JP2004347532A - Biosensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly selective biosensor having sensitivity far better than that of conventional ones. <P>SOLUTION: In the biosensor, a carbon nanotube is connected with a channel section of a field effect transistor or a single-electron type transistor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a biosensor, and more particularly, to a biosensor having a field-effect transistor or single-electron transistor structure. .
[0002]
[Prior art]
The conventionally proposed biosensor forms a thin film having a reactive group selectively reacting with a specific molecule on an electrode, and measures a change in potential when the thin film adsorbs the specific molecule. ing. Specifically, this method detects a glucose amount by forming a thin film having a glucose oxidase on an electrode and measuring a change in a current value accompanying an oxidation reaction with glucose. Regarding this type of biosensor, for example, the following Patent Document 1 and Non-Patent Documents 1 and 2 can be cited.
[0003]
[Patent Document 1]
JP-A-10-260156
[Non-patent document 1]
Aizawa, Chemical Communication. 945 pages (1989)
[0005]
[Non-patent document 2]
Alexander Star, Jean-Christophe P, Gabriel. Keith Bradley, and George Gruner, Vol. 3, No. 4, 459-463 (2003)
[0006]
[Problems to be solved by the invention]
However, since the conventional biosensor is a method of directly detecting the current value associated with the chemical reaction as described above, the sensitivity is low and it is difficult to detect a low concentration of glucose. However, it had a drawback that it was not possible to sufficiently exhibit the characteristic of the property.
[0007]
An object of the present invention is to eliminate such disadvantages in the prior art and to provide a highly selective biosensor with much higher sensitivity than the conventional one.
[0008]
[Means for Solving the Problems]
To achieve the above object, a first means of the present invention is characterized in that a carbon nanotube is connected to a channel portion of a field effect transistor or a single electron transistor.
[0009]
According to a second aspect of the present invention, in the first aspect, a defect is introduced inside the carbon nanotube.
[0010]
According to a third aspect of the present invention, in the first or the second aspect, a protective film such as SiO ₂ is provided on the channel portion, and for example, DNA or the like to be detected is to be detected on the protective film. A biopolymer probe, such as a DNA probe, that selectively reacts or adsorbs with a target biopolymer is formed.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, the present invention employs a field-effect or single-electron transistor structure in which a carbon nanotube is connected to a channel portion, whereby a highly sensitive and highly selective biosensor can be obtained.
[0012]
Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a single-electron biosensor according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing how DNA is detected using the single-electron biosensor.
[0013]
In these figures, 1 is a chip-shaped silicon substrate, 2 is a thin film made of SiO ₂ coated on the silicon substrate 1, and 3 and 4 are source electrodes formed on the thin film 1 at predetermined intervals. Further, in the drain electrode, a pointed end 5, 6 is formed at a portion facing the two electrodes 3, 4. Carbon nanotubes 7 having defects introduced between the tips 5 and 6 of the electrodes 3 and 4 are grown and formed. A channel electrode 8 is formed on the surface of the substrate 1 opposite to the thin film 1. Thus, a biosensor having a single-electron transistor structure is configured.
[0014]
Next, the control of the basic conductivity characteristics of the carbon nanotube will be described.
(1) A catalyst used when applying an electric field or a magnetic field and growing carbon nanotubes in order to arbitrarily design the growth position, direction, number, chirality, characteristics, etc. of the carbon nanotubes which are basic elements of the biosensor device. Optimize the type and shape.
[0015]
FIG. 3 is a schematic configuration diagram showing a method of patterning the catalyst and controlling the position and direction of the carbon nanotube while applying an electric field. In the figure, 1 is a silicon substrate, 2 is a thin film made of SiO ₂ coated on the silicon substrate 1, 9a and 9b are catalyst layers made of nickel or the like patterned on the SiO ₂ thin film 2, and 7 is a catalyst layer. The growth position, direction, number, chirality, characteristics, and the like are arbitrarily controlled by the carbon nanotubes formed between the catalyst layers 9a and 9b by applying an electric field. Reference numeral 10 denotes a reaction vessel, and reference numeral 11 denotes methane gas as a raw material for carbon nanotubes. The length of the grown carbon nanotube is about several μm (for example, about 3 μm), and the diameter is about several nm.
