The response is ca. 0.28 at 100 ppm formaldehyde, which is much lower than that of the nanocomposites at 25 ppm formaldehyde. In other words, the response of the ZnO QDs/graphene composite sensor is ca. 4 times better than the pure graphene sensor at 100 ppm formaldehyde, suggesting that the decorated ZnO QDs play an important role in the room temperature gas sensing properties.