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Nanomedicine moves one step closer to reality

Colorectal cancer represents the third most commonly diagnosed cancer in the U.S. But early detection of cancer - for example, by imaging methods such as colonoscopy - has markedly lowered mortality rates from this disease.

But, as Stanford radiologist Sam Gambhir, MD, PhD, notes, "Colonoscopy relies on the human eye. So this screening tool, while extremely useful, still misses many cancer lesions such as those that are too tiny, obscure or flat to be noticed."

Gambhir and his associates have turned to nanoparticles as imaging agents that may allow the detection even of minuscule tumors well before they would otherwise become observable. In a just-out mouse study, the researchers have proven the nanoparticles safe enough to allow them to proceed to human experiments.

Gambhir's group is filing for FDA permission to use the new agents in clinical trials for colorectal cancer. Here's how they work: Almost all the time, light bounces off a surface at the exact same wavelength, or color, at which it came in. But maybe one ten-millionth of the time, it bounces back slightly off-color.

The Gambhir lab's nanoparticles are designed to hugely amplify this minuscule off-color reflection. These particles, which measure 100 nanometers in diameter (somewhere between the size of a virus and a bulky protein molecule), can be coated with different specialized materials, each with its own off-color reflection "signature." The differently coated particles can, in turn, be attached to different molecules known to target specific cell-surface features common to various cancer types.

This approach could allow the simultaneously detection of as many as 15 such signatures at once on inspection by a specialized instrument called a Raman microscope, which can be configured to explore body cavities, "light up" the nanoparticles wherever they "stick," and monitor the color of light they give off.

All in all, a dramatic illustration of applied quantum mechanics' ability to improve the quality of medical applications.

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