A new technique that sticks individual DNA molecules to a gold surface works at the flick of an electrochemical switch. The technique could help provide greater control in the building of nano-scale structures and devices, according to researchers. 

Previous methods required DNA to be modified in some way for it to chemically bind to a surface. But as Ann Fornof of Munich's Ludwigs-Maximilians University in Germany explains, her team's electrochemically controlled technique is far simpler. 'We don't have to build into the DNA any specific structure,' she says. 'By changing the potential, we can just attach the DNA to the surface, or make the surface not attractive to the DNA.' 

Fornof and co-workers bound a double stranded DNA molecule to an atomic force microscope (AFM) tip and moved the tip with the molecule attached towards a gold microelectrode. When they adjusted the surface potential of the electrode and then moved the tip away slightly, they measured an increased force on the tip, suggesting that the DNA was stretching after becoming covalently bound to the surface. 

As the team observed, DNA is only anchored to a reduced gold surface, produced at negative potentials. Although DNA is negatively charged, magnesium ions from the experimental solution help attract it to the negatively polarised electrode. The bonds form between gold atoms and primary amine (RNH₂­) groups in the nucleotide bases of the DNA - the duplex tends to fray a little at the end, exposing a few bases to the gold surface. 

Fornof thinks there are a broad range of possibilities for their technique. 'You could trigger deposition in a single molecule and, from there, build up any sort of nanostructure that you might be interested in,' she says. 'We could envision using it as a way to turn on or off adhesion.' 

Robert Henderson, who studies biological molecules using AFM approaches at the University of Cambridge, UK, says the authors may have solved a tricky problem. 'It has always proved difficult to accurately place DNA molecules on surfaces - to lay the foundations for fabrication,' he says. 'This technique has potential to make much easier the production of nano-devices that use DNA as building blocks.' 

Hayley Birch 

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