Yuquan Zhang, Junfeng Shen, Changjun Min, Yunfeng Jin, Yuqiang Jiang, Jun Liu, Siwei Zhu, Yunlong Sheng, Anatoly V. Zayats, and Xiaocong Yuan
Optical trapping and manipulation of atoms, nanoparticles, and biological entities are widely employed in quantum technology, biophysics, and sensing. Single traps are typically achieved with linearly polarized light, while vortex beams form rotationally unstable symmetric traps. Here we demonstrate multiplexed optical traps reconfigurable with intensity and polarization of the trapping beam using intensity-dependent polarizability of nanoparticles. Nonlinearity combined with a longitudinal field of focused femtosecond vortex beams results in a stable optical force potential with multiple traps, in striking contrast to a linear trapping regime. The number of traps and their orientation can be controlled by the cylindrical vector beam order, polarization, and intensity. The nonlinear trapping demonstrated here on the example of plasmonic nanoparticles opens up opportunities for deterministic trapping and polarization-controlled manipulation of multiple dielectric and semiconductor particles, atoms, and biological objects since most of them exhibit a required intensity-dependent refractive index.
DOI
Friday, August 31, 2018
Response to Bianco et al.: Interaction Forces between F-actin and Titin PEVK Domain Measured with Optical Tweezers
Kenneth S. Campbell, Martin Lakie
A recent publication in Biophysical Journal by Bianco et al. (“Interaction forces between F-actin and titin PEVK domain measured with optical tweezers”) shows that the PEVK domain of titin molecules interacts with F-actin. This newly discovered behavior could influence the mechanical properties of striated muscles, and Bianco et al. suggest that the interactions between actin and titin could modulate thixotropic behavior. In this Comment to the Editor, we suggest that the thixotropic properties of striated muscles in vivo are more likely to reflect dynamic changes in the proportion of myosin cross-bridges bound between the myofilaments.
DOI
A recent publication in Biophysical Journal by Bianco et al. (“Interaction forces between F-actin and titin PEVK domain measured with optical tweezers”) shows that the PEVK domain of titin molecules interacts with F-actin. This newly discovered behavior could influence the mechanical properties of striated muscles, and Bianco et al. suggest that the interactions between actin and titin could modulate thixotropic behavior. In this Comment to the Editor, we suggest that the thixotropic properties of striated muscles in vivo are more likely to reflect dynamic changes in the proportion of myosin cross-bridges bound between the myofilaments.
DOI
Pause sequences facilitate entry into long-lived paused states by reducing RNA polymerase transcription rates
Ronen Gabizon, Antony Lee, Hanif Vahedian-Movahed, Richard H. Ebright & Carlos J. Bustamante
Transcription by RNA polymerase (RNAP) is interspersed with sequence-dependent pausing. The processes through which paused states are accessed and stabilized occur at spatiotemporal scales beyond the resolution of previous methods, and are poorly understood. Here, we combine high-resolution optical trapping with improved data analysis methods to investigate the formation of paused states at enhanced temporal resolution. We find that pause sites reduce the forward transcription rate of nearly all RNAP molecules, rather than just affecting the subset of molecules that enter long-lived pauses. We propose that the reduced rates at pause sites allow time for the elongation complex to undergo conformational changes required to enter long-lived pauses. We also find that backtracking occurs stepwise, with states backtracked by at most one base pair forming quickly, and further backtracking occurring slowly. Finally, we find that nascent RNA structures act as modulators that either enhance or attenuate pausing, depending on the sequence context.
DOI
Transcription by RNA polymerase (RNAP) is interspersed with sequence-dependent pausing. The processes through which paused states are accessed and stabilized occur at spatiotemporal scales beyond the resolution of previous methods, and are poorly understood. Here, we combine high-resolution optical trapping with improved data analysis methods to investigate the formation of paused states at enhanced temporal resolution. We find that pause sites reduce the forward transcription rate of nearly all RNAP molecules, rather than just affecting the subset of molecules that enter long-lived pauses. We propose that the reduced rates at pause sites allow time for the elongation complex to undergo conformational changes required to enter long-lived pauses. We also find that backtracking occurs stepwise, with states backtracked by at most one base pair forming quickly, and further backtracking occurring slowly. Finally, we find that nascent RNA structures act as modulators that either enhance or attenuate pausing, depending on the sequence context.
DOI
Liquid–liquid phase separation and evaporation of a laser-trapped organic–organic airborne droplet using temporal spatial-resolved Raman spectroscopy
Aimable Kalume, Chuji Wang, Joshua Santarpia and Yong-Le Pan
Chemical reactions in aerosol particles can occur between the reactive components of the particle or between the particle and its surrounding media. The fate of atmospheric aerosols depends on the environment, the composition and the distribution of components within a particle. It could be very interesting to see how a liquid aerosol particle behaves in ambient air if the particle is composed of mixed chemicals. Do the chemical components remain homogeneously mixed within a particle or separate as the mixed liquid is aerosolized? How do the chemicals within a droplet separate and interact with the air? In this paper, a single microdroplet formed from an organic–organic mixture of diethyl phthalate (DEPh) and glycerol was investigated using laser-trapped position-resolved temporal Raman spectroscopy. For the first time, we were able to directly observe the gradient distributions of the two chemicals at different positions within such an airborne droplet, their time-resolved processes of liquid–liquid phase-separation, and changes of the physical microstructure and chemical micro-composition in the droplet. The results revealed that DEPh migrated to the surface and formed an outer layer and glycerol was more concentrated in the interior of the droplet, DEPh evaporated faster than glycerol, and both organic chemicals within the mixed droplet evaporated faster than either of them within their pure droplets. This technique also provides a new method for studying the fine structure and chemical reactions of different molecules taking place inside a particle and at the interface of a particle with the surrounding microenvironment.
DOI
Chemical reactions in aerosol particles can occur between the reactive components of the particle or between the particle and its surrounding media. The fate of atmospheric aerosols depends on the environment, the composition and the distribution of components within a particle. It could be very interesting to see how a liquid aerosol particle behaves in ambient air if the particle is composed of mixed chemicals. Do the chemical components remain homogeneously mixed within a particle or separate as the mixed liquid is aerosolized? How do the chemicals within a droplet separate and interact with the air? In this paper, a single microdroplet formed from an organic–organic mixture of diethyl phthalate (DEPh) and glycerol was investigated using laser-trapped position-resolved temporal Raman spectroscopy. For the first time, we were able to directly observe the gradient distributions of the two chemicals at different positions within such an airborne droplet, their time-resolved processes of liquid–liquid phase-separation, and changes of the physical microstructure and chemical micro-composition in the droplet. The results revealed that DEPh migrated to the surface and formed an outer layer and glycerol was more concentrated in the interior of the droplet, DEPh evaporated faster than glycerol, and both organic chemicals within the mixed droplet evaporated faster than either of them within their pure droplets. This technique also provides a new method for studying the fine structure and chemical reactions of different molecules taking place inside a particle and at the interface of a particle with the surrounding microenvironment.
DOI
Thermal bath engineering for swift equilibration
Marie Chupeau, Benjamin Besga, David Guéry-Odelin, Emmanuel Trizac, Artyom Petrosyan, and Sergio Ciliberto
We provide a theoretical and experimental protocol that dynamically controls the effective temperature of a thermal bath, through a well-designed noise engineering. We use this powerful technique to shortcut the relaxation of an overdamped Brownian particle in a quadratic potential by a joint time engineering of the confinement strength and of the noise. For an optically trapped colloid, we report an equilibrium recovery time reduced by about two orders of magnitude compared to the natural relaxation time. Our scheme paves the way towards reservoir engineering in nanosystems.
DOI
We provide a theoretical and experimental protocol that dynamically controls the effective temperature of a thermal bath, through a well-designed noise engineering. We use this powerful technique to shortcut the relaxation of an overdamped Brownian particle in a quadratic potential by a joint time engineering of the confinement strength and of the noise. For an optically trapped colloid, we report an equilibrium recovery time reduced by about two orders of magnitude compared to the natural relaxation time. Our scheme paves the way towards reservoir engineering in nanosystems.
DOI
Enhancing plasmonic trapping with a perfect radially polarized beam
Xianyou Wang, Yuquan Zhang, Yanmeng Dai, Changjun Min, and Xiaocong Yuan
Strong plasmonic focal spots, excited by radially polarized light on a smooth thin metallic film, have been widely applied to trap various micro- and nano-sized objects. However, the direct transmission part of the incident light leads to the scattering force exerted on trapped particles, which seriously affects the stability of the plasmonic trap. Here we employ a novel perfect radially polarized beam to solve this problem. Both theoretical and experimental results verify that such a beam could strongly suppress the directly transmitted light to reduce the piconewton scattering force, and an enhanced plasmonic trapping stiffness that is 2.6 times higher is achieved in experiments. The present work opens up new opportunities for a variety of research requiring the stable manipulations of particles.
DOI
Strong plasmonic focal spots, excited by radially polarized light on a smooth thin metallic film, have been widely applied to trap various micro- and nano-sized objects. However, the direct transmission part of the incident light leads to the scattering force exerted on trapped particles, which seriously affects the stability of the plasmonic trap. Here we employ a novel perfect radially polarized beam to solve this problem. Both theoretical and experimental results verify that such a beam could strongly suppress the directly transmitted light to reduce the piconewton scattering force, and an enhanced plasmonic trapping stiffness that is 2.6 times higher is achieved in experiments. The present work opens up new opportunities for a variety of research requiring the stable manipulations of particles.
DOI
Thursday, August 30, 2018
FEATHER: Automated Analysis of Force Spectroscopy Unbinding and Unfolding Data via a Bayesian Algorithm
Patrick R. Heenan, Thomas T. Perkins
Single-molecule force spectroscopy (SMFS) provides a powerful tool to explore the dynamics and energetics of individual proteins, protein-ligand interactions, and nucleic acid structures. In the canonical assay, a force probe is retracted at constant velocity to induce a mechanical unfolding/unbinding event. Next, two energy landscape parameters, the zero-force dissociation rate constant (ko) and the distance to the transition state (Δx‡), are deduced by analyzing the most probable rupture force as a function of the loading rate, the rate of change in force. Analyzing the shape of the rupture force distribution reveals additional biophysical information, such as the height of the energy barrier (ΔG‡). Accurately quantifying such distributions requires high-precision characterization of the unfolding events and significantly larger data sets. Yet, identifying events in SMFS data is often done in a manual or semiautomated manner and is obscured by the presence of noise. Here, we introduce, to our knowledge, a new algorithm, FEATHER (force extension analysis using a testable hypothesis for event recognition), to automatically identify the locations of unfolding/unbinding events in SMFS records and thereby deduce the corresponding rupture force and loading rate. FEATHER requires no knowledge of the system under study, does not bias data interpretation toward the dominant behavior of the data, and has two easy-to-interpret, user-defined parameters. Moreover, it is a linear algorithm, so it scales well for large data sets. When analyzing a data set from a polyprotein containing both mechanically labile and robust domains, FEATHER featured a 30-fold improvement in event location precision, an eightfold improvement in a measure of the accuracy of the loading rate and rupture force distributions, and a threefold reduction of false positives in comparison to two representative reference algorithms. We anticipate FEATHER being leveraged in more complex analysis schemes, such as the segmentation of complex force-extension curves for fitting to worm-like chain models and extended in future work to data sets containing both unfolding and refolding transitions.
DOI
Single-molecule force spectroscopy (SMFS) provides a powerful tool to explore the dynamics and energetics of individual proteins, protein-ligand interactions, and nucleic acid structures. In the canonical assay, a force probe is retracted at constant velocity to induce a mechanical unfolding/unbinding event. Next, two energy landscape parameters, the zero-force dissociation rate constant (ko) and the distance to the transition state (Δx‡), are deduced by analyzing the most probable rupture force as a function of the loading rate, the rate of change in force. Analyzing the shape of the rupture force distribution reveals additional biophysical information, such as the height of the energy barrier (ΔG‡). Accurately quantifying such distributions requires high-precision characterization of the unfolding events and significantly larger data sets. Yet, identifying events in SMFS data is often done in a manual or semiautomated manner and is obscured by the presence of noise. Here, we introduce, to our knowledge, a new algorithm, FEATHER (force extension analysis using a testable hypothesis for event recognition), to automatically identify the locations of unfolding/unbinding events in SMFS records and thereby deduce the corresponding rupture force and loading rate. FEATHER requires no knowledge of the system under study, does not bias data interpretation toward the dominant behavior of the data, and has two easy-to-interpret, user-defined parameters. Moreover, it is a linear algorithm, so it scales well for large data sets. When analyzing a data set from a polyprotein containing both mechanically labile and robust domains, FEATHER featured a 30-fold improvement in event location precision, an eightfold improvement in a measure of the accuracy of the loading rate and rupture force distributions, and a threefold reduction of false positives in comparison to two representative reference algorithms. We anticipate FEATHER being leveraged in more complex analysis schemes, such as the segmentation of complex force-extension curves for fitting to worm-like chain models and extended in future work to data sets containing both unfolding and refolding transitions.
DOI
Crystallization of Methylammonium Lead Halide Perovskites by Optical Trapping
Vasudevan BIJU, Ken-ichi Yuyama, Md Jahidul Islam, Kiyonori Takahashi, Takayoshi Nakamura
Single crystals of organo‐lead halide perovskites attract much attention to electrooptical and photovoltaic applications. They are usually prepared in precursor solutions incubated at controlled temperatures or under optimized vapor atmosphere conditions, nucleating multiple perovskite crystals all over the solution. Multiple nucleation of crystals prevents efficient use of precursors in the preferential growth of large single crystals, Here, we show an innovative approach for spatio‐temporally controlled, selective nucleation and growth of single crystals of lead halide perovskites by optical trapping with a focused laser beam. Upon such a trapping in unsaturated precursor solutions, nucleation of MAPbX3 (MA = CH3NH3+, X = Cl‐, Br‐, or I‐) is induced at the focal spot through increase in the concentration of perovskite precursors in the focal volume. The rate at which the nucleated crystal grows depends upon whether the perovskite absorbs the trapping laser or not. These findings suggest that optical trapping would be useful to prepare various perovskite single crystals and modify their optical and electronic properties, offering new methodologies to engineer perovskite crystals.
DOI
Single crystals of organo‐lead halide perovskites attract much attention to electrooptical and photovoltaic applications. They are usually prepared in precursor solutions incubated at controlled temperatures or under optimized vapor atmosphere conditions, nucleating multiple perovskite crystals all over the solution. Multiple nucleation of crystals prevents efficient use of precursors in the preferential growth of large single crystals, Here, we show an innovative approach for spatio‐temporally controlled, selective nucleation and growth of single crystals of lead halide perovskites by optical trapping with a focused laser beam. Upon such a trapping in unsaturated precursor solutions, nucleation of MAPbX3 (MA = CH3NH3+, X = Cl‐, Br‐, or I‐) is induced at the focal spot through increase in the concentration of perovskite precursors in the focal volume. The rate at which the nucleated crystal grows depends upon whether the perovskite absorbs the trapping laser or not. These findings suggest that optical trapping would be useful to prepare various perovskite single crystals and modify their optical and electronic properties, offering new methodologies to engineer perovskite crystals.
DOI
Dynamic Features of Plectoneme Formation of Twisted DNA at Low Force
Kotaro Yoshida, Daisuke Ando, Masahiro Makuta, and Yoshihiro Murayama
We investigated dynamic features of plectoneme formation of a twisted DNA at a low force (smaller than 0.3 pN) using a novel tweezer, developed to independently control the stretching and twisting of a single DNA molecule. Several peaks appear in an extension–turn curve in both DNA winding and unwinding. The extension difference for a peak corresponds to the length of a loop in the plectoneme formation. Estimation of the torsional strain suggests that a transient structure is formed by twisting of a few Hertz. Our results are consistent with the theoretical prediction of plectoneme formation in the low-force regime. Repeatedly appearing peaks in the extension–turn curves suggest that some plectonemic domains appear more frequently than other domains.
DOI
We investigated dynamic features of plectoneme formation of a twisted DNA at a low force (smaller than 0.3 pN) using a novel tweezer, developed to independently control the stretching and twisting of a single DNA molecule. Several peaks appear in an extension–turn curve in both DNA winding and unwinding. The extension difference for a peak corresponds to the length of a loop in the plectoneme formation. Estimation of the torsional strain suggests that a transient structure is formed by twisting of a few Hertz. Our results are consistent with the theoretical prediction of plectoneme formation in the low-force regime. Repeatedly appearing peaks in the extension–turn curves suggest that some plectonemic domains appear more frequently than other domains.
DOI
Plant organelle dynamics: cytoskeletal control and membrane contact sites
Chiara Perico, Imogen Sparkes
Organelle movement and positioning are correlated with plant growth and development. Movement characteristics are seemingly erratic yet respond to external stimuli including pathogens and light. Given these clear correlations, we still do not understand the specific roles that movement plays in these processes. There are few exceptions including organelle inheritance during cell division and photorelocation of chloroplasts to prevent photodamage. The molecular and biophysical components that drive movement can be broken down into cytoskeletal components, motor proteins and tethers, which allow organelles to physically interact with one another. Our understanding of these components and concepts has exploded over the past decade, with recent technological advances allowing an even more in‐depth profiling. Here, we provide an overview of the cytoskeletal and tethering components and discuss the mechanisms behind organelle movement in higher plants.
