A molecule of DNA is recognized more as a nanomaterial rather than a biological material, in the field of nanotechnology. This paper looks at the structure of DNA, its material properties such a mechanical and electrical and its widespread applications. It is undoubtedly a strong fact that the DNA molecule is one of the most promising functional nanomaterials to date. DNA is in fact the most central substance in the workings of all life on Earth.
DNA which stands for Deoxyribonucleic acid is a nucleic acid that comprises the genetic instructions for the growth and function of living organisms. And the key part of DNA in the cell is the ability for long-term storage of information. This could often be compared to a blueprint, as it contains the instructions to construct other parts of the cell, namely proteins and RNA molecules 
DNA makes up the genetic component of all eukaryotes, bacteria and many viruses. Many biotechnology techniques, including recombinant DNA, anti-sense DNA and RNA, anti-gene technology, DNA vaccines, etc., have been developed over the past 30 years. Recently, other studies on DNA have focused on its potential use as a nanomaterial 
Structure of DNA
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The most important fact that DNA is of interest to nanotechnology is its size. It is a long polymer that is made up of repeating units called nucleotides. In general the DNA chain is 22 to 24 angstroms wide. And one nucleotide unit is 3.3 angstroms long. Even though these repeating units are very small, DNA polymers could be vast molecules containing millions of nucleotides. For example the largest human chromosome is said to be 220 million base pairs long.
In order to gain an intuitive feeling for the size of DNA to the sizes of things in general, and especially to the sizes of other things that are too small to be seen by the naked eye, we look at the figure below.
Figure : The relative lengths of things on a microscope scale
Every DNA molecule is made up of two long polymers that are connected by hydrogen bonding of atoms and are coiled in the shape of a double helix. Each polymer contains many structures called nucleotides that are further broken down into three parts namely,
Deoxyribose (a five carbon sugar).
A phosphate group.
A nitrogenous base.
There are 4 different nitrogenous bases which are named: thymine, cytosine, adenine, and guanine. And these four bases makes the foundation of the genetic code. Sometimes represented as T, C, A, and G, these chemicals act as the cell's memory, instructing it on how to synthesize enzymes and other proteins, as can be seen in figure 3.
An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell 
Figure : The structure of DNA 
The above figure shows a general cell and the whereabouts of the DNA in relation to the structure of the cell. The following diagram shows a DNA thread making two coils around each of a series of protein spools. The DNA double helix is followed showing its base-pairs which are illustrated more in detail in figure 3.
Figure : The DNA double helix showing base-pairs
Through this paper we will look at current application of DNA as a promising nanomaterial. The following are some of the interesting characteristics of DNA that make it ideal for such applications. These applications will be discussed further in detail.
Facile synthesis by solid-phase method
Natural information device
Switching (Inter/Intra molecular pairing)
Nanobioelectronics - DNA as a conductive nanowire
Based on the above characteristic properties, DNA is of great interest for applications in bioelectronics.
Presently there is a great interest and research to create bioelectronic devices for the use in biosensing, drug discovery, and even curing certain diseases.
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PNNL's Zhiwen Tang, Yuehe Lin and colleagues from both PNNL and Princeton University have built nanostructures of graphene and DNA. A fluorescent molecule was attached to the DNA to track its interaction. The ability for DNA to turns their fluorescent lights switch on and off when near graphene can be used to create a biosensor. And it may be possible to apply this technology for diagnosing diseases like cancer, and detecting toxins in tainted food and could also be extended to detecting pathogens from biological weapons.
The DNA molecule offers a promising template through the bottom-up assembly of nanoelectronic devices. This is a result of the well-defined chemical structure and the mass of electrostatic and chemical binding sites exploitable for modification with molecules, metal ions and other metal nanoparticles.
It has been established that DNA has the ability to show many conductivity features. Fascinatingly DNA would be an insulator, a good conductor, or a semiconductor with a large band gap, depending on the sequence of the DNA and the environments in which the assessment is carried out.
There have been reports of a conducting nanowire derived from DNA.
DNA of different sequences is attached onto two microelectrodes respectively and a connection made between the two electrodes as seen in Fig. 4a. A silver ion is doped to the DNA which is to be wired as seen in Fig. 4b.
Figure : Conductive DNA nanowire. (a) DNA only and (b) DNA with metals
Nanomechanics - DNA in Nanomechanics
Nature bases its operation on proteins to perform actions of any sort. DNA by nature has the ability to encode and transfer the information to fabricate proteins through a spontaneous process.
In the past the development of nanomechanical devices was focused mainly on motor proteins, such as actin, kinesin, and myosin. Lately research is being carried out to the construction of nanomechanical devices from DNA.
