Amin Mousavi, Fahimeh Hosseinibalam, Smaeyl Hassanzadeh, Zahra Taghaviyan
In this study, the behavior of charged particles within a fluid is investigated when exposed to the radiation of a Laguerre-Gaussian beam as an optical tube. Optical forces (e.g., Photophoretic, Radiation pressure and Lorentz forces) and non-optical forces (e.g., Drag and gravitational forces) determine the trajectories of ions movement within these beams. Trapping of charged particles in the direction of the beam axis in an optical tubes depends on the superiority of the radial component of the photophoretic force on the electromagnetic force. The factors affecting this, such as the amount and type of electrostatic charge and the radius of the particle, and the shape and power of the beam are studied. As a result, the charged particle can be guided to various paths based on their electrostatic charge and particle diameter. This could be done in the study of ions within a fluid by optical methods. One of the applications proposed in this regard is that we can counted charged and uncharged particles within a fluid (e.g., liquid ions or aerosols) by separating them in an optical tube.
DOI
Wednesday, July 31, 2019
Multi-parameter measurements of conformational dynamics in nucleic acids and nucleoprotein complexes
Ivan E. Ivanov, Zev Bryant
Biological macromolecules undergo dynamic conformational changes. Single-molecule methods can track such structural rearrangements in real time. However, while the structure of large macromolecules may change along many degrees of freedom, single-molecule techniques only monitor a limited number of these axes of motion. Advanced single-molecule methods are being developed to track multiple degrees of freedom in nucleic acids and nucleoprotein complexes at high resolution, to enable better manipulation and control of the system under investigation, and to collect measurements in massively parallel fashion. Combining complementary single-molecule methods within the same assay also provides unique measurement opportunities. Implementations of magnetic and optical tweezers combined with fluorescence and FRET have demonstrated results unattainable by either technique alone. Augmenting other advanced single-molecule methods with fluorescence detection will allow us to better capture the multidimensional dynamics of nucleic acids and nucleoprotein complexes central to biology.
DOI
Biological macromolecules undergo dynamic conformational changes. Single-molecule methods can track such structural rearrangements in real time. However, while the structure of large macromolecules may change along many degrees of freedom, single-molecule techniques only monitor a limited number of these axes of motion. Advanced single-molecule methods are being developed to track multiple degrees of freedom in nucleic acids and nucleoprotein complexes at high resolution, to enable better manipulation and control of the system under investigation, and to collect measurements in massively parallel fashion. Combining complementary single-molecule methods within the same assay also provides unique measurement opportunities. Implementations of magnetic and optical tweezers combined with fluorescence and FRET have demonstrated results unattainable by either technique alone. Augmenting other advanced single-molecule methods with fluorescence detection will allow us to better capture the multidimensional dynamics of nucleic acids and nucleoprotein complexes central to biology.
DOI
Enantioselective optical trapping of chiral nanoparticles by tightly focused vector beams
Manman Li, Shaohui Yan, Yanan Zhang, Peng Zhang, and Baoli Yao
Two enantiomers (mirror images) can show drastically different behaviors, resulting in the enantiomers’ identification and separation being in high demand in biomedical research and industry. Here, we introduce an optical approach in which, by using a tightly focused vector beam with radially varied polarizations, we realize the selective trapping of both enantiomeric forms. Numerical results show that such a focused field exhibits bifocal spot intensity distribution and can simultaneously stably trap one enantiomer in one focal spot and the other enantiomer in the other spot in three dimensions, achieving an effective separation of the chiral entities. The trapping distance and position of the enantiomeric pairs can be changed by separately varying the magnitude and sign of the polarization topological charge of the vector beam. And the difference in trapping potentials of the particles with different chirality provides a further identification of the chirality. Our theory indicates that the enantiomers’ identification and separation can be mediated by the same incident beam, providing a possible route to detect, separate, and manipulate chiral objects at nanometer scales.
DOI
Two enantiomers (mirror images) can show drastically different behaviors, resulting in the enantiomers’ identification and separation being in high demand in biomedical research and industry. Here, we introduce an optical approach in which, by using a tightly focused vector beam with radially varied polarizations, we realize the selective trapping of both enantiomeric forms. Numerical results show that such a focused field exhibits bifocal spot intensity distribution and can simultaneously stably trap one enantiomer in one focal spot and the other enantiomer in the other spot in three dimensions, achieving an effective separation of the chiral entities. The trapping distance and position of the enantiomeric pairs can be changed by separately varying the magnitude and sign of the polarization topological charge of the vector beam. And the difference in trapping potentials of the particles with different chirality provides a further identification of the chirality. Our theory indicates that the enantiomers’ identification and separation can be mediated by the same incident beam, providing a possible route to detect, separate, and manipulate chiral objects at nanometer scales.
DOI
Radiation force and torque on perfect electrically–conducting (PEC) corrugated circular and elliptical cylinders in TE or TM polarized plane progressive waves with arbitrary incidence
F.G.Mitri
In this work, theoretical modeling and numerical computations for the electromagnetic (EM) radiation force and torque (per-length) on perfect electrically conducting (PEC) cylinders of corrugated circular and elliptical geometrical cross-sections are developed and presented. A TE-polarized or TM-polarized plane progressive wave illumination with arbitrary incidence (in the polar plane) is assumed at normal incidence with respect to the axis of the cylindrical particle. The multipole expansion method in cylindrical coordinates is used and the scattering coefficients of the object of arbitrary shape (in 2D) are determined by imposing appropriate boundary conditions and solving numerically a linear system of equations by matrix inversion. Numerical computations are performed for the non-dimensional longitudinal and transverse radiation force functions as well as the axial radiation torque function. Suitable convergence plots confirm the validity of the multipole expansion approach to evaluate the radiation force and torque with no limitation to a particular frequency range (i.e. Rayleigh, Mie or geometrical optics regimes can be considered using the presented formalism). Particular emphases are given on the shape of the particle (i.e., circular or elliptical), its non-dimensional size, the corrugation/waviness characteristic of its surface, the polarization of the incident plane wave field, and the angle of incidence in the polar plane. The numerical predictions show that the longitudinal and transverse components of the radiation force vector are positive regardless of particle shape, size, corrugation properties, polarization and incidence angle [0 ≤ α ≤ 90°], while the axial torque component reverses sign at particular values of these parameters. The results are predominantly relevant in understanding the fundamentals of the optical/EM radiation force and torque theories and possible applications dealing with the interactions of EM waves with elongated tubular particles with circular or noncircular ribbed surfaces in particle manipulation and other areas. The acoustical analogue is also noted, which shows the universal characteristic of the radiation force and torque phenomena.
DOI
In this work, theoretical modeling and numerical computations for the electromagnetic (EM) radiation force and torque (per-length) on perfect electrically conducting (PEC) cylinders of corrugated circular and elliptical geometrical cross-sections are developed and presented. A TE-polarized or TM-polarized plane progressive wave illumination with arbitrary incidence (in the polar plane) is assumed at normal incidence with respect to the axis of the cylindrical particle. The multipole expansion method in cylindrical coordinates is used and the scattering coefficients of the object of arbitrary shape (in 2D) are determined by imposing appropriate boundary conditions and solving numerically a linear system of equations by matrix inversion. Numerical computations are performed for the non-dimensional longitudinal and transverse radiation force functions as well as the axial radiation torque function. Suitable convergence plots confirm the validity of the multipole expansion approach to evaluate the radiation force and torque with no limitation to a particular frequency range (i.e. Rayleigh, Mie or geometrical optics regimes can be considered using the presented formalism). Particular emphases are given on the shape of the particle (i.e., circular or elliptical), its non-dimensional size, the corrugation/waviness characteristic of its surface, the polarization of the incident plane wave field, and the angle of incidence in the polar plane. The numerical predictions show that the longitudinal and transverse components of the radiation force vector are positive regardless of particle shape, size, corrugation properties, polarization and incidence angle [0 ≤ α ≤ 90°], while the axial torque component reverses sign at particular values of these parameters. The results are predominantly relevant in understanding the fundamentals of the optical/EM radiation force and torque theories and possible applications dealing with the interactions of EM waves with elongated tubular particles with circular or noncircular ribbed surfaces in particle manipulation and other areas. The acoustical analogue is also noted, which shows the universal characteristic of the radiation force and torque phenomena.
DOI
Non-equilibrium dynamics of a nascent polypeptide during translation suppress its misfolding
Lisa M. Alexander, Daniel H. Goldman, Liang M. Wee & Carlos Bustamante
Protein folding can begin co-translationally. Due to the difference in timescale between folding and synthesis, co-translational folding is thought to occur at equilibrium for fast-folding domains. In this scenario, the folding kinetics of stalled ribosome-bound nascent chains should match the folding of nascent chains in real time. To test if this assumption is true, we compare the folding of a ribosome-bound, multi-domain calcium-binding protein stalled at different points in translation with the nascent chain as is it being synthesized in real-time, via optical tweezers. On stalled ribosomes, a misfolded state forms rapidly (1.5 s). However, during translation, this state is only attained after a long delay (63 s), indicating that, unexpectedly, the growing polypeptide is not equilibrated with its ensemble of accessible conformations. Slow equilibration on the ribosome can delay premature folding until adequate sequence is available and/or allow time for chaperone binding, thus promoting productive folding.
DOI
Protein folding can begin co-translationally. Due to the difference in timescale between folding and synthesis, co-translational folding is thought to occur at equilibrium for fast-folding domains. In this scenario, the folding kinetics of stalled ribosome-bound nascent chains should match the folding of nascent chains in real time. To test if this assumption is true, we compare the folding of a ribosome-bound, multi-domain calcium-binding protein stalled at different points in translation with the nascent chain as is it being synthesized in real-time, via optical tweezers. On stalled ribosomes, a misfolded state forms rapidly (1.5 s). However, during translation, this state is only attained after a long delay (63 s), indicating that, unexpectedly, the growing polypeptide is not equilibrated with its ensemble of accessible conformations. Slow equilibration on the ribosome can delay premature folding until adequate sequence is available and/or allow time for chaperone binding, thus promoting productive folding.
DOI
A New Twist for Materials Science: The Formation of Chiral Structures Using the Angular Momentum of Light
Takashige Omatsu, Katsuhiko Miyamoto, Kohei Toyoda, Ryuji Morita, Yoshihiko Arita, Kishan Dholakia
Recent work has shown that irradiation with light possessing orbital angular momentum (OAM) and an associated phase singularity, that is an optical vortex, twists a variety of materials. These include silicon, azo‐polymer, and even liquid‐phase resins to form various helically structured materials. This article provides a review of the unique helical‐structured materials created and the novel fundamental phenomena enabled by this interaction between both the spin angular momentum and the OAM of light with matter. Such light‐induced helical‐structured materials will potentially lead to advanced photonic devices, for instance, metamaterials for ultrasensitive detection and reactions for chiral chemical composites.
DOI
Recent work has shown that irradiation with light possessing orbital angular momentum (OAM) and an associated phase singularity, that is an optical vortex, twists a variety of materials. These include silicon, azo‐polymer, and even liquid‐phase resins to form various helically structured materials. This article provides a review of the unique helical‐structured materials created and the novel fundamental phenomena enabled by this interaction between both the spin angular momentum and the OAM of light with matter. Such light‐induced helical‐structured materials will potentially lead to advanced photonic devices, for instance, metamaterials for ultrasensitive detection and reactions for chiral chemical composites.
DOI
Investigation on the Volatility of Ammonium Nitrate Using Optical Tweezers
Lü Xi-juan, GAO Xiao-yan, MA Jia-bi, ZHANG Yun-hong
Abstract Measurements of the particle-to-gas partitioning of semi-volatile atmospheric aerosols are crucial for providing more accurate descriptions of the compositional and size distributions of atmospheric aerosol. As a major component of semi-volatile aerosol species, ammonium nitrate (NH4NO3) is ubiquitous in the sub-micron particulate matter, particularly in high pollution episodes. In order to further understand gas-particle partitioning of NH4NO3, determination of the saturated vapor pressure of NH4NO3 is needed. Here, we investigate the volatility of NH4NO3 at different relative humidities (RHs) using aerosol optical tweezers coupled with Raman spectroscopy as an instrument for sampling and detecting. According to the Maxwell equation, the vapor pressures at different RHs are calculated, and the values are (1.67±0.24)×10-3, (1.82±0.19)×10-3, (2.91±0.13)×10-3, (3.5±0.28)×10-3, (4.59±0.22)×10-3 and (6.64±0.3)×10-3 Pa, when the RH is 80%, 73%, 68%, 57.3%, 55.4%, 44.8% respectively. Obviously, the vapor pressures of NH4NO3 increase with RH decreasing, i.e. low RH promotes the evaporation of ammonium nitrate. Additionally, we also calculate the volatilizing flux of NH4NO3 at different RHs, and the values are in the range of (4.01±0.79)×10-7~(3.32±0.77)×10-8 mol·(s·m2)-1. The results obtained herein are of important significance in understanding the partitioning processes of semi-volatile aerosols.
DOI
Abstract Measurements of the particle-to-gas partitioning of semi-volatile atmospheric aerosols are crucial for providing more accurate descriptions of the compositional and size distributions of atmospheric aerosol. As a major component of semi-volatile aerosol species, ammonium nitrate (NH4NO3) is ubiquitous in the sub-micron particulate matter, particularly in high pollution episodes. In order to further understand gas-particle partitioning of NH4NO3, determination of the saturated vapor pressure of NH4NO3 is needed. Here, we investigate the volatility of NH4NO3 at different relative humidities (RHs) using aerosol optical tweezers coupled with Raman spectroscopy as an instrument for sampling and detecting. According to the Maxwell equation, the vapor pressures at different RHs are calculated, and the values are (1.67±0.24)×10-3, (1.82±0.19)×10-3, (2.91±0.13)×10-3, (3.5±0.28)×10-3, (4.59±0.22)×10-3 and (6.64±0.3)×10-3 Pa, when the RH is 80%, 73%, 68%, 57.3%, 55.4%, 44.8% respectively. Obviously, the vapor pressures of NH4NO3 increase with RH decreasing, i.e. low RH promotes the evaporation of ammonium nitrate. Additionally, we also calculate the volatilizing flux of NH4NO3 at different RHs, and the values are in the range of (4.01±0.79)×10-7~(3.32±0.77)×10-8 mol·(s·m2)-1. The results obtained herein are of important significance in understanding the partitioning processes of semi-volatile aerosols.
DOI
Tuesday, July 30, 2019
Optical-force laws for guided light in linear media
Thales Fernando Damasceno Fernandes and Pierre-Louis de Assis
The mechanical response of transparent materials to optical forces is a topic that concerns a wide range of fields, from the manipulation of biological material by optical tweezers to the design of nano-optomechanical systems. However, the fundamental aspects of such forces have always been surrounded by controversies, and several different formulations have been proposed. In this paper, we propose a general stress tensor formalism to put all optical forces in a consistent presentation that allows us to study how different predictions emerge, and use the specific case of light propagating as a superposition of guided modes in lossless dielectric waveguides as a physical example. We use this formalism to calculate optical forces for straight and curved waveguide sections and all possible excitation configurations for a given set of coupled eigenmodes, and then compare the results for each of the known proposed optical-force laws in a framework that permits distinguishing where there will be differences between the force laws proposed. The general formalism also allows us to show that proper use of the divergence theorem is crucial to account for all force terms, many of which vanish if the procedure most commonly used is applied for situations other than eigenmodes in straight waveguides in vacuum. Finally, it is known that discrepancies in the predicted forces arise from the incompleteness of each stress tensor with respect to the total-energy-momentum tensor of the system. A better understanding of how different stress tensors predict very different forces for certain waveguide geometries should open a pathway to identifying how to properly assemble the full tensor, as well as for experimental tests to confirm the predictions.
DOI
The mechanical response of transparent materials to optical forces is a topic that concerns a wide range of fields, from the manipulation of biological material by optical tweezers to the design of nano-optomechanical systems. However, the fundamental aspects of such forces have always been surrounded by controversies, and several different formulations have been proposed. In this paper, we propose a general stress tensor formalism to put all optical forces in a consistent presentation that allows us to study how different predictions emerge, and use the specific case of light propagating as a superposition of guided modes in lossless dielectric waveguides as a physical example. We use this formalism to calculate optical forces for straight and curved waveguide sections and all possible excitation configurations for a given set of coupled eigenmodes, and then compare the results for each of the known proposed optical-force laws in a framework that permits distinguishing where there will be differences between the force laws proposed. The general formalism also allows us to show that proper use of the divergence theorem is crucial to account for all force terms, many of which vanish if the procedure most commonly used is applied for situations other than eigenmodes in straight waveguides in vacuum. Finally, it is known that discrepancies in the predicted forces arise from the incompleteness of each stress tensor with respect to the total-energy-momentum tensor of the system. A better understanding of how different stress tensors predict very different forces for certain waveguide geometries should open a pathway to identifying how to properly assemble the full tensor, as well as for experimental tests to confirm the predictions.
DOI
Hybrid photonic-plasmonic platform for high-throughput single-molecule studies
Mina Mossayebi, Alberto Parini, Amanda J. Wright, Mike G. Somekh, Gaetano Bellanca, and Eric C. Larkins
We present the design and numerical characterization of a hybrid photonic-plasmonic nanoresonator comprised of a 2D photonic crystal (PhC) cavity, a gold bowtie nanoantenna (BNA) and a silicon dioxide, SiO2, spacer. This device is designed to serve as the building block of a multicomponent platform capable of running multiple single-molecule experiments such as optical trapping and sample interrogation simultaneously. The thickness and structure of the spacer layer are adjusted to maximize the energy in the externally accessible hot-spot in the BNA gap. Suitability of the device for photonic integration is demonstrated by exciting it through a PhC waveguide.
