Sensor system and detection method

Abstract

To provide a sensor element that can selectively detect a target material that has been difficult to detect.SOLUTION: A sensor element 1 can detect a target material in an atmosphere. The sensor element 1 includes a graphene 14, a drain electrode 15 attached to the graphene 14, and a source electrode 16 attached to the graphene 14. A current flowing between a source electrode 16 and a drain electrode 15 is measured in a period of time when application of light and stopping the application are repeated on the sensor element 114. This enables detection of the target material.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present invention relates to a sensor element, a sensor device, a sensor system and a detection method. [Background technology]

[0002] Graphene FETs, which use graphene, are known as a sensor element for detecting gases and odors. However, the types of target substances that can be detected by conventional graphene FETs are limited, and it has been difficult to identify the types of target substances through selective detection. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-046196 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a sensor element, a sensor device, a sensor system, and a detection method that are capable of selectively detecting a target substance that was difficult to detect with conventional techniques. [Means for solving the problem]

[0005] The sensor element of the embodiment includes graphene, a drain electrode attached to the graphene, a source electrode attached to the graphene, and a first substance provided on the graphene, the charge state of which can be changed by irradiation and cessation of light. During a period in which the light irradiation and cessation of light irradiation are repeated on the graphene, the sensor element is capable of detecting the target substance by measuring a current flowing between the source electrode and the drain electrode. [Brief description of the drawings]

[0006] [Figure 1]FIG. 1 is a plan view of a graphene FET according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the graphene FET of FIG. 1 taken along the arrow AA. [Diagram 3] FIG. 3 is a diagram showing a first substance and a second substance. [Figure 4] FIG. 4 is a diagram showing the time change in source-drain current of the graphene FET according to the embodiment, depending on whether or not a target substance is present. [Diagram 5] FIG. 5 is a diagram showing the change over time in source-drain current when the graphene FET of the embodiment is exposed to a dry atmosphere. [Figure 6] FIG. 6 is a diagram showing the change over time in source-drain current when the graphene FET according to the embodiment is placed in a container filled with pure water. [Figure 7] FIG. 7 shows the results of investigating the time variation of the source-drain current for a number of different gate voltages. [Figure 8] FIG. 8 shows the results of investigating the relationship between the source-drain current and the gate voltage during the light irradiation period and the non-light irradiation period. [Figure 9] FIG. 9 is a graph showing the time changes in source-drain current when nitrogen gas containing DMTS and nitrogen gas are supplied to the graphene FET of the embodiment. [Figure 10] Figure 10 shows the configuration of the experimental apparatus used in the experiment to investigate the source-drain current of the graphene FET. [Figure 11] FIG. 11 shows experimental results when a conventional graphene FET is used. [Figure 12] FIG. 12 is a graph showing changes over time in source-drain current when nitrogen gas containing 2-phenylethylamine and nitrogen gas are supplied to the graphene FET of the embodiment. [Figure 13] FIG. 13 is a block diagram showing a sensor circuit and a light source circuit according to an embodiment. [Figure 14] FIG. 14 is a block diagram showing a sensor system according to the embodiment. [Figure 15] FIG. 15 is a diagram illustrating an example of the configuration of a humidification unit. [Figure 16] FIG. 16 is a diagram showing the change in source-drain current with time to explain another testing method. [Figure 17] FIG. 17 is an enlarged view of a part of the change in source-drain current shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, the embodiments will be described with reference to the drawings. The drawings are schematic or conceptual, and are not necessarily the same as the actual ones. In the drawings, the same reference numerals are used to designate the same or corresponding parts, and duplicated explanations will be made as necessary. For simplification, there are cases where the same or corresponding parts are not designated by reference numerals.

[0008] Fig. 1 is a plan view of a graphene FET1 (sensor element) according to an embodiment of the present invention, Fig. 2 is a cross-sectional view of the graphene FET1 taken along the line AA in Fig. 1.

[0009] The graphene FET 1 includes a silicon substrate 11 , an insulating film 12 , an insulating film 13 , graphene 14 , a drain electrode 15 , a source electrode 16 , an insulating film 17 , a gate electrode 18 , a first substance 19 , and a highly resistive conductive layer 20 .

[0010] The insulating film 12 is provided on the front surface of the silicon substrate 11 and is, for example, a silicon oxide film. The insulating film 13 is provided on the back surface of the silicon substrate 11 and is, for example, a silicon oxide film.

[0011] The graphene 14 is provided on a partial region of the insulating film 12. The graphene 14 may be in the form of a single layer film or a multilayer film. The graphene 14 is used as a channel of the FET.

[0012] The drain electrode 15 is provided on one end of the graphene 14. The drain electrode 15 is attached to the graphene 14.

[0013] A source electrode 16 is provided on the other end of the graphene 14. The source electrode 16 is attached to the graphene 14.

[0014] The first substance 19 is provided on the graphene 14 between the drain electrode 15 and the source electrode 16. Note that, as shown in Figures 3(a) to 3(e), a second substance 19a may be adsorbed or bonded to the first substance 19, or the second substance 19a may be adsorbed or bonded on the graphene 14.

[0015] In FIG. 3( a ), a second material 19 a is adsorbed or bonded to a first material 19 , and the first material 9 and the second material 19 a are covered with a highly resistive conductive layer 20 .

[0016] In FIG. 3( b ), a second material 19 a is adsorbed or bonded to the first material 19 and the graphene 14 , and the first material 19 and the second material 19 a are covered with a highly resistive conductive layer 20 .

[0017] 3(c), a second material 19a is adsorbed or bonded to the graphene 14, and the first material 19 and the second material 19a are covered with a highly resistive conductive layer 20. The second material 19a is not adsorbed or bonded to the first material 19.

[0018] In FIG. 3( d ), the second material 19 a is adsorbed or bonded to the first material 19 and the graphene 14, the first material 19 is covered with a highly resistive conductive layer 20, and the second material 19 a is covered with the highly resistive conductive layer 20 such that its upper end portion protrudes from the highly resistive conductive layer 20.

[0019] In FIG. 3( e ), a second material 19 a is adsorbed or bonded to the first material 19 , but the first material 9 and the second material 19 a are not covered with a highly resistive conductive layer 20 .

[0020] The second substance 19a is a substance that specifically binds to a target substance (a substance to be detected). The second substance 19a is, for example, a molecular probe. The molecular probe includes, for example, an aptamer such as a nucleic acid aptamer or a peptide aptamer.

[0021] 1 and 2 covers the drain electrode 15 and the source electrode 16, and has an opening that exposes at least a part of the graphene 14 between the drain electrode 15 and the source electrode 16. The insulating film 17 is an insulating film that protects the drain electrode 15 and the drain electrode 15, and is, for example, an inorganic insulating film such as a silicon nitride film, an alumina film, or a silicon oxide film, or an organic insulating film such as a polyimide film, a polybenzoxazole film, a parylene film, a BCB (benzocyclobutene) film, or a PDMS (polydimethylsiloxane) film.

