Synthesis, biocompatibility and cell labeling of L-arginine-functional beta-cyclodextrin-modified quantum dot probes

A series of quantum dots (QDs), CdSe, CdSe/CdS and CdSe/ZnSe, coated with L-arginine-modified beta-cyclodextrin (beta-CD-L-Arg) were prepared in a solution of H2O and hexane by ultrasonic method and characterized using PL, UV-vis, TEM, EDX and FTIR techniques. We observed that beta-CD-L-Arg-coated QDs are water-soluble and stable with high colloidal properties in water. Their photophysical properties are similar to those of trioctylphosphine oxide (TOPO)-coated nanocrystals. The quantum yield (QY) of beta-CD-L-Arg/CdSe/ZnSe QDs in water is 68%, which is much higher than those of beta-CD-L-Arg/CdSe/CdS (26%) and beta-CD-L-Arg/CdSe (13%). The in vitro cytotoxicity of these QDs was evaluated in ECV-304, SH-SY5Y and Hela cells and low cytotoxicity was observed. In particular, the beta-CD-L-Arg/CdSe/ZnSe QDs presented lower cytotoxicity to these cells (CC(50) value is 173 microg/mL in ECV-304 cells for 48h). This may be due to the presence of the ZnSe and beta-CD-L-Arg outlayer, which may improve the biocompatibility of QDs. The QDs were further investigated for biological labeling in ECV-304 cells using confocal laser scanning fluorescence microscopy. We found that these QDs were capable of localing to the cytoplasm of cells. These results demonstrate that the beta-CD-L-Arg-coated QDs could be used as a potential photoluminescent nanocrystal probing agent with good biocompatibility.