Velocity Gradient Focusing in a Free-Flow Electrophoresis Device for Protein Fractionation*

Free-flow electrophoresis (FFE) devices enable the separation and collection of chemical species for applications in protein and DNA analysis. FFE operation is achieved by applying an electric field perpendicular to the flow of a liquid solution that is pressure-driven through a separation chamber. Analytes are injected at the beginning of the chamber, and then separate in the transverse direction based on their electrophoretic mobility. The fractions of analytes are then collected at different outlets. The present work highlights a novel FFE device that introduces a velocity gradient to counteract the electrophoretic migration, and therefore allows analytes to focus at unique positions in the chamber, where they experience a net force of zero in the transverse direction. This electrofocusing method, which serves to enhance resolution and sensitivity, is more versatile than traditional techniques, such as isoelectric focusing. The FFE device uses a simple fabrication approach for a microfluidic chamber that reduces Joule heating, and operates in the laminar flow regime. For validation, COMSOL simulations will be presented, followed by experimental results for the separation of different dyes and biomolecules.