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In this study, immobilization of laccase (L) enzyme on magnetite (Fe 3 O 4 ) nanoparticles was achieved, so that the immobilized enzyme could be used repeatedly. For this purpose, Fe 3 O 4 nanoparticles were coated and functionalized with chitosan (CS) and laccase from Trametes versicolor was immobilized onto chitosancoated magnetic nanoparticles (Fe 3 O 4 -CS) by adsorption or covalent binding after activating the hydroxyl groups of chitosan with carbodiimide (EDAC) or cyanuric chloride (CC). For chitosan-coated magnetic nanoparticles, the thickness of CS layer was estimated as 1.0-4.8 nm by TEM, isoelectric point was detected as 6.86 by zeta (f)-potential measurements, and the saturation magnetization was determined as 25.2 emu g À1 by VSM, indicating that these nanoparticles were almost superparamagnetic. For free laccase and immobilized laccase systems, the optimum pH, temperature, and kinetic parameters were investigated; and the change of the activity against repeated use of the immobilized systems were examined. The results indicated that all immobilized systems retained more than 71% of their initial activity at the end of 30 batch uses.

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