High catalytic activity of immobilized laccase on core-shell magnetic nanoparticles by dopamine self-polymerization

A facile and efficient method is developed for enzyme immobilization on silica-coated magnetic nanoparticles (Fe3O4@SiO2 NPs) via dopamine (DA) self-polymerization process. The scanning electron microscope images indicate that Fe3O4@SiO2 NPs have a spherical and uniform size distribution, and the high saturation magnetization (14.68 emu g(-1)) makes it easily to be separated from the reaction system under an extra magnetic field. Fourier-transform infrared spectroscopy and thermogravimetric analysis reveal that polydopamine (PDA) has been successfully coated on Fe3O4@SiO2 NPs surface. During in situ polymerization of DA, laccase is also firmly immobilized on Fe3O4@SiO2 NPs, and the total activity recovery can reach to 43.28%. However, the laccase immobilized by glutaraldehyde (GA) crosslinking method only keeps 3.33% of the total activity recovery under the optimized condition. Compared with free laccase and laccase immobilized by GA, the laccase immobilized by DA exhibits superior resistance to a broader pH value and obviously enhanced stability. After 10 times reusing cycles, the activity of laccase immobilized by DA still retains 65% of its initial activity, whereas the laccase immobilized by GA has 35% of its original activity. After 70 days of storage at 4 degrees C, the laccase immobilized by DA keeps about 80% of its initial activity, but the free laccase and the laccase immobilized by GA only remained 7.8% and 37%, respectively. Thus, this work provides a method for laccase immobilization with advantages of environmentally friendly, low cost and high catalytic activity. (C) 2014 Elsevier B.V. All rights reserved.