Three-dimensional nitrogen-doped graphene-based metal-free electrochemical sensors for simultaneous determination of ascorbic acid, dopamine, uric acid, and acetaminophen.

Three-dimensional nitrogen-doped graphene (3D-NG) networks, yielded by hydrothermal reaction and freeze-drying treatment, were used as building blocks to construct a metal-free quadruplet electrochemical sensor for simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA), and acetaminophen (AP). The introduced 3D-NG materials with a 3D porous structure and a nitrogen doping effect were beneficial for the generation of multidimensional electron transfer pathways and the improvement of electrocatalytic activities by modulating their electronic properties, which could contribute to the effective differentiation of the four analytes in their quaternary mixture. Well-resolved oxidation peaks and enhanced response currents of AA, DA, UA, and AP were obtained from the 3D-NG-based electrodes. For the individual determination of one analyte, the linear concentration ranges of AA, DA, UA, and AP were 20-10 000, 1-1000, 0.5-1000, and 0.1-600 μM with detection limits of 3.91, 0.26, 0.12, and 0.02 μM (S/N = 3), respectively. After the synchronous change of the concentrations of AA, DA, UA, and AP, desirable linear relationships were observed in the ranges of 100-7000, 2-600, 1-800, and 10-550 μM with detection limits of 24.33, 0.37, 0.21, and 1.87 μM (S/N = 3), respectively. This sensitive sensing platform was successfully used to monitor AA, DA, UA, and AP in human urine samples, which indicated that 3D-NG could become a promising electrode material for the simultaneous monitoring of multiple electroactive species.