A simple and robust method based on pneumatic PDMS microvalve that can be used to manipulate and process individual droplets in microfluidic devices was presented. By incorporating pneumatic microvalves into microfluidic devices, we developed modules that enable to control the formation of droplets, variation of droplets size and composition, reproducible and efficient fusion of droplets. By intermittently switching on and off microvalve, individual droplets can be generated on demand. The size of individual droplets can be flexibly and precisely tuned from hundreds of picoliter to a few nanoliter by varying the time of on-state of microvalve. By expanding the number of aqueous flow channels and building the corresponding microvalves, arrays of chemically distinct droplets can be easily produced via switching on the corresponding microvalves sequentially. When a pair of droplets are generated synchronously and then brought together in a confluence channel, controlled fusion of droplets can be achieved reproducibly and efficiently. (Figure 1)

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