Multi-functional Fe-metallohydrogel with peroxidase/oxidase activities for dye degradation and nitrite detection

A metallohydrogel designated as 2-PY-Fe was synthesized via a straightforward method, exhibiting both peroxidase-like and oxidase-like activities. On one hand, based on its peroxidase-like activity, 2-PY-Fe can serve as a catalyst for the degradation of various dyes. On the other hand, 2-PY-Fe metallohydrogel was used as an oxidase-like nanozyme to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to oxTMB. The addition of nitrite can trigger the diazotization of oxTMB, resulting in a decrease in the absorption peak at 654 nm and the emergence of a new signal peak at 446 nm resulting from the diazotization of oxTMB. Simultaneously, the existence of nitrite induces the decrease of the electro-oxidation signal of TMB and presents a new electrochemical signal from nitrite itself. A ratiometric colorimetric/electrochemical method and a smartphone-assisted detection method were established, combining the oxidase-mimicking catalysis and diazotization reaction. Additionally, this developed method was applied to monitor nitrite in real samples.