JP6035087B2 - Gas sensor, gas measuring device, and gas sensor manufacturing method - Google Patents

Description

  The present invention relates to a gas sensor that detects a gas using carbon nanotubes, a gas measuring device including the gas sensor, and a method for manufacturing the gas sensor.

In recent years, there has been a movement to strengthen regulations on gases exhausted from, for example, factories and cars from the awareness of problems surrounding the global environment. In practice, there are acceptable concentrations of gases harmful to the environment, and standards such as the order of ppb to ppm or less are defined. Accordingly, there is a need for a gas sensor that can detect very small amounts of these gases. Conventionally, an oxide semiconductor sensor such as SnO ₂ or ZnO that detects gas adsorption as a change in electrical conductivity has been used as a gas sensor for detecting gas, but it is insufficient in terms of detection sensitivity and response speed. Met.

Therefore, in recent years, attention has been focused on carbon nanotubes (hereinafter simply referred to as CNT) as a new gas sensor material.
In particular, a single-walled CNT (hereinafter simply referred to as SW-CNT (single wall carbon nanotube)) among these CNTs has a hollow structure with a diameter of several angstroms to several nanometers, and has a very large surface area per unit volume. For this reason, detection with extremely high sensitivity to gas adsorption on the CNT surface is possible.
SW-CNTs are known to have metallic or semiconductor electrical characteristics due to their chirality, and when semiconducting SW-CNTs are used, the gas adsorption reaction is performed by the electrical conductivity of SW-CNTs. It is possible to detect this as a change.

The following Non-Patent Document 1 is known as a technique that uses SW-CNT as a gas sensor for the first time, paying attention to the above points, and the electrical properties of SW-CNT (P-type semiconductor property) formed between electrodes are known. It is disclosed that _{2 to} 200 ppm of NO ₂ (nitrogen dioxide), 0.1 to 1% of NH ₃ (ammonia) and the like are measured in a room temperature environment.
Moreover, what is shown by the following patent document 1 is known as what actualized the gas sensor using SW-CNT.

Jing Kong, 6 others, “Nanotube Molecular Wires as Chemical Sensors”, SIGMA Life Science, VOL287, 28 JANUARY 2000, P622-P625

JP 2006-329802 A

According to the gas sensor shown in the above-mentioned Patent Document 1, it is formed so that semiconducting CNTs are bridged between a pair of electrodes, and the resistance change between the electrodes changes as the gas adsorbs to the CNTs. Based on this, the gas concentration is detected.
However, this gas sensor can detect whether the type of gas to be detected is an oxidizing gas or a reducing gas by using different CNT materials (P-type and N-type), but more than that. It was difficult to detect while classifying. Therefore, for example, it was not possible to detect only a specific gas from the mixed gas.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a gas sensor capable of selectively measuring a specific gas, a gas measuring device including the gas sensor, and a method of manufacturing the gas sensor. It is to be.

The present invention provides the following means in order to solve the above problems.
(1) A gas sensor according to the present invention is formed so as to be bridged between a support substrate, a pair of metal electrodes disposed on the support substrate so as to face each other with a space therebetween, and the pair of metal electrodes. , A bundle of nanotubes in which a plurality of semiconducting carbon nanotubes are aggregated, and on the surface of the carbon nanotubes, nanoparticles made of a metal material or a semiconductor are modified via a biomolecule, The carbon nanotubes and the nanoparticles are specifically bonded to each other.

According to the gas sensor of the present invention, when the gas to be detected is adsorbed to the nanotube bundle, the electrical characteristics of the nanotube bundle change in accordance with the adsorption. Therefore, the gas detection is performed by monitoring the change in the electrical characteristics. In addition, characteristics such as gas concentration can be measured.
In particular, the surface of each carbon nanotube constituting the nanotube bundle is modified with nanoparticles via a biomolecule. At this time, the biomolecule has bispecificity and specifically binds to both the carbon nanotube and the nanoparticle, so that the nanoparticle is securely held and secured. Moreover, the biomolecules are not bound to a part of the surface of the carbon nanotube, but are easily bound uniformly over the entire surface. Therefore, for these reasons, the nanoparticles are uniformly modified with a certain bonding force on the entire surface of the carbon nanotube.

  Therefore, at the time of gas adsorption, the gas is selectively adsorbed or decomposed with respect to each nanoparticle. Therefore, it is possible to select a gas that is easily adsorbed to the nanoparticles by appropriately selecting the nanoparticles to be modified. Thereby, it is possible to measure by targeting a specific gas, and the measurement can be performed while selecting the gas.

(2) In the gas sensor according to the present invention, the support substrate protrudes upward from the main surface of the substrate main body and the substrate main body, and is arranged to face each other with a gap therebetween. The pair of metal electrodes are respectively formed on the pair of base portions, and the nanotube bundle is formed between the pair of metal electrodes in a non-contact state with respect to the substrate body. It is preferable.

