Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1998-04-16
2001-04-10
Beisner, William H. (Department: 1744)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S415000, C205S778000, C435S287900, C435S288700
Reexamination Certificate
active
06214185
ABSTRACT:
The present invention is concerned with a sensor (biosensor) for the determination of the concentration and the detection of an enzyme substrate in a liquid sample, which sensor comprises an enzyme capable of reacting with said enzyme substrate while producing a substance directly or indirectly detectable, a detection device and a cover membrane or cover layer from a polymer permeable to the enzyme substrate.
BACKGROUND OF THE INVENTION
Today, sensors provided as amperometric sensors or enzyme electrodes or as optical sensors (optodes) are widely used to determine the amount of or to detect certain substances such as glucose, oxygen, CO
2
, in the blood and in other body liquids.
The construction and the function of an amperometric enzyme electrode is known for example from EP-A 0 603 154 of the applicant. The construction and the function of an optode is known for instance from Biosensors & Bioelectronics 5(1990) pp 137-148.
Amperometric sensors for the determination of glucose, lactate or creatinine are preferably constructed with oxidoreductases and a detection device to determine hydrogen peroxide (base electrode). They function in such a way that the oxidase such as glucose oxidase, lactate oxidase and sarcosin oxidase oxidizes the analyte to be determined with oxygen to the correspondent oxidation product and hydrogen peroxide, the concentration of hydrogen peroxide produced being proportional to the concentration of the analyte and being measured by anodic oxidation at approximately 650 mV versus Ag/AgCl at stainless steel or carbon electrodes (base electrodes). Alternatively, measuring may also be carried out at electrodes having a catalytical effect such as platinized carbon and mangane dioxide, at a reduced oxidation voltage (approximately 300 mV).
Further possibilities of determination are measuring the oxygen consumption or using mediators which may be measured by oxidation at the electrode instead of the hydrogen peroxide and also serve, in an oxidized form, as a substitute for oxygen.
The classical amperometric sensor comprises four layers: a base electrode, an interference-blocking layer, an enzyme layer and a cover membrane or cover layer respectively. This construction is schematically shown in the attached
FIG. 1
, reference number
1
indicating an electroconductive layer, e.g. from silver, applied onto a support (not shown). The base electrode
2
is applied onto the electroconductive layer
1
. On top of the base electrode
2
, the interference-blocking layer
3
, the enzyme layer
4
and the cover membrane
5
are provided. The cover membrane
5
is in contact with the sample.
The interference-blocking layer
3
of an amperometric sensor serves to keep away from the electrode any electroactive substances of the sample such as paracetamole, uric acid, ascorbic acid, which may be oxidized directly at the electrode surface and thus show wrong, excessive signals. As the interference-blocking layer, layers from cellulose acetate and polyphenylene diamine are of preferred use, the polyphenylene diamine layer being produced by polymerisation of phenylene diamine directly onto the base electrode. Unplasticised polyvinyl chloride (PVC) and nafion may also be applied directly from their solution.
As the cover layer
5
, a polycarbonate membrane made microporous by etching is frequently used, the pore width typically being 0.03&mgr;m at a porosity of less than 5%. This cover membrane is biocompatible and limits diffusion due to its reduced porosity, but does not prevent enzymes from being transported through the pores. To improve the diffusion properties, this layer is frequently laminated and/or additionally coated. By wetting with hydrophobe plasticisers, a so-called supported liquid membrane may be prepared.
A cover layer
5
of a porous polycarbonate membrane has the drawback of being incapable of sufficiently protecting the underlying enzyme layer
4
from proteases. Moreover, it is incapable of preventing the washing out of enzymes from the enzyme layer
4
, since enzymes are capable of diffusing through pores 0.03 &mgr;m wide.
Cover layers are often mechanically attached to the enzyme layer. When the cover layer is combined with the enzyme layer, this layer has to be mechanically attached to the base electrode. Such mechanical attachments are expensive, technically complex and frequently cause problems insofar as it is difficult to apply the membrane onto the underlying layer without producing air bubbles. This usually restricts the constructive freedom when designing sensors, since an embossed electrode surface is required to attach a membrane under mechanical tension to the electrode. The tension required frequently causes fissures and creases. Additionally, sheet membranes are relatively thick, and therefore the sensors produced have comparatively low electric currents and long response times.
To prepare the cover membrane it is further known to apply a solution of the polymer onto the enzyme layer and to evaporate the solvent. Thus for example, cover membranes of nafion, PVC, polyurethane, silicone, polyacrylate (p-HEMA) and cellulose acetate which stick to the underlying layer without any mechanical attachment, i.e. only by adhesion, may be prepared.
The polymers used so far which may be applied directly from their solution onto the enzyme layer or the electrode include only a few, such as nafion and cellulose acetate, which are selective towards electrochemically active interferents. Additionally, many polymers are soluble only in volatile, aggressive or toxic solvents, such as cellulose acetate in DMSO and acetone, and PVC in tetrahydrofurane and cyclohexanone. This circumstance is relevant for the production process as well as for safety reasons. It is also relevant for the electrode itself, since plastic portions may be deteriorated or enzymes present in the enzyme layer may be destroyed by these solvents. From plasticised PVC, plasticisers may diffuse into surrounding plastic portions or into the enzyme layer.
Another drawback consists in that in most polymers, particularly in plasticised PVC, permeability to the analytes such as glucose or lactate may be adjusted only by varying the layer thickness, since permeability is primarily due to faults in the membrane and the porosity thus produced. Even slight differences in the layer thickness may cause a total loss in permeability.
SUMMARY OF THE INVENTION
It is the object of the present invention to overcome the drawbacks cited above in a sensor mentioned above and in particular to provide a sensor wherein it is not necessary to mechanically attach the cover layer. Moreover, when applying the cover layer from the solution, none of the aggressive, toxic or extremely volatile solvents used in the state of the art are to be employed.
The sensor according to the invention for the determination of the concentration and the detection of an enzyme substrate in a liquid sample, which sensor comprises an enzyme capable of reacting with said enzyme substrate while producing a substance directly or indirectly detectable, a detection device and a cover membrane of a polymer permeable to the enzyme substrate is characterised in that said polymer is a polyvinyl chloride copolymer, i.e. a copolymer of vinyl chloride and a further monomer, which copolymer comprises hydrophilic groups. The copolymer used according to the invention to prepare the cover membrane may be a block copolymer, an alternating copolymer or a random copolymer.
As the hydrophilic groups, hydroxy, ester and/or carboxyl groups , are preferred.
The PVC copolymer used according to the invention is easily soluble in high-boiling esters. This permits an automatized discharge for several hours. In contrast, pure PVC is usually dissolved in tetrahydrofurane, which due to its high volatility does not permit a reproducible, automatized mass production.
A further advantage is that the dissolved polymer may be applied from this solution directly onto the enzyme layer. Inactivation of the enzyme layer caused by the cover layer according to the invention is v
Dolezal Andreas Martin
Offenbacher Helmut
Pestitschek Gabriela
Schaffar Bernhard Peter Harald
Wiedner Nicole
AVL Medical Instruments
Baker & Botts L.L.P.
Beisner William H.
LandOfFree
Sensor with PVC cover membrane does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sensor with PVC cover membrane, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sensor with PVC cover membrane will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2457327