Fig. 4. Operation modes and measurement protocol.
a Delta measurements to mitigate the sensor drift issue across different VGS voltage and swatch modes. MB Delta refers to the IDS difference between the malodour (M) swatch and blank (B) swatch modes at the same VGS. BB Delta and MM Delta refer to the IDS difference at the two VGS voltages in the same mode. b The basic measurement protocol is shown for collecting the sensor outputs in the experiments where the wet blank swatch is used as a reference. First, the sensors are exposed to wet blank swatch and two readings of IDS at two VGS voltages (i.e., −3 and −3.5 V) are recorded. Then the sensors are exposed to the malodour swatch and two readings of IDS at the same two VGS voltages are recorded.