Copper-modified poly(3,4-ethylenedioxythiophene) layers for selective determination of dopamine in the presence of ascorbic acid: I. Role of the polymer layer thickness.

The oxidation of ascorbic acid (AA) and dopamine (DA) is studied on non-modified and copper crystal-modified poly(3,4-ethylenedioxythiophene) (PEDOT)-coated electrodes. Both oxidation reactions are studied for different thickness of the polymer layers. For several microns thick PEDOT layers both PEDOT and Cu-modified PEDOT show the largest currents. A stable voltammetric response for AA oxidation is observed together with a linear dependence of the peak currents on concentration in the 0.3 to 6.0 mM range. For DA oxidation, however, a gradual loss of electroactivity is found with increasing number of voltammetric scans and concentration. This problem is overcome by using thinner (<1 µm) polymer layers. In the presence of both AA and DA, the Cu-modified PEDOT-coated electrodes provide better selectivity with respect to DA in comparison to non-modified PEDOT due to partial suppression of the AA oxidation currents. Thin PEDOT layers modified with electrodeposited Cu crystals show a stable and sensitive response for DA oxidation in the micromolar concentration range. A linear dependence of the voltammetric peak currents is found in a wide concentration range (from 6 to about 200 µM) of DA in the presence of a large excess (1 mM concentration) of AA. The sensitivity is 0.013 µA µM. [ABSTRACT FROM AUTHOR]