Simple graphene chemiresistors as pH sensors: fabrication and   characterization
  We report the fabrication and characterization of a simple gate-free graphene device as a pH sensor. The graphene sheets are made by mechanical exfoliation. Platinum contact electrodes are fabricated with a mask-free process using focused ion beam, and then expanded by silver paint. Annealing is used to improve the electrical contact. The experiment on the fabricated graphene device shows that the resistance of the device decreases linearly with increasing pH values (in the range of 4-10)in the surrounding liquid environment. The resolution achieved in our experiments is approximately 0.3 pH in alkali environment. The sensitivity of the device is calculated as approximately 2 k\Omega /pH. The simple configuration, miniaturized size and the integration ability make graphene-based sensors promising candidates for future micro/nano applications. 
Nan Lei, Pengfei Li, Wei Xue, Jie Xu
cond-mat.mtrl-sci cond-mat.mes-hall