This work provides novel methods for applications in optomechanical modulation and sensing.
DOI
Experimental and theoretical energetics of walking molecular motors under fluctuating environments
Takayuki Ariga, Michio Tomishige & Daisuke Mizuno
Molecular motors are nonequilibrium open systems that convert chemical energy to mechanical work. Their energetics are essential for various dynamic processes in cells, but largely remain unknown because fluctuations typically arising in small systems prevent investigation of the nonequilibrium behavior of the motors in terms of thermodynamics. Recently, Harada and Sasa proposed a novel equality to measure the dissipation of nonequilibrium small systems. By utilizing this equality, we have investigated the nonequilibrium energetics of the single-molecule walking motor kinesin-1. The dissipation from kinesin movement was measured through the motion of an attached probe particle and its response to external forces, indicating that large hidden dissipation exists. In this short review, aiming to readers who are not familiar with nonequilibrium physics, we briefly introduce the theoretical basis of the dissipation measurement as well as our recent experimental results and mathematical model analysis and discuss the physiological implications of the hidden dissipation in kinesin. In addition, further perspectives on the efficiency of motors are added by considering their actual working environment: living cells.
DOI
Molecular motors are nonequilibrium open systems that convert chemical energy to mechanical work. Their energetics are essential for various dynamic processes in cells, but largely remain unknown because fluctuations typically arising in small systems prevent investigation of the nonequilibrium behavior of the motors in terms of thermodynamics. Recently, Harada and Sasa proposed a novel equality to measure the dissipation of nonequilibrium small systems. By utilizing this equality, we have investigated the nonequilibrium energetics of the single-molecule walking motor kinesin-1. The dissipation from kinesin movement was measured through the motion of an attached probe particle and its response to external forces, indicating that large hidden dissipation exists. In this short review, aiming to readers who are not familiar with nonequilibrium physics, we briefly introduce the theoretical basis of the dissipation measurement as well as our recent experimental results and mathematical model analysis and discuss the physiological implications of the hidden dissipation in kinesin. In addition, further perspectives on the efficiency of motors are added by considering their actual working environment: living cells.
DOI
Subwavelength optical trapping and transporting using a Bloch mode
Lin Wang, Yongyin Cao, Bojian Shi, Hang Li, Rui Feng, Fangkui Sun, Lih Y. Lin, and Weiqiang Ding
Multi-functional optical manipulations, including optical trapping and transporting of subwavelength particles, are proposed using the Bloch modes in a dielectric photonic structure. We show that the Bloch modes in a periodic structure can generate a series of subwavelength trapping wells that are addressable by tuning the incident wavelength. This feature enables efficient optical trapping and transportation in a peristaltic way. Since we are using the guiding Bloch mode in a dielectric structure, rather than using plasmonic or dielectric resonant cavities, these operations are wide band and free from joule loss. The Bloch mode in a simple periodic dielectric structure provides a new platform for multi-functional optical operations and may find potential applications in nanophotonics and biomedicine.
DOI
Multi-functional optical manipulations, including optical trapping and transporting of subwavelength particles, are proposed using the Bloch modes in a dielectric photonic structure. We show that the Bloch modes in a periodic structure can generate a series of subwavelength trapping wells that are addressable by tuning the incident wavelength. This feature enables efficient optical trapping and transportation in a peristaltic way. Since we are using the guiding Bloch mode in a dielectric structure, rather than using plasmonic or dielectric resonant cavities, these operations are wide band and free from joule loss. The Bloch mode in a simple periodic dielectric structure provides a new platform for multi-functional optical operations and may find potential applications in nanophotonics and biomedicine.
DOI
Monday, September 21, 2020
Optimization of nonlinear optical tweezers suitable to stretch DNA molecules without broken state
Quy Ho Quang, Thanh Thai Doan, Tuan Doan Quoc, Le Ly Nguyen & Thang Nguyen Manh
The positioning of the trapped bead and DNA’s stretching dynamics in the nonlinear optical tweezers are numerically simulated by finite difference method using general Langevin. From the performance of longitudinal position-pulling time curves of bead and evolution of forces controlled by average laser power, the trapping time, possible maximum stretched length, and laser intensity threshold of to broken DNA molecule are found. We also discussed the suitable conditions to avoid broken and overstretched states for longitudinally optical stretched DNA molecule. Finally, the optimized configuration of NOT for DNA molecules having different contour lengths is proposed.
DOI
The positioning of the trapped bead and DNA’s stretching dynamics in the nonlinear optical tweezers are numerically simulated by finite difference method using general Langevin. From the performance of longitudinal position-pulling time curves of bead and evolution of forces controlled by average laser power, the trapping time, possible maximum stretched length, and laser intensity threshold of to broken DNA molecule are found. We also discussed the suitable conditions to avoid broken and overstretched states for longitudinally optical stretched DNA molecule. Finally, the optimized configuration of NOT for DNA molecules having different contour lengths is proposed.
DOI
Spin momentum-dependent orbital motion
Shaohui Yan, Manman Li, Yansheng Liang, Yanan Cai and Baoli Yao
We present a theoretic analysis on (azimuthal) spin momentum-dependent orbital motion experienced by particles in a circularly-polarized annular focused field. Unlike vortex phase-relevant (azimuthal) orbital momentum flow whose direction is specified by the sign of topological charge, the direction of (azimuthal) spin momentum flow is determined by the product of the field's polarization ellipticity and radial derivative of field intensity. For an annular focused field with a definite polarization ellipticity, the intensity's radial derivative has opposite signs on two sides of the central ring (intensity maximum), causing the spin momentum flow to reverse its direction when crossing the central ring. When placed in such a spin momentum flow, a probe particle is expected to response to this flow configuration by changing the direction of orbital motion as it traversing from one side to the other. The reversal of the particle's orbital motion is a clear sign that spin momentum flow can affect particles' orbital motion alone even without orbital momentum flow. More interestingly, for dielectric particles the spin momentum-dependent orbital motion tends to be 'negative', i.e., in the opposite direction of the spin momentum flow. This arises mainly because of spin–orbit interaction during the scattering process. For the purpose of experimental observation, we suggest the introduction of an auxiliary radially-polarized illumination to adjust the particle's radial equilibrium position, for the radial gradient force of the circularly-polarized annular focused field tends to constrain the particle at the ring of intensity maximum.
DOI
We present a theoretic analysis on (azimuthal) spin momentum-dependent orbital motion experienced by particles in a circularly-polarized annular focused field. Unlike vortex phase-relevant (azimuthal) orbital momentum flow whose direction is specified by the sign of topological charge, the direction of (azimuthal) spin momentum flow is determined by the product of the field's polarization ellipticity and radial derivative of field intensity. For an annular focused field with a definite polarization ellipticity, the intensity's radial derivative has opposite signs on two sides of the central ring (intensity maximum), causing the spin momentum flow to reverse its direction when crossing the central ring. When placed in such a spin momentum flow, a probe particle is expected to response to this flow configuration by changing the direction of orbital motion as it traversing from one side to the other. The reversal of the particle's orbital motion is a clear sign that spin momentum flow can affect particles' orbital motion alone even without orbital momentum flow. More interestingly, for dielectric particles the spin momentum-dependent orbital motion tends to be 'negative', i.e., in the opposite direction of the spin momentum flow. This arises mainly because of spin–orbit interaction during the scattering process. For the purpose of experimental observation, we suggest the introduction of an auxiliary radially-polarized illumination to adjust the particle's radial equilibrium position, for the radial gradient force of the circularly-polarized annular focused field tends to constrain the particle at the ring of intensity maximum.
DOI
Formation of pre-pore complexes of pneumolysin is accompanied by a decrease in short-range order of lipid molecules throughout vesicle bilayers
Bayan H. A. Faraj, Liam Collard, Rachel Cliffe, Leanne A. Blount, Rana Lonnen, Russell Wallis, Peter W. Andrew & Andrew J. Hudson
Oligomers of pneumolysin form transmembrane channels in cholesterol-containing lipid bilayers. The mechanism of pore formation involves a multistage process in which the protein, at first, assembles into a ring-shaped complex on the outer-bilayer leaflet. In a subsequent step, the complex inserts into the membrane. Contrary to most investigations of pore formation that have focussed on protein changes, we have deduced how the lipid-packing order is altered in different stages of the pore-forming mechanism. An optical tweezing apparatus was used, in combination with microfluidics, to isolate large-unilamellar vesicles and control exposure of the bilayer to pneumolysin. By monitoring Raman-scattered light from a single-trapped liposome, the effect of the protein on short-range order and rotational diffusion of lipids could be inferred from changes in the envelope of the C–H stretch. A significant change in the lipid-packing order takes place during assembly of pre-pore oligomers. We were not able to detect a change in the lipid-packing order during the initial stage of protein binding, or any further change during the insertion of oligomers. Pre-pore complexes induce a transformation in which a bilayer, resembling a liquid-ordered phase is changed into a bilayer resembling a fluid-liquid-disordered phase surrounding ordered microdomains enriched in cholesterol and protein complexes.
DOI
Oligomers of pneumolysin form transmembrane channels in cholesterol-containing lipid bilayers. The mechanism of pore formation involves a multistage process in which the protein, at first, assembles into a ring-shaped complex on the outer-bilayer leaflet. In a subsequent step, the complex inserts into the membrane. Contrary to most investigations of pore formation that have focussed on protein changes, we have deduced how the lipid-packing order is altered in different stages of the pore-forming mechanism. An optical tweezing apparatus was used, in combination with microfluidics, to isolate large-unilamellar vesicles and control exposure of the bilayer to pneumolysin. By monitoring Raman-scattered light from a single-trapped liposome, the effect of the protein on short-range order and rotational diffusion of lipids could be inferred from changes in the envelope of the C–H stretch. A significant change in the lipid-packing order takes place during assembly of pre-pore oligomers. We were not able to detect a change in the lipid-packing order during the initial stage of protein binding, or any further change during the insertion of oligomers. Pre-pore complexes induce a transformation in which a bilayer, resembling a liquid-ordered phase is changed into a bilayer resembling a fluid-liquid-disordered phase surrounding ordered microdomains enriched in cholesterol and protein complexes.
DOI
Brownian fluctuations and hydrodynamics of a microhelix near a solid wall
Silvio Bianchi, Viridiana Carmona Sosa, Gaszton Vizsnyiczai & Roberto Di Leonardo
We combine two-photon lithography and optical tweezers to investigate the Brownian fluctuations and propeller characteristics of a microfabricated helix. From the analysis of mean squared displacements and time correlation functions we recover the components of the full mobility tensor. We find that Brownian motion displays correlations between angular and translational fluctuations from which we can directly measure the hydrodynamic coupling coefficient that is responsible for thrust generation. By varying the distance of the microhelices from a no-slip boundary we can systematically measure the effects of a nearby wall on the resistance matrix. Our results indicate that a rotated helix moves faster when a nearby no-slip boundary is present, providing a quantitative insight on thrust enhancement in confined geometries for both synthetic and biological microswimmers.
DOI
We combine two-photon lithography and optical tweezers to investigate the Brownian fluctuations and propeller characteristics of a microfabricated helix. From the analysis of mean squared displacements and time correlation functions we recover the components of the full mobility tensor. We find that Brownian motion displays correlations between angular and translational fluctuations from which we can directly measure the hydrodynamic coupling coefficient that is responsible for thrust generation. By varying the distance of the microhelices from a no-slip boundary we can systematically measure the effects of a nearby wall on the resistance matrix. Our results indicate that a rotated helix moves faster when a nearby no-slip boundary is present, providing a quantitative insight on thrust enhancement in confined geometries for both synthetic and biological microswimmers.
DOI
Measuring Stepwise Binding of Thermally Fluctuating Particles to Cell Membranes without Fluorescence
Alexander Rohrbach, Tim Meyer, Ernst H.K. Stelzer, Holger Kress
Thermal motions enable a particle to probe the optimal interaction state when binding to a cell membrane. However, especially on the scale of microseconds and nanometers, position and orientation fluctuations are difficult to observe with common measurement technologies. Here, we show that it is possible to detect single binding events of immunoglobulin-G-coated polystyrene beads, which are held in an optical trap near the cell membrane of a macrophage. Changes in the spatial and temporal thermal fluctuations of the particle were measured interferometrically, and no fluorophore labeling was required. We demonstrate both by Brownian dynamic simulations and by experiments that sequential stepwise increases in the force constant of the bond between a bead and a cell of typically 20 pN/μm are clearly detectable. In addition, this technique provides estimates about binding rates and diffusion constants of membrane receptors. The simple approach of thermal noise tracking points out new strategies in understanding interactions between cells and particles, which are relevant for a large variety of processes, including phagocytosis, drug delivery, and the effects of small microplastics and particulates on cells.
