Method of measuring blood component, sensor used in the method, and measuring device
The present invention provides a method of measuring a component in blood, by which an amount of the component can be corrected accurately by measuring a hematocrit (Hct) value of the blood with high accuracy and high reliability and also provides a sensor used in the method. The sensor for measuring a component in blood has a first analysis portion and a second analysis portion. The first analysis portion has a first electrode system ( 11,12 ) and a reagent layer ( 14 ), and the reagent layer ( 14 ) has an oxidoreductase that acts on the component and a mediator. In the first analysis portion, the component in the blood is measured by causing a redox reaction of the component with the oxidoreductase in the presence of the mediator and detecting a redox current caused when a voltage is applied by the first electrode ( 11,12 ). The second analysis portion has a working electrode and a counter electrode, and a mediator is provided on the counter electrode but not on the working electrode. In the second analysis portion, a Hct value of the blood is measured by supplying the blood to the electrode system, applying a voltage to cause a current to flow, and detecting a value of the current. Using this Hct value, the amount of the component is corrected.
1. A measuring device for measuring a component in blood, comprising:
a sensor, comprising:
a first analysis portion for measuring the component in the blood sample, comprising an electrode system, an oxidoreductase that acts upon the component, and a mediator are provided; and
a second analysis portion for measuring a Hct value of the blood sample, comprising an electrode system that comprises a working electrode and a counter electrode, a mediator being provided on the counter electrode but not on the working electrode for measuring the Hct value, wherein
the first analysis portion measures the component in the blood with a redox reaction between the component and the oxidoreductase in the presence of the mediator by application of a voltage to the electrode system of the first analyzing portion and detecting an oxidation current or a reduction current caused to flow,
the second analysis portion measures the Hct value of the blood sample by application of a voltage to the blood supplied to the second analysis portion, and detecting a value of the oxidation current or the reduction current, and
the oxidoreductase and the mediator of the first analysis portion are present on the counter electrode of the second analysis portion;
a holder that holds the sensor;
a voltage source for the first analysis portion of the sensor;
a detector that detects an oxidation current or a reduction current of the first analysis portion;
a calculator that calculates an amount of the component from a value of the detected current of the first analysis portion;
a voltage source for the second analysis portion of the sensor;
a detector that detects an oxidation current or a reduction current of the second analysis portion;
a calculator that calculates a Hct value of the blood from a value of the detected oxidation or reduction current of the second analysis portion, the calculated amount of the component being corrected using the Hct value; and
a controller configured to direct application of a voltage by the voltage source for the first analysis portion, communicate with the detector of the first analysis portion, direct application of a voltage by the voltage source for the second analysis portion, and communicate with the detector of the second analysis portion.
2. The device according to claim 1 , wherein the working electrode and the counter electrode in the second analysis portion are provided on a common insulating base material so as to be coplanar and spaced apart from each other.
3. The device according to claim 1 , wherein the sensor further comprises a channel for leading blood to the sensor,
wherein the second analysis portion is on an upstream side and the first analysis portion is on a downstream side with respect to flow of the blood supplied from one end of the channel.
4. The device according to claim 1 , wherein the sensor further comprises a channel for leading blood to the sensor,
wherein the working electrode of the second analysis portion is on an upstream side and the counter electrode of the second analysis portion is on a downstream side with respect to flow of the blood supplied from one end of the channel.
5. The device according to claim 1 , wherein the mediator of the second analysis portion is a ferricyanide.
6. The device according to claim 5 , wherein the ferricyanide is potassium ferricyanide.
7. The device according to claim 1 , wherein the working electrode of the second analysis portion, on which the mediator is not provided, is coated with a polymeric material.
8. The device according to claim 7 , wherein the polymeric material is carboxymethylcellulose.
9. The device according to claim 1 , wherein the voltage source is controlled to apply a voltage for measuring the Hct value that is equal to or higher than a voltage causing electrolysis of water.
10. The device according to claim 9 , wherein the applied voltage for measuring the Hct value is in a range of 1 to 10 V.
11. The device according to claim 10 , wherein the applied voltage for measuring the Hct value is in a range of 1 to 6.5 V.
12. The device according to claim 1 , wherein the first analysis portion comprises a working electrode and a counter electrode.
13. The device to claim 12 , wherein at least one of the electrodes of the first analysis portion serves as the counter electrode of the second analysis portion.
14. The device according to claim 13 , wherein only the working electrode of the first analysis portion serves as the counter electrode of the second analysis portion.
15. The device according to claim 1 , wherein the mediator of the first analysis portion is a ferricyanide.
16. The device according to claim 15 , wherein the ferricyanide is potassium ferricyanide.
17. The device according to claim 1 , wherein the sensor further comprises an insulating substrate on which the first and second analysis portions are provided, and a channel for leading the blood to the analysis portions is provided on the insulating substrate, with one end of the channel being open toward an outside of the sensor so as to serve as a blood supply port.
18. The device according to claim 17 , wherein there is only one blood supply port, and
the channel branches so that ends of branched portions communicate with the first and second analysis portions, respectively.
19. The device to claim 17 , wherein the second analysis portion is located in the channel, and
the first analysis portion is located farther from the blood supply port than the second analysis portion.
20. The device according to claim 17 , wherein the sensor further comprises, a spacer and a cover, wherein the cover is disposed on the insulating substrate via the spacer.
21. The device according to claim 1 , which measures at least one component selected from the group consisting of glucose, lactic acid, uric acid, bilirubin, and cholesterol.
22. The device according to claim 21 , which measures glucose, and the oxidoreductase is at least one of glucose oxidase and glucose dehydrogenase.
23. The device according to claim 1 , wherein a polymeric material, an enzyme stabilizer, and a crystal homogenizing agent are provided on the electrode system of the first analysis portion.
24. The device according to claim 17 , wherein the sensor further comprises a blood detecting electrode,
wherein the blood detecting electrode is located farther from the blood supply port than at least one of the analysis portions so that whether or not the blood is supplied to the at least one of the analysis portions can be detected by the blood detecting electrode.
25. The device according to claim 1 , wherein the voltage source for the second analysis portion applies the voltage for measuring Hct for a period in the range of from 0.01 to 10 seconds.