Nano-transistor self-assembles using biology
20 November 2003
NewScientist.com news service
A functional electronic nano-device has been manufactured using biological self-assembly for the first time.
Israeli scientists harnessed the construction capabilities of DNA and the electronic properties of carbon nanotubes to create the self-assembling nano-transistor. The work has been greeted as "outstanding" and "spectacular" by nanotechnology experts.
The push to shrink electronic circuits to ever smaller dimensions is relentless. Carbon nanotubes, which have remarkable electronic properties and only about one nanometre in diameter, have been touted as a highly promising material to help drive miniaturisation. But manufacturing nano-scale transistors has proved both time-consuming and labour-intensive.
The team, at the Technion-Israel Institute of Technology, overcame these problems with a two step process. First they used proteins to allow carbon nanotubes to bind to specific sites on strands of DNA. They then turned the remainder of the DNA molecule into a conducting wire.
Proof of principle
"DNA is very good at building things in molecular biology, but unfortunately, it does not conduct electricity. We had to get a metal conductor on the DNA," explains physicist Erez Braun, who led the research.
"This is spectacular work," says Cees Dekker, a nanoscience expert at Delft University in the Netherlands. "It demonstrates that it's possible to use biology to build an inorganic device that works."
"But while it is a first step towards molecular computing based on this type of DNA configuration, we are still many years way from large scale self-assembly electronic devices, such as computers," Dekker cautions.
Braun's team began their manufacturing process by coating a central part of a long DNA molecule with proteins from an E. coli bacterium. Next, graphite nanotubes coated with antibodies were added, which bound onto the protein.
After this, a solution of silver ions was added. The ions chemically attach to the phosphate backbone of the DNA, but only where no protein has attached. Aldehyde then reduces the ions to silver metal, forming the foundation of a conducting wire.
To complete the device, gold was added. This nucleates on the silver and creates a fully conducting wire. The end result is a carbon nanotube device connected a both ends by a gold and silver wire.
The device operates as a transistor when a voltage applied across the substrate is varied. This causes the nanotubes to either bridge the gap between the wires - completing the circuit - or not.
Out of 45 nanoscale devices created in three batches, almost a third emerged as self-assembled transistors. They work at room temperature and the only restriction for future devices is that the components must be compatible with the biological reactions and the metal-plating process.
The team have already connected two of the devices together, using the biological technique. "The same process could allow us to create elaborate self-assembling DNA sculptures and circuitry," says Braun.