A single-molecule chain pH sensor based on a graphene electrode and a preparation method thereof

Abstract

The present invention relates to the field of semiconductor technology, and particularly to a single-molecule chain pH sensor based on a graphene electrode and a preparation method thereof. The pH sensor includes a graphene source electrode, a single-molecule chain, and a graphene drain electrode sequentially connected by an amide bond; the single-molecule chain includes a starting unit, a single-molecule polymer, and a termination unit connected in sequence. The starting unit and the termination unit are selected from aniline or phenylenediamine, and the single-molecule polymer is formed by electrochemically polymerizing monomer molecules. The monomer molecules are selected from aniline or aniline derivatives. The electrochemically polymerization method enables the polymerization process of the monomer molecules to be controllable, combines static electrodes with dynamic assembly, and can optimize the performance of the pH sensor; at the same time, the electrochemically polymerization method can significantly improve the size adaptability between the single-molecule chain and the static graphene electrode by flexibly adjusting the number of monomer molecules during the dynamic assembly process, thereby improving the connection success rate.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly 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, which can miniaturize the size of semiconductor devices and provide a new development path for dealing with the "Moore's Dilemma". Single-molecule devices use single molecules, a small number of molecules, and the conductive polymers composed of them to construct functional devices to achieve functions such as information detection, conversion, transmission, storage, and processing at the molecular level, providing broad development space and application prospects for constructing functionalized electronic devices.

[0003] Whether an efficient and reliable single-molecule semiconductor device can be prepared and the assembly of its functional core that can achieve large-scale integration is crucial. At present, the methods for assembling the functional core mainly include dynamic assembly and static assembly. Dynamic assembly achieves a high connection rate through the precise matching of molecules and electrodes, but the operation is complex and the cost is high, restricting 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, affecting 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 a graphene electrode; the second object of the present invention is to provide a preparation method of a single-molecule chain pH sensor.

[0005] To achieve the first object, the technical solution adopted by the present invention is as follows:

[0006] 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;

[0007] Wherein, the single-molecule chain includes a starting unit, a single-molecule polymer, and a terminating unit connected in sequence;

[0008] The starting unit and the terminating unit are selected from or ;

[0009] The single-molecule polymer is formed by electrochemical polymerization of monomer molecules, and the monomer molecules are selected from aniline or aniline derivatives;

[0010] A single-molecule chain pH sensor based on a graphene electrode can construct a single-chain functional core with spatial orientation between the graphene source electrode and the graphene drain electrode by using aniline or its derivatives and taking advantage of the ability of an electric field to oxidize monomer molecules into cation radicals and the Coulomb traction effect on the cation radical intermediates. The starting unit and the terminating unit are covalently grafted to the edges of the graphene source electrode and the graphene drain electrode by an amidation reaction, providing a starting site and a terminating site for the polymerization reaction. Under the condition of precisely controlling the electrochemical reaction, an input pulse voltage signal is used to carry out the electro-polymerization of monomer molecules in a two-electrode system, so as to achieve the construction of a polyaniline molecular chain or a polyaniline derivative molecular chain bridging the graphene dot electrode pair with a high connection rate. These single-molecule chains are used as the functional core of the graphene-based single-molecule device, and conductive single-molecule polymers are used to construct functional units to realize functions such as information detection, conversion, transmission, storage, and processing at the molecular level.

[0011] A single-molecule chain pH sensor based on a graphene electrode provided by the present invention can detect and quantify trace molecular markers in a timely and accurate manner at the molecular level. By using the sensitivity of the single-molecule chain as the functional core unit to protons, it can realize the conversion of the change in proton concentration into an electrical signal, thereby achieving precise sensing of pH.

[0012] The conductivity of polyaniline and its derivatives depends on proton doping on the main chain, and the conductivity will increase with the increase in the doping degree. When the pH value of the environment changes, the conductivity of polyaniline also changes accordingly, showing good pH responsiveness. Therefore, it can be used to construct a pH sensor.

[0013] Further, the monomer molecule is selected from any one of the following structural formulas:

[0014] 、 、 、 、 、 、 、 、 、 、 。

[0015] Further, the graphene source electrode and the graphene drain electrode are graphene dot electrodes.

[0016] Further, the graphene dot electrode is a graphene dot electrode with a nano-gap.

