Trimetallic Mn/Ni/Fe-MOF as a peroxidase-mimic nanozyme for ratiometric colorimetric sensing of nitrite

A ratiometric colorimetric sensing platform was developed for nitrite detection, featuring a trimetallic metal-framework (MOF) nanozyme (Mn/Ni/Fe-MOF) synthesized via a facile one-pot solvothermal method. Comprehensive characterization revealed its successful fabrication and superior structural properties. The rational design of the trimetallic system creates a synergistic electron transfer network, endowing it with significantly enhanced peroxidase-like activity that surpasses its mono- (Fe-MOF) and bimetallic counterparts (Mn/Fe -MOF and Ni/Fe -MOF). This advancement leads to a low detection limit of 1.39 μM and a wide linear range of 2.0–150 μM for nitrite sensing, improving the sensitivity of nanozyme-based colorimetric method. Leveraging this high activity, Mn/Ni/Fe-MOF catalyzed H 2 O 2 -mediated oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue product (oxTMB). Subsequently, a robust ratiometric platform (A 450 /A 652 ) was constructed based on a specific diazotization reaction between nitrite and oxTMB, which induced a distinct color change and an absorbance shift. Unlike single-signal assays prone to fluctuations, this internal reference mechanism automatically corrects for common interferences, ensuring high accuracy and reliability in complex matrices, as evidenced by excellent recoveries (97.9%–102.3%) in real samples (tap water and sausage). The entire system is characterized by remarkable simplicity: the nanozyme is synthesized via a facile one-pot method, and the detection requires only a single-step addition of nitrite to the pre-formed oxTMB system under mild acidic condition. This streamlined, “mix-and-detect” protocol avoids complex modifications, multi-step reactions, or sophisticated instruments, offering practical advantages for potential on-site application. This work presents a reliable, high-performance sensing strategy and highlights the great potential of multi-metal MOF nanozymes in designing advanced sensors.