Chao Zhang, Thejaswi Tumkur, Jian Yang, Minhan Lou, Liangliang Dong, Linan Zhou, Peter Nordlander, and Naomi J. Halas
The optical reshaping of metallic nanostructures typically requires intense laser pulses to first approach or achieve melting, followed by surface-tension-dominated reshaping, transforming the original nanostructures into more spherical morphologies. Here, we report the directional optical reshaping of the Au nanodisk of an Al–Au heterodimer in the illuminated junction of an atomic force microscope (AFM). Both the heightening and the repositioning of the Au nanodisk component are induced, reducing the gap between the two nanodisks. There are three contributors to this process: the photothermal softening of the Au lattice, the optical force applied to the Au nanodisk by the Al nanodisk, and the optical force from the nearby AFM tip. The asymmetric reshaping of the heterodimer is observable structurally, through electron microscopic imaging, and through changes in the heterodimer optical response. This optical-force-directed shape manipulation may have potential applications in nanofabrication, optically induced nanomanufacturing, sensing, and quality control.
DOI
Wednesday, October 10, 2018
Optimized stereo matching algorithm for integral imaging microscopy and its potential use in precise 3-D optical manipulation
Xiaohui Ma, Shulu Wang, Weiwei Liu, Fenghua Ma, Anting Wang, Yunlong, Sheng, Yinmei Li, Hai Ming
In this paper, we present an integral imaging microscopy, which can achieve continuous depth extraction. The multiple stereo matching algorithm is optimized with data point interpolation and calculation range correction, which can improve the computing efficiency and accuracy. A water suspension of silica-embedded magnetic particles in light-trap environment is used as a specimen. The elementary image array is obtained through sequentially imaging the specimen by the objective lens and microlens array, which contains continuous depth information that can give the optical tweezers a feedback for precise 3-D manipulation. Experimental and calculated results show the feasibility of our method.
DOI
In this paper, we present an integral imaging microscopy, which can achieve continuous depth extraction. The multiple stereo matching algorithm is optimized with data point interpolation and calculation range correction, which can improve the computing efficiency and accuracy. A water suspension of silica-embedded magnetic particles in light-trap environment is used as a specimen. The elementary image array is obtained through sequentially imaging the specimen by the objective lens and microlens array, which contains continuous depth information that can give the optical tweezers a feedback for precise 3-D manipulation. Experimental and calculated results show the feasibility of our method.
DOI
Tuesday, October 9, 2018
Optical Assembling of Micro-Particles at a Glass–Water Interface with Diffraction Patterns Caused by the Limited Aperture of Objective
Min-Cheng Zhong, Ai-Yin Liu and Rong Zhu
Optical tweezers can manipulate micro-particles, which have been widely used in various applications. Here, we experimentally demonstrate that optical tweezers can assemble the micro-particles to form stable structures at the glass–solution interface in this paper. Firstly, the particles are driven by the optical forces originated from the diffraction fringes, which of the trapping beam passing through an objective with limited aperture. The particles form stable ring structures when the trapping beam is a linearly polarized beam. The particle distributions in the transverse plane are affected by the particle size and concentration. Secondly, the particles form an incompact structure as two fan-shaped after the azimuthally polarized beam passing through a linear polarizer. Furthermore, the particles form a compact structure when a radially polarized beam is used for trapping. Thirdly, the particle patterns can be printed steady at the glass surface in the salt solution. At last, the disadvantage of diffraction traps is discussed in application of optical tweezers. The aggregation of particles at the interfaces seriously affects the flowing of particles in microfluidic channels, and a total reflector as the bottom surface of sample cell can avoid the optical tweezers induced particle patterns at the interface. The optical trapping study utilizing the diffraction gives an interesting method for binding and assembling microparticles, which is helpful to understand the principle of optical tweezers.
