DEVICE, TUNNEL CURRENT MEASURING APPARATUS, NUCLEIC ACID SEQUENCE READING APPARATUS, TUNNEL CURRENT MEASURING METHOD, AND NUCLEIC ACID SEQUENCE READING METHOD

Provided is a device that facilitates a sample to enter a sample measurement channel in which measuring electrodes are arranged. A device used in measurement of tunnel current includes: a base material; a channel formed in the base material; and a pair of measuring electrodes for measuring tunnel current occurring when a sample passes between the pair of measuring electrodes. The channel includes a sample supply channel, a sample measurement channel in which the measuring electrodes are arranged, a first taper channel arranged between the sample supply channel and the sample measurement channel and having a channel width that decreases from the sample supply channel to the sample measurement channel, and a sample collection channel used for collecting a sample that passed through the sample measurement channel. The width of a connection part between the first taper channel and the sample measurement channel is 20 nm to 200 nm.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from Japanese Patent Application No. 2021-034256, filed Mar. 4, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The disclosure in the present application relates to a device, a tunnel current measuring apparatus, a nucleic acid sequence reading apparatus, a tunnel current measuring method, and a nucleic acid sequence reading method.

Description of the Related Art

Memories using DNA that is a biopolymer are paid attention for their high storage density and storage retention stability. Commercialization of DNA memories requires a technology to read a DNA sequence at a high rate. As a method of reading a DNA sequence, a known exemplary method is to optically detect an elongation reaction in a PCR amplification process by using an optical probe. Devices used for such a method are called a sequencer and have already been commercialized. However, since such a method requires an amplification process such as a PCR, there is a problem of inability of achieving a reading rate exceeding an elongation time (about one second per one base) due to the amplification process. Further, since a PCR is effective only for DNA and thus is not applicable to biomolecules, artificial bases, and the like other than DNA, there also is a problem of a limited storage density that can be achieved with storage in combination of only four types of bases.

As a nucleic acid reading apparatus (method) other than the PCR, there is a method of forming a nanopore (micro through hole) in a thin film and measuring tunnel current when a nucleic acid passes through the nanopore (see Japanese Patent Application Laid-Open No. 2017-509899).

Further, it is desirable to elongate a nucleic acid when reading the nucleic acid. As a technology to elongate a nucleic acid, for example, a technology to provide a base material with a channel having nanowires formed therein and pass a nucleic acid through the spacing between the nanowires to be elongated (see Japanese Patent Application Laid-Open No. 2016-103979) is also known.

It is desirable that a reading apparatus (reading method) of a DNA memory can improve the reading rate of a nucleic acid and read a nucleic acid sequence even with a small amount of a sample. In the reading apparatus (reading method) disclosed in Japanese Patent Application Laid-Open No. 2017-509899, a chamber is formed by a thin film as a boundary in which a nanopore is formed, and tunnel current occurring when a nucleic acid supplied into the chamber passes through the nanopore is measured. However, the opening of the nanopore is formed so as to be substantially perpendicular to the thin film, and the area of the opening to the thin film is significantly small. Thus, a sample liquid containing nucleic acids comes into contact with the entire thin film, and this causes a problem that the nucleic acids in the sample liquid have difficulty in entering the opening.

SUMMARY OF THE INVENTION

An object of the disclosure of the present application is to provide a device that solves the above problem, a tunnel current measuring apparatus and a tunnel current measuring method using the device, and a nucleic acid sequence reading apparatus and a nucleic acid sequence reading method.

The disclosure of the present application relates to a device, a tunnel current measuring apparatus, a nucleic acid sequence reading apparatus, a tunnel current measuring method, and a nucleic acid sequence reading method illustrated below.

(1) A device used in measurement of tunnel current, the device including:

a base material;

a channel formed in the base material; and

a pair of measuring electrodes for measuring tunnel current occurring when a sample passes between the pair of measuring electrodes,

wherein the channel includes

a sample supply channel,

a sample measurement channel in which the measuring electrodes are arranged,

a first taper channel arranged between the sample supply channel and the sample measurement channel and having a channel width that decreases from the sample supply channel to the sample measurement channel, and

a sample collection channel used for collecting a sample that passed through the sample measurement channel,

wherein the first taper channel has a shape that suppresses occurrence of an electroosmotic flow, and

wherein a width of a connection part between the first taper channel and the sample measurement channel is 20 nm to 200 nm.

(2) The device according to (1) described above,

wherein W2/W1is 10 to 20, where W1denotes the width of the connection part between the first taper channel and the sample measurement channel, and W2denotes the width of a connection part between the first taper channel and the sample supply channel, and

wherein L1/W2is 0.5 to 5, where L1denotes a length between the connection part between the first taper channel and the sample measurement channel and the connection part between the first taper channel and the sample supply channel.

(3) The device according to (1) or (2) described above, wherein the length of the sample measurement channel is 20 nm to 1000 nm.

(4) The device according to any one of (1) to (3) described above further including a second taper channel arranged between the sample measurement channel and the sample collection channel and having a channel width that increases from the sample measurement channel to the sample collection channel.

(5) The device according to any one of (1) to (4) described above, wherein W1=W1a, W2=W2a, and L1=L1aare satisfied, where W1adenotes a width of a connection part between the sample measurement channel and the second taper channel, W2adenotes a width of a connection part between the second taper channel and the sample collection channel, and L1adenotes a length between the connection part between the second taper channel and the sample measurement channel and the connection part between the second taper channel and the sample collection channel.

(6) A tunnel current measuring apparatus including: the device according to any one of (1) to (5) described above; an electrophoresis power source; and a measuring unit,

wherein the electrophoresis power source applies a voltage of 10 mV to 5 V to an electrophoresis electrode.

(7) A nucleic acid sequence reading apparatus including: the tunnel current measuring apparatus according to (6) described above; and an analysis unit,

wherein the sample is a nucleic acid, and

wherein the analysis unit identifies a nucleic acid sequence from a measurement result of tunnel current acquired by the tunnel current measuring apparatus.

