The possibility to synergise two-dimensional (2D) materials with 0D nanoparticles has sparked a surge in high performance futuristic electronic devices. Here, we decorated plasmonic Au nanoparticles on surface of chemical vapor deposition (CVD) grown 2D MoS2 nanosheet and demonstrated bifunctional sensing behaviour within a single device. The plasmonic Au nanoparticles functionalized MoS2 device showed about 5 times higher sensitivity to NO2 than that of pristine MoS2 at room temperature. The enhanced gas sensing performance was attributed to a combination of Schottky barriers modulation at Au/MoS2 nanointerfaces and catalytic effects upon exposing the gas analyte. In addition, the device also exhibited enhanced photoresponse with a high photo-responsivity of 17.6 A/W and a moderate detectivity of 6.6 × 1011 Jones due to enhanced local plasmonic effects. Finally, photons and gas molecules are detected in sequence, which proved that only a single Au-MoS2 device exhibited remarkable bifunctional sensing characteristics. Such excellent bifunctional sensing ability of a single Au-MoS2 device paves the way to integrate the 2D material with plasmonic nanostructures for developing an advanced multifunctional sensor. © 2001-2012 IEEE.