parts make versatile nanotubes
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
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
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
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,"
“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
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
Search scheme treads
set up desktop chipmaking
DNA parts make
Watermarks hide in plain
Material bends sound waves
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link