Adarsh Lalitha Ravindranath, Mirali Seyed Shariatdoust, Samuel Mathew, and Reuven Gordon
Double-nanoholes fabricated by colloidal lithography were used for trapping single colloidal particles and single proteins. A gap separation of 60 nm between the cusps of the double-nanohole was achieved in a gold film of 70 nm thickness sputter coated onglass. The cusp separation was reduced steadily down to 10 nm by plasma etching the colloidal particles prior to sputter coating. Scanning electron microscopy was used to locate a particular double-nanohole and it was registered for later microscopy experiments. 30 nm polystyrene particles, the rubisco protein and bovine serum albumin were trapped using a laser focused through the aperture. Compared to other methods that require top-down nanofabrication, this approach is inexpensive and produces high-quality samples.
DOI
Wednesday, May 29, 2019
Force-Regulated Refolding of the Mechanosensory Domain in the Platelet Glycoprotein Ib-IX Complex
X. Frank Zhang, Wei Zhang, M. Edward Quach, Wei Deng, Renhao Li
In platelets, the glycoprotein (GP) Ib-IX receptor complex senses blood shear flow and transmits the mechanical signals into platelets. Recently, we have discovered a juxtamembrane mechanosensory domain (MSD) within the GPIb α subunit of GPIb-IX. Mechanical unfolding of the MSD activates GPIb-IX signaling into platelets, leading to their activation and clearance. Using optical tweezer-based single-molecule force measurement, we herein report a systematic biomechanical characterization of the MSD in its native, full-length receptor complex and a recombinant, unglycosylated MSD in isolation. The native MSD unfolds at a resting rate of 9 × 10 −3 s −1. Upon exposure to pulling forces, MSD unfolding accelerates exponentially over a force scale of 2.0 pN. Importantly, the unfolded MSD can refold with or without applied forces. The unstressed refolding rate of MSD is ∼17 s −1 and slows exponentially over a force scale of 3.7 pN. Our measurements confirm that the MSD is relatively unstable, with a folding free energy of 7.5 k BT. Because MSD refolding may turn off GPIb-IX’s mechanosensory signals, our results provide a mechanism for the requirement of a continuous pulling force of >15 pN to fully activate GPIb-IX.
DOI
In platelets, the glycoprotein (GP) Ib-IX receptor complex senses blood shear flow and transmits the mechanical signals into platelets. Recently, we have discovered a juxtamembrane mechanosensory domain (MSD) within the GPIb α subunit of GPIb-IX. Mechanical unfolding of the MSD activates GPIb-IX signaling into platelets, leading to their activation and clearance. Using optical tweezer-based single-molecule force measurement, we herein report a systematic biomechanical characterization of the MSD in its native, full-length receptor complex and a recombinant, unglycosylated MSD in isolation. The native MSD unfolds at a resting rate of 9 × 10 −3 s −1. Upon exposure to pulling forces, MSD unfolding accelerates exponentially over a force scale of 2.0 pN. Importantly, the unfolded MSD can refold with or without applied forces. The unstressed refolding rate of MSD is ∼17 s −1 and slows exponentially over a force scale of 3.7 pN. Our measurements confirm that the MSD is relatively unstable, with a folding free energy of 7.5 k BT. Because MSD refolding may turn off GPIb-IX’s mechanosensory signals, our results provide a mechanism for the requirement of a continuous pulling force of >15 pN to fully activate GPIb-IX.
DOI
Back-focal-plane interferometric detection of nanoparticles in spatially confined microfluidic channels
Abhay Kotnala, Yi Zheng, Jianping Fu, and Wei Cheng
Nanoparticles are important in several areas of modern biomedical research. However, detection and characterization of nanoparticles is challenging due to their small size. Back-focal-plane interferometry (BFPI) is a highly sensitive technique that has been used in laser tweezers for quantitative measurement of force and displacement. The utility of BFPI for detection and characterization of nanoparticles, however, has not yet been achieved. Here we show that BFPI can be used for rapid probing of a suspension of nanoparticles in a spatially confined microfluidic channel. We show that the Gaussian Root-mean-squared noise of the BFPI signal is highly sensitive to the nanoparticle size and can be used as a parameter for rapid detection of nanoparticles at a single-particle level and characterization of particle heterogeneities in a suspension. By precisely aligning the optical trap relative to the channel boundaries, individual polystyrene particles with a diameter as small as 63 nm can be detected using BFPI with a high signal-to-noise ratio.
DOI
Nanoparticles are important in several areas of modern biomedical research. However, detection and characterization of nanoparticles is challenging due to their small size. Back-focal-plane interferometry (BFPI) is a highly sensitive technique that has been used in laser tweezers for quantitative measurement of force and displacement. The utility of BFPI for detection and characterization of nanoparticles, however, has not yet been achieved. Here we show that BFPI can be used for rapid probing of a suspension of nanoparticles in a spatially confined microfluidic channel. We show that the Gaussian Root-mean-squared noise of the BFPI signal is highly sensitive to the nanoparticle size and can be used as a parameter for rapid detection of nanoparticles at a single-particle level and characterization of particle heterogeneities in a suspension. By precisely aligning the optical trap relative to the channel boundaries, individual polystyrene particles with a diameter as small as 63 nm can be detected using BFPI with a high signal-to-noise ratio.
DOI
Generalized Lorenz--Mie theories and mechanical effects of laser light, on the occasion of Arthur Ashkin’s receipt of the 2018 Nobel prize in physics for his pioneering work in optical levitation and manipulation: A review
Gérard Gouesbet
Among the many works of Arthur Ashkin, many have been devoted to optical tweezers, optical levitation and optical manipulation of macroscopic particles (“macroscopic” being here to beunderstood as opposed to atoms or molecules). From a theoretical point of view, these experiments have been studied in the framework of two limiting regimes, namely Rayleigh regime for small size parameter and ray optics for large size parameter. The generalized Lorenz-Mie theory (GLMT, and more generally GLMTs) bridges the gap between these two regimes. The present paper therefore reviews GLMTs and mechanical effects of laser light, in Rouen where the GLMT had originally been built, but also worldwide. A story in the review concerns the first experimental validations of GLMT using optical levitation experiments.
DOI
Among the many works of Arthur Ashkin, many have been devoted to optical tweezers, optical levitation and optical manipulation of macroscopic particles (“macroscopic” being here to beunderstood as opposed to atoms or molecules). From a theoretical point of view, these experiments have been studied in the framework of two limiting regimes, namely Rayleigh regime for small size parameter and ray optics for large size parameter. The generalized Lorenz-Mie theory (GLMT, and more generally GLMTs) bridges the gap between these two regimes. The present paper therefore reviews GLMTs and mechanical effects of laser light, in Rouen where the GLMT had originally been built, but also worldwide. A story in the review concerns the first experimental validations of GLMT using optical levitation experiments.
