“Spontaneous self-assembly of nucleic acid bases occurs on a variety of inorganic surfaces,” Ming Zheng of DuPont told nanotechweb.org. “This phenomenon, considered as an important prebiotic process relevant to the origin of life, has led us to seek a new function for nucleic acids in the manipulation of inorganic nanomaterials, where interfacial interactions dominate.”

Zheng and colleagues found that a specific single-stranded DNA - d(GT)n, where n=10 to 45 - self-assembled into a helical structure around individual carbon nanotubes in such a way that the electrostatic properties of the resulting hybrid depended on the nanotube’s diameter and electronic properties. As a result, the scientists were able to separate the nanotubes by anion-exchange chromatography. Early fractions from the process contained more smaller diameter and metallic tubes, while late fractions were enriched in larger diameter and semiconducting nanotubes.

“The separation of carbon nanotubes is the single greatest impediment to their technological application,” said Zheng. “Many attempts at nanotube separation have yielded only length sorting.”

Zheng believes that nanotube species obtained by the team’s separation process should enable applications such as nanoelectronics and biotechnology that require carbon nanotubes with defined electronic properties and band gap: the band gap of a semiconducting nanotube is inversely proportional to its diameter. “What’s more, fundamental physical and chemical studies of carbon nanotubes can now be conducted on materials with much better defined chemical identity,” he said.

The scientists are now aiming to improve the resolution of their technique and are working on scale-up. The researchers reported their work in Science.