(8) A tunnel current measuring method using a device,

wherein a device includes

a base material,

a channel formed in the base material, and

a pair of measuring electrodes for measuring tunnel current occurring when a sample passes between the pair of measuring electrodes,

wherein the channel includes

a sample supply channel,

a sample measurement channel in which the measuring electrodes are arranged,

a first taper channel arranged between the sample supply channel and the sample measurement channel and having a channel width that decreases from the sample supply channel to the sample measurement channel, and

a sample collection channel used for collecting a sample that passed through the sample measurement channel,

wherein the first taper channel has a shape that suppresses occurrence of an electroosmotic flow, and

wherein a width of a connection part between the first taper channel and the sample measurement channel is 20 nm to 200 nm,

the tunnel current measuring method including:

a sample electrophoresis step of causing electrophoresis of a sample in the sample supply channel toward the sample collection channel by applying a voltage to the sample supply channel and the sample collection channel; and

a measuring step of measuring tunnel current occurring when a sample passes through a gap between the pair of measuring electrodes arranged in the sample measurement channel.

(9) The tunnel current measuring method according to (8) described above, wherein in the sample electrophoresis step, a voltage of 10 mV to 5 V is applied.

(10) The tunnel current measuring method according to (8) or (9) described above,

wherein W2/W1is 10 to 20, where W1denotes the width of the connection part between the first taper channel and the sample measurement channel, and W2denotes the width of a connection part between the first taper channel and the sample supply channel, and

wherein L1/W2is 0.5 to 5, where L1denotes a length between the connection part between the first taper channel and the sample measurement channel and the connection part between the first taper channel and the sample supply channel.

(11) A nucleic acid sequence reading method, wherein the sample is a nucleic acid,

the method including a nucleic acid sequence reading step of identifying a nucleic acid sequence from a measurement result of tunnel current acquired by the measuring step of the tunnel current measuring method according to any one of (8) to (10) described above.

The use of the device disclosed in the present application facilitates a sample to enter the sample measurement channel in which the measuring electrodes are arranged.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

A device, a tunnel current measuring apparatus, a nucleic acid sequence reading apparatus, a tunnel current measuring method, and a nucleic acid sequence reading method will be described below in detail with reference to the drawings.

In this specification, members having the same type of function are labeled with the same or similar reference symbols. Further, repeated description for the members labeled with the same or similar reference symbols may be omitted.

In this specification, a numerical range expressed by using “to” means a range including numerical values preceding and subsequent to “to” as the lower limit and the upper limit, respectively. A numerical value, a numerical range, and a qualitative expression (for example, an expression of “the same”, “substantially”, or the like) is to be construed as indicating a numerical value, a numerical range, and a nature including an error generally tolerated in the field of the art.

Further, the position, the size, the range, or the like of each component illustrated in the drawings may not necessarily represent an actual position, an actual size, an actual range, or the like for easier understanding. Thus, the disclosure of the present application is not necessarily limited to the position, the size, the range, or the like disclosed in the drawings.

First Embodiment of Device

A device1according to a first embodiment will be described with reference toFIG. 1AtoFIG. 1C.FIG. 1Ais a top view of the device1,FIG. 1Bis a sectional view on arrow X-X ofFIG. 1A, andFIG. 1Cis a sectional view on arrow Y-Y ofFIG. 1A.FIG. 2is a schematic diagram illustrating an example of a fabrication procedure for the device1.

The device1includes a base material2, a channel3formed in the base material2, and a pair of measuring electrodes4aand4bused for measuring tunnel current occurring when a sample passes therebetween (hereafter, the pair of measuring electrodes4aand4bmay be referred to as “measuring electrode(s)4”). The channel3includes a sample supply channel31, a sample measurement channel32in which the measuring electrodes4are arranged, a first taper channel33arranged between the sample supply channel31and the sample measurement channel32and having a channel width decreasing from the sample supply channel31to the sample measurement channel32, and a sample collection channel34used for collecting a sample that has passed through the sample measurement channel32. The width W1of a connection part between the first taper channel33and the sample measurement channel32is 20 nm to 200 nm.

Although a second taper channel35is depicted in the example illustrated inFIG. 1A, the second taper channel35is an optional, additional feature in the device1according to the first embodiment. The sample collection channel34may be directly coupled to the sample measurement channel32as long as a sample flowing out of the sample measurement channel32can be collected.

The device1can be manufactured by using nanochannel-integrated mechanically controllable break junction, for example. An example of a manufacturing procedure for the device1will be illustrated with reference toFIG. 2. Note that mechanically controllable break junction (MCBJ) to fabricate the pair of measuring electrodes4is described in Japanese Patent Application Laid-Open No. 2019-525766, Japanese Patent Application Laid-Open No. 2017-509899 described above, M. Tsutsui, K., Shoji, M. Taniguchi, T. Kawai, Nano Lett., 345(2008), M. Tsutsui, M. Taniguchi, T. Kawai, Appl. Phys. Lett. 93, 163115(2008), and the like, for example.

(1) An insulating layer2bmade of an insulating material such as polyimide is formed on a substrate2amade of silicon or the like.

(2) A metal layer used for forming the measuring electrode4is deposited on the insulating layer2bby electron beam lithography (EB lithography).

(3) A deposition layer2cmade of SiO2or the like is formed by chemical deposition. A resist layer2dis laminated on the deposition layer2cby spin-coating.

(4) A pattern of the channel3including the sample measurement channel32is formed by electron beam lithography so as to be overlapped with the metal layer used for forming the measuring electrode4.

(5) The channel3is formed by dry etching. The measuring electrode4is then formed by forming a gap (nanogap G) in the metal layer by MCBJ. Note that, although the sample measurement channel32is etched up to a part under the measuring electrode4in the example illustrated inFIG. 2, there may be no channel in a portion under the measuring electrode4. Further, although one measuring electrode4is provided in the example illustrated inFIG. 2, two or more measuring electrodes4may be formed.

(6) A cover member5is attached, and one or more holes used for supply of a sample liquid, insertion of an electrophoresis electrode, or the like are formed in the cover member5, if necessary. Note that the cover member5can be attached at least when ion current is measured.

The substrate2ais not particularly limited as long as it is a material generally used in the field of semiconductor manufacturing technologies. The material of the substrate2amay be, for example, Si, SiOx, SiNx, Ge, Se, Te, GaAs, GaP, GaN, InSb, InP, or the like.

The insulating layer2bis also not particularly limited as long as it is a material generally used in the field of semiconductor manufacturing technologies. The material of the insulating layer2bmay be, for example, an insulating polymer such as polyimide, polypropylene, polyvinyl chloride, polystyrene, high density polyethylene (HDPE), polyacetal (POM), polyepoxy, or the like; an insulating semiconductor metal oxide such as SiO2, aluminum oxide, or the like; or the like.

