Augmenting Enzyme Mimic Activity of Magnesium Ferrite Nanoparticles by Manganese and Cerium Ion Doping

Enzyme mimics can serve as efficient substitutes to address the challenges posed bynatural enzymes. Magnesium ferrite nanoparticles (MgFe 2 O 4 NPs) have attracted interest as enzyme mimics because of their good catalytic activity and stability. Manganese and cerium ions are promising dopants because of the high reduction potentials of the Mn 3+ /Mn 2+ and Ce 4+ /Ce 3+ pairs, which can enhance the catalytic activity. In the present work, pristine and doped Mg 0.8 Mn 0.2– x Ce x Fe 2 O 4+δ ( x = 0.0, 0.1, and 0.2) NPs were synthesized by using the sol–gel method and assessed comparatively as polyphenol oxidase (PPO) and peroxidase mimics. The single-phase spinel structure was validated by the X-ray diffraction patterns. Transmission electron microscopy analysis confirmed that the size of the NPs was less than 30 nm. SEM displayed agglomeration of NPs, and Energy-Dispersive X-ray Spectroscopy confirmed the effective doping of MgFe 2 O 4 NPs. Brunauer–Emmett–Teller analysis revealed that the surface area of ferrite NPs increased from 34.1 to 41.3 m 2 g –1 upon doping. Electrochemical impedance spectroscopy revealed faster electron transfer in Mg 0.8 Mn 0.2 Fe 2 O 4+δ NPs, which correlated with their best PPO and peroxidase-like activities. The effect of parameters, such as pH, temperature, enzyme mimic dose, and substrate concentration, was ascertained. The Mg 0.8 Mn 0.2 Fe 2 O 4+δ NPs showed high enzyme mimic activity due to the efficient redox cycling of Mn 3+ /Mn 2+ . The lower activity of the Mg 0.8 Ce 0.2 Fe 2 O 4+δ NPs is explained on the basis of slower charge transfer. Catechol, H 2 O 2, and glucose were detected using the Mg 0.8 Mn 0.2 Fe 2 O 4+δ NPs within linear ranges of 200–1000 μM, 20–1000 μM, and 20–1000 μM with detection limits of 7.7 μM, 7.0 μM, and 9.3 μM, respectively. The kinetic studies under optimal conditions showed a higher binding affinity for Mg 0.8 Mn 0.2 Fe 2 O 4+δ than for pristine MgFe 2 O 4 NPs. Mg 0.8 Mn 0.2 Fe 2 O 4+δ NPs were successfully used for the estimation of the phenolic content and H 2 O 2 in different samples. This work provides insights into the rational design of doped spinel ferrite nanozymes with tunable redox properties for advanced catalytic and sensing applications.