Self-assembled peptide template directed synthesis of one-dimensional inorganic nanostructures and their applications

Abstract

Engineering at the nano scale has been an active area of science and technology over the last decade. Inspired by nature, synthesis of functional inorganic materials using synthetic organic templates constitutes the theme of this thesis. Developing organic template directed synthesis approach for inorganic nanomaterial synthesis was aimed. For this purpose, an amyloid like peptide sequence which is capable of self-assembling into nanofibers in convenient conditions was designed and decorated with functional groups showing relatively high affinity to special inorganic ions, which are presented at the periphery of the one-dimensional peptide nanofiber. These chemical groups facilitated the deposition of targeted inorganic monomers onto the nanofibers yielding one-dimensional organic-inorganic core-shell nanostructures. The physical and chemical properties of the synthesized peptide nanofibers and inorganic nanostructures were characterized using both qualitative and quantitative methods. First, silica nanotubes were obtained by silica mineralization around these peptide nanofiber templates for the construction of sensors for explosives. The fluorescence dye was used to coat the silica nanotubes to detect explosive vapor. The surface of the silica nanotubes were porous enough to adsorb more dye compared to the silica nanoparticles and silica film, and causes faster fluorescence quenching in the presence of explosives like trinitrotoluene and dinitrotoluene. The silica nanotubes which synthesized with this peptide nanofiber templates can be used in catalysis and sensors in which high surface area is advantageous. In the second part of the thesis, titanium dioxide nanotubes were obtained from titania mineralization. They are wellknown with their fascinating properties as a result of the one-dimensional nanostructure, such as more efficient electron transfer and less electron-hole recombination. The sufficient photoactivity of titanium dioxide makes them suitable materials for Dye-Sensitized Solar-Cell construction. It is demonstrated that the peptide nanofiber templated titanium dioxide nanotubes have more than two times more efficiency compared to template-free synthesized titanium dioxide particles. Finally, designed peptide sequence was conducted to a multi-step seeding mediated growth method for gold mineralization around peptide nanofibers. The gold-peptide hybrid nanostructures with different packing characteristics and sizes were synthesized and fully characterized. Further, it was demonstrated that the dry film of these nanostructures showed a resistive switching dominant conductivity, due to the nanogaps in between gold nanoparticles as a result of particle alignment driven by the peptide nanofiber. The results obtained in this thesis encourage use of a new “bottom-up” synthesis approach. Specially designed peptides with desired properties and functional groups were synthesized and peptide nanofibers formed were further used as templates for inorganic mineralization. Not only it is possible to synthesis high amount of nanostructure with this approach, but also formed one-dimensional nanostructures show advance functionalities used in several applications as a part of the thesis scope. This methodology is suitable for many metals and metal oxide based applications.