Chao Zhan, Gan Wang, Jun Yi, Jun-Ying Wei, Zhi-Hao Li, Zhao-Bin Chen, Jia Shi, Yang Yang, Wenjing Hong, Zhong-Qun Tian
The volume of the object that can be manipulated in solution is continuously decreasing toward an ultimate goal of a single molecule. However, Brownian motions suppress the molecular trapping. To date, free-molecule trapping in solution has not been accomplished. Here, we develop a strategy to directly trap, investigate, and release single molecules (∼2 nm) in solution by using an adjustable plasmonic optical nanogap, which has been further applied for selective single-molecule trapping. Comprehensive experiments and theoretical simulations demonstrated that the trapping force originated from plasmonic nanomaterials. This technique opens an avenue to manipulate single molecules and other objects in the size range of primary interest for physics, chemistry, and life and material sciences without the limitations of strong bonding group, ultra-high vacuum, and ultra-low temperature, and makes possible controllable single-molecule manipulation and investigation as well as bottom-up construction of nanodevices and molecular machines.
DOI
Wednesday, September 9, 2020
Observation of Collisions between Two Ultracold Ground-State CaF Molecules
Lawrence W. Cheuk, Loïc Anderegg, Yicheng Bao, Sean Burchesky, Scarlett S. Yu, Wolfgang Ketterle, Kang-Kuen Ni, and John M. Doyle
We measure inelastic collisions between ultracold CaF molecules by combining two optical tweezers, each containing a single molecule. We observe collisions between 2Σ CaF molecules in the absolute ground state |X,v=0,N=0,F=0⟩, and in excited hyperfine and rotational states. In the absolute ground state, we find a two-body loss rate of 7(4)×10−11 cm3/s, which is below, but close to, the predicted universal loss rate.
DOI
We measure inelastic collisions between ultracold CaF molecules by combining two optical tweezers, each containing a single molecule. We observe collisions between 2Σ CaF molecules in the absolute ground state |X,v=0,N=0,F=0⟩, and in excited hyperfine and rotational states. In the absolute ground state, we find a two-body loss rate of 7(4)×10−11 cm3/s, which is below, but close to, the predicted universal loss rate.
DOI
Tuesday, September 8, 2020
Spheroidal trap shell beyond diffraction limit induced by nonlinear effects in femtosecond laser trapping
Lu Huang, Yaqiang Qin, Yunfeng Jin, Hao Shi, Honglian Guo, Liantuan Xiao and Yuqiang Jiang
Beyond diffraction limit, multitrapping of nanoparticles is important in numerous scientific fields, including biophysics, materials science and quantum optics. Here, we demonstrate the 3-dimensional (3D) shell-like structure of optical trapping well induced by nonlinear optical effects in the femtosecond Gaussian beam trapping for the first time. Under the joint action of gradient force, scattering force and nonlinear trapping force, the gold nanoparticles can be stably trapped in some special positions, or hop between the trap positions along a route within the 3D shell. The separation between the trap positions can be adjusted by laser power and numerical aperture (NA) of the trapping objective lens. With a high NA lens, we achieved dual traps with less than 100 nm separation without utilizing complicated optical systems or any on-chip nanostructures. These curious findings will greatly extend and deepen our understanding of optical trapping based on nonlinear interaction and generate novel applications in various fields, such as microfabrication/nanofabrication, sensing and novel micromanipulations.
DOI
Beyond diffraction limit, multitrapping of nanoparticles is important in numerous scientific fields, including biophysics, materials science and quantum optics. Here, we demonstrate the 3-dimensional (3D) shell-like structure of optical trapping well induced by nonlinear optical effects in the femtosecond Gaussian beam trapping for the first time. Under the joint action of gradient force, scattering force and nonlinear trapping force, the gold nanoparticles can be stably trapped in some special positions, or hop between the trap positions along a route within the 3D shell. The separation between the trap positions can be adjusted by laser power and numerical aperture (NA) of the trapping objective lens. With a high NA lens, we achieved dual traps with less than 100 nm separation without utilizing complicated optical systems or any on-chip nanostructures. These curious findings will greatly extend and deepen our understanding of optical trapping based on nonlinear interaction and generate novel applications in various fields, such as microfabrication/nanofabrication, sensing and novel micromanipulations.
