Over-oxidized polypyrrole-modified carbon fibre ultramicroelectrode with an integrated silver/silver chloride reference electrode for the selective voltammetric measurement of dopamine in extremely small sample volumes

Abstract

The fabrication and characterization of carbon fibre cone nanometre-sized ultramicroelectrodes (nanoelectrodes, CFCNEs), modified with an over-oxidized polypyrrole (OPPY) film and equipped with an integrated micro Ag/AgCl reference electrode, is reported. The OPPY-modified CFCNEs are suitable for the anodic stripping voltammetric determination of a neurotransmitter, dopamine (DA), in extremely small sample volumes in the presence of ascorbic acid (AA). The observed high selectivity for DA and the ability for its accumulation were found to be a consequence of the exclusion of anionic species by the negative charges in the OPPY film. The OPPY film was prepared via electropolymerization by cycling the potential between –0.2 and 0.7 V versus Ag/AgCl, which also allowed control over its thickness. The permselectivity of the OPPY membrane was thoroughly evaluated. The anodic stripping voltammetric response for DA was found to be dependent on the film thickness, accumulation time and potential and on the pH of the measurement medium. A good linear relationship between the anodic stripping peak current and DA concentration was obtained over the range 2.5 × 10^–6–5.0 × 10^–4 mol l^–1, using a CFCNE modified with 15 OPPY coatings and a 2 min preconcentration time. The reproducibility of the measurement cycles (accumulation–detection–regeneration) was satisfactory, with an RSD of 5.6%(n= 10), and the limit of detection achieved with a 2 min preconcentration time was 1.0 × 10^–7 mol l^–1 of DA in phosphate buffer solution (pH 7.1). Owing to their ultra small size, and the integrated micro reference electrodes, the proposed OPPY-modified CFCNEs permitted the detection of DA in remarkably small sample volumes (as small as 10 nl), and in the presence of high concentrations of AA.