The term "bad breath" usually means your mouth smells bad. But excess ammonia compounds in an exhale may also signal liver and kidney disease, elevated acetone levels can indicate diabetes and nitric oxide levels can imply asthma. By blasting a person’s breath with a laser light, scientists can now detect molecules that may indicate the presence of such diseases.
When breathing, people inhale a complex mixture of gases, including nitrogen, oxygen, carbon dioxide, water vapor and traces of other gases like carbon monoxide, nitrous oxide and methane, said Jun Ye, an adjoint professor of physics at University of Colorado-Boulder who leads the research. Exhaled breath contains less oxygen, more carbon dioxide and a rich collection of more than a thousand types of other molecules, most of which are present in only trace amounts, he says.
Laser light can detect and distinguish specific molecules because different molecules vibrate and rotate at distinct frequencies that depend on their composition and structure, Ye said. He likens the concept to different radio stations broadcasting on separate radio frequencies.
Current breath analysis for biomarkers is a noninvasive and low-cost procedure, but the approaches are limited because the equipment is either not selective enough to detect a diverse set of rare markers or not sensitive enough to detect particular trace amounts of molecules exhaled in human breath. The new technique, known as optical frequency comb spectroscopy, "has the potential to be low-cost, rapid and reliable, and is sensitive enough to detect a much wider array of biomarkers all at once for a diverse set of diseases," Ye said.
The optical frequency comb is a very precise laser for measuring different colors, or frequencies, of light. Each comb line, or "tooth," is tuned to a distinct frequency of a particular molecule's vibration or rotation, and the entire comb covers a broad spectral range—much like a rainbow of color—that can identify thousands of different molecules.
When many breath molecules are detected simultaneously, highly reliable, disease-specific information can be collected, said Ye. Asthma, for example, can be detected much more reliably when carbonyl sulfide, carbon monoxide and hydrogen peroxide are all detected simultaneously with nitric oxide.
To test the technology, Ye's team from JILA—a joint institute of the National Institute of Standards and Technology and CU-Boulder—had several volunteer students breathe into a space between two curved mirrors and then directed sets of ultrafast laser pulses into the cavity. As the light pulses ricocheted around the cavity tens of thousands of times, the researchers determined which frequencies of light the molecules soaked up. That told them which molecules, and how much, were present in the breath.
They detected trace signatures of gases like ammonia, carbon monoxide and methane from the samples of volunteers. In one measurement, they detected carbon monoxide in a student smoker that was five times higher compared to a nonsmoking student.
The researchers described their work in an article in the Feb. 18 online edition of Optics Express.
The project was supported by the National Science Foundation and other government and non-profit agencies.
—By Jim Scott/CU-Boulder and Leslie Fink/NSF
This report is provided by the National Science Foundation, an independent federal agency that supports fundamental research and education across all fields of science and engineering, in partnership with U.S. News and World Report.