A microchip device for enhancing capillary zone electrophoresis using pressure-driven backflow.

A reduction in the electroosmotic flow (EOF) is often desirable in glass microchannels for realizing high resolutions in capillary zone electrophoresis (CZE). While static and dynamic coatings have been commonly employed to accomplish this goal, such chemicals can introduce unwanted interactions of the analyte molecules with the separation medium and/or channel surface. In this article, we report a microfluidic device that can enhance the resolving power of CZE analysis by generating a pressure-driven backflow in the separation channel. This backflow was generated in our current work by fabricating a shallow segment (0.5-4 μm deep) downstream of the separation duct (5 μm deep) and applying an electric field across it. A mismatch in EOF transport rate at the interface of this segment was shown to yield a pressure-gradient that counteracted electroosmosis and diminished the net fluid flow in the separation conduit by nearly an order of magnitude. Although the resulting pressure-driven backflow also somewhat increased the band broadening in the analysis channel, overall it allowed us to separate an amino acid mixture with an 8-fold higher resolution. The microchip device presented here is particularly suitable for miniaturization of the CZE method and may be easily integrated into other analytical procedures making it an attractive module for lab-on-a-chip applications.