Chemical sensor

Abstract

To provide a chemical sensor capable of detecting a chemical substance by a more convenient method.SOLUTION: A chemical sensor 1 is a sensor that measures a predetermined chemical substance contained in an object to be inspected. The chemical sensor 1 includes a sensing electrode 21, a counter electrode 22, and a reference electrode 23. The sensing electrode 21 contains metal oxide particles 41 carrying a noble metal. A molecularly imprinted film 42, which uses the chemical substance to be measured as a template, is provided around the metal oxide particles 41.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a chemical sensor for detecting chemical substances contained in an object to be inspected. [Background technology]

[0002] The musty odor of tap water and other water used for daily life is a problem in Japan and around the world. It is known that this musty odor is caused by chemicals such as geosmin and 2-methylisoborneol (2-MIB), which are produced by bacteria living in the water source.

[0003] Gas chromatography-mass spectrometry (GS-MS) is used to detect chemical substances that cause mold odors. However, analyzing chemical substances using GS-MS has some issues, such as the large size of the equipment used, the time it takes to obtain analytical results, and the complex operation that requires specialized knowledge. For this reason, it is difficult to immediately determine at the sampling site whether a specific chemical substance is present in a sample collected from a water source far from a water purification plant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-124643 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses an odor detection device that detects trace amounts of mold-smelling substances, etc. This odor detection device is configured so that an odor collector is installed above the water-receiving tank, a metal oxide semiconductor whose resistance value changes depending on the gas is installed above that, and an intake fan blows the odor of raw water from the water-receiving tank onto the metal oxide semiconductor.

[0006] The odor detection device disclosed in Patent Document 1 is also relatively large, and it is considered difficult to move the device, which makes it difficult to detect chemical substances in a short time at different sample collection locations each time a sample is collected.

[0007] An object of the present invention is to provide a chemical sensor that can detect chemical substances in a simpler manner. [Means for solving the problem]

[0008] A chemical sensor according to one aspect of the present invention is a chemical sensor for measuring a predetermined chemical substance contained in a test object, and includes a sensing electrode, a counter electrode, and a reference electrode. The sensing electrode includes metal oxide particles supporting a precious metal, and a molecular template film formed around the metal oxide particles using the chemical substance as a template.

[0009] According to the above configuration, the concentration of a chemical substance can be measured by placing the test object on each electrode and measuring the current value between the electrodes. Therefore, compared to measuring the concentration of a chemical substance using gas chromatography or the like, this is a simpler method for detecting the concentration of a chemical substance. In addition, the measuring device can be made smaller.

[0010] In the chemical sensor according to one aspect of the present invention, the chemical substance may be any one of geosmin, 2-methylisoborneol, halogenated anisole, octa-1,3-diene, α-terpineol, 4,4,6-trimethyl-1,3-dioxane, trimethylanisole, and 1-octen-3-ol. Specific examples of halogenated anisoles include 2,4,6-trichloroanisole.

[0011] According to the above configuration, the concentration of chemical substances that cause the musty odor of water can be confirmed in a simpler manner, and therefore, the concentration of a specific chemical substance contained in a sample can be confirmed quickly and easily at a sampling site such as a water source.

[0012] In the chemical sensor according to the above aspect of the present invention, the molecular template film may be conductive.

[0013] According to the above configuration, the sensitivity and selectivity of the sensing electrode to a predetermined chemical substance can be improved.

[0014] In the chemical sensor according to one aspect of the present invention, the noble metal may be any one of platinum (Pt), palladium (Pd), and gold (Au). Among these noble metals, platinum (Pt) or palladium (Pd) is preferred.

[0015] According to the above configuration, by selecting platinum (Pt) or palladium (Pd) as the precious metal supported on the metal oxide particles, a chemical sensor having higher sensitivity to a specific chemical substance (e.g., geosmin) can be obtained. [Effects of the Invention]

[0016] According to a chemical sensor according to one aspect of the present invention, chemical substances can be detected in a simpler manner. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view showing an external configuration of a chemical sensor according to an embodiment. [Figure 2] FIG. 1 is a block diagram showing an internal configuration of a chemical sensor according to an embodiment. [Figure 3] 2 is a schematic diagram showing a cross-sectional structure of a material particle contained in a sensing electrode of the chemical sensor shown in FIG. 1. FIG. [Figure 4] 1 is a graph showing the correlation between the geosmin concentration (μg / L) of each sample solution and the detected current value (A) in the examples. [Figure 5] 1 is a graph showing the results of evaluating the selectivity of geosmin in chemical sensors in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of the components are also the same. Therefore, detailed description thereof will not be repeated.

