Facile synthesis and characterization of highly fluorescent and biocompatible N-acetyl-l-cysteine capped CdTe/CdS/ZnS core/shell/shell quantum dots in aqueous phase

The synthesis of water-soluble quantum dots (QDs) in aqueous phase has received much attention recently. To date various kinds of QDs such as CdTe, CdSe, CdTe/CdS and CdSe/ZnS have been synthesized by aqueous methods. However, generally poor-quality QDs (photoluminescent quantum yield (PLQY) lower than 30%) are obtained via this method and the 3-mercaptopropionic acid stabilizer is notorious for its toxicity and awful odor. Here we introduce a novel thiol ligand, N-acetyl-l-cysteine, as an ideal stabilizer that is successfully employed to synthesize high-quality CdTe/CdS/ZnS QDs via a simple aqueous phase. The core/shell/shell structures of the CdTe/CdS/ZnS QDs were verified by x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, x-ray powder diffraction and transmission electron microscopy. These QDs not only possess a high PLQY but also have excellent photostability and favorable biocompatibility, which is vital for many biological applications. This type of water-dispersed QD is a promising candidate for fluorescent probes in biological and medical fields.