Graphene as an allotrope of carbon is promising for the detection of gaseous molecules due to its extremely high surface-to-volume ratio. However, its low selectivity poses a major problem for practical applications. The work presented in this thesis addresses the selectivity problem by depositing metal/metal oxide nanoparticles (NPs) on the surface of graphene. For this purpose, gas sensors with multiple multi-layer graphene (MLG) strips were fabricated. Four types of metal/metal oxide nanoparticles were investigated: Gold (Au), Platinum (Pt), Copper (Cu), and Iron (Fe). Various techniques were developed to study the properties of graphene and NPs. In addition, an automatic measurement setup with multi-strips switching is developed for data acquisition. Finally, the sensors decorated with different metal types and coverages are investigated for their response to H2O and NO2. The study shows that both the pristine devices and the sensors decorated with NPs hardly response to water molecules, while the responses to NO2 are larger and vary depending on the NPs. The results are promising for the development of a gas sensor array based on this methodology with improved selectivity for gas detection.