Honors College Thesis

Self Assembly of GeO₂ Nanoparticles: A Biomimetic Approach

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  • Diatoms are single celled eukaryotic microalgae that self-assemble complex SiO₂ nanostructures by sillafin proteins within their cell wall. There has been increasing interest in mimicking the diatom’s silica self-assembly process for fabricating metal oxide nanoparticles, namely germanium dioxide (GeO₂). GeO₂ has a higher refractive index than silica, enabling it to be applied in a range of technologies such as fiber optics, optoelectronic devices, and complimentary metal oxide semiconductors. Current GeO₂ nano-fabrication methods require high pressure, temperature, and a great deal of time and resources. Our investigation offers a new approach, one based on the diatom’s natural process to manipulate GeO₂. We demonstrated that with this approach, GeO₂ nanoparticles could be fabricated under ambient conditions with a simple protocol. A metal oxide precursor, germanium (IV) ethoxide (GTE), and the protein poly-L-lysine as the biomimetic template (a simplified model of the diatom derived silaffin protein) were placed in artificial seawater (PBS). Three sets of GeO₂ nanoparticles were selfassembled from solutions that contained high (54 mg/mL), medium (28 mg/mL) and low (14 mg/mL) GTE concentrations. Scanning electron microscopy revealed that at high GTE concentrations, only oval shaped GeO₂ nanoparticles (160 nm diam.) were produced while at medium GTE concentrations, cubic (200 nm diam.) and oval (160 nm diam.) shaped nanoparticles were self-assembled. At low GTE concentrations, indefinite shapes were assembled, described as round agglomerates. Energy dispersive x-ray spectroscopy (EDAX) data at this low GTE concentration reveal elemental nitrogen within the sample, confirming the presence of –NH and/or –N-C bonds and therefore PLL. We hypothesized that the PLL protein acts as a template for the self-assembly of GeO₂ nanoparticles. This has been confirmed by EDAX assay revealing the presence of PLL in nanoparticle samples.
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