JP2014157097A - Spectrometry and spectral device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spectrometry and a spectral device capable of simply, quickly and accurately detecting and identifying a substance.SOLUTION: A sample is analyzed by: a first step of placing a sample between electrode pairs to which direct current voltage V is applied; a second step of measuring a value of direct current I which flows between the electrode pairs, while changing the direct current voltage V; and a third step of determining a value Vp 1 of the direct current voltage V when a gradient of an I-V curve changes.

Description

  The present invention relates to a spectroscopic method and a spectroscopic device using a direct current voltage and direct current.

  In recent years, in various fields, development of a technique for detecting and identifying a substance (for example, one molecule) simply and quickly has been demanded.

  For example, techniques for detecting and identifying substances such as nucleotides or polynucleotides are widely used in fields such as medicine, drug discovery and criminal investigation, and are attracting increasing interest in the development of this technique.

  In order to realize tailor-made medical treatment that matches the individuality of a patient, it is necessary to accurately read the base sequence of the individual genome in a short time and accurately grasp the feature points in the base sequence of the individual genome. In this respect as well, there is an increasing interest in the development of technology for detecting and identifying substances such as nucleotides or polynucleotides.

  Under such circumstances, a tunnel current flowing between the electrode pair is measured when a substance (for example, a nucleotide or a polynucleotide) moves and passes through a minute space between the electrode pair. Development of a technique for detecting and identifying a substance based on the above is progressing (for example, see Non-Patent Document 1 and Non-Patent Document 2).

  More specifically, in the above-described technique, the tunnel current flowing between the electrode pair is reduced in a short time (for example, several milliseconds) from when the substance enters the minute space between the electrode pair and exits the space. To detect. Then, after detecting a plurality of tunnel currents, the frequency of occurrence of a tunnel current having a specific value is grasped, and the substance is identified based on the value of the tunnel current that appears most frequently.

  In the above-described technique, it is difficult to accurately determine the value of the tunnel current that appears most frequently only by detecting a small number (for example, one or two) of tunnel currents. That is, in the technique based on the tunnel current described above, in order to identify a substance with high accuracy, it is necessary to detect the tunnel current as much as possible and determine the value of the tunnel current that appears most frequently.

  Therefore, in order to accurately detect and identify a substance by the above-described technique, it takes a long time to accurately grasp the appearance frequency of a tunnel current having a specific value. In this respect, the above-described technique has room for further improvement.

  By the way, as another technique for detecting and identifying a substance using a tunnel current, inelastic tunneling spectroscopy (IETS) has been conventionally known (see, for example, Non-Patent Document 3).

  FIG. 16 shows an outline of conventional inelastic electron tunneling spectroscopy. In conventional inelastic electron tunneling spectroscopy, the electrical conductivity of an electrode pair is measured by an alternating current method using a lock-in amplifier (a method using an alternating voltage and an alternating current), and the substance is identified by this.

  The present inventor conducted research based on an original hypothesis that a substance (for example, a single molecule) could be detected and identified more easily, quickly and accurately if the above two techniques can be combined. Continued.

M. Tsutsui et al., Nature Nanotechnology 5,286-290 (2010) M. Tsutsui et al., Scientific Reports 1,46,1-6 (2011) B. C. Stipe et al., Science 280, 1732-1735 (1998)

  However, it is impossible to simply combine the two techniques described above, and in order to detect and identify a substance simply, quickly and accurately, a completely new technique different from the conventional technique is required.

  Specifically, in the technique of measuring a tunnel current flowing between a pair of electrodes when the substance moves and passes through the minute space between the electrode pair, the substance stays in the minute space between the electrode pair. The time is an extremely short time of several milliseconds. In order to measure the IETS spectrum in such a short time, for example, it is necessary to collect current data every 0.2 mV while performing voltage sweep from 0 V to 0.2 V. In this case, 1 m It is necessary to measure about 1000 points of current during a second.

  However, the conventional inelastic electron tunneling spectroscopy based on the AC method using a lock-in amplifier has a high-frequency signal generated by multiplying a noise signal other than the input signal that matches the frequency of the reference signal by a low-pass filter and the reference signal. It is essential to cut. Therefore, inelastic electron tunneling spectroscopy based on the AC method using a lock-in amplifier is not suitable for high-speed current measurement (the sample rate of a commercially available lock-in amplifier is approximately 10 kHz or less).

  In other words, the conventional inelastic electron tunneling spectroscopy based on the alternating current method using a lock-in amplifier cannot be combined with a technique that requires approximately 1000 current measurements in 1 msec. Have.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a spectroscopic method and a spectroscopic device capable of detecting and identifying a substance simply, quickly and accurately.

  As a result of intensive studies in view of the above problems, the present inventors applied a DC voltage to an electrode pair without using a lock-in amplifier, placed a sample between the electrode pair, and placed between the electrode pair. By measuring the flowing direct current (tunnel current), it was found that a small direct current (tunnel current) of picoampere level could be measured at a high speed of 10 MHz or more, and the direct current and direct current voltage thus measured were used. Even in such a case, the present inventors have found that the molecular structure can be accurately identified as in the measurement result of the conventional IETS method, and have completed the present invention.

  In order to solve the above problems, the spectroscopy of the present invention includes a first step of applying a DC voltage Vb to an electrode pair in which a sample is disposed between a positive electrode and a negative electrode, and changing the DC voltage Vb. However, the slope of the IV curve changes in the second step of measuring the value of the DC I flowing between the electrode pair and the IV curve in which the DC I is plotted against the DC voltage Vb. And a third step of determining the value Vp1 of the DC voltage Vb at the time.

  According to the above configuration, after the sample is placed between the electrode pair to which the DC voltage Vb is applied, the value of the DC I flowing between the electrode pair is measured while changing the DC voltage Vb. At this time, as the DC voltage Vb is changed, the value of the DC I changes.

  The slope of the IV curve (in other words, the amount of change in DC I when the DC voltage Vb changes by a certain amount) is the time when the DC voltage Vb corresponding to the energy of the molecular vibration mode is applied to the electrode pair. It changes with. In other words, if the value Vp1 of the DC voltage Vb when the slope of the IV curve in which the DC I is plotted with respect to the DC voltage Vb changes, the value Vp1 corresponds to the energy of the molecular vibration mode. DC voltage.

  That is, if the value Vp1 is determined based on the IV curve, the molecular vibration mode derived from the sample, in other words, the molecular structure contained in the sample can be estimated. Thus, the sample can be detected and identified simply, quickly and accurately.

  In the third method, the first differential dI / dVb of the direct current I with respect to the direct current voltage Vb is calculated for the IV curve in which the direct current I is plotted with respect to the direct current voltage Vb. Thus, it is preferable to determine the value Vp1.

  According to the said structure, an IV curve can be converted into a substantially step-like graph. As a result, the value Vp1 of the DC voltage Vb when the slope of the IV curve changes can be determined more accurately. As a result, the molecular structure of the sample can be determined more accurately.

  It may be difficult to directly determine the Vp1 from the IV curve. For example, when the slope of the IV curve changes only slightly, it becomes difficult to directly determine the Vp1 from the IV curve. However, even in such a case, if the value Vp1 is determined as the value of the DC voltage Vb when the value of the primary differential dI / dVb changes, the value Vp1 can be determined more accurately. it can.

In the spectroscopic method of the present invention, in the third step, the second derivative d ² I / dVb ^{2 of the} direct current I with respect to the direct current voltage Vb with respect to an IV curve in which the direct current I is plotted with respect to the direct current voltage Vb. It is preferable to determine the value Vp1 by calculating.

