In this study, we demonstrated that graphene could selectively absorb/desorb NO x molecules at room temperature. Chemical doping with NO 2 molecules changed the conductivity of the graphene layers, which was quantified by monitoring the current–voltage characteristics at various NO 2 gas concentrations. The adsorption rate was found to be more rapid than the desorption rate, which can be attributed to the reaction occurred on the surface of the graphene layer. The sensitivity was 9% when an ambient of 100 ppm NO 2 was used. Graphene-based gas sensors showed fast response, good reversibility, selectivity and high sensitivity. Optimization of the sensor design and integration with UV-LEDs and Silicon microelectronics will open the door for the development of nano-sized gas sensors that are extremely sensitive.