JP4774476B2 - sensor - Google Patents

Description

  The present invention relates to a sensor, and more particularly to a sensor such as a biosensor having a structure of a field effect transistor (hereinafter abbreviated as FET) or a single electron transistor (hereinafter abbreviated as SET).

The conventionally proposed biosensor forms a thin film on the electrode with a reactive group that selectively reacts with a specific molecule, and measures the change in potential when the thin film adsorbs the specific molecule. ing. Specifically, this is a method of detecting the amount of glucose by forming a thin film having glucose oxidase on an electrode and measuring a change in current value accompanying an oxidation reaction with glucose. With respect to this type of biosensor, for example, the following Patent Document 1 and Non-Patent Documents 1 and 2 can be cited.
JP-A-10-260156 Aizawa, chemical communication. 945 pages (1989) Alexander Star, Jean-Christophe P, Gabriel. Keith Bradley, and George Gruner, Vol. 3, No. 4, 459-463 (2003)

  However, since the conventional biosensor is a method that directly detects the current value associated with the chemical reaction as described above, the detection sensitivity is low and it is difficult to detect low concentrations of glucose. There was a drawback that the feature of selectivity could not be fully exhibited.

An object of the present invention is to eliminate such drawbacks in the prior art and provide a sensor having a sensitivity far superior to that of the prior art.

In order to achieve the above object, a first means of the present invention comprises: a substrate; and a channel having a source electrode and a drain electrode provided on the insulating film formed on the upper surface of the substrate so as to face each other at a predetermined interval. At least with the sensor
The channel is composed of ultrafine fibers;
An insulating thin film is formed on a surface of the substrate opposite to the channel, a back gate electrode is provided outside the insulating thin film, and the insulating thin film is modified with a specific substance that interacts with a substance to be detected. The substance to be detected is interposed between a modified portion and the back gate electrode .

According to a second means of the present invention, in the first means, the ultrafine fiber is a carbon nanotube .

According to a third means of the present invention, in the first means, the detected substance and the specific substance are biopolymers that interact with each other .

According to a fourth means of the present invention, in the third means, the substance to be detected is an antigen or an antibody, and the specific substance is an antibody or an antigen .

Since the present invention has the above-described configuration and uses ultrafine fibers such as carbon nanotubes in the channel , an ultrasensitive sensor can be provided.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a SET biosensor according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of the SET biosensor.

In these figures, 1 is a chip-like insulating substrate, 2 is a thin film coated on the insulating substrate 1 and having a functional group such as a hydroxyl group, an amino group, or a carboxylic acid group on the surface (having a hydroxyl group in this embodiment). (Thin film made of SiO ₂ ) 3 and 4 are a source electrode and a drain electrode formed on the thin film 2 at a predetermined interval, and pointed parts 5 and 6 are formed at opposite portions of the electrodes 3 and 4. (See FIG. 1). A carbon nanotube (hereinafter abbreviated as CNT) 7 in which a defect is introduced is grown between the tip portions 5 and 6 of both electrodes 3 and 4. A gate electrode 8 is formed on the surface of the substrate 1 opposite to the thin film 2.

  For the insulating substrate 1, for example, an inorganic compound such as silicon oxide, silicon nitride, aluminum oxide, or titanium oxide, or an organic compound such as acrylic resin or polyimide is used. For the electrodes 3, 4, and 8, for example, a metal such as gold, platinum, or titanium is used. The electrical connection relationship between the electrodes 3, 4 and 8 is as shown in FIG.

In this embodiment, CNT is used as the nanotube-like structure. By using this nanotube-like structure, a very fine channel can be formed, and a highly sensitive sensor can be obtained.

Note that a gap G is formed under the CNT 7 as shown in FIG. In this way, a sensor having a SET structure is configured. The basic configuration of SET and FET is the same, but in the channel used as a current path, the SET channel has a quantum dot structure, and the FET channel does not have a quantum dot structure. ing.

  In this transistor (SET and FET), the current value between the source electrode 3 and the drain electrode 4 changes sensitively to changes in the charge (more strictly, the spin electron state) on the gate electrode 8 and the CNT 7. Generally, SET is more sensitive than FET. In addition, SET characteristics are rarely observed without modification after CNT generation, but by making FET-like CNT the CNT generation temperature (high temperature of about 900 ° C.), the CNT is partially Breaks to form an island and exhibits SET current characteristics. Further, the same result can be obtained by flowing a current (up to several mA) larger than the operating current (up to several μA).

  In the present invention, when a molecule is attached to the gate electrode 8 or the CNT 7 of these transistors, the spin electron state on the CNT changes indirectly or directly. The attached molecule can be detected from the change in current. In addition, the modified molecule can be detected from a change in current when the gate electrode 8 or the CNT 7 itself is molecularly modified, or the reaction between the modified molecule and another molecule can be detected.

  In particular, when the gate electrode 8 or the CNT 7 is modified with an antibody (or antigen), it is possible to detect a specific antigen (or antibody) using an antibody-antigen reaction. Can detect microorganisms such as viruses and bacteria with high sensitivity and high speed. This method can be effectively used for prevention by early detection of infectious diseases and research of microorganisms, and since the element (sensor) itself is remarkably small, it is taken to the field and used for detection of infectious disease viruses and for these studies. be able to.

FIG. 3 is a schematic view showing a state of detection using the sensor. As shown in the figure, the sensor has a molecule detection portion 18 and a signal conversion portion 19, which are closely related. In the figure, 12 is a protective film made of SiO ₂ , 13 is a specific substance (for example, an antibody) that selectively reacts or adsorbs (interacts with) the substance to be detected, and 14 selectively reacts with the specific substance 13. Alternatively, a substance to be detected (for example, an antigen) adsorbed (interacted), 15 is a sample solution containing the substance 14 to be detected.