  According to the said structure, an IV curve can be converted into a substantially peak-shaped graph. As a result, the value Vp1 of the DC voltage Vb when the slope of the IV curve changes is more accurately compared with the case where the value Vp1 is determined by calculating the primary differential dI / dVb. Can be determined. Further, the molecular structure of the sample can be estimated more accurately as compared with the case where the value Vp1 is determined by calculating the first derivative dI / dV.

It may be difficult to directly determine the Vp1 from the IV curve. For example, when the slope of the IV curve changes only slightly, it becomes difficult to directly determine the Vp1 from the IV curve. However, even in such a case, if the value Vp1 is determined as the value of the DC voltage Vb when the value of the secondary differential d ² I / dVb ² changes, the value Vp1 is determined more accurately. can do. Moreover, the determination can be more accurate than the case where the value Vp1 is determined by calculating the first derivative dI / dVb.

  In the spectroscopic method of the present invention, the direct current I is preferably obtained by subtracting the value of the elastic tunnel current flowing between the electrode pair from the measured direct current value.

  According to the above configuration, since the value Vp1 can be determined substantially based only on the inelastic tunnel current, the value Vp1 can be determined more accurately. Therefore, according to the above configuration, the molecular structure of the sample can be estimated more accurately.

  The spectroscopic method of the present invention preferably includes, after the third step, a fourth step of comparing the sample value Vp1 with a predetermined reference sample value Vp2 corresponding to the Vp1. .

  According to the above configuration, similarity or identity between the molecular structure of the sample and the molecular structure of the reference sample can be determined.

The spectroscopic method of the present invention preferably has a fifth step of determining at least one of the following (A) to (C) after the fourth step. That means
(A) When the value Vp1 of the sample and the value Vp2 of the reference sample are the same, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are the same;
(B) When the value Vp1 of the sample and the value Vp2 of the reference sample are partially the same, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are partially the same. ;
(C) When the value Vp1 of the sample and the value Vp2 of the reference sample are different, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are different.

  According to the above configuration, the similarity or identity between the molecular structure of the sample and the molecular structure of the reference sample can be determined in more detail. Moreover, according to the said structure, when the molecular structure of a sample is unknown, the molecular structure of the said sample can be estimated.

  For example, the molecular structure of the sample is unknown, and the sample value Vp1 (which may be one or more Vp1s) and the reference sample value Vp2 (one or more Vp2s). Is the exact same case).

  In this case, it can be determined that the molecular structure of the sample and the molecular structure of the reference sample are completely the same. At this time, if a molecule having a known molecular structure is used as the reference sample, the molecular structure of the sample can be determined.

  On the other hand, the molecular structure of the sample is unknown, and the sample value Vp1 (which may be one or more Vp1s) and the reference sample value Vp2 (one or more Vp2s). Is present) may be partially or completely different.

  In this case, it can be determined that the molecular structure of the sample is different from the molecular structure of the reference sample. At this time, if a molecule having a known molecular structure is used as the reference sample, a specific molecular structure can be excluded from the molecular structure candidates of the sample.

  In the spectroscopic method of the present invention, the sample may be moving in a space between the electrode pair.

  According to the present invention, a minute direct current of picoampere level can be measured at a high speed of 10 MHz or higher, so that even if the sample is moving, the amount of data necessary for analysis can be obtained.

  In the spectroscopic method of the present invention, it is preferable that the space between the electrode pair is formed in such a size that only one molecule of substance is arranged as the sample.

  According to the above configuration, simple, rapid and accurate detection and identification can be performed for one molecule.

  In the spectroscopic method of the present invention, in the second step, the DC voltage Vb is preferably changed by a constant value.

  According to the above configuration, since the value of the direct current I is measured without unevenness, there is no possibility of overlooking the point where the slope of the IV curve changes. As a result, the molecular structure of the sample can be estimated more accurately.

  In order to solve the above problems, the spectroscopic device of the present invention includes a voltage source that applies a DC voltage V while changing a value with respect to an electrode pair in which a sample is arranged between a positive electrode and a negative electrode, and the electrode The DC voltage when the slope of the IV curve changes for an ammeter that measures the value of the DC I flowing between the pair and an IV curve in which the DC I is plotted against the DC voltage V. And an analysis unit for determining the value Vp1 of Vb.

  According to the above configuration, after the sample is placed between the electrode pair to which the DC voltage Vb is applied, the value of the DC I flowing between the electrode pair is measured while changing the DC voltage Vb. At this time, as the DC voltage Vb is changed, the value of the DC I changes.

  The slope of the IV curve (in other words, the amount of change in DC I when the DC voltage Vb changes by a certain amount) is the time when the DC voltage Vb corresponding to the energy of the molecular vibration mode is applied to the electrode pair. It changes with. In other words, if the value Vp1 of the DC voltage Vb when the slope of the IV curve in which the DC I is plotted with respect to the DC voltage Vb changes, the value Vp1 corresponds to the energy of the molecular vibration mode. DC voltage.

  That is, if the value Vp1 is determined based on the IV curve, the molecular vibration mode derived from the sample, in other words, the molecular structure contained in the sample can be estimated. Thus, the sample can be detected and identified simply, quickly and accurately.

  Since the present invention is a method capable of detecting the molecular vibration of a single molecule, it can detect and identify a single molecule.

  Since the present invention can measure a minute direct current of picoampere level at a high speed of 10 MHz or more, it can detect a molecule (for example, a moving molecule) that exists in a space between electrode pairs only for a short time. Identification can be made.

  In the present invention, since the size (for example, width) of the electrode pair can be set to a desired size, various substances (for example, nucleic acids, proteins, sugar chains, etc.) ranging from low molecules to high molecules can be used. Detection and identification can be done at the level of one molecule.

  Since the present invention can obtain detailed information on the molecular structure, the structure of an unknown molecule can be predicted.

(A) And (b) is a figure which shows an example of a structure of the electrode pair used for this invention. (A)-(c) is a figure explaining the basic principle of the 3rd process of this invention. (A)-(d) is a figure explaining the basic principle of the 3rd process of this invention. It is a block diagram which shows an example of a structure in one Embodiment of the spectroscopy apparatus of this invention. It is a flowchart which shows an example of the operation | movement in one Embodiment of the spectroscopic device of this invention. (A) And (b) is a figure which shows the preparation methods of the gold electrode pair which the single molecule joined in the Example of this invention. (A)-(d) is a graph which shows the test result at the time of using the electrode pair which 1, 4- benzenedithiol joined in the Example of this invention. (A)-(d) is a graph which shows the test result at the time of using the electrode pair which 1, 4- benzenedithiol joined in the Example of this invention. It is a figure which shows the energy of the molecular vibration mode characteristic of 1, 4-benzenedithiol in the Example of this invention. (A)-(d) is a graph which shows the test result at the time of using the electrode pair which 2,5-dimercapto-1,3,4-thiadiazole joined in the Example of this invention. (A)-(d) is a graph which shows the test result at the time of using the electrode pair which 2,5-dimercapto-1,3,4-thiadiazole joined in the Example of this invention. It is a figure which shows the energy of the molecular vibration mode characteristic of 2,5-dimercapto-1,3,4-thiadiazole in the Example of this invention. (A)-(d) is a graph which shows the test result at the time of using the electrode pair which 1,6-hexanedithiol joined in the Example of this invention. (A)-(d) is a graph which shows the test result at the time of using the electrode pair which 1,6-hexanedithiol joined in the Example of this invention. (A)-(d) is a graph which shows the test result at the time of using the electrode pair which the single gold atom joined in the Example of this invention. It is a figure which shows the outline of the conventional inelastic electron tunneling spectroscopy.

