Introduction
Droplet microfluidics showed great potential to facilitate many chemical and biomedical applications [1]–[4]. Different from conventional continuous-flow microfluidics, droplet microfluidics compartmentalizes reactions into massive pico- to nanoliter volume water-in-oil emulsion droplets, which achieves shorter reaction time, low reagent consumptions, high sensitivity, and enhanced signal to background ratio [1]–[4]. Those advantages have made droplet microfluidics a great platform to perform high-throughput screening (HTS) [2], [4]. However, the current tubing-based sample-to-droplet interfaces have hindered the feasibility of droplet microfluidics toward HTS due to the significant sample wastages from the prepared samples, low scalability with a large sample library, and length idle time when switching samples.