High throughput screening of active compounds using droplet microfluidics
High throughput screening (HTS) is a powerful tool for identifying new compounds for various pharmaceutical applications. HTS is mainly used to assay activity or functions of chemical libraries of millions of molecules against biological targets. It is useful for identifying ligands, enzymes, antibodies, and genes that modulate a particular biomolecular pathway. The pharmacological data obtained by HTS provides important information for the design of new drugs and for understanding the role of biochemical processes.
HTS assays are typically performed in microtiter plates. A typical screen using conventional robotics involves pipetting few microliters of reagents into each well of a microtiter plate, and adding few microliters of each variant from a library into different wells. This results in a total reagent volume on the order of millilitres for one microtiter plate, and significantly higher as the number of plates increases. These large volumes of samples make compound screens extremely expensive and time-consuming. To address these limitations, we perform screening reactions using droplet microfluidics, where aqueous droplets dispersed in an immiscible carrier oil, typically a fluorinated oil act as the functional equivalent of microtiter plate wells. In contrast to conventional HTS, we emulsify few picoliters of each variant from a library, and add few picoliters of reagents to each variant droplet. By reducing the reagent volumes by up to 7 orders of magnitude we can reduce the cost and the time for a screen assay and achieve extremely high throughput.
To track the library contents inside the droplets, we encode each compound using fluorophore combinations or nucleic acid sequences. To perform a screen, we reinject an aliquot of encoded library droplets into a microfluidic device, a target such as a microbial organism or a cell is added to each droplet. After an incubation step, the droplets are then detected and sorted at about 1000 Hz.
Guo, M. T., Rotem A., Heyman J. A., and Weitz D. A., Droplet Microfluidics for high-throughput biological assays, Lab on a Chip, 12, 2146-2155, 2012.