  An example of the embodiment of the present invention will be described below. It should be noted that the present invention is not limited to the configurations described below, and various modifications are possible within the scope indicated in the claims, and techniques disclosed in different embodiments and examples, respectively. Embodiments and examples obtained by appropriately combining technical means are also included in the technical scope of the present invention.

[1. Electrode pair)
An example of the configuration of the electrode pair used in the spectroscopy of this embodiment will be described below.

  FIGS. 1A and 1B show an example of the configuration of an electrode pair used in the spectroscopy of the present embodiment.

  The electrode pair used in the spectroscopic method of the present embodiment is formed by the pair of electrode 1 and electrode 2. A voltage source 5 is connected to the electrode 1, and an electrometer 6 is connected to the electrode 2. A sample 7 is placed in a space formed between the electrode 1 and the electrode 2.

  The voltage source 5 only needs to be able to apply the DC voltage Vb to the electrode pair, and a commercially available voltage source can be used as appropriate. For example, a 6487 type inter-voltage built-in picoammeter manufactured by Keithley Instruments Inc. can be used, but the present invention is not limited to this.

  The voltage source 5 is in increments of 0.01 mV, 0.05 mV, 0.1 mV, 0.2 mV, 0.3 mV, 0.4 mV, 0.5 mV, 0.5 mV, 0.6 mV, and 0.7 mV. , 0.8 mV increments, 0.9 mV increments, or 1.0 mV increments while increasing or decreasing the voltage can be used so that the DC voltage Vb can be applied to the electrode pair.

  The voltage source 5 is preferably one that can apply the direct-current voltage Vb to the electrode pair while increasing or decreasing the voltage at intervals of 0.2 mV or less. According to the above configuration, it is possible to measure current of approximately 1000 points or more in 1 msec, and it is possible to detect and identify a substance more accurately.

  The electrometer 6 is not particularly limited, and a commercially available electrometer can be used as appropriate. For example, a 6487 type inter-voltage built-in picoammeter manufactured by Keithley Instruments Inc. can be used, but the present invention is not limited to this.

  As an example of a specific configuration of the electrometer 6, an electrometer including a high-speed current amplifier, a high-speed RAID, and a high-speed digitalizer can be cited. If it is the said structure, the micro electric current of the picoampere level can be measured at a high speed of 10 MHz or more. As the high-speed current amplifier, the high-speed RAID, and the high-speed digitalizer, commercially available configurations can be used as appropriate.

  The electrode pair shown in FIG. 1B shows a state of the electrode pair when the electrode pair shown in FIG. 1A is viewed from the lower side to the upper side of the drawing. In the case where the sample 7 is movable, the sample 7 is, for example, the extending direction of the length (L) shown in FIG. 1B (in other words, in FIG. In the direction from the back to the front, or the direction from the front to the back of the paper).

  The size of the space formed between the electrode 1 and the electrode 2 is not particularly limited, and may be set as appropriate according to the size of the sample. For example, the space can be designed to be small enough to contain only one molecule.

  For example, the width (W) illustrated in FIG. 1B may be 1 nm to 1000 nm, 1 nm to 100 nm, 1 nm to 60 nm, or 1 nm to 20 nm. 20 nm to 60 nm or 50 nm to 60 nm. Of course, the width (W) may be 1 nm or less, or 1000 nm or more.

  Since the molecular diameter of nucleotides is known to those skilled in the art, the size of the width (W) can be set based on the molecular diameter. For example, since the molecular diameter of the nucleotide in the form of monophosphate is about 1 nm, the width (W) is set to, for example, 0.5 nm to 2 nm, 1 nm to 1.5 nm, or 1 nm to 1.2 nm. Is also possible.

  The height (H) shown in FIG. 1 (b) may be 1 nm to 1000 nm, 1 nm to 100 nm, 1 nm to 60 nm, 1 nm to 20 nm, It may be 20 nm to 60 nm, or 50 nm to 60 nm. Of course, the height (H) may be 1 nm or less, or 1000 nm or more.

  The height (H) can be set to 0.5 nm to 2 nm, 1 nm to 1.5 nm, or 1 nm to 1.2 nm, similarly to the width (W) described above.

  The length (L) shown in FIG. 1 (b) may be 1 nm to 1000 nm, 1 nm to 100 nm, 1 nm to 60 nm, 1 nm to 20 nm, It may be 20 nm to 60 nm, or 50 nm to 60 nm. Of course, the height (H) may be 1 nm or less, or 1000 nm or more.

  The height (H) can be set to 0.5 nm to 2 nm, 1 nm to 1.5 nm, or 1 nm to 1.2 nm, similarly to the width (W) described above.

The specific material of the electrode 1 and the electrode 2 is not particularly limited, and the electrode 1 and the electrode 2 can be made of a known material. For example, as the electrode 1 and the electrode 2, an Au electrode, a Cr / Au electrode, a Pt / Au / Pt / SiO ₂ electrode, or the like can be used.

[2. Spectroscopy)
An example of the configuration of the spectroscopy of this embodiment will be described below.

  The spectroscopic method of this embodiment has a first step, a second step, and a third step. The spectroscopic method of the present embodiment preferably further includes a fourth step or a fifth step. Below, each process is demonstrated.

[2-1. First step]
The first step is a step of applying a DC voltage Vb to an electrode pair in which a sample is disposed between the positive electrode and the negative electrode. The DC voltage Vb is applied to the electrode pair by the voltage source 5 described above.

  The state of the sample arranged between the electrode pairs is not particularly limited, and the sample may be arranged so as to be movable in the space between the electrode pairs, or may be arranged so as not to move in the space between the electrode pairs. . For example, when analyzing a plurality of types of samples continuously, the samples may be arranged so as to be movable in the space between the electrode pair. On the other hand, in order to increase the accuracy of the analysis, the sample may be arranged so as not to move in the space between the electrode pairs, in other words, to exist in the space between the electrode pairs for as long as possible.

  When the sample is arranged so as to be movable in the space between the electrode pairs, the sample may be moved by applying an electric force to the sample. In this case, the sample may be moved by an electrode pair different from the electrode pair (electrode 1 and electrode 2) described above.

  Further, when the sample is arranged so as to be movable in the space between the electrode pairs, the sample may be moved by applying pressure to the sample. In this case, a force may be applied to the gas or liquid by a pump and the sample may be moved by the gas or liquid.

  When the sample is arranged so as to be movable in the space between the electrode pair, the sample may be moved by Brownian motion.

  Of course, the method of moving the sample is not limited to the method described above.

  Since the spectroscopic method of this embodiment can measure a small direct current of picoampere level at a high speed of 10 MHz or more, even if it is a moving sample, the amount of data necessary for the analysis is obtained. Can be obtained.

  On the other hand, when the sample is arranged so as not to move in the space between the electrode pair, the sample may be immobilized on the electrode pair by forming a bond between the sample and the electrode pair. In addition, although the mode of the coupling | bonding formed between a sample and an electrode pair is not limited, a covalent bond is preferable from a viewpoint of fixing a sample firmly on an electrode pair and analyzing a sample more accurately.

  The sample is not particularly limited, and for example, various molecules (for example, a low molecule (nucleotide, amino acid, sugar, etc.) or a polymer (polynucleotide, protein, sugar, etc.)) can be used.

  For example, the sample may be a molecule having a functional group that can form a bond with an electrode pair. In this case, since the direct current I flowing between the electrode pair can be measured with the sample fixed between the electrode pair, the direct current I can be measured more stably.