[0022] The gate electrode 18 is provided on the insulating film 12. In FIG. 1 and FIG. 2, the gate electrode 18 is disposed on the insulating film 12 in a region spaced a certain distance to the right from the source electrode 16. A high-resistance conductive layer 20 is formed between the gate electrode 18 and the graphene 14. The conductive layer 20 preferably covers the exposed surfaces of the gate electrode 16 and the graphene 14 that are not covered by the insulating film 17 as shown in the figures, but may be formed under the gate electrode 16 and the graphene 14. The conductive layer 20 may also cover the surfaces of the first substance 19 and the second substance 19a (FIG. 3(a) to FIG. 3(c)). The resistance of the conductive layer 20 between the gate electrode 18 and the graphene 5 must be sufficiently larger than the resistance between the source electrode 16 and the drain electrode 15 of the graphene 14. Generally, the resistance between the source electrode 16 and the drain electrode 15 of the graphene 14 is about several kΩ, so the resistance between the gate electrode 16, 18, and the graphene 14 is preferably in the range of 10 MΩ to 100 GΩ. In addition, since the sensor element of the embodiment is used in a high humidity atmosphere as described later, the conductive layer 20 may be one that exhibits conductivity by absorbing moisture. Examples of the material (material) of the conductive layer 20 include those having polar groups such as carboxyl groups, phosphate groups, sulfonic acid groups, silanol groups, hydroxyl groups, and amino groups, dried salts, and ultrathin ionic liquids. The polar groups may be formed on the surfaces of the insulating films 12 and 17 to form a layer in which surface leakage occurs. Such a surface leakage layer may be obtained by, for example, UV ozone treatment. Alternatively, metal nanoparticles may be arranged and conducted using plasmons. Of course, a conductive material is used for the gate electrode 16, but it is more preferable to form gold, platinum, silver, silver chloride, or the like on the surface of the gate electrode 16, since this improves the transfer of charges with the conductive layer 20.

[0023] When the sensor element of the embodiment is repeatedly irradiated with light and then stopped, a charge fluctuation may occur in the first substance 19 during a first period during which light is irradiated and a second period during which light is not irradiated. Hereinafter, the period during which light (irradiated light) is irradiated is referred to as a light irradiation period, and the period during which light (irradiated light) is not irradiated is referred to as a non-light irradiation period.

[0024] For example, when light is irradiated onto the sensor element, graphene is excited, generating excited electrons and holes. If the energy level of the first substance 19 is at an appropriate position to induce charge transfer, either the excited electrons or holes in the graphene undergo charge transfer, and the charge of the first substance 19 changes. In this case, the first substance 19 behaves as an acceptor. When the light irradiation is stopped, the charge is discharged from the first substance 19.

[0025] Alternatively, when the first substance 19 is irradiated with light having a wavelength that excites the first substance 19, the first substance 19 is excited to generate excited electrons and holes. Here, if the relationship between the energy levels of the excited electrons and holes of the first substance 19, the Fermi level of graphene, and the energy levels of the excited electrons and holes of graphene is such that charge transfer is induced, either the excited electrons or the holes of the first substance 19 undergoes charge transfer to the graphene, and the charge of the first substance 19 changes. In this case, the first substance 19 behaves as a donor. When the irradiation of light is stopped, the charge of the first substance 19 is discharged.

[0026] Alternatively, when the first substance 19 is a metal nanoparticle, plasmon is excited by irradiation with light. If the relationship between the energy level of the plasmon, the Fermi level of graphene, and the energy levels of the excited electrons and holes of graphene is such that charge transfer is induced, plasmon-induced charge transfer occurs, and the charge of the first substance 19 changes. In this case, the metal nanoparticle behaves as either a donor or an acceptor. When the irradiation with light is stopped, the charge of the first substance 19 is discharged.

[0027] As described above, if a substance that acts as a donor or an acceptor is used for the first substance 19, the charge of the first substance 19 changes depending on whether or not light is turned on and off (whether or not light is irradiated). That is, the first substance is provided on the graphene, and the charge state can be changed by irradiating light and then stopping the irradiation. When the charge of the first substance 19 changes, a charge opposite to the charge of the first substance 19 is electrostatically induced in the graphene, and the Fermi level of the graphene changes. In addition, if the conductive layer covers the entire graphene surface, the charge of the first substance 19 causes electrostatic induction in the entire graphene, and a change in the Fermi level is caused in the entire graphene. When the Fermi level of graphene changes, the carrier density changes, and the source-drain current changes. The above behavior is called the photogating effect. The first substance 19 is a substance that can cause charge transfer between the graphene and the first substance 19. The first substance may be, for example, a substance having a carboxyl group, a phosphate group, a sulfonic acid group, a silanol group, a hydroxyl group, an amino group, or the like, or a metal particle. The metal particle may be, for example, a gold nanoparticle. Alternatively, the first substance may be a substance having a band gap such as a semiconductor material or a dielectric material, a substance made of a crystal having lattice defects, a substance having delocalized π electrons, or a molecule having a strong electron-withdrawing portion such as a halogen.

[0028] Graphene FET1 can be used, for example, as an odor sensor. Gas sensors using graphene FETs have been known for some time, but conventional gas sensors use a method of reading changes in the current (hereinafter referred to as source-drain current) flowing between the source and drain electrodes due to gas adsorption. In this method, the gas must be strongly charged when it is adsorbed on graphene, and the gases that can be detected are limited. Specifically, they are limited to NOX gas, which is a strong acceptor molecule, and ammonia, which is a strong donor molecule. When these molecules are adsorbed on graphene, charge transfer occurs between them and the graphene, causing them to become charged. As a result, a charge opposite to the charge of the adsorbed molecule is electrostatically induced in the graphene, changing the Fermi level and changing the source-drain current.

[0029] The graphene FET 1 is different from conventional gas sensors using graphene in that it detects target substances such as odors by utilizing the photogating effect. In the case of the sensor element of the embodiment, the substance whose charge changes to cause electrostatic induction in graphene is not the odor molecule to be detected but the first substance 19. The odor molecule to be detected can be detected by inhibiting or promoting the change in the charge of the first substance 19, so the odor molecule does not necessarily have to be a strong donor or acceptor. The change in the charge of the first substance 19 can be caused by changes in various processes that cause the change in the charge of the first substance 19, such as a change in the resistance of the conductive layer 20, inhibition or promotion of charge transfer between the graphene and the first substance 19, a change in the energy level of the graphene and the first substance 19, or a change in the excitation wavelength of the first substance 19. Therefore, even odor molecules that have no charge at all, such as dimethyl trisulfide and limonene, can be detected using the sensor element of the embodiment. In addition, odor molecules that can be dissociated in an aqueous solution and have a charge can also be detected using the sensor element of the embodiment. For example, 2-phenylethylamine is a monovalent cation with an acid dissociation constant of 9.9 (estimated value), but even if a graphene FET is exposed to a 2-phenylethylamine atmosphere, the source-drain current of the graphene FET changes only slowly, and noise due to disturbance factors such as humidity fluctuations is large, making detection difficult. By using the sensor element of the embodiment, the presence of 2-phenylethylamine can be clearly detected.

[0030] FIG. 4 is a diagram showing the time change of the source-drain current (detection current) of the graphene FET of this embodiment depending on the presence or absence of a target substance. "On" and "off" on the horizontal axis indicate the light irradiation period and the non-light irradiation period, respectively. The on / off cycle of the light irradiation is, for example, within the range of 10 milliseconds to several tens of seconds. The wavelength of the light is, for example, 650 nm.

[0031] As shown in Figure 4, the source-drain current during the light irradiation period is different from the source-drain current during the non-light irradiation period. The reason for this is thought to be as follows.

[0032] During the light irradiation period, the graphene is excited by the light, and excited electrons and holes are generated in the graphene 14. Furthermore, during the light irradiation period, charges remain in the first substance 19 on the graphene 14. For example, in the case of a donor, during the light irradiation period, the donor generates excited electrons and holes. The excited electrons or holes do not remain at the place where they were generated, but are transferred to the graphene. As a result, the charges that remain without being transferred remain in the donor.