The material forming the deposition layer2cmay be an insulating polymer such as polyimide, polypropylene, polyvinyl chloride, polystyrene, high density polyethylene (HDPE), polyacetal (POM), polyepoxy, or the like; an insulating semiconductor metal oxide such as SiO2, aluminum oxide, or the like; or the like.

The material forming the measuring electrode4is not particularly limited as long as it can be used for measuring tunnel current. The material may be, for example, gold, platinum, silver, palladium, tungsten, an alloy of these metals, or the like.

A photoresist used in electron beam lithography and a reagent used in development, etching, and the like are not particularly limited as long as they are materials generally used in the field of micromachining technologies. Further, a spin coater and an apparatus used for etching are also not particularly limited as long as they are devices generally used in the field of micromachining technologies.

The cover member5is not particularly limited as long as it is made of a material that can be attached to the base material2in which the channel3is formed. The material of the cover member5may be, for example, polymethyl disiloxane (PDMS) or the like. The cover member5and the base material2can be attached to each other by ozone plasma treatment or the like, for example.

Note that, in this specification, the term “base material” means a material part that serves as a base used for forming the channel3. In the example illustrated inFIG. 2, the base material2includes the substrate2a, the insulating layer2b, the deposition layer2c, and the resist layer2d. Note thatFIG. 2merely illustrates one example of the fabrication procedure for the device1in which the measuring electrodes4are arranged in the sample measurement channel32. There may be addition of another step or deletion of some of the above steps as long as the device1achieves the advantageous effect disclosed in the present application. For example, the resist layer2dmay be removed after the channel3is formed by etching. In such a case, the resist layer2dis not included in the base material2. Further, the device1may be fabricated by an electron beam engraving method, nano-printing, or the like.

Further, for easier understanding, detailed depiction of the substrate2a, the insulating layer2b, the deposition layer2c, and the resist layer2dis omitted in the example illustrated inFIG. 1AtoFIG. 1C, and these components are depicted as the base material2.

Application of a voltage to the sample supply channel31and the sample collection channel34causes electrophoresis force to be provided to a sample and increases the moving velocity of the sample. This results in an improved measuring rate of a sample compared to a case where no electrophoresis force is provided. In contrast, when a voltage is applied to the channel3to provide electrophoresis force to a sample, a larger sectional area of the channel3requires a larger voltage.

Reading of a nucleic acid from tunnel current is performed by identifying a difference in the measured current value in the order of picoampere. The present inventors have newly found from various experiment results that, when a voltage at a level that can provide electrophoresis force is applied to a nucleic acid supplied in the channel of the order of micrometer disclosed in Application Laid-Open No. 2016-103979, the measuring electrode4detects noise due to the voltage applied for electrophoresis and is unable to identify a nucleic acid. The disclosure of the present application is based on this finding.

The device1disclosed in the present application can provide electrophoresis force to a sample at a low voltage and thus can measure tunnel current with less noise due to the voltage applied for electrophoresis. Therefore, the device1can be preferably used for identifying a nucleic acid as described above, and the sample is not limited to a nucleic acid. With any sample having surface charges and moved by electrophoresis, tunnel current with less noise due to a voltage applied for electrophoresis can be measured. The sample may be, for example, a peptide, a lipid, a glycan, a synthetic polymer, or the like. Note that, in this specification, when “sample liquid” is referred to, the “sample liquid” means a liquid in which the sample described above is dissolved or dispersed in a solvent used for electrophoresis.

The device1requires the sample supply channel31having a predetermined size for supplying a sample liquid thereto. Thus, the device1employs the structure in which the width of the sample measurement channel32in which the measuring electrodes4are arranged is made narrower (smaller) and the sample supply channel31and the sample measurement channel32are connected via the first taper channel33.

As described above, to reduce noise due to a voltage applied for electrophoresis, it is preferable that the width of the sample measurement channel32be narrower. When the width of the connection part between the first taper channel33and the sample measurement channel32is denoted as W1, W1can be 200 nm or less, 180 nm or less, 160 nm or less, 140 nm or less, 120 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less. On the other hand, there is no limitation in the lower limit of W1as long as it is within a manufacturable range, and the lower limit of W1can be, but is not limited to, 20 nm or greater, 25 nm or greater, or 30 nm or greater, for example.

The width of the sample measurement channel32may be the same along the entire length or may vary along the length as long as it is within a range that does not affect analysis of a measurement result or the like. In the example illustrated inFIG. 1A, when the end opposite to the width W1of the sample measurement channel32is denoted as W1a, W1amay be the same as W1or may be larger or smaller than W1.

The gap between the pair of measuring electrodes4aand4b(gap G, seeFIG. 1B) is not particularly limited as long as it is within the range that enables measurement of tunnel current occurring when a sample passes therebetween. The gap G can be, but is not limited to, 0.1 nm or greater, 0.3 nm or greater, 0.5 nm or greater, 0.7 nm or greater, or 0.9 nm or greater, for example. On the other hand, the upper limit of the gap G can be, but is not limited to, 50 nm or less, 30 nm or less, 10 nm or less, 8 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm or less, or 1 nm or less, for example.

The length of the measuring electrode4(the length of the gap G in the same direction as L2ofFIG. 1A) is also not particularly limited as long as it is within a range that enables measurement of tunnel current occurring when a sample passes therebetween. The length can be, but is not limited to, 1000 nm or less, 800 nm or less, 600 nm or less, 400 nm or less, 200 nm or less, 100 nm or less, 80 nm or less, or 60 nm or less, for example.

Note that, for easier cutting in MCBJ, a smaller deposition amount of the measuring electrodes4(in a direction orthogonal to the direction of the length of the measuring electrode4or in the direction H inFIG. 1B, hereafter, which may be denoted as “thickness”) is preferable. An increase in the thickness of the measuring electrode4may make it difficult to control a cutting place and result in a rough cut surface of the fabricated gap G. Thus, the thickness of the measuring electrode4can be, but is not limited to, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less, for example. The lower limit of the thickness of the measuring electrode4is not particularly limited as long as tunnel current can be measured and can be, but is not limited to, 2 nm or greater, 4 nm or greater, 6 nm or greater, 8 nm or greater, 10 nm or greater, 15 nm or greater, or 20 nm or greater, for example.

