Japanese researchers have improved the electrical conductivity of DNA through simple chemical modifications. Their work could pave the way for building DNA circuits and self-assembling, DNA-based electronics.

DNA has for decades been regarded as a potential building block for molecular electronics, but random sequences of DNA vary in their conductivity - charge transfer through G-C (guanine-cytosine) pairs is faster than through A-T (adenine-thymine) pairs. Charge can migrate along an A-T rich sequence by ’hopping’ between G-C pairs, but this decreases its electrical conductivity.

Now Tetsuro Majima and colleagues at Osaka University in Japan have found a way to tune the electronic characteristics of the A-T pairs, meaning charge transport is no longer sequence dependent. ’We can just change one nitrogen atom to C-H,’ explains Majima. ’This new deazaadenine base is the same from the genetic point of view. On the other hand, its electronic characteristics are quite similar to guanine, so then we get some very exciting results.’

To prove that replacing adenine with deazaadenine would increase electrical conductivity, the researchers made short sequences of A-T rich DNA modified at one end with a photosensitiser and at the other with a positive charge ’trap’ - phenothiazine (PTZ). After injecting charge at the photosensitive end using a laser, the researchers measured charge transfer rate by observing how quickly PTZ was oxidised to form a PTZ⁺ cation. Simply swapping the adenine bases for deazaadenines increased the rate of charge transfer by three orders of magnitude. In random DNA sequences, with mixed G-C and A-T pairs, charge transport was faster in those where adenine was replaced with deazaadenine.

’Before this work, DNA was considered not to be a very electrically conductive material.   Its electron mobility is very, very low compared with usual conductive materials,’ says Majima. ’Now we can say DNA is no longer so bad for charge mobility materials’. But he is wary of discussing applications just yet - work in this field is in its very early stages, he says.

Christoph Walti, a bionanoelectronics expert at the University of Leeds, believes Majima’s work has the potential to bring about a real step change in the field of DNA-based molecular electronics. Most importantly, he notes, the method leaves the self-assembly properties of DNA fully intact.

’G-C -only sequences show much increased charge-transport behaviour, but are severely limited in their use in terms of self-assembly applications,’ he says. ’This work clearly demonstrates that random sequences - A-T and G-C mixed - show a remarkably high conductivity compared to wild-type DNA.’

Hayley Birch