Experimental study of AC-driven flow through nanopores with single-side conductive coatings

Electroosmosis can turn a nanoporous material into a direct current (DC)- driven fluid pump with no moving parts. When the pumps are used to drive aqueous flow, electrolysis gases must be vented. Alternating current (AC) approaches including induced charge electroosmosis (ICEO) and AC electroosmosis (ACEO) use surface charges on asymmetric conductive films to rectify flows, avoiding the electrolysis problem. However, most designs demand metal features on the nonplanar surfaces of microfluidic channel walls, making it challenging to create nanoscale channels that can hold off back pressures comparable to insulator-based DC electrokinetic pumps. A through-substrate format makes different fabrication methods available including those from the domain of nanoporous membranes. Our results show that a nanoporous membrane with a metal coating on one side, placed in an AC electric field, can drive through-flows and create pressures up to 400 Pa. The pores are in the 200-800 nm diameter range, significantly larger than asymmetric conical nanopore pumps, and operate by a different mechanism. Larger-scale variants of the device filled with tracer particles show vortices resembling those in previous ICEO/ACEO devices.