# Breath Isoprene Sensor Based on Quartz-Enhanced Photoacoustic Spectroscopy

## TL;DR

A new sensor detects isoprene in human breath using a laser-based method, showing higher isoprene levels after exercise.

## Contribution

A novel off-beam QEPAS sensor for isoprene detection in breath with optimized laser modulation and interference analysis.

## Key findings

- The sensor achieved a detection limit of ~220 ppbv for isoprene with 1 s acquisition time.
- Isoprene levels in breath increased from ~250–350 ppbv at rest to ~450–650 ppbv after moderate exercise.
- Interfering gases like CO2 and H2O were evaluated and minimized through numerical simulations.

## Abstract

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.