Enzyme Immobilization On The Surface Of Titanate Nanotubes

Nanomaterials have attracted much attention in the enzyme immobilization fieldwith the development of nanotechnology in recent years. Nanomaterials have beenrecognized as the excellent enzyme scaffolds, because they can offer the special andfascinating characteristics for balancing the key factors that determine the biocatalysisefficiency, including high specific surface area, minimized mass transfer resistance,and effective enzyme loading over their bulk counterparts. Titanate nanotubes (TNTs)which possess considerable specific surface area, demonstrate attractivebiocompatibility, hydrophobicity and special chelation interactions with catecholgroups. In this study, TNTs were employed as the supporter for pursuing the efficientenzyme immobilization.The main contents in this study were summarized as follows:(1) Titanate nanotubes, which were used as immobilized enzyme carrier, weresynthsised by hydrothermal method. Catalase (CAT)was pre-modified by3-(3,4-dihydroxyphenyl) propionicacid (3,4-diHPP) via1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) andN-hydroxysuccinimide (NHS) coupling chemistry, and then covalently immobilizedon the TNTs surface by the chelation of catechol groups with Ti4+ions. It is found thatTNTs exhibits excellent performances asthe immobilized supporter of enzyme: theenzyme loading is as high as820mg g of support1; the relative activity ofimmobilized enzyme is about60%of that of free enzyme; the immobilized CATdemonstratesenhanced storage and recycling stability.(2) Inspired by biomimetic adhesion, the polydopamine layer on the surface ofTNTs was formed by self-polymerization under alkaline condition. Polydopamineendowed the TNTs the chemistry characteristic of interact with NH2in catalasemolecules. In this experiment, CAT was immobilized on the surface of TNTs bydopamine self-polymerization. The enzyme loading is311.7mg g of support1withoutany leaking after incubation72h, and the relative activity is52%. Simultaneously,TNTs-PDA-CAT demonstrated increased affinity between enzyme and substrate, andenhanced storage and recycling stabilities, After sixty-day storage, the free CAT only keeps44%of its initial activity, while TNTs-CAT preserves92%of its initial activity;TNTs-CAT retains more than50%of the initial activity after nine successive cycles.(3)Norepinephrine (NE), which possesses the similar catecholamine group asdopamine, could form polynorepinephrine on the TNTs surface byself-polymerization under alkaline condition. Compared to the rough morphology ofPDA, PNE demonstrated homogeneous surface. The loading efficiency of CATimmobilized on TNTs-PNE was245.6mg g of support-1, and the relative activity was56%. TNTs-PNE-CAT exhibited increased affinity to H2O2, and enhanced storage andrecycling stabilities. The controllable surface morphology of PNE which was superiorPDA showed promising industrial application.