Effect of surface ligands with different terminal group on the optical stability and cytotoxicity of CuInS₂/ZnS quantum dots with the crystal structure of sphalerite

A novel method for preparing CuInS₂/ZnS quantum dots (CuInS₂/ZnS QDs) with the crystal structure of sphalerite by one-pot hot injection was developed in this paper. The as-prepared core CuInS₂ quantum dots (CuInS₂ QDs) was uniform spherical nanoparticle with the average diameter of about 2 nm with the fluorescent quantum yields (QY) of about 2.6%. By capping a shell of ZnS on the surface of CuInS₂ QDs, the formed CuInS₂/ZnS QDs exhibited obvious enhanced fluorescent emission with the QY of about 20%. Intriguingly, the crystal structure of obtained CuInS₂/ZnS QDs is sphalerite, which was confirmed by XRD. Considering the different terminal group between these small organic molecules, mercaptoacetic acid (TGA), thioglycerol (TGC) and mercaptoethylamine (MEA) were further selected as capping molecules to exchange the surface ligands of CuInS₂/ZnS QDs. The obtained CuInS₂/ZnS QDs modified with TGC exhibited excellent photostability in physiological conditions. To investigate the effect of ligand molecules on the biocompatible of CuInS₂/ZnS QDs, the experiment on the cytotoxicity of CuInS₂/ZnS QDs to A549 cells were conducted. The results indicated that CuInS₂/ZnS QDs capped with TGC showed the lowest cytotoxicity while CuInS₂/ZnS QDs capped with MEA exhibited the highest cytotoxicity among the three types of CuInS₂/ZnS QDs modified with ligands with different terminal group. These results provided a sight on how to select surface ligands to modify CuInS₂/ZnS QDs when CuInS₂/ZnS QDs will apply in biological fields. (paper)