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December 15, 2008
‘Strained’ quantum dots show optical properties

By Quinn Eastman

Quantum dots, tiny luminescent particles made of semiconductors, hold promise for detecting and treating cancer earlier. However, if doctors were to use them in humans, quantum dots could have limitations related to their size and possible toxicity.

Biomedical engineers at Emory and Georgia Tech have found a way around those limitations by exploiting a property of semiconductors called “lattice strain.” By layering materials with different chemical compositions on top of each other, the researchers can create particles with new optical properties.

A description of the “strain-tuned” particles is in the December issue of Nature Nanotechnology.

In addition to their expected utility in biomedical imaging, the new type of quantum dots could find use in optoelectronics, advanced color displays, and more efficient solar panels, says biomedical engineer Shuming Nie.

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. The particles can be between four and six nanometers wide, allowing them pass through the kidneys — meaning less toxicity. The newer strain-tuned quantum dots have not been tested in living animals or people.

Strain-tuned quantum dots can be made that emit light at wavelengths in the near-infrared range, a “clear window” where the human body is relatively transparent, says author Andrew Smith, a postdoctoral fellow in Nie’s group.