Polyamine induced tannic acid co-deposition on magnetic nanoparticles for enzyme immobilization and its efficient biodiesel production under alternating magnetic field

Tannic acid (TA) as a natural polyphenol is widely modified on various supporting materials for enzyme immobilization, while the time-consuming formation of TA layer and poor mechanical stability on substrates seriously hinder its practical application. Herein, we report a facile, rapid and stable enzyme immobilization strategy based on polyamine induced tannic acid co-deposition on magnetic nanoparticles. Specifically, tannic acid/polyamine binary system was firstly deposited and polymerized on the surface of magnetic nanoparticles through a modified mussel-inspired method, and then enzyme can be immobilized on the formed polymer layer via spontaneous Schiff-base reaction. The physical properties study revealed that polyamine as an intramolecular cross-linker could significantly accelerate deposition of TA on supports and stabilize the structure of formed polymer layer. Meanwhile, CALB as a representative lipase for biodiesel production was successfully immobilized on such nanocomposite with 132.8 mg/g support of loading capacity and 56.7% activity recovery under optimal conditions. Furthermore, the physicochemical properties of immobilized CALB displayed many significant advantages, including the improved stability of pH, temperature and methanol tolerance compared to free CALB. In particular, the theoretical simulation and structure analysis of immobilized CALB demonstrated that such nanocomposite can effectively prevent CALB active pocket structure damage. For further application, the immobilized CALB exhibited high production efficiency and reusability in the production of biodiesel compared to free CALB. Interestingly, the immobilized CALB showed the very efficient catalytic properties under an alternating magnetic field than the control without an alternating magnetic field, and the reaction rate was enhanced with the increase of magnetic field frequency and strength. Therefore, such polyamine induced TA co-deposition and polymerization strategy may provide an improved nanoplatform for enzyme immobilization.