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(a) Schematic diagram of an OET device. The chamber consists of two ITO electrodes with an AC voltage applied across them. The black arrows show the non-uniform electric field resulting from the resistivity change caused by the illumination of the a-Si:H photoconductive layer. The particle is attracted to the illuminated area by positive DEP force or pushed away by negative DEP force depending on its effective permittivity; (b) schematic experimental setup; (c) SEM image of silver-coated PMMA microspheres at 700x magnification; microscope images of a metal microsphere (d) before and (e) after being trapped by a 200 μm diameter circular light pattern.
Source publication
Optoelectronic tweezers (OET) or light-patterned dielectrophoresis (DEP) has been developed as a micromanipulation technology for controlling micro- and nano-particles with applications such as cell sorting and studying cell communications. Additionally, the capability of moving small objects accurately and assembling them into arbitrary 2D pattern...
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... and experimental setup. As shown in Fig. 1(a), a typical OET device consists of two elec- trodes made of indium tin oxide (ITO) coated glass slides which form a sample chamber. The bottom electrodes has a further thin coating of photoconductive semiconductor material, typically hydrogenated amorphous silicon (a-Si:H). A liquid buffer containing micro-particles is placed between ...
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... optical setup used in the experiment is shown in Fig. 1(b). As shown, the light pattern from the DMD projector (Dell 1510X) is introduced into the microscope (Olympus BX51, with motorised Prior Scan111 stage) and imaged onto the OET device, which is driven by the amplified signal from the function generator (TG5011 LX1 with amplifier Thurlby Thandor Instrument WA31). The camera is used to ...
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... metallic microspheres used in this work are silver-coated PMMA beads with diameters around 50 μm (size range: 45 μm to 53 μm) and an average silver-shell thickness of 250 nm (Cospheric, PMPMS-AG-1.53). Figure 1(c) shows a Scanning Electron Microscopy (SEM) image of the silver-coated PMMA microspheres at 700x magnification. In this work, an aver- age bead diameter of 50 μm was used to calculate the DEP force. ...
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... voltage was used, which is similar to the bias conditions used to manipulate other silver nanoscale objects in OET devices 18 . After adding an AC voltage across the OET device and projecting a light pattern onto its photoconduc- tive layer, the metallic microspheres were attracted to the illumination region due to positive DEP force, as shown in Fig. 1 (d,e). In this work the heating effect was not taken into account for the following reasons. Firstly, the silver-coated beads trapped by light patterns did not move when the applied voltage was turned off, indicating the thermophoresis effect is not strong enough to move these beads. Secondly, the optical power density of the light ...
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... this case, Faxen's correction based on the radius of the microsphere (25 μm) was used to calculate the DEP force 10 . To further clarify the influence of the distance between the bead and the substrate to the force, viscous drag force for a metallic bead moving at 3200 μm/s was calculated using Faxen's correction based on different distances between the bead centre and the a-Si:H surface (see results in Supplementary Fig. S1). As shown, although the force changes as the distance changes, the expected separation (less than a few hundred nanometers 23 ) will have little effect on the forces calculated. ...
Citations
... (DEP) (rather than the forces generated by direct photon momentum), OET systems typically exert a stronger manipulation force for a given intensity of light compared to OT. [136,188] The applications of OET include trapping, [189] bead positioning, [190] and manipulation and assembly of micro particles. [191] More Advanced Trapping techniques have emerged, which use machine learning technologies to automatically localize and trap microrobots in the OT. [192] Applications such as the selection and isolation of single cells for clonal expansion and RNAsequencing, selection and targeting of cell-cell fusion partners, and collection of precious microtissue specimens from complex samples [136] are also being explored. ...
Maturation of robotics research and advances in the miniaturization of machines have contributed to the development of microbots and enabled new technological possibilities and applications. Microbots have a wide range of applications, including the navigation of confined spaces, environmental monitoring, micro-assembly and manipulation of small objects, and in vivo micro-surgeries and drug delivery. Actuators are among the most critical components that define the performance of robots. A comprehensive review of the actuation mechanisms that have been employed in mobile microbots is provided, including piezoelectric, magnetic, electrostatic, thermal, acoustic, biological, chemical, and optical actuation, with a focus on the most recent development and methodologies.
... The photoconductive substrate is used to induce a nonuniform electric field in the liquid medium above, and the electric field interacts with the sample in the medium to generate a DEP force that controls its motion [73,74]. Unlike the OT, the OET not only has a greater manipulation force that can control larger microrobots but also can operate multiple microrobots simultaneously [75][76][77][78]. Many scholars have recently combined the OET actuation with photopolymerization technology. ...
Field-controlled microrobots have attracted extensive research in the biological and medical fields due to the prominent characteristics including high flexibility, small size, strong controllability, remote manipulation, and minimal damage to living organisms. However, the fabrication of these field-controlled microrobots with complex and high-precision 2- or 3-dimensional structures remains challenging. The photopolymerization technology is often chosen to fabricate field-controlled microrobots due to its fast-printing velocity, high accuracy, and high surface quality. This review categorizes the photopolymerization technologies utilized in the fabrication of field-controlled microrobots into stereolithography, digital light processing, and 2-photon polymerization. Furthermore, the photopolymerized microrobots actuated by different field forces and their functions are introduced. Finally, we conclude the future development and potential applications of photopolymerization for the fabrication of field-controlled microrobots.
