Optical Fiber Volatile Organic Compound Vapor Sensor With ppb Detectivity for Breath Biomonitoring

The accurate monitoring of volatile organic compounds (VOCs) at low detection limits is critical for biomedical applications, as many VOCs serve as biomarkers for early disease detection and environmental exposure to harmful substances. This study presents the development and performance evaluation of a compact, easily produced, and low-cost, optical fiber sensor (OFS) for the detection of VOCs at parts per billion (ppb) levels. A 32- $\mu $ m cavity formed at the end face of a standard optical fiber, using a commercially available photopolymerizable resin, acts as a sensing Fabry-Perot (FP) interferometer registering the presence of methanol, ethanol, and isopropanol vapors with distinctive temporal and spectral response. A clear correlation between the molar mass of the examined compounds and the recorded temporal/refractive response of the sensor is established. The performance of the sensor was demonstrated in the detection of 200 ppb of methanol, while a potential limit of detection (LOD) for methanol vapor was estimated of the order of 1 ppb. Preliminary experiments in exhaled breath monitoring confirmed the ability of the sensor to perform breath alcohol content (BrAC) measurements.