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High-Throughput Generation of Durable Droplet Arrays for Single-Cell Encapsulation, Culture, and Monitoring

Wu, Han, Chen, Xinlian, Gao, Xinghua, Zhang, Mengying, Wu, Jinbo, Wen, Weijia
Analytical chemistry 2018 v.90 no.7 pp. 4303-4309
Escherichia coli, bioassays, capillarity, droplets, encapsulation, evaporation, mammals, microparticles, monitoring, oils, wettability
High-throughput measurements can be achieved using droplet-based assays. In this study, we exploited the principles of wetting behavior and capillarity to guide liquids sliding along a solid surface with hybrid wettability. Oil-covered droplet arrays with uniformly sized and regularly shaped picoliter droplets were successfully generated on hydrophilic-in-hydrophobic patterned substrates. More than ten thousand 31-pL droplets were generated in 5 s without any sophisticated instruments. Covering the droplet arrays with oil during generation not only isolated the droplets from each other but also effectively prevented droplet evaporation. The oil-covered droplet arrays could be stored for more than 2 days with less than 35% volume loss. Single microspheres, microbial cells, or mammalian cells were successfully captured in the droplets. We demonstrate that Escherichia coli could be encapsulated at a certain number (1–4) and cultured for 3 days in droplets. Cell population and morphology were dynamically tracked within individual droplets. Our droplet array generation method enables high-throughput processing and is facile, efficient, and low-cost; in addition, the prepared droplet arrays have enormous potential for applications in chemical and biological assays.