A comparative investigation has been undertaken of the electrosynthesis and electrochemical properties of three different electroactive polymers on carbon film electrode substrates: poly(neutral red) from the phenazine dye neutral red, and poly(methylene green) and poly(methylene blue), from the corresponding phenothiazine dyes. The formation of the radical cation at different potentials and the chemical structures of the monomers both influence the electropolymerisation process of the three polyaromatic dyes. Of the three, poly(neutral red) is shown to have the best adhesion at carbon film electrodes. The influence of the electrolyte and pH on film growth and on electrochemical properties was investigated. The formal potential decreased linearly with increase in pH, in the pH range from 1 to 7 for all three polymers. The modified electrodes were also characterised by electrochemical impedance spectroscopy. The bulk and interfacial characteristics of the two phenothiazine polymers were similar and oxygendependent, but different to those of the phenazine polymer, poly(neutral red), which were not significantly influenced by the presence of oxygen in solution. Perspectives for use in electrochemical biosensors are indicated.

A new conducting composite flexible material prepared from cellulose acetate (CA) polymer and graphite has been developed and used for the fabrication of electrodes, which were then characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) was used to provide information concerning the morphology of the composite electrode surface. The potential window, background currents and capacitance were evaluated by cyclic voltammetry in the pH range from 4.6 to 8.2. The voltammetry of model electroactive species demonstrates a close to reversible electrochemical behaviour, under linear diffusion control. The electroactive area of the composite electrodes increases after appropriate electrode polishing and electrochemical pre-treatment. The electrodes were used as substrate for the electropolymerisation of the phenazine dye neutral red, for future use as redox mediator in electrochemical biosensors. The composite electrodes were also successfully used for the amperometric detection of ascorbate at 0.0 V vs. SCE, and applied to the measurement of ascorbate in Vitamin C tablets; the sensor exhibits high sensitivity and a low detection limit of 7.7 microM. Perspectives for use as a versatile, mechanically flexible and robust composite electrode of easily adaptable dimensions are indicated.

A graphite-polyurethane composite electrode has been used for the determination of furosemide, a antihypertensive drug, in pharmaceutical samples by anodic oxidation. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrooxidation process at þ 1.0 V vs. SCE over a wide pH range, with the result that no adsorption of analyte or products occurs, unlike at other carbon-based electrode materials. Quantification was carried out using cyclic voltammetry, differential pulse voltammetry, and square-wave voltammetry. Linear ranges were determined (up to 21 mmol L À1 with cyclic voltammetry) as well as limits of detection (0.15 mmol L À1 by differential pulse voltammetry). Four different types of commercial samples were successfully analyzed. Recovery tests were performed which agreed with those obtained by spectrophotometric evaluation. The advantages of this electrode material for repetitive analyzes, due to the fact that no electrode surface renewal is needed owing to the lack of adsorption, are highlighted.

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Self-assembled multilayer films of hyaluronic acid (HA) and the protein myoglobin (Mb) were built up layer by layer on Au covered quartz crystal microbalance (AuQCM) electrode substrates. Film formation and growth were monitored by an electrochemical quartz crystal microbalance (EQCM), and the step-by-step construction was investigated through quantification of the mass variation corresponding to adsorption of each monolayer together with cyclic voltammetry. A decrease of friction at the liquid/electrode interface was observed, indicating that the electrode surface becomes less rough after deposition of several monolayers. The properties of the {HA/Mb}(n) films were evaluated by electrochemical impedance spectroscopy (EIS). Modeling of the impedance spectra shows smoothing of the modified electrode surface with reorganization of the film structure after few monolayers, and the contribution of each layer to the electron transfer process was analyzed. The smoothing of the surfaces and the structural differences between successive bilayers was confirmed by morphological observations by using atomic force microscopy.