Electrokinetic 'ratchet' pumps for microfiuidics

The symmetry argument underlying 'ratchet' schemes for the motion of molecular motors and for selective transport of particles is shown to yield new means for the pumping of liquids. A practical realization consists in using surfaces bearing polar periodic arrays of electrodes addressed by an ac voltage difference. The resulting surface-induced pumping remains efficient under miniaturization and may find application in microfluidics.