Examples of the functional group include “—SH”, “—NH ₂ ”, and “—COOH”. When the functional group is “—SH”, the sample can be bonded to gold, which is a component of the electrode pair, via the functional group. When the functional group is “—NH ₂ ”, the sample can be bonded to gold, which is a component of the electrode pair, via the functional group. When the functional group is “—COOH”, the sample can be bonded to gold as a constituent component of the electrode pair via the functional group.

  The sample may be a molecule having a charge (for example, a nucleotide, a polynucleotide, an amino acid having a dissociable side chain, or a protein). In this case, the molecule having the charge can be moved so as to pass through the space between the electrode pair by an electrode pair different from the electrode pair (electrode 1 and electrode 2) described above. And when the molecule | numerator which has the said electric charge passes the space between electrode pairs, the direct current which flows between electrode pairs can be measured.

  Since the spectroscopic method of this embodiment can measure a small direct current of picoampere level at a high speed of 10 MHz or more, even if it is a moving sample, the amount of data necessary for the analysis is obtained. Can be obtained.

  The amount of the sample disposed between the electrode pair is not particularly limited, and one molecule may be disposed between the electrode pair, or 1 to 5 molecules may be disposed. 10 to 10 molecules may be arranged, or 10 or more molecules may be arranged. In addition, the quantity of the sample arrange | positioned between electrode pairs can be determined by designing the size of the space between electrode pairs to a desired size.

  With the spectroscopic method of the present embodiment, even if it is a single molecule, it is possible to obtain the amount of data necessary for the analysis. In addition, with the spectroscopic method of the present embodiment, detailed analysis on individual molecules can be performed.

[2-2. Second step]
The second step is a step of measuring the value of the direct current I flowing between the electrode pair while changing the direct current voltage Vb. That is, in the second step, after the sample is disposed between the electrode pair in the first step described above, the DC voltage Vb applied to the electrode pair is changed while the sample is disposed between the electrode pair. This is a step of measuring the value of the direct current I flowing between the electrode pair.

  The DC voltage Vb is applied to the electrode pair by the voltage source 5 described above, and the DC I is measured by the ammeter 6 described above. Since specific configurations of the voltage source 5 and the ammeter 6 have already been described, description thereof is omitted here.

  The change mode of the DC voltage Vb applied to the electrode pair is not particularly limited, and may be 0.01 mV, 0.05 mV, 0.1 mV, 0.2 mV, 0.3 mV, 0.4 mV, The DC voltage Vb may be increased or decreased in 0.5 mV increments, 0.6 mV increments, 0.7 mV increments, 0.8 mV increments, 0.9 mV increments, or 1.0 mV increments.

  It is preferable that the change mode of the DC voltage Vb applied to the electrode pair rises or falls at intervals of 0.2 mV or less. According to the above configuration, it is possible to measure current of approximately 1000 points or more in 1 msec, and it is possible to detect and identify a substance more accurately.

[2-3. Third step]
First, the basic principle of the third step will be described with reference to FIGS. 2 (a) to 2 (c).

  FIG. 2A shows a state in which a sample is arranged between a pair of electrodes formed of gold. Note that a DC voltage Vb is applied to the electrode pair, and the value of the DC I flowing between the electrode pair is measured by an ammeter.

  When the value of the DC voltage Vb applied to the electrode pair is gradually changed (for example, increased), the type of current flowing between the electrode pair changes according to the value of the DC voltage Vb. This point will be described in more detail with reference to FIGS. 2B and 2C.

  The sample has various molecular vibration modes corresponding to its molecular structure. Then, when the DC voltage Vb applied to the electrode pair is made smaller than the value Vp corresponding to the energy of the molecular vibration mode and when it is made larger than the value Vp corresponding to the energy of the molecular vibration mode. The type of current flowing between the electrode pair changes.

  Specifically, as shown in FIG. 2B, when a DC voltage Vb having a value smaller than the value Vp corresponding to the energy of the molecular vibration mode of the sample is applied to the electrode pair, An elastic tunnel current (elasticity) flows as a direct current between them.

  On the other hand, when a DC voltage Vb having a value larger than the value Vp corresponding to the energy of the molecular vibration mode of the sample is applied to the electrode pair, as shown in FIG. Elastic tunnel current (elastic) and inelastic tunnel current (inelastic) flow as direct current.

  Therefore, when the value of the DC voltage Vb is small and the value of the DC voltage is large with the value Vp as a boundary, the slope of the IV curve (in other words, when the DC voltage Vb changes by a certain amount). Change amount of the direct current I) changes.

  In the spectroscopic method according to the present embodiment, the value Vp is calculated based on the IV curve created based on the actual measurement value, so that the sample can be detected and identified simply, quickly and accurately. .

  The basic principle of the third step will be described in more detail with reference to FIGS. 3 (a) to 3 (d). In addition, the specific structure for performing the said 3rd process is not specifically limited, It can be performed using well-known structures, such as a computer suitably.

  As shown in FIG. 3A, in the third step, for the IV curve in which the DC I is plotted against the DC voltage Vb, the slope of the IV curve (shown by a solid line in FIG. 3A). This is a step of determining the value Vp of the DC voltage Vb when the slope of the graph changes.

  As already described, the above-described value Vp corresponds to the energy of the molecular vibration mode. Therefore, if the value Vp is determined, information on the molecular structure of the sample can be obtained, and thereby the sample can be identified.

  FIG. 3A shows an example of a typical IV curve. Note that the IV curve can be created by plotting the measured DC I value against the actual value of the DC voltage Vb applied to the electrode pair.

  As shown in FIG. 3A, when the direct current I flowing through the electrode pair is only an elastic tunnel current (elastic), the direct current I flowing through the electrode pair is an elastic tunnel current (elastic) and an inelastic tunnel current (inelastic). ), The slope of the graph (shown by a solid line in FIG. 3A) is different. Then, the value of the DC voltage Vb when the inclination changes is a value Vp to be obtained.

  As shown in FIG. 3C, the third step calculates the first derivative dI / dVb of the direct current I by the direct current voltage Vb with respect to the IV curve in which the direct current I is plotted against the direct current voltage Vb. It may be a step of determining the value Vp.

  In the case of the method shown in FIG. 3A, if the change in the slope of the graph is slight, it may be difficult to accurately determine the value Vp. However, as is clear from FIG. 3C, the IV curve can be converted into a substantially stepped graph by using the first-order differential dI / dVb. In the substantially step-like graph, the value of the DC voltage Vb when the value of the primary differential dI / dVb changes can be determined easily and accurately. In the substantially step-like graph, the value of the DC voltage when the value of the primary differential dI / dVb changes is the value Vp to be obtained.

As shown in FIG. 3D, the third step calculates the ^second derivative d ² I / dVb ² of the direct current I by the direct current voltage Vb with respect to the IV curve in which the direct current I is plotted against the direct current voltage Vb. This may be a step of determining the value Vp.

In the case of the method shown in FIGS. 3 (a) and 3 (c), if the change in the graph (shown by the solid line in FIGS. 3 (a) and 3 (c)) is slight, the value Vp is accurately set. It can be difficult to determine. However, as is apparent from FIG. 3D, using the ^second derivative d ² I / dVb ² , the IV curve can be converted into a substantially peak graph. In the substantially peak-shaped graph, the value of the DC voltage Vb when the secondary differential d ² I / dVb ² changes can be easily and accurately determined. In the substantially peak-shaped graph, the value of the DC voltage when the secondary differential d ² I / dVb ² changes is the value Vp to be obtained.

  As shown in FIG. 3B, in the third step, the direct current I is obtained by subtracting the value of the elastic tunnel current flowing between the electrode pairs from the measured direct current value (specifically, FIG. 3). It may be ΔI shown in (b).