  FIG. 4 and FIG. 5 are schematic views showing another state of detection using the sensor of the present invention, and FIG. 5 is an enlarged schematic view between the insulating substrate 1 and the gate electrode 8 of the sensor. In this example, the sample solution 15 containing the substance to be detected 14 is interposed between the insulating substrate 1 and the gate electrode 8 to detect the substance 14 to be detected. In FIG. 5, reference numeral 20 is a molecule that maintains the orientation of a specific substance (for example, an antibody), and 21 is a substance other than the substance to be detected that exists in the sample solution 15. FIG. 5 shows a state in which a substance to be detected (for example, antigen) 14 is selectively reacted or adsorbed by a specific substance (for example, antibody) 13.

Next, control of basic conductivity characteristics of CNT will be described.
(1) The type of catalyst used when applying CNT growth, applying an electric or magnetic field to arbitrarily design the growth position, direction, number, chirality, characteristics, etc. of the CNTs that are the basic elements of a biosensor device Optimize the shape and shape.

FIG. 6 is a schematic configuration diagram showing a method of patterning a catalyst and controlling the position and direction of CNTs while applying an electric field. In the figure, 1 is an insulating substrate, 2 is a thin film made of SiO ₂ coated on the insulating substrate 1, 9a and 9b are catalyst layers made of iron or the like patterned on the SiO ₂ thin film 2, and 7 is With the CNT formed between the catalyst layers 9a and 9b by applying an electric field, the growth position, direction, number, chirality, characteristics, and the like are arbitrarily controlled. 10 is a reaction vessel, 11 is a hydrocarbon gas such as methane gas which is a raw material of CNT. The grown CNT has a length of about several μm (for example, about 3 μm), a diameter of about several nm, and is an ultrafine fibrous aggregate.

(2) The shape of the four-probe method is created using CNTs with controlled positions, directions, and characteristics as non-invasive electrodes.

  In the four-probe method, four needle-shaped electrodes (for example, electrodes A, B, C, and D) are installed on a straight line on a sample, and the distance between two outer probes (for example, electrodes A and D) is constant. A current is passed and the potential difference generated between the two inner probes (for example, electrode B and electrode C) is measured to obtain a resistance value. The obtained resistance value is multiplied by the thickness of the sample and the correction coefficient RCF to obtain the volume resistance of the sample. This is a method for calculating a value.

(3) The portion where the electrode and channel (CNT) wrap is used by using a high electric field electron beam, or STM (Scanning Tunneling Microscopy) / AFM (Atomic Force Microscope). Welding is performed by a locally applied electric field to integrate the electrode and the channel (CNT).

(4) Next, the transport characteristics of the CNT are evaluated. The electrical conductivity characteristics to be evaluated include ballistic conductivity characteristics, whether spin injection is possible, and whether spin transport is possible.

(5) It has already been confirmed in our preliminary experiments that the electrical characteristics of CNTs change drastically by introducing defects into CNTs (by introducing defects into CNTs, ~ Preliminary experiments confirm that a SET having a high Coulomb energy of 5000 K and operating at room temperature can be formed).

  Therefore, by introducing defects to the CNTs arbitrarily by STM / AFM processing or electron beams, CNTs whose conductivity characteristics can be controlled can be obtained.

  As a specific example of this CNT defect introduction method, for example, there is a method in which annealing is performed at substantially the same temperature (for example, about 800 ° C.) as when CNT is produced, and then natural cooling is performed. And the defect of CNT refers to a change in the shape of CNT, such as a part of carbon atoms popping out by heat and barely connected in a state where the CNT is cut off. It is not clear at present whether this is the structure.

(6) The correlation between the defects in the CNT and the electrical characteristics of the CNT is examined. For example, the density, distribution, and size (size, energy barrier, etc.) of defects are evaluated by the scanning probe method (Kelvin probe method, Maxwell probe method, etc.), and the correlation between this and the electrical characteristics of CNT is clarified. To do. Thus, by grasping the correlation between the defects in the CNTs and the electrical characteristics, it is possible to manufacture a SET with good reproducibility and uniformity of characteristics.

(7) The electrical characteristics of the carbon nanotube can be controlled by controlling the introduction of defects according to (6).

  In the present invention, a SET that operates at room temperature can be manufactured using CNTs into which defects are introduced. Although the case where CNTs with defects are used is described here, CNTs without introducing defects can also be used.

  In order to avoid malfunctions due to floating charges and mobile charges, which were problems in conventional SETs, in the present invention, when two CNT-based SETs are made close to each other and a single charge is detected, both SETs are detected. The AND of the output characteristics (room temperature) is taken. As a result, both SETs operate only when there is a true charge, thereby avoiding malfunctions due to floating charges and mobile charges.

  In order to further increase the measurement speed, a system that uses a resonance circuit to operate with an alternating current is employed instead of the conventional direct current method using the above-described method. As described above, a single charge distribution can be measured at room temperature and at high speed without malfunction.

  FIG. 7 is a diagram showing room temperature coulomb diamond characteristics by SET using CNT. From this room temperature Coulomb diamond characteristic, it can be proved that the SET using the CNT of the present invention can operate at room temperature.

