Ultraviolet-​Induced Fluorescence of Polydopamine-​Coated Emulsion Droplets

Polydopamine (PDA)​, a multifunctional biomaterial with strong adhesion and coating properties, exhibits melanin-​like optoelectronic properties but is virtually devoid of intrinsic fluorescence. Herein we disclose the first PDA-​based system that can develop fluorescence without chem. manipulation. The polymn. of dopamine in the presence of oil microdroplets results in the formation of smooth PDA-​coated core-​shell droplets, which develop a bright and persistent fluorescence upon UVA illumination. The fluorescence induction depends on the excitation wavelength, the nature of the oil, and oxidn. and buffer conditions, suggesting photo-​oxidn. of PDA components within the oil matrix, which shields the developing fluorophores from water quenching. Peroxyl radical scavengers enhance the fluorescence, whereas hydrogen peroxide induces quenching. The new system holds potential interest for imaging and tocopherol sensing applications.