Scientists at University College Dublin are utilising DNA technology in order to grow infinitesimal wires for future computers, writes Dick Ahlstrom.
An Irish research team is "growing" microscopic wires and switches that in time could find their way into the next generation of miniaturised computers. The delicate process involves the use of DNA strands, the building blocks of all life on this planet.
Prof Donald Fitzmaurice heads the work as director of the nanochemistry group at University College Dublin. His team is working in the nanometre range where things are measured down to billionths of a metre or millionths of a millimetre.
These dimensions are almost impossible to comprehend, Fitzmaurice admits. A single human hair at about half a millimetre across is a mammoth structure by comparison.
The research is all about finding ways to produce in a predictable way tiny wires and functional switches and transistors, essential components in any computer. Electronic devices this small cannot be manufactured, they are better grown in solution, Fitzmaurice explains.
He and his team have developed a process that can reliably produce these components on a standard silicon chip template. "We are getting something like 60 to 70 per cent yields on the template which is higher than we thought," says Fitzmaurice. "It shows it is possible to build nanostructures with great precision that are important to the design of computer circuits using biological processes."
Their discovery has landed the group the cover story in the current edition of Advanced Materials, a leading international journal reporting on new materials. The cover (pictured right) shows the tiny junction point between two gold wires with a spherical particle of gold sitting in the gap between them.
"This is a nanometre scale switch," explains Fitzmaurice. "It is a very small switch and has been built using the simplest methodologies."
Small is too big a word for the device pictured here. It is measured in nanometres (nm), billionths of a metre. The two wires produced by Fitzmaurice's group measure about 40nm long and 20nm wide.
The minute gap between their ends is about 15nm across. The gold particle that sits fixed in this gap is about 10nm across, leaving spaces between the wire and the particle of between two and three nm.
The gaps are important, says Fitzmaurice because it allows the nanostructure to function like a conventional transistor. These are the electronic components built into microchips to power computer systems.
What is most striking about the research is that despite its precision, the nanostructure is made by dipping a piece of DNA attached to a silicon wafer into a series of solutions. "We have done all of that with beaker chemistry," says Fitzmaurice.
Fitzmaurice uses biochemicals as a way to dictate the nanostructure. Without these biological molecules the structure wouldn't form.
It begins with a strand of DNA, the genetic material from which all life on Earth is built, Fitzmaurice explains. DNA sequencers are now commonplace in modern labs so any DNA sequence required can be produced automatically to serve as a template. "We take a piece of DNA which is 90nm long that has a molecule called biotin attached to its middle," says Fitzmaurice. Biotin is a type of vitamin that in turn binds strongly to a protein called streptavidin.
The UCD team developed tiny gold particles that recognise DNA and can line up along it. When the silicon carrying the DNA strand is dipped in the first beaker containing the gold particles they form a gold chain 90nm long and 10nm across.
"We then expose that gold particle chain to streptavidin," says Fitzmaurice. It binds so strongly to the biotin that it actually shoves some gold particles in the chain out of the way to produce a gap about 10nm to 15nm across. At this stage there are two gold chains lined up end to end with a small gap between.
The next step is a form of electroplating that deposits extra gold along the chain, fusing the individual particles together to form two solid wires end to end with the gap still in place.
The final stage involves dipping this structure into a beaker containing individual gold particles each of which carries a small amount of biotin. This biotin fuses strongly to the streptavidin in the gap, in turn fixing the gold particle into position between the two wire ends. The electronic switch is complete, says Fitzmaurice. "This is a classic motif in the creation of nanostructures."