High Performance, Low Voltage Electroosmotic Pumps With Molecularly Thin Nanoporous Silicon Membranes

We have developed electroosmotic pumps (EOPs) fabricated from 15 nm thick porous nanocrystalline silicon (pnc-Si) membranes. Ultrathin pnc-Si membranes enable high electroosmotic flow per unit voltage. We demonstrate that electroosmosis theory compares well to the observed pnc-Si flow rates. We attribute the high flow rates to high electrical fields present across the 15 nm span of the membrane. Surface modications, such as plasma oxidation or silanization, can influence the electroosmotic flow rates through pnc-Si membranes by alteration of the zeta potential of the material. A prototype EOP that utilizes pnc-Si membranes and Ag/AgCl electrodes was shown to pump uL/min flow though capillary tubing with as little as 1 V of applied voltage. The high hydraulic permeability of pnc-Si membrane reduces the ability of this EOP to pump fluids in cases of high back pressure. However, the silicon-based platform of pnc-Si membranes allows for straight-forward integration into devices, and pnc-Si EOPs can be used as low voltage, on-chip EOPs in portable microfluidic devices with low back pressures.