Jianhua Zhang, Jingjing Guo, Fangzhi Mou and Jianguo Guan
Swarms and assemblies are ubiquitous in nature and they can perform complex collective behaviors and cooperative functions that they cannot accomplish individually. In response to light, some colloidal particles (CPs), including light active and passive CPs, can mimic their counterparts in nature and organize into complex structures that exhibit collective functions with remote controllability and high temporospatial precision. In this review, we firstly analyze the structural characteristics of swarms and assemblies of CPs and point out that light-controlled swarming and assembly of CPs are generally achieved by constructing light-responsive interactions between CPs. Then, we summarize in detail the recent advances in light-controlled swarming and assembly of CPs based on the interactions arisen from optical forces, photochemical reactions, photothermal effects, and photoisomerizations, as well as their potential applications. In the end, we also envision some challenges and future prospects of light-controlled swarming and assembly of CPs. With the increasing innovations in mechanisms and control strategies with easy operation, low cost, and arbitrary applicability, light-controlled swarming and assembly of CPs may be employed to manufacture programmable materials and reconfigurable robots for cooperative grasping, collective cargo transportation, and micro- and nanoengineering.
Wednesday, April 11, 2018
Experimental Test of the Differential Fluctuation Theorem and a Generalized Jarzynski Equality for Arbitrary Initial States
Thai M. Hoang, Rui Pan, Jonghoon Ahn, Jaehoon Bang, H. T. Quan, and Tongcang Li
Nonequilibrium processes of small systems such as molecular machines are ubiquitous in biology, chemistry, and physics but are often challenging to comprehend. In the past two decades, several exact thermodynamic relations of nonequilibrium processes, collectively known as fluctuation theorems, have been discovered and provided critical insights. These fluctuation theorems are generalizations of the second law and can be unified by a differential fluctuation theorem. Here we perform the first experimental test of the differential fluctuation theorem using an optically levitated nanosphere in both underdamped and overdamped regimes and in both spatial and velocity spaces. We also test several theorems that can be obtained from it directly, including a generalized Jarzynski equality that is valid for arbitrary initial states, and the Hummer-Szabo relation. Our study experimentally verifies these fundamental theorems and initiates the experimental study of stochastic energetics with the instantaneous velocity measurement.
DOI
Nonequilibrium processes of small systems such as molecular machines are ubiquitous in biology, chemistry, and physics but are often challenging to comprehend. In the past two decades, several exact thermodynamic relations of nonequilibrium processes, collectively known as fluctuation theorems, have been discovered and provided critical insights. These fluctuation theorems are generalizations of the second law and can be unified by a differential fluctuation theorem. Here we perform the first experimental test of the differential fluctuation theorem using an optically levitated nanosphere in both underdamped and overdamped regimes and in both spatial and velocity spaces. We also test several theorems that can be obtained from it directly, including a generalized Jarzynski equality that is valid for arbitrary initial states, and the Hummer-Szabo relation. Our study experimentally verifies these fundamental theorems and initiates the experimental study of stochastic energetics with the instantaneous velocity measurement.
DOI
Optimal integration of wide field illumination and holographic optical tweezers for multimodal microscopy with ultimate flexibility and versatility
Sang-Hyuk Lee
We introduce one-of-a-kind optical microscope that we have developed through optimized integration of wide-field and focused-light microscopies. This new instrument has accomplished operation of the same laser for both wide field illumination and holographic focused beam illumination interchangeably or simultaneously in a way scalable to multiple lasers. We have demonstrated its powerful capability by simultaneously carrying out Epi-fluorescence, total internal reflection fluorescence microscopy, selective plane illumination microscopy, and holographic optical tweezers with five lasers. Our instrument and the optical design will provide researchers across diverse fields, cell-biology and biophysics in particular, with a practical guidance to build an all-around multimodal microscope that will further inspire the development of novel hybrid microscopy experiments.
