Abstract
Optically induced electrokinetics (OEK)-based technologies, which integrate the high-resolution dynamic addressability of optical tweezers and the high-throughput capability of electrokinetic forces, have been widely used to manipulate, assemble, and separate biological and non-biological entities in parallel on scales ranging from micrometers to nanometers. However, simultaneously introducing optical and electrical energy into an OEK chip may induce a problematic temperature increase, which poses the potential risk of exceeding physiological conditions and thus inducing variations in cell behavior or activity or even irreversible cell damage during bio-manipulation. Here, we systematically measure the temperature distribution and changes in an OEK chip arising from the projected images and applied alternating current (AC) voltage using an infrared camera. We have found that the average temperature of a projected area is influenced by the light color, total illumination area, ratio of lighted regions to the total controlled areas, and amplitude of the AC voltage. As an example, optically induced thermocapillary flow is triggered by the light image-induced temperature gradient on a photosensitive substrate to realize fluidic hydrogel patterning. Our studies show that the projected light pattern needs to be properly designed to satisfy specific application requirements, especially for applications related to cell manipulation and assembly.
Highlights
1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Introduction In the past two decades, optically induced electrokinetics (OEK)-based technologies have rapidly extended into research fields such as manipulation, fabrication and assembly on the micro/nanoscale because of their superior ability to provide flexible, dynamic, non-invasive, high-resolution, and high-throughput approaches compared to traditional modalities[1]
Experimental setup The OEK chip photoconductive electrode used in our experiments is comprised of a 120 nm indium tin oxide (ITO) layer sputtered onto 600-μm-glass and a ~1 μm a-Si:H layer deposited onto the ITO layer through plasma-enhanced chemical vapor deposition (PECVD)
The OEK chip is placed between a 50× objective (Nikon TU Plan EPI ELWD, Japan) focusing the light images generated by a commercial projector (VPL-F400X, Sony, Japan) and an optical microscope (Zoom 160, Optem, USA), as shown in Fig. 1a and Supplementary Figure S1
Summary
In the past two decades, optically induced electrokinetics (OEK)-based technologies have rapidly extended into research fields such as manipulation, fabrication and assembly on the micro/nanoscale because of their superior ability to provide flexible, dynamic, non-invasive, high-resolution, and high-throughput approaches compared to traditional modalities (e.g., electrophoresis, dielectrophoresis, optical tweezers, magnetic tweezers, and acoustic traps)[1]. As a representative application of the light image-induced temperature gradient on a photosensitive substrate, fluidic hydrogel patterning driven by optically induced thermocapillary flow is proposed.
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