As described above, it is preferable that the length of the measuring electrode4be larger than the thickness thereof in order to reduce the thickness of the measuring electrode4to form the gap G by MCBJ. The ratio of length/thickness may be, but is not limited to,10to100, for example.

Electrodes are formed by MCBJ also for the device disclosed in Japanese Patent Application Laid-Open No. 2017-509899. Thus, the thickness of the electrode deposited on the thin film is thin for the reason described above. Further, in the device disclosed in Japanese Patent Application Laid-Open No. 2017-509899, since nanopores are formed in the thin film, a sample moves in the thickness direction of the gap G of the electrodes. On the other hand, when the device1disclosed in the present application is used to measure tunnel current of a sample, the sample moves in the longitudinal direction of the measuring electrodes4. That is, the moving direction of a sample with respect to the gap G differs between the device1disclosed in the present application and the device disclosed in Japanese Patent Application Laid-Open No. 2017-509899. In the case of the device disclosed in the present application, since an electric field is applied in the longitudinal direction of the measuring electrodes4, this results in a gradual intensity of the electric field and easier control of the moving velocity of a sample. In contrast, in the case of the device of Japanese Patent Application Laid-Open No. 2017-509899, since an electric field is applied in the thickness direction of the electrode (the thickness of the electrode is smaller than the length of the electrode), this results in a steep electric field and makes it difficult to control the moving velocity of a sample. As set forth, the device1disclosed in the present application achieves an advantageous effect of easier control of the moving velocity of a sample passing through the gap G of the measuring electrodes4compared to the device disclosed in Japanese Patent Application Laid-Open No. 2017-509899.

The length L2of the sample measurement channel32is not particularly limited as long as it is within a range that enables measurement of tunnel current occurring when a sample passes therethrough. If the length L2is too long, the entire channel of the device1will be longer. In contrast, if the length L2is too short, when the sample is an elongate sample (hereafter, also referred to as “elongate sample”) such as a nucleic acid or a peptide, it will be difficult to maintain a state where an elongate sample is elongated. The length L2can be, but is not limited to, 20 nm or greater, 25 nm or greater, 30 nm or greater, 35 nm or greater, 40 nm or greater, 45 nm or greater, or 50 nm or greater. Further, the length L2can be 2000 nm or less, 1500 nm or less, 1000 nm or less, 800 nm or less, 600 nm or less, 400 nm or less, 200 nm or less, 180 nm or less, 160 nm or less, 140 nm or less, 120 nm or less or 100 nm or less. The length L2is naturally required to be longer than the length of the gap G part of the measuring electrodes4.

To reduce noise due to a voltage applied for electrophoresis, it is preferable that the depth H of the channel3be also smaller. The depth H of the channel3can be, but is not limited to, 200 nm or less, 180 nm or less, 160 nm or less, 140 nm or less, 120 nm or less, 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, or 50 nm or less, for example. On the other hand, the depth H of the channel3can be 20 nm or greater, 25 nm or greater, or 30 nm or greater, for example.

In the device1according to the first embodiment, while the length of the first taper channel33(L1inFIG. 1A) and the width of the sample supply channel31(the connection part to the first taper channel33, W2inFIG. 1A) are not particularly limited, the width of the channel3is desirably as small as possible. Note that the sample supply channel31may have a wider part having a width larger than W2, if necessary, for supplying a sample liquid.

In the device1according to the first embodiment, while the width of the sample collection channel34and the length of the optionally, additionally provided second taper channel35(L1ainFIG. 1A) are not particularly limited, the width of the channel3is desirably as small as possible. Note that, to collect a sample, the sample collection channel34may have a wider part having a width larger than W2a, if necessary.

In comparison to the devices disclosed in Japanese Patent Application Laid-Open No. 2017-509899 and Japanese Patent Application Laid-Open No. 2016-103979, the following advantageous effects are achieved when the device1according to the first embodiment is used to measure tunnel current.

(1) A sample contained in a sample liquid supplied to the sample supply channel31is guided to the sample measurement channel32via the first taper channel33by electrophoresis. Therefore, even with a small amount of a sample such as a nucleic acid contained in the sample liquid, the sample can be more reliably guided to the measuring electrodes4than in the nanopore scheme disclosed in Japanese Patent Application Laid-Open No. 2017-509899.

(2) The nanopore of the device disclosed in Japanese Patent Application Laid-Open No. 2017-509899 is a three-dimensional hole formed in a thin film. It is thus very difficult to change the size of the hole inside the nanopore. Further, in the device disclosed in Japanese Patent Application Laid-Open No. 2017-509899, a chamber is formed such that a sample liquid comes into contact with the thin film. It is thus very difficult to design openings of the chamber and the nanopore without a level difference therebetween. That is, there is a limitation in channel design to facilitate a sample such as a nucleic acid contained in a sample liquid to flow into the openings. In contrast, in the device1, since the channel3is formed in the base material2, the channel3having a desired shape can be easily formed by electron beam lithography.

(3) The value of the width of the sample measurement channel32is made significantly small and a taper is formed from the sample supply channel31to the sample measurement channel32, and thereby the sectional area of the channel3can be smaller than in the embodiment disclosed in Japanese Patent Application Laid-Open No. 2016-103979. Thus, a voltage for providing electrophoresis force to a sample can be reduced, and noise caused by the voltage applied for electrophoresis can be reduced when tunnel current is measured.

Optional, Additional Modified Example of Device1

An optional, additional modified example (limitation) of the device1will be described with reference toFIG. 1AtoFIG. 1C. Note that the optional, additional modified example of the device1is an embodiment that further limits each feature of the embodiment of the device1. Thus, only the limitations will be described for the optional, additional modified example of the device1, and repeated description for the features already described in the first embodiment will be omitted.

Modified Example 1

In the device1, when the width of the connection part between the first taper channel33and the sample measurement channel32is denoted as W1, and the width of the connection part between the first taper channel33and the sample supply channel31is denoted as W2, the lower limit of W2/W1may be 2 or greater, 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, 9 or greater, or 10 or greater, and the upper limit of W2/W1may be 50 or less, 40 or less, 30 or less, or 20 or less. Further, when the length between the connection part between the first taper channel33and the sample measurement channel32and the connection part between the first taper channel and the sample supply channel is denoted as L1, the lower limit of L1/W2may be 0.3 or greater, 0.4 or greater, or 0.5 or greater, and the upper limit of L1/W2may be 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, or 5 or less.

