Nanofabrication using TMV and other templates
Nanofabrication involves creating, combining and assembling individual nanoparticles to make functional materials and devices, which can be used in a great variety of areas ranging from computer memory to biomedical sensors.
Innhold
The process of nanofabrication entails the making of complex and carefully aligned structures at the nanometer scale, which involves many difficulties, like shape-determination and site-specific modification. One way to overcome such difficulties is by using templates, which can function as a set of instructions or a «skeleton» for the emerging structures.
Viruses
Recently, there has been an increase in the use of naturally occurring biological nanoparticles for this purpose, among them viruses.<ref name=tmv1>N. F. Steinmetz, D. J. Evans, Utilisation of plant viruses in bionanotechnology, 2007</ref> A virus have several favorable properties when it comes to nanofabrication: The virions have a tendency to self-assemble into discrete, monodisperse nanoparticles, which are highly symmetrical. In addition, these viral nanoparticles have a propensity for self-organisation on the mesoscale. Both two-dimensional and three-dimensional crystals can easily be obtained by standard crystallisation procedures involving viral nanoparticles.<ref name=tmv1/> Some viruses can even function as natural templates for nanodevices because of their unique structures. Because of this it is clear that viruses may be well suited for nanofabrication.
Structure
A virus is in general many times smaller than a bacteria, with diameters ranging from 20 to 400 nanometres. It consists roughly of a nucleic acid (DNA or RNA), which is surrounded by a capsid; a protective coat of protein.<ref name=tmv7>http://www.britannica.com/EBchecked/topic/630244/virus/32742/Size-and-shape</ref> This capsid is of great interest because of its exceptional robustness: It can tolerate both high temperatures and wide pH-variations as well as it remains intact in many organic solvent-water mixtures.<ref name=tmv1/>
Plant viruses
We shall here discuss the present and future use of plant viruses as nanotemplates, by considering the tobacco mosaic virus (TMV), the red clover necrotic mosaic virus (RCNMV), the cowpea chlorotic mottle virus (CCMV) and the brome mosaic virus (BMV), focusing particularly on TMV and RCNMV. Plant viruses are viruses which only affect plants. Since plant viruses need living plant cells to reproduce, they are non-infectious to both humans and other mammals.<ref name=tmv8>http://www.disknet.com/indiana_biolab/v030.htm</ref> This is of course advantageous regarding production, research and prospective consumption of technologies involving such viruses.
The production of plant viruses is in itself simple and effective because of the natural tendency of viruses to replicate. It is for example possible to «harvest» amounts of plant virus on the gram scale within 2-4 weeks, when starting with 1 kg of infected leaves.<ref name=tmv1/> In the future, this can be exploited for making industrial nanofabrication effective.
TMV
There are generally two ways of nanofabricating: “top-down” and “bottom-up”. (Making big systems smaller, and the self-assembly of smaller systems into larger structures, respectively.) Tobacco mosaic virus (TMV) is used in both techniques.
Structure
TMV is a helical of a rod shaped virus composed of around 6400 bases and 2130 identical coat proteins. It has an outer diameter of 4 nanometres and a central channel with a diameter of 4 nanometres, and is a clad of flexible loops of the protein structure.<ref name=tmv5>Mato Knez et al., Biotemplate Synthesis of 3-nm Nickel and Cobalt Nanowires, 2003</ref> TMV has also a strong surface and stability against pH change and high temperature.<ref name=tmv5/> <ref name=tmv6>Erik Dujardin et al., Organization of Metallic Nanoparticles Using Tobacco Mosaic Virus Templates, 2003</ref> Because of this, the conditions for experiments in reduction of metals are suitable for the TMV.
Adsorption from solutions
For the producing of TMV, an infected nicotiana tabacum plant with a plasmid DNA that comprised the code for the movement and coat protein of the TMV genome as well for the replicas.<ref name=tmv5/> This virus can act as an attacker for metal ions. It has a chemical functionality that also can make metal wires from metal ion solutions. The TMV has also many adsorption properties of materials, for example silicon, glass, wafers and mica. TMV is then a template for nanofabrication, and the results of the adsorption of the solutions will result in particles in nanometer scale, and nanowires with length up to 600 nanometres in the central channel.<ref name=tmv5/> <ref name=tmv6/> The diameter of the particles is about 3-5 nanometres, and for nanowires about 3 nanometres.<ref name=tmv5/> <ref name=tmv6/> When considering this, it could be possible to fabricate gold, aluminum, silicon, or cobber in nanowires or nanoparticles.
By attaching gold particles on the edges of TMV, two or more virions can aggregate together.
The way these particles and nanowires are linked with the TMV is achieved by chemical or photochemical reduction of these materials. It is chemically controlling the surface charge of the virus by keeping parameters such as pH and temperature in a suitable level for the metallization. The “tricky thing” is to let the nanowires grow in continuous arrays. But TMV allows us to bind the modified vision to a specified target, for example to a small area on a solid substrate. This can open up possibilities for nanodevices in electronics.<ref name=tmv5/> After the TMV is bounded by chemical coding, there is an induction of the disassembly of proteins and RNA.
With high pH or with enzymes used on TMV, we have the nanowires or particles left on the specified place.<ref name=tmv5/> There are numerous perspectives in this case, and the contact can also be done in a top-down fashion. By modifying the coat protein of TMV, we can make different shapes and sizes of metal wires. So the coat protein can shape the wire instead of using bottom-up fashion like when putting wires on a surface.
