András Libál, Dong Yun Lee, Antonio Ortiz-Ambriz, Charles Reichhardt, Cynthia J. O. Reichhardt, Pietro Tierno & Cristiano Nisoli
Artificial particle ices are model systems of constrained, interacting particles. They have been introduced theoretically to study ice-manifolds emergent from frustration, along with domain wall and grain boundary dynamics, doping, pinning-depinning, controlled transport of topological defects, avalanches, and memory effects. Recently such particle-based ices have been experimentally realized with vortices in nano-patterned superconductors or gravitationally trapped colloids. Here we demonstrate that, although these ices are generally considered equivalent to magnetic spin ices, they can access a novel spectrum of phenomenologies that are inaccessible to the latter. With experiments, theory and simulations we demonstrate that in mixed coordination geometries, entropy-driven negative monopoles spontaneously appear at a density determined by the vertex-mixture ratio. Unlike its spin-based analogue, the colloidal system displays a “fragile ice” manifold, where local energetics oppose the ice rule, which is instead enforced through conservation of the global topological charge. The fragile colloidal ice, stabilized by topology, can be spontaneously broken by topological charge transfer.
DOI
Tuesday, October 30, 2018
Tunable size selectivity and nanoparticle immobilization on a photonic crystal optical trap
Aravind Krishnan, Shao-Hua Wu, and Michelle Povinelli
We harness residual thermal effects in a low-absorptivity system to manipulate parallel optical trapping of particles on the nanoscale. A photonic crystal is used to generate a 2D array of optical traps. We show that the size selectivity of the trap can be tuned by adding a non-ionic surfactant to the solution, altering the thermophoretic effect that delivers nanoparticles to trapping sites. We further show that particles can be permanently immobilized on the photonic crystal via photopolymerization of the trapping medium.
DOI
We harness residual thermal effects in a low-absorptivity system to manipulate parallel optical trapping of particles on the nanoscale. A photonic crystal is used to generate a 2D array of optical traps. We show that the size selectivity of the trap can be tuned by adding a non-ionic surfactant to the solution, altering the thermophoretic effect that delivers nanoparticles to trapping sites. We further show that particles can be permanently immobilized on the photonic crystal via photopolymerization of the trapping medium.
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Vectorial motion of matter induced by light fueled molecular machines
Zouheir Sekkat
A theory of vectorial, photochemically-induced motion of matter is reported. Molecules become mobile when they are photo-selected in a gradient of light intensity. The motion occurs in the direction of the vector of the intensity gradient, and its efficiency depends on the respective orientations of the vectors of light polarization and intensity gradient. Directional motion is imparted into materials containing such smart molecules. The theory well describes experimental observations, and its application to different types of gradients and light polarization excitations is considered. The theory opens important perspectives for the transport of matter by light.
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A theory of vectorial, photochemically-induced motion of matter is reported. Molecules become mobile when they are photo-selected in a gradient of light intensity. The motion occurs in the direction of the vector of the intensity gradient, and its efficiency depends on the respective orientations of the vectors of light polarization and intensity gradient. Directional motion is imparted into materials containing such smart molecules. The theory well describes experimental observations, and its application to different types of gradients and light polarization excitations is considered. The theory opens important perspectives for the transport of matter by light.
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Optical forces in optical nanofibers
Y Zhang, H Yu and Z Li
Optical forces exerted upon the endface of optical nanofiber have been carefully investigated numerically. Detailed spatial optical force distributions along the fiber axis are obtained. Dependence of optical force on fiber diameters, input modal polarizations, oblique-cut endfaces are carefully taken into considerations. It is clear now that oblique-cut fiber endface should be responsible for sideways deflection of nanofiber.
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Optical forces exerted upon the endface of optical nanofiber have been carefully investigated numerically. Detailed spatial optical force distributions along the fiber axis are obtained. Dependence of optical force on fiber diameters, input modal polarizations, oblique-cut endfaces are carefully taken into considerations. It is clear now that oblique-cut fiber endface should be responsible for sideways deflection of nanofiber.
DOI
Prospects and physical mechanisms for photonic space propulsion
Igor Levchenko, Kateryna Bazaka, Stephane Mazouffre & Shuyan Xu
An abundant source of energy in space, electromagnetic radiation can provide spacecraft with a gentle yet persistent thrust for interplanetary and interstellar missions. Early successes with microlaser and solar propulsion platforms confirm their potential for near-Earth and deep space exploration, although practical realization of reliable photonic devices is not trivial. This Perspective outlines the recent achievements and future outlook in the field of photonic space propulsion. We highlight several light-enabled mechanisms of thrust generation via photon–matter interactions such as photonic pressure and ablation, optical gradient forces, light-induced electron emission and others. Finally, we outline some of the key challenges in the area and possible solutions for practical applications.
DOI
An abundant source of energy in space, electromagnetic radiation can provide spacecraft with a gentle yet persistent thrust for interplanetary and interstellar missions. Early successes with microlaser and solar propulsion platforms confirm their potential for near-Earth and deep space exploration, although practical realization of reliable photonic devices is not trivial. This Perspective outlines the recent achievements and future outlook in the field of photonic space propulsion. We highlight several light-enabled mechanisms of thrust generation via photon–matter interactions such as photonic pressure and ablation, optical gradient forces, light-induced electron emission and others. Finally, we outline some of the key challenges in the area and possible solutions for practical applications.
DOI
Single-cell Raman spectroscopy reveals microsporidia spore heterogeneity in various insect hosts
Shenghui Huang, Xuhua Huang, Shengsheng Dai, Xiaochun Wang, and Guiwen Wang
Single-cell Raman spectroscopy was used to analyze the spore heterogeneity of 16 microsporidia strains from various insect hosts in order to better understand the basic biology of microsporidia. The Raman spectrum of a single spore revealed basic spore composition, and microsporidia spores in various hosts were found to be rich in trehalose. Principal component analysis and Raman intensity showed obvious heterogeneity in the trehalose, nucleic acid, and protein content of various spores; however, there was no correlation between various spore groups and host type. Trehalose content correlated with spore infectivity on Bombyx mori. Raman spectroscopy is an excellent tool for label-free investigation of intercellular molecular constituents, providing insight into the heterogeneity of microsporidia spores.
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Single-cell Raman spectroscopy was used to analyze the spore heterogeneity of 16 microsporidia strains from various insect hosts in order to better understand the basic biology of microsporidia. The Raman spectrum of a single spore revealed basic spore composition, and microsporidia spores in various hosts were found to be rich in trehalose. Principal component analysis and Raman intensity showed obvious heterogeneity in the trehalose, nucleic acid, and protein content of various spores; however, there was no correlation between various spore groups and host type. Trehalose content correlated with spore infectivity on Bombyx mori. Raman spectroscopy is an excellent tool for label-free investigation of intercellular molecular constituents, providing insight into the heterogeneity of microsporidia spores.
DOI
Thursday, October 25, 2018
Inexpensive Design of Bio‐Chip for Disease Diagnostics: Microchip Patterned from a Soft oxometalate‐Perylene based Hybrid Composite using Thermo‐optical Laser Tweezers
Soumyajit Roy, Preethi Thomas, Subhrokoli Ghosh, Apabrita Mallick, Ayan Banerjee, Soumyajit Roy
In this work, we have developed linear micro‐patterns of phosphotungstic acid soft oxometalate (SOM) and perylene (as fluorophore) hybrid composite on a glass substrate using a thermo‐optical tweezers set‐up, and used it for sensing of biologically important molecules such as glucose, uric acid and ascorbic acid. Bulk scale studies on the SOM‐fluorophore hybrid were initially performed to optimize the fabrication of the pattern. The aqueous dispersion of the hybrid composite was subjected to UV and fluorescence measurements. The linear micro‐patterns were characterized using Raman spectroscopy and AFM. The ability of the patterns to sense different biomarkers was monitored by fluorescence microscopy at different time intervals and could open up possibilities for inexpensive and facile detection of biologically important molecules, and thus introduce a new paradigm in reliable, robust, and low cost disease diagnostics.
DOI
In this work, we have developed linear micro‐patterns of phosphotungstic acid soft oxometalate (SOM) and perylene (as fluorophore) hybrid composite on a glass substrate using a thermo‐optical tweezers set‐up, and used it for sensing of biologically important molecules such as glucose, uric acid and ascorbic acid. Bulk scale studies on the SOM‐fluorophore hybrid were initially performed to optimize the fabrication of the pattern. The aqueous dispersion of the hybrid composite was subjected to UV and fluorescence measurements. The linear micro‐patterns were characterized using Raman spectroscopy and AFM. The ability of the patterns to sense different biomarkers was monitored by fluorescence microscopy at different time intervals and could open up possibilities for inexpensive and facile detection of biologically important molecules, and thus introduce a new paradigm in reliable, robust, and low cost disease diagnostics.
DOI
Tunable optical pulling force mediated by resonant electromagnetic coupling
Guangtao Guo, Tianhua Feng, and Yi Xu
In terms of the law of momentum conservation, the optical pulling force (OPF) is a counterintuitive phenomenon for optical manipulation. We investigate analytically and numerically the tunable OPF exerted on the low refractive index nanoparticle (NP) in a hybrid dimer system when it is illuminated by a plane wave based on the coupled dipole approximation method and the finite-difference time-domain method, respectively. The underlying physical mechanism relies on the near-field electromagnetic coupling between the low refractive index dielectric NP and the plasmonic NP. We further evaluate the dependence of the OPF on the geometrical parameters of the system. It is also numerically demonstrated that a Gaussian beam can be used to achieve pure OPF with no transverse force component. The proposed OPF offers an additional degree of freedom for optical sorting, transport, and trapping of NPs.
DOI
In terms of the law of momentum conservation, the optical pulling force (OPF) is a counterintuitive phenomenon for optical manipulation. We investigate analytically and numerically the tunable OPF exerted on the low refractive index nanoparticle (NP) in a hybrid dimer system when it is illuminated by a plane wave based on the coupled dipole approximation method and the finite-difference time-domain method, respectively. The underlying physical mechanism relies on the near-field electromagnetic coupling between the low refractive index dielectric NP and the plasmonic NP. We further evaluate the dependence of the OPF on the geometrical parameters of the system. It is also numerically demonstrated that a Gaussian beam can be used to achieve pure OPF with no transverse force component. The proposed OPF offers an additional degree of freedom for optical sorting, transport, and trapping of NPs.
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Large Diameter Fiber-Optics Tweezers forEscherichia ColiBacteria Manipulation
Qiangzhou Rong; Yajie Wang; Zhihua Shao; Xueguang Qiao
Large diameter fiber-optics tweezers are proposed in this paper, and their ability to trap and deliver Escherichia coli ( E. coli ) bacteria was characterized. The tweezers were formed by tapering four-mode fiber (FMF) with 8.7 μ m diameter, allowing the resonance field of the extended high-order modes to be used for manipulating the micro-objects. The diameter of the FMF taper was much larger than that of reported fiber-optic devices with nanoscale diameter, thereby making the device work as sturdier tweezers. The key factor for success is that, along the light transmission axis, the higher order modes have a unique mode field that extends longer and with a larger range around the fiber waist than the fundamental mode. At wavelengths ranging from 1500 to 1600 nm, especially close to 1560 nm, trapping and delivering of E. coli along the fiber was observed. In addition, a further demonstration for operation time shows a larger tapered fiber diameter was able to extend the service life of tweezers. The higher order micro-fiber modes offer a new opportunity for optical manipulation at the single-cell level.
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Large diameter fiber-optics tweezers are proposed in this paper, and their ability to trap and deliver Escherichia coli ( E. coli ) bacteria was characterized. The tweezers were formed by tapering four-mode fiber (FMF) with 8.7 μ m diameter, allowing the resonance field of the extended high-order modes to be used for manipulating the micro-objects. The diameter of the FMF taper was much larger than that of reported fiber-optic devices with nanoscale diameter, thereby making the device work as sturdier tweezers. The key factor for success is that, along the light transmission axis, the higher order modes have a unique mode field that extends longer and with a larger range around the fiber waist than the fundamental mode. At wavelengths ranging from 1500 to 1600 nm, especially close to 1560 nm, trapping and delivering of E. coli along the fiber was observed. In addition, a further demonstration for operation time shows a larger tapered fiber diameter was able to extend the service life of tweezers. The higher order micro-fiber modes offer a new opportunity for optical manipulation at the single-cell level.
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Photothermal dynamics of micro-glass beads coated with gold nanoparticles in water: Fine bubble generation and fluid-induced laser trapping
Shin-ichiro Yanagiya, Naoya Sekimoto and Akihiro Furube
In this study, gold nanoparticles were heterogeneously deposited onto the surfaces of glass beads through a gold ion reduction method to obtain "plasmonic beads". Plasmonic beads in pure water were illuminated with a visible continuous-wave laser through an objective lens. Using a relatively low-power laser, plasmonic beads were optically trapped and aggregated the other beads over an area much greater than the focal point. On the other hand, using a high-power laser (>20 mW/µm2), microbubbles were produced in water. Thus, the plasmonic beads studied herein can act as optically controllable fluid and microbubble generators.
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In this study, gold nanoparticles were heterogeneously deposited onto the surfaces of glass beads through a gold ion reduction method to obtain "plasmonic beads". Plasmonic beads in pure water were illuminated with a visible continuous-wave laser through an objective lens. Using a relatively low-power laser, plasmonic beads were optically trapped and aggregated the other beads over an area much greater than the focal point. On the other hand, using a high-power laser (>20 mW/µm2), microbubbles were produced in water. Thus, the plasmonic beads studied herein can act as optically controllable fluid and microbubble generators.
DOI
Controlling the Trajectories of Nano/Micro Particles Using Light-Actuated Marangoni Flow
Cunjing Lv, Subramanyan Namboodiri Varanakkottu, Tobias Baier, and Steffen Hardt
The ability to manipulate small objects and to produce patterns on the nano- and microscale is of great importance, both with respect to fundamentals and technological applications. The manipulation of particles with diameters of the order of 100 nm or below is a challenge because of their Brownian motion but also because of the scaling behavior of methods such as optical trapping. The unification of optical and hydrodynamic forces is a potential route toward the manipulation of tiny objects. Herein we demonstrate the trapping and manipulation of nano- and microparticles based on interfacial flows controlled by visible light, a method we denote as “Light-Actuated Marangoni Tweezer (LAMT)”. We experimentally study the manipulation of particles having diameters ranging from 20 nm to 10 μm, including quantum dots and polystyrene nano/microparticles. The particles can be manipulated by scanning a light beam along a liquid surface. In this way, we are able to define almost arbitrary particle trajectories, for example, in the form of letters. In addition, we are able to handle a number of particles in parallel by creating an optical “landscape” consisting of a multitude of laser spots. The inherent advantages of LAMTs are the linear scaling of the trapping force with the particle diameter and the fact that the force is less dependent on particle properties than in the case of conventional methods.
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Crystal Growth and Dissolution Dynamics of l-Phenylalanine Controlled by Solution Surface Laser Trapping
Ken-ichi Yuyama, Ding-Shiang Chiu, Yen-En Liu, Teruki Sugiyama, and Hiroshi Masuhara
We present sequential behavior of nucleation, growth, and dissolution of an l-phenylalanine plate-like crystal which is induced by a focused continuous-wave near-infrared laser beam in unsaturated solution. Upon the laser irradiation into the air/solution interface, the single crystal is generated from the focus and continuously grows two-dimensionally while being trapped by the laser. The crystal growth is stopped when the laser power is decreased. The crystal size is kept constant for a certain time period, and then the crystal starts dissolution. The dissolution is also induced by moving the crystal from the focus at the air/solution interface. When the crystal is shifted far from the original position where the crystallization is induced, the crystal starts dissolution at a certain distant position. Based on the demonstrations of the crystal size change during the laser manipulation, we conclude that the l-phenylalanine crystal is surrounded by a highly concentrated domain of a few hundreds of micrometers consisting of l-phenylalanine liquid-like clusters.
DOI
We present sequential behavior of nucleation, growth, and dissolution of an l-phenylalanine plate-like crystal which is induced by a focused continuous-wave near-infrared laser beam in unsaturated solution. Upon the laser irradiation into the air/solution interface, the single crystal is generated from the focus and continuously grows two-dimensionally while being trapped by the laser. The crystal growth is stopped when the laser power is decreased. The crystal size is kept constant for a certain time period, and then the crystal starts dissolution. The dissolution is also induced by moving the crystal from the focus at the air/solution interface. When the crystal is shifted far from the original position where the crystallization is induced, the crystal starts dissolution at a certain distant position. Based on the demonstrations of the crystal size change during the laser manipulation, we conclude that the l-phenylalanine crystal is surrounded by a highly concentrated domain of a few hundreds of micrometers consisting of l-phenylalanine liquid-like clusters.
