Ratiometric colorimetric detection of nitrite using CoMnO3 nanofibers as an oxidase-like enzyme to induce diazotization reaction

Nitrite is a typical food additive and preservative used in the food industry, which has attracted considerable attention due to its severe adverse effects on human health. Herein, a sensitive and highly selective ratiometric colorimetric sensing platform for the detection of nitrite was created based on a polymetallic oxide nanozyme, CoMnO₃ nanofibers (CMO) catalysis integrated with the particular diazotization reaction. The nanozyme has superior oxidase-like activity (K_m was 0.105 mM and V_max was 63.7 × 10^-8 M S^-1) and could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to oxidized TMB (oxTMB), as CMO could achieve the conversion of oxygen in the solution to superoxide anion (O₂˙^-). In addition, it is interesting to note that oxTMB can be diazotized in the presence of nitrite under acidic conditions, causing a shift in the ratio of nitrite concentration to the absorbance peaks at 450 and 652 nm (A₄₅₀/A₆₅₂). The ratio of A₄₅₀/A₆₅₂ exhibited a positive linear relationship with the concentration of nitrite within the concentration range of 0.2-200 μM, with a detection limit of 0.094 μM. Simultaneously, this method was also successful in quantifying the nitrite produced by brined and pickled foods and the dynamic tracking of the nitrite levels in various types of dishes. The analysis method not only offers dual-signal ratio sensing with high sensitivity but also holds the benefit of outstanding selectivity for the use of the particular reaction, which has a wide range of application prospects in food safety management.