Several kinds of nanomechanical motions of DNA motifs are possible such as opening/closing of a DNA tweezer, crawling shrinking/extention linear movement and simple rotations around a central DNA axis. These mechanical actions can be implementation to the construction of hybrid devices which contain functional moieties.
The Fig. 5 below shows a conventional molecular beacon, a nanomechanical motion of nucleic acid motifs with a hairpin structure.
Figure : Nano mechanical motion of nucleic acid motifs with a hairpin structure. A conventional molecular beacon 
DNA-based mechanical device have the ability to be fueled by DNA itself through the use of its elastic responses, according to Yurke, Turberfield, Mills, Simmel, and Neumann 2000.
Figure : A DNA Nanomechanical Device- Source Ned Seeman's Lab
The DNA nanomechanical device above in Fig 7. is a device that works by utilizing the B-Z transition of DNA. Two double crossover molecules (red and blue regions below) by a bridge segment that contains a region that can be converted from right-handed B-DNA to left-handed Z-DNA. This convertible segment is shown in yellow. Fig 8. below shows some examples of Nanomechanical devices.
Figure : Examples of molecular devices using DNAzymes. (a) Immobilized DNAzyme, (b) DNAzyme-immobilized electrode, (c) sensor containing DNAzyme, its activity is changed in the presence of the complementary DNA sequence, (d) enzyme immunoassay device containing both regions for recognition of thyroxine (T4) and DNAzyme.
DNA as a Nanoarchitecture
DX arrays have been used in the formation of hollow nanotubes of 4-20 nm diameter. These DNA nanotubes can be somewhat compared to carbon nanotubes interms of size and shape. But carbon nanotubes are known to very strong and better conductors, while the DNA nanotubes can be more simply adjusted and connected to other structures. There are several methods of constructing DNA nanotubes. One method uses the inherent curvature of DX tiles and forms a DX lattice that would curl around it and close into a tube. The other method uses single-stranded "tiles".
Nanotechnology involves two strategies. One is the 'top-down' approach that atoms or molecules should be functioned upon directly by a fine manipulation method. And the second is the 'bottom-up' approach, based on self-integration of molecules.
DNA has been used as a template in the architecture of nanoparticles. Soto et al. have been successful in synthesizing a photo-band gap in a photonic crystal by the use of DNA as an intercalating agent of nanoparticles . Others have made numerous nanoparticle assemblies using 'DNA recognition protein' and 'DNA' [,]. Maeda et al. have been successful in the precise control of positioning gold particles using DNA .
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Warner and Hutchison have assembled a ribbon shape and a linear structure from the use of cationic gold particles and DNA. It has also been reported that copper nanowire and platinum cluster aggregation has been carried out using DNA as a template [,].
A cube and a truncated octahedron from DNA Fig.9 and Fig.10 respectively have been made possible by the ability of specific sticky ends to attach to a branched DNA junction whose edges are double-stranded DNA. There is great expectation that DNA sticky ends could be used to assemble DNA cages containing oriented guests. If this goal can be achieve goal, there will be a great potential on the crystallization of all biological molecules.
Figure : DNA cube - Source Ned SeemanHYPERLINK "http://seemanlab4.chem.nyu.edu/index.html"'HYPERLINK "http://seemanlab4.chem.nyu.edu/index.html"s Lab
The above illustration of a DNA cube shows that it has six different cyclic strands. Their backbones are shown in red (front), green (right), yellow (back), magenta (left), cyan (top) and dark blue (bottom). And each of the nucleotides are characterised by a single colored dot for the backbone, and a white dot expressive the base. The helix axes of the molecule shows the connectivity of a cube and the strands are linked to each other twice on every edge. Therefore, this molecule is a hexacatenane.
Figure : Truncated Octahedron - Source Ned SeemanHYPERLINK "http://seemanlab4.chem.nyu.edu/index.html"'HYPERLINK "http://seemanlab4.chem.nyu.edu/index.html"s Lab
DNA and its remarkable characteristics make life and all living functions possible. So there is no doubt that it has great potential in the application in many fields of which nanotechnology is a major candidate, as the size of DNA puts it automatically in that category making possible technologies such as nanobioelectronics to functioning as nanocatalyst. DNA has many functions and multiple functions of DNA could be used simultaneously. These could be activated independently by molecular switching. The DNA molecule is indeed the most promising functional nanomaterial. Nevertheless in order to apply DNA molecules and its functionality in nanotechnology, there is still work to be carried out because of a large gap between theory and practice. It will not be long before we see a ground breaking achievement in the field of DNA nanotechnology.