Samuel B. Adeloju

Conducting polymers and the bioanalytical sciences: new tools for biomolecular communications. A review

This review covers the evolution of conducting polymers and their use in the bioanalytical sciences. It is the controlled dynamic behaviour of these unique materials that enables such diverse and high-level performance to be achieved. The construction and application of conducting polymers for use as biosensors are the particular emphasis of this paper. Biocompatibility is briefly discussed.

Polypyrrole-based amperometric flow injection biosensor for urea

Abstract A novel flow injection amperometric urea biosensor, based on the incorporation of urease into a conductive polypyrrole film, has been developed. The amperometric detection of as little as 3 ppm of urea by flow injection analysis (FIA) was accomplished in 0.05 M phosphate buffer (pH 7.0) with the application of an electrode potential of 3s- 70 mV vs. Ag AgCl to the biosensor. Optimum interaction between urea and the immobilized enzyme was accomplished by use of a relatively slow flow-rate of 0.1 ml/min. Under these conditions, the amperometric response was linear between 3 and 15 mg/l. Potential interferants such as potassium nitrate and potassium chloride did not have any effect on the biosensor when present up to 0.01 M, but ammonia and ammonium ions gave similar response to that of urea. This observation confirms that the biocatalytic reaction product contained either ammonia or ammonium ions.

Fabrication of ultra-thin polypyrrole-glucose oxidase film from supporting electrolyte-free monomer solution for potentiometric biosensing of glucose

A simple electropolymerisation process is described for the fabrication of an ultra-thin ( approximately 55 nm) polypyrrole (PPy)-glucose oxidase (GOD) film in a supporting electrolyte-free monomer solution for potentiometric biosensing of glucose. The optimum conditions for growing the ultra-thin film include 0.1 M pyrrole, 55-110 U/ml GOD, an applied current density of 0.05 mA/cm(2) and an electrical charge of 25 mC/cm(2). Long-term storage of the biosensor in acetate buffer improved the sensitivity of the biosensor by a factor of approximately two. The biosensor can also be used repeatedly for over 2 months with little or no loss in sensitivity. The interference effect of ascorbic acid was successfully reduced by inclusion of an outer PPy-Cl layer.

Polypyrrole-based potentiometric biosensor for urea Part 1. Incorporation of urease

Abstract A method is described for the incorporation of urease into a polypyrrole film by galvanostatic polymerisation on gold-coated plastic films and solid gold electrodes. The presence of urease in the polypyrrole film was verified by x-ray photoelectron spectroscopy, amino acid analysis, scanning microscopy and cyclic voltammetry. The enzyme activity in the polypyrrole-urease film was confirmed by its catalytic conversion of urea to carbon dioxide and ammonia. The use of both spectrophotometric and potentiometric methods for the detection of the catalytic activity of the polypyrrole-urease film and their potential use for the determination of urea is discussed.

Polypyrrole-based potentiometric biosensor for urea Part 2. Analytical optimisation

Abstract A novel potentiometric biosensor for urea, based on the entrapment of urease into a polypyrrole film, has been developed via galavanostatic film formation. The electrochemical polymerization was achieved by the application of a current density of 0.5 mA cm −2 to a working platinum disc electrode for 3 min in a solution containing 0.5 M pyrrole and 4000 μ ml −1 urease. The optimum conditions for the reliable performance of this sensor were 1 mM phosphate buffer at pH 7.0 and 35°C. A Nerstein response was observed for increasing concentration of urea in the linear range of 0.5 to 100mM. Trace concentrations of Hg 2+ and K + were both found to inhibit the response of the biosensor.

