Graphene (GR) is a single-atom-thick sheet of sp2-bonded carbon atoms (Li et al, 2011). Since the discovery of GR, it has attracted considerable attention because of its unique and novel properties such as high surface area, high electrical conductivity, strong mechanical strength and good chemical stability (Du et al. was po 2011). Therefore. it has received more and more interest for applications in many technological fields such as nanocomposites, bioelectronics and biosensing (Sun et al., 2011:Chen et al., 2011).