Measuring device

Abstract

Even when transmitting data wirelessly, the system should accurately measure the concentration of the substance being measured based on the electrical signal detected by the electrochemical sensor. [Solution] A measuring device comprising an electrochemical sensor having a working electrode containing a substance capable of recognizing a substance to be measured, a differential circuit for differentiating the electrical signal output from the electrochemical sensor, and a wireless transmitter connected to the output of the differential circuit.

Description

Technical Field

[0001] The present invention relates to an apparatus for measuring a substance to be measured in a solution using an electrochemical method, the apparatus comprising a wireless transmission unit.

Background Art

[0002] In recent years, with the increasing health awareness, there has been a growing need to selectively detect substances in biological fluids such as sweat, saliva, urine, tears, and blood in order to monitor the physical condition of the body. Among these, non-invasive measurements that do not involve procedures that harm the subject's body, such as blood collection, have attracted attention. In such non-invasive measurements, the substance to be measured may be monitored while the measuring device is attached to the subject's body. In order to facilitate attachment to the body, a small-sized measuring device is required.

[0003] There is an electrochemical sensor that measures a specific substance to be measured, such as a biological substance, by an electrical signal from an electrode in contact with a solution containing the substance to be measured. Furthermore, when a film containing a substance having the ability to selectively recognize the substance to be measured is formed on the electrode of the electrochemical sensor, more selective and sensitive detection of the substance to be measured becomes possible. Such an electrochemical sensor has a simple structure and can be miniaturized.

[0004] Non-Patent Document 1 discloses a wireless and body-wearable electrochemical sensor for non-invasively measuring electrolytes and metabolites in biological fluids such as sweat, saliva, and urine by an electrochemical method. Patent Document 1 discloses that a device for measuring the concentration of an analyte such as glucose includes a sensor having a film containing an enzyme such as glucose oxidase on an electrode, and that the device is configured to include a transdermal analyte sensor and an electronic device unit for wirelessly transmitting analyte information to a receiver.

[0005] Patent Document 2 discloses a concentration measurement method in which a first-order differential signal is generated from an electrical signal from an enzyme electrode, and the concentration of a target substance is measured based on the maximum value of the first-order differential signal. In order to suppress the influence of noise caused by the contact of the target substance with the enzyme membrane attached to the enzyme electrode, the concentration measurement is performed by ignoring the corresponding maximum value of the first-order differential signal within a predetermined time after the measurement point in which the target substance comes into contact with the enzyme membrane. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2024-26364 [Patent Document 2] Japanese Patent Application Publication No. 7-113783 [Non-patent literature]

[0007] [Non-Patent Document 1] Y. Bi et. al., Anal. Chem. 2023, 95, 6690-6699 [Overview of the project] [Problems that the invention aims to solve]

[0008] The inventors of this invention believed that by transmitting electrochemical measurement data wirelessly to an external device and performing complex data processing on the external device, it would be possible to create a smaller, more easily wearable measuring device. In other words, for measuring biological substances and the like, it is desirable that the device be able to transmit measurement data wirelessly in order to facilitate portability and wearability. However, wireless transmission is susceptible to noise.

[0009] On the other hand, in the measurement of biological substances, the rate of change in the concentration of the substance being measured (time derivative) is sometimes more useful than the concentration of the substance itself. Also, depending on the measurement principle of the electrochemical sensor, the time derivative of the electrical signal, rather than the electrical signal of the electrode itself, may reflect the concentration of the substance being measured. Therefore, the derivative of an electrical signal can be useful information for measuring biological substances and the like. However, the differentiation of an electrical signal is basically a high-pass filter process, which is susceptible to noise. In particular, when data is transmitted wirelessly, the transmitted data is prone to noise, and therefore the differentiation process is affected by the noise. For example, when performing differentiation processing on measurement data from a sensor disclosed in Patent Document 1 or Non-Patent Document 1 after wireless transmission, there was a problem that the measurement accuracy was reduced due to the influence of noise.

[0010] By making the time interval for wireless transmission considerably shorter than the time interval for data measurement, and by averaging the wirelessly transmitted data before differential processing, the accuracy of the differential value can be improved. However, increasing the frequency of wireless transmission increases the power consumption of the sensor, leading to the problem of reduced operating time due to battery depletion.

[0011] The sensor disclosed in Patent Document 2 has a differential circuit for generating a first-order differential signal, as well as a switch, a peak detection circuit, etc., to ignore the maximum value of the first-order differential signal for a certain period of time. Therefore, the circuit is large and unsuitable for body wear.

[0012] The present invention provides a small, wearable measuring device that can be attached to the body or other body parts, enabling high-precision measurement of data regarding the concentration of a substance to be measured based on electrical signals detected by an electrochemical sensor, while suppressing the effects of noise associated with wireless transmission, even when transmitting data wirelessly. [Means for solving the problem]

