Single potential electrophoresis on-chip using pressure pulse injection

We propose two new injection techniques for use in electrophoresis microchips, which we call 'front gate pressure injection' and 'back gate pressure injection'. Both techniques enable a controlled and variable size sample introduction with reduced bias compared to electrokinetic gated injection. A continuous flow of sample and buffer solution is electrokinetically driven near to the entrance of the separation channel, using a single voltage that is constant in time. A short sample plug is then injected in the separation channel by a 0.1 sec pressure pulse. The latter is generated using the mechanical deflection of a poly(dimethylsiloxane) membrane that is loosely placed on a dedicated chip reservoir. Back gate pressure injection was found to significantly decrease the injection bias compared to a classical gate flow injection while keeping the separation efficiency for fluorescein/rhodamine B solutions.