[0033] In graphene 14, charges opposite to those of the first material 19 are attracted by electrostatic induction. As a result, the position of the Fermi level of graphene 14 changes, and the source-drain current changes. In addition, during non-light irradiation periods, charges are removed from the first material 19, and electrostatic induction ceases to occur. As a result, the Fermi level returns to its original position, and the source-drain current also returns to its original state. Note that if the first material has a work function different from that of graphene, it may have charges even without light irradiation. Even in that case, if the charge transfer occurs as described above, the charge of the first material changes. As a result, the Fermi level of graphene changes due to the change in electrostatic induction, and this can be detected as a change in the source-drain current.

[0034] FIG. 4 shows an image of the change in source-drain current when a target odor molecule is detected using the sensor element of the embodiment. The source-drain current changes significantly depending on the presence or absence of irradiated light. The change in source-drain current due to the difference in the presence or absence of irradiated light is clearly manifested as a difference in amplitude between the absence and presence of the target substance. That is, according to the intensive research of the present inventor, the graphene FET of the embodiment utilizing the photogating effect can easily detect the target substance based on the magnitude of the change in source-drain current due to the difference in the presence or absence of light irradiation. That is, the target substance can be detected by measuring the current flowing between the source electrode and the drain electrode.

[0035] In addition, in the case of FIG. 4, a case is shown in which the first difference (with target material), which is a change in source-drain current, is smaller than the second difference (without target material), but depending on the first material 19, the first difference (with target material) may be larger than the second difference (without target material).

[0036] FIG. 5 is a diagram showing the change over time in source-drain current when the graphene FET of the embodiment is exposed to a dry atmosphere (an environment in which the amount or ratio of water vapor in the atmosphere is less than a certain level).

[0037] From Figure 5, it was confirmed that when the graphene FET of the embodiment was exposed to a dry atmosphere, the change in source-drain current due to the presence or absence of irradiated light was small. This is believed to be because one of the processes that causes the photogating effect (photoresponse) is inhibited in a dry atmosphere.

[0038] Next, the graphene FET according to the embodiment was subjected to a high humidity atmosphere (an environment in which the amount or ratio of water vapor in the atmosphere exceeds a certain value) to examine the time change in source-drain current. More specifically, the graphene FET according to the embodiment was placed in a sealed container together with a cup filled with pure water, and the time change in source-drain current was examined.

[0039] FIG. 6 is a diagram showing the change over time in source-drain current when the graphene FET according to the embodiment is accommodated in a sealed container together with pure water.

[0040] From Figure 6, we can see that the difference in source-drain current due to the presence or absence of light irradiation is small before a certain time has passed, but the difference in source-drain current becomes large after a certain time has passed. This result can be explained as follows.

[0041] It takes a certain amount of time for the pure water in the container to change into water vapor. Therefore, before a certain amount of time has passed, the amount or ratio of water vapor in the container is less than a certain value, and after the certain amount of time has passed, the amount or ratio of water vapor in the container exceeds the certain value. In other words, after the certain amount of time has passed, the graphene FET of the embodiment is exposed to a high humidity atmosphere. Therefore, it can be said that the measurement results in FIG. 6 indicate that when a high humidity gas is supplied to the graphene FET (graphene) of the embodiment, the photogating effect (photoresponse) of the graphene FET of the embodiment is amplified.

[0042] The photogating effect is amplified in a high humidity atmosphere for the following reasons. When the first substance 19 is a donor, the donor generates excited electrons and holes during the light irradiation period. Either the excited electrons or the holes do not remain at the place where they were generated, but are transferred to the graphene, and the remaining charge is trapped in the donor. It is considered that the high humidity gas promotes this charge transfer or the trapping of the remaining charge, or both. Alternatively, it is considered that the excitation wavelength of the donor is changed to promote this. In addition, in the graphene, a charge opposite to the charge of the donor is attracted by electrostatic induction. Furthermore, when a conductive layer is formed on the graphene, the charge of the donor extends to the entire graphene, so that electrostatic induction occurs throughout the entire graphene. It is considered that the high humidity gas promotes this electrostatic induction process.

[0043] That is, it is believed that high humidity promotes at least one of donor excitation, charge transfer, charge trapping, and electrostatic induction, resulting in an amplification of the photogating effect.

[0044] Here, the reason why the photogating effect is amplified in the case where the first substance 19 is a donor has been explained, but even in the case where the first substance 19 is an acceptor, at least one of charge transfer, charge trapping, and electrostatic induction is promoted, and the photogating effect is considered to be amplified. Furthermore, in the case of metal nanoparticles, the plasmon excitation wavelength may change, and the photogating effect may be amplified.

[0045] Furthermore, when a target substance is adsorbed to the graphene 14 or the first substance 19, or when a target substance is captured by the second substance 19a such as a molecular probe, causing a change in the structure of the second substance 19a, at least one of the excitation, charge transfer, charge trapping, and electrostatic induction of the first substance is inhibited or promoted. Therefore, the photogating effect (photoresponse) also changes due to the adsorption of the target substance or the change in the structure of the second substance 19a.

[0046] Figure 7 shows the results of investigating the time change of the source-drain current for several different gate voltages (Vg). To avoid the complexity of illustrating the on / off of the irradiated light, the timing of the irradiated light is shown with an arrow. The gate voltages are -350mV, -250mV, -150mV, -50mV, and 50mV.

[0047] From Figure 7, we can see that the gate voltage affects the photogating effect (photoresponse) because the value and waveform of the source-drain current also change when the gate voltage is different. This means that the photogating effect (photoresponse) can be amplified by adjusting the gate voltage to an appropriate value. When the gate voltage is increased from -350mV to -50mV, the absolute value of the source-drain current decreases, and in the range from -250mV to -50mV, the change in the source-drain current due to the blinking of the irradiated light also becomes smaller. In addition, from -350mV to -50mV, the source-drain current changes in the direction of decreasing due to the light irradiation, but from -50mV, the change in the opposite direction, that is, the source-drain current changes in the direction of increasing due to the light irradiation, and when the gate voltage is further increased to +50mV, the increase in the source-drain current due to the light irradiation becomes larger. This phenomenon can be understood by reading the source-drain current value when the light irradiation is performed and the source-drain current value when the light irradiation is stopped from this figure, and illustrating the relationship with the gate voltage.

[0048] Figure 8 shows the results of investigating the relationship between the source-drain current and the gate voltage with and without light irradiation. The results for the light irradiation period are shown by open diamonds and dashed lines, and the results for the non-light irradiation period are shown by black circles and solid lines.

[0049] When the gate voltage (Vg) is -350 mV, the source-drain current during the light irradiation period is smaller than the source-drain current during the non-light irradiation period.

[0050] When the gate voltage is -250 mV, the source-drain current during the light irradiation period is smaller than the source-drain current during the non-light irradiation period.

[0051] Here, if the current difference ΔI is the source-drain current during the non-illumination period minus the source-drain current during the illumination period, the current difference ΔI when Vg = -250 mV is larger than the current difference ΔI when Vg = -350 mV.

[0052] When the gate voltage is -150mV, the source-drain current during the light irradiation period is smaller than the source-drain current during the non-light irradiation period. However, the current difference ΔI when Vg=-150mV is smaller than the current difference ΔI when Vg=-350mV and Vg=-250mV.

[0053] When the gate voltage is -50mV, the magnitude relationship between the source-drain current during the light irradiation period and the source-drain current during the non-light irradiation period is reversed over time. Furthermore, the absolute value of the current difference ΔI when Vg=-50mV is smaller than the current differences ΔI when Vg=-350mV, Vg=-250mV, and Vg=-150mV both before and after the reversal.

