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

Development of an Alcohol Dehydrogenase Biosensor for Ethanol Determination with Toluidine Blue O Covalently Attached to a Cellulose Acetate Modified Electrode

In this work, a novel voltammetric ethanol biosensor was constructed using alcohol dehydrogenase (ADH). Firstly, alcohol dehydrogenase was immobilized on the surface of a glassy carbon electrode modified by cellulose acetate (CA) bonded to toluidine blue O (TBO). Secondly, the surface was covered by a glutaraldehyde/bovine serum albumin (BSA) cross-linking procedure to provide a new voltammetric sensor for the ethanol determination. In order to fabricate the biosensor, a new electrode matrix containing insoluble Toluidine Blue O (TBO) was obtained from the process, and enzyme/coenzyme was combined on the biosensor surface. The influence of various experimental conditions was examined for the characterization of the optimum analytical performance. The developed biosensor exhibited sensitive and selective determination of ethanol and showed a linear response between 1 × 10−5 M and 4 × 10−4 M ethanol. A detection limit calculated as three times the signal-to-noise ratio was 5.0 × 10−6 M. At the end of the 20th day, the biosensor still retained 50% of its initial activity

Microwire chronoamperometric determination of concentration, diffusivity, and salinity for simultaneous oxygen and proton reduction

A microwire chronoamperometric method is reported employing a 25μm diameter platinum microwire for multi-parameter electroanalysis with digital simulation-based evaluation (employing DigiElch 4.F). Concentration and diffusion coefficient data are obtained for the reduction of oxygen and for the reduction of protons individually and simultaneously in saline (0.1M to 4.0M NaCl) electrolyte media. The diffusion coefficient and concentration data for oxygen allows salinity levels to be estimated. The microwire chronoamperometry method offers versatility and precision due to (i) a slow approach to steady state (when compared to microdisc methods) and (ii) insignificant viscosity effects (when compared to hydrodynamic methods).</p

Electrochemistry of metal complexes and their use in amperometric sensors

This thesis concerns the utilization of metal complexes in amperometric sensors. Chapter One provides a general introduction to the area. The electrochemical theories relating to the development and use of amperometric sensors, are described, and applications for such sensors are outlined. These include trace element analysis for environmental and clinical use and the determination of NADH for the detection of clinical analytes. In Chapter Two, the electrochemical changes occurring in a ligand upon complexation, are examined as a possible method of selective metal ion detection. Screen-printing is used to produce disposable, single-use electrodes modified with the ligand bis- cyclohexanone oxaldihydrazone. At +250 mV vs SCE, the electrodes give a linear response to copper(II) across the range 30-300 pM (r = 0.983, n= 13). The effect on the electrode response of variations in pH, temperature, ligand content and storage time are outlined; as well as the effect of competing cations. In Chapter Three, pre-formed metal complexes are used as electron-transfer mediators. Part I considers homogeneous mediation from the enzyme NADH oxidase, using the Ru(lII/IV) redox couple. A scheme for enzyme amplification of the NADH response is outlined using alcohol dehydrogenase (ADH) and NADH oxidase. Additionally, ethanol determination is performed using an ADH/NADH oxidase bilayer. In Part 11, mediator immobilisation is examined using a novel ion-exchange/hydrogel composite (Nf/PVA). The structure of the composite is investigated by following the diffusional characteristics of both hydrophobic and hydrophilic mediators, incorporated within the film. An analytical application of the Nf(PVA layer is illustrated following the co-immobilisation of a mediator with glucose oxidase. The effect of protein adsorption onto the composite is also examined. Part HI of Chapter Three considers a possible alternative to mediated electrocatalysis, by using an electro- deposited film of poly(indole-5-carboxylic acid) (PICA). The overpotential. for the oxidation of ascorbate and NADH is lowered, apparently without the action of a redox mediating species. Strategies for the development of a PICA-based biosensor are outlined. Chapter Four provides an overview and general discussion of the experimental results and suggests areas for further work. These include further improvements to the design of the screen-printed electrodes in Chapter 2; the preferable choice of mediator for the immobilisation matrix in Chapter 3 Part 11, as well as possible methods of improving the biocompatability of the matrix; and a possible route to the immobilisation of NAD,, for the PICA-based system described in Chapter 3 Part III