Graphene is a 2D material composed of a monolayer of sp2-bonded carbon atoms. Due to its structure, graphene is sensitive to Fermi level changes, as discussed in several reviews. When the graphene sheet is made into the electrochemical or field effect transistor sensor, its conductivity can be easily modified by scanning a voltage range or doping and applying a gate voltage. Thus, graphene has several advantages for making sensors. Single-layer graphene has a large surface-tovolume ratio, which provides many binding sites per unit volume, resulting in high sensitivity.