DOI
Simultaneous Generation of Multiple Three-Dimensional Tractor Curve Beams
Jun Wu, Xinquan Tang and Jun Xia
A tractor beam, which has the ability to attract objects, is a class of special optical beams. Currently, people are using the holographic technology to shape complex optical tractor beams for both fundamental research and practical applications. However, most of the work reported is focusing on generating two-dimensional (2D) tractor beams and simple three-dimensional (3D) tractor beams, which has limitations in the further development on mechanism and application of beam shaping. In the present work, we are introducing our study in designing multiple 3D tractor beams with spatial location regulated independently. Meanwhile, each individual beam could be prescribed along arbitrary geometric curve and twisted at arbitrary angles as desired. In our method, the computer-generated hologram (CGH) of each curve is calculated, and all the CGHs are multiplexed and encoded into one phase-only hologram by adding respective linear phase grating such that different 3D curves appeared in the different positions of the focal regions. We experimentally prove that the generation of optical tractor beams at 3D configuration can be readily achieved. The generated beams in the present study are especially useful for applications such as multiple micro-machining optical trapping and complex 3D manipulation.
DOI
A tractor beam, which has the ability to attract objects, is a class of special optical beams. Currently, people are using the holographic technology to shape complex optical tractor beams for both fundamental research and practical applications. However, most of the work reported is focusing on generating two-dimensional (2D) tractor beams and simple three-dimensional (3D) tractor beams, which has limitations in the further development on mechanism and application of beam shaping. In the present work, we are introducing our study in designing multiple 3D tractor beams with spatial location regulated independently. Meanwhile, each individual beam could be prescribed along arbitrary geometric curve and twisted at arbitrary angles as desired. In our method, the computer-generated hologram (CGH) of each curve is calculated, and all the CGHs are multiplexed and encoded into one phase-only hologram by adding respective linear phase grating such that different 3D curves appeared in the different positions of the focal regions. We experimentally prove that the generation of optical tractor beams at 3D configuration can be readily achieved. The generated beams in the present study are especially useful for applications such as multiple micro-machining optical trapping and complex 3D manipulation.
DOI
All-fiber interferometer for displacement and velocity measurement of a levitated particle in fiber-optic traps
Wei Xiong, Guangzong Xiao, Xiang Han, Xinlin Chen, Kaiyong Yang, and Hui Luo
We propose an all-fiber interferometer based on laser Doppler velocimetry in a dual-beam fiber-optic trap to measure the displacement and velocity of a trapped particle. ABCD matrices are used to compute the contrast ratio of the interference. The influence of the reflectivity of the fiber end face is discussed. We have designed an optimized reflectivity based on the parameters of our setup. The antireflective coatings on the fiber end face are employed to achieve the given reflectivity. The displacement and velocity of the trapped microparticle are successfully measured by the period and frequency of the interference signal, respectively. The sensitivity of the displacement detection is 368 nm. By describing the miniaturization of the detection system, this paper provides a simple and practical scheme to achieve the integration of the entire optical trapping setup.
DOI
We propose an all-fiber interferometer based on laser Doppler velocimetry in a dual-beam fiber-optic trap to measure the displacement and velocity of a trapped particle. ABCD matrices are used to compute the contrast ratio of the interference. The influence of the reflectivity of the fiber end face is discussed. We have designed an optimized reflectivity based on the parameters of our setup. The antireflective coatings on the fiber end face are employed to achieve the given reflectivity. The displacement and velocity of the trapped microparticle are successfully measured by the period and frequency of the interference signal, respectively. The sensitivity of the displacement detection is 368 nm. By describing the miniaturization of the detection system, this paper provides a simple and practical scheme to achieve the integration of the entire optical trapping setup.
DOI
Controlling the dynamics of colloidal particles by critical Casimir forces
Alessandro Magazzù, Agnese Callegari, Juan Pablo Staforelli, Andrea Gambassi, Siegfried Dietrich and Giovanni Volpe
Critical Casimir forces can play an important role for applications in nano-science and nano-technology, owing to their piconewton strength, nanometric action range, fine tunability as a function of temperature, and exquisite dependence on the surface properties of the involved objects. Here, we investigate the effects of critical Casimir forces on the free dynamics of a pair of colloidal particles dispersed in the bulk of a near-critical binary liquid solvent, using blinking optical tweezers. In particular, we measure the time evolution of the distance between the two colloids to determine their relative diffusion and drift velocity. Furthermore, we show how critical Casimir forces change the dynamic properties of this two-colloid system by studying the temperature dependence of the distribution of the so-called first-passage time, i.e., of the time necessary for the particles to reach for the first time a certain separation, starting from an initially assigned one. These data are in good agreement with theoretical results obtained from Monte Carlo simulations and Langevin dynamics.
DOI
Critical Casimir forces can play an important role for applications in nano-science and nano-technology, owing to their piconewton strength, nanometric action range, fine tunability as a function of temperature, and exquisite dependence on the surface properties of the involved objects. Here, we investigate the effects of critical Casimir forces on the free dynamics of a pair of colloidal particles dispersed in the bulk of a near-critical binary liquid solvent, using blinking optical tweezers. In particular, we measure the time evolution of the distance between the two colloids to determine their relative diffusion and drift velocity. Furthermore, we show how critical Casimir forces change the dynamic properties of this two-colloid system by studying the temperature dependence of the distribution of the so-called first-passage time, i.e., of the time necessary for the particles to reach for the first time a certain separation, starting from an initially assigned one. These data are in good agreement with theoretical results obtained from Monte Carlo simulations and Langevin dynamics.
DOI
Friday, May 24, 2019
Self-stabilizing photonic levitation and propulsion of nanostructured macroscopic objects
Ognjen Ilic & Harry A. Atwater
Light is a powerful tool to manipulate matter, but existing approaches often necessitate focused, high-intensity light that limits the manipulated object’s shape, material and size. Here, we report that self-stabilizing optical manipulation of macroscopic—millimetre-, centimetre- and even metre-scale—objects could be achieved by controlling the anisotropy of light scattering along the object’s surface. In a scalable design that features silicon resonators on silica substrate, we identify nanophotonic structures that can self-stabilize when rotated and/or translated relative to the optical axis. Nanoscale control of scattering across a large area creates restoring behaviour by engineering the scattered phase, without needing to focus incident light or excessively constrain the shape, size or material composition of the object. Our findings may lead to platforms for manipulating macroscopic objects, with applications ranging from contactless wafer-scale fabrication and assembly, to trajectory control for ultra-light spacecraft and even laser-propelled light sails for space exploration.
DOI
Light is a powerful tool to manipulate matter, but existing approaches often necessitate focused, high-intensity light that limits the manipulated object’s shape, material and size. Here, we report that self-stabilizing optical manipulation of macroscopic—millimetre-, centimetre- and even metre-scale—objects could be achieved by controlling the anisotropy of light scattering along the object’s surface. In a scalable design that features silicon resonators on silica substrate, we identify nanophotonic structures that can self-stabilize when rotated and/or translated relative to the optical axis. Nanoscale control of scattering across a large area creates restoring behaviour by engineering the scattered phase, without needing to focus incident light or excessively constrain the shape, size or material composition of the object. Our findings may lead to platforms for manipulating macroscopic objects, with applications ranging from contactless wafer-scale fabrication and assembly, to trajectory control for ultra-light spacecraft and even laser-propelled light sails for space exploration.