[0017] To achieve the second object, the technical solution adopted by the present invention is:

[0018] A preparation method of a single-molecule chain pH sensor for preparing the single-molecule chain pH sensor based on a graphene electrode described in any one of the above, comprising the following steps:

[0019] S100. Prepare a graphene electrode array on a substrate by using micro-nano processing technology;

[0020] S200. Modify the graphene electrode array into a graphene drain electrode and a graphene source electrode with carboxyl groups at the ends by using reactive ion etching;

[0021] S300. Connect the starting unit and the terminating unit to the carboxyl ends of the graphene source electrode and the graphene drain electrode respectively by using an amide condensation reaction;

[0022] S400. Polymerize monomer molecules through an electrochemical polymerization reaction to form a single-molecule polymer. Utilize the potential difference between the graphene source electrode and the graphene drain electrode to connect the single-molecule polymer to the starting unit and the terminating unit respectively under the action of electric field polarization, and obtain a single-molecule chain pH sensor based on a graphene electrode.

[0023] Further, the process of step S300 is as follows:

[0024] Add monomer molecules, a graphene electrode array with carboxyl groups at the ends, and a dehydrating agent to the reaction system. Under a nitrogen atmosphere, add pyridine, let it stand, and carry out an amide condensation reaction for 24 - 72 h. Rinse and dry to obtain a graphene source electrode and a graphene drain electrode respectively connected with the starting unit and the terminating unit.

[0025] Further, the dehydrating agent is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride.

[0026] Further, in step S400, the potential difference is 0.5 - 1.5 V or -0.5 - -1.5 V.

[0027] Further, the electrolyte introduced in step S400 is selected from at least one of tetrabutylammonium hexafluorophosphate solution and morpholineethanesulfonic acid solution.

[0028] Further, in step S400, an electrolyte is introduced in 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.

[0029] One or more of the above technical solutions in the embodiments of the present invention have at least one of the following technical effects:

[0030] A single-molecule chain pH sensor based on a graphene electrode and a preparation method thereof provided by the present invention utilize the excellent electrochemical activity of aniline molecules and their derivatives, which have good electrical conductivity, electrocatalytic performance, electrochromic behavior, and optoelectronic properties. Using the single-molecule chain of aniline and its derivatives as a functional unit, a bridged single-molecule chain pH sensor based on a graphene electrode is constructed, which is expected to simultaneously realize a single-molecule functional device with a high connection rate while retaining the functional characteristics of a molecular film device. At the same time, the electrochemical polymerization method enables the polymerization of monomer molecules to be controllable, combining a static electrode and dynamic assembly, which is expected to optimize the performance of the single-molecule chain pH sensor based on a graphene electrode. Meanwhile, the electrochemical polymerization method can significantly improve the dimensional adaptability between the single-molecule chain and the static graphene electrode by flexibly adjusting the number of monomers during the dynamic assembly process, thereby increasing the success rate of connection.

[0031] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 is a schematic structural diagram of a single-molecule chain pH sensor based on a graphene electrode provided by an embodiment of the present invention.

[0034] Figure 2 is a cyclic voltammogram of aniline monomers in an electrolyte within a voltage range of -2 V to 2 V provided by Embodiment 1 of the present invention.

[0035] Figure 3 is a pulsed square wave image of ±1 V using the pulsed voltage method used in Embodiment 1 of the present invention.

[0036] Figure 4 is an image of the change in current over time during the electrochemical polymerization of aniline under the pulsed voltage method provided by Embodiment 1 of the present invention.

[0037] Figure 5 is an I-V characteristic curve of aniline after electrochemical polymerization in 15 graphene electrode pairs provided by Embodiment 1 of the present invention.

[0038] Figure 6 is the response of a single-molecule chain pH sensor based on a graphene electrode provided by Embodiment 1 of the present invention to different pH values.

[0039] Figure 7 It is a schematic diagram of the conductance switch change of the single-molecule chain pH sensor based on a graphene electrode provided in Embodiment 1 of the present invention after being cycled through different pH solutions.

[0040] Figure 8 It is the response of the single-molecule chain pH sensor based on a graphene electrode provided in Embodiment 2 of the present invention to different pH values.

[0041] Figure 9 It is the response of the single-molecule chain pH sensor based on a graphene electrode provided in Embodiment 3 of the present invention to different pH values.

[0042] Reference numerals:

[0043] 1. Graphene source-terminal electrode; 2. Single-molecule chain; 21. Starting unit; 22. Single-molecule polymer; 23. Terminating unit; 3. Graphene drain-terminal electrode. Detailed implementation manners

[0044] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts fall 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.

