A wearable sweat ascorbic acid sensor based on N-rGO-supported Ni3N/Ni heterostructure with enhanced electrochemical sensing properties

Abstract

Accurate quantification of ascorbic acid (AA) levels in human sweat is critical for the application of wearable sensor technology in health monitoring. However, the performance of current sensors often deteriorates due to decreased enzyme activity. Non-enzymatic electrochemical sensors, particularly those based on transition metals, transition metal nitride nanocomposites, and two-dimensional materials, have emerged as promising alternatives for AA detection. In this study, we used graphite oxide (GO) as a carbon source, NaCl crystals as a solid dispersant, and nickel acetate as a precursor. A composite material of nitrogen-doped reduced graphene oxide with a porous structure and a surface-loaded Ni₃N/Ni heterojunction (Ni₃N/Ni/N-rGO) was prepared via ammonia nitridation. During the nitridation process, nitrogen doping effectively regulates the charge distribution of the sp² carbon skeleton, induces structural defects, and enhances the electron transfer rate. By adjusting the GO content, nitridation temperature, and calcination time, a porous nano-biomimetic enzyme was successfully synthesized, and a high-performance electrochemical sensing system was developed. Electrochemical tests demonstrated that Ni₃N/Ni/N-rGO exhibits a large electrochemically active surface area and enhanced electrochemical sensing activity. In addition, the biomimetic enzyme accelerates the oxidation of vitamin C due to the vitamin C-like enzymatic activity of Ni₃N/Ni, its excellent interfacial electron transfer properties, and the high conductivity of N-rGO. Density functional theory (DFT) simulations were employed to elucidate the reaction mechanism and Gibbs free energy change during the electrocatalytic oxidation of vitamin C. The sensor exhibits a wide detection range (0.5–1937.5 μM), high sensitivity (663.87 μA mM⁻¹ cm⁻²), and a low detection limit (0.25 μM). Combined with a wearable electrochemical sensing system, the vitamin C content data in sweat can be collected and analyzed, demonstrating the potential of Ni₃N/Ni/N-rGO as a promising material for vitamin C sensing applications.