Normal breath consists of trillions of molecules, only a few of which are actual biomarkers. And finding just one isn't enough. There needs to be a pattern consisting of several different types of biomarkers that are all associated with a particular medical problem.
What's necessary, he said, is to create a device that will find a few molecules in a sea of background noise consisting of trillions of harmless molecules. He calls it "seeing the forest all at once, but also seeing individual trees extremely clearly."
And that, he said, is exactly what his team has accomplished.
The technology builds on the device that won a Nobel Prize in 2005, called optical frequency comb. Ye and his group applied the technology to spectroscopy, which is used to identify distinct molecules by their emission and absorption of light.
The heart of Ye's machine, which is about the size of a microwave oven, is a cavity between two curved mirrors. Laser pulses are shot into the cavity and reflect back and forth between the mirrors tens of thousands of times, bombarding any molecules in their way, before finally escaping. To test the device, the researchers recruited several students and had them breathe into the cavity.
The bouncing laser beam interacted with the billions of exhaled molecules, identifying the entire composition of the breath. The findings were very precise, Ye said. One of the participants was a smoker, and his test revealed five times the normal level of carbon monoxide.
The beauty of the system, Ye said, is the fact that it sees the entire spectrum, not just a few specific molecules. And that's important because a single molecule would mean little.
"If you have asthma, your breath will have nitrous oxide, but nitrous oxide does not necessarily mean you have asthma," he said. "But if you see several different molecules all at once, and they are associated with asthma, then you have found a real fingerprint of a certain disease."
The technology is still in its infancy, and for now it appears to be limited to diseases that somehow involve the lungs. But Ye thinks that could change, and the applications could broaden, as the technology develops further.
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