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Biosensor

  • US 4,950,378 A
  • Filed: 07/06/1988
  • Issued: 08/21/1990
  • Est. Priority Date: 07/17/1987
  • Status: Expired due to Term
First Claim
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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.

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