DNA is new god of small things

Researchers are using strands of DNA to build structures - pyramids, cubes and octahedrons - 2,000 times smaller than the width of a hair, writes Dick Ahlstrom

DNA carries the blueprint of all life. It might now also serve as scaffolding that will allow scientists to build impossibly small structures measuring just dozens of atoms across.

The striking image that accompanies this report is an actual "photo" of a structure made entirely of DNA and measuring only 22 billionths of a metre across. That is about 2,000 times smaller than the width of a human hair.

The team that created this octahedron believes DNA could provide a handy scaffolding system used in nanotechnology, the science of the incomprehensibly small. DNA shapes could be used to provide a template, a scaffold that could position other material at uniquely defined locations.

Details of the research by Dr Gerald Joyce and colleagues from the Scripps Research Institute, La Jolla, California, are published this morning in Nature.

Nanotechnology grew out of the need to produce smaller and smaller components for the computer industry. As components get smaller, however, it becomes more difficult to control their formation, and equally difficult to know for sure the device is what is intended.

The best option is to imitate nature and grow the components you want, an approach that would help ensure conformity, to maintain the consistency of the components you are attempting to produce. This why the use of DNA to produce shapes and scaffolds is promising. Structures made of DNA could provide a way to ensure this consistency given the molecule's well-understood properties and characteristics.

Dr Joyce, whose grandfather emigrated to the US from Co Mayo, argues that molecular self-assembly based on DNA "offers a means of spontaneously forming complex and well-defined structures from simple components". His octahedron is just such a self-folding structure, produced using a DNA strand just 1,669 base pairs long.

It was formed using one long chain and five shorter chains in a succession of heating and cooling steps. The assembly procedure could readily be modified, according to Joyce, to produce other shapes including cubes. These, too, would be self-forming, with the starting recipe being modified to produce a stronger or weaker structure to order.

Importantly, because the scaffold is made of DNA, the stuff of life, it would be a simple matter to modify a bacterium to produce large numbers of these structures by clonal production.

Until now, other three-dimensional DNA structures have resisted cloning "because they contain topologies that prevent copying by polymerases", the authors write. The use of polymerases is nature's own way of producing predetermined strands of genetic material.

The structure produced by Dr Joyce and the Scripps team is readily copied by polymerases and will fold into the required shape so long as the five shorter chains are in the presence of the long 1,669 base pair chain.

"Manipulation of the basic octahedron structure could produce a family of scaffold variants whose function is to position other material at uniquely defined locations," the authors propose. The rigidity of the structures could also be varied.

These specific starting shapes in turn would become tools in the construction of miniature devices by directing the assembly of additions to the scaffold. Controlled and consistent structure doesn't get much smaller than this, given the octahedron is about the same size as a small virus.