[0016]
(2) Using the carbon nanotubes whose positions, directions, characteristics, and the like are controlled as non-invasive electrodes, create a four-probe shape.
[0017]
In the four-probe method, four needle-like electrodes (for example, electrodes A, B, C, and D) are placed on a sample in a straight line, and a constant distance is provided between two outer probes (for example, electrodes A and D). A current is applied, and a potential difference between two inner probes (for example, electrode B and electrode C) is measured to determine a resistance value. This is a method of calculating the volume resistance value of the sample by multiplying the obtained resistance value by the thickness of the sample and the correction coefficient RCF.
[0018]
(3) The part where the electrode and the channel (carbon nanotube) overlap is 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 (carbon nanotube).
[0019]
(4) Next, the transport characteristics of the carbon nanotube are evaluated. The electric conduction characteristics to be evaluated include ballistic electric conduction characteristics, whether spin injection is possible, and whether spin transport is possible.
[0020]
(5) It has already been confirmed by preliminary experiments by the present inventors that the introduction of defects into carbon nanotubes significantly changes the electrical properties of carbon nanotubes (introducing defects into carbon nanotubes). It has been confirmed in preliminary experiments that a single-electron transistor having a high Coulomb energy of up to 5000 K and operating at room temperature can be formed.
[0021]
Therefore, by introducing defects into the carbon nanotube arbitrarily by STM / AFM processing or electron beam, a carbon nanotube whose electric conductivity can be controlled can be obtained.
[0022]
As a specific example of the method for introducing defects into carbon nanotubes, for example, there is a method in which annealing is performed at substantially the same temperature (for example, about 800 ° C.) as when carbon nanotubes are formed, and then natural cooling is performed. Defects in carbon nanotubes refer to changes in the shape of carbon nanotubes, such as the fact that some of the carbon atoms pop out due to heat and are barely connected in a state where the carbon nanotubes are cut. It is not clear at this time what the structure is.
[0023]
(6) A correlation between the defects in the carbon nanotube and the electrical characteristics of the carbon nanotube is examined. For example, the scanning probe method (Kelvin probe method, Maxwell probe method, etc.) evaluates the density, distribution, and size (size, energy barrier, etc.) of defects, and clarifies the correlation between these and the electrical properties of carbon nanotubes To By grasping the correlation between the defects in the carbon nanotube and the electrical characteristics in this way, a single-electron transistor with good reproducibility and uniformity of the characteristics can be manufactured.
[0024]
(7) The electrical characteristics of the carbon nanotubes can be controlled by controlling the introduction of defects according to the above (6).
[0025]
In the present invention, a single-electron transistor that operates at room temperature can be manufactured using a carbon nanotube into which a defect has been introduced.
[0026]
In order to avoid malfunction due to floating charge or mobile charge, which is a problem in conventional single-electron transistors, the present invention fabricates two carbon nanotube single-electron transistors in close proximity and detects a single charge. In doing so, the output characteristics (room temperature) of both carbon nanotube single electron transistors are ANDed. As a result, both carbon nanotube single-electron transistors operate only when there is a true charge, so that malfunctions due to floating charges and mobile charges can be avoided.
[0027]
In order to further increase the measurement speed, a system that uses the above-described method and operates with an alternating current using a resonance circuit instead of the conventional direct current system was adopted. As described above, a single charge distribution can be measured at room temperature and at high speed without malfunction.
[0028]
FIG. 4 is a diagram showing room temperature Coulomb diamond characteristics of a carbon nanotube single electron transistor. From this room temperature Coulomb diamond characteristic, it can be proved that the carbon nanotube single electron type transistor of the present invention can operate at room temperature.
