Here, we have designed, fabricated and characterized solutiongated graphene FETs based on using high-quality single layer graphene, for highly sensitive and selective K+ detection. The enhanced specificity ofits responseto thetargetsequencewasenabled viacoating ofthe graphene surface with G-quadruplex, which is a G-rich DNA molecule with strong binding affinity to K+. FETs based on graphene without O2 plasma pre-processing achieved a LOD of 0.74pM and a linear dynamic range of up to 1μM. Interestingly, after an optimized 10-s plasma pretreatmentstep,alowerLODbelow0.058pMcanbeachieved,which