... The primary cell manipulation principle is the DEP forces led by light-induced local electric-field gradients on photoconductive layer. Moreover, the sandwich structure OET chip containing two indium tin oxides (ITO) glasses, medium layer and photoconductive layer has manipulated different targets including cells [3], protists [4], micro-robots [5], metal beads [6], etc. Typically, Christian et al. [7] defined robust photoresist sandwiched microfludic channel in OET device and produced optimal conditions for high speed particle focusing. ...
Optoelectronic tweezers (OETs) based on dielectrophoresis (DEP) force is a valuable tool for the manipulation of particles and cells. However, DEP-based methods that can measure the electrical parameters are always preformed on static metal electrode DEP systems. Here, we present a partitioned single-sided OET chip that combines an OET system and microfluidic channel. Unlike classical sandwich-structure OET chip, the single-sided chip is close to the metal electrode DEP system but can switch functions easily. Numerical simulations are studied to analyze the electric field on a microfluidic chip and pro-vide data for characterizing cell electric properties. The focusing and electro-rotation are successfully realized by partitioned multi-signal OET system. By analyzing the rotation speed, some specific electric param-eters of Raw cells are characterized. The work has laid a foundation for OET-based single-sided chip fabrication and experiment validation.
... The former approach only allows the manipulation of objects within the field of view, while the later approach allows the manipulation of objects beyond the field of view. In addition, motorized positioning stage allows accurate control of the translational speed of the trapped object, [75][76][77] which is important to study the exerted manipulation force by the OET system. In some cases [ Fig. 3(a)], light patterns are projected onto the OET device from the top of the device, which shares the same objective lens for observation and brightfield illumination. ...
... Commercially-available DMD projector and liquid crystal display (LCD) projector are the commonly used light sources for an OET platform. [74][75][76][77][78][79][80][81][82] Self-built optical systems consisting of a DMD chip and a light source (e.g. LED, laser, and Hg lamp) have also be used for OET research. ...
... Non-specific surface-particle adherence 119,120 and electrostatic particle-particle interactions 121 can undermine the manipulation performance of OET. To minimize these effects, various methods were developed, such as using a chemical surfactant, 77 antifouling coating, 119 lipid bilayer, 83 and novel device structure. 120 It is also worth mentioning that the OET manipulation force for a specific target can be adjusted by a variety of parameters, such as optical power density, light pattern distribution, medium conductivity, frequency and magnitude of applied electric field. ...
The rapid development of micromanipulation technologies has opened exciting new opportunities for the actuation, selection and assembly of a variety of non-biological and biological nano/micro-objects for applications ranging from microfabrication, cell analysis, tissue engineering, biochemical sensing, to nano/micro-machines. To date, a variety of precise, flexible and high-throughput manipulation techniques have been developed based on different physical fields. Among them, optoelectronic tweezers (OET) is a state-of-art technique that combines light stimuli with electric field together by leveraging the photoconductive effect of semiconductor materials. Herein, the behavior of micro-objects can be directly controlled by inducing the change of electric fields on demand in an optical manner. Relying on this light-induced electrokinetic effect, OET offers tremendous advantages in micromanipulation such as programmability, flexibility, versatility, high-throughput and ease of integration with other characterization systems, thus showing impressive performance compared to those of many other manipulation techniques. A lot of research on OET have been reported in recent years and the technology has developed rapidly in various fields of science and engineering. This work provides a comprehensive review of the OET technology, including its working mechanisms, experimental setups, applications in non-biological and biological scenarios, technology commercialization and future perspectives.
... The primary cell manipulation principle is the DEP forces led by lightinduced local electric-field gradients on photoconductive layer. Moreover, the sandwich structure OET chip containing two indium tin oxides (ITO) glasses, medium layer and photoconductive layer has manipulated different targets including cells [3], protists [4], micro-robots [5], metal beads [6], etc. Apart from sandwich structure, Aaron T. Ohta et al. [7] introduced a single-sided lateral-field OET chip to facilitate its integration with microfluidic channels. Shuailong Zhang et al. [8] removed photoconductive layer parts and created a patterned OET chip to keep cells immobilized for a long time. ...
... This nonuniform electric field interacts with the samples in the liquid medium, producing DEP force that can control their positions [62]. OETs are capable of exerting stronger manipulation force (nanonetwons, 10 −9 N) and actuating larger objects (sizes over 100 microns) compared with OTs [63][64][65], and in addition, by projecting independently varying illumination patterns, it is particularly straightforward to use OET for parallel manipulation (e.g., creating 10,000 traps at the same time) [59]. These features make OETs an ideal optical tool to control microrobots. ...
