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
Monday, October 5, 2020
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
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