1. A preparation method for forming a nanogap electrode pair is characterized by comprising the following steps of:

step 1: drawing the multi-channel tubule into a nanopipette (3) with a sharp end at one end by applying external force;

step 2: preparing an electrode pair with a nanogap at the tip of a nanopipette (3);

and step 3: and (3) soaking the electrode pair prepared in the step (2) in a solvent for storage, thereby preparing the nano liquid-moving device (3) with the nano gap electrode pair.

2. The method of claim 1, wherein in step 1), a wire is inserted into the multi-channel tubule before the multi-channel tubule is drawn.

3. The method according to claim 2, wherein the step 2) is specifically: the nanogap electrode pair is prepared at the tip of the metal wire, namely at the tip of the nanopipette (3) by electrochemical deposition, chemical etching, mechanical controlled cracking or electroetching.

4. The method according to claim 3, wherein the chemical etching, mechanical controlled cracking or electrical etching is performed by:

firstly, preparing a contact electrode pair at the tip of a metal wire, namely the tip of the nanopipette (3) by an electrochemical deposition method, and then preparing the electrode pair contacted with the tip of the nanopipette (3) into the electrode pair with a nanogap by a chemical etching method, a mechanical controllable junction method or an electric etching method.

5. The method according to claim 1, wherein the step 2) is specifically:

2.1) after the drawing of the nano liquid transfer machine (3) in the step 1) is finished, forming a carbon nano electrode (2) on the head of the nano liquid transfer machine by adopting a carbon deposition method;

2.2) inserting a metal wire from the other end of the nano-pipette, wherein the metal wire does not extend out of the tip of the nano-pipette (3);

2.3) etching the end part of the carbon nano electrode by an electroetching method so as to facilitate electrochemical deposition;

2.4) preparing the electrode pair with the nanogap at the end of the carbon nano-electrode, namely the tip of the nanopipette (3) by an electrochemical deposition method.

6. The method of any one of claims 3 to 5, wherein during the preparation of the nanogap electrode pair at the tip of the nanopipette (3), the preparation is terminated by detecting a tunneling current between the electrode pairs or by detecting a conductance between the electrode pairs to a predetermined value.

7. The method according to claim 1, wherein the multi-channel tubule is a thin glass tube, and the number of channels of the multi-channel tubule is not less than two.

8. The method of claim 1, wherein the size of the nanogap is sub-10 nm, and the specific size range is 0.1 nm to 10 nm; the nanogap is the smallest diameter of the gap between the two electrodes in the electrode pair.

9. The manufacturing method of forming a pair of nanogap electrodes according to claim 1, wherein the inner diameter of each channel in the nanopipette (3) is 1 nm to 200 nm.

10. The method of claim 1, wherein the solvent used in step 3) is 18.2M Ω -cm of ultrapure water or ethanol, and the soaking time is 12-48 hours.

Background

The sub-10 nm gap electrode pair is an electrode having a gap size between counter electrodes within 10 nm. With the push of miniaturization development, nanogap electrodes have received worldwide attention as important platforms for detecting various small molecules and as basic members for constructing multifunctional molecular devices and systems. Nanogap electrodes below 10 nm have shown great advantages in many respects. Fields of application, such as sensing, optics, molecules and electronics. The gap spacing is reduced to below 10 nanometers, which will thoroughly change the existing nano gap related research and lead to valuable new physical phenomena, such as non-local electromagnetic effect, quantum interference, nuclear spin and electron tunneling, and have application prospects with high scientific and social influences, including the fields of molecular electronics, quantum tunneling, plasmon nano optics, highly sensitive sequencing and the like.

Although sub-10 nm gap electrodes hold great promise, they still face a number of fundamental challenges, namely how to efficiently and controllably fabricate sub-10 nm gap electrodes. To date, there are a variety of techniques for fabricating sub-10 nm gap electrodes, such as sub-10 nm electrodes fabricated by fracture junction techniques, electromigration and photolithography techniques, the latter typically combined with electrochemical deposition. However, all these techniques have in common that the manufacturing process is time consuming, cumbersome and the process has a limited degree of controllability. This results in poor repeatability from device to device, which is not conducive to scale up. This immature manufacturing method is not conducive to the wide application of tunneling nanoelectrodes, and hinders the commercial development prospects thereof. An innovative approach to address these problems and facilitate the application and development of sub-10 nm gap-based electrodes is urgently needed.

Disclosure of Invention

In order to solve the problems in the background art, the invention provides a preparation method for forming a nano-gap electrode pair, which combines the technologies of laser drawing, electrochemical deposition and the like, and can prepare the nano-gap electrode pair with the gap length of sub-10 nanometers in high precision with high yield by means of tunneling current feedback and the like.

