Cysteine mediated synthesis of quantum dots: Mechanism and application in visual detection of hydrogen peroxide and glucose

•A novel straightforward, cost-effective and homogeneous visual sensor is developed for H2O2 and glucose detection.•The mechanism of the ligand effect during QDs synthesis was carefully studied by theoretical calculation.•Biomimetic synthesis of CdTe QDs was applied here for direct visual detection of H2O2 and glucose.•This system revealed good performance and nM level limit of detection could be obtained solely via visual observation. A novel visual detection method was developed for H2O2 and glucose detection via the L-Cysteine (L-Cys) mediated synthesis of quantum dots (QDs). The mechanism of the ligand effect during QDs synthesis was also studied by theoretical calculation. This strategy is based on that L-Cys can be used as both H2O2 substrate and ligand to mediate biomimetic synthesis of luminescent CdTe QDs. Iodide (I−) can catalytic oxidized L-Cys to L-cystine in the presence of H2O2, which inhibits the synthesis of QDs. Hence, the degree of inhibition for the QDs synthesis is proportional to the H2O2 concentration. Additionally, the ligand effect of L-Cys and L-cystine for CdTe QDs synthesis was studied. The density functional theory (DFT) calculations showed that the combination of CdTe QDs with L-Cys had higher energy and more stable configuration than that with L-cystine, indicating that L-Cys is the more stable ligand of QDs. Under the optimized conditions, a low limit of detection (LOD) was obtained for H2O2 (0.3 nM). Then, we used H2O2 as a bridge for glucose detection, with a LOD of 5 nM. The feasibility of this sensor was demonstrated by rapid detection of H2O2 and glucose by naked-eye at a level of 10 nM.