Low-Voltage Pump Drives Fluid Flow

For microfluidic devices, bulky mechanical pumps are undesirable. Potential substitutes are electroosmotic pumps, which harness the interaction of an electric field with ions on a surface to drive fluid through a channel or porous material. But electroosmotic pumps can require high voltages—and therefore large power supplies—to achieve desired flow rates. Now, a new design achieves high flow rates without high voltages. James L. McGrath of the University of Rochester and coworkers constructed the new pumps with 15-nm-thick membranes made of porous nanocrystalline silicon (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1308109110). The thin material achieves extremely high electric fields across the membrane, which enable desired flow rates with applied voltages as low as 250 mV. The researchers show that modifying the membrane’s surface changes the rate but not the direction of flow. They incorporated the electroosmotic pumps into prototype devices that they used to drive fluid through capillary tubing at a flow rate of 1 μL per minute, a typical value for microfluidic devices.