Development of a Smart and Ultrafast Flexible Humidity Sensor Using the 0D/2D Au/GeS Heterostructure for Human Respiration Rate Monitoring

We have developed a smart, Internet of Things (IoT)-enabled, intelligent, and flexible humidity sensor for human respiration rate monitoring by using a heterostructure of two-dimensional (2D) germanium(II) sulfide (GeS) and zero-dimensional (0D) gold nanoparticles (Au NPs). The 2D GeS was synthesized by a facile liquid-phase exfoliation process, followed by the post-functionalization of Au NPs. Furthermore, the chemical and structural integrities of the heterostructure were corroborated by microscopic and spectroscopic techniques. The as-prepared heterostructure (termed Au-GeS) exhibited a maximum sensor response of 7102% at 90% of relative humidity (RH) level compared to the pristine GeS sensor response of 2700% at the same RH level. Finally, we demonstrate the use of the Au-GeS flexible humidity sensor for human respiration rate monitoring. The sensor showed an ultrafast response and recovery times of 0.69 and 0.73 s, respectively, during exhalation and inhalation. The sensor was further integrated into a portable electronic system to facilitate IoT-enabled real-time wireless sensing at the smartphone application interface. In our study, the excellent sensor performance with a simple fabrication process offers utilization of the flexible sensor in personal health monitoring.