Electrodeposition of Rhein and Its Electrocatalytic Activity Toward Hemoglobin Reduction

A stable electroactive thin film of rhein has been deposited on the surface of a glassy carbon electrode by cyclic voltammetry from an acetate buffer solution containing 1.0×10−5 mol/L rhein. Cyclic voltammograms of rhein indicate the presence of a pair of redox peaks with a formal potential of −0.184 V at a scan rate of 50 mV/s, with the cathodic peak potential shifting linearly in the negative direction with increasing solution pH (with a slope of 62 mV per pH unit). The rhein modified electrode shows electrocatalytic activity for hemoglobin reduction in 0.06 M H2SO4 solution. The peak currents are proportional to the concentrations of hemoglobin over the range of 6.0×10−8 to 1.3×10−6 mol/L. The detection limit is 1.0×10−8 mol/L at optimal conditions. The relative standard deviation is 3.5% for 6 successive determinations of 1.0×10−7 mol/L hemoglobin. The mechanism of the electrode reaction is discussed.