WASHINGTON, May 23 -- Chemists at Clemson University say they have developed
a new type of quantum dot that is the first to be made from carbon. Like their
metal-based counterparts, these nano-sized "carbon dots" glow brightly when
exposed to light and show promise for a broad range of applications, including
improved biological sensors, medical imaging devices and tiny light-emitting
diodes (LEDs), the researchers say.
The development, which could help broaden the use
of quantum dot technologies, is described in a research
communications published online today by the Journal
of the American Chemical Society . The paper
will appear in the journal's June 7 print edition.
The carbon-based quantum dots show less potential
for toxicity and environmental harm and have the
potential to be less expensive than metal-based quantum
dots, the scientists say. Cheap disposable sensors
that can detect hidden explosives and biological
warfare agents such as anthrax also are among the
possibilities envisioned by the researchers.
"Carbon is hardly considered to be a semiconductor,
so luminescent carbon nanoparticles are very interesting
both fundamentally and practically," says study leader
Ya-Ping Sun, Ph.D., a chemist at the university,
located in Clemson, S.C. "It represents a new platform
for the development of luminescent nanomaterials
for a wide range of applications."
Quantum dots have generated much interest in recent
years, especially for potential applications in biology
and medicine. These tiny particles -- thousands of
times smaller than the width of a human hair -- have
been developed from compounds composed of lead, cadmium
and, more recently, silicon. But these materials
have raised concerns over potential toxicity and
environmental harm. As a result, scientists have
begun to look for more benign compounds for making
quantum dots.
Researchers have known for some time that carbon
nanoparticles, due partly to their enormous surface
area, have unusual chemical and physical properties
quite different from their bulk form. Using nanoparticles
produced from graphite, Sun and his associates demonstrated
that when these carbon nanoparticles are covered
with special polymers, they glow brightly when exposed
to light, behaving as tiny light bulbs. The dots
glow continuously as long as a light source is present,
they say.
The scientists believe that this photoluminescence
may be due to the presence of "pockets" or holes
on the surface of the carbon dots that trap energy.
The polymer coating acts as a "molecular band-aid," enabling
light emission from the inside of the polymer casing,
they say. Scientists believe that metal-based quantum
dots emit light by a somewhat different mechanism.
The two-sided polymer coating allows researchers
to attach antibodies or other labeling materials
to the carbon dot, says Sun. This could lead to improved
dyes for medical imaging and also the development
of sensors that light up in the presence of a target,
such as anthrax or even food-borne pathogens. In
lab studies, the researchers successfully labeled
anthrax-like spores with luminescent carbon dots,
resulting in glowing spores that were easily viewed
under a microscope.
Funding for the current study is primarily provided
by Clemson University. The project is also supported
with some funding from the federal government.
The American Chemical Society -- the world's largest
scientific society -- is a nonprofit organization
chartered by the U.S. Congress and a global leader
in providing access to chemistry-related research
through its multiple databases, peer-reviewed journals
and scientific conferences. Its main offices are
in Washington, D.C., and Columbus, Ohio.
The online version of the research paper cited
above was published May 23 on the journal's Web
site. Journalists can arrange access to this site
by sending an e-mail to newsroom@acs.org or
calling the contact person for this release.
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