Selective detection of dopamine and its metabolite, DOPAC, in the presence of ascorbic acid using diamond electrode modified by the polymer film

The surface of boron-doped diamond (BDD) electrode is modified by the polymer film for the first time. The cationic polymer film of N,N-dimethylaniline (DMA) is electrochemically deposited on BDD electrode surface. This polymer (PDMA) film-coated BDD electrode is used as a sensor which selectively detect dopamine (DA) in the presence of ascorbic acid (AA). This electrode also can detect both DA and its metabolite, 3,4-dihydroxy phenyl acetic acid (DOPAC) in the presence of AA in the range of the physiological concentrations of these species. Favorable ionic interaction (i.e., electrostatic attraction) between the PDMA film and AA or DOPAC lowers their oxidation potentials and enhances the current response for AA and DOPAC compared to that at the bare electrode. The PDMA film also shows a hydrophobic interaction with DA and DOPAC. In cyclic voltammetric measurements, the PDMA film-coated electrode can successfully separate the oxidation potentials for AA and DA coexisting in the same solution and the separation is about 200 mV. AA oxidizes at more negative potential than DA. In square-wave voltammetry, the sensitivity of the PDMA film-coated BDD electrode for DA in the presence of higher concentration of AA is higher than that of the PDMA film-coated glassy carbon electrode. The hydrodynamic amperometric experiments confirm that the oxidation of AA is not affected by the oxidized product of DA and vice versa. So, unlike the bare electrode the catalytic oxidation of AA by the oxidized DA is eliminated at the PDMA film-coated BDD electrode. The sensitivities of the modified electrode for AA, DA and DOPAC, which are present in the same solution with their physiological concentration ratios, are calculated to be 0.070, 0.363 and 0.084 muA muM(-1), respectively. The modified electrode exhibits a stable and sensitive response to DA.