Wang et al. Nanoscale Research Letters 2012, 7:161 http://www.nanoscalereslett.com/content/7/1/161 Page 5 of 7 Figure 4 CV curves of C-rGO and E-rGO in the mixture of AA, DA, and UA. CV curves of (A) C-rGO and (B) E-rGO in (a) the mixture of AA (1.0 mM), DA (0.1 mM), and UA (0.1 mM), (b) 1.0 mM AA, (c) 0.1 mM DA, and (d) 0.1 mM UA. Electrolyte, 0.01 M PBS buffer (pH 7.4). and UA located at 52, 220 and 350 mV, respectively, showed up (Figure 4B), indicating the independently electrochemical oxidation of each analyte. However, with C-rGO, the oxidation peaks for the mixed analytes did not separate well (Figure 4A). The oxygen-contain- ing species present on the graphene sheets are responsi- ble for the electron transfer as well as the adsorption/ desorption of molecules [56]. The better electrocatalytic Figure 5 DPV profiles of E-rGO and the plot of DPV peak as function of DA concentration. (A) DPV profiles of E-rGO in the solution of 0.01 M PBS (pH 7.4) containing 1 mM AA, 0.1 mM UA, and different concentration of DA (from 0 to 50 μM). (B) The plot of DPV peak current as function of DA concentration.