Single molecular chain pH sensor based on graphene electrode and preparation method thereof

Abstract

The invention relates to the technical field of semiconductors, in particular to a graphene electrode-based monomolecular chain pH sensor and a preparation method thereof, the pH sensor comprises a graphene source terminal electrode, a monomolecular chain and a graphene drain terminal electrode which are sequentially connected through amido bonds; the monomolecular chain comprises a starting unit, a monomolecular polymer and a terminating unit which are connected in sequence, the starting unit and the terminating unit are selected from aniline or phenylenediamine, the monomolecular polymer is formed by electrochemical polymerization of monomer molecules, the monomer molecules are selected from aniline or aniline derivatives, and the polymerization process of the monomer molecules is controllable through an electrochemical polymerization method; the static electrode is combined with the dynamic assembly, so that the performance optimization of the pH sensor can be realized; meanwhile, according to the electrochemical polymerization method, the number of monomer molecules can be flexibly adjusted in the dynamic assembly process, the size adaptability of a single molecular chain and the static graphene electrode is remarkably improved, and therefore the connection success rate is increased.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a single-molecule chain pH sensor based on a graphene electrode and a preparation method thereof. Background Art

[0002] In the semiconductor industry, as the size of semiconductor devices approaches the physical limit, Moore's Law begins to face difficulties. Single-molecule devices provide a new solution that can miniaturize the size of semiconductor devices and provide a new development path to deal with the "Moore's Dilemma". Single-molecule devices use single molecules, a small number of molecules and their conductive polymers to build functional devices to achieve information detection, conversion, transmission, storage and processing at the molecular level, providing broad development space and application prospects for building functional electronic devices.

[0003] Whether efficient and reliable single-molecule semiconductor devices can be prepared and the assembly of their functional cores can be achieved on a large scale is crucial. At present, the methods for assembling functional cores mainly include dynamic assembly and static assembly. Dynamic assembly achieves high connection rate through precise matching of molecules and electrodes, but the operation is complicated and costly, limiting its large-scale application. Static assembly focuses on channels that rely on molecular size matching and is suitable for graphene devices, but there are limitations in precise matching, which affects the connection success rate and performance. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the related art. To this end, the first object of the present invention is to provide a single molecule chain pH sensor based on graphene electrode; the second object of the present invention is to provide a method for preparing a single molecule chain pH sensor.

[0005] In order to achieve the first purpose, the technical solution adopted by the present invention is: A single molecule chain pH sensor based on a graphene electrode, comprising a graphene source electrode, a single molecule chain and a graphene drain electrode connected in sequence through an amide bond; Wherein, the monomolecular chain comprises a starting unit, a monomolecular polymer and a terminating unit connected in sequence; The initiator unit and the terminating unit are selected from or ; The monomolecular polymer is formed by electrochemical polymerization of monomer molecules, and the monomer molecules are selected from aniline or aniline derivatives; The single-molecule chain pH sensor based on graphene electrode can construct a single-chain functional core in a spatial orientation between the graphene source electrode and the graphene drain electrode by using aniline or its derivatives, utilizing the ability of the electric field to oxidize monomer molecules into cationic free radicals and the Coulomb traction effect on the cationic free radical intermediates. The initiation unit and the termination unit are covalently grafted on the edges of the graphene source electrode and the graphene drain electrode by the amidation reaction, providing the starting site and the termination site for the polymerization reaction. Under the condition of precise control of the electrochemical reaction, the input pulse voltage signal is used to carry out the electropolymerization of the monomer molecules in the double electrode system, so as to achieve the construction of polyaniline molecular chains or polyaniline derivative molecular chains bridged in the graphene point electrode pair with a high connection rate, and use these single-molecule chains as the functional core of the graphene-based single-molecule device, and use conductive single-molecule polymers to construct functional units to realize the functions of information detection, conversion, transmission, storage and processing at the molecular level.

[0006] The single-molecule chain pH sensor based on graphene electrodes provided by the present invention can detect and quantify trace molecular markers timely and accurately at the molecular level. By utilizing the sensitivity of the single-molecule chain as a functional core unit to protons, the change in proton concentration can be converted into an electrical signal, thereby realizing accurate sensing of pH. The conductivity of polyaniline and its derivatives depends on proton doping on the main chain. The conductivity increases with the increase of the doping degree. When the pH value of the environment changes, the conductivity of polyaniline also changes accordingly. It has good pH response and can therefore be used to construct pH sensors.

