FIG. 1.

(a) Schematic of the microfluidic channel used in the droplet-based viral fusion assay. The components include a droplet generator, a pH switch, a micromixer, and detection cavities. The inset shows the pH switch, a structure that allows the rapid drop of droplet pH by introducing oil with an acid that is soluble in both the oil and aqueous phases. (b) The dimensions of the entire microfluidic device are 8 mm × 10 mm. (c) Schematic of the experimental assay. In this assay, droplets act as reaction chambers in which virus and receptor carrying liposome (host membrane mimic) fuse upon acidification. This process is visualized by fluorescence microscopy.