Steam detection sensor-purpose sensitive membrane, steam detection sensor having the same, and moisture measurement device and water content measurement device having the sensor

Abstract

To make it possible to measure moisture and / or water content with ease and high accuracy without requiring a complicated device, expensive reagent or cumbersome operation.SOLUTION: A steam detection sensor-purpose sensitive membrane according to one embodiment of the present invention is a membrane mainly composed of DNA, which substantially does not contain a material other than the DNA as a sensitive membrane material. Therefore, the steam detection sensor-purpose sensitive membrane that exhibits extremely high detection sensitivity and selectivity to steam can be provided. The DNA as the sensitive membrane material is not required to have a specific base sequence or fall within a specific length range, and may be a double strand, single strand, or in a state where the double strand and single strand mix at an arbitrary ratio. Therefore, the sensitive membrane of the present invention can be fabricated inexpensively using the naturally derived DNA.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a sensitive film for a water vapor detection sensor, a water vapor detection sensor having this sensitive film, and a humidity measuring device and a moisture measuring device each including this water vapor detection sensor. [Background technology]

[0002] 2. Description of the Related Art Various devices have been developed so far for measuring the humidity in an environment (humidity measuring devices, also called hygrometers) or for measuring the moisture content in a sample (substance) (moisture measuring devices, also called moisture meters).

[0003] For example, electric hygrometers are currently widely used, and polymer film humidity sensors are used in these electric hygrometers. Polymer film humidity sensors measure relative humidity by changing the amount of water contained in the polymer film of the sensor element in response to changes in relative humidity, which in turn changes the dielectric constant.

[0004] The present inventors have been conducting research and development with a focus on nanomechanical sensors. A nanomechanical sensor has a sensitive film (also called a receptor layer) that selectively adsorbs and absorbs a substance (or a group of substances) to be measured that exists in a gas or liquid phase, and performs analysis based on changes in various physical parameters caused in the sensor by this adsorption or the like. Nanomechanical sensors have the advantages of being relatively sensitive despite their small size and simple structure, and being able to handle a wide range of substances to be measured by appropriately selecting the sensitive film. Among nanomechanical sensors, the present inventors have focused on a surface stress sensor that detects changes in the surface stress of a sensitive film caused by the adsorption or the like of a substance to be measured to the sensitive film, and have been searching for a sensitive film material that shows high selectivity for various substances to be measured. Specifically, Non-Patent Document 1 discloses that a membrane-type surface stress sensor (MSS) can function as a humidity sensor when cellulose acetate butyrate (CAB) is used as a sensitive film material. Non-Patent Document 2 discloses that an MSS using graphene oxide (GO) as a sensitive film material can detect humidity (moisture content) of about several tens of ppm in gas detection. Note that the specific structure, manufacturing method, operation, characteristics, etc. of the MSS are already well known, so they will not be described in detail in this application, but please refer to Patent Document 1 as necessary.

[0005] However, many conventional humidity sensors have problems with their accuracy because they are affected to a certain extent by impurity gases that are inevitably contained in the gas to be measured.In addition, due to the need to add components such as filters to the device configuration to remove such impurity gases and the response speed of the sensor element, conventional humidity sensors have the problem that they take a long time until the measured value stabilizes, that is, they have a long measurement time.

[0006] Meanwhile, in recent years, research into the use of DNA as a functional material has been actively conducted, and many chemical and biosensors using DNA, including nanomechanical sensors, have been reported. However, most of them are liquid sensors that measure substances present in the liquid phase, and their application as gas sensors that measure substances present in the gas phase is limited. As an example of the latter, Non-Patent Document 3 discloses that a sensor in which a network of carbon nanotubes is constructed on a substrate using a material (DNA functionalized single walled CNT, DFC) made by wrapping the surface of single-walled carbon nanotubes (SWNTs) with single-stranded DNA (ssDNA) can function as a humidity sensor. However, Non-Patent Document 3 does not consider the above-mentioned contaminant gases, and there is a concern that the accuracy may decrease due to the contaminant gases, as with the above-mentioned problem.

[0007] Currently, the Karl Fischer moisture meter is widely used as a moisture meter. The Karl Fischer moisture meter measures the moisture content of a sample by utilizing the specific reaction of an electrolyte (Karl Fischer reagent) consisting mainly of iodide ions, sulfur dioxide, and alcohol with water in the presence of methanol in a titration cell. There are two typical methods for measuring moisture content using the Karl Fischer reagent: volumetric titration, which determines the moisture content from the titration volume, and coulometric titration, which measures the moisture content by generating iodine from iodide ions by electrolytic oxidation. In both titration methods, the solvent in which the sample to be measured is dissolved is anhydrousized with iodine, and then the sample to be measured is placed in this anhydrous solvent and titrated with the Karl Fischer reagent to calculate the moisture content.

[0008] As described above, the Karl Fischer method for measuring moisture content is based on the principle of measuring trace amounts of moisture in a sample by titration using a chemical reaction with the Karl Fischer reagent, and therefore has the problem that it cannot be applied to methanol or amine-based solvents, which are reaction substrates in commonly used electrolytes. To address this issue, various electrolytes have been developed and reported, but each has its own strengths and weaknesses, and there is also the problem of time and labor involved in being unable to measure unless the electrolyte is replaced and cleaned each time. In addition, although the Karl Fischer method can measure moisture content with high accuracy, it cannot fully meet the demands for simplicity, speed, and low cost on-site. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2011 / 148774 [Non-patent literature]

[0010] [Non-Patent Document 1] F. Loizeau et al., "Membrane-Type Surface Stress Sensor with Piezoresistive Readout," Procedia Engineering, 47 (2012) 1085-1088. [Non-Patent Document 2] G. Imamura et al., "Graphene Oxide as a Sensing Material for Gas Detection Based on Nanomechanical Sensors in the Static Mode," Chemosensors 2020, 8, 82. [Non-Patent Document 3] A. Paulet al., "Fabrication and Performance of Solution-Based Micropatterned DNA Functionalized Carbon Nanotube Network as Humidity Sensors," in IEEE Transactions on Nanotechnology, vol. 13, no. 2, pp. 335-342, March 2014. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in consideration of the above-mentioned state of the art, and its purpose is to enable humidity and / or moisture to be measured simply and with high accuracy without the need for complicated equipment, expensive reagents, or complicated operations. [Means for solving the problem]

[0012] The features of the present invention for achieving the above object are as follows.

