Modulating the growth of cysteine-capped cadmium sulfide quantum dots with enzymatically produced hydrogen peroxide

Cysteine (CSH) readily stabilizes cadmium sulfide quantum dots (CdS QDs) that grow in aqueous buffered solutions. The oxidation of CSH by hydrogen peroxide (H₂O₂) at room temperature yields cystine (CSSC), which is less efficient in stabilizing CdS QDs compared to CSH. Herein, we demonstrate that such oxidation causes a decrease in the formation rate of CSH-capped CdS QDs from Cd²⁺ and S²⁻ ions. For the first time, we combined the oxidation of CSH with the glucose oxidase (GO_x)-assisted biocatalytic oxidation of D-glucose, which leads to a buildup of H₂O₂ in the reaction mixture. The enzymatically modulated in situ growth of CdS QDs was monitored using two techniques: fluorescence spectroscopy and photoelectrochemical (PEC) analysis. This system enables quantification of GO_x and glucose in human serum. [Figure not available: see fulltext.].