Abstract
Preanodization of the Nafion-coated glassy carbon electrode (NCGCE) results in a large increase in the square-wave voltammetric peak current of dopamine (DA) with an excellent detection limit of 4.7 nM (S/N = 3) in pH 7.4 phosphate buffer solution. Chronocoulometry showed an increase in double-layer charge and the adsorption control of charge transfer. The surface coverage was calculated to be 3.1 × 10-10 mol/cm2, reminiscent of a monolayer coverage. The cause for such an increase in peak current on preanodization is unraveled using impedance measurements. The result reveals that the bulk resistance of Nafion is reduced progressively, and hence more solvent is found to permeate into the NCGCE, at more anodic preanodization potentials. The increase in the fraction of ion clusters in the bulk polymer exposing more SO3- and thus more cationic DA is exchanged to maintain the electroneutrality. The GCE/Nafion interfacial charge also increased with the preanodization potential due to the induction of >CO on the GCE surface. The interaction of the >CO with DA, possibly through hydrogen bonding, is envisaged to further increase the sensitivity in DA detection.
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