ABSTRACT
Cholinesterase sensors based on glassy carbon and planar epoxy graphite electrodes modified with processed polyaniline have been developed and examined for pesticide detection. The modification of electrode surface with polyaniline provides high operational stability and sensitivity towards the pesticides investigated. The detection limits found (coumaphos, 0.002, trichlorfon, 0.04, aldicarb, 0.03, methiocarb, 0.08 mg l(-1)) make it possible to detect the pollutants in the waters on the level of limited threshold levels without sample preconcentration.
Subject(s)
Aniline Compounds/chemistry , Cholinesterases/chemistry , Enzymes, Immobilized/chemistry , Pesticides/analysis , Electrodes , Sensitivity and SpecificityABSTRACT
Glucose biosensors based on lyophilised, crystalline and cross-linked glucose oxidase (GOx, CLEC(R)) and commercially available lyophilised GOx immobilised on top of glassy carbon electrodes modified with electrodeposited Prussian Blue are critically compared. Two procedures were carried out for preparing the biosensors: (1) deposition of one layer of adsorbed GOx dissolved in an aqueous solution followed by deposition of two layers of low molecular weight Nafion(R) dissolved in 90% ethanol, and (2) deposition of two layers of a mixture of GOx with Nafion dissolved in 90% ethanol. The performance of the biosensors was evaluated in terms of linear response range for hydrogen peroxide and glucose, detection limit, and susceptibility to some common interfering species (ascorbic acid, acetaminophen and uric acid). The operational stability of the biosensors was evaluated by applying a steady potential of -50 mV versus Ag/AgCl to the glucose biosensor and injecting standard solutions of hydrogen peroxide and glucose (50 muM and 1.0 mM, respectively, in phosphate buffer) for at least 5 h in a flow-injection system. Scanning electron microscopy was used for visualisation of the Prussian Blue redox catalyst and in the presence of the different GOx preparations on the electrode surface.
ABSTRACT
An advanced potentiometric pH transducer based on processible polyaniline (PCPAn) is reported on. Both glassy carbon and screen-printed carbon electrodes modified with PCPAn by dip-coating exhibited a fully reversible potentiometric response of approximately 90 mV/pH unit over the range from pH 3 to 9. Such a significantly higher potentiometric response of PCPAn-modified electrodes as compared with those of existing devices is explained on the basis of the thermodynamics of polyaniline redox reactions. The PCPAn-based pH transducers exhibit both good operational stability and prolonged shelf life and display a negligible response toward singly charged cations. The new thick-film pH transducer was employed for designing a potentiometric biosensor for urea. In the model solution which mimics blood serum, the urea-sensitive electrode has a detection limit of 10(-5) M urea and a maximum response of approximately 120 mV. The attractive performance characteristics are advantageous over those of existing pH sensors and offer great promise for sensing and biosensing applications.
Subject(s)
Aniline Compounds/chemistry , Biosensing Techniques/methods , Hydrogen-Ion Concentration , Polymers/chemistry , Potentiometry , TransducersABSTRACT
The formation of Nafion membranes containing glucose oxidase and dimethylferrocene as a mediator was optimized using a previously reported non-aqueous enzymology approach for biosensor development. Enzyme immobilization in Nafion membranes was carried out from water-organic mixtures with a high content of organic solvent. The mediator based reagentless glucose electrode was tested in a flow injection system. The response towards glucose addition was stable: the reproducibility during 50 assays exceeded 95%. The response was linear over the glucose concentration range 0.5-50 mM.