The SET of CNT used as well as formed on the substrate 1 as shown in FIG. 1, and coated with a protective film 12 made of a chip of SiO ₂ in order to operate in solution, as shown in FIG. 3, the SiO ₂ protective film A specific substance 13 such as an antibody is immobilized on 12. In this example, the protective film 12 is provided, but the protective film 12 may not be provided in some cases.

  A biosensor according to the present embodiment is installed in a sample solution 15 in which a substance to be detected 14 such as DNA is dissolved, and is operated with an alternating current using a resonance circuit. By measuring the single electron interaction, the detection target substance 14 can be detected (evaluation of surface charge distribution characteristics).

  Next, the creation of the signal conversion part of the sensor using CNT will be described in detail. FET and SET type transistors are created using the semiconductor properties of CNTs. The production method includes a process of vapor deposition of a catalyst by a general lithographic method, CNT growth by thermal CVD, and an electrode production process.

  However, this has the following problems. First, control of CNT growth is not easy. Several CNT growth methods have been proposed, but when creating an element that connects the electrodes of the signal conversion part with a single CNT, the yield of CNT bridging between the catalysts and the structural stability are important. is there. For this reason, it is important to determine the conditions (temperature, type of gas, flow rate, electric field, magnetic field, etc.) of the catalyst (mutual position, structure, size, etc.) and thermal CVD method.

  In addition, electrodes are created after CNT growth on the catalyst, but phenomena such as peeling of the electrodes from the substrate and cracks in the electrodes occur, and the contact potential with the CNTs affects the characteristics and strength of the device. In order to obtain stable current characteristics, it is necessary to study electrode materials.

  In the embodiment of the present invention, a novel technique (first technique to be described later) is used particularly for various elements of the catalyst. In addition, when the CNT is directly modified with molecules, the solvent containing the electrode and the molecule may cover the electrode, and the influence of the solvent covering the electrode surface on the connection between the electrode and a measuring instrument such as a probe occurs. A technique for preventing this (second technique described later) was used. Further, even when the back gate electrode or the side gate electrode of the element is used, the sample or vapor containing the sample may affect the gate electrode. This could be avoided by protecting the CNT (third method described later). In fact, in the detection results of various reactions using the back gate electrode and the side gate electrode, there is an example in which the current value changed because the detected substance was vaporized and adhered not only to the gate electrode but also to the CNT surface. is there.

Specifically, in the first method, a catalyst is deposited on the SiO ₂ film using an electron beam lithographic method in order to form nuclei for the growth of CNTs. In this embodiment, both surfaces of the Si substrate having a thickness of 380 μm are covered with SiO ₂ films having a thickness of about 300 nm. The present invention relates to a method of using CNT growth nuclei using a transition metal such as iron, nickel, cobalt, molybdenum and tungsten or a catalyst containing these transition metal fine particles on the SiO ₂ film.

FIG. 8 is a diagram for explaining a conventional method. In FIG. 8, 1 is an Si insulating substrate having SiO ₂ films formed on both surfaces, 7 is CNT, 9a and 9b are catalysts, and 22a and 22b are electrodes later. Is the position where is formed. In the conventional method, as shown in the figure, the catalysts 9a and 9b are formed by vapor deposition one by one at a predetermined interval, and the CNT 7 grown from one catalyst 9a reaches the paired catalyst 9b. Connection between the catalysts 9a and 9b by the CNT 7 can be made.

  FIG. 9 is a diagram for explaining an embodiment (first method) of the present invention. As shown in FIG. 9, a plurality of dot-shaped catalysts (9a-1) are formed at a position 22a where one electrode is formed. , 9a-2,... 9a-n) are formed side by side, and a plurality of dot-shaped catalysts (9b-1, 9b-2,... 9b- are also formed at the position 22b where the other electrode is formed. n) is formed to face the catalyst (9a-1, 9a-2, ... 9a-n). Thus, by increasing the number of installed catalysts 9, that is, the growth nuclei of CNTs and arranging them closely, it is possible to remarkably increase the probability that CNTs that originally tend to grow randomly from the catalyst 9 reach the paired catalysts 9. By this method, the yield can be increased by 10 times or more as compared with the prior art.

  FIG. 10 is a diagram illustrating an arrangement example of the catalyst 9 according to the present embodiment. 6 adjacent to each other so that the distance L1 between the adjacent catalysts is 2 μm, one catalyst row (9a-1, 9a-2,... 9a-n) and the other catalyst row ( The distance L2 between 9b-1, 9b-2,... 9b-n) is 4 μm. Note that the number of installed catalysts 9, the interval L1, and the interval L2 can be arbitrarily set.

  FIG. 11 is an enlarged perspective view of the catalyst 9. As shown in the figure, the catalyst 9 includes a support layer 25 made of Si or the like having a thickness of 50 nm, an intermediate layer 26 made of a transition metal such as Mo, Ta, or W having a thickness of 10 nm formed on the support layer 25. The formed top layer 27 is made of a transition metal such as Fe, Ni, and Co having a thickness of 3 nm. Therefore, the total height H of the catalyst 9 is 63 nm, and the direct light D is 2 μm. The catalyst 9 having a multilayer structure is patterned by a thin film forming technique such as vapor deposition, sputtering, or ion plating.

  After the insulating substrate 1 on which the catalyst 9 is formed is placed in a reaction vessel 10 of a thermal CVD apparatus as shown in FIG. 6, a hydrocarbon gas 11 such as methane or ethane is injected to grow CNT 7 on the catalyst 9. .

