MoS2 monolayers functionalized with gold nanoparticles using microwave absorption for FET-type NO2 gas sensors in ppb-levels

Molybdenum disulfide (MoS2) monolayers functionalized with nanometals using microwave absorption are developed in this study to realize high-performance field-effect transistor (FET)-type gas sensors detecting NO2 molecules in ppb-levels for health monitoring bioelectronics. The optimized microwave-induced functionalization of chemical vapor deposition-grown MoS2 monolayer films with gold nanoparticles (Au NPs) solution-processed at low temperatures (∼120 °C) for a short time periods (∼1 min), is investigated. The FET-type gas sensor exhibited a threshold voltage shift of ∼0.5 V and a sensing response of ∼10 % with a theoretical detection limit of 0.183 ppb when exposed to 200 ppb of NO2 gas at 30 °C for 15 s, as compared to that reported in the literature. In addition, the functionalization mechanism of Au NPs in the developed NO2 gas sensors is investigated to reveal high selectivity toward different gas species in exhaled breath and excellent stability against environmental factors, such as humidity and temperature, which are crucial for the practical analysis of human breath. Finally, the effect of ultraviolet irradiation on the photo-induced surface reactions is demonstrated to enhance the recovery characteristics of the FET-type gas sensors with recovery times spanning a few seconds.