Preparation of Cu-doped CdS quantum dots coated with biocompatible carboxymethyl chitosan for near infrared fluorescence imaging

In this study, water soluble Cu-doped CdS quantum dots (Cu:CdS QDs) were synthesized by one-pot method. The effect of reaction conditions on the Cu:CdS QDs were studied systematically, and the Cu:CdS QDs synthesized under optimizing condition possessed a small size (similar to 4 nm), high luminance and good self-fluorescence performance. Compared with CdS QDs, the fluorescence emission was redshifted from 627 nm to 720 nm. To reduce cytotoxicity of Cu:CdS QDs, carboxymethyl chitosan (CMCS) molecules were selected to be grafting onto the surface of Cu:CdS QDs through amide bonds and the CMCS modification would greatly impede the release of cadmium ions. Both in vitro cellular cytotoxicity and hemolysis assay demonstrated that the CMCS/Cu:CdS QDs were highly biocompatible and the CMCS/Cu:CdS QDs as fluorescent probes were successfully applied in vivo imaging of small animals and this QDs can be easily metabolized by mice over time without adverse reactions. This new nanoprobes open up exciting opportunities for future biomedical applications.