Effective Enzyme Immobilization onto a Magnetic Chitin Nanofiber Composite

In this study, a novel biocompatible magnetic chitin nanofiber composite (MCNC) was developed as a support for enzyme immobilization, and the enzyme-immobilizing ability was elucidated using chymotrypsin (CT) as a model enzyme. Chitin nanofibers (CNFs) were prepared via 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of chitin and then further modified with magnetic nanoparticles. Glutaraldehyde was used to cross-link the additional CT molecules and aggregate them onto the MCNCs. The CNFs were characterized by transmission electron microscopy, and Fourier transform infrared spectroscopy. The results showed that the CNFs were properly formed and that the CT molecules immobilized on the MCNCs presented excellent properties. After heating the composites at 60 degrees C for 3 h, the non-cross linked and cross-linked immobilized CTs retained 51.6% and 70.7% of the initial activity, respectively, whereas the free CTs retained only 29.6% of the initial activity. In addition, non-cross-linked and cross-linked immobilized CTs retained 85.7% and 84.9% of the initial activity, respectively, after 20 days, whereas the free CTs retained only 18.8% of the initial activity. When the MCNCs were used to immobilize the CT molecules, the enzyme loading capacity was enhanced up to 6.3-fold upon cross-linking. Moreover, the immobilized CTs could be easily separated and recycled from the reaction system by a magnetic force.