# Synthesis and characterization of ZrFe2O4 and ZrFe2O4@UiO-66-NH2 nanoparticles for efficient immobilization of Humicola insolens lipase: a comparative study of precipitation-crosslinking versus covalent binding methods

## TL;DR

Researchers compared two methods for attaching an enzyme to magnetic nanoparticles, finding that covalent binding improved enzyme stability and reuse.

## Contribution

The study introduces a comparative analysis of precipitation-crosslinking and covalent binding for enzyme immobilization on ZrFe2O4 and ZrFe2O4@UiO-66-NH2 nanoparticles.

## Key findings

- Covalent binding on ZrFe2O4@UiO-66-NH2 achieved over 80% immobilization efficiency.
- The covalently bound biocatalyst retained 70% activity after five reuse cycles.
- Precipitation-crosslinking showed lower enzyme loading and reduced thermal stability.

## Abstract

This study focused on immobilizing Humicola insolens lipase onto magnetic nanoparticles of ZrFe2O4 and ZrFe2O4@UiO-66-NH2 using precipitation-crosslinking and covalent binding methods. Characterization techniques, including FT-IR, SEM, energy-dispersive X-ray spectroscopy, X-ray diffraction, BET, DLS, and thermogravimetric analysis, confirmed the successful synthesis and functionalization of the supports. Enzyme immobilization was assessed using different buffer systems, and Tris–HCl buffer at a low concentration was chosen as the optimal medium due to its compatibility with the support structure. The precipitation-crosslinking method resulted in enzyme loadings of 260 mg g−1 for ZrFe2O4 and 226 mg g−1 for ZrFe2O4@UiO-66-NH2, achieving immobilization efficiencies of about 40% and 60%, respectively. In contrast, the covalent binding technique significantly improved the enzyme loading and immobilization efficiency, with ZrFe2O4 achieving 305 mg g−1 and 65% efficiency. ZrFe2O4@UiO-66-NH2 demonstrated even greater performance, with the immobilization efficiency exceeding 80%. The reusability and thermal stability of the immobilized lipase improved markedly with covalent binding, particularly for the biocatalyst obtained by immobilizing lipase on ZrFe2O4@UiO-66-NH2 nanoparticles. This biocatalyst retained over 70% of its activity after five reuse cycles and retained 40% activity at 80 °C. In contrast, the precipitation-crosslinking method led to a significant decline in activity during successive cycles, with no observable enhancement in enzyme thermal stability using this technique.

This study focused on immobilizing Humicola insolens lipase onto magnetic nanoparticles of ZrFe2O4 and ZrFe2O4@UiO-66-NH2 using precipitation-crosslinking and covalent binding methods.