Simultaneous detection of methane and carbon dioxide in human exhalation based on photoacoustic spectroscopy.

To address the demand for simultaneous multi-gas detection in medical diagnostics, this work develops an online breath sensing system based on photoacoustic spectroscopy (PAS), achieving real-time simultaneous monitoring of multiple exhaled gases using PAS. The system exploits the inherent difference in response amplitude between the fundamental and overtone resonances of the photoacoustic cell, where the highly sensitive fundamental signal is used to detect trace methane (CH), while the weak overtone response enables the measurement of high-concentration carbon dioxide (CO). This approach allows a single photoacoustic cell to simultaneously detect multi-component gases spanning several orders of magnitude in concentration. The minimum detection limits for CH and CO reach 320 ppb and 450 ppm, respectively. Real-time breath measurements from multiple volunteers demonstrate excellent stability, sensitivity, and repeatability of the system, confirming its feasibility and application potential for early disease screening.