DOI
Distributed Force Control for Microrobot Manipulation via Planar Multi‐Spot Optical Tweezer
Dandan Zhang Antoine Barbot Benny Lo Guang‐Zhong Yang
Optical tweezers (OT) represent a versatile tool for micro‐manipulation. To avoid damages to living cells caused by illuminating laser directly on them, microrobots controlled by OT can be used for manipulation of cells or living organisms in microscopic scale. Translation and planar rotation motion of microrobots can be realized by using a multi‐spot planar OT. However, out‐of‐plane manipulation of microrobots is difficult to achieve with a planar OT. This paper presents a distributed manipulation scheme based on multiple laser spots, which can control the out‐of‐plane pose of a microrobot along multiple axes. Different microrobot designs have been investigated and fabricated for experimental validation. The main contributions of this paper include: i) development of a generic model for the structure design of microrobots which enables multi‐dimensional (6D) control via conventional multi‐spot OT; ii) introduction of the distributed force control for microrobot manipulation based on characteristic distance and power intensity distribution. Experiments are performed to demonstrate the effectiveness of the proposed method and its potential applications, which include indirect manipulation of micro‐objects.
DOI
Optical tweezers (OT) represent a versatile tool for micro‐manipulation. To avoid damages to living cells caused by illuminating laser directly on them, microrobots controlled by OT can be used for manipulation of cells or living organisms in microscopic scale. Translation and planar rotation motion of microrobots can be realized by using a multi‐spot planar OT. However, out‐of‐plane manipulation of microrobots is difficult to achieve with a planar OT. This paper presents a distributed manipulation scheme based on multiple laser spots, which can control the out‐of‐plane pose of a microrobot along multiple axes. Different microrobot designs have been investigated and fabricated for experimental validation. The main contributions of this paper include: i) development of a generic model for the structure design of microrobots which enables multi‐dimensional (6D) control via conventional multi‐spot OT; ii) introduction of the distributed force control for microrobot manipulation based on characteristic distance and power intensity distribution. Experiments are performed to demonstrate the effectiveness of the proposed method and its potential applications, which include indirect manipulation of micro‐objects.
DOI
Evanescent Wave Optical Trapping and Sensing on Polymer Optical Fibers for Ultra-Trace Detection of Glucose
Tahereh Azargoshasb, H. Ali Navid, Roghaieh Parvizi, and Hadi Heidari
Graphene sensitization of glucose-imprinted polymer (G-IP)-coated optical fiber has been introduced as a new biosensor for evanescent wave trapping on the polymer optical fiber to detect low-level glucose. The developed sensor operates based on the evanescent wave modulation principle. Full characterization via atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and N2 adsorption/desorption of as-prepared G-IP-coated optical fibers was experimentally tested. Accordingly, related operational parameters such as roughness and diameter were optimized. Incorporating graphene into the G-IP not only steadily promotes the electron transport between the fiber surface and as-proposed G-IP but also significantly enhances the sensitivity by acting as a carrier for immobilizing G-IP with specific imprinted cavities. The sensor demonstrates a fast response time (5 s) and high sensitivity, selectivity, and stability, which cause a wide linear range (10–100 nM) and a low limit of detection (LOD = 2.54 nM). Experimental results indicate that the developed sensor facilitates online monitoring and remote sensing of glucose in biological liquids and food samples.
DOI
Graphene sensitization of glucose-imprinted polymer (G-IP)-coated optical fiber has been introduced as a new biosensor for evanescent wave trapping on the polymer optical fiber to detect low-level glucose. The developed sensor operates based on the evanescent wave modulation principle. Full characterization via atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and N2 adsorption/desorption of as-prepared G-IP-coated optical fibers was experimentally tested. Accordingly, related operational parameters such as roughness and diameter were optimized. Incorporating graphene into the G-IP not only steadily promotes the electron transport between the fiber surface and as-proposed G-IP but also significantly enhances the sensitivity by acting as a carrier for immobilizing G-IP with specific imprinted cavities. The sensor demonstrates a fast response time (5 s) and high sensitivity, selectivity, and stability, which cause a wide linear range (10–100 nM) and a low limit of detection (LOD = 2.54 nM). Experimental results indicate that the developed sensor facilitates online monitoring and remote sensing of glucose in biological liquids and food samples.
