An electrochemical oxidation of dopamine (DA) and tyrosine (Tyr) by metal oxide (MO) modified electrode where M=Cu and Ni in phosphate buffer solution (PBS), pH 7.0 has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. CuO and NiO nanoparticles were prepared by sol-gel process and co-precipitation method respectively and their structure, composition and surface morphology were examined by SEM, XRD, FTIR, UV and Raman techniques. A simple drop cast

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... d is employed for the surface modification of graphite electrode to prepare MO modified electrode and it exhibited good electrocatalytic activity towards detection of DA and Tyr. The present investigation on CV studies of DA at CuO modified electrode showed a reversible oxidation process with an anodic peak potential at +0.249V vs. SCE. However, no specific anodic oxidation peak identified with NiO modified electrode. Subsequent CV studies with Tyr at MO modified electrode (M=Cu, Ni) shows an irreversible oxidation process and both modified electrodes exhibited an anodic peak at a potential of +0.80V against very low or no anodic peak currents obtained at bare graphite electrode. Moreover, the CuO modified electrode (CMG) successfully separated the anodic signals of dopamine (DA), Ascorbic acid (AA) and Tyrosine in their ternary mixture whereas on bare graphite a single, overlapped oxidative peak was observed. In CV studies, the peak potential difference between AA-DA, DA-Tyr and AA-Tyr is 166 mV, 323 mV and 489 mV respectively and the corresponding peak potential separations are 209 mV, 400 mV and 609 mV respectively in differential pulse voltammetry (DPV). Owing to good stability, selectivity and simple low cost fabrication method, CuO modified electrode is found to be well suited for simultaneous determination of DA, AA and Tyr in their ternary mixture. Additionally, NiO modified electrode also shows good sensitivity towards the detection of tyrosine, so it acts as a good electrochemical sensor to assay tyrosine in the biological sample.