Water-soluble chitosan-quantum dot hybrid nanospheres toward bioimaging and biolabeling

A facile approach to prepare CdSe/ZnS quantum dot-encapsulated chitosan hybrid nanospheres (CS-QD) is developed by utilizing ethanol-aided counterion complexation in aqueous solution. The obtained CS-QD hybrid nanospheres have not only the loading space provided by the chitosan spherical matrix for loading multiply QDs but also unique fluorescent properties provided by the encapsulated QDs. Moreover, these hybrid nanospheres possess good biocompatibility and optical stability in physiological environment. It is demonstrated that CS-QD hybrid nanospheres can be internalized by tumor cells and hence act as labeling agent in cell imaging by optical microscopy. In addition, CS-QD hybrid nanospheres can be used for imaging of tumor in tumor-bearing mice via intratumoral administration and can accumulate at tumor site via the blood circulation based on intravenous injection. Thus, on the one hand, chitosan nanospheres provide the protection in both colloidal and optical stability arising from QDs and offer biocompatibility. On the other hand, the encapsulated QDs light up polymer nanospheres and display the fate of polymer nanospheres in cells and bodies.