Fig. 3

Droplet-based microfluidic screening platform. 1. Single cell encapsulation: yeast cells were encapsulated in 20 pl droplets at 1200 droplets/s by flow-focusing of a cell suspension with two streams of Novec7500 oil containing 2.5% (w/w) KryJeffD surfactant. Droplets were collected off-chip in a glass vial. 2. Cell growth and enzyme secretion: droplets were incubated for 16 h at 28 °C. 3. Enzymatic screening: droplets were loaded into an integrated device and spaced using Novec7500 oil containing 2.5% (w/w) KryJeffD₉₀₀ surfactant. To initiate the enzymatic reaction, a fluorogenic substrate was picoinjected in each droplet at a rate of 300 droplets/s by applying an AC field (20 kHz, 200 V _pp ). Droplets were incubated on-chip along a delay line and spaced with Novec7500 oil for fluorescence detection (i.e. enzymatic activity). Droplets could be sorted based on fluorescence at 300 droplets/s by applying AC field pulses (30 kHz; 1200 V _pp ; 0.3–0.6 ms). a–f Microscopic images of the different steps of the microfluidic system. The red arrows indicate encapsulated Y. lipolytica cells. Unless specified, scale bars are 30 μm