Protein-Mediated Layer-by-Layer Syntheses of Freestanding Microscale Titania Structures with Biologically Assembled 3-D Morphologies

A simple protein-mediated approach for preparing freestanding (silica free) microscale titania structures with morphologies inherited from complex-shaped, three-dimensional (3-D) biosilica templates (diatom frustules) is demonstrated. The silica diatom frustules were exposed in a repetitive alternating fashion to a silica-binding, titania-forming protein (protamine) and then to an aqueous titania precursor to build up a conformal titania-bearing coating. After organic pyrolysis at 500 degrees C, the conformal, continuous nature of the resulting crystalline anatase titania coating was confirmed by (i) demonstrating that a titania-coated frustule acted as a sensitive electrochemical hydrogen detector and (ii) selectively removing the silica templates to yield freestanding titania structures that retained the 3-D diatom frustule shape.