Surface tension monitoring in a “soft” interface using electrowetting on dielectric

We report the first demonstration of interfacial tension monitoring across two immiscible liquids using electrowetting on dielectric (EWOD). Impedance measurement during EWOD reveals the variation of surfactant concentration at the liquid-liquid interface in real time. The discrepancy with optical method was within 3.5 mN/m and the noise level was under 0.5 mN/m. We also show such approach can be used for label-free monitoring of DNA hybridization. Our approach opens a new horizon of EWOD used as a molecular sensing mechanism across a “soft” interface between liquids.