  In this embodiment, the growth of CNT 7 was performed according to the following procedure. The insulating substrate 1 on which the catalyst 9 was formed was heated from room temperature to 900 ° C. for 15 minutes. At this time, Ar was caused to flow into the container 10 at a flow rate of 1,000 sccm (gas flow rate for 1 minute). While maintaining this temperature, methane and hydrogen are introduced at a flow rate of 1,000 sccm and 500 sccm, respectively, for 10 minutes, and then the reactor 10 is cooled to room temperature over 120 minutes. At this time, Ar gas was introduced at 1,000 sccm.

  Thus, after producing | generating CNT, the electrode (the source electrode 3, the drain electrode 4) was vapor-deposited. For the electrode, Au is vapor-deposited or Ti is vapor-deposited, and then the surface is covered with Au. In particular, the latter has a feature that the peeling from the substrate and the generation of cracks in the electrode are small. The width of the electrode covering the catalyst is about 10 μm.

  Next, the second method described above will be described. A large number of electrodes (about 50 to 400) are formed simultaneously. When the CNT is directly modified, a solution containing the decorative molecule may be dropped on the CNT, and depending on the amount of the solution, the entire electrode may be covered. Once the surface of the electrode is covered with a solution, when measuring the current between the electrodes connected by CNT, a film is formed between the probe of the measuring device such as a prober and the electrode, and an accurate current value is obtained. There is no possibility.

12 and 13 are diagrams for explaining a sensor not subjected to the second method. FIG. 12 shows a state before the solution is dropped, and FIG. 13 shows a state after the solution is dropped. In both figures, (a) is a plan view and (b) is a cross-sectional view. In the conventional sensor, since the size of the electrodes 3 and 4 is small, as shown in FIG. 13, there are many cases where the entire electrodes 3 and 4 are covered with the coating 28 formed by dropping the solution. Since the value of the current flowing between the electrodes 3 and 4 is as small as about 1 μA, if the film 28 exists between the probe of the measuring apparatus and the electrodes 3 and 4, accurate current measurement cannot be performed.
Therefore, in the present invention, as shown in FIGS. 14 and 15, the length L3 of the electrodes 3 and 4 [see FIG. 14 (a)] is about 1.5 to 3 times longer than that of FIG. In this way, by increasing the length L3 of the electrodes 3 and 4, even if the molecular coating 28 that modifies the CNT 7 is formed, the end 29 of the electrodes 3 and 4 is not covered with the coating 28 (FIG. 15). See). The current flowing between the electrodes 3 and 4 can be accurately measured by applying a probe of a measuring device such as a prober to the portion 29 not covered with the coating 28 using an optical microscope. In the present embodiment, in FIG. 14A, the width w1 of the tip portion of the electrodes 3 and 4 is 10 μm, the width W2 of the portion to which the probe is applied is 150 μm, and the length L3 is 500 μm. As shown in FIG. 14 (b), the CNT 7 is in a slightly curved state between the electrodes 3 and 4, and a gap G is provided between the outermost surface on the substrate 1 side. The difference in expansion coefficient is absorbed by the slack of the CNTs 7.

  Next, the above-described third method will be described. CNTs are said to be 2,000 times stronger than iron of the same size. In fact, CNTs are hardly damaged even if they are cleaned after direct molecular modification. However, CNT easily interacts with various molecules including water and changes its spin electronic state, which appears as a change in current value. This can be positively used as a gas sensor, and at the same time becomes a noise source when a back gate electrode, a side gate electrode or the like is used as a sensor.

  Therefore, in the present invention, the CNT and a part of the electrode are covered with an insulating protective film to reduce noise. An insulating adhesive can be used to form the insulating film, but a passivation film widely used for spin coating can also be used. In particular, the increase in current observed when water was applied to the back gate electrode was not observed due to the formation of the insulating protective film. In addition, the formation of this insulating protective film makes it possible to ultrasonically clean the entire device and to clean the back gate electrode and the like with a stronger cleaning agent than ever before.

  The gate electrode of the sensor can be formed at various positions, and can have various structures depending on the use of the sensor and the ease of manufacture. Next, each structure will be described.

(A) Structure in which the gate electrode is molecularly modified When a molecule adheres to the SiO ₂ film formed on the substrate, the value of the current flowing between the source electrode and the drain electrode changes. For example, the current value changes by applying a fluorescent molecule FITC (Fluorescein isothiocyanate) to the gate electrode. As an example of the antibody-antigen reaction, the SiO ₂ film is molecularly modified with an antibody (or antisource) and reacted with the corresponding antisource (or antibody) to detect a change in electrical signal. Since the molecule can be modified in a larger region than CNT, it is suitable for detection of many molecules. In addition, since the CNTs are not directly modified, damage to the CNTs due to cleaning after use can be avoided.

FIG. 16 is a diagram showing this structure. As shown in the figure, the SiO ₂ film opposite to the CNT 7 on the insulating substrate 1 is molecularly modified with a specific substance (for example, antibody) 13, and a substance to be detected (for example, an anti-antibody) is interposed between the insulating substrate 1 and the gate electrode 8. The sample solution 15 containing the source) is interposed.

(B) Structure obtained by direct molecular modification of CNT FIG. 17 is a diagram showing a structure obtained by direct molecular modification of CNT7. By directly molecularly modifying the CNT7, the change of the spin electronic state on the CNT7 by the modifying molecule is larger than that in the case where the backgate electrode 8 is molecularly modified and has high sensitivity.