DOI
We present the design and numerical characterization of a hybrid photonic-plasmonic nanoresonator comprised of a 2D photonic crystal (PhC) cavity, a gold bowtie nanoantenna (BNA) and a silicon dioxide, SiO2, spacer. This device is designed to serve as the building block of a multicomponent platform capable of running multiple single-molecule experiments such as optical trapping and sample interrogation simultaneously. The thickness and structure of the spacer layer are adjusted to maximize the energy in the externally accessible hot-spot in the BNA gap. Suitability of the device for photonic integration is demonstrated by exciting it through a PhC waveguide.
DOI
Elastic modulus and migration capability of drug treated leukemia cells K562
Kui Wang, Yuntian Xu, Ying Peng, Xiangchao Pang, Yuanjun Zhang, L.I. Ruiz-Ortega, Ye Tian, A.H.W. Ngan, Bin Tang
Leukemia is a commonly seen disease caused by abnormal differentiation of hematopoietic stem cells and blasting in bone marrow. Despite drugs are used to treat the disease clinically, the influence of these drugs on leukemia cells’ biomechanical properties, which are closely related to complications like leukostasis or infiltration, is still unclear. Due to non-adherent and viscoelastic nature of leukemia cells, accurate measurement of their elastic modulus is still a challenging issue. In this study, we adopted rate-jump method together with optical tweezers indentation to accurately measure elastic modulus of leukemia cells K562 after phorbol 12-myristate 13-acetate (PMA), all-trans retinoic acid (ATRA), Cytoxan (CTX), and Dexamethasone (DEX) treatment, respectively. We found that compared to control sample, K562 cells treated by PMA showed nearly a threefold increase in elastic modulus. Transwell experiment results suggested that the K562 cells treated with PMA have the lowest migration capability. Besides, it was shown that the cytoskeleton protein gene α-tubulin and vimentin have a significant increase in expression after PMA treatment by qPCR. The results indicate that PMA has a significant influence on protein expression, stiffness, and migration ability of the leukemia cell K562, and may also play an important role in the leukostasis in leukemia.
DOI
Leukemia is a commonly seen disease caused by abnormal differentiation of hematopoietic stem cells and blasting in bone marrow. Despite drugs are used to treat the disease clinically, the influence of these drugs on leukemia cells’ biomechanical properties, which are closely related to complications like leukostasis or infiltration, is still unclear. Due to non-adherent and viscoelastic nature of leukemia cells, accurate measurement of their elastic modulus is still a challenging issue. In this study, we adopted rate-jump method together with optical tweezers indentation to accurately measure elastic modulus of leukemia cells K562 after phorbol 12-myristate 13-acetate (PMA), all-trans retinoic acid (ATRA), Cytoxan (CTX), and Dexamethasone (DEX) treatment, respectively. We found that compared to control sample, K562 cells treated by PMA showed nearly a threefold increase in elastic modulus. Transwell experiment results suggested that the K562 cells treated with PMA have the lowest migration capability. Besides, it was shown that the cytoskeleton protein gene α-tubulin and vimentin have a significant increase in expression after PMA treatment by qPCR. The results indicate that PMA has a significant influence on protein expression, stiffness, and migration ability of the leukemia cell K562, and may also play an important role in the leukostasis in leukemia.
DOI
Study of adhesivity of surfaces using rotational optical tweezers
Rahul V R, Dhanush Bhatt, Anand Dev Ranjan and Basudev Roy
Optical tweezers are powerful tools for high resolution study of surface properties. Such experiments are traditionally performed by studying the active or the brownian fluctuation of trapped particles in the X, Y and Z directions. Here we find that employing the fourth dimension, rotation, allows for sensitive and fast probing of the surface, and happen when birefringent microparticles are applied with circularly polarized light, thus called the Rotational Optical Tweezers. When the trapped birefringent microparticle is far away from the surface, the rotation rate is dependent only on the laser power. However, we find that if one traps close to a surface, the rotation rate goes to zero even at finite tweezers laser powers for some specific type of substrates. We suspect this to be due to the interaction between the substrate and the birefringent particle, keeping in mind that the faxen correction for this mode of rotation cannot increase beyond 1.2 times. We use this to probe some surfaces and find that there is no binding for hydrophobic ones but hydrophilic ones particularly tend to show a laser power threshold to start rotating. We calculate that the threshold energy of the tweezers is consistent with the Van der Waals potential energy, when the mode of interaction with the surface is purely physical. We also find that for chitosan, the mode of interaction is possibly different from Van der Waals. Further, we place the particle on the threshold and observe "stick-slip" kind of rotational behaviour.
DOI
Optical tweezers are powerful tools for high resolution study of surface properties. Such experiments are traditionally performed by studying the active or the brownian fluctuation of trapped particles in the X, Y and Z directions. Here we find that employing the fourth dimension, rotation, allows for sensitive and fast probing of the surface, and happen when birefringent microparticles are applied with circularly polarized light, thus called the Rotational Optical Tweezers. When the trapped birefringent microparticle is far away from the surface, the rotation rate is dependent only on the laser power. However, we find that if one traps close to a surface, the rotation rate goes to zero even at finite tweezers laser powers for some specific type of substrates. We suspect this to be due to the interaction between the substrate and the birefringent particle, keeping in mind that the faxen correction for this mode of rotation cannot increase beyond 1.2 times. We use this to probe some surfaces and find that there is no binding for hydrophobic ones but hydrophilic ones particularly tend to show a laser power threshold to start rotating. We calculate that the threshold energy of the tweezers is consistent with the Van der Waals potential energy, when the mode of interaction with the surface is purely physical. We also find that for chitosan, the mode of interaction is possibly different from Van der Waals. Further, we place the particle on the threshold and observe "stick-slip" kind of rotational behaviour.
DOI
Photoluminescence Activation of Organic Dyes via Optically Trapped Quantum Dots
Héctor Rodríguez-Rodríguez, María Acebrón, Francisco J. Iborra, J. Ricardo Arias-Gonzalez, Beatriz H. Juárez
Laser tweezers afford quantum dot (QD) manipulation for use as localized emitters. Here, we demonstrate fluorescence by radiative energy transfer from optically trapped colloidal QDs (donors) to fluorescent dyes (acceptors). To this end, we synthesized silica-coated QDs of different compositions and triggered their luminescence by simultaneous trapping and two-photon excitation in a microfluidic chamber filled with dyes. This strategy produces a near-field light source with great spatial maneuverability, which can be exploited to scan nanostructures. In this regard, we demonstrate induced photoluminescence of dye-labeled cells via optically trapped silica-coated colloidal QDs placed at their vicinity. Allocating nanoscale donors at controlled distances from a cell is an attractive concept in fluorescence microscopy because it dramatically reduces the number of excited dyes, which improves resolution by preventing interferences from the whole sample, while prolonging dye luminescence lifetime due to the lower power absorbed from the QDs.
DOI
Laser tweezers afford quantum dot (QD) manipulation for use as localized emitters. Here, we demonstrate fluorescence by radiative energy transfer from optically trapped colloidal QDs (donors) to fluorescent dyes (acceptors). To this end, we synthesized silica-coated QDs of different compositions and triggered their luminescence by simultaneous trapping and two-photon excitation in a microfluidic chamber filled with dyes. This strategy produces a near-field light source with great spatial maneuverability, which can be exploited to scan nanostructures. In this regard, we demonstrate induced photoluminescence of dye-labeled cells via optically trapped silica-coated colloidal QDs placed at their vicinity. Allocating nanoscale donors at controlled distances from a cell is an attractive concept in fluorescence microscopy because it dramatically reduces the number of excited dyes, which improves resolution by preventing interferences from the whole sample, while prolonging dye luminescence lifetime due to the lower power absorbed from the QDs.
DOI
Plasmofluidic Microlenses for Label-Free Optical Sorting of Exosomes
Xiangchao Zhu, Ahmet Cicek, Yixiang Li & Ahmet Ali Yanik
Optical chromatography is a powerful optofluidic technique enabling label-free fractionation of microscopic bioparticles from heterogenous mixtures. However, sophisticated instrumentation requirements for precise alignment of optical scattering and fluidic drag forces is a fundamental shortcoming of this technique. Here, we introduce a subwavelength thick (<200 nm) Optofluidic PlasmonIC (OPtIC) microlens that effortlessly achieves objective-free focusing and self-alignment of opposing optical scattering and fluidic drag forces for selective separation of exosome size bioparticles. Our optofluidic microlens provides a self-collimating mechanism for particle trajectories with a spatial dispersion that is inherently minimized by the optical gradient and radial fluidic drag forces working together to align the particles along the optical axis. We demonstrate that this facile platform facilitates complete separation of small size bioparticles (i.e., exosomes) from a heterogenous mixture through negative depletion and provides a robust selective separation capability for same size nanoparticles based on their differences in chemical composition. Unlike existing optical chromatography techniques that require complicated instrumentation (lasers, objectives and precise alignment stages), our OPtIC microlenses with a foot-print of 4 μm × 4 μm open up the possibility of multiplexed and high-throughput sorting of nanoparticles on a chip using low-cost broadband light sources.
DOI
Optical chromatography is a powerful optofluidic technique enabling label-free fractionation of microscopic bioparticles from heterogenous mixtures. However, sophisticated instrumentation requirements for precise alignment of optical scattering and fluidic drag forces is a fundamental shortcoming of this technique. Here, we introduce a subwavelength thick (<200 nm) Optofluidic PlasmonIC (OPtIC) microlens that effortlessly achieves objective-free focusing and self-alignment of opposing optical scattering and fluidic drag forces for selective separation of exosome size bioparticles. Our optofluidic microlens provides a self-collimating mechanism for particle trajectories with a spatial dispersion that is inherently minimized by the optical gradient and radial fluidic drag forces working together to align the particles along the optical axis. We demonstrate that this facile platform facilitates complete separation of small size bioparticles (i.e., exosomes) from a heterogenous mixture through negative depletion and provides a robust selective separation capability for same size nanoparticles based on their differences in chemical composition. Unlike existing optical chromatography techniques that require complicated instrumentation (lasers, objectives and precise alignment stages), our OPtIC microlenses with a foot-print of 4 μm × 4 μm open up the possibility of multiplexed and high-throughput sorting of nanoparticles on a chip using low-cost broadband light sources.
DOI
Optical vortex fiber laser based on modulation of transverse modes in two mode fiber
Dong Mao, Mingkun Li, Zhiwen He, Xiaoqi Cui, Hua Lu, Wending Zhang, Han Zhang, and Jianlin Zhao
Optical vortices, characterized by helical phase fronts, are usually generated outside the laser cavity using passive modulation methods. Here, we demonstrate an all-fiber laser to directly deliver mode-locked and continuous-wave vortex beams based on modulation of transverse modes in the two mode fiber. The mode couplers and reflectors for three schemes are long period fiber grating (LPFG) and fiber mirror, fiber taper and fiber Bragg grating, and LPFG and fiber Bragg grating, respectively. The laser is switchable between ±1 order vortex operations by tuning the intracavity polarization controller, and the optical vortex can directly work as an optical tweezer to manipulate rhenium diselenide nanosheets. The pulse duration at the mode-locked state is tunable from subpicoseconds to several picoseconds by spectral filters, and the maximum output power at the continuous-wave state exceeds 35 mW. The cost-effective all-fiber vortex laser is quite attractive for research of micromanipulation, spatiotemporal soliton, and optical communication.
DOI
Optical vortices, characterized by helical phase fronts, are usually generated outside the laser cavity using passive modulation methods. Here, we demonstrate an all-fiber laser to directly deliver mode-locked and continuous-wave vortex beams based on modulation of transverse modes in the two mode fiber. The mode couplers and reflectors for three schemes are long period fiber grating (LPFG) and fiber mirror, fiber taper and fiber Bragg grating, and LPFG and fiber Bragg grating, respectively. The laser is switchable between ±1 order vortex operations by tuning the intracavity polarization controller, and the optical vortex can directly work as an optical tweezer to manipulate rhenium diselenide nanosheets. The pulse duration at the mode-locked state is tunable from subpicoseconds to several picoseconds by spectral filters, and the maximum output power at the continuous-wave state exceeds 35 mW. The cost-effective all-fiber vortex laser is quite attractive for research of micromanipulation, spatiotemporal soliton, and optical communication.
DOI
Separation of chiral enantiomers by optical force and torque induced by tightly focused vector polarized hollow beams
Xingguang Liu, Junqing Li, Qiang Zhang and Mamo Gebeyehu Dirbeba
Enantioseparation is important for biology, chemistry and even pharmaceutical industries. We propose an approach for discriminating and separating chiral enantiomers by tightly focused vector polarized hollow beams, which possess a transverse spin angular momentum that can rotate the chiral particles along the transverse direction. We demonstrate the different optomechanical behaviours of the particles upon illumination with different vector polarized (azimuthally and radially) hollow beams by numerically calculating the optical force and spin torque. It is believed that this interesting approach may have potential applications in enantioseparation due to its simplicity and accessibility.
DOI
Enantioseparation is important for biology, chemistry and even pharmaceutical industries. We propose an approach for discriminating and separating chiral enantiomers by tightly focused vector polarized hollow beams, which possess a transverse spin angular momentum that can rotate the chiral particles along the transverse direction. We demonstrate the different optomechanical behaviours of the particles upon illumination with different vector polarized (azimuthally and radially) hollow beams by numerically calculating the optical force and spin torque. It is believed that this interesting approach may have potential applications in enantioseparation due to its simplicity and accessibility.
DOI
Friday, July 26, 2019
Surface Interactions of Gold Nanoparticles Optically Trapped against an Interface
Daniel Andrén, Nils Odebo Länk, Hana Šípová-Jungová, Steven Jones, Peter Johansson, Mikael Käll
Particles that diffuse in close proximity to a surface are expected to behave differently than in free solution because the surface interaction will influence a number of physical properties, including the hydrodynamic, optical, and thermal characteristics of the particle. Understanding the influence of such effects is particularly important in view of the increasing interest in laser tweezing of colloidal resonant nanoparticles for applications such as nanomotors and optical printing and for investigations of unconventional optical forces. Therefore, we used total internal reflection microscopy to probe the interaction between a glass surface and individual ∼100 nm gold nanoparticles trapped by laser tweezers. The results show that particles can be optically confined at controllable distances ranging between ∼30 and ∼90 nm from the surface, depending on the radiation pressure of the trapping laser and the ionic screening of the surrounding liquid. Moreover, the full particle–surface distance probability distribution can be obtained for single nanoparticles by analyzing temporal signal fluctuations. The experimental results are in excellent agreement with Brownian dynamics simulations that take the full force field and photothermal heating into account. At the observed particle–surface distances, translational friction coefficients increase by up to 60% compared to freely diffusing particles, whereas the rotational friction and thermal dissipation are much less affected. The methodology used here is general and can be adapted to a range of single nanoparticle–surface interaction investigations.
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Particles that diffuse in close proximity to a surface are expected to behave differently than in free solution because the surface interaction will influence a number of physical properties, including the hydrodynamic, optical, and thermal characteristics of the particle. Understanding the influence of such effects is particularly important in view of the increasing interest in laser tweezing of colloidal resonant nanoparticles for applications such as nanomotors and optical printing and for investigations of unconventional optical forces. Therefore, we used total internal reflection microscopy to probe the interaction between a glass surface and individual ∼100 nm gold nanoparticles trapped by laser tweezers. The results show that particles can be optically confined at controllable distances ranging between ∼30 and ∼90 nm from the surface, depending on the radiation pressure of the trapping laser and the ionic screening of the surrounding liquid. Moreover, the full particle–surface distance probability distribution can be obtained for single nanoparticles by analyzing temporal signal fluctuations. The experimental results are in excellent agreement with Brownian dynamics simulations that take the full force field and photothermal heating into account. At the observed particle–surface distances, translational friction coefficients increase by up to 60% compared to freely diffusing particles, whereas the rotational friction and thermal dissipation are much less affected. The methodology used here is general and can be adapted to a range of single nanoparticle–surface interaction investigations.
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Regulating, measuring and modelling the viscoelasticity of bacterial biofilms
Samuel G.V. Charlton, Michael A. White, Saikat Jana, Lucy E. Eland, Pahala Gedara Jayathilake, J. Grant Burgess, Jinju Chen, Anil Wipat, Thomas P. Curtis
Biofilms occur in a broad range of environments with heterogeneous physico-chemical conditions, such as in bio-remediation plants, on surfaces of biomedical implants and in the lungs of cystic fibrosis patients. In these scenarios, biofilms are subjected to shear forces, but the mechanical integrity of these aggregates often prevents their disruption or dispersal. Their physical robustness is the result of the multiple bio-polymers secreted by constituent microbial cells which are also responsible for numerous biological functions. A better understanding of the role of these bio-polymers and their response to dynamic forces is therefore crucial for understanding the interplay between biofilm structure and function. In this manuscript, we review experimental techniques in rheology, which help quantify the viscoelasticity of biofilms, and modelling approaches from soft matter physics, that can assist our understanding of the rheological properties. We describe how these methods could be combined with synthetic biology approaches to control and investigate the effects of secreted polymers on the physical properties of biofilms. We argue that without an integrated approach of the three disciplines the links between genetics, composition and interaction of matrix biopolymers and the viscoelastic properties of biofilms will be much harder to uncover.
Biofilms occur in a broad range of environments with heterogeneous physico-chemical conditions, such as in bio-remediation plants, on surfaces of biomedical implants and in the lungs of cystic fibrosis patients. In these scenarios, biofilms are subjected to shear forces, but the mechanical integrity of these aggregates often prevents their disruption or dispersal. Their physical robustness is the result of the multiple bio-polymers secreted by constituent microbial cells which are also responsible for numerous biological functions. A better understanding of the role of these bio-polymers and their response to dynamic forces is therefore crucial for understanding the interplay between biofilm structure and function. In this manuscript, we review experimental techniques in rheology, which help quantify the viscoelasticity of biofilms, and modelling approaches from soft matter physics, that can assist our understanding of the rheological properties. We describe how these methods could be combined with synthetic biology approaches to control and investigate the effects of secreted polymers on the physical properties of biofilms. We argue that without an integrated approach of the three disciplines the links between genetics, composition and interaction of matrix biopolymers and the viscoelastic properties of biofilms will be much harder to uncover.
