Biotemplate Synthesis of Ag Nanoparticles and Nanowires
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Biotemplate Synthesis of Ag Nanoparticles and Nanowires S. Behrens,1 E. Unger,2 J. Wu,1,3 W. Habicht,1 E. Dinjus1 1 Institute for Technical Chemistry, Forschungszentrum Karlsruhe, Hermann-von-HelmholtzPlatz 1, 76344 Eggenstein-Leopoldshafen, Germany. 2 Institute for Molecular Biotechnology, Beutenbergstrasse 11, 7708 Jena, Germany. 3 Department of Chemistry, Graduate School of Chinese Academy of Sciences, Beijing 100039, P. R. China. ABSTRACT We address the template-directed deposition of metals on microtubule supports for generating metal nanostructures with different morphologies. Microtubules are highly ordered protein assemblies of tubular structure with a high aspect ratio. In this approach, the biostructure serves as a functionalised scaffold where the metal is generated in situ and shaped into a nanostructure with its morphology complementary to that of the biotemplate. When the biotemplate is coupled to an appropriate chemical reaction, different Ag / protein structures are produced, ranging from microtubules densely covered by small Ag nanoparticles to continuous Ag nanowires. INTRODUCTION Biological systems exhibit typical size dimensions from the lower nanometer size range up to several micrometers, well-defined surface functionalities, and molecular recognition capabilities. However, often they do not posses the desired physical properties, e.g., many among them display poor electric conductivities, others are insulators. Recently, the unique features of biological systems have been explored as building blocks for bottom-up assembly or controlled deposition of novel inorganic materials and devices with advanced structures and functionalities.[1,2,3] Among bulk phase metals, silver exhibits a very high electric conductivity, and, thus, has been broadly applied in modern electronic industry. The fabrication of silver nanowires has a large potential application, e.g. for wiring individual devices in nanoelectronics. Inspired by their unique physical and chemical properties, a lot of effort has been made to tailor defined one, two, or three-dimensional nanostructures. EXPERIMENTAL Microtubule assembly: Tubulin protein was isolated from porcine brain by temperature dependent assembly-disassembly cycles. Microtubules were assembled from tubulin protein (final protein concentration ~1 mg/ml) in PIPES buffer (1,4-piperazine diethane sulfonic acid, 20 mM, pH 6.8), NaNO3 (80 mM), Mg(NO3)2 (0.5 mM) and ethylene glycol bis (2-aminoethyl ether) tetra acetic acid (1 mM) by adding guanosine-5’-triphosphate lithium salt (0.25 M) and after 20 min taxol (from Taxus brevifolia, 10 mM) and warming up the sample to 37 °C. Prior to metallization experiments, microtubules have been fixed by 0.1% glutaric dialdehyde to suppress their dynamic instability.
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Metallization of microtubules: All metallization procedures were carried out in the dark. Microtubules were incubated with AgNO3 for 1 min. Reducing Ag ions by an excess of NaBH4 at 0°C yielded microtubules decorated with small Ag nanoparticles (final concentr
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