Spectroscopic Properties and Biocompatibility Studies of CdTe Quantum Dots Capped with Biological Thiols

CdTe quantum dots (QDs) capped with two relevant biological thiols, glutathione (GSH) or cysteine (Cys) were synthesized in aqueous solution using CdCl₂, K₂TeO₃ and NaBH₄ and their chemical, spectroscopic and biocompatibility properties were assessed. Synthesized nanoparticles (NPs) are 3–6 nm in diameter, with emission spectra between 480–580 nm depending on QDs size, and emission quantum yields between 0.35–0.65. The toxicity of thiol-capped CdTe NPs to different bacterial strains was determined. Increased biocompatibility for Cys-capped QDs was observed. In addition, QDs uptake by eukaryotic cells was evaluated by fluorescence microscopy. CdTe-GSH NPs were incorporated into MKN45 cells only in the presence of lipofectamine. On the other hand, although CdTe-Cys NPs were freely incorporated into these cells, the amount of incorporation as well as the number of fluorescent cells was lower than that observed with GSH-capped QDs. Finally, no significant changes in cell morphology as a consequence of GSH- or Cys-capped QDs incorporation were observed. Summarizing, our results indicate that the as-synthesized GSH- and Cys-capped QDs display differential spectroscopic properties and cellular interactions, being CdTe-Cys more biocompatible than CdTe-GSH NPs.