DOI
Thermal motions enable a particle to probe the optimal interaction state when binding to a cell membrane. However, especially on the scale of microseconds and nanometers, position and orientation fluctuations are difficult to observe with common measurement technologies. Here, we show that it is possible to detect single binding events of immunoglobulin-G-coated polystyrene beads, which are held in an optical trap near the cell membrane of a macrophage. Changes in the spatial and temporal thermal fluctuations of the particle were measured interferometrically, and no fluorophore labeling was required. We demonstrate both by Brownian dynamic simulations and by experiments that sequential stepwise increases in the force constant of the bond between a bead and a cell of typically 20 pN/μm are clearly detectable. In addition, this technique provides estimates about binding rates and diffusion constants of membrane receptors. The simple approach of thermal noise tracking points out new strategies in understanding interactions between cells and particles, which are relevant for a large variety of processes, including phagocytosis, drug delivery, and the effects of small microplastics and particulates on cells.
DOI
Wednesday, September 16, 2020
Efficiencies of molecular motors: a comprehensible overview
Chun-Biu Li & Shoichi Toyabe
Many biological molecular motors can operate specifically and robustly at the highly fluctuating nano-scale. How these molecules achieve such remarkable functions is an intriguing question that requires various notions and quantifications of efficiency associated with the operations and energy transduction of these nano-machines. Here we give a short review of some important concepts of motor efficiencies, including the thermodynamic, Stokes, and generalized and transport efficiencies, as well as some implications provided by the thermodynamic uncertainty relations recently developed in nonequilibrium physics.
DOI
Many biological molecular motors can operate specifically and robustly at the highly fluctuating nano-scale. How these molecules achieve such remarkable functions is an intriguing question that requires various notions and quantifications of efficiency associated with the operations and energy transduction of these nano-machines. Here we give a short review of some important concepts of motor efficiencies, including the thermodynamic, Stokes, and generalized and transport efficiencies, as well as some implications provided by the thermodynamic uncertainty relations recently developed in nonequilibrium physics.
DOI
Improving Flow Bead Assay: Combination of Near-Infrared Optical Tweezers Stabilizing and Upconversion Luminescence Encoding
Bei Zheng, Ya-Feng Kang, Ting Zhang, Cheng-Yu Li, Sha Huang, Zhi-Ling Zhang, Qiong-Shui Wu, Chu-Bo Qi, Dai-Wen Pang, and Hong-Wu Tang
To enhance signal acquisition stability and diminish background interference for conventional flow bead-based fluorescence detection methods, we demonstrate here an exceptional microfluidic chip assisted platform by integrating near-infrared optical tweezers with upconversion luminescence encoding. For the former, a single 980 nm laser is employed to perform optical trapping and concurrently excite upconversion luminescence, avoiding the fluctuation of the signals and the complexity of the apparatus. By virtue of the favorable optical properties of upconversion nanoparticles (UCNPs), the latter is carried out by employing two-color UCNPs (Er-UCNPs and Tm-UCNPs) with negligible spectral overlaps. With the assistance of the double key techniques, we fabricated complex microbeads referred to a UCNPs–miRNAs–microbead sandwich construct by a one-step nucleic acid hybridization process and then obtained uniform terrace peaks for the automatic and simultaneous quantitative determination of miRNA-205 and miRNA-21 sequences with a detection limit of pM level on the basis of a special home-built flow bead platform. Furthermore, the technique was successfully applied for analyzing complex biological samples such as cell lysates and human tissue lysates, holding certain potential for disease diagnosis. In addition, it is expected that the flow platform can be utilized to investigate many other biomolecules of single cells and to allow analysis of particle heterogeneity in biological fluid by means of optical tweezers.
DOI
To enhance signal acquisition stability and diminish background interference for conventional flow bead-based fluorescence detection methods, we demonstrate here an exceptional microfluidic chip assisted platform by integrating near-infrared optical tweezers with upconversion luminescence encoding. For the former, a single 980 nm laser is employed to perform optical trapping and concurrently excite upconversion luminescence, avoiding the fluctuation of the signals and the complexity of the apparatus. By virtue of the favorable optical properties of upconversion nanoparticles (UCNPs), the latter is carried out by employing two-color UCNPs (Er-UCNPs and Tm-UCNPs) with negligible spectral overlaps. With the assistance of the double key techniques, we fabricated complex microbeads referred to a UCNPs–miRNAs–microbead sandwich construct by a one-step nucleic acid hybridization process and then obtained uniform terrace peaks for the automatic and simultaneous quantitative determination of miRNA-205 and miRNA-21 sequences with a detection limit of pM level on the basis of a special home-built flow bead platform. Furthermore, the technique was successfully applied for analyzing complex biological samples such as cell lysates and human tissue lysates, holding certain potential for disease diagnosis. In addition, it is expected that the flow platform can be utilized to investigate many other biomolecules of single cells and to allow analysis of particle heterogeneity in biological fluid by means of optical tweezers.
DOI
Realization of finite-rate isothermal compression and expansion using optical feedback trap
John A. C. Albay, Pik-Yin Lai, and Yonggun Jun
We experimentally realize the finite-rate isothermal process of a Brownian particle in a breathing harmonic potential. For the compression process, finite-rate equilibration can be achieved by increasing and then decreasing the stiffness of the potential to the final stiffness according to the shortcuts-to-isothermal (ScI) protocol. On the other hand, the realization of the ScI expansion is experimentally impossible with optical tweezers due to the requirement of a negative stiffness. Here, we propose a simple and elegant method to resolve this problem and demonstrate the ScI expansion by using the optical feedback trap capable of creating an arbitrary spatiotemporal potential even with a negative stiffness. In addition, we check the thermodynamic energetics such as work, heat, and internal energy, which indeed obey stochastic thermodynamics. Our method provides the possibility of a Brownian heat engine with maximum efficiency but non-vanishing power.
DOI
We experimentally realize the finite-rate isothermal process of a Brownian particle in a breathing harmonic potential. For the compression process, finite-rate equilibration can be achieved by increasing and then decreasing the stiffness of the potential to the final stiffness according to the shortcuts-to-isothermal (ScI) protocol. On the other hand, the realization of the ScI expansion is experimentally impossible with optical tweezers due to the requirement of a negative stiffness. Here, we propose a simple and elegant method to resolve this problem and demonstrate the ScI expansion by using the optical feedback trap capable of creating an arbitrary spatiotemporal potential even with a negative stiffness. In addition, we check the thermodynamic energetics such as work, heat, and internal energy, which indeed obey stochastic thermodynamics. Our method provides the possibility of a Brownian heat engine with maximum efficiency but non-vanishing power.
DOI
Method of optical manipulation of gold nanoparticles for surface-enhanced Raman scattering in a microcavity
Kun Xin, Xiaofeng Shi, Yi Liu, Zimeng Zhang, Wenjie Jia, and Jun Ma
In this study, an optical manipulation and micro-surface-enhanced Raman scattering (microSERS) setup based on a microcavity was developed for efficient capture of gold nanoparticles using the photothermal effect. In addition, optical manipulation of gold nanoparticles and SERS signal detection were performed using only one laser. The results show that the SERS enhancement effect based on the microcavity was more than 20 times that based on a gold colloid solution. The laser power and velocity of nanoparticles exhibited a good linear relationship, and the velocity of nanoparticles decreased with decreasing radius r, which verifies the detriment of the radial thermophoresis in this study. This method can be used to quickly and efficiently drive metal nanoparticles and provides a promising approach for analysis of substances in the fields of chemistry and biology.
DOI
In this study, an optical manipulation and micro-surface-enhanced Raman scattering (microSERS) setup based on a microcavity was developed for efficient capture of gold nanoparticles using the photothermal effect. In addition, optical manipulation of gold nanoparticles and SERS signal detection were performed using only one laser. The results show that the SERS enhancement effect based on the microcavity was more than 20 times that based on a gold colloid solution. The laser power and velocity of nanoparticles exhibited a good linear relationship, and the velocity of nanoparticles decreased with decreasing radius r, which verifies the detriment of the radial thermophoresis in this study. This method can be used to quickly and efficiently drive metal nanoparticles and provides a promising approach for analysis of substances in the fields of chemistry and biology.
DOI
Diffraction-limited axial double foci and optical traps generated by optimization-free planar lens
Long Ma, Jian Guan, Yiqun Wang, Chen Chen, Jianlong Zhang, Jie Lin, Jiubin Tan and Peng Jin
Axial diffraction-limited multiple foci are a kind of investigated focal field for trapping multiple nano-particles. We first experimentally generated diffraction-limited axial double foci by optimization-free binary planar lens and theoretically demonstrated it, which can be applied in multi-particle trapping. The proposed binary planar lens was analytically designed. The BPL has a numerical aperture of 0.9 and a focal length of 150 μm. The focal field of the binary planar lens, which is composed of diffraction-limited axial double foci, was first experimentally validated. The measured maximum lateral full widths at half maximum of the two generated focal spots were diffraction-limited and consistent with the theoretical. The axial double foci formed two stable optical traps that can trap two Rayleigh dielectric particles simultaneously. The radial, azimuthal and axial optical forces of the double optical traps are in good uniformity, which are 0.98, 0.99 and 0.96, respectively.
DOI
Axial diffraction-limited multiple foci are a kind of investigated focal field for trapping multiple nano-particles. We first experimentally generated diffraction-limited axial double foci by optimization-free binary planar lens and theoretically demonstrated it, which can be applied in multi-particle trapping. The proposed binary planar lens was analytically designed. The BPL has a numerical aperture of 0.9 and a focal length of 150 μm. The focal field of the binary planar lens, which is composed of diffraction-limited axial double foci, was first experimentally validated. The measured maximum lateral full widths at half maximum of the two generated focal spots were diffraction-limited and consistent with the theoretical. The axial double foci formed two stable optical traps that can trap two Rayleigh dielectric particles simultaneously. The radial, azimuthal and axial optical forces of the double optical traps are in good uniformity, which are 0.98, 0.99 and 0.96, respectively.
DOI
Tuesday, September 15, 2020
Combined Morpho-Chemical Profiling of Individual Extracellular Vesicles and Functional Nanoparticles without Labels
Yichuan Dai, Suwen Bai, Chuanzhen Hu, Kaiqin Chu, Bing Shen, and Zachary J. Smith
Biological nanoparticles are important targets of study, yet their small size and tendency to aggregate makes their heterogeneity difficult to profile on a truly single-particle basis. Here we present a label-free system called ‘Raman-enabled nanoparticle trapping analysis’ (R-NTA) that optically traps individual nanoparticles, records Raman spectra and tracks particle motion to identify chemical composition, size, and refractive index. R-NTA has the unique capacity to characterize aggregation status and absolute chemical concentration at the single-particle level. We validate the method on NIST standards and liposomes, demonstrating that R-NTA can accurately characterize size and chemical heterogeneity, including determining combined morpho-chemical properties such as the number of lamellae in individual liposomes. Applied to extracellular vesicles (EVs), we find distinct differences between EVs from cancerous and noncancerous cells, and that knockdown of the TRPP2 ion channel, which is pathologically highly expressed in laryngeal cancer cells, leads the EVs to more closely resemble EVs from normal epithelial cells. Intriguingly, the differences in EV content are found in small subpopulations of EVs, highlighting the importance of single-particle measurements. These experiments demonstrate the power of the R-NTA system to measure and characterize the morpho-chemical heterogeneity of bionanoparticles.
DOI
Biological nanoparticles are important targets of study, yet their small size and tendency to aggregate makes their heterogeneity difficult to profile on a truly single-particle basis. Here we present a label-free system called ‘Raman-enabled nanoparticle trapping analysis’ (R-NTA) that optically traps individual nanoparticles, records Raman spectra and tracks particle motion to identify chemical composition, size, and refractive index. R-NTA has the unique capacity to characterize aggregation status and absolute chemical concentration at the single-particle level. We validate the method on NIST standards and liposomes, demonstrating that R-NTA can accurately characterize size and chemical heterogeneity, including determining combined morpho-chemical properties such as the number of lamellae in individual liposomes. Applied to extracellular vesicles (EVs), we find distinct differences between EVs from cancerous and noncancerous cells, and that knockdown of the TRPP2 ion channel, which is pathologically highly expressed in laryngeal cancer cells, leads the EVs to more closely resemble EVs from normal epithelial cells. Intriguingly, the differences in EV content are found in small subpopulations of EVs, highlighting the importance of single-particle measurements. These experiments demonstrate the power of the R-NTA system to measure and characterize the morpho-chemical heterogeneity of bionanoparticles.