[0007] Furthermore, the monomer molecule is selected from any one of the following structural formulas: , , , , , , , , , , .

[0008] Furthermore, the graphene source terminal electrode and the graphene drain terminal electrode are graphene point electrodes.

[0009] Furthermore, the graphene point electrode is a graphene point electrode with a nanogap.

[0010] In order to achieve the second purpose, the technical solution adopted by the present invention is: A method for preparing a single molecule chain pH sensor, for preparing any of the above-mentioned single molecule chain pH sensors based on graphene electrodes, comprising the following steps: S100, preparing a graphene electrode array on a substrate using micro-nano processing technology; S200, modifying the graphene electrode array into a graphene drain electrode and a graphene source electrode with carboxyl groups at the ends by using a reactive ion etching method; S300, connecting the starting unit and the terminating unit to the carboxyl ends of the graphene source terminal electrode and the graphene drain terminal electrode respectively by an amide condensation reaction; S400, polymerizing monomer molecules to form single-molecule polymers through electrochemical polymerization reaction, and utilizing the potential difference between the graphene source terminal electrode and the graphene drain terminal electrode to connect the single-molecule polymers to the starting unit and the terminating unit respectively under the action of electric field polarization, thereby obtaining a single-molecule chain pH sensor based on graphene electrodes.

[0011] Furthermore, the process of step S300 is as follows: The monomer molecules, the graphene electrode array with carboxyl terminals and the dehydrating agent are added to the reaction system. Pyridine is added under a nitrogen atmosphere, and the system is allowed to stand for amide condensation reaction for 24 to 72 hours. The system is then rinsed and dried to obtain a graphene source terminal electrode and a graphene drain terminal electrode connected to the starting unit and the terminating unit, respectively.

[0012] Furthermore, the dehydrating agent is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride.

[0013] Further, in step S400, the potential difference is 0.5 to 1.5V or -0.5 to -1.5V.

[0014] Furthermore, the electrolyte introduced in step S400 is selected from at least one of tetra-n-butylammonium hexafluorophosphonate solution and morpholineethanesulfonic acid solution.

[0015] Furthermore, in step S400, an electrolyte is introduced into the electrochemical polymerization reaction, and the solvent of the electrolyte is selected from at least one of water, dimethyl sulfoxide, acetonitrile and N,N-dimethylformamide.

[0016] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: The present invention provides a single-molecule chain pH sensor based on graphene electrode and a preparation method thereof. The single-molecule chain of aniline and its derivatives is used as a functional unit to construct a bridge-type single-molecule chain pH sensor based on graphene electrode, which is expected to achieve a single-molecule functional device with a high connection rate while retaining the functional characteristics of the molecular film device. At the same time, the electrochemical polymerization method makes the polymerization of monomer molecules controllable, and combines the static electrode with the dynamic assembly, which is expected to achieve the performance optimization of the single-molecule chain pH sensor based on the graphene electrode. At the same time, the electrochemical polymerization method can significantly improve the size adaptability of the single-molecule chain and the static graphene electrode by flexibly adjusting the number of monomers during the dynamic assembly process, thereby improving the success rate of the connection.

[0017] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a schematic diagram of the structure of a single molecule chain pH sensor based on graphene electrode provided in an embodiment of the present invention.

[0020] Figure 2 This is the cyclic voltammetry curve of aniline monomer in electrolyte within the voltage range of -2 V to 2 V provided in Example 1 of the present invention.

[0021] Figure 3 This is a pulse square wave image of ±1 V used in the pulse voltage method of Example 1 of the present invention.

[0022] Figure 4 This is an image of the change of current over time during the electrochemical polymerization of aniline under the pulse voltage method provided in Example 1 of the present invention.

[0023] Figure 5 This is the IV characteristic curve of aniline after electrochemical polymerization in 15 graphene electrode pairs provided in Example 1 of the present invention.

[0024] Figure 6 This is the response of the single-molecule chain pH sensor based on graphene electrode provided in Example 1 of the present invention to different pH values.

[0025] Figure 7 It is a schematic diagram of the change in conductivity switch of the single-molecule chain pH sensor based on graphene electrode provided in Example 1 of the present invention after being circulated through solutions with different pH values.

[0026] Figure 8 This is the response of the single-molecule chain pH sensor based on graphene electrode provided in Example 2 of the present invention to different pH values.

[0027] Fig. 9 This is the response of the single-molecule chain pH sensor based on graphene electrode provided in Example 3 of the present invention to different pH values.

