Self-assembled monolayer modified electrode and preparation method and use thereof

Abstract

The present invention provides a self-assembled monomolecular film modified electrode and its preparation method and use. We use shielding molecules and conductor molecules to modify the electrode at the same time, which not only ensures the conductivity of the electrode, but also effectively avoids the generation of false positives and improves the detection accuracy of the electrode.

Description

Technical Field

[0001] The invention relates to the field of biotechnology, in particular to a self-assembled monomolecular film modified electrode and a preparation method and application thereof. Background Art

[0002] Unmodified gold electrodes have excellent electrical conductivity. However, in the electrochemical detection of molecules, it is usually through the specific binding of probes and target substances that electrical signals can be obtained or changed after the binding, thereby achieving molecular detection. If the gold electrode is not modified, substances with electrical signals that have not undergone specific binding can also be detected by the electrode in electrochemical detection.

[0003] Self-assembled monolayer (SAM) refers to a two-dimensional monolayer of molecules that is spontaneously formed through physical and chemical interactions between molecules and substrate surfaces and between molecules. It has the characteristics of uniformity, consistency, and close arrangement. Self-assembled monolayers (SAMs) have been widely studied, among which gold has a strong affinity with thiol compounds and is often used as a substrate to prepare SAMs. The core molecular structure in the self-assembled monolayer can be regarded as two parts: the head group and the tail group. The head group is the group on the side away from the substrate, usually the functional end of the monolayer; while the tail group is the group on the side close to the substrate. If the substrate is a gold material, the tail group is usually a thiol, and if it is combined with a silicon surface, chlorosilane is selected.

[0004] Another important feature of self-assembled monolayers is that molecules with different structures can be connected on the same substrate to form a monolayer mixed film. The common synthesis method is to prepare a solution of the molecular films to be connected in a certain proportion, and then immerse gold in the solution to complete the self-assembly.

[0005] Self-assembled monolayers have been studied in the prior art. The main application scenarios of this technology include self-assembled thin films and coating materials; constructing hydrophobic surfaces in MEMS components; forming thin film coatings for drugs for targeted cancer treatment; and fixing DNA chains in biological analysis. These applications usually use a single self-assembly solution to modify the surface of the material to achieve a certain effect. Research on modifying several different self-assembled monolayers on the same substrate is relatively scarce. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, the technical solution of the present invention adds a shielding self-assembled monolayer film on the electrode surface to isolate the contact between the substance with electrical signal that has not undergone specific binding and the gold electrode, and at the same time adds conductor molecules to improve the detection performance of the electrode.

[0007] One aspect of the present invention provides an electrode for electrochemical detection of nucleic acid molecules, comprising an electrode, the surface of which is modified with shielding molecules and conductor molecules, the length of the conductor molecules is less than or equal to the length of the shielding molecules, the shielding molecules include a head group and a tail group, the head group is a shielding group, and the tail group is a connecting group for connecting the electrode.

[0008] Typically, the length of the shielding molecule can range from 12-40 carbon chain lengths.

[0009] Furthermore, the electrode can be any electrode in the prior art that can self-assemble with sulfur-hydrogen bonds, such as a silver electrode, a copper electrode, a gold electrode, or a platinum electrode, preferably a gold electrode.

[0010] Furthermore, a common shielding group can be a long carbon chain alcohol (more than 12 carbon chains), and the tail group can be a thiol (-SH). The head shielding group can block the binding of non-target molecules to the electrode, and the tail group can form a chemical bond between the shielding molecule and the electrode to achieve the purpose of fixing the shielding molecule.

[0011] Furthermore, the head group is composed of a plurality of ethylene glycols and 10-20 carbon alkane chains connected in sequence, as shown in Figure 4a , the tail group is a thiol group.

[0012] Furthermore, the conductor molecule is a benzene ring chain structure or a long chain of benzene rings and alkynyl groups connected alternately.

[0013] Another aspect of the present invention provides the use of the above-mentioned electrode for detecting nucleic acid molecules. The nucleic acid molecules can be DNA or RNA from organisms.

[0014] Another aspect of the present invention provides a product for detecting nucleic acid molecules, wherein the product comprises the electrode and a biological probe.

