Micro air bubble manipulation by electrowetting on dielectric (EWOD): transporting, splitting, merging and eliminating of bubbles

This paper describes various manipulations of micro air bubbles using electrowetting on dielectric (EWOD): transporting, splitting, merging and eliminating. First, in order to understand the response of bubbles to EWOD, the contact angle modulation is measured in a capped air bubble and confirmed to be in good agreement with the Lippmann-Young equation until saturation. Based on the contact angle measurement, testing devices for the bubble manipulations are designed and fabricated. Sequential activations of patterned electrodes generate continuous bubble transportations. Bubble splitting is successfully realized by activating a single electrode positioned in the middle of bubble base. However, it is found that there are criteria that make splitting possible only in certain conditions. For successful splitting, smaller channel gap, larger bubble size, wider splitting electrode and/or larger contact angle changes by EWOD are preferred. These criteria are verified by a series of experiments as well as a static analysis. Bubble merging is achieved by moving bubbles towards each other in two different channel configurations: (1) channel I, where bubbles are in contact with the bottom channel plate only, and (2) channel II, where bubbles in contact with the top as well as bottom channel plates. Furthermore, eliminating a bubble to the ambient air is accomplished. All the bubble manipulation techniques may provide a versatile integrated platform not only to manipulate micro objects by utilizing micro bubbles as micro carriers, but also to enable a discrete bubble-based gas analysis system.