Aqueous Synthesis And Characterization For Optical And Chemical Properties Of CdTe/CdS/ZnS Quantum Dots

Quantum dots (QDs), also referred to as semiconductor nanocrystals, have attracted tremendous attention due to their unique electrical and optical properties in recent years. Compared with organic dyes, QDs have great advantages, such as size-dependent emission wavelength, a broad and continuous absorption spectrum, a narrow and symmetric emission spectrum and good photo and chemical stability. So far, QDs as luminescent probes have been successfully used in biological and medical fields such as immunoassay, DNA hybridization, cell imaging and potential photodynamic therapy. Currently, great progress has been made in preparation of QDs, and certain high-quality QDs, such as CdSe, CdTe, and some alloy nanocrystals, were successfully synthesized by organometallic approach and aqueous approach.To date, some core/shell-structured QDs, such as CdSe/ZnS, CdTe/CdSe and CdSe/ZnTe, have been successfully synthesized by organometallic routes. Especially, ZnS is non-toxic, chemically stable, and is often employed as the outer layer for QDs. Thus, as-prepared core/shell QDs are more preferable for their use in biomedical applications because they exhibit good stability and biocompatibility with low toxicity.In this paper, we described a strategy for synthesis of thiol-coated CdTe/CdS/ZnS (core-shell-shell) quantum dots (QDs) in the aqueous phase via conventional hydrothermal approach. The synthesis conditions were systematically optimized, which included the size of CdTe core, the refluxing time, the number of monolayers and the ligands. The chemical and optical properties of the as-prepared products were investigated. We found that the MPA-coated CdTe/CdS/ZnS QDs using CdTe QDs as the core presented highly photoluminescent quantum yields (PLQYs), good photostability and chemical stability, good salt tolerance and pH tolerance and favorable biocompatibility. The characterization of HRTEM, XRD and fluorescence correlation spectroscopy (FCS) showed that the CdTe/CdS/ZnS QDs had good monodispersity and nice crystal structure. The fluorescence life time spectra demonstrated that CdTe/CdS/ZnS QDs had a longer lifetime in contrast to fluorescent dyes and CdTe QDs. Furthermore, the MPA-stabilized CdTe/CdS/ZnS QDs were applied for the imaging of cells. Compared to current synthesis methods, our synthesis approach was reproducible and simple, and the reaction condition was mild. More importantly, our method was cost-effective, and was very suitable for large-scale synthesis of CdTe/CdS/ZnS QDs for the future applications.