(153c) Concentration Enhancement of Polyelectrolytes in a Microfluidic Device

We report experimental measurements of DNA concentration profiles in a microfluidic channel, using an electric field to drive the polyelectrolyte through the channel, while simultaneously applying a pressure gradient. These two fields combine to drive a net migration of the polymer in a direction transverse to the field lines. If the fields act in the same direction the polyelectrolyte will migrate towards the center of the channel, while if the fields are opposed it migrates towards the walls. Migration only occurs in the presence of both fields and vanishes when either field is removed. Our experiments are consistent with the hypothesis that migration is caused by an electrically induced hydrodynamic interaction acting on a polymer that is distorted from its equilibrium conformations by the shearing flow. It is conceivable that lateral migration can be used to enhance the concentration of DNA and other polyelectrolytes in microfluidic devices.