Self-monitoring of Metabolic Status with a Smartphone-assisted Breath Sensing Device

Human metabolism can be monitored through exhaled breath analysis, which is well suited for home-use due to its non-invasive nature. Despite strong research efforts, its potential outside research laboratories has hardly been exploited due to the lack of accurate and user-friendly sensing devices. Here, we present a fully integrated handheld breath acetone detector designed for smartphone-guided metabolic self-monitoring at home. The device enables volumecontrolled, end-tidal breath sampling through visual guidance, ensuring reproducible and accurate quantification of breath acetone. Small inter-device variability was identified (±5.6% for 3 devices at 1 parts-per-million; ppm), with high humidity robustness (≤4.2% bias across 0-90% relative humidity) and stable performance over 8 months (6.1% inter-day variability). We tested the detector for metabolic tracking during exercise and dietary interventions in 12 volunteers, capturing rapid subject-specific changes in breath acetone levels, in agreement with blood ketone and interstitial glucose assessment. Validation against proton transfer reaction time-of-flight mass spectrometry demonstrated excellent agreement across a physiologically relevant range of 0.2-45 ppm (e.g. 7.5% bias at 2 ppm) in 312 breath samples. This work establishes a comprehensive validation framework for translating breath detectors from laboratory prototypes into healthcare, for instance, for weight management, ketogenic diet guidance or preventive health monitoring.