An L-cysteine based sensor for Cu²⁺ detection applicable for both environmental water and human plasma

A flexible electrochemical sensor with high sensitivity and specificity is developed using gold nanoparticles (AuNPs) and a reduced graphene oxide/molybdenum disulfide (rGo-MoS₂) composite modified screen printed carbon electrode (SPCE), with L-cysteine (L-Cys) as a probe for Cu²⁺ target recognition. Owing to the AuNPs/rGo-MoS₂, the electron transference ability is improved by increasing the specific surface area of the working electrode, and a high sensitivity is achieved. Meanwhile, the bidentate chelation of L-Cys to Cu²⁺ contributes to a good selectivity. Using differential pulse voltammetry (DPV) for spiked standard Cu²⁺, the test results show a dynamic range from 0.1 μM to 100 μM, a detection limit of 0.020 μM, and a high sensitivity of 1.190 μA μM^-1. Furthermore, detection in both environmental water and human plasma samples demonstrates a wide applicability of this sensor in various matrices, and an excellent feasibility for environmental and clinical applications.