Hierarchical Fe3O4@C@MnO2 nanozymes: bridging structural engineering to on-site biosensing of tannic acid

Manganese dioxide (MnO 2 )-based heterogeneous catalysts have gained significant attention in nanozyme research due to their exceptional oxidase-mimicking capabilities. This work reports the rational design of MnO 2 functionalized magnetic carbon nanotubes (Fe 3 O 4 @C@MnO 2 ) through a multistep synthesis strategy. The magnetic N-doped hollow carbon substrate (Fe 3 O 4 @C) was first synthesized via controlled pyrolysis of FeOOH-coated polydopamine precursors. Subsequent interfacial redox reaction with KMnO 4 enabled the in situ deposition of ultrathin MnO 2 nanosheets on the nanotube substrate, forming a triple-component coaxial architecture. This hollow structure not only facilitates dense MnO 2 deposition but also maintains robust magnetic responsiveness. The obtained Fe 3 O 4 @C@MnO 2 exhibits remarkable enzyme-mimetic capability, catalyzing TMB chromogenic conversion with 0.92-fold enhanced catalytic performance relative to pristine MnO 2 . Systematic mechanistic studies reveal that tannic acid (TA) competitively inhibits ·OH radical generation via MnO 2 -TA complexation, while the carbon interlayer enhances electron transfer efficiency. Owing to the superior enzyme-mimetic performance of Fe 3 O 4 @C@MnO 2 and their inhibition effect by TA, a sensitive colorimetric biosensing assay was fabricated, achieving a TA detection limit of 0.029 μM with a 0.096–4.82 μM linear concentration range. This work exemplifies the synergy of structural engineering and component optimization in designing multifunctional nanozymes, showing potential applications in food quality monitoring, environmental analysis, and point-of-care diagnostics. Graphical