The display of unique electronic features by graphene has made it a reliable material for nano-electronic device application. Apart from graphene reliability due to its sensitivity, it shows uncommon electronic properties such as huge surface-to-volume ratio which allow it to utilize in the creation of gas sensors with low power requirements. It has exposed to transport features in graphene which can be adjusted by adsorbing and desorbing the gas molecules. Graphene-based sensors are utilized to determine the reliance of the density of states on the nitrogen dioxide to speed up the rate of response. In this study, the promise of graphene in generating small-scale NO2 gas sensor for environmental monitoring is investigated. For an in-depth knowledge of the electronic features of intrinsic and doped graphene systems, we find the electronic density of states for the graphene and also its dependence to the factor of NO2 concentration. Conductance model of graphene-based detector is adopted to derive current-voltage characteristic of device at different concentrations of NO2 gas. Finally, the proposed model indicates a concentration dependence of current-voltage characteristic showing that the I-V curve of presented model is evaluated with experimental data and good agreement is reported