Exploring dual catalytic functionality of MnO₂ nanozymes through coupled colorimetric and electrochemical responses

In this work, MnO₂ nanorods (MnO₂) were synthesized and demonstrated as a versatile dual-functional nanozyme platform for integrated colorimetric and electrochemical sensing pathways. Using furazolidone (FZD) as a model probe, we unraveled a unique kinetic modulation mechanism where FZD acts as an interfacial electron-transfer modulator rather than a simple enzyme inhibitor. Spectroscopic investigations reveal that FZD selectively suppresses the over-oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to its diimine form (TMB²⁺, 450 nm), promoting the accumulation of the stable radical cation (TMB^.+, 652 nm). Concurrently, the redox-active surface of MnO₂ accelerates the direct electrochemical reduction of FZD's nitro groups via a multi-electron pathway. Density functional theory (DFT) calculations confirm that the low-lying lowest unoccupied molecular orbital (LUMO) of FZD (-3.62 eV) facilitates reactive oxygen species capture, while facet-dependent adsorption energetics (E_ads = -75.1 kJ.mol^-1 on {100}) support the adsorption-controlled catalysis. Under optimized conditions, the platform achieved reliable dual-mode detection for FZD. This study provides a fundamental framework for designing single-material nanozyme systems with coupled catalytic outputs.