Target gas acetone was first diluted in the air and then a calculated amount of test gas was introduced by a microsyringe into the testing chamber on Chemical Gas Sensor-8 (CGS-8, Ailite Technology Co., Ltd., Beijing, China) at a relative humidity of 20–30%. The sensor sensitivity signal S, was defined as the ratio Ra/Rg, where Ra and Rg were the electrical resistances
of the sensor in air and in test gas, respectively.