Biosensor, biosensor chip and biosensor device

1. A biosensor device, comprising:

a biosensor, comprising:

a working electrode;

a counter electrode;

a working electrode terminal;

a counter electrode terminal; and

a reference terminal;

the working electrode being connected to the working electrode terminal; and

the counter electrode being connected to the counter electrode terminal and to the reference terminal; and

a measurement circuit configured to be connected to the biosensor for performing an assay of a fluid to determine the concentration of a substance in the fluid, the measurement circuit comprising:

a first voltage application section coupled to the working electrode terminal; and

a second voltage application section coupled to the counter electrode terminal and to the reference terminal;

wherein the second voltage application section uses a voltage at the reference terminal to control a voltage applied to the counter electrode terminal.

2. The biosensor device of claim 1 , wherein the first voltage application section outputs a signal representative of the level of a current flowing through the working electrode terminal.

3. The biosensor device of claim 1 , wherein:

the connection between the counter electrode and the counter electrode terminal has a resistance; and

the second voltage application section controls the voltage applied to the counter electrode terminal so that a voltage drop caused by the resistance is compensated.

4. The biosensor device of claim 1 , wherein substantially no current flows through the reference terminal during the assay.

5. The biosensor device of claim 1 , wherein the second voltage application section comprises a first amplifier having an output coupled to the counter electrode terminal and an input.

6. The biosensor device of claim 5 , wherein the second voltage application section further comprises a second amplifier having an output coupled to the input of the first amplifier and an input coupled to the reference terminal.

7. The biosensor device of claim 1 , wherein the second voltage application section comprises an amplifier having an input coupled to the reference terminal and an output coupled to the counter electrode terminal.

8. A device configured to be connected to a biosensor for assaying a concentration of a substance in an assayed fluid based on a current flowing between a working electrode and a counter electrode of the biosensor, the device comprising:

a first terminal configured to be connected to the working electrode of the biosensor, and a second terminal and a third terminal that are configured to be connected to the counter electrode of the biosensor,

a first voltage application section coupled to the first terminal; and

a second voltage application section coupled to the second terminal and to the third terminal;

wherein:

substantially no current flows through the third terminal during the assay; and

the second voltage application section uses a voltage at the third terminal to control a voltage applied to the second terminal.

9. The device of claim 8 , wherein the first voltage application section outputs a signal representative of the level of a current flowing through the first terminal.

10. The device of claim 8 , wherein

the connection between the counter electrode and the second terminal has a resistance; and

the second voltage application section controls the voltage applied to the second terminal so that a voltage drop caused by the resistance is compensated.

11. The device of claim 8 , wherein the second voltage application section comprises a first amplifier having an output coupled to the second terminal and an input.

12. The device of claim 11 , wherein the second voltage application section further comprises a second amplifier having an output coupled to the input of the first amplifier and an input coupled to the third terminal.

13. The device of claim 8 , wherein the second voltage application section comprises an amplifier having an input coupled to the third terminal and an output coupled to the second terminal.

14. A method for assaying a concentration of a substance in an assayed fluid based on a current flowing between a working electrode and a counter electrode of a biosensor, the biosensor having a working electrode terminal connected to the working electrode, and a counter electrode terminal and a reference terminal that are connected to the counter electrode, the method comprising the steps of:

connecting the biosensor to a measurement circuit having a first voltage application section and a second voltage application section;

applying a voltage from the first voltage application section to the working electrode terminal;

applying a voltage from the second voltage application section to the counter electrode terminal;

using a voltage at the reference terminal to control the voltage applied to the counter electrode terminal by the second voltage application section; and

detecting a current flowing through the working electrode terminal.

15. The method of claim 14 , further comprising the step of outputting from the first voltage application section a signal representative of the level of the current detected in the detecting step.

16. The method of claim 14 , wherein the step of applying a voltage from the second application section comprises the step of the second voltage application section applying the voltage to the counter electrode terminal to compensate for a voltage drop caused by a resistance in the connection between the counter electrode and the counter electrode terminal.

17. The method of claim 14 , wherein substantially no current flows at the reference terminal during the assay.