Rapid modulation of droplet composition with pincer microvalves

Single-layer membrane valves are simple to fabricate and to integrate into microfluidic devices. However, due to their rectangular flow channel geometry, they do not fully seal. Here, we show that liquid flow can be reduced by over 3 orders of magnitude, enabling the contents of forming droplets to be dynamically modulated. We use this precision control to perform combinatorial DNA synthesis in the droplets. We present single layer membrane valves capable of precisely modulating droplet composition for applications in synthetic biology and multiplex encoding.