In Situ Microscopic Observation on Surface Kinetics in Optical Trapping-Induced Crystal Growth: Step Formation, Wetting Transition, and Nonclassical Growth
Hiromasa Niinomi, Teruki Sugiyama, Toru Ujihara, Suxia Guo, Jun Nozawa, Junpei Okada, Takashige Omatsu, Satoshi Uda
Optical trapping-induced crystallization (OTIC) has provided significant impacts on the control of crystallization. Although consecutive research studies have implied that the optical potential formed on the crystalline surface by light propagation contributes to the crystal growth by observing bulk crystal growth, direct observation from the viewpoint of the surface kinetics represented as Burton, Cabrera, and Frank theory is still lacking. Here, we directly show the surface state modification by microscopically observing step formation/dissolution and wetting transition of a solution thin layer over a sodium chlorate crystalline surface upon turning on/off the laser irradiation. Irradiating/stopping of the laser irradiation to the crystal led to the formation/dissociation of several tens of micron-sized islands constructed by bunched steps. It was also found that the wetting transition of the solution thin film over the entire crystal surface took place simultaneously with the laser irradiation, evidencing that the interfacial potential was modified from repulsive to attractive potential by light propagation. Moreover, the observation visualized nonclassical crystal growth like the cluster assimilation scenario. Our observation not only leads to a deeper understanding of the mechanism of OTIC but also can provide the opportunity to reach unusual crystal growth phenomena beyond the classical limit and has implications for crystal growth modified by an external field.
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Optical trapping of inorganic oxide nanosheets colloidally dispersed in water: effects of refractivity
Teruyuki Nakato, Kanji Saito, Akira Ikeda, Yuki Higashi, Yasutaka Suzuki, Jun Kawamata
Optical trapping of three oxide nanosheets prepared by exfoliation of layered lepidocrocite-type titanate, hexaniobate, and fluorohectorite was carried out by the irradiation of linearly polarized laser beam, and their trapping behavior was compared in relation to the refractivity of oxide nanosheets. All of the nanosheets showed similar two-stage trapping process in enough dilute colloids where single nanosheets with their area around 50–100 µm2 were trapped. The first stage was arrestment of a single nanosheet by the laser beam at the focus and orientation with its in-plane direction parallel to the propagation direction of the incident laser beam. The second stage was the rotation of arrested nanosheet with keeping the orientation parallel to the propagation direction of the laser beam to reach the alignment of nanosheet edge (longitudinal) direction in parallel to the polarization direction of the incident irradiation. Higher trapping efficiency, evaluated by trapping with weaker laser beam and shorter time for the completion of orientational change, was found for the nanosheet species with larger refractive index.
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Optical trapping of three oxide nanosheets prepared by exfoliation of layered lepidocrocite-type titanate, hexaniobate, and fluorohectorite was carried out by the irradiation of linearly polarized laser beam, and their trapping behavior was compared in relation to the refractivity of oxide nanosheets. All of the nanosheets showed similar two-stage trapping process in enough dilute colloids where single nanosheets with their area around 50–100 µm2 were trapped. The first stage was arrestment of a single nanosheet by the laser beam at the focus and orientation with its in-plane direction parallel to the propagation direction of the incident laser beam. The second stage was the rotation of arrested nanosheet with keeping the orientation parallel to the propagation direction of the laser beam to reach the alignment of nanosheet edge (longitudinal) direction in parallel to the polarization direction of the incident irradiation. Higher trapping efficiency, evaluated by trapping with weaker laser beam and shorter time for the completion of orientational change, was found for the nanosheet species with larger refractive index.
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Polarization-dependent non-uniform rotation rates of rhombohedral calcite
Catherine M. Herne, Johanna R. Levey, and Tom R. McCausland
We demonstrate the polarization-dependent torque on rhombohedral calcite in an optical trap. Our precipitate technique produces regular crystals approximately 10μm on all edges. The regularity of the crystal shape makes it possible to visually identify the optical axis as well as the orientation of the polarization axes. When a rhombohedral crystal is trapped in an elliptically polarized beam, it orients itself with its optic axis approximately parallel to the beam axis. While in this orientation, the total torque increases and decreases relative to three extraordinary and ordinary axes of the crystal. We measure this axis-dependent calcite rotation through video analysis and model the dependence of the torque on the crystal orientation. The ability to predict the motion of calcite gives an analytical tool for applications such as fluid stirring or “lab on a chip” systems.
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We demonstrate the polarization-dependent torque on rhombohedral calcite in an optical trap. Our precipitate technique produces regular crystals approximately 10μm on all edges. The regularity of the crystal shape makes it possible to visually identify the optical axis as well as the orientation of the polarization axes. When a rhombohedral crystal is trapped in an elliptically polarized beam, it orients itself with its optic axis approximately parallel to the beam axis. While in this orientation, the total torque increases and decreases relative to three extraordinary and ordinary axes of the crystal. We measure this axis-dependent calcite rotation through video analysis and model the dependence of the torque on the crystal orientation. The ability to predict the motion of calcite gives an analytical tool for applications such as fluid stirring or “lab on a chip” systems.
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Monitoring of individual bacteria using electro-photonic traps
Donato Conteduca, Giuseppe Brunetti, Francesco Dell’Olio, Mario N. Armenise, Thomas F. Krauss, and Caterina Ciminelli
Antimicrobial resistance (AMR) describes the ability of bacteria to become immune to antimicrobial treatments. Current testing for AMR is based on culturing methods that are very slow because they assess the average response of billions of bacteria. In principle, if tests were available that could assess the response of individual bacteria, they could be much faster. Here, we propose an electro-photonic approach for the analysis and the monitoring of susceptibility at the single-bacterium level. Our method employs optical tweezers based on photonic crystal cavities for the trapping of individual bacteria. While the bacteria are trapped, antibiotics can be added to the medium and the corresponding changes in the optical properties and motility of the bacteria be monitored via changes of the resonance wavelength and transmission. Furthermore, the proposed assay is able to monitor the impedance of the medium surrounding the bacterium, which allows us to record changes in metabolic rate in response to the antibiotic challenge. For example, our simulations predict a variation in measurable electrical current of up to 40% between dead and live bacteria. The proposed platform is the first, to our knowledge, that allows the parallel study of both the optical and the electrical response of individual bacteria to antibiotic challenge. Our platform opens up new lines of enquiry for monitoring the response of bacteria and it could lead the way towards the dissemination of a new generation of antibiogram study, which is relevant for the development of a point-of-care AMR diagnostics.
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Antimicrobial resistance (AMR) describes the ability of bacteria to become immune to antimicrobial treatments. Current testing for AMR is based on culturing methods that are very slow because they assess the average response of billions of bacteria. In principle, if tests were available that could assess the response of individual bacteria, they could be much faster. Here, we propose an electro-photonic approach for the analysis and the monitoring of susceptibility at the single-bacterium level. Our method employs optical tweezers based on photonic crystal cavities for the trapping of individual bacteria. While the bacteria are trapped, antibiotics can be added to the medium and the corresponding changes in the optical properties and motility of the bacteria be monitored via changes of the resonance wavelength and transmission. Furthermore, the proposed assay is able to monitor the impedance of the medium surrounding the bacterium, which allows us to record changes in metabolic rate in response to the antibiotic challenge. For example, our simulations predict a variation in measurable electrical current of up to 40% between dead and live bacteria. The proposed platform is the first, to our knowledge, that allows the parallel study of both the optical and the electrical response of individual bacteria to antibiotic challenge. Our platform opens up new lines of enquiry for monitoring the response of bacteria and it could lead the way towards the dissemination of a new generation of antibiogram study, which is relevant for the development of a point-of-care AMR diagnostics.
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Review of optical tweezers in vacuum
Nan Li, Xun-min Zhu, Wen-qiang Li, Zhen-hai Fu, Meng-zhu Hu, Hui-zhu Hu
As a versatile tool for trapping and manipulating neutral particles, optical tweezers have been studied in a broad range of fields such as molecular biology, nanotechnology, and experimentally physics since Arthur Ashkin pioneered the field in the early 1970s. By levitating the “sensor” with a laser beam instead of adhering it to solid components, excellent environmental decoupling is achieved. Furthermore, unlike levitating particles in liquid or air, optical tweezers operating in vacuum are isolated from environmental thermal noise, thus eliminating the primary source of dissipation present for most inertial sensors. This attracted great attention in both fundamental and applied physics. In this paper we review the history and the basic concepts of optical tweezers in vacuum and provide an overall understanding of the field.
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As a versatile tool for trapping and manipulating neutral particles, optical tweezers have been studied in a broad range of fields such as molecular biology, nanotechnology, and experimentally physics since Arthur Ashkin pioneered the field in the early 1970s. By levitating the “sensor” with a laser beam instead of adhering it to solid components, excellent environmental decoupling is achieved. Furthermore, unlike levitating particles in liquid or air, optical tweezers operating in vacuum are isolated from environmental thermal noise, thus eliminating the primary source of dissipation present for most inertial sensors. This attracted great attention in both fundamental and applied physics. In this paper we review the history and the basic concepts of optical tweezers in vacuum and provide an overall understanding of the field.
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Microrheological quantification of viscoelastic properties with photonic force optical coherence elastography
Nichaluk Leartprapun, Yuechuan Lin, and Steven G. Adie
Photonic force optical coherence elastography (PF-OCE) is a new approach for volumetric characterization of microscopic mechanical properties of three-dimensional viscoelastic medium. It is based on measurements of the complex mechanical response of embedded micro-beads to harmonically modulated radiation-pressure force from a weakly-focused beam. Here, we utilize the Generalized Stokes-Einstein relation to reconstruct local complex shear modulus in polyacrylamide gels by combining PF-OCE measurements of bead mechanical responses and experimentally measured depth-resolved radiation-pressure force profile of our forcing beam. Data exclusion criteria for quantitative PF-OCE based on three noise-related parameters were identified from the analysis of measurement noise at key processing steps. Shear storage modulus measured by quantitative PF-OCE was found to be in good agreement with standard shear rheometry, whereas shear loss modulus was in agreement with previously published atomic force microscopy results. The analysis and results presented here may serve to inform practical, application-specific implementations of PF-OCE, and establish the technique as a viable tool for quantitative mechanical microscopy.
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Photonic force optical coherence elastography (PF-OCE) is a new approach for volumetric characterization of microscopic mechanical properties of three-dimensional viscoelastic medium. It is based on measurements of the complex mechanical response of embedded micro-beads to harmonically modulated radiation-pressure force from a weakly-focused beam. Here, we utilize the Generalized Stokes-Einstein relation to reconstruct local complex shear modulus in polyacrylamide gels by combining PF-OCE measurements of bead mechanical responses and experimentally measured depth-resolved radiation-pressure force profile of our forcing beam. Data exclusion criteria for quantitative PF-OCE based on three noise-related parameters were identified from the analysis of measurement noise at key processing steps. Shear storage modulus measured by quantitative PF-OCE was found to be in good agreement with standard shear rheometry, whereas shear loss modulus was in agreement with previously published atomic force microscopy results. The analysis and results presented here may serve to inform practical, application-specific implementations of PF-OCE, and establish the technique as a viable tool for quantitative mechanical microscopy.
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Thursday, July 25, 2019
An electro-osmotic microfluidic system to characterize cancer cell migration under confinement
T. H. Hui , W. C. Cho , H. W. Fong , M. Yu , K. W. Kwan , K. C. Ngan , K. H. Wong , Y. Tan , S. Yao , H. Jiang , Z. Gu and Y. Lin
We have developed a novel electro-osmotic microfluidic system to apply precisely controlled osmolarity gradients to cancer cells in micro-channels. We observed that albeit adhesion is not required for cells to migrate in such a confined microenvironment, the migrating velocity of cells is strongly influenced by the interactions between the cells and the channel wall, with a stronger adhesion leading to diminished cell motility. Furthermore, through examining more than 20 different types of cancer cells, we found a linear positive correlation between the protein concentration of the aquaporin-4 (AQP4) and the cell migrating speed. Knockdown of AQP4 in invasive re-populated cancer stem cells reduced their migration capability down to the level that is comparable to their parental cancer cells. Interestingly, these observations can all be quantitatively explained by the osmotic engine model where the cell movement is assumed to be driven by cross-membrane ion/water transport, while adhesion acts as a frictional resistance against the cell motility. By providing versatile and controllable features in regulating and characterizing the migration capability of cells, our system may serve as a useful tool in quantifying how cell motility is influenced by different physical and biochemical factors, as well as elucidating the mechanisms behind, in the future.
We have developed a novel electro-osmotic microfluidic system to apply precisely controlled osmolarity gradients to cancer cells in micro-channels. We observed that albeit adhesion is not required for cells to migrate in such a confined microenvironment, the migrating velocity of cells is strongly influenced by the interactions between the cells and the channel wall, with a stronger adhesion leading to diminished cell motility. Furthermore, through examining more than 20 different types of cancer cells, we found a linear positive correlation between the protein concentration of the aquaporin-4 (AQP4) and the cell migrating speed. Knockdown of AQP4 in invasive re-populated cancer stem cells reduced their migration capability down to the level that is comparable to their parental cancer cells. Interestingly, these observations can all be quantitatively explained by the osmotic engine model where the cell movement is assumed to be driven by cross-membrane ion/water transport, while adhesion acts as a frictional resistance against the cell motility. By providing versatile and controllable features in regulating and characterizing the migration capability of cells, our system may serve as a useful tool in quantifying how cell motility is influenced by different physical and biochemical factors, as well as elucidating the mechanisms behind, in the future.
Curvature- and Phase-Induced Protein Sorting Quantified in Transfected Cell-Derived Giant Vesicles
Guillermo Moreno-Pescador, Christoffer D. Florentsen, Henrik Østbye, Stine L. Sønder, Theresa L. Boye, Emilie L. Veje, Alexander K. Sonne, Szabolcs Semsey, Jesper Nylandsted, Robert Daniels, Poul Martin Bendix
Eukaryotic cells possess a dynamic network of membranes that vary in lipid composition. To perform numerous biological functions, cells modulate their shape and the lateral organization of proteins associated with membranes. The modulation is generally facilitated by physical cues that recruit proteins to specific regions of the membrane. Analyzing these cues is difficult due to the complexity of the membrane conformations that exist in cells. Here, we examine how different types of membrane proteins respond to changes in curvature and to lipid phases found in the plasma membrane. By using giant plasma membrane vesicles derived from transfected cells, the proteins were positioned in the correct orientation and the analysis was performed in plasma membranes with a biological composition. Nanoscale membrane curvatures were generated by extracting nanotubes from these vesicles with an optical trap. The viral membrane protein neuraminidase was not sensitive to curvature, but it did exhibit strong partitioning (coefficient of K = 0.16) disordered membrane regions. In contrast, the membrane repair protein annexin 5 showed a preference for nanotubes with a density up to 10–15 times higher than that on the more flat vesicle membrane. The investigation of nanoscale effects in isolated plasma membranes provides a quantitative platform for studying peripheral and integral membrane proteins in their natural environment.
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Eukaryotic cells possess a dynamic network of membranes that vary in lipid composition. To perform numerous biological functions, cells modulate their shape and the lateral organization of proteins associated with membranes. The modulation is generally facilitated by physical cues that recruit proteins to specific regions of the membrane. Analyzing these cues is difficult due to the complexity of the membrane conformations that exist in cells. Here, we examine how different types of membrane proteins respond to changes in curvature and to lipid phases found in the plasma membrane. By using giant plasma membrane vesicles derived from transfected cells, the proteins were positioned in the correct orientation and the analysis was performed in plasma membranes with a biological composition. Nanoscale membrane curvatures were generated by extracting nanotubes from these vesicles with an optical trap. The viral membrane protein neuraminidase was not sensitive to curvature, but it did exhibit strong partitioning (coefficient of K = 0.16) disordered membrane regions. In contrast, the membrane repair protein annexin 5 showed a preference for nanotubes with a density up to 10–15 times higher than that on the more flat vesicle membrane. The investigation of nanoscale effects in isolated plasma membranes provides a quantitative platform for studying peripheral and integral membrane proteins in their natural environment.
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Stable Casimir equilibria and quantum trapping
Rongkuo Zhao, Lin Li, Sui Yang, Wei Bao, Yang Xia, Paul Ashby, Yuan Wang, Xiang Zhang
The Casimir interaction between two parallel metal plates in close proximity is usually thought of as an attractive interaction. By coating one object with a low–refractive index thin film, we show that the Casimir interaction between two objects of the same material can be reversed at short distances and preserved at long distances so that two objects can remain without contact at a specific distance. With such a stable Casimir equilibrium, we experimentally demonstrate passive Casimir trapping of an object in the vicinity of another at the nanometer scale, without requiring any external energy input. This stable Casimir equilibrium and quantum trapping can be used as a platform for a variety of applications such as contact-free nanomachines, ultrasensitive force sensors, and nanoscale manipulations.
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The Casimir interaction between two parallel metal plates in close proximity is usually thought of as an attractive interaction. By coating one object with a low–refractive index thin film, we show that the Casimir interaction between two objects of the same material can be reversed at short distances and preserved at long distances so that two objects can remain without contact at a specific distance. With such a stable Casimir equilibrium, we experimentally demonstrate passive Casimir trapping of an object in the vicinity of another at the nanometer scale, without requiring any external energy input. This stable Casimir equilibrium and quantum trapping can be used as a platform for a variety of applications such as contact-free nanomachines, ultrasensitive force sensors, and nanoscale manipulations.
