Biosensor

Details Biosensor Biosensor

2002-03-26

2004-08-17

Noguerola, Alex (Department: 1753)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S403060

Reexamination Certificate

active

06776888

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a biosensor that carries out high-speed, highly-accurate, simple determination of a target object in a sample.
BACKGROUND ART
A biosensor has been proposed to determine a specific component in a sample by a simple procedure without any dilution or stirring the sample solution (Japanese Laid-Open Patent Publication No. 2-062952).
In this biosensor, an electrode system including a measurement electrode or a working electrode, a counter electrode, and a reference electrode is formed on an insulating base plate, for example, by screen printing. An enzyme reaction layer including a hydrophilic polymer, an oxidation-reduction enzyme, and an electron mediator is then formed on the electrode system. A buffer may be added to this enzyme reaction layer according to the requirements.
When a sample solution containing a substrate is added dropwise onto the enzyme reaction layer in the biosensor thus constructed, the enzyme reaction layer is dissolved to cause a reaction of the enzyme with the substrate, which results in reduction of the electron mediator. After completion of the enzyme reaction, the reduced electron mediator is oxidized electrochemically, and the concentration of the substrate included in the sample solution is calculated from the observed value of oxidation current.
In principle, the biosensor is applicable to measurement of diverse substances by selecting an appropriate enzyme that reacts with a target substance of measurement as the substrate. For example, when glucose oxidase is used as the oxidation-reduction enzyme, the biosensor is constructed to measure the concentration of glucose in blood. This is widely used as a glucose sensor. Application of cholesterol oxidase gives a biosensor that measures cholesterol in serum.
The value of serum cholesterol generally used for the index of diagnosis is the sum of the concentrations of cholesterol and cholesterol ester. The cholesterol ester is, however, not the substrate of the oxidation reaction with cholesterol oxidase. In order to measure the value of serum cholesterol as the index of diagnosis, an additional process is thus required to change the cholesterol ester to cholesterol. Cholesterol esterase is used as the enzyme that catalyzes this process.
The biosensor including cholesterol esterase and cholesterol oxidase in its enzyme reaction layer is used to measure the total concentration of cholesterol in serum.
The measurement of cholesterol is affected by cholesterol that is present in the cell membrane. The coexistence of a surface active agent with cholesterol esterase in the reaction reagent layer is preferable to enhance the reactivity. The surface active agent destroys the cell membrane in many cases, and there is a possibility that the substances inside the cell directly or indirectly affect the enzyme reaction or the electrode reaction. From this point of view, it is preferable that the enzyme reaction and the subsequent electrode reaction proceed in plasma or serum in the cholesterol sensor. In biosensors other than the cholesterol sensor, the presence of hemocytes in blood may also affect the response. It is accordingly ideal that the enzyme reaction and the electrode reaction proceed in a solution free of hemocytes.
Centrifugation is a known method to separate plasma or serum from whole blood. The centrifugation method, however, takes a rather long time and requires complicated operations.
U.S. Pat. No. 3,607,092 discloses a membrane used for testing blood. This membrane has a thin film layer that has permeability to liquids but impermeability to solids like hemocytes and giant molecules like protein. Namely this thin film functions to filter out the hemocytes. However, since the solid component is accumulated on the thin film with the passage of blood, a large area of the thin film layer is required to obtain filtrate of a certain amount sufficient for the reaction of the biosensor. The above-mentioned thin film is thus not sufficient.
U.S. Pat. No. 4,477,575 discloses an apparatus for and a method of separating serum from whole blood passing through a glass fiber filter. The method of separating serum from whole blood with a fiber or porous filter is applicable to the biosensor. This method, however, does not make the hemocytes kept in the filter but simply slows down the flow of hemocytes for separation of plasma. In the case of application of this method to the biosensor, a certain quantity of filtered plasma or serum sufficient for the reaction in the biosensor should be obtained, before the hemocytes are flown out of the filter. For this purpose, a specific setting that satisfies this condition should be applied for the length of the filter in the direction of blood flow.
The filter satisfying this condition is disposed between one portion of the biosensor with the electrode system and the reaction reagent system and another portion of the biosensor for supplying blood as a sample to construct the biosensor having the ability of filtering the hemocytes.
FIG. 9
shows a biosensor of such construction.
FIG. 9
is a decomposed perspective view of the biosensor without the reaction reagent layer.
In the example of
FIG. 9
, silver paste is printed on an insulating base plate
101
composed of polyethylene terephthalate by screen printing to form leads
102
and
103
and the base of an electrode system. Conductive carbon paste including a resin binder is printed on the base plate
101
to form the electrode system including a working electrode
104
and a counter electrode
105
, while insulting paste is printed to form an insulating layer
106
. The working electrode
104
is connected to the lead
102
, and the counter electrode
105
to the lead
103
. The insulating layer
106
makes the exposed area of the working electrode
104
and the counter electrode
105
constant, and partly covers the leads.
The process arranges the insulating base plate
101
with the electrode system, a cover
108
with an air vent
109
, a spacer
107
, and a filter
111
having the ability of filtering hemocytes at the positional relationship shown by the one-dot chain line and joins together to assemble a biosensor. The filter
111
is cut to fit a sample solution supply pathway, which is defined by a slit
110
of the spacer
107
between the cover
108
and the insulating base plate
101
. Numeral
113
a
represents a portion at which the filter
111
is in contact with the insulating base plate. The filter
111
is disposed between the electrode system and a sample supply unit
112
on the base plate without covering over the electrode system including the working electrode
104
and the counter electrode
105
in the sample solution supply pathway.
In the biosensor having the above construction, blood added dropwise onto the sample supply unit
112
soaks into an end of the filter
111
close to the sample supply unit. In the filter, the permeation rate of hemocytes is less than the permeation rate of plasma as the liquid component, and the plasma accordingly soaks out of the end of the filter close to the electrode system. The soak-out plasma dissolves reaction reagents, which include enzymes and are carried at a specific position covering over the electrode system or on the rear face of the cover immediately above the specific position, and fills the whole sample solution supply pathway from the vicinity of the electrode system to the air vent
109
. When the whole sample solution supply pathway is filled with the liquid, the flow of the liquid in the filter
111
stops, so that the hemocytes do not reach the end of the filter close to the electrode system but are retained at the current position.
Through the filtration of hemocytes, the reaction reagent layer dissolved in plasma chemically reacts with a target component included in the plasma, cholesterol in the case of the cholesterol sensor. After elapse of a preset time, the value of electric current is measured by means of the electrode reaction. This determines the component in the plasma.
In this prior art

Affiliated with

Also associated with

Rating

Biosensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Biosensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Biosensor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3280778