DOI
Optical tweezers can manipulate micro-particles, which have been widely used in various applications. Here, we experimentally demonstrate that optical tweezers can assemble the micro-particles to form stable structures at the glass–solution interface in this paper. Firstly, the particles are driven by the optical forces originated from the diffraction fringes, which of the trapping beam passing through an objective with limited aperture. The particles form stable ring structures when the trapping beam is a linearly polarized beam. The particle distributions in the transverse plane are affected by the particle size and concentration. Secondly, the particles form an incompact structure as two fan-shaped after the azimuthally polarized beam passing through a linear polarizer. Furthermore, the particles form a compact structure when a radially polarized beam is used for trapping. Thirdly, the particle patterns can be printed steady at the glass surface in the salt solution. At last, the disadvantage of diffraction traps is discussed in application of optical tweezers. The aggregation of particles at the interfaces seriously affects the flowing of particles in microfluidic channels, and a total reflector as the bottom surface of sample cell can avoid the optical tweezers induced particle patterns at the interface. The optical trapping study utilizing the diffraction gives an interesting method for binding and assembling microparticles, which is helpful to understand the principle of optical tweezers.
DOI
Detection of Magnetic Field Gradient and Single Spin Using Optically Levitated Nano-Particle in Vacuum
Ke-Wen Xiao, Lei-Ming Zhou, Zhang-Qi Yin and Nan Zhao
Optically levitated nano-particle with spins is a promising system for high-precision measurement and quantum information processing. We theoretically analyze the ratio between the fluctuation of particleʼs displacement caused by spins in magnetic field and caused by molecular collisions of the residual air. When the ratio is larger than unity, the displacement fluctuation of spins flipping can be remarkably detected. By theoretical analysis and numerical simulation, we propose and validate a scheme for the detection of gradient of the magnetic field by levitating ferromagnetic nano-particle, and also put forward a realizable detection scheme of the single spin by levitating nano-diamond particle with single nitrogen-vacancy(NV) centers.
DOI
DOI
Spatiotemporal autofocused chirped Pearcey Pearcey Gaussian wave packets with an adjustable focus in a quadratic-index medium
Xingyu Chen, Jingli Zhuang, Xi Peng, Dongdong Li, Liping Zhang, Fang Zhao, Dongmei Deng
Here we investigate the propagation properties of spatiotemporal autofocused chirped Pearcey Pearcey Gaussian (PePeG) wavepackets by solving (3 + 1) D Schrdinger equation in a quadratic index medium. When the spatial distribution factor p and the temporal distribution factor f are the same, PePeG wavepackets can simultaneously autofocus in spatial and temporal domain and the peak intensity at the focus is more 28 times than that at the initial plane. With the increase of distribution factor p, the scope of the radius of trapped particles decreases.
DOI
Here we investigate the propagation properties of spatiotemporal autofocused chirped Pearcey Pearcey Gaussian (PePeG) wavepackets by solving (3 + 1) D Schrdinger equation in a quadratic index medium. When the spatial distribution factor p and the temporal distribution factor f are the same, PePeG wavepackets can simultaneously autofocus in spatial and temporal domain and the peak intensity at the focus is more 28 times than that at the initial plane. With the increase of distribution factor p, the scope of the radius of trapped particles decreases.
DOI
A force sensor that converts fluorescence signal into force measurement utilizing short looped DNA
Golam Mustafa, Cho-Ying Chuang, William A. Roy, Mohamed M.F arhath, Nilisha Pokhrel, Yue Ma, Kazuo Nagasawa, Edwin Antony, Matthew J. Comstock, Soumitra Basu, Hamza Balci
A force sensor concept is presented where fluorescence signal is converted into force information via single-molecule Förster resonance energy transfer (smFRET). The basic design of the sensor is a ~100 base pair (bp) long double stranded DNA (dsDNA) that is restricted to a looped conformation by a nucleic acid secondary structure (NAS) that bridges its ends. The looped dsDNA generates a tension across the NAS and unfolds it when the tension is high enough. The FRET efficiency between donor and acceptor (D&A) fluorophores placed across the NAS reports on its folding state. Three dsDNA constructs with different lengths were bridged by a DNA hairpin and KCl was titrated to change the applied force. After these proof-of-principle measurements, one of the dsDNA constructs was used to maintain the G-quadruplex (GQ) construct formed by thrombin binding aptamer (TBA) under tension while it interacted with a destabilizing protein and stabilizing small molecule. The force required to unfold TBA-GQ was independently investigated with high-resolution optical tweezers (OT) measurements that established the relevant force to be a few pN, which is consistent with the force generated by the looped dsDNA. The proposed method is particularly promising as it enables studying NAS, protein, and small molecule interactions using a highly-parallel FRET-based assay while the NAS is kept under an approximately constant force.
