Enzyme-Inhibitor Assay Using Microdroplets

We demonstrate a microdroplet enzyme-inhibitor assay based on a microfluidic device. Alternating microdrops of a buffer solution containing enzyme and inhibitor reagents and perfluorodecalin (PFD) are formed in a continuous flow of hexadecane. PFD microdrops act as spacers between the reagent microdrops and keep them from coalescence. A substrate solution is then introduced into the reagent microdrops after homogeneous mixing of the enzyme and the inhibitor. The fluorescence depends on the amount of product from the reaction between the substrate and the reagents. Reaction rates were measured with long time exposure using fluoresce microscopy. We also checked probability of inter-droplet contamination of reagents by measuring the fluorescence of each microdrops using an image intensified fast camera.