Facile synthesis of near-infrared CuInS2/ZnS quantum dots and glycol-chitosan coating for in vivo imaging

This study describes the synthesis method of water-soluble, low-toxicity, photostable highly luminescent probes based on I–III–VI2 type semiconductor quantum dots (QDs) and the possibility of tumor targeting in living animals. Cd-free high-quality CuInS2/ZnS core/shell QDs were synthesized, and their surfaces were reacted with mercaptoundecanoic acid for aqueous phase transfer followed by reaction with glycol-chitosan; lastly, Arg-Gly-Asp (RGD) integrin-binding peptide was covalently attached for in vivo tumor targeting. Dowtherm A, a highly viscous heat-transfer organic fluid, was used to control semiconductor crystal growth at high temperature (>230 °C) during organic synthesis. The structural and optical properties of the resulting CuInS2/ZnS QDs were investigated. The average diameters of CuInS2 and CuInS2/ZnS QDs were 3.0 and 3.7 nm, respectively. Cell toxicity and in vivo tumor targetability in RR1022 cancer cell-xenografted mice were further evaluated using cRGDyk-tagged glycol-chitosan-coated CuInS2/ZnS QDs. Glycol-chitosan-coated MUA-QDs displayed a Z-average diameter of 203.8 ± 7.67 nm in water by dynamic light scattering.