[0013] A representative embodiment of the present invention is described below. [1] An electrochemical sensor equipped with a working electrode containing a substance capable of recognizing the substance to be measured, A differentiating circuit for differentiating the electrical signal output from the electrochemical sensor, and A wireless transmitter connected to the output of the differential circuit, A measuring device equipped with the following features. [2] The measuring apparatus according to [1], further comprising a low-pass filter between the differential circuit and the wireless transmission unit. [3] The measuring device according to [1] or [2], wherein the electrode system of the electrochemical sensor is a two-electrode system consisting of the working electrode and the counter electrode, or a three-electrode system consisting of the working electrode, the counter electrode and the reference electrode. [4] The measuring device according to [1] or [2], wherein the electrical signal is a current or a voltage. [5] The measuring apparatus according to [1] or [2], wherein the substance having the ability to recognize the substance to be measured is an enzyme. [6] The measuring apparatus according to [5], wherein the enzyme is an enzyme that can exchange electrons with the electrode by reaction with the substance to be measured. [7] The measuring apparatus according to [6], wherein the working electrode contains a redox substance that can be reversibly oxidized and reduced. [8] The measuring apparatus according to [7], wherein the redox substance is oxidized or reduced by a product produced by the reaction between the substance to be measured and the enzyme. [9] The measuring apparatus according to [7], wherein the redox substance constitutes a redox layer arranged in contact with the surface of the conductive layer of the working electrode, and the substance having the ability to recognize the substance to be measured constitutes a layer arranged in direct contact with the redox layer.

[10] A method for measuring the concentration of the substance to be measured in a solution, Using an electrochemical sensor equipped with a working electrode containing a substance capable of recognizing the substance to be measured, an electrical signal containing information regarding the concentration of the substance to be measured is obtained. To obtain the differential value of the electrical signal, To wirelessly transmit an electrical signal relating to the said differential value, and The wirelessly transmitted data is acquired as data relating to the concentration of the substance being measured. Methods that include... [Effects of the Invention]

[0014] Since the measuring device provided by the present invention uses a configuration in which an electrical signal detected by an electrochemical sensor is wirelessly transmitted through a differential circuit, even when wireless transmission is used, it is possible to measure with high accuracy data regarding the concentration of a substance to be measured based on the electrical signal detected by the sensor. Further, since the electrical signal detected by the sensor in the measuring device of the present invention is wirelessly transmitted and processed by an external device, the device can be miniaturized, thereby having the advantage of being easy to carry and attach to the body. Therefore, the measuring device is suitable as a portable measuring device or as a wearable device for measuring biological substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] [Figure 1] A block diagram showing an embodiment of the measuring device of the present invention. [Figure 2] A block diagram showing another embodiment of the measuring device of the present invention. [Figure 3] A schematic diagram of a two-electrode system electrochemical sensor, which is an embodiment of the electrochemical sensor in the measuring device of the present invention. <00OO094> [Figure 4] A schematic diagram of a three-electrode system electrochemical sensor, which is an embodiment of the electrochemical sensor in the measuring device of the present invention. [Figure 5] Patterns (A) of electrodes and side views (B) of working electrodes used in Examples 1 to 2 and Comparative Examples 1 to 2. <OO00099>Schematic diagrams explaining glucose concentration measurement systems used in Example 1 and Comparative Example 1. A: Example 1, B: Comparative Example 1. [Figure 7] Changes in glucose concentration over time measured in Example 1 and Comparative Example 1. A: Example 1, B: Comparative Example 1. [Figure 8] Schematic diagrams explaining glucose concentration measurement systems used in Example 2 and Comparative Example 2. A: Example 2, B: Comparative Example 2. [Figure 9] Changes in glucose concentration over time measured in Example 2 and Comparative Example 2. A: Example 2, B: Comparative Example 2. [Figure 10]The electrode patterns used in Example 3 and Comparative Example 3. [Figure 11] A schematic diagram illustrating the glucose concentration measurement system used in Example 3 and Comparative Example 3. A: Example 3, B: Comparative Example 3. [Figure 12] The percentage change in glucose concentration measured in Example 3 and Comparative Example 3. A: Example 3, B: Comparative Example 3. [Modes for carrying out the invention]

[0016] The present invention provides a measuring device for measuring the concentration of a substance to be measured in a solution containing the substance. The measuring device of the present invention comprises an electrochemical sensor having a working electrode containing a substance having the ability to recognize the substance to be measured, a differentiating circuit for differentiating the electrical signal output from the electrochemical sensor, and a wireless transmitting unit connected to the output of the differentiating circuit.

[0017] Hereinafter, exemplary embodiments of the measuring device of the present invention will be described with reference to the drawings.

[0018] Figure 1 is a block diagram representing one embodiment of the measuring device of the present invention. In the measuring device shown in Figure 1, a differential circuit is connected to the output of an electrochemical sensor, and a wireless transmission unit is connected to the output of the differential circuit. The measuring device of the present invention transmits data to an external device (for example, an external information processing terminal in Figure 1) via wireless transmission from the wireless transmission unit.

[0019] The electrochemical sensor comprises electrodes, the electrodes including a working electrode containing a substance capable of recognizing the substance to be measured (also referred to herein as the "recognition substance"). When the electrochemical sensor is brought into contact with a solution containing the substance to be measured, the substance to be measured and the recognition substance react, or the electrochemical reaction of the substance produced by the reaction changes the electrical properties of the working electrode, thereby causing the electrochemical sensor to output an electrical signal containing information regarding the concentration of the substance to be measured. The differential circuit differentiates the electrical signal output from the electrochemical sensor and outputs an electrical signal corresponding to the obtained differential value. The electrical signal output from the differential circuit is input to the wireless transmission unit and wirelessly transmitted from the wireless transmission unit to an external device.

