Mobile oscillating bubble actuated by AC-electrowetting-on-dielectric (EWOD) for microfluidic mixing enhancement

Abstract

This paper describes a novel microfluidic mixing method using an alternating current electrowetting-on-dielectric (AC-EWOD)-driven mobile oscillating bubble. An AC-EWOD-driven bubble can generate a microstreaming flow and be simultaneously transported on the two-dimensional surface of patterned electrodes covered with a hydrophobic dielectric layer in a microfluidic chip filled with an aqueous medium. When a bubble is actuated by AC-EWOD at a certain frequency (100Hz), it oscillates and simultaneously generates a microstreaming flow around itself owing to its compressibility. The flow induced by the bubble oscillation is strong enough to be applied for enhancement of fluid mixing. The oscillating bubble also can be transported on the array of EWOD electrodes using the same AC-EWOD actuation. The bubble behavior under different AC-EWOD conditions has been investigated, and the bubble oscillation amplitudes are characterized by using a high-speed camera. The flow visualization experiments show that the strength of the microstreaming flow is proportional to the bubble oscillation amplitude. For a relative comparison of mixing enhancement, four cases with different combinations of the two actuations (bubble oscillation and transportation) have been tested; the results show that a bubble simultaneously actuated by both actuations shows overwhelming mixing performance with reduced mixing time. This method can be applied to efficient mixing tools in microfluidic systems, with the benefits of a small size and high compatibility.