DOI
Wednesday, October 24, 2018
Manipulating the Quantum Coherence of Optically Trapped Nanodiamonds
Lachlan W. Russell, Simon G. Ralph, Kazuma Wittick, Jean-Philippe Tetienne, David A. Simpson, and Peter J. Reece
The use of optical tweezers as a tool to facilitate nondestructive nanoscale sensing has been a growing area of research, particularly in the biological sciences. The nitrogen-vacancy (NV) center in diamond has attracted significant interest in this area due to the array of sensing modalities available and the biocompatibility of the material itself. Many of the diamond sensing modalities rely on the measurement and characterization of the NV spin. Recent work has demonstrated the utility of the spin–lattice relaxation time (T1) of NV centers in nanodiamond for nanoscale magnetic sensing and spectroscopy. Here, we demonstrate spin relaxometry with optically trapped nanodiamonds. The all-optical sensing protocol we developed eliminates the spin decoherence effects of the trapping laser and can determine spin–lattice relaxation times on the order of ms. Moreover, the protocol requires relatively low trapping powers <50 mW, making it particularly applicable to biological systems.
DOI
The use of optical tweezers as a tool to facilitate nondestructive nanoscale sensing has been a growing area of research, particularly in the biological sciences. The nitrogen-vacancy (NV) center in diamond has attracted significant interest in this area due to the array of sensing modalities available and the biocompatibility of the material itself. Many of the diamond sensing modalities rely on the measurement and characterization of the NV spin. Recent work has demonstrated the utility of the spin–lattice relaxation time (T1) of NV centers in nanodiamond for nanoscale magnetic sensing and spectroscopy. Here, we demonstrate spin relaxometry with optically trapped nanodiamonds. The all-optical sensing protocol we developed eliminates the spin decoherence effects of the trapping laser and can determine spin–lattice relaxation times on the order of ms. Moreover, the protocol requires relatively low trapping powers <50 mW, making it particularly applicable to biological systems.
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Three-Dimensional Optical Tweezers Tracking Resolves Random Sideward Steps of the Kinesin-8 Kip3
Michael Bugiel, Erik Schäffer
The budding yeast kinesin-8 Kip3 is a highly processive motor protein that walks to the ends of cytoskeletal microtubules and shortens them in a collective manner. However, how exactly Kip3 reaches the microtubule end is unclear. Although rotations of microtubules in multimotored Kip3 gliding assays implied directed sideward switching between microtubule protofilaments, two-dimensional, single-molecule, optical-tweezers assays indicated that Kip3 randomly switched protofilaments. Here, we topographically suspended microtubules such that Kip3 motors could freely access the microtubules in three dimensions. Tracking single-motor-driven microspheres with a three-dimensional, zero-load, optical-tweezers-based force clamp showed that Kip3 switched protofilaments in discrete steps equally frequent in both directions. A statistical analysis confirmed the diffusive sideward motion of Kip3, consistent with the two-dimensional single-molecule results. Furthermore, we found that motors were in one of three states: either not switching protofilaments or switching between them with a slow or fast sideward-stepping rate. Interestingly, this sideward diffusion was limited to one turn, suggesting that motors could not cross the microtubule seam. The diffusive protofilament switching may enable Kip3 to efficiently bypass obstacles and reach the microtubule end for length regulation.
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The budding yeast kinesin-8 Kip3 is a highly processive motor protein that walks to the ends of cytoskeletal microtubules and shortens them in a collective manner. However, how exactly Kip3 reaches the microtubule end is unclear. Although rotations of microtubules in multimotored Kip3 gliding assays implied directed sideward switching between microtubule protofilaments, two-dimensional, single-molecule, optical-tweezers assays indicated that Kip3 randomly switched protofilaments. Here, we topographically suspended microtubules such that Kip3 motors could freely access the microtubules in three dimensions. Tracking single-motor-driven microspheres with a three-dimensional, zero-load, optical-tweezers-based force clamp showed that Kip3 switched protofilaments in discrete steps equally frequent in both directions. A statistical analysis confirmed the diffusive sideward motion of Kip3, consistent with the two-dimensional single-molecule results. Furthermore, we found that motors were in one of three states: either not switching protofilaments or switching between them with a slow or fast sideward-stepping rate. Interestingly, this sideward diffusion was limited to one turn, suggesting that motors could not cross the microtubule seam. The diffusive protofilament switching may enable Kip3 to efficiently bypass obstacles and reach the microtubule end for length regulation.
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3D laser nano-printing on fibre paves the way for super-focusing of multimode laser radiation
Grigorii S. Sokolovskii, Vasileia Melissinaki, Ksenia A. Fedorova, Vladislav V. Dudelev, Sergey N. Losev, Vladislav E. Bougrov, Wilson Sibbett, Maria Farsari & Edik U. Rafailov
Multimode high-power laser diodes suffer from inefficient beam focusing, leading to a focal spot 10–100 times greater than the diffraction limit. This inevitably restricts their wider use in ‘direct-diode’ applications in materials processing and biomedical photonics. We report here a ‘super-focusing’ characteristic for laser diodes, where the exploitation of self-interference of modes enables a significant reduction of the focal spot size. This is achieved by employing a conical microlens fabricated on the tip of a multimode optical fibre using 3D laser nano-printing (also known as multi-photon lithography). When refracted by the conical surface, the modes of the fibre-coupled laser beam self-interfere and form an elongated narrow focus, usually referred to as a ‘needle’ beam. The multiphoton lithography technique allows the realisation of almost any optical element on a fibre tip, thus providing the most suitable interface for free-space applications of multimode fibre-delivered laser beams. In addition, we demonstrate the optical trapping of microscopic objects with a super-focused multimode laser diode beam thus rising new opportunities within the applications sector where lab-on-chip configurations can be exploited. Most importantly, the demonstrated super-focusing approach opens up new avenues for the ‘direct-diode’ applications in material processing and 3D printing, where both high power and tight focusing is required.
DOI
Multimode high-power laser diodes suffer from inefficient beam focusing, leading to a focal spot 10–100 times greater than the diffraction limit. This inevitably restricts their wider use in ‘direct-diode’ applications in materials processing and biomedical photonics. We report here a ‘super-focusing’ characteristic for laser diodes, where the exploitation of self-interference of modes enables a significant reduction of the focal spot size. This is achieved by employing a conical microlens fabricated on the tip of a multimode optical fibre using 3D laser nano-printing (also known as multi-photon lithography). When refracted by the conical surface, the modes of the fibre-coupled laser beam self-interfere and form an elongated narrow focus, usually referred to as a ‘needle’ beam. The multiphoton lithography technique allows the realisation of almost any optical element on a fibre tip, thus providing the most suitable interface for free-space applications of multimode fibre-delivered laser beams. In addition, we demonstrate the optical trapping of microscopic objects with a super-focused multimode laser diode beam thus rising new opportunities within the applications sector where lab-on-chip configurations can be exploited. Most importantly, the demonstrated super-focusing approach opens up new avenues for the ‘direct-diode’ applications in material processing and 3D printing, where both high power and tight focusing is required.
DOI
Opto-Thermophoretic Tweezers and Assembly
Jingang Li, Linhan Lin, Yuji Inoue and Yuebing Zheng
Opto-thermophoretic manipulation is an emerging field, which exploits the thermophoretic migration of particles and colloidal species under a light-controlled temperature gradient field. The entropically favorable photon–phonon conversion and widely applicable heat-directed migration make it promising for low-power manipulation of variable particles in different fluidic environments. By exploiting an optothermal substrate, versatile opto-thermophoretic manipulation of colloidal particles and biological objects can be achieved via optical heating. In this paper, we summarize the working principles, concepts, and applications of the recently developed opto-thermophoretic techniques. Opto-thermophoretic trapping, tweezing, assembly, and printing of colloidal particles and biological objects are discussed thoroughly. With their low-power operation, simple optics, and diverse functionalities, opto-thermophoretic manipulation techniques will offer great opportunities in materials science, nanomanufacturing, life sciences, colloidal science, and nanomedicine.
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Opto-thermophoretic manipulation is an emerging field, which exploits the thermophoretic migration of particles and colloidal species under a light-controlled temperature gradient field. The entropically favorable photon–phonon conversion and widely applicable heat-directed migration make it promising for low-power manipulation of variable particles in different fluidic environments. By exploiting an optothermal substrate, versatile opto-thermophoretic manipulation of colloidal particles and biological objects can be achieved via optical heating. In this paper, we summarize the working principles, concepts, and applications of the recently developed opto-thermophoretic techniques. Opto-thermophoretic trapping, tweezing, assembly, and printing of colloidal particles and biological objects are discussed thoroughly. With their low-power operation, simple optics, and diverse functionalities, opto-thermophoretic manipulation techniques will offer great opportunities in materials science, nanomanufacturing, life sciences, colloidal science, and nanomedicine.
DOI
On-chip optical trapping of extracellular vesicles using box-shaped composite SiO2-Si3N4 waveguides
Gyllion Brian Loozen and Jacob Caro
The application of on-chip optical trapping and Raman spectroscopy using a dual-waveguide trap has so far been limited to relatively big synthetic and biological particles (e.g., polystyrene beads and blood cells). Here, from simulations, we present the capabilities of dual-waveguide traps built from composite SiO2-Si3N4 waveguides for optical trapping of extracellular vesicles (EVs). EVs, tiny cell-derived particles of size in the range 30−1000 nm, strongly attract attention as potential biomarkers for cancer. EVs are hard to trap, because of their smallness and low index contract w.r.t. water. This poses a challenge for on-chip trapping. From finite-difference time-domain simulations we obtain the narrow beam emitted from the waveguide facet into water, for λ = 785 nm. For a pair of such beams, in a counter-propagating geometry and for facet separations of 5, 10 and 15 µm, we derive the inter-facet optical field, which has a characteristic interference pattern with hot spots for trapping, and calculate the optical force exerted on EVs of size in the range 50−1000 nm, as a function of EV position. We use two refractive index models for the EV optical properties. Integration of the force curves leads to the trapping potentials, which are well-shaped in the transverse and oscillatory in the longitudinal direction. By applying Ashkin’s criterion, the conditions for stable trapping are established, the central result of this work. Very small EVs can be stably trapped with the traps by applying a power also suitable for Raman spectroscopy, down to a smallest EV diameter of 115 nm. We thus argue that this dual-waveguide trap is a promising lab-on-a-chip device with clinical relevance for diagnosis of cancer.
DOI
The application of on-chip optical trapping and Raman spectroscopy using a dual-waveguide trap has so far been limited to relatively big synthetic and biological particles (e.g., polystyrene beads and blood cells). Here, from simulations, we present the capabilities of dual-waveguide traps built from composite SiO2-Si3N4 waveguides for optical trapping of extracellular vesicles (EVs). EVs, tiny cell-derived particles of size in the range 30−1000 nm, strongly attract attention as potential biomarkers for cancer. EVs are hard to trap, because of their smallness and low index contract w.r.t. water. This poses a challenge for on-chip trapping. From finite-difference time-domain simulations we obtain the narrow beam emitted from the waveguide facet into water, for λ = 785 nm. For a pair of such beams, in a counter-propagating geometry and for facet separations of 5, 10 and 15 µm, we derive the inter-facet optical field, which has a characteristic interference pattern with hot spots for trapping, and calculate the optical force exerted on EVs of size in the range 50−1000 nm, as a function of EV position. We use two refractive index models for the EV optical properties. Integration of the force curves leads to the trapping potentials, which are well-shaped in the transverse and oscillatory in the longitudinal direction. By applying Ashkin’s criterion, the conditions for stable trapping are established, the central result of this work. Very small EVs can be stably trapped with the traps by applying a power also suitable for Raman spectroscopy, down to a smallest EV diameter of 115 nm. We thus argue that this dual-waveguide trap is a promising lab-on-a-chip device with clinical relevance for diagnosis of cancer.
DOI
Colloidal rods in optical potential energy landscapes
Joshua L. Abbott, James A. Spiers, Yongxiang Gao, Dirk G A L Aarts and Roel P A Dullens
We study the static and dynamic behaviour of colloidal rods in an optical potential energy landscape. We explore the stable states of a colloidal rod in a single optical trap close to a flat wall. Here two metastable states are observed, horizontal and vertical, both of which experience a parabolic potential energy landscape. Next we place a colloidal rod into a one-dimensional sinusoidal optical potential energy landscape and introduce a constant driving velocity. When driven below the critical velocity, the particle is confined to a single potential energy minimum of the optical landscape and the equilibrium position of a particle is investigated. The equilibrium position of a rod is found to vary substantially from that of a sphere due to the drag coefficient of a rod, which is highly dependent on its proximity to an optical trap. The driving velocity is increased to enable the particle to traverse the periodic landscape and above the critical velocity, the average particle velocity increases as the square root of the driving velocity. When introducing oscillations to the driving velocity we observe dynamic mode locking and characterise the nature of synchronised motion of the rod-like particles.
DOI
We study the static and dynamic behaviour of colloidal rods in an optical potential energy landscape. We explore the stable states of a colloidal rod in a single optical trap close to a flat wall. Here two metastable states are observed, horizontal and vertical, both of which experience a parabolic potential energy landscape. Next we place a colloidal rod into a one-dimensional sinusoidal optical potential energy landscape and introduce a constant driving velocity. When driven below the critical velocity, the particle is confined to a single potential energy minimum of the optical landscape and the equilibrium position of a particle is investigated. The equilibrium position of a rod is found to vary substantially from that of a sphere due to the drag coefficient of a rod, which is highly dependent on its proximity to an optical trap. The driving velocity is increased to enable the particle to traverse the periodic landscape and above the critical velocity, the average particle velocity increases as the square root of the driving velocity. When introducing oscillations to the driving velocity we observe dynamic mode locking and characterise the nature of synchronised motion of the rod-like particles.
DOI
Tuesday, October 23, 2018
Laser-induced angular momentum of spheroidal metal nanoparticle in a medium
Nicolas I. Grigorchuk
A theory for the generation in a spheroidal metallic nanoparticle of an angular momentum under the action of ultrashort laser pulse is developed. We proposed the mechanism for generation of rotation force associated with nanoparticle polarization in the frequency region close to the surface plasmon resonances. Under illumination of the laser field the nanoparticle with an asymmetrical shape is polarized and becomes a dipole. The pair of electric field forces tends to turn the dipole along the field direction. As a result, the angular momentum arises. It is considered that the polarization becomes a tensor quantity for the nanoparticle sizes smaller than the electron mean free path in it. It is shown that the rotation direction can be controlled by varying the wavelength of the incident light. The expressions for the components of the polarization tensor and for the angular momentum of a spheroidal metal nanoparticle are obtained.
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A theory for the generation in a spheroidal metallic nanoparticle of an angular momentum under the action of ultrashort laser pulse is developed. We proposed the mechanism for generation of rotation force associated with nanoparticle polarization in the frequency region close to the surface plasmon resonances. Under illumination of the laser field the nanoparticle with an asymmetrical shape is polarized and becomes a dipole. The pair of electric field forces tends to turn the dipole along the field direction. As a result, the angular momentum arises. It is considered that the polarization becomes a tensor quantity for the nanoparticle sizes smaller than the electron mean free path in it. It is shown that the rotation direction can be controlled by varying the wavelength of the incident light. The expressions for the components of the polarization tensor and for the angular momentum of a spheroidal metal nanoparticle are obtained.
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Gram-type differentiation of bacteria with 2D hollow photonic crystal cavities
R. Therisod, M. Tardif, P. R. Marcoux, E. Picard, J.-B. Jager, E. Hadji, D. Peyrade, and R. Houdré
Fast and label-free techniques to analyze viruses and bacteria are of crucial interest in biological and bio-medical applications. For this purpose, optofluidic systems based on the integration of photonic structures with microfluidic layers were shown to be promising tools for biological analysis, thanks to their small footprint and to their ability to manipulate objects using low powers. In this letter, we report on the optical trapping of living bacteria in a 2D silicon hollow photonic crystal cavity. This structure allows for the Gram-type differentiation of bacteria at the single cell scale, in a fast, label-free, and non-destructive way.
DOI
Fast and label-free techniques to analyze viruses and bacteria are of crucial interest in biological and bio-medical applications. For this purpose, optofluidic systems based on the integration of photonic structures with microfluidic layers were shown to be promising tools for biological analysis, thanks to their small footprint and to their ability to manipulate objects using low powers. In this letter, we report on the optical trapping of living bacteria in a 2D silicon hollow photonic crystal cavity. This structure allows for the Gram-type differentiation of bacteria at the single cell scale, in a fast, label-free, and non-destructive way.