[0013] [1] A sensitive membrane for a water vapor detection sensor, which is a membrane composed mainly of DNA and contains substantially no materials other than DNA as a sensitive membrane material. [2] The sensitive film for a water vapor detection sensor according to [1], wherein the DNA is primarily double-stranded DNA, primarily single-stranded DNA, or a mixture of double-stranded DNA and single-stranded DNA. [3] The sensitive film for a water vapor detection sensor according to [1] or [2], wherein the water vapor detection sensor is a gas sensor using a nanomechanical sensor. [4] The sensitive film for a water vapor detection sensor according to [3], wherein the nanomechanical sensor is a surface stress sensor. [5] A water vapor detection sensor having a sensitive membrane that is mainly composed of DNA and contains substantially no materials other than DNA as the sensitive membrane material. [6] The water vapor detection sensor according to [5], wherein the DNA is primarily double-stranded DNA, primarily single-stranded DNA, or a mixture of double-stranded DNA and single-stranded DNA. [7] A water vapor detection sensor according to [5] or [6], which is a gas sensor using a nanomechanical sensor. [8] The water vapor detection sensor according to [7], wherein the nanomechanical sensor is a surface stress sensor. [9] A humidity measuring device comprising a water vapor detection sensor according to any one of [5] to [7], a means for supplying a sample gas containing a gas in an environment to be measured to the water vapor detection sensor, and an analytical means for analyzing a signal output from the water vapor detection sensor, and measuring the humidity in the environment.

[10] A moisture measuring device comprising a water vapor detection sensor according to any one of [5] to [7], a means for supplying a sample gas containing a sample gas to be measured to the water vapor detection sensor, and an analytical means for analyzing a signal output from the water vapor detection sensor, and measuring the moisture in the sample. Effect of the Invention

[0014] According to the present invention, a sensitive membrane for a water vapor detection sensor that exhibits extremely high detection sensitivity and selectivity to water vapor can be provided by constructing the sensitive membrane using substantially only DNA as the sensitive membrane material. The DNA as the sensitive membrane material is not required to have a specific base sequence or to be in a specific length range, and may be double-stranded, single-stranded, or a mixture of double-stranded and single-stranded in any ratio, so the sensitive membrane of the present invention can be produced inexpensively using naturally occurring DNA. Alternatively, the sensitive membrane of the present invention can be produced using chemically synthesized DNA according to practical requirements, etc.

[0015] According to the present invention, a water vapor detection sensor having the above-mentioned sensitive film for a water vapor detection sensor can be provided. Since the sensitive film of the water vapor detection sensor of the present invention is mainly composed of DNA and does not substantially contain any material other than DNA as the sensitive film material, the sensor can be produced by a simple method of applying a solution in which the required sensitive film material is dissolved in a solvent to a sensor such as a nanomechanical sensor.

[0016] Furthermore, according to the present invention, it is possible to provide a humidity measuring device and a moisture measuring device that include the water vapor detection sensor. The humidity measuring device and the moisture measuring device of the present invention are equipped with the water vapor detection sensor of the present invention, a means for supplying a sample gas to the water vapor detection sensor, and an analysis means for analyzing a signal output from the water vapor detection sensor, and thus can perform desired humidity and / or moisture measurements, thereby simplifying the configuration of the device. Furthermore, the humidity measuring device and the moisture measuring device of the present invention do not require complicated operations, and therefore enable easy and highly accurate measurement of humidity and / or moisture on site. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a diagram showing an optical microscope photograph of an MSS, which is one embodiment of the water vapor detection sensor of the present invention. [Diagram 2] FIG. 4 is a diagram showing a profile obtained by using a stylus-type thin film step gauge for the sensitive film for the water vapor detection sensor produced in the examples. [Diagram 3] FIG. 2 is a schematic diagram showing the configuration of an apparatus used in a water vapor detection experiment in the examples. [Figure 4] 1 shows the measurement results of the response characteristics of the MSS to various gases in “Measurement 1” of the embodiment: (a) water, (b) ethanol, (c) acetone, (d) toluene, and (e) n-hexane. [Diagram 5] FIG. 13 is a graph plotting the relationship between the number of days elapsed since the day the sensor chip was produced (day 0) and the signal intensity of the MSS for a sample gas containing water vapor, for the MSS used in "Measurement 1" in the example. [Figure 6]1 shows the measurement results of the response characteristics of the MSS to a sample gas prepared using a mixed solvent in which a certain amount of water was added to THF as a sample solvent for "Measurement 2" in Example 1. (a) A diagram showing the time change in the signal from the MSS, and (b) A graph plotting the maximum value of the signal from the MSS against the water concentration in each sample solvent. [Figure 7] 1 shows the measurement results of the response characteristics of the MSS to a sample gas prepared using a mixed solvent in which a certain amount of water was added to acetonitrile as a sample solvent for “Measurement 2” in Example 1. (a) A diagram showing the time change of the signal from the MSS, and (b) A graph plotting the maximum value of the signal from the MSS against the water concentration in each sample solvent. [Figure 8] 1 shows the measurement results of the response characteristics of the MSS to a sample gas prepared using a mixed solvent in which a certain amount of water was added to acetone as a sample solvent in “Measurement 2” in Example 1. (a) A diagram showing the time change of the signal from the MSS, and (b) A graph plotting the maximum value of the signal from the MSS against the water concentration in each sample solvent. [Figure 9] (a) A graph combining the graphs shown in Figures 5(b), 6(b), and 7(b), and (b) a graph showing the water concentration, which is the horizontal axis of (a), in molar ppm. [Figure 10] FIG. 1 shows optical microscope images of the MSS used in “Measurement 2” in the example (a) immediately after the sensor chip was fabricated, and (b) after measurement using a mixed solvent of THF and water, (c) after measurement using a mixed solvent of acetonitrile and water, and (d) after measurement using a mixed solvent of acetone and water. [Figure 11] FIG. 13 shows the results of measuring the height profile of a structure including a sensitive film using a laser microscope for an MSS produced in the examples: (a) immediately after the production of the sensor chip, (b) after measuring the response characteristics to water (water vapor) in measurement 1, and (c) after measuring the response characteristics to THF vapor (when the amount of water added to THF was 0 ppm) in measurement 2. [Figure 12]1 shows the measurement results of the response characteristics of the MSS to the sample gas prepared using the first set of sample solvents for "Measurement 3" in Example 1. (a) A diagram showing the time change of the signal from the MSS, and (b) A graph plotting the signal intensity of the MSS against the water concentration in each sample solvent. [Figure 13] 13 shows the measurement results of the response characteristics of the MSS to the sample gas prepared using the second set of sample solvents for "Measurement 3" in Example 1. (a) A diagram showing the time change of the signal from the MSS, and (b) A graph plotting the signal intensity of the MSS against the water concentration in each sample solvent. [Figure 14] A combined graph of the graphs shown in FIG. 12(b) and FIG. 13(b). [Figure 15] 13 shows the measurement results of the response characteristics of the MSS to sample gas with relative humidities of 10%, 20%, 40%, 60%, and 80% for "Measurement 4" in Example 1. (a) A diagram showing the time change in the signal from the MSS, (b) A graph plotting the signal from the MSS 60 seconds after the supply of the sample gas against the relative humidity of the sample gas, and (c) A graph plotting the signal from the MSS 2 seconds after the supply of the sample gas against the relative humidity of the sample gas. [Figure 16] FIG. 13 is a graph showing a comparison of the MSS signal intensity measured using other solvents for single-stranded DNA and double-stranded DNA in “Measurement 5” of the embodiment, with the MSS signal intensity for a sample gas containing water vapor as the standard. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail. The following description of the components may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment.

