Fe–N–C oxidase-mimicking nanozymes for discrimination of antioxidants and detection of Hg²⁺

Single-atom nanozymes (SAzymes) with high atom utilization efficiency and well-defined coordination structures have been extensively studied. However, research on the use of the enzyme-like activity of SAzymes for the detection and discrimination of antioxidants remains relatively limited. Herein, synthesized Fe-N-C SAzymes (FeN₄) display excellent oxidase-like activity with a maximum reaction rate of 1.083 × 10^-7 M s^-1, which is 40.85 times higher than that for NC nanozymes. Experimental studies and density functional theory (DFT) calculations revealed that the high catalytic performance arises from the efficient absorption and activation of O₂ at highly exposed Fe sites. Based on the different inhibitory effects of ascorbic acid (AA), glutathione (GSH), and cysteine (Cys), a colorimetric sensor array for identifying antioxidants was developed. AA, GSH, and Cys were effectively distinguished through linear discriminant analysis (LDA). Moreover, a colorimetric platform for the rapid detection of trace Hg²⁺ was successfully presented, taking advantage of the strong binding ability between -SH of Cys and Hg²⁺, and achieving an impressive limit of detection (LOD) of 9.29 nM. This work not only provides a novel concept for distinguishing antioxidants but also expands the application of nanozymes in heavy metal ion detection.