JP5807500B2 - Biological sample measuring device and measuring method - Google Patents

Description

  The present invention relates to a biological sample measuring apparatus and measuring method capable of measuring a substrate concentration in a biological sample.

  Accurate measurement of the concentration of a specific substance in a biological sample is an important issue from a medical point of view. Among them, measurement of glucose concentration in blood, that is, blood glucose level is frequently performed for the prevention and treatment of diabetes, and is particularly important.

  In the treatment of diabetes, for example, there is insulin therapy. Insulin is known as a drug that controls blood sugar levels. In this therapy, insulin, which is a therapeutic agent for diabetes, is administered to diabetic patients. The need to administer insulin is determined based on the blood glucose level of the diabetic patient. For this reason, it is essential for a diabetic patient to grasp the blood glucose level. Therefore, development of simple self-blood glucose measuring devices that can be easily handled by diabetic patients at home has been actively conducted.

  A method using a biosensor in a simple self-blood glucose measurement device as described above is known (Patent Documents 1 to 4). An enzyme is used for the biosensor. Glucose in the blood is quantified using a specific reaction of the enzyme. The glucose determination method includes a GOD method in which glucose is decomposed into gluconic acid by glucose oxidase (hereinafter sometimes abbreviated as “GOD”), and glucose is abbreviated as glucose dehydrogenase (hereinafter abbreviated as “GDH”). GDH method of decomposing into gluconolactone is known.

  The enzyme is attached to the working electrode of the electrode pair of the biosensor. Electrons are generated when the enzyme specifically breaks down glucose. The generated electrons move to the working electrode of the electrode pair. This movement of electrons causes a current to flow through the electrode pair of the biosensor. This current is detected by the blood glucose measurement device, and the glucose content in the blood is calculated. That is, a blood sugar level is obtained. Moreover, a stable measurement value can be obtained by attaching an electron mediator carrying electrons to the electrode pair. Examples of the electron mediator include organic compounds such as potassium ferricyanide, hexaammineruthenium and quinone derivatives, or organic-metal complexes.

  The enzyme's activity on glucose is affected by environmental temperature. For this reason, an error may occur in the measurement result depending on the environment in which the measurement is performed. In order to solve this problem, there is known a measuring instrument that compensates for a measurement result based on temperature information obtained from a plurality of temperature sensors (Patent Document 5).

JP 2009-97877 A JP 2005-43280 A JP-A-2005-37335 JP 2002-107325 A JP 2010-25926 A

  In the configuration having a plurality of temperature sensors as described in Patent Document 5, the measuring instrument becomes complicated, large, and expensive. Further, in the simple self blood glucose measurement device, the position where the temperature sensor is arranged is particularly problematic. Details will be described below.

  In a general simplified self blood glucose measuring device, the biosensor is configured in a rod shape and is detachable from the slot of the self blood glucose measuring device main body. In other words, the biosensor is disposable. It is desirable that a biosensor provided in a disposable form is simply configured and inexpensive. However, when a temperature sensor is provided in the biosensor, the structure of the biosensor becomes complicated and the biosensor becomes expensive.

  On the other hand, when a temperature sensor is provided in the body of the self-blood glucose measuring device, the distance between the electrode pair of the biosensor and the temperature sensor becomes longer, so the ambient temperature around the electrode pair and the ambient temperature indicated by the temperature sensor are different There is. Thereby, the compensation for the measurement result may not be performed accurately. In particular, the temperature sensor is in an environment where heat is easily trapped inside the casing, and is further affected by heat generated by the electronic circuit, so that the accuracy of compensation for the measurement result is further reduced.

  This invention is made | formed in view of the said situation, The objective is to provide the biological sample measuring device and measuring method which can measure a substrate concentration with high precision irrespective of environmental temperature.

  (1) The biological sample measurement apparatus according to the present invention can introduce the biological sample into the first electrode to which an enzyme that reacts with a substrate in the biological sample to generate electrons is attached, and the first electrode. A second electrode provided in a separated sample space, first data indicating a substrate concentration in the biological sample, and an estimated value of a potential difference between the first electrode and the second electrode based on the reaction. A data table in which second data to be shown and third data indicating an estimated value of a current that flows when a first level voltage is applied to the biological sample via the first electrode and the second electrode are associated with each other. And a control unit electrically connected to each of the first electrode, the second electrode, and the storage unit. The control unit includes a first control for measuring a potential difference between the first electrode and the second electrode in the enzyme reaction, and a first level voltage between the first electrode and the second electrode. , The second control for measuring the current value flowing through the first electrode and the second electrode, the second data corresponding to the potential difference measured by the first control, and the second Based on the third data corresponding to the current value measured by the control, a third control for retrieving the first data from the data table is executed.

  The biological sample measuring device in the present invention generates a unique electric signal based on the substrate concentration in the biological sample, and enables the subject to recognize information on the substrate concentration. A biological sample is a substance collected from the body of an organism, and examples thereof include blood. Examples of the substrate include glucose, glycated albumin, and glycated hemoglobin when blood is used as a biological sample. Moreover, when saliva is used as a biological sample, saliva amylase is mentioned, for example. When urine is used as the biological sample, for example, albumin (including denatured and fragmented) can be mentioned.

  When a biological sample is introduced into the sample space, the enzyme attached to the first electrode reacts with the substrate, electrons are generated by the reaction, and the electrons move to the first electrode. As the second electrode, for example, a reference electrode (standard electrode) such as a silver-silver chloride electrode is used. When the first electrode and the second electrode are connected with a potentiometer, a potential difference is observed between the electrodes. The control unit measures a potential difference between the first electrode and the second electrode in the first control.

Further, in the second control, the control unit applies a voltage between the first electrode and the second electrode, and measures the inflowing current value. When a positive voltage is applied from the power source to the first electrode and the second electrode, electrons move from the first electrode to the second electrode via the power source, and in the second electrode, hydrogen ions, oxygen, Alternatively, unreacted mediator is reduced. Thereby, this movement of electrons is measured as a current value in the second control by the control unit.

  The potential difference generated between the first electrode and the second electrode by the reaction between the enzyme and the substrate at a certain substrate concentration depends on the environmental temperature. Similarly, the value of the current that flows when a voltage is applied to the biological sample via the first electrode and the second electrode also depends on the environmental temperature. Here, it is possible to specify the environmental temperature and the substrate concentration in the biological sample using the temperature-dependent characteristics of these potential differences and current values.

  Details will be described below. For example, when the potential difference E is obtained in the first control, the candidates for the set of the environmental temperature T and the substrate concentration C corresponding to the potential difference E are limited. Similarly, when the current I is obtained in the second control, the candidates for the set of the environmental temperature T and the substrate concentration C corresponding to the current I are limited. If a pair in which the environmental temperature T and the substrate concentration C are identical is found from these two sets of candidates, those values become the actual environmental temperature and the substrate concentration in the biological sample. That is, when the potential E and the current I are determined, the substrate concentration C is determined.

  The data table of the storage unit includes the substrate concentration (first data) in the biological sample, the potential (second data) and the current value (third data) obtained from the biological sample having the substrate concentration by the above method. It is associated. In the third control, the control unit uses the first data from the data table based on the second data corresponding to the potential measured in the first control and the third data corresponding to the current value measured in the second control. And the substrate concentration in the biological sample is specified from the first data.

  According to this configuration, the influence of temperature on the measured value can be eliminated without using a temperature sensor. That is, highly accurate measurement is possible with a simple configuration.

  (2) The data table includes a first table in which the first data, the second data, and the fourth data indicating the environmental temperature of the sample space are associated with each other, the first data, the third data, And a second table associated with the fourth data.

  Thus, the data table may be composed of a plurality of tables.

(3) the control unit in the third control, the first based control and the potential difference measured by the corresponding said second data, said first said first data and a set of candidates for the fourth data Based on the third data corresponding to the current value measured by the second control by searching from the table, the candidate of the first data and the fourth data set is searched from the second table, and the first From the set candidates retrieved from the table and the set candidates retrieved from the second table, a set in which both the first data and the fourth data match is retrieved, and the first of the sets is retrieved. The substrate concentration in the biological sample may be specified from one data.

  The search for the first data indicating the substrate concentration may be performed based on the above procedure referring to the two tables.

  (4) The second data in the data table indicates an estimated value of a potential difference after the first time has elapsed since the biological sample was introduced into the sample space, and the third data in the data table is When the application of the first level voltage to the biological sample is started via the first electrode and the second electrode after a lapse of a second time on the basis of the time point when the biological sample is introduced into the sample space, The estimated value of the electric current which flows into the said 1st electrode and the said 2nd electrode after 3rd time progress is shown. The control unit has detection means for detecting that the biological sample has been introduced into the sample space. The control unit executes the first control after a lapse of a first time after the detection unit detects that the biological sample has been introduced into the sample space, and the detection unit stores the sample in the sample space. After the second time has elapsed since the detection of the introduction of the biological sample, the voltage application in the second control is executed, and the detection means detects that the biological sample has been introduced into the sample space. After the third time has elapsed, the current measurement in the second control is performed.

  The potential difference measured by the first control depends on the time after the biological sample is introduced into the sample space. Further, the current value measured by the second control further depends on the time from the start of the application of the voltage between the electrodes. In this configuration, since the first control and the second control are executed based on a predetermined time after the biological sample is introduced into the sample space, highly accurate measurement is possible.

  (5) The enzyme may decompose glucose, and an electron mediator may be further attached to the first electrode.

  By using an enzyme that degrades glucose, blood glucose can be measured using blood as a biological sample. Moreover, a stable measurement result can be obtained by attaching an electron mediator to the first electrode.

(6) The substrate concentration measurement method in a biological sample according to the present invention is a first step of introducing a biological sample between an electrode pair to which an enzyme that generates electrons by reacting with a substrate in the biological sample is attached. A second step of measuring a potential difference between the electrode pair in the enzyme reaction, a third step of measuring a current value output by applying a voltage between the electrode pair, and a computer, First data indicating a substrate concentration in the biological sample, second data indicating an estimated value of a potential difference between the electrode pair in the reaction of the enzyme, and a first level voltage applied to the biological sample via the electrode pair Measured by the second data corresponding to the potential difference measured by the second step and the third step from the data table associated with the third data indicating the estimated value of the current flowing when the voltage is applied And a fourth step of searching for the first data based on the third data corresponding to the current value.

  The present invention can also be interpreted as a method for measuring a substrate concentration in a biological sample as described above.

  According to the biological sample measuring device and the measuring method according to the present invention, the substrate concentration in the biological sample can be measured with high accuracy regardless of the environmental temperature.

FIG. 1 is an external perspective view of a blood glucose measurement device 10 according to an embodiment of the present invention. FIG. 2 is a functional block diagram of the blood glucose measurement device 10. FIG. 3 is an external perspective view of the biosensor 12. FIG. 4 is an exploded view of the biosensor 12. FIG. 5 is a diagram showing the contents of the data table 81 stored in the EEPROM 33. FIG. 6 is a flowchart showing a flow of control performed by the control unit 23 for measuring the blood sugar level. FIG. 7 is a diagram illustrating a state in which blood 80 is introduced into the sample space 72 of the biosensor 12. FIG. 8 is a diagram showing the contents of the data table 88 stored in the EEPROM 33 in the modified example of the blood glucose measurement device 10.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as appropriate. In the embodiment described below, an embodiment is described in which the biological sample is blood and the specific component in the biological sample is glucose, that is, an aspect of measurement using a so-called blood glucose measurement device. It goes without saying that the embodiments of the present invention can be modified as appropriate without departing from the scope of the present invention.

[Schematic configuration of blood glucose measurement device 10]
As shown in FIG. 1, a blood glucose measurement device 10 (an example of a biological sample measurement device of the present invention) is configured such that a biosensor 12 is detachably attached to a main body 11. The main body 11 has a thin box shape. The main body 11 is provided with a display 13 and three operation buttons 14A, 14B, and 14C. The display 13 is a part of the display unit 21 described later, and displays various characters and images necessary for the operation of the blood glucose measurement device 10. The operation buttons 14A, 14B, and 14C form part of the operation unit 22 described later, and generate predetermined operation signals when pressed by an operator (hereinafter also referred to as a diabetic patient). Let

  A sensor insertion port 15 is provided on the side surface of the main body 11. The sensor insertion port 15 is for the biosensor 12 to be inserted and held. Although not shown in the figure, an electrode is provided in the back of the sensor insertion port 15, and a control unit 23 of the main body 11 described later and the biosensor 12 are electrically connected through the electrode. The biosensor 12 introduces blood, which is a living sample to be measured, and causes a chemical reaction to glucose (an example of the substrate of the present invention) in the blood. As a result of the electric current generated by the chemical reaction of glucose being electrically processed by the control unit 23, the glucose concentration in blood, that is, the blood sugar level is displayed on the display 13.

  Subsequently, the detailed configuration of the blood glucose measurement device 10 will be described.

  As shown in FIG. 2, the blood glucose measurement device 10 is broadly functionally divided into a display unit 21, an operation unit 22, a control unit 23, and a sensor unit 24. The display unit 21, the operation unit 22, and the sensor unit 24 are connected to the control unit 23 through the bus 25 so as to be able to transmit and receive electrical signals. A main body 11 is an electronic circuit in which a display unit 21, an operation unit 22, a control unit 23, and a sensor unit 24 are housed in a thin box-shaped housing. The display unit 21, the operation unit 22, the control unit 23, and the sensor unit 24 may be integrally formed on a common electronic substrate. The biosensor 12 described above forms a part of the sensor unit 24 in a state where the biosensor 12 is attached to the sensor insertion port 15. In FIG. 2, a power supply system that supplies driving power to each unit is omitted. The detail of each part which comprises the blood glucose measuring device 10 is demonstrated below.

[Display unit 21]
The display unit 21 includes the display 13 described above and a peripheral circuit 26 that is electrically connected to the control unit 23 and controls display on the display 13. The display 13 is, for example, a liquid crystal display or an organic EL display. Characters and images can be displayed on the display 13 by the control from the control unit 23 and the peripheral circuit 26. For example, the display 13 displays characters and graphics used by the diabetic patient to operate the blood glucose measurement device 10. The display on the display is dynamically changed by control from the control unit 23 and the peripheral circuit 26. For example, the display may be switched for each group of related operations. A diabetic patient can perform an operation suitable for each display content by pressing the operation buttons 14A, 14B, and 14C, or can switch the display content to one corresponding to another function. A diabetic patient can start measuring blood sugar levels or display the measured blood sugar levels on the display 13 by operating the operation buttons 14A, 14B, and 14C while confirming the display on the display 13.

[Operation unit 22]
The operation unit 22 includes operation buttons 14A, 14B, and 14C provided on the main body 11, and a peripheral circuit 27 that generates predetermined operation signals corresponding to pressing of the operation buttons 14A, 14B, and 14C. The diabetic patient presses the operation buttons 14A, 14B, and 14C while confirming the operation screen. For example, the operation button 14C receives an input for moving the cursor on the operation screen, the operation button 14B receives an input for cancellation, and the operation button 14A receives an input for determination. Further, a shortcut for directly calling a specific function may be assigned to the operation buttons 14A, 14B, and 14C. The operation unit 22 outputs various operation signals by pressing the operation buttons 14A, 14B, and 14C in a predetermined order on each operation screen. Upon receiving the operation signal, the control unit 23 executes various controls according to the operation signal. The number of operation buttons 14A, 14B, 14C and the like are appropriately designed. Further, the operation buttons 14A, 14B, and 14C do not necessarily need to be pushbutton switches independent of each other. For example, a pressure-sensitive or electrostatic touch panel sensor may be superimposed on the display 13, and the operation buttons 14A, 14B, 14C and the display 13 may be configured as a touch panel display.

[Sensor part 24]
The sensor unit 24 includes the biosensor 12 described above and a peripheral circuit 28 that is provided inside the main body 11 and is electrically connected to the biosensor 12 inserted into the sensor insertion port 15. The sensor unit 24 shapes and processes the electrical signal generated by the biosensor 12 as necessary, and transmits it to the control unit 23. The sensor unit 24 can apply a specified voltage between the electrodes of the biosensor 12 based on the control of the control unit 23. The detailed configuration of the biosensor 12 will be described below.

[Biosensor 12]
As shown in FIGS. 3 and 4, the biosensor 12 has a generally flat plate shape in which the front-rear direction 92 is the longitudinal direction, the left-right direction 93 is the short direction, and the vertical direction 91 is the thickness direction. The biosensor 12 includes a first substrate 30, a first electrode 41, a second electrode 42, a spacer 50, and a second substrate 60. In order from the top, the second substrate 60, the spacer 50, the first electrode 41 and the second electrode 42, and the first substrate 30 are stacked and integrated in the vertical direction 91 in this order. Here, the 1st board | substrate 30, the spacer 50, and the 2nd board | substrate 60 are each comprised with the insulating material.

  From the rear end side of the biosensor 12 in the front-rear direction 92, the first electrode 41 and the second electrode 42 are exposed upward. The biosensor 12 is inserted into the sensor insertion port 15 from the rear end side. At that time, the exposed portions of the first electrode 41 and the second electrode 42 are in contact with electrodes (not shown) provided at the back of the sensor insertion port 15, respectively. Accordingly, the first electrode 41 and the second electrode 42 are electrically connected to the control unit 23 through the sensor unit 24.

  On the front end side of the biosensor 12 in the front-rear direction 92, there is a region (intermittent portion 51) in which a part of the spacer 50 is cut into a groove. A sample space 72 is formed between the first electrode 41 and the second electrode 42 that face each other in the vertical direction 91 via the intermittent portion 51. The sample space 72 is a space into which blood as a sample is introduced. The first electrode 41 and the second electrode 42 are exposed to the sample space 72, respectively. The blood is introduced from the introduction port 71 opened at the front end of the biosensor 12 by the intermittent portion 51. The blood introduced into the sample space 72 comes into contact with the first electrode 41 and the second electrode 42, respectively. The first substrate 30 has a vent 61 for releasing the air in the sample space 72 to the outside when blood is introduced.

  An enzyme that decomposes glucose in blood is immobilized on the portion where the first electrode 41 is exposed to the sample space 72. Examples of this enzyme include GOD and GDH. In addition to these enzymes, coenzymes and electron mediators may be immobilized. Examples of such coenzymes include pyrroloquinoline quinone, nicotinamide adenine dinucleotide, flavin adenine dinucleotide, and nicotinamide adenine dinucleotide phosphate that function as an electron carrier. Moreover, as an electron mediator, the compound containing transition metals, such as ruthenium, osmium, molybdenum, tungsten, iron, cobalt, is mentioned, for example. The immobilization of these enzymes and the like is realized by applying a solution containing the enzymes and the like to the first electrode 41 and drying it.

[Control unit 23]
The control unit 23 (an example of the control unit and the computer of the present invention) includes a CPU 31 (Central Processing Unit) for performing various controls and operations, a RAM 32 (Random Access Memory) for temporarily storing data, and a power supply for the device It has an EEPROM 33 (Electrically Erasable Programmable Read Only Memory) that stores data to be retained even after it is turned off. These are electrically connected to the display unit 21, the operation unit 22, and the sensor unit 24 via an ASIC 34 (Application Specific Integrated Circuit) and the bus 25. The control unit 23 controls the operation of each unit by the CPU 31 performing calculations based on a program stored in the EEPROM 33. In addition, the control unit 23 has a timer function that counts time based on a program stored in the EEPROM 33. For example, the time may be counted based on a system clock included in the circuit of the control unit 23. In addition, the control unit 23 may include a coprocessor, an ALU, or the like that assists the CPU 31 as necessary.

  In response to an operation signal from the operation unit 22 when the operation buttons 14A, 14B, and 14C are pressed, the control unit 23 loads various programs stored in the EEPROM 33 to the RAM 32 and executes them. An example of a program stored in the EEPROM 33 is a program for executing blood glucose level measurement. The program for executing the measurement of the blood sugar level is based on the electrical signal from the sensor unit 24, and performs a prescribed control for the control unit 23 to calculate the blood sugar level. The calculated blood glucose level is displayed on the display 13 by a predetermined display method. Details of the control performed by the control unit 23 based on a program for executing blood glucose level measurement will be described later.

  The program for executing blood glucose level measurement uses a lower module group that controls the overall operation of the blood glucose measurement device 10. Examples of the module include a module that controls display on the display 13, a module that interprets an operation signal from the operation unit 22, and a module for communication control via the bus 25. Since these modules can be appropriately designed by those skilled in the art as needed, details are omitted.

[Data table 81]
Further, the EEPROM 33 stores a data table 81 that is referred to based on a program that executes blood glucose level measurement. As shown in FIG. 5, the data table 81 includes a first table 82 and a second table 83. In the first table 82, the environmental temperature T (an example of the fourth data of the present invention), the glucose concentration C (an example of the first data of the present invention), and the potential difference E (an example of the second data of the present invention) Are associated. In the second table 83, the environmental temperature T, the glucose concentration C, and the current I (an example of the third data of the present invention) are associated with each other. These data tables may be constructed as, for example, a relational database managed by an RDBMS (Relational DataBase Management System).

  The environmental temperature T stored in the first table 82 and the second table 83 indicates the environmental temperature of the sample space 72, respectively. The glucose concentration C indicates the glucose concentration in the blood introduced into the sample space 72, that is, the blood glucose level. As for the environmental temperature T and the glucose concentration C, values in a range assumed at the time of normal measurement are stored for each fixed value. In the example of FIG. 5, the environmental temperature T is stored for each 1K from 283K to 300K. As for the glucose concentration C, values from 20 mg / dl to 600 mg / dl are stored for every 1 mg / dl. However, these values are examples, and those skilled in the art may appropriately change them according to the design requirements of the device. In the first table 82 and the second table 83, a record is constituted by a direct product of the environmental temperature T and the glucose concentration C.

  When blood glucose is measured, if blood is introduced into the sample space 72, a potential difference is generated between the first electrode 41 and the second electrode 42 due to the reaction between the enzyme and glucose. Here, the potential difference after the elapse of a predetermined time after blood is introduced depends on the glucose concentration in the introduced blood and the environmental temperature. The potential difference E stored in the first table 82 is the potential difference between the electrodes after elapse of time t1 (an example of the first time of the present invention) after blood having a glucose concentration C is introduced into the sample space 72 at the environmental temperature T. Is an estimated value. Here, t1 is a value set by those skilled in the art, and a common value is used for calculation of all potential differences E. A more detailed reason why the potential difference occurs and a method of calculating the estimated value will be described later.

  When a voltage is applied between the first electrode 41 and the second electrode 42 after blood is introduced into the sample space 72, the electrons emitted by the mediator. A current flows through the first electrode 41 and the second electrode 42. Here, the current when a voltage is applied after a predetermined time has elapsed since the introduction of blood depends on the glucose concentration C and the environmental temperature T in the introduced blood. The current I stored in the second table 83 is an electrode after the elapse of time t2 (an example of the second time of the present invention) at the ambient temperature T with reference to the time when blood having a glucose concentration C is introduced into the sample space 72. When application of the voltage V (an example of the first level voltage of the present invention) is started in the meantime, an estimation of the current flowing through each electrode after the elapse of time t3 (an example of the third time of the present invention, t2 <t3) Value. Here, the voltage V is a value set by a person skilled in the art, and a common value is used for calculation of all the currents I. A more detailed reason why the current flows and a method of calculating the estimated value will be described later.

[Reaction of glucose at the first electrode 41 and the second electrode 42]
The reaction of glucose in the sample space 72 is described in detail below. When blood is introduced into the sample space 72, the enzyme immobilized on the first electrode 41 reacts with glucose. For example, when GOD is used as an enzyme, GOD oxidizes glucose to generate gluconic acid and electrons. The electrons move to the first electrode 41 via the electron mediator. As the second electrode, for example, a reference electrode (standard electrode) such as a silver-silver chloride electrode is used. When the first electrode and the second electrode are connected by a potentiometer, a potential difference is generated between the first electrode 41 and the second electrode 42. Is observed. This potential difference is called the natural potential of the first electrode or the open circuit potential.

The natural potential E _WE of the first electrode 41 at this time is expressed by the following formula 1.

  Equation 1 is called the Nernst equation, and is an equation showing the potential of the electrode in the oxidation-reduction reaction. Here, E0 is a reference potential (formula potential). R is a gas constant (8.31 J / (K · mol)). F is the Faraday constant (96500 C / mol). T is the absolute temperature (K). cO is the oxidant concentration at the first electrode, and in this embodiment, it is the concentration of the dissolved oxide mediator previously applied on the first electrode, for example, ferricyan ion. cR is a reductant concentration at the first electrode, and in this embodiment, a concentration of a reduced mediator that has received electrons from an enzyme, for example, ferrocyan ion. Both cO and cR depend on time t. n is the number of electrons that move from one molecule of the reduced mediator to the first electrode.

  That is, based on Equation 1, it is possible to calculate the potential between the electrodes at an arbitrary time. The person skilled in the art calculates the potential difference E (second data of the present invention) corresponding to each environmental temperature T and glucose concentration C after the elapse of time t1 from the introduction of blood into the sample space 72, and the first table. 82 records are created.

  Further, when a voltage is applied between the first electrode 41 and the second electrode 42 by the control unit 23, ferrocyan ions are oxidized again and returned to ferricyan ions. At this time, electrons are emitted and a current flows through the first electrode 41 and the second electrode 42.

  The current I flowing at this time is an oxidation-reduction current of the electron mediator and is expressed by the following formula 2.

Equation 2 is called the Cottrell equation, and is an equation showing the current flowing through the electrode due to the redox reaction. Here, t is an elapsed time (s) from the start of voltage application. n is the number of electrons transferred from one molecule of the reduced mediator to the first electrode. F is the Faraday constant (96500 C / mol). A is the surface area (cm ² ) of the electrode. c _R is the concentration of reduced mediator at the first electrode (mol / cm ^3). D is the diffusion coefficient (cm ² / s) of the electron mediator in the sample solution introduced into the sample space. D has temperature dependence. π is the circumference ratio.

The current I stored in advance in the second table 83 can be calculated by the following method using Equation 2. In the set environment temperature T, the first electrode surface area A is known, to introduce the test solution was pre-adjusted glucose concentration to produce a reduced mediator concentration c _R. After a lapse of properly configured reaction time (t2 described above), a positive voltage is applied from sufficiently formula weight potential E ⁰ of the mediator to the first electrode, the set time t (s) (described above t3-t2 ) for measuring the current I _T of time has elapsed. Placing this IT the left side of the number 2, number 2 becomes equation for diffusion coefficient D, by solving this diffusion coefficient D _T at a temperature T is obtained. Substituting D _T obtained at each T required temperature range of the number 2, further known the parameters n, F, A, the set time t, by substituting each c _R required concentration ranges, each T required temperature range, the estimated value of the current I in each c _R required concentration range (third data of the present invention) are calculated.

The diffusion coefficient _DT is desirably obtained at a temperature interval as fine as possible in a necessary temperature range. From each value obtained at a coarser temperature interval, a function that approximates them is derived, You may make it obtain _DT in a desired temperature interval based on a function. Such a function can be derived, for example, by applying a fitting algorithm based on the least square method or the like to each obtained value.

  A person skilled in the art assumes a situation in which the voltage V is applied between the electrodes after the elapse of time t2 with respect to the time when blood is introduced into the sample space 72, and sets the environmental temperature T and the glucose concentration C after the elapse of time t3. The corresponding current I is calculated and a record in the second table 83 is created.

  However, the potential difference E and the current I used for each table may be determined by an experimental method in addition to being calculated by theoretical calculation. For example, a person skilled in the art may measure the potential difference and the current by using the samples having different glucose concentrations, reproducing the above reaction while sequentially changing the environmental temperature.

[Measure blood glucose level]
As described above, the control unit 23 executes control for blood glucose level measurement based on a program for executing blood glucose level measurement. Details of the control are set to the following details with reference to the flowchart of FIG. Note that the control described below does not necessarily have to be executed entirely based on a program, and at least a part thereof may be executed based on connection logic.

  Before starting the blood glucose measurement, the diabetic patient inserts the biosensor 12 into the sensor insertion port 15 of the blood glucose measurement device 10. As a result, a part of the first electrode 41 and the second electrode 42 come into contact with the contact inside the sensor insertion port 15, respectively, and the first electrode 41 and the second electrode 42 are electrically connected to the control unit 23, respectively. It becomes a state.

  Based on the determination that the biosensor 12 has been inserted, the control unit 23 loads the program of the EEPROM 33 (program for executing blood sugar level measurement) into the RAM 32 and executes it. Thereby, control of the flowchart of FIG. 6 is started. In order to enable the controller 23 to recognize the insertion of the biosensor 12, the sensor insertion port 15 may be provided with a mechanical, optical, or electrical sensor.

  First, the control unit 23 activates a circuit necessary for measurement and prepares for measurement (S1). That is, the blood glucose measuring device 10 is shifted to a state in which the blood glucose level can be measured. Moreover, the control part 23 applies the weak voltage for a detection between the 1st electrode 41 and the 2nd electrode 42, and measures the electric current based on the said voltage repeatedly (S2, S3). The controller 23 monitors whether blood is introduced into the sample space 72 based on this current.

  When the diabetic patient does not introduce blood into the sample space 72, the current is not detected because the first electrode 41 and the second electrode 42 are open (S3: No). Meanwhile, the control unit 23 maintains the monitoring state.

  When a diabetic patient introduces blood into the sample space 72, the patient pierces the palm or the like with a needle to exude blood. A diabetic patient holds the blood glucose measurement device 10 and brings the inlet 71 of the biosensor 12 into contact with the exuded blood. The blood is introduced into the sample space 72 from the inlet 71 by capillary action. Note that the act of a diabetic patient introducing blood into the sample space 72 is an example of the first step of the present invention.

  As shown in FIG. 7, the blood 80 introduced into the sample space 72 comes into contact with the first electrode 41 and the second electrode 42, respectively. Thereby, between electrodes will be in an energized state and a weak electric current will flow into control part 23 (S3: Yes). Based on the current, the control unit 23 determines that blood has been introduced into the sample space 72 and stops applying the detection voltage. That is, the monitoring state is interrupted.

  The control unit 23 interrupts the monitoring state and starts counting time, and stops the control of the flowchart during the counting (S5). Since the glucose reaction described above is started when the blood 80 is in contact with the first electrode 41, the reaction is promoted in parallel with the counting, and a potential difference is generated between the first electrode 41 and the second electrode 42. Arise. When the time count reaches t1, the control unit 23 measures the potential difference between the first electrode 41 and the second electrode 42 (S6). At this time, the control unit 23 rounds up the obtained potential difference value to a predetermined format, thereby matching the potential difference E stored in the first table 82 with the closest value. The control unit 23 temporarily stores the obtained potential difference in the RAM 32. Here, the time t1 is the same as the value used when the potential difference E of the first table 82 is determined. The value of t1 is stored in the EEPROM 33 when the blood glucose measurement device 10 is manufactured. The control of S6 is an example of the first control and the second step of the present invention.

  The control unit 23 continues to count the time even after the time t1 has elapsed (S7). When the time count reaches t2, the control unit 23 starts applying the voltage V between the first electrode 41 and the second electrode 42 (S8). By this voltage, the oxidation reaction of the ferrocyan ion described above is promoted. The control unit 23 measures the current flowing through the first electrode 41 and the second electrode 42 when the count reaches t3 (S9, S10). At this time, the control unit 23 rounds the obtained current value into a predetermined format to match the current I stored in the second table 83 with the closest value. The control unit 23 temporarily stores the obtained current in the RAM 32. Here, the time t2 and the voltage V are the same as the values used when the current I of the second table 83 is determined. The values of the time t2 and the voltage V are stored in the EEPROM 33 when the blood glucose measuring device 10 is manufactured. After measuring this current, the control unit 23 stops applying the voltage V (S11). The control of S8 and S10 is an example of the second control and the third step of the present invention.

  Subsequently, the control unit 23 refers to the first table 82 and searches for a record in which the potential difference E matches the potential difference measured in the control of S6 (S12). There may be a plurality of records that satisfy this condition. Hereinafter, a set of records extracted from the first table 82 by this inquiry is referred to as a first candidate record 84. Further, the control unit 23 refers to the second table 83 and searches for a record in which the current I matches the current measured in the control of S10 (S13). There may be a plurality of records that satisfy this condition. Hereinafter, a set of records extracted from the second table 83 by this inquiry is referred to as a second candidate record 85.

  FIG. 5 shows an example of the first candidate record 84 and the second candidate record 85 extracted under the control of S12 and S13. The figure shows an example in which the potential difference 293 mv is measured under the control of S6 and the current 15.16 mA is measured under the control of S10. That is, as the first candidate record 84, a record having a potential difference E of 293 mv is extracted, and there are three records corresponding to this. Further, as the second candidate record 85, a record having a current I of 15.16 mA is extracted, and there are three records corresponding to this.

  The control unit 23 searches the first candidate record 84 and the second candidate record 85 for a record in which both the environmental temperature T and the glucose concentration C match (S14). One record that satisfies this condition exists for each candidate record. Hereinafter, a record extracted from the first candidate record 84 by this inquiry is referred to as a first purpose record 86, and a record extracted from the second candidate record 85 is referred to as a second purpose record 87.

  FIG. 5 shows an example of the first purpose record 86 and the second purpose record 87 extracted by the control of S14. In the example shown in the figure, the records in which the environmental temperature T and the glucose concentration C are identical between the first candidate record 84 and the second candidate record 85 are only records in which the environmental temperature T is 283K and the glucose concentration C is 100 mg / dL. It is. The records extracted from each candidate record so as to satisfy this condition are a first purpose record 86 and a second purpose record 87, respectively. In addition, control of S12-S14 is an example of the 3rd control and 4th step of this invention.

  The control unit 23 displays the glucose concentration C indicated by the first purpose record 86 and the second purpose record 87 on the display 13 through the display unit 21 as the measured blood glucose level (S15). The diabetic patient can check the blood glucose level by visually checking the display 13. Note that the blood glucose level may be stored in the EEPROM 33 so that the diabetic patient can confirm the blood glucose level later.

[Effects of Embodiment]
According to this embodiment, since the first table 82 and the second table 83 are associated with each other by the environmental temperature T and the glucose concentration C, it is possible to eliminate the influence of the temperature on the blood glucose level measurement value without using the temperature sensor. it can. That is, the blood sugar level can be measured with high accuracy by a simple configuration.

  The potential difference E stored in the first table 82 and the value of the current I stored in the second table 83 can be determined by experiments in addition to calculations based on theory. That is, those skilled in the art can easily configure each table.

  Further, the potential difference and current value between the electrodes to be measured may change depending on the time after blood is introduced into the sample space 72. In this configuration, the potential difference between the electrodes is measured after a lapse of time t1 after blood is introduced into the sample space 72, and the current is measured by applying a voltage between the electrodes after the lapse of time t2. . Therefore, the potential difference E stored in the first table 82 and the value of the current I stored in the second table 83 can be brought close to values obtained by actual measurement. That is, the blood sugar level can be measured with higher accuracy.

  In addition to the enzyme, an electron mediator is attached to the first electrode 41, whereby more stable measurement is realized.

[Modification 1]
In the embodiment described above, the data table 81 is configured by the first table 82 and the second table 83. However, in the present modification, the data table is configured by one table, and the first table 82 and the second table 83 are configured. The two tables 83 collected as one table are stored in the EEPROM 33 as the data table 88. Details of the data table 88 according to this modification will be described below.

  In the embodiment described above, the control unit 23 refers to the first table 82 and the second table 83 based on the potential difference measured by the control of S6 and the current measured by the control of S10, respectively. The value was specified. Here, since the glucose concentration C is uniquely determined when the potential difference E and the current I are determined, it is possible to create a data table 88 having the potential difference E and the current I as a main key and the glucose concentration C as a subordinate key. . Records in the data table 88 can be obtained by extracting all record combinations between the first table 82 and the second table 83 that have the same environmental temperature T and glucose concentration C. The data table 88 can be created using, for example, a database operation language such as SQL (Structured Query Language).