DOI
Positive cardiac inotrope omecamtiv mecarbil activates muscle despite suppressing the myosin working stroke
Michael S. Woody, Michael J. Greenberg, Bipasha Barua, Donald A. Winkelmann, Yale E. Goldman & E. Michael Ostap
Omecamtiv mecarbil (OM) is a positive cardiac inotrope in phase-3 clinical trials for treatment of heart failure. Although initially described as a direct myosin activator, subsequent studies are at odds with this description and do not explain OM-mediated increases in cardiac performance. Here we show, via single-molecule, biophysical experiments on cardiac myosin, that OM suppresses myosin’s working stroke and prolongs actomyosin attachment 5-fold, which explains inhibitory actions of the drug observed in vitro. OM also causes the actin-detachment rate to become independent of both applied load and ATP concentration. Surprisingly, increased myocardial force output in the presence of OM can be explained by cooperative thin-filament activation by OM-inhibited myosin molecules. Selective suppression of myosin is an unanticipated route to muscle activation that may guide future development of therapeutic drugs.
DOI
Omecamtiv mecarbil (OM) is a positive cardiac inotrope in phase-3 clinical trials for treatment of heart failure. Although initially described as a direct myosin activator, subsequent studies are at odds with this description and do not explain OM-mediated increases in cardiac performance. Here we show, via single-molecule, biophysical experiments on cardiac myosin, that OM suppresses myosin’s working stroke and prolongs actomyosin attachment 5-fold, which explains inhibitory actions of the drug observed in vitro. OM also causes the actin-detachment rate to become independent of both applied load and ATP concentration. Surprisingly, increased myocardial force output in the presence of OM can be explained by cooperative thin-filament activation by OM-inhibited myosin molecules. Selective suppression of myosin is an unanticipated route to muscle activation that may guide future development of therapeutic drugs.
DOI
Co-Entangled Actin-Microtubule Composites Exhibit Tunable Stiffness and Power-Law Stress Relaxation
Shea N.Ricketts, Jennifer L.Ross, Rae M.Robertson-Anderson
We use optical tweezers microrheology and fluorescence microscopy to characterize the nonlinear mesoscale mechanics and mobility of in vitro co-entangled actin-microtubule composites. We create a suite of randomly oriented, well-mixed networks of actin and microtubules by co-polymerizing varying ratios of actin and tubulin in situ. To perturb each composite far from equilibrium, we use optical tweezers to displace an embedded microsphere a distance greater than the lengths of the filaments at a speed much faster than their intrinsic relaxation rates. We simultaneously measure the force the filaments exert on the bead and the subsequent force relaxation. We find that the presence of a large fraction of microtubules (>0.7) is needed to substantially increase the measured force, which is accompanied by large heterogeneities in force response. Actin minimizes these heterogeneities by reducing the mesh size of the composites and supporting microtubules against buckling. Composites also undergo a sharp transition from strain softening to stiffening when the fraction of microtubules (ϕT) exceeds 0.5, which we show arises from faster poroelastic relaxation and suppressed actin bending fluctuations. The force after bead displacement relaxes via power-law decay after an initial period of minimal relaxation. The short-time relaxation profiles (t < 0.06 s) arise from poroelastic and bending contributions, whereas the long-time power-law relaxation is indicative of filaments reptating out of deformed entanglement constraints. The scaling exponents for the long-time relaxation exhibit a nonmonotonic dependence on ϕT, reaching a maximum for equimolar composites (ϕT = 0.5), suggesting that reptation is fastest in ϕT = 0.5 composites. Corresponding mobility measurements of steady-state actin and microtubules show that both filaments are indeed the most mobile in ϕT = 0.5 composites. This nonmonotonic dependence of mobility on ϕT demonstrates the important interplay between mesh size and filament rigidity in polymer networks and highlights the surprising emergent properties that can arise in composites.
We use optical tweezers microrheology and fluorescence microscopy to characterize the nonlinear mesoscale mechanics and mobility of in vitro co-entangled actin-microtubule composites. We create a suite of randomly oriented, well-mixed networks of actin and microtubules by co-polymerizing varying ratios of actin and tubulin in situ. To perturb each composite far from equilibrium, we use optical tweezers to displace an embedded microsphere a distance greater than the lengths of the filaments at a speed much faster than their intrinsic relaxation rates. We simultaneously measure the force the filaments exert on the bead and the subsequent force relaxation. We find that the presence of a large fraction of microtubules (>0.7) is needed to substantially increase the measured force, which is accompanied by large heterogeneities in force response. Actin minimizes these heterogeneities by reducing the mesh size of the composites and supporting microtubules against buckling. Composites also undergo a sharp transition from strain softening to stiffening when the fraction of microtubules (ϕT) exceeds 0.5, which we show arises from faster poroelastic relaxation and suppressed actin bending fluctuations. The force after bead displacement relaxes via power-law decay after an initial period of minimal relaxation. The short-time relaxation profiles (t < 0.06 s) arise from poroelastic and bending contributions, whereas the long-time power-law relaxation is indicative of filaments reptating out of deformed entanglement constraints. The scaling exponents for the long-time relaxation exhibit a nonmonotonic dependence on ϕT, reaching a maximum for equimolar composites (ϕT = 0.5), suggesting that reptation is fastest in ϕT = 0.5 composites. Corresponding mobility measurements of steady-state actin and microtubules show that both filaments are indeed the most mobile in ϕT = 0.5 composites. This nonmonotonic dependence of mobility on ϕT demonstrates the important interplay between mesh size and filament rigidity in polymer networks and highlights the surprising emergent properties that can arise in composites.
Inhomogeneity-Induced Casimir Transport of Nanoparticles
Fanglin Bao, Kezhang Shi, Guanjun Cao, Julian S. Evans, and Sailing He
We propose a scheme for transporting nanoparticles immersed in a fluid, relying on quantum vacuum fluctuations. The mechanism lies in the inhomogeneity-induced lateral Casimir force between a nanoparticle and a gradient metasurface and the relaxation of the conventional Dzyaloshinskiǐ-Lifshitz-Pitaevskiǐ constraint, which allows quantum levitation for a broader class of material configurations. The velocity for a nanosphere levitated above a grating is calculated and can be up to a few microns per minute. The Born approximation gives general expressions for the Casimir energy which reveal size-selective transport. For any given metasurface, a certain particle-metasurface separation exists where the transport velocity peaks, forming a “Casimir passage.” The sign and strength of the Casimir interactions can be tuned by the shapes of liquid-air menisci, potentially allowing real-time control of an otherwise passive force, and enabling interesting on-off or directional switching of the transport process.
DOI
We propose a scheme for transporting nanoparticles immersed in a fluid, relying on quantum vacuum fluctuations. The mechanism lies in the inhomogeneity-induced lateral Casimir force between a nanoparticle and a gradient metasurface and the relaxation of the conventional Dzyaloshinskiǐ-Lifshitz-Pitaevskiǐ constraint, which allows quantum levitation for a broader class of material configurations. The velocity for a nanosphere levitated above a grating is calculated and can be up to a few microns per minute. The Born approximation gives general expressions for the Casimir energy which reveal size-selective transport. For any given metasurface, a certain particle-metasurface separation exists where the transport velocity peaks, forming a “Casimir passage.” The sign and strength of the Casimir interactions can be tuned by the shapes of liquid-air menisci, potentially allowing real-time control of an otherwise passive force, and enabling interesting on-off or directional switching of the transport process.
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Carboplatin as an alternative to Cisplatin in chemotherapies: New insights at single molecule level
L.Oliveira, J.M.Caquito Jr, M.S. Rocha
Here we report a new study performed at single molecule level on the interaction of the antineoplastic drug Carboplatin and the DNA molecule - the main target of the drug inside cells in cancer chemotherapies. By using optical tweezers, we measure how the mechanical properties of the DNA-Carboplatin complexes changes as a function of the drug concentration in the sample, for two different ionic strengths ([Na] = 150 mM and [Na] = 1 mM). From these measurements, the binding mechanism and the physicochemical (binding) parameters of the interaction were inferred and directly compared to those obtained for the precursor drug Cisplatin under equivalent conditions. As the main conclusion, we show that Carboplatin binds preferentially forming covalent monoadducts in contrast to Cisplatin, which is hydrolyzed easier and presents a higher efficiency in forming covalent diadducts along the double-helix. In addition, we explicitly show that Carboplatin is much less sensitive to ionic strength changes when compared to Cisplatin. These findings provide new insights on the interactions of platinum-based compounds with the DNA molecule, being important to improve the current treatments and in the development of new antineoplastic agents.
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Here we report a new study performed at single molecule level on the interaction of the antineoplastic drug Carboplatin and the DNA molecule - the main target of the drug inside cells in cancer chemotherapies. By using optical tweezers, we measure how the mechanical properties of the DNA-Carboplatin complexes changes as a function of the drug concentration in the sample, for two different ionic strengths ([Na] = 150 mM and [Na] = 1 mM). From these measurements, the binding mechanism and the physicochemical (binding) parameters of the interaction were inferred and directly compared to those obtained for the precursor drug Cisplatin under equivalent conditions. As the main conclusion, we show that Carboplatin binds preferentially forming covalent monoadducts in contrast to Cisplatin, which is hydrolyzed easier and presents a higher efficiency in forming covalent diadducts along the double-helix. In addition, we explicitly show that Carboplatin is much less sensitive to ionic strength changes when compared to Cisplatin. These findings provide new insights on the interactions of platinum-based compounds with the DNA molecule, being important to improve the current treatments and in the development of new antineoplastic agents.
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Monday, October 22, 2018
Spatial multiplexing for tailored fully-structured light
E Otte, K Tekce and C Denz
Fully-structured light is an emerging approach to sculpt light in all its degrees of freedom, i.e. amplitude, phase and polarization with a high transverse resolution and complex modulation patterns. Such an attractive and versatile approach for advanced optical trapping or fabricating novel materials still poses fundamental as well as technical challenges. Though the implementation of spatial light modulators (SLMs) has opened up a promising path for this task, up to now, fully-structured light can only be achieved using interferometric methods, multiple SLMs, or split-screen techniques reducing spatial resolution. We present a sophisticated single-beam approach based on spatial multiplexing, which does not only allow joint customization of phase and polarization combined with natural and prospectively even on-demand amplitude modulation, but also ensures high spatial resolution by the use of a single standard SLM in the full-screen mode. We demonstrate the capabilities of our approach realizing double phase modulated light fields, as well as first- and higher-order vector modes with additional global phase modulation and natural amplitude shaping. These findings open new perspectives to optically trap polarization-sensitive, i.e. magnetic particles and advance laser material machining in anisotropic, birefingent matter.
DOI
Fully-structured light is an emerging approach to sculpt light in all its degrees of freedom, i.e. amplitude, phase and polarization with a high transverse resolution and complex modulation patterns. Such an attractive and versatile approach for advanced optical trapping or fabricating novel materials still poses fundamental as well as technical challenges. Though the implementation of spatial light modulators (SLMs) has opened up a promising path for this task, up to now, fully-structured light can only be achieved using interferometric methods, multiple SLMs, or split-screen techniques reducing spatial resolution. We present a sophisticated single-beam approach based on spatial multiplexing, which does not only allow joint customization of phase and polarization combined with natural and prospectively even on-demand amplitude modulation, but also ensures high spatial resolution by the use of a single standard SLM in the full-screen mode. We demonstrate the capabilities of our approach realizing double phase modulated light fields, as well as first- and higher-order vector modes with additional global phase modulation and natural amplitude shaping. These findings open new perspectives to optically trap polarization-sensitive, i.e. magnetic particles and advance laser material machining in anisotropic, birefingent matter.
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Optimization of a spatial light modulator driven by digital video interface graphics to generate holographic optical traps
Deepak K. Gupta, B. V. R. Tata, and T. R. Ravindran
We propose a method to optimize spatial light modulators (SLMs) driven by digital video interface graphics in a holographic optical tweezers system. A method analogous to that used to optimize LCD televisions is used to optimize the properties of the graphics card through a diffraction-based experiment and develop a lookup table for the SLM. The optimization allows the SLM to function with its full phase modulation depth with improved diffraction efficiency. Further, we propose a simple and robust method to correct for the spatially varying phase response of the SLM to enhance its diffraction efficiency. The optimization results in an improvement of uniformity in the intensity and quality of the trap spots.
DOI
We propose a method to optimize spatial light modulators (SLMs) driven by digital video interface graphics in a holographic optical tweezers system. A method analogous to that used to optimize LCD televisions is used to optimize the properties of the graphics card through a diffraction-based experiment and develop a lookup table for the SLM. The optimization allows the SLM to function with its full phase modulation depth with improved diffraction efficiency. Further, we propose a simple and robust method to correct for the spatially varying phase response of the SLM to enhance its diffraction efficiency. The optimization results in an improvement of uniformity in the intensity and quality of the trap spots.
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Raman characterizations of red blood cells with β-thalassemia using laser tweezers Raman spectroscopy
Jia, Wenguang, MS; Chen, Ping, MD; Chen, Wenqiang, MD; Li, Yongqing, MD
This study aimed to study the differences in Raman spectra of red blood cells (RBCs) among patients with β-thalassemia and controls using laser tweezers Raman spectroscopy (LTRS) system. A total of 33 patients with β-thalassemia major, 49 with β-thalassemia minor, and 65 controls were studied. Raman spectra of RBCs for each sample were recorded. Principal component analysis (PCA), one-way analysis of variance (ANOVA), and independent-sample t test were performed. The intensities of Raman spectra of β-thalassemia (major and minor) RBCs were lower than those of controls, especially at bands 1546, 1603, and 1619 cm–1. The intensity ratio of band 1546 cm–1 to band 1448 cm–1 demonstrated that there was a significant difference between the spectra of β-thalassemia major (mostly below 2.15) and those of controls. The spectra of controls could be well distinguished from those of β-thalassemia major using PCA. After normalization, the spectra of two different genotypes with β0/β0 mutations mainly overlapped, while those with β+/β+ mutations had lower intensity at bands 1546, 1603, and 1619 cm–1. The present study provided Raman characteristics of RBCs in patients with β-thalassemia major and supported the use of LTRS as a method for screening β-thalassemia major. The recognition rate for β-thalassemia minor needs to be further improved.
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Optical force decoration of 3D microstructures with plasmonic particles
M. G. Donato, V. P. Rajamanickam, A. Foti, P. G. Gucciardi, C. Liberale, and O. M. Maragò
Optical forces are used to push and aggregate gold nanorods onto several substrates creating surface-enhanced Raman scattering (SERS) active hot spots for Raman-based identification of proteins. By monitoring the increase of the protein SERS signal, we observe different aggregation times for different curvatures of the substrates. The slower aggregation dynamics on curved surfaces is justified by a simple geometrical model. In particular, this technique is used to decorate three-dimensional microstructures and to quickly realize hybrid micro/nanosensors for highly sensitive detection of biological material directly in a liquid environment.
DOI
Optical forces are used to push and aggregate gold nanorods onto several substrates creating surface-enhanced Raman scattering (SERS) active hot spots for Raman-based identification of proteins. By monitoring the increase of the protein SERS signal, we observe different aggregation times for different curvatures of the substrates. The slower aggregation dynamics on curved surfaces is justified by a simple geometrical model. In particular, this technique is used to decorate three-dimensional microstructures and to quickly realize hybrid micro/nanosensors for highly sensitive detection of biological material directly in a liquid environment.
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Highly Resolved Brownian Motion in Space and in Time
Jianyong Mo and Mark G. Raizen
Since the discovery of Brownian motion in bulk fluids by Robert Brown in 1827, Brownian motion at long timescales has been extensively studied both theoretically and experimentally for over a century. The theory for short-timescale Brownian motion was also well established in the last century, while experimental studies were not accessible until this decade. This article reviews experimental progress on short-timescale Brownian motion and related applications. The ability to measure instantaneous velocity enables new fundamental tests of statistical mechanics of Brownian particles, such as the Maxwell–Boltzmann velocity distribution and the energy equipartition theorem. In addition, Brownian particles can be used as probes to study boundary effects imposed by a solid wall, wettability at solid–fluid interfaces, and viscoelasticity. We propose future studies of fluid compressibility and nonequilibrium physics using short-duration pulsed lasers. Lastly, we also propose that an optically trapped particle can serve as a new testing ground for nucleation in a supersaturated vapor or a supercooled liquid.
DOI
Since the discovery of Brownian motion in bulk fluids by Robert Brown in 1827, Brownian motion at long timescales has been extensively studied both theoretically and experimentally for over a century. The theory for short-timescale Brownian motion was also well established in the last century, while experimental studies were not accessible until this decade. This article reviews experimental progress on short-timescale Brownian motion and related applications. The ability to measure instantaneous velocity enables new fundamental tests of statistical mechanics of Brownian particles, such as the Maxwell–Boltzmann velocity distribution and the energy equipartition theorem. In addition, Brownian particles can be used as probes to study boundary effects imposed by a solid wall, wettability at solid–fluid interfaces, and viscoelasticity. We propose future studies of fluid compressibility and nonequilibrium physics using short-duration pulsed lasers. Lastly, we also propose that an optically trapped particle can serve as a new testing ground for nucleation in a supersaturated vapor or a supercooled liquid.
