(714d) Biological Fabrication of Photoluminescent Nanocomb Structures by Metabolic Incorporation of Germanium into the Biosilica of the Diatom Pinnularia Sp

Diatoms are single-celled algae that make microscale silica shells or ?frustules? with intricate nanoscale features such as two-dimensional pore arrays. In this study, the metabolic insertion of low levels of germanium into the frustule biosilica of the pennate diatom Pinnularia sp. by a two-stage cultivation process induced the formation of frustules which strongly resembled double-sided nanocomb structures. The final product contained 0.2 to 1.0 wt% Ge in biosilica, depending upon the amount of soluble germanium added to the cultivation process. The 30 micron frustules consisted of a mixture of parent valves possessing a normal two-dimensional array of 200 nm pores, and daughter valves possessing the nanocomb structure formed by the fusion of the pore arrays. After thermal annealing in air, the Ge-doped frustules possessed blue photoluminescence (PL) with peak wavelength of 440-460 nm. The PL intensity was controlled by the annealing temperature and the level of Ge in the biosilica. The optimal PL intensity was obtained at a thermal annealing temperature of 400 ^oC. XPS and TEM/electron diffraction measurements confirmed that Ge-doped diatom biosilica consisted of amorphous GeO₂ after thermal annealing at 400 ^oC. This nanostructured GeO₂ was the likely the origin of the blue photoluminescence. This is the first reported study of using a cell culture system to biologically fabricate a Ge-doped silica nanocomb structure with controllable photoluminescent properties.