DOI
Organelle movement and positioning are correlated with plant growth and development. Movement characteristics are seemingly erratic yet respond to external stimuli including pathogens and light. Given these clear correlations, we still do not understand the specific roles that movement plays in these processes. There are few exceptions including organelle inheritance during cell division and photorelocation of chloroplasts to prevent photodamage. The molecular and biophysical components that drive movement can be broken down into cytoskeletal components, motor proteins and tethers, which allow organelles to physically interact with one another. Our understanding of these components and concepts has exploded over the past decade, with recent technological advances allowing an even more in‐depth profiling. Here, we provide an overview of the cytoskeletal and tethering components and discuss the mechanisms behind organelle movement in higher plants.
DOI
Double-arm optical tweezer system for precise and dexterous handling of micro-objects in 3D workspace
Yoshio Tanaka
Double-arm manipulators are unfamiliar as equipment used in microscopic work in biomedical laboratories, whereas they are prevalent in factory automation and humanoids. For non-contact micromanipulation in three-dimensional (3D) workspaces, we propose and design a double-arm optical tweezer system that can easily exchange two types of end-effectors (i.e., optical landscapes for laser trapping) with a focus tunable lens and a microlens array. With a time-shared scanning approach under interactive personal computer (PC) mouse controls, the system can perform the precise and dexterous handling of micro-objects in a 3D workspace. As a proof of concept, we demonstrate the two-dimensional (2D) and 3D dexterous handling of microbeads in the motions of solving puzzle rings. We also demonstrate the precise and periodic patterning of microbeads for massive dynamic arrays. This double-arm system can be applied with versatile tools used for various non-contact micromanipulations in the biomedical field and for dynamic arrays in single cell and 3D biology.
DOI
Double-arm manipulators are unfamiliar as equipment used in microscopic work in biomedical laboratories, whereas they are prevalent in factory automation and humanoids. For non-contact micromanipulation in three-dimensional (3D) workspaces, we propose and design a double-arm optical tweezer system that can easily exchange two types of end-effectors (i.e., optical landscapes for laser trapping) with a focus tunable lens and a microlens array. With a time-shared scanning approach under interactive personal computer (PC) mouse controls, the system can perform the precise and dexterous handling of micro-objects in a 3D workspace. As a proof of concept, we demonstrate the two-dimensional (2D) and 3D dexterous handling of microbeads in the motions of solving puzzle rings. We also demonstrate the precise and periodic patterning of microbeads for massive dynamic arrays. This double-arm system can be applied with versatile tools used for various non-contact micromanipulations in the biomedical field and for dynamic arrays in single cell and 3D biology.
DOI
Sensing Static Forces with Free-Falling Nanoparticles
Erik Hebestreit, Martin Frimmer, René Reimann, and Lukas Novotny
Miniaturized mechanical sensors rely on resonant operation schemes, unsuited to detect static forces. We demonstrate a nanomechanical sensor for static forces based on an optically trapped nanoparticle in vacuum. Our technique relies on an off-resonant interaction of the particle with a weak static force, and a resonant readout of the displacement caused by this interaction. We demonstrate a sensitivity of 10 aN to static gravitational and electric forces. Our work provides a tool for the closer investigation of short-range forces, and marks an important step towards the realization of matter-wave interferometry with macroscopic objects.
DOI
Miniaturized mechanical sensors rely on resonant operation schemes, unsuited to detect static forces. We demonstrate a nanomechanical sensor for static forces based on an optically trapped nanoparticle in vacuum. Our technique relies on an off-resonant interaction of the particle with a weak static force, and a resonant readout of the displacement caused by this interaction. We demonstrate a sensitivity of 10 aN to static gravitational and electric forces. Our work provides a tool for the closer investigation of short-range forces, and marks an important step towards the realization of matter-wave interferometry with macroscopic objects.
DOI
Monday, August 27, 2018
Photoinduced Tip–Sample Forces for Chemical Nanoimaging and Spectroscopy
Brian T. O’Callahan , Jun Yan, Fabian Menges, Eric A. Muller , and Markus B. Raschke
Control of photoinduced forces allows nanoparticle manipulation, atom trapping, and fundamental studies of light-matter interactions. Scanning probe microscopy enables the local detection of photoinduced effects with nano-optical imaging and spectroscopy modalities being used for chemical analysis and the study of physical effects. Recently, the development of a novel scanning probe technique has been reported with local chemical sensitivity attributed to the localization and detection of the optical gradient force between a probe tip and sample surface via infrared vibrationally resonant coupling. However, the magnitude and spectral line shape of the observed signals disagree with theoretical predictions of optical gradient forces. Here, we clarify this controversy by resolving and analyzing the interplay of several photoinduced effects between scanning probe tips and infrared resonant materials through spectral and spatial force measurements. Force spectra obtained on IR-active vibrational modes of polymer thin films are symmetric and match the material absorption spectra in contrast to the dispersive spectral line shape expected for the optical gradient force response. Sample thickness dependence shows continuous increase in force signal beyond the thickness where the optical dipole force would saturate. Our results illustrate that photoinduced force interactions between scanning probe tips and infrared-resonant materials are dominated by short-range thermal expansion and possibly long-range thermally induced photoacoustic effects. At the same time, we provide a guideline to detect and discriminate optical gradient forces from other photoinduced effects, which opens a new perspective for the development of new scanning probe modalities exploiting ultrastrong opto-mechanical coupling effects in tip–sample cavities.
DOI
Control of photoinduced forces allows nanoparticle manipulation, atom trapping, and fundamental studies of light-matter interactions. Scanning probe microscopy enables the local detection of photoinduced effects with nano-optical imaging and spectroscopy modalities being used for chemical analysis and the study of physical effects. Recently, the development of a novel scanning probe technique has been reported with local chemical sensitivity attributed to the localization and detection of the optical gradient force between a probe tip and sample surface via infrared vibrationally resonant coupling. However, the magnitude and spectral line shape of the observed signals disagree with theoretical predictions of optical gradient forces. Here, we clarify this controversy by resolving and analyzing the interplay of several photoinduced effects between scanning probe tips and infrared resonant materials through spectral and spatial force measurements. Force spectra obtained on IR-active vibrational modes of polymer thin films are symmetric and match the material absorption spectra in contrast to the dispersive spectral line shape expected for the optical gradient force response. Sample thickness dependence shows continuous increase in force signal beyond the thickness where the optical dipole force would saturate. Our results illustrate that photoinduced force interactions between scanning probe tips and infrared-resonant materials are dominated by short-range thermal expansion and possibly long-range thermally induced photoacoustic effects. At the same time, we provide a guideline to detect and discriminate optical gradient forces from other photoinduced effects, which opens a new perspective for the development of new scanning probe modalities exploiting ultrastrong opto-mechanical coupling effects in tip–sample cavities.
DOI
Optical Tweezers Microrheology: From the Basics to Advanced Techniques and Applications
Rae M. Robertson-Anderson
Over the past few decades, microrheology has emerged as a widely used technique to measure the mechanical properties of soft viscoelastic materials. Optical tweezers offer a powerful platform for performing microrheology measurements and can measure rheological properties at the level of single molecules out to near macroscopic scales. Unlike passive microrheology methods, which use diffusing microspheres to extract rheological properties, optical tweezers can probe the nonlinear viscoelastic response, and measure the space- and time-dependent rheological properties of heterogeneous, nonequilibrium materials. In this Viewpoint, I describe the basic principles underlying optical tweezers microrheology, the instrumentation and material requirements, and key applications to widely studied soft biological materials. I also describe several sophisticated approaches that include coupling optical tweezers to fluorescence microscopy and microfluidics. The described techniques can robustly characterize noncontinuum mechanics, nonlinear mechanical responses, strain-field heterogeneities, stress propagation, force relaxation dynamics, and time-dependent mechanics of active materials.
DOI
Over the past few decades, microrheology has emerged as a widely used technique to measure the mechanical properties of soft viscoelastic materials. Optical tweezers offer a powerful platform for performing microrheology measurements and can measure rheological properties at the level of single molecules out to near macroscopic scales. Unlike passive microrheology methods, which use diffusing microspheres to extract rheological properties, optical tweezers can probe the nonlinear viscoelastic response, and measure the space- and time-dependent rheological properties of heterogeneous, nonequilibrium materials. In this Viewpoint, I describe the basic principles underlying optical tweezers microrheology, the instrumentation and material requirements, and key applications to widely studied soft biological materials. I also describe several sophisticated approaches that include coupling optical tweezers to fluorescence microscopy and microfluidics. The described techniques can robustly characterize noncontinuum mechanics, nonlinear mechanical responses, strain-field heterogeneities, stress propagation, force relaxation dynamics, and time-dependent mechanics of active materials.
DOI
A Single Large Assembly with Dynamically Fluctuating Swarms of Gold Nanoparticles Formed by Trapping Laser
Tetsuhiro Kudo, Shang-Jan Yang, and Hiroshi Masuhara
Laser trapping has been utilized as tweezers to three-dimensionally trap nanoscale objects and has provided significant impacts in nanoscience and nanotechnology. The objects are immobilized at the position where the tightly focused laser beam is irradiated. Here, we report the swarming of gold nanoparticles in which component nanoparticles dynamically interact with each other, keeping their long interparticle distance around the trapping laser focus at a glass/solution interface. A pair of swarms are directionally extended outside the focal spot perpendicular to the linear polarization like a radiation pattern of dipole scattering, while a doughnut-shaped swarm is prepared by circularly polarized trapping laser. The light field is expanded as scattered light through trapped nanoparticles; this modified light field further traps the nanoparticles, and scattering and trapping cooperatively develop. Due to these nonlinear dynamic processes, the dynamically fluctuating swarms are evolved up to tens of micrometers. This finding will open the way to create various swarms of nanoscale objects that interact and bind through the scattered light depending on the properties of the laser beam and the nanomaterials.
DOI
Laser trapping has been utilized as tweezers to three-dimensionally trap nanoscale objects and has provided significant impacts in nanoscience and nanotechnology. The objects are immobilized at the position where the tightly focused laser beam is irradiated. Here, we report the swarming of gold nanoparticles in which component nanoparticles dynamically interact with each other, keeping their long interparticle distance around the trapping laser focus at a glass/solution interface. A pair of swarms are directionally extended outside the focal spot perpendicular to the linear polarization like a radiation pattern of dipole scattering, while a doughnut-shaped swarm is prepared by circularly polarized trapping laser. The light field is expanded as scattered light through trapped nanoparticles; this modified light field further traps the nanoparticles, and scattering and trapping cooperatively develop. Due to these nonlinear dynamic processes, the dynamically fluctuating swarms are evolved up to tens of micrometers. This finding will open the way to create various swarms of nanoscale objects that interact and bind through the scattered light depending on the properties of the laser beam and the nanomaterials.
DOI
Plasmonic response of graphene-like metallic-molecular nanocluster for optical applications
Aydin Amini; Saeed Golmohammadi; Sina Aghili
Three periodic structures based on arrays of graphene-like nanocluster have been proposed and their plasmonic response has been investigated. In the first step, plasmonic response of each periodic structure has been investigated using the hybridization diagram for a proposed single unit cell. In the second step, according to obtained results, appropriate applications for each structure have been introduced. The study is divided into three sections. In the first section, we have considered a periodic array of triangular-shaped nanoparticles to form a graphene-like nanocluster. This configuration shows considerable capabilities to act as a nanoscale waveguide. Alternatively, in the second section, we have replaced triangular nanoparticles with nanospheres. Results of this configuration show considerable enhancements in optical forces and hence, represent it as an acceptable candidate for tweezing and optical manipulations. Finally, we have replaced nanospheres with ring nanoparticles in each node of such a similar nanocluster. This change leads to create states of plasmonic resonances in spectral response, which is sensitive to surrounding medium and can be used as a sensing tool to detect medium perturbations.
DOI
Three periodic structures based on arrays of graphene-like nanocluster have been proposed and their plasmonic response has been investigated. In the first step, plasmonic response of each periodic structure has been investigated using the hybridization diagram for a proposed single unit cell. In the second step, according to obtained results, appropriate applications for each structure have been introduced. The study is divided into three sections. In the first section, we have considered a periodic array of triangular-shaped nanoparticles to form a graphene-like nanocluster. This configuration shows considerable capabilities to act as a nanoscale waveguide. Alternatively, in the second section, we have replaced triangular nanoparticles with nanospheres. Results of this configuration show considerable enhancements in optical forces and hence, represent it as an acceptable candidate for tweezing and optical manipulations. Finally, we have replaced nanospheres with ring nanoparticles in each node of such a similar nanocluster. This change leads to create states of plasmonic resonances in spectral response, which is sensitive to surrounding medium and can be used as a sensing tool to detect medium perturbations.
DOI
Label‐Free Optical Single‐Molecule Micro‐ and Nanosensors
Sivaraman Subramanian, Hsin‐Yu Wu, Tom Constant, Jolly Xavier, Frank Vollmer
Label‐free optical sensor systems have emerged that exhibit extraordinary sensitivity for detecting physical, chemical, and biological entities at the micro/nanoscale. Particularly exciting is the detection and analysis of molecules, on miniature optical devices that have many possible applications in health, environment, and security. These micro‐ and nanosensors have now reached a sensitivity level that allows for the detection and analysis of even single molecules. Their small size enables an exceedingly high sensitivity, and the application of quantum optical measurement techniques can allow the classical limits of detection to be approached or surpassed. The new class of label‐free micro‐ and nanosensors allows dynamic processes at the single‐molecule level to be observed directly with light. By virtue of their small interaction length, these micro‐ and nanosensors probe light–matter interactions over a dynamic range often inaccessible by other optical techniques. For researchers entering this rapidly advancing field of single‐molecule micro‐ and nanosensors, there is an urgent need for a timely review that covers the most recent developments and that identifies the most exciting opportunities. The focus here is to provide a summary of the recent techniques that have either demonstrated label‐free single‐molecule detection or claim single‐molecule sensitivity.
DOI
Label‐free optical sensor systems have emerged that exhibit extraordinary sensitivity for detecting physical, chemical, and biological entities at the micro/nanoscale. Particularly exciting is the detection and analysis of molecules, on miniature optical devices that have many possible applications in health, environment, and security. These micro‐ and nanosensors have now reached a sensitivity level that allows for the detection and analysis of even single molecules. Their small size enables an exceedingly high sensitivity, and the application of quantum optical measurement techniques can allow the classical limits of detection to be approached or surpassed. The new class of label‐free micro‐ and nanosensors allows dynamic processes at the single‐molecule level to be observed directly with light. By virtue of their small interaction length, these micro‐ and nanosensors probe light–matter interactions over a dynamic range often inaccessible by other optical techniques. For researchers entering this rapidly advancing field of single‐molecule micro‐ and nanosensors, there is an urgent need for a timely review that covers the most recent developments and that identifies the most exciting opportunities. The focus here is to provide a summary of the recent techniques that have either demonstrated label‐free single‐molecule detection or claim single‐molecule sensitivity.
DOI
Self-induced back action actuated nanopore electrophoresis (SANE)
Muhammad Usman Raza, Sai Santosh Sasank Peri, Liang-Chieh Ma, Samir M Iqbal and George Alexandrakis
We present a novel method to trap nanoparticles in double nanohole (DNH) nanoapertures integrated on top of solid-state nanopores (ssNP). The nanoparticles were propelled by an electrophoretic force from the cis towards the trans side of the nanopore but were trapped in the process when they reached the vicinity of the DNH-ssNP interface. The self-induced back action (SIBA) plasmonic force existing between the tips of the DNH opposed the electrophoretic force and enabled simultaneous optical and electrical sensing of a single nanoparticle for seconds. The novel SIBA actuated nanopore electrophoresis (SANE) sensor was fabricated using two-beam GFIS FIB. Firstly, Ne FIB milling was used to create the DNH features and was combined with end pointing to stop milling at the metal-dielectric interface. Subsequently, He FIB was used to drill a 25 nm nanopore through the center of the DNH. Proof of principle experiments to demonstrate the potential utility of the SANE sensor were performed with 20 nm silica and Au nanoparticles. The addition of optical trapping to electrical sensing extended translocation times by four orders of magnitude. The extended electrical measurement times revealed newly observed high frequency charge transients that were attributed to bobbing of the nanoparticle driven by the competing optical and electrical forces. Frequency analysis of this bobbing behavior hinted at the possibility of distinguishing single from multi-particle trapping events. We also discuss how SANE sensor measurement characteristics differ between silica and Au nanoparticles due to differences in their physical properties and how to estimate the charge around a nanoparticle. These measurements show promise for the SANE sensor as an enabling tool for selective detection of biomolecules and quantification of their interactions.
DOI
We present a novel method to trap nanoparticles in double nanohole (DNH) nanoapertures integrated on top of solid-state nanopores (ssNP). The nanoparticles were propelled by an electrophoretic force from the cis towards the trans side of the nanopore but were trapped in the process when they reached the vicinity of the DNH-ssNP interface. The self-induced back action (SIBA) plasmonic force existing between the tips of the DNH opposed the electrophoretic force and enabled simultaneous optical and electrical sensing of a single nanoparticle for seconds. The novel SIBA actuated nanopore electrophoresis (SANE) sensor was fabricated using two-beam GFIS FIB. Firstly, Ne FIB milling was used to create the DNH features and was combined with end pointing to stop milling at the metal-dielectric interface. Subsequently, He FIB was used to drill a 25 nm nanopore through the center of the DNH. Proof of principle experiments to demonstrate the potential utility of the SANE sensor were performed with 20 nm silica and Au nanoparticles. The addition of optical trapping to electrical sensing extended translocation times by four orders of magnitude. The extended electrical measurement times revealed newly observed high frequency charge transients that were attributed to bobbing of the nanoparticle driven by the competing optical and electrical forces. Frequency analysis of this bobbing behavior hinted at the possibility of distinguishing single from multi-particle trapping events. We also discuss how SANE sensor measurement characteristics differ between silica and Au nanoparticles due to differences in their physical properties and how to estimate the charge around a nanoparticle. These measurements show promise for the SANE sensor as an enabling tool for selective detection of biomolecules and quantification of their interactions.
DOI
Friday, August 17, 2018
Spherical Spontaneous Capillary-Wave Resonance on Optically Trapped Aerosol Droplet
Takuya Endo, Kyohei Ishikawa, Mao Fukuyama, Masaru Uraoka, Shoji Ishizaka, and Akihide Hibara
We report a contactless in situ surface tension measurement method of micrometer-sized aerosol droplets. In this method, we assume spherical spontaneous resonance of a thermally induced capillary wave. First, an aerosol droplet with a radius ranging from 4.7 to 12.4 µm is trapped by means of a simple single-beam optical-trapping configuration, and the frequency shift power spectrum of the light passing the droplet is measured. The spectrum in each case exhib-its several peaks in a frequency range of several tens to several hundred kilohertz. The peak frequencies agree well with theoretical ones predicted by the spherical resonant modes. After validating the above mentioned assumption, we measure the surface tension of aerosol droplets containing sodium dodecyl sulfate, and we successfully obtain the surface tension value. The present method utilizes just two phenomena, that is, the droplet-surface light scattering and spontaneous resonance of the capillary wave. These can be easily observed in aerosol droplets, and they can be utilized to gain scientific insights. The present method based on the nature of droplets can be used in various applications in aerosol science.
DOI
We report a contactless in situ surface tension measurement method of micrometer-sized aerosol droplets. In this method, we assume spherical spontaneous resonance of a thermally induced capillary wave. First, an aerosol droplet with a radius ranging from 4.7 to 12.4 µm is trapped by means of a simple single-beam optical-trapping configuration, and the frequency shift power spectrum of the light passing the droplet is measured. The spectrum in each case exhib-its several peaks in a frequency range of several tens to several hundred kilohertz. The peak frequencies agree well with theoretical ones predicted by the spherical resonant modes. After validating the above mentioned assumption, we measure the surface tension of aerosol droplets containing sodium dodecyl sulfate, and we successfully obtain the surface tension value. The present method utilizes just two phenomena, that is, the droplet-surface light scattering and spontaneous resonance of the capillary wave. These can be easily observed in aerosol droplets, and they can be utilized to gain scientific insights. The present method based on the nature of droplets can be used in various applications in aerosol science.
DOI
Lessons from optical tweezers: quantifying organelle interactions, dynamics and modelling subcellular events
Imogen Sparkes
Optical tweezers enable users to physically trap organelles and move them laterally within the plant cell. Recent advances have highlighted physical interactions between functionally related organelle pairs, such as ER–Golgi and peroxisome–chloroplast, and have shown how organelle positioning affects plant growth. Quantification of these processes has provided insight into the force components which ultimately drive organelle movement and positioning in plant cells. Application of optical tweezers has therefore revolutionised our understanding of plant organelle dynamics.
DOI
Optical tweezers enable users to physically trap organelles and move them laterally within the plant cell. Recent advances have highlighted physical interactions between functionally related organelle pairs, such as ER–Golgi and peroxisome–chloroplast, and have shown how organelle positioning affects plant growth. Quantification of these processes has provided insight into the force components which ultimately drive organelle movement and positioning in plant cells. Application of optical tweezers has therefore revolutionised our understanding of plant organelle dynamics.
DOI
Optical gradient forces between evanescently coupled waveguides
Mohammad-Ali Miri, Michele Cotrufo, and Andrea Alu
Evanescently coupled dielectric waveguides exert optical forces on each other, which may be attractive or repulsive as a function of the excited optical mode. Through energy conservation considerations, it is possible to show that the optical force between two waveguides is proportional to the derivative of the effective propagation index with respect to the separation between waveguides. Here, we prove analytically that the lateral force calculated from the spatial derivative of the propagation index is equivalent to the one obtained from a formal calculation based on the Maxwell’s stress tensor. Interestingly, this latter approach reveals that the sign and magnitude of the force depend only on the field intensity at the channel interfaces. In addition, our derivation provides insights into the design of the waveguide profile in order to increase or decrease the optical forces between coupled channels.
DOI
Evanescently coupled dielectric waveguides exert optical forces on each other, which may be attractive or repulsive as a function of the excited optical mode. Through energy conservation considerations, it is possible to show that the optical force between two waveguides is proportional to the derivative of the effective propagation index with respect to the separation between waveguides. Here, we prove analytically that the lateral force calculated from the spatial derivative of the propagation index is equivalent to the one obtained from a formal calculation based on the Maxwell’s stress tensor. Interestingly, this latter approach reveals that the sign and magnitude of the force depend only on the field intensity at the channel interfaces. In addition, our derivation provides insights into the design of the waveguide profile in order to increase or decrease the optical forces between coupled channels.
DOI
The temperature of an optically trapped, rotating microparticle
Paloma Rodríguez Sevilla, Yoshihiko Arita, Xiaogang Liu, Daniel Jaque, and Kishan Dholakia
The measurement of temperature at the mesoscopic scale is challenging but important in a wide variety of research fields, including the investigation of single molecule and cell mechanics and interactions as well as fundamental studies in heat transfer and Brownian dynamics on this scale. In this letter we present a route that determines temperature at the nano- to microscale with three independent measurements performed on a single trapped, rotating luminescent microparticle. We measure temperature changes using both the internal and external degrees of freedom, via (i) the upconverted luminescence, (ii) the rotation rate, and (iii) the Brownian dynamics of the particle. This novel tripartite approach allows us to cross-correlate the temperature for both the internal and external (center-of-mass) degree of freedom for the particle. In addition, our approach provides a measure of the temperature increase without the need of a precise knowledge of the particle dimensions, shape or any previous calibration of the sample or the experimental set-up. The developed technique opens up prospects for stringent tests of nanothermometry.
DOI
The measurement of temperature at the mesoscopic scale is challenging but important in a wide variety of research fields, including the investigation of single molecule and cell mechanics and interactions as well as fundamental studies in heat transfer and Brownian dynamics on this scale. In this letter we present a route that determines temperature at the nano- to microscale with three independent measurements performed on a single trapped, rotating luminescent microparticle. We measure temperature changes using both the internal and external degrees of freedom, via (i) the upconverted luminescence, (ii) the rotation rate, and (iii) the Brownian dynamics of the particle. This novel tripartite approach allows us to cross-correlate the temperature for both the internal and external (center-of-mass) degree of freedom for the particle. In addition, our approach provides a measure of the temperature increase without the need of a precise knowledge of the particle dimensions, shape or any previous calibration of the sample or the experimental set-up. The developed technique opens up prospects for stringent tests of nanothermometry.
DOI
Wednesday, August 15, 2018
Single-Molecule Mechanical Folding and Unfolding of RNA Hairpins: Effects of Single A-U to A·C Pair Substitutions and Single Proton Binding and Implications for mRNA Structure-Induced −1 Ribosomal Frameshifting
Lixia Yang, Zhensheng Zhong, Cailing Tong, Huan Jia, Yiran Liu, and Gang Chen
A wobble A·C pair can be protonated at near physiological pH to form a more stable wobble A+·C pair. Here, we constructed an RNA hairpin (rHP) and three mutants with one A-U base pair substituted with an A·C mismatch on the top (near the loop, U22C), middle (U25C), and bottom (U29C) positions of the stem, respectively. Our results on single-molecule mechanical (un)folding using optical tweezers reveal the destabilization effect of A-U to A·C pair substitution and protonation-dependent enhancement of mechanical stability facilitated through an increased folding rate, or decreased unfolding rate, or both. Our data show that protonation may occur rapidly upon the formation of an apparent mechanical folding transition state. Furthermore, we measured the bulk −1 ribosomal frameshifting efficiencies of the hairpins by a cell-free translation assay. For the mRNA hairpins studied, −1 frameshifting efficiency correlates with mechanical unfolding force at equilibrium and folding rate at around 15 pN. U29C has a frameshifting efficiency similar to that of rHP (∼2%). Accordingly, the bottom 2–4 base pairs of U29C may not form under a stretching force at pH 7.3, which is consistent with the fact that the bottom base pairs of the hairpins may be disrupted by ribosome at the slippery site. U22C and U25C have a similar frameshifting efficiency (∼1%), indicating that both unfolding and folding rates of an mRNA hairpin in a crowded environment may affect frameshifting. Our data indicate that mechanical (un)folding of RNA hairpins may mimic how mRNAs unfold and fold in the presence of translating ribosomes.
DOI
A wobble A·C pair can be protonated at near physiological pH to form a more stable wobble A+·C pair. Here, we constructed an RNA hairpin (rHP) and three mutants with one A-U base pair substituted with an A·C mismatch on the top (near the loop, U22C), middle (U25C), and bottom (U29C) positions of the stem, respectively. Our results on single-molecule mechanical (un)folding using optical tweezers reveal the destabilization effect of A-U to A·C pair substitution and protonation-dependent enhancement of mechanical stability facilitated through an increased folding rate, or decreased unfolding rate, or both. Our data show that protonation may occur rapidly upon the formation of an apparent mechanical folding transition state. Furthermore, we measured the bulk −1 ribosomal frameshifting efficiencies of the hairpins by a cell-free translation assay. For the mRNA hairpins studied, −1 frameshifting efficiency correlates with mechanical unfolding force at equilibrium and folding rate at around 15 pN. U29C has a frameshifting efficiency similar to that of rHP (∼2%). Accordingly, the bottom 2–4 base pairs of U29C may not form under a stretching force at pH 7.3, which is consistent with the fact that the bottom base pairs of the hairpins may be disrupted by ribosome at the slippery site. U22C and U25C have a similar frameshifting efficiency (∼1%), indicating that both unfolding and folding rates of an mRNA hairpin in a crowded environment may affect frameshifting. Our data indicate that mechanical (un)folding of RNA hairpins may mimic how mRNAs unfold and fold in the presence of translating ribosomes.
DOI
Experimental characterization and modeling of optical tweezer particle handling dynamics
Michael D. Porter, Brian Giera, Robert M. Panas, Lucas A. Shaw, Maxim Shusteff, and Jonathan B. Hopkins
We report a new framework for a quantitative understanding of optical trapping (OT) particle handling dynamics. We present a novel three-dimensional particle-based model that includes optical, hydrodynamic, and inter-particle forces. This semi-empirical colloid model is based on an open-source simulation code known as LAMMPS (large-scale atomic/molecular massively parallel simulator) and properly recapitulates the full OT force profile beyond the typical linear approximations valid near the trap center. Simulations are carried out with typical system parameters relevant for our experimental holographic optical trapping (HOT) system, including varied particle sizes, trap movement speeds, and beam powers. Furthermore, we present a new experimental method for measuring both the stable and metastable boundaries of the optical force profile to inform or validate the model’s underlying force profile. We show that our framework is a powerful tool for accurately predicting particle behavior in a practical experimental OT setup and can be used to characterize and predict particle handling dynamics within any arbitrary OT force profile.
DOI
We report a new framework for a quantitative understanding of optical trapping (OT) particle handling dynamics. We present a novel three-dimensional particle-based model that includes optical, hydrodynamic, and inter-particle forces. This semi-empirical colloid model is based on an open-source simulation code known as LAMMPS (large-scale atomic/molecular massively parallel simulator) and properly recapitulates the full OT force profile beyond the typical linear approximations valid near the trap center. Simulations are carried out with typical system parameters relevant for our experimental holographic optical trapping (HOT) system, including varied particle sizes, trap movement speeds, and beam powers. Furthermore, we present a new experimental method for measuring both the stable and metastable boundaries of the optical force profile to inform or validate the model’s underlying force profile. We show that our framework is a powerful tool for accurately predicting particle behavior in a practical experimental OT setup and can be used to characterize and predict particle handling dynamics within any arbitrary OT force profile.
DOI
Optical trapping and manipulation of plasmonic nanoparticles: fundamentals, applications, and perspectives
Alexander S. Urban, Sol Carretero-Palacios, Andrey A. Lutich, Theobald Lohmüller, Jochen Feldman and Frank Jäckel
This feature article discusses the optical trapping and manipulation of plasmonic nanoparticles, an area of current interest with potential applications in nanofabrication, sensing, analytics, biology and medicine. We give an overview over the basic theoretical concepts relating to optical forces, plasmon resonances and plasmonic heating. We discuss fundamental studies of plasmonic particles in optical traps and the temperature profiles around them. We place a particular emphasis on our own work employing optically trapped plasmonic nanoparticles towards nanofabrication, manipulation of biomimetic objects and sensing.
DOI
This feature article discusses the optical trapping and manipulation of plasmonic nanoparticles, an area of current interest with potential applications in nanofabrication, sensing, analytics, biology and medicine. We give an overview over the basic theoretical concepts relating to optical forces, plasmon resonances and plasmonic heating. We discuss fundamental studies of plasmonic particles in optical traps and the temperature profiles around them. We place a particular emphasis on our own work employing optically trapped plasmonic nanoparticles towards nanofabrication, manipulation of biomimetic objects and sensing.
DOI
Impact of Lanthanide Nanomaterials on Photonic Devices and Smart Applications
Jiajia Zhou, Julius L. Leaño Jr., Zhenyu Liu, Dayong Jin, Ka‐Leung Wong, Ru‐Shi Liu, Jean‐Claude G. Bünzli
Half a century after its initial emergence, lanthanide photonics is facing a profound remodeling induced by the upsurge of nanomaterials. Lanthanide‐doped nanomaterials hold promise for bioapplications and photonic devices because they ally the unmatched advantages of lanthanide photophysical properties with those arising from large surface‐to‐volume ratios and quantum confinement that are typical of nanoobjects. Cutting‐edge technologies and devices have recently arisen from this association and are in turn promoting nanophotonic materials as essential tools for a deeper understanding of biological mechanisms and related medical diagnosis and therapy, and as crucial building blocks for next‐generation photonic devices. Here, the recent progress in the development of nanomaterials, nanotechnologies, and nanodevices for clinical uses and commercial exploitation is reviewed. The candidate nanomaterials with mature synthesis protocols and compelling optical uniqueness are surveyed. The specific fields that are directly driven by lanthanide doped nanomaterials are emphasized, spanning from in vivo imaging and theranostics, micro‐/nanoscopic techniques, point‐of‐care medical testing, forensic fingerprints detection, to micro‐LED devices.
DOI
Half a century after its initial emergence, lanthanide photonics is facing a profound remodeling induced by the upsurge of nanomaterials. Lanthanide‐doped nanomaterials hold promise for bioapplications and photonic devices because they ally the unmatched advantages of lanthanide photophysical properties with those arising from large surface‐to‐volume ratios and quantum confinement that are typical of nanoobjects. Cutting‐edge technologies and devices have recently arisen from this association and are in turn promoting nanophotonic materials as essential tools for a deeper understanding of biological mechanisms and related medical diagnosis and therapy, and as crucial building blocks for next‐generation photonic devices. Here, the recent progress in the development of nanomaterials, nanotechnologies, and nanodevices for clinical uses and commercial exploitation is reviewed. The candidate nanomaterials with mature synthesis protocols and compelling optical uniqueness are surveyed. The specific fields that are directly driven by lanthanide doped nanomaterials are emphasized, spanning from in vivo imaging and theranostics, micro‐/nanoscopic techniques, point‐of‐care medical testing, forensic fingerprints detection, to micro‐LED devices.
DOI
A review on phospholipid vesicles flowing through channels
Fikret Aydin, Xiaolei Chu, Joseph Greenstein and Meenakshi Dutt
The flow of particles through confined volumes has appeared under different contexts in nature and technology. Some examples include the flow of red blood cells or drug delivery vehicles through capillaries, or surfactant-based particles in nano- or microfluidic cells. The molecular composition of the particles along with external conditions and the characteristics of the confined volume impact the response of the particle to flow. This review focuses on the problem of phospholipid vesicles constrained to flowing in channels. The review examines how experimental and computational approaches have been harnessed to study the response of these particles to the flow.
DOI
The flow of particles through confined volumes has appeared under different contexts in nature and technology. Some examples include the flow of red blood cells or drug delivery vehicles through capillaries, or surfactant-based particles in nano- or microfluidic cells. The molecular composition of the particles along with external conditions and the characteristics of the confined volume impact the response of the particle to flow. This review focuses on the problem of phospholipid vesicles constrained to flowing in channels. The review examines how experimental and computational approaches have been harnessed to study the response of these particles to the flow.
DOI
Tuesday, August 14, 2018
Dynamic Clustering of Dyneins on Axonal Endosomes: Evidence from High-Speed Darkfield Imaging
Praveen D. Chowdary, Luke Kaplan, Daphne L. Che, Bianxiao Cui
One of the fundamental features that govern the cooperativity of multiple dyneins during cargo trafficking in cells is the spatial distribution of these dyneins on the cargo. Geometric considerations and recent experiments indicate that clustered distributions of dyneins are required for effective cooperation on micron-sized cargos. However, very little is known about the spatial distribution of dyneins and their cooperativity on smaller cargos, such as vesicles or endosomes <200 nm in size, which are not amenable to conventional immunostaining and optical trapping methods. In this work, we present evidence that dyneins can dynamically be clustered on endosomes in response to load. Using a darkfield imaging assay, we measured the repeated stalls and detachments of retrograde axonal endosomes under load with <10 nm localization accuracy at imaging rates up to 1 kHz for over a timescale of minutes. A three-dimensional stochastic model was used to simulate the endosome motility under load to gain insights on the mechanochemical properties and spatial distribution of dyneins on axonal endosomes. Our results indicate that 1) the distribution of dyneins on endosomes is fluid enough to support dynamic clustering under load and 2) the detachment kinetics of dynein on endosomes differs significantly from the in vitro measurements possibly due to an increase in the unitary stall force of dynein on endosomes.
