<p> A Mn-doped Fe₃O₄ (Mn-Fe₃O₄) nanozyme was synthesized using a one-step solvothermal method. Compared to pristine Fe₃O₄, Mn-Fe₃O₄ exhibits unique oxidase (OXD)-like activity and enhanced peroxidase (POD)-like activity. The superior catalytic performance arises from the incorporated Mn species and the associated oxygen vacancies facilitate oxygen adsorption and activation, establishing an efficient self-cascade catalytic system. In this system, hydrogen peroxide (H₂O₂) generated in-situ through OXD-like catalysis can trigger mimic-POD reactions. A dual-mode antioxidant detection platform was subsequently constructed using melatonin (MT) as a proof of concept, with 3,3’,5,5’-tetramethylbenzidine (TMB) serving as the substrate for the Mn-Fe₃O₄ nanozyme. The colorimetric mode enables rapid visual screening by monitoring the oxidation of TMB to a blue-colored product, achieving a detection limit of 0.13 µM. The electrochemical mode features the novel utilization of mesoporous silica nanochannels for the selective enrichment of oxidized TMB (oxTMB), enabling highly sensitive quantification of MT with a detection limit as low as 0.6 nM. The assay applied to commercial tablets shows excellent recovery and reproducibility. This work combines engineered nanozymes with nanofilm-modified electrodes, offering an innovative approach for constructing advanced multimodal sensing systems.</p> Graphical Abstract <p></p>