Measurements of the Transverse Migration of Polyelectrolytes in Microfluidic Channels Induced By Combined Electric and Flow Fields

In a straight microfluidic channel, a dilute polyelectrolyte solution such as DNA can be focused towards the center of the device by applying an electric field and pressure gradient simultaneously. We report on systematic measurements of the effects of flow velocity, electric field, and ionic strength on the degree of migration. Our experiments show that migration increases with increasing shear and electric field, but eventually saturates; the addition of salt reduces the strength of the migration. Comparisons are made between experimentally measured concentration profiles and numerical models based upon the hypothesis that migration is caused by an electrically induced hydrodynamic interaction.