DOI
One of the fundamental features that govern the cooperativity of multiple dyneins during cargo trafficking in cells is the spatial distribution of these dyneins on the cargo. Geometric considerations and recent experiments indicate that clustered distributions of dyneins are required for effective cooperation on micron-sized cargos. However, very little is known about the spatial distribution of dyneins and their cooperativity on smaller cargos, such as vesicles or endosomes <200 nm in size, which are not amenable to conventional immunostaining and optical trapping methods. In this work, we present evidence that dyneins can dynamically be clustered on endosomes in response to load. Using a darkfield imaging assay, we measured the repeated stalls and detachments of retrograde axonal endosomes under load with <10 nm localization accuracy at imaging rates up to 1 kHz for over a timescale of minutes. A three-dimensional stochastic model was used to simulate the endosome motility under load to gain insights on the mechanochemical properties and spatial distribution of dyneins on axonal endosomes. Our results indicate that 1) the distribution of dyneins on endosomes is fluid enough to support dynamic clustering under load and 2) the detachment kinetics of dynein on endosomes differs significantly from the in vitro measurements possibly due to an increase in the unitary stall force of dynein on endosomes.
DOI
Optical lattices and optical vortex arrays in clustered speckles
Changwei He, Li Ma, Ruirui Zhang, Xing Li, Yuqin Zhang, and Chuanfu Cheng
Clustered speckle, optical lattices, and their optical vortex array are subjects of interest in optical wave manipulation. In this study, disordered optical lattices and vortex arrays with different unit structures were found in the clustered speckles generated by a circularly-distributed multi-pinhole scattering screen when it was illuminated by coherent light. These structures included hexagonal lattices, kagome lattices, and honeycomb lattices. Moreover, optical lattices with asymmetric units generated by modulation of phases with non-integer multiples of 2π were discussed. Theoretical analysis and numerical calculations demonstrated that optical lattices in clustered speckles in the observation plane were generated by the phase modulations of the random scattering screen. The lattice type depended on the number of 2π multiples of the summed phase difference between the pinholes. Additionally, the conditions for the formation of periodical optical lattices and their vortex arrays were given. Different optical lattices and their vortex arrays appearing simultaneously in the clustered speckle were difficult to generate using the common multi-beam interference system. This phenomenon is of great significance in the study of the orbital angular momentum of photons and other fields.
DOI
Clustered speckle, optical lattices, and their optical vortex array are subjects of interest in optical wave manipulation. In this study, disordered optical lattices and vortex arrays with different unit structures were found in the clustered speckles generated by a circularly-distributed multi-pinhole scattering screen when it was illuminated by coherent light. These structures included hexagonal lattices, kagome lattices, and honeycomb lattices. Moreover, optical lattices with asymmetric units generated by modulation of phases with non-integer multiples of 2π were discussed. Theoretical analysis and numerical calculations demonstrated that optical lattices in clustered speckles in the observation plane were generated by the phase modulations of the random scattering screen. The lattice type depended on the number of 2π multiples of the summed phase difference between the pinholes. Additionally, the conditions for the formation of periodical optical lattices and their vortex arrays were given. Different optical lattices and their vortex arrays appearing simultaneously in the clustered speckle were difficult to generate using the common multi-beam interference system. This phenomenon is of great significance in the study of the orbital angular momentum of photons and other fields.
DOI
Using single molecule force spectroscopy to facilitate a rational design of Ca2+-responsive β-roll peptide-based hydrogels
Lichao Liu, Han Wang, Yueying Han, Shanshan Lv and Jianfeng Chen
This study demonstrated that incorporation of Ca2+-responsive β-roll peptides arising from repeat-in-toxin (RTX) into elastomeric proteins provided an approach to construct hydrogels that exhibit Ca2+-responsive mechanical properties through a force analysis-based approach. Use of circular dichroism spectroscopy confirmed that there was a Ca2+-induced conformational change of RTX-based recombinant polyproteins. The polyproteins could be crosslinked into solid hydrogels. Shrinking/swelling measurements showed a Ca2+-responsive dimensional change of the RTX-based hydrogels. Mechanical measurements at constant pulling speed and at constant extension suggested that the mechanical properties of the RTX-based hydrogels were Ca2+-responsive. Experimental single molecule force spectroscopies were used to investigate the nano-mechanical stability of the RTX domains. Single molecule atomic force microscopy and optical tweezers provided evidence that the Ca2+-dependent refolding of the intrinsically disordered RTX led to the force increase. The results indicated that the unique Ca2+-responsive mechanical properties of the RTX-based hydrogels at the macroscopic level could be attributed to the nano-mechanical properties of the RTX domains engineered into individual polyproteins at the single molecule level.
DOI
This study demonstrated that incorporation of Ca2+-responsive β-roll peptides arising from repeat-in-toxin (RTX) into elastomeric proteins provided an approach to construct hydrogels that exhibit Ca2+-responsive mechanical properties through a force analysis-based approach. Use of circular dichroism spectroscopy confirmed that there was a Ca2+-induced conformational change of RTX-based recombinant polyproteins. The polyproteins could be crosslinked into solid hydrogels. Shrinking/swelling measurements showed a Ca2+-responsive dimensional change of the RTX-based hydrogels. Mechanical measurements at constant pulling speed and at constant extension suggested that the mechanical properties of the RTX-based hydrogels were Ca2+-responsive. Experimental single molecule force spectroscopies were used to investigate the nano-mechanical stability of the RTX domains. Single molecule atomic force microscopy and optical tweezers provided evidence that the Ca2+-dependent refolding of the intrinsically disordered RTX led to the force increase. The results indicated that the unique Ca2+-responsive mechanical properties of the RTX-based hydrogels at the macroscopic level could be attributed to the nano-mechanical properties of the RTX domains engineered into individual polyproteins at the single molecule level.
DOI
Generation of reconfigurable optical traps for microparticles spatial manipulation through dynamic split lens inspired light structures
Angel Lizana, Haolin Zhang, Alex Turpin, Albert Van Eeckhout, Fabian A. Torres-Ruiz, Asticio Vargas, Claudio Ramirez, Francesc Pi & Juan Campos
We present an experimental method, based on the use of dynamic split-lens configurations, useful for the trapping and spatial control of microparticles through the photophoretic force. In particular, the concept of split-lens configurations is exploited to experimentally create customized and reconfigurable three-dimensional light structures, in which carbon coated glass microspheres, with sizes in a range of 63–75 μm, can be captured. The generation of light spatial structures is performed by properly addressing phase distributions corresponding to different split-lens configurations onto a spatial light modulator (SLM). The use of an SLM allows a dynamic variation of the light structures geometry just by modifying few control parameters of easy physical interpretation. We provide some examples in video format of particle trapping processes. What is more, we also perform further spatial manipulation, by controlling the spatial position of the particles in the axial direction, demonstrating the generation of reconfigurable three-dimensional photophoretic traps for microscopic manipulation of absorbing particles.
DOI
We present an experimental method, based on the use of dynamic split-lens configurations, useful for the trapping and spatial control of microparticles through the photophoretic force. In particular, the concept of split-lens configurations is exploited to experimentally create customized and reconfigurable three-dimensional light structures, in which carbon coated glass microspheres, with sizes in a range of 63–75 μm, can be captured. The generation of light spatial structures is performed by properly addressing phase distributions corresponding to different split-lens configurations onto a spatial light modulator (SLM). The use of an SLM allows a dynamic variation of the light structures geometry just by modifying few control parameters of easy physical interpretation. We provide some examples in video format of particle trapping processes. What is more, we also perform further spatial manipulation, by controlling the spatial position of the particles in the axial direction, demonstrating the generation of reconfigurable three-dimensional photophoretic traps for microscopic manipulation of absorbing particles.
DOI
Pseudopolymorph Control of l-Phenylalanine Achieved by Laser Trapping
Chi-Shiun Wu, Pei-Yun Hsieh, Ken-ichi Yuyama, Hiroshi Masuhara, and Teruki Sugiyama
The pseudopolymorphism of l-phenylalanine, monohydrate and anhydrous crystals, was arbitrarily controlled by laser trapping with a focused continuous-wave near-infrared laser beam. Crystallization was realized even from unsaturated solution, when laser trapping always produced the anhydrous crystal. Contrarily, the monohydrate crystal was constantly formed from supersaturated solution. In saturated solution, the pseudopolymorphism strongly depended on laser power and polarization.
DOI
The pseudopolymorphism of l-phenylalanine, monohydrate and anhydrous crystals, was arbitrarily controlled by laser trapping with a focused continuous-wave near-infrared laser beam. Crystallization was realized even from unsaturated solution, when laser trapping always produced the anhydrous crystal. Contrarily, the monohydrate crystal was constantly formed from supersaturated solution. In saturated solution, the pseudopolymorphism strongly depended on laser power and polarization.
DOI
Monday, August 13, 2018
GHz Rotation of an Optically Trapped Nanoparticle in Vacuum
René Reimann, Michael Doderer, Erik Hebestreit, Rozenn Diehl, Martin Frimmer, Dominik Windey, Felix Tebbenjohanns, and Lukas Novotny
We report on rotating an optically trapped silica nanoparticle in vacuum by transferring spin angular momentum of light to the particle’s mechanical angular momentum. At sufficiently low damping, realized at pressures below 10−5 mbar, we observe rotation frequencies of single 100 nm particles exceeding 1 GHz. We find that the steady-state rotation frequency scales linearly with the optical trapping power and inversely with pressure, consistent with theoretical considerations based on conservation of angular momentum. Rapidly changing the polarization of the trapping light allows us to extract the pressure-dependent response time of the particle’s rotational degree of freedom.
DOI
We report on rotating an optically trapped silica nanoparticle in vacuum by transferring spin angular momentum of light to the particle’s mechanical angular momentum. At sufficiently low damping, realized at pressures below 10−5 mbar, we observe rotation frequencies of single 100 nm particles exceeding 1 GHz. We find that the steady-state rotation frequency scales linearly with the optical trapping power and inversely with pressure, consistent with theoretical considerations based on conservation of angular momentum. Rapidly changing the polarization of the trapping light allows us to extract the pressure-dependent response time of the particle’s rotational degree of freedom.
DOI
Interactions between micro-scale oil droplets in aqueous surfactant solution determined using optical tweezers
An Chen, Shao-Wei Li, Fu-Ning Sang, Hong-Bo Zeng, Jian-Hong Xu
The stability of the emulsions is crucial, which relies on a well-developed understanding of dynamic interaction forces between single dispersed droplets. In the previous studies, many interests focus on the oil droplets of size range of 20–200 µm. However, emulsion droplets with diameter below 10 µm are rarely mentioned, which is the size scale of real emulsion droplets in various applications, such as toners, spacers for liquid crystal displays, and materials in biomedical and biochemical analysis. The micro-scale droplets have many differences on the deformation, internal pressure and hydrodynamic effects. It is necessary to understand the interaction mechanisms between two real size scales of oil droplets for guiding practical production and application.
DOI
The stability of the emulsions is crucial, which relies on a well-developed understanding of dynamic interaction forces between single dispersed droplets. In the previous studies, many interests focus on the oil droplets of size range of 20–200 µm. However, emulsion droplets with diameter below 10 µm are rarely mentioned, which is the size scale of real emulsion droplets in various applications, such as toners, spacers for liquid crystal displays, and materials in biomedical and biochemical analysis. The micro-scale droplets have many differences on the deformation, internal pressure and hydrodynamic effects. It is necessary to understand the interaction mechanisms between two real size scales of oil droplets for guiding practical production and application.
DOI
Opto-Thermophoretic Manipulation and Construction of Colloidal Superstructures in Photocurable Hydrogels
Xiaolei Peng, Jingang Li, Linhan Lin, Yaoran Liu, and Yuebing Zheng
Light-based manipulation of colloidal particles holds great promise in fabrication of functional devices. Construction of complex colloidal superstructures using traditional optical tweezers is limited by high operation power and strong heating effect. Herein, we demonstrate low-power opto-thermophoretic manipulation and construction of colloidal superstructures in photocurable hydrogels. By introducing cationic surfactants into a hydrogel solution under a light-directed temperature field, we create both thermoelectric fields and depletion attraction forces to control the suspended colloidal particles. The particles of various sizes and compositions are thus trapped and organized into various superstructures. Furthermore, the colloidal superstructures are immobilized and patterned onto solid-state substrates through UV-induced photopolymerization of the hydrogel. Our opto-thermophoretic technique will open up avenues for bottom-up assembly of colloidal materials and devices.
DOI
Light-based manipulation of colloidal particles holds great promise in fabrication of functional devices. Construction of complex colloidal superstructures using traditional optical tweezers is limited by high operation power and strong heating effect. Herein, we demonstrate low-power opto-thermophoretic manipulation and construction of colloidal superstructures in photocurable hydrogels. By introducing cationic surfactants into a hydrogel solution under a light-directed temperature field, we create both thermoelectric fields and depletion attraction forces to control the suspended colloidal particles. The particles of various sizes and compositions are thus trapped and organized into various superstructures. Furthermore, the colloidal superstructures are immobilized and patterned onto solid-state substrates through UV-induced photopolymerization of the hydrogel. Our opto-thermophoretic technique will open up avenues for bottom-up assembly of colloidal materials and devices.
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Improving the throughput of automated holographic optical tweezers
Lucas A. Shaw, Samira Chizari, and Jonathan B. Hopkins
The purpose of this work is to introduce three improvements to automated holographic-optical-tweezers systems that increase the number and speed of particles that can be manipulated simultaneously. First, we address path planning by solving a bottleneck assignment problem, which can reduce total move time by up to 30% when compared with traditional assignment problem solutions. Next, we demonstrate a new strategy to identify and remove undesired (e.g., misshapen or agglomerated) particles. Finally, we employ a controller that combines both closed- and open-loop automation steps, which can increase the overall loop rate and average particle speeds while also utilizing necessary process monitoring checks to ensure that particles reach their destinations. Using these improvements, we show fast reconfiguration of 100 microspheres simultaneously with a closed-loop control rate of 6, and 10 Hz by employing both closed- and open-loop steps. We also demonstrate the closed-loop assembly of a large pattern in a continuously flowing microchannel-based particle-delivery system. The proposed approach provides a promising path toward automatic and scalable assembly of microgranular structures.
DOI
The purpose of this work is to introduce three improvements to automated holographic-optical-tweezers systems that increase the number and speed of particles that can be manipulated simultaneously. First, we address path planning by solving a bottleneck assignment problem, which can reduce total move time by up to 30% when compared with traditional assignment problem solutions. Next, we demonstrate a new strategy to identify and remove undesired (e.g., misshapen or agglomerated) particles. Finally, we employ a controller that combines both closed- and open-loop automation steps, which can increase the overall loop rate and average particle speeds while also utilizing necessary process monitoring checks to ensure that particles reach their destinations. Using these improvements, we show fast reconfiguration of 100 microspheres simultaneously with a closed-loop control rate of 6, and 10 Hz by employing both closed- and open-loop steps. We also demonstrate the closed-loop assembly of a large pattern in a continuously flowing microchannel-based particle-delivery system. The proposed approach provides a promising path toward automatic and scalable assembly of microgranular structures.
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Optical binding of two cooled micro-gyroscopes levitated in vacuum
Yoshihiko Arita, Ewan M. Wright, and Kishan Dholakia
Coupling between mesoscopic particles levitated in vacuum is a prerequisite for the realization of a large-scale array of particles in an underdamped environment as well as potential studies at the classical–quantum interface. Here, we demonstrate for the first time, to the best of our knowledge, optical binding between two rotating microparticles mediated by light scattering in vacuum. We investigate autocorrelations between the two normal modes of oscillation determined by the center-of-mass and the relative positions of the two-particle system. The inter-particle coupling, as a consequence of optical binding, removes the degeneracy of the normal mode frequencies, which is in good agreement with theory. We further demonstrate that the optically bound array of rotating microparticles retains their optical coupling during gyroscopic cooling, and exhibits cooperative motion whose center-of-mass is stabilized.
DOI
Coupling between mesoscopic particles levitated in vacuum is a prerequisite for the realization of a large-scale array of particles in an underdamped environment as well as potential studies at the classical–quantum interface. Here, we demonstrate for the first time, to the best of our knowledge, optical binding between two rotating microparticles mediated by light scattering in vacuum. We investigate autocorrelations between the two normal modes of oscillation determined by the center-of-mass and the relative positions of the two-particle system. The inter-particle coupling, as a consequence of optical binding, removes the degeneracy of the normal mode frequencies, which is in good agreement with theory. We further demonstrate that the optically bound array of rotating microparticles retains their optical coupling during gyroscopic cooling, and exhibits cooperative motion whose center-of-mass is stabilized.
