Selective droplet splitting using single layer microfluidic valves

Droplet microfluidics, with its small scale isolated samples, offers huge potential in the further miniaturisation of high throughput screening. The challenge is to deliver multiple samples in a manner such that reactions can be performed in numerous permutations. The present study investigates the use of single layer valves to break up individual droplets selectively. This splitting of large droplets, allows the main sample volume to navigate around the chip, with smaller daughter droplets being removed at desired locations. As such, the mother droplet is no longer an isolated sample akin to an on-chip test tube, but rather a mobile sample delivery system akin to an on-chip pipette. The partitioning takes place at the entrance to a bypass loop of the main channel. Under normal operating conditions the droplet passes the entrance intact, however, when a valve located at the entrance to the bypass loop is actuated, the geometry changes causes the droplet to split. We analyse this transition in behaviour for a range of oil and water inlets, and valve actuation pressures, showing that the valve can be actuated such that the next droplet to pass the bypass loop will be split, but subsequent droplets will not be.