DNA-based routes to metal, inorganic and polymer nanowires

Abstract

This thesis describes the preparation and characterization of conductive nanowires. The synthesis of the nanowires was achieved using a DNA-templating strategy. The chemical identity of the nanowires was characterized using FTIR, XPS and XRD, while the structural character, electronic properties and magnetic behavior were probed using AFM, EFM and MFM, respectively. The formation of Fe3O4 nanowires involved initial association of Fe²+ and Fe³+ ions to the DNA, and subsequent co-precipitation of the Fe3O4 material, upon addition of NaOH. Chemical characterization confirmed the formation of Fe3O4 within the product material. AFM data revealed one-dimensional (1-D) nanostructures with diameters up to 30 nm, whilst EFM and MFM showed that the nanowire structures are electrically conducting and exhibit magnetic behaviour. The preparation of Fe and Rh nanowires, respectively, was achieved by DNA-templating approach in conjunction with either chemical or electrochemical reduction. Chemical characterization confirmed a metal/oxide core/shell structure. AFM data showed 1-D nanostructures with granular character, and diameters up to 26 nm for Fe and 31 and 23 nm for Rh, respectively. The structures were confirmed to be electrically conducting and to display magnetic behaviour as indicated by EFM and MFM, respectively. Finally, DNA-templating of 2,6-diaminopurine-propyl-2,5 bis-dithenyl pyrrole and thymine-propyl-pyrrole by chemical oxidation using FeCl3 yielded supramolecular polymers. FTIR and XPS studies confirmed the presence and interaction of the component polymer chains. The DNA/CPs nanowires showed smooth and uniform structures with diameters up to 25 and 35 nm, and they were found to be electrically conducting. The attempted formation of larger structures based on the base pair hydrogen bonding between the two types of nanowires was investigated by AFM studies. However, reliable evidence for larger structures formation based on this specific interaction was not found.