[0054] When the gate voltage is 50 mV, the source-drain current during the light irradiation period is larger than the source-drain current during the non-light irradiation period. When Vg=50 mV, the current difference ΔI is a negative value, and its absolute value is larger than the current difference ΔI after inversion at Vg=-50 mV.

[0055] The above results can be explained as follows.

[0056] First, the difference in the source-drain current value between the light irradiation period and the non-light irradiation period is thought to be due to the charge of the first substance 19 changing to a positive charge side upon light irradiation, resulting in a photogating effect (photoresponse).

[0057] It is known that the gate voltage dependence of the source-drain current of graphene generally shows a V-shaped characteristic. The point at the bottom of the V where the current is the lowest is called the Dirac point, and is the state where the carrier density is the lowest. To the right of the Dirac point (the side where the gate voltage is high), electrons are the carriers (electron conduction region), and the further away from the Dirac point (the higher the gate voltage), the higher the carrier density becomes, and the source-drain current increases. On the other hand, to the left of the Dirac point (the side where the gate voltage is low), holes are the carriers (hole conduction region), and the further away from the Dirac point (the lower the gate voltage), the higher the carrier density becomes, and the source-drain current increases. Since the theoretical carrier density is low near the Dirac point, even if the carriers increase slightly due to thermal excitation, the effect is large, so the shape is slightly raised and U-shaped, and the change in the source-drain current with respect to the change in gate voltage is sluggish. As the carrier density increases away from the Dirac point, this phenomenon becomes negligible, and the change in the source-drain current with respect to the gate voltage becomes large. As the gate voltage increases, the increase in the carrier density slows down, and the change in the source-drain current with respect to the gate voltage becomes small again.

[0058] These electrical properties of graphene are due to the modulation of the Fermi level of graphene by changing the gate voltage. That is, when the Fermi level is at the Dirac point, the carrier density of graphene is the lowest. When the gate voltage is increased from there and the Fermi level is raised, the graphene enters the electron conduction region. When the gate voltage is further increased and the Fermi level is raised, the carrier density increases. When the gate voltage is lowered and the Fermi level is lower than the Dirac point, the graphene enters the hole conduction region. When the gate voltage is further decreased and the Fermi level is lowered, the carrier density increases.

[0059] The gate voltage dependence of the source-drain current in Figure 8 shows the typical V-shaped electrical characteristics of graphene mentioned above in both the light irradiation and non-light irradiation periods. In addition, the V-shaped curve during the light irradiation period is shifted to the left (lower gate voltage side) compared to the V-shaped curve during the non-light irradiation period, which indicates that negative charges are injected into the graphene by light irradiation. If positive charges appear on the graphene, negative charges are attracted into the graphene by electrostatic induction, which can create this situation. Here, it can be explained that this change in electrical characteristics is caused by the first substance being positively charged by light irradiation (or more precisely, the charge amount changes to the positive charge side).

[0060] The reason why the current difference ΔI was negative at Vg=50mV is that the Fermi level was higher than the Dirac point and in the electronic conduction region. In the electronic conduction state, when negative charges are injected into graphene by light irradiation, the density of electrons that become carriers increases.

[0061] The current difference ΔI at Vg = -50 mV was generally small in absolute value and reversed from a positive value to a negative value over time. This is thought to be because the Fermi level was slightly lower than the Dirac point and rose above the Dirac point over time.

[0062] The measurements in FIG. 8 were taken in the order of Vg=-350mV, -250mV, -150mV, -50mV, and 50mV. Before Vg=-350mV, measurements were taken at Vg=0mV. The gate voltage is applied to the sensor element of the embodiment through a high-resistance conductive layer on the surface of the element, so it takes a certain amount of time for the gate voltage to stabilize. The source-drain current at Vg=-350mV gradually increases because the potential at the previous Vg=0mV remains, and the source-drain current at Vg=-250mV and after gradually decreases because the potential at the previous measurement remains.

[0063] In the measurement at Vg=-50mV, it can be assumed that the Fermi level gradually increased as the gate voltage was gradually applied due to the above phenomenon, and as a result, the Fermi level, which was slightly below the Dirac point, exceeded the Dirac point.

[0064] At Vg = -150mV and -250mV, the change in source-drain current due to light irradiation becomes larger as the gate voltage moves away from the Dirac point. This is because, according to the general electrical properties of graphene mentioned above, the change in source-drain current with respect to the gate voltage, i.e., the slope, becomes larger as the gate voltage moves away from the Dirac point.

[0065] At Vg=-350mV, the change in source-drain current due to light irradiation starts to become smaller than at -250mV. This is also because, according to the general electrical properties of graphene mentioned above, when one moves too far from the Dirac point, the change in source-drain current with respect to the gate voltage, i.e., the slope, becomes sluggish.

[0066] As described above, the magnitude of the photogating effect changes when the Fermi level of graphene changes. In addition, the Fermi level of graphene can be modulated by changing the gate voltage. Therefore, by controlling the gate voltage, the Fermi level can be adjusted so that the photogating effect is maximized, and the Fermi level can be fixed so that the photogating effect is constant. For example, if the gate voltage is feedback-controlled so that the source-drain current value during the non-illumination period is constant, the Fermi level of the ground state of graphene is fixed, and a constant photogating effect can be obtained when light is irradiated.

[0067] The present inventors investigated whether dimethyl trisulfide (DMTS) can be detected using the graphene FET of the embodiment. DMTS is a sulfide compound having the structure CH3-SSS-CH3.

[0068] Gold nanoparticles and dried citric acid were used as the first substance and the conductive layer. To mount such gold nanoparticles and dried citric acid on a graphene FET, for example, the following process is performed. First, for example, 10 μL of a dispersion solution containing gold nanoparticles and citric acid is dropped onto the graphene, and then the dispersion solution is evaporated by natural drying.

[0069] FIG. 9 shows the time-dependent change in source-drain current when nitrogen gas containing DMTS and nitrogen gas are supplied to the graphene FET of the embodiment, and FIG. 10 shows the configuration of an apparatus used in an experiment to examine the time-dependent change in source-drain current. Dry nitrogen is supplied from a nitrogen cylinder 70, and the flow rate is controlled to 200 mL / min by a mass flow controller 71. The nitrogen is then humidified to a relative humidity of 98% or more by a humidification unit 72, and sent to a sensor element set in an acrylic transparent cassette 76. An LED light source 77 is placed on the transparent cassette 76, and light 78 with a wavelength of 660 nm can be emitted and stopped. The acrylic cassette 76 and the LED light source 77 were installed in a darkroom. In addition, the piping between the humidification unit 72 and the transparent cassette 76 is provided with a path for directly sending humidified nitrogen to the transparent cassette 76 by a three-way cock 73, and a path for sending humidified nitrogen containing DMTS to the transparent cassette 76 via an impinger 74 containing DMTS.

[0070] As shown in FIG. 9, after supplying high humidity nitrogen gas to the graphene FET of the embodiment, high humidity nitrogen gas containing DMTS was supplied, and then high humidity nitrogen gas was supplied again. The gate voltage was set to 0 mV, and the on / off cycle of the LED light was set to 5 seconds / 5 seconds. Although not shown to avoid cluttering the figure, the behavior of the source-drain current increasing due to the irradiation of the LED light is shown. The source-drain current fluctuates up and down in the figure, which is an observation of the change caused by turning the LED light on and off.

