Believe it or not, out there somewhere, in a brightly lit laboratory, is a person in a lab coat, folding DNA, proteins and other biological compounds to provide innovative new medicines, tackle microengineering problems and create intriguing art. Welcome to the world of nantechnology.
The structure of DNA
Nanotechnology is the study of materials and devices smaller than 100 nanometers (10-5 or 0.000001 cm), and it is being applied to a diverse set of problems including drug delivery, nanorobotics, gene therapy, microelectronics and molecular computing. DNA nanotechnology involves the construction of self-assembling minute artificial structures from nucleic acids (the building blocks of DNA). DNA can be used to form a functional nanostructure itself, or it can be used as a scaffold to direct the assembly of other molecules (e.g. carbon, protein, peptides) into a functional structure. This is possible because of the strict base pairing rules of DNA, which means that strands will only bind together if they share complementary sequences. Base sequences can be therefore designed that will form specific structures. This is a major advantage over other materials used in nanotechnology such as proteins and nanoparticles. Dynamic DNA nanostructures can also be designed that react to certain chemical or physical stimuli, and DNA engineering is allowing scientists to design sequences that catalyse reactions, influence gene expression and modify the properties of natural DNA. Even more amazingly, DNA ‘printers’ have now been developed which can produce DNA strands with specific sequences, and bind them to a surface.
In 1991, Scientists in New York, Nadrian Seeman and Junghuei Chen, began folding short strands of DNA into cubes, tubes and lattices. These early designs were simple and extremely difficult to construct. Research continued into DNA origami, however, and in 2006 scientists from the California Institute of Technology reported more complex DNA origami using much longer strands held together with DNA ‘staples’. Scientists can now fold DNA into pretty much any shape they like – hollow cages, lattices, honeycomb, and complex irregular shapes – last year Wei and colleagues in Boston wrote out the entire alphabet, as well as a series of emoticons, in single stranded DNA. Each strand is 42 base pairs long and folds on itself to form a rectangular tile, like a brick, which is then used to build tiny DNA walls. Ultimately these walls can be shaped into whatever 2 dimensional image you like. More recently, steps have been made towards creating more complex three-dimensional structures, and methods have been refined, massively increasing the speed of assembly. Han and colleagues have successfully created cross-shaped structures that can be assembled to form large, complex 3D designs. These cross-shaped nanostructures are based upon a naturally occurring DNA formation known as a Holliday junction, which is a transient step in the process of recombination during meiotic cell division. Artificial Holliday junctions can be formed between non-identical sequences, making them more stable. They hope this technique could be used to create cages that might carry drugs to the correct site.