Effects of L-cysteine on the photoluminescence, electronic and cytotoxicity properties of ZnS:O quantum dots

L-cysteine capped ZnS:O quantum dots (QDs) were prepared by two steps. The effects of L-cysteine (L-cys) on the crystal structure, size, water-dispersibility, photoluminescence (PL) and cytotoxicity were studied. It was found that the surface modification of L-cys on ZnS:O QDs did not change the crystal structure, and their average crystallite size increased with the increase of L-cys content. Moreover, the water-dispersibility and photostability of ZnS:O QDs can be improved by L-cys modification. The results displayed that the PL intensity was remarkably enhanced with the increase of L-cys concentration. The most intense emission was obtained when the mass ratio of L-cys:ZnS:O = 1.2:1, and was about 5 times stronger than that of uncoated ZnS:O QDs. First-principles calculations were used to explain the origin of high PL intensity. Also, it showed that the L-cys capped ZnS:O QDs were nontoxic and maintained remarkable cell viability and morphology up to the concentration of QDs was 200 mg/mL for HeLa cells. This work suggested that L-cys capped ZnS:O QDs had favorable biocompatibility and may be used for in vitro cell imaging of HeLa cells. (C) 2020 Elsevier B.V. All rights reserved.