[0028] Reference numerals: 1. Graphene source electrode; 2. Single molecule chain; 21. Starting unit; 22. Single molecule polymer; 23. Terminating unit; 3. Graphene drain electrode. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0030] like Figure 1 As shown, a single molecule chain pH sensor based on graphene electrode comprises a graphene source electrode 1, a single molecule chain 2 and a graphene drain electrode 3 connected in sequence through amide bonds; Wherein, the monomolecular chain comprises a starting unit 21, a monomolecular polymer 22 and a terminating unit 23 connected in sequence; The starting unit 21 and the terminating unit 23 are selected from or ; The monomolecular polymer 22 is formed by electrochemical polymerization of monomer molecules, wherein the monomer molecules are selected from aniline or aniline derivatives; Preferably, the monomer molecule is selected from any one of the following structural formulas: , , , , , , , , , , .

[0031] In the following examples, the experimental methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0032] Example 1 Preparation of a single-molecule chain pH sensor based on graphene electrodes.

[0033] 1. Prepare graphene electrode array on substrate using micro-nano processing technology. The preparation process is as follows: A copper foil with a thickness of 25 µm was used. It was first immersed in an acetic acid solution for 20 minutes to remove the surface oxide, then rinsed and dried, and further annealed in a tube furnace. Then, a single layer of graphene was generated on the copper foil by chemical vapor deposition using CH4 gas as a carbon source. On the resulting graphene-covered copper foil, a layer of PMMA950 (model A5, from Microchem) was first spin-coated, and then heated and cured at 180 degrees Celsius for 2 minutes to form a tight film protective layer on the top of the graphene. The copper substrate was removed by etching with a 2 mol / L ferric chloride solution for 30 minutes, and the ferric chloride remaining on the film surface was removed by multiple washings with hydrochloric acid solution and water. Afterwards, the treated graphene film was transferred to a clean silicon wafer with a 300 nm silicon dioxide layer and dried naturally to completely remove moisture. Then, the graphene / PMMA film on the silicon wafer was rinsed with acetone to remove PMMA and obtain a silicon wafer covered with graphene.

[0034] Place the above-mentioned silicon wafer covered with graphene on the central suction cup of the glue machine, and add 1 to 2 drops of photoresist (model AR-P 5350 All Resist). The glue machine first rotates at a speed of 600 rpm for 6 seconds, then accelerates to 4000 rpm for 45 seconds, and then heats on a hot plate at 110°C for 3 minutes to cure the photoresist. Use a 365nm UV exposure machine to expose the mask pattern on the surface of the silicon wafer for 25 seconds. Then carry out a development process for about 20 seconds, and fix it in deionized water for about 10 seconds, and finally clean the residue on the surface of the silicon wafer and dry it.

[0035] Using thermal evaporation coating technology, 8 nm of chromium and 60 nm of gold were deposited in sequence. After coating, the silicon wafer was immersed in acetone for more than 10 hours to dissolve and remove the photoresist. After drying with nitrogen, marks consisting of crosses and numbers were left on the silicon wafer, and the spacing between these marks was 200 µm.

[0036] Furthermore, a graphene strip with a width of 40 µm was produced by photolithography, and the rest of the graphene was removed by oxygen plasma etching. On this basis, a layer of metal electrode was deposited on the graphene strip using photolithography and metal deposition technology to form a graphene electrode array.

[0037] 2. The graphene electrode array is modified into a graphene drain electrode and a graphene source electrode with carboxyl groups at the ends by using a reactive ion etching method. The specific process is as follows: A layer of PMMA950 is applied as a protective coating on the graphene electrode array prepared above. Subsequently, an electron beam exposure technique is used to draw a dotted line pattern with a width of 5 nm in a direction orthogonal to the graphene strip. After being treated with a developer and fixed with a fixer, a series of fine dotted windows are formed on this PMMA950 protective layer. Then, the graphene partially exposed in these windows is etched using oxygen plasma etching technology. During the etching process, the line width of these dotted windows will gradually widen due to the action of oxygen plasma. In order to accurately grasp the timing of graphene cutting, the conductivity change of the graphene electrode array is monitored synchronously. When the conductivity value gradually decreases to zero, it means that the graphene has been cut off. At this time, a carboxyl group will be formed at the end of the graphene point electrode (including the graphene source electrode and the graphene drain electrode). By finely controlling the etching time of oxygen plasma, the spacing between the graphene source electrode and the graphene drain electrode can be accurately adjusted.