  In this case, the nanotube bundle can be brought into a non-contact state with respect to the substrate body, and can be formed between the pair of metal electrodes in a state of being floated. Therefore, the surface area of the nanotube bundle can be increased, and gas can be more easily adsorbed. Therefore, it is easy to make the gas sensor more sensitive and respond at high speed.

(3) In the gas sensor according to the present invention, the nanoparticles are preferably palladium or platinum.

  In this case, palladium (Pd) that easily adsorbs hydrogen-based gas or platinum (Pt) that easily adsorbs hydrocarbon-based gas is used as the nanoparticles. Measurement can be performed while selecting only gas or hydrocarbon-based gas.

(4) In the gas sensor according to the present invention, the metal electrode is preferably formed of any material of aluminum, gold, titanium, or nickel.

  In this case, by forming the metal electrode with any of the materials described above, even if the gas is adsorbed to the metal electrode, it is possible to suppress the resistance change of the metal electrode itself due to the adsorption. . Therefore, the change in the electrical characteristics of the nanotube bundle can be monitored more accurately, and the measurement accuracy can be increased.

(5) In the gas sensor according to the present invention, the biomolecule is preferably at least one selected from peptides, DNA, saccharides, and lipid molecules.

  In this case, since at least one selected from peptides, DNA, saccharides, and lipid molecules is used as the biomolecule, for example, the most suitable one depending on the affinity with the nanoparticle, etc. is widely used as the biomolecule it can.

(6) In the gas sensor according to the present invention, an insulating layer is preferably formed between the support substrate and the metal electrode.

  In this case, since the insulating layer is formed between the support substrate and the metal electrode, it may be a support substrate having conductivity, and the material selectivity as the support substrate is increased to increase the degree of design freedom. It can be improved.

(7) The gas measurement device according to the present invention is based on the gas sensor according to the present invention, a power supply unit that applies a measurement voltage between the pair of metal electrodes, and a change in electrical characteristics of the nanotube bundle. And a measuring unit that measures at least one of the types and characteristics.

  According to the gas measuring apparatus according to the present invention, since the above-described gas sensor is provided, it is possible to accurately measure the characteristics of the targeted specific gas, the concentration of the gas, and the like for various applications. It is possible to apply.

(8) In the method for manufacturing a gas sensor according to the present invention, the support substrate, the pair of metal electrodes disposed on the support substrate so as to face each other with a space therebetween, and the pair of metal electrodes are bridged. And a bundle of nanotubes formed by collecting a plurality of semiconducting carbon nanotubes, wherein the pair of metal electrodes are disposed in a solution in which the carbon nanotubes are dispersed. After immersing the support substrate, an AC voltage is applied between a pair of metal electrodes to cause dielectrophoresis of the carbon nanotubes, and the carbon nanotubes are bonded so as to crosslink between the pair of metal electrodes. A nanotube bundle forming step for forming a bundle, and the carbon nanotube is formed on the surface of the carbon nanotube during the nanotube bundle forming step. Via a carbon nanotube, a nano-particles made of a metal material or a semiconductor, a biological molecule that specifically binds respectively, characterized in that for modifying the nanoparticles.

According to the gas sensor manufacturing method of the present invention, by applying an AC voltage between a pair of metal electrodes in a solution in which carbon nanotubes are dispersed, the carbon nanotubes dispersed in the solution are turned into a pair of metal electrodes. Can be dielectrophoresed. At this time, since both ends of the carbon nanotube are polarized, the carbon nanotube can be oriented along the electric field direction connecting the pair of metal electrodes during dielectrophoresis.
In addition, since the electric field is likely to be locally concentrated at the tip of a pair of metal electrodes facing each other, one end of each carbon nanotube that has undergone dielectrophoresis with the above orientation is attached to the tip of the pair of metal electrodes. And combine. In addition, the carbon nanotubes are successively bonded in this way to form a nanotube bundle, and the nanotube bundle can be bonded so as to be bridged between the pair of metal electrodes.

  In the nanotube formation step, the nanoparticle is modified on the surface of the carbon nanotube via a biomolecule that specifically binds to the carbon nanotube and the nanoparticle (having bispecificity). Thereby, the gas sensor which comprises the nanotube bundle which consists of the carbon nanotube by which the nanoparticle was uniformly modified on the surface via the biomolecule can be obtained. According to this gas sensor, the same operational effects as those described above can be achieved. That is, it is possible to obtain a gas sensor that can measure while selecting a specific gas.

  In particular, since the carbon nanotubes are aligned using a dielectrophoresis and can be bonded so as to be bridged between a pair of metal electrodes, a bundle of nanotubes can be formed easily and efficiently, and productivity can be improved. This can lead to improvement of the cost and cost reduction. Moreover, since it can manufacture in the temperature environment of about normal temperature, it is excellent also in mass productivity.

