Subsecond Electrophoretic Separations from Droplet Samples for Screening of Enzyme Modulators

High-throughput screening (HTS) using multiwell plates and fluorescence plate readers is a powerful tool for drug discovery and evaluation by allowing tens of thousands of assays to be completed in 1 day. Although this method has been successful, electrophoresis-based methods for screening are also of interest to avoid difficulties associated fluorescence assays such as requirements to engineer fluorogenic reactions and false positives. We have developed a method using droplet microfluidics to couple multiwell plate-based assays to microchip electrophoresis (MCE) to screen enzyme modulators. Samples contained in multiwell plates are reformatted in to plugs with a sample volume of 8 nL segmented by an immiscible oil. The segmented flow sample streams are coupled to a hybrid polydimethylsiloxane-glass microfluidic device capable of selectively extracting the aqueous samples from the droplet stream and rapidly analyzing by MCE with laser-induced fluorescence detection. This system was demonstrated by screening a test library of 140 compounds against using protein kinase A. For each sample in the screen, two droplets are generated, allowing approximately 6 MCE injections per sample. Using a 1 s separation at 2000 V/cm, we are able to analyze 96 samples in 12 min. Separation resolution between the internal standard, substrate, and product is 1.2 and average separation efficiency is 16,000 plates/s using real samples. Twenty-five compounds were identified as modulators during primary screening and verified using dose-response curves.