DOI
Bacterial-nanostructure interactions: The role of cell elasticity and adhesion forces
Aaron Elbourne, James Chapman, Amy Gelmi, Daniel Cozzolino, Russell J.Crawford, Vi Khanh Truong
The attachment of single-celled organisms, namely bacteria and fungi, to abiotic surfaces is of great interest to both the scientific and medical communities. This is because the interaction of such cells has important implications in a range of areas, including biofilm formation, biofouling, antimicrobial surface technologies, and bio-nanotechnologies, as well as infection development, control, and mitigation. While central to many biological phenomena, the factors which govern microbial surface attachment are still not fully understood. This lack of understanding is a direct consequence of the complex nature of cell-surface interactions, which can involve both specific and non-specific interactions. For applications involving micro- and nano-structured surfaces, developing an understanding of such phenomenon is further complicated by the diverse nature of surface architectures, surface chemistry, variation in cellular physiology, and the intended technological output. These factors are extremely important to understand in the emerging field of antibacterial nanostructured surfaces. The aim of this perspective is to re-frame the discussion surrounding the mechanism of nanostructured-microbial surface interactions. Broadly, the article reviews our current understanding of these phenomena, while highlighting the knowledge gaps surrounding the adhesive forces which govern bacterial-nanostructure interactions and the role of cell membrane rigidity in modulating surface activity. The roles of surface charge, cell rigidity, and cell-surface adhesion force in bacterial-surface adsorption are discussed in detail. Presently, most studies have overlooked these areas, which has left many questions unanswered. Further, this perspective article highlights the numerous experimental issues and misinterpretations which surround current studies of antibacterial nanostructured surfaces.
DOI
The attachment of single-celled organisms, namely bacteria and fungi, to abiotic surfaces is of great interest to both the scientific and medical communities. This is because the interaction of such cells has important implications in a range of areas, including biofilm formation, biofouling, antimicrobial surface technologies, and bio-nanotechnologies, as well as infection development, control, and mitigation. While central to many biological phenomena, the factors which govern microbial surface attachment are still not fully understood. This lack of understanding is a direct consequence of the complex nature of cell-surface interactions, which can involve both specific and non-specific interactions. For applications involving micro- and nano-structured surfaces, developing an understanding of such phenomenon is further complicated by the diverse nature of surface architectures, surface chemistry, variation in cellular physiology, and the intended technological output. These factors are extremely important to understand in the emerging field of antibacterial nanostructured surfaces. The aim of this perspective is to re-frame the discussion surrounding the mechanism of nanostructured-microbial surface interactions. Broadly, the article reviews our current understanding of these phenomena, while highlighting the knowledge gaps surrounding the adhesive forces which govern bacterial-nanostructure interactions and the role of cell membrane rigidity in modulating surface activity. The roles of surface charge, cell rigidity, and cell-surface adhesion force in bacterial-surface adsorption are discussed in detail. Presently, most studies have overlooked these areas, which has left many questions unanswered. Further, this perspective article highlights the numerous experimental issues and misinterpretations which surround current studies of antibacterial nanostructured surfaces.
DOI
Colloidal analogues of polymer chains, ribbons and 2D crystals employing orientations and interactions of nano-rods dispersed in a nematic liquid crystal
Muhammed Rasi M, Ravi Kumar Pujala & Surajit Dhara
Robust control over the position, orientation and self-assembly of nonspherical colloids facilitate the creation of new materials with complex architecture that are important from technological and fundamental perspectives. We study orientation, elastic interaction and co-assembly of surface functionalized silica nano-rods in thin films of nematic liquid crystal. With homeotropic boundary condition, the nano-rods are predominantly oriented perpendicular to the nematic director which is different than the mostly parallel orientation of the micro-rods. The percentage of perpendicular nano-rods are significantly larger than the parallel nano-rods. The perpendicular nano-rods create very weak elastic deformation and exhibit unusual, out-of-plane, attractive interaction. On the other hand, the nano-rods oriented parallel to the director create strong elastic deformation and shows anisotropic, in-plane, dipolar interaction. In both orientations, the induced defects reside in the nano-rods. With the help of a dynamic laser tweezers and using nano-rods as building blocks we demonstrate colloidal analogues of linear polymer chains, ribbons and two-dimensional binary crystals.
DOI
Robust control over the position, orientation and self-assembly of nonspherical colloids facilitate the creation of new materials with complex architecture that are important from technological and fundamental perspectives. We study orientation, elastic interaction and co-assembly of surface functionalized silica nano-rods in thin films of nematic liquid crystal. With homeotropic boundary condition, the nano-rods are predominantly oriented perpendicular to the nematic director which is different than the mostly parallel orientation of the micro-rods. The percentage of perpendicular nano-rods are significantly larger than the parallel nano-rods. The perpendicular nano-rods create very weak elastic deformation and exhibit unusual, out-of-plane, attractive interaction. On the other hand, the nano-rods oriented parallel to the director create strong elastic deformation and shows anisotropic, in-plane, dipolar interaction. In both orientations, the induced defects reside in the nano-rods. With the help of a dynamic laser tweezers and using nano-rods as building blocks we demonstrate colloidal analogues of linear polymer chains, ribbons and two-dimensional binary crystals.
DOI
Microdeformation of RBCs under oxidative stress measured by digital holographic microscopy and optical tweezers
Jiaqi Liu, Lianqing Zhu, Fan Zhang, Mingli Dong, and Xinghua Qu
This paper utilized digital holographic microscopy and optical tweezers to study microdeformation of red blood cells (RBCs) dynamically under oxidative stress. RBCs attached with microbeads were stretched by dual optical tweezers to generate microdeformation. Morphology of RBCs under manipulation were recorded dynamically and recovered by off-axis digital holographic microscopy method. RBCs treated with H2O2 at different concentrations were measured to investigate the mechanical properties under oxidative stress. Use of optical tweezers and off-axis digital holographic microscopy enhanced measuring accuracy compared with the traditional method. Microdeformation of RBCs is also more consistent with the physiological situation. This proposal is meaningful for clinical applications and basic analysis of Parkinson’s disease research.
DOI
This paper utilized digital holographic microscopy and optical tweezers to study microdeformation of red blood cells (RBCs) dynamically under oxidative stress. RBCs attached with microbeads were stretched by dual optical tweezers to generate microdeformation. Morphology of RBCs under manipulation were recorded dynamically and recovered by off-axis digital holographic microscopy method. RBCs treated with H2O2 at different concentrations were measured to investigate the mechanical properties under oxidative stress. Use of optical tweezers and off-axis digital holographic microscopy enhanced measuring accuracy compared with the traditional method. Microdeformation of RBCs is also more consistent with the physiological situation. This proposal is meaningful for clinical applications and basic analysis of Parkinson’s disease research.
DOI
Optical transportation and accumulation of microparticles by self-accelerating cusp beams
Weiwei Liu, Xiaodong Yang, and Jie Gao
Most of the self–accelerating beams have monotonous single-channel bending structures, which greatly limit their applications in many fields such as microscopic imaging and particle manipulation. In this paper, the self-accelerating cusp beams with variable numbers of multichannel bending structures are generated to demonstrate the optical transportation and accumulation of micrometer polystyrene particles. The transportation velocity and optical force profiles of the microparticles moving along the bending channels of cusp beams are analyzed. Parallel particle transportation and particle accumulation manipulation from all the bending channels are further demonstrated. These results will inspire a lot of promising applications for self-accelerating beams especially in three-dimensional optical micromanipulation.
