Figure 4.

Droplet manipulation for mixing, adding, or diluting reagents. (A) Mixing of reagents can be accomplished on chip at the time of generation or by addition of reagents to droplets at a later stage. (B) Merging or fusion of droplets can be done either passively using various device designs or by electrocoalescence. (C) Dilution of the droplet content can be done directly on chip by varying the flow rates of the mixed aqueous phases during generation, controlling the flow and mixing via valve systems, separating a laminar flow in a tree-like design, fusing varying proportions of droplet pairs, simultaneously adding and removing reagents or generating droplets from sequentially diluting a concentrated initial reagent.