[0015] Furthermore, the biological probe is a single-stranded nucleic acid containing a nucleotide sequence that can bind to and complementarily pair with a target sequence in a target gene. For the design of the probe, those skilled in the art can refer to the design method of biological probes in the prior art. The main purpose of the biological probe is to capture the target nucleic acid and pull the target nucleic acid close to the electrode.

[0016] Furthermore, the biological probe is modified with a redox molecule, such as a ferrocene molecule.

[0017] Furthermore, the tail end of the biological probe is also modified with a molecule that can be connected to the electrode. For example, if the electrode is a gold electrode, the tail end of the biological probe can be modified with a thiol group.

[0018] Another aspect of the present invention provides a method for preparing the above electrode, the method comprising the following steps:

[0019] The electrode is immersed in a self-assembly solution, wherein the self-assembly solution refers to a solution containing shielding molecules and conductor molecules.

[0020] Furthermore, the method further comprises cleaning the electrode and then immersing it in the self-assembly solution. The cleaning method may be: cleaning the electrode with acetone isopropanol; and heating the electrode at 120-180 degrees in a nitrogen environment for 1-2 hours.

[0021] Furthermore, the electrode immersed in the self-assembly solution is taken out and rinsed with alcohol.

[0022] Furthermore, the final concentration of the shielding molecules is 1-3 mM, and the final concentration of the conductor molecules is 0.5-2 mM.

[0023] Usage: After the electrode is added to the self-assembly solution to complete the modification, the gene solution to be tested and the probe solution are added above the electrode, and then the electrical signal is detected by square wave voltammetry. For details, please refer to the following examples.

[0024] As described above, the electrode for electrochemical detection of nucleic acid molecules of the present invention has the following beneficial effects:

[0025] We modified the surface of the electrode with shielding molecules and conductor molecules, which can effectively avoid false positives from non-target genes and accurately detect target molecules, thereby improving the accuracy of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Shown is a schematic diagram of screen-printed electrodes.

[0027] Figure 2 The square wave voltammetric signal is shown after the shielding molecules form a self-assembled monolayer on the gold electrode surface. The solid line represents the result before the shielding molecules are added, and the dotted line represents the signal after the shielding molecules self-assembled monolayer is added.

[0028] Figure 3 Shown are schematic diagrams of the molecular structures of two conductor molecules.

[0029] Figure 4a Shown is a schematic diagram of the molecular structure of the shielding molecules and conductor molecules we use.

[0030] Figure 4b Shown is a schematic diagram of the monolayer structure formed by modifying the shielding molecules and conductor molecules on the electrode surface.

[0031] Figure 5The square wave voltammetric signal diagram after the self-assembled monolayer film is formed on the gold electrode surface using different molecules is shown, where the solid line represents the result after the conductor molecules are added to form the self-assembled film, the long dashed line represents the result after a certain proportion of conductor molecules and shielding molecules are added to form the self-assembled film, and the short dashed line represents the result after the shielding molecules are added to form the self-assembled film.

[0032] Figure 6 The target genes with signaling probes we used and the non-target genes with signaling probes are shown.

[0033] Figure 7 A schematic diagram showing the principle of detecting target genes and non-target genes using a fully modified electrode (modified with shielding molecules and conductor molecules).

[0034] Figure 8 The electrochemical signal diagram showing the detection of target genes and non-target genes by the fully modified electrode (shielding molecule and conductor molecule modification).

[0035] Fig. 9 The schematic diagram of the detection of target genes and non-target genes using electrodes modified only with shielding molecules is shown.

[0036] Fig.10 The electrochemical signal diagram of the target gene and non-target gene detection using an electrode modified with only shielding molecules is shown.

[0037] Fig.11 Display as Figure 8 and Fig.10 The results are combined into one figure. The thick solid line and the thick dashed line represent Figure 8 The electrochemical signals of the target gene and non-target gene in the graph are shown in Figure 2. The thick solid line and thick dashed line represent Fig.10 Electrochemical signals of target genes and non-target genes in .

[0038] Fig.12 Schematic diagram showing the detection principle of target and non-target genes on unmodified electrodes.