DOI
Measurement and simulation of atomic motion in nanoscale optical trapping potentials
Signe B. Markussen, Jürgen Appel, Christoffer Østfeldt, Jean-Baptiste S. Béguin, Eugene S. Polzik & Jörg H. Müller
Atoms trapped in the evanescent field around a nanofiber experience strong coupling to the light guided in the fiber mode. However, due to the intrinsically strong positional dependence of the coupling, thermal motion of the ensemble limits the use of nanofiber trapped atoms for some quantum tasks. We investigate the thermal dynamics of such an ensemble using short light pulses to make a spatially inhomogeneous population transfer between atomic states. As we monitor the wave packet of atoms created by this scheme, we find a damped oscillatory behavior which we attribute to sloshing and dispersion of the atoms. Oscillation frequencies range around 100 kHz, and motional dephasing between atoms happens on a timescale of 10μs. Comparison to Monte Carlo simulations of an ensemble of 1000 classical particles yields reasonable agreement for simulated ensemble temperatures between 25 and 40μK.
DOI
Atoms trapped in the evanescent field around a nanofiber experience strong coupling to the light guided in the fiber mode. However, due to the intrinsically strong positional dependence of the coupling, thermal motion of the ensemble limits the use of nanofiber trapped atoms for some quantum tasks. We investigate the thermal dynamics of such an ensemble using short light pulses to make a spatially inhomogeneous population transfer between atomic states. As we monitor the wave packet of atoms created by this scheme, we find a damped oscillatory behavior which we attribute to sloshing and dispersion of the atoms. Oscillation frequencies range around 100 kHz, and motional dephasing between atoms happens on a timescale of 10μs. Comparison to Monte Carlo simulations of an ensemble of 1000 classical particles yields reasonable agreement for simulated ensemble temperatures between 25 and 40μK.
DOI
Single-Molecule Studies of Protein Folding with Optical Tweezers
Carlos Bustamante, Lisa Alexander, Kevin Maciuba, and Christian M. Kaiser
Manipulation of individual molecules with optical tweezers provides a powerful means of interrogating the structure and folding of proteins. Mechanical force is not only a relevant quantity in cellular protein folding and function, but also a convenient parameter for biophysical folding studies. Optical tweezers offer precise control in the force range relevant for protein folding and unfolding, from which single-molecule kinetic and thermodynamic information about these processes can be extracted. In this review, we describe both physical principles and practical aspects of optical tweezers measurements and discuss recent advances in the use of this technique for the study of protein folding. In particular, we describe the characterization of folding energy landscapes at high resolution, studies of structurally complex multidomain proteins, folding in the presence of chaperones, and the ability to investigate real-time cotranslational folding of a polypeptide.
DOI
Manipulation of individual molecules with optical tweezers provides a powerful means of interrogating the structure and folding of proteins. Mechanical force is not only a relevant quantity in cellular protein folding and function, but also a convenient parameter for biophysical folding studies. Optical tweezers offer precise control in the force range relevant for protein folding and unfolding, from which single-molecule kinetic and thermodynamic information about these processes can be extracted. In this review, we describe both physical principles and practical aspects of optical tweezers measurements and discuss recent advances in the use of this technique for the study of protein folding. In particular, we describe the characterization of folding energy landscapes at high resolution, studies of structurally complex multidomain proteins, folding in the presence of chaperones, and the ability to investigate real-time cotranslational folding of a polypeptide.
DOI
Rapid tilted-plane Gerchberg-Saxton algorithm for holographic optical tweezers
Yanan Cai, Shaohui Yan, Zhaojun Wang, Runze Li, Yansheng Liang, Yuan Zhou, Xing Li, Xianghua Yu, Ming Lei, and Baoli Yao
Benefitting from the development of commercial spatial light modulator (SLM), holographic optical tweezers (HOT) have emerged as a powerful tool for life science, material science and particle physics. The calculation of computer-generated holograms (CGH) for generating multi-focus arrays plays a key role in HOT for trapping of a bunch of particles in parallel. To realize dynamic 3D manipulation, we propose a new tilted-plane GS algorithm for fast generation of multiple foci. The multi-focal spots with a uniformity of 99% can be generated in a tilted plane. The computation time for a CGH with 512×512 pixels is less than 0.1 second. We demonstrated the power of the algorithm by simultaneously trapping and rotating silica beads with a 7×7 spots array in three dimensions. The presented algorithm is expected as a powerful kernel of HOT.
DOI
Benefitting from the development of commercial spatial light modulator (SLM), holographic optical tweezers (HOT) have emerged as a powerful tool for life science, material science and particle physics. The calculation of computer-generated holograms (CGH) for generating multi-focus arrays plays a key role in HOT for trapping of a bunch of particles in parallel. To realize dynamic 3D manipulation, we propose a new tilted-plane GS algorithm for fast generation of multiple foci. The multi-focal spots with a uniformity of 99% can be generated in a tilted plane. The computation time for a CGH with 512×512 pixels is less than 0.1 second. We demonstrated the power of the algorithm by simultaneously trapping and rotating silica beads with a 7×7 spots array in three dimensions. The presented algorithm is expected as a powerful kernel of HOT.