[0029]
As shown in FIG. 1, a carbon nanotube single electron type transistor is formed on a substrate 1, and as shown in FIG. 2, a chip is coated with a protective film 12 made of SiO ₂ to operate in a solution. _{(2) The} DNA probe 13 is immobilized on the protective film 12. Although the protective film 12 is provided in this example, the protective film 12 may not be provided in some cases.
[0030]
The biosensor according to the present embodiment is installed in a solution 15 in which a target biopolymer 14 such as DNA is dissolved, and the biosensor is operated with an alternating current using a resonance circuit. By measuring the single electron interaction, it is possible to detect the target biopolymer 14 (evaluate the surface charge distribution characteristics).
[0031]
FIG. 5 is a schematic configuration diagram for explaining another embodiment of the present invention. In the case of the present embodiment, the substrate 1 itself is used as a channel (back channel), and electrodes 3 and 4 are provided on the substrate 1 with a carbon nanotube (CNT) 7 interposed therebetween. A concave portion 16 serving as a channel is formed on the rear surface of the substrate 1, and the concave portion 16 can be detected on the rear surface of the substrate 1 by wetting the concave portion 16 with a liquid containing a substance to be detected.
[0032]
FIG. 6 is a schematic configuration diagram for explaining still another embodiment of the present invention. In this embodiment, the substrate 1 itself is used as a channel (back channel), but a probe 17 made of carbon nanotube (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.
[0033]
In the above embodiment, one type of biosensor having a DNA probe was described. However, for example, three carbon nanotube single electron type transistors with an SiO ₂ film are provided on a substrate, and a DNA probe is provided on each SiO ₂ film. It is also possible to separately form a protein probe and a glycolipid probe and simultaneously measure different biopolymers (DNA, protein, glycolipid).
[0034]
In the above embodiment, the case where the surface charge distribution characteristics of DNA are evaluated has been described. However, the present invention is also applicable to detection of other biopolymers such as sugar chains, RNA, amino acids, sugars, and viruses. It is also possible to detect a change in the electronic state in the process of a protein such as rhodopsin emitting protons in response to light, or a change in the electronic state due to a change in the structure of the dye.
[0035]
In the above-described embodiment, an example in which the carbon nanotube is connected to the channel portion of the single-electron transistor is shown. However, the carbon nanotube can be connected to the channel portion of the field-effect transistor.
[0036]
【The invention's effect】
As described above, the present invention connects a carbon nanotube to the channel portion of a field-effect transistor or a single-electron transistor, thereby providing a biosensor with much higher sensitivity and higher selectivity than before. Can be provided.
[Brief description of the drawings]
FIG. 1 is a perspective view of a single-electron biosensor according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing how DNA is detected using the single-electron biosensor.
FIG. 3 is a schematic configuration diagram showing a method for controlling the position and direction of a carbon nanotube in an embodiment of the present invention.
FIG. 4 is a diagram showing room temperature Coulomb diamond characteristics of a carbon nanotube single electron transistor.
FIG. 5 is a schematic configuration diagram of a single-electron biosensor according to another embodiment of the present invention.
FIG. 6 is a schematic configuration diagram of a single-electron biosensor according to still another embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 1 substrate 2 thin film 3 source electrode 4 drain electrode 5, 6 tip 7 carbon nanotube 8 channel electrode 9a, 9b catalyst layer 10 reaction vessel 11 methane gas 12 SiO ₂ protective film 13 DNA probe 14 target biopolymer 15 solution 16 recess 17 needle.

Claims (3)

A biosensor comprising a carbon nanotube connected to a channel of a field effect transistor or a single electron transistor. 2. The biosensor according to claim 1, wherein a defect is introduced inside the carbon nanotube. 3. The biosensor according to claim 1, wherein a protective film is provided on the channel portion, and the biopolymer probe selectively reacts or adsorbs with a target biopolymer to be detected on the protective film. A biosensor characterized in that a biosensor is formed.

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