The technical scheme adopted by the invention is as follows:

a method of forming a nanogap electrode pair, comprising the steps of:

step 1: drawing the multi-channel thin tube into a nano liquid transfer device with a tip at one end by applying external force;

step 2: preparing an electrode pair with a nanogap at the tip of a nanopipette;

and step 3: and (3) soaking the electrode pair prepared in the step (2) in a solvent to store so as to stabilize the electrode structure, thereby preparing the nano pipette with the nano gap electrode pair.

The external force is applied by drawing with a laser drawing instrument.

In the step 1), a metal wire is inserted into the multi-channel tubule before the multi-channel tubule is drawn.

The step 2) is specifically as follows: the nanogap electrode pair is prepared at the tip of the metal wire, namely at the tip of the nanopipette by electrochemical deposition, chemical etching, mechanical controlled crack Junction (mechanical controlled Break Junction) or electrical etching.

The wire is inserted to provide continuity of the electrically conductive medium.

The chemical etching, mechanical controllable crack or electric etching method specifically comprises the following steps:

firstly, preparing a contact electrode pair at the tip of a metal wire, namely at the tip of the nanopipette by an electrochemical deposition method, and then preparing the electrode pair contacted with the tip of the nanopipette into the electrode pair with a nanogap by a chemical etching method, a mechanical controllable junction method or an electric etching method.

The step 2) is specifically as follows:

2.1) after the drawing of the nanopipette in the step 1) is finished, forming a carbon nano electrode on the head of the nanopipette (namely, the position close to the tip of the nanopipette) by adopting a carbon deposition method;

2.2) inserting a metal wire from the other end of the nano-pipette, wherein the metal wire does not extend out of the tip of the nano-pipette and is fixed through silica gel;

2.3) etching the end part of the carbon nano electrode by an electroetching method so as to facilitate electrochemical deposition;

2.4) preparing an electrode pair with a nanogap at the end of the carbon nanoelectrode, i.e., the nanopipette tip, by means of electrochemical deposition.

The carbon nanoelectrodes provide a robust electrical channel for the nanopipette.

In the process of preparing the electrode pair with the nanogap at the tip of the nanopipette, the sign of the preparation termination is that tunneling current is detected between the electrode pairs or the conductance value between the electrode pairs reaches a set value.

The multi-channel thin tube is a thin glass tube, and the number of channels of the multi-channel thin tube is not less than two; when the number of the channels is odd, the other channels are symmetrically arranged by taking the middle channel as a center; when the number of the channels is even, all the channels are symmetrically arranged.

The size of the nanometer gap is sub-10 nanometers, and the specific size range is 0.1 to 10 nanometers; the nanogap is the smallest diameter of the gap between the two electrodes in the electrode pair.

The inner diameter of each channel in the nanometer liquid transfer device is 1 nanometer to 200 nanometers.

The solvent in the step 3) adopts ultrapure water or ethanol with the concentration of 18.2M omega cm, and the soaking time is 12-48 hours.

The invention has the beneficial effects that:

compared with other nano electrodes, the electrode prepared by the invention has good stability and high controllability of electrode spacing. The sub-10 nanometer gap electrode pair prepared by the method can be used for manufacturing nanometer devices with nanometer gaps, such as molecular junctions, tunneling probes, Raman probes and the like.

The invention overcomes the problem that the sub-10 nanometer gap electrode can not be accurately prepared by the selection of a multi-channel thin tube, the design of drawing parameters, the selection of electrochemical materials, the control of current feedback and the parameter selection of voltage.

Drawings

FIG. 1 is a schematic view of the structure of a sub-10 nm gap electrode pair according to the present invention.

Fig. 2 is a schematic view of the apparatus for carbon deposition of the nanopipette of example 1.

Fig. 3 is a schematic view of an apparatus for electrochemical deposition of nanogap electrodes according to example 1.

Figure 4 is a graph of the tunneling current observed during electrochemical deposition of the nanogap electrode of example 1.

FIG. 5 is a graph of the results of tunneling current bias (I-V) for electrode pairs of different nanogap sizes of example 1.

FIG. 6 is a scanning electron micrograph of the nanogap electrode pair of example 1, wherein A is a side view and B is a top view.

In the figure: 1-conductive metal wire, 2-carbon nano electrode, 3-nano pipette, 4-gold electrode, 5-butane, 6-butane flame, 7-quartz capillary, 8-argon, 9-rubber tube, 10-reference electrode and counter electrode, and 11-electroplating solution.