[0071] From FIG. 9, the difference between the minimum and maximum values ​​of the source-drain current when high-humidity nitrogen gas containing DMTS is supplied is clearly smaller than the difference between the minimum and maximum values ​​of the source-drain current when high-humidity nitrogen gas not containing DMTS is supplied. In addition, since the amplitude changes from the cycle immediately after DMTS is supplied, it is shown that the graphene FET of the embodiment can detect the presence of DMTS in real time in about several seconds. On the other hand, it was found that it takes about several tens of seconds to dissociate the adsorbed DMTS, since it takes 2 to 3 cycles to respond when DMTS is gone. However, as a sensor for detecting DMTS, it is more important to respond quickly when DMTS increases than to respond quickly when DMTS decreases, so this result shows that the graphene FET of the embodiment is sufficiently useful as a DMTS detection sensor.

[0072] On the other hand, the results of an attempt to detect DMTS using a graphene FET of the conventional technology are shown in Figure 11. A graphene FET that had not been treated with any chemicals such as gold nanoparticles was enclosed in a sealed container with various odor components in an air-conditioned room without humidification, and the source-drain current was measured. The gate voltage was set to 0 mV, and light irradiation was performed in an on / off cycle of 30 seconds / 30 seconds (not shown to avoid complication). First, the measurement was performed with air alone without any odor components, then the container was opened and packed with methyl benzoate and resealed, and the measurement was performed, and then the container was opened and packed with menthol and resealed, and the source-drain current was measured in the same manner, with acetonitrile sealed, 1-octen-3-ol sealed, and DMTS sealed. By sealing the container with various odor molecules, the odor molecules gradually vaporize and the air concentration increases, so if conventional technology could detect them, the source-drain current should gradually change, but such behavior was not observed for all odor components. In addition, the photogating effect caused by turning light on and off was hardly observed, and no changes due to various odor components were observed. This result shows that many odor components cannot be detected with conventional technology, especially DMTS. It also shows that it would be difficult to use the photogating effect for odor detection using conventional technology.

[0073] In addition, since it is expected that the graphene FET of the embodiment detects sulfide compounds by adsorption to gold nanoparticles, it is also possible to detect sulfide compounds other than DTMS. For example, when the photogating effect was measured in a dark room using a rubber blackout curtain (not shown), the photogating effect was found to attenuate halfway through the measurement. This is presumed to be a change caused by the sulfur-containing components of the rubber vulcanizing agent filling the dark room as odor components and adsorbing to the metal nanoparticles.

[0074] The inventors investigated whether 2-phenylethylamine and methyl benzoate can be detected using the graphene FET of the embodiment. 2-Phenylethylamine is a molecule similar to amphetamine, a type of stimulant, and methyl benzoate is the odor molecule of cocaine.

[0075] Additionally, gold nanoparticles and dried citric acid were used as the first substance and conductive layer. Furthermore, an anti-methamphetamine aptamer was used as the second substance. The anti-methamphetamine aptamer is a DNA that binds to the stimulants methamphetamine and amphetamine, and in this experiment, a thiol group (-SH) was added to the 5' end to attach it to the gold nanoparticles. The base sequence is "5' SH - TTT ACT GGA GCT CAA TCA GTA CAC GAC GGT TGC AAG TGG GAC TCT GGT AGG CTG GGT TAA TTT GGG ACA AGC TTC AAC CAT GGA GTA 3'".

[0076] To mount such gold nanoparticles, dried citric acid, and anti-methamphetamine aptamer on a graphene FET, for example, the following process is performed. First, for example, 10 μL of a dispersion solution containing gold nanoparticles and citric acid is dropped onto the graphene, and then the dispersion solution is naturally dried. Next, 5 μL of a 1 μM solution of anti-methamphetamine aptamer is dropped onto the graphene, and then the graphene FET is left for 1 hour in a sealed high humidity atmosphere so that the aptamer solution does not dry. Next, a part of the dropped solution is absorbed with moisture-absorbing paper, and then the remaining solution is evaporated by natural drying.

[0077] Prior to the sensor experiment, the binding strength with 2-phenylethylamine was measured using isothermal titration calorimetry (ITC). When ITC was performed using an anti-methamphetamine aptamer without thiol group modification, the dissociation constant was 10 μM. This means that when the concentration of 2-phenylethylamine is 10 μM, half the number of molecules bind to the anti-methamphetamine aptamer, indicating that the binding strength of the aptamer is standard.

[0078] FIG. 12 is a diagram showing the time change of each source-drain current when nitrogen gas containing 2-phenylethylamine, nitrogen gas containing methyl benzoate, and nitrogen gas are supplied to the graphene FET of the embodiment. The experiment was performed with the same configuration as the DMTS detection experiment shown in FIG. 10, and the odor molecules put into the impinger were changed from DMTS to 2-phenylethylamine and methyl benzoate. The flow rate was 200 mL / min as in the case of FIG. 10, and the nitrogen gas containing 2-phenylethylamine, the nitrogen gas containing methyl benzoate, and the nitrogen gas were all supplied to the graphene FET of the embodiment with a relative humidity of 98% or more via a humidification unit. The LED light source also had the same 660 nm wavelength, and the on / off cycle was 5 seconds / 5 seconds. The gate voltage was set to 0 mV.

[0079] As shown in FIG. 12, a piping system connected to an impinger containing 2-phenylethylamine is first assembled in the graphene FET of the embodiment, and then high-humidity nitrogen gas is supplied, then high-humidity nitrogen gas containing 2-phenylethylamine is supplied, then high-humidity nitrogen gas is supplied, and then the piping system is reconnected to an impinger containing methyl benzoate, after which high-humidity nitrogen gas is supplied, then high-humidity nitrogen gas containing methyl benzoate is supplied, and then high-humidity nitrogen gas is supplied.

[0080] From FIG. 12, it can be seen that the difference between the minimum and maximum values ​​of the source-drain current when high humidity nitrogen gas containing 2-phenylethylamine is supplied is clearly smaller than the difference between the minimum and maximum values ​​of the source-drain current when high humidity nitrogen gas is supplied. It can also be seen that the response occurs within a few seconds after the gas is switched. Therefore, from FIG. 12, it can be said that the graphene FET of the embodiment can easily detect 2-phenylethylamine in real time based on the change in the source-drain current due to the photogating effect.

[0081] On the other hand, the difference between the minimum and maximum values ​​of the source-drain current when humidified methyl benzoate gas was supplied was not very different from the difference between the minimum and maximum values ​​of the source-drain current when humidified nitrogen gas was supplied. This result indicates that this experiment selectively detects 2-phenylethylamine.

[0082] From the above, it is possible to use the graphene FET of the embodiment to detect 2-phenylethylamine by distinguishing it from methyl benzoate. In other words, it shows that it is possible to selectively detect stimulants without mistaking them for cocaine.

[0083] It is possible to detect methyl benzoate by using a second substance 19a that specifically binds to methyl benzoate.

[0084] The graphene FET of the embodiment can detect target substances other than those mentioned above that are difficult or impossible to detect with known graphene FETs, such as ecgonine derivatives, which are other odor components of cocaine, stimulants such as methamphetamine and amphetamine, caryophyllene and its derivatives, which are odor components of cannabis, and heliotropin and MDP2P (3,4-methylenedioxyphenylpropan-2-one), which are odor components of MDMA (methylenedioxymethamphetamine, a hallucinogen commonly known as ecstasy). In addition, the presence of cocaine, stimulants, cannabis, and MDMA, which are the sources of odor, can be detected by detecting these odor components. When detecting these other target substances, a second substance 19a that binds to the target substances is used. In order to obtain a second substance that binds to a specific target substance, if the second substance is a nucleic acid aptamer, for example, it can be obtained by a method called SELEX (Systematic Evolution of Ligands by EXponential enrichment). In the SELEX method, 10 14 A nucleic acid library with about 100 sequences is mixed with the target substance, and the bound sequences are extracted and amplified by PCR (polymerase chain reaction). Since sequences that bind to the target substance are present in high concentrations in the PCR-amplified nucleic acid pool, this is mixed again with the target substance, and the bound sequences are extracted and amplified by PCR (polymerase chain reaction). By repeating this process, sequences with high binding ability are gradually concentrated.

