A new optical technique for breath analysis

A schematic of the cavity-enhanced optical frequency comb spectrometer breath-analysis system. (Adapted with permission. Copyright 2008 Optical Society of America.)
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Breath can be analyzed for a variety of compounds by an array of techniques. For example, GC/MS can separate and measure a large number of biomarkers in human breath. However, GC/MS instruments are large and complex and require a long period of time to perform a measurement. Now, Jun Ye, Michael Thorpe, and colleagues at the University of Colorado have developed a fast breath-analysis system based on cavity-enhanced optical frequency comb spectroscopy.

In this form of spectroscopy, an ultrafast laser creates a wide-bandwidth optical frequency comb, which includes a multitude of frequencies in the visible and NIR regions of the electromagnetic spectrum. The comb is coupled to an optical cavity containing one or more molecules, which absorb photons of particular frequencies. The pattern of photon absorption is unique for each kind of atom or molecule.

The instrument analyzes not only which frequencies of light are missing photons but also how many photons of a particular frequency have disappeared. From these data, researchers can identify the components in a sample by the unique molecular fingerprint of each individual analyte.

As a proof of principle, Ye, Thorpe, and colleagues analyzed H₂O, CO₂, CO, CH₄, and NH₃ by this method in samples of human breath. They could identify each component, even though the signals for these molecules occur in a highly congested region of the spectrum. The authors note that their system can also be used to look for other biomarkers relevant to particular diseases and that their instrument can be packaged into a box roughly the size of a large microwave oven, making it portable and easy to use in a field setting. (Opt. Express 2008, 16, 2387–2397)