| Summary: | Bioremediation with immobilized enzymes has several advantages, such as the enhancement of selectivity, activity, and stability of biocatalysts, as well as enzyme reusability. Laccase has proven to be a good candidate for the removal of a wide range of contaminants. In this study, naked or modified MnFe<sub>2</sub>O<sub>4</sub> magnetic nanoparticles (MNPs) were used as supports for the immobilization of laccase from <i>Trametes versicolor</i>. To increase enzyme loading and stability, MNPs were coated with chitosan both after the MNP synthesis (MNPs-CS) and during their formation (MNPs-CS<sub>in situ</sub>). SEM analysis showed different sizes for the two coated systems, 20 nm and 10 nm for MNPs-CS and MNPs-CS<sub>in situ</sub>, respectively. After covalent immobilization of laccase by glutaraldehyde, the MNPs-CS<sub>in situ</sub>-<i>lac</i> and MNPs-CS-<i>lac</i> systems showed a good resistance to temperature denaturation and storage stability. The most promising system for use in repeated batches was MNPs-CS<sub>in situ</sub>-<i>lac</i>, which degraded about 80% of diclofenac compared to 70% of the free enzyme. The obtained results demonstrated that the MnFe<sub>2</sub>O<sub>4</sub>-CS<sub>in situ</sub> system could be an excellent candidate for the removal of contaminants.
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