Traffic light. Quantum dots injected under the skin of mice glow red, yellow, and green.

Quantum Dots Light Up Tumors

Researchers have found a way to make cancer cells announce their locations by glowing bright red. By injecting so-called quantum dots into mice, a group of biomedical engineers gave mouse prostate tumors the equivalent of neon signs that could one day ease diagnosis and guide surgeon's hands.

Quantum dots are tiny nanometer-sized crystals made out of metals like silver or gold or semiconductors. Because they're comparable in diameter to the wavelength of light, quantum dots interact with light in odd ways. Change the size of a quantum dot, and its color changes. When light shines on a quantum dot, it will shine back, emitting bright light of its own.

In the 18 July online issue of Nature Biotechnology, Shuming Nie of Emory University in Atlanta and colleagues describe a way to take advantage of quantum dots' optical talents. The researchers coated cadmium-selenide quantum dots with an antibody that binds to a protein found in prostate gland tumors. When these dots were injected into the tails of mice with prostate tumors, they homed in on cancerous prostate cells. When the mice were exposed to bright light, the dots began to glow, indicating the site and size of tumors with at least 1000 cells. This is the first time that quantum dots have sought out target cells and revealed their location within a living animal.

Warren Chan of the University of Toronto envisions a future where various colors of quantum dots correspond to different proteins, and tumors of different types can be diagnosed by color coding. It's feasible because quantum dots can glow in the full range of visible light. "That's the thing that's great about quantum dots in comparison with dyes," Chan says.

The quantum dots also glow far more brightly than fluorescent marker proteins commonly used in biomedical research. But Nie says that in order to be practical for use in humans, quantum dots should glow in the infrared, which penetrates tissues better than visible light. And both Nie and Chan caution that the quantum dots have yet to be proven safe in living creatures.

Related site
Introduction to quantum dots