Study of Heterogeneous Electron Transfer on the Graphene/Self-Assembled Mono layer Modified Gold Electrode by Electrochemical Approaches

The electrochemical behaviors of graphene sheets attached to a self-assembled monolayer (SAM) on a gold electrode have been investigated. A gold electrode is sequentially modified by the SAM of n-octadecyl mercaptan (C18H37SH), followed by controllable adsorption of graphene sheets to obtain a graphene/SAM modified Au electrode. The graphene/SAM modified Au electrode is characterized electrochemically by using ruthenium hexaammine (Ru(NH3)(6)(3+)) as a redox probe, and by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The experimental results indicate that the heterogeneous electron transfer (ET) blocked by the SAM can be restored by graphene sheets and that the graphene/SAM modified Au electrode has a smaller interfacial capacitance, as compared with that of a bare Au electrode. The apparent ET rate constant of Ru(NH3)(6)(3+), k(app), on the graphene/SAM modified Au electrode has been also evaluated quantitatively by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM), and is equal to 4.2 x 10(-2) and 6.8 x 10(-2) cm s(-1), respectively. In addition, the electrochemical responses of free bases of DNA (guanine (G), adenine (A), thymine (T), and cytosine (C)) on the graphene/SAM modified Au electrode show that the graphene/SAM modified Au electrode possesses electrochemical properties similar to those of a graphene modified electrode rather than an Au electrode.