Isotopic Gas Analysis By Means Of Mid-Infrared Photoacoustic Spectroscopy Targeting Human Exhaled Air

There is a great need for cost-efficient non-invasive medical diagnostic tools for analyzing humanly exhaled air. Compared to present day methods, photoacoustic spectroscopy (PAS) can provide a compact and portable (bed-side), sensitive and inexpensive solution. We demonstrate a novel portable photoacoustic spectroscopic platform for isotopic measurements of methane (CH4). We identify and discriminate the (CH4)-C-12- and (CH4)-C-13 isotopologues and determine their mixing ratio. An Allan deviation analysis shows that the noise equivalent concentration for CH4 is 200 ppt (pmol/mol) at 100 s of integration time, corresponding to a normalized noise equivalent absorption coefficient of 5.1 x 10(-9) W cm(-1) Hz(-1/2), potentially making the PAS sensor a truly disruptive instrument for bedside monitoring using isotope tracers by providing real-time metabolism data to clinical personnel. (C) 2021 Optical Society of America