DOI
We introduce one-of-a-kind optical microscope that we have developed through optimized integration of wide-field and focused-light microscopies. This new instrument has accomplished operation of the same laser for both wide field illumination and holographic focused beam illumination interchangeably or simultaneously in a way scalable to multiple lasers. We have demonstrated its powerful capability by simultaneously carrying out Epi-fluorescence, total internal reflection fluorescence microscopy, selective plane illumination microscopy, and holographic optical tweezers with five lasers. Our instrument and the optical design will provide researchers across diverse fields, cell-biology and biophysics in particular, with a practical guidance to build an all-around multimodal microscope that will further inspire the development of novel hybrid microscopy experiments.
DOI
Remotely controlled fusion of selected vesicles and living cells: a key issue review
Azra Bahadori, Guillermo Moreno-Pescador, Lene B Oddershede and Poul M Bendix
Remote control over fusion of single cells and vesicles has a great potential in biological and chemical research allowing both transfer of genetic material between cells and transfer of molecular content between vesicles. Membrane fusion is a critical process in biology that facilitates molecular transport and mixing of cellular cytoplasms with potential formation of hybrid cells. Cells precisely regulate internal membrane fusions with the aid of specialized fusion complexes that physically provide the energy necessary for mediating fusion. Physical factors like membrane curvature, tension and temperature, affect biological membrane fusion by lowering the associated energy barrier. This has inspired the development of physical approaches to harness the fusion process at a single cell level by using remotely controlled electromagnetic fields to trigger membrane fusion. Here, we critically review various approaches, based on lasers or electric pulses, to control fusion between individual cells or between individual lipid vesicles and discuss their potential and limitations for present and future applications within biochemistry, biology and soft matter.
DOI
Remote control over fusion of single cells and vesicles has a great potential in biological and chemical research allowing both transfer of genetic material between cells and transfer of molecular content between vesicles. Membrane fusion is a critical process in biology that facilitates molecular transport and mixing of cellular cytoplasms with potential formation of hybrid cells. Cells precisely regulate internal membrane fusions with the aid of specialized fusion complexes that physically provide the energy necessary for mediating fusion. Physical factors like membrane curvature, tension and temperature, affect biological membrane fusion by lowering the associated energy barrier. This has inspired the development of physical approaches to harness the fusion process at a single cell level by using remotely controlled electromagnetic fields to trigger membrane fusion. Here, we critically review various approaches, based on lasers or electric pulses, to control fusion between individual cells or between individual lipid vesicles and discuss their potential and limitations for present and future applications within biochemistry, biology and soft matter.
DOI
Tuesday, April 10, 2018
A remote laboratory for optical levitation of charged droplets
Daniel Galan, Oscar Isaksson, Mats Rostedt, Jonas Enger, Dag Hanstorp and Luis de la Torre
We present a remotely controlled experiment in which liquid droplets are levitated by a vertically aligned focused laser beam. The droplets levitate at the point where the photon pressure of the focused laser beam balances the gravitational force. The size of a trapped droplet can be measured by detecting the diffraction pattern created by the trapping laser light. The charge on the trapped droplet can thereafter be determined by observing its motion when a vertically directed electrical field is applied. This experiment allows a student to study many fundamental physics processes, such as photon pressure, diffraction of light, or the motion of charged particles in electrical fields. The complexity of the experiments and the concept studied make this suitable for advanced studies in physics. The laser power required in the experiment is about 1 W, which is a thousand times greater than the value of 1 mW at which lasers begin to be capable of causing harm to eyes; high voltages are also used. Further, the cost of the equipment is relatively high, which limits its availability to most undergraduate teaching laboratories. It thus constitutes an ideal experiment for remote control.
