Figure 3: Dipole-detection-based sensing mechanism for a graphene heterodyne sensor.

(a) Measured mixing current response for a pair of cis- and trans-isomers, 1,2-dichloroethene, with the same injected mass of 1.28 μg. Only the polar cis-1,2-dichloroethene shows strong sensor response. The analytes were measured on a device with L=1 μm, W=1 μm, at . (b) Graphene sensor response and the corresponding illustration of the orientation of vapour molecules. Left panel—(top) measured mixing current response for hexane and benzene with an injected mass of 131 and 43.8 ng, respectively. (Bottom) schematic illustration of an analyte with zero dipole moment on graphene. Middle panel—(top) measured mixing current response for chloroform and chlorobenzene with an injected mass of 296 and 55 ng, respectively. (Bottom) schematic illustration of an analyte on graphene with the electronegative cloud (blue) closer to the graphene surface. Right panel—(top) measured mixing current response for acetone and 1,4-dioxane with an injected mass of 156 and 51.5 ng, respectively. (Bottom) schematic illustration of an analyte on graphene with the electropositive cloud (red) closer to the graphene surface. is the molecular dipole moment vector. The analytes were measured on a device with L=7 μm, W=2 μm, at .