An electrochemical biosensor has been developed evaluation of antioxidant capacity. In this biosensor, the damage a ds-DNA modified graphite electrode has been monitored by measurement electrochemical signal from of couple DNA-Ru(bpy) 3 2+ before and after treatment whit antioxidant by SWV method. The oxidizing mediator, Ru(bpy) 3 3+ , is electrogenerated on the graphite electrode that oxidize modified DNA on the surface and damage it, the decreasing in the redox signal of the DNA by Ru(bpy) 2 3+ is proinhibited by antioxidant. In this research several parameters affect on the intensity and electrochemical peak current were optimized. Then, the catalytic rate constant was measured for reaction of Ru(bpy) 3 3+ with DNA and Ru(bpy) 3 3+ with rutin and ascorbic acid by chronoamperometry and SWV methods. An electrochemical method is described for the cyclic voltammetric determination of isoproterenol. The method is based on catalyst effect of p-chloranil as a mediator for the electrocatalytic oxidation of isoproterenol on the surface of modified carbon paste electrode. The oxidation of isoproterenol occur at potentials about 600 mV less positive than with the unmodified carbon paste electrode at pH=10.5. Under the optimal conditions, the peaks current was linear with concentration of isoproterenol in the range of 30.0 to 1500.0 µmol L -1 .The detection limits (S/N = 3) was 19.95 µmol L -1 isoproterenol with relative standard deviations of less than 3%. The chronoamperometry was used to determine the catalytic rate constant for the catalytic reaction and diffusion coefficient also was measured. The proposed method has been successfully applied to the determination of isoproterenol in pharmaceutical and human serum samples.