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Three-dimensional position measurement of a levitated nanoparticle in a vacuum by a Dove prism
Yu Zheng and Fangwen Sun
Forward-scattering-light interferometry has become the most commonly used position detection scheme in optical levitation systems. Usually, three-set detectors are required to obtain the three-dimensional motion information. Here, we simplify the three-set detectors to one set by inserting a Dove prism. We investigate the role of a Dove prism in the position measurement process with an optical levitation system in vacuum. The relationship between the power spectral density and the rotation angle of a Dove prism is experimentally demonstrated and analyzed. This work shows that the Dove prism can greatly reduce the complexity of the experimental setup, which can be applied to compact optical levitation systems for studies in metrology, quantum physics, and biology.
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Forward-scattering-light interferometry has become the most commonly used position detection scheme in optical levitation systems. Usually, three-set detectors are required to obtain the three-dimensional motion information. Here, we simplify the three-set detectors to one set by inserting a Dove prism. We investigate the role of a Dove prism in the position measurement process with an optical levitation system in vacuum. The relationship between the power spectral density and the rotation angle of a Dove prism is experimentally demonstrated and analyzed. This work shows that the Dove prism can greatly reduce the complexity of the experimental setup, which can be applied to compact optical levitation systems for studies in metrology, quantum physics, and biology.
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2 × 2 microparticles curvilinear transport channel based on dual self-accelerating beams
Zhihai Liu, Tong Wang, Yu Zhang, Xiaoyun Tang, Wenjie Su, Wanming Dong, Siyu Lin, Xinghua Yang, Jianzhong Zhang, Jun Yang, and Libo Yuan
We propose and demonstrate a 2 × 2 microparticles curvilinear transport channel based on a dual self-accelerating beam generator. The device is composed of a dual-core fiber, a hollow capillary fiber, and a coreless silica fiber. The dual self-accelerating beams produced by the device propagate along the curvilinear trajectory due to the transverse accelerating property and then cross at the front of the fiber probe. The experimental results show that the yeast cell is transported along the curvilinear trajectory. By adjusting the optical power ratio of dual beams, we may control and ensure the yeast cell steers at the cross point. The proposed 2 × 2 curvilinear microparticles transport channel based on dual self-accelerating beams can realize microparticles sorting and obstacle avoidance, which means that it would be a useful tool in biology and colloidal science.
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We propose and demonstrate a 2 × 2 microparticles curvilinear transport channel based on a dual self-accelerating beam generator. The device is composed of a dual-core fiber, a hollow capillary fiber, and a coreless silica fiber. The dual self-accelerating beams produced by the device propagate along the curvilinear trajectory due to the transverse accelerating property and then cross at the front of the fiber probe. The experimental results show that the yeast cell is transported along the curvilinear trajectory. By adjusting the optical power ratio of dual beams, we may control and ensure the yeast cell steers at the cross point. The proposed 2 × 2 curvilinear microparticles transport channel based on dual self-accelerating beams can realize microparticles sorting and obstacle avoidance, which means that it would be a useful tool in biology and colloidal science.
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Temperature Measurement in Plasmonic Nanoapertures Used for Optical Trapping
Quanbo Jiang, Benoît Rogez, Jean-Benoît Claude, Guillaume Baffou, Jérôme Wenger
Plasmonic nanoapertures generate strong field gradients enabling efficient optical trapping of nano-objects. However, because the infrared laser used for trapping is also partly absorbed into the metal leading to Joule heating, plasmonic nano-optical tweezers face the issue of local temperature increase. Here, we develop three independent methods based on molecular fluorescence to quantify the temperature increase induced by a 1064 nm trapping beam focused on single and double nanoholes milled in gold films. We show that the temperature in the nanohole can be increased by 10 °C even at the moderate intensities of 2 mW/μm2 used for nano-optical trapping. The temperature gain is found to be largely governed by the ohmic losses into the metal layer, independently of the aperture size, double-nanohole gap, or laser polarization. The techniques developed therein can be readily extended to other structures to improve our understanding of nano-optical tweezers and explore heat-controlled chemical reactions in nanoapertures.
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Plasmonic nanoapertures generate strong field gradients enabling efficient optical trapping of nano-objects. However, because the infrared laser used for trapping is also partly absorbed into the metal leading to Joule heating, plasmonic nano-optical tweezers face the issue of local temperature increase. Here, we develop three independent methods based on molecular fluorescence to quantify the temperature increase induced by a 1064 nm trapping beam focused on single and double nanoholes milled in gold films. We show that the temperature in the nanohole can be increased by 10 °C even at the moderate intensities of 2 mW/μm2 used for nano-optical trapping. The temperature gain is found to be largely governed by the ohmic losses into the metal layer, independently of the aperture size, double-nanohole gap, or laser polarization. The techniques developed therein can be readily extended to other structures to improve our understanding of nano-optical tweezers and explore heat-controlled chemical reactions in nanoapertures.
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Unique transmembrane domain interactions differentially modulate integrin αvβ3 and αIIbβ3 function
Rustem I. Litvinov, Marco Mravic, Hua Zhu, John W. Weisel, William F. DeGrado, and Joel S. Bennett
Lateral transmembrane (TM) helix–helix interactions between single-span membrane proteins play an important role in the assembly and signaling of many cell-surface receptors. Often, these helices contain two highly conserved yet distinct interaction motifs, arranged such that the motifs cannot be engaged simultaneously. However, there is sparse experimental evidence that dual-engagement mechanisms play a role in biological signaling. Here, we investigate the function of the two conserved interaction motifs in the TM domain of the integrin β3-subunit. The first motif uses reciprocating “large-large-small” amino acid packing to mediate the interaction of the β3 and αIIb TM domains and maintain the inactive resting conformation of the platelet integrin αIIbβ3. The second motif, S-x3-A-x3-I, is a variant of the classical “G-x3-G” motif. Using site-directed mutagenesis, optical trap-based force spectroscopy, and molecular modeling, we show that S-x3-A-x3-I does not engage αIIb but rather mediates the interaction of the β3 TM domain with the TM domain of the αv-subunit of the integrin αvβ3. Like αIIbβ3, αvβ3 on circulating platelets is inactive, and in the absence of platelet stimulation is unable to interact with components of the subendothelial matrix. However, disrupting any residue in the β3 S-x3-A-x3-I motif by site-directed mutations is sufficient to induce αvβ3 binding to the αvβ3 ligand osteopontin and to the monoclonal antibody WOW-1. Thus, the β3-integrin TM domain is able to engage in two mutually exclusive interactions that produce alternate α-subunit pairing, creating two integrins with distinct biological functions.
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Lateral transmembrane (TM) helix–helix interactions between single-span membrane proteins play an important role in the assembly and signaling of many cell-surface receptors. Often, these helices contain two highly conserved yet distinct interaction motifs, arranged such that the motifs cannot be engaged simultaneously. However, there is sparse experimental evidence that dual-engagement mechanisms play a role in biological signaling. Here, we investigate the function of the two conserved interaction motifs in the TM domain of the integrin β3-subunit. The first motif uses reciprocating “large-large-small” amino acid packing to mediate the interaction of the β3 and αIIb TM domains and maintain the inactive resting conformation of the platelet integrin αIIbβ3. The second motif, S-x3-A-x3-I, is a variant of the classical “G-x3-G” motif. Using site-directed mutagenesis, optical trap-based force spectroscopy, and molecular modeling, we show that S-x3-A-x3-I does not engage αIIb but rather mediates the interaction of the β3 TM domain with the TM domain of the αv-subunit of the integrin αvβ3. Like αIIbβ3, αvβ3 on circulating platelets is inactive, and in the absence of platelet stimulation is unable to interact with components of the subendothelial matrix. However, disrupting any residue in the β3 S-x3-A-x3-I motif by site-directed mutations is sufficient to induce αvβ3 binding to the αvβ3 ligand osteopontin and to the monoclonal antibody WOW-1. Thus, the β3-integrin TM domain is able to engage in two mutually exclusive interactions that produce alternate α-subunit pairing, creating two integrins with distinct biological functions.
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Bacterial Single Cell Whole Transcriptome Amplification in Microfluidic Platform Shows Putative Gene Expression Heterogeneity
Yuguang Liu, Patricio Jeraldo, Jin Sung Jang, Jin Sung Jang
Single cell RNA sequencing is a technology that provides the capability of analyzing the transcriptome of a single cell from a population. So far, single cell RNA sequencing has been focused mostly on human cells due to the larger starting amount of RNA template for subsequent amplification. One of the major challenges of applying single cell RNA sequencing to microbial cells is to amplify the femtograms of the RNA template to obtain sufficient material for downstream sequencing with minimal contamination. To achieve this goal, efforts have been focused on multiround RNA amplification, but would introduce additional contamination and bias. In this work, we for the first time coupled a microfluidic platform with multiple displacement amplification technology to perform single cell whole transcriptome amplification and sequencing of Porphyromonas somerae, a microbe of interest in endometrial cancer, as a proof-of-concept demonstration of using single cell RNA sequencing tool to unveil gene expression heterogeneity in single microbial cells. Our results show that the bacterial single-cell gene expression regulation is distinct across different cells, supporting widespread heterogeneity.
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Single cell RNA sequencing is a technology that provides the capability of analyzing the transcriptome of a single cell from a population. So far, single cell RNA sequencing has been focused mostly on human cells due to the larger starting amount of RNA template for subsequent amplification. One of the major challenges of applying single cell RNA sequencing to microbial cells is to amplify the femtograms of the RNA template to obtain sufficient material for downstream sequencing with minimal contamination. To achieve this goal, efforts have been focused on multiround RNA amplification, but would introduce additional contamination and bias. In this work, we for the first time coupled a microfluidic platform with multiple displacement amplification technology to perform single cell whole transcriptome amplification and sequencing of Porphyromonas somerae, a microbe of interest in endometrial cancer, as a proof-of-concept demonstration of using single cell RNA sequencing tool to unveil gene expression heterogeneity in single microbial cells. Our results show that the bacterial single-cell gene expression regulation is distinct across different cells, supporting widespread heterogeneity.
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Tuesday, July 23, 2019
Cold Damping of an Optically Levitated Nanoparticle to Microkelvin Temperatures
Felix Tebbenjohanns, Martin Frimmer, Andrei Militaru, Vijay Jain, and Lukas Novotny
We implement a cold-damping scheme to cool one mode of the center-of-mass motion of an optically levitated nanoparticle in ultrahigh vacuum (10−8 mbar) from room temperature to a record-low temperature of 100μK. The measured temperature dependence on the feedback gain and thermal decoherence rate is in excellent agreement with a parameter-free model. For the first time, we determine the imprecision-backaction product for a levitated optomechanical system and discuss the resulting implications for ground-state cooling of an optically levitated nanoparticle.
We implement a cold-damping scheme to cool one mode of the center-of-mass motion of an optically levitated nanoparticle in ultrahigh vacuum (10−8 mbar) from room temperature to a record-low temperature of 100μK. The measured temperature dependence on the feedback gain and thermal decoherence rate is in excellent agreement with a parameter-free model. For the first time, we determine the imprecision-backaction product for a levitated optomechanical system and discuss the resulting implications for ground-state cooling of an optically levitated nanoparticle.
Strong light confinement and gradient force in parallel infinite-width monolayer graphene pairs
Chunyu Lu, Zheng-Da Hu, Jin Cui, Jicheng Wang and Liang Pan
We study high light confinement, field enhancement, and strong gradient force between graphene nanoribbons. Influence of the wavelength of incident light on the gradient force, which is rare in previous studies, is presented. Results of light field confinement are achieved, which are much better than those in the slot waveguides based on artificial hyperbolic metamaterials. The propagation length and enhancement ratio can be up to 79.5 μm and 16, respectively. It is worth mentioning that the light confinement ratio can reach an astonishing 97%. Finally, we analyze the gradient force of different intensity in terms of the electric field.
DOI
We study high light confinement, field enhancement, and strong gradient force between graphene nanoribbons. Influence of the wavelength of incident light on the gradient force, which is rare in previous studies, is presented. Results of light field confinement are achieved, which are much better than those in the slot waveguides based on artificial hyperbolic metamaterials. The propagation length and enhancement ratio can be up to 79.5 μm and 16, respectively. It is worth mentioning that the light confinement ratio can reach an astonishing 97%. Finally, we analyze the gradient force of different intensity in terms of the electric field.
DOI
Photothermal biological effects of monomeric erythrocyte using optical tweezers
Hao Lu, Ying Wu, Wenjing Xie, Qi Tang, Caiqin Han, and Ying Liu
The changes of mechanical properties and biological activities of monomeric erythrocytes are studied using optical tweezers micromanipulation technology. Firstly, the mechanical properties of irradiated erythrocyte membranes are obtained. Weaker power laser irradiation can delay the decay of the mechanical properties of erythrocytes and promote the biological activity of erythrocytes, while higher power laser irradiation damages erythrocytes. The stronger the laser irradiation is, the more obvious and rapid the damage will be. The temperature of the cell surface will be changed by regulating the laser power and irradiation time, so the biological functions of erythrocyte can be controlled. Secondly, the finite element simulation of the temperature change on the cell surface under the condition of laser irradiation is carried out using simulation software, and the precise temperature of the cell surface irradiated cumulatively by a laser with different powers is obtained. Finally, the processes of abscission, unfolding, and denaturation of hemoglobins in erythrocytes at different temperatures due to the photothermal effect are analyzed using the model. The mechanism of laser irradiation on the elasticity of erythrocyte membranes is also obtained.
DOI
The changes of mechanical properties and biological activities of monomeric erythrocytes are studied using optical tweezers micromanipulation technology. Firstly, the mechanical properties of irradiated erythrocyte membranes are obtained. Weaker power laser irradiation can delay the decay of the mechanical properties of erythrocytes and promote the biological activity of erythrocytes, while higher power laser irradiation damages erythrocytes. The stronger the laser irradiation is, the more obvious and rapid the damage will be. The temperature of the cell surface will be changed by regulating the laser power and irradiation time, so the biological functions of erythrocyte can be controlled. Secondly, the finite element simulation of the temperature change on the cell surface under the condition of laser irradiation is carried out using simulation software, and the precise temperature of the cell surface irradiated cumulatively by a laser with different powers is obtained. Finally, the processes of abscission, unfolding, and denaturation of hemoglobins in erythrocytes at different temperatures due to the photothermal effect are analyzed using the model. The mechanism of laser irradiation on the elasticity of erythrocyte membranes is also obtained.
DOI
Photon momentum induced precision small forces: a static and dynamic check
Eberhard Manske, Thomas Fröhlich and Suren Vasilyan
Practical means of generation and calibration of the small precision forces in static and dynamic regimes around 1 Hz by the usage of radiation pressure effect from 1 W continuous wave visible (diode) laser light is presented. The additive effect of the transfer of photon momentum, caused by non-overlapping multiply reflecting laser beam locked within quasi-passive and/or active macroscopic cavity system, is employed. The effective laser power (partially trapped experimentally) is amplified such that the optically generated forces are increased from hundreds of pN up to sub-µN level. The results presented in this paper should be seen as a means for extending the edge of practically verifiable lower limits of SI-traceable force metrology.
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Practical means of generation and calibration of the small precision forces in static and dynamic regimes around 1 Hz by the usage of radiation pressure effect from 1 W continuous wave visible (diode) laser light is presented. The additive effect of the transfer of photon momentum, caused by non-overlapping multiply reflecting laser beam locked within quasi-passive and/or active macroscopic cavity system, is employed. The effective laser power (partially trapped experimentally) is amplified such that the optically generated forces are increased from hundreds of pN up to sub-µN level. The results presented in this paper should be seen as a means for extending the edge of practically verifiable lower limits of SI-traceable force metrology.
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Resonant dielectric metasurfaces: active tuning and nonlinear effects
Chengjun Zou, Jürgen Sautter, Frank Setzpfandt and Isabelle Staude
Resonant dielectric metasurfaces were extensively studied in the linear and static regime of operation, targeting mainly wavefront shaping, polarization control and spectral filtering applications. Recently, an increasing amount of research focused on active tuning and nonlinear effects of these metasurfaces, unveiling their potential for novel nonlinear and reconfigurable optical devices. These may find many applications in imaging systems, compact adaptive optical systems, beam steering, holographic displays, and quantum optics, to just name a few. This review provides an overview of the recent progress in this field. Following a general introduction to resonant dielectric metasurfaces, the current state-of-the-art regarding the enhancement and tailoring of nonlinear frequency conversion processes using such metasurfaces is discussed. Next, we review different approaches to realize tunable dielectric metasurfaces, including ultrafast all-optical switching of the metasurface response. Finally, future directions and possible applications of nonlinear and tunable dielectric metasurfaces will be outlined.
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Resonant dielectric metasurfaces were extensively studied in the linear and static regime of operation, targeting mainly wavefront shaping, polarization control and spectral filtering applications. Recently, an increasing amount of research focused on active tuning and nonlinear effects of these metasurfaces, unveiling their potential for novel nonlinear and reconfigurable optical devices. These may find many applications in imaging systems, compact adaptive optical systems, beam steering, holographic displays, and quantum optics, to just name a few. This review provides an overview of the recent progress in this field. Following a general introduction to resonant dielectric metasurfaces, the current state-of-the-art regarding the enhancement and tailoring of nonlinear frequency conversion processes using such metasurfaces is discussed. Next, we review different approaches to realize tunable dielectric metasurfaces, including ultrafast all-optical switching of the metasurface response. Finally, future directions and possible applications of nonlinear and tunable dielectric metasurfaces will be outlined.
