“…In the past decades, researchers from all over the world have developed various types of gas sensors based on different sensing materials and physical principles, including catalytic combustion, electrochemistry, thermal conductivity, infrared absorption, fiber optic, paramagnetism, solid electrolyte and metal oxide semiconductor (MOS) sensors [1][2][3][4][5][6]. According to the sensing mode and measurement method, gas sensors can be divided into chemiresistive gas sensors, field effect transistor (FET) gas sensors, mass-sensitive gas sensors, photoluminescence (PL) gas sensors, micro electro mechanical system (MEMS) gas sensors, etc.…”