  In this embodiment, instead of the IV curve, a ΔI-V curve in which a value ΔI obtained by subtracting the value of the elastic tunnel current from the measured DC value is plotted with respect to the DC voltage Vb. The value Vp described above may be determined in the third step.

  In this case, as shown in FIG. 3B, the value Vp may be determined directly from the ΔIV curve.

  Further, the value Vp may be determined after first-order differentiation of the ΔI-V curve. Even in this case, the ΔIV curve can basically be converted into a graph similar to the graph shown in FIG.

  The value Vp may be determined after second-order differentiation of the ΔI-V curve. Even in this case, the ΔI-V curve can basically be converted into a graph similar to the graph shown in FIG.

  When the value Vp is determined using the ΔI-V curve, the value Vp is determined in a state in which the influence of the elastic tunnel current is removed, so that the value Vp can be determined more accurately. As a result, the sample can be detected and identified more accurately.

[2-4. Fourth step]
In the fourth step, the value Vp1 of the sample to be detected and identified and the value Vp2 of the reference sample determined in advance corresponding to the value Vp1 (in other words, the value Vp determined for the reference sample). Is a step of comparing According to the above configuration, the similarity or identity between the molecular structure of the sample to be detected and identified and the molecular structure of the reference sample can be determined.

  The reference sample is not particularly limited, and for example, a molecule whose molecular structure is known can be used.

  As a reference sample, it is possible to use the same type of molecule as the sample to be detected and identified. For example, when it is known that a sample to be detected and identified is a nucleotide, amino acid, or sugar, it is preferable to use a nucleotide, an amino acid, or a sugar, respectively, as a reference sample. According to the above configuration, the sample can be detected and identified more accurately.

  In the fourth step, the value Vp2 previously determined for the above-described reference sample is compared with the value Vp1 of the sample to be detected and identified.

  As a method for determining the reference sample value Vp2 in advance, for example, the reference sample value Vp2 may be determined by analyzing the reference sample in advance through the first to third steps described above.

  Alternatively, the energy of the molecular vibration mode can be calculated for a molecule with a known molecular structure (see, for example, Nano Lett. 5, 2257-2263 (2011)). As described above, since the value Vp corresponds to the energy of the molecular vibration mode, it is possible to determine the Vp of the reference sample by calculating the energy of the molecular vibration mode.

[2-5. Step 5]
The fifth step is a step that can be performed after the fourth step, and is a step of determining at least one of the following (A) to (C). That means
(A) When the value Vp1 of the sample (sample to be detected and identified) and the value Vp2 of the reference sample are the same, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are the same;
(B) When the value Vp1 of the sample (sample to be detected and identified) and the value Vp2 of the reference sample are partially the same, the molecular structure of the sample and the molecular structure of the reference sample are partially Determine that they are the same;
(C) When the value Vp1 of the sample (sample to be detected and identified) and the value Vp2 of the reference sample are different, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are different.

  According to the above configuration, the similarity or identity between the molecular structure of the sample to be detected and identified and the molecular structure of the reference sample can be determined in more detail. Further, according to the above configuration, when the molecular structure of a sample to be detected and identified is unknown, the molecular structure of the sample can be predicted.

  For example, the molecular structure of the sample is unknown, and the sample value Vp1 (which may be one or more Vp1s) and the reference sample value Vp2 (one or more Vp2s). Is the exact same case).

  In this case, it can be determined that the molecular structure of the sample and the molecular structure of the reference sample are completely the same. At this time, if a molecule having a known molecular structure is used as the reference sample, the molecular structure of the sample can be determined.

  On the other hand, when the molecular structure of the sample is unknown, the value Vp1 of the sample (which may be a case where a plurality of Vp1 exists) and the value Vp2 of the reference sample (a case where a plurality of Vp2 exist) ) Is partly the same.

  In this case, it can be determined that the molecular structure of the sample and the molecular structure of the reference sample are partially the same. At this time, if a molecule having a known molecular structure is used as the reference sample, at least a part of the molecular structure of the sample can be determined. More specifically, when a molecule having a known molecular structure is used as the reference sample, the energy of molecular vibration modes of various portions in the molecular structure of the reference sample can be calculated. Based on the energy of the molecular vibration mode, at least a part of the molecular structure of the sample can be determined.

  On the other hand, the molecular structure of the sample is unknown, and the sample value Vp1 (which may be one or more Vp1s) and the reference sample value Vp2 (one or more Vp2s). Is completely different).

  In this case, it can be determined that the molecular structure of the sample and the molecular structure of the reference sample are completely different. At this time, if a molecule having a known molecular structure is used as the reference sample, a specific molecular structure can be excluded from the molecular structure candidates of the sample.

  For example, the molecular structure of the reference sample is “A-B-C” (A, B, and C are different molecular skeletons (eg, benzene ring, long-chain alkane), and are linked to each other by chemical bonds. Assuming that one molecule is formed, the value Vp resulting from the molecular skeleton “A” is “a”, the value Vp resulting from the molecular skeleton “B” is “b”, and the molecular skeleton It is assumed that the value Vp resulting from “C” is “c”.

  At this time, if the value Vp of the sample to be detected and identified is “a”, “b”, and “c”, the molecular structure of the sample to be detected and identified is “ABC”. It can be determined that there is.

  On the other hand, if the value Vp of the sample to be detected and identified is “a”, “d”, and “e”, the sample to be detected and identified has the molecular skeleton “A”. Can be determined.

  On the other hand, if the value Vp of the sample to be detected and identified is “d”, “e”, and “f”, “A-B-C” is obtained from the molecular structure candidates of the sample to be detected and identified. "Can be excluded.

[3. Spectroscope]
[3-1. Spectrometer configuration)
An example of the configuration of the spectroscopic device of the present embodiment will be described with reference to FIG.

  The spectroscopic device 100 according to the present embodiment includes a voltage source 10 that applies a DC voltage Vb while changing a value between an electrode pair 20 in which a sample is disposed between a positive electrode and a negative electrode, and the electrode pair 20. The value Vp1 of the DC voltage Vb when the slope of the IV curve changes with respect to the ammeter 30 that measures the value of the DC I flowing through the IV and the IV curve in which the DC I is plotted against the DC voltage Vb. And an analysis unit 40 to be determined.

  The voltage source 10 has the same configuration as the voltage source 5 already described, the electrode pair 20 has the same configuration as the electrode pair already formed by the electrode 1 and the electrode 2, and the ammeter 30 has The configuration is the same as that of the ammeter 6 already described, and the analysis unit 40 is a configuration for performing the already-described third step. Since the details of these configurations have already been described, the detailed description thereof is omitted here.

  The voltage source 10 is configured to apply a DC voltage Vb to the electrode pair 20. The voltage source 10 can change (increase or decrease) the value of the DC voltage Vb applied to the electrode pair 20.

  When the value of the DC voltage Vb applied to the electrode pair 20 is changed, the value of the DC I flowing through the electrode pair 20 also changes with the change. Then, the ammeter 30 measures the value of the direct current I.

  Both the information related to the DC voltage Vb applied to the electrode pair 20 by the voltage source 10 and the information related to the DC I measured by the ammeter 30 are sent to the analysis unit 40.

  The analysis unit 40 is configured to determine the value Vp1 of the DC voltage Vb when the slope of the IV curve in which the DC I is plotted with respect to the DC voltage Vb changes.

  In this case, the analysis unit 40 creates an IV curve shown in FIG. 3A, for example, and determines a value Vp1 of the DC voltage Vb when the slope of the IV curve changes from the IV curve. You may do.

