‘Strained’ quantum dots promising in cancer detection

December 8th, 2008 - 5:32 pm ICT by IANS  

Washington, Dec 8 (IANS) Quantum dots, the tiny shiny particles made of semiconductors, hold promise for early detection and treatment of cancer. However, if doctors were to use them in humans, quantum dots could have limitations related to their size and possible toxicity. Scientists at Emory University and Georgia Institute of Technology have overcome those limitations by exploiting a property of semiconductors called “lattice strain”.

By layering materials with different chemical compositions on top of one another, researchers can create particles with new optical properties, said a Georgia release.

“The first generation of quantum dots had optical properties that could be tuned by their size,” said senior co-author Shuming Nie, a professor at Georgia Tech and Emory University.

“We have discovered another way to tune quantum dots’ properties: by modulating lattice strain.”

Strain-tuned quantum dots can be made that emit light at wavelengths in the near-infrared range while remaining small in size. Near-infrared wavelengths around 750 nanometres represent a “clear window” where the human body is relatively transparent, said Andrew Smith, co-author of the paper and a postdoctoral fellow in Nie’s group.

While the newer strain-tuned quantum dots have not been tested in living animals or people, they could probably pass through the kidneys, meaning less toxicity, if they are less than five nanometres in diameter, Smith added.

“Using near-infrared wavelengths, there’s less difficulty in seeing through the body’s tissues. Older quantum dots that emit in the near-infrared range are rod-shaped and large enough to get trapped in the kidneys, while smaller particles can both clear the kidneys and have less of a tendency to bind proteins in the blood,” he explained.

Besides their expected utility in biomedical imaging, the new type of quantum dots could find use in opto-electronics, advanced colour displays, and more efficient solar panels, Nie said.

Previous quantum dots contained cadmium, a toxic heavy metal. Strain-tuned quantum dots can be made mostly of the less toxic elements zinc and selenium, although some cadmium remains at the core of the particle. The particles can be between four and six nanometres wide.

The study on “strain-tuned” particles is scheduled for publication in the December issue of Nature Nanotechnology.

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