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First Carbon-Based Quantum Dots Created

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CLEMSON, N.C., May 26, 2006 -- A new type of quantum dot, the first to be made from carbon, is showing promise for a broad range of applications, including biosensors, medical imaging devices and tiny LEDs, and could be more environmentally friendly than its metal-based counterpart, the dots' creators said.

The nano-sized (billionths of a meter) "carbon dots" glow brightly when exposed to light, said the chemists at Clemson University who developed them. The carbon dots show less potential for toxicity and environmental harm and have the potential to be less expensive than metal-based quantum dots, they said. 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,” said study leader and chemist Ya-Ping Sun. “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, Sun said.

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 said.

The scientists said they 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 said. The current thinking among scientists, they said, is 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, said 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.

The research, funded by Clemson and the federal government, will appear in the June 7 edition of the Journal of the American Chemical Society. For more information, visit: www.clemson.edu


Published: May 2006
Glossary
american chemical society
The American Chemical Society (ACS) is a scientific society based in the United States that supports scientific inquiry in the field of chemistry. Founded in 1876 and chartered by the U.S. Congress, the ACS is one of the world's largest scientific organizations, with more than 152,000 members as of 2023. Publishing scientific journals: The ACS publishes numerous peer-reviewed scientific journals and periodicals, which are highly respected in the field of chemistry and related...
polymer
Polymers are large molecules composed of repeating structural units called monomers. These monomers are chemically bonded together to form long chains or networks, creating a macromolecular structure. The process of linking monomers together is known as polymerization. Polymers can be classified into several categories based on their structure, properties, and mode of synthesis. Some common types of polymers include: Synthetic polymers: These are human-made polymers produced through...
quantum dots
A quantum dot is a nanoscale semiconductor structure, typically composed of materials like cadmium selenide or indium arsenide, that exhibits unique quantum mechanical properties. These properties arise from the confinement of electrons within the dot, leading to discrete energy levels, or "quantization" of energy, similar to the behavior of individual atoms or molecules. Quantum dots have a size on the order of a few nanometers and can emit or absorb photons (light) with precise wavelengths,...
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