Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1989-07-19
1990-11-06
Kaplan, G. L.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
357 25, 435291, 435517, G01N 2726, C12M 134, C12Q 100
Patent
active
049684000
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an enzyme sensor and, more particularly, to an enzyme sensor for measuring the concentration of a biological substrate by potentiometric response.
BACKGROUND ART
Examples of enzyme sensors known in the art are glucose sensors, urea sensors and uric acid sensors. These sensors are for measuring the concentration of a biological substrate after the concentration of hydrogen peroxide (H.sub.2 O.sub.2) produced by an enzyme reactor or the concentration of oxygen (O.sub.2) consumed by the reaction is measured amperometrically using an oxygen sensor or hydrogen peroxide sensor. For this reason, enzyme sensors generally are difficult to miniaturize. Another drawback is that these sensors cannot be utilized in enzyme reactions that are not accompanied by the consumption of oxygen or the production of hydrogen peroxide. One expedient for solving these problems is a sensor which determines the concentration of a biological substrate by measuring a change in pH that accompanies the progress of an enzyme reaction.
In recent years attempts have been made to fabricate miniature enzyme sensors by utilizing ISFET (ion-selective field-effect transistor)-type pH sensors. However, the adhesion between an enzyme film and the surface of a gate insulating film (such as a film of Si.sub.3 N.sub.4, Al.sub.2 O.sub.3 or Ta.sub.2 O.sub.5) used in these ISFET's is poor. As a result, these sensors exhibit a somewhat low sensitivity, a large amount of drift and possess but a short service life.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a miniature enzyme sensor for measuring the concentration of a biological substrate potentiometrically, which sensor exhibits a high sensitivity, little drift and possesses a long service life.
As means for solving the foregoing problems, the enzyme sensor of the present invention comprises an insulating substrate, an electrically conductive layer coating the insulating substrate, a redox layer having an oxidation-reduction function coating a surface of the electrically conductive layer, and an enzyme-fixed layer coating a surface of the redox layer and having an enzyme fixed thereto.
In another aspect, the enzyme sensor of the present invention comprises a MOSFET, an electrically conductive layer coating a gate insulating film of the MOSFET, a redox layer having an oxidation-reduction function coating a surface of the electrically conductive layer, and an enzyme-fixed layer coating a surface of the redox layer and having an enzyme fixed thereto.
In the arrangement of the first aspect of the invention, the concentration of a biological substrate is converted into a corresponding hydrogen ion concentration by the enzyme-fixed layer, and the hydrogen ion concentration is converted into a corresponding electric field by the redox layer. The electric field thus produced is measured by the electrically conductive layer as a potential difference across the sensor and a reference electrode.
In the arrangement of the second aspect of the invention, the electric field is transmitted onto the gate insulating film of the MOSFET by the electrically conductive layer and is measured by the MOSFET.
The invention thus provides a miniature enzyme sensor for measuring the concentration of a biological substrate potentiometrically. The sensor exhibits a high sensitivity, little drift and possesses a long service life.
More specifically, the enzyme sensor of the present invention has the following advantages:
(1) Since the enzyme sensor is constructed on the gate portion of an ISFET, the sensor can be ultra-miniaturized and adapted for multiple enzymes.
(2) Since the the redox layer is used as a pH-sensitive film, sensitivity is high. (3) Since film formation is carried out by electrolytic polymerization, adhesion is excellent and film formation with good adhesion is possible even on irregular portion of the electrically conductive substrate. As a result, the sensor excels in durability and has a long lifetime.
(4) Since the enzyme is fixed
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Shimomura Takeshi
Uchida Naoto
Yamaguchi Shuichiro
Kaplan G. L.
Terumo Kabushiki Kaisha
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