[0019] In this embodiment, a chemical sensor 1, which is an example of a chemical sensor, will be described as an example. Chemical sensors are mainly used to measure predetermined chemical substances contained in a liquid test object. In the chemical sensor 1 according to this embodiment, the test object (sample liquid) is, for example, water collected from a water source such as tap water.

[0020] The substances that cause the moldy odor contained in this sample liquid are then taken as the predetermined chemical substance to be measured. More specifically, the predetermined chemical substance to be measured (i.e., the substances that cause the moldy odor) is geosmin, 2-methylisoborneol (2-MIB), etc. This makes it possible to confirm the concentration of the substances that cause the moldy odor contained in the sample liquid.

[0021] (Chemical sensor configuration) 1 shows the external configuration of the chemical sensor 1. FIG. 2 shows the internal configuration of the chemical sensor 1.

[0022] The chemical sensor 1 is mainly composed of a main body 10 having a substantially rectangular parallelepiped shape and a control unit 50 connected to the main body 10. In this embodiment, the control unit 50 is configured separately from the main body 10, but in another embodiment, the control unit 50 may be integrated with the main body 10.

[0023] The main body 10 forms the sensor portion of the chemical sensor 1. The main body 10 is provided with a plurality of electrodes (specifically, a sensing electrode 21, a counter electrode 22, and a reference electrode 23) and terminals (specifically, a first terminal 31, a second terminal 32, and a third terminal 33) that are electrically connected to the respective electrodes.

[0024] The main body 10 can be formed of an insulating material such as a ceramic material. For example, the main body 10 is formed of a ceramic substrate obtained by stacking and sintering multiple ceramic green sheets. However, the material of the main body 10 is not limited to ceramic.

[0025] The multiple electrodes (specifically, the sensing electrode 21, the counter electrode 22, and the reference electrode 23) are conductive. Each electrode can be formed, for example, by forming a space (hole) at a predetermined position in the main body 10 formed of a ceramic substrate and filling this space with a conductive electrode material.

[0026] The electrode material for the counter electrode 22 may be any known electrode material for a counter electrode. Specifically, platinum (Pt) paste or the like may be used as the electrode material for the counter electrode 22. The electrode material for the reference electrode 23 may be any known electrode material for a reference electrode. Specifically, silver (Ag) / silver chloride (AgCl) paste or the like may be used as the electrode material for the reference electrode 23. The electrode material for the sensing electrode 21 will be described later.

[0027] The multiple terminals (specifically, the first terminal 31, the second terminal 32, and the third terminal 33) are conductive. Each terminal is formed, for example, on the surface of the main body 10. As shown in FIG. 1, the terminals 31, 32, and 33 are arranged side by side on one end side in the longitudinal direction of the upper surface of the substantially rectangular parallelepiped-shaped main body 10.

[0028] The first terminal 31 is connected to the sensing electrode 21 via a wire 12 or the like. The second terminal 32 is connected to the counter electrode 22 via a wire 12 or the like. The third terminal 33 is connected to the reference electrode 23 via a wire 12 or the like. The wire 12 is formed inside the main body 10, which is formed of, for example, a ceramic substrate.

[0029] Each of the terminals 31, 32, and 33 is connected to a control unit 50 located outside the main body 10 via wiring 13 or the like (see FIG. 2). As a result, each of the electrodes 21, 22, and 23 is connected to a circuit within the control unit 50 via each of the terminals 31, 32, and 33.

[0030] The three electrodes included in the chemical sensor 1 (i.e., the sensing electrode 21, the counter electrode 22, and the reference electrode 23) have the configuration of a so-called three-electrode electrochemical cell. In the chemical sensor 1 according to this embodiment, the sensing electrode 21 corresponds to the working electrode.

[0031] These three electrodes are arranged in a sample placement section 11 provided near the end opposite to the side where the terminals are arranged on the top surface of the main body 10. A part of each electrode is exposed on the sample placement section 11.

[0032] The sample placement section 11 is an area where the sample liquid is placed. The sample placement section 11 preferably has a shape recessed from the upper surface of the main body section 10. The three electrodes (i.e., the detection electrode 21, the counter electrode 22, and the reference electrode 23) are arranged, for example, on the bottom surface of the recess of the sample placement section 11, spaced apart from each other to form a triangle (see FIG. 1). The sample liquid is dropped into the recess of the sample placement section 11.

[0033] The sample placement unit 11 has the above-described configuration, so that the liquid sample can be placed in a stable state for a certain period of time on the three electrodes arranged on the bottom surface of the sample placement unit 11. This makes it easier to measure the concentration of chemical substances in the sample liquid.

