JP2009174870A - Measuring display device to be mounted with biosensor mounted - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring display device capable of measurements, regardless of the height of the concentration of a substrate having specificity to an enzyme carried by a biosensor. <P>SOLUTION: This measuring display device 10 includes a voltage source 12 for applying a voltage to an electrode 104 of the biosensor 100; a current-voltage conversion circuit 14 for converting a current flowing in the electrode 104 into a voltage; an amplifying circuit 16 for amplifying an output from the current-voltage conversion circuit 14; and an operation control part 18a into which the output from the current-voltage conversion circuit 14 and an output from the amplifying circuit 16 are input. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a measurement display device that is connected to a biosensor and measures a component amount of a substrate.

  Conventionally, various biosensors and measurement display devices including Patent Document 1 have been disclosed. For example, a part of the biosensor 100 is shown in FIG. Two platinum electrodes 104 are laminated on the PET resin 102. A coating solution containing an enzyme is applied onto the two electrodes 104 by a dispenser to form an enzyme film 106. Electrons are exchanged by the reaction between the enzyme and blood and the two electrodes 104 are conducted. The value of the current flowing through the electrode 104 varies depending on the blood sugar level contained in blood or the like. That is, an electrical signal proportional to the component amount (or concentration) of the substrate having specificity for the enzyme can be obtained. This electric signal is measured and displayed by a measurement display device. The biosensor is not limited to the blood glucose level of blood, and various components can be tested by appropriately selecting an enzyme.

  FIG. 3 shows a circuit configuration of the measurement display device 30. The biosensor 100 used is a blood glucose level sensor. The voltage output from the arithmetic control unit 18 b of the voltage source 12 is converted into an analog value by a digital / analog converter (DAC) 22 and applied to one electrode 104 of the biosensor 100. As shown in FIG. 4, the application of voltage is as follows: (1) First, a predetermined value is set and a current is detected. (2) Wait for a predetermined time after the current is detected, and proceed with the reaction between the enzyme and blood. (3) After a predetermined time has elapsed, the potential is lowered to E1 with time, and then the potential is raised to E2.

As described above, the reaction between the enzyme and blood causes the transfer of electrons, and the two electrodes 104 are conducted. The potential V _out of the output terminal P3 of the operational amplifier OP1 is i × Rx + V _GND . This potential _Vout is converted into digital data by an analog / digital converter (ADC) 24 and input to the arithmetic control unit 18a. The arithmetic control unit 18a performs a predetermined calculation from the input potential value to obtain a blood sugar level.

  When measuring a blood glucose level, it is required to increase measurement accuracy in a low concentration range. Even if the accuracy of the resistor Rx, the operational amplifier OP1, etc. is increased, if the accuracy and resolution of the two converters 22 and 24 are the same as the conventional one, the measurement accuracy is not improved. It is conceivable to change the resolution of the two converters 22 and 24 to a high bit number (for example, change from 10 bits to 12 bits) or use ΔΣ type analog-digital conversion (see Patent Document 2). There is a limit due to noise.

  Further, as shown in FIG. 5, a measurement display device 40 in which an amplifier circuit 42 is added between the operational amplifier OP1 and the arithmetic control unit 18a can be considered. Amplification increases the measurement accuracy in the low concentration range. However, as shown in FIG. 6, the current varies greatly depending on the blood glucose level. Therefore, even if amplification is possible in the low concentration region, the high concentration region is saturated quickly due to amplification, and measurement in the high concentration region cannot be performed. The blood glucose level may be higher or lower than the predetermined range, and it is necessary to accurately measure both the high concentration and the low concentration. However, at present, only one of them can be measured as described above.

  Although the blood glucose level sensor has been described as an example, the above-described problem occurs depending on the concentration of the substrate having specificity for the enzyme even with other biosensors.

JP 2000-162176 A JP 2002-340853 A

  An object of the present invention is to provide a measurement display device that can perform measurement regardless of the concentration of a substrate having specificity for an enzyme of a biosensor.

  In the measurement display device of the present invention, a biosensor having an enzyme is attached on at least two electrodes. The measurement display device receives a voltage source that applies a voltage to the electrode, a current-voltage conversion circuit that converts a current flowing through the electrode into a voltage, and an output voltage of the current-voltage conversion circuit, and amplifies the output voltage. The amplifier circuit includes an arithmetic control unit to which the output voltage of the current-voltage conversion circuit and the output voltage of the amplifier circuit are input.

  When the enzyme and the substrate of the sample react with each other, when a voltage is applied from the power source to the electrodes, electrons are transferred between the electrodes. The current flowing through the electrode is converted into a voltage by a current-voltage conversion circuit. Further, the output of the current-voltage conversion circuit is amplified by an amplifier circuit. Both the output of the current-voltage conversion circuit and the output of the amplifier circuit are input to the arithmetic control unit.

  The arithmetic control unit selects the output voltage of the amplifier circuit if the output voltage of the amplifier circuit is within a pre-stored threshold range, and the output voltage of the amplifier circuit is outside the pre-stored threshold range. If so, the output voltage of the current-voltage conversion circuit is selected.

  A switch for alternately inputting the output voltage of the current-voltage conversion circuit and the output voltage of the amplifier circuit to the arithmetic control unit may be included. When input to the arithmetic control unit, both outputs are alternately input by the switch.

  In the present invention, the output voltage of the current-voltage conversion circuit and the output voltage of the amplifier circuit are input to the calculation control unit for obtaining the concentration of the substrate. When determining the concentration of the substrate, it is possible to appropriately select which output voltage is used, and calculation is possible regardless of the concentration of the substrate.

  The measurement display device of the present invention will be described with reference to the drawings. The biosensor connected to the measurement display device will be described using the biosensor 100 of FIG. 2 described in the related art.

  The measurement display device 10 shown in FIG. 1 includes a voltage source 12 that applies a voltage to the electrode 104 of the biosensor 100, a current-voltage conversion circuit 14 that converts a current flowing through the electrode 104 into a voltage, and a current-voltage conversion circuit 14. It includes an amplifier circuit 16 that amplifies the output voltage, and an arithmetic control unit 18a to which the output voltage of the current-voltage conversion circuit 14 and the output voltage of the amplifier circuit 16 are input.

  The voltage source 12 includes an arithmetic control unit 18 b and a digital / analog converter (DAC) 22. The voltage source 12 applies a voltage to the electrode 104 of the biosensor 100. The voltage specified by the arithmetic control unit 18 b is converted from a digital value to an analog voltage by the DAC 22 and applied to the electrode 104. The applied voltage changes with time after a lapse of a certain time. Specifically, as shown in FIG. 4, (1) wait at a constant potential until a current where the enzyme has reacted with blood is detected, and (2) turn off the power supply 12 until the reaction between the enzyme and blood proceeds. Wait for a certain period of time (3) After the power supply 12 is turned on, the potential is lowered linearly to E1 and then raised linearly to E2. Note that the calculation control unit 18b of the voltage source 12 may be the same as the calculation control unit 18a on the right side of FIG. 1 that calculates the component amount of the substrate by calculation.

The current-voltage conversion circuit 14 includes an operational amplifier OP1 and a resistor Rx. A resistor Rx is connected to the inverting input terminal (−) of the operational amplifier OP1, and the non-inverting input terminal (+) is the ground level V _GND . Negative feedback is applied from the output terminal P3 of the operational amplifier OP1 through the resistor Rx. Since the input impedance of the operational amplifier OP1 itself is very high, most of the current flowing through the electrode 104 flows through the resistor Rx. The potential V _out1 of the output terminal P3 of the operational amplifier OP1 is expressed by the following formula 1.

The amplifier circuit 16 includes an operational amplifier OP2 and resistors Rf and Rs. The output of the current-voltage conversion circuit 14 is input to the non-inverting input terminal (+) of the operational amplifier OP2. The inverting input terminal (−) is grounded by connecting the resistor Rs, and negative feedback is applied from the output terminal P4 by the resistor Rf. The potential V _out2 of the output terminal P4 of the operational amplifier OP2 is _expressed by the following mathematical formula 2.

  The amplification factor of the amplifier circuit 16 is 1 + Rf / Rs, and the resistors Rf and Rs are appropriately selected so that desired amplification can be performed. If it is too large, the concentration range of the substrate that can be amplified becomes narrow. If it is small, the range of substrate concentration that can be amplified is expanded, but sufficient amplification cannot be performed. For example, resistors Rf and Rs that can be amplified four times are selected.

  The output voltage of the current-voltage conversion circuit 14 and the output voltage of the amplifier circuit 16 are input to the arithmetic control unit 18a via an analog / digital converter (ADC) 24. The arithmetic control unit 18a is a microcomputer that calculates a blood sugar level by performing a predetermined calculation from the input output voltage. The required substrate value varies depending on the type of biosensor. The ADC 24 may be connected to each of the output terminals P3 and P4.

The arithmetic control unit 18a has two inputs. Arithmetic control unit 18a selects the output voltage _{V out2} of the amplifying circuit 16 as long as it is within the range of the output voltage _{V out2} of the amplifying circuit 16 is stored in advance threshold. Output voltage V _out2 of the amplifying circuit 16 selects the output voltage V _out1 of the current-voltage conversion circuit 14 if outside the range of the threshold value stored in advance. The threshold value is a value when the output V _out2 is not saturated when amplified by the amplifier circuit 16. The threshold value is a value having a certain range, and is set in advance according to the specifications of the biosensor 100 and the amplifier circuit 16 to be used. Therefore, if it is not saturated when it is amplified, that value is used, and if it is saturated when it is amplified, a value that is not amplified is used. The arithmetic control unit 18a uses the selected value to determine the amount of a substrate component such as a blood glucose level.

