Engineered Tobacco mosaic virus mutants with distinct physical characteristics in planta and enhanced metallization properties

TMV nanorods with programmed longitudinal domains of differently addressable coat proteins

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.

Integration of plant viruses in electron beam lithography nanostructures

Tobacco mosaic virus (TMV) is the textbook example of a virus, and also of a self-assembling nanoscale structure. This tubular RNA/protein architecture has also found applications as biotemplate for the synthesis of nanomaterials such as wires, as tubes, or as nanoparticle assemblies. Although TMV is, being a biological structure, quite resilient to environmental conditions (temperature, chemicals), it cannot be processed in electron beam lithography (eBL) fabrication, which is the most important and most versatile method of nanoscale structuring. Here we present adjusted eBL-compatible processes that allow the incorporation of TMV in nanostructures made of positive and negative tone eBL resists. The key steps are covering TMV by polymer resists, which are only heated to 50 °C, and development (selective dissolution) in carefully selected organic solvents. We demonstrate the post-lithography biochemical functionality of TMV by selective immunocoating of the viral particles, and the use of immobilized TMV as direct immunosensor. Our modified eBL process should be applicable to incorporate a wide range of sensitive materials in nanofabrication schemes.

pH control of the electrostatic binding of gold and iron oxide nanoparticles to tobacco mosaic virus

We report the binding of nanoparticles (NPs) to wild type (unmodified) tobacco mosaic virus (TMV). The viruses are simply mixed with citrate-coated, negatively charged gold and iron oxide nanoparticles (IONPs) in acidic solution. This results in TMV decorated along its whole length by the respective particles. Such a decoration usually requires chemical modification or mutation of TMV (e.g., cysteine residues), but here we simply reduce TMV's natural negative charge by protonation. The particles are protonated to a much smaller extent. This charge-based mechanism does not operate for neutral particles.

Fabrication and characterization of gold nano-wires templated on virus-like arrays of tobacco mosaic virus coat proteins

The rod-shaped plant virus tobacco mosaic virus (TMV) is widely used as a nano-fabrication template, and chimeric peptide expression on its major coat protein has extended its potential applications. Here we describe a simple bacterial expression system for production and rapid purification of recombinant chimeric TMV coat protein carrying C-terminal peptide tags. These proteins do not bind TMV RNA or form disks at pH 7. However, they retain the ability to self-assemble into virus-like arrays at acidic pH. C-terminal peptide tags in such arrays are exposed on the protein surface, allowing interaction with target species. We have utilized a C-terminal His-tag to create virus coat protein-templated nano-rods able to bind gold nanoparticles uniformly. These can be transformed into gold nano-wires by deposition of additional gold atoms from solution, followed by thermal annealing. The resistivity of a typical annealed wire created by this approach is significantly less than values reported for other nano-wires made using different bio-templates. This expression construct is therefore a useful additional tool for the creation of chimeric TMV-like nano-rods for bio-templating.

Nanoscale science and technology with plant viruses and bacteriophages

Nanoscale science refers to the study and manipulation of matter at the atomic and molecular scales, including nanometer-sized single objects, while nanotechnology is used for the synthesis, characterization, and for technical applications of structures up to 100 nm size (and more). The broad nature of the fields encompasses disciplines such as solid-state physics, microfabrication, molecular biology, surface science, organic chemistry and also virology. Indeed, viruses and viral particles constitute nanometer-sized ordered architectures, with some of them even able to self-assemble outside cells. They possess remarkable physical, chemical and biological properties, their structure can be tailored by genetic engineering and by chemical means, and their production is commercially viable. As a consequence, viruses are becoming the basis of a new approach to the manufacture of nanoscale materials, made possible only by the development of imaging and manipulation techniques. Such techniques reach the scale of single molecules and nanoparticles. The most important ones are electron microscopy and scanning probe microscopy (both awarded with the Nobel Prize in Physics 1986 for the engineers and scientists who developed the respective instruments). With nanotechnology being based more on experimental than on theoretical investigations, it emerges that physical virology can be seen as an intrinsic part of it.

New approaches for bottom-up assembly of tobacco mosaic virus-derived nucleoprotein tubes on defined patterns on silica- and polymer-based substrates

The capability of some natural molecular building blocks to self-organize into defined supramolecular architectures is a versatile tool for nanotechnological applications. Their site-selective integration into a technical context, however, still poses a major challenge. RNA-directed self-assembly of tobacco mosaic virus-derived coat protein on immobilized RNA scaffolds presents a possibility to grow nucleoprotein nanotubes in place. Two new methods for their site-selective, bottom-up assembly are introduced. For this purpose, isothiocyanate alkoxysilane was used to activate oxidic surfaces for the covalent immobilization of DNA oligomers, which served as linkers for assembly-directing RNA. Patterned silanization of surfaces was achieved (1) on oxidic surfaces via dip-pen nanolithography and (2) on polymer surfaces (poly(dimethylsiloxane)) via selective oxidization by UV-light irradiation in air. Atomic force microscopy and X-ray photoelectron spectroscopy were used to characterize the surfaces. It is shown for the first time that the combination of the mentioned structuring methods and the isothiocyanate-based chemistry is appropriate (1) for the site-selective immobilization of nucleic acids and, thus, (2) for the formation of viral nanoparticles by bottom-up self-assembly after adding the corresponding coat proteins.

Electroless synthesis of 3 nm wide alloy nanowires inside Tobacco mosaic virus

We show that 3 nm wide cobalt-iron alloy nanowires can be synthesized by simple wet chemical electroless deposition inside tubular Tobacco mosaic virus particles. The method is based on adsorption of Pd(II) ions, formation of a Pd catalyst, and autocatalytic deposition of the alloy from dissolved metal salts, reduced by a borane compound. Extensive energy-filtering TEM investigations at the nanoscale revealed that the synthesized wires are alloys of Co, Fe, and Ni. We confirmed by high-resolution TEM that our alloy nanowires are at least partially crystalline, which is compatible with typical Co-rich alloys. Ni traces bestow higher stability, presumably against corrosion, as also known from bulk CoFe. Alloy nanowires, as small as the ones presented here, might be used for a variety of applications including high density data storage, imaging, sensing, and even drug delivery.

Inducible site-selective bottom-up assembly of virus-derived nanotube arrays on RNA-equipped wafers

Tobacco mosaic virus (TMV) is a tube-shaped, exceptionally stable plant virus, which is among the biomolecule complexes offering most promising perspectives for nanotechnology applications. Every viral nanotube self-assembles from a single RNA strand and numerous identical coat protein (CP) subunits. Here we demonstrate that biotechnologically engineered RNA species containing the TMV origin of assembly can be selectively attached to solid surfaces via one end and govern the bottom-up growth of surface-linked TMV-like nanotubes in situ on demand. SiO(2) wafers patterned by polymer blend lithography were modified in a chemically selective manner, which allowed positioning of in vitro produced RNA scaffolds into predefined patches on the 100-500 nm scale. The RNA operated as guiding strands for the self-assembly of spatially ordered nanotube 3D arrays on the micrometer scale. This novel approach may promote technically applicable production routes toward a controlled integration of multivalent biotemplates into miniaturized devices to functionalize poorly accessible components prior to use. Furthermore, the results mark a milestone in the experimental verification of viral nucleoprotein complex self-assembly mechanisms.