Bubble-induced streaming for micro-object manipulation

A novel micromanipulation method has been developed where alternating current electrowetting-on-dielectric (AC-EWOD)-driven twin bubbles manipulate micro/bio-objects in a microfluidic chip filled with aqueous solution. First, the behavior of a bubble sitting on an EWOD electrode submerged in a water chamber was investigated under different AC-EWOD actuation conditions such as frequencies and voltages. The results show that the bubble oscillation amplitude highly depended on the applied frequency and was proportional to the strength of bubble-induced streaming. To improve the controllability of manipulating objects, twin bubbles-induced streaming patterns in the different distances between the twin bubbles were experimentally studied on patterned EWOD electrodes. To transport bubbles in a microfluidic chip, the arrays of EWOD electrodes were microfabricated and EWOD signals were controlled by a digital I/O board through a custom-made Labview code. The transportation of twin bubbles was successfully demonstrated by sequentially activating the arrays of EWOD electrodes. Finally, as proof of the feasibility of the proposed method, the manipulation of a fish egg by AC-EWOD-driven twin bubbles was experimentally achieved.