A new diazotization-like phenomenon catalyzed by Mn3O4 vacancy nanozyme for smartphone-assisted visual detection of nitrite in food

The presence of excessive nitrite in foodstuffs poses significant risks to human health, underscoring the critical importance of developing rapid detection methods. This study synthesizes a Mn₃O₄ vacancy-rich nanozyme exhibiting exclusive oxidase-mimicking activity, capable of catalyzing the oxidation of N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium salt (TOPS). Intriguingly, TOPS oxidation derivatives demonstrate nitrite concentration-dependent color variations through a diazotization-like phenomenon. Thus, we establish dual detection platforms incorporating both visual and smartphone-assisted sensing modalities. Mechanistic investigations reveal that both the catalytic oxidation and diazotization-like processes involve reactive oxygen species ( • O₂ − and 1 O₂). Sensitivity studies demonstrate a linear detection range of 20–160 μM, with calculated limits of detection (LOD) at 1.9 μM (visual) and 0.01 μM (smartphone), respectively. Comparative analysis with national standard methods validates the reliability and accuracy of our approach in real food matrices. This work presents a robust analytical platform combining operational simplicity with laboratory-grade precision for food safety monitoring.