Detailed Description

In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.

The term "nanopipette" as used herein generally refers to a multi-channel tubule of pipette-like shape with a single side tip and a tip size on the order of nanometers.

The term "gap" as used herein generally refers to a void, channel, or passage formed or otherwise provided in a material. The material may be a solid material, such as a substrate. The gap may be disposed adjacent or proximate to the sensing circuit or an electrode coupled to the sensing circuit. In an embodiment, the gap has a characteristic width or diameter on the order of 0.1 nanometers to about 10 nanometers. A gap having a width of a nanometer order may be referred to as a "nanogap". In some cases, the width of the nanogap can be less than the diameter of the biomolecule or a subunit of the biomolecule (e.g., a monomer).

The term "electrode" as used herein generally refers to a material or component that can be used to measure an electrical current. An electrode (or electrode assembly) may be used to measure current into and out of another electrode. In some cases, electrodes may be disposed in a channel (e.g., a nanogap) and used to measure current across the channel. The current may be a tunneling current. Such a current can be detected when a biomolecule (e.g., a protein) flows through the nanogap. In some cases, a sensing circuit coupled with an electrode provides an applied voltage across the electrode to generate a current. Alternatively or additionally, the electrodes may be used to measure and/or identify the conductance associated with a biomolecule (e.g., an amino acid subunit or a protein monomer). In this case, the tunneling current may be related to the conductance.

In an embodiment, the nanoelectrode pairs comprise individual nanoelectrodes separated by a gap having a length of 0.1 to 10 nanometers. The nanoelectrodes may be of any convenient shape or size and may comprise any conductive material. Each of the electrodes disclosed herein may be made of a different material or from a mixture of materials, such as an alloy.

Nanoelectrodes are used to measure the current that can travel through and/or across a molecule. The current may be a tunneling current. Measuring the current can be used to determine the sequence of a biopolymer, such as a nucleic acid molecule (e.g., DNA or RNA) or a protein. For mass measurement, the gap spacing between the electrodes of one or more nanoelectrode pairs can be stable and controllable.

For the purpose of facilitating an understanding of the embodiments of the present invention, embodiments of the present invention will be described below with reference to the accompanying drawings. The various embodiments are not to be construed as limiting the embodiments of the invention.

Example 1

The structure of the nanogap electrode pair prepared in example 1 of the present invention is shown in fig. 1, a conductive metal wire 1 in a channel of a nanopipette is made of a copper wire, a carbon electrode 2 at the tip of the nanopipette obtained by carbon deposition, a nanopipette 3 with a tip on one side of a drawn double channel, and a nanogap gold electrode 4 electrochemically deposited on the carbon nanoelectrode.

The preparation process comprises the following steps:

step one, drawing a nanometer liquid shifter with a tip on one side

Drawing the cleaned thin tube by a two-step method, wherein the drawing adopts a P-2000 laser drawing instrument: first, applying laser beam to Heat the middle part of a thin glass tube, heating and simultaneously drawing, wherein drawing parameters are set as Heat: 850, Filament: 4, Velocity: 30, Delay: 160, Pull: 100, respectively; secondly, setting parameters as Heat: 860, fragment: 3, Velocity: 20, Delay: 140, Pull: 160. the drawing procedure is ended, forming two identical nanopipette 3 with single-sided tip.

The cleaning steps are as follows: the tubules were rinsed clean with 18.2 M.OMEGA.cm of ultrapure water, and the tubes were placed in a plasma cleaner to clean surface impurities for 30 minutes.

The thin tube is a double-channel thin glass tube, the outer diameter of the thin glass tube is 1.2mm, the inner diameter of the thin glass tube is 0.90mm, and the length of the thin glass tube is 100 mm.

Step two, preparing carbon nano-electrode at the tip of the nano-pipette

As shown in fig. 2, the tip of the nanopipette 3 prepared in the first step is placed in a quartz capillary 7, and 0.2m is introduced³Argon for a/min of 8. The other end of the nanometer liquid transfer device 3 is connected with a rubber tube 9 and is filled with 0.2m³Butane 5 gas/min. The quartz capillary 7 was preheated with a butane flame 6 and the butane flame was moved along the quartz capillary 7 to adjust the flame position until the tip of the nanopipette 3 appeared bright yellow. After the state of preheating was maintained for 10 seconds, the butane flame was moved from the tip to the distal end along the nanopipette 3, and the probe was heated for 30 seconds, thereby forming the carbon nanoelectrode 2 at the tip of the nanopipette 3.

