# Study on the Immobilization of Horseradish Peroxidase on a Multi-Level Composite Carrier SiO2@MnO2@MAF-7

## TL;DR

This study develops a new composite material to stabilize and reuse the enzyme horseradish peroxidase, improving its efficiency and durability for industrial applications.

## Contribution

The first use of SiO2@MnO2@MAF-7 for HRP immobilization, combining three strategies to enhance stability and reusability.

## Key findings

- MAF-7 encapsulation achieved 85.03% immobilization efficiency and 42% lower Km, showing better substrate affinity.
- The composite carrier retained 65% activity after five reuse cycles and improved activity retention by 35–50% under harsh conditions.
- MAF-7’s mesopores (12.47 nm) matched HRP size, and π-π stacking and H-bonds stabilized the enzyme.

## Abstract

What are the main findings?
Hierarchical Immobilization Superiority: The SiO2@MnO2@MAF-7 carrier immobilized HRP via three strategies (adsorption/cross-linking/encapsulation), with MAF-7 encapsulation showing the highest efficiency (85.03%) and 42% lower Km, indicating enhanced substrate affinity.Synergistic Stability Enhancement: MnO2’s peroxidase-like activity combined with MAF-7’s confinement effect improved HRP’s activity retention by 35–50% at 80 °C/pH 4–9, maintaining 65% activity after five reuse cycles.Structure-Mechanism Correlation: BET/XRD confirmed MAF-7’s mesopores (12.47 nm) matched HRP size, while FTIR/docking revealed HRP-MAF-7 stabilization via π-π stacking and H-bonds, clarifying the molecular-level protection mechanism.

Hierarchical Immobilization Superiority: The SiO2@MnO2@MAF-7 carrier immobilized HRP via three strategies (adsorption/cross-linking/encapsulation), with MAF-7 encapsulation showing the highest efficiency (85.03%) and 42% lower Km, indicating enhanced substrate affinity.

Synergistic Stability Enhancement: MnO2’s peroxidase-like activity combined with MAF-7’s confinement effect improved HRP’s activity retention by 35–50% at 80 °C/pH 4–9, maintaining 65% activity after five reuse cycles.

Structure-Mechanism Correlation: BET/XRD confirmed MAF-7’s mesopores (12.47 nm) matched HRP size, while FTIR/docking revealed HRP-MAF-7 stabilization via π-π stacking and H-bonds, clarifying the molecular-level protection mechanism.

What are the implications of the main findings?
Industrial Potential: The composite carrier addresses free HRP’s instability and unrecoverability, offering a scalable solution for oxidoreductase applications.Generalizable Design: The “rigid core-catalytic shell-porous framework” strategy can be extended to other enzymes (e.g., laccase or glucose oxidase).Mechanistic Insight: The revealed Mn2+/Zn2+ dual-metal coordination with HRP guides future designs of bioinspired catalysts and stimuli-responsive carriers.

Industrial Potential: The composite carrier addresses free HRP’s instability and unrecoverability, offering a scalable solution for oxidoreductase applications.

Generalizable Design: The “rigid core-catalytic shell-porous framework” strategy can be extended to other enzymes (e.g., laccase or glucose oxidase).

Mechanistic Insight: The revealed Mn2+/Zn2+ dual-metal coordination with HRP guides future designs of bioinspired catalysts and stimuli-responsive carriers.

This study addresses the issues of poor stability and difficulty in recovery of free horseradish peroxidase (HRP) by developing a multi-level composite immobilized carrier that combines high loading capacity with long-term stability. The SiO2@MnO2@MAF-7 core–shell structured carrier was prepared via a solvothermal self-assembly method. Three immobilization strategies—adsorption, covalent cross-linking, and encapsulation—were systematically compared for their immobilization efficacy on HRP. The material structure was analyzed using techniques such as specific surface area analysis (BET), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) to characterize the material structure. Enzyme kinetic parameter determination experiments were conducted to systematically evaluate the performance advantages of the immobilized enzyme. BET analysis showed that SiO2@MnO2@MAF-7 had a specific surface area of 251.99 m2/g and a mesoporous area of 12.47 nm, and its HRP loading was 50.37 U/mg (immobilization efficiency 85.03%). Compared with free HRP, the Km value of the immobilized enzyme was decreased by 42%, the activity retention rate was increased by 35–50% at 80 °C and pH 4–9, and the activity was maintained by 65% after five repeated uses. In this study, MAF-7 was combined with MnO2/SiO2 for HRP immobilization for the first time, and the triple effect of rigid support-catalytic synergy-confined protection synergistically improved the stability of the enzyme, providing a new strategy for the industrial application of oxidoreductases.