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Ramanome technology platform for label-free screening and sorting of microbial cell factories at single-cell resolution
Yuehui He, Xixian Wang, Bo Ma, Jian Xu
Phenotypic profiling of natural, engineered or synthetic cells has increasingly become a bottleneck in the mining and engineering of cell factories. Single-cell phenotyping technologies are highly promising for tackling this hurdle, yet ideally they should allow non-invasive live-cell probing, be label-free, provide landscape-like phenotyping capability, distinguish complex functions, operate with high speed, sufficient throughput and low cost, and finally, couple with cell sorting so as to enable downstream omics analysis. This review focuses on recent progress in Ramanome Technology Platform (RTP), which consists of Raman spectroscopy based phenotyping, sorting and sequencing of single cells, and discuss the key challenges and emerging trends. In addition, we propose ramanome, a collection of single-cell Raman spectra (SCRS) acquired from individual cells within a cellular population or consortium, as a new type of biological phenome datatype at the single-cell resolution. By establishing the phenome-genome links in a label-free, single-cell manner, RTP should find wide applications in functional screening and strain development of live microbial, plant and animal cell factories.
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Phenotypic profiling of natural, engineered or synthetic cells has increasingly become a bottleneck in the mining and engineering of cell factories. Single-cell phenotyping technologies are highly promising for tackling this hurdle, yet ideally they should allow non-invasive live-cell probing, be label-free, provide landscape-like phenotyping capability, distinguish complex functions, operate with high speed, sufficient throughput and low cost, and finally, couple with cell sorting so as to enable downstream omics analysis. This review focuses on recent progress in Ramanome Technology Platform (RTP), which consists of Raman spectroscopy based phenotyping, sorting and sequencing of single cells, and discuss the key challenges and emerging trends. In addition, we propose ramanome, a collection of single-cell Raman spectra (SCRS) acquired from individual cells within a cellular population or consortium, as a new type of biological phenome datatype at the single-cell resolution. By establishing the phenome-genome links in a label-free, single-cell manner, RTP should find wide applications in functional screening and strain development of live microbial, plant and animal cell factories.
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The base pair-scale diffusion of nucleosomes modulates binding of transcription factors
Sergei Rudnizky, Hadeel Khamis, Omri Malik, Philippa Melamed, and Ariel Kaplan
The structure of promoter chromatin determines the ability of transcription factors (TFs) to bind to DNA and therefore has a profound effect on the expression levels of genes. However, the role of spontaneous nucleosome movements in this process is not fully understood. Here, we developed a single-molecule optical tweezers assay capable of simultaneously characterizing the base pair-scale diffusion of a nucleosome on DNA and the binding of a TF, using the luteinizing hormone β subunit gene (Lhb) promoter and Egr-1 as a model system. Our results demonstrate that nucleosomes undergo confined diffusion, and that the incorporation of the histone variant H2A.Z serves to partially relieve this confinement, inducing a different type of nucleosome repositioning. The increase in diffusion leads to exposure of a TF’s binding site and facilitates its association with the DNA, which, in turn, biases the subsequent movement of the nucleosome. Our findings suggest the use of mobile nucleosomes as a general transcriptional regulatory mechanism.
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The structure of promoter chromatin determines the ability of transcription factors (TFs) to bind to DNA and therefore has a profound effect on the expression levels of genes. However, the role of spontaneous nucleosome movements in this process is not fully understood. Here, we developed a single-molecule optical tweezers assay capable of simultaneously characterizing the base pair-scale diffusion of a nucleosome on DNA and the binding of a TF, using the luteinizing hormone β subunit gene (Lhb) promoter and Egr-1 as a model system. Our results demonstrate that nucleosomes undergo confined diffusion, and that the incorporation of the histone variant H2A.Z serves to partially relieve this confinement, inducing a different type of nucleosome repositioning. The increase in diffusion leads to exposure of a TF’s binding site and facilitates its association with the DNA, which, in turn, biases the subsequent movement of the nucleosome. Our findings suggest the use of mobile nucleosomes as a general transcriptional regulatory mechanism.
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Multiplicative noise effects in an optically trapped aerosol
R.F. Rodríguez, E. Salinas-Barrios
We develop a stochastic model to describe the effects of external noise on the position and power spectrum fluctuations of the particles of an optically confined aerosol. We propose that externally imposed fluctuations may induce a random frequency of the confining laser. Our analysis is based on a linear multiplicative Langevin equation and on the cumulant method. We also derive the associated Fokker-Planck equation and the mean square displacement of the particles. Our model predicts that these multiplicative fluctuations may produce a large effect on these correlations and on the corresponding fluctuations spectra which might be measurable.
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We develop a stochastic model to describe the effects of external noise on the position and power spectrum fluctuations of the particles of an optically confined aerosol. We propose that externally imposed fluctuations may induce a random frequency of the confining laser. Our analysis is based on a linear multiplicative Langevin equation and on the cumulant method. We also derive the associated Fokker-Planck equation and the mean square displacement of the particles. Our model predicts that these multiplicative fluctuations may produce a large effect on these correlations and on the corresponding fluctuations spectra which might be measurable.
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Monday, July 22, 2019
Disappearance and reappearance of an optical trap for silver nanoparticles under femtosecond pulsed excitation: A theoretical investigation
Anita Devi, Shruthi S Nair and Arijit K. De
Recently, the role of ultrafast pulsed excitation in laser trapping of dielectric nanoparticles has been explored and it was observed that the optical Kerr effect (OKE) plays an important role in determining the stability of the trap. Here, we theoretically investigate the trapping behaviour of metallic (silver) nanoparticles and study the effect of OKE (up to sixth order) under high repetition rate femtosecond pulsed excitation. We observe that the trapping potential is first stabilized, then destabilized and again stabilized with an increase in laser power. This work shows how one can fine-tune the stability of an optical trap for metallic nanoparticles through OKE.
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Recently, the role of ultrafast pulsed excitation in laser trapping of dielectric nanoparticles has been explored and it was observed that the optical Kerr effect (OKE) plays an important role in determining the stability of the trap. Here, we theoretically investigate the trapping behaviour of metallic (silver) nanoparticles and study the effect of OKE (up to sixth order) under high repetition rate femtosecond pulsed excitation. We observe that the trapping potential is first stabilized, then destabilized and again stabilized with an increase in laser power. This work shows how one can fine-tune the stability of an optical trap for metallic nanoparticles through OKE.
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Are microtubules tension sensors?
Olivier Hamant, Daisuke Inoue, David Bouchez, Jacques Dumais & Eric Mjolsness
Mechanical signals play many roles in cell and developmental biology. Several mechanotransduction pathways have been uncovered, but the mechanisms identified so far only address the perception of stress intensity. Mechanical stresses are tensorial in nature, and thus provide dual mechanical information: stress magnitude and direction. Here we propose a parsimonious mechanism for the perception of the principal stress direction. In vitro experiments show that microtubules are stabilized under tension. Based on these results, we explore the possibility that such microtubule stabilization operates in vivo, most notably in plant cells where turgor-driven tensile stresses exceed greatly those observed in animal cells.
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Mechanical signals play many roles in cell and developmental biology. Several mechanotransduction pathways have been uncovered, but the mechanisms identified so far only address the perception of stress intensity. Mechanical stresses are tensorial in nature, and thus provide dual mechanical information: stress magnitude and direction. Here we propose a parsimonious mechanism for the perception of the principal stress direction. In vitro experiments show that microtubules are stabilized under tension. Based on these results, we explore the possibility that such microtubule stabilization operates in vivo, most notably in plant cells where turgor-driven tensile stresses exceed greatly those observed in animal cells.
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Translational and rotational manipulation of filamentous cells using optically driven microrobots
Songyu Hu, Ruifeng Hu, Xiaobin Dong, Tanyong Wei, Shuxun Chen, and Dong Sun
Optical cell manipulation has become increasingly valuable in cell-based assays. In this paper, we demonstrate the translational and rotational manipulation of filamentous cells using multiple cooperative microrobots automatically driven by holographic optical tweezers. The photodamage of the cells due to direct irradiation of the laser beam can be effectively avoided. The proposed method will enable fruitful biomedical applications where precise cell manipulation and less photodamage are required.
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Optical cell manipulation has become increasingly valuable in cell-based assays. In this paper, we demonstrate the translational and rotational manipulation of filamentous cells using multiple cooperative microrobots automatically driven by holographic optical tweezers. The photodamage of the cells due to direct irradiation of the laser beam can be effectively avoided. The proposed method will enable fruitful biomedical applications where precise cell manipulation and less photodamage are required.
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Light‐Controlled Micromotors and Soft Microrobots
Stefano Palagi, Dhruv P. Singh, Peer Fischer
Mobile microscale devices and microrobots can be powered by catalytic reactions (chemical micromotors) or by external fields. This report is focused on the role of light as a versatile means for wirelessly powering and controlling such microdevices. Recent advances in the development of autonomous micromotors are discussed, where light permits their actuation with unprecedented control and thereby enables advances in the field of active matter. In addition, structuring the light field is a new means to drive soft microrobots that are based on (photo‐) responsive polymers. The behavior of the two main classes of thermo‐ and photoresponsive polymers adopted in microrobotics (poly(N‐isopropylacrylamide) and liquid‐crystal elastomers) is analyzed, and recent applications are reported. The advantages and limitations of controlling micromotors and microrobots by light are reviewed, and some of the remaining challenges in the development of novel photo‐active materials for micromotors and microrobots are discussed.
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Mobile microscale devices and microrobots can be powered by catalytic reactions (chemical micromotors) or by external fields. This report is focused on the role of light as a versatile means for wirelessly powering and controlling such microdevices. Recent advances in the development of autonomous micromotors are discussed, where light permits their actuation with unprecedented control and thereby enables advances in the field of active matter. In addition, structuring the light field is a new means to drive soft microrobots that are based on (photo‐) responsive polymers. The behavior of the two main classes of thermo‐ and photoresponsive polymers adopted in microrobotics (poly(N‐isopropylacrylamide) and liquid‐crystal elastomers) is analyzed, and recent applications are reported. The advantages and limitations of controlling micromotors and microrobots by light are reviewed, and some of the remaining challenges in the development of novel photo‐active materials for micromotors and microrobots are discussed.
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Single-photon controlled switch based on the giant Kerr nonlinearity in the single-spin coupled to levitated nanodiamonds
Jian Liu, Ka-Di Zhu
The photonic devices play a key role in optical communication networks and quantum networks. Here we analyze an optomechanical coupling between levitated nano-mechanical resonator and a nitrogen-vacancy(NV) center that exhibits a giant enhanced nonlinearity. Then we propose an experimentally accessible optical switch scheme at the single-photon level due to the optomechanically induced Kerr effect and show the pump power for the switch is reduced to 10^-19 W. This is a promising device for future optomechanics-based photonic quantum computing and quantum networks.
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The photonic devices play a key role in optical communication networks and quantum networks. Here we analyze an optomechanical coupling between levitated nano-mechanical resonator and a nitrogen-vacancy(NV) center that exhibits a giant enhanced nonlinearity. Then we propose an experimentally accessible optical switch scheme at the single-photon level due to the optomechanically induced Kerr effect and show the pump power for the switch is reduced to 10^-19 W. This is a promising device for future optomechanics-based photonic quantum computing and quantum networks.
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The 2018 Nobel Prize in Physics: optical tweezers and chirped pulse amplification
Matthew C. Asplund, Jeremy A. Johnson, James E. Patterson
The 2018 Nobel Prize in Physics was awarded to Arthur Ashkin (prize share ½), Gérard Mourou (prize share ¼), and Donna Strickland (prize share ¼) for “groundbreaking inventions in the field of laser physics.” This feature article summarizes the development of “optical tweezers and their application to biological systems” by Arthur Ashkin, as well as the Mourou/Strickland method of “generating high-intensity, ultrashort optical pulses” known as chirped pulse amplification. Further developments are also briefly discussed.
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The 2018 Nobel Prize in Physics was awarded to Arthur Ashkin (prize share ½), Gérard Mourou (prize share ¼), and Donna Strickland (prize share ¼) for “groundbreaking inventions in the field of laser physics.” This feature article summarizes the development of “optical tweezers and their application to biological systems” by Arthur Ashkin, as well as the Mourou/Strickland method of “generating high-intensity, ultrashort optical pulses” known as chirped pulse amplification. Further developments are also briefly discussed.
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Defect-Free Assembly of 2D Clusters of More Than 100 Single-Atom Quantum Systems
Daniel Ohl de Mello, Dominik Schäffner, Jan Werkmann, Tilman Preuschoff, Lars Kohfahl, Malte Schlosser, and Gerhard Birkl
We demonstrate the defect-free assembly of versatile target patterns of up 111 neutral atoms, building on a 361-site subset of a micro-optical architecture that readily provides thousands of sites for single-atom quantum systems. By performing multiple assembly cycles in rapid succession, we drastically increase achievable structure sizes and success probabilities. We implement repeated target pattern reconstruction after atom loss and deterministic transport of partial atom clusters necessary for distributing entanglement in large-scale systems. This technique will propel assembled-atom architectures beyond the threshold of quantum advantage and into a regime with abundant applications in quantum sensing and metrology, Rydberg-state mediated quantum simulation, and error-corrected quantum computation.
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We demonstrate the defect-free assembly of versatile target patterns of up 111 neutral atoms, building on a 361-site subset of a micro-optical architecture that readily provides thousands of sites for single-atom quantum systems. By performing multiple assembly cycles in rapid succession, we drastically increase achievable structure sizes and success probabilities. We implement repeated target pattern reconstruction after atom loss and deterministic transport of partial atom clusters necessary for distributing entanglement in large-scale systems. This technique will propel assembled-atom architectures beyond the threshold of quantum advantage and into a regime with abundant applications in quantum sensing and metrology, Rydberg-state mediated quantum simulation, and error-corrected quantum computation.
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Wednesday, July 17, 2019
The mixing-demixing phase diagram of ultracold heteronuclear mixtures in a ring trimer
Andrea Richaud, Alessandro Zenesini & Vittorio Penna
We derive the complete mixing-demixing phase-diagram relevant to a bosonic binary mixture confined in a ring trimer and modeled within the Bose-Hubbard picture. The mixing properties of the two quantum fluids, which are shown to be strongly affected by the fragmented character of the confining potential, are evaluated by means of a specific indicator imported from Statistical Thermodynamics and are shown to depend only on two effective parameters incorporating the asymmetry between the heteronuclear species. To closely match realistic experimental conditions, our study is extended also beyond the pointlike approximation of potential wells by describing the systems in terms of two coupled Gross-Pitaevskii equations. The resulting mean-field analysis confirms the rich scenario of mixing-demixing transitions of the mixture and also constitutes an effective springboard towards a viable experimental realization. We additionally propose an experimental realization based on a realistic optical-tweezers system and on the bosonic mixture 23Na + 39K, thanks to the large tunability of their intra- and inter-species scattering lengths.
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We derive the complete mixing-demixing phase-diagram relevant to a bosonic binary mixture confined in a ring trimer and modeled within the Bose-Hubbard picture. The mixing properties of the two quantum fluids, which are shown to be strongly affected by the fragmented character of the confining potential, are evaluated by means of a specific indicator imported from Statistical Thermodynamics and are shown to depend only on two effective parameters incorporating the asymmetry between the heteronuclear species. To closely match realistic experimental conditions, our study is extended also beyond the pointlike approximation of potential wells by describing the systems in terms of two coupled Gross-Pitaevskii equations. The resulting mean-field analysis confirms the rich scenario of mixing-demixing transitions of the mixture and also constitutes an effective springboard towards a viable experimental realization. We additionally propose an experimental realization based on a realistic optical-tweezers system and on the bosonic mixture 23Na + 39K, thanks to the large tunability of their intra- and inter-species scattering lengths.
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Single and double box HMGB proteins differentially destabilize nucleosomes
Micah J McCauley, Ran Huo, Nicole Becker, Molly Nelson Holte, Uma M Muthurajan, Ioulia Rouzina, Karolin Luger, L James Maher, III, Nathan E Israeloff, Mark C Williams
Nucleosome disruption plays a key role in many nuclear processes including transcription, DNA repair and recombination. Here we combine atomic force microscopy (AFM) and optical tweezers (OT) experiments to show that high mobility group B (HMGB) proteins strongly disrupt nucleosomes, revealing a new mechanism for regulation of chromatin accessibility. We find that both the double box yeast Hmo1 and the single box yeast Nhp6A display strong binding preferences for nucleosomes over linker DNA, and both HMGB proteins destabilize and unwind DNA from the H2A–H2B dimers. However, unlike Nhp6A, Hmo1 also releases half of the DNA held by the (H3–H4)2 tetramer. This difference in nucleosome destabilization may explain why Nhp6A and Hmo1 function at different genomic sites. Hmo1 is enriched at highly transcribed ribosomal genes, known to be depleted of histones. In contrast, Nhp6A is found across euchromatin, pointing to a significant difference in cellular function.
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Nucleosome disruption plays a key role in many nuclear processes including transcription, DNA repair and recombination. Here we combine atomic force microscopy (AFM) and optical tweezers (OT) experiments to show that high mobility group B (HMGB) proteins strongly disrupt nucleosomes, revealing a new mechanism for regulation of chromatin accessibility. We find that both the double box yeast Hmo1 and the single box yeast Nhp6A display strong binding preferences for nucleosomes over linker DNA, and both HMGB proteins destabilize and unwind DNA from the H2A–H2B dimers. However, unlike Nhp6A, Hmo1 also releases half of the DNA held by the (H3–H4)2 tetramer. This difference in nucleosome destabilization may explain why Nhp6A and Hmo1 function at different genomic sites. Hmo1 is enriched at highly transcribed ribosomal genes, known to be depleted of histones. In contrast, Nhp6A is found across euchromatin, pointing to a significant difference in cellular function.