(C) Structure obtained by indirectly molecularly modifying CNT FIG. 18 shows a structure obtained by indirectly molecularly modifying CNT7. In order to indirectly modify the CNT7, the CNT7 is covered with an insulating thin film 30 made of an organic compound such as an adhesive as shown in FIG. The change of the spin electronic state caused by the modifying molecule or the molecule attached to the surface in the thin film 30 causes the change of the spin electronic state of the CNT 7, resulting in the change of the current. Both the back gate electrode 8 is molecularly modified and the CNT 7 is directly molecularly modified, and has high sensitivity and stability.

(D) Structure using sol-gel For each of the cases (A) to (C), a sol-gel containing a substance to be detected is used instead of the solution 15. As with the solution, changes in the electrical signal can be detected.

(E) Structure using a side gate An island is formed in the vicinity of the CNT on the substrate, and this is used as a gate. This structure has the advantage that the CNT7 itself is not damaged by modifying the CNT7 directly without taking the trouble of molecular modification of the back surface (back gate electrode). It is a structure suitable for SET.

  In the case of the structure in which the aforementioned (A) back gate electrode is molecularly modified, it is preferable to stabilize current characteristics by covering a part of the CNT and the electrode with an insulating protective film. In the case of the structure in which (B) CNT is directly molecularly modified and the structure in which (C) CNT is indirectly molecularly modified as described above, the portion not covered with the film on the electrodes 3 and 4 as described with reference to FIG. 29 may be formed.

  FIG. 19 is a schematic configuration diagram for explaining still another structure. In this structure, the substrate 1 itself is used as a channel (back channel), and the electrodes 3 and 4 are provided on the substrate 1 with the CNTs 7 interposed therebetween. A recess 16 serving as a channel is formed on the back surface of the substrate 1, and the recess 16 can be detected on the back surface of the substrate 1 by wetting it with a liquid containing a substance to be detected.

  FIG. 20 is a schematic configuration diagram for explaining still another structure. Even in this structure, the substrate 1 itself is used as a channel (back channel), but a probe 17 made of CNT or the like is provided in the channel of the substrate 1. The integrated back channel and probe 17 can be used, for example, as a probe of a scanning probe microscope.

Next, specific examples of the present invention will be described. As a preliminary experiment, a solution containing the fluorescent molecule FITC was dropped onto the SiO ₂ film back gate electrode, and changes in current characteristics were observed. FIG. 21 shows IV characteristics when the gate voltage is −20 V and the concentration of the fluorescent molecule FITC is 0.64 nM. In the figure, the vertical axis represents the current value (A) flowing between the source electrode and the drain electrode, and the horizontal axis represents the voltage value (V) between the source electrode and the drain electrode. Also, the dotted line in the figure is the IV characteristic curve before attaching the fluorescent molecule FITC, and the solid line is the IV characteristic curve after attaching the fluorescent molecule FITC.

  As is apparent from this figure, it can be seen that the IV characteristics greatly change before and after the attachment of the fluorescent molecule FITC.

(Specific example 1)
Next, detection of divalent ions using ion reaction will be described. The CNT of the CNT biosensor was directly modified with pyrene, and N- [5- (3′-maleimidopropylamino) -1-carboxypentyliminodiacetic acid {N- [5- (3′-Maleimidopropylamimo) -1-carboxypentyl] ] After binding to the back gate electrode, a solution containing Ni ions was dropped, and the conduction characteristics were examined based on the IV characteristics in each case. FIG. 22 shows IV characteristics when no electric field is applied to the gate electrode. The vertical axis represents the current value (A) flowing between the source electrode and the drain electrode, and the horizontal axis represents the voltage value (V) between the source electrode and the drain electrode. In the figure, di is an IV characteristic curve after cleaning the back gate electrode, nta is an IV characteristic curve after NTA bonding, and ni is an IV characteristic curve after dropping a solution containing Ni ions.

  As is apparent from this figure, the current increases by increasing the voltage between the source electrode and the drain electrode. However, in all systems (di, nta, and ni systems), the current increases almost in the vicinity of dv = 0V. However, semiconductor properties are seen.

  Compared to the IV characteristic curve after cleaning, the IV characteristic curve after NTA is bound to the back gate electrode shows a significant decrease in current. In contrast, when Ni ions are added to the system, the current increases. Since NTA reacts not only with Ni ions but also with other divalent positive ions, other divalent positive ions can also be detected.

(Specific example 2)
Next, detection of hemagglutinin (HA) using an antigen-antibody reaction will be described. The C-terminal of HA was cleaved at various levels (220, 250, 290, 320) and expression was attempted. Genes were introduced into 293T cells, and the expression of HA protein in the cells was confirmed using monoclonal antibody E2 / 3 and polyclonal antibodies. It was confirmed that the HA protein was secreted into the supernatant by Western blotting. HA _1-290 was expressed in large quantities and purified from the supernatant with a Ni ²⁺ column. Fractions containing the target HA protein were confirmed by ELISA and SDS-PAGE, and this fraction was collected and dialyzed with PBS to obtain HA. Although expression was also _observed for the shorter HA _1-220 , it was not used because it did not react with the monoclonal antibody.

After binding the NTA to the SiO ₂ film back gate electrode of the CNT biosensor, adding Ni ions to the system, a dilution of the stock ^solution, giving HA antibody at a concentration of from ^{10 -10} to ^{10 -5} sought IV characteristic curve It was. At this time, since the back gate electrode has no HA, the HA antibody does not bind to the back gate electrode with orientation.

Next, it was immobilized on NTA on the back gate electrode of the SiO ₂ film by means of a His tag preliminarily attached with HA, and similarly, an HA antibody was given to obtain an IV characteristic curve. These IV characteristic curve diagrams are shown in FIGS. The gate voltage was −20V.