DOI
Digital Microfluidics for Single Bacteria Capture and Selective Retrieval Using Optical Tweezers
Phalguni Tewari Kumar, Deborah Decrop, Saba Safdar, Ioannis Passaris, Tadej Kokalj, Robert Puers, Abram Aertsen, Dragana Spasic, and Jeroen Lammertyn
When screening microbial populations or consortia for interesting cells, their selective retrieval for further study can be of great interest. To this end, traditional fluorescence activated cell sorting (FACS) and optical tweezers (OT) enabled methods have typically been used. However, the former, although allowing cell sorting, fails to track dynamic cell behavior, while the latter has been limited to complex channel-based microfluidic platforms. In this study, digital microfluidics (DMF) was integrated with OT for selective trapping, relocation, and further proliferation of single bacterial cells, while offering continuous imaging of cells to evaluate dynamic cell behavior. To enable this, magnetic beads coated with Salmonella Typhimurium-targeting antibodies were seeded in the microwell array of the DMF platform, and used to capture single cells of a fluorescent S. Typhimurium population. Next, OT were used to select a bead with a bacterium of interest, based on its fluorescent expression, and to relocate this bead to a different microwell on the same or different array. Using an agar patch affixed on top, the relocated bacterium was subsequently allowed to proliferate. Our OT-integrated DMF platform thus successfully enabled selective trapping, retrieval, relocation, and proliferation of bacteria of interest at single-cell level, thereby enabling their downstream analysis.
DOI
When screening microbial populations or consortia for interesting cells, their selective retrieval for further study can be of great interest. To this end, traditional fluorescence activated cell sorting (FACS) and optical tweezers (OT) enabled methods have typically been used. However, the former, although allowing cell sorting, fails to track dynamic cell behavior, while the latter has been limited to complex channel-based microfluidic platforms. In this study, digital microfluidics (DMF) was integrated with OT for selective trapping, relocation, and further proliferation of single bacterial cells, while offering continuous imaging of cells to evaluate dynamic cell behavior. To enable this, magnetic beads coated with Salmonella Typhimurium-targeting antibodies were seeded in the microwell array of the DMF platform, and used to capture single cells of a fluorescent S. Typhimurium population. Next, OT were used to select a bead with a bacterium of interest, based on its fluorescent expression, and to relocate this bead to a different microwell on the same or different array. Using an agar patch affixed on top, the relocated bacterium was subsequently allowed to proliferate. Our OT-integrated DMF platform thus successfully enabled selective trapping, retrieval, relocation, and proliferation of bacteria of interest at single-cell level, thereby enabling their downstream analysis.
DOI
Fundamental investigation of photoacoustic signal generation from single aerosol particles at varying relative humidity
Matus E. Diveky, Sandra Roy, Grégory David, Johannes W. Cremer, Ruth Signorell
Photoacoustic (PA) spectroscopy enjoys widespread applications across atmospheric sciences. However, experimental biases and limitations originating from environmental conditions and particle size distributions are not fully understood. Here, we combine single-particle photoacoustics with modulated Mie scattering to unravel the fundamental physical processes occurring during PA measurements on aerosols. We perform measurements on optically trapped droplets of varying sizes at different relative humidity. Our recently developed technique – photothermal single-particle spectroscopy (PSPS) – enables fundamental investigations of the interplay between the heat flux and mass flux from single aerosol particles. We find that the PA phase is more sensitive to water uptake by aerosol particles than the PA amplitude. We present results from a model of the PA phase, which sheds further light onto the dependence of the PA phase on the mass flux phenomena. The presented work provides fundamental insights into photoacoustic signal generation of aerosol particles.
DOI
Photoacoustic (PA) spectroscopy enjoys widespread applications across atmospheric sciences. However, experimental biases and limitations originating from environmental conditions and particle size distributions are not fully understood. Here, we combine single-particle photoacoustics with modulated Mie scattering to unravel the fundamental physical processes occurring during PA measurements on aerosols. We perform measurements on optically trapped droplets of varying sizes at different relative humidity. Our recently developed technique – photothermal single-particle spectroscopy (PSPS) – enables fundamental investigations of the interplay between the heat flux and mass flux from single aerosol particles. We find that the PA phase is more sensitive to water uptake by aerosol particles than the PA amplitude. We present results from a model of the PA phase, which sheds further light onto the dependence of the PA phase on the mass flux phenomena. The presented work provides fundamental insights into photoacoustic signal generation of aerosol particles.
DOI
Controlled Optofluidic Crystallization of Colloids Tethered at Interfaces
Alessio Caciagli, Rajesh Singh, Darshana Joshi, R. Adhikari, and Erika Eiser
We report experiments that show rapid crystallization of colloids tethered to an oil-water interface in response to laser illumination. This light-induced transition is due to a combination of long-ranged thermophoretic pumping and local optical binding. We show that the flow-induced force on the colloids can be described as the gradient of a potential. The nonequilibrium steady state due to local heating thus admits an effective equilibrium description. The optofluidic manipulation explored in this work opens novel ways to manipulate and assemble colloidal particles.
DOI
We report experiments that show rapid crystallization of colloids tethered to an oil-water interface in response to laser illumination. This light-induced transition is due to a combination of long-ranged thermophoretic pumping and local optical binding. We show that the flow-induced force on the colloids can be described as the gradient of a potential. The nonequilibrium steady state due to local heating thus admits an effective equilibrium description. The optofluidic manipulation explored in this work opens novel ways to manipulate and assemble colloidal particles.
DOI
Casimir spring and dilution in macroscopic cavity optomechanics
J. M. Pate, M. Goryachev, R. Y. Chiao, J. E. Sharping & M. E. Tobar
The Casimir force was predicted in 1948 as a force arising between macroscopic bodies from the zero-point energy. At finite temperatures, it has been shown that a thermal Casimir force exists due to thermal rather than zero-point energy and there are a growing number of experiments that characterize the effect at a range of temperatures and distances. In addition, in the rapidly evolving field of cavity optomechanics, there is an endeavour to manipulate phonons and enhance coherence. We demonstrate a way to realize a Casimir spring and engineer dilution in macroscopic optomechanics, by coupling a metallic SiN membrane to a photonic re-entrant cavity. The attraction of the spatially localized Casimir spring mimics a non-contacting boundary condition, giving rise to increased strain and acoustic coherence through dissipation dilution. This provides a way to manipulate phonons via thermal photons leading to ‘in situ’ reconfigurable mechanical states, to reduce loss mechanisms and to create additional types of acoustic nonlinearity—all at room temperature.
DOI
The Casimir force was predicted in 1948 as a force arising between macroscopic bodies from the zero-point energy. At finite temperatures, it has been shown that a thermal Casimir force exists due to thermal rather than zero-point energy and there are a growing number of experiments that characterize the effect at a range of temperatures and distances. In addition, in the rapidly evolving field of cavity optomechanics, there is an endeavour to manipulate phonons and enhance coherence. We demonstrate a way to realize a Casimir spring and engineer dilution in macroscopic optomechanics, by coupling a metallic SiN membrane to a photonic re-entrant cavity. The attraction of the spatially localized Casimir spring mimics a non-contacting boundary condition, giving rise to increased strain and acoustic coherence through dissipation dilution. This provides a way to manipulate phonons via thermal photons leading to ‘in situ’ reconfigurable mechanical states, to reduce loss mechanisms and to create additional types of acoustic nonlinearity—all at room temperature.
DOI
Thursday, September 10, 2020
Determinants for Fusion Speed of Biomolecular Droplets
Dr. Archishman Ghosh Prof. Huan‐Xiang Zhou
Biomolecular droplets formed through phase separation have a tendency to fuse. The speed with which fusion occurs is a direct indicator of condensate liquidity, which is key to both cellular functions and diseases. Using a dual‐trap optical tweezers setup, we found the fusion speeds of four types of droplets to differ by two orders of magnitude. The order of fusion speed correlates with the fluorescence of thioflavin T, which in turn reflects the macromolecular packing density inside droplets. Unstructured protein or polymer chains pack loosely and readily rearrange, leading to fast fusion. In contrast, structured protein domains pack more closely and have to break extensive contacts before rearrangement, corresponding to slower fusion. This molecular interpretation for disparate fusion speeds provides mechanistic insight into the assembly and aging of biomolecular droplets.
DOI
Biomolecular droplets formed through phase separation have a tendency to fuse. The speed with which fusion occurs is a direct indicator of condensate liquidity, which is key to both cellular functions and diseases. Using a dual‐trap optical tweezers setup, we found the fusion speeds of four types of droplets to differ by two orders of magnitude. The order of fusion speed correlates with the fluorescence of thioflavin T, which in turn reflects the macromolecular packing density inside droplets. Unstructured protein or polymer chains pack loosely and readily rearrange, leading to fast fusion. In contrast, structured protein domains pack more closely and have to break extensive contacts before rearrangement, corresponding to slower fusion. This molecular interpretation for disparate fusion speeds provides mechanistic insight into the assembly and aging of biomolecular droplets.
DOI
Optical trapping of single nano-size particles using a plasmonic nanocavity
Jiachen Zhang, Fanfan Lu, Wending Zhang, Weixing Yu, Weiren Zhu, Malin Premaratne, Ting Mei, Fajun Xiao and Jianlin Zhao
Trapping and manipulating micro-size particles using optical tweezers has contributed to many breakthroughs in biology, materials science, and colloidal physics. However, it remains challenging to extend this technique to a few nanometers particles owing to the diffraction limit and the considerable Brownian motion of trapped nanoparticles. In this work, a nanometric optical tweezer is proposed by using a plasmonic nanocavity composed of the closely spaced silver coated fiber tip and gold film. It is found that the radial vector mode can produce a nano-sized near field with the electric-field intensity enhancement factor over 103 through exciting the plasmon gap mode in the nanocavity. By employing the Maxwell stress tensor formalism, we theoretically demonstrate that this nano-sized near field results in a sharp quasi-harmonic potential well, capable of stably trapping 2 nm quantum dots beneath the tip apex with the laser power as low as 3.7 mW. Further analysis reveals that our nanotweezers can stably work in a wide range of particle-to-tip distances, gap sizes, and operation wavelengths. We envision that our proposed nanometric optical tweezers could be compatible with the tip-enhanced Raman spectroscopy to allow simultaneously manipulating and characterizing single nanoparticles as well as nanoparticle interactions with high sensitivity.
DOI
Trapping and manipulating micro-size particles using optical tweezers has contributed to many breakthroughs in biology, materials science, and colloidal physics. However, it remains challenging to extend this technique to a few nanometers particles owing to the diffraction limit and the considerable Brownian motion of trapped nanoparticles. In this work, a nanometric optical tweezer is proposed by using a plasmonic nanocavity composed of the closely spaced silver coated fiber tip and gold film. It is found that the radial vector mode can produce a nano-sized near field with the electric-field intensity enhancement factor over 103 through exciting the plasmon gap mode in the nanocavity. By employing the Maxwell stress tensor formalism, we theoretically demonstrate that this nano-sized near field results in a sharp quasi-harmonic potential well, capable of stably trapping 2 nm quantum dots beneath the tip apex with the laser power as low as 3.7 mW. Further analysis reveals that our nanotweezers can stably work in a wide range of particle-to-tip distances, gap sizes, and operation wavelengths. We envision that our proposed nanometric optical tweezers could be compatible with the tip-enhanced Raman spectroscopy to allow simultaneously manipulating and characterizing single nanoparticles as well as nanoparticle interactions with high sensitivity.
DOI
Multipole interplay controls optical forces and ultra-directional scattering
Andrei Kiselev, Karim Achouri, and Olivier J. F. Martin
We analyze the superposition of Cartesian multipoles to reveal the mechanisms underlying the origin of optical forces. We show that a multipolar decomposition approach significantly simplifies the analysis of this problem and leads to a very intuitive explanation of optical forces based on the interference between multipoles. We provide an in-depth analysis of the radiation coming from the object, starting from low-order multipole interactions up to quadrupolar terms. Interestingly, by varying the phase difference between multipoles, the optical force as well as the total radiation directivity can be well controlled. The theory developed in this paper may also serve as a reference for ultra-directional light steering applications.
DOI
We analyze the superposition of Cartesian multipoles to reveal the mechanisms underlying the origin of optical forces. We show that a multipolar decomposition approach significantly simplifies the analysis of this problem and leads to a very intuitive explanation of optical forces based on the interference between multipoles. We provide an in-depth analysis of the radiation coming from the object, starting from low-order multipole interactions up to quadrupolar terms. Interestingly, by varying the phase difference between multipoles, the optical force as well as the total radiation directivity can be well controlled. The theory developed in this paper may also serve as a reference for ultra-directional light steering applications.
DOI
Fano-Resonant, Asymmetric, Metamaterial-Assisted Tweezers for Single Nanoparticle Trapping
Domna G. Kotsifaki, Viet Giang Truong, and Síle Nic Chormaic
Plasmonic nanostructures overcome Abbe’s diffraction limit to create strong gradient electric fields, enabling efficient optical trapping of nanoparticles. However, it remains challenging to achieve stable trapping with low incident laser intensity. Here, we demonstrate Fano resonance-assisted plasmonic optical tweezers for single nanoparticle trapping in an array of asymmetrical split nanoapertures on a 50 nm gold thin film. A large normalized trap stiffness of 8.65 fN/nm/mW for 20 nm polystyrene particles at a near-resonance trapping wavelength of 930 nm was achieved. The trap stiffness on-resonance is enhanced by a factor of 63 compared to that of off-resonance due to the ultrasmall mode volume, enabling large near-field strengths and a cavity effect contribution. These results facilitate trapping with low incident laser intensity, thereby providing new options for studying transition paths of single molecules such as proteins.