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On-the-Fly Calibrated Measure and Remote Control of Temperature and Viscosity at Nanoscale
Dipankar Mondal, Soumendra Nath Bandyopadhyay, Paresh Mathur, and Debabrata Goswami
A novel on-the-fly calibration method of optical tweezers is presented, which enables in situ control and measure of absolute temperature and viscosity at nanoscale dimensions. Such noncontact measurement and control at the nanoscale are challenging as the present techniques only provide off-line measurements that do not provide absolute values. Additionally, some of the present methods have a low spatial resolution. We simultaneously apply the high temporal sensitivity of position autocorrelation and equipartition theorem to precisely measure and control in situ temperature and the corresponding microrheological property around the focal volume of the trap at high spatial resolution. The femtosecond optical tweezers (FOTs) use a single-beam high repetition rate laser for optical trapping to result in finer temperature gradients in comparison to the continuous-wave laser tweezers. Such finer temperature gradients are due to the additional nonlinear optical (NLO) phenomena occurring only at the nanoscale focal plane of the FOTs. Because NLO processes are laser peak power-dependent, they promote an effective study of physical properties occurring only at the focal plane. Using FOTs at optically benign near-infrared wavelengths, we demonstrate microrheological control and measurement in water by adding a highly absorbing yet low fluorescent dye (IR780).
DOI
A novel on-the-fly calibration method of optical tweezers is presented, which enables in situ control and measure of absolute temperature and viscosity at nanoscale dimensions. Such noncontact measurement and control at the nanoscale are challenging as the present techniques only provide off-line measurements that do not provide absolute values. Additionally, some of the present methods have a low spatial resolution. We simultaneously apply the high temporal sensitivity of position autocorrelation and equipartition theorem to precisely measure and control in situ temperature and the corresponding microrheological property around the focal volume of the trap at high spatial resolution. The femtosecond optical tweezers (FOTs) use a single-beam high repetition rate laser for optical trapping to result in finer temperature gradients in comparison to the continuous-wave laser tweezers. Such finer temperature gradients are due to the additional nonlinear optical (NLO) phenomena occurring only at the nanoscale focal plane of the FOTs. Because NLO processes are laser peak power-dependent, they promote an effective study of physical properties occurring only at the focal plane. Using FOTs at optically benign near-infrared wavelengths, we demonstrate microrheological control and measurement in water by adding a highly absorbing yet low fluorescent dye (IR780).
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Determining the size and refractive index of single aerosol particles using angular light scattering and Mie resonances
Alison Bain, Aidan Rafferty, Thomas C. Preston
Optical trapping allows for high precision studies of many microphysical and chemical processes as it enables measurements on the single-particle level. This has been a tremendous benefit to fundamental aerosol research. In the vast majority of these experiments, trapped particles are characterized using light scattering – most often angular light scattering (phase functions) or Mie resonance spectroscopy. In this report, we compare the radii and refractive indices of best-fit found with these two light scattering methods by trapping single aerosol particles in a relative humidity-controlled cell where we can simultaneously measure both phase functions and Mie resonances, the latter of which are found using cavity-enhanced Raman scattering. Additionally, we compare best-fits found using both one- and two-dimensional phase functions. The application of Mie theory to these light scattering problems is thoroughly reviewed. Both the accuracy and uncertainty of the best-fits that these light scattering techniques produce are investigated using a model aqueous inorganic aerosol particle.
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Optical trapping allows for high precision studies of many microphysical and chemical processes as it enables measurements on the single-particle level. This has been a tremendous benefit to fundamental aerosol research. In the vast majority of these experiments, trapped particles are characterized using light scattering – most often angular light scattering (phase functions) or Mie resonance spectroscopy. In this report, we compare the radii and refractive indices of best-fit found with these two light scattering methods by trapping single aerosol particles in a relative humidity-controlled cell where we can simultaneously measure both phase functions and Mie resonances, the latter of which are found using cavity-enhanced Raman scattering. Additionally, we compare best-fits found using both one- and two-dimensional phase functions. The application of Mie theory to these light scattering problems is thoroughly reviewed. Both the accuracy and uncertainty of the best-fits that these light scattering techniques produce are investigated using a model aqueous inorganic aerosol particle.
DOI
Thursday, October 18, 2018
Living Nanospear for Near-Field Optical Probing
Yuchao Li, Hongbao Xin, Yao Zhang, Hongxiang Lei, Tianhang Zhang, Huapeng Ye, Juan Jose Saenz, Cheng-Wei Qiu, and Baojun Li
Optical nanoprobes, designed to emit or collect light in the close proximity of a sample, have been extensively used to sense and image at nanometer resolution. However, the available nanoprobes, constructed from artificial materials, are incompatible and invasive when interfacing with biological systems. In this work, we report a fully biocompatible nanoprobe for subwavelength probing of localized fluorescence from leukemia single-cells in human blood. The bioprobe is built on a tapered fiber tip apex by optical trapping of a yeast cell (1.4 μm radius) and a chain of Lactobacillus acidophilus cells (2 μm length and 200 nm radius), which act as a high-aspect-ratio nanospear. Light propagating along the bionanospear can be focused into a spot with a full width at half-maximum (fwhm) of 190 nm on the surface of single cells. Fluorescence signals are detected in real time at subwavelength spatial resolution. These noninvasive and biocompatible optical probes will find applications in imaging and manipulation of biospecimens.
DOI
Optical nanoprobes, designed to emit or collect light in the close proximity of a sample, have been extensively used to sense and image at nanometer resolution. However, the available nanoprobes, constructed from artificial materials, are incompatible and invasive when interfacing with biological systems. In this work, we report a fully biocompatible nanoprobe for subwavelength probing of localized fluorescence from leukemia single-cells in human blood. The bioprobe is built on a tapered fiber tip apex by optical trapping of a yeast cell (1.4 μm radius) and a chain of Lactobacillus acidophilus cells (2 μm length and 200 nm radius), which act as a high-aspect-ratio nanospear. Light propagating along the bionanospear can be focused into a spot with a full width at half-maximum (fwhm) of 190 nm on the surface of single cells. Fluorescence signals are detected in real time at subwavelength spatial resolution. These noninvasive and biocompatible optical probes will find applications in imaging and manipulation of biospecimens.
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Temperature elevation and fluid convection under optical trapping condition as revealed by fluorescence correlation spectroscopy
Kenji Setoura; Keisuke Fujita; Syoji Ito; Hiroshi Miyasaka
Temperature of matter increases under intense photoirradiation owing to photothermal conversion. The photothermal effect is sometimes a significant issue in optical manipulation usually requiring intense optical fields. Quantitative evaluation of local temperature under photoirradiation can, therefore, provide indispensable information for optical manipulation. In a previous work, we have applied fluorescence correlation spectroscopy (FCS) to monitor the temperature under the optical trapping condition in water, ethanol, and ethylene glycol. We pointed out that analyses of diffusion time of fluorescent dyes could provide information about temperature on the basis of temperature-dependent viscosities of the solvents. In the present work, the FCS thermometry was applied to seven solvents including primary aliphatic alcohols, to examine universal applicability of the method. To verify the experimental results, numerical simulations were performed on the basis of two-dimensional heat conduction at a stationary state. The numerical results on the temperature field satisfactorily reproduced the experimental data, proving that the FCS thermometry is applicable to ordinary solvents. In addition, we also performed numerical simulations on velocity fields in the solvent, to evaluate contribution of natural convection under typical optical trapping condition at light intensity of ∼MW cm − 2. It was revealed that the contribution of the natural convection is not negligible for mass transfer in the solvents.
DOI
Temperature of matter increases under intense photoirradiation owing to photothermal conversion. The photothermal effect is sometimes a significant issue in optical manipulation usually requiring intense optical fields. Quantitative evaluation of local temperature under photoirradiation can, therefore, provide indispensable information for optical manipulation. In a previous work, we have applied fluorescence correlation spectroscopy (FCS) to monitor the temperature under the optical trapping condition in water, ethanol, and ethylene glycol. We pointed out that analyses of diffusion time of fluorescent dyes could provide information about temperature on the basis of temperature-dependent viscosities of the solvents. In the present work, the FCS thermometry was applied to seven solvents including primary aliphatic alcohols, to examine universal applicability of the method. To verify the experimental results, numerical simulations were performed on the basis of two-dimensional heat conduction at a stationary state. The numerical results on the temperature field satisfactorily reproduced the experimental data, proving that the FCS thermometry is applicable to ordinary solvents. In addition, we also performed numerical simulations on velocity fields in the solvent, to evaluate contribution of natural convection under typical optical trapping condition at light intensity of ∼MW cm − 2. It was revealed that the contribution of the natural convection is not negligible for mass transfer in the solvents.
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Nonparaxial propagation of abruptly autofocusing circular Pearcey Gaussian beams
Xingyu Chen, Dongmei Deng, Jingli Zhuang, Xiangbo Yang, Hongzhan Liu, and Guanghui Wang
We introduce a new class of abruptly autofocusing circular Pearcey Gaussian beams (AAFCPGBs) which tend to be abruptly autofocusing circular Pearcey beams with a small distribution factor, or Gaussian beams with a larger distribution factor. The nonparaxial propagation of the AAFCPGBs is investigated by numerical calculation. The radiation force of the AAFCPGBs exerted on a Rayleigh particle is analyzed in detail.
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We introduce a new class of abruptly autofocusing circular Pearcey Gaussian beams (AAFCPGBs) which tend to be abruptly autofocusing circular Pearcey beams with a small distribution factor, or Gaussian beams with a larger distribution factor. The nonparaxial propagation of the AAFCPGBs is investigated by numerical calculation. The radiation force of the AAFCPGBs exerted on a Rayleigh particle is analyzed in detail.
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Electromagnetic binding and radiation force reversal on a pair of electrically conducting cylinders of arbitrary geometrical cross-section with smooth and corrugated surfaces
F. G. Mitri
The electromagnetic (EM) radiation force-per-length exerted on a pair of electrically-conducting cylindrical particles of circular and non-circular cross-sections is examined using a formal semi-analytical method based on boundary matching in cylindrical coordinates. Initially, the scattering coefficients of the particle pair are determined by imposing suitable boundary conditions leading linear systems of equations computed via matrix inversion and numerical integration procedures. Standard cylindrical (Bessel and Hankel) wave functions are used and closed-form expressions for the dimensionless longitudinal and transverse radiation force functions are evaluated assuming either magnetic (TE) or electric (TM) plane wave incidences. Particle pairs with smooth and corrugated surfaces are considered and numerical computations are performed with emphasis on the distance separating their centers of mass, the angle of incidence of the incident illuminating field and the surface roughness. Adequate convergence plots confirm the validity of the method to evaluate the radiation force functions, and the model is adaptable to any frequency range (i.e. Rayleigh, Mie or geometrical optics regimes). The results can find potential applications in optical tweezers and other related applications in fluid dynamics. In addition, the acoustical analogue is discussed.
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The electromagnetic (EM) radiation force-per-length exerted on a pair of electrically-conducting cylindrical particles of circular and non-circular cross-sections is examined using a formal semi-analytical method based on boundary matching in cylindrical coordinates. Initially, the scattering coefficients of the particle pair are determined by imposing suitable boundary conditions leading linear systems of equations computed via matrix inversion and numerical integration procedures. Standard cylindrical (Bessel and Hankel) wave functions are used and closed-form expressions for the dimensionless longitudinal and transverse radiation force functions are evaluated assuming either magnetic (TE) or electric (TM) plane wave incidences. Particle pairs with smooth and corrugated surfaces are considered and numerical computations are performed with emphasis on the distance separating their centers of mass, the angle of incidence of the incident illuminating field and the surface roughness. Adequate convergence plots confirm the validity of the method to evaluate the radiation force functions, and the model is adaptable to any frequency range (i.e. Rayleigh, Mie or geometrical optics regimes). The results can find potential applications in optical tweezers and other related applications in fluid dynamics. In addition, the acoustical analogue is discussed.
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Sizing and identification of nanoparticles by a tapered fiber
Huiling Pan, Weina Zhang and Hongxiang Lei
There is a strong desire for sizing and identification of nanoparticles in fields of advanced nanotechnology and environmental protection. Although existing approaches can size the nanoparticles, or identify nanoparticles with different refractive indexes, a fast and simple method that combines the two functions still remains challenges. Here, we propose a versatile optical method to size and identify nanoparticles using an optical tapered fiber. By detecting reflection signals in real time, 400–600 nm SiO2 nanoparticles can be sized and 500 nm SiO2, PMMA, PS nanoparticles can be identified. This method requires only an optical tapered fiber, avoiding the use of elaborate nanostructures and making the device highly autonomous, flexible and compact. The demonstrated method provides a potentially powerful tool for biosensing, such as identification of nano-contaminant particles and biological pathogens.
DOI
There is a strong desire for sizing and identification of nanoparticles in fields of advanced nanotechnology and environmental protection. Although existing approaches can size the nanoparticles, or identify nanoparticles with different refractive indexes, a fast and simple method that combines the two functions still remains challenges. Here, we propose a versatile optical method to size and identify nanoparticles using an optical tapered fiber. By detecting reflection signals in real time, 400–600 nm SiO2 nanoparticles can be sized and 500 nm SiO2, PMMA, PS nanoparticles can be identified. This method requires only an optical tapered fiber, avoiding the use of elaborate nanostructures and making the device highly autonomous, flexible and compact. The demonstrated method provides a potentially powerful tool for biosensing, such as identification of nano-contaminant particles and biological pathogens.
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Cooperative and mobile manipulation of multiple microscopic objects based on micro-hands and laser-stage control☆
Quang MinhTa, Chien Chern Cheah
While various techniques have been developed for manipulation of biological cells or micro-objects using optical tweezers, the performance and feasibility of these techniques are mostly dependent on the physical properties of the target objects to be manipulated. In these existing techniques, direct trapping and manipulation of the manipulated objects using laser traps are performed, and therefore, existing techniques for optical manipulation are not capable of coordinating and manipulating various types of objects in the micro-world, including untrappable micro-objects, relatively large micro-objects, and laser sensitive biological cells. In this paper, a cooperative control technique is proposed for coordinative and mobile manipulation of multiple microscopic objects using micro-hands with multiple laser-driven fingertips and robot-assisted stage control. Several virtual micro-hands are formed by coordinating multiple optically trapped micro-particles that serve as the laser-driven fingertips, and then utilized for individual and coordinative manipulation of the target micro-objects. Simultaneously, global transportation of all the grasped target objects is performed by controlling the robot-assisted stage. While it is difficult to design multi-fingered hands in micro-scale due to scaling effect, this paper presents the first result on cooperative and mobile manipulation of multiple micro-objects using multiple micro-hands with laser-driven fingertips and robot-assisted stage control. In this paper, a primary study on repositioning strategy of the laser-driven fingertips is also introduced to allow the fingertips in a grasping formation to be repositioned. Rigorous mathematical formulations and solutions are derived to achieve the control objective, and experimental results are presented to demonstrate the effectiveness of the proposed control technique.
DOI
While various techniques have been developed for manipulation of biological cells or micro-objects using optical tweezers, the performance and feasibility of these techniques are mostly dependent on the physical properties of the target objects to be manipulated. In these existing techniques, direct trapping and manipulation of the manipulated objects using laser traps are performed, and therefore, existing techniques for optical manipulation are not capable of coordinating and manipulating various types of objects in the micro-world, including untrappable micro-objects, relatively large micro-objects, and laser sensitive biological cells. In this paper, a cooperative control technique is proposed for coordinative and mobile manipulation of multiple microscopic objects using micro-hands with multiple laser-driven fingertips and robot-assisted stage control. Several virtual micro-hands are formed by coordinating multiple optically trapped micro-particles that serve as the laser-driven fingertips, and then utilized for individual and coordinative manipulation of the target micro-objects. Simultaneously, global transportation of all the grasped target objects is performed by controlling the robot-assisted stage. While it is difficult to design multi-fingered hands in micro-scale due to scaling effect, this paper presents the first result on cooperative and mobile manipulation of multiple micro-objects using multiple micro-hands with laser-driven fingertips and robot-assisted stage control. In this paper, a primary study on repositioning strategy of the laser-driven fingertips is also introduced to allow the fingertips in a grasping formation to be repositioned. Rigorous mathematical formulations and solutions are derived to achieve the control objective, and experimental results are presented to demonstrate the effectiveness of the proposed control technique.