[0019] [Sensing membrane for water vapor detection sensor] The sensitive membrane for a water vapor detection sensor according to one embodiment of the present invention (hereinafter also simply referred to as the "sensitive membrane of the present invention") is a membrane composed primarily of DNA and contains substantially no materials other than DNA as sensitive membrane materials.

[0020] In this specification, the term "a film mainly composed of DNA" means that the majority of the components of the sensitive film are DNA. In the sensitive film of the present invention, components other than DNA include, for example, binders that improve adhesion to the substrate (sensor body) on which the sensitive film is formed, and impurities that may be inevitably included when the sensitive film is formed. In addition, in this specification, the term "the sensitive film does not substantially contain materials other than DNA as sensitive film materials" means that, among the components of the sensitive film, only DNA is intended as a material that has sensitivity (the property of responding to the measured substance) to the measured substance (in this invention, water vapor (water in a gaseous state)), and the components other than DNA do not have sensitivity to the measured substance, or even if they have such sensitivity, it is negligible compared to the sensitivity of DNA, that is, they do not substantially function as sensitive film materials.

[0021] For example, when the water vapor detection sensor is a surface stress sensor, the sensitive film is formed on the sensor body (coated on the sensor body). Here, the sensitive film may be composed of only DNA, or may be composed of components other than DNA. In the former case, except for impurities that may be inevitably contained when the sensitive film is formed, the component of the sensitive film is DNA, and the sensitive film material is DNA. In the latter case, the components other than DNA are binders that improve adhesion with the sensor body, and the components are intended to occupy only a part of the components of the sensitive film and not substantially function as sensitive film materials.

[0022] In nanomechanical sensors such as surface stress sensors, a film-like material such as a self-assembled film may be interposed between the sensor body surface and the sensitive film in order to improve the adhesion between the sensor body and the sensitive film. In such cases, the film-like material and the sensitive film are distinguished as separate structures, and then the configuration of the sensitive film is determined. On the other hand, if it is difficult to distinguish them as separate structures, it may not be possible to say that DNA accounts for the majority of the components of the sensitive film when the film-like material is included. In such cases, it may be possible to determine whether the condition of the sensitive film of the present invention is met by determining the material intended to be sensitive to the substance to be measured among the components, and then regarding the part (range) in which the material is mainly included as the sensitive film.

[0023] Specifically, the material described in Non-Patent Document 3 is a material (DFC) in which single-stranded DNA is fixed (non-covalently) to the surface of a carbon nanotube via van der Waals forces. According to Non-Patent Document 3, DFC has been reported to be used as a molecular recognition material for compounds such as methanol, triethylamine (TMA), and propionic acid (PA), and therefore DFC itself is treated as a sensitive membrane material. Therefore, in relation to the above-mentioned conditions of the sensitive membrane of the present invention, a membrane-like structure composed of a DFC network corresponds to the sensitive membrane, the constituent element of the structure is DFC, and the sensitive membrane material is DFC. Therefore, it can be understood that the structure is not mainly composed of DNA, and that the sensitive membrane material does not substantially contain materials other than DNA.

[0024] In addition, in the sensitive film for the water vapor detection sensor of the present invention, the DNA as the sensitive film material is not required to have a specific base sequence or to be in a specific length range. In other words, the sensitive film of the present invention is not intended to have DNA with a specific base sequence and / or within a specific length range, so that the DNA exhibits specificity for water molecules. Rather, the sensitive film of the present invention utilizes the physical adsorption of water molecules to DNA, and may be composed of DNA with random base sequences and lengths, and the orientation of the DNA in a film-like state is not particularly important. This should be understood as one of the features of the sensitive film of the present invention, which is different from the conventional chemical and biosensors using DNA, in which the base sequence and length of the DNA are set under specific conditions, or the DNA is fixed on the substrate (sensor body) so as to have a specific orientation (via an anchor structure as necessary) to exhibit the desired sensor function.

[0025] In one embodiment of the sensitive membrane for the water vapor detection sensor of the present invention, the DNA constituting the sensitive membrane may be substantially double-stranded DNA. Here, the DNA constituting the sensitive membrane of the present invention is "substantially double-stranded DNA" is not limited to a state in which all of the DNA has a double-stranded structure, but is intended to include a state in which the majority of the DNA (typically 80% or more) has a double-stranded structure and some of the DNA is in a single-stranded state. Here, double-stranded DNA includes not only DNA that is completely double-stranded, but also DNA in which at least several bases at either end are single-stranded.

[0026] In another embodiment of the sensitive membrane for the water vapor detection sensor of the present invention, the DNA constituting the sensitive membrane may be substantially single-stranded DNA. Here, the DNA constituting the sensitive membrane of the present invention is "substantially single-stranded DNA" is not limited to a state in which all of the DNA has a single-stranded structure, but is intended to include a state in which the majority of the DNA (typically 80% or more) has a single-stranded structure and some of it is in a double-stranded state. Here, single-stranded DNA includes not only completely single-stranded DNA, but also DNA in which at least several bases at either end are double-stranded.

[0027] In other words, in the sensitive film for the water vapor detection sensor of the present invention, the DNA as the sensitive film material may be mainly double-stranded DNA, may be mainly single-stranded DNA, or may be a mixture of double-stranded and single-stranded DNA in any ratio (a mixture of double-stranded and single-stranded DNA). In other words, as described above, the DNA as the sensitive film material is not required to have a specific base sequence or to be within a specific length range, so the sensitive film of the present invention can be produced at low cost using naturally occurring DNA. Alternatively, the sensitive film of the present invention can be produced using chemically synthesized DNA depending on practical requirements, etc.

