Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1990-07-27
1993-02-16
Niebling, John
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204403, 204415, 204416, G01N 2726
Patent
active
051868083
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a film-coated sensor and, more particularly, to a solid-film-type, miniature film-coated sensor capable of being used upon being inserted into a living body.
BACKGROUND ART
A solid-film-type film-coated sensor has long been desired in the fields of medicine and foods. Film-coated sensors of the coated wire electrode-type, in which a platinum electrode is directly coated with a polymeric film (e.g., a cellulose film), have recently appeared on the market. However, these sensors exhibit problems in terms of durability.
For example, in a solid-film-type oxygen sensor, the rate at which oxygen in a specimen solution is determined by an internal response electrode is limited. Though this problem can be solved if the film thickness of a gas-permeable membrane is reduced and the area of the responsive portion of the sensor is increased, the sensor is readily influenced by flow of the specimen solution, and this is a cause of response drift. Accordingly, in a case where a small amount (on the order of 1 .mu.l ) of a specimen solution is to be measured, it is preferred that the form of the sensor be such that the area having the oxgyen-reducing function be very small (on the order of square microns). In particular, in a case where a miniature sensor is directly inserted into a living body to continuously measure the partial pressure of oxygen in a solution containing a substance to be reduced, it is preferred that the oxygen sensor be one in which coexisting substances are excluded and only the oxygen is acted upon by the oxygen-reducing reaction efficiently by way of an oxygen-reducing membrane. It is especially desired that the sensor have a very small area also from the standpoint of excluding the coexisting substances.
With an oxygen sensor in which the gas-permeable membrane is further coated with an enzyme-fixing membrane, time is required for the permeation of oxygen gas and response time (a 90% response) takes more than one minute.
Thus, there is increasing demand for a quick-response, miniaturized film-coated sensor in which a solid film coating is readily controlled, and in which there is little drift.
Furthermore, when measurement is performed in a blood component, accurate measurement is made impossible owing to adhesion of protein to the surface of a platinum electrode.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the foregoing problems of the prior art and provide a miniature film-coated sensor in which the surface is uniform, the film coating is readily controlled and there is little drift because the sensor is not readily influenced by the flow of the specimen solution.
A further object of the invention is to provide a film-coated sensor which has a quick response and which is not readily influenced by electrode-activated substances other than substances to be measured that are present in solution. In particular, an object of the invention is to provide a film-coated sensor having a quick response of less than 10 seconds.
Thus, there is provided a film-coated sensor capable of measuring trace amounts (less than 10 .mu.l) of a sample and of performing measurement upon being directly inserted into a living body or tissue.
In order to attain the foregoing objects, a film-coated sensor according to the present invention comprises a capillary, an electrically conductive substrate connected to a lead wire at one end of the capillary and inscribed in the capillary, and a solid coating film which coats, to a predetermined depth, an end face of the electrically conductive substrate at another end, which is open, of the capillary.
The electrically conductive substrate is composed of carbon fibers, a carbon rod-shaped member, gold wire or a metal oxide.
The sectional area of the electrically conductive substrate is less than 10.sup.-5 cm.sup.2.
The solid coating film has a film which responds only to a gas or electrolyte from an activated substance of interest contained in blood or a related biological fluid.
According to the presen
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Kasai Satoru
Oyama Noboru
Shimomura Takeshi
Uchida Naoto
Yamaguchi Shuichiro
Bell Bruce F.
Niebling John
Terumo Kabushiki Kaisha
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