Programmable Control of Multiscale Droplets using V‐Valves

Abstract Contemporary droplet‐based microfluidic platforms generate large numbers of sub‐nanoliter (<10⁻⁹ L) volume droplets on short timescales. The controllable generation of femtoliter (10⁻¹⁵ L) volume droplets is however a far more challenging task. Herein, the design, fabrication, and testing of a valve‐based droplet‐on‐demand generator that enables the robust and controllable production of femtoliter‐volume water‐in‐oil droplets is described, where droplet size is determined by on‐chip pressure. This generator enables the sequential supply of femtoliter droplets to much larger “mother” droplets stored on‐chip, which in turn allows for high‐precision droplet dilution and programmable droplet pairing/merging operations. Such an approach can generate in excess of 700 fL‐volume droplets of variable content and with dilution factors of almost three orders of magnitude. Using the same principle, the microfluidic platform can also perform rapid, low‐volume consumption titrations. Accordingly, the valve‐based droplet‐on‐demand generator allows for a range of automated and multi‐step droplet‐based manipulations.