The gases you breathe out may provide a mirror of what's going on inside your body. In an effort to detect the minute traces of gases that may point to diseases such as cancer and asthma, researchers have developed a laser for low-cost, highly sensitive breath analysis.
CU-Boulder physics doctoral student Michael Thorpe stands next to a novel laser apparatus. Image credit: University of Colorado at Boulder.
The scientists, a collaboration from the National Institute of Standards and Technology and the University of Colorado at Boulder, hope that the system will someday allow doctors to screen people for certain diseases simply by sampling their breath. They explain that the technique is powerful enough to sort through all the molecules in human breath and sensitive enough to distinguish rare molecules that may be biomarkers for specific diseases.
Physicist Jun Le, who led the research, explains that people inhale a complex mixture of gases, including nitrogen, oxygen, carbon dioxide, water vapor and small amounts of other gases like carbon monoxide, nitrous oxide and methane. Exhaled breath contains less oxygen, more carbon dioxide, and a wide variety of more than a thousand types of other molecules, most of which occur only in trace amounts.
Certain molecules can signify the potential for diseases. For example, excess methylamine may point to liver and kidney disease, ammonia may signal renal failure, elevated acetone levels can indicate diabetes, and nitric oxide levels can signify asthma.
As the scientists explain, laser light can detect specific molecules because different molecules vibrate at distinct resonant frequencies due to their composition and structure. The light takes the form of an "optical frequency comb" where each tooth of the comb is tuned to a distinct frequency to detect a particular molecule. Ye, along with other researchers, originally helped develop the optical frequency comb in the 1990s, winning a Nobel Prize for the achievement.
Optical frequency combs have also been applied to spectroscopy, allowing researchers to analyze the light emitted or absorbed by matter.
In practice, the laser breath analysis technique works by individuals breathing into an optical cavity enclosed by curved mirrors. Then, laser pulses are directed into the cavity, ricocheting around the cavity tens of thousands of times. Depending on which frequencies of light are absorbed, the researchers can determine the presence of the corresponding molecules.
In one measurement with student volunteers, the scientists detected carbon monoxide levels in an individual who smoked that were five times higher than the levels of a non-smoker.
Although current breath analysis techniques can detect some molecules, the laser method is unique in that it can detect a diverse set of molecules simultaneously, even if they occur in very small amounts. The study is published in Optics Express, the free, open-access journal published by the Optical Society of America.
via: University of Colorado at Boulder