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Dynamics of two levitated nanospheres nonlinearly coupling with non-Markovian environment
Li Xun, Xiong Biao, Chao Shilei, Jin Jiasen, Zhou Ling
The dynamics of two nanospheres nonlinearly coupling with non-Markovian reservoir is investigated. A master equation of the two nanospheres is derived by employing quantum state diffusion method. It is shown that the nonlinear coupling can improve the non-Markovianity. Due to the sharing of the common non-Markovian environment, the state transfer between the two nanospheres can be realized. The entanglement and the squeezing of the individual mode, as well as the jointed two-mode are analyzed. The present system can be realized by trapping two nanospheres in a wideband cavity, which might provide a method to study adjustable non-Markovian dynamics of mechanical motion.
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The dynamics of two nanospheres nonlinearly coupling with non-Markovian reservoir is investigated. A master equation of the two nanospheres is derived by employing quantum state diffusion method. It is shown that the nonlinear coupling can improve the non-Markovianity. Due to the sharing of the common non-Markovian environment, the state transfer between the two nanospheres can be realized. The entanglement and the squeezing of the individual mode, as well as the jointed two-mode are analyzed. The present system can be realized by trapping two nanospheres in a wideband cavity, which might provide a method to study adjustable non-Markovian dynamics of mechanical motion.
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Optical pulling forces on Rayleigh particles using ambient optical nonlinearity
Liping Gong, Xiaohe Zhang, Bing Gu, Zhuqing Zhu, Guanghao Rui, Jun He, Qiwen Zhan, Yiping Cui
Optical pulling forces exerted on small particles can be achieved by tailoring the properties of the electromagnetic field, the particles themselves, or the surrounding environment. However, the nonlinear optical effect of the surrounding environment has been largely neglected. Herein, we report the optical pulling forces on a Rayleigh particle immersed in a nonlinear optical liquid using high-repetition-rate femtosecond laser pulses. The analytic expression of time-averaged optical forces allows us to better understand the underlying mechanism of the particle transportation. It is shown that the two-photon absorption of the surrounding liquid gives rise to a negative radiation force. Transversely confined Rayleigh particles can be continuously dragged towards the light source during a pulling process.
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Optical pulling forces exerted on small particles can be achieved by tailoring the properties of the electromagnetic field, the particles themselves, or the surrounding environment. However, the nonlinear optical effect of the surrounding environment has been largely neglected. Herein, we report the optical pulling forces on a Rayleigh particle immersed in a nonlinear optical liquid using high-repetition-rate femtosecond laser pulses. The analytic expression of time-averaged optical forces allows us to better understand the underlying mechanism of the particle transportation. It is shown that the two-photon absorption of the surrounding liquid gives rise to a negative radiation force. Transversely confined Rayleigh particles can be continuously dragged towards the light source during a pulling process.
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On‐chip technology for single‐cell arraying, electrorotation‐based analysis and selective release
Kevin Keim, Mohamed Z. Rashed, Samuel C. Kilchenmann, Aurélien Delattre, António F. Gonçalves, Paul Éry, Carlotta Guiducci
This paper reports a method for label‐free single‐cell biophysical analysis of multiple cells trapped in suspension by electrokinetic forces. Tri‐dimensional pillar electrodes arranged along the width of a microfluidic chamber define actuators for single cell trapping and selective release by electrokinetic force. Moreover, a rotation can be induced on the cell in combination with a negative DEP force to retain the cell against the flow. The measurement of the rotation speed of the cell as a function of the electric field frequency define an electrorotation spectrum that allows to study the dielectric properties of the cell. The system presented here shows for the first time the simultaneous electrorotation analysis of multiple single cells in separate micro cages that can be selectively addressed to trap and/or release the cells. Chips with 39 micro‐actuators of different interelectrode distance were fabricated to study cells with different sizes. The extracted dielectric properties of Henrietta Lacks, human embryonic kidney 293, and human immortalized T lymphocytes cells were found in agreements with previous findings. Moreover, the membrane capacitance of M17 neuroblastoma cells was investigated and found to fall in in the range of 7.49 ± 0.39 mF/m2.
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This paper reports a method for label‐free single‐cell biophysical analysis of multiple cells trapped in suspension by electrokinetic forces. Tri‐dimensional pillar electrodes arranged along the width of a microfluidic chamber define actuators for single cell trapping and selective release by electrokinetic force. Moreover, a rotation can be induced on the cell in combination with a negative DEP force to retain the cell against the flow. The measurement of the rotation speed of the cell as a function of the electric field frequency define an electrorotation spectrum that allows to study the dielectric properties of the cell. The system presented here shows for the first time the simultaneous electrorotation analysis of multiple single cells in separate micro cages that can be selectively addressed to trap and/or release the cells. Chips with 39 micro‐actuators of different interelectrode distance were fabricated to study cells with different sizes. The extracted dielectric properties of Henrietta Lacks, human embryonic kidney 293, and human immortalized T lymphocytes cells were found in agreements with previous findings. Moreover, the membrane capacitance of M17 neuroblastoma cells was investigated and found to fall in in the range of 7.49 ± 0.39 mF/m2.
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Molecular Assembly of Ground-State Cooled Single Atoms
L. R. Liu, J. D. Hood, Y. Yu, J. T. Zhang, K. Wang, Y.-W. Lin, T. Rosenband, and K.-K. Ni
We demonstrate full quantum state control of two species of single atoms using optical tweezers and assemble the atoms into a molecule. Our demonstration includes 3D ground-state cooling of a single atom (Cs) in an optical tweezer, transport by several microns with minimal heating, and merging with a single Na atom. Subsequently, both atoms occupy the simultaneous motional ground state with 61(4)% probability. This realizes a sample of exactly two cotrapped atoms near the phase-space-density limit of one, and allows for efficient stimulated-Raman transfer of a pair of atoms into a molecular bound state of the triplet electronic ground potential a3Σ+. The results are key steps toward coherent creation of single ultracold molecules for future exploration of quantum simulation and quantum information processing.
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We demonstrate full quantum state control of two species of single atoms using optical tweezers and assemble the atoms into a molecule. Our demonstration includes 3D ground-state cooling of a single atom (Cs) in an optical tweezer, transport by several microns with minimal heating, and merging with a single Na atom. Subsequently, both atoms occupy the simultaneous motional ground state with 61(4)% probability. This realizes a sample of exactly two cotrapped atoms near the phase-space-density limit of one, and allows for efficient stimulated-Raman transfer of a pair of atoms into a molecular bound state of the triplet electronic ground potential a3Σ+. The results are key steps toward coherent creation of single ultracold molecules for future exploration of quantum simulation and quantum information processing.
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Passive and active microrheology of a lyotropic chromonic nematic liquid crystal disodium cromoglycate
Ahlem Habibi, Christophe Blanc, Nadia Ben Mbarek, Taoufik Soltani
Rheological properties of isotropic fluids are frequently probed by microrheology, a set of techniques that uses the dynamics of micron scale particles to extract the viscoelastic properties either in a passive or in an active approach. For an anisotropic fluid like a nematic phase, these techniques are often applied but the mechanical properties of mesophases cannot be straightforwardly related to the dynamics of the beads. We have illustrated this by focusing on the microrheology of solutions of disodium cromoglycate, a lyotropic chromonic liquid crystal. We have probed this system with beads of several sizes with both passive and active methods and confronted our results to recent but apparently contradictory data present in the literature.
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True one cell chemical analysis: a review
Imesha W. De Silva, Amanda R. Kretsch, Holly-May Lewis, Melanie Bailey and Guido F. Verbeck
The constantly growing field of True One Cell (TOC) analysis has provided important information on the direct chemical composition of various cells and cellular components. Since the heterogeneity of individual cells has been established, more researchers are interested in the chemical differences between individual cells; TOC is the only form of analysis that can provide this information. This has resulted in the constant development of new technologies and methods. This review highlights the common techniques for micro- and nanomanipulation, Raman spectroscopy, microscopy, and mass spectrometric imaging as they pertain to TOC chemical analysis.
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The constantly growing field of True One Cell (TOC) analysis has provided important information on the direct chemical composition of various cells and cellular components. Since the heterogeneity of individual cells has been established, more researchers are interested in the chemical differences between individual cells; TOC is the only form of analysis that can provide this information. This has resulted in the constant development of new technologies and methods. This review highlights the common techniques for micro- and nanomanipulation, Raman spectroscopy, microscopy, and mass spectrometric imaging as they pertain to TOC chemical analysis.
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Tuesday, July 16, 2019
Ultra-fast force-clamp spectroscopy data on the interaction between skeletal muscle myosin and actin
Manuela Maffei, Diego Beneventi, Monica Canepari, Roberto Bottinelli, Francesco Saverio Pavone, Marco Capitanio
Ultrafast force-clamp spectroscopy is a single molecule technique based on laser tweezers with sub-millisecond and sub-nanometer resolution. The technique has been successfully applied to investigate the rapid conformational changes that occur when a myosin II motor from skeletal muscle interacts with an actin filament. Here, we share data on the kinetics of such interaction and experimental records collected under different forces [1]. The data can be valuable for researchers interested in the mechanosensitive properties of myosin II, both from an experimental and modeling point of view. The data is related to the research article “ultrafast force-clamp spectroscopy of single molecules reveals load dependence of myosin working stroke” [2].
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Ultrafast force-clamp spectroscopy is a single molecule technique based on laser tweezers with sub-millisecond and sub-nanometer resolution. The technique has been successfully applied to investigate the rapid conformational changes that occur when a myosin II motor from skeletal muscle interacts with an actin filament. Here, we share data on the kinetics of such interaction and experimental records collected under different forces [1]. The data can be valuable for researchers interested in the mechanosensitive properties of myosin II, both from an experimental and modeling point of view. The data is related to the research article “ultrafast force-clamp spectroscopy of single molecules reveals load dependence of myosin working stroke” [2].
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Dynamics analysis of nanoparticles optically driven by a Laguerre-Gaussian beam with optical spin
Mamoru Tamura, Takashige Omatsu and Takuya Iida
We theoretically discover that the spin angular momentum (SAM) enables to modulate the orbital torque through the inter-particle light-induced force (IP-LIF). Laguerre - Gaussian beam with the orbital angular momentum (OAM) can induce the orbital motion for the optically trapped objects. In addition, the SAM can also accelerate or decelerate the orbital motion due to the IP-LIF. Our discovery provides a new physical aspect, i.e. the IP-LIF plays an important role in the many-body dynamics of nanoparticles via the SAM-OAM coupling.
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We theoretically discover that the spin angular momentum (SAM) enables to modulate the orbital torque through the inter-particle light-induced force (IP-LIF). Laguerre - Gaussian beam with the orbital angular momentum (OAM) can induce the orbital motion for the optically trapped objects. In addition, the SAM can also accelerate or decelerate the orbital motion due to the IP-LIF. Our discovery provides a new physical aspect, i.e. the IP-LIF plays an important role in the many-body dynamics of nanoparticles via the SAM-OAM coupling.
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Formation of a single poly(N,N-diethylacrylamide) micro-droplet in water by coupling of photothermal effects and an optical force
M Matsumoto, T Asoh, T Shoji, T Nishiyama, Hideo Horibe, Yukiteru Katsumoto and Yasuyuki Tsuboi
Poly(N-isopropylacrylamide) (PNIPAM) exhibits phase separation with lower critical solution temperature (LCST). In the 1990s, Masuhara and co-workers reported the first demonstration of optical trapping of PNIPAM forming a micrometer-sized polymer droplet. Since then, this technique has attracted much attention to create a molecular assembly in a microspace. In the present study, we targeted poly(N,N-diethylacrylamide) (PDEA), which has an analogous chemical structure to PNIPAM. We demonstrated that optical tweezers formed the unique micro-morphologies of a phase separated PDEA droplet. Fluorescence microscopic images and Raman spectra of the PDEA droplet showed that a lot of smaller-sized water-rich micro-domains were inhomogeneously formed in the droplet. Such unique phase separation behavior was never observed in steady-state heating of an aqueous PDEA solution above its LCST. Our results indicate that a novel micro-structure can be formed by coupling of an optical gradient force and a local temperature elevation.
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Poly(N-isopropylacrylamide) (PNIPAM) exhibits phase separation with lower critical solution temperature (LCST). In the 1990s, Masuhara and co-workers reported the first demonstration of optical trapping of PNIPAM forming a micrometer-sized polymer droplet. Since then, this technique has attracted much attention to create a molecular assembly in a microspace. In the present study, we targeted poly(N,N-diethylacrylamide) (PDEA), which has an analogous chemical structure to PNIPAM. We demonstrated that optical tweezers formed the unique micro-morphologies of a phase separated PDEA droplet. Fluorescence microscopic images and Raman spectra of the PDEA droplet showed that a lot of smaller-sized water-rich micro-domains were inhomogeneously formed in the droplet. Such unique phase separation behavior was never observed in steady-state heating of an aqueous PDEA solution above its LCST. Our results indicate that a novel micro-structure can be formed by coupling of an optical gradient force and a local temperature elevation.
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Detection of optical force due to multiphoton absorption
S Nakamura, R Sunakawa, K Setoura, S Ito and H Miyasaka
Resonant optical manipulation using absorption force so far has been based on the linear (one-photon) absorption by target material, while optical forces due to multiphoton absorption have not been much investigated. As multiphoton absorption obeys different selection rule from that of one-photon absorption, and also shows non-linear dependence on light intensity, a larger variety of photo-mechanical responses of small particles can be expected by using multiphoton absorption force. In this study, we focused femtosecond laser pulses to a single polymer microparticle containing fluorescence dyes to exert multiphoton absorption force on the particle. We successfully observed the three-dimensional motion of the photo-irradiated microparticle due to the multiphoton absorption.
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Resonant optical manipulation using absorption force so far has been based on the linear (one-photon) absorption by target material, while optical forces due to multiphoton absorption have not been much investigated. As multiphoton absorption obeys different selection rule from that of one-photon absorption, and also shows non-linear dependence on light intensity, a larger variety of photo-mechanical responses of small particles can be expected by using multiphoton absorption force. In this study, we focused femtosecond laser pulses to a single polymer microparticle containing fluorescence dyes to exert multiphoton absorption force on the particle. We successfully observed the three-dimensional motion of the photo-irradiated microparticle due to the multiphoton absorption.
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Time-scale dependent Brownian motion of nanoparticles in clusters at a solid-liquid interface by laser trapping
Itsuo Hanasaki and Chie Hosokawa
Nanoparticles in a cluster trapped by laser-induced force field show Brownian motion at solid-liquid interfaces. The cluster formation means that the particles are highly concentrated. In general, the diffusion coefficients of particles in fluids decrease with substantially high concentration and also in the vicinity of solid walls due to the hydrodynamic effect. The particle trajectory data obtained from the experimental measurements show that the longer time span of observation leads to smaller diffusion coefficient due to the confinement effect. However, they also exhibit higher diffusion coefficient compared to the the bulk condition when evaluated at a sufficiently short time span of the frame interval under the condition of sufficiently high laser powers.
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Nanoparticles in a cluster trapped by laser-induced force field show Brownian motion at solid-liquid interfaces. The cluster formation means that the particles are highly concentrated. In general, the diffusion coefficients of particles in fluids decrease with substantially high concentration and also in the vicinity of solid walls due to the hydrodynamic effect. The particle trajectory data obtained from the experimental measurements show that the longer time span of observation leads to smaller diffusion coefficient due to the confinement effect. However, they also exhibit higher diffusion coefficient compared to the the bulk condition when evaluated at a sufficiently short time span of the frame interval under the condition of sufficiently high laser powers.
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Anisotropic dynamics of nanoparticles in clusters at a solid-liquid interface by laser trapping
Itsuo Hanasaki and Chie Hosokawa
It is well-recognized that the Brownian motion of particles in fluids is random. Nevertheless, there can be characteristics depending on the specific physical conditions. We analyze the system of nanoparticle clusters formed by the laser trapping force field at the solid-liquid interface, based on the microscopy movie data. Since the laser trapping force field is basically a function of radial distance from the focal point in the two dimension at the liquid-solid interface, we examine the difference of displacement distributions in the radial and circumferential directions. The results show that the basic characteristics in this system depends on the laser power, and there is an anisotropy in the stochastic motion of the nanoparticles.
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It is well-recognized that the Brownian motion of particles in fluids is random. Nevertheless, there can be characteristics depending on the specific physical conditions. We analyze the system of nanoparticle clusters formed by the laser trapping force field at the solid-liquid interface, based on the microscopy movie data. Since the laser trapping force field is basically a function of radial distance from the focal point in the two dimension at the liquid-solid interface, we examine the difference of displacement distributions in the radial and circumferential directions. The results show that the basic characteristics in this system depends on the laser power, and there is an anisotropy in the stochastic motion of the nanoparticles.
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Plasmonic optical trapping of pyrene-pendant polymer chains by controlling thermophoretic force
Kenta Ushiro, Tatsuya Shoji and Yasuyuki Tsuboi
Plasmonic optical tweezers (POT) has a high potential for manipulation of nanomaterials due to an enhanced optical force. However, unfavorable thermal effects induced by plasmon excitation have frequently hindered the manipulation. For this issue, we have recently developed a novel non-plasmonic optical tweezers using a nanostructured silicon substrate (B-Si). We called it "Nano-Structured Semi-Conductor-Assisted Optical Tweezers (NASSCA-OT)". In the present study, we trapped pyrene-pendant polymer chains homogeneously dissolved in water for POT or NASSCA-OT. We used plasmonic gold nanopyramidal dimer arrays or B-Si in contact with the aqueous polymer solution. During plasmon excitation with a near-infrared laser light, any sign of optical trapping was never detected in fluorescence micro-spectroscopy. By contrast, trapping of the polymer chains was obviously observed for NASSCA-OT. Upon laser irradiation, pyrene excimer fluorescence was dramatically increased at the focal spot. These results indicate that NASSCA-OT is a powerful tool for manipulation of molecular materials.
