ABSTRACT
As previously reported the batch electrochemical cell was used with the electrodes of B type to separately determine the Catechol or Bisphenol A concentrations in aqueous solutions. In particular, with the B1, B2 and B3 electrodes we have studied the electrochemical response to BPA in the concentration range from 3 to 20 µM. The results of this investigation are displayed in Fig. 5.5A, where the electrochemical currents are reported as a function of BPA concentration for three different enzyme percentages. Data in Fig. 5.5A show that: (i) each electrode type displays their own linear behaviour; (ii) at each BPA concentration the electrochemical signals are not linear function of enzyme concentration, but increase faster than enzyme concentration (Fig. 5.5B). This behaviour indicates that under the conditions used to prepare the electrodes, no protein-protein interactions occurred. Similar results have been obtained by other authors (Erdem et al. 2000) who observed a non-linear increase in electrochemical signal when different percentages of horseradish peroxidase were entrapped in a carbon paste electrode. The same non-linear behaviour is observed when the slopes of the straight lines in Fig. 5.5A (i.e. the electrode sensitivities: 10.02 nA µM−1 for 2.5% tyrosinase, 22.82 nA µM−1 for 5% tyrosinase and 64.48 nA µM−1 for 10% tyrosinase) are reported (Fig. 5.5C) as a function of enzyme concentration in the carbon paste. The results above appear to indicate that it is possible to modulate both the electrochemical response of a carbon paste biosensor to BPA and its relative sensitivity on the basis of the amount of immobilized tyrosinase, and consequently on the basis of the carbon paste composition.
