Guar Gum/Ethyl Cellulose-Polyvinyl Pyrrolidone Composite-Based Quartz Crystal Microbalance Humidity Sensor for Human Respiration Monitoring

In this work, the guar gum (GG) and the electro-spinned ethyl cellulose-polyvinyl pyrrolidone (EC-PVP) nanofibers were used as humidity-sensitive materials for fabricating a quartz crystal microbalance (QCM) sensor. Fourier transform infrared spectroscopy, scanning electron microscopy, water contact angle test, and X-ray photoelectron spectra were used to characterize the synthesized GG/EC-PVP composite material, confirming its successful preparation and good hydrophilicity. The humidity sensitivity experiments were performed at room temperature. The GG/EC-PVP-coated QCM sensor has high sensitivity (55.72 Hz/% RH) and low hysteresis (2.8% RH) in a wide relative humidity range (0-97% RH), short response/recovery time (26/2 s), excellent selectivity, good repeatability, and stability. The combined action of hydrophilic groups and porous structure enhances the humidity sensitivity. The GG/EC-PVP sensor can be used to capture and measure typical breathing patterns in different human basic emotions due to its good performance. Furthermore, a lie-detector system was also designed for judging the lying through detecting the emotional breathing pattern of the subjects.

Automated summary

In this study, a quartz crystal microbalance (QCM) sensor was fabricated using guar gum (GG) and electro-spun ethyl cellulose-polyvinyl pyrrolidone (EC-PVP) nanofibers as humidity-sensitive materials. The GG/EC-PVP-coated QCM sensor exhibited high sensitivity, low hysteresis, excellent selectivity, good repeatability, and stability in a wide range of relative humidity. The sensor's hydrophilic groups and porous structure contributed to its enhanced humidity sensitivity. The GG/EC-PVP sensor could capture and measure typical breathing patterns in different human emotions, and could also be used for lie detection.