[0028] In a preferred embodiment, the water vapor detection sensor is a gas sensor using a nanomechanical sensor. A preferred embodiment of the nanomechanical sensor is a surface stress sensor. In the following, a surface stress sensor is taken up as a representative example of a nanomechanical sensor, and a membrane-type surface stress sensor (MSS) is taken as an example of a specific type of surface stress sensor, but it should be noted that there is no intention to limit the sensor to this.

[0029] [Water vapor detection sensor] The water vapor detection sensor according to one embodiment of the present invention has the above-mentioned sensitive film for the water vapor detection sensor of the present invention. Since the specific features of the sensitive film have already been described, the description thereof will be omitted below.

[0030] FIG. 1 is an optical microscope photograph of an MSS having a sensitive film for a water vapor detection sensor of the present invention. The MSS chip (sensor chip) including the MSS (sensor element) shown in FIG. 1 is formed from a silicon wafer used in the field of semiconductor element technology, which is cut from a silicon single crystal, and the sensor element has a structure in which a circular part (which may be another shape such as a square) shown in the center is connected and fixed at four points on the top, bottom, left and right of the circular part to a frame-shaped part around it. When a gas component given to the sensor element is adsorbed and desorbed by the sensitive film applied to the surface of the circular part (thin film), the surface stress applied to the sensor element is concentrated in these four fixed areas (narrow parts), and the electrical resistance of the piezoresistance elements provided in these fixed areas is changed. These piezoresistance elements are interconnected by a conductive area provided in the frame-shaped part to form a Wheatstone bridge. A voltage is applied between two opposing nodes of this Wheatstone bridge, and the voltage appearing between the remaining two nodes is taken out of the sensor element as a signal output from the sensor element and the required analysis is performed. The structure and operation of such a sensor element are described in detail in, for example, Patent Document 1. In FIG. 1, the sensitive film is applied to the circular portion of the sensor element by an inkjet method. In the examples described later, an example of specific conditions for applying the sensitive film for the water vapor detection sensor of the present invention using an inkjet device is shown. Of course, the method and means for applying the sensitive film are not limited to this, and a liquid constant volume discharge device such as a dispenser may be used, and it is also possible to adopt a spray coating method using a spray coater.

[0031] [Water vapor detection sensor applications] The sensitive film for a water vapor detection sensor of the present invention has high selectivity to water vapor, and a water vapor detection sensor having the sensitive film responds with high sensitivity to water vapor. Therefore, the water vapor detection sensor of the present invention is suitable for use in applications for detecting water vapor in gas. Specifically, the water vapor detection sensor of the present invention can be suitably used in humidity measuring devices (hygrometers) and moisture measuring devices (moisture meters). However, it should be noted that the applications of the water vapor detection sensor of the present invention are not limited to humidity measuring devices and moisture measuring devices having the configurations shown below.

[0032] [Humidity measuring device] A humidity measuring device according to one embodiment of the present invention comprises a water vapor detection sensor of the present invention, a means for supplying a sample gas containing gas in an environment to be measured to the water vapor detection sensor, and an analysis means for analyzing a signal output from the water vapor detection sensor, and measures the humidity in the environment.

[0033] [Moisture measuring device] A moisture measuring device according to one embodiment of the present invention comprises a water vapor detection sensor of the present invention, a means for supplying a sample gas containing a sample gas to be measured to the water vapor detection sensor, and an analysis means for analyzing a signal output from the water vapor detection sensor, and measures the moisture in the sample.

[0034] An example of a specific configuration of the humidity measuring device and moisture measuring device can be the configuration described in the embodiment described below with reference to Fig. 3. However, the configuration of the humidity measuring device and moisture measuring device of the present invention is not limited to this, and a person skilled in the art will understand that various modifications are possible based on the exemplified device configuration.

[0035] The present invention will be described in more detail below with reference to examples. Note that the following examples are not intended to limit the present invention, but are intended to aid in understanding the present invention. EXAMPLES

[0036] In this example, the characteristics of an MSS having a configuration similar to that of the MSS described with reference to the optical microscope photograph shown in Fig. 1 are measured as a water vapor detection sensor, and it is described that this MSS exhibits extremely high detection sensitivity and selectivity for water vapor. Note that the MSS used here has a circular portion (a thin film on which a sensitive film is applied, which is fixed to the surrounding frame-shaped portion by a narrow portion provided with a piezoresistance element) with a diameter of 300 μm and a film thickness of approximately 3 μm.

[0037] Sodium deoxyribonucleic acid (derived from salmon testis) obtained from Tokyo Chemical Industry Co., Ltd. was dissolved in water to make a 200 μg / mL solution, which was then applied to the MSS chip (sensor chip) by the inkjet method and the solvent was dried to prepare a sensitive film. The details of the application conditions are as follows. Inkjet device: LaboJet-500SP (Microjet) Pretreatment: Oxygen plasma exposure (30 W, 2 minutes). The above solution was applied to the sensor chip within 1 hour after the treatment. Drop speed: 3~4s / shot Number of drops: 100-1000 shots Sensor chip temperature: Room temperature (25℃) Pulse voltage: 30.0V Pulse width: 100.0μs

[0038] In addition, since the solvent of the solution applied to the sensor chip was dried under the above-mentioned room temperature conditions, it is considered that the double-stranded structure of DNA is hardly converted to a single-stranded structure (denatured) by the drying process.

[0039] Figure 2 shows a profile obtained by scanning an area including the circular part (main body) of the MSS and the fixed areas (narrow parts) on both sides of the MSS using a stylus-type thin film step gauge (Dektak, manufactured by Bruker) for a sensitive film prepared by dropping 500 shots of the coating liquid onto a sensor chip. From the profile shown in Fig. 2, it was confirmed that the obtained sensitive film had a cone-like shape with a thickness of about 1.5 μm at the periphery of the circular part of the MSS. This is considered to be due to the coffee ring effect that occurred when water, the solvent of the coating solution, evaporated under heating conditions.

[0040] Here, in the present invention, the sensitive film formed on the sensor chip does not need to be flat. In other words, there is no need to add additives other than DNA to the coating solution in order to suppress the above-mentioned coffee ring effect when the sensitive film is produced. The shape of the sensitive film of the present invention has almost no effect on the detection sensitivity and selectivity to water vapor, which is evident from the fact that the MSS having the sensitive film produced in this embodiment exhibits extremely high detection sensitivity and selectivity to water vapor.