(9) In the method for producing a gas sensor according to the present invention, the nanotube bundle forming step mixes the nanoparticles and the biomolecules in a solution in which the carbon nanotubes are dispersed, and the biomolecules are put on the surface of the carbon nanotubes. A preliminary step in which nanoparticles are modified in advance, and a main step in which the nanotube bundles are formed by dielectrophoresis of the carbon nanotubes in which the nanoparticles have been modified through the biomolecules by application of the alternating voltage. And are preferably provided.

  In this case, since the nanoparticles and the biomolecule are mixed in the solution in which the carbon nanotubes are dispersed, the nanoparticles can be uniformly bonded to the entire surface of the carbon nanotubes via the biomolecules in advance. Therefore, a plurality of carbon nanotubes whose nanoparticles are reliably modified can be aggregated by subsequent dielectrophoresis, and a higher quality nanotube bundle can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, it can be set as the highly convenient gas sensor which can measure a specific gas selectively and can respond flexibly to the various uses for which gas detection is required.

It is a figure showing a 1st embodiment concerning the present invention, and is a lineblock diagram of a gas measuring device. It is a perspective view of the gas sensor shown in FIG. It is an enlarged view of CNT which comprises the nanotube bundle | flux shown in FIG. It is the figure which showed how the sensor response of the nanotube bundle | flux in the gas sensor shown in FIG. 2 changes with the difference in gas concentration. FIG. 3 is a process diagram when the gas sensor shown in FIG. 2 is manufactured, and shows a state in which a metal film is formed on an SOI substrate. It is a figure which shows the state which formed the photoresist film corresponding to a pair of metal electrode on the metal film from the state shown in FIG. FIG. 7 is a diagram illustrating a state where the photoresist film is removed after the SOI substrate is etched using the photoresist film as a mask from the state illustrated in FIG. 6. It is a figure which shows the state which immersed the SOI substrate shown in FIG. 7 in the solution in which CNT was disperse | distributed. It is a figure which shows the state which is applying the alternating voltage between a pair of metal electrodes from the state shown in FIG. 8, and dielectrophoreses CNT with which the nanoparticle was modified through the biomolecule. It is a figure which shows the modification of the manufacturing method of a gas sensor, Comprising: It is a figure which shows the state which is carrying out the dielectrophoresis of CNT with which the nanoparticle is not modified. It is a figure which shows 2nd Embodiment which concerns on this invention, Comprising: It is a block diagram of a gas measuring device. It is a perspective view of the gas sensor shown in FIG. It is a figure which shows 3rd Embodiment which concerns on this invention, Comprising: It is a perspective view of the gas sensor in which the nanotube bundle was formed between a pair of metal electrodes formed on the support substrate with uniform thickness. FIG. 14 is a process diagram when the gas sensor shown in FIG. 13 is manufactured, and shows a state in which a metal film is formed on an SOI substrate and a photoresist film corresponding to a pair of metal electrodes is formed on the metal film. is there. It is a figure which shows the state which removed the photoresist film, after etching a metal film by using a photoresist film as a mask from the state shown in FIG.

<First Embodiment>
Hereinafter, a first embodiment according to the present invention will be described with reference to the drawings.
(Configuration of gas measuring device)
As shown in FIG. 1, the gas measuring apparatus 1 of the present embodiment includes a gas sensor 2, a power supply unit 3 that applies a measurement voltage between a pair of metal electrodes 15 (to be described later) of the gas sensor 2, and the gas sensor 2 at the time of voltage application. The measurement unit 4 is configured to measure at least one of the type or characteristics of the gas to be detected based on the change in the electrical characteristics of the nanotube bundle 20 described later, and the power source unit 3 and the measurement unit 4 And a control unit 5 for controlling.

The measurement unit 4 is a power source that applies a DC voltage or an AC voltage as the measurement voltage, and measures a gas concentration or the like by measuring a change in conductance (change in electrical characteristics) of the nanotube bundle 20 when the voltage is applied. Is possible.
The sensor response (ΔG / G ₀ ) is obtained by normalizing the change in conductance (ΔG) with the initial conductance (G ₀ ).

(Configuration of gas sensor)
The gas sensor 2 will be described.
As shown in FIG. 2, the gas sensor 2 is bridged between the support substrate 10, a pair of metal electrodes 15 disposed on the support substrate 10 so as to face each other with a space therebetween, and the pair of metal electrodes 15 ( And a nanotube bundle 20 formed so as to be bridged).

The support substrate 10 has a rectangular shape in plan view that is long in the first direction L1 and short in the second direction L2 orthogonal to the first direction L1 in plan view. A pair of base portions 12 that protrude upward from the surface 11a and that face each other with a gap in the first direction L1 are integrally formed.
The pair of base portions 12 are disposed at a portion of the support substrate 10 that is located in the middle of the second direction L <b> 2, and one end portion (base end portion) coincides with the edge portion of the substrate body 11. Moreover, the other edge part (front-end | tip part) in a pair of base part 12 is made into the opposing part 12a which faces each other at intervals. In addition, this opposing part 12a is formed in the planar view triangle shape so that it may sharpen.

  In the support substrate 10 of this embodiment, an SOI substrate 13 in which an oxide layer (silicon oxide film) 13b is formed on a silicon support layer 13a and a silicon active layer 13c is thermally bonded to the oxide layer 13b. The case where it is formed by is taken as an example. The substrate body 11 is mainly formed of a silicon support layer 13a, and the pair of base portions 12 are formed of a silicon support layer 13a, an oxide layer 13b, and a silicon active layer 13c. However, the support substrate 10 is not limited to the case where it is formed of the SOI substrate 13.

The metal electrode 15 is an electrode film formed over the entire surface of the pair of base portions 12, and is formed by, for example, a vapor deposition method or a sputtering method. Therefore, the opposing part 15a which faces each other among the metal electrodes 15 is formed in a triangular shape in plan view so as to be sharpened. The metal electrode 15 is preferably formed of any material such as aluminum, gold, titanium, or nickel.
Since the base portion 12 on which the pair of metal electrodes 15 is formed has the oxide layer 13b, the pair of metal electrodes 15 are not electrically connected to each other through the base portion 12 and the substrate body 11.

The nanotube bundle 20 is an aggregate of carbon nanotubes 21 formed into a bundle (bundle shape) by gathering together a plurality of semiconducting carbon nanotubes 21 in a non-contact state with respect to the substrate body 11. A pair of metal electrodes 15 are formed between opposing portions 15 a.
Therefore, the nanotube bundle 20 is arranged in parallel along the first direction L1 and is in a state of floating in the air.

  The carbon nanotubes 21 include carbon nanohorns, carbon nano-onions, carbon nanofibers and the like that have a long configuration. The structure may be single-layer, double-layer, or multi-layer, but in the present embodiment, a single-wall carbon nanotube is used as an example, and is simply referred to as CNT 21 below.

By the way, on the surface of each CNT 21 constituting the nanotube bundle 20, nanoparticles 25 are modified via biomolecules 26 as shown in FIG.
The nanoparticles 25 are ultra-fine particles made of a metal material or a semiconductor. The nano particles 25 are not limited to the nano size, but may be a micro size or a size of nano or smaller.
As the nanoparticles 25, for example, particles of noble metals such as palladium (Pd) and platinum (Pt), and semiconductor particles such as cadmium selenide (CdSe), zinc oxide (ZnO), and silicon (Si) are used. Is preferred.

The biomolecule 26 has bispecificity capable of specifically binding to the CNT 21 and the nanoparticle 25, respectively, and the binding force (chemical binding force) ensures the nanoparticle 25 on the surface of the CNT 21. It is tied to In particular, the biomolecule 26 is uniformly bonded to the entire surface of the CNT 21 without unevenness. Therefore, the entire surface of each CNT 21 is in a state where the nanoparticles 25 are uniformly modified (coated) with a reliable bonding force.
The biomolecule 26 is preferably at least one selected from, for example, peptides, DNA, saccharides and lipid molecules. Further, FIG. 3 illustrates a case where the biomolecules 26 are bound so as to be wound around the surface of the CNT 21 in a continuous line, but the present invention is not limited to this case.

(Operation of gas measuring device)
Next, the case where gas is measured using the gas measuring device 1 configured as described above will be described.
First, the gas sensor 2 shown in FIG. 1 is installed at a measurement point, and a measurement voltage is applied between the pair of metal electrodes 15 by the power supply unit 3. Here, when there are gases to be detected at the measurement points, these gases are adsorbed on the nanotube bundle 20. Then, the conductance of the nanotube bundle 20 changes (electrical characteristics change) by this adsorption. Therefore, gas can be detected by the measurement unit 4 monitoring this change.

  In particular, the surface of each CNT 21 constituting the nanotube bundle 20 is in a state where the nanoparticles 25 are uniformly modified with a certain binding force through the biomolecules 26 over the entire surface. Therefore, at the time of gas adsorption, the gas is mainly selectively adsorbed or decomposed with respect to the nanoparticles 25. Therefore, it is possible to select a gas that is easily adsorbed to the nanoparticles 25 by appropriately selecting the nanoparticles 25 to be modified. Thereby, it can measure aiming at specific gas, and can measure it, selecting.

  Therefore, according to the gas measuring device 1 including the gas sensor 2 of the present embodiment, for example, it is possible to detect only a specific type of gas from a mixed gas. Further, since the nanotube bundle 20 is in a non-contact state with respect to the substrate body 11 and is formed between the pair of metal electrodes 15 in a state of floating in the hollow, the surface area of the nanotube bundle 20 can be increased. It is easier to adsorb gas. Therefore, it can be set as the gas sensor 2 which responds more rapidly with high sensitivity.

Further, not only gas detection but also characteristics such as gas concentration can be measured.
For example, the case where the CNT 21 is P-type semiconducting and NO ₂ gas that is an oxidizing gas is measured will be described as an example.
When a specific concentration (× 1) of NO ₂ gas is present around the gas sensor 2, the NO ₂ gas is attracted by the nanoparticles 25 and adsorbed on the surface of the CNT 21. Then, electrons in the CNT 21 move to NO ₂ and the hole density of the CNT 21 increases, whereby the electric resistance of the CNT 21 changes and the conductance increases. Therefore, the sensor response (ΔG / G ₀ ) increases as in the period T1 shown in FIG.

After the NO ₂ gas is adsorbed, the NO ₂ gas can be desorbed from the nanotube bundle 20 by heating the gas sensor 2 to a temperature at which the NO ₂ gas is desorbed or irradiating with ultraviolet rays. The sensor response (ΔG / G ₀ ) can be reduced and restored to the original state as in the period T2 shown in FIG.

Next, when NO ₂ gas having twice the concentration (× 2 times) of the previous gas is present around the gas sensor 2, the hole density of the CNT 21 further increases, so that the period T 3 shown in FIG. The sensor response (ΔG / G ₀ ) rises more than when (× 1).
Further, when the NO ₂ gas having a concentration 4 times that of the previous gas (× 4 times) is present around the gas sensor 2, the hole density of the CNT 21 further increases, so that the period T 4 shown in FIG. The sensor response (ΔG / G ₀ ) is higher than when (× 2).

Thus, when the gas concentration increases, the sensor response (ΔG / G ₀ ) increases in proportion to the concentration. Therefore, the measurement unit 4 can accurately measure the gas concentration based on the magnitude of the sensor response (ΔG / G ₀ ) of the nanotube bundle 20.

Incidentally, NO ₂ gas is one example, but is not limited to this case.
For example, it is possible to measure NH ₃ gas which is a reducing gas. In this case, contrary to the case described above, when NH ₃ gas is adsorbed, electrons move from NH ₃ to CNT 21, and the hole density of CNT 21 decreases, so that the electrical resistance of CNT 21 changes and conductance increases. To do. Accordingly, when the gas concentration increases, the sensor response (ΔG / G ₀ ) also increases in proportion thereto. Therefore, it is possible to measure the gas concentration similarly.
Even with other gases, the gas concentration can be measured.

As described above, according to the gas sensor 2 of the present embodiment, it is possible to accurately measure the characteristics of a target specific gas and the characteristics such as the concentration of the gas, and for various applications that require gas detection. It is possible to provide a highly convenient gas sensor that can be flexibly handled.
Moreover, according to the gas measuring apparatus 1 provided with this gas sensor 2, it can be applied to various uses. For example, air pollution gas such as NOx and SOx, toxic gas _(SF 6, NH ₃₎ in the semiconductor processes and, measurement of volatile organic (VOC) gas, a wide range of applications can be expected.

(Gas sensor manufacturing method)
Next, a method for manufacturing the gas sensor 2 described above will be described below.
First, the formation process of forming the support substrate 10 having the substrate body 11 and the pair of base portions 12 from the SOI substrate 13 and forming the pair of metal electrodes 15 is performed.

  Specifically, first, as shown in FIG. 5, a metal film 30 is formed over the entire surface of the silicon active layer 13c of the SOI substrate 13 by vapor deposition or sputtering. Next, as shown in FIG. 6, a photoresist film 31 is patterned on the metal film 30 so as to correspond to the pair of metal electrodes 15.

Next, the metal film 30 is wet-etched, for example, using the photoresist film 31 as a mask by a semiconductor process or a MEMS process using a general etching technique, and then the SOI substrate 13 is dry-etched from the silicon support layer 13a side. Drill down. As a result, as shown in FIG. 7, the SOI substrate 13 can be formed in a step structure to form the support substrate 10 including the substrate body 11 and the pair of base portions 12, and at the same time, a metal is formed on the pair of base portions 12. Electrode 15 can be formed.
FIG. 7 shows a state where the photoresist film 31 used as a mask is removed.

  Next, an alternating voltage is applied between the pair of metal electrodes 15 in the solution in which the CNT 21 is dispersed to form the nanotube bundle 20 by dielectrophoresis, and at the same time, the nanoparticles 25 are modified on the surface of the CNT 21 via the biomolecule 26. A nanotube bundle forming step is performed.

  Specifically, first, a liquid tank (not shown) is prepared in which a CNT 21 is mixed in advance with an aqueous solvent or an organic solvent (alcohol or the like) and a solution W (see FIG. 8) in which the CNT 21 is dispersed is stored. At this time, the biomolecules 26 and the nanoparticles 25 are mixed in the solution W. Further, the metallic property is a semiconducting CNT 21 whose electrical properties are separated and purified, and a solution W in which the semiconducting CNT 21 is dispersed is prepared.