In-situ electrochemical studies on the redox properties of polypyrrole in aqueous solutions

Two electropolymerization techniques have been used in preliminary research on polypyrrole, such as potential cycling and galvanostatic modes. The cyclic voltammograms and chronopotentiograms can describe the proceeding of the growth of polypyrrole from various aqueous solutions. The cyclic voltammetry of a polypyrrole film in an electrolyte solution can further characterize the polypyrrole films electrochemically. Some evidence has been shown of doping with cations. Polypyrrole differs with respect to the extent of oxidation, doping anions, and also reduction, doping cations. Such properties can be switched dynamically between anion and cation coupling or hopping through electrochemical oxidation and reduction of the polypyrrole backbone.

Constant current cathodic stripping potentiometric determination of arsenic on a mercury film electrode in the presence of copper ions

Abstract A method is described for the cathodic stripping potentiometric determination of arsenic on a mercury film electrode in 1xa0M HCl which contained copper (II) ions. Optimum determination of arsenic in this medium was accomplished with an electrolysis potential of −600xa0mV vs Ag/AgCl (1xa0M HCl) and application of a small constant reducing current (−1.5xa0μA) during the stripping step. As little as 2xa0μg/l of arsenic can be detected by this method in the presence of 5xa0mg/l copper (II) ions with an electrolysis time of 30xa0s. A linear concentration range of 10–200xa0μg/l was achieved under these conditions. Effective reduction of As(V) to As(III) in water, bovine liver and dogfish muscle samples was accomplished with l -cysteine prior to the CSP determination of arsenic.

Evaluation of some wet decomposition methods for mercury determination in biological and environmental materials by cold vapour atomic absorption spectroscopy

Four of the most commonly used wet digestion methods were evaluated for the accurate determination of mercury in biological and environmental materials by cold vapour atomic absorption spectroscopy. The method based on the ue of HNO3-H2SO4 mixture was found to be most suitable for the reliable determination of the element. The recovery efficiencies of the method for mercury in fish homogenate and horse kidney samples were 95.9 and 105.7%, respectively for the inorganic form, and 89.0 and 99.8% for the organic form. The method based on the use of HNO3-H2O2 mixture also gave similar recoveries for the organic and inorganic mercury in these samples. In comparison, the recoveries of the organic mercury in the fish and kidney samples by the use of HNO3 only and HNO3-HClO4 mixture were < 50%, but their recovery efficiencies for the inorganic mercury were close to 100%. The application of the method utilizing the HNO3-H2SO4 mixture to a range of biological and environmental standard reference materials gave the most accurate and reproducible analytical data. The suitability of the digestion method for the reliable determination of mercury in soil samples was also demonstrated.

Study on the formation of the Prussian blue films on the polypyrrole Surface as a potential mediator system for biosensing applications

Abstract The formation of a Prussian blue film under and above a polypyrrole film containing formate dehydrogenase and β-nicotinamide adenine dinucleotide has been investigated by electrochemical quartz crystal microbalance and cyclic voltammetry techniques. Two different deposition mechanisms of Prussian blue were identified and explained when the polypyrrole coated substrate electrode was used. Very stable current and frequency responses were obtained when the Prussian blue film was deposited under the polypyrrole film. This layered structure is potentially useful in solving the leakage problems of a biosensing system involves immobilised mediator. This advantage has been demonstrated using a formate biosensor fabricated with the enzyme, formate dehydrogenase, a co-factor, β-nicotinamide adenine dinucleotide and a Prussian blue mediator.

Electroimmobilisation of sulphite oxidase into a polypyrrole film and its utilisation for flow amperometric detection of sulphite

The immobilisation of sulphite oxidase into a polypyrrole film by galvanostatic polymerisation has been investigated. The properties of the film were characterised by radiolabelling technique, cyclic voltammetry, resistometry, electrochemical quartz crystal microbalance, scanning electron microscopy and atomic force microscopy. The radiolabelling measurements revealed that the amount of enzyme incorporated into the polypyrrole film is influenced by the enzyme concentration, film thickness and current density. The interaction of sulphite with the immobilised enzyme was confirmed by cyclic voltammetry, resistometry and electrochemical quartz crystal microbalance. Quantification of sulphite can be made from the amperometric response resulting from this interaction by flow injection analysis.