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, Internetof Things (IoT)-enabled, intelligent,and flexible humidity sensor for human respiration rate monitoringby using a heterostructure of two-dimensional (2D) germanium(II) sulfide(GeS) and zero-dimensional (0D) gold nanoparticles (Au NPs). The 2DGeS was synthesized by a facile liquid-phase exfoliation process,followed by the post-functionalization of Au NPs. Furthermore, thechemical and structural integrities of the heterostructure were corroboratedby 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 sensorresponse of 2700% at the same RH level. Finally, we demonstrate theuse of the Au-GeS flexible humidity sensor for human respiration ratemonitoring. The sensor showed an ultrafast response and recovery timesof 0.69 and 0.73 s, respectively, during exhalation and inhalation.The sensor was further integrated into a portable electronic systemto facilitate IoT-enabled real-time wireless sensing at the smartphoneapplication interface. In our study, the excellent sensor performancewith a simple fabrication process offers utilization of the flexiblesensor in personal health monitoring.