Poly(vinylidene fluoride-hexafluoropropylene) composite sensors for volatile organic compounds detection in breath

This paper presents three poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) composite-based sensors for detecting volatile organic compunds (VOCs) in the presence of water vapor applicable in breath based sensing. Three sensors with varying sensitivities to acetone, water, ethanol, isoprene, and 2-ethylhexyl acetate (2-EHA), representing VOCs found in breath, have been developed. A sensor fabricated by spray coating PVDF-HFP/C65 composite (Sensor-1) exhibited a 52.6% increase in resistance when exposed to acetone, while the change was less than 0.34% for water. The resistance changes for ethanol, isoprene, and 2-EHA, were 5.6%, 3%, and 0.11%, respectively. The second sensor (Sensor-2), with a two-layer design of PVDF-HFP and PVDF-HFP/C65, was fabricated by a spin coating method, which exhibited improved response times. The response times of Sensor-2 compared to Sensor-1 decreased by 52% for acetone, 92% for water, 30% for ethanol, and 61% for isoprene. In the third sensor (Sensor-3), the addition of carbon nanotube (CNT) in the composite (PVDF-HFP/C65/CNT) caused a decrease in resistance when exposed to water. This is in contrast to Sensors 1 & 2 where resistance increased for all VOCs, and provides a higher selectivity for the system. The results from the three sensors were analyzed using principal component analysis (PCA) and it was demonstrated that the combined responses of these sensors provide a high selectivity. The sensor fabrication, testing methods, and results are presented and discussed.