Evaluation of physically small p-phenylacetate-modified carbon electrodes against fouling during dopamine detection in vivo

In this paper, the effectiveness of anionic p-phenylacetate film was evaluated in protecting physically small conical-tip carbon electrodes (∼2 μm radius and ∼4 μm axial length) from fouling during dopamine detection in vivo. After characterising p-phenylacetate film-modified carbon electrodes in several redox systems in vitro, they were found to exhibit an 11% loss in dopamine oxidation signal over a 40-day storage period in ambient laboratory conditions, compared to over a 90% loss at bare carbon electrodes. In addition, by incubating in a synthetic laboratory solution containing the fouling reagents, 1.0% (v/v) caproic acid (a lipid), 0.1% (w/v) bovine serum albumin and 0.01% (w/v) cytochrome C (both are protein) and 0.002% (w/v) human fibrinopeptide B (a peptide), film-modified carbon electrodes showed a 29% reduction in the limit of detection and a 25% decrease in sensitivity for dopamine over 7 days, compared to undeterminable results arising from a severely degraded surface at bare carbon electrodes. During dopamine detection in vivo, 70-95% of the dopamine oxidation current remained after the first 40 min of the experiment, and at least 50% over the next 20 min. In contrast, constant degradation in the dopamine oxidation signal was observed at bare carbon electrodes throughout the experiment. An average electrode surface fouling rate of 0.54% min^-1 was estimated at the p-phenylacetate film-modified carbon electrodes during the first 40 min of the experiments.