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Acidosis and Phosphate Directly Reduce Myosin’s Force-Generating Capacity Through Distinct Molecular Mechanisms
Mike Woodward and Edward P. Debold
Elevated levels of the metabolic by-products, including acidosis (i.e., high [H+]) and phosphate (Pi) are putative agents of muscle fatigue; however, the mechanism through which they affect myosin’s function remain unclear. To elucidate these mechanisms, we directly examined the effect of acidosis (pH 6.5 vs. 7.4), alone and in combination with elevated levels of Pi on the force-generating capacity of a mini-ensemble of myosin using a laser trap assay. Acidosis decreased myosin’s average force-generating capacity by 20% (p < 0.05). The reduction was due to both a decrease in the force generated during each actomyosin interaction, as well as an increase in the number of binding events generating negative forces. Adding Pi to the acidic condition resulted in a quantitatively similar decrease in force but was solely due to an elimination of all high force-generating events (>2 pN), resulting from an acceleration of the myosin’s rate of detachment from actin. Acidosis and Pi also had distinct effects on myosin’s steady state ATPase rate with acidosis slowing it by ∼90% (p > 0.05), while the addition of Pi under acidic conditions caused a significant recovery in the ATPase rate. These data suggest that these two fatigue agents have distinct effects on myosin’s cross-bridge cycle that may underlie the synergistic effect that they have muscle force. Thus these data provide novel molecular insight into the mechanisms underlying the depressive effects of Pi and H+ on muscle contraction during fatigue.
DOI
Elevated levels of the metabolic by-products, including acidosis (i.e., high [H+]) and phosphate (Pi) are putative agents of muscle fatigue; however, the mechanism through which they affect myosin’s function remain unclear. To elucidate these mechanisms, we directly examined the effect of acidosis (pH 6.5 vs. 7.4), alone and in combination with elevated levels of Pi on the force-generating capacity of a mini-ensemble of myosin using a laser trap assay. Acidosis decreased myosin’s average force-generating capacity by 20% (p < 0.05). The reduction was due to both a decrease in the force generated during each actomyosin interaction, as well as an increase in the number of binding events generating negative forces. Adding Pi to the acidic condition resulted in a quantitatively similar decrease in force but was solely due to an elimination of all high force-generating events (>2 pN), resulting from an acceleration of the myosin’s rate of detachment from actin. Acidosis and Pi also had distinct effects on myosin’s steady state ATPase rate with acidosis slowing it by ∼90% (p > 0.05), while the addition of Pi under acidic conditions caused a significant recovery in the ATPase rate. These data suggest that these two fatigue agents have distinct effects on myosin’s cross-bridge cycle that may underlie the synergistic effect that they have muscle force. Thus these data provide novel molecular insight into the mechanisms underlying the depressive effects of Pi and H+ on muscle contraction during fatigue.
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Friday, August 10, 2018
Plasmonic nano-tweezer based on square nanoplate tetramers
Qijian Jin, Li Wang, Sheng Yan, Hua Wei, and Yingzhou Huang
The research fields of trapping nanoparticles have experienced a huge development in recent years, which mainly benefits from the unique field enhancement in plasmonic nanomaterials. Since the large field enhancement originates from the excited localized surface plasmon at the metal surface, exploring novel metal nanostructures with high trapping efficiency is always the main goal in this field. In this work, the plasmonic trapping of nanoparticles based on the gold periodic square tetramers (PST) was investigated through full-wave simulations using the finite-difference time-domain (FDTD) method. The electric field and surface charge distributions on the surface of PST indicate that both the trapping position and efficiency are influenced by orientations of the square nanoplates. The maximum electromagnetic enhancement is achieved when all square nanoplates rotate 45° along the 𝑧 axis. Therefore, the gradient force and trapping potential of this PST with optimal orientation were further studied, and the results indicate that a dielectric nanoparticle of 15 nm radius can be stably captured. Furthermore, the calculation results show that the plasmonic trapping with this PST exhibits strong polarization dependence. It is easy to change the trapping position and the field intensity by tuning the polarization of the incident wave. Our work enables a deeper understanding of this kind of plasmonic trapping and could have potential applications in biomedical research and life science.
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MEMS Resonant Mass Sensor With Integrated Optical Manipulation
Ethan G. Keeler ; Peifeng Jing ; Jingda Wu ; Chen Zou ; Lih Y. Lin
We investigate optical manipulation of particles in fluid as a viable method to achieve better experimental fidelity and extend the application of integrated-fluidic resonant-mass sensing. Fluctuations in sample position or trajectory can lead to measurement error, thereby degrading the resolution with which these devices can accurately characterize mass. Optical trapping offers precise location control in such fluidic environments and can define and fix position to mitigate variability, but requires a novel approach to design, fabrication, and biological viability concerns. Optical considerations are especially imperative when working with biological cells, organic matter, or other materials adversely affected by imposing high intensity laser light, and mandate the use of a photonic-crystal structure. Given these requirements, this letter details a design and fabrication approach embodied by unique devices that demonstrate compatibility with optical trapping and mass sensing. Accordingly, the effects of optical manipulation on the measurement are disclosed, toward long-term biological mass monitoring and sensing. Ultimately, precise measurement of singular cell mass could answer many fundamental biological questions, with implications in cell biology, pharmacology, and medicine.
DOI
We investigate optical manipulation of particles in fluid as a viable method to achieve better experimental fidelity and extend the application of integrated-fluidic resonant-mass sensing. Fluctuations in sample position or trajectory can lead to measurement error, thereby degrading the resolution with which these devices can accurately characterize mass. Optical trapping offers precise location control in such fluidic environments and can define and fix position to mitigate variability, but requires a novel approach to design, fabrication, and biological viability concerns. Optical considerations are especially imperative when working with biological cells, organic matter, or other materials adversely affected by imposing high intensity laser light, and mandate the use of a photonic-crystal structure. Given these requirements, this letter details a design and fabrication approach embodied by unique devices that demonstrate compatibility with optical trapping and mass sensing. Accordingly, the effects of optical manipulation on the measurement are disclosed, toward long-term biological mass monitoring and sensing. Ultimately, precise measurement of singular cell mass could answer many fundamental biological questions, with implications in cell biology, pharmacology, and medicine.
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Three-Dimensional Enantiomeric Recognition of Optically Trapped Single Chiral Nanoparticles
Gabriel Schnoering, Lisa V. Poulikakos, Yoseline Rosales-Cabara, Antoine Canaguier-Durand, David J. Norris, and Cyriaque Genet
We optically trap freestanding single metallic chiral nanoparticles using a standing-wave optical tweezer. We also incorporate within the trap a polarimetric setup that allows us to perform in situ chiral recognition of single enantiomers. This is done by measuring the S3 component of the Stokes vector of a light beam scattered off the trapped nanoparticle in the forward direction. This unique combination of optical trapping and chiral recognition, all implemented within a single setup, opens new perspectives towards the control, recognition, and manipulation of chiral objects at nanometer scales.
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We optically trap freestanding single metallic chiral nanoparticles using a standing-wave optical tweezer. We also incorporate within the trap a polarimetric setup that allows us to perform in situ chiral recognition of single enantiomers. This is done by measuring the S3 component of the Stokes vector of a light beam scattered off the trapped nanoparticle in the forward direction. This unique combination of optical trapping and chiral recognition, all implemented within a single setup, opens new perspectives towards the control, recognition, and manipulation of chiral objects at nanometer scales.
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Natural convection induced by an optically fabricated and actuated microtool with a thermoplasmonic disk
Einstom Engay, Ada-Ioana Bunea, Manto Chouliara, Andrew Bañas, and Jesper Glückstad
Two-photon polymerization was employed for fabricating microtools amenable to optical trapping and manipulation. A disk feature was included as part of the microtools and further functionalized by electron-beam deposition. The nanostructured gold layer on the disk facilitates off-resonant plasmonic heating upon illumination with a laser beam. As a consequence, natural convection characterized by the typical toroidal shape resembling that of Rayleigh–Bénard flow can be observed. A velocity of several μm·s−1 is measured for 2 μm microspheres dispersed in the surroundings of the microtool. To the best of our knowledge, this is the first time that thermoplasmonic-induced natural convection is experimentally demonstrated using a mobile heat source.
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Two-photon polymerization was employed for fabricating microtools amenable to optical trapping and manipulation. A disk feature was included as part of the microtools and further functionalized by electron-beam deposition. The nanostructured gold layer on the disk facilitates off-resonant plasmonic heating upon illumination with a laser beam. As a consequence, natural convection characterized by the typical toroidal shape resembling that of Rayleigh–Bénard flow can be observed. A velocity of several μm·s−1 is measured for 2 μm microspheres dispersed in the surroundings of the microtool. To the best of our knowledge, this is the first time that thermoplasmonic-induced natural convection is experimentally demonstrated using a mobile heat source.
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Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System
Daniel Andrén, Pawel Karpinski, Mikael Käll
The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.
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The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.
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Thursday, August 9, 2018
Patterning of graphene oxide with optoelectronic tweezers
Matthew B. Lim, Robert G. Felsted, Xuezhe Zhou, Bennett E. Smith, and Peter J. Pauzauskie
Optoelectronic tweezers (OET) offer a means for parallel trapping and dynamic manipulation of micro-scale particles using low-intensity light. Such capabilities can facilitate the formation of bulk materials with a precisely tailored microstructure. Here, we report the use of OET to vertically align, trap, and reposition sheets of graphene oxide (GO) in liquids, paving the way for textured and patterned graphene macroassemblies that could offer superior performance for applications in energy storage, catalysis, and electronic devices. Trapping can be achieved with low-power light from inexpensive digital projectors and diode lasers, making it simple for users to create and apply patterns while avoiding undesirable photothermal heating effects. To give users a quantitative idea of trap stiffness, we also present a theoretical framework for predicting the maximum achievable speed of a GO platelet in an OET trap.
DOI
Optoelectronic tweezers (OET) offer a means for parallel trapping and dynamic manipulation of micro-scale particles using low-intensity light. Such capabilities can facilitate the formation of bulk materials with a precisely tailored microstructure. Here, we report the use of OET to vertically align, trap, and reposition sheets of graphene oxide (GO) in liquids, paving the way for textured and patterned graphene macroassemblies that could offer superior performance for applications in energy storage, catalysis, and electronic devices. Trapping can be achieved with low-power light from inexpensive digital projectors and diode lasers, making it simple for users to create and apply patterns while avoiding undesirable photothermal heating effects. To give users a quantitative idea of trap stiffness, we also present a theoretical framework for predicting the maximum achievable speed of a GO platelet in an OET trap.
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Free and confined Brownian motion in viscoelastic Stokes–Oldroyd B fluids
Shuvojit Paul, Basudev Roy and Ayan Banerjee
We linearize the Stokes–Oldroyd B model for small perturbations and instantaneous hydrodynamic friction to simulate the environment for a free and confined Brownian particle. We use the standard Green's function approach to determine the viscoelasticity, and show that the expression obtained for the frequency dependent viscosity is similar to that given by the Jeffrey's model, though the latter describes viscoelasticity by the bulk storage and loss moduli that is represented by a complex elastic modulus of the fluid concerned. In contrast, we consider the characteristics of the polymer chains and the Newtonian solvent of the complex fluid individually, and determine an expression for frequency-dependent viscosity that would be useful for microrheology performed from Brownian trajectories measured in experiments. Finally, we evaluate the trajectory of a free Brownian particle in a viscoelastic environment using our formalism, and calculate various important parameters quantifying Brownian dynamics, which we then extend to the particle confined in a harmonic potential as provided by optical tweezers.
DOI
We linearize the Stokes–Oldroyd B model for small perturbations and instantaneous hydrodynamic friction to simulate the environment for a free and confined Brownian particle. We use the standard Green's function approach to determine the viscoelasticity, and show that the expression obtained for the frequency dependent viscosity is similar to that given by the Jeffrey's model, though the latter describes viscoelasticity by the bulk storage and loss moduli that is represented by a complex elastic modulus of the fluid concerned. In contrast, we consider the characteristics of the polymer chains and the Newtonian solvent of the complex fluid individually, and determine an expression for frequency-dependent viscosity that would be useful for microrheology performed from Brownian trajectories measured in experiments. Finally, we evaluate the trajectory of a free Brownian particle in a viscoelastic environment using our formalism, and calculate various important parameters quantifying Brownian dynamics, which we then extend to the particle confined in a harmonic potential as provided by optical tweezers.
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Dissecting myosin-5B mechanosensitivity and calcium regulation at the single molecule level
Lucia Gardini, Sarah M. Heissler, Claudia Arbore, Yi Yang, James R. Sellers, Francesco S. Pavone & Marco Capitanio
Myosin-5B is one of three members of the myosin-5 family of actin-based molecular motors. Despite its fundamental role in recycling endosome trafficking and in collective actin network dynamics, the molecular mechanisms underlying its motility are inherently unknown. Here we combine single-molecule imaging and high-speed laser tweezers to dissect the mechanoenzymatic properties of myosin-5B. We show that a single myosin-5B moves processively in 36-nm steps, stalls at ~2 pN resistive forces, and reverses its directionality at forces >2 pN. Interestingly, myosin-5B mechanosensitivity differs from that of myosin-5A, while it is strikingly similar to kinesin-1. In particular, myosin-5B run length is markedly and asymmetrically sensitive to force, a property that might be central to motor ensemble coordination. Furthermore, we show that Ca2+ does not affect the enzymatic activity of the motor unit, but abolishes myosin-5B processivity through calmodulin dissociation, providing important insights into the regulation of postsynaptic cargoes trafficking in neuronal cells.
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Myosin-5B is one of three members of the myosin-5 family of actin-based molecular motors. Despite its fundamental role in recycling endosome trafficking and in collective actin network dynamics, the molecular mechanisms underlying its motility are inherently unknown. Here we combine single-molecule imaging and high-speed laser tweezers to dissect the mechanoenzymatic properties of myosin-5B. We show that a single myosin-5B moves processively in 36-nm steps, stalls at ~2 pN resistive forces, and reverses its directionality at forces >2 pN. Interestingly, myosin-5B mechanosensitivity differs from that of myosin-5A, while it is strikingly similar to kinesin-1. In particular, myosin-5B run length is markedly and asymmetrically sensitive to force, a property that might be central to motor ensemble coordination. Furthermore, we show that Ca2+ does not affect the enzymatic activity of the motor unit, but abolishes myosin-5B processivity through calmodulin dissociation, providing important insights into the regulation of postsynaptic cargoes trafficking in neuronal cells.
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Counter‐Propagating Optical Trapping of Resonant Nanoparticles Using a Uniaxial Crystal
Pawel Karpinski Steven Jones Daniel Andrén Mikael Käll
Laser tweezing of optically resonant nanostructures, such as plasmonic nanoparticles and high‐index dielectric nanoresonators, is extremely challenging because the enhanced light–matter interaction usually amplifies radiation pressure to an extent where conventional single beam gradient trapping in three dimensions becomes impossible. Such particles are therefore typically trapped off resonance or in two dimensions only. To extend the application potential of optical tweezers to the resonant case, focus splitting inside a uniaxial birefringent crystal and reflection from a mirror is used to develop a counter‐propagating beam configuration based on a single microscope objective. The setup allows one to trap and rapidly rotate resonant gold nanorods in water far from any interface, thereby opening a range of possibilities for novel studies of resonantly enhanced optical forces and interactions in uniform environments.
DOI
Laser tweezing of optically resonant nanostructures, such as plasmonic nanoparticles and high‐index dielectric nanoresonators, is extremely challenging because the enhanced light–matter interaction usually amplifies radiation pressure to an extent where conventional single beam gradient trapping in three dimensions becomes impossible. Such particles are therefore typically trapped off resonance or in two dimensions only. To extend the application potential of optical tweezers to the resonant case, focus splitting inside a uniaxial birefringent crystal and reflection from a mirror is used to develop a counter‐propagating beam configuration based on a single microscope objective. The setup allows one to trap and rapidly rotate resonant gold nanorods in water far from any interface, thereby opening a range of possibilities for novel studies of resonantly enhanced optical forces and interactions in uniform environments.
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Ion Coulomb crystal in a polychromatic optical superlattice
I V Krasnov and L P Kamenshchikov
We demonstrate that the earlier suggested new all-optical method of creating long-term small (containing two or three particles) ion clusters using the rectified optical forces (RFs) can be used to create cold trapped Coulomb crystals (consisting of several tens of resonant ions). The results of the supercomputer simulations of the dynamics of a mercury ion cloud in a polychromatic optical superlattice (induced by RFs) are presented and analysed. Such a cloud (including 49 ions) in the absence of the optical field expands rapidly (during the characteristic time of the order of ) as a result of the Coulomb explosion. It is shown that the polychromatic optical field can result in the 'quenching' of the Coulomb explosion and crystallisation of the ion cloud: creation of a quasi-2D array of ordered and strongly coupled cold ions (with the Coulomb coupling parameter and temperature ~10−3 K). The mean destruction time of the studied metastable crystal is of the order of 10 s. Moreover, the central core of the ion cloud can retain its crystalline configuration for a much longer time.
DOI
We demonstrate that the earlier suggested new all-optical method of creating long-term small (containing two or three particles) ion clusters using the rectified optical forces (RFs) can be used to create cold trapped Coulomb crystals (consisting of several tens of resonant ions). The results of the supercomputer simulations of the dynamics of a mercury ion cloud in a polychromatic optical superlattice (induced by RFs) are presented and analysed. Such a cloud (including 49 ions) in the absence of the optical field expands rapidly (during the characteristic time of the order of ) as a result of the Coulomb explosion. It is shown that the polychromatic optical field can result in the 'quenching' of the Coulomb explosion and crystallisation of the ion cloud: creation of a quasi-2D array of ordered and strongly coupled cold ions (with the Coulomb coupling parameter and temperature ~10−3 K). The mean destruction time of the studied metastable crystal is of the order of 10 s. Moreover, the central core of the ion cloud can retain its crystalline configuration for a much longer time.
DOI
Wednesday, August 8, 2018
Molecular switch-like regulation enables global subunit coordination in a viral ring ATPase
Sara Tafoya, Shixin Liu, Juan P. Castillo, Rockney Atz, Marc C. Morais, Shelley Grimes, Paul J. Jardine, and Carlos Bustamante
Subunits in multimeric ring-shaped motors must coordinate their activities to ensure correct and efficient performance of their mechanical tasks. Here, we study WT and arginine finger mutants of the pentameric bacteriophage φ29 DNA packaging motor. Our results reveal the molecular interactions necessary for the coordination of ADP-ATP exchange and ATP hydrolysis of the motor's biphasic mechanochemical cycle. We show that two distinct regulatory mechanisms determine this coordination. In the first mechanism, the DNA up-regulates a single subunit's catalytic activity, transforming it into a global regulator that initiates the nucleotide exchange phase and the hydrolysis phase. In the second, an arginine finger in each subunit promotes ADP-ATP exchange and ATP hydrolysis of its neighbor. Accordingly, we suggest that the subunits perform the roles described for GDP exchange factors and GTPase-activating proteins observed in small GTPases. We propose that these mechanisms are fundamental to intersubunit coordination and are likely present in other ring ATPases.
Subunits in multimeric ring-shaped motors must coordinate their activities to ensure correct and efficient performance of their mechanical tasks. Here, we study WT and arginine finger mutants of the pentameric bacteriophage φ29 DNA packaging motor. Our results reveal the molecular interactions necessary for the coordination of ADP-ATP exchange and ATP hydrolysis of the motor's biphasic mechanochemical cycle. We show that two distinct regulatory mechanisms determine this coordination. In the first mechanism, the DNA up-regulates a single subunit's catalytic activity, transforming it into a global regulator that initiates the nucleotide exchange phase and the hydrolysis phase. In the second, an arginine finger in each subunit promotes ADP-ATP exchange and ATP hydrolysis of its neighbor. Accordingly, we suggest that the subunits perform the roles described for GDP exchange factors and GTPase-activating proteins observed in small GTPases. We propose that these mechanisms are fundamental to intersubunit coordination and are likely present in other ring ATPases.
Mutual interaction of red blood cells assessed by optical tweezers and scanning electron microscopy imaging
Tatiana Avsievich, Alexey Popov, Alexander Bykov, and Igor Meglinski
The adhesion of red blood cells (RBC) has been studied extensively in frame of cell-to-cell interaction induced by dextran macromolecules, whereas the data are lacking for native plasma solution. We apply optical tweezers to investigate the induced adhesion of RBC in plasma and in dextran solution. Two hypotheses, cross-bridges and depletion layer, are typically used to describe the mechanism of cell interaction; however, both mechanisms need to be confirmed experimentally. These interactions in fact are very much dependent on the size and concentration of dextran and proteins in plasma. The results show that in different dextran solutions, the interaction of adhering RBC agrees well with the quantitative predictions obtained based on the depletion-induced cells adhesion model, whereas the migrating cross-bridges model is more appropriate for plasma. Despite the different mechanisms of RBC interaction in a mixture of dextran with the size ranges and volume fraction proportional to plasma proteins, the dependence of RBC adhering tends to be close to the cross-bridges model. The induced aggregation of RBC in the dextran solutions and in native plasma are observed by direct visualization utilizing scanning electron microscopy.
DOI
The adhesion of red blood cells (RBC) has been studied extensively in frame of cell-to-cell interaction induced by dextran macromolecules, whereas the data are lacking for native plasma solution. We apply optical tweezers to investigate the induced adhesion of RBC in plasma and in dextran solution. Two hypotheses, cross-bridges and depletion layer, are typically used to describe the mechanism of cell interaction; however, both mechanisms need to be confirmed experimentally. These interactions in fact are very much dependent on the size and concentration of dextran and proteins in plasma. The results show that in different dextran solutions, the interaction of adhering RBC agrees well with the quantitative predictions obtained based on the depletion-induced cells adhesion model, whereas the migrating cross-bridges model is more appropriate for plasma. Despite the different mechanisms of RBC interaction in a mixture of dextran with the size ranges and volume fraction proportional to plasma proteins, the dependence of RBC adhering tends to be close to the cross-bridges model. The induced aggregation of RBC in the dextran solutions and in native plasma are observed by direct visualization utilizing scanning electron microscopy.
DOI
Strong cytoskeleton activity on millisecond timescales upon particle binding revealed by ROCS microscopy
Felix Jünger, Alexander Rohrbach
Cells change their shape within seconds, cellular protrusions even on subsecond timescales enabling various responses to stimuli of approaching bacteria, viruses or pharmaceutical drugs. Typical response patterns are governed by a complex reorganization of the actin cortex, where single filaments and molecules act on even faster timescales. These dynamics have remained mostly invisible due to a superposition of slow and fast motions, but also due to a lack of adequate imaging technology. Whereas fluorescence techniques require too long integration times, novel coherent techniques such as ROCS microscopy can achieve sufficiently high spatiotemporal resolution. ROCS uses rotating back‐scattered laser light from cellular structures and generates a consistently high image contrast at 150nm resolution and frame rates of 100 Hz ‐ without fluorescence or bleaching. Here, we present an extension of ROCS microscopy that exploits the principles of dynamic light scattering for precise localization, visualization and quantification of the cytoskeleton activity of mouse macrophages. The locally observed structural reorganization processes, encoded by dynamic speckle patterns, occur upon distinct mechanical stimuli, such as soft contacts with optically trapped beads. We find that a substantial amount of the near‐membrane cytoskeleton activity takes place on millisecond timescales, which is much faster than reported ever before.
DOI
Cells change their shape within seconds, cellular protrusions even on subsecond timescales enabling various responses to stimuli of approaching bacteria, viruses or pharmaceutical drugs. Typical response patterns are governed by a complex reorganization of the actin cortex, where single filaments and molecules act on even faster timescales. These dynamics have remained mostly invisible due to a superposition of slow and fast motions, but also due to a lack of adequate imaging technology. Whereas fluorescence techniques require too long integration times, novel coherent techniques such as ROCS microscopy can achieve sufficiently high spatiotemporal resolution. ROCS uses rotating back‐scattered laser light from cellular structures and generates a consistently high image contrast at 150nm resolution and frame rates of 100 Hz ‐ without fluorescence or bleaching. Here, we present an extension of ROCS microscopy that exploits the principles of dynamic light scattering for precise localization, visualization and quantification of the cytoskeleton activity of mouse macrophages. The locally observed structural reorganization processes, encoded by dynamic speckle patterns, occur upon distinct mechanical stimuli, such as soft contacts with optically trapped beads. We find that a substantial amount of the near‐membrane cytoskeleton activity takes place on millisecond timescales, which is much faster than reported ever before.
DOI
Phragmoplast Orienting Kinesin 2 Is a Weak Motor Switching between Processive and Diffusive Modes
Mayank Chugh, Maja Reißner, Michael Bugiel, Elisabeth Lipka, Arvid Herrmann, Basudev Roy, Sabine Müller, Erik Schäffer
Plant development and morphology relies on the accurate insertion of new cell walls during cytokinesis. However, how a plant cell correctly orients a new wall is poorly understood. Two kinesin class-12 members, phragmoplast orienting kinesin 1 (POK1) and POK2, are involved in the process, but how these molecular machines work is not known. Here, we used in vivo and single-molecule in vitro measurements to determine how Arabidopsis thaliana POK2 motors function mechanically. We found that POK2 is a very weak, on average plus-end-directed, moderately fast kinesin. Interestingly, POK2 switches between processive and diffusive modes characterized by an exclusive-state mean-squared-displacement analysis. Our results support a model that POK motors push against peripheral microtubules of the phragmoplast for its guidance. This pushing model may mechanically explain the conspicuous narrowing of the division site. Together, our findings provide mechanical insight into how active motors accurately position new cell walls in plants.
DOI
Plant development and morphology relies on the accurate insertion of new cell walls during cytokinesis. However, how a plant cell correctly orients a new wall is poorly understood. Two kinesin class-12 members, phragmoplast orienting kinesin 1 (POK1) and POK2, are involved in the process, but how these molecular machines work is not known. Here, we used in vivo and single-molecule in vitro measurements to determine how Arabidopsis thaliana POK2 motors function mechanically. We found that POK2 is a very weak, on average plus-end-directed, moderately fast kinesin. Interestingly, POK2 switches between processive and diffusive modes characterized by an exclusive-state mean-squared-displacement analysis. Our results support a model that POK motors push against peripheral microtubules of the phragmoplast for its guidance. This pushing model may mechanically explain the conspicuous narrowing of the division site. Together, our findings provide mechanical insight into how active motors accurately position new cell walls in plants.
DOI
Calibration of force detection for arbitrarily shaped particles in optical tweezers
Ann A. M. Bui, Anatolii V. Kashchuk, Marie Anne Balanant, Timo A. Nieminen, Halina Rubinsztein-Dunlop & Alexander B. Stilgoe
Force measurement with an optical trap requires calibration of it. With a suitable detector, such as a position-sensitive detector (PSD), it is possible to calibrate the detector so that the force can be measured for arbitrary particles and arbitrary beams without further calibration; such a calibration can be called an “absolute calibration”. Here, we present a simple method for the absolute calibration of a PSD. Very often, paired position and force measurements are required, and even if synchronous measurements are possible with the position and force detectors used, knowledge of the force–position curve for the particle in the trap can be highly beneficial. Therefore, we experimentally demonstrate methods for determining the force–position curve with and without synchronous force and position measurements, beyond the Hookean (linear) region of the trap. Unlike the absolute calibration of the force and position detectors, the force–position curve depends on the particle and the trapping beam, and needs to be determined in each individual case. We demonstrate the robustness of our absolute calibration by measuring optical forces on microspheres as commonly trapped in optical tweezers, and other particles such a birefringent vaterite microspheres, red blood cells, and a deformable “blob”.
DOI
Force measurement with an optical trap requires calibration of it. With a suitable detector, such as a position-sensitive detector (PSD), it is possible to calibrate the detector so that the force can be measured for arbitrary particles and arbitrary beams without further calibration; such a calibration can be called an “absolute calibration”. Here, we present a simple method for the absolute calibration of a PSD. Very often, paired position and force measurements are required, and even if synchronous measurements are possible with the position and force detectors used, knowledge of the force–position curve for the particle in the trap can be highly beneficial. Therefore, we experimentally demonstrate methods for determining the force–position curve with and without synchronous force and position measurements, beyond the Hookean (linear) region of the trap. Unlike the absolute calibration of the force and position detectors, the force–position curve depends on the particle and the trapping beam, and needs to be determined in each individual case. We demonstrate the robustness of our absolute calibration by measuring optical forces on microspheres as commonly trapped in optical tweezers, and other particles such a birefringent vaterite microspheres, red blood cells, and a deformable “blob”.
DOI
HACF-based optical tweezers available for living cells manipulating and sterile transporting
Yu Zhang, Yan Li, Yaxun Zhang, Chuanzhen Hu, Zhihai Liu, Xinghua Yang, Jianzhong, Zhang, Jun Yang, Libo Yuan
We propose and demonstrate a single fiber optical tweezers based on a hollow annular-core fiber (HACF), which is available for living cells manipulating and sterile transporting due to the hollow structure, there exists a fluidic channel in the fiber, which is naturally a microfluidic passageway in the fluidic environment, both the optical trapping forces (OTF) and the liquid viscous resistances (LVR) play the important roles. We perform the particles manipulating and transporting by adjusting and controlling the net forces of OTF and LVR. We employ the fiber grinding–polishing technology to fabricate the HACF probe, producing the OTFs. We employ the micropump to perform the positive or negative pressure in the hollow hole of the HACF, changing the liquid velocity and direction, adjusting the LVRs. It is ideally suited for rare cells manipulating and sterile transporting. The implantation of the hollow hole and annular waveguide in a HACF provides the availability for particles manipulating and transporting, constitutes a new development for single fiber optical trapping and makes possible of more practical applications in particles manipulating and transporting fields.
DOI
We propose and demonstrate a single fiber optical tweezers based on a hollow annular-core fiber (HACF), which is available for living cells manipulating and sterile transporting due to the hollow structure, there exists a fluidic channel in the fiber, which is naturally a microfluidic passageway in the fluidic environment, both the optical trapping forces (OTF) and the liquid viscous resistances (LVR) play the important roles. We perform the particles manipulating and transporting by adjusting and controlling the net forces of OTF and LVR. We employ the fiber grinding–polishing technology to fabricate the HACF probe, producing the OTFs. We employ the micropump to perform the positive or negative pressure in the hollow hole of the HACF, changing the liquid velocity and direction, adjusting the LVRs. It is ideally suited for rare cells manipulating and sterile transporting. The implantation of the hollow hole and annular waveguide in a HACF provides the availability for particles manipulating and transporting, constitutes a new development for single fiber optical trapping and makes possible of more practical applications in particles manipulating and transporting fields.
DOI
Tuesday, August 7, 2018
Analysis of tunable and highly confined surface wave in the photonic hypercrystals containing graphene-based hyperbolic metamaterial
Min Cheng, Ping Fu, Yingting Lin, Xiyao Chen, Shengyu Chen, Xiaoteng Tang, Shangyuan Feng
The property of surface wave at the interface between a dielectric half-space and a photonic hypercrystals (PHC) containing graphene-based hyperbolic metamaterial (GHMM) is investigated. It is observed that the propagation length, figure-of-merit (FOM), absorption resonance, nanoscale mode confinement and penetration depth of surface wave can be tuned by varying the Fermi energy of graphene sheets via electrostatic biasing. It is also found that the surface states in the hypercrystal containing GHMM allow for both high wave numbers and long propagation lengths at the same time. It is shown that the surface wave in the PHC has extremely low group velocity and the magnitude of group velocity can be well regulated. Here we also analyse the optical forces from the surface wave in the case of Rayleigh particles, and large and tunable radiation force component has been observed.
DOI
The property of surface wave at the interface between a dielectric half-space and a photonic hypercrystals (PHC) containing graphene-based hyperbolic metamaterial (GHMM) is investigated. It is observed that the propagation length, figure-of-merit (FOM), absorption resonance, nanoscale mode confinement and penetration depth of surface wave can be tuned by varying the Fermi energy of graphene sheets via electrostatic biasing. It is also found that the surface states in the hypercrystal containing GHMM allow for both high wave numbers and long propagation lengths at the same time. It is shown that the surface wave in the PHC has extremely low group velocity and the magnitude of group velocity can be well regulated. Here we also analyse the optical forces from the surface wave in the case of Rayleigh particles, and large and tunable radiation force component has been observed.
DOI
Optical Trapping of Single Nanostructures in a Weakly Focused Beam. Application to Magnetic Nanoparticles
Héctor Rodríguez-Rodríguez, Sara de Lorenzo, Leonor de la Cueva, Gorka Salas, and J. Ricardo Arias-Gonzalez
Optical trapping of individual particles is believed to be only effective under highly focused beams because these conditions strengthen the gradient forces. This is especially critical in the beam propagating direction, where the scattering and absorption forces must be counterbalanced. Here, we demonstrate that optical trapping of nanostructures is also possible in a weakly focused beam. We study the theoretical conditions for effective three-dimensional optical confinement and verify them experimentally on iron-oxide-based nanoparticles with and without a silica coating, for which scattering, absorption, and gradient forces exist. This chemical approach to their all-optical control is, in turn, convenient for making magnetic nanostructures biocompatible. Weakly focused beams reduce the irradiance in the focal region and therefore the photon damage to the samples, which is further important to delay quantum dot quenching in the trap or to prevent artifacts in the study of biomolecular motor dynamics.
DOI
Optical trapping of individual particles is believed to be only effective under highly focused beams because these conditions strengthen the gradient forces. This is especially critical in the beam propagating direction, where the scattering and absorption forces must be counterbalanced. Here, we demonstrate that optical trapping of nanostructures is also possible in a weakly focused beam. We study the theoretical conditions for effective three-dimensional optical confinement and verify them experimentally on iron-oxide-based nanoparticles with and without a silica coating, for which scattering, absorption, and gradient forces exist. This chemical approach to their all-optical control is, in turn, convenient for making magnetic nanostructures biocompatible. Weakly focused beams reduce the irradiance in the focal region and therefore the photon damage to the samples, which is further important to delay quantum dot quenching in the trap or to prevent artifacts in the study of biomolecular motor dynamics.
DOI
Single Molecule Studies Enabled by Model Based Controller Design
Shreyas Bhaban; Saurav Talukdar; Mingang Li; Thomas Hays; Peter Seiler; Murti Salapaka
Optical tweezers have enabled important insights into intracellular transport through the investigation of motor proteins, with their ability to manipulate particles at the microscale, affording femto newton force resolution. Its use to realize a constant force clamp has enabled vital insights into the behavior of motor proteins under different load conditions. However, the varying nature of disturbances and the effect of thermal noise pose key challenges to force regulation. Furthermore, often the main aim of many studies is to determine the motion of the motor and the statistics related to the motion, which can be at odds with the force regulation objective. In this article, we propose a mixed objective H2/H∞ optimization framework using a model-based design, that achieves the dual goals of force regulation and real time motion estimation with quantifiable guarantees. Here, we minimize the H∞ norm for the force regulation and error in step estimation while maintaining the H2 norm of the noise on step estimate within user specified bounds. We demonstrate the efficacy of the framework through extensive simulations and an experimental implementation using an optical tweezer setup with live samples of the motor protein ‘kinesin’; where regulation of forces below 1 piconewton with errors below 10% is obtained while simultaneously providing real time estimates of motor motion.
