Carla Gouveia-Caridade

Enzyme immobilisation on electroactive nanostructured membranes (ENM): Optimised architectures for biosensing

Electroactive nanostructured membranes have been produced by the layer-by-layer (LbL) technique, and used to make electrochemical enzyme biosensors for glucose by modification with cobalt hexacyanoferrate redox mediator and immobilisation of glucose oxidase enzyme. Indium tin oxide (ITO) glass electrodes were modified with up to three bilayers of polyamidoamine (PAMAM) dendrimers containing gold nanoparticles and poly(vinylsulfonate) (PVS). The gold nanoparticles were covered with cobalt hexacyanoferrate that functioned as a redox mediator, allowing the modified electrode to be used to detect H(2)O(2), the product of the oxidase enzymatic reaction, at 0.0 V vs. SCE. Enzyme was then immobilised by cross-linking with glutaraldehyde. Several parameters for optimisation of the glucose biosensor were investigated, including the number of deposited bilayers, the enzyme immobilisation protocol and the concentrations of immobilised enzyme and of the protein that was crosslinked with PAMAM. The latter was used to provide glucose oxidase with a friendly environment, in order to preserve its bioactivity. The optimised biosensor, with three bilayers, has high sensitivity and operational stability, with a detection limit of 6.1 microM and an apparent Michaelis-Menten constant of 0.20mM. It showed good selectivity against interferents and is suitable for glucose measurements in natural samples.

Strategies, Development and Applications of Polymer-Modified Electrodes for Stripping Analysis

Recent progress in polymer modified electrodes for stripping analysis is surveyed, mainly concerned with ion- exchange polymer and conducting polymer coatings on mercury thin film electrodes and other solid electrode substrates. Film preparation methods are discussed and applications involving different types of polymer film or polymer film com- posites illustrated, with emphasis on recent literature published in the last five years.

Development and Interfacial Properties of Novel Polymer-Modified Carbon Film Electrodes

The surface properties of carbon film electrode sensors covered by coating with Nafion polymer film, before and after electrochemical analysis of sub-micromolar traces of lead and cadmium ions, were investigated. These protective polymer films are applied to the electrode surfaces to prevent the irreversible adsorption of chemical species, such as proteins and surfactants present in natural media, which leads to a decrease in response. Electrochemical impedance spectroscopy and voltammetric techniques were used for characterisation. The effect of non-ionic surfactant molecules in solution on the behaviour of the polymer-coated electrode was also investigated. It is shown that permanent changes to the structure and morphology of the Nafion film and of the carbon-Nafion interface occur after deposition of the trace metal ions, an effect which is lessened in the presence of surfactant.

Influence of Protein Adsorption on the Passivation of Dental Amalgams

Abstract The influence of protein adsorption on the surface properties and corrosion resistance of the high copper dental amalgam Tytin® has been investigated, using the model protein bovine serum albumin, in chloride-containing and artificial saliva solutions by employing voltammetric techniques and electrochemical impedance. It is demonstrated that the effect of this protein can be to inhibit oxide formation and increase the amalgam corrosion rate. The results are discussed and compared with others obtained without protein in solutions of artificial saliva with and without the addition of the organic components.