[0038] 3. Connecting the starting unit and the terminating unit to the carboxyl terminal of the graphene source terminal electrode and the graphene drain terminal electrode respectively by amide condensation reaction, the specific process is as follows: The edge carboxylation treated graphene dot electrode was placed in a three-necked flask, followed by the addition of 1 mg of p-phenylenediamine and 25 mg of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCl). To ensure that the reaction environment was dry and oxygen-free, the three-necked flask was sealed and replaced with argon gas to replace the original air in the flask. The internal and external pressures were balanced by connecting nitrogen. After that, 10 ml of pyridine was introduced by syringe, and the reaction was allowed to stand for 48 hours under lightless conditions. The graphene electrode was taken out and washed three times with acetone and deionized water respectively, and finally dried with nitrogen to obtain the graphene source electrode and graphene drain electrode modified with the start unit and the termination unit, respectively.

[0039] Fourth, the monomer molecules are polymerized through electrochemical polymerization reaction to form a single molecule polymer. The two ends of the single molecule polymer are respectively connected to the starting unit and the ending unit of the graphene point electrode to form a single molecule chain in the nanogap of the graphene point electrode pair as the functional core. The specific process is as follows: Prepare a 0.02 M aniline monomer solution containing 900 µL of water and 100 µL of dimethylsulfoxide (DMSO), add concentrated hydrochloric acid to adjust the pH of the solution to about 1, and further disperse it evenly by ultrasonication. Place a micro liquid tank that runs through the top and bottom on the surface of the graphene dot electrode modified with the starter unit and the termination unit, add a small amount of the prepared electrolyte and cover it. Select a graphene dot electrode pair and use a semiconductor parameter instrument to perform a cyclic voltammetry test on the two-electrode system, such as Figure 2 As shown in the figure, the redox peak of aniline appears at ±1 V, which determines that the polymerization potential of aniline is ±1 V. Then, a positive and negative pulse voltage of 1 V is applied, and the interval between each pulse is 10 s. Figure 3 As shown in the figure, under the action of the pulse voltage, the current curve is relatively smooth in the initial 8 time periods (each time period is 10s); as the electropolymerization continues, the current signal jitters in the time periods of 80-90s, 100-110s and 120-130s; further application of the pulse voltage causes a significant increase in the time periods of 140-150s and 160-170s, at which time the interrupted graphene source electrode and the graphene drain electrode are connected through the single molecule chain functional core, as shown in the figure. Figure 4 As shown, a single-molecule chain pH sensor based on graphene electrode was obtained.

[0040] 5. Test the IV curve of the single-molecule chain pH sensor based on graphene electrode prepared above from -1V to 1V to determine whether the sensor is successfully connected. The specific process is as follows: 15 pairs of graphene dot electrodes connected to polyaniline molecular chains were selected, and the conductivity between each pair of electrodes was tested using a probe station. The IV curve of the electrode pair from -1 V to 1 V was tested three times, and the current at ±1 V was read, and whether the curve passed the origin was observed. After test statistics, the current at ±1 V of the 15 graphene dot electrode pairs after three repeated tests was greater than 1nA. Figure 5 , A to O in the figure are the detection results of the 1st to 15th graphene dot electrode pairs, respectively. The results show that the single-molecule chain pH sensor based on graphene electrode provided in this embodiment is successfully connected.

[0041] 6. Test the pH response of the single-molecule chain pH sensor based on graphene electrode after treatment with different pH aqueous solutions. The specific process is as follows: treat the pH sensor with aqueous solutions of pH 1, 3, 5 and 7, and test its IV curve which increases from -1V to 1V after treatment, such as Figure 6 As shown, the results show that the single-molecule chain pH sensor based on graphene electrode provided in this embodiment can sense different pH; The single-molecule chain pH sensor based on the graphene electrode provided in this embodiment was further treated alternately with a pure aqueous solution and a hydrochloric acid aqueous solution with a pH of 1, and the IV curve of the pH sensor after treatment was tested from -1 V to +1 V. The current change after 10 alternating treatments was statistically analyzed, as shown in FIG. Figure 7 As shown, the results indicate that the pH sensor has good reversibility to alternating treatments of acid and water.

[0042] Example 2 Preparation of a single-molecule chain pH sensor based on graphene electrodes.

[0043] In this embodiment, except that the starting unit and the terminating unit are replaced by aniline hydrochloride, the rest of the preparation process is the same as that of Example 1.

