Metal and metaloxide nanostructures on and in plant viruses

Tobacco Mosaic Virus (TMV) is composed of 2130 identical coat protein subunits following the right-handed helix of an accompanying RNA strand to produce a 300 nm hollow cylinder with an outer diameter of 18 nm and a 4 nm wide central channel. In this work, TMV is used as a bionanotemplate for the synthesis of interesting nanomaterials. When the TMV is activated with a catalyst (Pd (II)), nickel, copper, and cobalt nanowires can be grown within the central channel of the virion. In the same way alloy nanowires (cobalt-iron) are produced inside the central channel. Due to the non-galvanic protocol, the deposition method is called electroless deposition (ELD). Apart from the deposition of metals (Ni, Co, Cu, CoFe alloy), zinc oxide, a large band gap semiconductor, is deposited on the exterior surface of the virus. The chemical compositions of the nanomaterials are revealed at the nanoscale by energy-filtering transmission electron microscopy. Various physical properties of some of the synthesized nanomaterials are measured: Electrical transport measurements on the TMV rods, contacted by gold electrodes, indicate that the TMV rods show insulating behavior at room temperature. High-resolution transmission electron microscopy images of individual nickel nanowires show the crystalline bulk phase, confined to a 3 nm wide wire, with (111) planes perpendicular to the wire axis. Cathodoluminescence measurements from individual zinc oxide rods exhibit ultraviolet emission with a photon energy of around ∼3.4 eV, which is equal to the band gap of the bulk material. Furthermore, 6 nm diameter gold nanoparticles (Au-nps) are selectively attached to the ends of the TMV particles, and they are enlarged by electroless deposition of gold. The RNA strand plays an important role in the selective attachment of the Au-nps. It is possible to print and align TMV particles on a variety of surfaces by the microcontact printing method. Several micrometer long end-to-end assembled TMV rods can be placed close to the edges within the recessed regions of polydimethysiloxane stamp structures. The reason for the selective assembly of the virions is the dewetting of the inking solvent (water) on the stamp surface. By printing, the virion pattern is transferred to solid surfaces. Alternatively, TMV particles can be selectively assembled on flat rectangular submicrometer patches with amine groups, which are generated by electron beam lithography. The experimental results show that TMV can be a model system for new bionanotemplates with huge potential in nanoscale science and possibly technology.


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