A rapid field-free electroosmotic micropump incorporating charged microchannel surfaces

A rapid field-free electroosmotic micropump (RFEP) was constructed incorporating separate anionic and cationic glass microchannel surface modifications and its performance was investigated. Two of the arms of the devised Y-shaped RFEP were coated with anionic and cationic polymers, respectively. Different charges localized on these interior surfaces produced electroosmotic flow in opposite directions when an electric field was applied along the two coated arms. The hydrodynamic pressure developed at the common junction of the three arms generated field-free flow, which responded rapidly and reversibly to the applied electric field. The flow rate of the devised RFEP was 262.4 nL min−1 when 1.0 kV cm−1 was applied in 10 mM phosphate buffer at pH 7.0. Field-free flow in the vertical channel was quickly and precisely controlled by an external voltage program, as previously demonstrated by field-free gated injection and microbead sorting experiments. Gated field-free injection was achieved by combining two RFEPs at a simple cross. The devised RFEP was found to produce rapid short hydrodynamic pulses, which allowed the sorting of microbeads at up to 120 objects per minute in a biocompatible manner.