FIG. 23 is an IV characteristic curve diagram when a solution containing Ni ions is given after NTA binding, FIG. 24 is an IV characteristic curve diagram when HA antibody having a dilution ratio of 10 ⁻¹⁰ is given, and FIG. FIG. 26 is an IV characteristic curve when HA antibody having a dilution ratio of 10 ⁻⁸ is given, FIG. 26 is an IV characteristic curve chart when HA antibody having a dilution ratio of 10 ⁻⁷ is given, and FIG. 27 is a dilution ratio of the stock solution. There Figure IV characteristic curve when gave ^10-6 HA antibody, FIG. 28 is a IV characteristic diagram when the dilution ratio of the stock solution gave ^{10 -5} HA antibody for. In these figures, the dotted line in the figure indicates that the former SiO ₂ film back gate electrode has no HA, and the solid line indicates that the latter HA is fixed to the NTA on the SiO ₂ film back gate electrode with a His tag previously attached. It is.

  As is clear from these figures, when the voltage between the source electrode and the drain electrode is changed from 0 V to 1 V, there is almost no difference in the current value between the source electrode and the drain electrode (solid line and dotted line). When the voltage is increased to 1 V or higher, the current value rapidly increases in a system (solid line) in which HA is assumed to be fixed.

  From this, it is possible to detect HA antibody even in a highly diluted region as compared with conventional methods such as ELISA (e (nzyme-) l (inked) i (mmuno) s (orbent) a (say))). It turns out that it is.

(Specific example 3)
The detection of hemagglutinin (HA) using these antigen-antibody reactions gave similar results even when using the sol-gel method. Their IV characteristics are shown in FIGS. In all systems before the experiment of antigen-antibody reaction, a solution containing Ni ions is given after NTA binding. The gate voltage was −20V.

FIG. 29 is an IV characteristic curve diagram when HA antibody at a dilution rate of 10 ⁻⁷ was given without adding HA antigen, and FIG. 30 was IV at the time when HA antibody at a dilution rate of 10 ⁻⁶ was given without adding HA antigen. Fig. 31 is a characteristic curve diagram, Fig. 31 is a IV characteristic curve diagram when HA antibody at a dilution rate of ^10-5 is given without ^adding an HA antigen, and Fig. 32 is an HA antibody at a dilution rate of ^10-6 after giving an HA antigen. FIG. 33 shows an IV characteristic curve when an HA antibody having a dilution rate of 10 ⁻⁵ is given after attaching the HA antigen, and FIG. 34 shows a dilution rate of 10 ⁻⁴ after attaching the HA antigen. It is IV characteristic curve figure when HA antibody is given. In these figures, ni is an IV characteristic curve when a solution containing Ni ions is given after NTA binding, and HA is immobilized on NTA on the SiO ₂ film back gate electrode with a hystag pre-attached with HA. is there.

As is clear from these figures, a large change appeared in the current value between the source electrode and the drain electrode particularly when the dilution ratios of the stock solution were 10 ⁻⁵ and 10 ⁻⁴ . Moreover, the detection sensitivity was about ELISA.

(Specific example 4)
Next, detection of calmodulin (CaM) using an antigen-antibody reaction will be described. A DNA fragment containing the rat calmodulin gene cDNA was inserted into the SacI-XbaI site of the expression vector pBAD / gIII (manufactured by Invitrogen) to construct a calmodulin expression vector (pBAD / gIII / calmodulin). The vector was introduced into Escherichia coli LMG194 strain to obtain a calmodulin expression clone. This claw was inoculated into 2 ml of LB / Ampicillin medium and cultured overnight.

5 ml of this culture solution is inoculated into LB / Ampicillin medium and cultured with shaking at 37 ° C. until OD ₆₀₀ reaches 0.5, and then L-arabinose is added to a final concentration of 0.02%. The culture was shaken at 37 ° C for a time. Then, the cells are collected by centrifugation, suspended in Native Binding Buffer (manufactured by Invitrogen), ultrasonically pulverized, and partially purified using Probond ^™ Purification System (manufactured by Invitrogen), and then HiLoad26 / 60 Superdex75pg (Amersmece) manufactured by Biomers And purified to homogeneity by SDS / polyacrylamide electrophoresis to obtain calmodulin.

After binding the NTA to the SiO ₂ film back gate electrode of the CNT biosensor was NTA immobilized on SiO ₂ film back gate electrode by His tag (His tag) previously marked with the HA, dilution of stock solution, from ^{10 -8} It was obtained IV characteristic curve giving HA antibody at a concentration of up to ^10-2. The result is shown in FIG. The gate voltage was −20V.

Curve (A) in the figure is an IV characteristic curve when washed after NTA binding, curve (B) is an IV characteristic curve when CaM is attached to NTA with a Histag previously attached, and curve (C) is dilution of the stock solution. IV characteristic curve when CaM antibody with a rate of 10 ⁻⁸ was given, curve (2) is IV characteristic curve when CaM antibody with a dilution ratio of 10 ⁻⁷ was given, and curve (e) was dilution of the stock solution IV characteristic curve when CaM antibody having a rate of 10 ⁻⁶ is given, curve (f) is IV characteristic curve when CaM antibody having a dilution ratio of 10 ⁻⁴ is given, and curve (g) is dilution of the stock solution It is IV characteristic curve when a CaM antibody with a rate of 10 ⁻² is given.

  As is apparent from this figure, when the voltage between the source electrode and the drain electrode is changed from 0 V to 0.5 V, the current value changes according to each concentration. From this, it can be seen that the CaM antibody can be detected even in a region where the dilution of the stock solution is very high, like the HA antibody.

