Figure ) shows selected baseline-corrected resistive transient responses to different r.h. levels. At low r.h. changes (2%), the sensor with the highest GO content shows a positive signal response, in agreement with the r.h. responses measured at higher baseline r.h. (see above). On the other hand, the resistive sensors of higher degrees of reduction (increasing from left to right), exhibit negative signals of down to -5%. An increase in resistance during r.h. exposure, has been reported in the literature for rGO, and was attributed to perturbations of the p-type conductivity of rGO. Water can act as electron donor, resulting in a decrease of charge carrier density. For increasing r.h. transient exposures, the negative sensor signals invert and become positive (cf. figure ). The r.h. value of inversion depends on the degree of reduction: For instance, at 16% r.h., two resistors of high GO content show a positive signal of up to ∼60%, while the sensors that experienced longer UV exposure, still respond with negative signals of -7%, each. Finally, at higher r.h. level (∼80%), all sensors show positive responses. In the low r.h. range up to ∼40%, the sensor with the highest degree of reduction shows only negative responses, while films with more GO content show signal inflection points at lower r.h. values, demonstrating the ability to tailor and optimize the r.h. sensing ranges of the material. A similar trend with an observable point of inversion was reported by Tai et al. for rGO humidity sensors obtained by gradual thermal reduction for up to 13 h. At high r.h. (∼80%), the sensors exposed to DUV light for 2 and 4 h