Strands of DNA can be easily made into nanoscale fibre optic cables (Image: Wikimedia Commons)

Thanks to a new technique, DNA strands can be easily converted into tiny fibre optic cables that guide light along their length. Optical fibres made this way could be important in optical computers, which use light rather than electricity to perform calculations, or in artificial photosynthesis systems that may replace today’s solar panels.

Both kinds of device need small-scale light-carrying “wires” that pipe photons to where they are needed. Now Bo Albinsson and his colleagues at Chalmers University of Technology in Gothenburg, Sweden, have worked out how to make them. The wires build themselves from a mixture of DNA and molecules called chromophores that can absorb and pass on light.

The result is similar to natural photonic wires found inside organisms like algae, where they are used to transport photons to parts of a cell where their energy can be tapped. In these wires, chromophores are lined up in chains to channel photons.


Light wire

Albinsson’s team used a single type of chromophore called YO as their energy mediator. It has a strong affinity for DNA molecules and readily wedges itself between the “rungs” of bases that make up a DNA strand. The result is strands of DNA with YO chromophores along their length, transforming the strands into photonic wires just a few nanometres in diameter and 20 nanometres long. That’s the right scale to function as interconnects in microchips, says Albinsson.

To prove this was happening, the team made DNA strands with an “input” molecule on one end to absorb light, and on the other end a molecule that emits light when it receives it from a neighbouring molecule. When the team shone UV light on a collection of the DNA strands after they had been treated with YO, the finished wires transmitted around 30% of the light received by the input molecule along to the emitting molecule.

Physicists have corralled chromophores for their own purposes in the past, but had to use a “tedious” and complex technique that chemically attaches them to a DNA scaffold, says Niek van Hulst, at the Institute of Photonic Sciences in Barcelona, Spain, who was not involved in the work.

The Gothenburg group’s ready-mix approach gets comparable results, says Albinsson. Because his wires assemble themselves, he says they are better than wires made by the previous chemical method as they can self-repair: if a chromophore is damaged and falls free of the DNA strand, another will readily take its place. It should be possible to transfer information along the strands encoded in pulses of light, he told New Scientist.

Variable results

Philip Tinnefeld at the Ludwig Maximilian University of Munich in Germany says a price has been paid for the added simplicity.

Because the wire is self-assembled, he says, it’s not clear exactly where the chromophores lie along the DNA strand. They are unlikely to be spread out evenly and the variation between strands could be large.

Van Hulst agrees and is investigating whether synthetic molecules made from scratch can be more efficient than modified DNA.

But both researchers think that with improvements, “molecular photonics” could have a wide range of applications, from photonic circuitry in molecular computers to light harvesting in artificial photosynthetic systems.

Journal reference: Journal of the American Chemical Society (DOI: 10.1021/ja803407t)