"This is the first example of a photoconducting nanostructure," says Takanori Fukushita of the University of Tokyo, Japan, a member of the team that built the cables.
The hollow cables can grow up to several micrometres long. To build them, Fukushita and colleagues created a compound containing hexabenzocoronene (HBC), two carbon-12 chains, and trinitrofluorenone (TNF). They placed the compound in a solution of tetrahydrofuran and bubbled methane vapour though it, causing the compound to self-assemble into hollow cables.
The HBC, which sheds electrons when hit by light, formed the inside of the cable wall, and the TNF, which readily accepts electrons, coated the outside of the wall.
At the moment, the cables cannot produce usable electricity from sunlight alone, as current does not flow well through the outer layer of TNF. The next step, Fukushita says, is to modify the outer layer, perhaps by attaching carbon-60 molecules (buckyballs), so it acts as a semiconductor and allows more current to flow.
Once this has been achieved, the nanocables could be fitted to nano-sized robots or micro-machines and power their movements, suggests Franz Würthner at the University of Würzburg in Germany. Their similarity in size and function to the antennae used by bacteria for photosynthesis means it might also be possible to connect them to such organisms, creating hybrid devices, he says.