A comparison of amperometric screen-printed, carbon electrodes and their application to the analysis of phenolic compounds present in beers

In this paper a comparison between three commercially-available, screen-printable graphite inks for the construction of phenolic biosensors is made. The enzyme tyrosinase was immobilised within a polymer matrix and the substrate catechol was used to characterise the bio-electroanalytical response of each electrode. Biosensors fabricated from Gwent graphite inks exhibited the greatest sensitivity (5740 mA mol cm−2) compared to Dupont and Acheson graphite-based inks. This difference in sensitivity was attributed to a combination of a larger electroactive surface area, and thus a greater number of immobilised enzyme molecules. However, the dynamic range was considerably smaller (0.025–14 μM) indicating that the enzyme molecules were easily accessible to the substrate catechol. The surface properties of the biosensors were characterised using ac impedance, which indicated that the presence of the polymer on the electrode surface not only increased the charge-transfer kinetics of the three biosensors, but also increased the surface roughness of biosensors fabricated from Gwent inks. On the basis of these results Gwent graphite-based inks were used for analysis of phenolic compounds in lager beers by flow-injection analysis. The biosensor displayed favourable response characteristics, but cannot differentiate between the various phenolic compounds present in the samples. Nevertheless, the biosensor maybe suitable for indicating the phenolic status of beer or brew samples compared to time-consuming traditional methods, e.g. colorimetric or chromatographic methods.