3,4-ethylenedioxythiophene (EDOT) was electropolymerized in the presence of sodium lignosulfonate (LS) at constant current density of 0.25 mA cm^-2. As a result, a thin composite film consisting of poly(3,4-ethylenedioxythiophene) and LS (PEDOT/LS) was deposited on the electrode surface. Unlike PEDOT, PEDOT/LS shows appreciable redox activity due to LS-derived quinone moieties (Fig. 1A) with diffusion-like charge propagation across the film thickness. We used pulsed chronoamperometry to determine the apparent charge transport diffusion coefficient and we found that for at sufficiently short times the current decay response conforms to the Cottrell equation. From this dependence, for the film polymerized at 50 mC cm^-2 we found the D_ct value to be 1.6 x 10^-9 cm² s^-1. The film-modified gold electrodes can be used as voltammetric sensor of uric acid (UA) in the presence of ascorbic acid (AA). Interestingly, the UA response is catalysed by the presence of AA and for high AA/UA concentration ratios more that 10-fold enhancement of the UA peak currents are apparent (Fig. 1B).

Fig. 1 (A) Comparison of cyclic voltammograms of PEDOT films electropolymerized in the absence (black line) and presence of LS (red line). LS concentration in the plating bath – 1 mg cm^-3. Scan rate – 10 mV s^-1. Electrolyte – phosphate buffer (pH 7.4). (B) AA-induced peak current enhancement of UA on PEDOT/ClO4 (red line) and PEDOT/LS film (black line) as a function of UA concentration.

Works are in progress to evaluate the performance of the proposed composite toward electrochemical sensing of other biomolecules.

Acknowledgement This work was financially supported by Polish Ministry of Science and Higher Education under project No N N209 450939.

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