Light, as an external stimulus or energy source, is capable of driving the motion of microrobots with the advantages of dynamic programmable, wireless, and remote manipulation on demand with high spatial and temporal resolution. The focus of this chapter is on the state-of-the-art light-driven microrobots, which can do mechanical work by harvesting light energy or use light to control the use of other energy sources. Based on different operating principles, light-driven microrobots are classified into three categories, namely, optical microrobot, opto-mechanical soft microrobot, and opto-chemical microrobot. The working mechanisms and applications of each category of light-driven microrobots are presented and discussed, including their advantages and limitations. Finally, we provide a critical outlook for this field and highlight the challenges together with some perspectives and solutions. By providing a comprehensive review of the light-driven microrobotic technology, this chapter is expected to incubate innovative ideas and promote future development and new applications of light-driven microrobots.
... Optoelectronic tweezer (OET) is an optical micromanipulation technology that relies on optically induced-dielectrophoresis (ODEP) force for the control of micro-/nano-scale objects [1][2][3][4][5]. Based on light patterned electric fields, OET is capable of exerting pico-to-nano Newton manipulation forces [6,7], and is well suited for parallel and independent control of multiple objects [1,3,8,9]. Because of these outstanding micromanipulation capabilities, OET has been widely used to manipulate and assemble bio-analytes and molecules [10][11][12], cells of different species [13][14][15][16][17][18][19][20], nano-/microparticles [8,[21][22][23][24][25][26], electronic/ photonic components [27][28][29][30][31][32][33], and microrobots [9], thus offering a powerful scientific tool to investigate the microscopic world for physical, chemical, and biological studies. ...
... In this case, the light pattern was kept stationary while the motorized stage was programmed to move linearly, which propelled the trapped bead to move in the opposite direction. Due to the viscous damped nature of the experiment, the beads quickly equilibrate to a constant velocity at which the DEP actuation force exerted on the bead is equal to the viscous drag force given by Stokes law [7,17,25,38], i.e., ...
... To probe the phenomenon of reduced force found for thick doughnut rings and to clarify the physical mechanism for the observed experimental results, simulations were carried out in COMSOL Multiphysics using the AC/DC module (COMSOL Inc., Burlington, MA, accessed via license obtained through CMC Microsystems, Kingston, Canada) [6][7][8][9]. The model length (x axis) and height (y axis) were set to 500 μm and 150 μm, respectively. ...
Optoelectronic tweezer (OET) is a useful optical micromanipulation technology that has been demonstrated for various applications in electrical engineering and most notably cell selection for biomedical engineering. In this work, we studied the use of light patterns with different shapes and thicknesses to manipulate dielectric micro-particles with OET. It was demonstrated that the maximum velocities of the microparticles increase to a peak and then gradually decrease as the light pattern’s thickness increases. Numerical simulations were run to clarify the underlying physical mechanisms, and it was found that the observed phenomenon is due to the co-influence of horizontal and vertical dielectrophoresis forces related to the light pattern’s thickness. Further experiments were run on light patterns with different shapes and objects of different sizes and structures. The experimental results indicate that the physical mechanism elucidated in this research is an important one that applies to different light pattern shapes and different objects, which is useful for enabling users to optimize OET settings for future micro-manipulation applications.
... A longpass filter (DHC GCC-300116) and a shortpass filter (YIZHENG LASER YZ-400-550LGP-Y5) are placed in light path. The longpass filter is placed in projected light path to filter blue light that heat a-Si:H film and retain green red light with good photoelectric effect [19] . The shortpass filter is placed in front of the CCD camera can filter out strong red light so that the image can be clearly recorded. ...
... A longpass filter (DHC GCC-300116) and a shortpass filter(YIZHENG LASER YZ-400-550LGP-Y5) are placed in light path. The longpass filter is placed in projected light path to filter blue light that heat a-Si:H film and retain green red light with good photoelectric effect [19] . The shortpass filter is placed in front of the CCD camera can filter out strong red light so that the image can be clearly recorded. ...
... By projecting illuminated and dark regions onto the photoconductive substrate, lightactivated virtual electrodes can be formed in OET, which induce nonuniform electric fields producing DEP forces [42][43][44][45][46][47][48][49][50][51][52] . OET is capable of generation of forces on the order of nanoNetwons (10 −9 N) 53 , which permits the manipulation of objects with sizes >100 μm 54,55 . In addition, it is particularly straightforward to use OET for parallel manipulation [41][42][43][44][45] , simply by projecting movies of moving shapes into a microscope. ...
There is great interest in the development of micromotors which can convert energy to motion in sub-millimeter dimensions. Micromachines take the micromotor concept a step further, comprising complex systems in which multiple components work in concert to effectively realize complex mechanical tasks. Here we introduce light-driven micromotors and micromachines that rely on optoelectronic tweezers (OET). Using a circular micro-gear as a unit component, we demonstrate a range of new functionalities, including a touchless micro-feed-roller that allows the programming of precise three-dimensional particle trajectories, multi-component micro-gear trains that serve as torque- or velocity-amplifiers, and micro-rack-and-pinion systems that serve as microfluidic valves. These sophisticated systems suggest great potential for complex micromachines in the future, for application in microrobotics, micromanipulation, microfluidics, and beyond.