[0041] In this embodiment, the thickness of the sensitive film refers to the thickness of the thickest part of the film. That is, the thickness of the sensitive film having the profile shown in Fig. 2 is about 1.5 μm. In this embodiment, as described above, the number of drops of the coating liquid was set in the range of 100 shots to 1000 shots to produce the sensitive film, and as a result, the sensitive film had a thickness in the range of about 100 nm to 10 μm.

[0042] Here, from the results of measuring the infrared absorption spectrum of the coating solution (DNA solution), it was estimated that most of the DNA used had a double-stranded structure, with some single-stranded DNA included. In addition, as mentioned above, the DNA used was derived from salmon testes, that is, it was naturally derived DNA, so it is understood that its length varies within a certain range.

[0043] FIG. 3 is a schematic diagram showing the configuration of the apparatus used in the water vapor detection experiment in this embodiment. In FIG. 3, the sample to be measured is contained in a vial. Specifically, 2 mL of a given sample solution is placed in a 10 mL vial, and dry nitrogen gas is poured into the vial at a flow rate of 20 sccm as a carrier gas, so that the headspace gas of the vial, which is the saturated vapor of the sample solution, is sent out from the vial, and mixed with dry nitrogen gas at a flow rate of 80 sccm to prepare a mixed gas with a total flow rate of 100 sccm, which is used as the sample gas. Here, the flow rate of the dry nitrogen gas is controlled by two mass flow controllers (MFC1, MFC2) connected to two nitrogen gas cylinders (not shown), respectively. That is, when the above-mentioned sample gas is supplied, the flow rate of the gas path (L11) from MFC1 is controlled to 20 sccm, and the flow rate of the gas path (L2) from MFC2 is controlled to 80 sccm. The gas sent out through the head space (volume 8 mL) of the vial passes through the downstream gas path (L12) and merges with the gas path (L2) from MFC2 at the valve section, and the mixed gas with a flow rate of 100 sccm is supplied to the sensor section equipped with a sensor chip (MSS chip) through the gas path (L31), and then the mixed gas is discharged through the gas exhaust path (L32) of the sensor section. In addition, when dry nitrogen gas not containing the sample gas is supplied as a purge gas, only dry nitrogen gas with a flow rate of 100 sccm is supplied to the sensor section through the gas path (L2) from MFC2. In the following, in a series of measurement cycles, the period during which the above-mentioned sample gas is supplied is also referred to as the "sampling period", and the period during which only the above-mentioned dry nitrogen gas is supplied is also referred to as the "purge period".

[0044] In the sensor section, the change in surface stress caused by the components in the gas supplied to the sensor chip (MSS chip) is recorded as a signal from the MSS (sensor element) by a recorder (also called a data logger or data recorder), and is further analyzed by an analysis device (such as a personal computer). Of course, the device of this embodiment may also include an interface or communication device for exchanging information, commands, etc. with devices outside the device, but these are not shown in the figure.

[0045] Using such an experimental apparatus, the following measurements were carried out.

[0046] <Measurement 1: Measurement of response characteristics for various gases> In measurement 1, the vapors of five kinds of solvents, water, ethanol, acetone, toluene, and n-hexane, were used as the sample gas. Dry nitrogen gas was used as the carrier gas and purge gas. In the measurement of each sample gas, a measurement sequence was set in which the purge gas was first flowed for 30 seconds, then the sample gas was flowed for 60 seconds, and then the purge gas was flowed again for 90 seconds. This was counted as one cycle, and the measurement cycle was repeated several times. In addition, for the four kinds of solvents other than water, a dehydration treatment (static method, 24 hours or more) was performed using 20% ​​(m / v) molecular sieves (3A, Nacalai Tesque, Inc.) for each solvent before the measurement.

[0047] The MSS used in measurement 1 had a sensitive film prepared under the condition that the number of drops of the coating liquid on the sensor chip was 500 shots. The MSS was placed in an incubator set at 25°C and the measurement was performed in the same manner for measurements 2 and 3 described below.

[0048] The results are shown in Figure 4(a) to Figure 4(e), which show the change in signal (unit: mV) from the MSS over time (unit: seconds) in one representative cycle out of the multiple measurement cycles described above.

[0049] As shown in FIG. 4(a), the MSS prepared in this embodiment immediately showed a signal of about 40 mV when the sample gas containing water vapor was supplied after the end of the purge period (i.e., immediately after the start of the sampling period), and although the signal gradually decreased thereafter, the signal was maintained between about 35 mV and 40 mV throughout the entire sampling period. In addition, when the gas supplied was switched back to the purge gas after the end of the sampling period, the signal quickly returned to the baseline (a line based on the signal in the first purge period). Thus, from the signal waveform shown in FIG. 4(a), it can be seen that the rate of adsorption and desorption of water vapor contained in the sample gas to the sensitive film of the MSS prepared in this embodiment is fast, and that the change in surface stress caused by the adsorption of water vapor to the sensitive film is detected with high sensitivity.

[0050] In contrast, as shown in Figures 4(b) to 4(e), when sample gas containing ethanol, acetone, toluene, and n-hexane vapor was supplied, in all cases, only a slight increase in signal (approximately 1 mV) from the baseline was observed when the purge period was switched to the sampling period.

[0051] From these results, it was confirmed that the MSS prepared in this example exhibits extremely high detection sensitivity and selectivity for water vapor. Note that, in some of the molecular recognition methods using DNA proposed in the past, the main detection principle is that the target molecule intercalates between the base pairs of the double-stranded structure of DNA, but in the nanomechanical sensor to which the present invention is applied, even if such intercalation occurs, it is considered that it does not affect the change in the physical parameters detected by the sensor, and therefore it can be said that the change in surface stress detected by the MSS prepared in this example can be considered to be caused solely by the physical adsorption of water molecules to the DNA, which is the sensitive film material.

[0052] [Evaluation of the stability of the sensitive film] Figure 5 is a graph plotting the relationship between the number of days elapsed since the sensor chip was produced (day 0) and the signal strength of the MSS for the sample gas containing water vapor for the MSS used in measurement 1. Here, the signal strength of the MSS means a feature value that indicates the response characteristics of the MSS, extracted based on the waveform of the signal from the MSS obtained during the sampling period. For details, see the explanations of Figures 12(b) and 13(b) described later.

