Figure 1.

Microfluidic high-throughput screening platform. Initially, cells in PBS are mixed with cell culture media. Droplets are formed by combining this aqueous stream with two streams containing a fluorinated oil and surfactant mixture. The 0.3-nl droplets formed in this device are collected in a syringe that provides a microaerobic environment when capped. The syringe is placed in an incubator for cell culturing. After culturing for a predetermined amount of time, droplets from the incubated syringe are reinjected into a second device (lower panel) where they are combined with another set of droplets containing fluorescent enzymatic assay reagents. After droplet coalescence, the resulting droplets flow through channels for 30 s to allow the assay reaction to proceed. The extracellular concentration of the metabolite of interest is quantified by measuring the droplet fluorescence with a laser/photomultiplier tube system. Based on this measurement, droplets are sorted into one of two channels. This system as currently configured can screen ~1 to 2 clones per second so that 10⁴ clones can be screened in less than 3 h.