Scanning Optical Tweezers Research Articles

Light‐Driven Micronavigators for Directional Migration of Cells

AbstractCell migration is an essential physiological process in the life cycle of cells, playing a crucial role in cancer metastasis, neural development, and cellular immune response. However, achieving precise control of cell migration at single‐cell level is challenging due to the intricate and diverse microenvironments of cells. Here, an optical technique is presented that utilizes light‐actuated micronavigators to guide the directional migration of individual cells both in vitro and in vivo. Employing high‐speed scanning optical tweezers, micronavigators near target cells are trapped and rotated at a rotation speed of up to 12 000 rpm, which, to the best of knowledge, represents the fastest rotation of light‐driven micromotors in a biological environment to date. The micronavigators generate a powerful fluid shear force (up to 40 pN) which can guide the migration of immune and nerve cells in a predetermined direction. Furthermore, micronavigators are employed to guide cell migration in various biological systems, including lab‐on‐a‐chip devices and blood vessels within living animals. This technique offers new opportunities for controlling cell migration, enabling precise immune activation, and neuron repair at the single‐cell level.

Optically Programmable Living Microrouter in Vivo.

With high reconfigurability and swarming intelligence, programmable medical micromachines (PMMs) represent a revolution in microrobots for executing complex coordinated tasks, especially for dynamic routing of various targets along their respective routes. However, it is difficult to achieve a biocompatible implantation into the body due to their exogenous building blocks. Herein, a living microrouter based on an organic integration of endogenous red blood cells (RBCs), programmable scanning optical tweezers and flexible optofluidic strategy is reported. By harvesting energy from a designed optical force landscape, five RBCs are optically rotated in a controlled velocity and direction, under which, a specific actuation flow is achieved to exert the well-defined hydrodynamic forces on various biological targets, thus enabling a selective routing by integrating three successive functions, i.e., dynamic input, inner processing, and controlled output. Benefited from the optofluidic manipulation, various blood cells, such as the platelets and white blood cells, are transported toward the damaged vessel and cell debris for the dynamic hemostasis and targeted clearance, respectively. Moreover, the microrouter enables a precise transport of nanodrugs for active and targeted delivery in a large quantity. The proposed RBC microrouter might provide a biocompatible medical platform for cell separation, drug delivery, and immunotherapy.

Measurement of red blood cell deformability during morphological changes using rotating-glass-plate-based scanning optical tweezers.

It is important to measure the deformability of red blood cells (RBCs) before transfusion, which is a key factor in the gas transport ability of RBCs and changes during storage of RBCs in vitro. Moreover, the morphology of RBCs also changes during storage. It is proposed that the change in morphology is related to the change in deformability. However, the efficiency of typical methods that use particles as handles is low, especially in the deformability measurement of echinocyte and spherocytes. Therefore, the deformability of RBCs with different morphologies is hard to be measured and compared in the same experiment. In this study, we developed a cost-effective and efficient rotating-glass-plate-based scanning optical tweezers device for the measurement of deformability of RBCs. The performance of this device was evaluated, and the deformability of three types of RBCs was measured using this device. Our results clearly show that the change of erythrocyte morphology from discocyte to echinocyte and spherocyte during storage in vitro is accompanied by a decrease in deformability.

Optical manipulation of neuronal mitochondria using scanning optical tweezers

Mitochondria play a crucial role in the physiological functions and energy metabolism of neurons, which can help in the understanding of complex biochemical reactions associated with various neurodegenerative diseases. Neurons, being highly differentiated terminal cells, require a greater number of mitochondria than ordinary cells to generate significant amounts of ATP, which is necessary for the growth of differentiated neuronal structures like axons and dendrites and the transmission of electrical signals along neuronal axons. Advancements in imaging technology, electrophysiology, and fluorescence targeting labeling have facilitated the study of mitochondrial movements in neurons and axons. However, disordered mitochondrial movements can hinder their analysis and characterization. Thus, it becomes necessary to artificially control their transport. Here, we demonstrate the utilization of scanning optical tweezers (SOTs) on the stable trapping and precise transport of soma or axon of neurons and enable. The presented method provides an optical approach to the control of mitochondria or other organelles in complex and variable biological environment.

Using time-shared scanning optical tweezers assisted two-photon fluorescence imaging to establish a versatile CRISPR/Cas12a-mediated biosensor

Based on the admirable precision to identify target nucleic acids and the particular trans-cleavage feature, CRISPR/Cas12a system is a useful means to further improve the sensing accuracy and the design flexibility of fluorescence biosensors. However, the current construction concepts still suffer from insufficient sensitivity, unsuitable for complicated real samples and limited detection species. In this work, much efforts are achieved to address these obstacles. At first, we adopt a microsphere sustained signal enrichment, under which a home-made time-shared scanning optical tweezers assisted fluorescence imaging is employed to guarantee a stable excitation and also realize multiflux measurement. Furthermore, by taking advantage of the low background merit of the near-infrared light excited two-photon fluorescence, a commendable anti-interference capability is endowed to operate in complex media. After utilizing a functional DNA (e.g. aptamer and DNAzyme) regulated mediation pathway to respond non-nucleic acid analytes (alpha fetal protein and Pb2+), the newly-established CRISPR/Cas12a-mediated fluorescence biosensor is found to display favorable assay performance. More importantly, our analytical methodology can act as a versatile and reliable toolbox in various applications such as disease diagnosis and environmental analysis, propelling the development of CRISPR system in biosensing field.

Light-driven upconversion fluorescence micromotors

Light-driven micromotors with high spatial resolution are powerful tools for targeted drug delivery and biomedical diagnosis. To combine the function of biosensing, light-driven micromotors have been modified with fluorescence materials such as quantum dots or dyes. However, these fluorescence micromotors are generally driven and excited by ultraviolet or visible lights, which may cause photo-damage to biological cells or tissues. Here we propose upconversion fluorescence micromotors (UCFMs) constructed by lanthanide (NaYF4: Yb3+, Er3+) doped microrods that were driven and excited by near-infrared lights. The UCFMs were moved to the surfaces of the targeted cancer cells using scanning optical tweezers (SOTs). The upconversion fluorescence spectra were measured to determine the temperatures of the cells, with an absolute sensitivity from 1.71 × 10−3 to 1.74 × 10−3 K−1 and a relative sensitivity from 0.53% to 0.68% K−1. The UCFMs were then optically driven to actuate the local flow to deliver the polystyrene (PS) microparticles and doxorubicin-loaded mesoporous silica nanoparticles to the vicinity of the cancer cells. By integrating the actuator and sensor into a single device, the UCFMs hold great potential for applications to precise biosensing, single-cell biomedical analysis, and targeted drug delivery.

Dual-Arm Visuo-Haptic Optical Tweezers for Bimanual Cooperative Micromanipulation of Nonspherical Objects.

Cooperative manipulation through dual-arm robots is widely implemented to perform precise and dexterous tasks to ensure automation; however, the implementation of cooperative micromanipulation through dual-arm optical tweezers is relatively rare in biomedical laboratories. To enable the bimanual and dexterous cooperative handling of a nonspherical object in microscopic workspaces, we present a dual-arm visuo-haptic optical tweezer system with two trapped microspheres, which are commercially available end-effectors, to realize indirect micromanipulation. By combining the precise correction technique of distortions in scanning optical tweezers and computer vision techniques, our dual-arm system allows a user to perceive the real contact forces during the cooperative manipulation of an object. The system enhances the dexterity of bimanual micromanipulation by employing the real-time representation of the forces and their directions. As a proof of concept, we demonstrate the cooperative indirect micromanipulation of single nonspherical objects, specifically, a glass fragment and a large diatom. Moreover, the precise correction method of the scanning optical tweezers is described. The unique capabilities offered by the proposed dual-arm visuo-haptic system can facilitate research on biomedical materials and single-cells under an optical microscope.

Optically Manipulated Neutrophils as Native Microcrafts In Vivo.

As the first line of host defense against invading pathogens, neutrophils have an inherent phagocytosis capability for the elimination of foreign agents and target loading upon activation, as well as the ability to transmigrate across blood vessels to the infected tissue, making them natural candidates to execute various medical tasks in vivo. However, most of the existing neutrophil-based strategies rely on their spontaneous chemotactic motion, lacking in effective activation, rapid migration, and high navigation precision. Here, we report an optically manipulated neutrophil microcraft in vivo through the organic integration of endogenous neutrophils and scanning optical tweezers, functioning as a native biological material and wireless remote controller, respectively. The neutrophil microcrafts can be remotely activated by light and then navigated to the target position along a designated route, followed by the fulfillment of its task in vivo, such as active intercellular connection, targeted delivery of nanomedicine, and precise elimination of cell debris, free from the extra construction or modification of the native neutrophils. On the basis of the innate immunologic function of neutrophils and intelligent optical manipulation, the proposed neutrophil microcraft might provide new insight for the construction of native medical microdevices for drug delivery and precise treatment of inflammatory diseases.

In Vivo Optofluidic Switch for Controlling Blood Microflow.

Control of blood microflow is crucial for the prevention and therapy of blood disorders, such as cardiovascular diseases and their complications. Conventional control strategies generally implant exogenous synthetic materials into blood vessels as labeling markers or actuating sources, which are invasive and incompatible with biological systems. Here, a label‐free, noninvasive, and biocompatible device constructed from natural red blood cells (RBCs) for controlling blood microflow in vivo is reported. The RBCs, optically manipulated, arranged, and rotated using scanning optical tweezers, can function as an optofluidic switch for targeted switching, directional enrichment, dynamic redirecting, and rotary actuation of blood microflow inside zebrafish. The regulation precision of the switch is determined to be at the single‐cell level, and the response time is measured as ≈200 ms using a streamline tracking method. This in vivo optofluidic switch may provide a biofriendly device for exploring blood microenvironments in a noncontact and noninvasive manner.

Scanning holographic optical tweezers.

The aim of this Letter is to introduce a new optical tweezers approach, called scanning holographic optical tweezers (SHOT), which drastically increases the working area (WA) of the holographic-optical tweezers (HOT) approach, while maintaining tightly focused laser traps. A 12-fold increase in the WA is demonstrated. The SHOT approach achieves its utility by combining the large WA of the scanning optical tweezers (SOT) approach with the flexibility of the HOT approach for simultaneously moving differently structured optical traps in and out of the focal plane. This Letter also demonstrates a new heuristic control algorithm for combining the functionality of the SOT and HOT approaches to efficiently allocate the available laser power among a large number of traps. The proposed approach shows promise for substantially increasing the number of particles that can be handled simultaneously, which would enable optical tweezers additive fabrication technologies to rapidly assemble microgranular materials and structures in reasonable build times.

Study of in vitro RBCs membrane elasticity with AOD scanning optical tweezers.

The elasticity of red cell membrane is a critical physiological index for the activity of RBC. Study of the inherent mechanism for RBCs membrane elasticity transformation is attention-getting all along. This paper proposes an optimized measurement method of erythrocytes membrane shear modulus incorporating acousto-optic deflector (AOD) scanning optical tweezers system. By use of this method, both membrane shear moduli and sizes of RBCs with different in vitro times were determined. The experimental results reveal that the RBCs membrane elasticity and size decline with in vitro time extension. In addition, semi quantitative measurements of S-nitrosothiol content in blood using fluorescent spectrometry during in vitro storage show that RBCs membrane elasticity change is positively associated with the S-nitrosylation level of blood. The analysis considered that the diminished activity of the nitric oxide synthase makes the S-nitrosylation of in vitro blood weaker gradually. The main reason for worse elasticity of the in vitro RBCs is that S-nitrosylation effect of spectrin fades. These results will provide a guideline for further study of in vitro cells activity and other clinical applications.

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.

Influence of time delay on trap stiffness in computer-controlled scanning optical tweezers

In scanning optical tweezers, the positions of optically trapped particles are individually controlled by periodically updating the scan data, which make up the data set of time-shared positions of a single-beam optical trap. The scan data are usually generated from the computer and are then transferred to the controller that sends electrical signals to the scanner. During the data generation and transfer phases, a short but noticeable time delay, indicated by the updating of scan data, is incurred and the scanner momentarily stalls. In this paper, we investigate the influence of this time delay on the trapped beads in scanning optical tweezers having a low scanning frequency. To understand the influence of the time delay, we analyzed the motions of two beads, trapped by the scanning optical traps, having a finite distance between them. We found that the trapped beads undergo relatively large vibrations during scanning, and the trap stiffness for one of the two beads significantly decreases with the time delay. We anticipate that our observation is essential to design scanning optical traps that need to manipulate trapped beads in real-time.

Parametrization of trapping forces on microbubbles in scanning optical tweezers

We present the results of experiments to parametrize the trapping forces on microbubbles held in scanning optical tweezers. We determine the dependence on microbubble and trap dimensions of the maximum axial trapping force, and the dependence on bubble size of the maximum transverse drag force for which the bubble remains trapped. We have also determined the spring constant of the optical trap in the radial direction, which is the first measurement of this important parameter for a low refractive index particle, or for any object in a time-averaged optical potential.

Trapping and manipulation of microscopic bubbles with a scanning optical tweezer

The authors have demonstrated three-dimensional trapping of ultrasound contrast agent microbubbles using a circularly scanning optical tweezers to confine the microbubble in a time-averaged optical potential. They have measured the maximum transverse drag force that may be applied to the trapped microbubble before it escapes and found that this decreases significantly at small trap radii. They explain this in terms of the relative volumes of the microbubble and the trap and anticipate that this feature will be important in experiments involving the insonation of optically trapped microbubbles.

Diffusion of colloids in one-dimensional light channels

Single-file diffusion (SFD), prevalent in many chemical and biological processes,refers to the one-dimensional motion of interacting particles in pores whichare so narrow that the mutual passage of particles is excluded. Since thesequence of particles in such a situation remains unaffected over timet, this leads to strong deviations from normal diffusion, e.g. an increaseof the particle mean-square-displacement as the square root oft. We present experimental results of the diffusive behaviour of colloidal particles inone-dimensional channels with varying particle density. The channels are realizedby means of a scanning optical tweezers. Based on a new analytical approach(Kollmann 2003 Phys. Rev. Lett. 90 180602) for SFD, we can predict quantitatively thelong-time, diffusive behaviour from the short time density fluctuations in our systems.