  The detection results of CaM antibody and HA antibody using ELISA are shown in the following table. In this measurement procedure, the primary antibody was diluted at the following dilution ratio and allowed to stand for 1 hour, the secondary antibody (anti-mouse HRPO standard antibody) was diluted 5000 times and allowed to stand again for 1 hour, and then TMB. A substrate having an absorption wavelength of 450 nm was produced with a color former and the absorbance was measured.

table

(CaM antibody) (HA antibody)
PBS Neg. Con 0.034 0.030
2.5 × 10 ⁻² 2.000 1.722
6.3 × 10 ⁻³ 2.439 2.725
1.6 × 10 ⁻³ 2.899 3.378
3.9 × 10 ⁻⁴ 2.300 3.132
0.98 × 10 ⁻⁴ 0.650 2.839
2.4 × 10 ⁻⁵ 0.177 1.413
6.1 × 10 ⁻⁶ 0.051 0.290

A dilution of 6.1 × 10 ⁻⁶ has been shown to be difficult to detect by ELISA. On the other hand, in the specific examples 3 and 4, the sol-gel method shows sensitivity about ELISA, and the others are detected at a dilution of about 10 ⁻⁸ . CNT is grown on the Si substrate, electrodes are formed on both ends thereof, and the back surface of the Si substrate opposite to the surface on which the CNT is grown is activated with acid (sulfuric acid), and then a silanizing reagent ( 3-mercaptopropyltriethoxysilane) is reacted at 180 ° C. to immobilize NTA. Next, Ni ions were added to immobilize histidine-introduced antigens (CaM, HA), reacted with diluted antibodies, washed, and a negative bias was applied to the back of the substrate to measure IV characteristics.

FIG. 36 is a characteristic diagram showing changes in current value when 1.5 V is applied between the CNT electrodes after reacting the diluted CaM antibody with CaM immobilized as described above. As is clear from this figure, when the antigen was not immobilized, the current value hardly changed, but when immobilized, the current value increased as the antibody concentration increased. It was also found that antibody detection was possible in a dilution range of about 10 ⁻¹⁰ to 10 ⁻⁸ of the antibody stock solution.

When the detection limit of the antibody was examined using FLISA, it was found that the detection limit was obtained by diluting the antibody stock solution by about 10 ⁻⁶ . It was also found that the detection limit differs between CaM and HA and depends on the antigen and antibody.

  In each of the above specific examples, the case where the gate voltage is −20 V has been described. However, it has been found that detection is possible even with a gate voltage of about 0 V or a positive gate voltage with little change in the current value.

  When a CNT biosensor is applied to a solution, noise may be observed, causing a problem in data reliability. Therefore, noise can be remarkably reduced by evaporating the solvent (water) with a blower, a heater, a thermoelectric conversion element (Peltier element) or the like after dropping the sample solution (test solution) onto the sensor. The noise countermeasure is applied to a specific example in which the above solution is applied. In addition, the sample solution (test solution) can be cooled by a thermoelectric conversion element (Peltier element), liquid nitrogen, or the like, and the influence of a solvent such as water can be reduced. In particular, by freezing water to insulate, noise can be greatly reduced.

Conventional methods include ELISA and Western blotting, but their sensitivity is limited to a stock solution dilution ratio of about 10 ⁻⁵ . Sensitivity of the sensor of the present invention to which was subjected to a HA antibody detection, 10 ³ about the ELISA.

  In addition, since an electric signal is used, there are not many chemical reaction processes, and therefore the time required for detection is extremely short. Although the current characteristic was examined with an IV curve, it is possible to acquire the IV curve within a few seconds with a parameter analyzer.

  Conventionally known PCRs require temperature control because they involve temperature changes, but the sensor of the present invention can be used in a constant temperature environment, so temperature control is not required, and the configuration is simplified and miniaturized. Is possible. Examples that can be used in a constant temperature environment include the RT-PCR method, the ICAN method, and the LAMP method, but all of them have a drawback of requiring a long detection time.

  The sensor of the present invention can perform not only a single type of detection but also various types of sensing simultaneously on a single sample, and a plurality of types of detection at the same time. In addition, multiple samples can be detected in parallel using a plurality of sensors.

The sensor using the nanotube-like structure in the channel of the present invention is strong and can be used repeatedly. However, since it is inexpensive, it can be disposable for detection of dangerous viruses and the like.

  Although the case where CNT is used has been described in the embodiment, it is also possible to use ultrafine fibers that are not in a tube shape.

In the above embodiment, one type of biosensor in which a DNA probe is formed has been described. For example, three CNT biosensors with a SiO ₂ film are provided on a substrate, and a DNA probe, a protein probe, and a sugar are provided on each SiO ₂ film. It is also possible to form lipid probes individually and measure different biopolymers (DNA, protein, glycolipid) simultaneously.

In the above embodiment, the case where the surface charge distribution characteristics in DNA are evaluated has been described. However, the present invention can also be applied to detection of other biopolymers such as sugar chains, RNA, amino acids, sugars and viruses. It is also possible to detect changes in the electronic state in the process in which a protein such as rhodopsin emits protons in response to light, or changes in the electronic state due to structural changes in the dye.

  In the above-described embodiment, an example in which a nanotube-like structure is connected to the SET channel portion has been described. However, a nanotube-like structure can also be used for the FET channel portion.