DOI
We present a remotely controlled experiment in which liquid droplets are levitated by a vertically aligned focused laser beam. The droplets levitate at the point where the photon pressure of the focused laser beam balances the gravitational force. The size of a trapped droplet can be measured by detecting the diffraction pattern created by the trapping laser light. The charge on the trapped droplet can thereafter be determined by observing its motion when a vertically directed electrical field is applied. This experiment allows a student to study many fundamental physics processes, such as photon pressure, diffraction of light, or the motion of charged particles in electrical fields. The complexity of the experiments and the concept studied make this suitable for advanced studies in physics. The laser power required in the experiment is about 1 W, which is a thousand times greater than the value of 1 mW at which lasers begin to be capable of causing harm to eyes; high voltages are also used. Further, the cost of the equipment is relatively high, which limits its availability to most undergraduate teaching laboratories. It thus constitutes an ideal experiment for remote control.
DOI
Light‐Driven Rotation of Plasmonic Nanomotors
Lei Shao, Mikael Käll
Colloidal metal nanocrystals exhibit distinct plasmonic resonances that can greatly enhance optical forces and torques. This article highlights the recent application of such particles as light‐driven rotary motors at the nanoscale. By using laser tweezers, it is possible to achieve unprecedented rotation performance in solution, providing a variety of exciting possibilities for applications ranging from nanomechanics to biochemical sensing. Recent developments in this emerging field are discussed, and the physics behind the rotation mechanism, the Brownian dynamics, and the photothermal heating effects influencing the performance of the plasmonic nanomotors are introduced. Possible applications, open questions, and interesting future developments are also discussed.
DOI
Colloidal metal nanocrystals exhibit distinct plasmonic resonances that can greatly enhance optical forces and torques. This article highlights the recent application of such particles as light‐driven rotary motors at the nanoscale. By using laser tweezers, it is possible to achieve unprecedented rotation performance in solution, providing a variety of exciting possibilities for applications ranging from nanomechanics to biochemical sensing. Recent developments in this emerging field are discussed, and the physics behind the rotation mechanism, the Brownian dynamics, and the photothermal heating effects influencing the performance of the plasmonic nanomotors are introduced. Possible applications, open questions, and interesting future developments are also discussed.
DOI
A photophoretic-trap volumetric display
D. E. Smalley, E. Nygaard, K. Squire, J. Van Wagoner, J. Rasmussen, S. Gneiting, K. Qaderi, J. Goodsell, W. Rogers, M. Lindsey, K. Costner, A. Monk, M. Pearson, B. Haymore & J. Peatross
Free-space volumetric displays, or displays that create luminous image points in space, are the technology that most closely resembles the three-dimensional displays of popular fiction1. Such displays are capable of producing images in ‘thin air’ that are visible from almost any direction and are not subject to clipping. Clipping restricts the utility of all three-dimensional displays that modulate light at a two-dimensional surface with an edge boundary; these include holographic displays, nanophotonic arrays, plasmonic displays, lenticular or lenslet displays and all technologies in which the light scattering surface and the image point are physically separate. Here we present a free-space volumetric display based on photophoretic optical trapping2 that produces full-colour graphics in free space with ten-micrometre image points using persistence of vision. This display works by first isolating a cellulose particle in a photophoretic trap created by spherical and astigmatic aberrations. The trap and particle are then scanned through a display volume while being illuminated with red, green and blue light. The result is a three-dimensional image in free space with a large colour gamut, fine detail and low apparent speckle. This platform, named the Optical Trap Display, is capable of producing image geometries that are currently unobtainable with holographic and light-field technologies, such as long-throw projections, tall sandtables and ‘wrap-around’ displays.