And the nanopipette in the second step is manufactured on the same day of use and stored in a sealed culture dish.

Step three, electroetching the carbon nano electrode

1) And (3) inserting the metal wire 1 from the tail part of the nano pipettor 3 treated in the step two, and fixing the metal wire by using silica gel.

2) And etching the carbon nano-electrode in the etching solution. The etching process was carried out in a CHI760C instrument using a cyclic scan with the following parameters: initial potential: 0V, final potential: 2V, number of scans: 4-6 times, scanning speed: 0.1V/s. Both carbon nanoelectrodes serve as working electrodes. The reference electrode and the counter electrode are respectively made of silver wires and platinum wires.

The metal wire 1 is a copper wire, and the outer diameter is 0.5 mm.

The etching solution is 100mM KCl and 100mM KOH.

The outer diameter of the silver wire is 0.250mm, and the outer diameter of the platinum wire is 0.250 mm.

All electrochemical characterizations were performed in a faraday cage throughout the synthesis.

Step four, preparing the nanogap electrode pair on the carbon nanoelectrode by electrochemical deposition (as shown in FIG. 3)

1) Using a potentiostat, the nanopipette tip (the etched carbon nanoelectrode) was immersed in the plating solution 11, and gold pre-electrodeposition was performed for a certain period of time using a constant potential program.

2) Feedback-controlled electrodeposition was performed using a potentiostat, with a certain preset current being selected, and once tunneling current was observed, the nanopipette tip was immediately taken out of the solution and rinsed with 18.2M Ω · cm ultrapure water, which was then stored in a sealed vial filled with 18.2M Ω · cm ultrapure water until use.

The plating solution 11 was ECF64D diluted 10 times and contained 4.4mM NH₄AuSO₃And 52mM (NH)₄)₂SO₃。

The constant potential program is specifically as follows: the Ag/AgCl wire 10 is used as a reference electrode and a counter electrode, the two carbon nano electrodes are used as working electrodes, and the constant potential is set as a first potential: -730mV, potential two: 750mV and 20mV potential difference.

The Ag/AgCl wire is newly prepared and has an outer diameter of 0.125 mm.

The gold pre-electrodeposition time is 20-50 seconds.

The preset current is 10pA-1 nA.

The feedback control electrodeposition specifically comprises the following steps: in the constant current electrodeposition process, one carbon nano-electrode serves as a reference electrode and a counter electrode, and the other carbon nano-electrode serves as a working electrode.

As shown in fig. 4, for the tunneling current observed during electrodeposition.

The function of the gold nano electrode preserved in the ultrapure water is to rearrange and assemble the atomic structure of the gold nano electrode by utilizing the reforming effect.

Fig. 5 shows the results of tunneling current bias (I-V) measurements in air at room temperature (297K) for the prepared electrode pairs of different nanogap sizes.

FIG. 6 shows a scanning electron micrograph of the nanogap electrode pair.

Example 2

The method for preparing the nanogap electrode pair provided in embodiment 2 of the invention comprises the following steps:

step one, placing a metal wire in a thin glass tube;

drawing a thin glass tube with metal wires inside;

the second step is specifically as follows: drawing the cleaned thin glass tube with the gold wire inside by a three-step method by using a P-2000 laser drawing instrument: first, a laser beam is applied to Heat the middle part of a thin glass tube while drawing, and drawing parameters are set to be, Heat: 350, Filament: 4, Velocity: 15, Delay: 120, Pull: 0, heating and melting the middle part of the thin glass tube to form an hourglass-shaped structure; and step two, hermetically connecting two ends of the thin glass tube with a tetrafluoroethylene hose, and vacuumizing the interior of the thin glass tube for 6 minutes. The glass tube and wire were then Heat sealed and the drawing parameters were set to Heat: 390, file: 3, Velocity: 12, Delay: 120, Pull: 0; thirdly, reheating the thin glass tube after the metal wire is sealed, and simultaneously applying tension to two ends of the thin glass tube, wherein drawing parameters are set as Heat: 520, Filament: 3, Velocity: 36, Delay: 170, Pull: 50. the drawing procedure was completed and a nanopipette with a tip on one side and a wire inside was formed.

The cleaning steps are as follows: washing with 18.2M omega cm ultrapure water, putting into a plasma cleaning machine to clean impurities on the surface for 30 minutes.

The heating and sealing steps are as follows: the glass tube was heated for 4 seconds, cooled for 1 minute, and then heated for 7 seconds.

Because the most pointed wire is often wrapped in glass due to the difference in ductility between the glass capillary and the wire, it needs to be mechanically polished using a pin-grinding machine to expose the wire.

