Hybrid electrodes effective for both electrowetting- and dielectrowetting-driven digital microfluidics

Electrowetting on dielectric (EWOD) and dielectrowetting (DEW) are two major principles to drive droplets in digital microfluidics. EWOD is effective to manipulate (create, transport, split, and merge) conductive droplets being currently used for many biological, chemical, and optical applications. DEW can also manipulate droplets but more efficiently with dielectric (nonconductive) fluids. A digital microfluidic platform efficiently operable by both EWOD and DEW would offer higher versatility in handling a wide range of fluids, regardless of their conductivities. In this regard, this article presents a new hybrid electrode design enabling EWOD and DEW to drive various kinds of droplet fluids on a single platform. In addition, a slippery liquid-infused surface (SLIPS) is integrated with the hybrid electrodes. The SLIPS is well known to resist biofouling and repel sticky fluids, which endows the hybrid electrodes with much wider application spectra. As a result, the present SLIPS-integrated hybrid electrodes facilitate actuating various kinds of fluids which would not be driven by conventional EWOD and/or DEW electrodes. This paper presents the successful transportation of not only conductive fluids including water, protein solution, glycerol, and honey but also nonconductive fluids including dodecane, silicone oil, and light and heavy crude oil, all driven by the SLIPS-integrated hybrid electrodes. The performance comparisons among solid, interdigitating, and hybrid electrodes are made by testing both conductive and nonconductive droplets.