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A Breathalyzer for Cancer
By Sam Kean
ScienceNOW Daily News
31 August 2009
A team of researchers may have come up with a golden idea for diagnosing lung cancer. By coating tiny nuggets of gold with a thin layer of organic material, the researchers have developed an "electronic nose" that, with some additional work, could spot lung cancer instantly by analyzing someone's breath.
Hossam Haick and colleagues at the Technion-Israel Institute of Technology in Haifa embedded the 5-nanometer-long gold nanoparticles in a silicon wafer and then collected exhaled air from 40 cancer patients and 56 people with healthy lungs. All the subjects had to breathe deeply through a purifying filter for 5 minutes. After this "lung washout," they filled five 750-milliliter Mylar bags with air. A machine blew this air over the silicon-gold circuit, and the electrical resistance of the gold nanoparticles rose or fell depending on the presence or absence of certain compounds.
Cancer cells exude different compounds than healthy cells do, Haick explains, and the circuit picks up this difference. Tumor growth causes stress in cells, leading to a build up of free radical molecules that attack the lipids in cell walls, tearing out molecules with long chains of carbon atoms. The team identified 42 such molecules and settled on four to track with the nanoparticles: decane, trimethylbenzene, ethylbenzene, and heptanol. These four molecules appear at relatively high concentrations and, after binding to the organic coat on the nanoparticles, cause the resistance to electric current in the circuit to fluctuate in a predictable way. The sensors respond rapidly and are completely reusable, the team reported online 30 August in Nature Nanotechnology.
The gold circuit, now patented, is a big improvement over Haick's previous electronic nose, which used carbon nanotubes. The resistance of the nanotubes was too sensitive to water vapor, a major component of breath, whereas gold particles are unperturbed by water. After finishing the Nature Nanotechnology paper, Haick's team discovered a bonus: With gold, patients don't have to avoid alcohol, coffee, tobacco, or food before tests, all of which had confounded previous devices.
"This paper is the best one I've seen on the sensor technology," says David Smith, a physical chemist at Keele University in the United Kingdom. He says the breath diagnosis is especially promising for detecting lung cancers early, before they show up on x-rays. However, Smith says he has seen similar research unravel when scientists tried to develop tools for doctors, which ideally must be small, portable, and inexpensive. He also cautions that blinded clinical trials will be necessary to determine if the pricey nanoparticles can complement or replace existing tools, such as biopsies and x-rays.
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