Polydopamine-Coated Solid Silica Nanoparticles Encapsulating IR-783 Dyes: Synthesis and NIR Fluorescent Cell Imaging.

We report a simple and efficient synthetic method for polydopamine (PDA)-coated solid silica nanoparticles (s-SiO@PDA NPs) encapsulating anionic near-infrared (NIR) fluorescent dyes through physical adsorption. Despite the use of anionic NIR fluorescent dyes indocyanine green (ICG) and 2-[2-[2-chloro-3-[2-[1,3-dihydro-3,3-dimethyl-1-(4-sulfobutyl)-2-indol-2-ylidene]-ethylidene]-1-cyclohexen-1-yl]-ethenyl]-3,3-dimethyl-1-(4-sulfobutyl)-3-indolium (IR-783), they were successfully immobilized on anionic s-SiO@PDA NP surfaces under acidic aqueous conditions. After embedding in the s-SiO@PDA NPs, the fluorescence of ICG was almost quenched, while a diminished IR-783 fluorescence remained observable.