Individual graphene oxide sheets subjected to chemical reduction were electrically characterized as a function of temperature and external electric fields. The fully reduced monolayers exhibited conductivities ranging between 0.05 and 2 S/cm and field effect mobilities of 2-200 cm2/Vs at room temperature. Temperature-dependent electrical measurements and Raman spectroscopic investigations suggest that charge transport occurs via variable range hopping between intact graphene islands with sizes on the order of several nanometers. Furthermore, the comparative study of multilayered sheets revealed that the conductivity of the undermost layer is reduced by a factor of more than 2 as a consequence of the interaction with the Si/SiO2 substrate.

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Mid-infrared spectroscopy is a widely used tool for material identification and secondary structure analysis in chemistry, biology and biochemistry. However, the diffraction limit prevents nanoscale protein studies. Here we introduce mapping of protein structure with 30 nm lateral resolution and sensitivity to individual protein complexes by Fourier transform infrared nanospectroscopy (nano-FTIR). We present local broadband spectra of one virus, ferritin complexes, purple membranes and insulin aggregates, which can be interpreted in terms of their α-helical and/or β-sheet structure. Applying nano-FTIR for studying insulin fibrils—a model system widely used in neurodegenerative disease research—we find clear evidence that 3-nm-thin amyloid-like fibrils contain a large amount of α-helical structure. This reveals the surprisingly high level of protein organization in the fibril’s periphery, which might explain why fibrils associate. We envision a wide application potential of nano-FTIR, including cellular receptor in vitro mapping and analysis of proteins within quaternary structures.

Large biomolecules are attractive templates for the synthesis of metal 1-7 and inorganic 8-10 compound nanostructures. The well-defined chemical and structural heterogeneity of the biotemplates can be exploited for the precise control of the size and shape of the formed nanostructures. Here, we demonstrate that the central channel of the tobacco mosaic virus (TMV) can be used as a template to synthesize nickel and cobalt nanowires only a few atoms in diameter, with lengths up to the micrometer range.A key issue in nanotechnology is the development of conceptually simple construction techniques for the mass fabrication of identical nanoscale structures. Conventional "top-down" fabrication techniques are both energy-intensive and wasteful because many production steps involve depositing unstructured layers and then patterning them by removing most of the deposited films. Furthermore, increasingly expensive fabrication facilities are required as the feature size decreases. The natural alternative to top-down construction is the "bottom-up" approach, in which nanoscale structures are built from their atomic and molecular constituents by self-assembly. This approach relies on the exploitation of specific intermolecular interactions and is one of the key building principles of all living organisms. It is thus obvious to search for biological structures that can be used as templates for directing the self-assembly. An ideal biological nano-object for this purpose is the tobacco mosaic virus (TMV), which is a very stable tube-shaped complex of a helical RNA composed of ca. 6400 bases and 2130 identical coat proteins. The rigid virion is 300 nm long, but linear head-to-tail aggregation results in oligomers with lengths of 600, 900 nm, and so forth.11 TMV has an outer diameter of 18 nm; a central channel with a diameter of 4 nm is clad by flexible loops of the protein structure. TMV is thus a perfect molecular nanocylinder. The well-defined chemical groups at specific locations of the coat proteins can act as ligands for metal ions. We use this chemical functionality for the growth of metal wires from metal ion solutions. TMV is first activated by the selective binding of Pd(II) or Pt(II) ions, followed by metallization with boranecontaining nickel and cobalt solutions. Nickel and cobalt wires (3 nm wide) with lengths of up to 600 nm grow selectively in the central channel.To produce TMV, which is harmless to mammals, we infected Nicotiana tabacum cv. Samsun nn plants with plasmid DNA that comprised the code for the movement and coat protein of the TMV genome as well for the replicase. Systemically infected leaves were harvested, and virions were isolated by standard methods. Each virion is composed of the RNA, a helix with an 8-nm diameter, and the coat proteins that are arranged in a helical fashion. The RNA bases fit into pockets in the coat protein structure. Both the outer surface and the channel cladding are hydrophilic, as seen by the presence of water molecules 12 and by the adsorption properties. The oute...

Tobacco mosaic virus (TMV) is a very stable nanotube complex of a helical RNA and 2130 coat proteins. The special shape makes it an interesting nano‐object, especially as a template for chemical reactions. Here we use TMV as a chemically functionalized template for binding metal ions. Different chemical groups of the coat protein can be used as ligands or to electrostatically bind metal ions. Following this activation step, chemical reduction and electroless plating produces metal clusters of several nanometers in diameter. The clusters are attached to the virion without destroying its structure. Gold clusters generated from an ascorbic acid bath bind to the exterior surface as well as to the central channel of the hollow tube. Very high selectivity is reached by tuning PdII and PtII activations with phosphate: When TMV is first activated with PdII, and thereafter metallized with a nickel–phosphinate bath, 3 nm nickel clusters grow in the central channel; when TMV from phosphate‐buffered suspensions is employed, larger nickel clusters grow on the exterior surface. Phosphate buffers have to be avoided when 3 nm nickel and cobalt wires of several 100 nm in length are synthesized from borane‐based baths inside the TMV channel. The results are discussed with respect to the inorganic complex chemistry of precursor molecules and the distribution of binding sites in TMV.

We studied the adsorption behavior and surface chemistry of the tobacco mosaic virus (TMV) on well-defined metal and insulator surfaces. TMV serves as a tubular supramolecular model system with precisely known surface termination. We show that if the surface chemistry of the substrate and the pH-dependent chemistry of the molecular surface match, for example, by hydrogen bonding, a strong adsorption occurs, and lateral movement is impeded. Due to the immobilization, the virion can be imaged by atomic force microscopy (AFM) in contact mode. We also used self-assembled monolayers with an acyl chloride group to induce covalent bonding via ester formation. Noncontact AFM proved that TMV keeps its cylindrical cross section only under weak adsorption conditions, that is, on hydrophobic surfaces, while on hydrophilic substrates a deformation occurs to maximize the number of interacting chemical groups.

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