A highly sensitive electrochemical sensor based on N-MLG@Ni-Mn LDH/Cys nanocomposite for detection of trace copper ions in sweat

A novel N-MLG@Ni–Mn LDH/Cys electrode was constructed for Cu²⁺ detection in sweat. • Dual active sites significantly enhance Cu²⁺ adsorption and signal amplification. • The sensor exhibits a wide detection range and a low detection limit for Cu²⁺. • The synergistic effect of N-MLG and Ni–Mn LDH improves electrochemical performance. In this study, a highly sensitive electrochemical sensor based on a N-MLG@Ni-Mn LDH/Cys nanocomposite was fabricated for the detection of trace Cu²⁺ in sweat. Nitrogen-doped multilayer graphene (N-MLG) was electrostatically self-assembled with nickel-manganese layered double hydroxide (Ni-Mn LDH) via their charge complementarity, forming a uniform heterostructure. L -cysteine (Cys) was further introduced as a surface modifier to construct the N-MLG@Ni-Mn LDH/Cys nanocomposite-based electrochemical sensor. Based on the hard-soft acid-base (HSAB) theory, a synergistic adsorption mechanism involving dual active sites was established, which significantly enhanced the preconcentration efficiency and specific recognition ability toward copper ions. Electrochemical measurements were performed using square-wave anodic stripping voltammetry (SWASV). Electrochemical characterization demonstrated that the sensor possesses excellent conductivity and good electrochemical activity. Under optimized experimental conditions, the sensor exhibited outstanding analytical performance. A good linear relationship was obtained for Cu²⁺ in the concentration range of 0.1–500 ppb, with a low detection limit of 0.24 ppb. In addition, the sensor prepared by this method showed good anti-interference capability, repeatability, and long-term stability, and it also performed well in the detection of artificial sweat samples. Overall, these performance advantages provide a feasible technical strategy for noninvasive monitoring of Cu²⁺ in sweat, with broad application prospects. An electrochemical sensing platform was constructed for the sensitive detection of Cu²⁺ in sweat based on an N-MLG@Ni-Mn LDH/Cys composite-modified screen-printed electrode (SPE). The electrostatic self-assembly between negatively charged N-MLG nanosheets and positively charged Ni-Mn LDH laminates leads to a stable intercalated heterostructure with high conductivity and abundant active sites. Subsequent functionalization with L-cysteine introduces sulfhydryl (-SH) groups, enabling specific chelation toward Cu²⁺ and enhancing selectivity. During detection, Cu²⁺ is effectively preconcentrated via the synergistic interactions of hydroxyl (-OH) and sulfhydryl (-SH) groups, followed by electrochemical reduction to Cu⁰ under a negative potential. The deposited Cu⁰ is then oxidized during the stripping process, generating a characteristic current signal proportional to the Cu²⁺ concentration. Combined with SWASV, this dual-active-site strategy achieves high sensitivity, excellent selectivity, and reliable analytical performance, demonstrating its effectiveness for trace Cu²⁺ detection in sweat. Download: Download high-res image (221KB) Download: Download full-size image