Droplet Actuation by Electrowetting-on-Dielectric (EWOD): A Review

Abstract

This paper reviews publications that have fortified our understanding of the electrowetting-on-dielectric (EWOD) actuation mechanism. Over the last decade, growing interest in EWOD has led to a wide range of scientific and technological investigations motivated by its applicability in microfluidics, especially for droplet-based optical and lab-on-a-chip systems. At this point in time, we believe that it is helpful to summarize the observations, insights, and modeling techniques that have led to the current picture showing how forces act on liquid droplets and how droplets respond in EWOD microfluidic devices. We discuss the basic physics of EWOD and explain the mechanical response of a droplet using free-body diagrams. It is our hope that this review will inspire new research approaches and help design useful devices.

Keywords:

• Electrowetting
• electrowetting-on-dielectric
• EWOD
• droplet actuation
• digital microfluidics

Acknowledgements

This work was supported by the NIH (R01 RR020070), DOE (DE-SC0005056),and the UCLA Foundation from a donation made by Ralph & Marjorie Crump for the UCLA Crump Institute for Molecular Imaging. WN acknowledges further supports from the NSF Graduate Research Fellowship Program and an NSF Integrative Graduate Education and Research Traineeship (IGERT) through the UCLA Materials Creation Training Program (MCTP).

Notes

1. In digital microfluidics, droplets of sub-millimeter size are manipulated individually, i.e., each can be controlled independently (e.g., by EWOD actuation). Digital microfluidics can be classified as a subset of droplet microfluidics, which also includes manipulation of droplets as a group; a typical example is multiple droplets moving with a carrier fluid pumped in a microchannel.