Synthesis and Fabrication of Semiconductor Nanoparticles With Surfactant-Mixed Metal Oxides for Humidity Sensing in Respiratory Monitoring Devices

The humidity sensor plays a vital role in respiratory monitoring systems by measuring moisture content in exhaled breath, which is crucial for assessing various respiratory conditions. This study presents a resistive-type respiratory sensor utilizing surfactant-mixed SnO2 nanostructured thin film for real-time respiratory monitoring. X-ray diffraction (XRD) analysis confirms the formation of a tetragonal rutile-phase crystalline structure, with an average particle size of approximately 2.16 nm, as observed in the field-emission scanning electron microscopy (FESEM) images. A hole-collecting layer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) enhances the sensor’s performance. Operating effectively within a relative humidity (RH) range of 40%–80% RH, this sensor aligns well with the optimal indoor humidity levels (40%–60% RH) recommended for human health. The sensor demonstrates minimal hysteresis (8.1% RH), a rapid response time of 18 s, and a swift recovery within 14 s, alongside a high sensitivity of 0.5 MΩ/% RH. Real-time evaluations involving varied human breathing patterns illustrate the sensor’s capability to detect fluctuations in respiration rates and depths, making it a valuable tool in clinical scenarios.