Breath Isoprene Sensor Based on Quartz-Enhanced Photoacoustic Spectroscopy

Isoprene, the most abundant endogenous hydrocarbon in human breath, is a promising biomarker for metabolic and cardiovascular diseases. In this paper, we present the detection of isoprene in exhaled breath using the off-beam Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) method. The sensor employs a homemade quantum cascade laser emitting at 11.03 μm. We use numerical simulations to evaluate the impact of interfering gases (CO₂ and H₂O) and optimize the laser modulation parameters. The limit of detection reached for 1 s acquisition time is close to 220 parts per billion in volume (ppbv) with a normalized noise equivalent absorption (NNEA) of 1.1×10-8cm-1·W·Hz-1/2. Breath measurements conducted on healthy volunteers reveal a significant increase in isoprene concentration from resting levels (~250-350 ppbv) to elevated levels (~450-650 ppbv) after moderate physical exercise.