The thin glass tube is a double channel, the outer diameter is 1.2mm, the inner diameter is 0.90mm, the length is 100mm, and two same metal wires are respectively inserted from the tail part.

The metal wire is a gold wire, the length of the metal wire is 2cm, and the outer diameter of the metal wire is 25 micrometers;

and step three, preparing the nanogap electrode pair on the tip of the metal wire by adopting the electrochemical deposition method of the step four in the first embodiment.

1) Using a potentiostat, the nanopipette tip (wire tip) was immersed in the plating solution and gold pre-electrodeposition was performed for a certain time using a potentiostatic program.

2) Feedback-controlled electrodeposition was performed using a potentiostat, with a certain preset current being selected, and once tunneling current was observed, the nanopipette tip was immediately taken out of the solution and rinsed with 18.2M Ω · cm ultrapure water, which was then stored in a sealed vial filled with 18.2M Ω · cm ultrapure water until use.

Example 3

The method for preparing the nanogap electrode pair provided in embodiment 3 of the invention comprises the following steps:

wherein the first and second steps are the same as those of the first and second steps of the embodiment 2.

Step one, placing a metal wire in a thin glass tube;

drawing a thin glass tube with metal wires inside;

step three, contacting the tips of the metal wires through electrochemical deposition;

the third step is specifically as follows: the metal wire at the tip of the nanopipette is immersed in the electroplating solution, one of the two metal wires is used as a working electrode, the other metal wire is used as a reference electrode, a gold wire is inserted in the electroplating solution to be used as a counter electrode, and the three electrodes are respectively connected with a potentiostat. The potential of the working electrode relative to the reference electrode changes continuously as gold atoms are deposited on the working electrode during electrochemical deposition. When the distance between the working electrode and the reference electrode is continuously reduced, the potential of the working electrode relative to the reference electrode is obviously increased and finally reaches 0V, which indicates that the working electrode is just connected with the reference electrode, and the electrochemical deposition process is immediately stopped at the moment to obtain the contacted electrode pair.

The outer diameter of the gold wire is 0.25 mm.

And step four, preparing the nano-gap electrode pair by using a mechanical controllable cracking method.

The fourth step is specifically as follows: the tip of the nanopipette is fixed on a mechanical controllable crack device, and the two metal wires are respectively connected with an electrical measuring instrument. The mechanical controllable split device is an elastic chip, a mandril positioned right below the center of the chip is operated to move upwards to bend the chip, the bending stress of the chip is further transmitted to the contact position of the fixed electrode pair, the electrode pair is finally pulled back along two sides of the contact point to form a nanometer gap, and the mandril can recover the chip, so that the electrode pair is recovered to contact. During the process, whether the size of the nanometer gap is in the tunneling action range is judged through the tunneling current.

Example 4

The method for preparing the nanogap electrode pair provided in embodiment 4 of the invention comprises the following steps:

the first, second and third steps of the embodiment 4 of the present invention are the same as the first, second and third steps of the embodiment 3.

Step one, placing a metal wire in a thin glass tube;

drawing a thin glass tube with metal wires inside;

step three, contacting the tips of the metal wires through electrochemical deposition;

and step four, preparing the nano-gap electrode pair by using a chemical etching method.

The fourth step is specifically as follows: the nanopipette tip was immersed in the etching solution, and once a tunneling current was observed, the nanoelectrode was immediately taken out of the solution and washed with 18.2M Ω · cm ultrapure water, and then stored in a sealed vial filled with 18.2M Ω · cm ultrapure water until use.

The etching solution is a mixed solution of concentrated hydrochloric acid and ethanol with the volume ratio of 1: 10.

Example 5

The method for preparing the nanogap electrode pair provided in embodiment 5 of the invention comprises the following steps:

the first, second and third steps of the embodiment 5 of the present invention are the same as the first, second and third steps of the embodiment 3.

Step one, placing a metal wire in a thin glass tube;

drawing a thin glass tube with metal wires inside;

step three, contacting the tips of the metal wires through electrochemical deposition;

and step four, preparing the nano-gap electrode pair by using an electroetching method.

The fourth step is specifically as follows: and (3) placing the nano pipette in the air, taking one of the two metal wires as a working electrode and the other metal wire as a reference electrode, and connecting the two electrodes with a potentiostat respectively. A10V bias was applied across the electrodes, stopped when the voltage abruptly changed to 0, and then stored in a sealed vial filled with 18.2 M.OMEGA.cm of ultrapure water until use.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.