Shielding effects of Fe3+-tannic acid nanocoatings for immobilized enzyme on magnetic Fe3O4@silica core shell nanosphere

Enzyme immobilization on solid supports is a valuable approach to address enzyme stability and reuse for continuous operations. However, the enzymes immobilized on the external surface of solid supports may not be protected by carriers and suffer inactivation caused by denaturing stresses and hazard external environment. Herein, we describe for the first time a enzyme-shielding strategy to prepare hybrid organic/inorganic nano-biocatalysts; it exploits the self-assembly of supramolecular metal-organic coordination complex (tannic acid (TA) and Fe3+) at the surface of immobilized catalase on Fe3O4/silica core-shell nanospheres to grow a protective nanocoating (Fe3+-TA nanocoating). The nanocoatings around the immobilized catalase (Fe3+-TA@Fe3O4/SiO2-catalase) provide a "shield effect" to protect from biological, thermal and chemical degradation for enzyme. As a result, the stability of immobilized catalase against proteolytic agent, denaturants and heat were improved remarkably compared to the immobilized catalase without a protective nanocoating and free catalase. More importantly, the recycling of the immobilized catalase was improved remarkably. The Fe3+-TA@Fe3O4/SiO2-catalase still retained 55% of their original activity after 9 cycles, whereas the immobilized catalase without a protective nanocoating only retained 20% of original activity. These results demonstrated that the novel enzyme-shielding strategy is an efficient method to obtain stable and recycled biocatalyst with yolk-shell structure.