[0020] Since differentiating circuits are susceptible to noise, it is preferable that the electrical signal from the differentiating circuit be processed to reduce high-frequency noise before being sent to the wireless transmitter. In another embodiment of the measuring device of the present invention, as shown in Figure 2, a low-pass filter is provided between the differentiating circuit and the wireless transmitter. The electrical signal output from the differentiating circuit is subjected to high-frequency noise reduction by the low-pass filter before being wirelessly transmitted to the external device by the wireless transmitter. Therefore, in this specification, "connected to the output" of a component such as a sensor or circuit includes not only direct connections but also indirect connections via components that remove noise from the output of the differentiating circuit.

[0021] The external device receives data transmitted from the wireless transmission unit, processes the received data as needed, and records, displays, etc., the data. In this invention, the electrical signal detected by the electrochemical sensor of the measuring device is wirelessly transmitted to the external device, and complex data processing is performed by the external device. For this reason, the measuring device of the present invention can be miniaturized and is easy to carry or wear on the body. The measuring device of the present invention is suitable as a wearable device for measuring biological substances.

[0022] The components of the measuring device of the present invention are illustrated in more detail below.

[0023] <Electrochemical Sensor> An electrochemical sensor comprises a working electrode and a counter electrode (or reference electrode). The working electrode and the counter electrode are arranged so that they can each come into contact with a solution containing the substance to be measured, but they do not come into electrical contact with each other.

[0024] A substance capable of recognizing the substance to be measured (recognition substance in this specification) is immobilized on the working electrode used in the electrochemical sensor. When the electrochemical sensor is brought into contact with a solution containing the substance to be measured, the substance to be measured undergoes an electrochemical reaction at the working electrode, causing changes in the electrical state of the working electrode, such as the potential of the working electrode relative to the counter electrode, the current flowing when the working electrode and the counter electrode are electrically connected, and the impedance between the working electrode and the counter electrode. The electrochemical sensor outputs an electrical signal relating to the electrical state of the working electrode.

[0025] The electrical signal output by the electrochemical sensor may be any signal, such as voltage, current, power, or frequency and phase as an AC signal. However, for ease of processing in the differentiating circuit connected to the output of the electrochemical sensor, the electrical signal is preferably voltage or current.

[0026] When the electrochemical sensor converts the current flowing when the working electrode and the counter electrode are electrically connected into an electrical signal and outputs it, the electrochemical sensor may include a mechanism to set the potential of the working electrode relative to the counter electrode to a predetermined value. Furthermore, when the electrochemical sensor converts the impedance between the working electrode and the counter electrode into an electrical signal and outputs it, the electrochemical sensor may include a mechanism to apply a predetermined DC voltage, or an AC voltage with a predetermined amplitude and frequency, between the working electrode and the counter electrode.

[0027] In one embodiment, the electrode system of the electrochemical sensor in the measuring device of the present invention is a two-electrode system consisting of a working electrode and a counter electrode (reference electrode), as shown in Figure 3. In another embodiment, the electrode system of the electrochemical sensor in the measuring device of the present invention may be a three-electrode system, as shown in Figure 4, which further includes a reference electrode that can come into contact with a solution containing the substance to be measured, independently of the working electrode and the counter electrode. In such a three-electrode system, the reference electrode functions as the reference electrode.

[0028] In the two-electrode system, the working electrode and the counter electrode may be independent electrodes, as shown in Figure 3A, or they may be electrodes formed on the same substrate, as shown in Figure 3B. In the three-electrode system, the working electrode, the counter electrode, and the reference electrode may be independent electrodes, as shown in Figure 4A, or they may be electrodes formed on the same substrate, as shown in Figure 4B.

[0029] The three-electrode system described above may be equipped with a potential control mechanism that controls the potential of the counter electrode so that the potential of the working electrode relative to the reference electrode is a predetermined value (see Figure 4). The potential control mechanism is not particularly limited as long as it is a mechanism that can set the potential of the working electrode to a predetermined value relative to the reference electrode, and conventionally known mechanisms can be used. Examples of the potential control mechanism include a mechanism using an analog circuit with an operational amplifier, a mechanism using a microprocessor with a potentiostat function (for example, the ADuCM355 from Analog Devices), a mechanism that digitally converts the working electrode potential and inputs it to a microprocessor, the microprocessor calculates the counter electrode potential necessary to set the working electrode potential to a predetermined value, and applies the calculated potential to the counter electrode, and a mechanism that wirelessly receives the potential data of the working electrode from an external device (for example, using the wireless transmission unit configured to wirelessly receive signals from an external device), and applies the potential corresponding to the potential data to the counter electrode. Of these, from the viewpoint of miniaturizing the measuring device of the present invention, a mechanism using an analog circuit with an operational amplifier is preferred.

[0030] [Working electrode, reference electrode, counter electrode] The working electrode included in the electrochemical sensor may consist of a conductive layer formed on a substrate. The material of the conductive layer may be selected considering its reactivity with the solution and the reaction products between the substance to be measured and the recognition substance. For example, the material of the conductive layer is a material that does not react with the solution containing the substance to be measured. Typically, the material of the conductive layer includes metals such as gold, palladium, platinum, rhodium, indium, iridium, titanium, and copper, as well as carbon materials, with gold or platinum being preferred.

[0031] The conductive layer can be formed, for example, by depositing the metal at any position on the substrate. Alternatively, an electrode may be constructed by attaching a separately prepared thin metal film to the substrate. Alternatively, the conductive layer (or electrode) may be formed by conventionally known methods such as vacuum deposition, electron beam deposition, sputtering, plating, CVD, ion plating coating, inkjet printing, etc., depending on the material.