[0045] As Figure 1 shown, a single-molecule chain pH sensor based on a graphene electrode includes a graphene source-terminal electrode 1, a single-molecule chain 2, and a graphene drain-terminal electrode 3 that are sequentially connected by an amide bond;

[0046] Among them, the single-molecule chain includes a starting unit 21, a single-molecule polymer 22, and a terminating unit 23 that are sequentially connected;

[0047] The starting unit 21 and the terminating unit 23 are selected from or ;

[0048] The single-molecule polymer 22 is formed by electrochemical polymerization of monomer molecules, and the monomer molecules are selected from aniline or aniline derivatives;

[0049] Preferably, the monomer molecules are selected from any one of the following structural formulas:

[0050] , , , , , , , , , , 。

[0051] In the following examples, unless otherwise specified, the experimental methods used are conventional methods, and the materials, reagents, etc. used can be obtained from commercial sources unless otherwise specified.

[0052] Example 1 Preparation of a single-molecule chain pH sensor based on a graphene electrode.

[0053] I. Preparation of a graphene electrode array on a substrate using micro-nano processing technology. The preparation process is as follows:

[0054] A copper foil with a thickness of 25 µm is first immersed in an ice acetic acid solution for 20 minutes to remove surface oxides, then rinsed and dried, and further annealed in a tube furnace. Subsequently, using CH4 gas as a carbon source, monolayer graphene is grown on the copper foil through chemical vapor deposition technology. On the copper foil covered with the obtained graphene, a layer of PMMA950 (model A5, from Microchem) is first spin-coated, and then heated and cured at 180 °C for 2 minutes to form a tight thin film protective layer on the top layer of graphene. The copper substrate is removed by etching with a 2 mol / L ferric chloride solution for 30 minutes, and the residual ferric chloride on the film surface is removed by washing with hydrochloric acid solution and water multiple times. After that, the treated graphene film is transferred to a clean silicon wafer with a 300 nm silicon dioxide layer and air-dried to completely remove moisture. Then, the graphene / PMMA film on the silicon wafer is rinsed with acetone to remove PMMA, and a silicon wafer covered with graphene is obtained.

[0055] The above-mentioned silicon wafer covered with graphene is placed on the central chuck of a spin coater, and 1 to 2 drops of photoresist (model AR-P 5350 All Resist) are dropped. The spin coater first rotates at a speed of 600 revolutions per minute for 6 seconds, then accelerates to 4000 revolutions per minute and rotates for 45 seconds, and then heats on a hot plate at 110 °C for 3 minutes to cure the photoresist. A mask pattern is exposed on the surface of the silicon wafer using a 365 nm ultraviolet exposure machine, and the exposure duration is 25 seconds. Then, a development process is carried out for about 20 seconds, and fixed in deionized water for about 10 seconds. Finally, the residues on the surface of the silicon wafer are cleaned and dried.

[0056] Using the thermal evaporation coating technique, chromium with a thickness of 8 nm and gold with a thickness of 60 nm were deposited successively. After the coating was completed, the silicon wafer was immersed in acetone for more than 10 hours to dissolve and remove the photoresist. After drying with nitrogen, marks composed of crosses and numbers were left on the silicon wafer, and the spacing between these marks was 200 µm.

[0057] Furthermore, graphene strips with a width of 40 µm were fabricated through photolithography technology, and the remaining graphene was removed by oxygen plasma etching. On this basis, a metal electrode was deposited on the graphene strips using photolithography and metal deposition techniques to form a graphene electrode array.

[0058] II. Modify the graphene electrode array into a graphene drain electrode and a graphene source electrode with carboxyl groups at the ends by using the reactive ion etching method. The specific process is as follows:

[0059] A layer of PMMA950 was applied as a protective coating on the above-prepared graphene electrode array. Subsequently, using electron beam lithography technology, a dotted line pattern with a width of 5 nm was drawn in a direction orthogonal to the graphene strips. After being treated with a developer and fixed with a fixer, a series of fine dotted line windows were formed on this PMMA950 protective layer. Then, using oxygen plasma etching technology, the graphene exposed in these window parts was etched. During the etching process, the line width of these dotted line windows would gradually widen due to the action of oxygen plasma. In order to accurately control the timing of graphene cutting, the conductance change of the graphene electrode array was monitored synchronously. When the conductance value gradually decreased to zero, it meant that the graphene had been cut. At this time, carboxyl groups would be formed at the ends of the graphene dot electrodes (including the graphene source electrode and the graphene drain electrode). By precisely controlling the etching duration of oxygen plasma, the spacing between the graphene source electrode and the graphene drain electrode could be accurately adjusted.