  An example of the data table 88 is shown in FIG. In the data table 88, the potential difference E and the current I are the main keys, that is, there is no record in the data table 88 where the potential difference E and the current I are both the same value. In the example shown in the figure, the data table 88 does not hold the environmental temperature T, but may hold it as a subordinate key. In this modification, the control unit 23 refers to the data table 88 instead of executing the control of S12 to S14 in the above-described embodiment. At that time, the control unit 23 searches the record by associating the potential difference measured by the control of S6 with the potential difference E and the current measured by the control of S10 with the current I. The control unit 23 displays the glucose concentration C of the extracted record as a blood glucose level on the display 13 through the display unit 21.

  In the present modification, since the data table 88 is combined into one, the reference amount of the table is reduced, and the time until the blood sugar level is displayed on the display 13 can be shortened.

[Other variations]
In the above-described embodiment, only the blood glucose level is displayed on the display 13 after the blood glucose level is measured. However, even if the environmental temperature T indicated by the first objective record 86 and the second objective record 87 is also displayed. Good.

  In addition, the blood glucose measurement device 10 is not necessarily configured as a portable type as in the above-described embodiment, and may be configured as a stationary type on the assumption that it is installed in a hospital or the like. Moreover, the biosensor 12 does not necessarily need to be detachable, and the shapes of the first electrode 41 and the second electrode 42 can be appropriately changed according to the request of the device.

  Moreover, the flowchart of FIG. 6 mentioned above is an example, and if it has the same function, the order of detailed control may differ somewhat.

  In the embodiment described above, an example in which blood is used as a biological sample and glucose is used as a substrate is shown in the present invention. The biological sample of the present invention is saliva, sweat, urine, plasma, or the like. The substrate may be any component in the biological sample. Enzymes and mediators are appropriately used depending on the substrate to be measured.

10 ... blood glucose measurement device (biological sample measurement device)
23 ... Control unit 41 ... first electrode 42 ... second electrode 72 ... sample space 81 ... data table 82 ... first table 83 ... second table 88 ... Data table

Claims (6)

A first electrode to which an enzyme that reacts with a substrate in a biological sample to generate electrons is attached;
A second electrode provided apart from a sample space into which the biological sample can be introduced with respect to the first electrode;
First data indicating a substrate concentration in the biological sample, second data indicating an estimated value of a potential difference between the first electrode and the second electrode based on the reaction, and the first electrode and the second electrode A storage unit that stores a data table associated with third data indicating an estimated value of a current that flows when a first-level voltage is applied to the biological sample via
A control unit electrically connected to each of the first electrode, the second electrode, and the storage unit,
The control unit
A first control for measuring a potential difference between the first electrode and the second electrode in the enzyme reaction;
A second control for applying a first level voltage between the first electrode and the second electrode and measuring a current value flowing through the first electrode and the second electrode;
Searching the first data from the data table based on the second data corresponding to the potential difference measured by the first control and the third data corresponding to the current value measured by the second control. 3 is a biological sample measuring device that executes three controls. The above data table is
A first table in which the first data, the second data, and the fourth data indicating the environmental temperature of the sample space are associated with each other;
The biological sample measurement device according to claim 1, further comprising: a second table in which the first data, the third data, and the fourth data are associated with each other. In the third control, the control unit
Based on the second data corresponding to the potential difference measured by the first control, a candidate for the set of the first data and the fourth data is searched from the first table,
Based on the third data corresponding to the current value measured by the second control, a candidate for the set of the first data and the fourth data is searched from the second table,
From the set candidates retrieved from the first table and the set candidates retrieved from the second table, a set in which both the first data and the fourth data match is retrieved, The biological sample measuring device according to claim 2, wherein a substrate concentration in the biological sample is specified from the first data. The second data in the data table indicates an estimated value of a potential difference after the first time has elapsed since the biological sample was introduced into the sample space.
The third data in the data table is a first level in the biological sample via the first electrode and the second electrode after a lapse of a second time on the basis of the time when the biological sample is introduced into the sample space. When the application of the voltage is started, an estimated value of the current flowing through the first electrode and the second electrode after the third time has elapsed,
The control unit
Having detection means for detecting that the biological sample has been introduced into the sample space;
The first control is executed after a first time has elapsed since the detection means detects that the biological sample has been introduced into the sample space,
The application of the voltage in the second control is performed after the second time has elapsed since the detection means detects that the biological sample has been introduced into the sample space,
The living body according to any one of claims 1 to 3, wherein the current is measured in the second control after a lapse of a third time since the detecting means detects that the biological sample has been introduced into the sample space. Sample measuring device. The enzyme degrades glucose,
The biological sample measurement device according to claim 1, wherein an electron mediator is further attached to the first electrode. A first step of introducing the biological sample between a pair of electrodes to which an enzyme that reacts with a substrate in the biological sample to generate electrons is attached;
A second step of measuring a potential difference between the electrode pair in the enzyme reaction;
A third step of applying a voltage between the electrode pairs and measuring the output current value;
The computer receives first data indicating the substrate concentration in the biological sample, second data indicating an estimated value of a potential difference between the electrode pair in the enzyme reaction, and first data on the biological sample via the electrode pair. The second data corresponding to the potential difference measured in the second step, and the third step from the data table associated with the third data indicating the estimated value of the current flowing when the level voltage is applied And a fourth step of searching for the first data on the basis of the third data corresponding to the current value measured by the method of measuring a substrate concentration in a biological sample.

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