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-SiO₂@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)-2H-indol-2-ylidene]-ethylidene]-1-cyclohexen-1-yl]-ethenyl]-3,3-dimethyl-1-(4-sulfobutyl)-3H-indolium (IR-783), they were successfully immobilized on anionic s-SiO₂@PDA NP surfaces under acidic aqueous conditions. After embedding in the s-SiO₂@PDA NPs, the fluorescence of ICG was almost quenched, while a diminished IR-783 fluorescence remained observable. The fluorescence intensity of IR-783 embedded in s-SiO₂@PDA NPs remained almost constant over 2 weeks in a pseudobiological solution, with a slight reduction due to dye degradation and dye leakage from the s-SiO₂@PDA NPs. Finally, the s-SiO₂@PDA NPs encapsulating IR-783 were successfully used for NIR fluorescent imaging of African green monkey kidney cells.