DOI
Optical tweezers have enabled important insights into intracellular transport through the investigation of motor proteins, with their ability to manipulate particles at the microscale, affording femto newton force resolution. Its use to realize a constant force clamp has enabled vital insights into the behavior of motor proteins under different load conditions. However, the varying nature of disturbances and the effect of thermal noise pose key challenges to force regulation. Furthermore, often the main aim of many studies is to determine the motion of the motor and the statistics related to the motion, which can be at odds with the force regulation objective. In this article, we propose a mixed objective H2/H∞ optimization framework using a model-based design, that achieves the dual goals of force regulation and real time motion estimation with quantifiable guarantees. Here, we minimize the H∞ norm for the force regulation and error in step estimation while maintaining the H2 norm of the noise on step estimate within user specified bounds. We demonstrate the efficacy of the framework through extensive simulations and an experimental implementation using an optical tweezer setup with live samples of the motor protein ‘kinesin’; where regulation of forces below 1 piconewton with errors below 10% is obtained while simultaneously providing real time estimates of motor motion.
DOI
Optical tweezer system with no fluorescent confocal microscope for trapping colloidal nanoparticles
Nuansri R., Buranasiri P., Limsuwan P. and Ou-Yang H.D.
We describe two optical tweezer systems for the studies of laser trapping of fluorescent colloidal nanoparticles (NPs). The first one, conventional optical tweezer system widely used in laser trapping, requires a fluorescent confocal microscope for observing trapped NPs. The second system, with no microscope, is presented for the first time in this work. The quantity of trapped NPs for this system is estimated from the transmitted laser light intensity that passes through the fluorescent colloidal NPs. Then the transmitted laser light is converted into the voltage signal and measured by an oscilloscope. A small capillary tube to be filled by the colloidal NPs is developed and used in the second system. This tube can be used with light-sensitive cameras for which a danger of damaging by high light intensities exists. Finally, we show that the results obtained using the both tweezer systems are in good agreement.
DOI
We describe two optical tweezer systems for the studies of laser trapping of fluorescent colloidal nanoparticles (NPs). The first one, conventional optical tweezer system widely used in laser trapping, requires a fluorescent confocal microscope for observing trapped NPs. The second system, with no microscope, is presented for the first time in this work. The quantity of trapped NPs for this system is estimated from the transmitted laser light intensity that passes through the fluorescent colloidal NPs. Then the transmitted laser light is converted into the voltage signal and measured by an oscilloscope. A small capillary tube to be filled by the colloidal NPs is developed and used in the second system. This tube can be used with light-sensitive cameras for which a danger of damaging by high light intensities exists. Finally, we show that the results obtained using the both tweezer systems are in good agreement.
DOI
Direct Visualization of Barrier Crossing Dynamics in a Driven Optical Matter System
Patrick Figliozzi, Curtis W. Peterson, Stuart A. Rice, and Norbert F. Scherer
A major impediment to a more complete understanding of barrier crossing and other single-molecule processes is the inability to directly visualize the trajectories and dynamics of atoms and molecules in reactions. Rather, the kinetics are inferred from ensemble measurements or the position of a transducer (e.g., an AFM cantilever) as a surrogate variable. Direct visualization is highly desirable. Here, we achieve the direct measurement of barrier crossing trajectories by using optical microscopy to observe position and orientation changes of pairs of Ag nanoparticles, i.e. passing events, in an optical ring trap. A two-step mechanism similar to a bimolecular exchange reaction or the Michaelis–Menten scheme is revealed by analysis that combines detailed knowledge of each trajectory, a statistically significant number of repetitions of the passing events, and the driving force dependence of the process. We find that while the total event rate increases with driving force, this increase is due to an increase in the rate of encounters. There is no drive force dependence on the rate of barrier crossing because the key motion for the process involves a random (thermal) radial fluctuation of one particle allowing the other to pass. This simple experiment can readily be extended to study more complex barrier crossing processes by replacing the spherical metal nanoparticles with anisotropic ones or by creating more intricate optical trapping potentials.
DOI
A major impediment to a more complete understanding of barrier crossing and other single-molecule processes is the inability to directly visualize the trajectories and dynamics of atoms and molecules in reactions. Rather, the kinetics are inferred from ensemble measurements or the position of a transducer (e.g., an AFM cantilever) as a surrogate variable. Direct visualization is highly desirable. Here, we achieve the direct measurement of barrier crossing trajectories by using optical microscopy to observe position and orientation changes of pairs of Ag nanoparticles, i.e. passing events, in an optical ring trap. A two-step mechanism similar to a bimolecular exchange reaction or the Michaelis–Menten scheme is revealed by analysis that combines detailed knowledge of each trajectory, a statistically significant number of repetitions of the passing events, and the driving force dependence of the process. We find that while the total event rate increases with driving force, this increase is due to an increase in the rate of encounters. There is no drive force dependence on the rate of barrier crossing because the key motion for the process involves a random (thermal) radial fluctuation of one particle allowing the other to pass. This simple experiment can readily be extended to study more complex barrier crossing processes by replacing the spherical metal nanoparticles with anisotropic ones or by creating more intricate optical trapping potentials.
DOI
Influence of Enzyme Quantity and Distribution on the Self-Propulsion of Non-Janus Urease-Powered Micromotors
Tania Patiño, Natalia Feiner-Gracia, Xavier Arqué, Albert Miguel-López, Anita Jannasch, Tom Stumpp, Erik Schäffer, Lorenzo Albertazzi, and Samuel Sánchez
The use of enzyme catalysis to power micro- and nanomachines offers unique features such as biocompatibility, versatility, and fuel bioavailability. Yet, the key parameters underlying the motion behavior of enzyme-powered motors are not completely understood. Here, we investigate the role of enzyme distribution and quantity on the generation of active motion. Two different micromotor architectures based on either polystyrene (PS) or polystyrene coated with a rough silicon dioxide shell (PS@SiO2) were explored. A directional propulsion with higher speed was observed for PS@SiO2 motors when compared to their PS counterparts. We made use of stochastically optical reconstruction microscopy (STORM) to precisely detect single urease molecules conjugated to the micromotors surface with a high spatial resolution. An asymmetric distribution of enzymes around the micromotor surface was observed for both PS and PS@SiO2 architectures, indicating that the enzyme distribution was not the only parameter affecting the motion behavior. We quantified the number of enzymes present on the micromotor surface and observed a 10-fold increase in the number of urease molecules for PS@SiO2 motors compared to PS-based micromotors. To further investigate the number of enzymes required to generate a self-propulsion, PS@SiO2 particles were functionalized with varying amounts of urease molecules and the resulting speed and propulsive force were measured by optical tracking and optical tweezers, respectively. Surprisingly, both speed and force depended in a nonlinear fashion on the enzyme coverage. To break symmetry for active propulsion, we found that a certain threshold number of enzymes molecules per micromotor was necessary, indicating that activity may be due to a critical phenomenon. Taken together, these results provide new insights into the design features of micro/nanomotors to ensure an efficient development.
DOI
The use of enzyme catalysis to power micro- and nanomachines offers unique features such as biocompatibility, versatility, and fuel bioavailability. Yet, the key parameters underlying the motion behavior of enzyme-powered motors are not completely understood. Here, we investigate the role of enzyme distribution and quantity on the generation of active motion. Two different micromotor architectures based on either polystyrene (PS) or polystyrene coated with a rough silicon dioxide shell (PS@SiO2) were explored. A directional propulsion with higher speed was observed for PS@SiO2 motors when compared to their PS counterparts. We made use of stochastically optical reconstruction microscopy (STORM) to precisely detect single urease molecules conjugated to the micromotors surface with a high spatial resolution. An asymmetric distribution of enzymes around the micromotor surface was observed for both PS and PS@SiO2 architectures, indicating that the enzyme distribution was not the only parameter affecting the motion behavior. We quantified the number of enzymes present on the micromotor surface and observed a 10-fold increase in the number of urease molecules for PS@SiO2 motors compared to PS-based micromotors. To further investigate the number of enzymes required to generate a self-propulsion, PS@SiO2 particles were functionalized with varying amounts of urease molecules and the resulting speed and propulsive force were measured by optical tracking and optical tweezers, respectively. Surprisingly, both speed and force depended in a nonlinear fashion on the enzyme coverage. To break symmetry for active propulsion, we found that a certain threshold number of enzymes molecules per micromotor was necessary, indicating that activity may be due to a critical phenomenon. Taken together, these results provide new insights into the design features of micro/nanomotors to ensure an efficient development.
DOI
Monday, August 6, 2018
Measuring the Local Velocity along Transition Paths during the Folding of Single Biological Molecules
Krishna Neupane, Noel Q. Hoffer, and M. T. Woodside
Transition paths are the most interesting part of folding reactions but remain little studied. We measured the local velocity along transition paths in DNA hairpin folding using optical tweezers. The velocity distribution agreed well with diffusive theories, yielding the diffusion coefficient. We used the average velocity to calculate the transmission factor in transition-state theory (TST), finding observed rates that were ∼10 5-fold slower than predicted by TST. This work quantifies the importance of barrier recrossing events and highlights the effectiveness of the diffusive model of folding.
Transition paths are the most interesting part of folding reactions but remain little studied. We measured the local velocity along transition paths in DNA hairpin folding using optical tweezers. The velocity distribution agreed well with diffusive theories, yielding the diffusion coefficient. We used the average velocity to calculate the transmission factor in transition-state theory (TST), finding observed rates that were ∼10 5-fold slower than predicted by TST. This work quantifies the importance of barrier recrossing events and highlights the effectiveness of the diffusive model of folding.
Non-invasive Neurite Mechanics in Differentiated PC12 Cells
Fernanda Gárate, María Pertusa, Yahaira Arana and Roberto Bernal
Thermal Fluctuations Spectroscopy (TFS) in combination with novel optical-based instrumentation was used to study mechanical properties of cell-cultured neurites with a spatial resolution limited only by the light diffraction. The analysis of thermal fluctuations together with a physical model of cellular elasticity allow us to determine relevant mechanical properties of neurite as axial tension σ, flexural rigidity B, plasma membrane tension γ, membrane bending rigidity K, and cytoskeleton to membrane-coupling ρbk, whose values are consistent with previously reported values measured using invasive approaches. The value obtained for the membrane-coupling parameter was used to estimate the average number of coupling elements between the plasma membrane and the cytoskeleton that fell in the range of 30 elements per area of the laser spot used to record the fluctuations. Furthermore, to expand the TFS analysis, we investigate the correlation between F-actin linear density and the mechanical features of PC12 neurites. Using a hybrid instrument that combines TFS and a simple fluorescent technique, our results show that the fluctuations are related with the F-actin concentration. These measurements have an advantage of not requiring the application of an external force, allowing as to directly establish a correlation between changes in the mechanical parameters and cytoskeleton-protein concentrations. The sensibility of our method was also tested by the application of TFS technique to PC12 neurite under Paraformaldehyde and Latrunculin-A effect. These results show a dramatic modification in the fluctuations that are consistent with the reported effect of these drugs, confirming the high sensitivity of this technique. Finally, the thermal fluctuation approach was applied to DRG axons to show that its utility is not limited to studies of PC12 neurites, but it is suitable to measure the general characteristic of various neuron-like cells.
DOI
Thermal Fluctuations Spectroscopy (TFS) in combination with novel optical-based instrumentation was used to study mechanical properties of cell-cultured neurites with a spatial resolution limited only by the light diffraction. The analysis of thermal fluctuations together with a physical model of cellular elasticity allow us to determine relevant mechanical properties of neurite as axial tension σ, flexural rigidity B, plasma membrane tension γ, membrane bending rigidity K, and cytoskeleton to membrane-coupling ρbk, whose values are consistent with previously reported values measured using invasive approaches. The value obtained for the membrane-coupling parameter was used to estimate the average number of coupling elements between the plasma membrane and the cytoskeleton that fell in the range of 30 elements per area of the laser spot used to record the fluctuations. Furthermore, to expand the TFS analysis, we investigate the correlation between F-actin linear density and the mechanical features of PC12 neurites. Using a hybrid instrument that combines TFS and a simple fluorescent technique, our results show that the fluctuations are related with the F-actin concentration. These measurements have an advantage of not requiring the application of an external force, allowing as to directly establish a correlation between changes in the mechanical parameters and cytoskeleton-protein concentrations. The sensibility of our method was also tested by the application of TFS technique to PC12 neurite under Paraformaldehyde and Latrunculin-A effect. These results show a dramatic modification in the fluctuations that are consistent with the reported effect of these drugs, confirming the high sensitivity of this technique. Finally, the thermal fluctuation approach was applied to DRG axons to show that its utility is not limited to studies of PC12 neurites, but it is suitable to measure the general characteristic of various neuron-like cells.
DOI
Microfluidic Technology for Cell Manipulation
Jae-Sung Kwon and Je Hoon Oh
Microfluidic techniques for cell manipulation have been constantly developed and integrated into small chips for high-performance bioassays. However, the drawbacks of each of the techniques often hindered their further advancement and their wide use in biotechnology. To overcome this difficulty, an examination and understanding of various aspects of the developed manipulation techniques are required. In this review, we provide the details of primary microfluidic techniques that have received much attention for bioassays. First, we introduce the manipulation techniques using a sole driving source, i.e., dielectrophoresis, electrophoresis, optical tweezers, magnetophoresis, and acoustophoresis. Next, we present rapid electrokinetic patterning, a hybrid opto-electric manipulation technique developed recently. It is introduced in detail along with the underlying physical principle, operating environment, and current challenges. This paper will offer readers the opportunity to improve existing manipulation techniques, suggest new manipulation techniques, and find new applications in biotechnology. View Full-Text
DOI
Microfluidic techniques for cell manipulation have been constantly developed and integrated into small chips for high-performance bioassays. However, the drawbacks of each of the techniques often hindered their further advancement and their wide use in biotechnology. To overcome this difficulty, an examination and understanding of various aspects of the developed manipulation techniques are required. In this review, we provide the details of primary microfluidic techniques that have received much attention for bioassays. First, we introduce the manipulation techniques using a sole driving source, i.e., dielectrophoresis, electrophoresis, optical tweezers, magnetophoresis, and acoustophoresis. Next, we present rapid electrokinetic patterning, a hybrid opto-electric manipulation technique developed recently. It is introduced in detail along with the underlying physical principle, operating environment, and current challenges. This paper will offer readers the opportunity to improve existing manipulation techniques, suggest new manipulation techniques, and find new applications in biotechnology. View Full-Text
DOI
Processive Kinesin-14 HSET Exhibits Directional Flexibility Depending on Motor Traffic
Dana N. Reinemann, Stephen R. Norris, Ryoma Ohi, Matthew J .Lang
A common mitotic defect observed in cancer cells that possess supernumerary (more than two) centrosomes is multipolar spindle formation [1, 2]. Such structures are resolved into a bipolar geometry by minus-end-directed motor proteins, such as cytoplasmic dynein and the kinesin-14 HSET [3, 4, 5, 6, 7, 8]. HSET is also thought to antagonize plus-end-directed kinesin-5 Eg5 to balance spindle forces [4, 5, 7, 9]. However, the biomechanics of this force opposition are unclear, as HSET has previously been defined as a non-processive motor [10, 11, 12, 13, 14, 15, 16]. Here, we use optical trapping to elucidate the mechanism of force generation by HSET. We show that a single HSET motor has a processive nature with the ability to complete multiple steps while trapped along a microtubule and when unloaded can move in both directions for microns. Compared to other kinesins, HSET has a relatively weak stall force of 1.1 pN [17, 18]. Moreover, HSET’s tail domain and its interaction with the E-hook of tubulin are necessary for long-range motility. In vitro polarity-marked bundle assays revealed that HSET selectively generates force in anti-parallel bundles on the order of its stall force. When combined with varied ratios of Eg5, HSET adopts Eg5’s directionality while acting as an antagonizing force brake, requiring at least a 10-fold higher Eg5 concentration to surpass HSET’s sliding force. These results reveal HSET’s ability to change roles within the spindle from acting as an adjustable microtubule slider and force regulator to a processive motor that aids in minus end focusing.
DOI
A common mitotic defect observed in cancer cells that possess supernumerary (more than two) centrosomes is multipolar spindle formation [1, 2]. Such structures are resolved into a bipolar geometry by minus-end-directed motor proteins, such as cytoplasmic dynein and the kinesin-14 HSET [3, 4, 5, 6, 7, 8]. HSET is also thought to antagonize plus-end-directed kinesin-5 Eg5 to balance spindle forces [4, 5, 7, 9]. However, the biomechanics of this force opposition are unclear, as HSET has previously been defined as a non-processive motor [10, 11, 12, 13, 14, 15, 16]. Here, we use optical trapping to elucidate the mechanism of force generation by HSET. We show that a single HSET motor has a processive nature with the ability to complete multiple steps while trapped along a microtubule and when unloaded can move in both directions for microns. Compared to other kinesins, HSET has a relatively weak stall force of 1.1 pN [17, 18]. Moreover, HSET’s tail domain and its interaction with the E-hook of tubulin are necessary for long-range motility. In vitro polarity-marked bundle assays revealed that HSET selectively generates force in anti-parallel bundles on the order of its stall force. When combined with varied ratios of Eg5, HSET adopts Eg5’s directionality while acting as an antagonizing force brake, requiring at least a 10-fold higher Eg5 concentration to surpass HSET’s sliding force. These results reveal HSET’s ability to change roles within the spindle from acting as an adjustable microtubule slider and force regulator to a processive motor that aids in minus end focusing.
