Cavity-enhanced optical frequency comb spectroscopy: application to human breath analysis

To date, researchers have identified over 1000 different compounds contained in human breath.These molecules have both endogenous and exogenous origins and provide information about physiological processes occurring in the body as well as environment-related ingestion or absorption of contaminants 1,2 .While the presence and concentration of many of these molecules are poorly understood, many 'biomarker' molecules have been correlated to specific diseases and metabolic processes.Such correlations can result in non-invasive methods of health screening for a wide variety of medical conditions.In this article we present human breath analysis using an optical-frequency-comb-based trace detection system with excellent performance in all criteria: detection sensitivity, ability to identify and distinguish a large number of biomarkers, and measurement time.We demonstrate a minimum detectable absorption of 8 x 10 -10 cm -1 , a spectral resolution of 800 MHz, and 200 nm of spectral coverage from 1.5 to 1.7 µm where strong and unique molecular fingerprints exist for many biomarkers.We present a series of breath measurements including stable isotope ratios of CO 2 , breath concentrations of CO, and the presence of trace concentrations of NH 3 in high concentrations of H 2 O.