NO2is a major air pollutant that should be monitored due to its harmful effects on the environment and human health. Semiconducting metal oxide-based gas sensors have been widely explored owing to their superior sensitivity towards NO2, but their high operating temperature (>200 °C) and low selectivity still limit their practical use in sensor devices. In this study, we decorated graphene quantum dots (GQDs) with discrete band gaps onto tin oxide nanodomes (GQD@SnO2nanodomes), enabling room temperature (RT) sensing towards 5 ppm NO2gas with a noticeable response ((Ra/Rg) − 1 = 4.8), which cannot be matched using pristine SnO2nanodomes. In addition, the GQD@SnO2nanodome based gas sensor shows an extremely low detection limit of 1.1 ppb and high selectivity compared to other pollutant gases (H2S, CO, C7H8, NH3, and CH3COCH3). The oxygen functional groups in GQDs specifically enhance NO2accessibility by increasing the adsorption energy. Strong electron transfer from SnO2to GQDs widens the electron depletion layer at SnO2, thereby improving the gas response over a broad temperature range (RT–150 °C). This result provides a basic perspective for utilizing zero-dimensional GQDs in high-performance gas sensors operating over a wide range of temperatures.