The gas-sensing response curves of the Apicidin samples were measured using a gas sensing characterization station (QMCS-I, HUST, China). The details of the station configuration and gas-sensing test steps were described in our previous publications . The sensor samples were mounted over the test-board in a chamber of 0.7 L volume with controlled temperature for DC electrical measurement. The accuracy of the temperature control is ±2 °C. The static method was employed and the gas concentration was determined by the volume ratio. The gas-sensing tests throughout the work were performed under atmospheric pressure with a relative humidity of (45 ± 1)% at 25 °C. The gas-sensing response is defined as the ratio of the sensor resistance in clean air to that in the target gas. The response time (T90) and the recovery time (T10) are specified in terms of the time for the sensor to reach 90% of its final response upon target gas exposure and the time interval over which the sensor response reduces to 10% of its maximal value after gas release, respectively.