Bioinspired Design of Alcohol Dehydrogenase@nano TiO(2) Microreactors for Sustainable Cycling of NAD(+)/NADH Coenzyme

The bioinspired design and construction of enzyme@capsule microreactors with specific cell-like functionality has generated tremendous interest in recent years. Inspired by their fascinating complexity, scientists have endeavored to understand the essential aspects of a natural cell and create biomimicking microreactors so as to immobilize enzymes within the hierarchical structure of a microcapsule. In this study, simultaneous encapsulation of alcohol dehydrogenase (ADH) was achieved during the preparation of microcapsules by the Pickering emulsion method using amphiphilic modified TiO(2) nanoparticles (NPs) as building blocks for assembling the photocatalytic microcapsule membrane. The ADH@TiO(2) NP microreactors exhibited dual catalytic functions, i.e., spatially confined enzymatic catalysis and the membrane-associated photocatalytic oxidation under visible light. The sustainable cycling of nicotinamide adenine dinucleotide (NAD) coenzyme between NADH and NAD(+) was realized by enzymatic regeneration of NADH from NAD(+) reduction, and was provided in a form that enabled further photocatalytic oxidation to NAD(+) under visible light. This bioinspired ADH@TiO(2) NP microreactor allowed the linking of a semiconductor mineral-based inorganic photosystem to enzymatic reactions. This is a first step toward the realization of sustainable biological cycling of NAD(+)/NADH coenzyme in synthetic functional microsystems operating under visible light irradiation.