Droplet Microfluidic System with On-Demand Trapping and Releasing of Droplet for Drug Screening Applications.

96-Well plate has been the traditional method used for screening drug compounds libraries for potential bioactivity. Although this method has been proven successful in testing dose-response analysis, the microliter consumption of expensive reagents and hours of reaction and analysis time call for innovative methods for improvements. This work demonstrates a droplet microfluidic platform that has the potential to significantly reduce the reagent consumption and shorten the reaction and analysis time by utilizing nanoliter-sized droplets as a replacement of wells. This platform is evaluated by applying it to screen drug compounds that inhibit the tau-peptide aggregation, a phenomena related to Alzheimer's disease. In this platform, sample reagents are first dispersed into nanolitre-sized droplets by an immiscible carrier oil and then these droplets are trapped on-demand in the downstream of the microfluidic device. The relative decrease in fluorescence through drug inhibition is characterized using an inverted epifluorescence microscope. Finally, the trapped droplets are released on-demand after each test by manipulating the applied pressures to the channel network which allows continuous processing. The testing results agree well with that obtained from 96-well plates with much lower sample consumption (∼200 times lower than 96-well plate) and reduced reaction time due to increased surface volume ratio (2.5 min vs 2 h).