[0032] The counter electrode and, if necessary, the reference electrode included in the electrochemical sensor can each be composed of a conductive layer formed on a substrate, similar to the working electrode. Alternatively, the counter electrode or reference electrode can be formed without using a substrate and a conductive layer. For example, the counter electrode may be formed using a metal wire, a metal plate, etc., or the reference electrode may be a glass tube in which a reference electrode material such as silver / silver chloride is sealed, or a silver / silver chloride electrode obtained by printing silver / silver chloride paste on a conductive layer may be used. In one preferred embodiment of a two-electrode system, the conductive layer of the working electrode is gold, and the counter electrode (reference electrode) is a silver / silver chloride electrode formed using silver / silver chloride paste on a gold conductive layer. In one preferred embodiment of a three-electrode system, the counter electrode is platinum, the conductive layer of the working electrode is gold, and the reference electrode is a silver / silver chloride electrode formed on a gold conductive layer.

[0033] [Base material] Examples of materials for the substrate include flexible materials in the form of sheets or films, composed of materials such as polyimide (PI) resin, polyester resin, polyamide resin, epoxy resin, polysulfone resin, paper made from natural materials, and cloth.

[0034] [Recognition substance] The recognition substance immobilized on the working electrode has the ability to selectively recognize the substance to be measured, and from the viewpoint of availability and ease of handling, a biologically derived substance (such as a ligand) is preferred. Examples of such recognition substances include enzymes, nucleic acids, antibodies, receptors, organelles, microorganisms, cells, and tissues, and among these, enzymes are preferred from the viewpoint of ease of handling.

[0035] [enzyme] The enzyme used as the recognition substance can be either an enzyme that can directly exchange electrons with the electrode through a reaction with the substance to be measured, or an enzyme that can exchange electrons with the working electrode via the product of a reaction with the substance to be measured. Examples of such enzymes include glucose oxidase (GOD), glucose dehydrogenase (GDH), lactate oxidase, lactate dehydrogenase, fructose dehydrogenase, invertase, amylase, urease, uricase, amino acid oxidase, bilirubin oxidase, cholesterol oxidase, alcohol oxidase, alcohol dehydrogenase, and creatininase. However, there are no particular restrictions on the type of enzyme used, and it can be appropriately selected depending on the substance to be measured. For example, if glucose contained in blood, sweat, urine, etc., is the substance to be measured, examples of enzymes that can be used include glucose oxidase (GOD) and glucose dehydrogenase (GDH).

[0036] [Redox substances] If it is difficult for the recognition material to directly exchange electrons with the working electrode, a reversibly redoxable substance (also referred to herein as a "redox substance") may be further fixed to the working electrode, and electron exchange with the working electrode may occur via the redox substance. Alternatively, even if the recognition material can directly exchange electrons with the working electrode, the redox substance may be fixed to the working electrode to improve the sensitivity and accuracy of the measurement.

[0037] The redox substance immobilized on the working electrode is not particularly limited as long as it is a redox substance that can be oxidized or reduced by a recognition substance or a substance produced by a reaction between the recognition substance and the substance to be measured, and can transfer electrons to the electrode; conventionally known substances can be used. Examples of such redox substances include Prussian blue, Meldora blue, thionine, azur A, azur B, azur C, phenothiazine, tetrathiafulvalene, quinones such as hydroquinone and 1,4-naphthoquinone, ferrocene, ferrocene derivatives, potassium ferrocyanide, ferricyanide, osmium complex, p-aminophenol, ABTS(2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid)), and others.

[0038] To facilitate the transfer of electrons between the counter electrode and the solution, bio-derived substances, and even redox substances, may be immobilized on the counter electrode, similar to the working electrode. The bio-derived substance immobilized on the counter electrode does not need to have the ability to recognize the substance being measured. Examples of such bio-derived substances include bilirubin oxidase and laccase. Examples of redox substances immobilized on the counter electrode include the redox substances that can be used for the working electrode as described above.

[0039] In this specification, "fixed" of a substance, such as a recognition substance or a redox substance, to an electrode means that the substance is in a state where it does not move relative to the electrode. For example, the recognition substance may be directly fixed to the surface of the conductive layer of the working electrode, or it may be indirectly fixed via another substance, such as the redox substance. The redox substance is preferably fixed directly to the surface of the conductive layer. In one embodiment, the redox substance constitutes a redox layer positioned in direct contact with the surface of the conductive layer of the electrode, and the recognition substance constitutes a recognition substance fixed layer positioned in direct contact with the redox layer. In another embodiment, a layer of a mixture of the recognition substance and the redox substance is formed on the surface of the conductive layer of the electrode. Because the recognition substance is fixed to the electrode by chemical or physical bonding, it remains substantially fixed to the electrode even after the electrode has been brought into contact with a solution containing the substance to be measured.

[0040] [Other components] To selectively measure the substance to be measured, a film that selectively permeates the substance to be measured may be formed on the surface of the electrode on which the recognition substance is immobilized that comes into contact with the solution containing the substance to be measured. Examples of materials for the film include polymers that form hydrogels, and more specific examples of usable polymers include polycaprolactone, gelatin, gelatin methacrylate, alginate, alginate methacrylate, chitosan, chitosan methacrylate, glycol chitosan, glycol chitosan methacrylate, hyaluronic acid (HA), HA methacrylate, and other non-crosslinked natural or synthetic polymer chains. Examples of usable polymers include water-soluble photosensitive resins in which photosensitive groups are directly bonded to water-soluble polymers, and organic molecules and water-soluble polymers having crosslinkable reactive groups.

