Abstract

Putting Nanoliter Droplets in an Array for High-throughput Assays

Wenbin Du, Professor, State Key Laboratory of Microbial Resources, Institute of Microbiology, CAS

In this study, we introduced a simple and automated platform to generate droplet arrays for high throughput assays, especially single cell analysis. Compare with serial process of each droplet within a microfluidic channel, positioning droplets in a 2D array helps us to perform high throughput assays in droplets in parallel, and enables tracking of dynamic reactions in each droplet. We used a novel droplet generation method we called cross-interface emulsification to generate nanoliter droplets on well plates simply by a capillary tip. The platform we developed can deposit droplets of programmed volumes in microwells. We can also introduce multiple droplets in the same well, and mix them by centrifugation. This platform was used in single-cell whole genome amplification (WGA) of bacterial cells. The procedure included fluorescence activated cell sorting, single-cell lysis, and multiple displacement amplification (MDA) of the whole genome of cells. We successfully miniaturized the final reaction to 200 ~ 500 nL, which significantly eliminated contamination and improved the coverage of genome sequencing. Direct sequencing WGA products of Sulfolobus A20 (archaea) and E. coli K12 (bacteria) single cells shows highly specific assembly and mapping onto the reference genome. In summary, we believe that the droplet array generation methods we developed can provide versatile platforms for broad applications including single-cell analysis, protein crystallization screening, and high throughput drug screening.