[0039] Fig.13 The electrochemical signal diagram showing the detection of target genes and non-target genes on the unmodified electrode. DETAILED DESCRIPTION

[0040] We changed the electrical properties of the gold electrode by adding mixed solutions of strong and weak conductivity in different proportions to the gold electrode to form a self-assembled monolayer film.

[0041] According to the tests of different substances, the head group of the shielding molecule we selected is composed of several ethylene glycols and 10-20 carbon alkane chains, and the tail group is thiol. If the electrode surface is only covered with shielding molecules, it is likely to shield both useful signals and noise. Therefore, we added a conductor molecule with a certain conductivity to enable the modified gold electrode to filter out noise while receiving useful signals. Common conductor molecules include benzene ring chain structures and structures connected between benzene rings and alkynyl groups ( Figure 3 ), where the connection between the benzene ring and the alkynyl group has good conductivity, but the disadvantage is that the molecular stability is poor and it is easy to cross-link or oxidize, but it has good stability after being combined with the gold electrode immediately after preparation; the single benzene ring chain structure has better stability, but the corresponding conductivity is not as good as the former. In our test, we found that the wires of both structures can meet the experimental requirements, and the wires with strong conductivity can also obtain larger electrical signals.

[0042] It is important that the length of the conductor molecule must be less than the length of the shielding molecule. If the length of the conductor molecule is too long, the molecular layer after self-assembly will be higher than the thickness of the shielding layer, and the noise signal cannot be effectively shielded. Therefore, we choose a shorter molecular chain length so that the final conductor molecule self-assembled film is inside the shielding molecule film. From the perspective of the entire planar structure ( Figure 4b ), there is a certain gap between the arrangement of molecules. If the size of the signal molecule is smaller than or close to this gap, it can fall into the shielding molecule membrane and contact the conductor molecule membrane, thereby transferring electrons to generate electrical signals. Therefore, when performing subsequent molecular detection, a probe layer can be added. The function of the probe layer is to capture the target substance with electrical signal molecules. The captured substance is close to the self-assembled film of the entire electrode, and the smaller signal molecules on it enter the shielding molecule membrane and transmit electrical signals through the conductor molecules, while the non-target substances that are not captured are free in the entire solution, and the larger volume of the entire substance will be blocked outside the shielding molecule membrane and cannot be detected.

[0043] After certain electrochemical tests, we can determine the conductivity of the conductor molecules and the effect of adding conductor molecules on the electrochemical properties of the entire self-assembled monolayer. The results show that the conductor molecules we use have obvious conductivity compared to shielding molecules. When a certain proportion of conductor molecules are added to the shielding molecule solution and then immersed in the gold electrode for self-assembled monolayer, the current size is about 18 times that when there is only a shielding molecule film, indicating that the conductivity of the gold electrode has been improved to a certain extent.

[0044] The following is an explanation of the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the process equipment or devices not specifically noted in the following embodiments all adopt conventional equipment or devices in the art. In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the presence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combined connection relationship between one or more devices / devices mentioned in the present invention does not exclude the presence of other devices / devices before and after the combination device / device or the insertion of other devices / devices between these explicitly mentioned two devices / devices, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, rather than limiting the order of arrangement of each method step or limiting the scope of the present invention. The change or adjustment of its relative relationship, without substantial change in the technical content, should also be regarded as the scope of the present invention.

[0045] Materials and Methods :

[0046] Electrode (three-electrode system): The working electrode and auxiliary electrode materials are gold, and the reference electrode uses silver / silver chloride;

[0047] Screen-printed electrodes (Botan Technology (Weihai) Co., Ltd.), such as Figure 1 As shown; compared with traditional electrodes, screen-printed electrodes are disposable electrodes with low cost and no maintenance required. Each electrode has a high degree of repeatability, is small in size and flexible in use, and can be customized in different shapes and materials according to needs.

[0048] Detection method: square wave voltammetry. The input voltage of square wave voltammetry is a step voltage that rises or falls continuously, and a symmetrical equal-amplitude square wave with a small amplitude is superimposed on each step, and then the generated current signal is detected. All test results are realized on the electrochemical workstation Autolab of Metrohm Switzerland. Different parameters are adjusted in the software to obtain the optimal electrical signal curve.

[0049] Example 1: The conductivity of the electrode surface is reduced after modification with shielding molecules

[0050] First, clean the gold electrode purchased on the market: clean it with acetone and isopropanol for several minutes, blow it dry, and then heat it to 120-180 degrees in a nitrogen environment for 1-2 hours.

[0051] The gold electrode material was first used for square wave voltammetry measurement, and the measuring solution was a PBS solution of 500 μM potassium ferrocyanide; after being thoroughly rinsed with pure water, the electrode was immersed in a 1 mM shielding molecule solution (molecular structure such as Figure 4a As shown, the solvent used is anhydrous alcohol), and the immersion time at room temperature is 2-4 hours. Then, it is taken out of the solution and rinsed with anhydrous alcohol and blown dry to complete the self-assembled molecular film modification. The modified gold electrode is tested with potassium ferrocyanide solution of the same concentration and it is found that the peak electrical signal is reduced by about 150 times.

[0052] Test results such as Figure 2 As shown, the solid line represents the result before adding shielding molecules, and the dotted line represents the signal after adding shielding molecule self-assembled film, indicating that the conductivity of the gold electrode modified with shielding molecules is greatly reduced.

[0053] Example 2: Electrode conductivity is enhanced after adding conductor molecules

[0054] Three electrode construction methods: We used shielding molecules and conductor molecules as shown in Figure 4. All electrodes were cleaned with acetone and isopropanol before modification and heated to 120-180 degrees for 1-2 hours in a nitrogen environment.

[0055] To modify only the shielding molecule electrode: take the cleaned electrode and immerse it in a 1mM shielding molecule solution (dissolved in anhydrous alcohol) for 3 hours at room temperature. Then take it out of the solution and rinse it with anhydrous alcohol and blow it dry to complete the modification.

[0056] Electrode modified with conductor molecules only: Take the cleaned electrode and immerse it in 1mM conductor molecule solution (dissolved in anhydrous alcohol) for 3 hours at room temperature. Then take it out of the solution and rinse it with anhydrous alcohol and blow it dry to complete the modification.

[0057] Simultaneous modification of shielding molecules and conductor molecules: First, prepare a mixed solution of shielding molecules and conductor molecules. Take a certain amount of concentrated solution of shielding molecules and conductor molecules and add an appropriate amount of anhydrous alcohol, and finally obtain a mixed solution with a shielding molecule concentration of 1mM and a conductor molecule concentration of 1mM. Take the cleaned electrode and immerse it in the mixed solution for 3 hours at room temperature. Then take it out of the solution, rinse it with anhydrous alcohol and blow it dry to complete the modification.

[0058] Detection method: square wave voltammetry.

[0059] Test substance: PBS solution containing 500 μM potassium ferrocyanide.

[0060] Test results such as Figure 5As shown in the figure, the solid line represents the result after only adding conductor molecules to form a self-assembled film, the long dashed line represents the result after adding a certain proportion of conductor molecules and shielding molecules to form a self-assembled film, and the short dashed line represents the result after only adding shielding molecules to form a self-assembled film. From the peak current size, the current when only adding conductor molecules is about 40 times that of adding only shielding molecules, indicating that the conductor molecules we use have obvious conductivity compared to shielding molecules. When a certain proportion of conductor molecules are added to the shielding molecule solution and then immersed in the gold electrode for self-assembly of a single layer of film, the current size is about 18 times that of when there is only a shielding molecule film, indicating that the conductivity of the gold electrode has been improved to a certain extent, but the presence of shielding molecules will still prevent the transfer of electrons.

[0061] Example 3 Detection performance of modified electrode

[0062] Our method combined with specific biological probes can well distinguish target genes and non-target genes with charged signal molecules. The corresponding biological probe is usually a short DNA fragment that is complementary to the target gene sequence. One section of the DNA fragment can be connected to some long-chain alkanes, and a thiol group is added to the end of the alkane chain, so that the entire probe chain can be fixed on the electrode through the thiol group, similar to the above-mentioned shielding molecules and conductor molecules.