DOI
Plasmonic nanostructures overcome Abbe’s diffraction limit to create strong gradient electric fields, enabling efficient optical trapping of nanoparticles. However, it remains challenging to achieve stable trapping with low incident laser intensity. Here, we demonstrate Fano resonance-assisted plasmonic optical tweezers for single nanoparticle trapping in an array of asymmetrical split nanoapertures on a 50 nm gold thin film. A large normalized trap stiffness of 8.65 fN/nm/mW for 20 nm polystyrene particles at a near-resonance trapping wavelength of 930 nm was achieved. The trap stiffness on-resonance is enhanced by a factor of 63 compared to that of off-resonance due to the ultrasmall mode volume, enabling large near-field strengths and a cavity effect contribution. These results facilitate trapping with low incident laser intensity, thereby providing new options for studying transition paths of single molecules such as proteins.
DOI
Enantioselective optical trapping of chiral nanoparticles using a transverse optical needle field with a transverse spin
Ying Li, Guanghao Rui, Sichao Zhou, Bing Gu, Yanzhong Yu, Yiping Cui, and Qiwen Zhan
Since the fundamental building blocks of life are built of chiral amino acids and chiral sugar, enantiomer separation is of great interest in plenty of chemical syntheses. Light-chiral material interaction leads to a unique chiral optical force, which possesses opposite directions for specimens with different handedness. However, usually the enantioselective sorting is challenging in optical tweezers due to the dominating achiral force. In this work, we propose an optical technique to sort chiral specimens by use of a transverse optical needle field with a transverse spin (TONFTS), which is constructed through reversing the radiation patterns from an array of paired orthogonal electric dipoles located in the focal plane of a 4Pi microscopy and experimentally generated with a home-built vectorial optical field generator. It is demonstrated that the transverse component of the photonic spin gives rise to the chiral optical force perpendicular to the direction of the light’s propagation, while the transverse achiral gradient force would be dramatically diminished by the uniform intensity profile of the optical needle field. Consequently, chiral nanoparticles with different handedness would be laterally sorted by the TONFTS and trapped at different locations along the optical needle field, providing a feasible route toward all-optical enantiopure chemical syntheses and enantiomer separations in pharmaceuticals.
DOI
Since the fundamental building blocks of life are built of chiral amino acids and chiral sugar, enantiomer separation is of great interest in plenty of chemical syntheses. Light-chiral material interaction leads to a unique chiral optical force, which possesses opposite directions for specimens with different handedness. However, usually the enantioselective sorting is challenging in optical tweezers due to the dominating achiral force. In this work, we propose an optical technique to sort chiral specimens by use of a transverse optical needle field with a transverse spin (TONFTS), which is constructed through reversing the radiation patterns from an array of paired orthogonal electric dipoles located in the focal plane of a 4Pi microscopy and experimentally generated with a home-built vectorial optical field generator. It is demonstrated that the transverse component of the photonic spin gives rise to the chiral optical force perpendicular to the direction of the light’s propagation, while the transverse achiral gradient force would be dramatically diminished by the uniform intensity profile of the optical needle field. Consequently, chiral nanoparticles with different handedness would be laterally sorted by the TONFTS and trapped at different locations along the optical needle field, providing a feasible route toward all-optical enantiopure chemical syntheses and enantiomer separations in pharmaceuticals.
DOI
Wednesday, September 9, 2020
Microspheres with Atomic-Scale Tolerances Generate Hyperdegeneracy
Jacob Kher-Alden, Shai Maayani, Leopoldo L. Martin, Mark Douvidzon, Lev Deych, and Tal Carmon
Degeneracies play a crucial rule in precise scientific measurements as well as in sensing applications. Spherical resonators have a high degree of degeneracy thanks to their highest symmetry; yet, fabricating perfect spheres is challenging because even a stem to hold the sphere breaks the symmetry. Here we fabricate a levitating spherical resonator that is evanescently coupled to a standard optical fiber. We characterize the resonators to exhibit an optical quality factor exceeding a billion, 10 μm radius, and sphericity to within less than 1 Å. Using our high quality and sphericity, we experimentally lift degeneracies of orders higher than 200, which we resolve with optical finesse exceeding 10 000 000. We then present our experimentally measured degenerate modes as well as their density of states next to our corresponding theoretical calculation. Our contactless photonic resonator is compatible with standard telecom fiber technology, exhibits the highest resonance enhancement as defined by (quality factor)/(mode volume), and the modes populating our cavity show the highest order of degeneracy reported in any system ever studied. This is in comparison with other settings that typically utilize the lowest-order twofold degeneracy.
DOI
Degeneracies play a crucial rule in precise scientific measurements as well as in sensing applications. Spherical resonators have a high degree of degeneracy thanks to their highest symmetry; yet, fabricating perfect spheres is challenging because even a stem to hold the sphere breaks the symmetry. Here we fabricate a levitating spherical resonator that is evanescently coupled to a standard optical fiber. We characterize the resonators to exhibit an optical quality factor exceeding a billion, 10 μm radius, and sphericity to within less than 1 Å. Using our high quality and sphericity, we experimentally lift degeneracies of orders higher than 200, which we resolve with optical finesse exceeding 10 000 000. We then present our experimentally measured degenerate modes as well as their density of states next to our corresponding theoretical calculation. Our contactless photonic resonator is compatible with standard telecom fiber technology, exhibits the highest resonance enhancement as defined by (quality factor)/(mode volume), and the modes populating our cavity show the highest order of degeneracy reported in any system ever studied. This is in comparison with other settings that typically utilize the lowest-order twofold degeneracy.
DOI
Probing the optical chiral response of single nanoparticles with optical tweezers
Rfaqat Ali, F. A. Pinheiro, R. S. Dutra, F. S. S. Rosa, and P. A. Maia Neto
We propose an enantioselective scheme to sort homogeneous chiral particles using optical tweezers. For a certain range of material parameters, we show that a highly focused circularly polarized laser beam traps particles of a specific chirality selected by the handedness of the trapping beam. Furthermore, by applying a transverse Stokes drag force that displaces the trapped particle off-axis, we allow for the rotation of the particle center-of-mass around the trapping beam axis. The rotation angle is highly dependent on the handedness of the trapped particle and is easily measurable with standard video-microscopy techniques, allowing for an alternative mechanism for chiral resolution. Our platform not only allows for enantio selection of particles dispersed in solution but also paves the way to characterization of the chiral parameter of individual, homogeneous chiral microspheres using optical tweezing.
DOI
We propose an enantioselective scheme to sort homogeneous chiral particles using optical tweezers. For a certain range of material parameters, we show that a highly focused circularly polarized laser beam traps particles of a specific chirality selected by the handedness of the trapping beam. Furthermore, by applying a transverse Stokes drag force that displaces the trapped particle off-axis, we allow for the rotation of the particle center-of-mass around the trapping beam axis. The rotation angle is highly dependent on the handedness of the trapped particle and is easily measurable with standard video-microscopy techniques, allowing for an alternative mechanism for chiral resolution. Our platform not only allows for enantio selection of particles dispersed in solution but also paves the way to characterization of the chiral parameter of individual, homogeneous chiral microspheres using optical tweezing.
DOI
All-dielectric silicon metalens for two-dimensional particle manipulation in optical tweezers
Teanchai Chantakit, Christian Schlickriede, Basudeb Sain, Fabian Meyer, Thomas Weiss, Nattaporn Chattham, and Thomas Zentgraf
Dynamic control of compact chip-scale contactless manipulation of particles for bioscience applications remains a challenging endeavor, which is restrained by the balance between trapping efficiency and scalable apparatus. Metasurfaces offer the implementation of feasible optical tweezers on a planar platform for shaping the exerted optical force by a microscale-integrated device. Here we design and experimentally demonstrate a highly efficient silicon-based metalens for two-dimensional optical trapping in the near-infrared. Our metalens concept is based on the Pancharatnam–Berry phase, which enables the device for polarization-sensitive particle manipulation. Our optical trapping setup is capable of adjusting the position of both the metasurface lens and the particle chamber freely in three directions, which offers great freedom for optical trap adjustment and alignment. Two-dimensional (2D) particle manipulation is done with a relatively low-numerical-aperture metalens (NAML=0.6). We experimentally demonstrate both 2D polarization-sensitive drag and drop manipulation of polystyrene particles suspended in water and transfer of angular orbital momentum to these particles with a single tailored beam. Our work may open new possibilities for lab-on-a-chip optical trapping for bioscience applications and microscale to nanoscale optical tweezers.
DOI
Dynamic control of compact chip-scale contactless manipulation of particles for bioscience applications remains a challenging endeavor, which is restrained by the balance between trapping efficiency and scalable apparatus. Metasurfaces offer the implementation of feasible optical tweezers on a planar platform for shaping the exerted optical force by a microscale-integrated device. Here we design and experimentally demonstrate a highly efficient silicon-based metalens for two-dimensional optical trapping in the near-infrared. Our metalens concept is based on the Pancharatnam–Berry phase, which enables the device for polarization-sensitive particle manipulation. Our optical trapping setup is capable of adjusting the position of both the metasurface lens and the particle chamber freely in three directions, which offers great freedom for optical trap adjustment and alignment. Two-dimensional (2D) particle manipulation is done with a relatively low-numerical-aperture metalens (NAML=0.6). We experimentally demonstrate both 2D polarization-sensitive drag and drop manipulation of polystyrene particles suspended in water and transfer of angular orbital momentum to these particles with a single tailored beam. Our work may open new possibilities for lab-on-a-chip optical trapping for bioscience applications and microscale to nanoscale optical tweezers.
DOI
Single-Molecule Plasmonic Optical Trapping
Chao Zhan, Gan Wang, Jun Yi, Jun-Ying Wei, Zhi-Hao Li, Zhao-Bin Chen, Jia Shi, Yang Yang, Wenjing Hong, Zhong-Qun Tian
The volume of the object that can be manipulated in solution is continuously decreasing toward an ultimate goal of a single molecule. However, Brownian motions suppress the molecular trapping. To date, free-molecule trapping in solution has not been accomplished. Here, we develop a strategy to directly trap, investigate, and release single molecules (∼2 nm) in solution by using an adjustable plasmonic optical nanogap, which has been further applied for selective single-molecule trapping. Comprehensive experiments and theoretical simulations demonstrated that the trapping force originated from plasmonic nanomaterials. This technique opens an avenue to manipulate single molecules and other objects in the size range of primary interest for physics, chemistry, and life and material sciences without the limitations of strong bonding group, ultra-high vacuum, and ultra-low temperature, and makes possible controllable single-molecule manipulation and investigation as well as bottom-up construction of nanodevices and molecular machines.
DOI
The volume of the object that can be manipulated in solution is continuously decreasing toward an ultimate goal of a single molecule. However, Brownian motions suppress the molecular trapping. To date, free-molecule trapping in solution has not been accomplished. Here, we develop a strategy to directly trap, investigate, and release single molecules (∼2 nm) in solution by using an adjustable plasmonic optical nanogap, which has been further applied for selective single-molecule trapping. Comprehensive experiments and theoretical simulations demonstrated that the trapping force originated from plasmonic nanomaterials. This technique opens an avenue to manipulate single molecules and other objects in the size range of primary interest for physics, chemistry, and life and material sciences without the limitations of strong bonding group, ultra-high vacuum, and ultra-low temperature, and makes possible controllable single-molecule manipulation and investigation as well as bottom-up construction of nanodevices and molecular machines.
DOI
Observation of Collisions between Two Ultracold Ground-State CaF Molecules
Lawrence W. Cheuk, Loïc Anderegg, Yicheng Bao, Sean Burchesky, Scarlett S. Yu, Wolfgang Ketterle, Kang-Kuen Ni, and John M. Doyle
We measure inelastic collisions between ultracold CaF molecules by combining two optical tweezers, each containing a single molecule. We observe collisions between 2Σ CaF molecules in the absolute ground state |X,v=0,N=0,F=0⟩, and in excited hyperfine and rotational states. In the absolute ground state, we find a two-body loss rate of 7(4)×10−11 cm3/s, which is below, but close to, the predicted universal loss rate.
DOI
We measure inelastic collisions between ultracold CaF molecules by combining two optical tweezers, each containing a single molecule. We observe collisions between 2Σ CaF molecules in the absolute ground state |X,v=0,N=0,F=0⟩, and in excited hyperfine and rotational states. In the absolute ground state, we find a two-body loss rate of 7(4)×10−11 cm3/s, which is below, but close to, the predicted universal loss rate.
