Time-shared Optical Tweezers Research Articles

Improving the multi-functionality of optical tweezers with FPGA integration.

The development of optical tweezers aims to extend their operating function and pattern. However, excessive programming can lead to a decrease in the system's operating speed and introduce bugs or data transmission delays. In this study, we present a time-shared optical tweezers system that allows for parallel operation of multiple functions. To enable efficient data transmission, we employ a queue structure and a buffer. To assess the system's performance, we utilize a biological sample in conjunction with the optical tweezers system and scanning imaging technique. We quantify the trapping parameter while concurrently running power stabilization programs. As a result, the standard deviation of the measured stiffness is reduced by 60% in the x and y directions and 30% in the z direction, indicating a significant improvement in calibration precision. Throughout the program execution, the system maintains an operating rate of 110kHz, and the data are continuously updated in real time on the host. The system's performance demonstrates its potential for quantification and morphological reconstruction of biological samples.

Acousto-holographic optical tweezers.

Acousto-optic deflectors (AODs) allow the creation of multiple optical traps by time-sharing, that is, by rapidly cycling the laser focus between designated spatial locations. The traps thus formed are not permanent. In this Letter, we successfully demonstrate the creation of multiple and permanent traps by means of AODs driven by specially encoded radio frequency signals. The generation of complex acoustic signals allows us to treat such devices as super-fast spatial light modulators. Using this technique, it is possible to generate several static optical trap arrays and switch them at kilohertz (kHz) rates, allowing independent control of each trap group. Additionally, we discuss the compatibility of this method with precise force and position measurements, and the improvement in their frequency bandwidth compared to time-sharing optical tweezers, especially when many objects are trapped.

Time-shared optical tweezers with a microlens array for dynamic microbead arrays.

Dynamic arrays of microbeads and cells offer great flexibility and potential as platforms for sensing and manipulation applications in various scientific fields, especially biology and medicine. Here, we present a simple method for assembling and manipulating dense dynamic arrays based on time-shared scanning optical tweezers with a microlens array. Three typical examples, including the dynamic and simultaneous bonding of microbeads in real-time, are demonstrated. The optical design and the hardware setup for our approach are also described.

Optical runaway evaporation for the parallel production of multiple Bose-Einstein condensates

We report on parallel production of Bose-Einstein condensates (BECs) in steerable, multi-plexed crossed optical dipole traps. Using a conventional trap-weakening evaporation scheme, where the optical trapping power is lowered, we obtain an array of up to four independent BECs. To improve evaporation efficiency, we propose to target each crossed trap site with a narrow auxiliary laser beam, creating an escape channel for energetic atoms. We experimentally demonstrate runaway evaporation using this scheme, which is characterized by very modest weakening in atomic confinement such that high densities and elastic collision rates can be maintained. Based on discretely time-shared optical tweezers, our approach is particularly suited for addressing the problem of simultaneously cooling atoms in multiple traps clouds, providing the freedom to act locally and in a tailored fashion at individual trap sites.

Mechanical analysis of the optical tweezers in time-sharing regime

Time-sharing optical tweezers is a versatile technique to realize multiple traps for manipulating biological cells and macromolecules. It has been based on an intuitive hypothesis that the trapped viscoelastic object does not "sense" blinking of the optical beam. We present a quantitative analysis using mechanical modeling and numerical simulation, showing that the local stress and strain are jumping all the time and at all locations with the jumping amplitude independent of the recovery time of the viscoelastic material and the jumping frequency. Effects of the stress and strain jumping on the object deformation and the internal energy dissipation are analyzed.

Weak Electrolyte Dependence in the Repulsion of Colloids at an Oil–Water Interface

The two-particle interaction between 3.1-μm-diameter polystyrene latex particles at a decane-water interface was measured with time-shared optical tweezers. The water subphase contained either 0.103 mM RbCl or 0.0342 mM MgCl2, which have hydrated cations of different size but identical anions. The choice of both the anion and the concentrations makes a comparison with published data on NaCl possible and also isolates the effect of the nature of the cation on the electrostatic interaction. The measured magnitude of the dipolar force and the relative changes as a function of electrolyte were in quantitative agreement with predictions from a recently published model that uses the Langevin-Poisson-Boltzmann equation including steric effects and the polarization saturation of the medium to predict the dipolar interaction (Frydel, D.; Oettel, M. Phys. Chem. Chem. Phys. 2011, 13, 4109-4118). These results support the hypothesis that a condensed layer of counterions contributes to the electrostatic interaction between colloidal particles at an oil-water interface. Although it has been suggested that the electrostatic interactions between particles at liquid interfaces could serve as a sensitive probe of the structural details of the electric double layer, both the model predictions and experimental measurements showed a maximum change of only ~25% in the magnitude of the interaction with a change in electrolyte under the conditions tested. The ability to resolve this small change was confounded by the heterogeneous nature of the interaction. Thus, despite the apparent importance of the choice of electrolyte, the subtlety of competing effects makes it unlikely that colloidal force measurements could be used to probe the fine structure of the electric double layer.

