Zone sculpting using partitioned electrokinetic injections

Narovlyansky, M.1, Squires, T.M.2, Whitesides, G.M.1
1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, U.S.A.
2 Departments of Physics and Applied Mathematics, Caltech, Pasadena, CA

In electrokinetic separations, the narrower and more homogeneous the initial sample plug, the higher the ultimate resolution of the separation. Here we describe a general and versatile method to sculpt low-dispersion, high-fidelity sample zones in microfluidic devices for high resolution electrokinetic separations. In a simple channel intersections microfabricated partitions act to reduce each channel’s permeability to transverse electric fields, yet maintain permeability to parallel fields, allowing one to sculpt injection fields and plugs. For steady-state sample containment at intersections using only two electrodes one also has to use sheath flow.

To demonstrate, we create and separate narrow (2:1) bands in a PDMS device. Partitioned injections do not depend on device material or separation medium, and their resolution is limited only by fabrication capabilities.