Peptide-mediated deposition of nanostructured TiO₂ into the periodic structure of diatom biosilica

Diatoms are single-celled algae that make silica shells called frustules that possess periodic structures ordered at the micro- and nanoscale. Nanostructured titanium dioxide (TiO₂) was deposited onto the frustule biosilica of the diatom Pinnularia sp. Poly-l-lysine (PLL) conformally adsorbed onto surface of the frustule biosilica. The condensation of soluble Ti-BALDH to TiO₂ by PLL-adsorbed diatom biosilica deposited 1.32 ± 0.17 g TiO₂/g SiO₂ onto the frustule. The periodic pore array of the diatom frustule served as a template for the deposition of the TiO₂ nanoparticles, which completely filled the 200-nm frustule pores and also coated the frustule outer surface. Thermal annealing at 680 °C converted the as-deposited TiO₂ to its anatase form with an average nanocrystal size of 19 nm, as verified by x-ray diffraction, electron diffraction, and SEM/TEM. This is the first reported study of directing the peptide-mediated deposition of TiO₂ into a hierarchical nanostructure using a biologically fabricated template.