Electroosmotically induced hydraulic pumping on microchips: Differential ion transport

The theory behind and operation of an electroosmotically induced hydraulic pump for microfluidic devices is reported. This microchip functional elemen t consists of a tee intersection with one inlet channel and two outlet chan nels. The inlet channel is maintained at high voltage while one outlet chan nel is kept at ground and the other channel has no electric potential appli ed. A pressure-induced now of buffer is created in both outlet channels of the tee by reducing electroosmosis in the ground channel relative to that o f the inlet channel. Spatially selective reduction of electroosmosis is acc omplished by coating the walls of the ground channel with a viscous polymer . The pump is shown to differentially transport ions down the two outlet ch annels. This ion discrimination ability of the pump is examined as a functi on of an analyte's electrophoretic velocity. In addition, we demonstrate th at an anion can be rejected from the ground channel and made to flow only i nto the field-free channel if the electrophoretic velocity of the anion is greater than the pressure-generated now in the ground channel. The velocity threshold at which anion rejection occurs can be selectively tuned by chan ging the flow resistance in the field-free channel relative to the ground c hannel.