Liquid–liquid phase separated FG-Nup49 droplets in the microfluidic device. (A) Scheme of the microfluidic device/chip. (B) COMSOL color image (flow simulations, see Fig. S1 for details) of the working principle of the device. (C) First mixer of the device (MI) where the denatured FG-Nup protein solution is buffer exchanged into a physiological buffer, and the formation of droplets is triggered that then flow toward MII. The image shows a bright field view of the device overlaid with a fluorescent snapshot of FG-Nup49 droplet formation. (D) Fluorescence image of FG-Nup49 droplets flowing along the snake-like observation channel after their formation (10×, air objective, epifluorescence microscopy). Scale bar is 50 µm. (E) Snapshots of a coalescence event between two liquid FG-Nup49 droplets (20×, air objective, epifluorescence microscopy). Scale bar is 10 µm. (F) FRAP experiment of one droplet in the device (63×, oil objective, confocal microscopy). Each frame corresponds to a 2-s interval acquisition. Scale bar is 3 µm.