Microfabricated porous membrane structure for sample concentration and electrophoretic analysis

A microfabricated injection valve incorporating a porous membrane structure is reported that enables electrokinetic concentration of DNA samples using homogeneous buffer conditions followed by injection into a channel for ele ctrophoretic analysis. The porous membrane was incorporated in the microcha nnel manifold by having two channels separated from each other by 3-12 mu m and connected by a thin porous silicate layer. This design allows the pass age of current to establish an electrical connection between the separated channels but prevents large molecules, e.g., DNA, from traversing the membr ane. Concentrated DNA can be injected into the separation channel and elect rophoretically analyzed. Experiments exhibit a nonlinear increase in concen tration with time, and DNA fragments can be concentrated up to 2 orders of magnitude as shown by comparison of peak intensities for analysis performed with and without concentration.