Then, since the biomolecule 26 has bispecificity with respect to each of the CNT 21 and the nanoparticle 25, the nanoparticle 25 can be uniformly bonded to the entire surface of the CNT 21 via the biomolecule 26. it can.
As a result, a plurality of CNTs 21 in which the nanoparticles 25 are modified (chemically bonded) via the biomolecules 26 are dispersed in the solution W (preliminary step).

Note that it is generally known that when the CNTs 21 are simply mixed into the solution, the CNTs 21 are likely to stick to each other (easily entangled), and thus may not be uniformly dispersed in the solution. As a countermeasure, there are many cases where a treatment such as adding a dispersant or a surfactant to the solution is performed.
In contrast, in the case of the present embodiment, the biomolecules 26 are quickly and uniformly bonded to the CNTs 21, so that the CNTs 21 can be prevented from sticking to each other, and the same function as the above-described surfactant and the like can be achieved. Can be made. Accordingly, it is possible to omit the trouble of putting a surfactant or the like and the trouble of managing it.

Next, as shown in FIG. 8, after the support substrate 10 on which the pair of metal electrodes 15 is formed is immersed in the solution W, the pair of metal electrodes 15 is connected by the AC power supply 32 connected to the pair of metal electrodes 15. An AC voltage is applied between them. Thereby, as shown in FIG. 9, the CNT 21 in which the nanoparticles 25 are modified via the biomolecule 26 can be moved toward the pair of metal electrodes 15 by dielectrophoresis.
In addition, in FIG. 9, illustration of the biomolecule 26 and the nanoparticle 25 is simplified.

  At this time, since both ends of the CNT 21 are polarized, the CNT 21 can be oriented along the electric field direction (arrow F direction) connecting the pair of metal electrodes 15 during dielectrophoresis. In addition, since the electric field is likely to be locally concentrated on the facing portions 15 a of the pair of metal electrodes 15 facing each other, the CNT 21 that has undergone dielectrophoresis in the above orientation posture has one end portion with respect to the facing portions 15 a of the pair of metal electrodes 15. Each adheres and binds.

Then, the CNTs 21 are successively bonded in this way, thereby forming a nanotube bundle 20 in which a plurality of CNTs 21 in which the nanoparticles 25 are reliably modified are assembled together, and the nanotube bundle 20 is paired with a pair of metals. The electrodes 15 can be bonded so as to crosslink (this step). At this point, the nanotube bundle forming process is completed.
As a result, the gas sensor 2 shown in FIG. 2 can be obtained.

  According to the manufacturing method of the present embodiment described above, the nanotube bundle 20 can be easily and efficiently bonded to the pair of metal electrodes 15 while adjusting the orientation of the CNTs 21 using dielectrophoresis. Can be reliably formed, leading to improvement in productivity and cost reduction. Moreover, since it can manufacture in the temperature environment of about normal temperature, it is excellent also in mass productivity.

  As a method of forming the nanotube bundle 20 between the pair of metal electrodes 15, for example, a thermal chemical vapor deposition method (CVD) in which a source gas such as methane is flowed using a Fe, Ni-based metal catalyst is used. However, in this case, there are problems in that it is difficult to control the growth conditions and in terms of cost and manufacturing throughput. In addition, the nanotube bundle obtained by the thermal CVD method contains a large amount of metal catalyst particles and carbon-based impurities. Therefore, the gas detection capability may be deteriorated. Furthermore, in the thermal CVD method, it is difficult to control the electrical properties of CNTs such as semiconductivity and metallic properties, so it is difficult to efficiently form semiconducting nanotube bundles that can be used as gas sensors.

On the other hand, in this embodiment, since the nanotube bundle 20 is formed by using dielectrophoresis, there is no possibility that the above problems caused by the thermal CVD method occur.
That is, since the solution W in which the semiconducting CNTs 21 are dispersed in advance is used, the nanotube bundle 20 in which the semiconducting CNTs 21 are efficiently gathered can be formed without impurities that lead to deterioration of the detection capability of the gas sensor 2. The shape, density, and the like of the nanotube bundle 20 can be precisely controlled by the shape of the pair of metal electrodes 15, the amplitude, frequency, application time, and the like of the alternating voltage. Furthermore, the apparatus necessary for forming the nanotube bundle 20 is mainly the solution W in which the AC power supply 32 and the CNT 21 are dispersed, and the time spent for the dielectrophoresis can be as short as about several minutes.

  Therefore, according to the manufacturing method of the present embodiment, the nanotube bundle 20 can be formed by cross-linking the CNT 21 between the pair of metal electrodes 15 by a simple process. A gas sensor 2 capable of high-speed response and room temperature operation can be realized. In addition, since the nanoparticles 25 are uniformly modified on the surface of each CNT 21 via the biomolecules 26, it is possible to selectively detect a specific gas.