[0060] III. Connect the starting unit and the terminating unit to the carboxyl ends of the graphene source electrode and the graphene drain electrode respectively by using the amide condensation reaction. The specific process is as follows:

[0061] Place the graphene dot electrode with edge carboxylation treatment in a three-neck flask, and then add 1 mg of p-phenylenediamine and 25 mg of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCl). To ensure a dry and oxygen-free reaction environment, seal the three-neck flask and perform three gas replacements to replace the original air in the flask with argon, while maintaining the internal and external air pressure balance by connecting nitrogen. Then, introduce 10 ml of pyridine using a syringe and let it react statically for 48 hours in the dark. Take out the graphene electrode and wash it three times with acetone and deionized water respectively, and finally dry it with nitrogen to obtain the graphene source electrode and graphene drain electrode modified with the starting unit and the terminating unit respectively.

[0062] IV. Polymerize monomer molecules through electrochemical polymerization reaction to form single-molecule polymers. The two ends of the single-molecule polymers are respectively connected to the starting unit and the terminating unit of the graphene dot electrode to form a single-molecule chain in the nano-gap of the graphene dot electrode pair, serving as the functional core. The specific process is as follows:

[0063] Prepare a 0.02 M aniline monomer solution containing a mixture of 900 µL of water and 100 µL of dimethylsulfoxide (DMSO), and adjust the pH of the solution to about 1 by dropping concentrated hydrochloric acid, and further disperse it evenly by ultrasonic wave. Place it in a micro-liquid tank with upper and lower through-holes on the surface of the graphene dot electrode modified with the starting unit and the terminating unit, drop a small amount of the prepared electrolyte solution and cover the lid. Select the graphene dot electrode pair and perform cyclic voltammetry testing on the two-electrode system using a semiconductor parameter analyzer. As Figure 2 shown, the results show that oxidation-reduction peaks of aniline appear at ±1 V, and thus the polymerization potential of aniline is determined to be ±1 V. Then apply positive and negative pulse voltages of 1 V, with a pulse interval of 10 s for each segment. As Figure 3 shown, under the action of the pulse voltage, within the initial 8 time periods (each time period is 10 s), the current curve is relatively smooth; as the electro-polymerization continues, current signal jitters occur in the time periods of 80 - 90 s, 100 - 110 s, and 120 - 130 s; further apply the pulse voltage, and in the time periods of 140 - 150 s and 160 - 170 s, the current signal rises to a large extent. At this time, the interrupted graphene source electrode and graphene drain electrode are connected through the single-molecule chain functional core. As Figure 4 shown, a single-molecule chain pH sensor based on graphene electrodes is obtained.

[0064] V. To test the I-V curve of the single-molecule chain pH sensor based on graphene electrodes prepared above when varying from -1V to 1V and determine whether the sensor is successfully connected. The specific process is as follows:

[0065] Select 15 pairs of graphene dot electrodes connected with polyaniline molecular chains, and use a probe station to test the conductivity between each pair of electrodes. When testing, repeat the measurement of the I-V curve of the electrode pair from -1V to 1V three times, read the current at ±1V, and simultaneously observe whether the curve passes through the origin. After test statistics, for the 15 pairs of graphene dot electrodes after three repeated tests, the current at ±1V is greater than 1nA. As Figure 5 shown, in the figure, from A to O are the detection results of the 1st to the 15th pairs of graphene dot electrodes respectively, and the results show that the single-molecule chain pH sensor based on graphene electrodes provided in this embodiment is successfully connected.

[0066] VI. To test the pH response of the single-molecule chain pH sensor based on graphene electrodes after being treated with aqueous solutions of different pH values. The specific process is as follows: Treat the pH sensor with aqueous solutions of pH 1, 3, 5, and 7 respectively, and test its I-V curve from -1V to 1V after treatment. As Figure 6 shown, the results show that the single-molecule chain pH sensor based on graphene electrodes provided in this embodiment can sense different pH values;

[0067] Furthermore, alternately treat the single-molecule chain pH sensor based on graphene electrodes provided in this embodiment with pure aqueous solution and hydrochloric acid aqueous solution of pH 1, test its I-V curve from -1V to +1V after treatment, and statistically analyze the current change situation after 10 times of alternate treatment. As Figure 7 shown, the results show that the pH sensor has good reversibility to the alternate treatment of acid and water.

[0068] Example 2 Preparation of a single-molecule chain pH sensor based on graphene electrodes.

[0069] In this embodiment, except for replacing the starting unit and the terminating unit with aniline hydrochloride, the remaining preparation process is the same as that in Example 1.

[0070] