JP7576528B2 - Measurement method and device - Google Patents

Description

The present invention relates to a measurement method and a measurement device for measuring a measurement target in blood.

The techniques disclosed in Patent Documents 1 and 2 measure the glucose concentration using a pair of glucose electrodes that are provided with a reagent for measuring glucose in a flow path of an analytical tool (biosensor), and correct the glucose concentration using a hematocrit value measured using a pair of hematocrit electrodes that are not provided with such a reagent.

The technology disclosed in Patent Document 3 involves preparing multiple working electrodes in the flow path of a biosensor, using one of the working electrodes to measure the amount of blood components, and using the other working electrodes to measure the amount of blood cells (hematocrit) and the amount of interfering substances, thereby measuring the amount of blood cells and the amount of interfering substances, and using this to correct the amount of blood components.

In the technology disclosed in Patent Document 4, the counter electrode, measurement electrode, and detection electrode are formed along the sample supply path of the biosensor in the direction of sample flow from the sample supply port, with the detection electrode being the most downstream electrode, and whether or not a sufficient amount of sample liquid required for measurement has been supplied is determined based on whether or not the currents output from the first and second sets of electrodes exceed a predetermined threshold value, and if the current from the second set does not exceed the predetermined threshold value within a predetermined elapsed time after the current from the first set exceeds the predetermined threshold value, it is determined that there is a shortage of sample liquid.

The technology disclosed in Patent Document 5 discloses a method for detecting blood using alternating current.

JP 2014-232102 A JP 2019-35748 A Patent No. 4689601 WO 02/44705 A1 Special Publication No. 2001-527215

The objective of the embodiment of the present disclosure is to detect whether an appropriate amount of blood has been applied to a biosensor correctly in a measurement method that uses a biosensor to measure a measurement target in blood.

One aspect of the present disclosure is a measurement method for measuring a measurement target using a biosensor having a flow path into which blood containing a measurement target is introduced, a first electrode pair consisting of a first working electrode and a first counter electrode formed in the flow path to measure the measurement target in the blood, a second electrode pair formed upstream of the first electrode pair in the flow path and consisting of a second working electrode and a second counter electrode, a blood detection electrode formed downstream of the first electrode pair in the flow path, and a reagent placed on at least the first working electrode and reacting with the measurement target, the first conductor being the introduction of blood up to the first upstream electrode between a second downstream electrode, which is the electrode located downstream of the second electrode pair, and a first upstream electrode, which is the electrode located upstream of the first electrode pair and on which a reagent is placed. The method includes a first detection step of detecting the introduction of blood, a second detection step of detecting the introduction of blood to the blood detection electrode between the reference electrode, which is one of the electrodes of the first electrode pair, and the blood detection electrode, a time determination step of determining whether the time from the detection of the first introduction to the detection of the second introduction is equal to or less than a predetermined time threshold, a first measurement step of acquiring first information related to the object to be measured using the first electrode pair, a second measurement step of acquiring second information related to the object to be measured using the second electrode pair, a calculation step of calculating the concentration of the object to be measured from the first information and the second information if the determination in the time determination step is equal to or less than the predetermined time threshold, and an error processing step of performing error processing if the determination in the time determination step exceeds the predetermined time threshold.

According to an embodiment of the present disclosure, in a measurement method that uses a biosensor to measure a measurement target in blood, it is possible to detect that an appropriate amount of blood has been applied correctly to the biosensor.

1 is a perspective view showing an external appearance of a measuring device according to an embodiment; FIG. 1 is a schematic diagram showing a schematic configuration of a biosensor. FIG. 2 is a block diagram showing the functions of the measuring device. 4 is a flowchart showing an example of a measurement method according to the embodiment. 1 is a graph showing the relationship between pulse voltage application and the corresponding response current. 13 is a graph showing the reduction rates of response current values in patterns 2 and 3 relative to pattern 1.

The following describes a measurement method and a measurement device according to an embodiment of the present disclosure. In the following description, the "upstream side" and the "downstream side" are defined according to the direction in which blood applied to the biosensor flows in the flow path.

(1) Measurement Method The measurement method according to this embodiment is a method for measuring a target substance using a biosensor having: a flow path into which blood containing a target substance is introduced; a first electrode pair consisting of a first working electrode and a first counter electrode formed in the flow path in order to measure the target substance in the blood; a second electrode pair formed upstream of the first electrode pair in the flow path and consisting of a second working electrode and a second counter electrode; a blood detection electrode formed downstream of the first electrode pair in the flow path; and a reagent placed on at least the first working electrode and reacting with the target substance. The measurement method includes introducing blood up to the first upstream electrode between a second downstream electrode which is the electrode located downstream of the second electrode pair, and a first upstream electrode which is the electrode located upstream of the first electrode pair and on which a reagent is placed. The method includes a first detection step of detecting a first introduction, a second detection step of detecting a second introduction, which is the introduction of blood to the blood detection electrode, between a reference electrode which is one of the first electrode pair and the blood detection electrode, a time determination step of determining whether the time from the detection of the first introduction to the detection of the second introduction is equal to or less than a predetermined time threshold, a first measurement step of acquiring first information related to the object to be measured using the first electrode pair, a second measurement step of acquiring second information related to the object to be measured using the second electrode pair, a calculation step of calculating the concentration of the object to be measured from the first information and the second information if the determination in the time determination step is equal to or less than the predetermined time threshold, and an error processing step of performing error processing if the determination in the time determination step exceeds the predetermined time threshold.

The measurement target refers to a chemical component contained in blood, such as glucose (blood glucose) or lactate (lactic acid). The first electrode pair is composed of a first working electrode and a first counter electrode, and a reagent is placed on at least the first working electrode, and preferably the entire surface of the first working electrode exposed to the flow path is covered with the reagent. The reagent is a chemical substance that reacts with the measurement target, and may include, for example, an enzyme and a mediator. The reagent may be placed on the first counter electrode, but must not come into contact with the electrodes constituting the second electrode pair located upstream of the first working electrode. The second electrode pair is located upstream of the first electrode pair and is composed of a second working electrode and a second counter electrode.

The electrode of the second electrode pair located downstream, in other words, the electrode closer to the first electrode pair, is the second downstream electrode. In the second electrode pair, either the second working electrode or the second counter electrode may be located upstream, but when the second working electrode is located downstream, the second working electrode becomes the second downstream electrode, and when the second counter electrode is located downstream, the second counter electrode becomes the second downstream electrode. On the other hand, in the first electrode pair, the electrode located upstream and on which the reagent is placed is the first upstream electrode. Here, in the first electrode pair, when the reagent is placed only on the first working electrode, the first working electrode is provided on the upstream side, and this first working electrode becomes the first upstream electrode. On the other hand, in the first electrode pair, when the reagent is placed on both the first working electrode and the first counter electrode, the first counter electrode may be provided on the upstream side, in which case the first counter electrode becomes the first upstream electrode. When electrical conduction occurs between the second downstream electrode and the first upstream electrode via blood, a first introduction is detected, which means that blood has been introduced up to the first upstream electrode. The process of detecting this first introduction is the first detection process.

This first detection step preferably includes a step of applying a pulse voltage between the second downstream electrode and the first upstream electrode, a step of measuring a peak value of a response current corresponding to the applied pulse voltage, and an introduction detection step of judging whether or not the measured peak value exceeds a predetermined current threshold, and detecting the first introduction when the number of times the peak value exceeds the predetermined number of times or more. That is, when measuring the peak value of the response current with a pulse wave generated by a pulse voltage, a higher value can be obtained compared to when a DC voltage of the same value is applied. For example, it is preferable that the frequency of the pulse wave is 1 to 2000 Hz (period is 0.5 ms to 1 s), the potential difference from the base to the peak of the pulse wave is 50 to 1000 mV, and the time it takes for the pulse wave to rise from the base to the peak is 30 μs or less. By making this time 30 μs or less, the peak value of the response signal can be generated with high accuracy. The above-mentioned predetermined number of times may be one time, but it is preferable that it is multiple times, or even three times, in order to avoid erroneous judgment due to a high peak value accidentally obtained by a noise component such as static electricity.

One of the electrodes in the first electrode pair is a reference electrode. The reference electrode may be the same electrode as the first upstream electrode used to detect the first introduction, but it is preferable that the electrode located downstream, not the first upstream electrode, is used as the reference electrode. When electrical conduction is established between this reference electrode and the blood detection electrode, which is the electrode located at the most downstream, via blood, the second introduction, which means that blood has been introduced up to the blood detection electrode, is detected. The process of detecting this second introduction is the second detection process. The blood detection electrode is provided near the most downstream of the flow path. Therefore, if it is detected that blood has been introduced up to the blood detection electrode, it can be considered that the entire flow path is filled with blood.

This second detection step preferably includes a step of applying a pulse voltage between the reference electrode and the blood detection electrode, a step of measuring a response current value corresponding to the applied voltage, and an introduction detection step of determining whether the measured response current value exceeds a predetermined current threshold and detecting the second introduction if it does. However, the voltage applied in the second detection step may be a DC voltage, and a determination may be made as to whether the measured response current value exceeds the predetermined current threshold.

In the time determination step, it is determined whether the time from the detection of the first introduction to the detection of the second introduction is equal to or less than a predetermined time threshold. Here, if the amount of blood applied to the biosensor is enough for the blood and the reagent to come into contact with each other, but is not enough to fill the entire flow path, and blood is applied again, the reagent dissolves during the few seconds that the blood and the reagent come into contact with each other in the first application, and the reagent that was present on the first electrode pair is swept downstream by the blood added in the second application. If the measurement of the measurement object is performed in this state, the reagent that was originally required for the reaction will be insufficient on the first electrode pair, and the response current value will be reduced. Therefore, in this embodiment, a time determination step is provided to determine whether the time from the detection of the first introduction to the detection of the second introduction is equal to or less than a predetermined time threshold, and if this determination is negative, that is, if the time from the detection of the first introduction to the detection of the second introduction exceeds the predetermined time threshold, an error process is performed in the error processing step. This error process may, for example, be a visual error message displayed on the display screen, a warning sound is generated by a voice display device, or processing is interrupted. If the amount of applied blood is insufficient and the second introduction is not detected, the time determination process determines that a predetermined time position has been exceeded, and an error processing process can be performed.

The first measurement step uses a first electrode pair to obtain first information related to the object to be measured. This first measurement step preferably includes a step of applying a DC voltage to the first electrode pair, and a step of measuring a response current value as the first information corresponding to the applied DC voltage. Furthermore, the second measurement step uses a second electrode pair to obtain second information related to the object to be measured. This second measurement step preferably includes a step of applying a DC voltage to the second electrode pair, and a step of measuring a response current value as the second information corresponding to the applied DC voltage.

The first information is the response current value applied to blood that has reacted with a reagent. The second information is the response current value applied to blood that has not reacted with a reagent. Here, since the second electrode pair is located upstream of the first electrode pair, the response current value measured by the second electrode pair is not affected by the reagent. The first information is information measured based on the reaction with the reagent, such as a glucose value or a lactate value. The second information is reference information for the first information, and specifically, information on the physical properties of blood measured without using a reagent, such as a hematocrit value. The second information may also be a response current value that is the same item as the item measured as the first information but is measured based on a different measurement principle.

In the calculation step, if the determination in the time determination step is positive, i.e., if the time from the detection of the first introduction to the detection of the second introduction is equal to or less than the time threshold, the final concentration of the object to be measured is calculated from the first information and the second information. For example, the final concentration of the object to be measured can be obtained by correcting the first information obtained as the concentration of the object to be measured with the second information obtained as reference information. Also, the final concentration of the object to be measured can be obtained by correcting the first information with the second information or by taking the average value of the first information and the second information from the first information obtained as the concentration of the object to be measured and the second information obtained as the concentration of the object to be measured using a measurement principle different from that of the first information.

(2) Measuring device An embodiment of a measuring device for carrying out the above-mentioned measuring method will be described below. FIG. 1 is a perspective view showing the appearance of a measuring device 1 according to this embodiment. In this embodiment, as an example, the measuring device 1 is a portable blood glucose meter. In FIG. 1, a portable blood glucose meter is provided as the measuring device 1, and a biosensor 2 configured to be detachable from the measuring device 1 is provided. The biosensor 2 is provided with a blood supply port 2d as an inlet of a flow path 2a so that a patient's blood as a sample can be introduced into a flow path 2a described later, and an air hole 2e for discharging air in the flow path 2a due to the introduction of blood, and is configured to have a function of detecting a blood glucose level (glucose level) in blood. The measuring device 1 shown in FIG. 1 can be used as a blood glucose meter such as a portable blood glucose meter or a blood glucose self-measurement meter.

The measuring device 1 also includes a main body 1a, which is provided with an insertion port 1b for inserting a strip-shaped biosensor 2. The main body 1a also includes a control unit 100, which is configured with, for example, a microprocessor and controls each part of the measuring device 1. As shown in FIG. 3, the main body 1a also includes a voltage applicator 50 that supplies a predetermined voltage signal to the biosensor 2 and receives a voltage signal indicating the measurement result from the biosensor 2 and performs A/D conversion, a measuring device 60 that generates measurement data indicating the measurement value, and a recording unit (not shown) that records the measurement data obtained by the measuring unit. The measurement data obtained by the measuring device 60 is recorded in the recording unit in association with the measurement time, patient ID, etc.

The main body 1a is also provided with a display screen 1c for displaying measurement data, and a connector 1d for data communication with an external device. This connector 1d is configured to transmit and receive data such as measurement data, measurement time, and patient ID between the external device, such as a mobile device such as a smartphone or a personal computer. In other words, the measurement device 1 is configured to be able to transfer measurement data and measurement time to an external device via the connector 1d, and to receive a patient ID, etc. from an external device and associate it with the measurement data, etc.

In addition to the above description, for example, the measuring device 60 may be provided at the end of the biosensor 2, and the measurement data may be generated on the biosensor 2 side. The main body 1a of the measuring device 1 may also be provided with a user interface including an input unit such as a button or a touch panel for a user such as a patient to input data. Also, the display screen 1c, recording unit, etc. may not be provided on the main body 1a, but may be provided on an external device that can be connected to the main body 1a.

Figure 2 is a schematic diagram of the biosensor 2 used in the measuring device 1 of this embodiment. In the figure, the upper side is the upstream side, and the lower side is the downstream side. In the biosensor 2, an electrode layer formed, for example, using a metal material such as gold (Au) or a carbon material such as carbon is formed on a substrate formed, for example, using synthetic resin (plastic). On the electrode layer, a spacer (not shown) having a rectangular cutout as the covering area 2b, and a synthetic resin cover (not shown) having an air hole 2e formed thereon are laminated. By laminating the substrate, spacer, and cover, a space having a blood supply port 2d formed by the cutout of the spacer is formed, and this space becomes the flow path 2a. The air hole 2e is formed near the downstream end of the flow path 2a.

In this embodiment, the electrode layer is formed so that five electrodes, the first working electrode 11 and the first counter electrode 12 as the first electrode pair 10, the second working electrode 21 and the second counter electrode 22 as the second electrode pair 20, and the blood detection electrode 30, are exposed in the flow path 2a in a rectangular shape parallel to each other in the longitudinal and transverse directions of the biosensor 2, and the first electrode pair 10, the second electrode pair 20, and the blood detection electrode 30 exposed in the flow path 2a come into contact with the introduced blood and function as a measurement region. Note that adjacent electrodes are insulated from each other. For example, when the electrode layer is formed from a metal material formed by physical vapor deposition, the electrodes are insulated from each other by drawing a predetermined electrode pattern with a laser beam (trimming). In addition, in the case of an electrode layer formed from a carbon material, the electrodes are formed at a predetermined interval. The electrode layer in this embodiment is formed from a nickel-vanadium alloy.

Each electrode is extended along the longitudinal direction of the biosensor 2 and is bent in the width direction at the upstream end. The bent portions are located in parallel in the width direction in the following order from the upstream side: second working electrode 21, second counter electrode 22, first working electrode 11, first counter electrode 12, and blood detection electrode 30. Each electrode is covered with the cover (not shown) in the covering region 2b from the upstream end of the biosensor 2 to the vicinity of the downstream end, but the downstream end portion is not covered and is exposed, and this portion forms the connector region 2c that is inserted into the insertion port 1b of the main body 1a. In this connector region 2c, the lead portion 11a of the first working electrode 11, the lead portion 12a of the first counter electrode 12, the lead portion 21a of the second working electrode 21, the lead portion 22a of the second counter electrode 22, and the lead portion 30a of the blood detection electrode 30 each form an exposed contact point.

In the widthwise center of the upstream part of the biosensor 2, a gap is formed between each electrode and a cover (not shown). This gap is a capillary-shaped flow path 2a through which blood is deposited and flows as described above. In addition, the non-conductive region 45 between the second counter electrode 22, which is the second electrode counting from the upstream side, and the first working electrode 11, which is the third electrode, is wider than the gap between the other electrodes. This non-conductive region 45 is an area formed by drawing a rectangular pattern on the electrode layer with laser light and is insulated from the other electrodes. Furthermore, a reagent 40 is placed on the first working electrode 11. The area in which this reagent 40 is placed reaches the middle of the first counter electrode 12 on the downstream side and the middle of the non-conductive region 45 on the upstream side, but does not reach the second counter electrode 22. In other words, the first working electrode 11 and the second counter electrode 22 are separated by the non-conductive region 45, preventing contact between the reagent 40 placed on the first working electrode 11 and the second counter electrode 22. When blood is deposited on the blood supply port 2d of the biosensor 2, it flows downstream in the flow path 2a by capillary force through the second counter electrode 22, the first working electrode 11, the first counter electrode 12, and the blood detection electrode 30 in that order. When the blood reaches the first working electrode 11, the reagent 40 placed on the first working electrode 11 is dissolved by the blood.

Figure 3 is a block diagram showing the functions of the measurement device 1 of this embodiment. As described above, the measurement device 1 of this embodiment includes a biosensor 2 having a first electrode pair 10 consisting of a first working electrode 11 and a first counter electrode 12 that measure the measurement target in blood, a second electrode pair 20 formed upstream of the first electrode pair 10 and consisting of a second working electrode 21 and a second counter electrode 22, a blood detection electrode 30 formed downstream of the first electrode pair 10, and a reagent 40 that is placed in contact with at least the first working electrode 11 and reacts with the measurement target.

The lead portions 11a, 12a, 21a, 22a, and 30a of the electrodes of the biosensor 2 are connected in parallel to the voltage applicator 50 and ground, which will be described later, by a connection circuit 200. The connection circuit 200 is provided with a first working electrode switch 211 between the voltage applicator 50 and the lead portion 11a, a first counter electrode switch 212 between the voltage applicator 50 and the lead portion 12a, a second working electrode switch 221 between the voltage applicator 50 and the lead portion 21a, a second counter electrode switch 222 between the voltage applicator 50 and the lead portion 22a, and a blood detection electrode switch 230 between the voltage applicator 50 and the lead portion 30a.

Furthermore, the lead portions 11a, 12a, 21a, 22a, and 30a of each electrode are branched from the corresponding switches 211, 212, 221, 222, and 230, and are connected in parallel to the ground. The connection circuit 200 between each branch point and the ground is provided with a ground switch 311 for the first working electrode, a ground switch 312 for the first counter electrode, a ground switch 321 for the second working electrode, a ground switch 322 for the second counter electrode, and a ground switch 330 for the blood detection electrode. Each switch is an electronic switch, and is controlled to be turned on and off by the control unit 100, as described below.

The measuring device 1 includes a voltage applicator 50 equipped with a power source. The voltage applicator 50 can be connected to each electrode through a connection circuit 200. The voltage applicator 50 also includes a current/voltage conversion circuit 51 that converts the current flowing between the electrodes into a voltage and outputs it, and an A/D conversion circuit 52 that converts the voltage value from the current/voltage conversion circuit 51 into a pulse. The control unit 100 turns on the desired switch corresponding to the electrode to be used and variably controls the voltage applied between each electrode at ground, so that the voltage applicator 50 can apply a voltage between the electrodes and obtain the value of the response current flowing between the electrodes.

The measuring device 1 further includes a control unit 100, which is a central control device that executes a predetermined program. The control unit 100 includes a measuring device 60 (referred to as a first measuring device 61 when acquiring the first information, and as a second measuring device 62 when acquiring the second information) that acquires measurement data indicating measurement values corresponding to the first information and the second information based on pulses from the A/D conversion circuit 52 of the voltage applicator 50, an introduction detector 65 (referred to as a first detector 66 when detecting the first introduction, and as a second detector 67 when detecting the second introduction) that detects the first introduction and the second introduction, a time determiner 70 that determines whether the time from the detection of the first introduction to the detection of the second introduction is equal to or less than a predetermined time threshold, and a calculator 80 that calculates the concentration of the object to be measured from the first information and the second information when the determination in the time determiner 70 is positive.

The measuring device 1 further includes an error indicator 90 that displays an error if the determination in the time determiner 70 is negative.

Each detection process and each measurement process will be explained below with reference to Table 1, which shows the open/closed state of each switch.

In the first detection step described in (1) above, the second downstream electrode 23 (the second counter electrode 22 in this embodiment) and the first upstream electrode 13 (the first working electrode 11 in this embodiment) are used. In the first detection step, the control unit 100 first controls the second counter electrode switch 222 and the first working electrode ground switch 311 to be in a connected state (CLOSE), and controls the other switches to be in a non-connected state (OPEN) (see Table 1). Next, the voltage applicator 50 applies a steady voltage (for example, 500 mV) between the second downstream electrode 23 (the second counter electrode 22) and the first upstream electrode 13 (the first working electrode 11). At this time, the control unit 100 controls the second counter electrode switch 222 to open and close at a predetermined period, so that a pulse voltage can be applied periodically between these electrodes. When blood is introduced up to the first upstream electrode 13 (the first working electrode 11), the measuring device 60 can measure the peak value of the response current corresponding to the applied pulse voltage. The introduction detector 65 ("first detector 66") determines whether the peak value of the response current measured by the measuring device 60 exceeds a predetermined current threshold, and if so, detects the first introduction.

In the above embodiment, the second downstream electrode 23 (second counter electrode 22) is used as the working electrode. When there is a shortage of blood deposited on the biosensor 2, a relatively large amount of blood is present on the electrode located on the upstream side, but the amount of blood is small on the electrode located on the downstream side. Therefore, by using the second downstream electrode 23 (second counter electrode 22) located on the upstream side as the working electrode, it becomes easier for a current to flow, and the accuracy of detecting a shortage of blood can be improved.

On the other hand, when the first upstream electrode 13 (first working electrode 11) located downstream is used as the working electrode, it is possible to use the same working electrode as the first working electrode 11 in the first measurement step described below. This simplifies the configuration of the electrical circuit. In this case, it is necessary to control the first working electrode switch 211 and the second counter electrode ground switch 322 so that they are connected.

In FIG. 3, the second counter electrode 22 located downstream of the second electrode pair 20 is the second downstream electrode 23, but when the second working electrode 21 is placed downstream, the second working electrode 21 becomes the second downstream electrode 23. In FIG. 3, the first working electrode 11 located upstream of the first electrode pair 10 is the first upstream electrode 13, but when the first counter electrode 12 is placed upstream and the reagent 40 is placed on the first counter electrode 12, the first counter electrode 12 becomes the first upstream electrode 13. The voltage value of the applied pulse voltage is desirably set, for example, in the range of 50 to 1000 mV, more preferably in the range of 100 to 600 mV. In addition, the peak value of the response current is desirably set, for example, to 0.3 μA or more, more preferably 0.7 μA or more.

In the second detection step described in (1) above, the reference electrode 14 (the first counter electrode 12 in this embodiment) and the blood detection electrode 30 are used. In the second detection step, the control unit 100 first controls the first counter electrode switch 212 and the blood detection electrode ground switch 330 to be in a connected state, and controls the other switches to be in a disconnected state (see Table 1). Next, the voltage applicator 50 applies a steady voltage (for example, 200 mV) between the reference electrode 14 (the first counter electrode 12) and the blood detection electrode 30. At this time, the control unit 100 controls the first counter electrode switch 212 to open and close at a predetermined period, so that a pulse voltage can be applied periodically between these electrodes. When blood is introduced up to the blood detection electrode 30, the measuring device 60 can measure the peak value of the response current corresponding to the applied pulse voltage. The introduction detector 65 ("second detector 67") determines whether the peak value of the response current measured by the measuring device 60 exceeds a predetermined current threshold, and if so, detects the second introduction.

In this embodiment, the first counter electrode 12 located downstream of the first electrode pair 10 is used as the reference electrode 14, but the first working electrode 11 located upstream may be used as the reference electrode 14. The voltage value of the applied pulse voltage is preferably set, for example, in the range of 50 to 1000 mV, more preferably in the range of 100 to 600 mV. The peak value of the response current is preferably set, for example, to 0.3 μA or more, more preferably 0.7 μA or more. In this embodiment, a pulse voltage is applied, but the control unit 100 can apply a DC voltage by keeping the first counter electrode switch 212 in a constant connection state. In this case, the measuring device 60 measures the peak value of the response current value responding to the DC voltage, or the current value after a predetermined time has elapsed since the initial response, and the introduction detector 65 ("second detector 67") can detect the second introduction by determining whether or not this current value exceeds a predetermined current threshold.

The time determiner 70 performs the time determination process described in (1) above. The time determiner 70 determines whether the time from the first introduction to the second introduction detected by the introduction detector 65 is equal to or less than a predetermined time threshold. The time determiner 70 can be allocated by a central processing unit (CPU) that executes a predetermined program in the control unit 100 of the measuring device. It is desirable to set this time threshold to, for example, 20 seconds, and more preferably 10 seconds. If the time from the first introduction to the second introduction is equal to or less than this time threshold, the time determiner 70 determines that the blood was applied normally. On the other hand, if the time from the detection of the first introduction to the detection of the second introduction exceeds this time threshold, the time determiner 70 determines that the application was not normal due to a lack of blood or a second application.

In the first measurement step described in (1) above, the first electrode pair 10, i.e., the first working electrode 11 and the first counter electrode 12, are used. In the first measurement step, the control unit 100 first controls the first working electrode switch 211 and the first counter electrode ground switch 312 to be in a connected state, and controls the other switches to be in a disconnected state (see Table 1). Next, when the voltage applicator 50 applies a DC voltage (e.g., 200 mV) to the first electrode pair 10, the meter 60 (first meter 61) measures a response current value as first information corresponding to the applied DC voltage. It is desirable to set the voltage value of the applied DC voltage in the range of, for example, 100 to 1000 mV, more preferably in the range of 200 to 500 mV.

The response current value measured by the first measuring device 61 may be used as the first information as is. Also, a value converted into the concentration of the object to be measured by referring to a calibration curve or comparison table created from current response values measured in advance for an object to be measured of a known concentration may be used as the first information.

In the second measurement step described in (1) above, the second electrode pair 20, i.e., the second working electrode 21 and the second counter electrode 22, are used. In the second measurement step, first, either before or after measuring the first information, the control unit 100 controls the second working electrode switch 221 and the second counter electrode ground switch 322 to be in a connected state and the other switches to be in a disconnected state (see Table 1). Next, when the voltage applicator 50 applies a DC voltage (e.g., 3.5 V) to the second electrode pair 20, the meter 60 (second meter 62) measures a response current value as second information corresponding to the applied DC voltage. It is desirable to set the voltage value of the applied DC voltage in the range of, for example, 2 to 20 V, more preferably in the range of 3 to 10 V.

The response current value measured by the second measuring device 75 may be used as the second information as is. Alternatively, the second information may be a value converted into a numerical value of a measurement item (e.g., hematocrit value) by referring to a calibration curve or comparison table created in advance using current response values measured with another blood sample that is known about the measurement item of the second measuring device 62.

The calculator 80 performs the calculation process described in (1) above. That is, when the determination in the time determiner 70 is positive, the calculator 80 calculates the concentration of the object to be measured from the first information and the second information. This calculator 80 can be realized by a central processing unit (CPU) that executes a predetermined program in the control section of the measuring device. The calculation of the object to be measured in the calculator 80 is the same as that described in the calculation process in (1) above.

The error indicator 90 is realized as a device that displays an error message or issues an audio warning sound when the time determiner 70 makes a negative judgment in the error processing step described in (1) above, i.e., when the time from the detection of the first introduction to the detection of the second introduction exceeds a predetermined time threshold. For example, the display screen 1c in the measuring device 1 in FIG. 1 can be used as the error indicator 90 to display an error message.

(3) Measurement Example Hereinafter, an example of the measurement method of this embodiment will be described with reference to the flowchart in Fig. 4. In this example, a glucose value is measured as the first information, and a hematocrit value is measured as the second information. Note that the glucose value obtained as the first information is a value influenced by the hematocrit value in the blood, and needs to be corrected based on the hematocrit value obtained as the second information.

The biosensor 2 shown in FIG. 2 is formed by providing each electrode on a substrate that is, for example, 6 mm wide and 30 mm long. The width of the flow channel 2a is, for example, 2 mm and the length is 4 mm.

First, an example of the composition of the reagent 40 placed on the first working electrode 11 is as follows.
Hexaammineruthenium(III) chloride: 38.9% by mass
1-Methoxy PES (Dojindo Laboratories): 0.2% by mass
SN Deformer 1315 (San Nopco): 0.1% by mass
0.6M phosphate buffer (pH 7.0): 8.8% by mass
CHAPS (Dojindo Chemical Research Institute): 4.0% by mass
Glycine: 4.0% by mass
Distilled water: 44.0% by mass

0.1 mg of reagent 40 with this composition is applied to an area 3 mm wide and 1 mm long, centered on the first working electrode 11. This area is adjusted so that it covers up to about the middle of the first counter electrode 12 on the downstream side and up to about the middle of the non-conductive area 45 on the upstream side. In addition, 4.1 units of glucose dehydrogenase (AMANO8, Amano Enzyme) are applied to the area where this reagent 40 has been applied.

This biosensor 2 is attached to the connector 1d of the main body 1a of the measuring device 1. Then, in the first detection step shown in S100 of FIG. 4, the control unit 100 first controls the second counter electrode switch 222 and the first working electrode ground switch 311 to be in a connected state, and the other switches to be in a disconnected state (see Table 1). Next, the voltage applicator 50 applies a steady voltage of 500 mV between the second downstream electrode 23 and the first upstream electrode 13. Next, blood is applied to the flow path 2a, and when the blood fills the second downstream electrode 23 and the first upstream electrode 13, the measuring device 60 measures a current of 0.7 μA or more. This detects that the electrodes are electrically connected. After detecting a current of 0.7 μA or more for the first time, the control unit 100 controls the second counter electrode switch 222 to open and close at a predetermined cycle of 2.5 ms, changing the voltage application method so that a pulse voltage is applied between the electrodes in which a voltage of 500 mV is applied for 2.5 ms and then stopped for 2.5 ms.

Figure 5 is a graph showing the relationship between voltage application and current. When an initial steady voltage or a second or subsequent pulse voltage is applied as in the upper graph, a current having a peak showing a transient response is generated as in the lower graph. At the stage shown in S110, the introduction detector 65 (first detector 66) judges whether the peak value, which is the current value of this peak, has been detected three times to be equal to or greater than the threshold value of 0.7 μA. The application of voltage is repeated until a peak value equal to or greater than the threshold value is detected three times. In this embodiment, the threshold value of 0.7 μA indicates the current threshold. Note that the initial voltage application method may not be a steady voltage of 500 mV, but may be a pulse voltage (AC voltage) in which a voltage of 500 mV is applied for 2.5 ms and then stopped for 2.5 ms, as in the second or subsequent times.

As shown in FIG. 5, the first peak value tends to be lower than subsequent peak values. This is thought to be because, at the time when the current having the first peak is generated, blood has not yet reached the entire surface of the first upstream electrode 13, and the reagent has not yet been completely dissolved by the blood. Therefore, it is preferable that the current threshold value (first current threshold value) at the first peak value is higher than the current threshold value (second current threshold value) at the subsequent peak value. The current threshold value at the first peak value can be, for example, 0.2 to 0.5 μA, and more preferably 0.35 μA.

When a peak value equal to or greater than the threshold is detected three times in the step shown in S110 and the first introduction is detected, in the second detection step shown in S120, the control unit 100 first controls the first counter electrode switch 212 and the blood detection electrode ground switch 330 to be in a connected state and the other switches to be in a disconnected state (see Table 1). At this time, the control unit 100 controls the first counter electrode switch 212 to be opened and closed at a predetermined cycle of 2.5 ms so that a pulse voltage can be applied between the electrodes. Then, the voltage applicator 50 repeatedly applies a voltage of 200 mV between the reference electrode 14 and the blood detection electrode 30 for 2.5 ms and stops the application for 2.5 ms. Then, the measuring device 60 detects a peak value of the current similar to that in FIG. 5. In the step shown in S130, the introduction detector 65 (second detector 67) determines whether the peak value has been detected to be equal to or greater than the threshold value of 0.7 μA three times. If these three detections are not made, in the time determination step shown in S140, the time determiner 70 determines whether the time threshold of 10 seconds has elapsed since the first introduction was detected. If not, the voltage application is repeated at the stage shown in S120. On the other hand, if it is determined that the time threshold has elapsed, an error process is performed by the error indicator 90 at the error processing step shown in S160, and subsequent processing is stopped.

On the other hand, if a peak value equal to or greater than the threshold is detected three times at the stage shown in S130 and a second introduction is detected, in the time determination step shown in S150, the time determiner 70 determines whether a time threshold of 10 seconds has elapsed between the detection of the first introduction and the detection of the second introduction. If it is determined that the time threshold has elapsed, in the error processing step shown in S160, an error is processed by the error indicator 90 and subsequent processing is stopped.

When it is determined at the stage shown in S150 that the time threshold has not elapsed, the first information is measured by the measuring device 60 (first measuring device 61) in the first measurement step shown in S170. At the same time, the second information is measured by the measuring device 60 (second measuring device 62) in the second measurement step.

In measuring the first information, the control unit 100 first controls the first working electrode switch 211 and the first counter electrode ground switch 312 to be in a connected state, and controls the other switches to be in a disconnected state (see Table 1). Next, the voltage applicator 50 applies a voltage of 200 mV to the first electrode pair 10 for 4.5 seconds, and the measurement device 60 (first measurement device 61) measures the first information as the corresponding response current value. In measuring the second information, the control unit 100 first controls the second working electrode switch 221 and the second counter electrode ground switch 322 to be in a connected state, and controls the other switches to be in a disconnected state (see Table 1). Next, the voltage applicator 50 applies a voltage of 3.5 V to the second electrode pair 20 for 1 second, and the measurement device 60 (second measurement device 62) measures the second information as the corresponding response current value.

Then, in the calculation step shown in S180, the calculator 80 calculates a corrected glucose value from the first information and the second information. In other words, the calculator 80 uses the hematocrit value obtained as the second information to correct the glucose value obtained as the first information, which is a value influenced by the hematocrit value in the blood. Note that an environmental temperature measurement may be performed between S170 and S180 and used as one of the parameters for the calculation by the calculator 80.

In this embodiment, the combination of the first electrode pair 10 for acquiring the glucose value, which is the first information, or the second electrode pair 20 for acquiring the hematocrit value, which is the second information, is not used as is to detect the introduction of blood. That is, the first introduction is detected using the first upstream electrode 13 of the first electrode pair 10 on which the reagent 40 is placed, and the second downstream electrode 23 of the second electrode pair for acquiring the hematocrit value, which is the second information. In addition, the second introduction is detected using the reference electrode 14 of the first electrode pair 10 and the blood detection electrode 30 provided at the most downstream of the flow path 2a, which does not contribute to acquiring the first information and the second information. In this way, an irregular electrical circuit configuration that intentionally changes the combination of electrodes to which a voltage is applied and switch control by the control unit 100 are performed.

By this process, while measuring the first information and the second information as before, it is possible to detect the time when the blood that has been deposited on the biosensor 2 and flowed through the flow path 2a first comes into contact with the reagent 40 by detecting the first introduction. In addition, it is now possible to detect the time when the blood fills the first electrode pair 10 and the second electrode pair 20 by detecting the second introduction. Then, in the time determination process, it is now possible to determine whether the time from the detection of the first introduction to the detection of the second introduction, i.e., the time from the first contact of the blood with the reagent 40 to the time when the blood fills the first electrode pair 10 and the second electrode pair 20 and is ready for measurement, is equal to or less than a predetermined time threshold.

According to the detection method of this embodiment, when the amount of blood dispensed on the biosensor 2 in the first dispense is introduced into the flow path 2a to such an extent that it does not come into contact with the reagent 40, i.e., does not reach the first upstream electrode 13, the reagent 40 is not dissolved. Therefore, as long as the blood fills all of the first electrode pair 10 and the second electrode pair 20 with blood in the second dispense, a correct measurement can be performed, and the biosensor will not be discarded unnecessarily. On the other hand, when the amount of blood dispensed on the biosensor in the first dispense is introduced into the flow path 2a to such an extent that it comes into contact with the reagent 40, i.e., it reaches the first upstream electrode 13 but does not fill all of the first electrode pair 10 and the second electrode pair 20, the reagent 40 is dissolved by the blood dispensed the first time. Therefore, when blood is dispensed again, the dissolved reagent 40 on the first upstream electrode 13 is swept downstream, and an accurate response current value cannot be measured. Therefore, in such a case, an error process is performed by the error indicator 90, and it is possible to prevent an inaccurate glucose value from being notified to the user.

(4) Verification of the first detection step Using the above-mentioned measuring device 1, the direction of current flow in the electrodes used in the first detection step was examined. Specifically, in the first detection step (see S100 in FIG. 4), a pulse voltage of 500 mV was applied for 2.5 ms and then stopped for 2.5 ms, and it was determined that the first introduction was detected when a peak value of the current above the threshold was detected three times. The amount of blood deposited on the biosensor 2 was adjusted to an amount that reached the first working electrode 11 (first upstream electrode 13) but did not reach the first counter electrode 12.

The first example was a configuration in which the first working electrode 11 (first upstream electrode 13) was used as the working electrode and the second counter electrode 22 (second downstream electrode 23) was used as the counter electrode, and the second example was a configuration in which the second counter electrode 22 (second downstream electrode 23) was used as the working electrode and the first working electrode 11 (first upstream electrode 13) was used as the counter electrode. Furthermore, the third example was a configuration in which the second counter electrode 22 was not used and a voltage was applied between the first working electrode 11 and the first counter electrode 12, and the fourth example was a configuration in which a voltage was applied between the first working electrode 11 and the blood detection electrode 30.

As a result, it was found that in both the first and second examples, the arrival of blood could be detected, and the first introduction could be detected regardless of whether the first working electrode 11 (first upstream electrode 13) or the second counter electrode 22 (second downstream electrode 23) was used as the working electrode. On the other hand, in the third and fourth examples, in which blood did not reach the first counter electrode 12, naturally no current flowed between the electrodes, and therefore no blood was detected.

(5) Verification of Pulse Voltage and DC Voltage in the First Detection Step Verification was conducted as to whether a pulse voltage or a DC voltage was more suitable for the voltage applied in the first measurement step, using the above-described measurement device 1. Specifically, in a state where a sufficient amount of blood was applied to the biosensor 2 to perform the first measurement, verification was conducted in a case where a pulse voltage of 500 mV was applied for 2.5 ms and then stopped for 2.5 ms, and in a case where a DC voltage of 500 mV was applied for 50 ms.

First, using biosensor 2 (hereafter referred to as the "normal sensor") that had just been adjusted, in pattern 1 where blood with a glucose level of 330 mg/dl was deposited, the response current value when a pulse voltage was applied was 14.9 μA, whereas the response current value when a DC voltage was applied was 0.04 μA.

Next, using biosensor 2 (hereinafter referred to as the "storage sensor") that had been adjusted and then stored in a 50°C temperature environment for three months to reduce the activity of the reagent, blood with a glucose level of 330 mg/dl was deposited in pattern 2, where the response current value was 14.7 μA when a pulse voltage was applied, whereas the response current value was 0.02 μA when a DC voltage was applied. The rate of decrease in the response current value of pattern 2 relative to the current response value of pattern 1 (i.e., the value calculated by "(X-Y)/X x 100" where the current response value of pattern 1 is X and the current response value of pattern 2 is Y) was 1.3% when a pulse voltage was applied, whereas it was 50% when a DC voltage was applied.

In pattern 3, where blood with a glucose level of 0 mg/dl was deposited using a normal sensor, the response current value when a pulse voltage was applied was 14.2 μA, whereas the response current value when a DC voltage was applied was 0.03 μA. The rate of decrease in the response current value of pattern 3 relative to the current response value of pattern 1 (i.e., the value calculated by "(X-Z)/X x 100" where the current response value of pattern 1 is X and the current response value of pattern 3 is Z) was 4.7% when a pulse voltage was applied, whereas it was 25% when a DC voltage was applied.

Figure 6 is a graph showing the rate of decrease in response current values in patterns 2 and 3 compared to pattern 1. This shows that the application of a pulse voltage has almost no effect on changes in glucose values or changes in the activity of reagents such as stored sensors, whereas the application of a DC voltage is highly sensitive to these changes. This means that the application of a DC voltage is suitable for detecting quantitative changes in the object being measured. On the other hand, the application of a pulse voltage is not significantly affected by the measurement conditions or measurement environment, so it can be said to be suitable for detecting the presence or absence of current conduction between electrodes.

(6) Others In the measuring device 1 of the above embodiment, one voltage applicator 50 applies a voltage between the electrodes in the first detection step, the second detection step, and the first measurement step, and the second measurement step. However, in the measuring device 1 of another embodiment, the present invention is not limited to this configuration, and the measuring device 1 may be provided with a plurality of voltage applicators 50 each responsible for applying a voltage for each step or for each of several steps.

In addition, in the measurement device of the above embodiment, when applying a pulse voltage to each electrode, the control unit 100 controls the opening and closing of each switch. However, in another embodiment of the measurement device 1, each switch may not be provided, and the pulse voltage may be applied directly to each electrode from the voltage applicator 50.

The present invention can be used as a portable blood glucose measurement device or blood glucose self-measurement meter that uses a biosensor. It can also be used as a measurement device that can measure items other than blood glucose.

1 Measuring device 1a Main body 1b Insertion port 1c Display screen 1d Connector 2 Biosensor 2a Flow path 2b Covered area 2c Connector area 2d Blood supply port 2e Air hole 10 First electrode pair 11 First working electrode 11a Lead portion 12 First counter electrode 12a Lead portion 13 First upstream electrode 14 Reference electrode 20 Second electrode pair 21 Second working electrode 21a Lead portion 22 Second counter electrode 22a Lead portion 23 Second downstream electrode 30 Blood detection electrode 30a Lead portion 40 Reagent 45 Non-conductive area 50 Voltage applicator 51 Current/voltage conversion circuit 52 A/D conversion circuit 60 Measuring device 61 First measuring device 62 Second measuring device 65 Introduction detector 66 First detector 67 Second detector 70 Time determination device 80 Calculating device 90 Error display 100 Control unit 200 Connection circuit 211 First working electrode switch 212 First counter electrode switch 221 Second working electrode switch 222 Second counter electrode switch 230 Blood detection electrode switch 311 First working electrode ground switch 312 First counter electrode ground switch 321 Second working electrode ground switch 322 Second counter electrode ground switch 330 Blood detection electrode ground switch

Claims (10)

a flow path into which blood containing a measurement target is introduced;
a first electrode pair including a first working electrode and a first counter electrode formed in the flow path for measuring a measurement target substance in blood;
a second electrode pair formed upstream of the first electrode pair in the flow path and including a second working electrode and a second counter electrode;
a blood detection electrode formed in the flow path downstream of the first electrode pair;
A reagent that is placed on at least the first working electrode and reacts with the object to be measured;
A measurement method for measuring a measurement object using a biosensor having
a first detection step of detecting a first introduction of blood between a second downstream electrode, which is an electrode located downstream of the second electrode pair, and a first upstream electrode, which is an electrode located upstream of the first electrode pair and on which the reagent is placed, to the first upstream electrode;
a second detection step of detecting a second introduction of blood between a reference electrode, which is one of the first electrode pair, and the blood detection electrode, the second introduction being the introduction of blood to the blood detection electrode;
a time determination step of determining whether a time from the detection of the first introduction to the detection of the second introduction is equal to or less than a predetermined time threshold;
a first measurement step of acquiring first information related to the object to be measured using the first electrode pair;
a second measurement step of acquiring second information related to the object to be measured using the second electrode pair;
a calculation step of calculating a concentration of the object to be measured from the first information and the second information when the determination in the time determination step is equal to or shorter than a predetermined time threshold value;
an error processing step of performing an error processing when the determination in the time determination step exceeds a predetermined time threshold;
The measuring method has the following features. The first detection step includes:
applying a pulse voltage between the second downstream electrode and the first upstream electrode;
measuring a peak value of a response current corresponding to the applied pulse voltage;
an introduction detection step of determining whether the measured peak value exceeds a predetermined current threshold value, and detecting the first introduction when the number of times the measured peak value exceeds a predetermined number of times or more;
The method of claim 1, comprising: The first measuring step includes:
applying a DC voltage to the first electrode pair;
measuring a response current value as the first information corresponding to the applied DC voltage;
comprising
The second measuring step includes:
applying a DC voltage to the second electrode pair;
measuring a response current value as the second information corresponding to the applied DC voltage;
The method of claim 1 or 2, comprising: a flow path into which blood containing a measurement target is introduced;
a first electrode pair including a first working electrode and a first counter electrode formed in the flow path for measuring a measurement target substance in blood;
a second electrode pair formed upstream of the first electrode pair in the flow path and including a second working electrode and a second counter electrode;
a blood detection electrode formed in the flow path downstream of the first electrode pair;
A reagent that is placed on at least the first working electrode and reacts with the object to be measured;
A biosensor having
a first detector that detects a first introduction of blood between a second downstream electrode, which is an electrode located downstream of the second electrode pair, and a first upstream electrode, which is an electrode located upstream of the first electrode pair and on which the reagent is placed, and the first introduction is the introduction of blood to the first upstream electrode;
a second detector that detects a second introduction of blood between a reference electrode, which is one of the first electrode pair, and the blood detection electrode, the second introduction being the introduction of blood to the blood detection electrode;
a time determiner that determines whether a time from the detection of the first introduction to the detection of the second introduction is equal to or less than a predetermined time threshold;
a first measuring device that acquires first information related to the measurement target using the first electrode pair;
a second measuring device that acquires second information related to the object to be measured using the second electrode pair;
a calculator that calculates a concentration of the object to be measured from the first information and the second information when the determination by the time determiner is equal to or shorter than a predetermined time threshold;
an error indicator that displays an error when the determination by the time determiner exceeds a predetermined time threshold;
A measuring device having a voltage applicator that applies a voltage between the electrodes of the biosensor;
a connection circuit having a switch for connecting between the voltage applicator and each of the electrodes;
A control unit that controls opening and closing of the switch;
5. The measuring device according to claim 4, further comprising a measuring device for measuring a response current corresponding to the voltage applied by the voltage applicator. the control unit controls a switch of the connection circuit so as to connect the second downstream electrode and the first upstream electrode;
the voltage applicator applies a pulse voltage between the second downstream electrode and the first upstream electrode;
The measuring device measures a peak value of a response current corresponding to the applied pulse voltage,
6. The measurement device of claim 5, wherein the first detector detects the first introduction when the measured peak value exceeds a predetermined current threshold. The measurement device according to claim 6, wherein the first detector detects the first introduction when the peak value measured the first time exceeds a predetermined first current threshold and when the peak value measured the second or subsequent time exceeds a second current threshold that is greater than the first current threshold. The measurement device according to claim 6 or 7, wherein the control unit periodically opens and closes a switch between the voltage applicator and the second downstream electrode or the first upstream electrode, while the voltage applicator applies a steady voltage, thereby applying the pulse voltage between the second downstream electrode and the first upstream electrode. the control unit controls a switch of the connection circuit so as to connect the reference electrode and the blood detection electrode;
The voltage applicator applies a voltage between the reference electrode and the blood detection electrode,
The measuring device measures a response current value corresponding to the applied voltage,
The measurement device according to claim 6 or 7, wherein the second detector detects the second introduction when the measured response current value exceeds a predetermined current threshold value. the control unit controls a switch of the connection circuit so as to connect the first electrode pair;
The voltage applicator applies a DC voltage to the first electrode pair,
The measuring device measures a response current value corresponding to the applied DC voltage as the first information, and
The control unit controls a switch of the connection circuit so that the second electrode pair is connected either before or after measuring the first information;
The voltage applicator applies a DC voltage to the second electrode pair,
The measurement device according to claim 5 , wherein the measurement device measures a response current value, as the second information, corresponding to the applied DC voltage.