  The analysis unit 40 determines the value Vp1 by calculating the first derivative dI / dVb of the direct current I based on the direct current voltage Vb with respect to the IV curve in which the direct current I is plotted against the direct current voltage Vb. May be.

  In this case, for example, the analysis unit 40 may create a graph shown in FIG. 3C and determine the value Vp1 from the graph.

The analysis unit 40 calculates the value Vp1 by calculating the ^second derivative d ² I / dVb ² of the direct current I with respect to the direct current voltage Vb with respect to the IV curve in which the direct current I is plotted with respect to the direct current voltage Vb. It may be determined.

  In this case, the analysis unit 40 may create, for example, a graph shown in FIG. 3D and determine the value Vp1 from the graph.

  The analysis unit 40 uses (or calculates) the direct current I obtained by subtracting the value of the elastic tunnel current flowing between the electrode pairs from the actually measured direct current value (ΔI). May be.

  In this case, the analysis unit 40 may create, for example, a ΔI-V curve shown in FIG. 3B and determine the value Vp1 directly from the ΔI-V curve, or the ΔI-V The value Vp1 may be determined after first-order differentiation of the curve, or the value Vp1 may be determined after second-order differentiation of the ΔI-V curve.

  The specific configuration of the analysis unit 40 is not particularly limited, and can be configured by a known arithmetic device such as a computer.

  In the spectroscopic device according to the present embodiment, the value Vp1 determined by the analysis unit 40 can be regarded as an analysis result as it is, and the value Vp1 can be further examined. Then, when further examination is performed, the information of the value Vp1 is sent to the comparison unit 50.

  The comparison unit 50 is configured to compare the sample value Vp1 with a predetermined reference sample value Vp2.

  The comparison unit 50 may have a configuration in which information about the reference sample value Vp2 is stored in advance, or may have a configuration in which information about the reference sample value Vp2 can be input from another configuration. Good.

  The specific configuration of the comparison unit 50 is not particularly limited, and can be configured by a known arithmetic device such as a computer.

  In the spectroscopic device of the present embodiment, the comparison result by the comparison unit 50 (for example, what percentage of Vp is the same, what value of Vp is matched, which value of Vp is not matched, etc.) The comparison result) can be regarded as an analysis result as it is, and further examination can be performed. When further examination is performed, the comparison result by the comparison unit 50 is sent to the determination unit 60.

The determination unit 60 is configured to determine at least one of the following (A) to (C). That means
(A) When the value Vp1 of the sample and the value Vp2 of the reference sample are the same, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are the same;
(B) When the value Vp1 of the sample and the value Vp2 of the reference sample are partially the same, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are partially the same. ;
(C) When the value Vp1 of the sample and the value Vp2 of the reference sample are different, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are different.

  The specific configuration of the determination unit 60 is not particularly limited, and can be configured by a known arithmetic device such as a computer.

[3-2. Example of operation flow of spectroscopic device]
FIG. 5 shows an example of an operation flow of the spectroscopic device of the present embodiment.

  In S101, a sample is placed in a space between the positive electrode and the negative electrode constituting the electrode pair 20. In the present invention, a sample may be arranged in advance in a space between the positive electrode and the negative electrode constituting the electrode pair 20.

  In S <b> 102, a DC voltage Vb is applied to the electrode pair 20 by the voltage source 10 with the sample placed. Further, in S102, the value of the DC voltage Vb applied to the electrode pair 20 is changed. The change in the value of the DC voltage Vb can be performed by adjusting the output of the voltage source 10 or the like.

  In S <b> 103, the direct current I flowing through the electrode pair 20 is measured by the ammeter 30.

  In S <b> 104, the value Vp <b> 1 is determined by the analysis unit 40 from the value of the DC voltage Vb applied to the electrode pair 20 by the voltage source 10 and the value of the DC I measured by the ammeter 30. At this time, an IV curve or a ΔI-V curve or the like can be created by the analysis unit 40.

  In S105, it is determined whether further information (or further analysis) regarding the molecular structure of the sample is necessary. If no further information is required, the operation of the spectroscopic device ends when the value Vp1 is obtained. On the other hand, when further information is required, information on the value Vp1 determined by the analysis unit 40 is sent to the comparison unit 50.

  In S106, the comparison unit 50 compares the value Vp1 of the sample to be analyzed with the value Vp2 of the reference sample determined in advance. In the comparison unit 50, for example, a comparison result such as what percentage of Vp is identical, which value of Vp is matched, and which value of Vp is not matched is obtained.

  In S107, it is determined whether further information (or further analysis) regarding the molecular structure of the sample is necessary. If no further information is required, the operation of the spectroscopic device is terminated. On the other hand, when further information is required, the comparison result obtained by the comparison unit 50 is sent to the determination unit 60.

  In S108, the determination unit 60 predicts the molecular structure of the sample (in other words, various determinations are made regarding the molecular structure of the sample).

  After the prediction (determination) is finished, the operation of the spectroscopic device is finished.

  The control block of the spectroscopic device (in particular, the analysis unit 40, the comparison unit 50, and the determination unit 60) may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or may be a CPU (Central It may be realized by software using a Processing Unit.

  In the latter case, the spectroscopic device includes a CPU that executes instructions of a program that is software that realizes each function, a ROM (Read Only Memory) or a storage in which the above-described program and various data are recorded so as to be readable by a computer (or CPU) An apparatus (these are referred to as “recording media”), a RAM (Random Access Memory) for expanding the program, and the like are provided. And the objective of this invention is achieved when a computer (or CPU) reads the said program from the said recording medium and runs it.

  As the recording medium, a “non-temporary tangible medium” such as a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like can be used. The program may be supplied to the computer via an arbitrary transmission medium (such as a communication network or a broadcast wave) that can transmit the program. The present invention can also be realized in the form of a data signal embedded in a carrier wave in which the program is embodied by electronic transmission.

  The following examples are based on direct current measurement using an ammeter. In the following examples, an IV curve was created using an electrode pair in which a single molecule was bonded between the electrode pair, and the IV curve was further analyzed.

  The method based on the direct current measurement of the present embodiment is capable of speeding up the measurement as compared with the method based on the alternating voltage and alternating current using the conventional lock-in amplifier. It allows biomolecules (eg, nucleic acids or proteins) dispersed therein to be identified at the level of a single molecule. Examples will be described in detail below.

<1. Fabrication of electrode pair with single molecule bonded>
When performing electrical measurement of one molecule based on the DC measurement method, an electrode pair in which one molecule is bonded between the electrode pair using nano-mechanical-controllable break junction (MCBJ) Produced. A method for manufacturing the electrode pair will be described below.

  After spin-coating polyimide on a phosphor bronze substrate having a thickness of 0.5 mm, a polyimide film having a thickness of 4 μm was formed by baking. Next, after drawing a microelectrode pattern by photolithography, a Cr / Au layer (thickness: 5 nm / 30 nm) was deposited on the polyimide film by high-frequency sputtering.

  The substrate produced as described above was immersed in N, N-dimethylformamide for half a day, and subjected to ultrasonic cleaning to remove the photoresist layer, thereby producing an electrode.

  Next, overlapping drawing was performed by an electron beam lithography method, and a fine line pattern was drawn so as to connect the electrodes. The fine line pattern had a notch in the center, and the minimum width was 20 nm as a design value.

  After drawing the fine line pattern, a Cr / Au layer (thickness 1 nm / 100 nm) was deposited by high frequency sputtering. The obtained substrate was immersed in N, N-dimethylformamide for half a day and then subjected to ultrasonic cleaning. By removing the electron beam resist layer, a thin line having a junction having a width of 100 nm at the center was obtained.

