Philippe M. Fauchet

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

Significance Electroosmotic pumps (EOPs) are a class of pumps in which fluid is driven through a capillary or porous media within an electric field. Current research on EOPs concerns the development of new materials in which high electroosmotic flow rates can be achieved for low voltages. Such pumps could be used for portable microfluidic devices. Porous nanocrystalline silicon (pnc-Si) is a material that is formed into a 15-nm-thick nanomembrane. pnc-Si membranes are shown here to have high electroosmotic flow rates at low applied voltages due to the high electric fields achieved over the ultrathin membrane. A prototype EOP was designed using pnc-Si membranes and shown to pressurize fluid through capillary tubing at voltages as low as 250 mV. 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 with the observed pnc-Si flow rates. We attribute the high flow rates to high electrical fields present across the 15-nm span of the membrane. Surface modifications, 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 uses pnc-Si membranes and Ag/AgCl electrodes was shown to pump microliter per minute-range flow through a 0.5-mm-diameter capillary tubing with as low as 250 mV of applied voltage. This silicon-based platform enables straightforward integration of low-voltage, on-chip EOPs into portable microfluidic devices with low back pressures.