Methods and devices are provided for focusing and/or sorting activated T cells. The device comprises a microfluidic channel comprising a plurality of electrodes arranged to provide dielectrophoretic (DEP) forces that are perpendicular to forces from hydrodynamic flows along the channel. The device may be configured to apply voltages to a plurality of electrodes in a first upper region of the microfluidic channel to focus the cells into a single flow, and to apply different voltages to a plurality of electrodes in a second downstream region of the microfluidic channel to sort cells based on size. The output of the microfluidic channel may diverge into multiple channels, wherein cells of various sorted sizes are directed into the appropriate output channel.