Highly bright silica-coated InP/ZnS quantum dot-embedded silica nanoparticles as biocompatible nanoprobes

Abstract Background Quantum dots (QDs) have outstanding optical properties such as strong fluorescence, excellent photostability, broad absorption spectra, and narrow emission bands, which make them useful for bioimaging. However, cadmium (Cd)-based QDs, which have been widely studied, have potential toxicity problems. Cd-free QDs have also been studied, but their weak photoluminescence (PL) intensity makes their practical use in bioimaging challenging. In this study, Cd-free QD nanoprobes for bioimaging were fabricated by densely embedding multiple indium phosphide/zinc sulfide (InP/ZnS) QDs onto silica templates and coating them with a silica shell. Results The fabricated silica-coated InP/ZnS QD-embedded silica nanoparticles (SiO 2 @InP QDs@SiO 2 NPs) exhibited hydrophilic properties because of the surface silica shell, and the maximum PL intensity of the SiO 2 @InP QDs@SiO 2 NPs was approximately 98.4 times higher than that of a single hydrophilic cadmium selenide/ZnS (CdSe/ZnS) QDs. Moreover, the brightness of the particles could be easily controlled by adjusting the amount of InP/ZnS QDs in the SiO 2 @InP QDs@SiO 2 NPs. When SiO 2 @InP QDs@SiO 2 NPs were administered to tumor syngeneic mice, the fluorescence signal was prominently detected in the tumor because of the preferential distribution of SiO 2 @InP QDs@SiO 2 NPs, demonstrating their applicability in bioimaging with NPs. Conclusion Thus, SiO 2 @InP QDs@SiO 2 NPs have the potential to successfully replace Cd-based QDs as highly bright and biocompatible fluorescent nanoprobes.