DEP microactuation of liquids

We report rapid actuation of nanoliter to microliter water volumes using the dielectrophoretic (DEP) force. This micro-electromechanical mechanism for manipulating, transporting, and metering liquids harnesses strong, nonuniform RF electric fields created by coplanar electrodes with 30 to 100 /spl mu/m feature size patterned on insulating substrates. Electrolysis is avoided by spin-coating the electrodes with /spl sim/10 /spl mu/m of polyimide. Transient liquid velocities exceed 25 cm/s, and droplets down to a few nanoliters in volume are formed in <30 ms. Because water responds rapidly, controlled DEP actuation can be achieved by very short bursts of rf voltage. An important benefit of minimized exposure of conductive liquids to strong rf fields is reduced Joule heating. A new microfluidic scheme for the "laboratory on a chip" is proposed, based on high-speed, programmable manipulation of discrete nanodroplets on smooth substrates.