DNA parts make versatile nanotubes

By Chhavi Sachdev, Technology Research News

The perfect material for a nanoscale circuit would not only readily assemble itself, but would also have adjustable physical and chemical properties. Researchers at Purdue University have come close to that ideal with organic nanotubes that can be mass-produced and whose properties can be predetermined.

The key to these prodigious nanotubes is that they are not made of carbon. Instead, the researchers’ rosette nanotubes are built from two of the bases that make up DNA.

Regular carbon nanotubes self-assemble when graphite sheets roll up. The organic rosette nanotubes, which, like DNA, form in water, self-assemble when rings of atoms stack up, forming a hollow channel in the middle.

Each stacked ring of the rosette nanotube is a supermacrocycle -- a ring of atoms held by non-covalent hydrogen bonds. Each supermacrocycle has six segments. Each segment, or module, is made of guanine and cytosine bases and amino acids. The rings are rosette-shaped, like a flower with six petals

The rosette nanotubes assemble spontaneously because parts of the module are water-repellent and parts are attracted to water. In trying to keep their water-repellent ends away from the water, the modules align themselves so that their water-loving ends face outside, and the water-repellent ends inside, forming a ring. The rings then stack together to form a tube.

“The reason they stack up is because they don’t like to get wet,” said researcher Hicham Fenniri, an assistant professor of chemistry at Purdue University. “They repel water and prefer to interact with themselves. The hydrophobic and electrostatic interactions help keep the nanotube stable."

Self-assembly is a key goal in making machines at the molecular scale because it allows fairly large and complex structures to come together in a single, largely error-free step. “It is almost a Darwinian chemistry,” said Fenniri. “If a module is not chemically fit, it will not be incorporated in the nanotube structure,” he said.

Another benefit of self-assembly is high yield. “The chemistry used to make these tubes is scalable using standard industrial processes,” said Fenniri. A small-scale industrial plant could produce up to 500 kilograms of the rosette nanotubes in a month, according to the researchers.

Rosette nanotubes are also chemically versatile. Researchers can specify the chemical properties of the nanotubes before production because “the properties of the modules they are made of can be altered at will,” said Fenniri. The modules can be tuned to transmit light or electricity, for instance, he said.

The researchers can also specify the dimensions of the tubes. “Our tubes vary in length from one nanometer to several microns,” he said.

Although rosette nanotubes are relatively strong, they are not as strong as carbon nanotubes. Where there is high mechanical stress, “carbon nanotubes may be more advantageous,” said Fenniri. “However, the rosette nanotubes can be modified to become mechanically very strong -- several orders of magnitude stronger than nylon, for instance,” he added.

Rosette nanotubes could eventually be used as fibers in new plastic-like materials or as electronic wires in computing devices, according to the researchers.

Rosette nanotubes with light-transmitting properties could be used in light-emitting devices or in solar energy transport and conversion. Since the tubes assemble in water, they could also have biological applications such as internal drug delivery, according to the researchers.

Another important use for the rosette nanotubes could be as a template for tiny nanowires, said Deepak Srivastava, a senior scientist at NASA's Ames Research Center. "If you can fill up the cavity with metal, then the metal will harden, and at that point you can wash away or dissolve the tube part [to leave behind] metal nanowires or semiconductor nanowires," he said.

“This is a major advance in the preparation of nanotubes in aqueous environments,” said Steven Kornguth, a professor of neurobiology at The University of Texas, Austin. The tubes’ adaptability is important, according to Kornguth. “The internal cavity of the rosette may serve as a locus for insertion of metals that will alter [their] conducting properties,” he said. Their ability to anchor on to surfaces for use in photonic or electronic conduction applications may also prove useful, he said.

The researchers are currently working on making the nanotubes as long as a millimeter. The research could be applied practically within the next two years, according to Fenniri.

Fenniri’s colleagues were Packiarajan Mathivanan, Kenrick L. Vidale, Debra M. Sherman, Klaas Hallenga, Karl V. Wood, and Joseph G. Stowell of Purdue University. The paper was published in the Journal of the American Chemical Society, April 25, 2001. The research was funded by the National Science Foundation (NSF), the American Chemical Society, the Showalter Foundation, Research Corporation, the American Cancer Society, 3M, and Purdue University.

Timeline: < 2 years
Funding:   Institute; Corporate; University
TRN Categories:   Biological, Chemical, DNA and Molecular Computing
Story Type:   News
Related Elements:  Technical paper, " Helical Rosette Nanotubes: Design, Self-Assembly, and Characterization," the Journal of the American Chemical Society, April 25, 2001: http://www.chem.purdue.edu/hf/NANOTUBEpaper.pdf


June 6, 2001

Page One

Search scheme treads lightly

Bug-eye lenses set up desktop chipmaking

DNA parts make versatile nanotubes

Watermarks hide in plain text

Material bends sound waves


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