  When microorganisms such as viruses enter the human body or other living organisms, antibodies against them start to interact. Therefore, viruses with antibodies can be detected from body fluids using the sensor of the present invention. For example, since the HA shown as the specific example is a protein called spike protein that covers the surface of influenza virus, it can be detected by the sensor of the present invention, and infectious diseases such as influenza, SARS, and BSE can be detected with high sensitivity and high speed. it can.

  Since the sensor of the present invention has a small detection portion and uses an electric signal, the detection circuit can be formed into a chip, and can be used as a portable and inexpensive detector. This enables testing in the field and can be provided to any medical institution. This not only helps prevent defense against early detection of infectious diseases, but also helps combat bioterrorism.

  Also in the basic science field, it is possible to detect the binding strength of intermolecular interactions at the single molecule level by the sensor of the present invention and classify viruses and proteins by current characteristics. Therefore, it is possible to conduct basic experiments for drug discovery by searching for and designing molecules similar to antibodies. One molecule can also be detected over time. Furthermore, it can also be used as a basic circuit of a spectroscopic antigen-antibody reaction detector.

  By directly modifying the gate electrode and CNT of the sensor of the present invention with DNA, complementary DNA can be detected electrically with extremely high sensitivity. In addition, identification is possible through ultrasensitive and high-speed measurement of microorganisms such as infectious disease viruses and bacteria caused by DNA.

  Furthermore, environmental hormones, toxins, and inorganic substances can be detected by the sensor of the present invention. In addition, since the influence of the vapor of the sample can be detected, the target is not limited to liquid but can be applied to gas, and the concentration of specific substances such as harmful substances in the atmosphere and other gases can be measured.

It is a perspective view of a sensor concerning an embodiment of the present invention. It is a schematic block diagram of the sensor. It is the schematic which shows a mode that it detects using the sensor. It is the schematic which shows the mode of other detection of the sensor which concerns on embodiment of this invention. FIG. 4 is an enlarged schematic view between an insulating substrate and a gate electrode of the sensor. It is a schematic block diagram which shows a mode that a carbon nanotube is grown and formed in embodiment of this invention. It is a figure which shows the room temperature Coulomb diamond characteristic by a carbon nanotube single electron type transistor. It is a schematic perspective view which shows a mode that a carbon nanotube is grown and formed by the conventional method. It is a schematic perspective view which shows a mode that a carbon nanotube is grown and formed by the method of this invention. It is a schematic perspective view which shows the example of an arrangement | sequence of the catalyst by the method of this invention. It is an expansion perspective view of the catalyst. It is the top view (a) and sectional drawing (b) of the sensor which do not give a 2nd method. It is the top view (a) and sectional drawing (b) of a sensor which show the state after dripping a solution on the sensor. It is the top view (a) and sectional drawing (b) of the sensor of this invention. It is the top view (a) and sectional drawing (b) of a sensor which show the state after dripping a solution on the sensor. It is sectional drawing which shows the state which modified the back gate electrode with the sensor of this invention. It is sectional drawing which shows the state which carried out the molecular modification of the carbon nanotube directly with the sensor of this invention. It is sectional drawing which shows the state which modified the carbon nanotube with the indirect molecule | numerator with the sensor of this invention. It is a schematic block diagram which shows the other structure of the sensor of this invention. It is a schematic block diagram which shows other structure of the sensor of this invention. It is IV characteristic curve figure at the time of FITC detection by the sensor of this invention. It is IV characteristic curve figure at the time of Ni ion detection by the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction by the sol gel method of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction by the sol gel method of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction by the sol gel method of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction by the sol gel method of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction by the sol gel method of the sensor of this invention. It is IV characteristic curve figure at the time of hemagglutinin detection by the antigen antibody reaction by the sol gel method of the sensor of this invention. It is IV characteristic curve figure at the time of calmodulin detection by the antigen antibody reaction of the sensor of this invention. It is IV characteristic curve figure at the time of calmodulin detection by the antigen antibody reaction of the sensor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Thin film 3 Source electrode 4 Drain electrode 5, 6 Point 7 Carbon nanotube 8 Gate electrode 9a, 9b Catalyst layer 10 Reaction vessel 11 Hydrocarbon gas 12 Protective film 13 Specific substance 14 Detected substance 15 Sample solution 16 Recess 17 Probe 18 Molecule detection part 19 Signal conversion part 20 Molecule that keeps orientation of specific substance 21 Substance other than specific substance 22a, 22b Position where electrode is formed later 25 Support layer 26 Intermediate layer 27 Top layer 28 Film 29 Covered with film Uninsulated portion 30 Insulating thin film G Gap L1 Distance between adjacent catalysts L2 Distance between catalyst rows L3 Electrode length W1 Width of electrode tip W2 Width of a portion to which a probe is applied.

Claims (4)

In a sensor comprising at least a substrate and a channel having a source electrode and a drain electrode provided facing each other at a predetermined interval on an insulating film formed on the upper surface of the substrate,
The channel is composed of ultrafine fibers;
An insulating thin film is formed on a surface of the substrate opposite to the channel, a back gate electrode is provided outside the insulating thin film, and the insulating thin film is modified with a specific substance that interacts with a substance to be detected. A sensor characterized in that the substance to be detected is interposed between a modification site and the back gate electrode . The sensor according to claim 1, wherein the ultrafine fiber is a carbon nanotube . The sensor according to claim 1, wherein the sensor is a biopolymer that interacts with the substance to be detected and the specific substance . 4. The sensor according to claim 3 , wherein the substance to be detected is an antigen or an antibody, and the specific substance is an antibody or an antigen .

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