When the shape of the first taper channel33is in accordance with the ratio described above, the following advantageous effects are achieved in addition to the advantageous effects described for the device1according to the first embodiment.

(1) With the first taper channel33being formed at the ratio described above, this can facilitate an elongate sample in a sample liquid to be straightened.

(2) While an electroosmotic flow (EOF) occurs inside the channel when the channel is filled with a solvent and a voltage is applied thereto, a reverse flow occurs in a region along the wall. When the first taper channel33is formed in the range described in the modified example 1, occurrence of the EOF is likely to be suppressed, and an acceleration effect due to an enhanced electric field is obtained because of the shape of the first taper channel33. Therefore, the elongate sample contained in a sample liquid is straightened and is likely to be introduced in the sample measurement channel32.

Modified Example 2

The device1may include the second taper channel35arranged between the sample measurement channel32and the sample collection channel34and having the channel width increasing from the sample measurement channel32to the sample collection channel34.

When the device1includes the second taper channel35, an advantageous effect of preventing an elongate sample from being stacked at the outlet of the sample measurement channel32to facilitate passage of the elongate sample is provided in addition to the advantageous effects described for the device1according to the first embodiment and modified example 1.

Modified Example 3

In addition to the limitation to modified example 2, the device1may satisfy W1=W1a, W2=W1, and L1=L1a, where W1adenotes the width of the connection part between the sample measurement channel32and the second taper channel35, W2adenotes the width of the connection part between the second taper channel35and the sample collection channel34, and L1adenotes the length between the connection part between the second taper channel35and the sample measurement channel32and the connection part between the second taper channel35and the sample collection channel34. In other words, the channel3may be formed to be symmetrical about the sample measurement channel32.

When the channel3of the device1is formed to be symmetrical about the sample measurement channel32, the following advantageous effects are achieved in addition to the advantageous effects described for the device1according to the first embodiment, modified example 1, and modified example 2.

(1) By exchanging the positive pole and the negative pole of the electrophoresis electrodes, it is also possible to measure a sample passing between the measuring electrodes4from the reverse direction. For example, since it is possible to confirm the same sequence from different directions when reading the sequence of a nucleic acid, a peptide, or the like, improvement in reading accuracy is expected.

Other Modified Examples

The device1disclosed in the present application is not limited to the first embodiment and modified examples 1 to 3 described above and may be modified or changed as appropriate within the scope of the technical concept disclosed in the present application. Also, some of the components can be omitted in each embodiment.

For example, the manufactured device1may be hydrophilized so as to facilitate flow of a sample liquid. The hydrophilizing method may be plasma treatment, surfactant treatment, polyvinyl pyrrolidone (PVP) treatment, photocatalytic treatment, SiO2film coating, or the like. For example, it is possible to introduce a hydroxy group to the surface by performing plasma treatment for 10 to 30 seconds on the surface of the device1on which the channel3is formed. Further, the device1may have the cover member5. Furthermore, electrodes for applying voltages for electrophoresis may be formed to the sample supply channel31and the sample collection channel34of the device1. The electrophoresis electrode will be described later.

Embodiment of Tunnel Current Measuring Apparatus

An embodiment of the tunnel current measuring apparatus100will be described with reference toFIG. 3.FIG. 3is a schematic diagram illustrating an overview of the embodiment of the tunnel current measuring apparatus100. The tunnel current measuring apparatus100includes an electrophoresis power source (hereafter, also referred to as “first power source”)6and a measuring unit7in addition to the device1. The measuring unit7includes a tunnel current detection unit (hereafter, also referred to as “detection unit”)7aand a tunnel current measuring power source (hereafter, also referred to as “second power source”)7b.

In the example illustrated inFIG. 3, an electrophoresis first electrode (hereafter, also referred to as “first electrode”)61is formed at a part in contact with a sample liquid inside the sample supply channel31, and an electrophoresis second electrode (hereafter, also referred to as “second electrode”)62is formed at a part in contact with a solvent inside the sample collection channel34. The first electrode61and the second electrode62may be components of the device1or may be components of the tunnel current measuring apparatus100.

The first electrode61and the second electrode62can be formed of a known conductive metal such as Ag/AgCl, aluminum, copper, platinum, gold, silver, titanium, or the like. The first electrode61and the second electrode62can may be formed on the base material2or may be a separate member from the device1and inserted via a hole of the cover member5.

FIG. 3illustrates an example in which two first power sources6of a first power source6aconnected to the first electrode61and a first power source6bconnected to the second electrode62are used to apply voltages for electrophoresis. In the example illustrated inFIG. 3, since two power sources are used as the first power source6, the voltages can be separately increased and decreased. Note that the example illustrated inFIG. 3is a mere example, and the disclosure is not limited thereto. A single first power source6may be provided, for example, as long as a voltage for electrophoresis described later can be applied. In the tunnel current measuring apparatus100disclosed in the present application, with a significantly smaller width of the channel3, in particular, the sample measurement channel32of the device1, a voltage required for electrophoresis of a sample can be reduced. Thus, the measuring unit7can obtain a measurement value of tunnel current with a small noise component when measuring tunnel current occurring when a sample passes through the gap between the measuring electrodes4. Therefore, the obtained measurement result can be preferably used for use of identification of the sequence of a nucleic acid or a peptide, analysis of a lipid, a glycan, or a synthetic polymer, or the like.

If the voltage applied by the first power source6is too low, the moving velocity of a sample is slow, and a long time is required for measurement. The voltage applied by the first power source6can be, but is not limited to, 10 mV or higher, 15 mV or higher, 20 mV or higher, 25 mV or higher, or 30 mV or higher, for example. On the other hand, the upper limit of the voltage applied by the first power source6can be set as appropriate taking into consideration of accuracy of an analysis unit when an obtained measurement result is analyzed, the width of the channel3, and the like. The upper limit of the voltage applied by the first power source6can be, but is not limited to, 5 V or lower, 3 V or lower, 1 V or lower, 500 mV or lower, 300 mV or lower, 100 mV or lower, 90 mV or lower, 80 mV or lower, 70 mV or lower, 60 mV or lower, or 50 mV or lower, for example. Note that a measurement result of tunnel current obtained by the tunnel current measuring apparatus100may be analyzed by an analysis unit that is a separate component from the tunnel current measuring apparatus100. Therefore, the analysis unit is not an essential component in the tunnel current measuring apparatus100.

