Micro-robotics is exploding in popularity, driven by the need to control the position of individual cells and other micronsized particles. There are many examples of optical tweezer-based micro-robots; here we introduce the first microrobotic system that relies on the related technology of optoelectronic tweezers (OET). The optoelectronic micro-robots described here are straightforward to manufacture and can be programmed to carry out sophisticated, multi-axis operations. One particularly useful program is a serial combination of “load,” “transport,” and “deliver,” which can be applied to manipulate a wide range of micron-dimension payloads. Importantly, micro-robots programmed in this manner are much gentler on fragile mammalian cells than conventional OET techniques. The micro-robotic system described here was demonstrated to be useful for single-cell isolation, clonal expansion and RNA sequencing, applications that are becoming increasingly important in the post-CRISPR life-science research landscape. We propose that the OET micro-robotic system, which can be implemented using a microscope and consumer-grade optical projector, will be useful for a wide range of applications in the life sciences and beyond.
Optoelectronic tweezers (OET) is an opto-electro-fluidic micromanipulation technology that uses light-induced dielectrophoresis (DEP) for touch-free actuation of micro-scale objects in physical, chemical and biomedical studies. In this work, we introduce a new method to evaluate the behavior of particles trapped in OET traps and used this technique to study their escape mechanism. Particles experiencing negative DEP were made to move in a circular path on a microscope stage, such that the particles’ velocities and trajectories could be observed under different conditions. At high velocities, particles were observed to escape the trap vertically (into the suspending medium) before settling back onto the surface. Three-dimensional numerical simulations of electrical field distribution indicated that the vertical displacement phenomenon occurs when the particle experiences the strongest DEP force at the boundary of the light pattern, lifting the trapped particle to a region where viscous drag exceeds the local horizontal DEP force, thereby forcing it to escape OET confinement. Similar ‘hopping’ phenomena were also observed for cells and particles of different sizes. We propose that the escape mechanism clarified in this work is a general one for objects manipulated by negative DEP in an OET trap, which will be important to consider in the future design of OET-enabled micromanipulation tools for a wide range of applications.
Light patterned dielectrophoresis or optoelectronic tweezers (OET) has been proved to be an effective micromanipulation technology for cell separation, cell sorting and control of cell interactions. Apart from being useful for cell biology experiments, the capability of moving small objects accurately also makes OET an attractive technology for other micromanipulation applications. In particular, OET has the potential to be used for efficiently and accurately assembling small optoelectronic/electronic components into circuits. This approach could produce a step change in the size of the smallest components that are routinely assembled; down from the current smallest standard component size of 400×200 μm (0402 metric) to components a few microns across and even nanostructured components. In this work, we have demonstrated the use of OET to manipulate conductive silver nanowires into different patterns. The silver nanowires (typical diameter: 60 nm; typical length: 10 μm) were suspended in a 15 mS/m solution of KCL in water and manipulated by positive dielectrophoresis force generated by OET. A proof-of-concept demonstration was also made to prove the feasibility of using OET to manipulate silver nanowires to form a 150-μm-long conductive path between two isolated electrodes. It can be seen that the resistance between two electrodes was effectively brought down to around 700 Ω after the silver nanowires were assembled and the solution evaporated. Future work in this area will focus on increasing the conductivity of these tracks, encapsulating the assembled silver nanowires to prevent silver oxidation and provide mechanical protection, which can be achieved via 3D printing and inkjet printing technology.
Micro light-emitting diode (micro-LED) arrays based on an AlInGaN structure have attracted much interest recently as
light sources for data communications. Visible light communication (VLC), over free space or plastic optical fibre (POF), has become a very important technique in the role of data transmission. The micro-LEDs which are reported here contain pixels ranging in diameter from 14 to 84μm and can be driven directly using a high speed probe or via complementary metal-oxide semiconductor (CMOS) technology. The CMOS arrays allow for easy, computer control of
individual pixels within arrays containing up to 16×16 elements. The micro-LEDs best suited for data transmission have
peak emissions of 450nm or 520nm, however various other wavelengths across the visible spectrum can also be used.
Optical modulation bandwidths of over 400MHz have been achieved as well as error-free (defined as an error rate of
<1x10-10) data transmission using on-off keying (OOK) non-return-to-zero (NRZ) modulation at data rates of over
500Mbit/s over free space. Also, as a step towards a more practical multi-emitter data transmitter, the frequency response of a micro-LED integrated with CMOS circuitry was measured and found to be up to 185MHz. Despite the reduction in bandwidth compared to the bare measurements using a high speed probe, a good compromise is achieved from the additional control available to select each pixel. It has been shown that modulating more than one pixel simultaneously can increase the data rate. As work continues in this area, the aim will be to further increase the data transmission rate by modulating more pixels on a single device to transmit multiple parallel data channels simultaneously.