[0041] [Measurement Process] The operation of the electrochemical sensor in the process of measuring the concentration of a substance to be measured using the measuring device of the present invention is illustrated below.

[0042] The substance to be measured can be any substance that is selectively recognized by the recognition substance, and its type is not particularly limited. Preferably, the substance to be measured is a biological substance, such as glucose, lactic acid, fructose, urea, uric acid, amino acids, bilirubin, cholesterol, alcohol, creatinine, ascorbic acid, etc. In the following examples, glucose is used as the substance to be measured, but the substances to be measured that can be used in the present invention are not limited to this.

[0043] In one embodiment, the electrochemical sensor is a two-electrode system consisting of a working electrode and a counter electrode (reference electrode). The glucose concentration is measured with the working electrode and the counter electrode in contact with a solution containing the substance to be measured (glucose), the working electrode and the counter electrode electrically connected, and without applying a voltage between the working electrode and the counter electrode, in a state where substantially no current is flowing. Here, a state where substantially no current is flowing means a state in which no current is flowing other than unintended current leakage such as leakage current. The working electrode has the redox substance and the enzyme (glucose oxidase) as the recognition substance immobilized on it. When the enzyme on the working electrode reacts with glucose in the presence of water and oxygen, glucose is converted to gluconic acid and hydrogen peroxide is produced. At the same time, the hydrogen peroxide converts the redox substance from its reduced form to its oxidized form. This causes a change in the ratio of oxidized to reduced forms of the redox substance, and the potential difference between the counter electrode and the working electrode changes in accordance with this change. In this embodiment, when the redox substance is oxidized by the reaction between glucose and the enzyme, the potential difference between the counter electrode and the working electrode shifts to the noble side, while when the redox substance is reduced, the potential difference shifts to the denominative side. From the viewpoint of more accurate measurement, it is preferable that the redox substance is oxidized or reduced by the product generated by the enzymatic reaction rather than being directly oxidized or reduced by the enzyme.

[0044] The potential difference signal between the counter electrode and the working electrode is output from the electrochemical sensor and enters a differentiating circuit, which will be described later. In this differentiating circuit, the time derivative of the potential difference signal is output sequentially. This time derivative is proportional to the concentration of the substance being measured (glucose).

[0045] In another embodiment, the electrochemical sensor is a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode. The glucose concentration is measured with the working electrode, counter electrode, and reference electrode in contact with a solution containing the substance to be measured (glucose), the working electrode and the counter electrode being electrically connected, and a voltage applied between the working electrode and the counter electrode so that the potential difference between them is a predetermined value. The working electrode is immobilized with the redox substance and an enzyme (glucose oxidase) as the recognition substance. The enzyme on the working electrode reacts with glucose in the presence of water and oxygen, converting glucose to gluconic acid and generating hydrogen peroxide. Simultaneously, the hydrogen peroxide converts the redox substance from its reduced form to its oxidized form. This causes a change in the ratio of oxidized to reduced forms of the redox substance, and in response to this change, a potential difference is generated between the counter electrode and the working electrode, causing a current to flow between the working electrode and the counter electrode. From the viewpoint of more accurate measurement, it is preferable that the redox substance is oxidized or reduced by a product generated by an enzymatic reaction rather than being directly oxidized or reduced by an enzyme.

[0046] The signal of the current flowing between the counter electrode and the working electrode is output from the electrochemical sensor and enters a differentiating circuit, which will be described later. In this differentiating circuit, the time derivative of the current signal is output sequentially. This time derivative is proportional to the rate of change of the concentration of the substance being measured (glucose).

[0047] <Differential circuit> The differentiating circuit of the measuring device of the present invention is not particularly limited in type, as long as it can sequentially calculate the differential value (rate of change of the electrical signal with respect to time) of the electrical signal output by the electrochemical sensor. Conventional known circuits can be used for the differentiating circuit. The differentiating circuit may be either a passive differentiating circuit or an active differentiating circuit. Examples of the passive differentiating circuit include a CR differentiating circuit using a capacitor and a resistor, and an RL differentiating circuit combining an inductor and a resistor. Examples of the active differentiating circuit include a differentiating circuit using an operational amplifier, a capacitor, and a resistor, and a differentiating circuit using an operational amplifier, an inductor, and a resistor. Of these, an active differentiating circuit is preferred from the viewpoint of the accuracy of the calculated differential value, and furthermore, a differentiating circuit using an operational amplifier, a capacitor, and a resistor is more preferred from the viewpoint of miniaturizing the circuit.

[0048] If the electrical signal output by the electrochemical sensor is minute, an amplification circuit may be inserted before the input of the differentiation circuit to differentiate the amplified electrical signal.

[0049] <Low-pass filter> Since the electrical signal output by the differentiation circuit often contains high-frequency noise, in a preferred embodiment of the present invention, a low-pass filter is inserted between the differentiation circuit and the wireless transmission unit. This reduces the high-frequency noise contained in the output signal from the differentiation circuit by processing it with the low-pass filter, and the signal with reduced noise can be wirelessly transmitted from the wireless transmission unit. From the viewpoint of miniaturizing the device, the measuring device of the present invention does not include any components or circuits other than the low-pass filter between the differentiation circuit and the wireless transmission unit.