DOI
Wednesday, October 17, 2018
Switching and Torque Generation in Swarming E. coli
Katie M. Ford, Jyot D. Antani, Aravindh Nagarajan, Madeline M. Johnson and Pushkar P. Lele
Escherichia coli swarm on semi-solid surfaces with the aid of flagella. It has been hypothesized that swarmer cells overcome the increased viscous drag near surfaces by developing higher flagellar thrust and by promoting surface wetness with the aid of a flagellar switch. The switch enables reversals between clockwise (CW) and counterclockwise (CCW) directions of rotation of the flagellar motor. Here, we measured the behavior of flagellar motors in swarmer cells. Results indicated that although the torque was similar to that in planktonic cells, the tendency to rotate CCW was higher in swarmer cells. This suggested that swarmers likely have a smaller pool of phosphorylated CheY. Results further indicated that the upregulation of the flagellin gene was not critical for flagellar thrust or swarming. Consistent with earlier reports, moisture added to the swarm surface restored swarming in a CCW-only mutant, but not in a FliG mutant that rotated motors CW-only (FliGCW). Fluorescence assays revealed that FliGCW cells grown on agar surfaces carried fewer flagella than planktonic FliGCW cells. The surface-dependent reduction in flagella correlated with a reduction in the number of putative flagellar preassemblies. These results hint toward a possibility that the conformational dynamics of switch proteins play a role in the proper assembly of flagellar complexes and flagellar export, thereby aiding bacterial swarming.
DOI
Escherichia coli swarm on semi-solid surfaces with the aid of flagella. It has been hypothesized that swarmer cells overcome the increased viscous drag near surfaces by developing higher flagellar thrust and by promoting surface wetness with the aid of a flagellar switch. The switch enables reversals between clockwise (CW) and counterclockwise (CCW) directions of rotation of the flagellar motor. Here, we measured the behavior of flagellar motors in swarmer cells. Results indicated that although the torque was similar to that in planktonic cells, the tendency to rotate CCW was higher in swarmer cells. This suggested that swarmers likely have a smaller pool of phosphorylated CheY. Results further indicated that the upregulation of the flagellin gene was not critical for flagellar thrust or swarming. Consistent with earlier reports, moisture added to the swarm surface restored swarming in a CCW-only mutant, but not in a FliG mutant that rotated motors CW-only (FliGCW). Fluorescence assays revealed that FliGCW cells grown on agar surfaces carried fewer flagella than planktonic FliGCW cells. The surface-dependent reduction in flagella correlated with a reduction in the number of putative flagellar preassemblies. These results hint toward a possibility that the conformational dynamics of switch proteins play a role in the proper assembly of flagellar complexes and flagellar export, thereby aiding bacterial swarming.
DOI
Optical Method for Formation of Nanostructure in Nanosuspension
Valerii Ivanovich Ivanov, Vladimir Kancherovich Khe, Vladimir Ivanovich Krylov, Denis Alexeyevich Syrnikov
It is proposed to use light pressure forces to form nanostructures in a transparent nanosuspension. We have discussed the theoretical model of formation of crystal from nanoparticles on a bottom of cuvette by using the laser effect in liquid. It was received the steady-state solution of one-dimensional task of the light induced mass transfer as depending on intensity of laser beam.
DOI
It is proposed to use light pressure forces to form nanostructures in a transparent nanosuspension. We have discussed the theoretical model of formation of crystal from nanoparticles on a bottom of cuvette by using the laser effect in liquid. It was received the steady-state solution of one-dimensional task of the light induced mass transfer as depending on intensity of laser beam.
DOI
Orientation-Control of Two Plasmonically Coupled Nanoparticles in an Optical Trap
Hamideh Kermani and Alexander Rohrbach
Optical monitoring of nanoparticle (NP) dynamics is typically beyond the spatial and temporal resolution limit of light microscopy. However, the orientation and assembly of NPs can be controlled by various light scattering methods. Here we demonstrate how two 80 nm silver NPs form a dimer inside an optical trap and orient along the electric field of the trapping laser, therefore allowing to rotate them stably in the horizontal plane. We built a dual-path spectrometer for two orthogonal polarization directions to determine the azimuthal dimer angle for different plasmonic coupling strengths by the difference in the measured spectral intensity maxima. The azimuthal angle of the dimer could be retrieved with an accuracy of a few degrees independent of the spectral frequency or the distance between the NPs. Our results coincide well with a developed theoretical model predicting polarization-dependent scattering spectra for dimers with different orientations and NP distances. Our study points out another strategy for a highly controlled assembly of single NPs using optical tweezers and multimodal scattered light.
DOI
Optical monitoring of nanoparticle (NP) dynamics is typically beyond the spatial and temporal resolution limit of light microscopy. However, the orientation and assembly of NPs can be controlled by various light scattering methods. Here we demonstrate how two 80 nm silver NPs form a dimer inside an optical trap and orient along the electric field of the trapping laser, therefore allowing to rotate them stably in the horizontal plane. We built a dual-path spectrometer for two orthogonal polarization directions to determine the azimuthal dimer angle for different plasmonic coupling strengths by the difference in the measured spectral intensity maxima. The azimuthal angle of the dimer could be retrieved with an accuracy of a few degrees independent of the spectral frequency or the distance between the NPs. Our results coincide well with a developed theoretical model predicting polarization-dependent scattering spectra for dimers with different orientations and NP distances. Our study points out another strategy for a highly controlled assembly of single NPs using optical tweezers and multimodal scattered light.
DOI
Optical funnel for living cells trap
Zhihai Liu, Lu Wang, Yu Zhang, Chao Liu, Jiaze Wu, Yaxun Zhang, Xinghua Yang, Jianzhong Zhang, Jun Yang, Libo Yuan
We proposed and experimentally demonstrated an optical funnel for living cells trap based on an annular-core optical fiber. The proposed optical funnel employed the annular dark field to trap the living cell to avoid the laser damages. To perform the dark field trap, we placed the living cells in the glycerol solution. The refractive index of glycerol liquid was higher than yeast cells, which helped to perform the dark field trap; the viscosity of glycerol was significant, which helped to perform the viscosity-assisted 3-D trapping. The experimental results showed that the donut shape intensity field introduced by a single fiber probe performed 3D trapping easily and efficiently. Such funnel-shaped hollow conical beam could find ample potentials in optical manipulation on biological living cells, avoiding optical damages. All-fiber and seamlessly integrated structure of the proposed scheme could find ample potentials in manipulating biological cells.
DOI
We proposed and experimentally demonstrated an optical funnel for living cells trap based on an annular-core optical fiber. The proposed optical funnel employed the annular dark field to trap the living cell to avoid the laser damages. To perform the dark field trap, we placed the living cells in the glycerol solution. The refractive index of glycerol liquid was higher than yeast cells, which helped to perform the dark field trap; the viscosity of glycerol was significant, which helped to perform the viscosity-assisted 3-D trapping. The experimental results showed that the donut shape intensity field introduced by a single fiber probe performed 3D trapping easily and efficiently. Such funnel-shaped hollow conical beam could find ample potentials in optical manipulation on biological living cells, avoiding optical damages. All-fiber and seamlessly integrated structure of the proposed scheme could find ample potentials in manipulating biological cells.
DOI
Dissipative Self‐Assembly of Anisotropic Nanoparticle Chains with Combined Electrodynamic and Electrostatic Interactions
Fan Nan, Fei Han, Norbert F. Scherer, Zijie Yan
Dissipative self‐assembly of colloidal nanoparticles offers the prospect of creating reconfigurable artificial materials and systems, yet the phenomenon only occurs far from thermodynamic equilibrium. Therefore, it is usually difficult to predict and control. Here, a dissipative colloidal solution system, where anisotropic chains with different interparticle separations in two perpendicular directions transiently arise among largely disordered silver nanoparticles illuminated by a laser beam, is reported. The optical field creates a nonequilibrium dissipative state, where a disorder‐to‐order transition occurs driven by anisotropic electrodynamic interactions coupled with electrostatic interactions. Investigation of the temporal dynamics and spatial arrangements of the nanoparticle system shows that the optical binding strength and entropy of the system are two crucial parameters for the formation of the anisotropic chains and responsible for adaptive behaviors, such as self‐replication of dimer units. Formation of anisotropic nanoparticle chains is also observed among colloidal nanoparticles made from other metal (e.g., Au), polymer (e.g., polystyrene), ceramic (e.g., CeO2), and hybrid materials (e.g., SiO2@Au core–shell), suggesting that light‐driven self‐organization will provide a wide range of opportunities to discover new dissipative structures under thermal fluctuations and build novel anisotropic materials with nanoscale order.
DOI
Dissipative self‐assembly of colloidal nanoparticles offers the prospect of creating reconfigurable artificial materials and systems, yet the phenomenon only occurs far from thermodynamic equilibrium. Therefore, it is usually difficult to predict and control. Here, a dissipative colloidal solution system, where anisotropic chains with different interparticle separations in two perpendicular directions transiently arise among largely disordered silver nanoparticles illuminated by a laser beam, is reported. The optical field creates a nonequilibrium dissipative state, where a disorder‐to‐order transition occurs driven by anisotropic electrodynamic interactions coupled with electrostatic interactions. Investigation of the temporal dynamics and spatial arrangements of the nanoparticle system shows that the optical binding strength and entropy of the system are two crucial parameters for the formation of the anisotropic chains and responsible for adaptive behaviors, such as self‐replication of dimer units. Formation of anisotropic nanoparticle chains is also observed among colloidal nanoparticles made from other metal (e.g., Au), polymer (e.g., polystyrene), ceramic (e.g., CeO2), and hybrid materials (e.g., SiO2@Au core–shell), suggesting that light‐driven self‐organization will provide a wide range of opportunities to discover new dissipative structures under thermal fluctuations and build novel anisotropic materials with nanoscale order.
DOI
Influenza virus replication raises the temperature of cells
Hisataka Maruyama, Takahiro Kimura, Hengiun Liu, Sumio Ohtsuki, Yukari Miyake, Masashi Isogai, Fumihito Arai, Ayae Honda
Influenza virus invades the cell by binding sialic acid on the cell membrane through haemagglutinin (HA), and then genome replication and transcription are carried out in the nucleus to produce progeny virus.
Multiplication of influenza virus requires metabolites, such as nucleotides and amino acids, as well as cellular machinery to synthesize its genome and proteins, thereby producing viral particles. Influenza virus infection forces the start of several metabolic systems in the cell, which consume or generate large amounts of energy. Thus, the viral multiplication processes involved in both genome replication and transcription are considered to require large numbers of nucleotides. The high-level consumption of nucleotides generates large amounts of energy, some of which is converted into heat, and this heat may increase the temperature of cells. To address this question, we prepared a tool based on rhodamine B fluorescence, which we used to measure the temperatures of influenza virus-infected and uninfected cells. The results indicated that influenza virus multiplication increased the temperature of cells by approximately 4 °C – 5 °C, ATP levels in the cells decreased at 3 h after infection, and mitochondrial membrane potential decreased with multiplication level. Thus, the increase in cellular temperature during influenza virus infection appears to be due to the massive consumption of ATP over a short period.
DOI
Influenza virus invades the cell by binding sialic acid on the cell membrane through haemagglutinin (HA), and then genome replication and transcription are carried out in the nucleus to produce progeny virus.
Multiplication of influenza virus requires metabolites, such as nucleotides and amino acids, as well as cellular machinery to synthesize its genome and proteins, thereby producing viral particles. Influenza virus infection forces the start of several metabolic systems in the cell, which consume or generate large amounts of energy. Thus, the viral multiplication processes involved in both genome replication and transcription are considered to require large numbers of nucleotides. The high-level consumption of nucleotides generates large amounts of energy, some of which is converted into heat, and this heat may increase the temperature of cells. To address this question, we prepared a tool based on rhodamine B fluorescence, which we used to measure the temperatures of influenza virus-infected and uninfected cells. The results indicated that influenza virus multiplication increased the temperature of cells by approximately 4 °C – 5 °C, ATP levels in the cells decreased at 3 h after infection, and mitochondrial membrane potential decreased with multiplication level. Thus, the increase in cellular temperature during influenza virus infection appears to be due to the massive consumption of ATP over a short period.
DOI
Thursday, October 11, 2018
Interactions between colliding oil drops coated with non-ionic surfactant determined using optical tweezers
An Chen, Shao-Wei Li, Dian Jing, Jian-Hong Xu
Non-ionic surfactants are widely used in many industrial applications such as detergents, oil recovery, and mineral flotation techniques. Non-ionic surfactants readily adsorb onto the oil-water interface, although they cannot dissociate in solutions like ionic surfactants can. Nonetheless, the electrostatic double-layer (EDL) repulsive force between oil drops coated with the non-ionic surfactant can still provide stability against coalescence. In this work, the interaction forces between two tetradecane drops with diameter of 6.5 µm were measured in the presence of the non-ionic fluorocarbon-based surfactant FS-30 in various salt solutions using optical tweezers. The measured force curves were consistent with the presence of a surface charge, even though the surfactant was non-ionic in nature. The results clearly show that the EDL repulsive force is gradually screened with increasing salt concentration. It was also found that the EDL repulsive force was significantly screened in the divalent cation salt solutions (Ca2+, Ba2+) in comparison to in the monovalent cation salt solutions (Na+). In addition, the absolute value of the measured zeta potential () of emulsified tetradecane drops gradually decreased with increasing FS-30 concentration. In all experimental processes, the emulsified tetradecane drops coated with FS-30 were stable against coalescence. These findings have significant implications for the stability of emulsions used in the food, cosmetic, and detergent industries.
DOI
Non-ionic surfactants are widely used in many industrial applications such as detergents, oil recovery, and mineral flotation techniques. Non-ionic surfactants readily adsorb onto the oil-water interface, although they cannot dissociate in solutions like ionic surfactants can. Nonetheless, the electrostatic double-layer (EDL) repulsive force between oil drops coated with the non-ionic surfactant can still provide stability against coalescence. In this work, the interaction forces between two tetradecane drops with diameter of 6.5 µm were measured in the presence of the non-ionic fluorocarbon-based surfactant FS-30 in various salt solutions using optical tweezers. The measured force curves were consistent with the presence of a surface charge, even though the surfactant was non-ionic in nature. The results clearly show that the EDL repulsive force is gradually screened with increasing salt concentration. It was also found that the EDL repulsive force was significantly screened in the divalent cation salt solutions (Ca2+, Ba2+) in comparison to in the monovalent cation salt solutions (Na+). In addition, the absolute value of the measured zeta potential () of emulsified tetradecane drops gradually decreased with increasing FS-30 concentration. In all experimental processes, the emulsified tetradecane drops coated with FS-30 were stable against coalescence. These findings have significant implications for the stability of emulsions used in the food, cosmetic, and detergent industries.
DOI
Time averages and their statistical variation for the Ornstein-Uhlenbeck process: Role of initial particle distributions and relaxation to stationarity
Andrey G. Cherstvy, Samudrajit Thapa, Yousof Mardoukhi, Aleksei V. Chechkin, and Ralf Metzler
How ergodic is diffusion under harmonic confinements? How strongly do ensemble- and time-averaged displacements differ for a thermally-agitated particle performing confined motion for different initial conditions? We here study these questions for the generic Ornstein-Uhlenbeck (OU) process and derive the analytical expressions for the second and fourth moment. These quantifiers are particularly relevant for the increasing number of single-particle tracking experiments using optical traps. For a fixed starting position, we discuss the definitions underlying the ensemble averages. We also quantify effects of equilibrium and nonequilibrium initial particle distributions onto the relaxation properties and emerging nonequivalence of the ensemble- and time-averaged displacements (even in the limit of long trajectories). We derive analytical expressions for the ergodicity breaking parameter quantifying the amplitude scatter of individual time-averaged trajectories, both for equilibrium and out-of-equilibrium initial particle positions, in the entire range of lag times. Our analytical predictions are in excellent agreement with results of computer simulations of the Langevin equation in a parabolic potential. We also examine the validity of the Einstein relation for the ensemble- and time-averaged moments of the OU-particle. Some physical systems, in which the relaxation and nonergodic features we unveiled may be observable, are discussed.
DOI
How ergodic is diffusion under harmonic confinements? How strongly do ensemble- and time-averaged displacements differ for a thermally-agitated particle performing confined motion for different initial conditions? We here study these questions for the generic Ornstein-Uhlenbeck (OU) process and derive the analytical expressions for the second and fourth moment. These quantifiers are particularly relevant for the increasing number of single-particle tracking experiments using optical traps. For a fixed starting position, we discuss the definitions underlying the ensemble averages. We also quantify effects of equilibrium and nonequilibrium initial particle distributions onto the relaxation properties and emerging nonequivalence of the ensemble- and time-averaged displacements (even in the limit of long trajectories). We derive analytical expressions for the ergodicity breaking parameter quantifying the amplitude scatter of individual time-averaged trajectories, both for equilibrium and out-of-equilibrium initial particle positions, in the entire range of lag times. Our analytical predictions are in excellent agreement with results of computer simulations of the Langevin equation in a parabolic potential. We also examine the validity of the Einstein relation for the ensemble- and time-averaged moments of the OU-particle. Some physical systems, in which the relaxation and nonergodic features we unveiled may be observable, are discussed.
