NIR light-triggered bursting of double-emulsion drops (DEDs) for microdroplet generation

Microdroplets have significant applications in microbiology, pharmaceuticals, cosmetics, and synthetic materials. Herein, we present for the first time, a near-infrared (NIR)-light-triggered double-emulsion drop (DED) bursting method for generating a large number of micro-droplets with a size of several microns. Under the irradiation of NIR light, the inner water phase of the DED containing a trace amount of Prussian blue (PB) rapidly heats up and evaporates rapidly to generate microbubbles due to the photothermal property of PB. By controlling the light intensity, the DED could be inflated by the constant coalescence of microbubbles, which then burst immediately and tear the middle oil phase to form a large number of microdroplets. The performance of the microdroplets generated by NIR-light-triggered DED bursting was investigated by varying the oil shell thickness (H_O), oil phase viscosity (η_O) and oil type. H_O and η_O were the key factors affecting the generation of microdroplets. DEDs with lower H_O and η_O generated lower polydispersity and a large number of microdroplets via NIR-triggered DED bursting. The proportion of microdroplets of sizes below 10 μm reached up to 95%. Furthermore, camellia oil, as the middle oil phase of the DEDs, generated lower polydispersity and a large number of microdroplets measuring several microns. The as-developed bursting method has great potential to generate micro-droplets for micro-/nano- and biotechnology applications.