Figure 4.

Producing and sorting drops that contained cells (image refers to drops that contain fluorescein only; see Ref. 35 for more details). (a) A microfluidic flow-focusing device is used to produce 12 pL aqueous monodisperse drops in oil. (b) The drops could be removed to a Pasteur pipette for incubation. (c) The drops could be reinjected into a microfluidic channel and space could be created between drops using surfactant-free oil. (d) An ac electric field can be applied between two electrodes located near the microfluidic channel. The field caused the drops to flow into the upper channel rather than the lower channel (inset: in the absence of an electric field the drops flow preferentially into the lower channel, because that channel has less hydraulic resistance). The scale bars are 100 μm, except in (b) where it is 1 mm. Reprinted with permission from J.-C. Baret et al., Lab Chip, 9, 1850 (2009). Copyright 2009 The Royal Society of Chemistry.