Researchers from Dupont and Lehigh University are using short stretches of single-stranded DNA sequences to accurately sort and separate mixtures of Carbon Nanotubes (CNTs) into distinct categories - previously a major hurdle in nanotube production. The details are published in an article found in the July 9 issue of Nature.

Carbon nanotubes are long, narrow cylinders of graphite with novel properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science. They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat. The properties of the nanotube vary according to the tubes' shape and structure.

Current methods of producing CNTs yield a mixture of tubes, with different diameters and symmetry, known as "chirality." Before the tubes can be utilized, however, they must be disentangled from a mixture and "purified" into separate species of CNTs of the same electronic type.

"A systematic method of purifying every single-chirality species of the same electronic type from a synthetic mixture of single-walled nanotubes is highly desirable," the DuPont-Lehigh group wrote in Nature, "but the task has proven to be insurmountable to date."

The Nature article is titled "DNA sequence motifs for structure-specific recognition and separation of carbon nanotubes." Its authors are Ming Zheng, Xiaomin Tu, Anand Jagota and Suresh Manohar. Zheng and Tu are scientists with DuPont Central Research and Development. Jagota is a professor of chemical engineering at Lehigh. Manohar is a graduate student in chemical engineering at Lehigh.

The new method utilizes tailored DNA sequences and "allows the purification of all 12 major single-chirality semiconducting species from a synthetic mixture, with sufficient yield for both fundamental studies and application development."

"The interesting discovery made by Tu and Zheng," says Jagota, "is that if you choose the DNA sequence correctly, it recognizes a particular type of CNT and enables us to sort that variety cleanly. This kind of practical improvement brings us closer to manufacturing possibility."

Source: http://www.eurekalert.org/pub_releases/2009-07/lu-red070809.php