[0063] like Figure 6 As shown, two gene fragments were customized and synthesized. Fragment a contains the target gene fragment we need to detect (nucleotide sequence SEQ ID NO.1: 5'-GACAACGGCTCCGGCATGTGCAAGG-3'), and fragment b contains a non-target gene fragment (nucleotide sequence SEQ ID NO.2: 5'-CCCATCACCATCTTCCAGGAGC-3'). Both gene fragments are composed of a small segment of DNA, a ferrocene molecule (black solid pentagon) and a carbon chain composed of more than a dozen alkanes. The difference between the two is that in addition to the difference in the nucleotide sequence, a thiol group (-SH) is added to the tail of the target gene fragment. When the fragment with the added thiol group is added to the self-assembly mixture, a self-assembly process can also occur and connect to the electrode. Gene detection in the prior art is to bind a DNA probe sequence to the electrode surface in advance, and then capture and fix the target gene on the surface of the electrode through hybridization with the target gene. In order to verify that our modified electrode can better identify the target gene, we designed Figure 6 The fragment shown in a in the figure is fixed on the electrode to simulate the process of the target gene being captured by the DNA probe; the non-target gene does not have a nucleotide sequence matching the DNA probe, so it will not bind to the probe during the gene detection process and will be free in the solution. Therefore, we designed Figure 6 The sequence in b does not contain a sulfhydryl group (-SH).

[0064] Specific operation method: first modify the shielding molecule and conductor molecule self-assembly layer on the electrode: take the concentrated solution of shielding molecules and conductor molecules and add an appropriate amount of anhydrous alcohol, and finally obtain a shielding molecule concentration of 1mM (usually 1-3mM) and a conductor molecule concentration of 1mM (usually 0.5-2mM) in the mixed solution. Take the cleaned electrode and immerse it in the mixed solution for 3 hours at room temperature, then take it out of the solution and rinse it with anhydrous alcohol and blow it dry to complete the modification. Prepare probe solutions containing target genes and non-target genes respectively, add the two solutions to PBS buffer respectively, and adjust the ratio so that the final gene probe concentration is 15μM (usually 10-20μM). Add the probe mixture of target genes and non-target genes to the modified electrode surface respectively, let it stand at room temperature for 0.5 hours, and then use square wave voltammetry for electrochemical detection.

[0065] Test results such as Figure 8 As shown, the solid line represents the electrochemical signal of the target gene, and the dotted line represents the electrochemical signal of the non-target gene. It can be seen that the current peak of the target gene is more than ten times that of the non-target gene, which can be well distinguished. We analyzed that this is due to the different structures of the two target molecules: Figure 7 The schematic diagram of the compounds on the modified electrode is shown, where a represents the target gene sequence with thiol (-SH). When the target gene sequence is fixed on the electrode, the signal molecule (ferrocene, represented by the solid pentagon) in the sequence can pass through the gap between the shielding molecule and the conductor molecule and approach the conductor molecule. Therefore, after providing a certain voltage, a redox reaction can occur to generate an electrical signal, while b in the middle represents that the non-target gene cannot be connected to the electrode, and is suspended in the solution and blocked by the shielding molecule layer on the outside of the electrode. It can be seen that the modified electrode can detect the target nucleic acid molecule in conjunction with the square wave voltammetry.

[0066] Example 4 Detection performance of electrodes modified with only shielding molecules

[0067] Based on the above experiment, we removed the conductor molecule component, leaving only the shielding molecule electrode for surface modification (adding shielding molecules such as long-chain alkanes to cover the remaining exposed parts of the electrode surface is a common method). Similarly, the probe solution containing the target gene and non-target gene was prepared, and the two gene probe mixtures were added to the modified electrode surface respectively, left to stand at room temperature for 0.5 hours, and then electrochemical detection was performed using square wave voltammetry. The structure after modification is as follows Fig. 9 The operation method is shown in Example 3.

[0068] The results are as follows Fig.10As shown, the ferrocene molecules modified on our target gene are at a certain distance from the electrode surface; but they can still be detected, while the non-target genes are isolated outside the electrode as before. The peak value of the electrical signal of the target gene is greater than that of the non-target gene, and can be clearly distinguished. However, combined with the two sets of data in Example 3, the absolute value of the peak value of the target gene after removing the conductor molecule is much smaller than the signal value obtained by our electrode modification method after adding the conductor molecule ( Fig.11 ). The greater the absolute difference between the peak values ​​of the target gene and the non-target gene, the easier it is to distinguish them. Therefore, it is shown that adding the conductor molecule during self-assembly modification can effectively enhance the electrochemical signal generated by the target gene and more effectively identify the target gene sequence.