[0034] The control unit 50 is connected to and controls each component in the main body 10. The control unit 50 has, for example, a control board. The control unit 50 includes a voltage application unit 51, a current detection unit 52, a memory (not shown), a timer (not shown), and the like.

[0035] The voltage application unit 51 applies a predetermined voltage between the sensing electrode 21 and the reference electrode 23 (i.e., between the first terminal 31 and the third terminal 33). The current detection unit 52 detects the value of the current flowing between the sensing electrode 21 and the counter electrode 22 (i.e., the value of the current flowing between the first terminal 31 and the second terminal 32) when the predetermined voltage is applied between the sensing electrode 21 and the reference electrode 23, that is, when the voltage between the sensing electrode 21 and the reference electrode 23 is constant.

[0036] The value of the current flowing between the sensing electrode 21 and the counter electrode 22 changes depending on the concentration of a predetermined chemical substance (for example, geosmin, 2-methylisoborneol (2-MIB), etc.) contained in the sample liquid.

[0037] The current detection unit 52 detects this current value, and the control unit 50 can calculate the concentration of a predetermined chemical substance in the sample liquid. The concentration calculated by the control unit 50 can be displayed on a display unit (not shown) in the chemical sensor 1.

[0038] Specifically, the value of the current flowing between the sensing electrode 21 and the counter electrode 22 is proportional to the concentration of a predetermined chemical substance contained in the sample liquid. In this case, information storing the relationship between the concentration of the chemical substance and the current value (for example, information like the graph shown in FIG. 4) is stored in a memory within the control unit 50, and the control unit 50 determines the concentration of the chemical substance from the current value detected by the current detection unit 52, thereby obtaining the concentration of the chemical substance.

[0039] (Detection electrode configuration) Next, a more detailed description will be given of the configuration of the sensing electrode 21. In the chemical sensor 1 according to this embodiment, the sensing electrode 21 contains metal oxide particles carrying a precious metal. A molecular template film is provided around the metal oxide particles, with a predetermined chemical substance (the chemical substance to be measured) as a template.

[0040] 3 is a schematic diagram showing the structure of material particles 40, which are an example of the electrode material of the sensing electrode 21. In the following, an example will be described in which the chemical substance to be measured is geosmin.

[0041] The material particle 40 has a metal oxide particle 41 and a molecular template film 42 formed on the surface of the metal oxide particle 41. The metal oxide particle 41 supports a noble metal.

[0042] Examples of metal oxides constituting the metal oxide particles 41 include cobalt oxide, tin oxide, tungsten oxide, iridium oxide, etc. Among these, cobalt oxide is preferred.

[0043] Examples of the noble metal supported on the metal oxide particles 41 include platinum (Pt), palladium (Pd), and gold (Au). Among these, platinum (Pt) and palladium (Pd) are preferred. As will be shown in the examples described later, by selecting platinum (Pt) or palladium (Pd) as the noble metal supported on the metal oxide particles 41, a chemical sensor 1 having higher sensitivity to a specific chemical substance (e.g., geosmin) can be obtained.

[0044] The molecular template film 42 is provided to cover the periphery (outer surface) of the metal oxide particle 41. The molecular template film 42 is formed of a molecular imprint material using the chemical substance to be measured (e.g., geosmin) as a template. That is, the molecular template film 42 has holes 42a formed therein, the holes having a structure that matches the structure of the geosmin to be measured. As a result, when a sample liquid is placed on the sample placement section 11, the geosmin contained in the sample liquid fits into the holes 42a in the molecular template film 42 of the material particle 40 contained in the sensing electrode 21.

[0045] When geosmin gets trapped in the holes 42a of the molecular template film 42 contained in the sensing electrode 21, the geosmin is oxidized, and the resulting current is measured. This current value is significantly higher than the current value detected with a sample solution containing a chemical substance other than geosmin (e.g., quinoclamine). This causes a current to flow between the sensing electrode and the counter electrode. The current value at this time is proportional to the concentration of geosmin.

[0046] The molecular template film 42 is preferably conductive, which can suppress an increase in resistance between the electrodes and improve output. Examples of materials for such a molecular template film 42 include conductive polymers such as polypyrrole and polyaniline.

[0047] Examples of methods for forming the molecular template film 42 around the metal oxide particles 41 include the following methods.

[0048] Metal oxide particles are immersed in a polypyrrole solution containing geosmin. The particles are then removed from the solution and heated. After heating, the particles are immersed in ethanol. After immersion, the particles are dried to form a molecular template film around the metal oxide particles.

