Synthesis of poly(ethylene glycol)-graft-chitosan and using as ligand for fabrication of water-soluble quantum dots

The synthesis of water-soluble, stable and biocompatible quantum dots (QDs) is of crucial importance for nanobiotechnology. A chitosan derivative, poly(ethylene glycol)-graft-chitosan (PEG-g-CS), was successfully synthesized and employed as ligand for the growth of CdSe QDs in aqueous solution. The bivalent Cd(2+) ions can coordinate with multiple amino-groups, thus they act as both inter- and intramolecular cross-linking agents. When the concentration of Cd(2+) was 0.2 mmol/L, the CdSe/PEG-g-CS aggregates formed an irregular cross-linked network; when the concentration was 1 mmol/L, a phenomenon of micro-phase separation emerged as a result of enrichment of CS phase; when the concentration was 2 mmol/L, spherical nanohybrids with the size of 30-50 nm were obtained. Moreover, a possible mechanism was proposed for the formation of CdSe/PEG-g-CS aggregates. Meantime, in vitro 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity tests against HepG2 cells were carried out, the corresponding results suggested that the CdSe QDs prepared using PEG-g-CS as ligand displayed very low cytotoxicity. Therefore, these water-soluble QD-polymer hybrids are expected to find promising applications in medical field.