DOI
Tuesday, September 8, 2020
Spheroidal trap shell beyond diffraction limit induced by nonlinear effects in femtosecond laser trapping
Lu Huang, Yaqiang Qin, Yunfeng Jin, Hao Shi, Honglian Guo, Liantuan Xiao and Yuqiang Jiang
Beyond diffraction limit, multitrapping of nanoparticles is important in numerous scientific fields, including biophysics, materials science and quantum optics. Here, we demonstrate the 3-dimensional (3D) shell-like structure of optical trapping well induced by nonlinear optical effects in the femtosecond Gaussian beam trapping for the first time. Under the joint action of gradient force, scattering force and nonlinear trapping force, the gold nanoparticles can be stably trapped in some special positions, or hop between the trap positions along a route within the 3D shell. The separation between the trap positions can be adjusted by laser power and numerical aperture (NA) of the trapping objective lens. With a high NA lens, we achieved dual traps with less than 100 nm separation without utilizing complicated optical systems or any on-chip nanostructures. These curious findings will greatly extend and deepen our understanding of optical trapping based on nonlinear interaction and generate novel applications in various fields, such as microfabrication/nanofabrication, sensing and novel micromanipulations.
DOI
Beyond diffraction limit, multitrapping of nanoparticles is important in numerous scientific fields, including biophysics, materials science and quantum optics. Here, we demonstrate the 3-dimensional (3D) shell-like structure of optical trapping well induced by nonlinear optical effects in the femtosecond Gaussian beam trapping for the first time. Under the joint action of gradient force, scattering force and nonlinear trapping force, the gold nanoparticles can be stably trapped in some special positions, or hop between the trap positions along a route within the 3D shell. The separation between the trap positions can be adjusted by laser power and numerical aperture (NA) of the trapping objective lens. With a high NA lens, we achieved dual traps with less than 100 nm separation without utilizing complicated optical systems or any on-chip nanostructures. These curious findings will greatly extend and deepen our understanding of optical trapping based on nonlinear interaction and generate novel applications in various fields, such as microfabrication/nanofabrication, sensing and novel micromanipulations.
DOI
Distributed Force Control for Microrobot Manipulation via Planar Multi‐Spot Optical Tweezer
Dandan Zhang Antoine Barbot Benny Lo Guang‐Zhong Yang
Optical tweezers (OT) represent a versatile tool for micro‐manipulation. To avoid damages to living cells caused by illuminating laser directly on them, microrobots controlled by OT can be used for manipulation of cells or living organisms in microscopic scale. Translation and planar rotation motion of microrobots can be realized by using a multi‐spot planar OT. However, out‐of‐plane manipulation of microrobots is difficult to achieve with a planar OT. This paper presents a distributed manipulation scheme based on multiple laser spots, which can control the out‐of‐plane pose of a microrobot along multiple axes. Different microrobot designs have been investigated and fabricated for experimental validation. The main contributions of this paper include: i) development of a generic model for the structure design of microrobots which enables multi‐dimensional (6D) control via conventional multi‐spot OT; ii) introduction of the distributed force control for microrobot manipulation based on characteristic distance and power intensity distribution. Experiments are performed to demonstrate the effectiveness of the proposed method and its potential applications, which include indirect manipulation of micro‐objects.
DOI
Optical tweezers (OT) represent a versatile tool for micro‐manipulation. To avoid damages to living cells caused by illuminating laser directly on them, microrobots controlled by OT can be used for manipulation of cells or living organisms in microscopic scale. Translation and planar rotation motion of microrobots can be realized by using a multi‐spot planar OT. However, out‐of‐plane manipulation of microrobots is difficult to achieve with a planar OT. This paper presents a distributed manipulation scheme based on multiple laser spots, which can control the out‐of‐plane pose of a microrobot along multiple axes. Different microrobot designs have been investigated and fabricated for experimental validation. The main contributions of this paper include: i) development of a generic model for the structure design of microrobots which enables multi‐dimensional (6D) control via conventional multi‐spot OT; ii) introduction of the distributed force control for microrobot manipulation based on characteristic distance and power intensity distribution. Experiments are performed to demonstrate the effectiveness of the proposed method and its potential applications, which include indirect manipulation of micro‐objects.
DOI
Evanescent Wave Optical Trapping and Sensing on Polymer Optical Fibers for Ultra-Trace Detection of Glucose
Tahereh Azargoshasb, H. Ali Navid, Roghaieh Parvizi, and Hadi Heidari
Graphene sensitization of glucose-imprinted polymer (G-IP)-coated optical fiber has been introduced as a new biosensor for evanescent wave trapping on the polymer optical fiber to detect low-level glucose. The developed sensor operates based on the evanescent wave modulation principle. Full characterization via atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and N2 adsorption/desorption of as-prepared G-IP-coated optical fibers was experimentally tested. Accordingly, related operational parameters such as roughness and diameter were optimized. Incorporating graphene into the G-IP not only steadily promotes the electron transport between the fiber surface and as-proposed G-IP but also significantly enhances the sensitivity by acting as a carrier for immobilizing G-IP with specific imprinted cavities. The sensor demonstrates a fast response time (5 s) and high sensitivity, selectivity, and stability, which cause a wide linear range (10–100 nM) and a low limit of detection (LOD = 2.54 nM). Experimental results indicate that the developed sensor facilitates online monitoring and remote sensing of glucose in biological liquids and food samples.
DOI
Graphene sensitization of glucose-imprinted polymer (G-IP)-coated optical fiber has been introduced as a new biosensor for evanescent wave trapping on the polymer optical fiber to detect low-level glucose. The developed sensor operates based on the evanescent wave modulation principle. Full characterization via atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and N2 adsorption/desorption of as-prepared G-IP-coated optical fibers was experimentally tested. Accordingly, related operational parameters such as roughness and diameter were optimized. Incorporating graphene into the G-IP not only steadily promotes the electron transport between the fiber surface and as-proposed G-IP but also significantly enhances the sensitivity by acting as a carrier for immobilizing G-IP with specific imprinted cavities. The sensor demonstrates a fast response time (5 s) and high sensitivity, selectivity, and stability, which cause a wide linear range (10–100 nM) and a low limit of detection (LOD = 2.54 nM). Experimental results indicate that the developed sensor facilitates online monitoring and remote sensing of glucose in biological liquids and food samples.
DOI
Measurement and simulation of atomic motion in nanoscale optical trapping potentials
Signe B. Markussen, Jürgen Appel, Christoffer Østfeldt, Jean-Baptiste S. Béguin, Eugene S. Polzik & Jörg H. Müller
Atoms trapped in the evanescent field around a nanofiber experience strong coupling to the light guided in the fiber mode. However, due to the intrinsically strong positional dependence of the coupling, thermal motion of the ensemble limits the use of nanofiber trapped atoms for some quantum tasks. We investigate the thermal dynamics of such an ensemble using short light pulses to make a spatially inhomogeneous population transfer between atomic states. As we monitor the wave packet of atoms created by this scheme, we find a damped oscillatory behavior which we attribute to sloshing and dispersion of the atoms. Oscillation frequencies range around 100 kHz, and motional dephasing between atoms happens on a timescale of 10μs. Comparison to Monte Carlo simulations of an ensemble of 1000 classical particles yields reasonable agreement for simulated ensemble temperatures between 25 and 40μK.
DOI
Atoms trapped in the evanescent field around a nanofiber experience strong coupling to the light guided in the fiber mode. However, due to the intrinsically strong positional dependence of the coupling, thermal motion of the ensemble limits the use of nanofiber trapped atoms for some quantum tasks. We investigate the thermal dynamics of such an ensemble using short light pulses to make a spatially inhomogeneous population transfer between atomic states. As we monitor the wave packet of atoms created by this scheme, we find a damped oscillatory behavior which we attribute to sloshing and dispersion of the atoms. Oscillation frequencies range around 100 kHz, and motional dephasing between atoms happens on a timescale of 10μs. Comparison to Monte Carlo simulations of an ensemble of 1000 classical particles yields reasonable agreement for simulated ensemble temperatures between 25 and 40μK.
DOI
Single-Molecule Studies of Protein Folding with Optical Tweezers
Carlos Bustamante, Lisa Alexander, Kevin Maciuba, and Christian M. Kaiser
Manipulation of individual molecules with optical tweezers provides a powerful means of interrogating the structure and folding of proteins. Mechanical force is not only a relevant quantity in cellular protein folding and function, but also a convenient parameter for biophysical folding studies. Optical tweezers offer precise control in the force range relevant for protein folding and unfolding, from which single-molecule kinetic and thermodynamic information about these processes can be extracted. In this review, we describe both physical principles and practical aspects of optical tweezers measurements and discuss recent advances in the use of this technique for the study of protein folding. In particular, we describe the characterization of folding energy landscapes at high resolution, studies of structurally complex multidomain proteins, folding in the presence of chaperones, and the ability to investigate real-time cotranslational folding of a polypeptide.
DOI
Manipulation of individual molecules with optical tweezers provides a powerful means of interrogating the structure and folding of proteins. Mechanical force is not only a relevant quantity in cellular protein folding and function, but also a convenient parameter for biophysical folding studies. Optical tweezers offer precise control in the force range relevant for protein folding and unfolding, from which single-molecule kinetic and thermodynamic information about these processes can be extracted. In this review, we describe both physical principles and practical aspects of optical tweezers measurements and discuss recent advances in the use of this technique for the study of protein folding. In particular, we describe the characterization of folding energy landscapes at high resolution, studies of structurally complex multidomain proteins, folding in the presence of chaperones, and the ability to investigate real-time cotranslational folding of a polypeptide.
DOI
Rapid tilted-plane Gerchberg-Saxton algorithm for holographic optical tweezers
Yanan Cai, Shaohui Yan, Zhaojun Wang, Runze Li, Yansheng Liang, Yuan Zhou, Xing Li, Xianghua Yu, Ming Lei, and Baoli Yao
Benefitting from the development of commercial spatial light modulator (SLM), holographic optical tweezers (HOT) have emerged as a powerful tool for life science, material science and particle physics. The calculation of computer-generated holograms (CGH) for generating multi-focus arrays plays a key role in HOT for trapping of a bunch of particles in parallel. To realize dynamic 3D manipulation, we propose a new tilted-plane GS algorithm for fast generation of multiple foci. The multi-focal spots with a uniformity of 99% can be generated in a tilted plane. The computation time for a CGH with 512×512 pixels is less than 0.1 second. We demonstrated the power of the algorithm by simultaneously trapping and rotating silica beads with a 7×7 spots array in three dimensions. The presented algorithm is expected as a powerful kernel of HOT.
DOI
Benefitting from the development of commercial spatial light modulator (SLM), holographic optical tweezers (HOT) have emerged as a powerful tool for life science, material science and particle physics. The calculation of computer-generated holograms (CGH) for generating multi-focus arrays plays a key role in HOT for trapping of a bunch of particles in parallel. To realize dynamic 3D manipulation, we propose a new tilted-plane GS algorithm for fast generation of multiple foci. The multi-focal spots with a uniformity of 99% can be generated in a tilted plane. The computation time for a CGH with 512×512 pixels is less than 0.1 second. We demonstrated the power of the algorithm by simultaneously trapping and rotating silica beads with a 7×7 spots array in three dimensions. The presented algorithm is expected as a powerful kernel of HOT.
DOI
Monday, September 7, 2020
Inverse integral transformation method to derive local viscosity distribution measured by optical tweezers†
Ruri Hidema, Zenji Yatabe, Hikari Takahashi, Ryusei Higashikawa and Hiroshi Suzuki
Complex fluids have a non-uniform local inner structure; this is enhanced under deformation, inducing a characteristic flow, such as an abrupt increase in extensional viscosity and drag reduction. However, it is challenging to derive and quantify the non-uniform local structure of a low-concentration solution. In this study, we attempted to characterize the non-uniformity of dilute and semi-dilute polymer and worm-like micellar solutions using the local viscosity at the micro scale. The power spectrum density (PSD) of the particle displacement, measured using optical tweezers, was analyzed to calculate the local viscosity, and two methods were compared. One is based on the PSD roll-off method, which yields a single representative viscosity of the solution. The other is based on our proposed method, called the inverse integral transformation method (IITM), for deriving the local viscosity distribution. The distribution obtained through the IITM reflects the non-uniformity of the solutions at the micro scale, i.e., the distribution widens above the entanglement concentrations of the polymer or viscoelastic worm-like micellar solutions.
DOI
Complex fluids have a non-uniform local inner structure; this is enhanced under deformation, inducing a characteristic flow, such as an abrupt increase in extensional viscosity and drag reduction. However, it is challenging to derive and quantify the non-uniform local structure of a low-concentration solution. In this study, we attempted to characterize the non-uniformity of dilute and semi-dilute polymer and worm-like micellar solutions using the local viscosity at the micro scale. The power spectrum density (PSD) of the particle displacement, measured using optical tweezers, was analyzed to calculate the local viscosity, and two methods were compared. One is based on the PSD roll-off method, which yields a single representative viscosity of the solution. The other is based on our proposed method, called the inverse integral transformation method (IITM), for deriving the local viscosity distribution. The distribution obtained through the IITM reflects the non-uniformity of the solutions at the micro scale, i.e., the distribution widens above the entanglement concentrations of the polymer or viscoelastic worm-like micellar solutions.
