ELECTRON-MICROSCOPIC AND VOLTAMMETRIC ANALYSIS OF CARBON-FIBER ELECTRODE PRETREATMENTS

The comparison between the differential pulse voltammetric capability of untreated or treated 12 mum or 30 mum diameter carbon fibre electrodes (CFE) to detect electroactive compounds in vitro has been analysed. Their affinity for ascorbic acid (AA), catechols (dopamine (DA); 3,4-dihydroxyphenylacetic acid (DOPAC)), indoles (serotonin (5HT); 5-hydroxyindoleacetic acid (5HIAA)) and uric acid (UA) has been quantified. It appeared that only the 12 mum CFE, when electrically pretreated, can selectively and simultaneously detect the oxidation of AA, catechols and indoles, while the electrically pretreated 30 mum CFE are specifically sensitive to the indoles. However, both electrodes displayed highest sensitivity for serotonin. To avoid the detection of acids and selectively monitor the oxidation of DA and 5HT the 12 mum CFE and the 30 mum CFE were chemically (chromic acid) and electrically pretreated then electrically coated with Nafion. However, the 30 mum CFE alone selectively measured these compounds in vitro as the 12 mum CFE did not accept the coat of Nafion. Using transmission electron microscopy (TEM) and scanning electron microscopy (SEM), we have investigated the effect of electrical and/or chemical pretreatments on the structural characteristics of the CFE. It appeared that both pretreatments increased the surface area of the carbon fibres by pitting, roughening and fracturing the carbon. Holes were also observed on the surface of the 30 mum dia. carbon fibres following the electrical pretreatment. The possibility of a correlation between these modifications and the pretreatment-induced voltammetric high sensitivity of the CFE is discussed.