Two-dimensional manipulation of droplets on a single-sided continuous optoelectrowetting digital microfluidic chip

Abstract

Digital microfluidic chips are liquid processors that perform biochemical assays by moving, merging and splitting droplets using the electrowetting effect. Yet, hardwiring electrowetting chips becomes tedious as soon as they include more than a few dozen electrodes. Single-sided continuous opto-electrowetting, where the electrowetting effect of a featureless semiconductor film is controlled by light patterns is a promising solution to this hardwiring bottleneck, but so far two-dimensional manipulation of droplets is still difficult. Here, we demonstrate the manipulation of droplets along arbitrary directions by using Z-shaped light patterns that rotate the electric field by an arbitrary angle. We provide a theoretical model for driving droplets in different directions. It is verified by Comsol simulations and experiments. Optimization of the width of the notches provides quite large increase of the driving voltage in the y-direction. The chip can move dyed water droplets in the y-direction at a maximum speed of 4.86 mm/s. Such multidimensional droplet driving opens new possibilities for single-sided continuous optoelectrowetting such as merging droplets that are not in line, efficient droplet mixing, and bypassing droplets to avoid coalescence.