Unveiling the Physicochemical Properties of Magnetic Nanoparticles as Solid Carriers for Laccase Immobilization Toward Different Reducing Substrates

Laccases are multicopper oxidases capable of oxidizing a wide range of substrates using molecular oxygen as the terminal electron acceptor, producing water as the sole by-product. High-redox potential fungal laccases, such as those from Trametes versicolor, are particularly attractive for industrial and environmental applications, although their use is often limited by sensitivity to operational conditions. Enzyme immobilization represents an effective strategy to enhance laccase stability and reusability. In this work, magnetic nanoparticles (MNPs) were investigated as support for laccase immobilization due to their high surface area, biocompatibility, and ease of magnetic recovery. Two modified co-precipitation synthetic routes were systematically evaluated, and the size, morphology, and chemical composition of the products were characterized by microscopy, light scattering, and spectroscopic methods, while both adsorption and covalent immobilization strategies were explored. The MNP surface was found to be highly reactive toward radical species generated during laccase-catalyzed reactions, especially in the presence of small Fe2+ excess. While this can enhance the enzyme catalytic activity, it challenges the inertness of the support and promotes, in some cases, strong interactions between reaction products and the nanoparticle surface. These findings highlight a previously unexplored role of magnetic supports in laccase-based biocatalytic systems.