Free-flow electrophoresis
Free-flow electrophoresis (FFE) separates and collects charged analytes continuously. As a result, FFE can be used for the purification of complex biological mixtures that contain analytes such as proteins, DNA, and small molecules.
Figure 1: An FFE device consists of a flow chamber that has an electric field applied perpendicular to the direction of fluid flow. A biological sample is injected with the fluid flow such that charged analytes migrate across the chamber according to their electrophoretic mobility. The separated analytes will then exit through different outlets at the end of the flow chamber.
Figure 2: The UW Microfluidics Lab studies the fluid dynamics of FFE to improve the separation resolution. New FFE concepts are validated through numerical simulations, device fabrication, and experiments. For example, a new FFE device has successfully separated and collected samples containing reference DNA markers as well as proteins.
Collection of separated proteins
A drawback of using capillary isoelectric focusing for collecting separated proteins is Taylor dispersion. As separated proteins are pumped out of the separation chamber, the electric field which kept them focusing is no longer present. Therefore as they are pumped, diffusion becomes a dominant force in their motion and causes the highly focused sample to spread. To prevent separated proteins from mixing, a separation chip was developed which uses a sheath flow and pressure system to direct highly concentrated samples to different regions for collection. The figure below illustrates this concept. Initially with equal pressures, the velocity profile is symmetric and directs the concentrated protein to the central path. Increasing the pressure ratio between the two sheath-flow streams changes the direction of the concentrated protein to the second collection path.
Figure 3. A separation chip has been developed which uses a sheath flow and pressure system to direct highly concentrated samples to different regions for collection.