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

Abstract

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.

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

“…According to the reported procedures, , with Cu 2+ as a metal ion and adenine as a ligand, the ellipsoid-shaped nanomaterial with average length of ca. 1.5–2 μm and width of ca.…”

“…According to the literature, − upon exploring the catalytic performance of nanozyme, the selected buffer system with concentration ranging from 10 to 200 mM is applied, respectively. A question appears: does buffer concentration affect the catalytic activity?…”

“…In the presence of Cu-Adenine, colorless PPD turns dark purple in 50 mM Tris–HCl, and a new absorption peak at 517 nm appears, indicating that PPD is catalytically oxidized (Figure A) . For 1,5-NDA, the solution switches to pink-purple in 50 mM Tris–HCl and a new absorption peak at 508 nm corresponding to oxidized 1,5-NDA is detected (Figure B) . For 1,8-NDA, such oxidation is also observed in 50 mM Tris–HCl, expressed as the appearance of a new absorption peak at 514 nm and the solution switching from colorless to brown (Figure C) .…”

“…Nanozymes are nanomaterial-based artificial enzymes. − Compared with natural enzymes, nanozyme exhibits various distinct advantages, such as low cost, high durability, adjustable activity, high tolerance to harsh environments, etc. − Nanozymes can be divided into peroxidase, oxidase, superoxide dismutase, catalase, etc., − among which, oxidase-mimicking nanozymes are widely applied in therapeutics, − biosensing, − bioimaging, , and also environmental monitoring and protection. − According to the literature, ,− the catalytic performance of oxidase mimics is explored in various buffer systems, and also the buffer concentrations range from 10 to 200 mM. Recently, it is found that oxidase mimics exhibit buffer species-dependent catalytic performance .…”

“…Polycyclic aromatic hydrocarbons (PAHs) are well-known persistent organic pollutants owing to their high mutagenicity, teratogenicity, and carcinogenicity, , among which, aromatic amines and phenols are two typical types of pollutants. − Aromatic amines could be specifically and catalytically oxidized by oxidase mimics in proper buffer solution, which is used for designing sensor array to identifying multiple aromatic amines . And also, phenols could be catalytically oxidized by laccase mimics (a kind of oxidase mimics), which are usually utilized to degrade phenols and to design sensors for detecting a single phenol (catechol, hydroquinone, 2-chlorophenol, 4-chlorophenol, and phenol) and even as a sensor array for multiple phenols − because multiple phenols are possibly coexisting in most cases. − As important synthetic industrial chemicals and intermediary products, aromatic amines and phenols are usually coexisting in water, , while the strategy that can simultaneously identify aromatic amines and phenols is rarely reported.…”