[0049] This results in material particles 40 having molecular template films 42 that are templated by a specific chemical substance such as geosmin. The material particles 40 are then made into a paste and solidified to form the sensing electrode 21.

[0050] (Summary of the embodiment) As described above, the chemical sensor 1 according to this embodiment is a sensor that measures a predetermined chemical substance contained in a test object. The chemical sensor 1 includes a sensing electrode 21, a counter electrode 22, and a reference electrode 23. The sensing electrode 21 includes metal oxide particles 41 supporting a precious metal. A molecular template film 42 is provided around the metal oxide particles 41, using the chemical substance to be measured as a template.

[0051] According to the chemical sensor 1 of this embodiment, the concentration of a chemical substance can be measured by placing a sample liquid to be tested in the sample placement section 11 and measuring the current value between the electrodes. Therefore, compared to measuring the concentration of a chemical substance using gas chromatography or the like, this is a simpler method for detecting the concentration of a chemical substance. In addition, the measuring device can be made smaller.

[0052] Furthermore, in the chemical sensor 1 according to this embodiment, a molecular template film 42 is formed on the surface of material particles 40 that serve as the electrode material for the sensing electrode 21. These material particles 40 are made into a paste and solidified to form the sensing electrode 21. This results in an electrode structure in which a thin molecular template film 42 is formed on the surface of each material particle 40.

[0053] Conventional chemical sensors detect chemical substances to be measured by using an electrode with a molecular template film formed on the surface of the electrode as a sensing electrode (see, for example, Patent Document 2: JP 2021-173625 A). With this type of electrode structure, it takes a certain amount of time for the chemical substance to be measured to become embedded in the molecular template film, which results in a long detection time.

[0054] In contrast, the sensing electrode 21 of the chemical sensor 1 according to this embodiment has an electrode structure in which a thin molecular template film 42 is formed on the surface of each material particle 40, as described above. Therefore, when a sample liquid is placed on the sensing electrode 21, the chemical substance to be measured quickly becomes embedded in the holes 42a of the molecular template film 42, increasing the current value. This allows the concentration of the chemical substance to be detected in a short time.

[0055] In this embodiment, the control unit 50 has a configuration separate from the main body unit 10, but in another embodiment, the control unit 50 may be arranged inside the main body unit 10. In the case where the control unit 50 is configured to be integrated with the main body unit 10, the wiring 13 is also arranged inside the main body unit 10.

[0056] [Example] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0057] In this example, a chemical sensor 1 having a sensing electrode 21 including metal oxide particles 41 supporting different noble metals was manufactured, and the sensitivity of the sensor to geosmin was confirmed.

[0058] (1) Manufacturing of chemical sensors In Example 1, fine particles of cobalt oxide carrying Pd as a precious metal were used as metal oxide particles 41. A molecular template film 42 was formed on these fine particles using polypyrrole as a molecular imprinting material. Geosmin was used as the template material. Geosmin was added together with the molecular imprinting material during the formation of the molecular template film 42, and the geosmin was removed after the film was formed, thereby forming a molecular template film 42 on the surface of metal oxide particles 41 using geosmin as a template.

[0059] The material particles 40 produced as described above were used as an electrode material to form a sensing electrode 21. A platinum (Pt) paste was used as an electrode material for a counter electrode 22, and a silver / silver chloride (Ag / AgCl) paste was used as an electrode material for a reference electrode 23, to form a reference electrode 23.

[0060] Using these three electrodes, the chemical sensor 1 described in the above embodiment was manufactured.

[0061] In Example 2, chemical sensor 1 was manufactured in the same manner as in Example 1, except that Pt was used instead of Pd as the precious metal. In Example 3, chemical sensor 1 was manufactured in the same manner as in Example 1, except that Au was used instead of Pd as the precious metal.

[0062] (2) Sensor sensitivity evaluation test 1 The geosmin concentration in water was measured using the chemical sensors 1 of Examples 1 to 3 manufactured in (1) above. Specifically, multiple sample solutions containing geosmin at different concentrations ranging from 0 μg / L to 5 μg / L were prepared. Geosmin was dissolved in a fixed amount of water, and sample solutions of different concentrations were prepared by diluting the resulting solution. The geosmin concentration (μg / L) of each sample solution was determined based on the dilution ratio of a geosmin aqueous solution of known concentration.

[0063] The geosmin concentrations of these sample solutions were measured using the chemical sensors 1 of Examples 1 to 3. The current values ​​detected by the current detection unit 52 in the control unit 50 were then confirmed. The results are shown in Figure 3. Figure 3 is a graph showing the correlation between the geosmin concentration (μg / L) of each sample solution and the detected current value (A).