[0085] The graphene FET of the embodiment can also detect limonene, which is the main component of citrus odor. Limonene is represented by the chemical formula C 10 H 16It is an uncharged monoterpene represented by the formula: and was difficult to detect using sensors of the prior art. The inventors have found that a peptide with the amino acid sequence N-terminus-RRWLLLW-C-terminus binds strongly to limonene as a molecular probe. Here, R is an abbreviation for arginine, W is tryptophan, and L is an abbreviation for leucine. The dissociation constant measured by the ITC method was 12 μM.

[0086] First, 10 μL of a 500 nM solution of a peptide with the amino acid sequence N-CGGGRGAGAGAR-C-terminus was dropped onto the graphene, left in a high humidity atmosphere for 1 hour, and then washed with pure water. Here, C is an abbreviation for cysteine, G is glycine, and A is alanine. It has been confirmed that the GAGAGA part of the peptide with this sequence forms a β-sheet structure and self-assembles a monolayer on the graphene. As a result, the thiol group (-SH group of the cysteine ​​side chain) that binds to the gold nanoparticles is aligned on the graphene, so 10 μL of the gold nanoparticle dispersion solution was dropped and naturally dried, and then a 1 μM solution of a peptide with the sequence N-RRWLLLWRRCC-C-terminus was dropped and left in a high humidity atmosphere for 1 hour, after which a part of the dropped solution was absorbed with absorbent paper, and the remaining solution was evaporated by natural drying. The reason for adding the amino acid RRCC to the C-terminus side is to increase the solubility of the peptide in water by RR and to fix it to the gold nanoparticles by CC. When the change in source-drain current due to the photogating effect when the graphene FET subjected to the above treatment is sealed with pure water and limonene is compared with the change in source-drain current due to the photogating effect when the graphene FET is sealed with only pure water, the former has a smaller current change (not shown), and it was confirmed that the graphene FET according to this embodiment can detect limonene. Furthermore, since limonene is the main component of the odor of citrus fruits, the graphene FET according to this embodiment can also detect the presence of citrus fruits, which are the source of limonene. In Japan, the import of citrus fruits is prohibited as a border control measure against fruit flies, an invasive species that causes serious damage to citrus cultivation. The graphene FET according to this embodiment can also be used as a detection sensor for citrus fruits illegally brought into airports, etc.

[0087] As described above, according to this embodiment, it is possible to detect various target substances in real time, and also possible to perform selective discrimination.

[0088] A sensor circuit, a sensor system, and a detection method using the graphene FET of this embodiment will be described below. By using the graphene FET of this embodiment, it is possible to provide a sensor circuit, a sensor system, and a detection method capable of detecting various odor components and objects that generate the odor components.

[0089] FIG. 13 is a block diagram showing a sensor circuit (sensor device) 2 and a light source circuit according to the embodiment.

[0090] The sensor circuit 2 includes a graphene FET 1, a drain voltage control unit 21, a source voltage control unit 22, a source-drain current measuring unit 23, a determination unit 24, and a gate voltage control unit 25. The elements 1, 21 to 25 constituting the sensor circuit 2 may be formed, for example, on a silicon substrate, on a module mounting a graphene FET chip, or in a system housing into which an exchange cartridge mounting a graphene FET chip is inserted. Note that, although the number of graphene FETs 1 is one in FIG. 13, the number may be two or more. Furthermore, a plurality of graphene FETs 1 having different types of target substances may be integrated into one chip, or a plurality of graphene FET chips may be densely mounted on a wiring chip using chip stacking technology. The light source circuit 51 includes an LED chip 55 as a light source, a power supply control circuit 56 that controls the drive current or drive voltage of the LED chip 55, and a photodetector (PD) 57 that measures the light quantity of the LED chip 55. The LED power supply control circuit 56 adjusts the current value or voltage value as necessary based on the light quantity information from the PD 57. The LED power control circuit 56 also controls blinking in accordance with a specified on / off cycle, and sends a synchronization signal to the determination unit 24 and gate voltage control unit 25 of the sensor circuit 2. The light source circuit 51 is formed inside a system housing into which a replacement cartridge on which components including the graphene FET chip 1 are mounted is inserted.

[0091] The drain voltage control unit 21 controls the voltage applied to the drain electrode of the graphene FET 1. The source voltage control unit 22 controls the voltage applied to the source electrode of the graphene FET 1. The source-drain current measurement unit 23 measures the source-drain current flowing between the source electrode and drain electrode of the graphene FET 1.

[0092] The determination unit 24 determines whether or not a target substance has been detected based on the measured source-drain current and the synchronization signal received from the light source circuit.

[0093] The time change (waveform) of the source-drain current when the graphene FET1 is exposed to a high-humidity atmosphere with different concentrations of the target substance is acquired in advance together with a synchronization signal of the light source. In addition, the time change (waveform) of the source-drain current when the graphene FET1 is exposed to a high-humidity atmosphere that does not contain the target substance is also acquired in advance together with a synchronization signal of the light source. The time change information of the source-drain current is stored, for example, in the determination unit 24 as reference data of concentration dependency. In addition, a predetermined threshold value is set and this is also stored, for example, in the determination unit 24.

[0094] The determination unit 24 determines the concentration of the target substance in the high humidity atmosphere based on the measured source-drain current and the reference data. If the fluctuation of the measured source-drain current with time associated with the on / off of the light source is greater than a set threshold, it determines that the target substance is included in the high humidity atmosphere. If the fluctuation of the measured source-drain current with time associated with the on / off of the light source is smaller than a set threshold, it determines that the target substance is not included in the high humidity atmosphere.

[0095] This determination is made, for example, by continuously calculating the absolute value of the difference between the measured source-drain current value after a predetermined time has elapsed since the light irradiation and the value after a predetermined time has elapsed since the light irradiation was stopped, and if the fluctuation of this value becomes larger than a threshold value, it is determined that the target substance is contained in the high humidity atmosphere, and if the fluctuation of the absolute value remains smaller than the threshold value, it is determined that the target substance is not contained in the high humidity atmosphere. Note that the cycle and duty ratio of the light source blinking, the time for measuring the source-drain current after the light irradiation, the time for measuring the source-drain current after the light irradiation is stopped, and the threshold value can be appropriately set to optimal values ​​according to the type of target substance and the type of graphene FET.

[0096] In the above embodiment, a simple on / off cycle is used as an example, but multiple periods may be superimposed on the heterodyne. An example is shown in Fig. 16 and Fig. 17. Fig. 17 is an enlarged view of the area surrounded by the solid line in Fig. 16. The duty ratio is 2:1, and first, 10 cycles of 20ms / 10ms on / off cycles are given for 300ms. Here, the light irradiation period is 200ms in total, while the non-light irradiation period is 100ms in total, so a non-light irradiation period of 50ms is given with a duty ratio of 2:1 for the difference of 100ms. This results in a cycle of a light blinking period of 300ms and a non-light irradiation period of 50ms, so this is given for 10 cycles, 3.5 seconds. At this time, the difference between the light irradiation period and the non-light irradiation period is 500ms, so a non-light irradiation period of 250ms is given with a duty ratio of 2:1. This creates a 3.75-second cycle of light blinking / non-illumination, and 10 more cycles of this, totaling 37.5 seconds, are added. By superimposing multiple different periods in this way, multiple pieces of information on the time response of changes in source-drain current due to the photogating effect can be obtained. For example, the fast response at the moment of blinking and the subsequent slow response can be obtained all at once. In this embodiment, a case where 10-cycle superimposition was performed with a duty ratio of 2:1 was introduced, but the duty ratio and number of cycles can be changed arbitrarily according to the information to be obtained.

[0097] The gate voltage control unit 25 controls the gate voltage based on the measured source-drain current. More details are as follows. In advance, the gate voltage is changed and the change in the source-drain current when the irradiated light is turned on and off is measured, and the optimal range of the gate voltage and source-drain current value at which the change in the source-drain current is maximum is measured. In this case, the source-drain current value for determining the range may be the value at the time of light irradiation or the value at the time of light irradiation being stopped. In addition, the value after a certain period of time has elapsed from the time of light irradiation, the value after a certain period of time has elapsed from the time of light irradiation being stopped, or both the value at the time of light irradiation and the value after the time of light irradiation being stopped may be used. Alternatively, the average value of the two values ​​or the average value of the blinking period may be used. In short, it is sufficient to use the value that is most convenient to use in fixing the Fermi level of graphene. The measured gate voltage and the optimal range of the source-drain current value are stored as reference data, for example, in the gate voltage control unit 25. When measuring next, the gate voltage control unit first applies the gate voltage in the optimal gate voltage range obtained in advance as reference data. At this time, based on the value of the source-drain current measured by the source-drain current measuring unit, the gate voltage is adjusted as necessary to be within the optimal source-drain current range obtained as reference data, using an on / off synchronization signal sent from the LED power control circuit as necessary. After the source-drain current has been adjusted to the optimal range, a signal is output to notify that the sensor is ready to start measurement. This signal is input to, for example, the judgment unit 24, which makes a judgment based on the source-drain current measuring unit 23. On the other hand, if the measured source-drain current cannot be adjusted to the optimal range, a signal is output to notify that the measurement is not ready to start. Based on these signals, the sensing system controls the operation and stop of measurement, or records the measurement results as the state when they were obtained.

[0098] Furthermore, it is expected that the source-drain current may fluctuate and deviate from the optimal range even during sensing due to various disturbances such as noise. Therefore, if necessary, the source-drain current value is monitored even during sensing, and the gate voltage is adjusted to keep the source-drain current value within the optimal range.

[0099] FIG. 14 is a block diagram showing a sensor system 3 according to the embodiment.

[0100] The sensor system 3 includes a humidification unit 30, a sensor unit 40, an irradiation unit 50, and pipes 61-65.

[0101] A pipe 61 is connected to the humidification unit 30. A gas (specimen gas) 9 that may possibly contain a target substance is introduced into the humidification unit 30 via the pipe 61. The humidification unit 30 humidifies the introduced gas 9.

[0102] The sample gas humidified by humidification unit 30 is introduced into sensor unit 40 via pipes 62 and 63. One end of pipe 63 is connected to pipe 62, and the other end of pipe 63 is connected to sensor unit 40.

[0103] The sensor unit 40 includes a graphene FET 1, a first member 41, and a second member .

[0104] A recess is provided on the surface of the first member 41, and a component 2 including a graphene FET 1 is provided in this recess.

[0105] The second member is provided on the first member 41. The second member includes a first gas flow passage 43, a cavity 44, a second gas flow passage 45, and a window portion .

[0106] In the cavity 44, the graphene of the graphene FET 1 is exposed within the cavity 44.

[0107] The first gas flow path 43 connects the cavity 44 and the pipe 63. Therefore, the specimen gas introduced from the pipe 63 and having an increased humidity is supplied to the graphene of the graphene FET 1.

[0108] The second gas flow path 45 is provided to exhaust the specimen gas supplied to the graphene of the graphene FET 1. The second gas flow path 45 is connected to a pipe 64, and the pipe 64 is connected to a pipe 65. The pipe 64 is provided in the second member 42. One end of the pipe 64 is connected to the second gas flow path 45, and the other end of the pipe 64 is connected to one end of the pipe 65.

[0109] The other end of the pipe 65 is connected to an exhaust system (not shown) including a suction pump, etc. As a result, the sample gas 9 introduced from the pipe 61 is exhausted from the pipe 65 via the humidification unit 30, the sensor unit 40, etc. The window portion 45 is provided above the hollow portion 44. The window portion 45 is transparent to the irradiated light. In other words, the irradiated light can pass through the window portion 45. Typical transparent materials include acrylic resin, glass, and quartz. On the other hand, the portion of the member 42 other than the window portion 45 is formed of a light-shielding material.

[0110] Furthermore, the sensor part 2 inserted into the recess of the first member 41 may be of a replaceable cartridge type. For example, the first member 41 and the second member 42 are openable and closable, and after the sensor part 2 is stored in the recess, when the first member 41 and the second member 42 are closed again, the graphene part of the sensor part 2 is aligned with the position of the cavity 44, and the electrical input / output terminal formed on the sensor part comes into contact with a connector terminal formed on either the first member 41 or the second member 42, so that electrical input / output can be performed from the sensor unit 40 or from outside thereof.

[0111] Furthermore, although not shown, if necessary, a temperature adjustment device can be incorporated in the sensor unit 40. As the temperature adjustment device, for example, a Peltier element or the like is used.

[0112] The irradiation unit 50 includes a light source 51 and an optical fiber 52 (light transmission path). The light source 51 generates light to be used as irradiation light. The light exit side of the optical fiber 52 is connected to the window portion 45 through a hole provided in the second member 42. Therefore, the light 53 emitted from the light source 51 is irradiated to the graphene of the graphene FET1 through the optical fiber 52. In addition, a device is used to fill the gap between the hole provided in the second member 42 and the optical fiber with a light-shielding material so that external light does not leak in through the gap. Specifically, a method is used in which a light-shielding rubber is provided at the exit portion of the hole in the second member 42, or a light-shielding adhesive is applied.

[0113] FIG. 15 is a diagram showing an example of the configuration of the humidification unit 30. As shown in FIG.

[0114] The humidifying unit 30 includes a pipe 31 , a hydrophilic nonwoven fabric 32 provided on the inner wall of the pipe 31 , and a water supply section 33 that supplies water to the hydrophilic nonwoven fabric 32 .

[0115] The water supply unit 33 includes a container 34 in which water is stored, and a thin, tubular supply unit 35 that supplies the water stored in the container 34 into the hydrophilic nonwoven fabric 32. The supply unit 36 ​​penetrates the piping 31 and comes into contact with the hydrophilic nonwoven fabric 32.

[0116] Although not shown, a thermometer and hygrometer can be installed in the sensor system. The installation location is, for example, midway along the pipe 65.

[0117] Next, a detection method according to an embodiment will be described. The detection method according to an embodiment uses a graphene FET according to an embodiment (hereinafter, simply referred to as a graphene FET).

[0118] The detection method of the embodiment includes a first step of blinking a light on the graphene of the graphene FET, a second step of collecting a gas (sample gas) that may contain a target substance, a third step of humidifying the collected sample gas, a fourth step of supplying the humidified sample gas to the graphene FET, a fifth step of measuring a source-drain current flowing through a source electrode and a drain electrode of the graphene FET, and a sixth step of determining whether or not the sample gas contains a target substance and, if so, its concentration based on the current measured in the fifth step.

[0119] The first step (blinking of light) is performed, for example, by using the irradiation unit 50 in FIG. 13 and the light source circuit 51 in FIG.

[0120] The second step (collection of sample gas) is carried out, for example, using pipe 61 in FIG. 14 and an inlet (not shown) provided at the tip of the pipe.