DOI
A force sensor concept is presented where fluorescence signal is converted into force information via single-molecule Förster resonance energy transfer (smFRET). The basic design of the sensor is a ~100 base pair (bp) long double stranded DNA (dsDNA) that is restricted to a looped conformation by a nucleic acid secondary structure (NAS) that bridges its ends. The looped dsDNA generates a tension across the NAS and unfolds it when the tension is high enough. The FRET efficiency between donor and acceptor (D&A) fluorophores placed across the NAS reports on its folding state. Three dsDNA constructs with different lengths were bridged by a DNA hairpin and KCl was titrated to change the applied force. After these proof-of-principle measurements, one of the dsDNA constructs was used to maintain the G-quadruplex (GQ) construct formed by thrombin binding aptamer (TBA) under tension while it interacted with a destabilizing protein and stabilizing small molecule. The force required to unfold TBA-GQ was independently investigated with high-resolution optical tweezers (OT) measurements that established the relevant force to be a few pN, which is consistent with the force generated by the looped dsDNA. The proposed method is particularly promising as it enables studying NAS, protein, and small molecule interactions using a highly-parallel FRET-based assay while the NAS is kept under an approximately constant force.
DOI
A microscopic Kapitza pendulum
Christopher J. Richards, Thomas J. Smart, Philip H. Jones & David Cubero
Pyotr Kapitza studied in 1951 the unusual equilibrium features of a rigid pendulum when its point of suspension is under a high-frequency vertical vibration. A sufficiently fast vibration makes the top position stable, putting the pendulum in an inverted orientation that seemingly defies gravity. Kapitza’s analytical method, based on an asymptotic separation of fast and slow variables yielding a renormalized potential, has found application in many diverse areas. Here we study Kapitza’s pendulum going beyond its typical idealizations, by explicitly considering its finite stiffness and the dissipative interaction with the surrounding medium, and using similar theoretical methods as Kapitza. The pendulum is realized at the micrometre scale using a colloidal particle suspended in water and trapped by optical tweezers. Though the strong dissipation present at this scale prevents the inverted pendulum regime, new ones appear in which the equilibrium positions are displaced to the side, and with transitions between them determined either by the driving frequency or the friction coefficient. These new regimes could be exploited in applications aimed at particle separation at small scales.
DOI
Pyotr Kapitza studied in 1951 the unusual equilibrium features of a rigid pendulum when its point of suspension is under a high-frequency vertical vibration. A sufficiently fast vibration makes the top position stable, putting the pendulum in an inverted orientation that seemingly defies gravity. Kapitza’s analytical method, based on an asymptotic separation of fast and slow variables yielding a renormalized potential, has found application in many diverse areas. Here we study Kapitza’s pendulum going beyond its typical idealizations, by explicitly considering its finite stiffness and the dissipative interaction with the surrounding medium, and using similar theoretical methods as Kapitza. The pendulum is realized at the micrometre scale using a colloidal particle suspended in water and trapped by optical tweezers. Though the strong dissipation present at this scale prevents the inverted pendulum regime, new ones appear in which the equilibrium positions are displaced to the side, and with transitions between them determined either by the driving frequency or the friction coefficient. These new regimes could be exploited in applications aimed at particle separation at small scales.
DOI
Effect of nanoscale roughness on optical trapping properties of surface plasmon polaritons exerted on nanoparticle
Ge Cheng-Xian, Wu Zhen-Sen, Bai Jing, Gong Lei
Based on the three-dimensional dispersive finite difference time domain method and Maxwell stress tensor equation, the effect of nanoscale surface roughness on the optical trapping properties of nanoparticle in a vicinity of the composite gold film with periodic structure is investigated numerically. The periodic structure is observed as circular holes which can excite the surface plasmon polaritons on the metal-dielectric interface with particular emphasis on its crucial role in tailoring the optical force acting on a nearby nanoparticle. Utilizing the Monte-Carlo method, the surface roughness is added into the calculation model of the proposed method to accurately investigate the optical performance of the film-tuned nanoparticle system. Selected calculations on the effects of root mean square height and correlation length of rough surface are analyzed in detail to demonstrate that the negative effect of the surface roughness on the optical trapping force can be eliminated when the ratio of correlation length to root mean square height is equal to 10. Accurate investigation of optical trapping properties of nanoparticle in a vicinity of the composite gold film could provide guidelines for further research on the optical system design and manipulation of arbitrary composite nanoparticles.
