Valence-Engineered Oxidase-Mimicking Nanozyme with Specificity for Aromatic Amine Oxidation and Identification

Oxidase-mimicking nanozymes with specificity for catalyzing oxidation of aromatic amines are of great significance for recognition of aromatic amines but rarely reported. Herein, Cu-A nanozyme (synthesized with Cu²⁺ as a node and adenine as a linker) could specifically catalyze oxidation of o-phenylenediamine (OPD) in Britton-Robinson buffer solution. Such a specific catalytic performance was also corroborated with other aromatic amines, such as p-phenylenediamine (PPD), 1,5-naphthalene diamine (1,5-NDA), 1,8-naphthalene diamine (1,8-NDA), and 2-aminoanthracene (2-AA). Moreover, the presence of salts (1 mM NaNO₂, NaHCO₃, NH₄Cl, KCl, NaCl, NaBr, and NaI) greatly mediated the catalytic activity with the order of NaNO₂ < blank ≈ NaHCO₃ < NH₄Cl ≈ KCl ≈ NaCl < NaBr < NaI, which was due to anions sequentially increasing interfacial Cu⁺ content via anionic redox reaction, while the effect of cations was negligible. With the increased Cu⁺ content, K_m decreased and V_max increased, indicating valence-engineered catalytic activity. Based on high specificity and satisfactory activity, a colorimetric sensor array with NaCl, NaBr, and NaI as sensing channels was constructed to identify five representative aromatic amines (OPD, PPD, 1,5-NDA, 1,8-NDA, and 2-AA) as low as 50 μM, quantitatively analyze single aromatic amine (with OPD and PPD as model analysts), and even identify 20 unknown samples with an accuracy of 100%. In addition, the performance was further validated through accurately recognizing various concentration ratios of binary, ternary, quaternary, and quinary mixtures. Finally, the practical applications were demonstrated by successfully discriminating five aromatic amines in tap, river, sewage, and sea water, providing a simple and feasible assay for large-scale scanning aromatic amine levels in environmental water samples.