Nanostructured Polyphenol-Mediated Coating: a Versatile Platform for Enzyme Immobilization and Micropollutant Removal

Catechol–amine codeposition can improve the stability of a mussel-inspired coating layer (e.g., dopamine, tannic acid, gallic acid) but its superior performance on enzyme immobilization has not been studied yet. For the first time, a tannic acid-3-aminopropyltriethoxysilane (TA–APTES) coating was investigated for carrier activation and subsequent enzyme loading via covalent bonding. During the coating process, nanoparticles were generated by the reaction between APTES and TA, and then in situ assembled and adhered to the carrier surface, resulting in a hierarchical nanostructure. The TA/APTES ratio and coating time greatly affected enzyme loading and specific activity by changing the nanoparticles' amount/size and available quinone groups of oxidized TA. The nanoparticles offered more area (i.e., specific surface area) for enzyme loading and reaction, while the quinone groups were responsible for covalently binding the enzyme. The TA–APTES coating showed much better performance in enzyme immobilization than glutaraldehyde, genipin, and polydopamine activation strategies, thanks to its special surface nanostructure and abundant quinone groups. Secondary grafting branched polymer γ-polyglutamic acid (γ-PGA) on the TA–APTES coating layer further increased enzyme loading (3.5–4.5 times). Finally, the universality of the TA/APTES coating was demonstrated by applying it on various materials for immobilizing different enzymes and removing five micropollutants (i.e., bisphenol A, 2,4,6-trichlorophenol, aflatoxin B1 (AFB1), deoxynivalenol (DON), and tetracycline (TC)). This work not only established a novel platform for facile and efficient enzyme immobilization but also clarified the effect of surface chemistry and morphology on enzyme immobilization and micropollutant removal.