[0053] As shown in FIG. 5, the MSS prepared in this embodiment maintained the same performance as on the day of preparation (day 0) even after 150 days or more had passed since the preparation of the sensor chip, and it was confirmed that the stability of the sensitive film was excellent. Note that the number of plots in FIG. 5 is six (i.e., the number of measurements using sample gas containing water vapor is six in total), but during the period when measurements using sample gas containing water vapor were not performed, the sensor chip was stored in the atmosphere (in an environment of about 25° C.) or was used for measurements using a different experimental system. From this, it can be said that the MSS prepared in this embodiment has a sensitive film stability to the extent that it can be repeatedly used for measurements using sample gas containing water vapor even after a long time has passed since the preparation of the sensor chip, and further, even if it is stored in the atmosphere, it does not deteriorate in a way that affects the measurement performance, and the durability of the sensor chip is excellent to the extent that it can be used for multiple measurements.

[0054] <Measurement 2: Measurement of response characteristics to water in various solvents> In measurement 2, a mixed solvent was prepared by adding a certain amount of water to THF, acetonitrile, and acetone, and the response characteristics of the MSS to the sample gas prepared using this mixed solvent as the sample solvent was measured. Here, THF was used that had been sufficiently dehydrated in advance by freeze degassing treatment. In addition, when preparing each sample solvent, each solvent was dehydrated in advance (static method, 24 hours or more) using 20% ​​(m / v) molecular sieves (3A, Nacalai Tesque, Inc.), and then a certain amount of water was added. In the measurement of each sample gas, a measurement sequence was set in which purge gas was first flowed for 30 seconds, then sample gas was flowed for 30 seconds, and then purge gas was flowed again for 150 seconds. This was set as one cycle, and the measurement cycle was repeated several times.

[0055] The results are shown in Figures 6 to 8. FIG. 6 shows the measurement results of the response characteristics of the MSS to a sample gas prepared using a mixed solvent in which a certain amount (0 ppm to 1000 ppm) of water was added to THF as the sample solvent. FIG. 6(a) shows the change in the signal from the MSS over time, and FIG. 6(b) is a graph plotting the maximum value of the signal from the MSS against the water concentration (weight ppm) in each sample solvent. 7 and 8 were prepared under the same conditions as FIG. 6, except that the THF in FIG. 6 was replaced with acetonitrile and acetone, respectively. Figures 6(a), 7(a) and 8(a) show the change in signal (in mV) from the MSS over time (in seconds) in a representative cycle out of the multiple measurement cycles described above.

[0056] As shown in Figure 6, in the MSS prepared in this example, the maximum signal value obtained during the sampling period increased as the amount of water contained in THF increased (Figure 6(a)), and it was confirmed that the maximum value was approximately linearly related to the concentration of water in the solvent (the amount of water vapor contained in the vapor of the mixed solvent of THF and water) (Figure 6(b)). Moreover, similar trends were also observed when a mixed solvent of acetonitrile and water was used (Figures 7(a) and 7(b)), and when a mixed solvent of acetone and water was used (Figures 8(a) and 8(b)).

[0057] From the results shown in Figs. 6(a), 7(a) and 8(a), in Measurement 2, even after a certain time has passed after switching from the sampling period to the purge period again, the signal from the MSS has not returned to the baseline, and at first glance, it seems that the water vapor (water molecules) adsorbed on the sensitive film has not been sufficiently desorbed by the purge gas (dry nitrogen gas). However, in comparison with Fig. 4 showing the results of Measurement 1, the scale of the vertical axis showing the signal value is about one-tenth or less, so it should be noted that even if the signal appears large, it may actually be a relatively small signal. In addition, unlike Measurement 1, in Measurement 2, due to the nature of the experiment in which the sensor response to water molecules in the vapor of a mixed solvent containing a certain amount of water is measured, the molecules or ions present in the sensitive film and the water molecules may be in a hydrated state, and this can also be understood as the reason why a longer purge period is required to return the signal from the MSS to the baseline.

[0058] Figure 9(a) shows a graph combining the graphs shown in Figures 6(b), 7(b), and 8(b). Figure 9(b) shows the relationship between the water concentration, which is the horizontal axis of Figure 9(a), and the maximum value of the MSS signal when expressed in molar ppm.

[0059] From the graphs shown in Figures 9(a) and 9(b), it can be seen that the results obtained in Measurement 2 agree well with Raoult's law ("The vapor pressure of each component in a mixed solution is expressed as the product of the vapor pressure of each pure liquid and the molar fraction in the mixed solution"). However, for acetone (ketone), there is a deviation from an ideal solution (perfect solution) for which Raoult's law applies, and the higher the concentration of water, the more difficult it is to regard the activity coefficients of all components as 1 in a real solution, which is thought to be why there is a deviation from the results for THF and acetonitrile.

[0060] [Evaluation of the stability of the sensitive film] FIG. 10(a) is an optical microscope photograph of the MSS used in measurement 2 immediately after the sensor chip was fabricated, and FIG. 10(b) to FIG. 10(d) are optical microscope photographs after measurements using a mixed solvent of THF and water, a mixed solvent of acetonitrile and water, and a mixed solvent of acetone and water, respectively.

[0061] As shown in Figures 10(a) to 10(d), even after the MSS produced in this example was subjected to various measurements, the sensor chip maintained almost the same appearance as immediately after production, and the sensitive film also maintained the same state as before the measurements even after a series of measurements were performed, and no defects such as detachment of the sensitive film from the circular part (main body) were observed.

[0062] 11 shows the height profile of the structure including the sensitive film obtained by scanning the circular part (main body) of the MSS and the fixing regions (narrow parts) on both sides of the circular part (main body) of the MSS produced in this example with a laser microscope. The laser microscope used for the measurement was a 3D Surface Profiler (VK-X1000, KEYENCE Corporation).

[0063] 11(a) to 11(c) respectively show the measurement results of the height profile of the sensitive film immediately after the sensor chip was fabricated, after measuring the response characteristics to water (water vapor) in Measurement 1, and after measuring the response characteristics to THF vapor (when the amount of water added to THF was 0 ppm) in Measurement 2. Comparing these measurement results, it is found that the MSS fabricated in this example showed almost no change in the height profile of the sensitive film even after being subjected to various measurements, indicating that the sensor chip including the sensitive film has excellent stability.

[0064] <Measurement 3: Measurement of performance as a moisture meter> In measurement 3, based on the results of measurement 2, the response characteristics of the MSS to sample gases prepared using mixed solvents with a wider range of moisture content as the sample solvent were measured with the intention of evaluating the performance as a moisture meter. The solvent used was THF. In the measurement of each sample gas, a measurement sequence was set up in which purge gas was first flowed for 30 seconds, then the sample gas was flowed for 300 seconds, and then the purge gas was flowed again for 300 seconds. This was counted as one cycle, and the measurement cycle was repeated several times.

