A Room-Temperature Dual-Gas Humidity/Ammonia Sensor Based on Gallium Oxide for Breath Analysis

The analysis of human breath to detect both respiration state and breath biomarkers is of great importance in the fields of exhaled noninvasive breath monitoring and diagnosis. Thus, we have elaborately synthesized gallium oxide (Ga₂O₃) with different oxygen species as humidity and gas sensitive materials to monitor respiratory function and ammonia (NH₃). In this work, the sensing characteristics and breath monitoring applications of the humidity/ammonia sensor based on the Ga₂O₃ are systematically investigated. The humidity sensor demonstrated high responsivity (over 3 orders of magnitude), low humidity hysteresis (1.83%) and good long-term stability. The ammonia sensor has a response of 1.2% to 2 ppm ammonia at 70% RH. To investigate the potential application of the sensor in detecting ammonia in exhaled gas, a simulated breath test was conducted.