DOI
Most of the self–accelerating beams have monotonous single-channel bending structures, which greatly limit their applications in many fields such as microscopic imaging and particle manipulation. In this paper, the self-accelerating cusp beams with variable numbers of multichannel bending structures are generated to demonstrate the optical transportation and accumulation of micrometer polystyrene particles. The transportation velocity and optical force profiles of the microparticles moving along the bending channels of cusp beams are analyzed. Parallel particle transportation and particle accumulation manipulation from all the bending channels are further demonstrated. These results will inspire a lot of promising applications for self-accelerating beams especially in three-dimensional optical micromanipulation.
DOI
Role of nonconservative scattering forces and damping on Brownian particles in optical traps
Matthieu Mangeat, Yacine Amarouchene, Yann Louyer, Thomas Guérin, and David S. Dean
We consider a model of a particle trapped in a harmonic optical trap but with the addition of a nonconservative radiation induced force. This model is known to correctly describe experimentally observed trapped particle statistics for a wide range of physical parameters, such as temperature and pressure. We theoretically analyze the effect of nonconservative force on the underlying steady state distribution as well as the power spectrum for the particle position. We compute perturbatively the probability distribution of the resulting nonequilibrium steady states for all dynamical regimes underdamped through to overdamped and give expressions for the associated currents in phase space (position and velocity). We also give the spectral density of the trapped particle's position in all dynamical regimes and for any value of the nonconservative force. Signatures of the presence of nonconservative forces are shown to be particularly strong for the underdamped regime at low frequencies.
DOI
We consider a model of a particle trapped in a harmonic optical trap but with the addition of a nonconservative radiation induced force. This model is known to correctly describe experimentally observed trapped particle statistics for a wide range of physical parameters, such as temperature and pressure. We theoretically analyze the effect of nonconservative force on the underlying steady state distribution as well as the power spectrum for the particle position. We compute perturbatively the probability distribution of the resulting nonequilibrium steady states for all dynamical regimes underdamped through to overdamped and give expressions for the associated currents in phase space (position and velocity). We also give the spectral density of the trapped particle's position in all dynamical regimes and for any value of the nonconservative force. Signatures of the presence of nonconservative forces are shown to be particularly strong for the underdamped regime at low frequencies.
DOI
Thursday, May 23, 2019
Force Generated by Two Kinesin Motors Depends on the Load Direction and Intermolecular Coupling
Hamid Khataee and Jonathon Howard
Kinesins are molecular motors that carry cellular cargoes. While the mechanics of single kinesins are well characterized experimentally, the behavior of multiple kinesins varies considerably among experiments. The basis for this variability is unknown. Here, we resolve single-motor force measurements into a vertical component, which accelerates kinesin detachment, and a horizontal component, which decelerates the detachment when resisting the motor. This directionality, when the different experimental geometries are considered, can account for much of the variation in multiple motor dynamics.
DOI
Kinesins are molecular motors that carry cellular cargoes. While the mechanics of single kinesins are well characterized experimentally, the behavior of multiple kinesins varies considerably among experiments. The basis for this variability is unknown. Here, we resolve single-motor force measurements into a vertical component, which accelerates kinesin detachment, and a horizontal component, which decelerates the detachment when resisting the motor. This directionality, when the different experimental geometries are considered, can account for much of the variation in multiple motor dynamics.
DOI
Nonequilibrium Dynamics Induced by Scattering Forces for Optically Trapped Nanoparticles in Strongly Inertial Regimes
Yacine Amarouchene, Matthieu Mangeat, Benjamin Vidal Montes, Lukas Ondic, Thomas Guérin, David S. Dean, and Yann Louyer
The forces acting on optically trapped particles are commonly assumed to be conservative. Nonconservative scattering forces induce toroidal currents in overdamped liquid environments, with negligible effects on position fluctuations. However, their impact in the underdamped regime remains unexplored. Here, we study the effect of nonconservative scattering forces on the underdamped nonlinear dynamics of trapped nanoparticles at various air pressures. These forces induce significant low-frequency position fluctuations along the optical axis and the emergence of toroidal currents in both position and velocity variables. Our experimental and theoretical results provide fundamental insights into the functioning of optical tweezers and a means for investigating nonequilibrium steady states induced by nonconservative forces.
DOI
The forces acting on optically trapped particles are commonly assumed to be conservative. Nonconservative scattering forces induce toroidal currents in overdamped liquid environments, with negligible effects on position fluctuations. However, their impact in the underdamped regime remains unexplored. Here, we study the effect of nonconservative scattering forces on the underdamped nonlinear dynamics of trapped nanoparticles at various air pressures. These forces induce significant low-frequency position fluctuations along the optical axis and the emergence of toroidal currents in both position and velocity variables. Our experimental and theoretical results provide fundamental insights into the functioning of optical tweezers and a means for investigating nonequilibrium steady states induced by nonconservative forces.
DOI
On-resonance photonic nanojets for nanoparticle trapping
Haotian Wang, Jianing Zhang, Xiang Wu, and Deyuan Shen
We present an optical-trapping scheme based on an on-resonance photonic nanojet (PNJ) excited using a plane wave. A two-dimensional numerical simulation demonstrates that a PNJ is enhanced through resonance with whispering gallery modes (WGMs) and achieves a larger spatial distribution, providing a stable trapping region for nanoparticles nearly four times larger than those of the WGM nodes without broadening by the PNJ. To further enlarge the trapping region, an asymmetric micro-resonator lengthens the mode field of the on-resonance PNJ. We also propose an effective method for addressing the nanoparticle-induced resonance detuning through exciting high-order WGMs of a larger-mode field volume.
DOI
We present an optical-trapping scheme based on an on-resonance photonic nanojet (PNJ) excited using a plane wave. A two-dimensional numerical simulation demonstrates that a PNJ is enhanced through resonance with whispering gallery modes (WGMs) and achieves a larger spatial distribution, providing a stable trapping region for nanoparticles nearly four times larger than those of the WGM nodes without broadening by the PNJ. To further enlarge the trapping region, an asymmetric micro-resonator lengthens the mode field of the on-resonance PNJ. We also propose an effective method for addressing the nanoparticle-induced resonance detuning through exciting high-order WGMs of a larger-mode field volume.
DOI
Geometrical-optics computer model of metal-knitted mesh for calculations of solar pressure on space deployable antenna reflectors
Yu. E. Geints, A. V. Klimkin, S. V. Latynsev, A. V. Ovchinnikov, I. V. Ptashnik, A. A. Solodov, A. M. Solodov, and E. N. Yakimov
A novel computer 3D model is presented for calculations of optical parameters (transmittance, reflectance, and absorbance) of a metal-knitted mesh textile as a structural element of deployable antenna reflectors for space satellites. The model is based on geometrical-optics ray tracing upon diffuse scattering of a broadband light source (Sun) at a complex knitted mesh structure with different inclinations to the radiative source. The proposed computer model is built for the special type of metal-wire textile (two-bar large void tricot) possessing extremely high transmittance and is verified by comparison with the experimental measurements of light scattering parameters of real antenna mesh samples of data-relaying satellites (Russian series “Loutch”). The model is used for calculations of solar radiation pressure exerted on a knitted mesh antenna reflector and gives the maximal pressure value of about 0.28 μN/m2.
