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Twinkle, Twinkle, Quantum Dot

Posted: December 22, 2011

By Pam Frost Gorder

nanoparticles Jessica Winter and her research colleagues have invented fluorescent nanoparticles that change color to tag molecules under the microscope. This series of photos shows a particle changing from red to green — and, at the 89-second mark, to yellow — over the course of two minutes.

Ohio State engineers have invented a new kind of nanoparticle that shines in different colors to tag molecules in biomedical tests.

These tiny plastic nanoparticles are stuffed with even tinier bits of electronics called quantum dots. Like little traffic lights, the particles glow brightly in red, yellow or green, so researchers can easily track molecules under a microscope.

Jessica Winter, assistant professor of chemical and biomolecular engineering and biomedical engineering, and chemical and biomolecular engineering research scientist Gang Ruan describe their patent-pending technology in the journal Nano Letters.

Researchers routinely tag molecules with fluorescent materials to see them under a microscope. Unlike the more common fluorescent molecules, quantum dots shine very brightly and could illuminate chemical reactions especially well, allowing researchers to see the inner workings of living cells.

“These new nanoparticles could be a great addition to the arsenal of biomedical engineers who are trying to find the roots of diseases,” Ruan says.

An obstacle to combating major diseases like cancer is the lack of molecular or cellular-level understanding of biological processes, the engineers explain. By tailoring particles with quantum dots to tag particular molecules, researchers could use the colors to track these processes.

Quantum dots are pieces of semiconductor that measure only a few nanometers, or billionths of a meter, across. When light shines on them, they absorb energy and begin to glow, making them good tags for molecules.

Due to quantum mechanical effects, quantum dots “twinkle” — they blink on and off at random moments. This blinking has been a problem for researchers, because it breaks up the trajectory of a moving particle or tagged molecule that they are trying to follow. Yet, blinking also is beneficial, because when dots come together and the collective blinking appears more like a constant, steady light, researchers know for certain that tagged molecules have aggregated.

Winter and Ruan have taken advantage of those characteristics by using polymers to create micelles, nano-sized spheres containing different combinations of red and green quantum dots.

The micelles stuffed with only red quantum dots glowed red, and those stuffed with green glowed green. But those stuffed with red and green dots alternated from red to green to yellow.

Because the particles glow continuously, researchers can use them to track tagged molecules continuously. They can also monitor color changes to detect when molecules come together.

Winter and Ruan say the particles also could be used in fluid mechanics; researchers who are developing tiny medical devices with fluid separation channels could use quantum dots to follow the fluid’s path.

Finding biocompatible materials to make their new nanoparticles safe to use in the body, Winter and Ruan will continue developing the technology. They also are developing magnetic particles to enhance medical imaging of cancer, and it may be possible to combine magnetism with the quantum dot technology for different kinds of imaging.

The university expects to license the technology for industry.

This research was supported by the National Science Foundation, an endowment from the William G. Lowrie family to the Department of Chemical and Biomolecular Engineering, and Ohio State’s Center for Emergent Materials.

Pam Frost Gorder is assistant director of research communications at Ohio State.