DNA sorts nanotubes

Carbon nanotubes -- rolled-up sheets of carbon atoms that have a variety of useful mechanical and electrical properties -- promise to be an important ingredient in nanotechnology. One challenge, however, is separating different types of nanotubes.

Researchers from DuPont Central Research and Development, the University of Illinois at Urbana-Champaign and the Massachusetts Institute of Technology have come up with a way to use DNA to separate carbon nanotubes by electrical type -- metallic or semi conducting -- and by diameter. A carbon nanotubes's electrical properties and diameter are related.

Nanotubes could eventually enable super-sensitive sensors, tiny electronics, and ultra-dense computer memory.

DNA is made up of four bases -- adenine, cytosine, guanine and thymine -- strung along a sugar-phosphate backbone. Adenine and thymine, and cytosine and guanine connect together, and given the right sequences, DNA can be made to assemble into various structures.

The researchers discovered that a certain sequence of single-stranded DNA self-assembles into an ordered structure around individual carbon nanotubes. The electrostatic profiles of the combined DNA and nanotube structure depends on the type of tube, and, for semiconducting tubes, on the tube's diameter. The work appeared in the November 28, 2003 issue of Science.