DOI
A novel computer 3D model is presented for calculations of optical parameters (transmittance, reflectance, and absorbance) of a metal-knitted mesh textile as a structural element of deployable antenna reflectors for space satellites. The model is based on geometrical-optics ray tracing upon diffuse scattering of a broadband light source (Sun) at a complex knitted mesh structure with different inclinations to the radiative source. The proposed computer model is built for the special type of metal-wire textile (two-bar large void tricot) possessing extremely high transmittance and is verified by comparison with the experimental measurements of light scattering parameters of real antenna mesh samples of data-relaying satellites (Russian series “Loutch”). The model is used for calculations of solar radiation pressure exerted on a knitted mesh antenna reflector and gives the maximal pressure value of about 0.28 μN/m2.
DOI
Optical pressure control with aperiodic nanostructured material
Yu-Chun Hsueh, Li-Fan Yang, and Kevin J. Webb
The electromagnetic force on matter depends on both the geometry and the material properties, and for a contiguous material with a periodic boundary condition, the pressure is a useful metric. We present a statistical method with example results that allows the evaluation of pressure in relation to a nanostructured material arrangement formed by populating pixels within a region one wavelength on a side. The two example materials considered are gold and silicon, both in a free-space background. We find that both the magnitude of the pressure and the direction can be regulated, depending on the geometry, and these effects are related to the specifics of the internal structure resonances. Control of positive and negative pressure can be understood as being due to the total field, a superposition of the incident and scattered fields, where the structure regulates the local scattered field and hence the pressure through an integral of the resulting force density. The statistical analysis provides physical insight into how to constrain the design framework for applications. The application space includes biophysics, where information is obtained about biomolecules from force and torque measurements, cavity optomechanics related to basic science and sensing, and optical remote control and actuation, where regulation of the magnitude and direction and the possibility of materials with multiple functionalities provide new opportunities.
DOI
The electromagnetic force on matter depends on both the geometry and the material properties, and for a contiguous material with a periodic boundary condition, the pressure is a useful metric. We present a statistical method with example results that allows the evaluation of pressure in relation to a nanostructured material arrangement formed by populating pixels within a region one wavelength on a side. The two example materials considered are gold and silicon, both in a free-space background. We find that both the magnitude of the pressure and the direction can be regulated, depending on the geometry, and these effects are related to the specifics of the internal structure resonances. Control of positive and negative pressure can be understood as being due to the total field, a superposition of the incident and scattered fields, where the structure regulates the local scattered field and hence the pressure through an integral of the resulting force density. The statistical analysis provides physical insight into how to constrain the design framework for applications. The application space includes biophysics, where information is obtained about biomolecules from force and torque measurements, cavity optomechanics related to basic science and sensing, and optical remote control and actuation, where regulation of the magnitude and direction and the possibility of materials with multiple functionalities provide new opportunities.
DOI
Optical trapping below the diffraction limit with a tunable beam waist using super-oscillating beams
Harel Nagar, Tamir Admon, Doron Goldman, Amir Eyal, and Yael Roichman
Super-oscillating beams can be used to create light spots whose size is below the diffraction limit with a side ring of high intensity adjacent to them. Optical traps made of the super-oscillating part of such beams exhibit superior localization of submicron beads compared to regular optical traps. Here we focus on the effect of the ratio of particle size to beam size on the localization and stiffness of optical traps made of super-oscillating beams. We find a nonmonotonic dependence of trapping stiffness on the ratio of particle size to beam size. Optimal trapping is achieved when the particle is larger than the beam waist of the super-oscillating feature but small enough not to overlap with the side ring.
DOI
Super-oscillating beams can be used to create light spots whose size is below the diffraction limit with a side ring of high intensity adjacent to them. Optical traps made of the super-oscillating part of such beams exhibit superior localization of submicron beads compared to regular optical traps. Here we focus on the effect of the ratio of particle size to beam size on the localization and stiffness of optical traps made of super-oscillating beams. We find a nonmonotonic dependence of trapping stiffness on the ratio of particle size to beam size. Optimal trapping is achieved when the particle is larger than the beam waist of the super-oscillating feature but small enough not to overlap with the side ring.
DOI
Microscope Observation of Morphology of Colloidally Dispersed Niobate Nanosheets Combined with Optical Trapping
Teruyuki Nakato, Yuki Higashi, Wataru Ishitobi, Takashi Nagashita, Makoto Tominaga, Yasutaka Suzuki, Toshiaki Iwai, and Jun Kawamata
Although inorganic nanosheets prepared by exfoliation (delamination) of layered crystals have attracted great attention as 2D nanoparticles, in situ real space observations of exfoliated nanosheets in the colloidally dispersed state have not been conducted. In the present study, colloidally dispersed inorganic nanosheets prepared by exfoliation of layered niobate are directly observed with bright-field optical microscopy, which detects large nanosheets with lateral length larger than several micrometers. The observed nanosheets are not strictly flat but rounded, undulated, or folded in many cases. Optical trapping of nanosheets by laser radiation pressure has clarified their uneven cross-sectional shapes. Their morphology is retained under the relation between Brownian motion and optical trapping.
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Tuesday, May 21, 2019
Size-Selective Optical Printing of Silicon Nanoparticles through Their Dipolar Magnetic Resonance
Cecilia Zaza, Ianina L. Violi, Julián Gargiulo, Germán Chiarelli, Ludmilla Schumacher, Jurij Jakobi, Jorge Olmos-Trigo, Emiliano Cortes, Matthias König, Stephan Barcikowski, Sebastian Schlücker, Juan José Sáenz, Stefan A. Maier, and Fernando D. Stefan
Silicon nanoparticles possess unique size-dependent optical properties due to their strong electric and magnetic resonances in the visible range. However, their widespread application has been limited, in comparison with other (e.g., metallic) nanoparticles, because their preparation on monodisperse colloids remains challenging. Exploiting the unique properties of Si nanoparticles in nano- and microdevices calls for methods able to sort and organize them from a colloidal suspension onto specific positions of solid substrates with nanometric precision. We demonstrate that surfactant-free silicon nanoparticles of a predefined and narrow (σ < 10 nm) size range can be selectively immobilized on a substrate by optical printing from a polydisperse colloidal suspension. The size selectivity is based on differential optical forces that can be applied on nanoparticles of different sizes by tuning the light wavelength to the size-dependent magnetic dipolar resonance of the nanoparticles.
DOI
Silicon nanoparticles possess unique size-dependent optical properties due to their strong electric and magnetic resonances in the visible range. However, their widespread application has been limited, in comparison with other (e.g., metallic) nanoparticles, because their preparation on monodisperse colloids remains challenging. Exploiting the unique properties of Si nanoparticles in nano- and microdevices calls for methods able to sort and organize them from a colloidal suspension onto specific positions of solid substrates with nanometric precision. We demonstrate that surfactant-free silicon nanoparticles of a predefined and narrow (σ < 10 nm) size range can be selectively immobilized on a substrate by optical printing from a polydisperse colloidal suspension. The size selectivity is based on differential optical forces that can be applied on nanoparticles of different sizes by tuning the light wavelength to the size-dependent magnetic dipolar resonance of the nanoparticles.
