Based on fluorescence microscopy, the electrophoretic transfer of proteins across the liquid–liquid interface in microfluidic aqueous two-phase systems (ATPS) was investigated. Specifically, the behavior of bovine serum albumine (BSA) and bovine γ-globulin (BγG) in an ATPS containing polyethylene glycol and dextran was observed. Both proteins, initially dissolved in the dextran phase, accumulated significantly close to the three-phase contact lines between the two aqueous phases and the solid surface upon application of an electric field. The accumulation process is superposed by crossing of the proteins into the PEG phase, which also occurs mainly at the three-phase contact line. Differences in their accumulation/transfer behavior allow a separation of the two proteins.

In this collection, we present the fluorescence images of the accumulation and transfer dynamics as observed with widefield and confocal microscopy. The matlab files contain the code that was used to evaluate the widefield images of protein accumulation at the phase boundary.