In the first embodiment, the nanoparticles 25 are modified via the biomolecules 26 on the surface of the CNTs 21 before the CNTs 21 are dielectrophoresised. However, the present invention is not limited to this case.
For example, as shown in FIG. 10, in the solution W in which only the CNTs 21 are dispersed, an alternating voltage is applied between the pair of metal electrodes 15 to cause dielectrophoresis of the CNTs 21 to form the nanotube bundle 20.
Next, a not-shown containing liquid containing the biomolecules 26 and the nanoparticles 25 is prepared, and the support substrate 10 in which the nanotube bundle 20 is formed between the pair of metal electrodes 15 is immersed in this containing liquid. In the contained liquid, the nanoparticles 25 are specifically bound to the biomolecules 26.

Then, by performing the immersion, the biomolecules 26 are specifically bonded one after another to the surface of each CNT 21 constituting the nanotube bundle 20. Thereby, the nanoparticle 25 can be modified via the biomolecule 26 on the surface of the CNT 21. Finally, the contained liquid is washed with ultrapure water and dried with N ₂ gas or the like, whereby the gas sensor 2 shown in FIG. 2 can be obtained.
Even with such a manufacturing method, the gas sensor 2 can be manufactured, and the same effects can be obtained.

Second Embodiment
Next, a second embodiment according to the present invention will be described with reference to the drawings. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

(Configuration of gas measuring device and gas sensor)
As shown in FIG. 11, the gas measuring device 45 of this embodiment includes a multi-sensing type gas sensor 40.
In this gas sensor 40, as shown in FIG. 12, a plurality of pairs of base portions 12 and a pair of metal electrodes 15 are formed on a common substrate body 11, and the nanotube bundle 20 is bridged between each pair of metal electrodes 15. It is formed so that.

In this case, since a plurality of nanotube bundles 20 are provided, for example, when measuring the gas concentration or the like, the gas concentration can be measured based on the measurement results obtained by the plurality of nanotube bundles 20 rather than the measurement results obtained by the single nanotube bundle 20. Therefore, measurement accuracy can be further increased.
In the illustrated example, the case where three nanotube bundles 20 are provided is described as an example. However, two nanotubes or four or more nanotube bundles may be provided.

<Third Embodiment>
Next, a third embodiment according to the present invention will be described with reference to the drawings. In the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

(Configuration of gas sensor)
As shown in FIG. 13, in the gas sensor 50 of the present embodiment, an insulating layer 52 is formed on the main surface 51 a of the support substrate 51 having a uniform thickness, and a pair of metal electrodes 15 is formed on the insulating layer 52. Thus, the nanotube bundle 20 is formed so as to be bridged between the facing portions 15 a of the pair of metal electrodes 15. Therefore, the nanotube bundle 20 is not formed in a state of floating in the hollow, but is formed so as to be bridged between the facing portions 15a of the pair of metal electrodes 15 in a state where a part thereof is in contact with the insulating layer 52. ing.
The support substrate 51 may be the SOI substrate 13 described above or a silicon wafer. The insulating layer 52 may be a glass film, a ceramic film, an oxide film, or the like.

  Even with the gas sensor 50 configured as described above, the same effects can be obtained. However, according to the first embodiment, it is more preferable because the surface area can be increased by making the nanotube bundle 20 float in a hollow state.

(Gas sensor manufacturing method)
In the case of manufacturing the gas sensor 50 configured as described above, as shown in FIG. 14, an insulating layer 52 is formed on the main surface 51a of the support substrate 51 by vapor deposition or sputtering, and the insulating layer 52 is formed on the insulating layer 52. After the metal film 30 is formed over the entire surface by the same method, a photoresist film 31 is patterned on the metal film 30 so as to correspond to the pair of metal electrodes 15.
Then, as shown in FIG. 15, the metal film 15 is etched by wet etching or the like using the photoresist film 31 as a mask to form the metal electrode 15. FIG. 15 shows a state where the photoresist film 31 used as a mask is removed.

Thereafter, similarly to the first embodiment, the gas sensor 50 shown in FIG. 13 can be manufactured by performing the nanotube bundle forming step.
In particular, in the third embodiment, since it is not necessary to dig down the support substrate 51, the gas sensor 50 can be manufactured more efficiently. Further, since the insulating layer 52 is formed between the support substrate 51 and the metal electrode 15, the support substrate 51 having conductivity may be used, and the material selectivity as the support substrate 51 is enhanced to allow freedom of design. The degree can be improved.
In the case where an insulating substrate such as a glass substrate is used as the support substrate 51, the insulating layer 52 does not need to be formed.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

For example, in each of the above embodiments, the nanoparticles 25 may be a metal material or a semiconductor, and may be appropriately selected according to the type of gas desired to be measured. In particular, when the palladium (Pd) mentioned in the first embodiment is selected as the nanoparticle 25, it becomes easy to adsorb a hydrogen-based gas. For example, while selecting a hydrogen-based gas from a mixed gas, It is possible to measure. Further, when platinum (Pt) is selected as the nanoparticle 25, it becomes easy to adsorb the hydrocarbon-based gas, and therefore it is possible to perform measurement while selecting the hydrocarbon-based gas.
Examples of the nanoparticles 25 include CdSe.

