Sensor element, sensor device, sensor system and detection method

A sensor element capable of detecting a target substance contained in an atmosphere, the sensor element comprising:

• a graphene;
• a drain electrode provided on the graphene;
• a source electrode provide on the graphene;
• a first substance provided on the graphene and having a charge condition and including carboxyl group, phosphate group, sulfonic group, silanol group, hydroxyl group, or amino group, wherein the charge condition is changed when irradiation of light and stopping of the irradiation of the light are performed;
• and
• a humidification mechanism configured to humidify the atmosphere,
• the target substance being detectable by measuring current that flows between the source electrode and the drain electrode, the measuring of the current being performed in a period during which the irradiation of the light and the stopping of the irradiation of the light are repeated above the sensor element, and
• the measuring of the current being performed after the atmosphere is humidified by the humidification mechanism.