Cells in Double Emulsions for FACS Sorting

Very high throughput can be achieved in molecular biology reactions by emulsifying or ‘dropletising’ the reaction in an oil carrier, so that millions of droplets each behave as discrete micro-reactors. Using microfluidic droplet generating chips, it is possible to capture individual cells in micro-droplets containing highly reproducible volumes of a reaction mix. If a fluorogenic substrate is available, and the droplets can be sorted in a FACS machine, then very large libraries can be screened, and multiple generations of screening can readily be carried out. Small double emulsion droplets, in the size range of 25 – 35 µm, can be useful for sorting, because the continuous ‘outer’ phase is aqueous and compatible with a FACS, and the 30 µm droplets are small enough to pass undamaged through the sorting cell. Here, we investigate the use of a two-chip system for making 30 µm double emulsion droplets.