Manipulation of Micro/Mini-objects by AC-Electrowetting-Actuated Oscillating Bubbles: Capturing, Carrying and Releasing

Abstract

This paper describes a new principle and experimental results of object manipulation using oscillating bubbles. AC-electrowetting is applied to oscillate an air bubble in a water medium in order to capture or repel neighboring micro/mini-objects. A series of experiments show capturing of various objects including glass beads and fish eggs, which is highly dependent on the oscillation frequency/amplitude and the density difference between the object and medium. In particular, it is shown that oscillating bubbles generate a repelling force when the density of neighboring objects is much lower than that of the medium. This result partially verifies the Nyborg/Miller’s prediction based on the radiation force, implying that the radiation force is responsible for capturing and repelling neighboring objects. In addition, the capturing force is indirectly measured by exposing the oscillating bubble along with the captured glass beads to the stream in a mini-channel. By measuring the maximum speed of the channel flow that makes all captured glass beads separated from the oscillating bubble, the capturing force is inferred based on the Stokes approximation. Finally, capturing and releasing are integrated with bubble transportation. AC-electrowetting not only oscillates a bubble, but also laterally transports the oscillating bubble on a 2-D surface. Using this scheme, a series of operations (capturing, carrying, and releasing) are achieved on a chip by sole AC-electrowetting without any acoustic excitations for bubble oscillation. This new manipulation method may provide an efficient tool for handling micro/mini-objects including biological cells.