Biosensing at Drop Scale Assisted by Electrowetting at Moderate Frequency

This paper addresses surface ageing of a functionalized substrate in digital microfluidics. A model system based on bovine serum albumin (BSA)-laden sessile drop is selected. AC ElectroWetting-On-Dielectrics (EWOD), increasingly used in digital micro-systems for medical assays, is implemented in coplanar configuration. The small frequency re- quired by EWOD actuation (f =100 - 1000 Hz) enables shape oscillations of the latter sessile drop and internal streaming. As demonstrated from dynamic contact angle (DCA) imaging, adsorption of BSA at the solid substrate is promoted un- der EWOD, as also shown from the time-dependent solid-liquid surface pressure. For an oscillating mode, n = 6, our numerical simulations show that corner eddies located near the oscillating contact line yield an efficient molecular re- newal. In this way, oscillating EWOD could be used purposely as a tool to speed up label-free detection from DCA measurements.