Monitoring the cellular uptake of silica-coated CdSe/ZnS quantum dots by time lapse confocal laser scanning microscopy

Abstract

In this study, we aimed to investigate the efficiency of silica coated CdSe/ZnS nanocrystals (CdSe/ZnS-SiO2 NCs) for imaging purposes. CdSe quantum dots (QDs) were synthesized by organometallic routes and were coated with ZnS shell by injecting solutions of diethylzinc (Zn (Et)2) and hexamethyldislathiane ((TMS)2 S) as precursors for zinc and sulfur ions respectively. Then, CdSe/ZnS QDs were rendered water soluble by overcoating with silica using tetraethyl orthosilicate (TEOS) as a silica precursor. QDs were characterized by UV-Vis absorption, emission spectroscopy TEM, XRD and DLS. The biocompatibility of silica-coated QDs (CdSe/ZnS-SiO2) was tested by evaluating mitochondrial activity of liver hepatocellular carcinoma (HepG2) cells exposed to different concentrations of CdSe/ ZnS-SiO2. CdSe/ZnS-SiO2 cytotoxicity was evaluated by investigating DNA damage using alkaline comet assay. The intracellular uptake and localization of QDs in HepG2 cells were monitored by fluorescence imaging using Confocal Laser Scanning Microscopy (CLSM) up to eight hours. Results showed that silica coating yielded final particles' size around 35 nm possessing strong luminescence property. The cytotoxicity test results showed that CdSe/ZnS-SiO2 were nontoxic at low concentrations. CLSM showed that HepG2 cells depicted fast internalization of CdSe/ZnS-SiO2 into the cells with very good fluorescence emission in the cytoplasmic portion.