Formation of droplets interface bilayer by coplanar EWOD device

Abstract

Droplet interface bilayer (DIB) is formed on a microfabricated aperture between two addressable encapsulated droplets driven by coplanar EWOD electrodes. The DIBs, or artificial bilayer lipid membranes (BLMs), are fundamental to the in vitro studies of purified membrane channel proteins. A sandwich device is designed with three plates: the top and bottom plates contain coplanar EWOD electrodes for individual encapsulated droplet manipulations; the middle silicon plate holds an aperture with proper dimension and wettability for DIB formation. For the amphiphilic characteristic of the lipid molecules, a lipid monolayer is assembled at the interface of the water (KCl) core and oil (decane) shell of the encapsulated droplet. The two lipid monolayers are driven to the aperture through manipulating the two encapsulated droplets by EWOD. After thinning the excess oil film in the aperture, the formation of the DIB is completed and confirmed by optical and electrical means. Ag/AgCl electrodes and a patch clamp amplifier are used for electrophysiological signal examinations, including the transmembrane capacitance and the ion current. The specific capacitance and the thickness of the DIB are 0.5 µF/cm2 and 6.8 nm, respectively. Ion channels are incorporated into the DIB by adding alpha-hemolysin (a-HL) molecules in one of the KCl core droplet. The ion current and the conductance of each incorporated ion channel at the 150 mV clamp voltage are monitored and measured to be 80 pA and 500 pS, respectively. Around 10 ion channels are successfully incorporated in the 100 µm × 100 µm aperture between two encapsulated droplets driven by EWOD. The demonstrated device exhibits precise control of the encapsulated droplets and the lipid monolayers, contributing to a stable DIB formation for in vitro membrane proteins studies in isolated droplet environments.