Insulin-based Nanowire Structures: Production, Characterization and Catalysis Potential.

Abstract

Use of proteins as bio-templates for production of nanowires and materials is a burgeoning field of research making use of intrinsic protein characteristics and tendencies to self-assemble nanostructures for use in a variety of applications. Proteins are known to self-associate into a variety of aggregate structures with interesting qualities including high aspect ratios and large effective surface areas that can be coated with metals. These protein-based nanowires are of potential interest as high surface area catalytic surfaces. Here we have developed a protocol for producing insulin-based protein-fibrils by heating and applying oscillatory strain to the proteins. Using this method we reliably produce numerous high aspect ratio fibrils that are characterized using TEM. The fibril structures and 2-D networks formed by deposition of the structures onto a substrate have been analyzed and a regime of appropriate applied strain has been identified for production of a large number of fibrils and highly connected networks upon deposition. Aggregate development is explored using sigmoidal analysis of rheological data tracking initial stages of growth during the heating and deforming protocol. Use of the sigmoidal model allows for extraction of kinetic constants associated with aggregate production in the solution resulting in increased viscosity. The sigmoidal model may be applied to a variety of experimental techniques tracking fibril development, although they measure different aspects of the denaturing, nucleation and fibril growth process. The sigmoidal model is applied to ThT assay data compiled from the literature and used to point to possible techniques for increased uniformity and better comparison amongst ThT assay tests. A protocol for metallizing insulin fibrils is developed for coating the produced insulin fibrils with platinum using an electroless plating technique. The platinum completely covers the fibrils and is well-adhered, forming a metallic nanowire based on the insulin template. Dispersions of nanowires are used as efficient catalysts in reducing 4-nitrophenol to 4-aminophenol. This reduction is tracked by UV-Visible Spectroscopy, and associated reaction constants compares favorably with reaction constants of similar platinum-coated substrates used in the literature. Subsequently, the immobilization of the protein-based nanowires onto textile substrates has been demonstrated for potential use as retrievable catalysts.