(640d) Protein Amyloid Fibrils As Template for the Synthesis of Silica Nanofibers

The preparation of silica fiber-like materials has captured the attention of scientists for the last decades. Their preparation requires the use of suitable templates. In this work, we show how protein fibrils can be used as templates for the preparation of long silica fibers, with a variety of aspect ratios. Protein amyloid fibrils are self-assembled structures resulting from partial denaturation of certain proteins, and their resulting aggregation mediated by $\beta$-sheets interactions. These structures are characterized by an extremely large aspect ratio, with a diameter that changes depending on the age of the fibrils, and on the degree of association of the different strands. Amyloid fibrils have an abundance of amino acid side chains at their surface that permit their dispersion in water and offer the chance to perform a wide range of simple derivatizations. We take advantage of these favorable features of amyloid fibrils and present a very simple procedure to coat them with silica. Starting with b-lactoglobulin fibrils with typical diameters of about 20nm , and a length of several micrometers, and by following two different strategies to grow silica (either in water at acidic pH values, or in ethanol-water mixtures under Stöber conditions) we have been able to control both the thickness and the roughness of the silica layer. Silica nanofibers with a thickness ranging from a few nanometers to hundreds of nanometers have been prepared. As an example of the flexibility offered by our approach, some of the rough silica-coated nano-fibers have been further functionalized to render them hydrophobic.

Such fibers have been further used for the fabrication of lotus-like surfaces. The surfaces have been prepared with a process consisting of four simple steps. First, ten microns colloidal particles have been arranged in either a single colloidal crystal, or in a binary colloidal crystal by combining them with smaller sub-micrometer particles. Large scale substrates have been coated with colloidal crystals. The hydrophobicity of the substrate has been measured by water contact angle, and found to be superior to that of the papillar structure of the lotus leaf deprived of the wax tubular structure. Then, silica nanotubes have been prepared by coating b -Lactoglobulin amyloid fibrils with silica by means of a Stober process. These silica nanotubes have been deposited on the binary colloidal crystal surfaces through a layer-by-layer deposition procedure, using positively-charged Ludox silica particles to reverse the sign of the charge on the surface of the substrate. Finally, the substrates have been hydrophobized by binding an alkyl chain on the surface of the fibrils. The final surfaces are superhydrophobic, with a water contact angle of 165.5 degrees, which is higher than that of the original Lotus leaf. The presented approach has two main advantages. It is easily scalable, and is based on a multi-step approach, which allows one a rational design of the nanostructure and microstructure impact on the final hydrophobicity of the surface.