DOI
Monday, September 7, 2020
Inverse integral transformation method to derive local viscosity distribution measured by optical tweezers†
Ruri Hidema, Zenji Yatabe, Hikari Takahashi, Ryusei Higashikawa and Hiroshi Suzuki
Complex fluids have a non-uniform local inner structure; this is enhanced under deformation, inducing a characteristic flow, such as an abrupt increase in extensional viscosity and drag reduction. However, it is challenging to derive and quantify the non-uniform local structure of a low-concentration solution. In this study, we attempted to characterize the non-uniformity of dilute and semi-dilute polymer and worm-like micellar solutions using the local viscosity at the micro scale. The power spectrum density (PSD) of the particle displacement, measured using optical tweezers, was analyzed to calculate the local viscosity, and two methods were compared. One is based on the PSD roll-off method, which yields a single representative viscosity of the solution. The other is based on our proposed method, called the inverse integral transformation method (IITM), for deriving the local viscosity distribution. The distribution obtained through the IITM reflects the non-uniformity of the solutions at the micro scale, i.e., the distribution widens above the entanglement concentrations of the polymer or viscoelastic worm-like micellar solutions.
DOI
Complex fluids have a non-uniform local inner structure; this is enhanced under deformation, inducing a characteristic flow, such as an abrupt increase in extensional viscosity and drag reduction. However, it is challenging to derive and quantify the non-uniform local structure of a low-concentration solution. In this study, we attempted to characterize the non-uniformity of dilute and semi-dilute polymer and worm-like micellar solutions using the local viscosity at the micro scale. The power spectrum density (PSD) of the particle displacement, measured using optical tweezers, was analyzed to calculate the local viscosity, and two methods were compared. One is based on the PSD roll-off method, which yields a single representative viscosity of the solution. The other is based on our proposed method, called the inverse integral transformation method (IITM), for deriving the local viscosity distribution. The distribution obtained through the IITM reflects the non-uniformity of the solutions at the micro scale, i.e., the distribution widens above the entanglement concentrations of the polymer or viscoelastic worm-like micellar solutions.
DOI
Controllable Cellular Micromotors Based on Optical Tweezers
Xiaobin Zou, Qing Zheng, Dong Wu, Hongxiang Lei
Micromotors hold exciting prospects in biomedical applications but still face a great challenge. To date, there have been few reports of micromotors with high safety, flexible controllability, and full biocompatibility. Here, a multifunctional method based on an optical tweezer system is presented to realize controllable cellular micromotors. The method not only satisfies all of the above criteria but is also independent of the cell types and materials. Optical tweezers are used to generate a dynamic scanning optical trap along a given circular trajectory, which can trap and drive a microparticle or a single cell to move along the trajectory and thus generate a microvortex. Cells within the microvortex will be controllably rotated under an action of shear stress or torque and their rotation rate and direction can be controlled by changing the scanning frequency and direction of the dynamic optical trap. The proposed method is effective for both immotile target cells and swimming target cells. Additionally, it is further applied to realize synchronous translation and rotation of cellular micromotors and to assemble controllable and fully biocompatible cellular micromotor assays. The proposed method is believed to have potential applications in targeted drug delivery, biological microenvironment monitoring and sensing, and biomedical treatment.
DOI
Micromotors hold exciting prospects in biomedical applications but still face a great challenge. To date, there have been few reports of micromotors with high safety, flexible controllability, and full biocompatibility. Here, a multifunctional method based on an optical tweezer system is presented to realize controllable cellular micromotors. The method not only satisfies all of the above criteria but is also independent of the cell types and materials. Optical tweezers are used to generate a dynamic scanning optical trap along a given circular trajectory, which can trap and drive a microparticle or a single cell to move along the trajectory and thus generate a microvortex. Cells within the microvortex will be controllably rotated under an action of shear stress or torque and their rotation rate and direction can be controlled by changing the scanning frequency and direction of the dynamic optical trap. The proposed method is effective for both immotile target cells and swimming target cells. Additionally, it is further applied to realize synchronous translation and rotation of cellular micromotors and to assemble controllable and fully biocompatible cellular micromotor assays. The proposed method is believed to have potential applications in targeted drug delivery, biological microenvironment monitoring and sensing, and biomedical treatment.
DOI
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