Evaluations of the chemical stability and cytotoxicity of CuInS₂ and CuInS₂/ZnS core/shell quantum dots

Recently, CuInS2 quantum dots (CIS QDs) are extensively applied in biological applications because of their distinctive optical property. These novel ternary semiconductor CIS QDs can be developed into good biomarkers or trackers because they do not contain cadmium, unlike CdTe and CdSe QDs with high risk for cytotoxicity. However, reports on toxicity and effective factors affecting CIS QDs are seldom developed, and in vivo chemical stability has not been clearly investigated. In this study, we focused on the fate, degradation, and exposure time of CIS QDs in Caenorhabditis elegans (C. elegans), which is used as a model organism in biology. Moreover, X-ray absorption near-edge structure (XANES) is used to identify the oxidation state of CIS and CIS/ZnS QDs in various exposure times. The purpose was to use different oxidation states of copper and zinc ions of QDs to achieve chemical stability in C. elegans. CIS and CIS/ZnS QDs were synthesized by hydrothermal method, and QDs were transferred to aqueous solution by coating with O-carboxymethylchitosan (OCMCS). Moreover, intracellular uptake and cell viability tests were estimated as preliminary experiments for in vitro cytotoxicity testing. Our results showed that the supported QD materials can be applied in biological systems. Consequently, we further considered the function of QD materials in C. elegans. The QD materials of coating OCMCS could be successfully delivered to the interior of the C. elegans through the alimentary system in a manner dependent on the exposure time. Most importantly, XANES results revealed that the oxidative state of CIS QDs did not change without an outer layer after treatment for 96 h in C. elegans. Therefore, the extreme chemical stability of CIS QDs may explain the low cytotoxicity in the organism and thus has potential biomedical applications.