DOI
Free-space volumetric displays, or displays that create luminous image points in space, are the technology that most closely resembles the three-dimensional displays of popular fiction1. Such displays are capable of producing images in ‘thin air’ that are visible from almost any direction and are not subject to clipping. Clipping restricts the utility of all three-dimensional displays that modulate light at a two-dimensional surface with an edge boundary; these include holographic displays, nanophotonic arrays, plasmonic displays, lenticular or lenslet displays and all technologies in which the light scattering surface and the image point are physically separate. Here we present a free-space volumetric display based on photophoretic optical trapping2 that produces full-colour graphics in free space with ten-micrometre image points using persistence of vision. This display works by first isolating a cellulose particle in a photophoretic trap created by spherical and astigmatic aberrations. The trap and particle are then scanned through a display volume while being illuminated with red, green and blue light. The result is a three-dimensional image in free space with a large colour gamut, fine detail and low apparent speckle. This platform, named the Optical Trap Display, is capable of producing image geometries that are currently unobtainable with holographic and light-field technologies, such as long-throw projections, tall sandtables and ‘wrap-around’ displays.
DOI
Combining Holographic Optical Tweezers with Upconversion Luminescence Encoding: Imaging-Based Stable Suspension Array for Sensitive Responding of Dual Cancer Biomarkers
Cheng-Yu Li, Di Cao, Chu-Bo Qi, Ya-Feng Kang, Chong-Yang Song, Dang-Dang Xu, Bei Zheng, Dai-Wen Pang, and Hong-Wu Tang
Establishment of a stable analytical methodology with high-quality results is an urgent need for screening cancer biomarkers in early diagnosis of cancer. In this study, we incorporate holographic optical tweezers with upconversion luminescence encoding to design an imageable suspension array and apply it to conduct the detection of two liver cancer related biomarkers, carcinoembryonic antigen and alpha fetal protein. This bead-based assay is actualized by forming a bead array with holographic optical tweezers and synchronously exciting the upconversion luminescence of corresponding trapped complex beads fabricated with a simple one-step sandwich immunological recognition. Owing to the fact that these flowing beads are stably trapped in the focal plane of the objective lens which tightly converges the array of the laser beams by splitting a 980 nm beam using a diffraction optical element, a fairly stable excitation condition is achieved to provide reliable assay results. By further taking advantage of the eminent encoding capability of upconversion nanoparticles and the extremely low background signals of anti-Stokes luminescence, the two targets are well-identified and simultaneously detected with quite sound sensitivity and specificity. Moreover, the potential on-demand clinical application is presented by employing this approach to respond the targets toward complex matrices such as serum and tissue samples, offering a new alternative for cancer diagnosis technology.
Establishment of a stable analytical methodology with high-quality results is an urgent need for screening cancer biomarkers in early diagnosis of cancer. In this study, we incorporate holographic optical tweezers with upconversion luminescence encoding to design an imageable suspension array and apply it to conduct the detection of two liver cancer related biomarkers, carcinoembryonic antigen and alpha fetal protein. This bead-based assay is actualized by forming a bead array with holographic optical tweezers and synchronously exciting the upconversion luminescence of corresponding trapped complex beads fabricated with a simple one-step sandwich immunological recognition. Owing to the fact that these flowing beads are stably trapped in the focal plane of the objective lens which tightly converges the array of the laser beams by splitting a 980 nm beam using a diffraction optical element, a fairly stable excitation condition is achieved to provide reliable assay results. By further taking advantage of the eminent encoding capability of upconversion nanoparticles and the extremely low background signals of anti-Stokes luminescence, the two targets are well-identified and simultaneously detected with quite sound sensitivity and specificity. Moreover, the potential on-demand clinical application is presented by employing this approach to respond the targets toward complex matrices such as serum and tissue samples, offering a new alternative for cancer diagnosis technology.
Surface Imaging Technique by an Optically Trapped Microsphere in Air Condition
Masaki Michihata, Jonggang Kim, Satoru Takahashi, Kiyoshi Takamasu, Yasuhiro Mizutanim, Yasuhiro Takaya
Recent advancement of fabrication technologies enables nanoscale surface patterning on microstructures, which requires multi-scale measurements for the determination of their geometric dimensions and surface texture in the same coordinate system. Previously, we have developed a micro-coordinate measuring machine with a laser-trapped microprobe that uses an optically trapped microsphere as a surface detecting sensor. In this paper, we propose a surface imaging technique using the optically trapped microsphere as a micro-lens, i.e., the surface imaging system is integrated into the coordinate measuring system. The optically trapped microsphere with a diameter of 8 μm was brought close to a measured surface to image the surface underneath it. Because there is an unknown gap between the microsphere and surface, the focal plane of the imaging system had to be adjusted to the measured surface by the developed imaging lens system. With the microsphere-based imaging system, an optical diffractive grating of sub-micrometer periodic structure with 417 nm pitch and 50 nm depth was successfully imaged and the defect on the grating was detected. Thus, we verified that development of an imaging system based on the optically trapped microsphere for multi-scale evaluation systems can be accomplished.
DOI
Recent advancement of fabrication technologies enables nanoscale surface patterning on microstructures, which requires multi-scale measurements for the determination of their geometric dimensions and surface texture in the same coordinate system. Previously, we have developed a micro-coordinate measuring machine with a laser-trapped microprobe that uses an optically trapped microsphere as a surface detecting sensor. In this paper, we propose a surface imaging technique using the optically trapped microsphere as a micro-lens, i.e., the surface imaging system is integrated into the coordinate measuring system. The optically trapped microsphere with a diameter of 8 μm was brought close to a measured surface to image the surface underneath it. Because there is an unknown gap between the microsphere and surface, the focal plane of the imaging system had to be adjusted to the measured surface by the developed imaging lens system. With the microsphere-based imaging system, an optical diffractive grating of sub-micrometer periodic structure with 417 nm pitch and 50 nm depth was successfully imaged and the defect on the grating was detected. Thus, we verified that development of an imaging system based on the optically trapped microsphere for multi-scale evaluation systems can be accomplished.
DOI
Sliding of a single lac repressor protein along DNA is tuned by DNA sequence and molecular switching
Alessia Tempestini, Carina Monico, Lucia Gardini, Francesco Vanzi, Francesco S Pavone, Marco Capitanio
In any living cell, genome maintenance is carried out by DNA-binding proteins that recognize specific sequences among a vast amount of DNA. This includes fundamental processes such as DNA replication, DNA repair, and gene expression and regulation. Here, we study the mechanism of DNA target search by a single lac repressor protein (LacI) with ultrafast force-clamp spectroscopy, a sub-millisecond and few base-pair resolution technique based on laser tweezers. We measure 1D-diffusion of proteins on DNA at physiological salt concentrations with 20 bp resolution and find that sliding of LacI along DNA is sequence dependent. We show that only allosterically activated LacI slides along non-specific DNA sequences during target search, whereas the inhibited conformation does not support sliding and weakly interacts with DNA. Moreover, we find that LacI undergoes a load-dependent conformational change when it switches between sliding and strong binding to the target sequence. Our data reveal how DNA sequence and molecular switching regulate LacI target search process and provide a comprehensive model of facilitated diffusion for LacI.
DOI
In any living cell, genome maintenance is carried out by DNA-binding proteins that recognize specific sequences among a vast amount of DNA. This includes fundamental processes such as DNA replication, DNA repair, and gene expression and regulation. Here, we study the mechanism of DNA target search by a single lac repressor protein (LacI) with ultrafast force-clamp spectroscopy, a sub-millisecond and few base-pair resolution technique based on laser tweezers. We measure 1D-diffusion of proteins on DNA at physiological salt concentrations with 20 bp resolution and find that sliding of LacI along DNA is sequence dependent. We show that only allosterically activated LacI slides along non-specific DNA sequences during target search, whereas the inhibited conformation does not support sliding and weakly interacts with DNA. Moreover, we find that LacI undergoes a load-dependent conformational change when it switches between sliding and strong binding to the target sequence. Our data reveal how DNA sequence and molecular switching regulate LacI target search process and provide a comprehensive model of facilitated diffusion for LacI.
DOI
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