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

Exploring Interdigitated Electrode Arrays Screen-Printed on Paper Substrates for Steady-State Electrochemical Measurements

This research explores the use of interdigitated electrode arrays (IDE) screen-printed on paper substrate for electrochemical measurements in steady state. Since the steady state is strongly related to IDE dimensions, the accuracy and reproducibility of the fabrication process were assessed for stencils of 120- and 200-mesh. Simulations were used to predict the limiting current and time response, and as a benchmark for comparison with the experimental results. For accurate an comparison, evaporation was prevented by using a homemade humidity box, which enabled measurements for periods as long as 30 min. Although cyclic voltammetry measurements in steady state were possible, this required at least 15 min per cycle when using the smallest electrodes (band width of 0.205 mm). Chronoamperometric measurements reaching steady state were also possible, requiring nearly 5 min for the largest electrodes (band width of 0.376 mm). Regarding the reproducibility of measurements, the relative standard deviations (RSD) of current and response time were near 12% and 26%, respectively. We attribute this mainly to the reproducibility of IDE fabrication (8% RSD). Experimental currents were approximately 30% to 34% of their simulated counterparts. Conversely, the simulated response times were about 30% to 50% of their experimental counterparts. We ascribe these discrepancies to the porosity of the paper (Whatman 2 CHR), estimated to be near 31% under wet conditions. This suggests that fibers inside the paper substrate block the passage of electrochemical species, thereby delaying their diffusion and decreasing the current. (C) 2022 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited

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