DOI
Efficient modulation of subwavelength focusing via meta-aperture-based plasmonic lens for multifunction applications
Kai-Hao Chang, Yen-Chun Chen, Wen-Hao Chang & Po-Tsung Lee
Subwavelength focusing is crucial for many applications in photonics including super-resolution micro/nanoscopy, nanolithography, and optical trapping. However, most nanostructures exhibit poor ability to modulate focusing spot, which makes them hard to achieve ultra-small resolution. Here, we propose three kinds of plasmonic lens (PL) by utilizing different meta-aperture designs for efficient subwavelength focusing modulation. The shape of nanoaperture strongly influences the diffraction properties. Spatial modulation of focusing spot by employing a circular array of proposed nanoapertures is explored. The best focusing performance among these PLs is the design of T-shape nanoaperture, which has great resolution achieving ultra-small focusing spot of 0.14 λ2 and 0.20 λ2 (λ = 633 nm) for simulation and experiment respectively, better than lots of focusing devices especially by using linear polarization. Multiple-object trapping can be realized by using T-shape nanoaperture-based PL. Our designed PLs with different nanoapertures demonstrate the capability to broaden and integrate different functionalities for on-chip nanotechnologies development.
DOI
Subwavelength focusing is crucial for many applications in photonics including super-resolution micro/nanoscopy, nanolithography, and optical trapping. However, most nanostructures exhibit poor ability to modulate focusing spot, which makes them hard to achieve ultra-small resolution. Here, we propose three kinds of plasmonic lens (PL) by utilizing different meta-aperture designs for efficient subwavelength focusing modulation. The shape of nanoaperture strongly influences the diffraction properties. Spatial modulation of focusing spot by employing a circular array of proposed nanoapertures is explored. The best focusing performance among these PLs is the design of T-shape nanoaperture, which has great resolution achieving ultra-small focusing spot of 0.14 λ2 and 0.20 λ2 (λ = 633 nm) for simulation and experiment respectively, better than lots of focusing devices especially by using linear polarization. Multiple-object trapping can be realized by using T-shape nanoaperture-based PL. Our designed PLs with different nanoapertures demonstrate the capability to broaden and integrate different functionalities for on-chip nanotechnologies development.
DOI
A microfluidic device for isolating intact chromosomes from single mammalian cells and probing their folding stability by controlling solution conditions
Tomohiro Takahashi, Kennedy O. Okeyo, Jun Ueda, Kazuo Yamagata, Masao Washizu & Hidehiro Oana
Chromatin folding shows spatio-temporal fluctuations in living undifferentiated cells, but fixed spatial heterogeneity in differentiated cells. However, little is known about variation in folding stability along the chromatin fibres during differentiation. In addition, effective methods to investigate folding stability at the single cell level are lacking. In the present study, we developed a microfluidic device that enables non-destructive isolation of chromosomes from single mammalian cells as well as real-time microscopic monitoring of the partial unfolding and stretching of individual chromosomes with increasing salt concentrations under a gentle flow. Using this device, we compared the folding stability of chromosomes between non-differentiated and differentiated cells and found that the salt concentration which induces the chromosome unfolding was lower (≤500 mM NaCl) for chromosomes derived from undifferentiated cells, suggesting that the chromatin folding stability of these cells is lower than that of differentiated cells. In addition, individual unfolded chromosomes, i.e., chromatin fibres, were stretched to 150–800 µm non-destructively under 750 mM NaCl and showed distributions of highly/less folded regions along the fibres. Thus, our technique can provide insights into the aspects of chromatin folding that influence the epigenetic control of cell differentiation.
DOI
Chromatin folding shows spatio-temporal fluctuations in living undifferentiated cells, but fixed spatial heterogeneity in differentiated cells. However, little is known about variation in folding stability along the chromatin fibres during differentiation. In addition, effective methods to investigate folding stability at the single cell level are lacking. In the present study, we developed a microfluidic device that enables non-destructive isolation of chromosomes from single mammalian cells as well as real-time microscopic monitoring of the partial unfolding and stretching of individual chromosomes with increasing salt concentrations under a gentle flow. Using this device, we compared the folding stability of chromosomes between non-differentiated and differentiated cells and found that the salt concentration which induces the chromosome unfolding was lower (≤500 mM NaCl) for chromosomes derived from undifferentiated cells, suggesting that the chromatin folding stability of these cells is lower than that of differentiated cells. In addition, individual unfolded chromosomes, i.e., chromatin fibres, were stretched to 150–800 µm non-destructively under 750 mM NaCl and showed distributions of highly/less folded regions along the fibres. Thus, our technique can provide insights into the aspects of chromatin folding that influence the epigenetic control of cell differentiation.
DOI
Analysis of lateral binding force exerted on multilayered spheres induced by high-order Bessel beams with arbitrary polarization angles
J.Bai, Z.S.Wu, C.X.Ge, Q.C.Shang, Z.J.Li, L.Gong
Based on the generalized multi-particle Mie equation (GMM) and Electromagnetic Momentum (EM) theory, the lateral binding force (BF) exerted on multilayered spheres induced by an arbitrary polarized high-order Bessel beam (HOBB) is investigated with particular emphasis on the half-conical angle of the wave number components and the order (or topological charge) of the beam. The illuminating HOBB with arbitrary polarization angle is described in terms of beam shape coefficients (BSCs) within the framework of generalized Lorenz-Mie theories (GLMT). Utilizing the addition theorem of the spherical vector wave functions (SVWFs), the interactive scattering coefficients are derived through the continuous boundary conditions on which the interaction of the multilayered spheres is considered. Numerical results concerning the influences of different parameters of the incident Bessel beam and of the binding body on the lateral BF are displayed in detail. The observed dependence of the separation of optically bound particles on the incidence of HOBB is in agreement with earlier theoretical prediction. Accurate investigation of BF induced by HOBB exerted on multilayered spheres could provide key support for further research on optical binding between more complex multilayered biological cells, which plays an important role in using optical manipulation on stratified particle self-assembly.
DOI
Based on the generalized multi-particle Mie equation (GMM) and Electromagnetic Momentum (EM) theory, the lateral binding force (BF) exerted on multilayered spheres induced by an arbitrary polarized high-order Bessel beam (HOBB) is investigated with particular emphasis on the half-conical angle of the wave number components and the order (or topological charge) of the beam. The illuminating HOBB with arbitrary polarization angle is described in terms of beam shape coefficients (BSCs) within the framework of generalized Lorenz-Mie theories (GLMT). Utilizing the addition theorem of the spherical vector wave functions (SVWFs), the interactive scattering coefficients are derived through the continuous boundary conditions on which the interaction of the multilayered spheres is considered. Numerical results concerning the influences of different parameters of the incident Bessel beam and of the binding body on the lateral BF are displayed in detail. The observed dependence of the separation of optically bound particles on the incidence of HOBB is in agreement with earlier theoretical prediction. Accurate investigation of BF induced by HOBB exerted on multilayered spheres could provide key support for further research on optical binding between more complex multilayered biological cells, which plays an important role in using optical manipulation on stratified particle self-assembly.
DOI
Do Actomyosin Single-Molecule Mechanics Data Predict Mechanics of Contracting Muscle?
Alf Månsson, Marko Ušaj, Luisa Moretto and Dilson E. Rassier
In muscle, but not in single-molecule mechanics studies, actin, myosin and accessory proteins are incorporated into a highly ordered myofilament lattice. In view of this difference we compare results from single-molecule studies and muscle mechanics and analyze to what degree data from the two types of studies agree with each other. There is reasonable correspondence in estimates of the cross-bridge power-stroke distance (7–13 nm), cross-bridge stiffness (~2 pN/nm) and average isometric force per cross-bridge (6–9 pN). Furthermore, models defined on the basis of single-molecule mechanics and solution biochemistry give good fits to experimental data from muscle. This suggests that the ordered myofilament lattice, accessory proteins and emergent effects of the sarcomere organization have only minor modulatory roles. However, such factors may be of greater importance under e.g., disease conditions. We also identify areas where single-molecule and muscle data are conflicting: (1) whether force generation is an Eyring or Kramers process with just one major power-stroke or several sub-strokes; (2) whether the myofilaments and the cross-bridges have Hookean or non-linear elasticity; (3) if individual myosin heads slip between actin sites under certain conditions, e.g., in lengthening; or (4) if the two heads of myosin cooperate.
DOI
In muscle, but not in single-molecule mechanics studies, actin, myosin and accessory proteins are incorporated into a highly ordered myofilament lattice. In view of this difference we compare results from single-molecule studies and muscle mechanics and analyze to what degree data from the two types of studies agree with each other. There is reasonable correspondence in estimates of the cross-bridge power-stroke distance (7–13 nm), cross-bridge stiffness (~2 pN/nm) and average isometric force per cross-bridge (6–9 pN). Furthermore, models defined on the basis of single-molecule mechanics and solution biochemistry give good fits to experimental data from muscle. This suggests that the ordered myofilament lattice, accessory proteins and emergent effects of the sarcomere organization have only minor modulatory roles. However, such factors may be of greater importance under e.g., disease conditions. We also identify areas where single-molecule and muscle data are conflicting: (1) whether force generation is an Eyring or Kramers process with just one major power-stroke or several sub-strokes; (2) whether the myofilaments and the cross-bridges have Hookean or non-linear elasticity; (3) if individual myosin heads slip between actin sites under certain conditions, e.g., in lengthening; or (4) if the two heads of myosin cooperate.
DOI
Wednesday, October 10, 2018
How light absorption modifies the radiative force on a microparticle in optical tweezers
Warlley H. Campos, Jakson M. Fonseca, Joaquim B. S. Mendes, Márcio S. Rocha, and Winder A. Moura-Melo
Reflection and refraction of light can be used to trap small dielectric particles in the geometrical optics regime. Absorption of light is usually neglected in theoretical calculations, but it is known that it occurs in the optical trapping of semi-transparent particles. Here, we propose a generalization of Ashkin’s model for the radiative force exerted on a spherical bead, including the contribution due to attenuation/absorption of light in the bulk of the particle. We discuss in detail the balance between refraction, reflection, and absorption for different optical parameters and particle sizes. Our findings contribute to the understanding of optical trapping of light-absorbing particles and may be used to predict whenever absorption is important in real experiments.
DOI
Reflection and refraction of light can be used to trap small dielectric particles in the geometrical optics regime. Absorption of light is usually neglected in theoretical calculations, but it is known that it occurs in the optical trapping of semi-transparent particles. Here, we propose a generalization of Ashkin’s model for the radiative force exerted on a spherical bead, including the contribution due to attenuation/absorption of light in the bulk of the particle. We discuss in detail the balance between refraction, reflection, and absorption for different optical parameters and particle sizes. Our findings contribute to the understanding of optical trapping of light-absorbing particles and may be used to predict whenever absorption is important in real experiments.
DOI
Enhancement of axial force of optical tweezers by utilizing a circular stop at the back focal plane of the objective
Hossein Gorjizadeh Alinezhad, Sajad Meydanloo, and S. Nader S. Reihani
Optical tweezers are indispensable force spectroscopes. The trap stiffness and the linear force range of the instrument determine the working force range of the instrument. Here we show both theoretically and experimentally that utilizing a circular obstruction at the back focal plane of the objective can significantly increase the maximum linear force. For instance, utilizing a disk with an obstruction ratio of 0.773 could increase the maximum linear force by a factor of ∼39 when a 3.4 μm polystyrene bead is trapped. We also show that this simple beam shaping method can significantly improve the maximum applicable force per unit power of the laser entering the objective lens.
DOI
Optical tweezers are indispensable force spectroscopes. The trap stiffness and the linear force range of the instrument determine the working force range of the instrument. Here we show both theoretically and experimentally that utilizing a circular obstruction at the back focal plane of the objective can significantly increase the maximum linear force. For instance, utilizing a disk with an obstruction ratio of 0.773 could increase the maximum linear force by a factor of ∼39 when a 3.4 μm polystyrene bead is trapped. We also show that this simple beam shaping method can significantly improve the maximum applicable force per unit power of the laser entering the objective lens.
DOI
Differential effect of multiple kinesin motors on run length, force and microtubule binding rate
Braulio Gutiérrez-Medina, Mónica Buendía Padilla, Alejandra Judith Gutiérrez-Esparza, Alma Rosa Oaxaca Camacho
The in vitro transport of cargo by motor proteins constitutes a model system to understand mechanisms of vesicle trafficking inside cells. Here we apply the classic bead assay with a short, stiff kinesin protein to test the effect of multiple motors on essential transport parameters: distance, force and microtubule binding rate. Measurements of unloaded run length show that the transition from single- to multiple-motor behavior can be characterized by the appearance of extended runs, in accordance with a recently proposed model that quantifies the probability of multiple-motor engagement. In this transition, application of mechanical load using optical tweezers allows us to register maximum force values above single kinesin levels (8 pN). Yet, averages of run length and maximum force undergo little change as the probability of multiple-motor participation increases. In contrast, the measured rate of bead binding to microtubules scales linearly with the average number of motors per bead. These observations suggest that multiple motors bound randomly to the same cargo mainly increase the probability of attachment of these cargoes to the cytoskeletal filament network.
DOI
The in vitro transport of cargo by motor proteins constitutes a model system to understand mechanisms of vesicle trafficking inside cells. Here we apply the classic bead assay with a short, stiff kinesin protein to test the effect of multiple motors on essential transport parameters: distance, force and microtubule binding rate. Measurements of unloaded run length show that the transition from single- to multiple-motor behavior can be characterized by the appearance of extended runs, in accordance with a recently proposed model that quantifies the probability of multiple-motor engagement. In this transition, application of mechanical load using optical tweezers allows us to register maximum force values above single kinesin levels (8 pN). Yet, averages of run length and maximum force undergo little change as the probability of multiple-motor participation increases. In contrast, the measured rate of bead binding to microtubules scales linearly with the average number of motors per bead. These observations suggest that multiple motors bound randomly to the same cargo mainly increase the probability of attachment of these cargoes to the cytoskeletal filament network.
DOI
Synthetic three-dimensional atomic structures assembled atom by atom
Daniel Barredo, Vincent Lienhard, Sylvain de Léséleuc, Thierry Lahaye & Antoine Browaeys
A great challenge in current quantum science and technology research is to realize artificial systems of a large number of individually controlled quantum bits for applications in quantum computing and quantum simulation. Many experimental platforms are being explored, including solid-state systems, such as superconducting circuits1 or quantum dots2, and atomic, molecular and optical systems, such as photons, trapped ions or neutral atoms3,4,5,6,7. The latter offer inherently identical qubits that are well decoupled from the environment and could provide synthetic structures scalable to hundreds of qubits or more8. Quantum-gas microscopes9 allow the realization of two-dimensional regular lattices of hundreds of atoms, and large, fully loaded arrays of about 50 microtraps (or ‘optical tweezers’) with individual control are already available in one10 and two11 dimensions. Ultimately, however, accessing the third dimension while keeping single-atom control will be required, both for scaling to large numbers and for extending the range of models amenable to quantum simulation. Here we report the assembly of defect-free, arbitrarily shaped three-dimensional arrays, containing up to 72 single atoms. We use holographic methods and fast, programmable moving tweezers to arrange—atom by atom and plane by plane—initially disordered arrays into target structures of almost any geometry. These results present the prospect of quantum simulation with tens of qubits arbitrarily arranged in space and show that realizing systems of hundreds of individually controlled qubits is within reach using current technology.
DOI
A great challenge in current quantum science and technology research is to realize artificial systems of a large number of individually controlled quantum bits for applications in quantum computing and quantum simulation. Many experimental platforms are being explored, including solid-state systems, such as superconducting circuits1 or quantum dots2, and atomic, molecular and optical systems, such as photons, trapped ions or neutral atoms3,4,5,6,7. The latter offer inherently identical qubits that are well decoupled from the environment and could provide synthetic structures scalable to hundreds of qubits or more8. Quantum-gas microscopes9 allow the realization of two-dimensional regular lattices of hundreds of atoms, and large, fully loaded arrays of about 50 microtraps (or ‘optical tweezers’) with individual control are already available in one10 and two11 dimensions. Ultimately, however, accessing the third dimension while keeping single-atom control will be required, both for scaling to large numbers and for extending the range of models amenable to quantum simulation. Here we report the assembly of defect-free, arbitrarily shaped three-dimensional arrays, containing up to 72 single atoms. We use holographic methods and fast, programmable moving tweezers to arrange—atom by atom and plane by plane—initially disordered arrays into target structures of almost any geometry. These results present the prospect of quantum simulation with tens of qubits arbitrarily arranged in space and show that realizing systems of hundreds of individually controlled qubits is within reach using current technology.
DOI
Optical-Force-Dominated Directional Reshaping of Au Nanodisks in Al–Au Heterodimers
Chao Zhang, Thejaswi Tumkur, Jian Yang, Minhan Lou, Liangliang Dong, Linan Zhou, Peter Nordlander, and Naomi J. Halas
The optical reshaping of metallic nanostructures typically requires intense laser pulses to first approach or achieve melting, followed by surface-tension-dominated reshaping, transforming the original nanostructures into more spherical morphologies. Here, we report the directional optical reshaping of the Au nanodisk of an Al–Au heterodimer in the illuminated junction of an atomic force microscope (AFM). Both the heightening and the repositioning of the Au nanodisk component are induced, reducing the gap between the two nanodisks. There are three contributors to this process: the photothermal softening of the Au lattice, the optical force applied to the Au nanodisk by the Al nanodisk, and the optical force from the nearby AFM tip. The asymmetric reshaping of the heterodimer is observable structurally, through electron microscopic imaging, and through changes in the heterodimer optical response. This optical-force-directed shape manipulation may have potential applications in nanofabrication, optically induced nanomanufacturing, sensing, and quality control.
DOI
The optical reshaping of metallic nanostructures typically requires intense laser pulses to first approach or achieve melting, followed by surface-tension-dominated reshaping, transforming the original nanostructures into more spherical morphologies. Here, we report the directional optical reshaping of the Au nanodisk of an Al–Au heterodimer in the illuminated junction of an atomic force microscope (AFM). Both the heightening and the repositioning of the Au nanodisk component are induced, reducing the gap between the two nanodisks. There are three contributors to this process: the photothermal softening of the Au lattice, the optical force applied to the Au nanodisk by the Al nanodisk, and the optical force from the nearby AFM tip. The asymmetric reshaping of the heterodimer is observable structurally, through electron microscopic imaging, and through changes in the heterodimer optical response. This optical-force-directed shape manipulation may have potential applications in nanofabrication, optically induced nanomanufacturing, sensing, and quality control.
DOI
Optimized stereo matching algorithm for integral imaging microscopy and its potential use in precise 3-D optical manipulation
Xiaohui Ma, Shulu Wang, Weiwei Liu, Fenghua Ma, Anting Wang, Yunlong, Sheng, Yinmei Li, Hai Ming
In this paper, we present an integral imaging microscopy, which can achieve continuous depth extraction. The multiple stereo matching algorithm is optimized with data point interpolation and calculation range correction, which can improve the computing efficiency and accuracy. A water suspension of silica-embedded magnetic particles in light-trap environment is used as a specimen. The elementary image array is obtained through sequentially imaging the specimen by the objective lens and microlens array, which contains continuous depth information that can give the optical tweezers a feedback for precise 3-D manipulation. Experimental and calculated results show the feasibility of our method.
DOI
In this paper, we present an integral imaging microscopy, which can achieve continuous depth extraction. The multiple stereo matching algorithm is optimized with data point interpolation and calculation range correction, which can improve the computing efficiency and accuracy. A water suspension of silica-embedded magnetic particles in light-trap environment is used as a specimen. The elementary image array is obtained through sequentially imaging the specimen by the objective lens and microlens array, which contains continuous depth information that can give the optical tweezers a feedback for precise 3-D manipulation. Experimental and calculated results show the feasibility of our method.
DOI
Tuesday, October 9, 2018
Optical Assembling of Micro-Particles at a Glass–Water Interface with Diffraction Patterns Caused by the Limited Aperture of Objective
Min-Cheng Zhong, Ai-Yin Liu and Rong Zhu
Optical tweezers can manipulate micro-particles, which have been widely used in various applications. Here, we experimentally demonstrate that optical tweezers can assemble the micro-particles to form stable structures at the glass–solution interface in this paper. Firstly, the particles are driven by the optical forces originated from the diffraction fringes, which of the trapping beam passing through an objective with limited aperture. The particles form stable ring structures when the trapping beam is a linearly polarized beam. The particle distributions in the transverse plane are affected by the particle size and concentration. Secondly, the particles form an incompact structure as two fan-shaped after the azimuthally polarized beam passing through a linear polarizer. Furthermore, the particles form a compact structure when a radially polarized beam is used for trapping. Thirdly, the particle patterns can be printed steady at the glass surface in the salt solution. At last, the disadvantage of diffraction traps is discussed in application of optical tweezers. The aggregation of particles at the interfaces seriously affects the flowing of particles in microfluidic channels, and a total reflector as the bottom surface of sample cell can avoid the optical tweezers induced particle patterns at the interface. The optical trapping study utilizing the diffraction gives an interesting method for binding and assembling microparticles, which is helpful to understand the principle of optical tweezers.
DOI
Optical tweezers can manipulate micro-particles, which have been widely used in various applications. Here, we experimentally demonstrate that optical tweezers can assemble the micro-particles to form stable structures at the glass–solution interface in this paper. Firstly, the particles are driven by the optical forces originated from the diffraction fringes, which of the trapping beam passing through an objective with limited aperture. The particles form stable ring structures when the trapping beam is a linearly polarized beam. The particle distributions in the transverse plane are affected by the particle size and concentration. Secondly, the particles form an incompact structure as two fan-shaped after the azimuthally polarized beam passing through a linear polarizer. Furthermore, the particles form a compact structure when a radially polarized beam is used for trapping. Thirdly, the particle patterns can be printed steady at the glass surface in the salt solution. At last, the disadvantage of diffraction traps is discussed in application of optical tweezers. The aggregation of particles at the interfaces seriously affects the flowing of particles in microfluidic channels, and a total reflector as the bottom surface of sample cell can avoid the optical tweezers induced particle patterns at the interface. The optical trapping study utilizing the diffraction gives an interesting method for binding and assembling microparticles, which is helpful to understand the principle of optical tweezers.
DOI
Detection of Magnetic Field Gradient and Single Spin Using Optically Levitated Nano-Particle in Vacuum
Ke-Wen Xiao, Lei-Ming Zhou, Zhang-Qi Yin and Nan Zhao
Optically levitated nano-particle with spins is a promising system for high-precision measurement and quantum information processing. We theoretically analyze the ratio between the fluctuation of particleʼs displacement caused by spins in magnetic field and caused by molecular collisions of the residual air. When the ratio is larger than unity, the displacement fluctuation of spins flipping can be remarkably detected. By theoretical analysis and numerical simulation, we propose and validate a scheme for the detection of gradient of the magnetic field by levitating ferromagnetic nano-particle, and also put forward a realizable detection scheme of the single spin by levitating nano-diamond particle with single nitrogen-vacancy(NV) centers.
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Spatiotemporal autofocused chirped Pearcey Pearcey Gaussian wave packets with an adjustable focus in a quadratic-index medium
Xingyu Chen, Jingli Zhuang, Xi Peng, Dongdong Li, Liping Zhang, Fang Zhao, Dongmei Deng
Here we investigate the propagation properties of spatiotemporal autofocused chirped Pearcey Pearcey Gaussian (PePeG) wavepackets by solving (3 + 1) D Schrdinger equation in a quadratic index medium. When the spatial distribution factor p and the temporal distribution factor f are the same, PePeG wavepackets can simultaneously autofocus in spatial and temporal domain and the peak intensity at the focus is more 28 times than that at the initial plane. With the increase of distribution factor p, the scope of the radius of trapped particles decreases.
DOI
Here we investigate the propagation properties of spatiotemporal autofocused chirped Pearcey Pearcey Gaussian (PePeG) wavepackets by solving (3 + 1) D Schrdinger equation in a quadratic index medium. When the spatial distribution factor p and the temporal distribution factor f are the same, PePeG wavepackets can simultaneously autofocus in spatial and temporal domain and the peak intensity at the focus is more 28 times than that at the initial plane. With the increase of distribution factor p, the scope of the radius of trapped particles decreases.
DOI
A force sensor that converts fluorescence signal into force measurement utilizing short looped DNA
Golam Mustafa, Cho-Ying Chuang, William A. Roy, Mohamed M.F arhath, Nilisha Pokhrel, Yue Ma, Kazuo Nagasawa, Edwin Antony, Matthew J. Comstock, Soumitra Basu, Hamza Balci
A force sensor concept is presented where fluorescence signal is converted into force information via single-molecule Förster resonance energy transfer (smFRET). The basic design of the sensor is a ~100 base pair (bp) long double stranded DNA (dsDNA) that is restricted to a looped conformation by a nucleic acid secondary structure (NAS) that bridges its ends. The looped dsDNA generates a tension across the NAS and unfolds it when the tension is high enough. The FRET efficiency between donor and acceptor (D&A) fluorophores placed across the NAS reports on its folding state. Three dsDNA constructs with different lengths were bridged by a DNA hairpin and KCl was titrated to change the applied force. After these proof-of-principle measurements, one of the dsDNA constructs was used to maintain the G-quadruplex (GQ) construct formed by thrombin binding aptamer (TBA) under tension while it interacted with a destabilizing protein and stabilizing small molecule. The force required to unfold TBA-GQ was independently investigated with high-resolution optical tweezers (OT) measurements that established the relevant force to be a few pN, which is consistent with the force generated by the looped dsDNA. The proposed method is particularly promising as it enables studying NAS, protein, and small molecule interactions using a highly-parallel FRET-based assay while the NAS is kept under an approximately constant force.
DOI
A force sensor concept is presented where fluorescence signal is converted into force information via single-molecule Förster resonance energy transfer (smFRET). The basic design of the sensor is a ~100 base pair (bp) long double stranded DNA (dsDNA) that is restricted to a looped conformation by a nucleic acid secondary structure (NAS) that bridges its ends. The looped dsDNA generates a tension across the NAS and unfolds it when the tension is high enough. The FRET efficiency between donor and acceptor (D&A) fluorophores placed across the NAS reports on its folding state. Three dsDNA constructs with different lengths were bridged by a DNA hairpin and KCl was titrated to change the applied force. After these proof-of-principle measurements, one of the dsDNA constructs was used to maintain the G-quadruplex (GQ) construct formed by thrombin binding aptamer (TBA) under tension while it interacted with a destabilizing protein and stabilizing small molecule. The force required to unfold TBA-GQ was independently investigated with high-resolution optical tweezers (OT) measurements that established the relevant force to be a few pN, which is consistent with the force generated by the looped dsDNA. The proposed method is particularly promising as it enables studying NAS, protein, and small molecule interactions using a highly-parallel FRET-based assay while the NAS is kept under an approximately constant force.
DOI
A microscopic Kapitza pendulum
Christopher J. Richards, Thomas J. Smart, Philip H. Jones & David Cubero
Pyotr Kapitza studied in 1951 the unusual equilibrium features of a rigid pendulum when its point of suspension is under a high-frequency vertical vibration. A sufficiently fast vibration makes the top position stable, putting the pendulum in an inverted orientation that seemingly defies gravity. Kapitza’s analytical method, based on an asymptotic separation of fast and slow variables yielding a renormalized potential, has found application in many diverse areas. Here we study Kapitza’s pendulum going beyond its typical idealizations, by explicitly considering its finite stiffness and the dissipative interaction with the surrounding medium, and using similar theoretical methods as Kapitza. The pendulum is realized at the micrometre scale using a colloidal particle suspended in water and trapped by optical tweezers. Though the strong dissipation present at this scale prevents the inverted pendulum regime, new ones appear in which the equilibrium positions are displaced to the side, and with transitions between them determined either by the driving frequency or the friction coefficient. These new regimes could be exploited in applications aimed at particle separation at small scales.
DOI
Pyotr Kapitza studied in 1951 the unusual equilibrium features of a rigid pendulum when its point of suspension is under a high-frequency vertical vibration. A sufficiently fast vibration makes the top position stable, putting the pendulum in an inverted orientation that seemingly defies gravity. Kapitza’s analytical method, based on an asymptotic separation of fast and slow variables yielding a renormalized potential, has found application in many diverse areas. Here we study Kapitza’s pendulum going beyond its typical idealizations, by explicitly considering its finite stiffness and the dissipative interaction with the surrounding medium, and using similar theoretical methods as Kapitza. The pendulum is realized at the micrometre scale using a colloidal particle suspended in water and trapped by optical tweezers. Though the strong dissipation present at this scale prevents the inverted pendulum regime, new ones appear in which the equilibrium positions are displaced to the side, and with transitions between them determined either by the driving frequency or the friction coefficient. These new regimes could be exploited in applications aimed at particle separation at small scales.
DOI
Effect of nanoscale roughness on optical trapping properties of surface plasmon polaritons exerted on nanoparticle
Ge Cheng-Xian, Wu Zhen-Sen, Bai Jing, Gong Lei
Based on the three-dimensional dispersive finite difference time domain method and Maxwell stress tensor equation, the effect of nanoscale surface roughness on the optical trapping properties of nanoparticle in a vicinity of the composite gold film with periodic structure is investigated numerically. The periodic structure is observed as circular holes which can excite the surface plasmon polaritons on the metal-dielectric interface with particular emphasis on its crucial role in tailoring the optical force acting on a nearby nanoparticle. Utilizing the Monte-Carlo method, the surface roughness is added into the calculation model of the proposed method to accurately investigate the optical performance of the film-tuned nanoparticle system. Selected calculations on the effects of root mean square height and correlation length of rough surface are analyzed in detail to demonstrate that the negative effect of the surface roughness on the optical trapping force can be eliminated when the ratio of correlation length to root mean square height is equal to 10. Accurate investigation of optical trapping properties of nanoparticle in a vicinity of the composite gold film could provide guidelines for further research on the optical system design and manipulation of arbitrary composite nanoparticles.
DOI
Based on the three-dimensional dispersive finite difference time domain method and Maxwell stress tensor equation, the effect of nanoscale surface roughness on the optical trapping properties of nanoparticle in a vicinity of the composite gold film with periodic structure is investigated numerically. The periodic structure is observed as circular holes which can excite the surface plasmon polaritons on the metal-dielectric interface with particular emphasis on its crucial role in tailoring the optical force acting on a nearby nanoparticle. Utilizing the Monte-Carlo method, the surface roughness is added into the calculation model of the proposed method to accurately investigate the optical performance of the film-tuned nanoparticle system. Selected calculations on the effects of root mean square height and correlation length of rough surface are analyzed in detail to demonstrate that the negative effect of the surface roughness on the optical trapping force can be eliminated when the ratio of correlation length to root mean square height is equal to 10. Accurate investigation of optical trapping properties of nanoparticle in a vicinity of the composite gold film could provide guidelines for further research on the optical system design and manipulation of arbitrary composite nanoparticles.
DOI
Monday, October 8, 2018
A myosin II nanomachine mimicking the striated muscle
Irene Pertici, Lorenzo Bongini, Luca Melli, Giulio Bianchi, Luca Salvi, Giulia Falorsi, Caterina Squarci, Tamás Bozó, Dan Cojoc, Miklós S. Z. Kellermayer, Vincenzo Lombardi & Pasquale Bianco
The contraction of striated muscle (skeletal and cardiac muscle) is generated by ATP-dependent interactions between the molecular motor myosin II and the actin filament. The myosin motors are mechanically coupled along the thick filament in a geometry not achievable by single-molecule experiments. Here we show that a synthetic one-dimensional nanomachine, comprising fewer than ten myosin II dimers purified from rabbit psoas, performs isometric and isotonic contractions at 2 mM ATP, delivering a maximum power of 5 aW. The results are explained with a kinetic model fitted to the performance of mammalian skeletal muscle, showing that the condition for the motor coordination that maximises the efficiency in striated muscle is a minimum of 32 myosin heads sharing a common mechanical ground. The nanomachine offers a powerful tool for investigating muscle contractile-protein physiology, pathology and pharmacology without the potentially disturbing effects of the cytoskeletal—and regulatory—protein environment.
DOI
The contraction of striated muscle (skeletal and cardiac muscle) is generated by ATP-dependent interactions between the molecular motor myosin II and the actin filament. The myosin motors are mechanically coupled along the thick filament in a geometry not achievable by single-molecule experiments. Here we show that a synthetic one-dimensional nanomachine, comprising fewer than ten myosin II dimers purified from rabbit psoas, performs isometric and isotonic contractions at 2 mM ATP, delivering a maximum power of 5 aW. The results are explained with a kinetic model fitted to the performance of mammalian skeletal muscle, showing that the condition for the motor coordination that maximises the efficiency in striated muscle is a minimum of 32 myosin heads sharing a common mechanical ground. The nanomachine offers a powerful tool for investigating muscle contractile-protein physiology, pathology and pharmacology without the potentially disturbing effects of the cytoskeletal—and regulatory—protein environment.
DOI
Lorentz gamma factor from vacuum to medium and Minkowski momentum of a photon
Dipok Saikia
Lorentz gamma factor is derived for a photon when it moves from vacuum to a dielectric medium of refractive index μ. This gamma factor can completely explain the increase of photon momentum (Minkowski momentum) in a medium. Covariance problem is resolved without violating energy conservation law and Lorentz invariance.
DOI
Lorentz gamma factor is derived for a photon when it moves from vacuum to a dielectric medium of refractive index μ. This gamma factor can completely explain the increase of photon momentum (Minkowski momentum) in a medium. Covariance problem is resolved without violating energy conservation law and Lorentz invariance.
