A novel gas sensor based on multi-layered graphene (MLG) functionalised with gold nanoparticles (Au-NPs) is presented. We demonstrate for the first time that: (1) the signal saturates during the analyte exposure, something which does not occur in the pristine material and in graphene-based gas sensors in general; (2) the sign of the device current response is inverted. MLG is grown by chemical vapour deposition on pre-patterned CMOS-compatible Mo catalyst. The sensor is fabricated directly on the growth substrate, without any transfer of MLG. The Au-NPs are later deposited from an aerosol on the sensor at a specific controlled location, mitigating any additional patterning steps. The functionalised sensor is tested with 1 ppm (part-per-million) of NO2 at room temperature.