[0065] The following two sets of sample solvents were prepared. (First set) Water addition amounts were 0 ppm, 10 ppm, 20 ppm, 50 ppm, 100 ppm and 200 ppm. (Second set) Water addition amounts were 0 ppm, 200 ppm, 400 ppm, 600 ppm, 1000 ppm, 2000 ppm, 3000 ppm and 4000 ppm.

[0066] Here, the sample solvents of the first and second sets were prepared independently. That is, the sample solvent in the first set with 200 ppm water added and the sample solvent in the second set with 200 ppm water added were prepared separately, although the amounts of water added were the same. In addition, in preparing the sample solvents of the first and second sets, THF that had been sufficiently dehydrated in advance by freeze-degassing treatment was further dehydrated (static method, 24 hours or more) using 20% ​​(m / v) molecular sieves (3A, Nacalai Tesque, Inc.), and a predetermined amount of water was added.

[0067] The results are shown in Figures 12 and 13. FIG. 12 shows the measurement results of the response characteristics of the MSS to a sample gas prepared using the first set of sample solvents, where FIG. 12(a) is a diagram showing the change in signal from the MSS over time, and FIG. 12(b) is a graph plotting the signal intensity of the MSS against the water concentration in each sample solvent. FIG. 13 shows the measurement results of the response characteristics of the MSS to a sample gas prepared using the second set of sample solvents, where FIG. 13(a) is a diagram showing the change in signal from the MSS over time, and FIG. 13(b) is a graph plotting the signal intensity of the MSS against the water concentration in each sample solvent. Note that Figures 12(a) and 13(a) show the change in signal (in mV) from the MSS over time (in seconds) in a representative cycle out of the multiple measurement cycles described above, but for the first purge period, only the signal (baseline) for 10 seconds before switching to the sampling period is shown. In addition, with respect to Fig. 12(b) and Fig. 13(b), the signal strength of the MSS means a feature value that indicates the response characteristics of the MSS, extracted based on the waveform of the signal from the MSS obtained during the sampling period. Specifically, for example, in a signal having a waveform as shown in Fig. 12(a), the value in a state in which the signal remains at a substantially constant value during the latter half of the sampling period is extracted as the feature value. For convenience, this value will be referred to as the saturation value below. In addition, in a signal having a waveform as shown by "+2000ppm", "+3000ppm", and "+4000ppm" in Fig. 13(a), the maximum value that can be read from the peaks observed during the first half of the sampling period is extracted as the feature value.

[0068] As shown in FIG. 12, in the MSS prepared in this example, when the amount of water contained in THF was in the range of 0 ppm to 200 ppm, the signal intensity (the characteristic value here is both the saturation value and the maximum value) increased as the amount of water increased (FIG. 12(a)). It was confirmed that these signal intensities were approximately linearly related to the concentration of water in the solvent (the amount of water vapor contained in the vapor of the mixed solvent of THF and water) (FIG. 12(b)).

[0069] This result shows that by using the sensitive membrane of the present invention, it is possible to measure moisture contents of 200 ppm or less with high accuracy, which was difficult to measure using the conventional moisture measurement method based on the Karl Fischer method.

[0070] In addition, as shown in FIG. 13, in the MSS prepared in this example, when the amount of water contained in THF was in the range of 0 ppm to 4000 ppm, the signal obtained during the sampling period was larger as the amount of water was greater (FIG. 13(a)), and it was confirmed that these signal intensities had a certain functional relationship with the concentration of water in the solvent (the amount of water vapor contained in the vapor of the mixed solvent of THF and water) (FIG. 13(b)).

[0071] Specifically, in the range of 0 ppm to 1000 ppm of water, the signal from MSS showed a sharp rise immediately after the start of the sampling period, and then increased toward the saturation value, or showed a behavior of remaining at a value almost equal to the saturation value, as in the first set of experiments in the range of 0 ppm to 200 ppm. In contrast, in the range of 2000 ppm to 4000 ppm, where the amount of water is greater than 1000 ppm, the signal from MSS showed a sharp rise immediately after the start of the sampling period, and then increased to a maximum value, and then gradually decreased. As a result, in the graph shown in FIG. 13(b), if the signal intensity when the amount of water is 1000 ppm is regarded as one boundary, the change in the signal intensity from MSS in the range of 0 ppm to 1000 ppm and the range of 1000 ppm to 4000 ppm can be regarded as separate functional relationships.

[0072] These results not only show that by using the sensitive film of the present invention, a moisture meter applicable to samples having a wide range of water contents can be produced, but also suggest that when it is required to analyze whether a certain sample meets a certain criterion (for example, a water content of 1000 ppm or less or more than 1000 ppm), if a preliminary measurement is performed on a sample containing water in a range that includes the criterion value and the characteristics of the signal from the sensor can be captured, it is possible to determine whether the criterion is met from the characteristics of the waveform of the signal from the sensor when an actual sample is measured.

[0073] Furthermore, as shown in Figure 14, when the graphs shown in Figure 12(b) and Figure 13(b) are combined into one, it is confirmed that the results obtained using the two sets of sample solutions prepared independently show almost the same functional relationship. This means that the results obtained using the MSS prepared in this example are highly reproducible, and that high-precision measurements are possible even when used as a moisture meter.

[0074] <Measurement 4: Measurement of performance as a hygrometer> In measurement 4, the response characteristics of the MSS to sample gas prepared so that the relative humidity was in the range of 10% to 80% was measured with the intention of evaluating the performance as a hygrometer. Specifically, in the preparation of the sample gas described with reference to FIG. 3, the flow rate of the gas path (L11) from the MFC1 was set to 10 sccm, 20 sccm, 40 sccm, 60 sccm, and 80 sccm, and the flow rate of the gas path (L2) from the MFC2 was set to 90 sccm, 80 sccm, 60 sccm, 40 sccm, and 20 sccm, thereby preparing sample gases with water vapor ratios of 10%, 20%, 40%, 60%, and 80% in the mixed gas with a total flow rate of 100 sccm. In the measurement of each sample gas, a measurement sequence was set in which first the purge gas was flowed for 30 seconds, then the sample gas was flowed for 60 seconds, and then the purge gas was flowed again for 60 seconds. This was regarded as one cycle, and the measurement cycle was repeated several times.

[0075] The MSS used in measurement 4 had a sensitive film prepared under the condition that the number of shots of the coating solution dropped onto the sensor chip was 1000. The MSS was placed in an incubator set at 25°C and the measurement was performed.