In each of the above embodiments, the biomolecule 26 is preferably at least one selected from peptides, DNAs, saccharides, and lipid molecules as mentioned in the first embodiment. At this time, for example, only one type of peptide may be selected, or two types of peptide and DNA may be selected. Therefore, an optimal one can be widely used as the biomolecule 26 according to the affinity with the nanoparticle 25 and the like.
That is, the nanoparticles 25 may be selected according to the type of gas to be measured, and the biomolecules 26 having a good affinity for the nanoparticles 25 may be selected and used.

  In each of the above embodiments, the material of the metal electrode 15 is not particularly limited. However, as described in the first embodiment, the metal electrode 15 is formed of any material of aluminum, gold, titanium, or nickel. Is preferred. In this case, even if the gas is adsorbed on the metal electrode 15, it is possible to suppress the resistance change of the metal electrode 15 itself due to the adsorption. Therefore, the change in conductance (change in electrical characteristics) of the nanotube bundle 20 can be monitored more accurately, and the measurement accuracy can be increased.

DESCRIPTION OF SYMBOLS 1, 45 ... Gas measuring apparatus 2, 40, 50 ... Gas sensor 3 ... Power supply part 4 ... Measuring part 10, 51 ... Supporting substrate 15 ... Metal electrode 20 ... Nanotube bundle 21 ... CNT (carbon nanotube)
25 ... Nanoparticle 26 ... Biomolecule 11 ... Substrate body 12 ... Base part 52 ... Insulating layer

Claims (7)

A support substrate;
A pair of metal electrodes disposed on the support substrate so as to face each other with a space therebetween;
A nanotube bundle formed by bridging between the pair of metal electrodes, and a plurality of semiconducting carbon nanotubes gathered together,
On the surface of the carbon nanotube, nanoparticles are modified through biomolecules,
The biomolecules are specifically bound to the carbon nanotubes and the nanoparticles, respectively .
The nanoparticles are palladium or platinum;
The gas sensor according to claim 1, wherein the biomolecule is at least one selected from peptides, DNA, saccharides, and lipid molecules . The gas sensor according to claim 1,
The support substrate is
A substrate body;
A pair of base portions that protrude upward from the main surface of the substrate body and are arranged to face each other with a gap therebetween,
The pair of metal electrodes are respectively formed on the pair of base portions.
The gas sensor according to claim 1, wherein the nanotube bundle is formed between the pair of metal electrodes in a non-contact state with respect to the substrate body. The gas sensor according to claim 1 or 2 ,
The gas sensor is characterized in that the metal electrode is made of any material of aluminum, gold, titanium, or nickel. The gas sensor according to any one of claims 1 to 3 ,
An insulating layer is formed between the support substrate and the metal electrode. A gas sensor according to claim 1;
A power supply unit for applying a measurement voltage between the pair of metal electrodes;
A gas measuring device comprising: a measuring unit that measures at least one of the type and the characteristics of the gas based on a change in electrical characteristics of the nanotube bundle. A support substrate, a pair of metal electrodes disposed on the support substrate so as to face each other with a space therebetween, and a plurality of semiconducting carbon nanotubes are formed to be bridged between the pair of metal electrodes. A method of manufacturing a gas sensor comprising a bundle of nanotubes,
After immersing the support substrate on which the pair of metal electrodes are disposed in a solution in which the carbon nanotubes are dispersed, an AC voltage is applied between the pair of metal electrodes to cause dielectrophoresis of the carbon nanotubes, A nanotube bundle forming step of forming the nanotube bundle by bonding the carbon nanotubes so as to be bridged between a pair of metal electrodes,
During the nanotube bundle forming step,
On the surface of the carbon nanotubes, through a said carbon nanotubes, nanoparticles, biological molecule that specifically binds respectively, by modifying the nanoparticles,
The nanoparticles are palladium or platinum;
The method for producing a gas sensor, wherein the biomolecule is at least one selected from peptides, DNA, saccharides, and lipid molecules . In the manufacturing method of the gas sensor according to claim 6 ,
The nanotube bundle forming step includes
A preliminary step of mixing the nanoparticle and the biomolecule in a solution in which the carbon nanotube is dispersed, and pre-modifying the nanoparticle via the biomolecule on the surface of the carbon nanotube;
And a step of forming the nanotube bundle by dielectrophoresis of the carbon nanotubes modified with the nanoparticles through the biomolecules by applying the alternating voltage. Method.

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