P–N Heterojunction formation: Metal Sulfide@Metal Oxide Chemiresistor for ppb H2S Detection from Exhaled Breath and Food Spoilage at Flexible Room Temperature

The development of a portable, low-cost sensor capable of accurately detecting H₂S gas in exhaled human breath at room temperature is highly anticipated in the fields of human health assessment and food spoilage evaluation. However, achieving outstanding gas sensing performance and applicability for flexible room-temperature operation with parts per billion H₂S gas sensors still poses technical challenges. To address this issue, this study involves the in situ growth of MoS₂ nanosheets on the surface of In₂O₃ fibers to construct a p-n heterojunction. The In₂O₃@MoS₂-2 sensor exhibits a high response of 460.61 to 50 ppm of H₂S gas at room temperature, which is 19.5 times higher than that of the pure In₂O₃ sensor and 322.1 times higher than that of pure MoS₂. The In₂O₃@MoS₂-2 also demonstrates a minimum detection limit of 3 ppb and maintains a stable response to H₂S gas even after being bent 50 times at a 60° angle. These exceptional gas sensing properties are attributed to the increase in oxygen vacancies and chemisorbed oxygen on In₂O₃@MoS₂-2 nanofibers as well as the formation of the p-n heterojunction, which modulates the heterojunction barrier. Furthermore, in this study, we successfully applied the In₂O₃@MoS₂-2 sensor for oral disease and detection of food spoilage conditions, thereby providing new design insights for the development of portable exhaled gas sensors and gas sensors for evaluating food spoilage conditions at room temperature.