Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1997-10-17
2000-07-04
Tung, T.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204400, 427 213, G01N 2726
Patent
active
060833661
DESCRIPTION:
BRIEF SUMMARY
This invention relates to sensors for analytes present in solution.
Conductimetric sensors based on redox state dependent conducting organic polymers such as polypyrrole, polyaniline and polyindole are well known. Such sensors commonly comprise a layer of the conducting organic polymer bridging two closely spaced electrodes, and commonly rely upon the detection of changes in the resistance or ac impedance of the polymer. This change in resistance is caused by the interaction between the analyte--which may be present in solution or in the gas phase--and the polymer. An important area of application lies in the incorporation of enzymes into the organic polymer to produce `biosensors` capable of quantitative sensing of biologically significant analytes. Exposure of the enzyme to the analyte induces catalytic activity which in turn induces conductivity changes within the enzyme trapping polymer matrix. Although the precise nature of the conductivity changes are unclear--and may well differ with different combinations of polymer and enzyme--local H.sup.+ concentration effects and, in the case of oxidases, ketones and aldehydes, H.sup.2 O.sup.2 generation have been implicated. Broadly speaking, the conductivity of the polymer is perturbed by the redox behaviour of the enzyme on exposure to the analyte. Since enzyme-substrate interactions are typically very specific, the associated biosensor represents a highly selective method of analyte detection.
However, it is usually only possible to bridge the electrodes by electrochemical growth of organic polymer if the electrodes are rather closely spaced (typically <20 .mu.m). This upper limit imposes restrictions on the magnitude of the measured signal and also requires precise electrode geometries which in turn requires technically demanding and expensive fabrication procedures such as screen printing or silicon chip fabrication techniques.
An appealing alternative which circumvents the problem of precise electrode alignment would involve measuring the impedance or admittance of a polymer bridging an analyte solution and a planar working electrode; in such an arrangement measurements would be made in the {working electrode.fwdarw.polymer.fwdarw.analyte solution.fwdarw.counter electrode} plane. Detection of the analyte would be accomplished by detecting changes in the impedance or admittance of the polymer induced by interaction between the polymer and the analyte. However, the linear mass transport regime operating in this arrangement would inevitably result in a detection signal of insufficient magnitude for useful measurement.
The present invention is based upon the concept of incorporating within the above described arrangement a working electrode assembly which comprises an array of conducting organic polymer coated micro-electrodes. Such an electrode results in radial transport of the analyte, rendering feasible the use of the arrangement as a sensor.
The present invention further provides examples of such arrays of micro-electrodes and methods of fabricating same.
International Publication WO 91/08474 describes a method for fabricating a microelectrode by photoablation. The microelectrode was used in an amperometric assay method for the detection of heavy metals.
According to one aspect of the invention there is provided a sensor for an analyte comprising a working electrode assembly itself comprising a micro-electrode array in which each micro-electrode is coated with a layer of redox state dependent conducting organic polymer; a counter electrode; a conductive medium containment into which the electrodes are disposed and a material for analysis may be introduced; means for applying an alternating electric polarising potential across the electrodes; and means for detecting a variation in a conductimetric property across the {working electrode.fwdarw.counter electrode} plane in the presence of the analyte.
The conductive medium containment may comprise a conducting solution.
The conductimetric property may be the impedance across the {working electrode.fwdarw
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Noguerola Alex
The Manchester Metropolitan University
Tung T.
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