Droplet Interface Oscillations using Electrowetting on Dielectric EWOD for Open Chip Microfluidic Applications

Abstract

Droplet manipulation on microfluidic platform has gained significant importance due to its applicability to various healthcare technologies, where larger equipment can be reduced to portable handheld systems based on microfluidic devices. Electrowetting-On-Dielectric (EWOD) has emerged as one of the most promising techniques for droplet manipulation in microfluidic devices because it is an easily programmable, cost effective, reconfigurable and reversible technique. Droplet creation, actuation, merging, mixing, and splitting are the fundamental operations which enable biochemical assays on EWOD based microfluidic platform. In conventional EWOD the droplet is sandwiched between two substrates. This however reduces the accessibility of the droplet to the device edges only. Recently, it has been demonstrated that EWOD based droplet actuation is also possible on single sided electrodes. Enhanced droplet accessibility on such an open-chip microfluidic platform holds promise for development of complex platforms with better integration of external sensors and actuators. In the quest to improve the fundamental EWOD operations for its open-chip version, we have studied the role of droplet interface oscillation in enhancing mixing and enabling localized sensing. The thesis work presented here focuses on two main aspects of interfacial oscillations: i) non-axisymmetric modes of droplet which appear due to the parametric coupling during oscillations. We have demonstrated the use of these modes for applications in mixing; and ii) localized electrowetting where only a part of droplet interface is actuated instead of full droplet by patterning the actuation electrodes. We have demonstrated the use of localized interface actuation for localized sensing application. In non-axisymmetric oscillations, droplets contact line loses its symmetrical shape during spreading and expands to form asymmetrical lobes. The number of lobes represent different mode shapes. These mode shapes were analyzed using image analysis. The extracted int...