Multipass Spectroscopy Seeks Disease Biomarkers in Breath

An optical sensing method developed by a research team at the University of Warsaw relies on highly sensitive spectroscopic measurements to detect the presence or absence of formaldehyde in a person’s breath. The breath test is based on multipass spectroscopy and can detect the presence of a single molecule of formaldehyde in 1 million air particles, even in the presence of gases that can obstruct precision optical measurements.

Formaldehyde is currently under investigation as a biomarker for cancers such as lung and breast. The ability to detect it quickly and noninvasively supports the development of an inexpensive and rapid screening test.

Multipass spectroscopy increases the extent to which light interacts with a sample, making it a useful application for detecting particularly low concentrations of gas molecules. In the research team’s system, the scientists shine a laser through a small hole in a mirror located at one end of an experimental cell. In the presence of a second mirror positioned at the other end of the experimental cell, light bounces back and forth. The interaction lengths extend up to hundreds of times the full length of the cell.

Researchers have developed an extremely sensitive, yet simple, optical method for detecting formaldehyde. Their approach is based on multipass spectroscopy, which introduces a laser through a small hole in a mirror. The laser light then bounces back and forth between mirrors, creating interaction lengths with the sample that are tens or hundreds of times the length of the cell. Courtesy of the University of Warsaw via Mateusz Winkowski.

Because the presence of multiple laser beams can lead to fringe interference and, in effect, decrease sensitivity and prevent scientists from using a multipass spectroscopy system to precisely determine biomarker concentration, the researchers also developed a technique called optical fringe quenching to combat the influence of noise in their setup.

By slightly modulating the laser emission over a predetermined set of wavelengths and averaging the emitted light from the sample over the wavelengths, the researchers successfully eliminated optical interference enough to acquire an accurate detection of formaldehyde. To further reduce interference from other constituents commonly found in breath samples, the researchers selected an optimal spectral range and sample pressure.

The team of Mateusz Winkowski and Tadeusz Stacewicz used calibrated artificial mixtures of formaldehyde in air to test with their method. The team reported results indicating that the technique is more than capable of detecting formaldehyde at levels the indicate the presence of disease. Moreover, the optical fringe quenching component of the work, Winkowski said, can improve any optical system using a multipass cell. Specific applications Winkowski identified included measuring formaldehyde gas emitted from household materials and/or industrial sources to understand the effects on human health.

The researcher said they next plan to apply their method to measure ethane gas in breath. Ethane is also under investigation as a possible biomarker for cancer and other diseases.

The research was published in Biomedical Optics Express (www.doi.org/10.1364/BOE.405384).