▎ 摘　　要

Graphene holds great promise in gas sensor applications due to its excellent electrical transport properties and extraordinarily large surface-to-bulk ratio, rendering the whole atomic-thin films easily affected by gaseous molecules. One unique feature of graphene-based gas sensors is their reversible molecular physical adsorption/desorption mechanism that does not noticeably cause structural distortion or property degradation that chemical reactions would. Given the underlying principle of graphene sensors is the charge transfer between gases and graphene, the initial graphene doping level should be critical in the final sensor performance; however, such knowledge has been largely missed in prior reports. Here, we fabricated graphene transistors to examine the sensor properties using prototypical testing gas NO2. We found that the distinct initial doping levels of graphene may lead to opposite electrical responses when graphene sensors are exposed to NO2. The electrical response is triggered by the charge transfer between graphene and NO2 (and its dimer N2O4). Our work highlights the role of graphene conditions in sensor performance, suggests the practical avenues to optimize graphene sensors, and unravels the complex interactions between adsorbed molecules and graphene, which provide valuable guidance for the mass production of commercialized graphene sensors.