Coupling diazotization with oxidase-mimetic catalysis to realize dual-mode double-ratiometric colorimetric and electrochemical sensing of nitrite

Nitrite is often utilized as coloring and preservative agents in food industry, but excessive nitrite in drinking water and food causes great threats to human health, requiring convenient and reliable methods for its monitoring. In comparison with common single-signal assays, multimodal detection can not only expand application scenarios but also offer self-correction and self-validation to obtain more reliable results. However, how to achieve the multimodal sensing of nitrite remains a challenge. Here we report a novel dual-mode double-ratiometric colorimetric and electrochemical method for nitrite quantification by coupling diazotization with oxidase-mimicking catalysis. Carbon-supported Mn3O4 particles were explored as an oxidase-like nanozyme with excellent activity to catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue TMBox. On the one hand, the presence of nitrite can induce the diazotization of TMBox, not only decreasing the visible signal of TMBox at 652 nm but also generating a new signal assigned to diazotized TMBox at 445 nm. On the other hand, the existence of nitrite triggers the decrease of the TMB homogeneous electro-oxidation signal, but offers a new electro-oxidation signal attributed to nitrite itself. With such an interesting sensing principle, a dual-mode double-ratiometric colorimetric and electrochemical approach was developed to detect nitrite with good sensitivity and specificity. Reliable applications of the method in monitoring nitrite in several matrices were also demonstrated, implying its great promise in food safety supervision and environmental monitoring.