[0050] The type of low-pass filter is not particularly limited, as long as it can reduce high-frequency noise contained in the electrical signal output by the differentiating circuit. Conventional known low-pass filters can be used. Examples of such low-pass filters include RC circuits using capacitors and resistors, LR circuits using inductors and resistors, and higher-order low-pass filters combining operational amplifiers with capacitors, inductors, and resistors. Of these, RC circuits or LR circuits are preferred from the viewpoint of miniaturizing the circuit.

[0051] From the viewpoint of sufficiently reducing high-frequency noise in wirelessly transmitted data, the cutoff frequency of the low-pass filter is preferably 20 times or less the reciprocal of the wireless transmission interval of the wireless transmission unit, more preferably 10 times or less. On the other hand, from the viewpoint of ensuring the accuracy of the data after wireless transmission, it is preferably 1 / 10 times or more the reciprocal of the wireless transmission interval of the wireless transmission unit, more preferably 1 / 2 times or more. The cutoff frequency of the low-pass filter is the frequency at which the gain of the low-pass filter output becomes 1 / 2 of the DC signal. For example, the cutoff frequency of a first-order low-pass filter in an RC circuit with a resistor of resistance R and a capacitor of capacitance C is 1 / 2πRC.

[0052] <Wireless Transmitter> The wireless transmitting unit of the measuring device of the present invention is not particularly limited in type, as long as it has the function of transmitting an electrical signal relating to the differential value output from the differential circuit or the low-pass filter to an external device (for example, an external information processing terminal in Figure 1) by wireless means. Conventional known types of wireless transmitting units and wireless transmission methods can be used.

[0053] The aforementioned wireless transmission may be either digital wireless communication, which digitally converts and transmits the wireless transmission data, or analog wireless communication, which transmits the data without digital conversion. However, from the viewpoint of noise reduction, digital wireless communication is preferred. Examples of digital wireless communication include Wi-Fi, Bluetooth®, ANT+, Bluetooth Low Energy (BLE®), Thread, Zigbee, Narrow Band IoT (NB-IoT), Long-Term Evolution for Machines (LTE-M), Sigfox, LoRaWAN, ELTRES, ZETA, and others. Furthermore, the digitally converted data can be stored in an RFID chip, and the data stored in the RFID chip can be read from an external device using near-field communication (NFC).

[0054] <Wireless transmission data> Data wirelessly transmitted from the measuring device of the present invention is received by an external device and acquired as data relating to the concentration of the substance to be measured. If necessary, the external device may process the wirelessly transmitted data (e.g., smoothing, comparison with a predetermined value, A / D conversion if the wireless transmission is analog, etc.). The obtained data may be recorded or displayed as data relating to the concentration of the substance to be measured, or may be used for further analysis.

[0055] As exemplary embodiments of the present invention, the following substances, manufacturing methods, uses, or methods are further disclosed herein. However, the present invention is not limited to these embodiments.

[0056] [1] An electrochemical sensor equipped with a working electrode containing a substance capable of recognizing the substance to be measured, A differentiating circuit for differentiating the electrical signal output from the electrochemical sensor, and A wireless transmitter connected to the output of the differential circuit, A measuring device equipped with the following features. [2] Preferably, the measuring device according to [1], comprising a low-pass filter between the differential circuit and the wireless transmission unit. [3] Preferably, the electrode system of the electrochemical sensor is a two-electrode system consisting of the working electrode and the counter electrode, or a three-electrode system consisting of the working electrode, the counter electrode and the reference electrode, according to [1] or [2]. [4] Preferably, the measuring device according to any one of [1] to [3], wherein the electrical signal is a current or a voltage. [5] Preferably, the measuring device according to any one of [1] to [4], wherein the substance having the ability to recognize the substance to be measured is an enzyme. [6] Preferably, the measuring apparatus according to [5], wherein the enzyme is an enzyme that can exchange electrons with the electrode by reaction with the substance to be measured. [7] Preferably, the measuring device according to [6], wherein the working electrode contains a redox substance that can be reversibly oxidized and reduced. [8] Preferably, the measuring apparatus according to [7], wherein the redox substance is oxidized or reduced by a product produced by the reaction of the substance to be measured with the enzyme. [9] Preferably, the measuring apparatus according to [7] or [8], wherein the redox substance constitutes a redox layer arranged in contact with the surface of the conductive layer of the working electrode, and the substance having the ability to recognize the substance to be measured constitutes a layer arranged in direct contact with the redox layer.

[10] Preferably, the measuring device according to any one of [2] to [9], wherein no components or circuits other than the low-pass filter are included between the differential circuit and the wireless transmission unit.

[11] A method for measuring the concentration of a substance to be measured in a solution, Using an electrochemical sensor equipped with a working electrode containing a substance capable of recognizing the substance to be measured, an electrical signal containing information regarding the concentration of the substance to be measured is obtained. To obtain the differential value of the electrical signal, To wirelessly transmit an electrical signal relating to the said differential value, and The wirelessly transmitted data is acquired as data relating to the concentration of the substance being measured. Methods that include...

[12] Preferably, the method according to

[11] , which includes processing the electrical signal for the differential value with a low-pass filter before wireless transmission.

[13] Preferably, the electrode system of the electrochemical sensor is a two-electrode system consisting of the working electrode and the counter electrode, or a three-electrode system consisting of the working electrode, the counter electrode and the reference electrode, according to

[11] or

[12] .

[14] Preferably, the method according to any one of

[11] to

[13] , wherein the electrical signal is a current or a voltage.

[15] Preferably, the method according to any one of

[11] to

[14] , wherein the substance having the ability to recognize the substance to be measured is an enzyme.

