Microfluidic device for generating uniform water-in-oil emulsions. (A) Schematic of the device, showing central aqueous input reservoir (Raq) with 110 radial nozzles that empty into an annular oil flow channel. An oil-surfactant mixture is supplied at the oil input reservoir (Rin), and the emulsion is collected at the output reservoir (Rout). The reservoirs are contacted by microbore tubing, which delivers material to and from the device. (B) Photograph of the device during operation, with magnified view on the left. For visualization, the aqueous phase contained bromophenol blue in a solution of 15 mM MgCl2, 50 mM KCl, and 50 mM EPPS (pH 7.5).