Buffer Concentration-Dependent Catalytic Performance of Cu-Adenine Oxidase Mimic for Constructing Sensor Array for Identifying Aromatic Amines and Phenols

Oxidase-mimicking nanozymes are some of the most important nanozymes, which are investigated in various buffer concentrations. However, buffer concentration-dependent catalytic performance is rarely investigated. Herein, with o-phenylenediamine (OPD) as a substrate, the catalytic performance of Cu-Adenine oxidase mimic (fabricated with Cu2+ as an active center and adenine as a ligand) gradually decreases upon Tris–HCl buffer concentration (CTris–HCl) increasing from 10 to 200 mM, exhibiting buffer concentration-dependent catalytic activity. Such buffer concentration-dependent catalytic activity is believed to be because Tris–HCl and OPD competitively bind with Cu-Adenine, leading to differences in catalytic activity. Similarly, with 2,4-dichlorophenol (2,4-DP) as a substrate and 4-aminoantipyrine (4-AP) as a chromogenic agent, the same results are obtained. However, with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 3,3′,5,5′-tetramethylbenzidine (TMB) as substrates, the catalytic oxidation cannot be observed at CTris–HCl ≥ 50 mM. Tris–HCl and substrate competitively binding with Cu-Adenine produces buffer concentration-dependent catalytic performance. Subsequently, substrates are successfully expanded to other aromatic amines (p-phenylenediamine (PPD), 1,5-naphthalenediamine (1,5-NDA), 1,8-naphthalenediamine (1,8-NDA)) and phenols (phenol, 3-cresol, 1-naphthol). Based on the results, with 50 and 150 mM Tris–HCl buffer solutions as sensing channels, a Cu-Adenine-based colorimetric sensor array is constructed for discriminating four representative aromatic amines (OPD, PPD, 1,5-NDA, 1,8-NDA) and four phenols (2,4-DP, phenol, 3-cresol, 1-naphthol) as low as 50 μM. The performance is further validated through accurately identifying binary, quaternary, and even senary and octonary mixtures. Finally, the designed sensor array is successfully applied for identifying eight representative aromatic amines and phenols in river water, seawater, and sewage water, presenting great potential and valuable applications for large-scale scanning levels of aromatic amines and phenols in water samples.