Improving the brightness and photostability of NIR fluorescent silica nanoparticles through rational fine-tuning of the covalent encapsulation methods.

Near-infrared (NIR) fluorescence imaging technology calls for highly bright and photostable emissive materials for long-term and real-time bioimaging and medical diagnosis. Herein, we report that four aminocyanine dyes were covalently encapsulated inside silica nanoparticles by reverse microemulsion using different linkage methods. The fluorescence brightness and photostability of the obtained fluorescent silica nanoparticles (FSNPs) were found to have direct correlation with the used covalent encapsulation methods, especially the number of anchoring sites of the encapsulated dyes. The aminocyanine dye 4-Si contains three anchoring sites for embedding into the silica nanoparticles, and provides FSNP-4- the FSNP with the best brightness and photostability.