Numerical Simulation of Electric Field Gradient Focusing and Separation of Analytes in Microchannels with Embedded Bipolar Electrode

A new method for simultaneously concentrating and separating analytes in a microfluidic channel with embedded floating electrode is proposed. The complex interplay of electrophoretic, electroosmotic, bulk convective, and diffusive mass/charge transport in the microchannel is analyzed by numerical simulations. The thin floating electrode attached locally to the wall of the straight microchannel results in a redistribution of local field strength after the application of an external electric field. Together with bulk convection based on cathodic electroosmotic flow, an extended field gradient is formed in the anodic microchannel segment. It imparts a spatially dependent electrophoretic force on charged analytes and, in combination with the bulk convection, results in electric field gradient focusing at analyte-specific positions. Analyte molecules having different electrophoretic mobilities are focused at different locations within the channel.