  The reason why the above two inputs are made to the arithmetic control unit 18a is that the biosensor 100 and the substrate to be measured are irreversible. For example, when only the amplified output voltage is acquired, the biosensor 100 is saturated. 100 must be replaced and restarted from the beginning without amplification. By obtaining both output voltages regardless of the presence or absence of amplification, it is possible to prevent redoing from the beginning.

  In addition, a display for displaying a value such as a blood glucose level and a button for starting / ending the measurement display device 10 are included. The arithmetic control unit 18a uses a memory as necessary to store the obtained substrate value.

  Even if the analog / digital conversion is performed with 10 bits and the offset voltages of the operational amplifiers OP1 and OP2 and the accuracy of the reference power supply are increased, a difference between devices occurs. When analog / digital conversion is performed with 12 bits, the difference between devices is improved.

  As described above, in the present invention, two values are input to the arithmetic control unit 18a. The arithmetic control unit 18a can switch the value to be used in accordance with the concentration of the substrate. If the concentration is low, the amplified value can be used to increase accuracy. If the concentration is high, saturation can be prevented by using a value that is not amplified. Since the optimum output can be used when determining the concentration of the substrate, the accuracy of the determined concentration of the substrate is increased.

As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment. For example, switches may be connected to the output terminal P3 of the current-voltage conversion circuit 14 and the output terminal P4 of the amplifier circuit 16, respectively. The switch uses a switching element such as a MOSFET. Pulses are input to both switches so that both switches are turned on alternately. You may make it output a pulse from the calculation control part 18a. By alternately turning on the switches, the outputs V _out1 and V _out2 are input to the arithmetic control unit 18a.

The reason why both switches are alternately turned on is that the outputs V _out1 and V _out2 are input to the arithmetic control unit 18a regardless of the presence or absence of amplification. As described above, the enzyme of the biosensor 100 can only perform an irreversible reaction. For example, if only the amplified output voltage is acquired, the biosensor 100 is replaced when it is saturated, and the process is repeated from the beginning without amplification. There must be. By switching at high speed, both output voltages can be obtained regardless of the presence or absence of amplification.

_Moreover, until the _{V out2} is saturated enter the _{V out2} to the calculation control unit 18a, it may be input to _{V out1} to the calculation control unit 18a when saturated. When the calculation control unit 18a obtains the component amount of the substrate, V _out2 is used until saturation, and V _out1 is used after saturation. If V _out2 is not saturated, the amount of the component of the substrate is determined only by V _out2 . A switch is connected to each of the output terminal P3 of the current-voltage conversion circuit 14 and the output terminal P4 of the amplifier circuit 16, and the arithmetic control unit 18a sends a signal to the switch so as to operate as described above. The arithmetic control unit 18a can switch the value to be used in accordance with the concentration of the substrate, and can determine the concentration of the substrate using the optimum value.

  In addition, the present invention can be carried out in a mode in which various improvements, modifications, and changes are added based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

It is a figure which shows the circuit structure of the measurement display apparatus of this invention. It is a figure which shows a part of biosensor, (a) is a front view, (b) is the YY sectional view taken on the line of (a). It is a figure which shows the circuit structure of the conventional measurement display apparatus. It is a graph which shows the time change of the applied voltage to a biosensor, and the electric current which flows into an electrode. It is a figure which shows the circuit structure which added the amplifier circuit to the measurement display apparatus of FIG. It is a graph which shows the relationship between the scanning electric potential at the time of test | inspecting a blood glucose level, and the electric current which flows into an electrode.

Explanation of symbols

10, 30, 40: Measurement display device 12: Voltage source 14: Current-voltage conversion circuit 16, 42: Amplification circuit 18a, 18b: Arithmetic control unit 22: Digital / analog converter 24: Analog / digital converter 100: Biosensor 102: PET resin 104: Electrode 106: Enzyme film OP1, OP2: Operational amplifiers Rx, Rf, Rs: Resistance

Claims (3)

A measurement display device in which a biosensor having an enzyme is mounted on at least two electrodes,
A voltage source for applying a voltage to the electrode;
A current-voltage conversion circuit for converting a current flowing through the electrode into a voltage;
An amplification circuit that receives an output voltage of the current-voltage conversion circuit and amplifies the output voltage;
An output controller of the current-voltage converter circuit and an output voltage of the amplifier circuit are input, and an arithmetic control unit for obtaining the amount of the substrate component of the sample that has reacted with the enzyme
Measuring display device including The arithmetic control unit selects the output voltage of the amplifier circuit if the output voltage of the amplifier circuit is within a pre-stored threshold range, and the output voltage of the amplifier circuit is outside the pre-stored threshold range. The measurement display device according to claim 1, wherein the output voltage of the current-voltage conversion circuit is selected. 3. The measurement display device according to claim 1, further comprising a switch for alternately inputting the output voltage of the current-voltage conversion circuit and the output voltage of the amplifier circuit to the arithmetic control unit.

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