[0044] The response of the single-molecule chain pH sensor based on graphene electrode provided in this embodiment to solutions with pH values ​​of 1, 2, 3, 4 and 7 was tested. The specific testing process was the same as that in Example 1. Figure 8 As shown, the results indicate that the single-molecule chain pH sensor based on graphene electrode provided in this embodiment is capable of sensing different pH values.

[0045] Example 3 Preparation of a single-molecule chain pH sensor based on graphene electrode.

[0046] In this embodiment, the monomer molecules undergoing polymerization reaction are replaced with 2-(3-methylpent-2-yl)aniline monomers, 1 mL of 0.002 M 2-(3-methylpent-2-yl)aniline monomers and 0.001 M p-toluenesulfonic acid (p-TSA) aqueous solution are prepared, hydrochloric acid is added dropwise to adjust the solution pH to about 1, and ultrasonic dispersion is further performed to make the solution uniform, and the solution is used as an electrolyte. The rest of the preparation process is the same as in Example 1.

[0047] The response of the single-molecule chain pH sensor based on graphene electrode provided in this embodiment to solutions with pH values ​​of 2, 4 and 6 was tested. The specific testing process was the same as that in Example 1. Fig. 9 As shown, the results indicate that the single-molecule chain pH sensor based on graphene electrode provided in this embodiment is capable of sensing different pH values.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single-molecule chain pH sensor based on graphene electrode, characterized in that: The method comprises sequentially connecting a graphene source terminal electrode, a single molecule chain and a graphene drain terminal electrode through an amide bond; Wherein, the monomolecular chain comprises a starting unit, a monomolecular polymer and a terminating unit connected in sequence; The initiator unit and the terminating unit are selected from or ; The monomolecular polymer is formed by electrochemical polymerization of monomer molecules, and the monomer molecules are selected from aniline or aniline derivatives.

2. The single-molecule chain pH sensor based on graphene electrode according to claim 1, characterized in that: The monomer molecule is selected from any one of the following structural formulas: 、 、 、 、 、 、 、 、 、 、 。 3. The single-molecule chain pH sensor based on graphene electrode according to claim 1, characterized in that: The graphene source terminal electrode and the graphene drain terminal electrode are graphene point electrodes.

4. The single-molecule chain pH sensor based on graphene electrode according to claim 3, characterized in that: The graphene point electrode is a graphene point electrode with a nano-gap.

5. A method for preparing a single molecule chain pH sensor, characterized in that: The method for preparing a single-molecule chain pH sensor based on a graphene electrode as claimed in any one of claims 1 to 4 comprises the following steps: S100, preparing a graphene electrode array on a substrate using micro-nano processing technology; S200, modifying the graphene electrode array into a graphene drain electrode and a graphene source electrode with carboxyl groups at the ends by using a reactive ion etching method; S300, connecting the starting unit and the terminating unit to the carboxyl ends of the graphene source terminal electrode and the graphene drain terminal electrode respectively by an amide condensation reaction; S400, polymerizing monomer molecules to form single-molecule polymers through electrochemical polymerization reaction, and utilizing the potential difference between the graphene source terminal electrode and the graphene drain terminal electrode to connect the single-molecule polymers to the starting unit and the terminating unit respectively under the action of electric field polarization, thereby obtaining a single-molecule chain pH sensor based on graphene electrodes.

6. The method for preparing a single molecule chain pH sensor according to claim 5, characterized in that: The process of step S300 is as follows: The monomer molecules, the graphene electrode array with carboxyl terminals and the dehydrating agent are added to the reaction system. Pyridine is added under a nitrogen atmosphere, and the system is allowed to stand for amide condensation reaction for 24 to 72 hours. The system is then rinsed and dried to obtain a graphene source terminal electrode and a graphene drain terminal electrode connected to the starting unit and the terminating unit, respectively.

7. The method for preparing a single molecule chain pH sensor according to claim 6, characterized in that: The dehydrating agent is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride.

8. The method for preparing a single molecule chain pH sensor according to claim 5, characterized in that: In step S400, the potential difference is 0.5 to 1.5V or -0.5 to -1.5V.

9. The method for preparing a single molecule chain pH sensor according to claim 5, characterized in that: The electrolyte introduced in step S400 is selected from at least one of tetra-n-butylammonium hexafluorophosphonate solution and morpholineethanesulfonic acid solution.

10. The method for preparing a single molecule chain pH sensor according to claim 9, characterized in that: In step S400, an electrolyte is introduced into the electrochemical polymerization reaction, wherein the solvent of the electrolyte is selected from at least one of water, dimethyl sulfoxide, acetonitrile and N,N-dimethylformamide.

Images