Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving antigen-antibody binding – specific binding protein...
Patent
1996-01-16
1998-12-08
Saunders, David
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving antigen-antibody binding, specific binding protein...
435 4, 435 6, 435 792, 435 18, 435 25, 435817, 436 37, 436151, 436806, C12Q 100, C12Q 168, G01N 3353
Patent
active
058467440
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The concept of sensors based on an electrochemical transducer sensitised with a biological moiety, such as an enzyme, is both simple and elegant and offers the prospect of reagentless clinical analysis with minimum sample preparation. The major advantage of this approach for medical use is ease of operation, thus obviating the requirement for trained laboratory personnel to carry out the measurement. This should allow deployment of sensors in decentralised laboratories and facilitate a more rapid return of clinical information to the clinician. The net benefit Clinical Chemistry, Vol.3, Alberti, KGMM and Price, CP (eds), Churchill Livingston 1985!. However, in few cases has the concept been translated into practical working devices suitable for near patient testing. Commercially available biosensors based on electrochemical methods are generally either potentiometric or amperometric and for certain clinically important analytes, both of these techniques have drawbacks for biosensor exploitation. In order to circumvent these problems and to produce specific, sensitive techniques suitable for deployment in decentralised laboratories we have demonstrated the feasibility of constructing sensors based on polymer membranes which are modified during operation due to the changes in pH and lead to highly sensitive changes in impedance at underlying electrodes.
Techniques in relation to this type of process have been disclosed for instance, in U.S. Pat. No. 4,352,884 and EP 0 311 768. U.S. Pat. No. 4,352,884 describes a pH electrode having an acrylate copolymer coating for the immobilisation of bioactive materials which was used for the measurement of urea.
This method is only for the immobilisation of bioactive materials such as antigens, antibodies and enzymes and does not play a part in the measurement process. The use of polymer coatings on pH electrodes has a disadvantage of a small dynamic range and poor sensitivity.
EP 0 311 768 describes the modification of a semi-conductive polymer coated on the electrode which becomes more conductive as a result of a homogeneous immunoassay using enzyme conjugates. The method is based on the measurement of resistance which applies a large voltage (500 mV) to the system which may perturb it. The method appears only to cause changes up to 1 order of magnitude and is therefore not as sensitive as the method disclosed in the present invention.
In the present invention, a novel sensor format is described based on the impedance analysis of polymer coatings on electrodes, which require simple fabrication and measurement techniques. The impedance of an electrode is sensitive to a number of factors. Changes in electrode impedance are often caused by changes in double layer capacity. The double layer capacity (C.sub.dl) arises from the separation at the surface of an electrode between the electronic charges in the metal and the (mobile) ionic charges in the solution in contact with the metal. For a metal (e.g. gold) in contact with a solution of aqueous potassium chloride, this separation is due to the presence of a layer of water molecules on the metal surface. This double layer capacity may be calculated from the standard formula for a parallel plate condenser,
If instead of a layer of water molecules, there is an insulating polymer layer between the metal and the aqueous solution, equation (1) still holds, but d represents the thickness of the polymer layer.
It has now been found that the production of minute imperfections in such a polymer layer give rise to a dramatic increase in capacity which can easily be measured.
The impedance of an electrode is determined by applying a sinusoidal potential of small peak to peak amplitude (typically <10 mV) to the electrode and measuring the resultant sinusoidal current. The range of frequencies which are employed lie between 10.sup.5 Hz and 10.sup.-3 Hz. There is generally a phase difference (q) between the potential and current so that the ratio of potential to current is essentially a vector quantity (Z)
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Armstrong Ronald D.
Athey Dale
McNeil Calum J.
Mullen William Henry
Cambridge Life Sciences PLC
Saunders David
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