الفهرس 
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Abstract
Quantum dots (QDs) are zero-dimensional systems wherein charge carriers (i.e., electrons and holes) are confined in all three dimensions. QDs are a very interesting nanomaterial with unique characteristics, which could help in many clinical and pharmaceutical purposes. In this study, we aimed to investigate the efficiency of silica-coated CdSe/ZnS (CdSe/ZnS-SiO2 NCs) and Graphene nanocrystals (GQDs) 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. On the other hand, GQDs were synthesized via glucose pyrolysis. Then, the prepared NCs overcoated 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 was tested by evaluating mitochondrial activity and alkaline comet assay of liver hepatocellular carcinoma (HepG2) cells exposed to different concentrations of QDs. The intracellular uptake and localization of QDs in HepG2 cells, Bacillus subtilis (B. subtilis) and Chlamydomonas reinhardtii (C. reinhardtii) 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 30 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 human, bacterial and algal cells. While GQDs showed higher biocompatibility and good ability to internalization inside human cells however it showed internalization inside neither bacteria nor algae.