DOI
Spin photonic forces in non-reciprocal waveguides
Sarang Pendharker, Farid Kalhor, Todd Van Mechelen, Saman Jahani, Neda Nazemifard, Thomas Thundat, and Zubin Jacob
Optical forces acting on particles - controlled by the intensity, polarization and direction of optical beams - have become an important tool in manipulation, sorting and analysis of nano/micro-particles. The nature of these forces has been well understood in reciprocal structures exhibiting time-reversal symmetries. Here, we investigate the nature of optical forces in non-reciprocal structures with non-degenerate counter-propagating modes. We consider the specific case of non-reciprocity induced via translational motion and show that the two counter-propagating modes in a moving slab-waveguide are not degenerate which results in a non-zero lateral and longitudinal force on a nanoparticle. We prove that these anomalous forces are fundamentally connected to near-field photonic spin in optical waveguides and explain their directionality using universal spin-momentum locking of evanescent waves. The presented results show that the interplay of photon spin and non-reciprocity can lead to unique avenues of controlling nanoscale optical forces on-chip.
DOI
Optical forces acting on particles - controlled by the intensity, polarization and direction of optical beams - have become an important tool in manipulation, sorting and analysis of nano/micro-particles. The nature of these forces has been well understood in reciprocal structures exhibiting time-reversal symmetries. Here, we investigate the nature of optical forces in non-reciprocal structures with non-degenerate counter-propagating modes. We consider the specific case of non-reciprocity induced via translational motion and show that the two counter-propagating modes in a moving slab-waveguide are not degenerate which results in a non-zero lateral and longitudinal force on a nanoparticle. We prove that these anomalous forces are fundamentally connected to near-field photonic spin in optical waveguides and explain their directionality using universal spin-momentum locking of evanescent waves. The presented results show that the interplay of photon spin and non-reciprocity can lead to unique avenues of controlling nanoscale optical forces on-chip.
DOI
Direct measurement of radiation pressure and circulating power inside a passive optical cavity
Ryan Wagner, Felipe Guzman, Akobuije Chijioke, Gurpreet Kaur Gulati, Matthias Keller, and Gordon Shaw
A mechanical force sensor coupled to two optical cavities is developed as a metrological tool. This system is used to generate a calibrated circulating optical power and to create a transfer standard for externally coupled optical power. The variability of the sensor as a transfer standard for optical power is less than 2%. The uncertainty in using the sensor to measure the circulating power inside the cavity is less than 3%. The force measured from the mechanical response of the sensor is compared to the force predicted from characterizing the optical spectrum of the cavity. These two forces are approximately 20% different. Potential sources for this disagreement are analyzed and discussed. The sensor is compact, portable, and can operate in ambient and vacuum environments. This device provides a pathway to novel nanonewton scale force and milliwatt scale laser power calibrations, enables direct measurement of the circulating power inside an optical cavity, and enhances the sensitivity of radiation pressure-based optical power transfer standards.
DOI
A mechanical force sensor coupled to two optical cavities is developed as a metrological tool. This system is used to generate a calibrated circulating optical power and to create a transfer standard for externally coupled optical power. The variability of the sensor as a transfer standard for optical power is less than 2%. The uncertainty in using the sensor to measure the circulating power inside the cavity is less than 3%. The force measured from the mechanical response of the sensor is compared to the force predicted from characterizing the optical spectrum of the cavity. These two forces are approximately 20% different. Potential sources for this disagreement are analyzed and discussed. The sensor is compact, portable, and can operate in ambient and vacuum environments. This device provides a pathway to novel nanonewton scale force and milliwatt scale laser power calibrations, enables direct measurement of the circulating power inside an optical cavity, and enhances the sensitivity of radiation pressure-based optical power transfer standards.
DOI
Optical trapping and axial shifting for strongly absorbing particle with single focused TEM00 Gaussian beam
Zhihai Liu, Jiaze Wu, Yu Zhang, Yaxun Zhang, Xiaoyun Tang, Xinghua Yang, Jianzhong Zhang, Jun Yang, and Libo Yuan
We propose and demonstrate a stable three-dimensional trap and manipulation of a micron-sized strongly absorbing particle in pure liquid glycerol by using a single tight focused TEM00 Gaussian beam. We employ a bottom-side bidirectional view observation system to observe the trapped particle. We use the light at 980 nm to trap the absorbing particle and the light at 532 nm to indicate the distribution of the temperature field around the trapped particle. The trapping position of the absorbing particle is related to the incident laser power; the lower the incident laser power, the longer the particle shift distance. Our approach provides full control over trapped absorbing particles and expands optical manipulation of strong absorbing particles into a liquid media.
DOI
We propose and demonstrate a stable three-dimensional trap and manipulation of a micron-sized strongly absorbing particle in pure liquid glycerol by using a single tight focused TEM00 Gaussian beam. We employ a bottom-side bidirectional view observation system to observe the trapped particle. We use the light at 980 nm to trap the absorbing particle and the light at 532 nm to indicate the distribution of the temperature field around the trapped particle. The trapping position of the absorbing particle is related to the incident laser power; the lower the incident laser power, the longer the particle shift distance. Our approach provides full control over trapped absorbing particles and expands optical manipulation of strong absorbing particles into a liquid media.
DOI
New Detector Sensitivity Calibration and the Calculation of the Interaction Force between Particles Using an Optical Tweezer
Pavel Yale, Jean-Michel Edoukoua Konin, Michel Abaka Kouacou and Jérémie Thouakesseh Zoueu
We propose a new approach to calculate the sensitivity factor of the detector in optical tweezers. In this work, we used a charge-coupled device (CCD) camera and a quadrant photodiode (QPD) for the extraction of the various positions occupied by the trapped object (in this case, silica beads of different diameters). Image-J software and the Boltzmann statistical method were then used to estimate the sensitivity of the detector. Silica beads of diameter 0.8 µm, 2 µm, a system of 2 µm bead stuck to 4.5 µm one and another system of 2 µm beads stuck to 2 µm one, were studied. This work contributes significantly to making better calibration of the detector without taking into account the geometry of the object imprisoned in the optical trap. We further developed an approach to calculate the interaction force between two microbeads. This approach does not require any knowledge of solvent viscosity and works for all types of samples.
DOI
We propose a new approach to calculate the sensitivity factor of the detector in optical tweezers. In this work, we used a charge-coupled device (CCD) camera and a quadrant photodiode (QPD) for the extraction of the various positions occupied by the trapped object (in this case, silica beads of different diameters). Image-J software and the Boltzmann statistical method were then used to estimate the sensitivity of the detector. Silica beads of diameter 0.8 µm, 2 µm, a system of 2 µm bead stuck to 4.5 µm one and another system of 2 µm beads stuck to 2 µm one, were studied. This work contributes significantly to making better calibration of the detector without taking into account the geometry of the object imprisoned in the optical trap. We further developed an approach to calculate the interaction force between two microbeads. This approach does not require any knowledge of solvent viscosity and works for all types of samples.
DOI
Thursday, October 4, 2018
Single Cell Isolation Using Optical Tweezers
Anusha Keloth, Owen Anderson, Donald Risbridger and Lynn Paterson
Optical tweezers offer a non-contact method for selecting single cells and translocating them from one microenvironment to another. We have characterized the optical tweezing of yeast S. cerevisiae and can manipulate single cells at 0.41 ± 0.06 mm/s using a 26.8 ± 0.1 mW from a 785 nm diode laser. We have fabricated and tested three cell isolation devices; a micropipette, a PDMS chip and a laser machined fused silica chip and we have isolated yeast, single bacteria and cyanobacteria cells. The most effective isolation was achieved in PDMS chips, where single yeast cells were grown and observed for 18 h without contamination. The duration of budding in S. cerevisiae was not affected by the laser parameters used, but the time from tweezing until the first budding event began increased with increasing laser energy (laser power × time). Yeast cells tweezed using 25.0 ± 0.1 mW for 1 min were viable after isolation. We have constructed a micro-consortium of yeast cells, and a co-culture of yeast and bacteria, using optical tweezers in combination with the PDMS network of channels and isolation chambers, which may impact on both industrial biotechnology and understanding pathogen dynamics.
DOI
Optical tweezers offer a non-contact method for selecting single cells and translocating them from one microenvironment to another. We have characterized the optical tweezing of yeast S. cerevisiae and can manipulate single cells at 0.41 ± 0.06 mm/s using a 26.8 ± 0.1 mW from a 785 nm diode laser. We have fabricated and tested three cell isolation devices; a micropipette, a PDMS chip and a laser machined fused silica chip and we have isolated yeast, single bacteria and cyanobacteria cells. The most effective isolation was achieved in PDMS chips, where single yeast cells were grown and observed for 18 h without contamination. The duration of budding in S. cerevisiae was not affected by the laser parameters used, but the time from tweezing until the first budding event began increased with increasing laser energy (laser power × time). Yeast cells tweezed using 25.0 ± 0.1 mW for 1 min were viable after isolation. We have constructed a micro-consortium of yeast cells, and a co-culture of yeast and bacteria, using optical tweezers in combination with the PDMS network of channels and isolation chambers, which may impact on both industrial biotechnology and understanding pathogen dynamics.
DOI
A fluorescent membrane tension probe
Adai Colom, Emmanuel Derivery, Saeideh Soleimanpour, Caterina Tomba, Marta Dal Molin, Naomi Sakai, Marcos González-Gaitán, Stefan Matile & Aurélien Roux
Cells and organelles are delimited by lipid bilayers in which high deformability is essential to many cell processes, including motility, endocytosis and cell division. Membrane tension is therefore a major regulator of the cell processes that remodel membranes, albeit one that is very hard to measure in vivo. Here we show that a planarizable push–pull fluorescent probe called FliptR (fluorescent lipid tension reporter) can monitor changes in membrane tension by changing its fluorescence lifetime as a function of the twist between its fluorescent groups. The fluorescence lifetime depends linearly on membrane tension within cells, enabling an easy quantification of membrane tension by fluorescence lifetime imaging microscopy. We further show, using model membranes, that this linear dependency between lifetime of the probe and membrane tension relies on a membrane-tension-dependent lipid phase separation. We also provide calibration curves that enable accurate measurement of membrane tension using fluorescence lifetime imaging microscopy.
DOI
Cells and organelles are delimited by lipid bilayers in which high deformability is essential to many cell processes, including motility, endocytosis and cell division. Membrane tension is therefore a major regulator of the cell processes that remodel membranes, albeit one that is very hard to measure in vivo. Here we show that a planarizable push–pull fluorescent probe called FliptR (fluorescent lipid tension reporter) can monitor changes in membrane tension by changing its fluorescence lifetime as a function of the twist between its fluorescent groups. The fluorescence lifetime depends linearly on membrane tension within cells, enabling an easy quantification of membrane tension by fluorescence lifetime imaging microscopy. We further show, using model membranes, that this linear dependency between lifetime of the probe and membrane tension relies on a membrane-tension-dependent lipid phase separation. We also provide calibration curves that enable accurate measurement of membrane tension using fluorescence lifetime imaging microscopy.
DOI
Influence of higher modes on plasmonic force in a narrow slit
Alexander Tusnin and David Shapiro
The plasmonic force due to electromagnetic waves between two metallic walls has been studied earlier for a subwavelength slit taking into consideration only zero mode. In the present paper, the effects of the second mode are analyzed. The higher modes are shown to decrease the attractive force. The magnetic field of the p-wave is compared with the model of a perfect conductor. The difference occurs maximal at the threshold, where the second mode changes its behavior from evanescent to propagating. The effect of possibly changing the attractive force to the repulsive force for a relatively wide slit is found.
DOI
The plasmonic force due to electromagnetic waves between two metallic walls has been studied earlier for a subwavelength slit taking into consideration only zero mode. In the present paper, the effects of the second mode are analyzed. The higher modes are shown to decrease the attractive force. The magnetic field of the p-wave is compared with the model of a perfect conductor. The difference occurs maximal at the threshold, where the second mode changes its behavior from evanescent to propagating. The effect of possibly changing the attractive force to the repulsive force for a relatively wide slit is found.
DOI
The kinetoplastid kinetochore protein KKT4 is an unconventional microtubule tip–coupling protein
Aida Llauró, Hanako Hayashi, Megan E. Bailey, Alex Wilson, Patryk Ludzia, Charles L. Asbury, Bungo Akiyoshi
Kinetochores are multiprotein machines that drive chromosome segregation by maintaining persistent, load-bearing linkages between chromosomes and dynamic microtubule tips. Kinetochores in commonly studied eukaryotes bind microtubules through widely conserved components like the Ndc80 complex. However, in evolutionarily divergent kinetoplastid species such as Trypanosoma brucei, which causes sleeping sickness, the kinetochores assemble from a unique set of proteins lacking homology to any known microtubule-binding domains. Here, we show that the T. brucei kinetochore protein KKT4 binds directly to microtubules and maintains load-bearing attachments to both growing and shortening microtubule tips. The protein localizes both to kinetochores and to spindle microtubules in vivo, and its depletion causes defects in chromosome segregation. We define a microtubule-binding domain within KKT4 and identify several charged residues important for its microtubule-binding activity. Thus, despite its lack of significant similarity to other known microtubule-binding proteins, KKT4 has key functions required for driving chromosome segregation. We propose that it represents a primary element of the kinetochore–microtubule interface in kinetoplastids.
DOI
Kinetochores are multiprotein machines that drive chromosome segregation by maintaining persistent, load-bearing linkages between chromosomes and dynamic microtubule tips. Kinetochores in commonly studied eukaryotes bind microtubules through widely conserved components like the Ndc80 complex. However, in evolutionarily divergent kinetoplastid species such as Trypanosoma brucei, which causes sleeping sickness, the kinetochores assemble from a unique set of proteins lacking homology to any known microtubule-binding domains. Here, we show that the T. brucei kinetochore protein KKT4 binds directly to microtubules and maintains load-bearing attachments to both growing and shortening microtubule tips. The protein localizes both to kinetochores and to spindle microtubules in vivo, and its depletion causes defects in chromosome segregation. We define a microtubule-binding domain within KKT4 and identify several charged residues important for its microtubule-binding activity. Thus, despite its lack of significant similarity to other known microtubule-binding proteins, KKT4 has key functions required for driving chromosome segregation. We propose that it represents a primary element of the kinetochore–microtubule interface in kinetoplastids.
DOI
Experimental test of ensemble inequivalence and the fluctuation theorem in the force ensemble in DNA pulling experiments
A. M. Monge, M. Manosas, and F. Ritort
We experimentally test the validity of the Crooks fluctuation theorem (CFT) in the force ensemble by pulling DNA hairpins, first with magnetic tweezers, next with optical tweezers using force feedback. The CFT holds when using the definition of work Wf=−∫xdf, where x is the molecular extension and f is the force. In contrast, it does not hold when using the usual definition, appropriate for the constant extension ensemble, Wx=∫fdx, showing the importance of the contribution of boundary terms to the full entropy production in a clear example of statistical ensemble inequivalence in small systems. We also evaluate the differences in the average dissipated work in the force ensemble as compared to the extension ensemble, highlighting ensemble inequivalence also at the level of molecular kinetics.
DOI
We experimentally test the validity of the Crooks fluctuation theorem (CFT) in the force ensemble by pulling DNA hairpins, first with magnetic tweezers, next with optical tweezers using force feedback. The CFT holds when using the definition of work Wf=−∫xdf, where x is the molecular extension and f is the force. In contrast, it does not hold when using the usual definition, appropriate for the constant extension ensemble, Wx=∫fdx, showing the importance of the contribution of boundary terms to the full entropy production in a clear example of statistical ensemble inequivalence in small systems. We also evaluate the differences in the average dissipated work in the force ensemble as compared to the extension ensemble, highlighting ensemble inequivalence also at the level of molecular kinetics.
DOI
Microfluidic-Based Single-Cell Study: Current Status and Future Perspective
Haiwa Wu, Jing Zhu, Yao Huang, Daming Wu and Jingyao Sun
Investigation of cell behavior under different environments and manual operations can give information in specific cellular processes. Among all cell-based analysis, single-cell study occupies a peculiar position, while it can avoid the interaction effect within cell groups and provide more precise information. Microfluidic devices have played an increasingly important role in the field of single-cell study owing to their advantages: high efficiency, easy operation, and low cost. In this review, the applications of polymer-based microfluidics on cell manipulation, cell treatment, and cell analysis at single-cell level are detailed summarized. Moreover, three mainly types of manufacturing methods, i.e., replication, photodefining, and soft lithography methods for polymer-based microfluidics are also discussed.
DOI
Investigation of cell behavior under different environments and manual operations can give information in specific cellular processes. Among all cell-based analysis, single-cell study occupies a peculiar position, while it can avoid the interaction effect within cell groups and provide more precise information. Microfluidic devices have played an increasingly important role in the field of single-cell study owing to their advantages: high efficiency, easy operation, and low cost. In this review, the applications of polymer-based microfluidics on cell manipulation, cell treatment, and cell analysis at single-cell level are detailed summarized. Moreover, three mainly types of manufacturing methods, i.e., replication, photodefining, and soft lithography methods for polymer-based microfluidics are also discussed.
DOI
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