DOI
Optical attraction of strongly absorbing particles in liquids
Yu Zhang, Xiaoyun Tang, Yaxun Zhang, Zhihai Liu, Xinghua Yang, Jianzhong Zhang, Jun Yang, and Libo Yuan
Although optical tweezers function well for the majority of transparent particles, the absorbing particles experience a considerably high absorption force that can destroy the stable optical traps. Photophoretic force is an alternative mechanism that can be used to trap the absorbing particles. The major difficulty that is associated with the utilization of photophoretic forces for trapping strongly absorbing particles in liquids is the presence of considerable absorption on the illuminated side; a positive photophoretic force is usually induced, thereby pushing away the absorbing particles from the high-intensity region of the laser source. Here, we demonstrate a novel principle for the optical trapping and manipulation of strongly absorbing particles by harnessing strong Δα-type photophoretic forces while suppressing their stochastic nature in pure liquid glycerol using a normal divergent Gaussian beam and a Bessel-like beam. Further, our approach expands the optical manipulation of strong absorbing particles to liquid media and provides position control over the trapped particles, including the optical transportation and pinpoint positioning of the 3-μm objects over a distance of a millimeter.
DOI
Although optical tweezers function well for the majority of transparent particles, the absorbing particles experience a considerably high absorption force that can destroy the stable optical traps. Photophoretic force is an alternative mechanism that can be used to trap the absorbing particles. The major difficulty that is associated with the utilization of photophoretic forces for trapping strongly absorbing particles in liquids is the presence of considerable absorption on the illuminated side; a positive photophoretic force is usually induced, thereby pushing away the absorbing particles from the high-intensity region of the laser source. Here, we demonstrate a novel principle for the optical trapping and manipulation of strongly absorbing particles by harnessing strong Δα-type photophoretic forces while suppressing their stochastic nature in pure liquid glycerol using a normal divergent Gaussian beam and a Bessel-like beam. Further, our approach expands the optical manipulation of strong absorbing particles to liquid media and provides position control over the trapped particles, including the optical transportation and pinpoint positioning of the 3-μm objects over a distance of a millimeter.
DOI
Indirect optical trapping using light driven micro-rotors for reconfigurable hydrodynamic manipulation
Unė G. Būtaitė, Graham M. Gibson, Ying-Lung D. Ho, Mike Taverne, Jonathan M. Taylor & David B. Phillips
Optical tweezers are a highly versatile tool for exploration of the mesoscopic world, permitting non-contact manipulation of nanoscale objects. However, direct illumination with intense lasers restricts their use with live biological specimens, and limits the types of materials that can be trapped. Here we demonstrate an indirect optical trapping platform which circumvents these limitations by using hydrodynamic forces to exert nanoscale-precision control over aqueous particles, without directly illuminating them. Our concept is based on optically actuated micro-robotics: closed-loop control enables highly localised flow-fields to be sculpted by precisely piloting the motion of optically-trapped micro-rotors. We demonstrate 2D trapping of absorbing particles which cannot be directly optically trapped, stabilise the position and orientation of yeast cells, and demonstrate independent control over multiple objects simultaneously. Our work expands the capabilities of optical tweezers platforms, and represents a new paradigm for manipulation of aqueous mesoscopic systems.
DOI
Optical tweezers are a highly versatile tool for exploration of the mesoscopic world, permitting non-contact manipulation of nanoscale objects. However, direct illumination with intense lasers restricts their use with live biological specimens, and limits the types of materials that can be trapped. Here we demonstrate an indirect optical trapping platform which circumvents these limitations by using hydrodynamic forces to exert nanoscale-precision control over aqueous particles, without directly illuminating them. Our concept is based on optically actuated micro-robotics: closed-loop control enables highly localised flow-fields to be sculpted by precisely piloting the motion of optically-trapped micro-rotors. We demonstrate 2D trapping of absorbing particles which cannot be directly optically trapped, stabilise the position and orientation of yeast cells, and demonstrate independent control over multiple objects simultaneously. Our work expands the capabilities of optical tweezers platforms, and represents a new paradigm for manipulation of aqueous mesoscopic systems.
DOI
Designing the measurement of the atomic mass density wave of a Gaussian mass-polariton pulse in optical fibers
Mikko Partanen, Jukka Tulkki
We have recently introduced the mass-polariton (MP) theory of light to describe the coupled dynamics of the field and matter when a light pulse propagates in a transparent medium. The theory is based on combining the electrodynamics of continuous media and continuum mechanics, which are both widely used standard theories in their fields of physics. The MP theory shows that a light pulse propagating in a transparent medium is accompanied by a mass density wave (MDW) of atoms set in motion by the optical force density of the light pulse. In the corresponding quantum picture, the covariant coupled state of the field and matter is described as the MP quasiparticle, which has coupled field and medium components. We study a schematic experimental setup that would enable measurements of the atomic displacements and the excess mass density related to the MDW of a Gaussian MP pulse propagating in an optical fiber made of fused silica.
DOI
We have recently introduced the mass-polariton (MP) theory of light to describe the coupled dynamics of the field and matter when a light pulse propagates in a transparent medium. The theory is based on combining the electrodynamics of continuous media and continuum mechanics, which are both widely used standard theories in their fields of physics. The MP theory shows that a light pulse propagating in a transparent medium is accompanied by a mass density wave (MDW) of atoms set in motion by the optical force density of the light pulse. In the corresponding quantum picture, the covariant coupled state of the field and matter is described as the MP quasiparticle, which has coupled field and medium components. We study a schematic experimental setup that would enable measurements of the atomic displacements and the excess mass density related to the MDW of a Gaussian MP pulse propagating in an optical fiber made of fused silica.
DOI
Strong and High-Precision Manipulation of Nanoparticle with Graphene-Coated Fiber Systems
Shu Yang, Kang Zhao, Zhengtian Xu
Two kinds of graphene-coated fiber systems are proposed and studied for optical trapping. Their plasmonic modes in uniform environment and close to the substrate are studied in the finite element method. The optical forces exerted on dielectric nanoparticle by these systems are calculated by standalone waveguide approximation. It is found that for the dielectric particle with diameter of 1 nm, the maximal optical forces generated by certain modes are more than 107 fN/W whereas their force ranges are only one to several nanometers. These results may have important applications in strong and high-precision optical tweezers.
DOI
Two kinds of graphene-coated fiber systems are proposed and studied for optical trapping. Their plasmonic modes in uniform environment and close to the substrate are studied in the finite element method. The optical forces exerted on dielectric nanoparticle by these systems are calculated by standalone waveguide approximation. It is found that for the dielectric particle with diameter of 1 nm, the maximal optical forces generated by certain modes are more than 107 fN/W whereas their force ranges are only one to several nanometers. These results may have important applications in strong and high-precision optical tweezers.
