Enzyme-Mediated Kinetic Control of Fe³⁺-Tannic Acid Complexation for Interface Engineering

Supramolecular self-assembly of Fe³⁺ and tannic acid (TA) has received great attention in the fields of materials science and interface engineering because of its exceptional surface coating properties. Although advances in coating strategies often suggest that kinetics in the generation of interface-active Fe³⁺-TA species is deeply involved in the film formation, there is no acceptable elucidation for the coating process. In this work, we developed the enzyme-mediated kinetic control of Fe²⁺ oxidation to Fe³⁺ in a Fe²⁺-TA complex in the iron-gall-ink-revisited coating method. Specifically, hydrogen peroxide, produced in the glucose oxidase (GOx)-catalyzed reaction of d-glucose, accelerated Fe²⁺ oxidation, and the optimized kinetics profoundly facilitated the film formation to be about 9 times thicker. We also proposed a perspective considering the coating process as nucleation and growth. From this viewpoint, the kinetics in the generation of interface-active Fe³⁺-TA species should be optimized because it determines whether the interface-active species forms a film on the substrate (i.e., heterogeneous nucleation and film growth) or flocculates in solution (i.e., homogeneous nucleation and particle growth). Moreover, GOx was concomitantly embedded into the Fe³⁺-TA films with sustained catalytic activities, and the GOx-mediated coating system was delightfully adapted to catalytic single-cell nanoencapsulation.