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Plasmonic optical tweezers (POT) has a high potential for manipulation of nanomaterials due to an enhanced optical force. However, unfavorable thermal effects induced by plasmon excitation have frequently hindered the manipulation. For this issue, we have recently developed a novel non-plasmonic optical tweezers using a nanostructured silicon substrate (B-Si). We called it "Nano-Structured Semi-Conductor-Assisted Optical Tweezers (NASSCA-OT)". In the present study, we trapped pyrene-pendant polymer chains homogeneously dissolved in water for POT or NASSCA-OT. We used plasmonic gold nanopyramidal dimer arrays or B-Si in contact with the aqueous polymer solution. During plasmon excitation with a near-infrared laser light, any sign of optical trapping was never detected in fluorescence micro-spectroscopy. By contrast, trapping of the polymer chains was obviously observed for NASSCA-OT. Upon laser irradiation, pyrene excimer fluorescence was dramatically increased at the focal spot. These results indicate that NASSCA-OT is a powerful tool for manipulation of molecular materials.
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Nanoscale integration of single cell biologics discovery processes using optofluidic manipulation and monitoring
Marsela Jorgolli, Tanner Nevill, Aaron Winters, Irwin Chen, Su Chong, Fen‐Fen Lin, Marissa Mock, Ching Chen, Kim Le, Christopher Tan, Philip Jess, Han Xu, Agi Hamburger, Jennitte Stevens, Trent Munro, Ming Wu, Philip Tagari, Les P. Miranda
The new and rapid advancement in the complexity of biologics drug discovery has been driven by a deeper understanding of biological systems combined with innovative new therapeutic modalities, paving the way to breakthrough therapies for previously intractable diseases. These exciting times in biomedical innovation require the development of novel technologies to facilitate the sophisticated, multifaceted, high‐paced workflows necessary to support modern large molecule drug discovery. A high‐level aspiration is a true integration of “lab‐on‐a‐chip” methods that vastly miniaturize cellulmical experiments could transform the speed, cost, and success of multiple workstreams in biologics development. Several microscale bioprocess technologies have been established that incrementally address these needs, yet each is inflexibly designed for a very specific process thus limiting an integrated holistic application. A more fully integrated nanoscale approach that incorporates manipulation, culture, analytics, and traceable digital record keeping of thousands of single cells in a relevant nanoenvironment would be a transformative technology capable of keeping pace with today's rapid and complex drug discovery demands. The recent advent of optical manipulation of cells using light‐induced electrokinetics with micro‐ and nanoscale cell culture is poised to revolutionize both fundamental and applied biological research. In this review, we summarize the current state of the art for optical manipulation techniques and discuss emerging biological applications of this technology. In particular, we focus on promising prospects for drug discovery workflows, including antibody discovery, bioassay development, antibody engineering, and cell line development, which are enabled by the automation and industrialization of an integrated optoelectronic single‐cell manipulation and culture platform. Continued development of such platforms will be well positioned to overcome many of the challenges currently associated with fragmented, low‐throughput bioprocess workflows in biopharma and life science research.
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The new and rapid advancement in the complexity of biologics drug discovery has been driven by a deeper understanding of biological systems combined with innovative new therapeutic modalities, paving the way to breakthrough therapies for previously intractable diseases. These exciting times in biomedical innovation require the development of novel technologies to facilitate the sophisticated, multifaceted, high‐paced workflows necessary to support modern large molecule drug discovery. A high‐level aspiration is a true integration of “lab‐on‐a‐chip” methods that vastly miniaturize cellulmical experiments could transform the speed, cost, and success of multiple workstreams in biologics development. Several microscale bioprocess technologies have been established that incrementally address these needs, yet each is inflexibly designed for a very specific process thus limiting an integrated holistic application. A more fully integrated nanoscale approach that incorporates manipulation, culture, analytics, and traceable digital record keeping of thousands of single cells in a relevant nanoenvironment would be a transformative technology capable of keeping pace with today's rapid and complex drug discovery demands. The recent advent of optical manipulation of cells using light‐induced electrokinetics with micro‐ and nanoscale cell culture is poised to revolutionize both fundamental and applied biological research. In this review, we summarize the current state of the art for optical manipulation techniques and discuss emerging biological applications of this technology. In particular, we focus on promising prospects for drug discovery workflows, including antibody discovery, bioassay development, antibody engineering, and cell line development, which are enabled by the automation and industrialization of an integrated optoelectronic single‐cell manipulation and culture platform. Continued development of such platforms will be well positioned to overcome many of the challenges currently associated with fragmented, low‐throughput bioprocess workflows in biopharma and life science research.
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Monday, July 15, 2019
The Small GTPase Rac1 Increases Cell Surface Stiffness and Enhances 3D Migration Into Extracellular Matrices
Tom Kunschmann, Stefanie Puder, Tony Fischer, Anika Steffen, Klemens Rottner & Claudia Tanja Mierke
Membrane ruffling and lamellipodia formation promote the motility of adherent cells in two-dimensional motility assays by mechano-sensing of the microenvironment and initiation of focal adhesions towards their surroundings. Lamellipodium formation is stimulated by small Rho GTPases of the Rac subfamily, since genetic removal of these GTPases abolishes lamellipodium assembly. The relevance of lamellipodial or invadopodial structures for facilitating cellular mechanics and 3D cell motility is still unclear. Here, we hypothesized that Rac1 affects cell mechanics and facilitates 3D invasion. Thus, we explored whether fibroblasts that are genetically deficient for Rac1 (lacking Rac2 and Rac3) harbor altered mechanical properties, such as cellular deformability, intercellular adhesion forces and force exertion, and exhibit alterations in 3D motility. Rac1 knockout and control cells were analyzed for changes in deformability by applying an external force using an optical stretcher. Five Rac1 knockout cell lines were pronouncedly more deformable than Rac1 control cells upon stress application. Using AFM, we found that cell-cell adhesion forces are increased in Rac1 knockout compared to Rac1-expressing fibroblasts. Since mechanical deformability, cell-cell adhesion strength and 3D motility may be functionally connected, we investigated whether increased deformability of Rac1 knockout cells correlates with changes in 3D motility. All five Rac1 knockout clones displayed much lower 3D motility than Rac1-expressing controls. Moreover, force exertion was reduced in Rac1 knockout cells, as assessed by 3D fiber displacement analysis. Interference with cellular stiffness through blocking of actin polymerization by Latrunculin A could not further reduce invasion of Rac1 knockout cells. In contrast, Rac1-expressing controls treated with Latrunculin A were again more deformable and less invasive, suggesting actin polymerization is a major determinant of observed Rac1-dependent effects. Together, we propose that regulation of 3D motility by Rac1 partly involves cellular mechanics such as deformability and exertion of forces.
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Membrane ruffling and lamellipodia formation promote the motility of adherent cells in two-dimensional motility assays by mechano-sensing of the microenvironment and initiation of focal adhesions towards their surroundings. Lamellipodium formation is stimulated by small Rho GTPases of the Rac subfamily, since genetic removal of these GTPases abolishes lamellipodium assembly. The relevance of lamellipodial or invadopodial structures for facilitating cellular mechanics and 3D cell motility is still unclear. Here, we hypothesized that Rac1 affects cell mechanics and facilitates 3D invasion. Thus, we explored whether fibroblasts that are genetically deficient for Rac1 (lacking Rac2 and Rac3) harbor altered mechanical properties, such as cellular deformability, intercellular adhesion forces and force exertion, and exhibit alterations in 3D motility. Rac1 knockout and control cells were analyzed for changes in deformability by applying an external force using an optical stretcher. Five Rac1 knockout cell lines were pronouncedly more deformable than Rac1 control cells upon stress application. Using AFM, we found that cell-cell adhesion forces are increased in Rac1 knockout compared to Rac1-expressing fibroblasts. Since mechanical deformability, cell-cell adhesion strength and 3D motility may be functionally connected, we investigated whether increased deformability of Rac1 knockout cells correlates with changes in 3D motility. All five Rac1 knockout clones displayed much lower 3D motility than Rac1-expressing controls. Moreover, force exertion was reduced in Rac1 knockout cells, as assessed by 3D fiber displacement analysis. Interference with cellular stiffness through blocking of actin polymerization by Latrunculin A could not further reduce invasion of Rac1 knockout cells. In contrast, Rac1-expressing controls treated with Latrunculin A were again more deformable and less invasive, suggesting actin polymerization is a major determinant of observed Rac1-dependent effects. Together, we propose that regulation of 3D motility by Rac1 partly involves cellular mechanics such as deformability and exertion of forces.
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TGFβ-induced cytoskeletal remodeling mediates elevation of cell stiffness and invasiveness in NSCLC
E. Gladilin, S. Ohse, M. Boerries, H. Busch, C. Xu, M. Schneider, M. Meister & R. Eils
Importance of growth factor (GF) signaling in cancer progression is widely acknowledged. Transforming growth factor beta (TGFβ) is known to play a key role in epithelial-to-mesenchymal transition (EMT) and metastatic cell transformation that are characterized by alterations in cell mechanical architecture and behavior towards a more robust and motile single cell phenotype. However, mechanisms mediating cancer type specific enhancement of cell mechanical phenotype in response to TGFβ remain poorly understood. Here, we combine high-throughput mechanical cell phenotyping, microarray analysis and gene-silencing to dissect cytoskeletal mediators of TGFβ-induced changes in mechanical properties of on-small-cell lung carcinoma (NSCLC) cells. Our experimental results show that elevation of rigidity and invasiveness of TGFβ-stimulated NSCLC cells correlates with upregulation of several cytoskeletal and motor proteins including vimentin, a canonical marker of EMT, and less-known unconventional myosins. Selective probing of gene-silenced cells lead to identification of unconventional myosin MYH15 as a novel mediator of elevated cell rigidity and invasiveness in TGFβ-stimulated NSCLC cells. Our experimental results provide insights into TGFβ-induced cytoskeletal remodeling of NSCLC cells and suggest that mediators of elevated cell stiffness and migratory activity such as unconventional cytoskeletal and motor proteins may represent promising pharmaceutical targets for restraining invasive spread of lung cancer.
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Importance of growth factor (GF) signaling in cancer progression is widely acknowledged. Transforming growth factor beta (TGFβ) is known to play a key role in epithelial-to-mesenchymal transition (EMT) and metastatic cell transformation that are characterized by alterations in cell mechanical architecture and behavior towards a more robust and motile single cell phenotype. However, mechanisms mediating cancer type specific enhancement of cell mechanical phenotype in response to TGFβ remain poorly understood. Here, we combine high-throughput mechanical cell phenotyping, microarray analysis and gene-silencing to dissect cytoskeletal mediators of TGFβ-induced changes in mechanical properties of on-small-cell lung carcinoma (NSCLC) cells. Our experimental results show that elevation of rigidity and invasiveness of TGFβ-stimulated NSCLC cells correlates with upregulation of several cytoskeletal and motor proteins including vimentin, a canonical marker of EMT, and less-known unconventional myosins. Selective probing of gene-silenced cells lead to identification of unconventional myosin MYH15 as a novel mediator of elevated cell rigidity and invasiveness in TGFβ-stimulated NSCLC cells. Our experimental results provide insights into TGFβ-induced cytoskeletal remodeling of NSCLC cells and suggest that mediators of elevated cell stiffness and migratory activity such as unconventional cytoskeletal and motor proteins may represent promising pharmaceutical targets for restraining invasive spread of lung cancer.
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Laser Raman tweezer spectroscopy to explore the bisphenol A-induced changes in human erythrocytes†
Jijo Lukose, Mithun N.a, Priyanka M.a, Ganesh Mohan, Shamee Shastry and Santhosh Chidangil
The dermal penetration of bisphenol-A (BPA) from thermal papers into the human skin is a matter of major health concern due to its extensive use in developing countries like India, one of its largest users in the world. Bisphenol A is widely used in the manufacture of many consumer goods like polycarbonate water bottles, baby bottles, food containers, home appliances, thermal papers used in billing and tickets, the inner lining of food cans, etc. BPA can be easily adsorbed into the blood rapidly. The integration of optical tweezers with Raman spectroscopic techniques has realized avenues for interpreting single cell investigations. In the present work, the impact of BPA from thermal papers on individual human erythrocytes (red blood cells) has been investigated using micro-Raman spectroscopy. Significant intensity variations were noticed for hemoglobin oxygenation markers in the Raman spectra of red blood cells (RBCs). Raman spectral variations supporting RBC hemoglobin depletion were also found in the presence of BPA. Evident morphological changes are also observed in RBCs due to BPA in vitro exposures, which ultimately lead to cell bursting at higher concentrations.
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The dermal penetration of bisphenol-A (BPA) from thermal papers into the human skin is a matter of major health concern due to its extensive use in developing countries like India, one of its largest users in the world. Bisphenol A is widely used in the manufacture of many consumer goods like polycarbonate water bottles, baby bottles, food containers, home appliances, thermal papers used in billing and tickets, the inner lining of food cans, etc. BPA can be easily adsorbed into the blood rapidly. The integration of optical tweezers with Raman spectroscopic techniques has realized avenues for interpreting single cell investigations. In the present work, the impact of BPA from thermal papers on individual human erythrocytes (red blood cells) has been investigated using micro-Raman spectroscopy. Significant intensity variations were noticed for hemoglobin oxygenation markers in the Raman spectra of red blood cells (RBCs). Raman spectral variations supporting RBC hemoglobin depletion were also found in the presence of BPA. Evident morphological changes are also observed in RBCs due to BPA in vitro exposures, which ultimately lead to cell bursting at higher concentrations.
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Simultaneous detection of two-photon fluorescence and backscatter in laser trapping of dielectric nanoparticles
Anita Devi; Arijit Kumar De
In recent past, high-repetition-rate, ultrafast pulse excitation has been identified to play an important role in stable trapping of dielectric nanoparticles assisted by optical nonlinearity due to its high peak power. We experimentally demonstrate trapping of 100-nm fluorescent polystyrene particles by simultaneous detection of both two-photon fluorescence (TPF) and backscattered signals. Here we show that TPF signal decays over time due to photobleaching, but this signal is useful to know whether a particle is dragged toward the trap while backscattered signal provides detailed information about the particle’s dynamics inside the trap. We also discuss pros and cons of moving-averaging method (used to smooth noisy experimental data). We conclude that both TPF and backscattered detection methods are needed to explore the dynamics of the particle inside the potential well.
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In recent past, high-repetition-rate, ultrafast pulse excitation has been identified to play an important role in stable trapping of dielectric nanoparticles assisted by optical nonlinearity due to its high peak power. We experimentally demonstrate trapping of 100-nm fluorescent polystyrene particles by simultaneous detection of both two-photon fluorescence (TPF) and backscattered signals. Here we show that TPF signal decays over time due to photobleaching, but this signal is useful to know whether a particle is dragged toward the trap while backscattered signal provides detailed information about the particle’s dynamics inside the trap. We also discuss pros and cons of moving-averaging method (used to smooth noisy experimental data). We conclude that both TPF and backscattered detection methods are needed to explore the dynamics of the particle inside the potential well.
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Non-uniform stochastic dynamics of nanoparticle clusters at a solid–liquid interface induced by laser trapping
Itsuo Hanasaki and Chie Hosokawa
We reveal the characteristics of Brownian motion in nanoparticle clusters formed by the optical force fields at a solid–liquid interface based on the trajectory analysis from the microscopy movie data. The characteristics of stochastic motion depend not only on the laser power but also on the location in the clusters. The particles at the focal points exhibit smaller displacements, compared to the surrounding particles that are nevertheless trapped. The nominal diffusion coefficient is larger than the bulk at sufficiently small time scale for sufficiently high laser powers, although it decreases as a function of time because of the confinement. Decomposition of radial and circumferential components of displacements reveals the anisotropy as well as non-uniformity of the dynamics.
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We reveal the characteristics of Brownian motion in nanoparticle clusters formed by the optical force fields at a solid–liquid interface based on the trajectory analysis from the microscopy movie data. The characteristics of stochastic motion depend not only on the laser power but also on the location in the clusters. The particles at the focal points exhibit smaller displacements, compared to the surrounding particles that are nevertheless trapped. The nominal diffusion coefficient is larger than the bulk at sufficiently small time scale for sufficiently high laser powers, although it decreases as a function of time because of the confinement. Decomposition of radial and circumferential components of displacements reveals the anisotropy as well as non-uniformity of the dynamics.
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Red-Blood-Cell-Based Microlens: Application to Single-Cell Membrane Imaging and Stretching
Xiaoshuai Liu, Yuchao Li, Xiaohao Xu, Yao Zhang, Baojun Li
The red blood cell (RBC)-based microlens has attracted extensive insights into biological applications due to its intrinsic advantages of total biocompatibility. Most of the currently available RBC microlenses are fixed on a substrate and cannot be moved in a flexible manner, which limits their applications to optical imaging. Here we present an RBC microlens assembled by launching a 980 nm laser beam into a tapered fiber probe. The RBC microlens was then used to scan a single-cell membrane in three dimensions for optical imaging with a magnification factor of 1.7. Moreover, the microlens was employed to stretch the cell membrane with an enhancement factor of 1.5 in a noncontact and noninvasive manner.
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The red blood cell (RBC)-based microlens has attracted extensive insights into biological applications due to its intrinsic advantages of total biocompatibility. Most of the currently available RBC microlenses are fixed on a substrate and cannot be moved in a flexible manner, which limits their applications to optical imaging. Here we present an RBC microlens assembled by launching a 980 nm laser beam into a tapered fiber probe. The RBC microlens was then used to scan a single-cell membrane in three dimensions for optical imaging with a magnification factor of 1.7. Moreover, the microlens was employed to stretch the cell membrane with an enhancement factor of 1.5 in a noncontact and noninvasive manner.