DOI
Testing Kinetic Identities Involving Transition-Path Properties Using Single-Molecule Folding Trajectories
Krishna Neupane, Noel Q. Hoffer, and Michael T. Woodside
Recent advances in single-molecule assays have allowed individual transition paths during the folding of single molecules to be observed directly. We used the transition paths of DNA hairpins having different sequences, measured with high-resolution optical tweezers, to test theoretical relations between the properties of the transition paths and the folding kinetics. We showed that folding and unfolding rates were related to the average transition-path times, as expected from theory, for all hairpins studied. We also found that the probability distribution of transition-path occupancies agreed with the profile of the average velocity along the transition paths for each of the hairpins, as expected theoretically. Finally, we used the latter result to show that the committor probability recovered from the velocity profile matches the committor measured empirically. These results validate the proposed kinetic identities.
DOI
Recent advances in single-molecule assays have allowed individual transition paths during the folding of single molecules to be observed directly. We used the transition paths of DNA hairpins having different sequences, measured with high-resolution optical tweezers, to test theoretical relations between the properties of the transition paths and the folding kinetics. We showed that folding and unfolding rates were related to the average transition-path times, as expected from theory, for all hairpins studied. We also found that the probability distribution of transition-path occupancies agreed with the profile of the average velocity along the transition paths for each of the hairpins, as expected theoretically. Finally, we used the latter result to show that the committor probability recovered from the velocity profile matches the committor measured empirically. These results validate the proposed kinetic identities.
DOI
Electrical and thermal properties of silver nanowire fabricated on a flexible substrate by two-beam laser direct writing for designing a thermometer
Gui-Cang He, Heng Lu, Xian-Zi Dong, Yong-Liang Zhang, Jie Liu, Chang-Qing Xie and Zhen-Sheng Zhao
Accurate knowledge of electrical conductivity and thermal conductivity temperature dependence plays a crucial role in the design of a thermometer. Here, by using a two-beam laser direct writing system, an individual silver nanowire (AgNW) with well-defined dimensions is fabricated on a polyethylene terephthalate (PET) substrate. The temperature dependence of the resistivity of the fabricated AgNW is measured ranging from 10 to 300 K, and fitted with the Bloch–Grüneisen formula. The residual resistivity ((1.62 ± 0.20) × 10−7 Ω m) of the AgNW is larger than that of the bulk material (1 × 10−11 Ω m). The electron–phonon coupling constant of the AgNW is (1.08 ± 0.13) × 10−7 Ω m, which is larger than that of the bulk silver (5.24 × 10−8 Ω m). Moreover, the Debye temperature of the AgNW is 199.30 K and is lower than that of the bulk silver (235 K). The Lorenz number of the fabricated AgNW is found to decrease as the temperature increases. Besides, the Lorenz number (2.66 × 10−7 W Ω K−2) is larger than the Sommerfeld value (2.44 × 10−8 W Ω K−2) at room temperature. The measurement results allow one to design a thermometer in the temperature range 40–300 K. The flexibility of the AgNW is also excellent, and the resistance increase of the AgNW is only 2.58% when the AgNW bending about 1000 times with a bending radius of 1 mm.
DOI
Accurate knowledge of electrical conductivity and thermal conductivity temperature dependence plays a crucial role in the design of a thermometer. Here, by using a two-beam laser direct writing system, an individual silver nanowire (AgNW) with well-defined dimensions is fabricated on a polyethylene terephthalate (PET) substrate. The temperature dependence of the resistivity of the fabricated AgNW is measured ranging from 10 to 300 K, and fitted with the Bloch–Grüneisen formula. The residual resistivity ((1.62 ± 0.20) × 10−7 Ω m) of the AgNW is larger than that of the bulk material (1 × 10−11 Ω m). The electron–phonon coupling constant of the AgNW is (1.08 ± 0.13) × 10−7 Ω m, which is larger than that of the bulk silver (5.24 × 10−8 Ω m). Moreover, the Debye temperature of the AgNW is 199.30 K and is lower than that of the bulk silver (235 K). The Lorenz number of the fabricated AgNW is found to decrease as the temperature increases. Besides, the Lorenz number (2.66 × 10−7 W Ω K−2) is larger than the Sommerfeld value (2.44 × 10−8 W Ω K−2) at room temperature. The measurement results allow one to design a thermometer in the temperature range 40–300 K. The flexibility of the AgNW is also excellent, and the resistance increase of the AgNW is only 2.58% when the AgNW bending about 1000 times with a bending radius of 1 mm.
DOI
Dynamic control of the interference pattern of surface plasmon polaritons and its application to particle manipulation
Chun-Fu Kuo and Shu-Chun Chu
This study proposes a method of dynamically controlling the interference pattern of surface plasmon polaritons (SPPs) within a four-slit structure by changing the phase difference between multiple-incident Gaussian beams. The theoretical analysis of the controlling mechanism of the SPP interference field and the numerical simulation of the generation and movement of both one-dimensional and two-dimensional SPP interference fields are provided. In addition, through simulation, this study demonstrates using the controllable two-dimensional SPP interference bright spots field for manipulating particles in static liquids.
DOI
This study proposes a method of dynamically controlling the interference pattern of surface plasmon polaritons (SPPs) within a four-slit structure by changing the phase difference between multiple-incident Gaussian beams. The theoretical analysis of the controlling mechanism of the SPP interference field and the numerical simulation of the generation and movement of both one-dimensional and two-dimensional SPP interference fields are provided. In addition, through simulation, this study demonstrates using the controllable two-dimensional SPP interference bright spots field for manipulating particles in static liquids.
DOI
Wednesday, August 1, 2018
Geometric Effects of Colloidal Particles on Stochastic Interface Adsorption
Dong Woo Kang, Byung Gyu Park, Kyu Hwan Choi, Jin Hyun Lim, Seong Jae Lee, and Bum Jun Park
The stochastic interface adsorption behaviors of ellipsoid particles were investigated using optical laser tweezers. The particles were brought close to the oil–water interface, attempting to attach forcefully to the interface. Multiple attempts of the particle attachments statistically quantified the dependence of the adsorption probability on the particle aspect ratio. It was found that the adsorption probability proportionally increased with the aspect ratio because of the decrease in electrostatic interactions between the charged particles and the charged interface for higher aspect ratio particles. In addition, the adsorption holding time required for the interface attachments was found to increase as the aspect ratio decreased. Notably, the probabilistic adsorption behaviors of the ellipsoid particles and the holding time dependence revealed that the particle adsorption to the interface occurred stochastically, not deterministically. We also demonstrated that the adsorption behaviors measured on a single-particle scale were consistent with the gravity-induced spontaneous adsorption properties performed on a large scale with regard to the nondeterministic adsorption behaviors and the aspect ratio dependence on the adsorption probability.
DOI
The stochastic interface adsorption behaviors of ellipsoid particles were investigated using optical laser tweezers. The particles were brought close to the oil–water interface, attempting to attach forcefully to the interface. Multiple attempts of the particle attachments statistically quantified the dependence of the adsorption probability on the particle aspect ratio. It was found that the adsorption probability proportionally increased with the aspect ratio because of the decrease in electrostatic interactions between the charged particles and the charged interface for higher aspect ratio particles. In addition, the adsorption holding time required for the interface attachments was found to increase as the aspect ratio decreased. Notably, the probabilistic adsorption behaviors of the ellipsoid particles and the holding time dependence revealed that the particle adsorption to the interface occurred stochastically, not deterministically. We also demonstrated that the adsorption behaviors measured on a single-particle scale were consistent with the gravity-induced spontaneous adsorption properties performed on a large scale with regard to the nondeterministic adsorption behaviors and the aspect ratio dependence on the adsorption probability.
DOI
Bubble generation and molecular crystallization at solution surface by intense continuous-wave laser irradiation
Jim Jui-Kai Chen, Ken-ichi Yuyama, Teruki Sugiyama and Hiroshi Masuhara
We demonstrate bubble generation outside the focus induced by irradiating a focused 1064 nm continuous-wave laser beam into the surface of water and l-phenylalanine H2O solutions. In the former case of water, bubbles stay at positions distant from the focus during the irradiation, and their size and location are controllable by the laser power. In the latter solution, bubbles move outward toward the surrounding area, and subsequently crystallization takes place at the focus. We discuss these behaviors from the viewpoints of the temperature elevation accompanying the decrease in air solubility as well as the optical trapping of l-phenylalanine clusters giving a single crystal.
DOI
We demonstrate bubble generation outside the focus induced by irradiating a focused 1064 nm continuous-wave laser beam into the surface of water and l-phenylalanine H2O solutions. In the former case of water, bubbles stay at positions distant from the focus during the irradiation, and their size and location are controllable by the laser power. In the latter solution, bubbles move outward toward the surrounding area, and subsequently crystallization takes place at the focus. We discuss these behaviors from the viewpoints of the temperature elevation accompanying the decrease in air solubility as well as the optical trapping of l-phenylalanine clusters giving a single crystal.
DOI
Mechanical Cooperativity in DNA Cruciform Structures
Shankar Mandal, Sangeetha Selvam, Yunxi Cui, Mohammed Enamul Hoque, Prof. Hanbin Mao
Unlike short‐range chemical bonds that maintain chemical properties of a biological molecule, long‐range mechanical interactions determine mechanochemical properties of molecules. Limited by experimental approaches, however, direct quantification of such mechanical interactions is challenging. Using magneto‐optical tweezers, herein we found torque can change the topology and mechanochemical property of DNA cruciform, a naturally occurring structure consisting of two opposing hairpin arms. Both mechanical and thermodynamic stabilities of DNA cruciforms increase with positive torque, which have been attributed to the topological coupling between DNA template and the cruciform. The coupling exists simultaneously in both arms of a cruciform, which coordinates the folding and unfolding of the cruciform, leading to a mechanical cooperativity not observed previously. As DNA torque readily varies during transcriptions, our finding suggests that DNA cruciforms can modulate transcriptions by adjusting their properties according to the torque.
DOI
Unlike short‐range chemical bonds that maintain chemical properties of a biological molecule, long‐range mechanical interactions determine mechanochemical properties of molecules. Limited by experimental approaches, however, direct quantification of such mechanical interactions is challenging. Using magneto‐optical tweezers, herein we found torque can change the topology and mechanochemical property of DNA cruciform, a naturally occurring structure consisting of two opposing hairpin arms. Both mechanical and thermodynamic stabilities of DNA cruciforms increase with positive torque, which have been attributed to the topological coupling between DNA template and the cruciform. The coupling exists simultaneously in both arms of a cruciform, which coordinates the folding and unfolding of the cruciform, leading to a mechanical cooperativity not observed previously. As DNA torque readily varies during transcriptions, our finding suggests that DNA cruciforms can modulate transcriptions by adjusting their properties according to the torque.
DOI
Experimental investigation on optical vortex tweezers for microbubble trapping
Xiaoming Zhou, Ziyang Chen, Zetian Liu, Jixiong Pu
In this paper, we investigated the microbubble trapping using optical vortex tweezers. It is shown that the microbubble can be trapped by the vortex optical tweezers, in which the trapping light beam is of vortex beam. We studied a relationship between the transverse capture gradient force and the topological charges of the illuminating vortex beam. For objective lenses with numerical aperture of 1.25 (100×), the force measurement was performed by the power spectral density (PSD) roll-off method. It was shown that transverse trapping forces of vortex optical tweezers increase with the increment of the laser power for fixed topological charge. Whereas, the increase in the topological charges of vortex beam for the same laser power results in the decrease of the transverse trapping forces. The experimental results demonstrated that the laser mode (topological charge) has significant influence on the lateral trapping force.
DOI
In this paper, we investigated the microbubble trapping using optical vortex tweezers. It is shown that the microbubble can be trapped by the vortex optical tweezers, in which the trapping light beam is of vortex beam. We studied a relationship between the transverse capture gradient force and the topological charges of the illuminating vortex beam. For objective lenses with numerical aperture of 1.25 (100×), the force measurement was performed by the power spectral density (PSD) roll-off method. It was shown that transverse trapping forces of vortex optical tweezers increase with the increment of the laser power for fixed topological charge. Whereas, the increase in the topological charges of vortex beam for the same laser power results in the decrease of the transverse trapping forces. The experimental results demonstrated that the laser mode (topological charge) has significant influence on the lateral trapping force.
DOI
Hacking CD/DVD/Blu-ray for Biosensing
Edwin En-Te Hwu and Anja Boisen
The optical pickup unit (OPU) within a CD/DVD/Blu-ray drive integrates 780, 650, and 405 nm wavelength lasers, diffraction-limited optics, a high-bandwidth optoelectronic transducer up to 400 MHz, and a nanoresolution x-, z-axis, and tilt actuator in a compact size. In addition, the OPU is a remarkable piece of engineering and could enable different scientific applications such as sub-angstrom displacement sensing, micro- and nanoimaging, and nanolithography. Although off-the-shelf OPUs can be easily obtained, manufacturers protect their datasheets under nondisclosure agreements to impede their availability to the public. Thus, OPUs are black boxes that few people can use for research, and only experienced researchers can access all their functions. This review details the OPU mechanism and components. In addition, we explain how to utilize three commercially available triple-wavelength OPUs from scratch and optimize sensing quality. Then, we discuss scientific research using OPUs, from standard optical drive-based turnkey-biomarker array reading and OPU direct bioapplications (cytometry, optical tweezing, bioimaging) to modified OPU-based biosensing (DNA chip fluorescence scanning, biomolecular diagnostics). We conclude by presenting future trends on optical storage devices and potential applications. Hacking low-cost and high-performance OPUs may spread micro- and nanoscale biosensing research from research laboratories to citizen scientists around the globe.
DOI
The optical pickup unit (OPU) within a CD/DVD/Blu-ray drive integrates 780, 650, and 405 nm wavelength lasers, diffraction-limited optics, a high-bandwidth optoelectronic transducer up to 400 MHz, and a nanoresolution x-, z-axis, and tilt actuator in a compact size. In addition, the OPU is a remarkable piece of engineering and could enable different scientific applications such as sub-angstrom displacement sensing, micro- and nanoimaging, and nanolithography. Although off-the-shelf OPUs can be easily obtained, manufacturers protect their datasheets under nondisclosure agreements to impede their availability to the public. Thus, OPUs are black boxes that few people can use for research, and only experienced researchers can access all their functions. This review details the OPU mechanism and components. In addition, we explain how to utilize three commercially available triple-wavelength OPUs from scratch and optimize sensing quality. Then, we discuss scientific research using OPUs, from standard optical drive-based turnkey-biomarker array reading and OPU direct bioapplications (cytometry, optical tweezing, bioimaging) to modified OPU-based biosensing (DNA chip fluorescence scanning, biomolecular diagnostics). We conclude by presenting future trends on optical storage devices and potential applications. Hacking low-cost and high-performance OPUs may spread micro- and nanoscale biosensing research from research laboratories to citizen scientists around the globe.
DOI
Optical tweezers and their applications
Paolo Polimeno, Alessandro Magazzù, Maria Antonia Iatì, Francesco Patti, Rosalba Saija, Cristian Degli Esposti Boschi, Maria Grazia Donato, Pietro G. Gucciardi, Philip H. Jones, Giovanni Volpe, Onofrio M. Maragò
Optical tweezers, tools based on strongly focused light, enable optical trapping, manipulation, and characterisation of a wide range of microscopic and nanoscopic materials. In the limiting cases of spherical particles either much smaller or much larger than the trapping wavelength, the force in optical tweezers separates into a conservative gradient force, which is proportional to the light intensity gradient and responsible for trapping, and a non-conservative scattering force, which is proportional to the light intensity and is generally detrimental for trapping, but fundamental for optical manipulation and laser cooling. For non-spherical particles or at intermediate (meso)scales, the situation is more complex and this traditional identification of gradient and scattering force is more elusive. Moreover, shape and composition can have dramatic consequences for optically trapped particle dynamics. Here, after an introduction to the theory and practice of optical forces with a focus on the role of shape and composition, we give an overview of some recent applications to biology, nanotechnology, spectroscopy, stochastic thermodynamics, critical Casimir forces, and active matter.
DOI
Optical tweezers, tools based on strongly focused light, enable optical trapping, manipulation, and characterisation of a wide range of microscopic and nanoscopic materials. In the limiting cases of spherical particles either much smaller or much larger than the trapping wavelength, the force in optical tweezers separates into a conservative gradient force, which is proportional to the light intensity gradient and responsible for trapping, and a non-conservative scattering force, which is proportional to the light intensity and is generally detrimental for trapping, but fundamental for optical manipulation and laser cooling. For non-spherical particles or at intermediate (meso)scales, the situation is more complex and this traditional identification of gradient and scattering force is more elusive. Moreover, shape and composition can have dramatic consequences for optically trapped particle dynamics. Here, after an introduction to the theory and practice of optical forces with a focus on the role of shape and composition, we give an overview of some recent applications to biology, nanotechnology, spectroscopy, stochastic thermodynamics, critical Casimir forces, and active matter.
DOI
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