DOI
Triggered disassembly and reassembly of actin networks induces rigidity phase transitions
Bekele J. Gurmessa, Nicholas Bitten, Dan T. Nguyen, Omar A. Saleh, Jennifer L. Ross, Moumita Das and Rae M. Robertson-Anderson
Non-equilibrium soft materials, such as networks of actin proteins, have been intensely investigated over the past decade due to their promise for designing smart materials and understanding cell mechanics. However, current methods are unable to measure the time-dependent mechanics of such systems or map mechanics to the corresponding dynamic macromolecular properties. Here, we present an experimental approach that combines time-resolved optical tweezers microrheology with diffusion-controlled microfluidics to measure the time-evolution of microscale mechanical properties of dynamic systems during triggered activity. We use these methods to measure the viscoelastic moduli of entangled and crosslinked actin networks during chemically-triggered depolymerization and repolymerization of actin filaments. During disassembly, we find that the moduli exhibit two distinct exponential decays, with experimental time constants of ∼169 min and ∼47 min. Conversely, during reassembly, measured moduli initially exhibit power-law increase with time, after which steady-state values are achieved. We develop toy mathematical models that couple the time-evolution of filament lengths with rigidity percolation theory to shed light onto the molecular mechanisms underlying the observed mechanical transitions. The models suggest that these two distinct behaviors both arise from phase transitions between a rigidly percolated network and a non-rigid regime. Our approach and collective results can inform the general principles underlying the mechanics of a large class of dynamic, non-equilibrium systems and materials of current interest.
DOI
Non-equilibrium soft materials, such as networks of actin proteins, have been intensely investigated over the past decade due to their promise for designing smart materials and understanding cell mechanics. However, current methods are unable to measure the time-dependent mechanics of such systems or map mechanics to the corresponding dynamic macromolecular properties. Here, we present an experimental approach that combines time-resolved optical tweezers microrheology with diffusion-controlled microfluidics to measure the time-evolution of microscale mechanical properties of dynamic systems during triggered activity. We use these methods to measure the viscoelastic moduli of entangled and crosslinked actin networks during chemically-triggered depolymerization and repolymerization of actin filaments. During disassembly, we find that the moduli exhibit two distinct exponential decays, with experimental time constants of ∼169 min and ∼47 min. Conversely, during reassembly, measured moduli initially exhibit power-law increase with time, after which steady-state values are achieved. We develop toy mathematical models that couple the time-evolution of filament lengths with rigidity percolation theory to shed light onto the molecular mechanisms underlying the observed mechanical transitions. The models suggest that these two distinct behaviors both arise from phase transitions between a rigidly percolated network and a non-rigid regime. Our approach and collective results can inform the general principles underlying the mechanics of a large class of dynamic, non-equilibrium systems and materials of current interest.
DOI
Monday, May 20, 2019
Transformation of the Nonprocessive Fast Skeletal Myosin II into a Processive Motor
Mamta Amrute‐Nayak Arnab Nayak Walter Steffen Georgios Tsiavaliaris Tim Scholz Bernhard Brenner
Myosin family motors play diverse cellular roles. Precise insights into how the light chains contribute to the functional variabilities among myosin motors, however, remain unresolved. Here, it is demonstrated that the fast skeletal muscle myosin II isoform myosin heavy chain (MHC‐IID) can be transformed into a processive motor, by simply replacing the native regulatory light chain MLC2f with the regulatory light chain variant MLC2v from the slow muscle myosin II. Single molecule kinetic analyses and optical trapping measurements of the hybrid motor reveal marked changes such as increased association rate of myosin toward adenosine triphosphate (ATP) and actin by more than twofold. The direct consequence of high adenosine diphosphate (ADP) affinity and increased actin rebinding is the altered overall actomyosin association time during the cross‐bridge cycle. The data indicate that the MLC2v influences the duty ratio in the hybrid motor, suggestive of promoting interhead communication and enabling processive movement. This finding establishes that the regulatory light chain fine‐tunes the motor's mechanical output that may have important implications under physiological conditions. Furthermore, the success of this approach paves the way to engineer motors from a known motor protein element to assemble highly specialized biohybrid machines for potential applications in nano‐biomedicine and engineering.
DOI
Myosin family motors play diverse cellular roles. Precise insights into how the light chains contribute to the functional variabilities among myosin motors, however, remain unresolved. Here, it is demonstrated that the fast skeletal muscle myosin II isoform myosin heavy chain (MHC‐IID) can be transformed into a processive motor, by simply replacing the native regulatory light chain MLC2f with the regulatory light chain variant MLC2v from the slow muscle myosin II. Single molecule kinetic analyses and optical trapping measurements of the hybrid motor reveal marked changes such as increased association rate of myosin toward adenosine triphosphate (ATP) and actin by more than twofold. The direct consequence of high adenosine diphosphate (ADP) affinity and increased actin rebinding is the altered overall actomyosin association time during the cross‐bridge cycle. The data indicate that the MLC2v influences the duty ratio in the hybrid motor, suggestive of promoting interhead communication and enabling processive movement. This finding establishes that the regulatory light chain fine‐tunes the motor's mechanical output that may have important implications under physiological conditions. Furthermore, the success of this approach paves the way to engineer motors from a known motor protein element to assemble highly specialized biohybrid machines for potential applications in nano‐biomedicine and engineering.
DOI
Spin to orbital light momentum conversion visualized by particle trajectory
Alejandro V. Arzola, Lukáš Chvátal, Petr Jákl & Pavel Zemánek
In a tightly focused beam of light having both spin and orbital angular momentum, the beam exhibits the spin-orbit interaction phenomenon. We demonstrate here that this interaction gives rise to series of subtle, but observable, effects on the dynamics of a dielectric microsphere trapped in such a beam. In our setup, we control the strength of spin-orbit interaction with the width, polarization and vorticity of the beam and record how these parameters influence radius and orbiting frequency of the same single orbiting particle pushed by the laser beam. Using Richard and Wolf model of the non-paraxial beam focusing, we found a very good agreement between the experimental results and the theoretical model based on calculation of the optical forces using the generalized Lorenz-Mie theory extended to a non-paraxial vortex beam. Especially the radius of the particle orbit seems to be a promising parameter characterizing the spin to orbital momentum conversion independently on the trapping beam power.
DOI
In a tightly focused beam of light having both spin and orbital angular momentum, the beam exhibits the spin-orbit interaction phenomenon. We demonstrate here that this interaction gives rise to series of subtle, but observable, effects on the dynamics of a dielectric microsphere trapped in such a beam. In our setup, we control the strength of spin-orbit interaction with the width, polarization and vorticity of the beam and record how these parameters influence radius and orbiting frequency of the same single orbiting particle pushed by the laser beam. Using Richard and Wolf model of the non-paraxial beam focusing, we found a very good agreement between the experimental results and the theoretical model based on calculation of the optical forces using the generalized Lorenz-Mie theory extended to a non-paraxial vortex beam. Especially the radius of the particle orbit seems to be a promising parameter characterizing the spin to orbital momentum conversion independently on the trapping beam power.
DOI
Miniaturized optical fiber tweezers for cell separation by optical force
Shaojing Liu, Zongbao Li, Zhe Weng, Yuqi Li, Lingling Shui, Zhongxing Jiao, Yilin Chen, Aiping Luo, Xiaobo Xing, and Sailing He
In advanced biomedicine and microfluidics, there is a strong desire to sort and manipulate various cells and bacteria based on miniaturized microfluidic chips. Here, by integrating fiber tweezers into a T-type microfluidic channel, we report an optofluidic chip to selectively trap Escherichia coli in human blood solution based on different sizes and shapes. Furthermore, we simulate the trapping and pushing regions of other cells and bacteria, including rod-shaped bacteria, sphere-shaped bacteria, and cancer cells based on finite-difference analysis. With the advantages of controllability, low optical power, and compact construction, the strategy may be possibly applied in the fields of optical separation, cell transportation, and water quality analysis.
