Droplet sample introduction to microchip gel and zone electrophoresis for rapid analysis of protein-protein complexes and enzymatic reactions.

Electrophoresis has demonstrated utility as tool for screening of small molecule modulators of protein-protein interactions and enzyme targets. Screening of large chemical libraries requires high-throughput separations. Such fast separation can be accessed by microchip electrophoresis. Here, microchip gel electrophoresis separations of proteins are achieved in 2.6 s with 1200 V/cm and 3-mm separation lengths. However, such fast separations can still suffer from limited overall throughput from sample introduction constraints. Automated introduction of microfluidic droplets has been demonstrated to overcome this limitation. Most devices for coupling microfluidic droplets to microchip electrophoresis are only compatible with free-solution separations. Here, we present a device that is compatible with coupling droplets to gel and free-solution electrophoresis. In this device, automated sample introduction is based on a novel mechanism of carrier phase separation using the difference in density of the carrier phase and the running buffer. This device is demonstrated for microchip gel electrophoresis and free-solution electrophoresis separations of protein-protein interaction and enzyme samples, respectively. Throughputs of about 10 s per sample are achieved and over 1000 separations are demonstrated without reconditioning of the device. Graphical abstract.