Dynamic microbead arrays for biosensing applications

In this paper we present the development of an optical tweezers platform capable of creating on-demand dynamic microbead arrays for the multiplexed detection of biomolecules. We demonstrate the use of time-shared optical tweezers to dynamically assemble arrays of sensing microspheres, while simultaneously recording fluorescence signals in real time. The detection system is able to achieve multiplexing by using quantum dot nanocrystals as both signaling probes and encoding labels on the surface of the trapped microbeads. The encoding can be further extended by using a range of bead sizes. Finally, the platform is used to detect and identify three genes expressed by pathogenic strains of Escherichia coli O157:H7. The in situ actuation enabled by the optical tweezers, combined with multiplexed fluorescence detection offers a new tool, readily adaptable to biosensing applications in microfluidic devices, and could potentially enable the development of on-demand diagnostics platforms.

Experimental analysis of Hb oxy–deoxy transition in single optically stretched red blood cells

Raman confocal microscopy, combined with an optical stretcher, is used to study the spatial distribution and the oxidation state of hemoglobin in erythrocytes under stretching condition. In particular, a near infrared laser ( λ = 1064 nm) is used to generate multiple time-sharing Optical Tweezers to trap and stretch a single erythrocyte, while a second laser ( λ = 532 nm) acts as Raman probe. Our study demonstrates that stretching induces hemoglobin transition to the deoxygenated state. Moreover, by using Principal Component Analysis we prove the reversibility of the oxy ↦ deoxy hemoglobin transition after application of the optically induced mechanical stress.

Stability of Novel Time-Sharing Dual Optical Tweezers Using a Rotating Tilt Glass Plate

A novel realization of time-sharing optical tweezers (TSOT) is demonstrated using a tilt glass plate. Objects are trapped in the time-sharing dual traps; each of them acts like a single beam gradient trap with an effective stiffness. The effective stiffness of TSOT is experimentally measured through analysis of dynamical images. In comparison, it is numerically calculated by adopting the Monte Carlo technique. Both simulation and experimental results agree well with each other and show a good linear relationship between the effective stiffness and trap switching frequency in the range from 5 Hz to 70 Hz.

Monte-Carlo simulation of effective stiffness of time-sharing optical tweezers

The Brownian motion of a polystyrene bead trapped in a time-sharing optical tweezers (TSOT) is numerically simulated by adopting Monte-Carlo technique. By analyzing the Brownian motion signal, the effective stiffness of a TSOT is acquired at different switching frequencies. Simulation results confirm that for a specific laser power and duty ratio, the effective stiffness varies with the frequency at low frequency range, while at high frequency range it keeps constant. Our results reveal that the switching frequency can be used to control the stability of time-sharing optical tweezers in a range.

Diffusion-Sensing versus Quorum Sensing in a Model Biofilm

Cell interactions through soluble signaling molecules control differentiation, immune response and other physiologically vital processes in everything from tissue to biofilms. We tested a model of a bacterial biofilm, which uses an autoinducer (AI), N-acyl-L-homoserine lactone (AHL) for signaling, to discriminate quorum-sensing (QS) and diffusion-sensing (DS). The AI induces the transcription of a set of genes that includes the gene-encoding the AI-producing enzyme, promoting a positive feed-back. We creating a synthetic biofilm using a microfluidic network, to convey cells to an assembly area where multiple, time-shared optical tweezers are used to array them. The cells are encapsulated in a 30μm×30μm×45μm volume of hydrogel mimicking an extra-cellular matrix. To extend the size, shape and constituency of the array, we then step to an adjacent location while maintaining registration with the reference array, and repeat the process as illustrated in Figure 1(a). Using this step-and-repeat method, we formed arrays of E. coli engineered to produce AHL, which is functionally linked to a fluorescence reporter. As shown in Fig. 1(d), the threshold to induce AI production and fluorescence depends on the number of cells and the mass-transfer, indicating that QS is a side effect of DS.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Live cell lithography: Using optical tweezers to create synthetic tissue

We demonstrate a new method for creating synthetic tissue that has the potential to capture the three-dimensional (3D) complexity of a multi-cellular organism with submicron precision. Using multiple laminar fluid flows in a microfluidic network, we convey cells to an assembly area where multiple, time-shared optical tweezers are used to organize them into a complex array. The cells are then encapsulated in a 30 microm x 30 microm x 45 microm volume of photopolymerizable hydrogel that mimicks an extra-cellular matrix. To extend the size, shape and constituency of the array without loss of viability, we then step to an adjacent location while maintaining registration with the reference array, and repeat the process. Using this step-and-repeat method, we formed a heterogeneous array of E. coli genetically engineered with a lac switch that is functionally linked to fluorescence reporters. We then induced the array using ligands through a microfluidic network and followed the space-time development of the fluorescence to evaluate viability and metabolic activity.

2P2-J14 画像処理と光ピンセットの融合による動的微粒子配列の作成(ナノ・マイクロバイオシステム)

We propose a method of automatic assembly of dynamic beads array using optical tweezers combined with computer vision. Time-sharing optical tweezers generates and changes multiple laser trap potentials based on results of real-time recognition of dispersed beads on a cover glass to automatically trap, transport, align and sort the beads without collision each other. We can also use PC mouse for user interface to translate, rotate and expand the array in real-time. Automated forming of silica and colored polystyrene beads arrays are demonstrated.