Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For corrosion
Patent
1997-06-11
1998-12-15
Bell, Bruce F.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For corrosion
2057775, 205778, 2057905, 205791, 205792, 2057935, 204403, 204415, 422 8201, 422 8202, 4352871, 4352891, 435817, G01N 2726
Patent
active
058491740
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application is a 371 of PCT/GB95/01818 filed on Aug. 1, 1995.
This invention relates to electrochemistry and in particular to novel electrode structures and their use in analysis for the detection of enzymes or their substrates. The invention is of particular utility in sensors for biomedical applications.
2. Description of the Related Art
There is a continuing need for improved immunoassay techniques particularly for the detection of low levels of analytes in small samples.
In recent years, a number of electrochemical techniques have been developed in the hope of avoiding the generally conventional use of radioisotope labels for the detection of low levels of analytes. Direct amperometric measurements of NADH and of phenol has been reported by Wright et al Anal. Chem., 58(1986) 2995 and by Wehmeyer et al Anal. Chem., 58(1986) 135 employing enzyme-labelled antigens. The use of redox-labelled drug conjugates, specifically ferrocenyl-lidocaine for similar direct amperometric measurements has also been reported by Di Gleria et al Anal. Chem. 58(1986) 1203. These direct amperometric measurement techniques tend to suffer from a sensitivity limitation and in general the techniques are limited to low micromolar concentration ranges.
Chambers and Walton in J. Electroanal. Chem., 250(1988) 417-425 report use of a poly(vinylferrocene)-modified glassy carbon electrode used as a charge-accumulating device to a accumulate charge from a solution of glucose/glucose oxidase via the intermediary of a redox-labelled antigen, which is cycled repeatedly between the enzyme and the electrode. Chambers and Walton were able reproducibly to detect 1,1'-dimethylferrocene-3-ethan-1-ol-2-amine at nanomolar concentrations. Although Chambers and Walton identified 8-ferrocenyl-theophylline as their preferred redox-active mediator for further work, they found that it possessed a significant disadvantage in that it appeared to be bound unspecifically to anti-theophylline antibodies and so was not ideal for use in a competitive immunoassay.
A different approach has been adopted by Bartlett and Birkin, (Anal. Chem. 1993, 65, 1118-1119), namely the production of a DC bioelectrochemical transistor in the form of an enzyme switch. In this prior enzyme switch system, to provide a switch responsive to glucose, glucose oxidase was immobilized in a thin insulating film of poly(1,2-diaminobenzene) deposited on top of a poly(aniline) film deposited across a gap between two carbon electrodes. The change in conductivity of poly(aniline) between its oxidised and reduced states is measured by applying a small DC voltage from one carbon electrode to the other across the film and is used to measure the presence of redox mediator shuttling charge between the enzyme and polymer film. One drawback of this system is the need to form a polymer film which bridges the two electrodes, taking into account the minimum distance which can be tolerated between the electrodes.
SUMMARY OF THE INVENTION
The present invention has arisen from the work of the present inventors in seeking to improve upon the prior techniques.
As will be seen from the detailed description below, the methods and apparatus of the present invention draw upon the technology developed in connection with the prior enzyme switches, but apply this technology in a quite new way, namely in an alternating current system using a single polymer coated electrode.
In accordance with a first aspect of the present invention, there is provided a method for indicating the concentration of a substance in solution comprising passing an alternating voltage between a first electrode structure having coated thereon a polymer, the polymer being in one of an oxidised and a reduced state between which states its conductivity varies, and a second separate counter electrode in said solution; and measuring the change in conductivity of the polymer coating, such measurement being representative of the state of the polymer and thereby of the concentration of sai
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Bartlett et al., "Enzyme Switch Responsive to Glucose," Anal. Chem. 1118 (1993) No Month Available.
Bartlett, "Modified Electrode Surface in Amperometric Biosensors," MBEC Biosensors special feature, p. B10, (May 1990).
Chambers et al., The Development of Redox-Modified Electrodes as Charg-Accumulating Devices For Use In Higher Sensitivity Detection Systems, J. Electroanal. Chem. 250:417 (1988) No Month Available.
DiGleria et al., "Homogeneous Ferrocene-Mediated Amperometric Immunoassay," Anal. Chem. 1203 (1986) No Month Available.
Wehmeyer et al., "Competitive Heterogeneous-Enzyme Immunoassay for Digoxin with Electrochemical Detection," Anal. Chem. 135 (1986) No Month Available.
Wright et al., "Digoxin Homogeneous Enzyme Immunoassay Using High-Performance Liquid Chromatographic Column Switching with Amperometric Detection," Anal. Chem. 295 (1986 ) No Month Available.
Bartlett Philip Nigel
Birkin Peter Robert
Sanghera Gurdial Singh
Bell Bruce F.
MediSense, Inc.
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