Our breath can carry signs of disease. Some animals with sensitive noses can even detect certain cancers on our breath before current screening devices. Researchers at the University of Adelaide think it is possible to go beyond relying on dogs' noses and instead use laser detectors to find astonishingly rare trace gasses for medical use or to detect pollution.
If we want to identify the presence of a molecule in a sample of gas today, all options have limitations, PhD student Sarah Scholten told IFLScience. Mass spectrometry provides accurate readings from small samples, but is slow, expensive, and requires equipment that is anything but portable. Detectors that are dependent on chemicals that react with the ones being sought do a poor job of measuring concentrations.
Every gas absorbs light at specific wavelengths, so shining a broad spectrum light through a sample can identify its contents. This is the technique we use to determine the composition of stars, and sometimes even the atmospheres of planets. However, Scholten explained that ordinary light, such as from an incandescent source, will interfere with itself, hindering detection of very low concentration samples.
Scholten and her co-authors, therefore, turned to optical frequency combs, a technology that converts a laser operating at a single frequency into millions of discrete frequencies while maintaining the extreme spatial coherence that is one of laser's defining features. The creators of frequency combs shared the 2005 Nobel Prize for Physics.
In the journal Physical Review Applied, Scholten announced that her product can detect carbon dioxide concentrations in gas with a precision of 0.04 percent, delivering on her team's promise to build an “optical dog's nose”.
Scholten bounced the light from a commercial model of an optical frequency comb backwards and forwards through a gas to increase the opportunities for the lasers to encounter rare molecules. Scholten told IFLScience the lasers are so coherent they can sustain being reflected through a 10-centimeter (4-inch) sample so many times that the laser has a 1.6-kilometer (1-mile) path within the gas.
The team's goal is to be able to detect substances down to concentrations of parts per billion. Scholten told IFLScience that while they are not there yet, they expect to be soon. “With further development, it opens the way for real-time and inexpensive monitoring and analysis that can be carried out in the field, or in the doctor’s surgery, by non-specialist operators,” she said in a statement.
Besides finding signs of disease on a patient's breath, the technology could be used to locate sources of pollution. A detector could identify molecules that shouldn't be present far from the source and even be so portable it could trace their path in reverse, identifying the emission site.