Cysteine-conjugated silicon quantum dots-based dual-mode sensors for highly sensitive and selective detection of heavy metal ions

Dual-mode detection methods have attracted great interest because of their low cost, excellent biocompatibility, and facile synthesis, which are special usefulness for sensing. Herein, a fluorescent/colorimetric dual-mode sensor based on L-cysteine-conjugated silicon quantum dots (L-Cys-Si QDs) was developed. The characterization results demonstrated that the carboxyl groups in cysteine can interact with the amino groups on Si QDs. Compared to Si QDs, the L-Cys-Si QDs showed a much higher selectivity for Co²⁺ detection. Moreover, due to the presence of thiol groups, L-Cys-Si QDs could also be applied to Hg²⁺ detection, while Si QDs had no such effect. The dual-mode sensor L-Cys-Si QDs had been used to the detection of Hg²⁺ and Co²⁺ in water samples with satisfied results. This work suggests an easy procedure for improving the sensors' capacity for heavy metal ions via cysteine conjugation, and will inspire more synthesis of modified Si QDs and other nanomaterials with marvelous properties.