Micro-cylinder biosensors for phenol and catechol based on layer-by-layer immobilization of tyrosinase on latex particles: Theory and experiment

Abstract Microelectrode sensors for phenol and catechol are described, based on the sequential immobilization of polystyrene sulphonate, polyallylamine, tyrosinase and polyallylamine again, onto micrometer scale latex spheres, followed by the adsorption of the spheres onto electrochemically pretreated carbon fibres. The steady state responses of the fibres are analyzed in terms of a cylindrical diffusionkinetic model. It is deduced that the adsorbed latex particles provide a relatively open film structure, resulting in a diffusion coefficient only one order of magnitude lower than the solution value, and that at minimum 2-3% of the immobilized enzyme is catalytically active. The optimised sensors exhibit linear ranges to phenol and catechol of 7-56.5 lM and 2-19.7 lM respectively, with sensitivities of 0.15 A M À1 cm À2 and 1.72 A M À1 cm À2 respectively. The limiting factor to sensor stability is desorption of latex from the fibres

Study of the Underlying Electrochemistry of Polycrystalline Gold in Aqueous Solution and Electrocatalysis by Large Amplitude Fourier Transformed Alternating Current Voltammetry

Polycrystalline gold electrodes of the kind that are routinely used in analysis and catalysis in aqueous media are often regarded as exhibiting relatively simple double-layer charging/discharging and monolayer oxide formation/ removal in the positive potential region. Application of the large amplitude Fourier transformed alternating current (FT-ac) voltammetric technique that allows the faradaic current contribution of fast electron-transfer processes to be emphasized in the higher harmonic components has revealed the presence of well-defined faradaic (premonolayer oxidation) processes at positive potentials in the double-layer region in acidic and basic media which are enhanced by electrochemical activation. These underlying quasi-reversible interfacial electron-transfer processes may mediate the course of electrocatalytic oxidation reactions of hydrazine, ethylene glycol, and glucose on gold electrodes in aqueous media. The observed responses support key assumptions associated with the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis