University of Pittsburgh researchers yesterday reported the discovery of hydrocarbon nanotubes, each about a thousand times thinner than a human hair, that can assemble themselves into what appears to be a teeny, tiny shag carpet.

This "nanocarpet," about a million times smaller than a conventional carpet, is more than just a curiosity, said Alan Russell, a professor of chemical and bioengineering at Pitt, as well as director of the McGowan Institute for Regenerative Medicine.

"I think there's a whole host of applications," he said, from artificial retinas to electronics. Moreover, the tiny tubes can self-assemble themselves into other structures, including nanocrackers that have the texture of a saltine cracker and nanoflowers.

The material also is designed to detect and kill bacteria and forms a so-called self-decontaminating coating.

"The carpet of self-assembled nanotubes is unique," said Hicham Fenniri, senior research officer at the National Institute for Nanotechnology in Alberta, Canada. Other researchers have shown they can fashion carbon nanotubes into a carpet, but Russell's nanotubes do that job themselves and are biocompatible, he noted.

"It's very impressive," agreed Tomasz Kowalewski, a chemist at Carnegie Mellon University who studies self-assembly of carbon nanotubes.

Nanotechnology ---- materials, structures and devices that are measured in billionths of meters ---- is a growing area of research. And because they are so small, getting these materials and machines to assemble themselves is a necessary feat.

The report by Russell and his Pitt colleagues was published online yesterday by the Journal of the American Chemical Society.

They also have started a spin-off company, NanoSembly, to further develop the nanotubes and explore their possible uses.

The work was part of a project funded by the Army Research Office to develop coatings that can both detect biological agents that might be used in biological weapons and destroy them.

Russell's team planned to combine the hydrocarbon diacetylene, which can change color in response to bacteria, with a quaternary amine salt, a substance that can kill cells by rupturing their membranes.

"We thought we'd just stick the two things together and away we go," Russell explained. But the resulting material had some unexpected properties. When post-doctoral researcher Sang Beom Lee put them under a microscope, he found they had created nanotubes.

This bit of serendipity ultimately was caused by a contaminant, a secondary amine salt.

The material, as the researchers reported in their paper yesterday, does indeed change color in the presence of E. coli bacteria and it does appear to disrupt the membranes of the bacteria. Russell said additional compounds that target other types of bacteria could also be added to the nanotubes.

"This is an unexpected combination of innovative ideas to address an important public health problem," Fenniri said, "a true example of nanomedicine in action."

Such a coating might be used on buildings, tanks, sensitive equipment ---- anywhere that might be subject to bacterial contamination.

But once the nanotubes were discovered, Russell and his team set about to see how they might manipulate the tubes and what structures might be self-assembled.

The nanocarpets can be created by mixing the nanotubes with a solvent, adding a little bit of a nonsolvent and then allowing the mixture to dry.

Self-assembled materials also tend to be materials that can easily fall apart, so the researchers are studying ways of strengthening the materials once they have formed.