[0069] Example 5 Comparison between the modified electrode and the commercial electrode

[0070] Based on the above experiments, we studied the differences between the modified electrodes and the unmodified electrodes. Existing commonly used commercial electrodes are usually pure metal material electrodes before modification. Take 2 unmodified electrodes and only perform cleaning treatment (refer to the above embodiment for the cleaning operation). Refer to the above embodiment for the subsequent operation method: prepare a solution of the gene probe, take the concentrated solution after dissolution and dilute it to 15uM (usually 10-20μM) with PBS buffer. Then add the prepared solution containing the target gene and non-target gene to the surface of the unmodified electrode, let it stand at room temperature for 0.5 hours, and then use square wave voltammetry to measure the electrical signal.

[0071] The results of the electrical signal are as follows Fig.13 As shown. It can be seen that the unmodified electrode has no screening effect on the target gene or non-target gene. We analyzed that this is because after adding the gene probe solution, the target gene will be connected to the gold electrode due to the thiol group, and the non-target gene will float on the surface of the gold electrode (such as Fig.12 As shown). However, due to the absence of interference from shielding molecules, conductor molecules and other substances, the ferrocene on the two gene probes can generate current signals generated by redox reactions. At the same time, it can be seen from the results in the above Example 3 that the modified electrode sheet cannot detect non-target genes, but has a better detection effect on target genes.

[0072] In summary, the modified electrode can effectively detect the target gene and also has a good shielding effect on non-target genes.

[0073] The above examples are for the purpose of illustrating the embodiments disclosed by the present invention and are not to be construed as limitations of the present invention. In addition, the various modifications listed herein and the variations of methods and compositions in the invention are obvious to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications obvious to those skilled in the art as described above to obtain the invention should be included within the scope of the present invention.

Claims

1. An electrode for electrochemical detection of nucleic acid molecules, characterized in that: The invention comprises an electrode, the surface of which is modified with shielding molecules and conductor molecules, the length of the conductor molecules is shorter than that of the shielding molecules, the shielding molecules comprise a head group and a tail group, the head group is a shielding group, and the tail group is a connecting group for connecting the electrode; the head group is a group far from the electrode substrate side, and the tail group is a group close to the electrode substrate side; the length of the shielding molecules ranges from 12 to 40 carbon chains, the shielding group is a long carbon chain alcohol, and the tail group is a thiol group; the conductor molecules are benzene ring chain structures or long chains of benzene rings and alkynyl groups alternately connected.

2. The electrode for electrochemical detection of nucleic acid molecules according to claim 1, characterized in that: The electrode is selected from any one of a silver electrode, a copper electrode, a gold electrode, or a platinum electrode.

3. The electrode for electrochemical detection of nucleic acid molecules according to claim 1, characterized in that: The head group is composed of a plurality of ethylene glycols and 10-20 carbon alkane chains connected in sequence.

4. Use of the electrode according to any one of claims 1 to 3 for detecting nucleic acid molecules.

5. A product for detecting nucleic acid molecules, characterized in that: The product contains the electrode as described in any one of claims 1 to 3 and a biological probe, wherein the biological probe is a single-stranded nucleic acid containing a nucleotide sequence that can bind to and complementarily pair with a target sequence in a target gene.

6. The method for preparing the electrode according to any one of claims 1 to 3, wherein the method comprises: immersing the electrode in a self-assembly solution, wherein the self-assembly solution refers to a solution containing shielding molecules and conductor molecules.

7. The preparation method according to claim 6, characterized in that: The method further includes cleaning the electrode and then immersing it in the self-assembly solution.

8. The preparation method according to claim 7, characterized in that: The method further comprises taking out the electrode immersed in the self-assembly solution and then rinsing it.

9. The preparation method according to claim 6, characterized in that: The final concentration of the shielding molecule is 1-3 mM, and the final concentration of the conductor molecule is 0.5-2 mM.

Images