Nagata, Yasuhiro;

Biosensor

An electrode refreshing arrangement of a biosensor includes a constant reverse bias voltage arranged to be supplied between a working electrode and a reference electrode, so as to thereby refresh the working electrode, that is, to remove the disturbance film or substance formed on the surface of the working electrode as a result of the enzyme reaction, thus reviving the activity of the working electrode.

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What is claimed is:

1. A biosensor comprising:

an enzyme electrode body;

a foundation electrode provided on the enzyme electrode body and including a working electrode, a counter electrode and a reference electrode;

an enzyme film provided on the surface of the foundation electrode and fixed with physiologically active material so that an electrical signal is generated in the foundation electrode on the basis of the result of the enzyme reaction to measure the density of an objective material, and an electrical circuit including:

a first operational amplifier having an inverting input and a non-inverting input and an output, said inverting input being connected to said reference electrode and said output being connected to said counter electrode;

a first constant voltage supplying means and a second constant voltage supplying means;

a switching means for selectively connecting said non-inverting input of said first operational amplifier to said first constant voltage supplying means and to ground;

a second operational amplifier having a non-inverting input and an inverting input and an output, said inverting input being connected to said working electrode and said non-inverting input being connected to said second constant voltage supplying means;

a resistance means connected between said inverting input of said second operational amplifier and said output of said second operational amplifier;

a unipolar current carrying device connected between said inverting and non-inverting inputs of said second operational amplifier and arranged to conduct current only if a potential at said inverting input of said second operational amplifier is greater than a potential at said non-inverting input of said second operational amplifier;

wherein said switching means, when selectively connecting said non-inverting input of said first operational amplifier to said first constant voltage supplying means, places the biosensor in a refresh state for refreshing said working electrode while keeping a voltage drop in a vicinity of a surface of said working electrode constant and wherein when said selecting means connects said non-inverting input of said first operational amplifier to ground, the biosensor is placed in a measuring state such that a signal present at said output of said second operational amplifier is proportional to said electrical signal generated in said foundation electrode.

2. A biosensor as recited in claim 1, wherein said second constant voltage supplying means comprises a third operational amplifier having an inverting input and a non-inverting input and an output and a constant voltage source, said constant voltage source being connected between said non-inverting input of said third operational amplifier and ground and said inverting input of said third operational amplifier being connected to said output of said third operational amplifier, wherein said output of said third operational amplifier is the output of said second constant voltage supplying means.

3. A biosensor as recited in claim 1 or 2, wherein said unipolar current carrying device comprises a diode.

4. A biosensor as recited in claims 1 or 2, wherein said reference electrode is made of silver.

5. A biosensor comprising:

an enzyme electrode body;

a foundation electrode provided on the enzyme electrode body and including a working electrode, a counter electrode and a reference electrode;

an enzyme film provided on the surface of the foundation electrode and fixed with physiologically active material so that an electrical signal is generated in the foundation electrode on the basis of the result of the enzyme reaction to measure the concentration of an objective material, and an electrical circuit including:

a first amplifier having a pair of inputs and an output, one of said inputs being connected to said reference electrode while said output is connected to said counter electrode;

a first constant voltage supplying means and a second constant voltage supply means;

a switching means for selectively connecting the other of said inputs of said first amplifier to said first constant voltage supplying means and to ground;

a second amplifier having a pair of inputs, one of which being connected to said working electrode while the other of which is connected to said second constant voltage supplying means;

a unipolar current carrying device connected between said inputs of said second amplifier and arranged to conduct current only if a potential at one of said inputs of said second amplifier is greater than a potential at the other of said inputs of said second amplifier;

wherein said switching means, when selectively connecting said other input of said first amplifier to said first constant voltage supplying means, places the biosensor in a refresh stat for refreshing said working electrode while keeping a voltage drop in the vicinity of a surface of said working electrode constant and wherein when said selecting means connects said other input of said first amplifier to ground, the biosensor is placed on a measuring state such that a signal present at said output of said second amplifier is proportional to said electrical signal generated in said foundation electrode.

6. A biosensor as recited in claim 5, wherein said second constant voltage supplying means comprises a third amplifier having a pair of inputs and an output and a constant voltage source, said constant voltage source being connected between one of said pair of inputs of said third amplifier and ground and the second of said pair of inputs of said third amplifier being connected to said output of said third amplifier, wherein said output of said third amplifier is the output of said second constant voltage supplying means.

7. A biosensor as recited in claims 5 or 6, wherein said unipolar current carrying device comprises a diode.

8. A biosensor as recited in claims 5 or 6, wherein said reference electrode is made of silver.