Comparison of enzyme immobilisation methods for potentiometric phosphate biosensors.

The development of two phosphate biosensors is described and compared for potentiometric detection of phosphate. Purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) were co-immobilised by chemical cross-linking with glutaraldehyde (GLA) and bovine serum albumin (BSA), and via entrapment into polypyrrole (PPy) films by galvanostatic polymerisation. The BSA-GLA film was made with 4.5% v/v GLA and 6.8% w/v BSA with a drying time of 30 min, while polypyrrole entrapment was achieved with 0.5M pyrrole by using a polymerisation time of 200s. A mole ratio of 1:8 (6.2U/mL XOD: 49.6 U/mL PNP) was used for both methods of enzyme immobilisation. Sensitive potentiometric measurements obtained for phosphate with the BSA-GLA-PNP-XOD biosensor were compared with those of PPy-PNP-XOD-Fe(CN)(6)(4-) biosensor. A minimum detectable concentration of 0.1mg/L phosphate and a linear concentration range of 0.5-2.5mg/L were achieved with the PPy-PNP-XOD-Fe(CN)(6)(4-) biosensor. In comparison, a minimum detectable concentration of 2mg/L and a linear concentration range of 4-12 mg/L were achieved with the BSA-GLA immobilisation. The presence of uric and ascorbic acids had the least effect on the performance of the PPy-PNP-XOD-Fe(CN)(6)(4-) biosensor, but will not have any effect on phosphate measurement with both biosensors at levels normally present in water.

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.

Slurry sampling for hydride generation atomic absorption spectrometric determination of arsenic in cigarette tobaccos.

The development of a slurry sampling hydride generation atomic absorption spectrometric (HGAAS) method for the determination of arsenic in cigarette tobacco samples is described. The method is relatively simple and has been shown to give values of total arsenic close to those obtained using methods requiring total dissolution and decomposition of all vegetable matter before analysis. Pre-treatment of samples slurried in nitric acid by ultrasonication permitted the extraction of about 90% of the total arsenic from tobacco samples. Further improvement in the recovery efficiency (up to 93-94%) was accomplished by the use of an additional step of short microwave-accelerated treatment. L-Cysteine was used as a pre-reduction agent. The accuracy and precision of the slurry sampling HGAAS method were studied using the certified reference material (CRM) CTA-OTL-1 Oriental Tobacco Leaves. Under the optimum conditions, as little as 2.6 ng of arsenic can be detected. The relative standard deviation of the overall procedure was calculated to be below 7.6% at arsenic concentration levels of 0.5-0.9 mg kg-1 and the analytical results obtained for the CRM agreed with the certified value. The main factors that influenced the reliability of the method were sample homogeneity, particle size and slurry concentration.

Conducting polymers and the bioanalytical sciences: new tools for biomolecular communication. 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.

Voltammetric determination of platinum in inorganic complexes and in water, geological and biological matrices using laboratory- and field-based instrumentation.

The extremely sensitive catalytic hydrogen ion reduction wave observed after the formation of a platinum-formazone complex at a mercury electrode in a hydrazine-formaldehyde-H2SO4 medium has been utilised to determine platinum voltammetrically in well characterised platinum inorganic complexes (oxidation states O, II and IV) and in biological, geological and water samples. Experimental conditions have been optimised and sample-treatment procedures for various matrices have been critically evaluated for the quantification of platinum by the standard additions method. The determination of platinum in geological samples by this method has been compared with an inductively coupled plasma mass spectrometric method. Both conventional and portable field-based instrumentation have been used in the studies, and the possibility of developing a field-based method for the determination of platinum has been investigated. Despite the inherent sensitivity of the method, which enables concentrations down to 0.01 p.p.b. to be detected in simple matrices, natural levels in water and biological materials, where matrix effects suppress the voltammetric response, are often below the detection limit.