DOI
Based on the three-dimensional dispersive finite difference time domain method and Maxwell stress tensor equation, the effect of nanoscale surface roughness on the optical trapping properties of nanoparticle in a vicinity of the composite gold film with periodic structure is investigated numerically. The periodic structure is observed as circular holes which can excite the surface plasmon polaritons on the metal-dielectric interface with particular emphasis on its crucial role in tailoring the optical force acting on a nearby nanoparticle. Utilizing the Monte-Carlo method, the surface roughness is added into the calculation model of the proposed method to accurately investigate the optical performance of the film-tuned nanoparticle system. Selected calculations on the effects of root mean square height and correlation length of rough surface are analyzed in detail to demonstrate that the negative effect of the surface roughness on the optical trapping force can be eliminated when the ratio of correlation length to root mean square height is equal to 10. Accurate investigation of optical trapping properties of nanoparticle in a vicinity of the composite gold film could provide guidelines for further research on the optical system design and manipulation of arbitrary composite nanoparticles.
DOI
Monday, October 8, 2018
A myosin II nanomachine mimicking the striated muscle
Irene Pertici, Lorenzo Bongini, Luca Melli, Giulio Bianchi, Luca Salvi, Giulia Falorsi, Caterina Squarci, Tamás Bozó, Dan Cojoc, Miklós S. Z. Kellermayer, Vincenzo Lombardi & Pasquale Bianco
The contraction of striated muscle (skeletal and cardiac muscle) is generated by ATP-dependent interactions between the molecular motor myosin II and the actin filament. The myosin motors are mechanically coupled along the thick filament in a geometry not achievable by single-molecule experiments. Here we show that a synthetic one-dimensional nanomachine, comprising fewer than ten myosin II dimers purified from rabbit psoas, performs isometric and isotonic contractions at 2 mM ATP, delivering a maximum power of 5 aW. The results are explained with a kinetic model fitted to the performance of mammalian skeletal muscle, showing that the condition for the motor coordination that maximises the efficiency in striated muscle is a minimum of 32 myosin heads sharing a common mechanical ground. The nanomachine offers a powerful tool for investigating muscle contractile-protein physiology, pathology and pharmacology without the potentially disturbing effects of the cytoskeletal—and regulatory—protein environment.
DOI
The contraction of striated muscle (skeletal and cardiac muscle) is generated by ATP-dependent interactions between the molecular motor myosin II and the actin filament. The myosin motors are mechanically coupled along the thick filament in a geometry not achievable by single-molecule experiments. Here we show that a synthetic one-dimensional nanomachine, comprising fewer than ten myosin II dimers purified from rabbit psoas, performs isometric and isotonic contractions at 2 mM ATP, delivering a maximum power of 5 aW. The results are explained with a kinetic model fitted to the performance of mammalian skeletal muscle, showing that the condition for the motor coordination that maximises the efficiency in striated muscle is a minimum of 32 myosin heads sharing a common mechanical ground. The nanomachine offers a powerful tool for investigating muscle contractile-protein physiology, pathology and pharmacology without the potentially disturbing effects of the cytoskeletal—and regulatory—protein environment.
DOI
Lorentz gamma factor from vacuum to medium and Minkowski momentum of a photon
Dipok Saikia
Lorentz gamma factor is derived for a photon when it moves from vacuum to a dielectric medium of refractive index μ. This gamma factor can completely explain the increase of photon momentum (Minkowski momentum) in a medium. Covariance problem is resolved without violating energy conservation law and Lorentz invariance.
DOI
Lorentz gamma factor is derived for a photon when it moves from vacuum to a dielectric medium of refractive index μ. This gamma factor can completely explain the increase of photon momentum (Minkowski momentum) in a medium. Covariance problem is resolved without violating energy conservation law and Lorentz invariance.
DOI
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