FIG. 4.

(a) Reaction scheme of enzymatic reaction between Amplex Red (AR) and H₂O₂, mediated by Horseradish Peroxidase (HRP), leading to the fluorescent product, resorufin. (b) Schematic of the DIB mass transfer experiment. One drop contained H₂O₂, the other AR. As soon as a DIB was formed, membrane permeable H₂O₂ transferred to the adjacent droplet, leading to the synthesis of a fluorescent product. (c) An extension of the assay to a five droplet network, where the enzymatic cascade reaction sequentially propagated through the droplets over time. (d) Graph showing fluorescence levels of the four dye-containing droplets over time. This shows that droplets increased in fluorescence as the reaction proceeded (black arrow) and that the droplets further away from the H₂O₂, source had smaller fluorescence levels (red arrow).