A detection unit7aof the measuring unit7is not particularly limited as long as it has a component that can measure a change in tunnel current occurring when a sample passes through the gap between the pair of measuring electrodes4aand4bacross which a voltage is applied by a tunnel current measuring power source (hereafter, also referred to as “second power source”)7b. For example, since a change in occurring tunnel current is of the order of picoampere, a known ammeter that can measure current of the order of picoampere can be used. Further, the current may be calculated from a voltage measured by a voltmeter. The measuring unit7may optionally, additionally include a current amplifier, a noise removal device, an analog-to-digital (A/D) converter, or the like. When the measuring unit7includes a current amplifier, a noise removal device, an A/D converter, or the like, data that will be easily analyzed can be provided instead of raw data of measured tunnel current values. Alternatively, the measuring unit7may have only the component that can measure a change in tunnel current, and the current amplifier, the noise removal device, the A/D converter, or the like may be components of the analysis unit8.

The second power source7bapplies a voltage across the pair of measuring electrodes4aand4b. The voltage applied by the second power source7bis not particularly limited as long as tunnel current can be measured. The lower limit of the voltage applied by the second power source7bcan be, but is not limited to, 20 mV or higher, 50 mV or higher, or 100 mV or higher, and the upper limit thereof can be, but is not limited to, 750 mV or lower, 500 mV or lower, 250 mV or lower, or the like, for example. A specific configuration of the second power source7bis not particularly limited, and a known power source device can be used.

The use of the tunnel current measuring apparatus100disclosed in the present application to measure tunnel current achieves an advantageous effect that a measurement result of tunnel current with a less noise component due to a voltage applied for electrophoresis can be obtained.

Embodiment of Nucleic Acid Sequence Reading Apparatus

An embodiment of a nucleic acid sequence reading apparatus100awill be described with reference toFIG. 4.FIG. 4is a schematic diagram illustrating an overview of the embodiment of the nucleic acid sequence reading apparatus100a. The nucleic acid sequence reading apparatus100ais the same as the tunnel current measuring apparatus100except that the nucleic acid sequence reading apparatus100aincludes, in addition to the tunnel current measuring apparatus100, the analysis unit8as an essential component that identifies a nucleic acid sequence from a measurement result of tunnel current acquired by the tunnel current measuring apparatus100. Thus, the analysis unit8will be mainly described in the embodiment of the nucleic acid sequence reading apparatus100a, and repeated description for the features already described in the embodiment of the tunnel current measuring apparatus100will be omitted. Thus, even without explicit description in the embodiment of the nucleic acid sequence reading apparatus100a, naturally, the features already described in the embodiment of the tunnel current measuring apparatus100can be employed.

The analysis unit8identifies a nucleic acid sequence from a measurement result of tunnel current acquired by the tunnel current measuring apparatus100. More specifically, the analysis unit8calculates conductance from a measurement value of tunnel current. When tunnel current is measured, the conductance can be calculated by dividing a measurement value of the tunnel current by a voltage applied across the pair of measuring electrodes4aand4b. The conductance calculated from tunnel current occurring when a nucleic acid passes between the pair of measuring electrodes4aand4bvaries in accordance with the type of the nucleic acid. Therefore, since the type of a nucleic acid can be identified based on calculated conductance, a nucleic acid sequence can be read through time series analysis of measurement values of tunnel current.

Note that the analysis unit8may perform up to the conductance analysis described above, and a separate device from the analysis unit8may perform identification of a specific nucleic acid name, such as adenine (A), guanine (G), cytosine (C), thymine (T), uracil (U), or the like. Alternatively, the analysis unit8may be provided with a storage unit that stores conductance corresponding to types of nucleic acids, and the analysis unit8may directly read a nucleic acid sequence from a measurement result of tunnel current by comparing calculated conductance with conductance written in the storage unit. In this specification, “identifying a nucleic acid sequence” encompasses providing conductance information that can identify a type of a nucleic acid in addition to specifically identifying a type of a nucleic acid.

Note that, in this specification, “nucleic acid” includes an artificial nucleic acid in addition to the nucleic acids described above forming DNA and RNA. Examples of the artificial nucleic acid may be, but is not limited to, the following artificial nucleic acids, for example.

Addition of different types of artificial nucleic acids to natural nucleic acids can increase the density of a nucleic acid memory by increased bits.

The nucleic acid sequence reading apparatus100amay optionally, additionally include a display unit9that displays a measured tunnel current value and/or a result analyzed by the analysis unit8, a program memory10that stores a program in advance that causes the analysis unit8or the display unit9to function, and a control unit11that reads and executes the program stored in the program memory10. The program may be stored in the program memory10in advance or may be stored in a storage medium and then stored in the program memory10by using installing means.

As the display unit9, a known display device such as a liquid crystal display, a plasma display, an organic EL display, or the like can be used.

Embodiment of Tunnel Current Measuring Method and Nucleic Acid Sequence Reading Method

Next, a tunnel current measuring method using the tunnel current measuring apparatus100and a nucleic acid sequence reading method using the nucleic acid sequence reading apparatus100awill be described with reference toFIG. 5.FIG. 5is a flowchart of the tunnel current measuring method and the nucleic acid sequence reading method. The embodiment of the tunnel current measuring method includes a sample electrophoresis step (ST1) and a tunnel current measuring step (ST2). The embodiment of the nucleic acid sequence reading method includes a nucleic acid sequence reading step (ST3) in addition to the sample electrophoresis step (ST1) and the tunnel current measuring step (ST2).

The sample electrophoresis step (ST1) is performed by supplying a sample liquid to the sample supply channel31, supplying a solvent to the sample collection channel34, and applying voltages to the first electrode61and the second electrode62. The supplied sample liquid or the solvent is permeated by capillary force and thereby liquid junction is provided in in the first taper channel33, the sample measurement channel32, and the second taper channel35formed if necessary. The solvent used for fabricating the sample liquid can be any conductive solvent. The solvent may be, but is not limited to, ultrapure water, a buffer liquid, or the like, for example. The ultrapure water can be manufactured by using Milli-Q (registered trademark) Integral 3 (device name) manufactured by EMD Millipore (Milli-Q (registered trademark) Integral 33/5/1015 (catalog number)), for example. The buffer liquid may be a known buffer for electrophoresis, such as TE buffer, TBE buffer, or the like. The concentration of the buffer can be adjusted as appropriate within a range that enables electrophoresis, such as 1 μM or less, for example, without being limited thereto. Further, the sample liquid may be a surfactant such as polyvinyl-pyrrolidone (PVP) or otherwise an amphiphilic chemical, if necessary, in order to reduce influence of an electroosmotic flow (EOF).

In the tunnel current measuring step (ST2), tunnel current occurring when the sample passes through the gap between the pair of measuring electrodes4aand4barranged in the sample measurement channel32is measured.

The nucleic acid sequence reading step (ST3) is performed when the sample is a nucleic acid. In the nucleic acid sequence reading step (ST3), a nucleic acid sequence is identified by the method described above (in the embodiment of the nucleic acid sequence reading apparatus) from the tunnel current value obtained by the tunnel current measuring step (ST2). Note that the electrophoresis step (ST1), the tunnel current measuring step (ST2), and the nucleic acid sequence reading step (ST3) may be performed in advance by using a nucleic acid having a known sequence, and the type of a nucleic acid and the calculated conductance may be associated with each other and stored in the storage unit, if necessary. Further, when the sample is a peptide, “nucleic acid” can be replaced with “amino acid”.

While details of the disclosure of the present application will be specifically described with Examples below, each Example is intended to provide a reference for a specific aspect. These illustrations are intended to neither limit nor express to limit the scope of the disclosure in the present application.

EXAMPLES

Fabrication of Device1

The device was fabricated in accordance with the procedure illustrated inFIG. 2. The specific procedure was as follows.

(1) The polyimide insulating layer2bwas formed on the silicon substrate2a.

(2) A metal layer used for forming the measuring electrode4on the insulating layer2bwas deposited on the insulating layer2bby using electron beam lithography and lift-off technology. ZEP520A was used for the resist, and gold was used for the material of the metal layer used for forming the measuring electrode4.

(3) The SiO2deposition layer2cwas formed by chemical deposition. The resist layer2dwas laminated on the deposition layer2cby spin-coating. ZEP520A was used for the resist.

(4) The pattern of the channel3including the sample measurement channel32was formed so as to overlap the metal layer used for forming the measuring electrode4by electron beam lithography.

(5) The channel3was formed by dry etching. The substrate2awas folded to form a gap (nanogap G) in the material layer by MCBJ, and thereby the measuring electrode4was formed.

(6) The cover member5made of PDMS in which a supply hole for a sample liquid and an insertion hole for an electrophoresis electrode were formed was fabricated by electron beam lithography. The base material2in which the channel3was formed and the cover member5were treated by ozone plasma and bonded to each other. Ag/AgCl was used for the electrophoresis electrode, and the electrophoresis electrode was inserted from a hole formed in the cover member5.

FIG. 6Ais a SEM photograph near the measuring electrodes4and the sample measurement channel32in which the measuring electrodes4are arranged of the device1fabricated in Example 1.FIG. 6Bis a photograph in which the cover member5is bonded to the device1and an electrophoresis electrode is inserted therein.

The dimensions of the device1illustrated inFIG. 6Awill be described with reference to the reference symbols ofFIG. 1A. The width W1of the connection part between the first taper channel33and the sample measurement channel32was 200 nm, the length L2of the sample measurement channel32was 8 μm, the width W2of the connection part between the first taper channel33and the sample supply channel31was 2 μm, and the length L1of the first taper channel33was 5 μm, and W1=W1a, W2=W2a, and L1=L1awere satisfied. Further, the gap G between the pair of the measuring electrodes4aand4bwas adjusted to be 0.55 nm to 1.0 nm. Further, the depth of the channel3was 50 nm.

The mask for electron beam lithography was changed to fabricate the device so that the same ratio as that of Example 1 is obtained while the width of the channel is smaller than that of Example 1. The size of the device fabricated in Example 2 satisfied W1=W1a=20 nm, W2=W2a=200 nm, L1=L1a=500 nm, and L2=800 nm. Further, the gap G between the pair of the measuring electrodes4aand4bwas 1 nm, and the depth of the channel3was 20 nm.

Fabrication of Nucleic Acid Sequence Reading Apparatus (Tunnel Current Measuring Apparatus)

A battery was used as the electrophoresis power source6and connected via lead wires to the electrophoresis electrodes of the device fabricated in Example 2. In the tunnel current detection unit7aof the measuring unit7, a scheme to obtain a current value by performing current/voltage amplification to measure a micro-current value as a voltage was used for the ammeter, and a digital oscilloscope by National Instrument that is an A/D converter was used as a voltmeter. Further, a feedback resistor was incorporated in a commercially available current amplifier to increase accuracy of a current amplifier.

Tunnel Current Measuring Method and Nucleic Acid Sequence Reading Method

(1) Preparation of a Sample Liquid

As a nucleic acid, λDNA (NIPPON GENE CO., LTD., Tokyo, Japan) having a known sequence was used. Water was used as a solvent, and the nucleic acid was dissolved in the solvent to prepare a sample liquid. The concentration of the nucleic acid was 1 micro-mol/l.

(2) Measurement of Tunnel Current (Acquisition of Nucleic Acid Information)

The sample liquid prepared in (1) described above was supplied to the sample supply channel, and the solvent was supplied to the sample collection channel. DC voltages 600 mV and −600 mV were applied to the electrophoresis electrodes61and62, respectively. A DC voltage of 100 mV was applied to the measuring electrodes4.FIG. 7indicates a measurement result.

(3) Reading of a Nucleic Acid Sequence

The conductance was calculated from the waveform of the tunnel current of (2) described above. The nucleic acid sequence was determined from the time axis and the calculated conductance and then confirmed to be the same as the sequence of λDNA used as the sample.

Example 5, Comparative Example 1

The tunnel current was measured in the same procedure as in Example 4 except that the DC voltages applied to the electrophoresis electrodes61and62were changed to 0.1 V (Example 5) and 1000 V (Comparative example 1).FIG. 8indicates a measurement result. As illustrated inFIG. 8A, when a voltage for electrophoresis of 1000 V was applied, a difference in tunnel current in the order of picoampere occurring when the nucleic acid passes through the gap G between the measuring electrodes4was not identified at all due to noise.FIG. 8Bis a graph of an enlarged part near the picoampere order range of the measurement result of the tunnel current value ofFIG. 8A. As illustrated inFIG. 8B, when the voltage was 0.1 V, a difference in tunnel current in the order of picoampere occurring when the nucleic acid passes through the gap G between the measuring electrodes4was identified.

It was confirmed from the above results that, if the voltage applied for electrophoresis is high, a difference in tunnel current in the order of picoampere occurring when the nucleic acid passes through the gap G between the measuring electrodes4is unable to be identified due to noise. As disclosed in Japanese Patent Application Laid-Open No. 2016-103979, when a channel formed in a substrate is used for elongation of a nucleic acid, the width of the channel and the applied voltage can be set to values that enable elongation of the nucleic acid. In general, however, a larger width of the channel requires a larger voltage value for the nucleic acid to move inside the channel by electrophoresis. It is known in the field of micromachining that a micro-channel can be formed in a substrate. However, the device disclosed in the present application achieves a significant advantageous effect that, with improved size and arrangement of the channel, a nucleic acid sequence can be read from tunnel current by using a channel formed in a base material.

Moving Velocity of Nucleic Acid in Accordance with Adjustment of Sample Liquid

Next, an experiment was performed to confirm a flow of a nucleic acid due to electrophoresis when the first taper channel33was formed.

(1) Fabrication of a Device

A device having a larger channel than the device fabricated in Example 2 was fabricated in order to observe a stained nucleic acid by using an optical microscope. Note that the measuring electrodes4were not formed in Example 6, because the experiment was not intended to read a nucleic acid sequence. The device was fabricated in accordance with the procedure of Example 1 except that the measuring electrodes4were not formed. The size of the device fabricated in Example 6 satisfied W1=W1a=1 μm, W2=W2a=10 μm, L1=L1a=20 μm, and L2=20 μm. The depth of the channel3was 20 nm.

(2) Adjustment of a Sample Liquid

Sample a: Without PVP

Sample b: With PVP

In both the samples, the pH of the TBE buffer was 7.8, and the concentration of λDNA was 0.1 μg/mL.

A DC voltage of 5 V was applied to the fabricated device. Motion of the nucleic acid was observed by an optical microscope.FIG. 9indicates a measurement result. Note that “position (x)” of the vertical axis ofFIG. 9corresponds to an intermediate position of the channel corresponding to the sample measurement channel32at which the width is narrowest. The moving velocity of λDNA contained in the sample b with PVP was higher than λDNA contained in the sample a without PVP. This is considered to be because the PVP suppressed an electroosmotic flow (EOF) occurring in the first taper channel33of the device1. It was revealed that, when the device1disclosed in the present application is used in the tunnel current measuring method or the nucleic acid sequence reading method, it is preferable to add a surfactant such as PVP in order to improve the reading rate of a nucleic acid.

Shape of First Taper Channel33

Next, an experiment was performed to confirm influence of the shape of the first taper channel33on the moving velocity of a sample.

(1) Fabrication of a Device

A device was fabricated in which W1and W1aof a device (hereafter, referred to as “Device b”) were changed as follows from the size described in Example 6. The sizes other than W1and W1awere the same as Device b.

(2) Adjustment of a Sample Liquid

A DC voltage of 5 V was applied to the fabricated device.

FIG. 10indicates a measurement result. The range X inFIG. 10represents a portion corresponding to the sample measurement channel32(L2ofFIG. 1A), and the range Y represents a portion corresponding to a part from the inlet of the first taper channel33to the outlet of the second taper channel35(L1+L2+L1aofFIG. 1A) (hereafter, a portion corresponding to Y may be referred to as “micro-channel portion”). Analysis illustrated inFIG. 11was performed from the measurement result ofFIG. 10.FIG. 11 (b)is a graph in which the position and the moving velocity when an individual bead of Devices a to c passes are plotted.FIG. 11 (c)is a graph in which the position and the acceleration when an individual bead of Devices a to c passes are plotted.FIG. 11 (d)is an enlarged view ofFIG. 11 (b), andFIG. 11 (e)is an enlarged view ofFIG. 11(c). Note that, sinceFIG. 11 (b) to (e)are diagrams illustrating an overview, all the plot symbols are represented by black solid circles.

An analysis result ofFIG. 11and what was revealed are as follows.

(1) The moving velocity and the acceleration of the beads differed depending on the shape of the first taper channel33.

(2) As illustrated inFIGS. 11 (b) and (d), although the moving velocity of the bead before and immediately after entering the micro-channel portion was stable in all the devices of Devices a to c, the moving velocity increased after fully entering the micro-channel portion. Then, the velocity decreased toward the outlet of the micro-channel portion after having a peak at Position 0. The velocities (the velocity at Position (x)) calculated from trace data on 10 beads are as follows.

In general, the velocity v of a sample particle is determined by the sum of an electrophoresis velocity vep and a velocity veo of an electroosmotic flow from a channel. Respective velocities, that is, vep and veo are in a proportional relationship between a DC electric field E and a velocity v and thus expressed by the following Equation.

It was implied that a stable electric field was formed in the micro-channel portion of all the devices of Devices a to c, and it was found that stable flow control is possible.

(3) From the data indicated byFIGS. 11 (c) and (e), the maximum accelerations in the acceleration region (the left side of Position 0) of the micro-channel portion are as follows.

As is clear from the above calculation result, a larger value of W2/W1(a larger angle of the taper of the first taper channel33) resulted in a larger acceleration. When the acceleration is larger, the force received by the micro-channel portion becomes larger, which contributes to entropy dissociation energy of an elongate sample such as a nucleic acid and can elongate the elongate sample. Further, when the acceleration is larger, the number of samples (the number of nucleic acids) per unit time that pass through the gap G between the measuring electrodes can be increased. Further, for the same number of samples (the number of nucleic acids) that pass between the measuring electrodes per unit time, a smaller value of W2/W1requires only a smaller value of the voltage applied for electrophoresis, and therefore measurement noise caused by the voltage applied for electrophoresis can be further reduced.

(4) As described above, it was confirmed that adjustment of the ratio of reducing the width of the first taper channel33from the sample supply channel31to the sample measurement channel32synergistically achieves the advantageous effects such as improvement in a reading rate of a sample and/or reduction in measurement noise caused by a voltage applied for electrophoresis, elongation of an elongate sample such as a nucleic acid, or the like.

The use of the device disclosed in the present application can reduce noise caused by the voltage applied for electrophoresis when measuring tunnel current occurring when a sample passes between the measuring electrodes4. Therefore, the disclosed device is useful in development of analysis devices in analysis instrument industry.

LIST OF REFERENCE SYMBOLS