DOI
Controllable Cellular Micromotors Based on Optical Tweezers
Xiaobin Zou, Qing Zheng, Dong Wu, Hongxiang Lei
Micromotors hold exciting prospects in biomedical applications but still face a great challenge. To date, there have been few reports of micromotors with high safety, flexible controllability, and full biocompatibility. Here, a multifunctional method based on an optical tweezer system is presented to realize controllable cellular micromotors. The method not only satisfies all of the above criteria but is also independent of the cell types and materials. Optical tweezers are used to generate a dynamic scanning optical trap along a given circular trajectory, which can trap and drive a microparticle or a single cell to move along the trajectory and thus generate a microvortex. Cells within the microvortex will be controllably rotated under an action of shear stress or torque and their rotation rate and direction can be controlled by changing the scanning frequency and direction of the dynamic optical trap. The proposed method is effective for both immotile target cells and swimming target cells. Additionally, it is further applied to realize synchronous translation and rotation of cellular micromotors and to assemble controllable and fully biocompatible cellular micromotor assays. The proposed method is believed to have potential applications in targeted drug delivery, biological microenvironment monitoring and sensing, and biomedical treatment.
DOI
Micromotors hold exciting prospects in biomedical applications but still face a great challenge. To date, there have been few reports of micromotors with high safety, flexible controllability, and full biocompatibility. Here, a multifunctional method based on an optical tweezer system is presented to realize controllable cellular micromotors. The method not only satisfies all of the above criteria but is also independent of the cell types and materials. Optical tweezers are used to generate a dynamic scanning optical trap along a given circular trajectory, which can trap and drive a microparticle or a single cell to move along the trajectory and thus generate a microvortex. Cells within the microvortex will be controllably rotated under an action of shear stress or torque and their rotation rate and direction can be controlled by changing the scanning frequency and direction of the dynamic optical trap. The proposed method is effective for both immotile target cells and swimming target cells. Additionally, it is further applied to realize synchronous translation and rotation of cellular micromotors and to assemble controllable and fully biocompatible cellular micromotor assays. The proposed method is believed to have potential applications in targeted drug delivery, biological microenvironment monitoring and sensing, and biomedical treatment.
DOI
The Mitotic Crosslinking Protein PRC1 Acts Like a Mechanical Dashpot to Resist Microtubule Sliding
Ignas Gaska, Mason E. Armstrong, April Alfieri, Scott Forth
Cell division in eukaryotes requires the regulated assembly of the spindle apparatus. The proper organization of microtubules within the spindle is driven by motor proteins that exert forces to slide filaments, whereas non-motor proteins crosslink filaments into higher-order motifs, such as overlapping bundles. It is not clear how active and passive forces are integrated to produce regulated mechanical outputs within spindles. Here, we employ simultaneous optical trapping and total internal reflection fluorescence (TIRF) microscopy to directly measure the frictional forces produced by the mitotic crosslinking protein PRC1 that resist microtubule sliding. These forces scale with microtubule sliding velocity and the number of PRC1 crosslinks but do not depend on overlap length or PRC1 density within overlaps. Our results suggest that PRC1 ensembles act similarly to a mechanical dashpot, producing significant resistance against fast motions but minimal resistance against slow motions, allowing for the integration of diverse motor activities into a single mechanical outcome.
DOI
Cell division in eukaryotes requires the regulated assembly of the spindle apparatus. The proper organization of microtubules within the spindle is driven by motor proteins that exert forces to slide filaments, whereas non-motor proteins crosslink filaments into higher-order motifs, such as overlapping bundles. It is not clear how active and passive forces are integrated to produce regulated mechanical outputs within spindles. Here, we employ simultaneous optical trapping and total internal reflection fluorescence (TIRF) microscopy to directly measure the frictional forces produced by the mitotic crosslinking protein PRC1 that resist microtubule sliding. These forces scale with microtubule sliding velocity and the number of PRC1 crosslinks but do not depend on overlap length or PRC1 density within overlaps. Our results suggest that PRC1 ensembles act similarly to a mechanical dashpot, producing significant resistance against fast motions but minimal resistance against slow motions, allowing for the integration of diverse motor activities into a single mechanical outcome.
DOI
Optical trapping in the presence of laser-induced thermal effects
J. A. Zenteno-Hernandez, J. Vázquez Lozano, J. A. Sarabia-Alonso, J. Ramírez-Ramírez, and R. Ramos-García
The inclusion of thermal effects in optical manipulation has been explored in diverse experiments, increasing the possibilities for applications in diverse areas. In this Letter, the results of combined optical and thermal manipulation in the vicinity of a highly absorbent hydrogenated amorphous silicon layer, which induces both the generation of convective currents and thermophoresis, are presented. In combination with the optical forces, thermal forces help reduce the optical power required to trap and manipulate micrometric polystyrene beads. Moreover, the inclusion of these effects allows the stacking and manipulation of multiple particles with a single optical trap along with the beam propagation, providing an extra tool for micromanipulation of a variety of samples.
DOI
The inclusion of thermal effects in optical manipulation has been explored in diverse experiments, increasing the possibilities for applications in diverse areas. In this Letter, the results of combined optical and thermal manipulation in the vicinity of a highly absorbent hydrogenated amorphous silicon layer, which induces both the generation of convective currents and thermophoresis, are presented. In combination with the optical forces, thermal forces help reduce the optical power required to trap and manipulate micrometric polystyrene beads. Moreover, the inclusion of these effects allows the stacking and manipulation of multiple particles with a single optical trap along with the beam propagation, providing an extra tool for micromanipulation of a variety of samples.
DOI
Single-Cell Multimodal Analytical Approach by Integrating Raman Optical Tweezers and RNA Sequencing
Teng Fang, Wenhao Shang, Chang Liu, Yaoyao Liu, and Anpei Ye
Single-cell analysis has become a state-of-art approach to heterogeneity profiling in tumor cells. Herein, we realize a kind of single-cell multimodal analytical approach by combining single-cell RNA sequencing (scRNA-seq) with Raman optical tweezers (ROT), a label-free single-cell identification and isolation technique, and apply it to investigate drug sensitivity. The drug sensitivity of human BGC823 gastric cancer cells toward different drugs, paclitaxel and sodium dichloroacetate, was distinguished in the conjoint analytical way including morphology monitoring, Raman identification, and transcriptomic profiling. Each individual BGC823 cancer cell was measured by Raman spectroscopy, then nondestructively isolated out by ROT, and finally RNA-sequenced. Our results demonstrate each analytical mode can reflect cell response to the drugs from different perspectives and is consistent and complementary with each other. Therefore, we believe the multimodal analytical approach offers an access to comprehensive characterizations of the unicellular complexity, which especially makes sense for studying tumor heterogeneity or a desired special cell from a mixture cell sample such as whole blood.
DOI
Single-cell analysis has become a state-of-art approach to heterogeneity profiling in tumor cells. Herein, we realize a kind of single-cell multimodal analytical approach by combining single-cell RNA sequencing (scRNA-seq) with Raman optical tweezers (ROT), a label-free single-cell identification and isolation technique, and apply it to investigate drug sensitivity. The drug sensitivity of human BGC823 gastric cancer cells toward different drugs, paclitaxel and sodium dichloroacetate, was distinguished in the conjoint analytical way including morphology monitoring, Raman identification, and transcriptomic profiling. Each individual BGC823 cancer cell was measured by Raman spectroscopy, then nondestructively isolated out by ROT, and finally RNA-sequenced. Our results demonstrate each analytical mode can reflect cell response to the drugs from different perspectives and is consistent and complementary with each other. Therefore, we believe the multimodal analytical approach offers an access to comprehensive characterizations of the unicellular complexity, which especially makes sense for studying tumor heterogeneity or a desired special cell from a mixture cell sample such as whole blood.
DOI
Optical trapping of antihydrogen towards an atomic anti-clock
P. Crivelli & N. Kolachevsky
The unprecedented flux of low energy antiprotons delivered by the Extra Low ENergy Antiprotons (ELENA) ring, being under commissioning at CERN, will open a new era for precision tests with antimatter including laser and microwave spectroscopy and tests ofits gravitational behaviour. Here we present an alternative to magnetic trapping to perform ultra-high precision laser spectroscopy of antihydrogen. The proposed scheme is to load the ultra cold anti-hydrogen atoms produced by the GBAR experiment in an optical trap tuned at the magicwavelength of the 1S–2S transition in order to measure this interval at a level comparable or even better than its matter counter part. This will provide a very accurate test of Lorentz/CPT violating effects which can be parametrised in the framework of the Standard Model Extension.
DOI
The unprecedented flux of low energy antiprotons delivered by the Extra Low ENergy Antiprotons (ELENA) ring, being under commissioning at CERN, will open a new era for precision tests with antimatter including laser and microwave spectroscopy and tests ofits gravitational behaviour. Here we present an alternative to magnetic trapping to perform ultra-high precision laser spectroscopy of antihydrogen. The proposed scheme is to load the ultra cold anti-hydrogen atoms produced by the GBAR experiment in an optical trap tuned at the magicwavelength of the 1S–2S transition in order to measure this interval at a level comparable or even better than its matter counter part. This will provide a very accurate test of Lorentz/CPT violating effects which can be parametrised in the framework of the Standard Model Extension.
DOI
Tuesday, September 1, 2020
Metallic particle manipulation with adjustable trapping range through customized field
Zhidong Bai, Shuoshuo Zhang, Yudong Lyu, Rui Zhao, Xifu Yue, Xiaolu Ge, Shenggui Fu, Zhongsheng Man
Since the invention of optical tweezers, optical manipulation has advanced significantly in many applications, including atomic physics, biochemistry and soft matter physics. Here, we propose a method to trap metallic particles with adjustable trapping range in the transverse plane with the help of customized field. By tailoring the polarization state of the incident field, the focal field with elongation in the direction perpendicular to optical axis can be turned in the 4 focusing system. As a result, optical trapping with tunable trapping range is possible when the metallic particle is interacted with such customized field.
DOI
Since the invention of optical tweezers, optical manipulation has advanced significantly in many applications, including atomic physics, biochemistry and soft matter physics. Here, we propose a method to trap metallic particles with adjustable trapping range in the transverse plane with the help of customized field. By tailoring the polarization state of the incident field, the focal field with elongation in the direction perpendicular to optical axis can be turned in the 4 focusing system. As a result, optical trapping with tunable trapping range is possible when the metallic particle is interacted with such customized field.
DOI
Femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles
Liping Gong, Xiaohe Zhang, Zhuqing Zhu, Guanghao Rui, Jun He, Yiping Cui, and Bing Gu
We investigate femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles with different volume fractions and two-photon absorption (TPA) coefficients. Numerical simulations show that the hollow-core particles with low and high-volume fractions can easily be trapped and bounced by the tightly focused Gaussian laser pulses, respectively. Further studies show that the hollow-core particles with and without TPA can be identified, because the TPA effect enhances the radiation force, and subsequently the longitudinal force destabilizes the trap by pushing the particle away from the focal point. The results may find direct applications in particle sorting and characterizing the TPA coefficient of single nanoparticles.
DOI
We investigate femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles with different volume fractions and two-photon absorption (TPA) coefficients. Numerical simulations show that the hollow-core particles with low and high-volume fractions can easily be trapped and bounced by the tightly focused Gaussian laser pulses, respectively. Further studies show that the hollow-core particles with and without TPA can be identified, because the TPA effect enhances the radiation force, and subsequently the longitudinal force destabilizes the trap by pushing the particle away from the focal point. The results may find direct applications in particle sorting and characterizing the TPA coefficient of single nanoparticles.
DOI
Precise capture and dynamic relocation of nanoparticulate biomolecules through dielectrophoretic enhancement by vertical nanogap architectures
Eui-Sang Yu, Hyojin Lee, Sun-Mi Lee, Jiwon Kim, Taehyun Kim, Jongsu Lee, Chulki Kim, Minah Seo, Jae Hun Kim, Young Tae Byun, Seung-Chul Park, Seung-Yeol Lee, Sin-Doo Lee & Yong-Sang Ryu
Toward the development of surface-sensitive analytical techniques for biosensors and diagnostic biochip assays, a local integration of low-concentration target materials into the sensing region of interest is essential to improve the sensitivity and reliability of the devices. As a result, the dynamic process of sorting and accurate positioning the nanoparticulate biomolecules within pre-defined micro/nanostructures is critical, however, it remains a huge hurdle for the realization of practical surface-sensitive biosensors and biochips. A scalable, massive, and non-destructive trapping methodology based on dielectrophoretic forces is highly demanded for assembling nanoparticles and biosensing tools. Herein, we propose a vertical nanogap architecture with an electrode-insulator-electrode stack structure, facilitating the generation of strong dielectrophoretic forces at low voltages, to precisely capture and spatiotemporally manipulate nanoparticles and molecular assemblies, including lipid vesicles and amyloid-beta protofibrils/oligomers. Our vertical nanogap platform, allowing low-voltage nanoparticle captures on optical metasurface designs, provides new opportunities for constructing advanced surface-sensitive optoelectronic sensors.
