NIRT: NER: Biosynthesis of Germanium Oxide Nanoparticles

Oregon State University, Corvallis OR

Investigators

Abstract

This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 01-157, category NER. This exploratory proposal embraces two themes of the NSF Nanoscale Science and Engineering Program, including 1) Biosystems at Nanoscale, 2) Manufacturing Processes at the Nanoscale. The overall goal of this proposed research is to demonstrate the feasibility of a process for biosynthesis of germanium oxide nanoparticles. The PIs specific objectives are to: 1) Establish cultures of photosynthetic marine diatoms known to co-assimilate soluble silicon (Si) and germanium (Ge), including Cylindrotheca fusimormis, Cyclotella nana,and Phaeodactylum tricornutum; 2) Develop a two-stage photobioreactor for biological manufacture Ge-oxide nanoparticles by marine diatoms, and identify soluble Si/Ge feeding strategies that sustain Ge- oxide nanoparticle formation; 3) Characterize the composition and size of nanoparticles by TEM/EDAX; and 4) characterize photonic properties of extracted nanoparticles by photoluminescence spectroscopy before and after thermal annealing or H2 reduction. The PI proposes that the biomineralization capacity of marine diatoms can be harnessed to manufacture germanium oxide nanoparticles that ultimately could be processed into photonic materials. The synthesis of quantum dots by the atomic assembly of Ge atoms or Ge-oxide nanocrystals on silicon substrates is an emerging area of nanotechnology, as these light-emitting nanomaterials have novel optical / electronic properties. Current technology for manufacture of Ge-oxide nanocrystals involves exotic and cumbersome processes at extreme conditions, such as laser ablation, cluster beam deposition, or DC magnetron sputtering. In contrast, diatoms could manufacture monodisperse Ge-oxide nanoparticles at the atomic scale by biologically-mediated processes at ambient conditions, using the nanobiochemical machinery of the cell itself. He proposes that Ge-oxide nanoparticle production by diatoms can be accomplished in two stages. In Stage 1, diatoms are grown to high cell density on a soluble Si substrate (e.g. silicic acid) to the point of Si depletion in the liquid medium. In Stage 2, soluble germanium (e.g. germanic acid) is continuously added to the dense diatom suspension at sub-lethal concentration. Diatoms assimilate soluble Ge, and then biologically polymerize soluble Ge to Ge-oxide nanospheres, which accumulate within the cell since they cannot be readily assimilated into the silica cell wall. If this proposed research is successful, then a biotechnology-derived route to synthesis of nanoparticles or nanocomposite materials with optoelectronic properties would be demonstrated and the impact will be significant. The research plan will be co-directed two chemical engineers with respective expertise in cell culture of marine organisms and semiconductor materials synthesis. Graduate students working with the PIs would be uniquely cross trained in two high-technology areas: biotechnology and electronic materials.