Atomic Engineering of a FeFe Dual Single-Atom Nanozyme for Enhanced Peroxidase-like Activities To Build Chemical Tongue for Discrimination of Aromatic Amines

Single-atom nanozymes have made important progress in the field of sensors, but their catalytic performance as natural enzyme substitutes is far from satisfactory. We describe here a FeFe dual single-atom nanozyme (Fe₂N_6/CN) with a Fe loading of 0.89 wt %, and it shows a synergistic effect and a peroxidase (POD)-like activity. Especially, the Fe₂N₆/CN nanozyme shows an excellent specific activity (315.4 U μmol^-1). The values of catalytic rate constant (<i>k</i>_cat) and catalytic efficiency (<i>k</i>_cat/<i>K</i>_m) for the Fe₂N₆/CN with 3,3',5,5'-tetramethylbenzidine (TMB) are 23.8 s^-1 and 8.24 × 10⁴ M^-1 s^-1, respectively, and with H₂O₂, they are 30.8 s^-1 and 0.919 × 10³ M^-1 s^-1, respectively. Density functional theory calculations reveal that Fe₂N_6/CN possesses excellent POD-like activity. Based on the POD-like activity of Fe₂N₆/CN, we design a Fe₂N₆/CN nanozyme chemical tongue for the colorimetric recognition of aromatic amines using three wavelengths as array's channels. The data interpretation using linear discriminant analysis, clustering heat map, etc., shows excellent clustering separation and classification of aromatic amines. Furthermore, this chemical tongue can simultaneously recognize mixtures of different molar ratios, quantitatively determine different concentrations of individual aromatic amines, and even identify unknown samples. This preparation strategy not only provides a promising pathway for the utilization of nanozymes but also highlights the potential of dual single atoms as an attractive platform for design of sensor arrays.