DOI
Toward the development of surface-sensitive analytical techniques for biosensors and diagnostic biochip assays, a local integration of low-concentration target materials into the sensing region of interest is essential to improve the sensitivity and reliability of the devices. As a result, the dynamic process of sorting and accurate positioning the nanoparticulate biomolecules within pre-defined micro/nanostructures is critical, however, it remains a huge hurdle for the realization of practical surface-sensitive biosensors and biochips. A scalable, massive, and non-destructive trapping methodology based on dielectrophoretic forces is highly demanded for assembling nanoparticles and biosensing tools. Herein, we propose a vertical nanogap architecture with an electrode-insulator-electrode stack structure, facilitating the generation of strong dielectrophoretic forces at low voltages, to precisely capture and spatiotemporally manipulate nanoparticles and molecular assemblies, including lipid vesicles and amyloid-beta protofibrils/oligomers. Our vertical nanogap platform, allowing low-voltage nanoparticle captures on optical metasurface designs, provides new opportunities for constructing advanced surface-sensitive optoelectronic sensors.
DOI
Large Submillimeter Assembly of Microparticles with Necklace-like Patterns Formed by Laser Trapping at Solution Surface
Jia-Syun Lu, Hsuan-Yin Wang, Tetsuhiro Kudo, and Hiroshi Masuhara
In colloidal solution, nanoparticles can be optically trapped by a tightly focused laser beam, and they are assembled in a focal spot whose diameter is typically about one micrometer. We herein report that a large submillimeter sized assembly of polystyrene microparticles with necklace-like patterns are prepared by laser trapping at a solution surface. The light propagation outside the focal spot is directly confirmed by 1064 nm backscattering images, and finite difference time domain simulation well supports the idea that an optical potential is expanded outside the focal spot based on light propagation through whispering gallery mode. This demonstration opens a new method for fabrication of a millimeter-order huge assembly by a single tightly focused laser beam.
DOI
In colloidal solution, nanoparticles can be optically trapped by a tightly focused laser beam, and they are assembled in a focal spot whose diameter is typically about one micrometer. We herein report that a large submillimeter sized assembly of polystyrene microparticles with necklace-like patterns are prepared by laser trapping at a solution surface. The light propagation outside the focal spot is directly confirmed by 1064 nm backscattering images, and finite difference time domain simulation well supports the idea that an optical potential is expanded outside the focal spot based on light propagation through whispering gallery mode. This demonstration opens a new method for fabrication of a millimeter-order huge assembly by a single tightly focused laser beam.
DOI
Specular-reflection photonic nanojet: physical basis and optical trapping application
I. V. Minin, Yu. E. Geints, A. A. Zemlyanov, and O. V. Minin
A specular-reflection photonic nanojet (s-PNJ) is a specific type of optical near-field subwavelength spatial localization originated from the constructive interference of direct and backward propagated optical waves focused by a transparent dielectric microparticle located near a flat reflecting mirror. The unique property of s-PNJ is reported for maintaining its spatial localization and high intensity when using microparticles with high refractive index contrast when a regular photonic nanojet is not formed. The physical principles of obtaining subwavelength optical focus in the specular-reflection mode of a PNJ are numerically studied and a comparative analysis of jet parameters obtained by the traditional schemes without and with reflection is carried out. Based on the s-PNJ, the physical concept of an optical tweezer integrated into the microfluidic device is proposed provided by the calculations of optical trapping forces of the trial gold nanosphere. Importantly, such an optical trap shows twice as high stability to Brownian motion of the captured nano-bead as compared to the conventional nanojet-based traps and can be relatively easy implemented.
DOI
A specular-reflection photonic nanojet (s-PNJ) is a specific type of optical near-field subwavelength spatial localization originated from the constructive interference of direct and backward propagated optical waves focused by a transparent dielectric microparticle located near a flat reflecting mirror. The unique property of s-PNJ is reported for maintaining its spatial localization and high intensity when using microparticles with high refractive index contrast when a regular photonic nanojet is not formed. The physical principles of obtaining subwavelength optical focus in the specular-reflection mode of a PNJ are numerically studied and a comparative analysis of jet parameters obtained by the traditional schemes without and with reflection is carried out. Based on the s-PNJ, the physical concept of an optical tweezer integrated into the microfluidic device is proposed provided by the calculations of optical trapping forces of the trial gold nanosphere. Importantly, such an optical trap shows twice as high stability to Brownian motion of the captured nano-bead as compared to the conventional nanojet-based traps and can be relatively easy implemented.
DOI
Monday, August 31, 2020
Molecular height measurement by cell surface optical profilometry (CSOP)
Sungmin Son, Sho C. Takatori, Brian Belardi, Marija Podolski, Matthew H. Bakalar, and Daniel A. Fletcher
The physical dimensions of proteins and glycans on cell surfaces can critically affect cell function, for example, by preventing close contact between cells and limiting receptor accessibility. However, high-resolution measurements of molecular heights on native cell membranes have been difficult to obtain. Here we present a simple and rapid method that achieves nanometer height resolution by localizing fluorophores at the tip and base of cell surface molecules and determining their separation by radially averaging across many molecules. We use this method, which we call cell surface optical profilometry (CSOP), to quantify the height of key multidomain proteins on a model cell, as well as to capture average protein and glycan heights on native cell membranes. We show that average height of a protein is significantly smaller than its contour length, due to thermally driven bending and rotation on the membrane, and that height strongly depends on local surface and solution conditions. We find that average height increases with cell surface molecular crowding but decreases with solution crowding by solutes, both of which we confirm with molecular dynamics simulations. We also use experiments and simulations to determine the height of an epitope, based on the location of an antibody, which allows CSOP to profile various proteins and glycans on a native cell surface using antibodies and lectins. This versatile method for profiling cell surfaces has the potential to advance understanding of the molecular landscape of cells and the role of the molecular landscape in cell function.
DOI
The physical dimensions of proteins and glycans on cell surfaces can critically affect cell function, for example, by preventing close contact between cells and limiting receptor accessibility. However, high-resolution measurements of molecular heights on native cell membranes have been difficult to obtain. Here we present a simple and rapid method that achieves nanometer height resolution by localizing fluorophores at the tip and base of cell surface molecules and determining their separation by radially averaging across many molecules. We use this method, which we call cell surface optical profilometry (CSOP), to quantify the height of key multidomain proteins on a model cell, as well as to capture average protein and glycan heights on native cell membranes. We show that average height of a protein is significantly smaller than its contour length, due to thermally driven bending and rotation on the membrane, and that height strongly depends on local surface and solution conditions. We find that average height increases with cell surface molecular crowding but decreases with solution crowding by solutes, both of which we confirm with molecular dynamics simulations. We also use experiments and simulations to determine the height of an epitope, based on the location of an antibody, which allows CSOP to profile various proteins and glycans on a native cell surface using antibodies and lectins. This versatile method for profiling cell surfaces has the potential to advance understanding of the molecular landscape of cells and the role of the molecular landscape in cell function.
DOI
Controlled rotation of cells using a single-beam anisotropic optical trap
Zihao Shan, Enfan Zhang, Dun Pi, Huiyao Gu, Wen Cao, Feng Lin, Zhen Cai, Xingkun Wu
Non-contact, noninvasive techniques to control the orientation of single living cells are highly valuable for biological research and clinical applications. We experimentally demonstrate a single-beam, single-fiber optical manipulation technique using an anisotropic, four-lobed light field propagated by low-order fiber mode LP21. The laser beam forms a rotationally non-axisymmetric optical multi-trap that may be directed to a spatial location on-demand, capable of cell translation, rotation, and orientation-holding with emitted power as low as 10 mW. We further developed a T-matrix based simulation method that can numerically model and optimize parameters that vary desired laser trap opto-mechanical properties, such as holding torque and capture efficiency. The demonstrated technique is easy to implement for cell micro-manipulation in complex research environments with multi-side occlusion, such as within a microfluidic channel in a lab-on-chip system, and may be used in conjunction with additional units for low-profile three-dimensional rotation and translation, or with other magnetic or electrical manipulation techniques.
DOI
Non-contact, noninvasive techniques to control the orientation of single living cells are highly valuable for biological research and clinical applications. We experimentally demonstrate a single-beam, single-fiber optical manipulation technique using an anisotropic, four-lobed light field propagated by low-order fiber mode LP21. The laser beam forms a rotationally non-axisymmetric optical multi-trap that may be directed to a spatial location on-demand, capable of cell translation, rotation, and orientation-holding with emitted power as low as 10 mW. We further developed a T-matrix based simulation method that can numerically model and optimize parameters that vary desired laser trap opto-mechanical properties, such as holding torque and capture efficiency. The demonstrated technique is easy to implement for cell micro-manipulation in complex research environments with multi-side occlusion, such as within a microfluidic channel in a lab-on-chip system, and may be used in conjunction with additional units for low-profile three-dimensional rotation and translation, or with other magnetic or electrical manipulation techniques.
DOI
Optothermal generation, trapping, and manipulation of microbubbles
J. A. Sarabia-Alonso, J. G. Ortega-Mendoza, J. C. Ramírez-San-Juan, P. Zaca-Morán, J. Ramírez-Ramírez, A. Padilla-Vivanco, F. M. Muñoz-Pérez, and R. Ramos-García
The most common approach to optically generate and manipulate bubbles in liquids involves temperature gradients induced by CW lasers. In this work, we present a method to accomplish both the generation of microbubbles and their 3D manipulation in ethanol through optothermal forces. These forces are triggered by light absorption from a nanosecond pulsed laser (λ = 532 nm) at silver nanoparticles photodeposited at the distal end of a multimode optical fiber. Light absorbed from each laser pulse quickly heats up the silver-ethanol interface beyond the ethanol critical-point (∼ 243 °C) before the heat diffuses through the liquid. Therefore, the liquid achieves a metastable state and owing to spontaneous nucleation converted to a vapor bubble attached to the optical fiber. The bubble grows with semi-spherical shape producing a counterjet in the final stage of the collapse. This jet reaches the hot nanoparticles vaporizing almost immediately and ejecting a microbubble. This microbubble-generation mechanism takes place with every laser pulse (10 kHz repetition rate) leading to the generation of a microbubbles stream. The microbubbles' velocities decrease as they move away from the optical fiber and eventually coalesce forming a larger bubble. The larger bubble is attracted to the optical fiber by the Marangoni force once it reaches a critical size while being continuously fed with each bubble of the microbubbles stream. The balance of the optothermal forces owing to the laser-pulse drives the 3D manipulation of the main bubble. A complete characterization of the trapping conditions is provided in this paper.
DOI
The most common approach to optically generate and manipulate bubbles in liquids involves temperature gradients induced by CW lasers. In this work, we present a method to accomplish both the generation of microbubbles and their 3D manipulation in ethanol through optothermal forces. These forces are triggered by light absorption from a nanosecond pulsed laser (λ = 532 nm) at silver nanoparticles photodeposited at the distal end of a multimode optical fiber. Light absorbed from each laser pulse quickly heats up the silver-ethanol interface beyond the ethanol critical-point (∼ 243 °C) before the heat diffuses through the liquid. Therefore, the liquid achieves a metastable state and owing to spontaneous nucleation converted to a vapor bubble attached to the optical fiber. The bubble grows with semi-spherical shape producing a counterjet in the final stage of the collapse. This jet reaches the hot nanoparticles vaporizing almost immediately and ejecting a microbubble. This microbubble-generation mechanism takes place with every laser pulse (10 kHz repetition rate) leading to the generation of a microbubbles stream. The microbubbles' velocities decrease as they move away from the optical fiber and eventually coalesce forming a larger bubble. The larger bubble is attracted to the optical fiber by the Marangoni force once it reaches a critical size while being continuously fed with each bubble of the microbubbles stream. The balance of the optothermal forces owing to the laser-pulse drives the 3D manipulation of the main bubble. A complete characterization of the trapping conditions is provided in this paper.
DOI
Nanoscale rotational optical manipulation
Masayuki Hoshina, Nobuhiko Yokoshi, and Hajime Ishihara
Light has momentum, and hence, it can move small particles. The optical tweezer, invented by Ashkin et al. [Opt. Lett. 11, 288 (1986)] is a representative application. It traps and manipulates microparticles and has led to great successes in the biosciences. Currently, optical manipulation of “nano-objects” is attracting growing attention, and new techniques have been proposed and realized. For flexible manipulation, push–pull switching [Phys. Rev. Lett. 109, 087402 (2012)] and super-resolution trapping by using the electronic resonance of nano-objects have been proposed [ACS Photonics 5, 318 (2017)]. However, regarding the “rotational operation” of nano-objects, the full potential of optical manipulation remains unknown. This study proposes mechanisms to realize rotation and direction switching of nano-objects in macroscopic and nanoscopic areas. By controlling the balance between the dissipative force and the gradient force by using optical nonlinearity, the direction of the macroscopic rotational motion of nano-objects is switched. Further, conversion between the spin angular momentum and orbital angular momentum by light scattering through localized surface plasmon resonance in metallic nano-complexes induces optical force for rotational motion in the nanoscale area. This study pieces out fundamental operations of the nanoscale optical manipulation of nanoparticles.