  Finally, the polyimide layer on the substrate is excavated by a reactive ion etching method (using a mixed gas of carbon tetrafluoride and oxygen) to completely remove the polyimide immediately below the electrode joint, and to perform self-supporting bonding. A structure was formed. The total length of the junction structure was about 2 μm.

  An MCBJ substrate was produced as described above.

  The MCBJ substrate described above was placed on two support points. A Teflon (registered trademark) container is attached on an MCBJ substrate using an adhesive (polyimide), and a molecule having a thiol group to be measured (specifically, 1,4-benzenedithiol, An organic solvent (toluene) containing 2,5-dimercapto-1,3,4-thiadiazole or 1,6-hexanedithiol) was added.

  Next, the Au nanojoint formed on the MCBJ substrate was broken by pushing and bending the MCBJ substrate from the back side using a piezo element (see FIG. 6A). In this example, the broken Au nanojunction functions as an electrode pair.

  At this time, a molecule having a thiol group to be measured comes into contact with the surface of a clean fracture surface exposed by the fracture of the Au nanojunction, and forms an Au-thiol bond with Au. As a result, the molecule to be measured can be strongly adsorbed on the fracture surface.

  Thereafter, evacuation was performed to evaporate the organic solvent (toluene), leaving only the molecules to be measured on the fractured Au nanojunction. Note that it is preferable to perform the vacuum evacuation within a few minutes after breaking the joint. According to this, it is possible to prevent an excessive number of molecules (specifically, more than one molecule) from aggregating on the fracture surface to form a large aggregate.

When the vacuum level becomes 10 ⁻⁵ Torr or less, the piezoelectric element is driven by GPIB (General Purpose interface Bus) control to bend the MCBJ substrate, and the Au nanojunction break and re-formation is repeated 200 times. It is possible to prevent a defect from occurring in the bonding and to stably produce an electrode pair in which a single molecule is bonded (see FIG. 6A).

  In the series of operations described above, a direct current passing through the Au nanojunction is measured with a voltage of 0.2 V applied to the Au nanojunction using a picoammeter source (Keithley 6487), and the obtained direct current data is used. At the same time as calculating the electrical conductivity of the Au nanojunction, drive control of the piezo element was performed using the electrical conductivity.

  In this example, the movement of the piezo element was controlled so that the pushing speed was reduced in multiple steps as the Au nanojunction was gradually narrowed as the substrate was bent. Thereby, an electrode pair in which a single molecule is bonded can be manufactured very stably.

  After breaking and re-forming the Au nanojunction 200 times, the broken Au nanojunction was cooled to a temperature of 77K using liquid nitrogen. In this cooling process, in order to prevent the distance between the fractured Au nanojunction (in other words, the distance between the positive electrode and the negative electrode of the electrode pair) from significantly increasing with the contraction of the MCBJ substrate, The drive of the piezo element was appropriately controlled so that the electrical conductivity of the junction was maintained so as to correspond to one molecular conductance to be measured.

After the temperature around the Au nano-contact reaches 77K, by driving the piezoelectric element, was fattened Au nano-contact until 10G ₀ or more electric conductivity (G ₀ is the quantization unit of conductance). After that, after breaking the Au nanojunction by the self-breaking joining method, the electric conductivity of the broken Au nanojunction is stably maintained at the electric conductivity corresponding to one molecule to be measured. It confirmed (refer FIG.6 (b)).

<2. Measurement of IV characteristics (current-voltage characteristics) using a pair of electrodes bonded with a single molecule>
Among the electrode pairs to which the produced single molecule is bonded, using an electrode pair in which the electrical conductivity of the electrode pair is stable for more than 10 seconds in the vicinity of the electrical conductivity corresponding to one molecule to be measured, I-V characteristics were measured.

  The IV characteristics are measured using a picoammeter source (Keithley 6487), and the DC voltage applied to the fractured Au nanojunction (in other words, the electrode pair) is incremented by 0.2 mV from 0 V in the positive direction. After sweeping at a constant speed to reach + aV (a is an arbitrary number), the sweep direction was reversed to reach -aV (a is an arbitrary number). Each time the DC voltage was changed by 0.2 mV, the direct current flowing through the fractured Au nanojunction was recorded. An IV curve (current-voltage curve) was created by plotting the DC against the DC voltage.

  In addition, the IV curve was created for each of 1,4-benzenedithiol, 2,5-dimercapto-1,3,4-thiadiazole, and 1,6-hexanedithiol.

<3. Test results>
Fig. 7 (a) to Fig. 7 (d) and Fig. 8 (a) to Fig. 8 (d) show test results when 1,4-benzenedithiol is used. FIG. 10 (a) to FIG. 10 (d) and FIG. 11 (a) to FIG. 11 (d) show test results when 2,5-dimercapto-1,3,4-thiadiazole is used. Fig. 13 (a) to Fig. 13 (d) and Fig. 14 (a) to Fig. 14 (d) show test results when 1,6-hexanedithiol is used.

  More specifically, FIG. 7A shows an example of a typical IV curve, and FIG. 7B shows an I-V actually obtained when 1,4-benzenedithiol is used. V curve is shown.

  FIG. 10 (a) shows an example of a typical IV curve, and FIG. 10 (b) shows the actual I obtained with 2,5-dimercapto-1,3,4-thiadiazole. -V curve is shown.

  FIG. 13A shows an example of a typical IV curve, and FIG. 13B shows an IV curve actually obtained when 1,6-hexanedithiol is used. .

  In any case, the value of the direct current I flowing between the electrode pair increased as the value of the direct current voltage Vb applied to the electrode pair increased.

  Next, linear fitting (least square method) is performed in a low bias region (in other words, a region where an elastic tunnel current flows between the electrode pair) of the obtained IV curve, and an IV straight line (linear function) is obtained. Obtained. Then, a difference ΔI between the DC value on the IV curve and the DC value on the IV line was calculated. At this time, if it is assumed that the elastic tunnel current flowing between the electrode pair is represented by a linear function of the DC voltage applied to the electrode pair, the difference ΔI corresponds to the inelastic tunnel current flowing between the electrode pair. Can think.

  FIG. 7C shows a relationship between a typical difference ΔI and a DC voltage Vb, and FIG. 7D shows a difference ΔI and a DC voltage actually obtained when 1,4-benzenedithiol is used. The relationship with Vb is shown.

  FIG. 10 (c) shows a typical relationship between the difference ΔI and the DC voltage Vb, and FIG. 10 (d) is actually obtained when 2,5-dimercapto-1,3,4-thiadiazole is used. The relationship between the obtained difference ΔI and the DC voltage Vb is shown.

  FIG. 13C shows a relationship between a typical difference ΔI and a DC voltage Vb, and FIG. 13D shows a difference ΔI and a DC voltage actually obtained when 1,6-hexanedithiol is used. The relationship with Vb is shown.

  When the value of the difference ΔI is plotted against the value of the DC voltage Vb, in any case of 1,4-benzenedithiol, 2,5-dimercapto-1,3,4-thiadiazole and 1,6-hexanedithiol, When the DC voltage Vb was swept in the positive (negative) direction, the difference ΔI started to increase (decrease) from zero at a certain value of the DC voltage Vb.

  On the other hand, in the measurement using a pair of electrodes bonded with a single gold atom, when the DC voltage Vb is swept in the positive (negative) direction, the difference ΔI decreases from zero at a certain value of the DC voltage Vb. There was a tendency to increase (see FIGS. 15A to 15D).

  This characteristic ΔI-V characteristic is that the fully accelerated electrons excite specific molecular vibrations that can interact strongly with the electrons, so that the electric current of the electrode pair is separated from the DC voltage Vb of a specific value. It can be interpreted as appearing because of the change in conductivity. It strongly suggests that the difference ΔI is a parameter corresponding to the inelastic tunnel current.