[0121] The third step (humidifying the sample gas) is performed, for example, using a humidifying unit 50 shown in FIG.

[0122] The fourth step (supply of humidified sample gas) is performed, for example, by using pipes 62 to 65 in FIG. 14 and an exhaust system (not shown).

[0123] The fifth step (measuring the source-drain current) is performed, for example, by using the sensor unit 40 in Fig. 14 (more specifically, the source-drain current measuring unit 23 in Fig. 13). The sixth step (determining the presence / absence and concentration of a target substance) is performed, for example, by using the sensor unit 40 in Fig. 14 (more specifically, the determining unit 24 in Fig. 13).

[0124] Furthermore, a seventh step may be added in which the gate voltage is adjusted so that the source-drain current value of the graphene of the graphene FET falls within an optimal range based on the source-drain current measured in the fifth step. The seventh step is performed, for example, by using the sensor unit 40 in FIG. 14 (more specifically, the gate voltage control unit 25 in FIG. 13).

[0125] 14 may perform the first to seventh steps using a plurality of sensor systems (or a plurality of devices) capable of performing all of the first to seventh steps. In other words, the steps performed by each of the plurality of sensor systems (or a plurality of devices) may be different.

[0126] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0127] 1...Graphene FET, 2...Sensor circuit, 3...Sensor system, 9...Sample gas, 11...Silicon substrate, 12, 13...Insulating film, 14...Graphene, 15...Drain electrode, 16...Source electrode, 17...Insulating film, 18...Gate electrode, 19...First insulating film, 19a...Second substance, 21...Drain voltage control section, 22...Source electrode voltage control section, 23...Source-drain current measuring section, 24...Determination section, 25...Gate voltage control unit, 30...humidification unit, 31...piping, 32...hydrophilic nonwoven fabric, 33...water supply unit, 34...container, 35...supply unit, 40...sensor unit, 41...first member, 42...second member, 43...first gas flow path, 44...cavity, 45...second gas flow path, 46...window portion, 50...irradiation unit, 51...light source, 52...optical fiber, 55...LED, 56...light intensity control unit, 57...onset control unit, 61-65...piping.

Claims

1. A sensor element capable of detecting a target substance contained in an atmosphere, comprising: Graphene, A drain electrode provided on the graphene; A source electrode provided on the graphene; and a sensor element provided on the graphene, the sensor element having a charge state that changes when light is irradiated and the light irradiation is stopped, and the sensor element includes a first substance that includes a carboxyl group, a phosphate group, a sulfonic acid group, a silanol group, a hydroxyl group, or an amino group; a humidification mechanism separate from the sensor element that humidifies the graphene of the sensor element; A gate electrode for applying a voltage to the graphene; one of gold, platinum, silver, and silver chloride disposed on a surface of the gate electrode; the target substance can be detected by measuring a current flowing between the source electrode and the drain electrode during a period in which the irradiation of the light and the cessation of the irradiation of the light are repeated on the sensor element; The measuring of the current is performed after the humidification mechanism humidifies the graphene of the sensor element. Sensor system.

2. The current during the period is different between a first case and a second case, In the first case, the sensor element is exposed to the atmosphere containing the target substance; In the second case, the sensor element is exposed to the atmosphere that does not contain the target substance. The sensor system of claim 1 .

3. The first substance includes a substance capable of causing charge transfer between the graphene or metal particles; The sensor system of claim 1 .

4. When the sensor element is exposed to an atmosphere containing the target substance, the current during the period when the light is irradiated and the current during the period when the light is not irradiated are different from the current during the period when the light is irradiated and the current during the period when the light is not irradiated when the sensor element is exposed to the atmosphere not containing the target substance. The sensor system of claim 1 .

5. a value of the current during the period when the light is irradiated and a value of the current during the period when the light is not irradiated are different between a third case and a fourth case, In the third case, the graphene and the first material are exposed to the atmosphere containing the target material; In the fourth case, the graphene and the first material are exposed to the atmosphere not containing the target material. The sensor system of claim 1 .

6. A sensor element capable of detecting a target substance contained in an atmosphere, Graphene, A drain electrode provided on the graphene; A source electrode provided on the graphene; A gate electrode for applying a voltage to the graphene; A conductive layer provided between the gate electrode and the graphene; and a sensor element provided on the graphene, the sensor element having a charge state that changes when light is irradiated and the light irradiation is stopped, and the sensor element includes a first substance that includes a carboxyl group, a phosphate group, a sulfonic acid group, a silanol group, a hydroxyl group, or an amino group; a humidification mechanism separate from the sensor element for humidifying the graphene of the sensor element; the target substance can be detected by measuring a current flowing between the source electrode and the drain electrode during a period in which the irradiation of the light and the cessation of the irradiation of the light are repeated on the sensor element; The measuring of the current is performed after the humidification mechanism humidifies the graphene of the sensor element. Sensor system.

7. The electrical resistance between the gate electrode and the graphene is between 10 MΩ and 100 GΩ. The sensor system of claim 1 .

8. A sensor element capable of detecting a target substance contained in an atmosphere, comprising: Graphene, A drain electrode provided on the graphene; A source electrode provided on the graphene; A gate electrode, and a sensor element provided on the graphene, the sensor element having a charge state that changes when light is irradiated and the light irradiation is stopped, and the sensor element includes a first substance that includes a carboxyl group, a phosphate group, a sulfonic acid group, a silanol group, a hydroxyl group, or an amino group; a humidification mechanism separate from the sensor element that humidifies the graphene of the sensor element; a measurement unit configured to measure a current flowing between a source electrode and a drain electrode of the sensor element; a determination unit configured to determine one of the presence or absence of the target substance and the concentration of the target substance; a gate voltage control unit configured to control a gate voltage applied to the gate electrode based on the current measured by the measurement unit; Equipped with the target substance can be detected by measuring a current flowing between the source electrode and the drain electrode during a period in which the irradiation of the light and the cessation of the irradiation of the light are repeated on the sensor element; The measuring of the current is performed after the humidification mechanism humidifies the graphene of the sensor element. Sensor system.

9. the gate voltage control unit is configured to adjust the gate voltage so that a value of a current flowing between the source electrode and the drain electrode of the sensor element falls within a predetermined range; and The value of the current is a first value of the current during light irradiation and a second value of the current when the light irradiation is stopped, or an average value of the first value and the second value. The sensor system of claim 8.

10. an illumination unit for illuminating the sensor element with light; Further comprising: The sensor system of claim 8.

11. The illumination unit includes a light source and a blinking control unit connected to the light source and configured to control blinking of the light generated by the light source. The sensor system of claim 10.

12. The sensor system detects one of sulfide compounds, limonene, methyl benzoate, ecgonine derivatives, methamphetamine, amphetamine, caryophyllene, amphetamine derivatives, caryophyllene derivatives, heliotropin, and 3,4-methylenedioxyphenylpropan-2-one (MDP2P). The sensor system of claim 10.

13. A detection method using the sensor system according to claim 1, Repeatedly irradiating and stopping light on the graphene of the sensor element; humidifying a gas that may contain a target substance by a humidification mechanism of the sensor system; providing the humidified gas to the graphene of the sensor element; Measuring a current flowing through a source electrode and a drain electrode of the sensor element; and determining one of the presence or absence of the target substance in the gas and the concentration of the target substance based on the measured current; Equipped with applying a voltage to the graphene so that a value of the current flowing between the source electrode and the drain electrode of the sensor element falls within a predetermined range; and A detection method, wherein the value of the current is a first value of the current when light is irradiated and a second value of the current when the light irradiation is stopped, or an average value of the first value and the second value.

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