An integrated flexible self-powered wearable respiration sensor

Highlights: • An all-in-one self-powered wearable respiration sensor was developed. • Respiratory patterns and NH₃ in exhaled gases can be simultaneously detected. • Breathing moisture dramatically enhances the sensitivity and selectivity toward NH₃. • Gas sensing mechanism was investigated via finite element simulation. -- Abstract: Human respiration is rich in physiological and pathological information for health assessment and illness prediction. In this work, an integrated triboelectric self-powered respiration sensor (TSRS) was developed for simultaneously monitoring human respiratory behaviors and NH₃ concentration in exhaled gases. The TSRS based on Ce-doping ratio of 0.004 M exhibits a better selectivity and larger sensitivity of 20.13 ppm⁻¹ compared with those synthesized in other doping ratios. Under the same moisture as the breathing gas (97.5%RH), the sensor holds greater sensitivity toward NH₃ at low concentration (0.1–1 ppm) than that at high concentration (1–10 ppm), implying the capability in detecting trace level NH₃ biomarker in human breathing gases. Furthermore, triggered by the expansion and contraction of chest during breathing, TSRS can spontaneously monitor human respiratory patterns and physiological process after physical exercise. Meanwhile, a theoretical modeling was established in terms of permittivity change under gas molecules adsorption and verified via finite element simulation to interpret the self-powered sensing behaviors. This research not only proposes a promising approach to develop an all-in-one wearable respiration monitoring system for personal health diagnosis but also sheds some light on the theoretical modeling of triboelectric self-powered gas-sensing in terms of permittivity change.