DOI
Light has momentum, and hence, it can move small particles. The optical tweezer, invented by Ashkin et al. [Opt. Lett. 11, 288 (1986)] is a representative application. It traps and manipulates microparticles and has led to great successes in the biosciences. Currently, optical manipulation of “nano-objects” is attracting growing attention, and new techniques have been proposed and realized. For flexible manipulation, push–pull switching [Phys. Rev. Lett. 109, 087402 (2012)] and super-resolution trapping by using the electronic resonance of nano-objects have been proposed [ACS Photonics 5, 318 (2017)]. However, regarding the “rotational operation” of nano-objects, the full potential of optical manipulation remains unknown. This study proposes mechanisms to realize rotation and direction switching of nano-objects in macroscopic and nanoscopic areas. By controlling the balance between the dissipative force and the gradient force by using optical nonlinearity, the direction of the macroscopic rotational motion of nano-objects is switched. Further, conversion between the spin angular momentum and orbital angular momentum by light scattering through localized surface plasmon resonance in metallic nano-complexes induces optical force for rotational motion in the nanoscale area. This study pieces out fundamental operations of the nanoscale optical manipulation of nanoparticles.
DOI
Miniature force sensor for absolute laser power measurements via radiation pressure at hundreds of watts
Alexandra B. Artusio-Glimpse, Ivan Ryger, Natalia A. Azarova, Paul A. Williams, Joshua A. Hadler, and John H. Lehman
We present a small power meter that detects the radiation pressure of an incident high-power laser. Given its small package and non-destructive interaction with the laser, this power meter is well suited to realizing a robust real-time, high-accuracy power measurement in laser-based manufacturing environments. The incident laser power is determined through interferometric measurement of displacement of a 20 mm diameter high reflectivity mirror, mounted at the center of a dual element spiral flexure. This device can measure laser power from 25 W to 400 W with a 260 mW/Hz−−−√ noise floor and ≤ 3.2% expanded uncertainty. We validate our device against a calibrated thermopile with simultaneous measurements of an unpolarized 1070 nm laser and report good agreement between the two systems. Finally, by referencing to an identical mechanical spring that does not see the incident laser, we suppress vibration noise in the power measurement by 14.8 dB over a 600 Hz measured bandwidth. This is an improvement over other radiation pressure based power meters that have previously been demonstrated.
DOI
We present a small power meter that detects the radiation pressure of an incident high-power laser. Given its small package and non-destructive interaction with the laser, this power meter is well suited to realizing a robust real-time, high-accuracy power measurement in laser-based manufacturing environments. The incident laser power is determined through interferometric measurement of displacement of a 20 mm diameter high reflectivity mirror, mounted at the center of a dual element spiral flexure. This device can measure laser power from 25 W to 400 W with a 260 mW/Hz−−−√ noise floor and ≤ 3.2% expanded uncertainty. We validate our device against a calibrated thermopile with simultaneous measurements of an unpolarized 1070 nm laser and report good agreement between the two systems. Finally, by referencing to an identical mechanical spring that does not see the incident laser, we suppress vibration noise in the power measurement by 14.8 dB over a 600 Hz measured bandwidth. This is an improvement over other radiation pressure based power meters that have previously been demonstrated.
DOI
Thursday, August 27, 2020
Establishment of an optical trapping curve for prediction of trapping parameters
Ayush Owhal, Dipankar Boruah, Sachin U. Belgamwar
Optical trapping is widely used to manipulate a small-sized particle freely suspended in the isotropic fluidic domain. Trapping is done by means of optical forces developed by conversing light beam. The active gradient forces, depends upon parameters like light wavelength, particle size, and refractive index of medium and particle. The viscous drag forces, depends upon parameter like viscosity of fluid, relative velocity of particle with respect to medium. The necessary condition for particle trapping is to maintain > . In this paper, a graphical approach is applied to predetermine the value of specific parameter such as relative velocity of particle and light wavelength under the necessary condition for optical trapping, while keeping other parameters are as fixed. Software simulation is performed with set of relative velocities on polystyrene small-sized particle in water channel to validate the graphical approach.
DOI
Optical trapping is widely used to manipulate a small-sized particle freely suspended in the isotropic fluidic domain. Trapping is done by means of optical forces developed by conversing light beam. The active gradient forces, depends upon parameters like light wavelength, particle size, and refractive index of medium and particle. The viscous drag forces, depends upon parameter like viscosity of fluid, relative velocity of particle with respect to medium. The necessary condition for particle trapping is to maintain > . In this paper, a graphical approach is applied to predetermine the value of specific parameter such as relative velocity of particle and light wavelength under the necessary condition for optical trapping, while keeping other parameters are as fixed. Software simulation is performed with set of relative velocities on polystyrene small-sized particle in water channel to validate the graphical approach.
DOI
Optical trapping Rayleigh particles with a twist effect
Yao Zhang, Haoran Yan, Daomu Zhao
We theoretically and numerically investigate the focusing properties and the radiation forces produced by a focused rotating anisotropic generalized multi-Gaussian Schell model (RAGMGSM) beam. We find that for different parameters at the trapped plane, the intensity distribution would evolve into an elliptical dark hollow or elongated Gaussian beam profile. Compared to the focal plane, the trapped plane has an axial displacement due to the twist effects. Further, we demonstrate that two types of particles at different positions of the trapped plane can be trapped and rotated simultaneously by such a focused beam. Moreover, the influences of the beam index M, the coherence width δ, and the twist factor u on the radiation forces is elucidated respectively. The limits of each parameter for stability of optical trapping under a certain condition are explicitly discussed.
DOI
We theoretically and numerically investigate the focusing properties and the radiation forces produced by a focused rotating anisotropic generalized multi-Gaussian Schell model (RAGMGSM) beam. We find that for different parameters at the trapped plane, the intensity distribution would evolve into an elliptical dark hollow or elongated Gaussian beam profile. Compared to the focal plane, the trapped plane has an axial displacement due to the twist effects. Further, we demonstrate that two types of particles at different positions of the trapped plane can be trapped and rotated simultaneously by such a focused beam. Moreover, the influences of the beam index M, the coherence width δ, and the twist factor u on the radiation forces is elucidated respectively. The limits of each parameter for stability of optical trapping under a certain condition are explicitly discussed.
DOI
Optical pulling forces and their applications
Hang Li, Yongyin Cao, Lei-Ming Zhou, Xiaohao Xu, Tongtong Zhu, Yuzhi Shi, Cheng-Wei Qiu, and Weiqiang Ding
Optical manipulations utilizing the mechanical effect of light have been indispensable in various disciplines. Among those various manipulations, optical pulling has emerged recently as an attractive notion and captivated the popular imagination, not only because it constitutes a rich family of counterintuitive phenomena compared with traditional manipulations but also due to the profound physics underneath and potential applications. Beginning with a general introduction to optical forces, related theories, and methods, we review the progresses achieved in optical pulling forces using different mechanisms and configurations. Similar pulling forces in other forms of waves, including acoustic, water, and quantum matter waves, are also integrated. More importantly, we also include the progresses in counterintuitive left-handed optical torque and lateral optical force as the extensions of the pulling force. As a new manipulation degree of freedom, optical pulling force and related effects have potential applications in remote mass transportation, optical rotating, and optical sorting. They may also stimulate the investigations of counterintuitive phenomena in other forms of waves.
DOI
Optical manipulations utilizing the mechanical effect of light have been indispensable in various disciplines. Among those various manipulations, optical pulling has emerged recently as an attractive notion and captivated the popular imagination, not only because it constitutes a rich family of counterintuitive phenomena compared with traditional manipulations but also due to the profound physics underneath and potential applications. Beginning with a general introduction to optical forces, related theories, and methods, we review the progresses achieved in optical pulling forces using different mechanisms and configurations. Similar pulling forces in other forms of waves, including acoustic, water, and quantum matter waves, are also integrated. More importantly, we also include the progresses in counterintuitive left-handed optical torque and lateral optical force as the extensions of the pulling force. As a new manipulation degree of freedom, optical pulling force and related effects have potential applications in remote mass transportation, optical rotating, and optical sorting. They may also stimulate the investigations of counterintuitive phenomena in other forms of waves.
DOI
Nanoplastic Analysis by Online Coupling of Raman Microscopy and Field-Flow Fractionation Enabled by Optical Tweezers
Christian Schwaferts, Vanessa Sogne, Roland Welz, Florian Meier, Thorsten Klein, Reinhard Niessner, Martin Elsner, and Natalia P. Ivleva
Nanoplastic pollution is an emerging environmental concern, but current analytical approaches are facing limitations in this size range. However, the coupling of nanoparticle separation with chemical characterization bears potential to close this gap. Here, we realize the hyphenation of particle separation/characterization (field-flow fractionation (FFF), UV, and multiangle light scattering) with subsequent chemical identification by online Raman microspectroscopy (RM). The problem of low Raman scattering was overcome by trapping particles with 2D optical tweezers. This setup enabled RM to identify particles of different materials (polymers and inorganic) in the size range from 200 nm to 5 μm, with concentrations in the order of 1 mg/L (109 particles L–1). The hyphenation was realized for asymmetric flow FFF and centrifugal FFF, which separate particles on the basis of different properties. This technique shows potential for application in nanoplastic analysis, as well as many other fields of nanomaterial characterization.
DOI
Nanoplastic pollution is an emerging environmental concern, but current analytical approaches are facing limitations in this size range. However, the coupling of nanoparticle separation with chemical characterization bears potential to close this gap. Here, we realize the hyphenation of particle separation/characterization (field-flow fractionation (FFF), UV, and multiangle light scattering) with subsequent chemical identification by online Raman microspectroscopy (RM). The problem of low Raman scattering was overcome by trapping particles with 2D optical tweezers. This setup enabled RM to identify particles of different materials (polymers and inorganic) in the size range from 200 nm to 5 μm, with concentrations in the order of 1 mg/L (109 particles L–1). The hyphenation was realized for asymmetric flow FFF and centrifugal FFF, which separate particles on the basis of different properties. This technique shows potential for application in nanoplastic analysis, as well as many other fields of nanomaterial characterization.
DOI
Vortex preserving statistical optical beams
Zhiheng Xu, Xiaofei Li, Xin Liu, Sergey A. Ponomarenko, Yangjian Cai, and Chunhao Liang
We establish a general form of the cross-spectral density of statistical sources that generate vortex preserving partially coherent beams on propagation through any linear ABCD optical system. We illustrate our results by introducing a class of partially coherent vortex beams with a closed form cross-spectral density at the source and demonstrating the beam vortex structure preservation on free space propagation and imaging by a thin lens. We also show the capacity of such vortex preserving beams of any state of spatial coherence to trap nanoparticles with the refractive index smaller than that of a surrounding medium.
DOI
We establish a general form of the cross-spectral density of statistical sources that generate vortex preserving partially coherent beams on propagation through any linear ABCD optical system. We illustrate our results by introducing a class of partially coherent vortex beams with a closed form cross-spectral density at the source and demonstrating the beam vortex structure preservation on free space propagation and imaging by a thin lens. We also show the capacity of such vortex preserving beams of any state of spatial coherence to trap nanoparticles with the refractive index smaller than that of a surrounding medium.
DOI
Wednesday, August 26, 2020
Opto-thermoelectric speckle tweezers
Abhay Kotnala, Pavana Siddhartha Kollipara and Yuebing Zheng
Opto-thermoelectric tweezers present a new paradigm for optical trapping and manipulation of particles using low-power and simple optics. New real-life applications of opto-thermoelectric tweezers in areas such as biophysics, microfluidics, and nanomanufacturing will require them to have large-scale and high-throughput manipulation capabilities in complex environments. Here, we present opto-thermoelectric speckle tweezers, which use speckle field consisting of many randomly distributed thermal hotspots that arise from an optical speckle pattern to trap multiple particles over large areas. By further integrating the speckle tweezers with a microfluidic system, we experimentally demonstrate their application for size-based nanoparticle filtration. With their low-power operation, simplicity, and versatility, opto-thermoelectric speckle tweezers will broaden the applications of optical manipulation techniques.
DOI
Opto-thermoelectric tweezers present a new paradigm for optical trapping and manipulation of particles using low-power and simple optics. New real-life applications of opto-thermoelectric tweezers in areas such as biophysics, microfluidics, and nanomanufacturing will require them to have large-scale and high-throughput manipulation capabilities in complex environments. Here, we present opto-thermoelectric speckle tweezers, which use speckle field consisting of many randomly distributed thermal hotspots that arise from an optical speckle pattern to trap multiple particles over large areas. By further integrating the speckle tweezers with a microfluidic system, we experimentally demonstrate their application for size-based nanoparticle filtration. With their low-power operation, simplicity, and versatility, opto-thermoelectric speckle tweezers will broaden the applications of optical manipulation techniques.
DOI
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