Low toxic and highly luminescent CdSe/Cd x Zn1−x S quantum dots with thin organic SiO2 coating for application in cell imaging

A silanization process was employed to transfer hydrophobic quantum dots (QDs) prepared via an organic route at high temperature into water phase. The QDs were further coated with a thin organic SiO 2 shell to form QDs@SiO 2 composite nanoparticles by ligand exchange or remaining initial organic ligands on the surface. In this study, QDs with different ligands, either trioctylphosphine oxide (TOPO) or oleic acid (OA), were employed to investigate the effects of ligands on the reverse micelles in preparing QDs@SiO 2 nanoparticles. In the preparing process, hydrophobic QDs were silanized by partially hydrolyzed tetraethyl orthosilicate (TEOS). For TOPO-capped CdSe QDs, surface TOPO ligands were completely replaced by partially hydrolyzed TEOS. As for OA-capped CdSe/Cd x Zn 1− x S QDs, surface OA ligands were partially replaced. It was found that the ligand exchange drastically reduced the photoluminescence (PL) efficiency of CdSe QDs. Furthermore, the cytotoxicity studies of QDs@SiO 2 have been carried out in detail. The results indicate that CdSe/Cd x Zn 1− x S QDs@SiO 2 composite nanoparticles exhibit lower cytotoxicity compared with CdSe QDs@SiO 2 , because the SiO 2 shell and remained OA ligand layer can effectively prevent the leakage of toxic Cd 2+ ions. Meanwhile, it was found that these CdSe/Cd x Zn 1− x S QDs@SiO 2 nanocomposites could keep excellent PL properties even for 24 h incubating with Siha cells, which indicating that our prepared composite nanoparticles are potentially applicable for cell imaging in biological systems.