[16] Preferably, the enzyme is an enzyme that can exchange electrons with the electrode by reaction with the substance to be measured, according to

[15] .

[17] Preferably, the method according to

[16] , wherein the working electrode contains a redox substance that can be reversibly oxidized and reduced.

[18] Preferably, the method according to

[17] , wherein the redox substance is oxidized or reduced by a product produced by the reaction of the substance to be measured with the enzyme.

[19] Preferably, the method according to

[17] or

[18] , wherein the redox substance constitutes a redox layer arranged in contact with the surface of the conductive layer of the working electrode, and the substance having the ability to recognize the substance to be measured constitutes a layer arranged in direct contact with the redox layer.

[20] Preferably, the method according to any one of

[12] to

[19] , wherein the electrical signal for the differential value is not subjected to any processing other than processing by the low-pass filter before wireless transmission. [Examples]

[0057] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] (Fabrication of an electrochemical sensor - 1) The electrochemical sensor was fabricated using the following method. [electrode] Electrodes with the pattern shown in Figure 5 were formed. Gold was vacuum deposited onto a substrate (polyimide film, 125 μm thick) through a metal mask using a vacuum deposition apparatus (SVC-700TMSG / 7PS80, manufactured by Sanyu Electronics Co., Ltd.) to a thickness of 50 nm.

[0059] [Working electrode] A mixed solution was prepared by mixing a 0.2% by mass aqueous dispersion of carbon nanotubes (CNTs) (manufactured by TUBALL) and an aqueous solution containing 1% by mass Prussian blue (PB) (redox substance, manufactured by Aldrich) in a volume ratio of 10:1 in the circular portion of the right electrode of the electrode pattern shown in Figure 5. 5 μL of this mixed solution was dropped onto a 3 mm diameter circular portion of the working electrode and dried in an 80°C constant temperature bath for 10 minutes to form a Prussian blue-containing carbon nanotube layer as a redox layer.

[0060] Next, a mixed solution was prepared by mixing a PBS solution (phosphate-buffered saline, pH 7.2, Life Technology) containing 1% by mass of enzyme (glucose oxidase, Aldrich) with a 2% by mass acetic acid solution (Fujifilm Wako Pure Chemical Industries) containing 1% by mass of chitosan (Aldrich) in a volume ratio of 1:2. 10 μL of this mixed solution was dropped onto the redox layer and dried at 25°C for 20 hours. After that, the unfixed enzyme was washed off with PBS solution, and the mixture was dried at room temperature to form an enzyme-immobilized layer, thereby obtaining an enzyme-modified electrode in which the enzyme and redox substances were immobilized on the working electrode.

[0061] [Counter electrode (reference electrode)] A silver / silver chloride paste (manufactured by SUN CHEMICAL) was screen-printed onto the left electrode of the electrode pattern in Figure 5 using a screen mask to form a silver / silver chloride electrode, which was then used as the counter electrode.

[0062] (Example 1) [Measurement System] A measurement system including the electrochemical sensor was constructed as shown in Figure 6A. The counter electrode was set to ground potential, the potential of the working electrode was used as the output of the electrochemical sensor, the output of the electrochemical sensor was amplified by a non-inverting amplifier circuit, and then the differential value of the amplified output was obtained as a voltage signal by a differentiating circuit. This signal was then digitally converted by a wireless device (BLE wireless module IMBLE2; manufactured by Interplan Corporation) and transmitted wirelessly.

[0063] [Measurement of glucose concentration] Using the aforementioned apparatus, the glucose concentration in the solution was measured as follows. The working electrode and counter electrode of the electrochemical sensor were immersed in 10 mL of PBS solution (the solution to be measured), and the solution to be measured was stirred at 500 rpm using a stirring bar. After 50 seconds, 10 μL of 100 mM D-glucose solution was added to the stirring PBS solution to adjust the glucose concentration in the solution to 100 μM. Subsequently, D-glucose solution was added again every 50 seconds to sequentially increase the glucose concentration in the solution to 200 μM, 300 μM, 500 μM, and 1 mM. The measurement data from the apparatus was wirelessly transmitted from a wireless device to a personal computer. The data transmission interval of the wireless device was set to 0.5 seconds. A graph showing the change in the received data over time was created on the personal computer that received the data. A graph showing the glucose concentration, as shown in Figure 7A, was obtained.

[0064] (Comparative Example 1) As shown in Figure 6B, the differentiating circuit was removed from the apparatus of Example 1, and a measurement system was constructed in which the wirelessly transmitted data from the apparatus was differentiated on a receiving PC. Using this measurement system, glucose concentration was measured in the same manner as in Example 1, and a graph showing the glucose concentration was created. As shown in Figure 7B, the obtained differential values ​​had more noise than those in Example 1 and could not be used as measured values ​​for glucose concentration.

[0065] (Example 2) As shown in Figure 8A, glucose concentration was measured and a graph showing glucose concentration was created in the same manner as in Example 1, except that a low-pass filter was inserted between the differentiating circuit and the wireless device. The cutoff frequency of the low-pass filter was 16 Hz. As shown in Figure 9A, a graph showing glucose concentration was obtained with even lower noise compared to Example 1.

[0066] (Comparative Example 2) As shown in Figure 8B, the differential circuit was removed from the apparatus of Example 2, and a measurement system was constructed in which the wirelessly transmitted data from the apparatus was differentiated on a receiving PC. Using this measurement system, glucose concentration was measured in the same manner as in Example 1, and a graph showing the glucose concentration was created. As shown in Figure 9B, the obtained differential values ​​were noisy, similar to Comparative Example 1, and could not be used as measured values ​​for glucose concentration.

[0067] (Fabrication of electrochemical sensors - 2) The electrochemical sensor was fabricated using the following method. [electrode] Electrodes with the pattern shown in Figure 10 were formed. Gold was vacuum deposited onto a substrate (polyimide film, 125 μm thick) through a metal mask using a vacuum deposition apparatus (SVC-700TMSG / 7PS80, manufactured by Sanyu Electronics Co., Ltd.) to a thickness of 50 nm. [Working electrode] An enzyme-modified electrode was fabricated in the central circular electrode portion of the electrode pattern shown in Figure 10, using the same procedure as described in (Fabrication of Electrochemical Sensor - 1) above, with the enzyme and redox substance immobilized on the working electrode. [Counter electrode] The left electrode in the electrode pattern shown in Figure 10 was used as the counter electrode. [Reference electrode] A silver / silver chloride electrode was formed by screen printing a silver / silver chloride paste (manufactured by SUN CHEMICAL) onto the electrode on the right side of the electrode pattern in Figure 10 using a screen mask, and this was used as a reference electrode.

[0068] (Example 3) [Measurement System] A measurement system including the electrochemical sensor was constructed as shown in Figure 11A. The working electrode was set to ground potential, and the working electrode potential relative to the reference electrode was determined by controlling the voltage applied to the reference electrode. At this time, the potential of the working electrode relative to the reference electrode was -0.1V. The current flowing from the working electrode to the counter electrode was used as the output of the electrochemical sensor. The current output of the electrochemical sensor was converted to a voltage by a current-voltage conversion circuit, and then the differential value of the output was obtained as a voltage signal by a differentiation circuit. This signal was then digitally converted by a wireless device (BLE wireless module IMBLE2; manufactured by Interplan Corporation) and transmitted wirelessly.

[0069] [Measurement of the rate of change in glucose concentration] Using the aforementioned apparatus, the glucose concentration in the solution was measured as follows. The working electrode, counter electrode, and reference electrode of the electrochemical sensor were immersed in 10 mL of PBS solution (the solution to be measured), and the solution to be measured was stirred at 500 rpm using a stirring bar. After 70 seconds, 20 μL of 100 mM D-glucose solution was added to the stirring PBS solution at a rate of 1 second, adjusting the glucose concentration in the solution to 200 μM. Subsequently, 20 μL, 40 μL, and 60 μL of D-glucose solution were added at 1 second each every 80 seconds, sequentially increasing the glucose concentration in the solution to 400 μM, 800 μM, and 1.4 mM. The measurement data from the apparatus was wirelessly transmitted from a wireless device to a personal computer. The data transmission interval of the wireless device was set to 0.5 seconds. A graph showing the change in the received data over time was created on the personal computer that received the data. A graph showing the rate of change in glucose concentration, as shown in Figure 12A, was obtained.

[0070] (Comparative Example 3) As shown in Figure 11B, the differential circuit was removed from the apparatus of Example 3, and a measurement system was constructed in which the wirelessly transmitted data from the apparatus was differentiated on a receiving PC. Using this measurement system, the rate of change of glucose concentration was measured in the same manner as in Example 3, and a graph showing the rate of change of glucose concentration was created. As shown in Figure 12B, the obtained differential values ​​had more noise than those in Example 3 and could not be used as measured values ​​for the amount of change in glucose concentration.

Claims

1. An electrochemical sensor equipped with a working electrode containing a substance capable of recognizing the substance to be measured. A differentiating circuit for differentiating the electrical signal output from the electrochemical sensor, and A wireless transmitter connected to the output of the differential circuit, A measuring device equipped with the following features.

2. The measuring device according to claim 1, further comprising a low-pass filter between the differential circuit and the wireless transmission unit.

3. The measuring device according to claim 1 or 2, wherein the electrode system of the electrochemical sensor is a two-electrode system consisting of the working electrode and the counter electrode, or a three-electrode system consisting of the working electrode, the counter electrode and the reference electrode.

4. The measuring device according to claim 1 or 2, wherein the electrical signal is a current or a voltage.

5. The measuring device according to claim 1 or 2, wherein the substance having the ability to recognize the substance to be measured is an enzyme.

6. The measuring apparatus according to claim 5, wherein the enzyme is an enzyme that can exchange electrons with an electrode through a reaction with the substance to be measured.

7. The measuring apparatus according to claim 6, wherein the working electrode contains a redox substance that can be reversibly oxidized and reduced.

8. The measuring apparatus according to claim 7, wherein the redox substance is oxidized or reduced by a product produced by the reaction between the substance to be measured and the enzyme.

9. The measuring apparatus according to claim 7, wherein the redox substance constitutes a redox layer arranged in contact with the surface of the conductive layer of the working electrode, and the substance having the ability to recognize the substance to be measured constitutes a layer arranged in direct contact with the redox layer.

10. A method for measuring the concentration of a substance to be measured in a solution, Using an electrochemical sensor equipped with a working electrode containing a substance capable of recognizing the substance to be measured, an electrical signal containing information regarding the concentration of the substance to be measured is obtained. To obtain the differential value of the electrical signal, To wirelessly transmit an electrical signal relating to the said differential value, and The wirelessly transmitted data is acquired as data relating to the concentration of the substance being measured. Methods that include...

Images