[0076] The results are shown in Figure 15. Figure 15 shows the measurement results of the response characteristics of the MSS to sample gas with relative humidities of 10%, 20%, 40%, 60%, and 80%, where Figure 15(a) shows the change in signal from the MSS over time, Figure 15(b) shows a graph plotting the signal from the MSS 60 seconds after the sample gas was supplied against the relative humidity of the sample gas, and Figure 15(c) shows a graph plotting the signal from the MSS 2 seconds after the sample gas was supplied against the relative humidity of the sample gas. Note that Figure 15(a) shows the change in signal (in mV) from the MSS over time (in seconds) in one representative cycle out of the multiple measurement cycles described above, but for the first purge period, only the signal (baseline) for 10 seconds before switching to the sampling period is shown.

[0077] As shown in Fig. 15(a), in the MSS prepared in this example, when the relative humidity of the sample gas was in the range of 10% to 80%, the higher the relative humidity was, the larger the maximum value and saturation value of the signal obtained during the sampling period was (Fig. 15(a)). Note that the maximum value and saturation value here have the same meanings as those in Figs. 12(b) and 13(b) described above.

[0078] Here, when the relative humidity of the sample gas was in the range of 10% to 40%, the signal from the MSS showed a sharp rise immediately after the start of the sampling period, and then increased toward the saturation value, or showed behavior of remaining at a value almost equal to the saturation value. In contrast, when the relative humidity of the sample gas was in the range of 60% to 80%, the signal from the MSS showed a sharp rise immediately after the start of the sampling period and rose to a maximum value. Thereafter, in the sample gas with a relative humidity of 60%, the signal from the MSS showed a gradual and gradual decrease, and in the sample gas with a relative humidity of 80%, the signal from the MSS showed an almost constant value.

[0079] Here, we focused on the signal from the MSS 60 seconds after the supply of the sample gas, which is the end of the sampling period, and plotted this against the relative humidity of the sample gas, and found that there was a certain functional relationship, as shown in Figure 15(b). We also focused on the signal from the MSS 2 seconds after the supply of the sample gas, which is the beginning of the sampling period, and plotted this against the relative humidity of the sample gas, and found that there was an almost linear relationship, as shown in Figure 15(c).

[0080] These results show that by using the sensitive film of the present invention, a hygrometer that can be applied to a wide range of humidity that can be envisioned in practical use can be produced.

[0081] <Measurement 5: Measurement using single-stranded DNA as the sensitive membrane material> In measurement 5, measurements were performed using double-stranded DNA and single-stranded DNA as the sensitive film material, and the results were compared. As in measurements 1 to 4 above, sodium deoxyribonucleic acid (derived from salmon testis) obtained from Tokyo Chemical Industry Co., Ltd. was used as the double-stranded DNA, and a 21-mer oligonucleotide (base sequence: 5'-GAC TAC CTC CTC CAC AGA CTC-3') was used as the single-stranded DNA. The fabrication method of the MSS using each sensitive film material (the application conditions of the DNA solution on the MSS chip) was the same as that of the MSS used in measurements 1 to 4 above. The experimental apparatus was also configured as shown in FIG. 3, and the response characteristics to the vapor of the five types of solvents (water, ethanol, acetone, toluene, and n-hexane) used in measurement 1 above were measured.

[0082] Fig. 16 is a graph showing a comparison of the signal intensity ratio of MSS measured using other solvents with respect to the signal intensity of MSS for a sample gas containing water vapor, for single-stranded DNA and double-stranded DNA. Note that the meaning of signal intensity here is the same as in Fig. 12(b) and Fig. 13(b) described above.

[0083] 16, in the MSS used in this measurement, whether the sensitive film material is single-stranded DNA or double-stranded DNA, the signal intensity of the MSS for the sample gas containing ethanol, acetone, n-hexane, or toluene vapor is less than 0.1 times the value measured using the sample gas containing water vapor, and is extremely small. Thus, from the results obtained in this measurement, it was confirmed that the MSS equipped with the sensitive film of the present invention has extremely high detection sensitivity and selectivity for water vapor. [Industrial Applicability]

[0084] According to the present invention, a sensitive film for a water vapor detection sensor that exhibits extremely high detection sensitivity and selectivity to water vapor is provided by using DNA derived from a living body or chemically synthesized DNA as a sensitive film material. By using a water vapor detection sensor having the sensitive film, anyone can easily measure humidity and / or moisture anywhere. By using a surface stress sensor, particularly a membrane-type surface stress sensor (MSS), as a water vapor detection sensor, humidity and / or moisture can be measured with an extremely fast response speed. According to the present invention, since it is not necessary to add a member such as a filter for removing impurity gases to the device configuration as in the past, a high economic effect can be expected as a hygrometer that can perform rapid and highly accurate measurements in real time on site. In addition, it is considered that the economic effect of the moisture meter that can easily perform measurements on site as an alternative device to the moisture measurement method by the Karl Fischer method in a laboratory is also high.

Claims

1. A sensitive membrane for a water vapor detection sensor, which is a membrane mainly composed of DNA and does not substantially contain any material other than DNA as a sensitive membrane material.

2. 2. The sensitive film for a water vapor detection sensor according to claim 1, wherein the DNA is primarily double-stranded DNA, primarily single-stranded DNA, or a mixture of double-stranded DNA and single-stranded DNA.

3. 3. The sensitive film for a water vapor detection sensor according to claim 1, wherein the water vapor detection sensor is a gas sensor using a nanomechanical sensor.

4. The sensitive film for a water vapor detection sensor according to claim 3 , wherein the nanomechanical sensor is a surface stress sensor.

5. A water vapor detection sensor having a sensitive film that is mainly composed of DNA and does not substantially contain any material other than DNA as the sensitive film material.

6. 6. The water vapor detection sensor of claim 5, wherein the DNA is primarily double-stranded DNA, primarily single-stranded DNA, or a mixture of double-stranded DNA and single-stranded DNA.

7. 6. The water vapor detection sensor according to claim 5, which is a gas sensor using a nanomechanical sensor.

8. The water vapor detection sensor of claim 7 , wherein the nanomechanical sensor is a surface stress sensor.

9. 9. A humidity measuring device comprising the water vapor detection sensor according to claim 5, a means for supplying a sample gas containing a gas in an environment to be measured to the water vapor detection sensor, and an analysis means for analyzing a signal output from the water vapor detection sensor, and measuring the humidity in the environment.

10. 9. A moisture measuring device comprising the water vapor detection sensor according to claim 5, a means for supplying a sample gas containing a sample gas to be measured to the water vapor detection sensor, and an analysis means for analyzing a signal output from the water vapor detection sensor, and for measuring moisture in the sample.

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