Provided are microfluidic designs and methods for rapid generation of monodisperse nanoliter volume droplets of reagent/target (e.g., molecule or cell) mix in emulsion oil. The designs and methods enable high-throughput encapsulation of a single target (e.g., DNA/RNA molecules or cells) in controlled size droplets of reagent mix. According to various embodiments, a microfabricated, 3-valve pump is used to precisely meter the volume of reagent/target mix in each droplet and also to effectively route microparticles such as beads and cells into the device, which are encapsulated within droplets at the intersection of the reagent channel and an oil channel. The pulsatile flow profile of the microfabricated pumps provides active control over droplet generation, thereby enabling droplet formation with oils that are compatible with biological reactions but are otherwise difficult to form emulsions with.