Breath test: infrared approach detects exhaled chemicals

IR breath

Trace analytes can be detected in the breath using near infrared Fourier transform broadband cavity enhanced absorption spectroscopy. This could open up a whole new area of medical diagnostics and health research.

Breath test diagnostics have been in development for many years, but researchers in the UK are now moving forward with a system that can detect acetone and other analytes at the sub 10 parts per million level. The technique might be applied to detecting acetone in the breath during an exercise workout to measure when body metabolism switches to so-called "fat burning" or to diagnose and monitor disease such as diabetes non-invasively.

Wolfgang Denzer, Gus Hancock, Cathryn Langley, Rob Peverall, Grant Ritchie and David Taylor of the Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford and at Oxford Medical Diagnostics Ltd in Yarnton, working with Meez Islam of the School of Science and Technology, University of Teesside, Borough Road, Middlesbrough, convey the need for a sophisticated cost effective analytical technique that can measure several analytes simultaneously at low levels, for example in human breath. Such a technique would be able to extract a great deal of information from a particular measurement, leading to greater precision and be specific even when target compounds have broad spectroscopic fingerprints. They suggest that cavity enhanced absorption spectroscopic (CEAS) measurements offer this and more to Fourier techniques.

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Proof is in the testing

Previously, the team demonstrated proof of principle using near infrared broadband CEAS with a superluminescent light emitting diode (SLED). SLEDs have a relatively high spectral power density and spatial coherence, the team explains and the preliminary data allowed them to detect butadiene, which absorbs the SLED radiation between 1.6 and 1.7 micrometres and could still be distinguished from the many other hydrocarbons that exhibit overtone and combination band absorptions at similar wavelengths.

The team has now obtained BB-CEAS absorption measurements for various compounds, including isoprene, butadiene, acetone and methane using both a supercontinuum source and a SLED. They describe their optical enhancement cavity as having relatively high finesse and consisting of mirrors with a reflectivity of 99.98%. A Fourier transform spectrometer records the data. They recently published details of the results, which highlighted spectral interferences and unambiguous concentration determinations.

They were able to detect acetone in a "breath-like" matrix with ppm precision at lower than 10 ppm acetone concentrations. The team also points out that enhancements are sufficiently high with the cavity technique to allow atmospheric levels of methane to be detected within minutes. In addition, coupling SLEDs together increases wavelength coverage and allowed them to simultaneously determine acetylene, carbon dioxide and butadiene.

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Breath test

The development of the research into a breathalyser diagnostic is underway thanks to Hancock's university spin out company Oxford Medical Diagnostics. "This is of great interest in sport studies and dietary studies to find out how people have worked out in the gym," he says. "That is an area we are trying to explore and we are trying to produce a monitor of how well you have burned off some body fat." He adds that the technology was originally being developed for disease detection. "Acetone is associated with diabetes and we have already developed a detection system that can see acetone at about the levels that are important for the diagnosis of diabetes," he says.

"We would like to set this up as a screening method for diabetes as there are so many people who suffer from it, particularly type 2 diabetes, but they don't know they have it." The team also hopes to determine whether breath levels of acetone reflect blood sugar concentration. Ultimately, a breath test device might be developed to allow diabetes patients to test their blood sugar without the need for frequent pin prick tests by simply breathing into a handheld monitor.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.