[0064] 3, it was confirmed that there was a linear relationship between the geosmin concentration and the current value for each of the chemical sensors 1 of Examples 1 to 3. Therefore, the chemical sensors 1 of Examples 1 to 3 can be suitably used as sensors for measuring the concentration of geosmin in a sample solution.

[0065] (3) Sensor sensitivity evaluation test 2 Using the chemical sensors 1 of Examples 1 to 3 produced in (1) above, the sensor sensitivity of geosmin relative to that of quinoclamine, another chemical substance, was evaluated.

[0066] Quinoclamine is a chemical known as an active ingredient in herbicides, etc. Quinoclamine is a substance that inhibits the detection of geosmin.

[0067] In this evaluation test, in addition to the chemical sensors 1 of Examples 1 to 3, a chemical sensor having a sensing electrode 21 formed using material particles 40 without a molecular template film as the electrode material was used as a comparison object.

[0068] Specifically, a chemical sensor was fabricated in the same manner as in Example 1 except that the sensing electrode was formed using material particles 40 that did not have a molecular template film, and this was designated Comparative Example 1. A chemical sensor was fabricated in the same manner as in Example 2 except that the sensing electrode was formed using material particles 40 that did not have a molecular template film, and this was designated Comparative Example 2. A chemical sensor was fabricated in the same manner as in Example 3 except that the sensing electrode was formed using material particles 40 that did not have a molecular template film, and this was designated Comparative Example 3.

[0069] The chemical sensors 1 according to Examples 1-3 and the chemical sensors according to Comparative Examples 1-3 were evaluated for their sensor sensitivity to geosmin at a concentration of 1 μg / L relative to their sensor sensitivity to quinoclamine at a concentration of 5 μg / L.

[0070] Specifically, using the chemical sensors of each Example and Comparative Example, the concentrations of a sample solution containing quinoclamine at a concentration of 5 μg / L and a sample solution containing geosmin at a concentration of 1 μg / L were measured. The measurements were performed twice for each chemical sensor.

[0071] The selectivity of geosmin in each chemical sensor was evaluated based on the S / N ratio, where S was the sensitivity of geosmin at 1 μg / L and N was the sensitivity of quinoclamine at 5 μg / L. The results are shown in Figure 5.

[0072] As shown in Fig. 5, it was confirmed that the sensor sensitivity of geosmin relative to quinoclamine was significantly higher for all of the chemical sensors 1 of Examples 1 to 3 compared to the chemical sensors of Comparative Examples 1 to 3. The chemical sensors of Comparative Examples 1 to 3 had S / N values ​​close to "1," confirming that they had almost no selectivity for geosmin relative to quinoclamine.

[0073] From the above results, it was confirmed that the chemical sensor 1 according to this example can be suitably used as a chemical sensor for detecting the concentration of geosmin. Furthermore, by changing the chemical substance used as the template in the process of forming the molecular template film 42, it is thought that the sensor can be used as a chemical sensor for detecting specific chemical substances other than geosmin.

[0074] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. Furthermore, configurations obtained by combining the configurations of the various embodiments described in this specification are also included in the scope of the present invention. [Explanation of symbols]

[0075] 1: Chemical sensors 10: Main body 11: Sample placement section 21: Detection pole 22: Opposite 23:Reference pole 31: 1st terminal 32: 2nd terminal 33: 3rd terminal 40: Material particles (of the sensing electrode) 41: Metal oxide particles 42: Molecularly templated membrane 42a: hole 50: Control unit 52: Current detection unit

Claims

1. A chemical sensor for measuring a predetermined chemical substance contained in an object to be inspected, A sensing electrode, a counter electrode, and a reference electrode are provided, the sensing electrode includes metal oxide particles carrying a noble metal; A chemical sensor in which a molecular template film using the chemical substance as a template is provided around the metal oxide particles.

2. The chemical substance is any one of geosmin, 2-methylisoborneol, halogenated anisole, octa-1,3-diene, α-terpineol, 4,4,6-trimethyl-1,3-dioxane, trimethylanisole, and 1-octen-3-ol. The chemical sensor of claim 1 .

3. The molecular template film is conductive. The chemical sensor according to claim 1 or 2.

4. The noble metal is any one of platinum (Pt), palladium (Pd), and gold (Au). The chemical sensor according to claim 1 or 2.

5. The noble metal is platinum (Pt) or palladium (Pd); The chemical sensor of claim 4 .

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