Assembling via nucleic hybridization
TMV is suitable for manipulating particles and wires in nanometers scale. But TMV is also been used as a template in a DNA link to electrodeposited chitosan. This has the potential for making devices and materials at nanometers. The idea is assembling of TMV nanotemplates via nucleic hybridization. The virion is disassembled partially to expose the end of the RNA sequence and hybridize to virus-specific probe DNA link to electrodeposited chitosan.<ref name=tmv4>Hyunmin Yi et al., Patterned Assembly of genetically modified viral nanotemplates via nucleic acid hybridization, 2005</ref> When TMV template is on chitosan, chitosan is utilized as an interface to direct the spatially selective assembly of the viral templates onto the surface of gold-patterned silicon chip by applying an electrical signal.<ref name=tmv4/> All these strategies provide the basis for further efforts to utilize TMV templates in the construction of nanodevices.<ref name=tmv4/> “Supercomputers” could be just around the corner if these devices can be constructed like transistors or just regular devices for digital memory.
RCMNV
Another plant virus which can be used as a nanotemplate is the red clover necrotic mosaic virus (RCNMV). The RCNMV capsid, consisting of 180 copies of a single protein, has an icosahedral structure, and a diameter of approximately 36 nanometres.<ref name=tmv9>http://www.ncsu.edu/research/results/vol7n3/02.html</ref>, <ref name=tmv1/> The main property of the RCNMV that makes it useful as a nanotemplate is the fact that it has a hollow 17 nanometer wide interior, which can contain up to 2000 molecules.<ref name=tmv10>http://news.ncsu.edu/news/2009/02/tp-lommelfranzen.php</ref>, <ref name=tmv11>http://ncsu.edu/nano/faculty/profiles/details.php/22</ref> There are several pores in the capsid leading into this inner cavity, which must function as transport channels for insertion of molecules. In general, the chemical character of the RCNMV capsid makes the pores close when calcium (Ca2+) is present, and open when calcium is absent.<ref name=tmv11/> In this way, the traffic in and out of the «storage space» can be controlled.
Drug-delivery system
If the RCNMV is to be used in a drug-delivery system within the human body, the virus needs to know when the drugs are supposed to be released from the capsid. This can be controlled by placing small proteins on the surface of the capsid; signal-peptides which are attracted to specific predetermined cells, like for example cancer cells. (Figure 6).<ref name=tmv10/> The human blood vessels contain concentrations of calcium high enough for automatic sealing of the capsid, but inside individual cells the concentration is much lower. This leads to emission of the content of the capsid as soon as it has entered the desired cell.<ref name=tmv10/> Such a target specific delivery of drugs will greatly reduce side effects of all kinds of chemotherapy.
Another potential application for RCNMV is in the fight against genetic diseases like for example sickle-cell anemia, a serious inborn disease which involves great reduction of life expectancy. By placing artificially modified RNA inside the capside, human cells containing disease developing information can be reprogrammed and evolve into healthy cells.<ref name=tmv9/> There has also been done research on the formation of RCNMV capsides around gold nanoparticles, in order to fabricate a hybrid metal. This may be used as the building block in the construction of new nanomaterials or as a tool in sensors for use in biotechnology.<ref name=tmv1/>
CCMV and BMV
Two other icosahedral viruses which also have potential «cargo holds» inside their protein capsides are the cowpea chlorotic mottle virus (CCMV) and the brome mosaic virus (BMV). Similar to RCNMV, various molecules can be attached to their protein capsides, but in this case the opening and closing of their pores is controlled by regulations of the pH-value in their surroundings.<ref name=tmv1/>
Because it has the ability to assemble into thin films as well as obtaining and releasing nanoparticles on command, CCMV can be used in functional membranes.<ref name=tmv1/> Research on BMV on the other hand, has shown that this virus can function as a template in creating two-dimensional and three-dimensional crystals, which can be potential components in various new materials. As with RCNMV, BMV capsids grown around gold nanoparticles may also be used in biosensing applications.<ref name=tmv1/>
NOTES
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REFERENCES
- Nicole F. Steinmetz, David J. Evans, Utilisation of plant viruses in bionanotechnology - www.rsc.org/obc, Advance Article 24/7 - 2007
- Sinan Balci, Kei Noda, Alexander M. Bittner, Anan Kadri, Christina Wege Holger Jeske, Klaus Kern, Self-Assembly of Metal-Virus Nanodumbbells - Angew. Chem. Int. Ed., 46 - 2007
- S. Balci, A.M. Bittner, K. Hahn, C. Scheu, M. Knez, A. Kadri, C. Wege, H. Jeske, K. Kern, Copper nanowires within the central channel of tobacco mosaic virus particles - Electrochimica Acta, 51 - 2006
- Hyunmin Yi, Saira Nisar, Sang-Yup Lee, Michael A. Powers, William E. Bentley, Gregory F. Payne, Reza Ghodssi, Gary W. Rubloff, Michael T. Harris, James N. Culver, Patterned Assembly of Genetically Modified Viral Nanotemplates via Nucleic Acid Hybridization - Nano Letters, 5 - 2005
- Mato Knez, Alexander M. Bittner, Fabian Boes, Christina Wege, Holger Jeske, E. Mai, Klaus Kern, Biotemplate Synthesis of 3-nm Nickel and Cobalt Nanowires - Nano Letters, 3 - 2003
- Erik Dujardin, Charlie Peet, Geald Stubbs, James N. Culver, Stephen Mann, Organization of Metallic Nanoparticles Using Tobacco Mosaic Virus Templates – Nano Letters, 3 - 2003
- Britannica Online Encyclopedia - http://www.britannica.com/
- Indiana Biolab - http://www.disknet.com/indiana_biolab/
- North Carolina State University - http://www.ncsu.edu
- North Carolina State University Newsroom - http://news.ncsu.edu