DOI
In advanced biomedicine and microfluidics, there is a strong desire to sort and manipulate various cells and bacteria based on miniaturized microfluidic chips. Here, by integrating fiber tweezers into a T-type microfluidic channel, we report an optofluidic chip to selectively trap Escherichia coli in human blood solution based on different sizes and shapes. Furthermore, we simulate the trapping and pushing regions of other cells and bacteria, including rod-shaped bacteria, sphere-shaped bacteria, and cancer cells based on finite-difference analysis. With the advantages of controllability, low optical power, and compact construction, the strategy may be possibly applied in the fields of optical separation, cell transportation, and water quality analysis.
DOI
An optical tweezer phonon laser
Robert M. Pettit, Wenchao Ge, P. Kumar, Danika R. Luntz-Martin, Justin T. Schultz, Levi P. Neukirch, M. Bhattacharya & A. Nick Vamivakas
Phonon lasers are mechanical analogues of the ubiquitous optical laser and have been realized in a variety of contexts1,2,3,4,5,6,7,8,9,10,11,12. However, no such demonstration exists for mesoscopic levitated optomechanical systems, which are emerging as important platforms for conducting fundamental tests of quantum mechanics13,14,15 and gravity16, as well as for developing sensing modalities that couple mechanical motion to electron spin17,18,19,20 and charge21. Inspired by the pioneering work of Arthur Ashkin on optical tweezers22,23, we introduce a mesoscopic, frequency-tunable phonon laser based on the centre-of-mass oscillation of a silica nanosphere levitated in an optical tweezer under vacuum. Unlike previous levitated realizations, our scheme is general enough to be used on single electrons, liquid droplets or even small biological organisms24. Our device thus provides a pathway for a coherent source of phonons on the mesoscale that can be applied to both fundamental problems in quantum mechanics as well as tasks of precision metrology25,26,27.
DOI
Phonon lasers are mechanical analogues of the ubiquitous optical laser and have been realized in a variety of contexts1,2,3,4,5,6,7,8,9,10,11,12. However, no such demonstration exists for mesoscopic levitated optomechanical systems, which are emerging as important platforms for conducting fundamental tests of quantum mechanics13,14,15 and gravity16, as well as for developing sensing modalities that couple mechanical motion to electron spin17,18,19,20 and charge21. Inspired by the pioneering work of Arthur Ashkin on optical tweezers22,23, we introduce a mesoscopic, frequency-tunable phonon laser based on the centre-of-mass oscillation of a silica nanosphere levitated in an optical tweezer under vacuum. Unlike previous levitated realizations, our scheme is general enough to be used on single electrons, liquid droplets or even small biological organisms24. Our device thus provides a pathway for a coherent source of phonons on the mesoscale that can be applied to both fundamental problems in quantum mechanics as well as tasks of precision metrology25,26,27.
DOI
Simultaneous Localization and Mapping-based In Vivo Navigation Control of Microparticles
Xiaojian Li, Shisan Xu, Shuk Han Cheng, Dong Sun
In vivo manipulation of microparticles, such as biological cells and drugs, has attracted considerable attention in recent years. This paper presents the development of robot-aided manipulation technology that can control targeted microparticles to move a relatively long distance in in vivo environment. The field of view can be updated online, such that the controlled micro-particle can be tracked automatically in transportation. Simultaneous localization and mapping for in vivo applications are first investigated. Based on the in vivo map, an artificial potential field-based controller with disturbance compensation is developed to navigate microparticles in vivo. Experiments on navigating single cells in living zebrafish embryos by using optical tweezers manipulators are performed to demonstrate the effectiveness of the proposed control approach in a dynamic in vivo environment.
DOI
In vivo manipulation of microparticles, such as biological cells and drugs, has attracted considerable attention in recent years. This paper presents the development of robot-aided manipulation technology that can control targeted microparticles to move a relatively long distance in in vivo environment. The field of view can be updated online, such that the controlled micro-particle can be tracked automatically in transportation. Simultaneous localization and mapping for in vivo applications are first investigated. Based on the in vivo map, an artificial potential field-based controller with disturbance compensation is developed to navigate microparticles in vivo. Experiments on navigating single cells in living zebrafish embryos by using optical tweezers manipulators are performed to demonstrate the effectiveness of the proposed control approach in a dynamic in vivo environment.
DOI
Force-detected nanoscale absorption spectroscopy in water at room temperature using an optical trap featured
Alexander Parobek, Jacob W. Black, Maria Kamenetska, and Ziad Ganim
Measuring absorption spectra of single molecules presents a fundamental challenge for standard transmission-based instruments because of the inherently low signal relative to the large background of the excitation source. Here we demonstrate a new approach for performing absorption spectroscopy in solution using a force measurement to read out optical excitation at the nanoscale. The photoinduced force between model chromophores and an optically trapped gold nanoshell has been measured in water at room temperature. This photoinduced force is characterized as a function of wavelength to yield the force spectrum, which is shown to be correlated to the absorption spectrum for four model systems. The instrument constructed for these measurements combines an optical tweezer with frequency domain absorption spectroscopy over the 400-800 nm range. These measurements provide proof-of-principle experiments for force-detected nanoscale spectroscopies that operate under ambient chemical conditions.
DOI
Measuring absorption spectra of single molecules presents a fundamental challenge for standard transmission-based instruments because of the inherently low signal relative to the large background of the excitation source. Here we demonstrate a new approach for performing absorption spectroscopy in solution using a force measurement to read out optical excitation at the nanoscale. The photoinduced force between model chromophores and an optically trapped gold nanoshell has been measured in water at room temperature. This photoinduced force is characterized as a function of wavelength to yield the force spectrum, which is shown to be correlated to the absorption spectrum for four model systems. The instrument constructed for these measurements combines an optical tweezer with frequency domain absorption spectroscopy over the 400-800 nm range. These measurements provide proof-of-principle experiments for force-detected nanoscale spectroscopies that operate under ambient chemical conditions.
DOI
Giant lateral optical forces on Rayleigh particles near hyperbolic and extremely anisotropic metasurfaces
N. K. Paul, D. Correas-Serrano, and J. S. Gomez-Diaz
We report a dramatic enhancement of the lateral optical forces induced on electrically polarizable Rayleigh particles near hyperbolic and extremely anisotropic metasurfaces under simple plane-wave illumination. Such enhancement is enabled by the interplay between the ultraconfined surface plasmons supported by these structures and the out-of-plane polarization spin acquired by the particle. The resulting giant lateral forces appear over a broad frequency range and may open unprecedented venues for routing, trapping, and assembling nanoparticles.
DOI
We report a dramatic enhancement of the lateral optical forces induced on electrically polarizable Rayleigh particles near hyperbolic and extremely anisotropic metasurfaces under simple plane-wave illumination. Such enhancement is enabled by the interplay between the ultraconfined surface plasmons supported by these structures and the out-of-plane polarization spin acquired by the particle. The resulting giant lateral forces appear over a broad frequency range and may open unprecedented venues for routing, trapping, and assembling nanoparticles.
DOI
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