DNA is a beautifully clever and complex molecule that holds all the genetic information necessary for growth and development, functioning and reproduction of all known living things. But DNA nanotechnology is not interested in these genetic instructions – instead it focusses on the design, study and application of synthetic structures that are based on DNA, making use of the nucleic acid’s physical and chemical characteristics.
The field of DNA nanotechnology was invented by American nanotechnologist and crystallographer Nadrian C. Seeman – also known as Ned – in the early 1980s. Seeman realised that a three-dimensional lattice could be created from DNA, which could then be used to position target molecules, thus making crystallographic study easier as the difficult process of obtaining pure crystals was no longer necessary. Seeman’s lab created a cube of DNA in 1991, which was an important step towards developing DNA origami. Seeman himself describes the technique as convenient and logical means of constructing new materials on the nanoscale.
DNA nanotechnology uses artificial nucleic acids as a non-biological engineering material for technological uses. Two-dimensional and three-dimensional crystal lattices, nanotubes, polyhedra and other shapes have all been created, as have functional devices such as molecular machines and DNA computers.
The strict base-pairing rules of nucleic acids – in which only the sections of strands with complementary base sequences selectively bond to form a double helix – makes their use in this technique possible. It enables the design of base sequences to selectively amass to create complex target structures with precisely controlled nanoscale features. There are several ways that the DNA can be assembled: a tile-based method where smaller structures aggregate; folding using the technique of DNA origami to create two- and three-dimensional shapes; and a dynamically reconfigurable method using strand displacement.
The technique offers the unparalleled ability to control function and structure on a molecular level, with the size of structures expanding towards the microlevel domain. But does it offer any solutions to real-life problems, or it is just some very interesting academic work?
DNA is an intricate molecule and its complexity can be both a gift and a curse. Any number of functional groups may be added to it, from proteins to small molecules to inorganic materials, in any desired orientation or pattern. However, the yield is low and production scale is small with the cost of synthetic DNA high. This isn’t such a problem is the technique is employed for academic purposes but it is something that will need to be considered if to be used commercially. Additionally, in some applications, DNA nanostructures are easily altered and highly sensitive to ion strength, temperature and nucleases. The are also soft and small, and it can be hard to address individual structures efficiently.
But DNA nanotechnology has been utilised on the small scale successfully. It has been recognized as a useful tool to solve basic problems in structural biology and biophysics, including x-ray crystallography and nuclear magnetic resonance spectroscopy of proteins in order to determine their structure. Indeed, DNA origami was used to determine the structure of membrane proteins by nuclear magnetic resonance (NMR), and an artificial DNA-origami membrane channel was utilised as a platform for single molecule sensors, something which may prove useful in interfacing and communicating with living cells.
In the future, it may also be used in molecular scale electronics to create nanowires and in nanomedicine to make smart drugs for targeted drug delivery. One such idea in progress employs a hollow DNA box containing proteins that induce apoptosis (programmed cell death) when in close proximity to cancerous cells. Some DNA nanostructures with several degrees of function have been integrated into DNA robots that can recognise diseased cells and encourage apoptosis.
Other uses include DNA robotics in nanomechanical sensors, switches and tweezers and DNA walkers that can be employed in nanoscale assembly lines to move nanoparticles and direct chemical synthesis, and in DNA computing.
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