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.

The size and shape of nanocarriers can affect their fate in vivo, but little is known about the effect of nanocarrier aspect ratio on biodistribution in the setting of cancer imaging and drug delivery. The production of nanoscale anisotropic materials is a technical challenge. A unique biotemplating approach based on of rod-shaped nucleoprotein nanoparticles with predetermined aspect ratios (AR 3.5, 7, and 16.5) is used. These rigid, soft-matter nanoassemblies are derived from tobacco mosaic virus (TMV) components. The role of nanoparticle aspect ratio is investigated, while keeping the surface chemistries constant, using either PEGylated stealth nanoparticles or receptor-targeted RGD-displaying formulations. Aspect ratio has a profound impact on the behavior of the nanoparticles in vivo and in vitro. PEGylated nanorods with the lowest aspect ratio (AR 3.5) achieve the most efficient passive tumorhoming behavior because they can diffuse most easily, whereas RGD-labeled particles with a medium aspect ratio (AR 7) are more efficient at tumor targeting because this requires a balance between infusibility and ligand–receptor interactions. The in vivo behavior of nanoparticles can therefore be tailored to control biodistribution, longevity, and tumor penetration by modulating a single parameter: the aspect ratio of the nanocarrier.

The spacing of functional nanoscopic elements may play a fundamental role in nanotechnological and biomedical applications, but is so far rarely achieved on this scale. In this study we show that tobacco mosaic virus (TMV) and the RNA-guided self-assembly process of its coat protein (CP) can be used to establish new nanorod scaffolds that can be loaded not only with homogeneously distributed functionalities, but with distinct molecule species grouped and ordered along the longitudinal axis. The arrangement of the resulting domains and final carrier rod length both were governed by RNA-templated two-step in vitro assembly. Two selectively addressable TMV CP mutants carrying either thiol (TMVCys) or amino (TMVLys) groups on the exposed surface were engineered and shown to retain reactivity towards maleimides or NHS esters, respectively, after acetic acid-based purification and re-assembly to novel carrier rod types. Stepwise combination of CP(Cys) and CP(Lys) with RNA allowed fabrication of TMV-like nanorods with a controlled total length of 300 or 330 nm, respectively, consisting of adjacent longitudinal 100-to-200 nm domains of differently addressable CP species. This technology paves the way towards rod-shaped scaffolds with pre-defined, selectively reactive barcode patterns on the nanometer scale.

Decoration of nanoparticles, in particular biomolecules, gathered high attention in recent years.(1-7) Of special interest is the potential use of biomolecules as templates for the fabrication of semiconducting or metallic nanostructures.(1-7,26) In this work we show the application of atomic layer deposition, a gas-phase thin film deposition process, to biological macromolecules, which are frequently used as templates in nanoscale science, and the possibility to fabricate metal oxide nanotubes and thin films with embedded biomolecules.(1-13).

Tobacco mosaic virus (TMV) is a robust nanotubular nucleoprotein scaffold increasingly employed for the high density presentation of functional molecules such as peptides, fluorescent dyes, and antibodies. We report on its use as advantageous carrier for sensor enzymes. A TMV mutant with a cysteine residue exposed on every coat protein (CP) subunit (TMVCys) enabled the coupling of bifunctional maleimide-polyethylene glycol (PEG)-biotin linkers (TMVCys/Bio). Its surface was equipped with two streptavidin [SA]-conjugated enzymes: glucose oxidase ([SA]-GOx) and horseradish peroxidase ([SA]-HRP). At least 50% of the CPs were decorated with a linker molecule, and all thereof with active enzymes. Upon use as adapter scaffolds in conventional “high-binding” microtiter plates, TMV sticks allowed the immobilization of up to 45-fold higher catalytic activities than control samples with the same input of enzymes. Moreover, they increased storage stability and reusability in relation to enzymes applied directly to microtiter plate wells. The functionalized TMV adsorbed to solid supports showed a homogeneous distribution of the conjugated enzymes and structural integrity of the nanorods upon transmission electron and atomic force microscopy. The high surface-increase and steric accessibility of the viral scaffolds in combination with the biochemical environment provided by the plant viral coat may explain the beneficial effects. TMV can, thus, serve as a favorable multivalent nanoscale platform for the ordered presentation of bioactive proteins.

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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