On-chip micromanipulation by AC-EWOD driven twin bubbles

Abstract

A novel on-chip micromanipulation method has been developed by which the streaming generated by oscillating twin bubbles actuated by alternating current electrowetting-on-dielectric (AC-EWOD) was used to manipulate micro/bio-objects in an aqueous medium. First, the behavior of a bubble placed on a plain EWOD electrode submerged in a water chamber was investigated under different AC-EWOD actuation conditions such as various frequencies and voltages using high-speed images. The results showed that the bubble oscillation amplitude highly depended on the applied frequency and was proportional to the strength of the bubble-induced streaming. To investigate the effect of the streaming, the forces generated by the oscillating bubble-induced streaming were indirectly measured using Stokes’ drag approximation under the different AC-EWOD actuation conditions at various distances between the bubble and a fish egg. The maximum force was calculated as 9μN. To improve the controllability for manipulating objects, a system of twin bubbles was proposed, and twin-bubble-induced streaming patterns at different distances between the twin bubbles were experimentally studied on microfabricated AC-EWOD chips to determine the optimum distance. To transport twin bubbles on microfluidic chips, the arrays of EWOD electrodes were microfabricated, and EWOD signals were controlled by a digital I/O board using custom-programmed 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.