  The value of the DC voltage Vb when the value of the difference ΔI changes takes a value corresponding to the energy of molecular vibration excited by the tunnel electrons, and the value of the DC voltage Vb is 1 on the ΔI-V curve as a DC voltage. Subsequent differentiation results in a substantially step shape, and the ΔI-V curve is secondarily differentiated with a DC voltage, resulting in a substantially peak shape, which can be detected more clearly.

  Specifically, FIG. 8A shows a typical graph obtained when the ΔI-V curve is first-order differentiated with respect to the DC voltage Vb, and FIG. 8B shows ΔI related to 1,4-benzenedithiol. The graph actually obtained when the -V curve is first-order differentiated with the DC voltage Vb is shown.

  FIG. 11 (a) shows a typical graph obtained when the ΔI-V curve is first-order differentiated with respect to the DC voltage Vb, and FIG. 11 (b) shows 2,5-dimercapto-1,3,4- The graph actually obtained when the ΔI-V curve related to thiadiazole is first-order differentiated with respect to the DC voltage Vb is shown.

  FIG. 14A shows a typical graph obtained when the ΔI-V curve is first-order differentiated with respect to the DC voltage Vb, and FIG. 14B shows the ΔI-V curve for 1,6-hexanedithiol. A graph actually obtained when first-order differentiation is performed with the DC voltage Vb is shown.

  FIG. 15C shows a graph that is actually obtained when the ΔI-V curve related to the gold atom is first-order differentiated with the DC voltage Vb.

  As shown in FIG. 8B, FIG. 11B, FIG. 14B, and FIG. 15C, when the value of the first derivative is plotted against the value of the DC voltage Vb, a substantially step-shaped graph is obtained. As a result, it was possible to more clearly detect the value of the DC voltage Vb when the value of the difference ΔI changes.

  FIG. 8C shows a typical graph obtained when the ΔI-V curve is second-order differentiated with the DC voltage Vb. FIG. 8D shows the ΔI-V for 1,4-benzenedithiol. A graph actually obtained when the curve is second-order differentiated with the DC voltage Vb is shown.

  FIG. 11 (c) shows a typical graph obtained when the ΔI-V curve is second-order differentiated with respect to the DC voltage Vb, and FIG. 11 (d) shows 2,5-dimercapto-1,3,4- The graph actually obtained when the ΔI-V curve relating to thiadiazole is second-order differentiated with respect to the DC voltage Vb is shown.

  FIG. 14 (c) shows a typical graph obtained when the ΔI-V curve is second-order differentiated with respect to the DC voltage Vb, and FIG. 14 (d) shows the ΔI-V curve for 1,6-hexanedithiol. A graph actually obtained when second-order differentiation is performed with the DC voltage Vb is shown.

  As shown in FIGS. 8 (d), 11 (d) and 14 (d), when the value of the second derivative is plotted against the value of the DC voltage Vb, a substantially peak graph is obtained. The value of the DC voltage Vb when the value of the difference ΔI changes can be detected more clearly than in the case of.

  8D and 11D, the value of the DC voltage Vb corresponding to the observed peak position was extracted by Gaussian fitting. In FIG. 8D and FIG. 11D, the position of the peak is indicated by an arrow.

  The value of the DC voltage Vb extracted by Gaussian fitting coincided with the energy of a characteristic molecular vibration mode having a strong vibronic interaction theoretically derived for all single-molecule junctions and single-atom contacts to be measured.

  For example, FIG. 9 shows molecular vibration mode energy (specifically, 0.05 eV, 0.10 eV, 0.14 eV, 0.20 eV) characteristic of 1,4-benzenedithiol. The molecular vibration mode energies 0.05 eV, 0.10 eV, 0.14 eV, and 0.20 eV are considered to correspond to the peaks indicated by arrows in FIG.

  In addition, FIG. 12 shows molecular vibration mode energy characteristic of 2,5-dimercapto-1,3,4-thiadiazole (specifically, 0.03 eV, 0.07 eV, 0.13 eV, 0.17 eV). Indicates. The molecular vibration mode energies of 0.03 eV, 0.07 eV, 0.13 eV, and 0.17 eV are considered to correspond to the peaks indicated by arrows in FIG.

  From the above results, it became clear that a ΔI spectrum applicable to the discrimination of one molecule can be derived by combining the IV curve created based on the DC voltage and DC and the numerical analysis. .

  The present invention can be used for detection, identification, identification, or structural analysis of various substances (for example, one molecule). More specifically, the present invention can be used for a sequencer for reading and understanding the base sequence of a polynucleotide.

DESCRIPTION OF SYMBOLS 1 ... Electrode 2 ... Electrode 5 ... Voltage source 6 ... Ammeter 7 ... Sample 10 ... Voltage source 20 ... Electrode pair 30 ... Ammeter 40 ... Analysis Unit 50: Comparison unit 60: Determination unit 100: Spectroscopic apparatus

Claims (10)

A first step of applying a DC voltage Vb to an electrode pair in which a sample is disposed between a positive electrode and a negative electrode;
A second step of measuring the value of the direct current I flowing between the electrode pair while changing the direct current voltage Vb;
A third step of determining a value Vp1 of the DC voltage Vb when the slope of the IV curve changes with respect to an IV curve in which the DC I is plotted with respect to the DC voltage Vb. Characteristic spectroscopy.   In the third step, the value Vp1 is determined by calculating a first derivative dI / dVb of the direct current I based on the direct current voltage Vb with respect to an IV curve in which the direct current I is plotted with respect to the direct current voltage Vb. The spectroscopic method according to claim 1, wherein: In the third step, the above value is obtained by calculating the ^second derivative d ² I / dVb ² of the direct current I with respect to the direct current voltage Vb with respect to the IV curve in which the direct current I is plotted with respect to the direct current voltage Vb. 3. The spectroscopic method according to claim 1, wherein Vp1 is determined.   4. The spectroscopic method according to claim 1, wherein the direct current I is obtained by subtracting a value of an elastic tunnel current flowing between the electrode pairs from a measured direct current value. 5. Law.   The method according to claim 1, further comprising a fourth step of comparing the value Vp1 of the sample with a predetermined value Vp2 of a reference sample corresponding to the value Vp1 after the third step. 5. The spectroscopic method according to any one of 4 above. 6. The spectroscopic method according to claim 5, further comprising a fifth step of determining at least one of the following (A) to (C) after the fourth step.
(A) When the value Vp1 of the sample and the value Vp2 of the reference sample are the same, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are the same;
(B) When the value Vp1 of the sample and the value Vp2 of the reference sample are partially the same, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are partially the same. ;
(C) When the value Vp1 of the sample and the value Vp2 of the reference sample are different, it is determined that the molecular structure of the sample and the molecular structure of the reference sample are different.   The spectroscopic method according to claim 1, wherein the sample moves in a space between the electrode pair.   The spectroscopic method according to any one of claims 1 to 7, wherein the space between the electrode pair is formed with a size in which only one molecule of substance is arranged as the sample.   The spectroscopic method according to claim 1, wherein in the second step, the DC voltage Vb changes by a constant value. A voltage source that applies a DC voltage V while changing a value with respect to an electrode pair in which a sample is disposed between a positive electrode and a negative electrode;
An ammeter for measuring the value of the direct current I flowing between the electrode pair;
An analysis unit that determines a value Vp1 of the DC voltage Vb when the slope of the IV curve changes with respect to an IV curve in which the DC I is plotted with respect to the DC voltage V. A spectroscopic device.