Tannic acid-doped polypyrrole (PPY/TA) films have been grown on gold electrodes for selective electrochemical detection of dopamine (DA). Electrochemical quartz crystal microbalance (EQCM) studies revealed that, in vivid contrast to perchlorate-doped polypyrrole films (PPY/ClO4-), the redox switching of PPY/TA films in aqueous solutions involved only cation transport if the solution pH was greater than 3∼4. The PPY/TA Au electrodes also exhibited attractive permselectivity for electroactive cations, namely, effectively blocking the electrochemical reactions of anionic ferricyanide and ascorbic acid (AA) while well retaining the electrochemical activities of hexaammineruthenium (III) and dopamine as cationic species. A 500 Hz PPY/TA film could effectively block the redox current of up to 5.0 mM AA. The coexistence of ascorbic acid in the measurement solution notably enhanced the current signal for dopamine oxidation, due probably to the chemical regeneration of dopamine through an ascorbic acid-catalyzed reduction of the electro-oxidation product of dopamine (EC’ mechanism), and the greatest amplification was found at an ascorbic acid concentration of 1.0 mM. The differential pulse voltammetry peak current for DA oxidation was linear with DA concentration in the range of 0 to 10 μM, with sensitivity of 0.125 and 0.268 μA/μM, as well as lower detection limit of 2.0 and 0.3 μM in a PBS solution without AA and with 1.0 mM coexisting AA, respectively.
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