Cellular uptake, elimination and toxicity of CdSe/ZnS quantum dots in HepG2 cells

In this work, the cellular uptake, elimination and toxicity of CdSe/ZnS QDs in HepG2 cells were comprehensively studied using inductively coupled plasma mass spectrometry (ICP-MS), MTT assay, AO/EB staining, and glutathione level and gene expression analysis. ICP-MS analytical results showed that the uptake efficiency of CdSe QDs by HepG2 cells was lower than that of Cd(II) and Se(IV), and the uptake was dose- and time-dependent. The uptake amount was related to the physicochemical properties of QDs, and NH2-QDs with smaller size were more easily taken up by cells. In combination with various biochemical methodologies, a systematic and thorough quantitative analysis of the in vitro effects of CdSe/ZnS QDs with different coatings was conducted, along with that of Cd (II) and Se (IV). Although Cd(II) above 8.9 μM exhibited obvious toxicity to the cells, no obvious toxicity of four CdSe/ZnS QDs was observed within the tested concentration range (10-100 nM), most likely due to the protection of the ZnS shell and the PEG coating. From the molecular level's point of view, QDs at concentration of 100 nM exhibit obvious impact on the cells, such as increased gene expression (MT1A and CYP1A1), which was positively correlated with the intracellular concentration of QDs.