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Breaking Through Bead-Supported Assay: Integration of Optical Tweezers Assisted Fluorescence Imaging and Luminescence Confined Upconversion Nanoparticles Triggered Luminescent Resonance Energy Transfer (LRET)
Cheng-Yu Li,Ya-Feng Kang, Chu-Bo Qi, Bei Zheng, Ming-Qiu Zheng, Chong-Yang Song, Zhen-Zhong Guo, Yi Lin, Dai-Wen Pang, Hong-Wu Tang
Herein, a conceptual approach for significantly enhancing a bead-supported assay is proposed. For the fluorescence imaging technology, optical tweezers are introduced to overcome the fluid viscosity interference and immobilize a single tested bead at the laser focus to guarantee a fairly precise imaging condition. For the selection of fluorescent materials and the signal acquisition means, a type of innovative luminescence confined upconversion nanoparticle with a unique sandwich structure is specially designed to act as an efficient energy donor to trigger the luminescent resonance energy transfer (LRET) process. By further combining the double breakthrough with a molecular beacon model, the newly developed detection strategy allows for achieving a pretty high LRET ratio (≈ 88%) to FAM molecules and offering sound assay performance toward miRNA analysis with a detection limit as low as the sub-fM level, and is capable of well identifying single-base mismatching. Besides, this approach not only is able to accurately qualify the low-abundance targets from as few as 30 cancer cells but also can be employed as a valid cancer early warning tool for performing liquid biopsy.
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Herein, a conceptual approach for significantly enhancing a bead-supported assay is proposed. For the fluorescence imaging technology, optical tweezers are introduced to overcome the fluid viscosity interference and immobilize a single tested bead at the laser focus to guarantee a fairly precise imaging condition. For the selection of fluorescent materials and the signal acquisition means, a type of innovative luminescence confined upconversion nanoparticle with a unique sandwich structure is specially designed to act as an efficient energy donor to trigger the luminescent resonance energy transfer (LRET) process. By further combining the double breakthrough with a molecular beacon model, the newly developed detection strategy allows for achieving a pretty high LRET ratio (≈ 88%) to FAM molecules and offering sound assay performance toward miRNA analysis with a detection limit as low as the sub-fM level, and is capable of well identifying single-base mismatching. Besides, this approach not only is able to accurately qualify the low-abundance targets from as few as 30 cancer cells but also can be employed as a valid cancer early warning tool for performing liquid biopsy.
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Regulating substrate mechanics to achieve odontogenic differentiation for dental pulp stem cells on TiO2 filled and unfilled polyisoprene
Ya-Chen Chuang, Yingjie Yu, Ming-Tzo Wei, Chung-Chueh Chang, Vincent Ricotta, Kuan-Che Feng, Likun Wang, Aneel K. Bherwani, H. Daniel Ou-Yang, Marcia Simon, Liudi Zhang, Miriam Rafailovich
We have shown that materials other than hydrogels commonly used in tissue engineering can be effective in enabling differentiation of dental pulp stem cells (DPSC). Here we demonstrate that a hydrophobic elastomer, polyisoprene (PI), a component of Gutta-percha, normally used to obturate the tooth canal, can also be used to initiate differentiation of the pulp. We showed that PI substrates without additional coating promote cell adhesion and differentiation, while their moduli can be easily adjusted either by varying the coating thickness or incorporation of inorganic particles. DPSC plated on those PI substrates were shown, using SPM and hysitron indentation, to adjust their moduli to conform to differentially small changes in the substrate modulus. In addition, optical tweezers were used to separately measure the membrane and cytoplasm moduli of DPSC, with and without Rho kinase inhibitor. The results indicated that the changes in modulus were attributed predominantly to changes within the cytoplasm, rather than the cell membrane. CLSM was used to identify cell morphology. Differentiation, as determined by qRT-PCR, of the upregulation of OCN, and COL1α1 as well as biomineralization, characterized by SEM/EDAX, was observed on hard PI substrates in the absence of induction factors, i.e. dexamethasone, with moduli 3–4 MPa, regardless of preparation. SEM showed that even though biomineralization was deposited on both spun cast thin PI and filled thick PI substrates, the minerals were aggregated into large clusters on thin PI, and uniformly distributed on filled thick PI, where it was templated within banded collagen fibers.
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We have shown that materials other than hydrogels commonly used in tissue engineering can be effective in enabling differentiation of dental pulp stem cells (DPSC). Here we demonstrate that a hydrophobic elastomer, polyisoprene (PI), a component of Gutta-percha, normally used to obturate the tooth canal, can also be used to initiate differentiation of the pulp. We showed that PI substrates without additional coating promote cell adhesion and differentiation, while their moduli can be easily adjusted either by varying the coating thickness or incorporation of inorganic particles. DPSC plated on those PI substrates were shown, using SPM and hysitron indentation, to adjust their moduli to conform to differentially small changes in the substrate modulus. In addition, optical tweezers were used to separately measure the membrane and cytoplasm moduli of DPSC, with and without Rho kinase inhibitor. The results indicated that the changes in modulus were attributed predominantly to changes within the cytoplasm, rather than the cell membrane. CLSM was used to identify cell morphology. Differentiation, as determined by qRT-PCR, of the upregulation of OCN, and COL1α1 as well as biomineralization, characterized by SEM/EDAX, was observed on hard PI substrates in the absence of induction factors, i.e. dexamethasone, with moduli 3–4 MPa, regardless of preparation. SEM showed that even though biomineralization was deposited on both spun cast thin PI and filled thick PI substrates, the minerals were aggregated into large clusters on thin PI, and uniformly distributed on filled thick PI, where it was templated within banded collagen fibers.
DOI
Thursday, July 4, 2019
Generalized Modeling of Optomechanical Forces Applied to PT-Symmetric Optical Microscale Resonators
Martino De Carlo; Francesco De Leonardis; Luciano Lamberti; Vittorio M. N. Passaro
We propose an innovative optomechanical device, exploiting the force enhancement due to a quasi-PT symmetry in resonant coupled optical cavities. In order to perform the study, we develop a generalized modeling of the response theory of optical forces, including the loss and the gain effects in optical systems. The enhancement of optical force appears to be limited only by non-linearity and by the resolution of the gain/loss mechanism.
DOI
We propose an innovative optomechanical device, exploiting the force enhancement due to a quasi-PT symmetry in resonant coupled optical cavities. In order to perform the study, we develop a generalized modeling of the response theory of optical forces, including the loss and the gain effects in optical systems. The enhancement of optical force appears to be limited only by non-linearity and by the resolution of the gain/loss mechanism.
DOI
Dissipation effect on optical force and torque near interfaces
Daigo Oue
The Fresnel–Snell law, which is one of the fundamental laws in optics and gives insights on the behaviour of light at interfaces, is violated if there exists dissipation in the transmitting media. In order to overcome this problem, we extend the angle of refraction from a real number to a complex number. We use this complex-angle approach to analyse the behaviour of light at interfaces between lossy media and lossless media. We reveal that dissipation makes the wavenumber of the light exceed the maximum allowed at lossless interfaces. This is surprising because, in general, dielectric loss only changes the intensity profiles of the light, so this excess wavenumber cannot be produced in the bulk even if there exists dielectric loss. Additionally, anomalous circular polarisation emerges with dissipation. The direction of the anomalous circular polarisation is transverse, whereas without dissipation the direction of circular polarisation has to be longitudinal. We also discuss how the excess wavenumber can increase optical force and how the anomalous circular polarisation can generate optical transverse torque. This novel state of light produced by dissipation will pave the way for a new generation of optical trapping and manipulation.
DOI
The Fresnel–Snell law, which is one of the fundamental laws in optics and gives insights on the behaviour of light at interfaces, is violated if there exists dissipation in the transmitting media. In order to overcome this problem, we extend the angle of refraction from a real number to a complex number. We use this complex-angle approach to analyse the behaviour of light at interfaces between lossy media and lossless media. We reveal that dissipation makes the wavenumber of the light exceed the maximum allowed at lossless interfaces. This is surprising because, in general, dielectric loss only changes the intensity profiles of the light, so this excess wavenumber cannot be produced in the bulk even if there exists dielectric loss. Additionally, anomalous circular polarisation emerges with dissipation. The direction of the anomalous circular polarisation is transverse, whereas without dissipation the direction of circular polarisation has to be longitudinal. We also discuss how the excess wavenumber can increase optical force and how the anomalous circular polarisation can generate optical transverse torque. This novel state of light produced by dissipation will pave the way for a new generation of optical trapping and manipulation.
DOI
Nonlinear refractive index measurement of a trapped particle with Shack–Hartmann wavefront sensor
Samaneh Birzhandi, Khosro Madanipour, Saeed Ghanbari
A technique for nonlinear refractive index measurement of a single trapped nanoparticle is investigated using Shack–Hartmann sensor. In this technique, trapping laser is used as a probe beam and an interacting green laser is illuminated as a pumping beam. Optical path difference and effective height of particle is measured with dual wavelength unwrapping technique. Using the absorption relation, we obtain the profile of nonlinear refractive index. Also, the results prove the quadric relation of the nonlinear refractive index to the nonlinear absorption. This result may have an enormous effect in investigating and characterization of nonlinear refractive index of Nano and Micro-sized particles. Also, measuring the thermal profile of the trapping site after illuminating the high power trapping laser leads to measuring the gradient intensity that could have an important role in nonconservative forces measurements. Another advantage is in having the effective thickness of particle which is important while geometry of the particle is crucial for determining trap stiffness. This measurement may lead to adaptive trap shape control and potential well measurement.
DOI
A technique for nonlinear refractive index measurement of a single trapped nanoparticle is investigated using Shack–Hartmann sensor. In this technique, trapping laser is used as a probe beam and an interacting green laser is illuminated as a pumping beam. Optical path difference and effective height of particle is measured with dual wavelength unwrapping technique. Using the absorption relation, we obtain the profile of nonlinear refractive index. Also, the results prove the quadric relation of the nonlinear refractive index to the nonlinear absorption. This result may have an enormous effect in investigating and characterization of nonlinear refractive index of Nano and Micro-sized particles. Also, measuring the thermal profile of the trapping site after illuminating the high power trapping laser leads to measuring the gradient intensity that could have an important role in nonconservative forces measurements. Another advantage is in having the effective thickness of particle which is important while geometry of the particle is crucial for determining trap stiffness. This measurement may lead to adaptive trap shape control and potential well measurement.
DOI
Colloidal Organosilica Spheres for Three-Dimensional Confocal Microscopy
Yanyan Liu, Taiki Yanagishima, Arran Curran, Kazem V. Edmond, Stefano Sacanna, Roel P. A. Dullens
We describe the synthesis and application of 3-(trimethoxysilyl)propyl methacrylate (TPM) particles as a colloidal model system for three-dimensional (3D) confocal scanning laser microscopy. The effect of the initial TPM concentration on the growth and polydispersity of the particles and a recently developed solvent transfer method to disperse particles in a refractive index and density-matching solvent mixture are reviewed and discussed. To fully characterize the system as a colloidal model, we measure the pair potential between the TPM particles directly using optical tweezers. Finally, we use 3D confocal microscopy to image a sedimentation–diffusion equilibrium of TPM particles to characterize the phase behavior and particle dynamics through successful detection and tracking of all particles in the field of view.
DOI
We describe the synthesis and application of 3-(trimethoxysilyl)propyl methacrylate (TPM) particles as a colloidal model system for three-dimensional (3D) confocal scanning laser microscopy. The effect of the initial TPM concentration on the growth and polydispersity of the particles and a recently developed solvent transfer method to disperse particles in a refractive index and density-matching solvent mixture are reviewed and discussed. To fully characterize the system as a colloidal model, we measure the pair potential between the TPM particles directly using optical tweezers. Finally, we use 3D confocal microscopy to image a sedimentation–diffusion equilibrium of TPM particles to characterize the phase behavior and particle dynamics through successful detection and tracking of all particles in the field of view.
DOI
Imaging: Gear up for mechano-immunology
Zhengpeng Wan, Samina Shaheen, Alicia Chau, Yingyue Zeng, Wanli Liu
Immune cells including B and T lymphocytes have a remarkable ability to sense the physical perturbations through their surface expressed receptors. At the advent of modern imaging technologies paired with biophysical methods, we have gained the understanding of mechanical forces exerted by immune cells to perform their functions. This review will go over the imaging techniques already being used to study mechanical forces in immune cells. We will also discuss the dire need for new modern technologies for future work.
DOI
Immune cells including B and T lymphocytes have a remarkable ability to sense the physical perturbations through their surface expressed receptors. At the advent of modern imaging technologies paired with biophysical methods, we have gained the understanding of mechanical forces exerted by immune cells to perform their functions. This review will go over the imaging techniques already being used to study mechanical forces in immune cells. We will also discuss the dire need for new modern technologies for future work.
DOI
Enhancement of optical force acting on vesicles via the binding of gold nanoparticles
Yumeki Tani and Takashi Kaneta
Here we found that gold nanoparticles (AuNPs) enhance the optical force acting on vesicles prepared from phospholipids via hydrophobic and electrostatic interactions. A laser beam was introduced into a cuvette filled with a suspension of vesicles and it accelerated them in its propagation direction via a scattering force. The addition of the AuNPs exponentially increased the velocity of the vesicles as their concentration increased, but polystyrene particles had no significant impact on velocity in the presence of AuNPs. To elucidate the mechanism of the increased velocity, the surface charges in the vesicles and the AuNPs were controlled; the surface charges of the vesicles were varied via the use of anionic, cationic and neutral phospholipids, whereas AuNPs with positive and negative charges were synthesized by coating with citrate ion and 4-dimethylaminopyridine, respectively. All vesicles increased the velocity at different degrees depending on the surface charge. The vesicles were accelerated more efficiently when their charges were opposite those of the AuNPs. These results suggested that hydrophobic and electrostatic interactions between the vesicles and the AuNPs enhanced the optical force. By accounting for the binding constant between the vesicles and the AuNPs, we proposed a model for the relationship between the concentration of the AuNPs and the velocity of the vesicles. Consequently, the increased velocity of the vesicles was attributed to the light scattering that was enhanced when AuNPs were adsorbed onto the vesicles.
DOI
Here we found that gold nanoparticles (AuNPs) enhance the optical force acting on vesicles prepared from phospholipids via hydrophobic and electrostatic interactions. A laser beam was introduced into a cuvette filled with a suspension of vesicles and it accelerated them in its propagation direction via a scattering force. The addition of the AuNPs exponentially increased the velocity of the vesicles as their concentration increased, but polystyrene particles had no significant impact on velocity in the presence of AuNPs. To elucidate the mechanism of the increased velocity, the surface charges in the vesicles and the AuNPs were controlled; the surface charges of the vesicles were varied via the use of anionic, cationic and neutral phospholipids, whereas AuNPs with positive and negative charges were synthesized by coating with citrate ion and 4-dimethylaminopyridine, respectively. All vesicles increased the velocity at different degrees depending on the surface charge. The vesicles were accelerated more efficiently when their charges were opposite those of the AuNPs. These results suggested that hydrophobic and electrostatic interactions between the vesicles and the AuNPs enhanced the optical force. By accounting for the binding constant between the vesicles and the AuNPs, we proposed a model for the relationship between the concentration of the AuNPs and the velocity of the vesicles. Consequently, the increased velocity of the vesicles was attributed to the light scattering that was enhanced when AuNPs were adsorbed onto the vesicles.
DOI
Whole genome amplification of single epithelial cells dissociated from snap-frozen tissue samples in microfluidic platform
Yuguang Liu, Janet Yao, and Marina Walther-Antonio
Single cell sequencing is a technology capable of analyzing the genome of a single cell within a population. This technology is mostly integrated with microfluidics for precise cell manipulation and fluid handling. So far, most of the microfluidic-based single cell genomic studies have been focused on lab-cultured species or cell lines that are relatively easy to handle following standard microfluidic-based protocols without additional adjustments. The major challenges for performing single cell sequencing on clinical samples is the complex nature of the samples which requires additional sample processing steps to obtain intact single cells of interest without using amplification-inhibitive agents. Fluorescent-activated cell sorting is a common option to obtain single cells from clinical samples for single cell applications but requires >100 000 viable cells in suspension and the need for specialized laboratory and personnel. In this work, we present a protocol that can be used to obtain intact epithelial cells from snap-frozen postsurgical human endometrial tissues for single cell whole genome amplification. Our protocol includes sample thawing, cell dissociation, and labeling for genome amplification of targeted cells. Between 80% and 100% of single cell replicates lead to >25 ng of DNA after amplification with no measurable contamination, sufficient for downstream sequencing.
DOI
Single cell sequencing is a technology capable of analyzing the genome of a single cell within a population. This technology is mostly integrated with microfluidics for precise cell manipulation and fluid handling. So far, most of the microfluidic-based single cell genomic studies have been focused on lab-cultured species or cell lines that are relatively easy to handle following standard microfluidic-based protocols without additional adjustments. The major challenges for performing single cell sequencing on clinical samples is the complex nature of the samples which requires additional sample processing steps to obtain intact single cells of interest without using amplification-inhibitive agents. Fluorescent-activated cell sorting is a common option to obtain single cells from clinical samples for single cell applications but requires >100 000 viable cells in suspension and the need for specialized laboratory and personnel. In this work, we present a protocol that can be used to obtain intact epithelial cells from snap-frozen postsurgical human endometrial tissues for single cell whole genome amplification. Our protocol includes sample thawing, cell dissociation, and labeling for genome amplification of targeted cells. Between 80% and 100% of single cell replicates lead to >25 ng of DNA after amplification with no measurable contamination, sufficient for downstream sequencing.
DOI
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