Biological Assembly and Synthesis of Inorganic Nanostructures

Field: Biochemistry, Genetics and Molecular Biology (Life Sciences)

Science technologies have been in pursuit of smaller, faster and more efficient devices and enormous efforts made by myriad numbers of scientists have provided us with electronics in reduced volumes with improved performances. Miniaturization of electronic circuits down to micrometer scale has been well-developed as industrial processes and it is easy to witness electronic products containing integrated circuits consisted of microstructures in our everyday life. However, miniaturization of circuit components down to nanometer scale has revealed new challenges not only for difficult handling of diminutive structures but also for unusual physical properties of nanomaterials. Countless numbers of conventional chemical and physical studies have been dedicated to exploit the benefit of the unique properties of nanostructures by developing efficient techniques for controlled synthesis and assembly of nanostructures. However, environmental concerns of using toxic solvent systems and high energy-consuming processes, and pursuit of highly selective molecular interactions for highly precise assemblies have averted the eyes of scientists to biological materials. Biorecognition properties of biological materials are attractive for achieving programmed self-assembly of nanostructures and biomolecules with metal-reducing ability are very inviting for developments of environmentally-acceptable synthesis processes. In the light of above discussion, this thesis takes the advantages of biological approaches to assemble and synthesize inorganic nanostructures in a controlled manner. DNA was used for the assembly processes due to their facilities of sequence programming and chemical modifications. Spatially controlled assembly of multi-segmented Au/Pd/Au nanowires across gold electrodes has been demonstrated using thiolated DNA strands functionalized on the gold surface of nanowires and electrodes. Electron transport properties of DNA-assisted assembled nanowires were demonstrated showing negligible blocking effect by DNA layers hybridized between nanowires and electrodes. The assembled Au/Pd/Au nanowire was used for hydrogen sensing manifesting the applicability of DNA-assisted assembly to build functional nanodevices. Amino acids are essential as building blocks for proteins and for metabolisms. Recently, amino acids have been given another important role as a reducing and capping agent for the synthesis of gold nanostructures. Amino acid-mediated synthesis of gold nanostructures has been demonstrated showing the capability of biological approaches to synthesize single crystalline gold nanostructures in 0-D, 1-D and 2-D dimensions by manipulating the reaction environment. Structural changes of gold nanostructures due to the speciation of gold complexes were systematically demonstrated by altering solvent conditions. The effect of the side chains of amino acids on the structural features of gold nanostructures was systematically demonstrated. Distinguished electron transport properties were observed for single crystalline nanoribbons showing resistivity lower by an order of magnitude than polycrystalline counterparts. Rapid reversible room temperature H2S gas sensor was fabricated using AC aligned gold nanoparticle ar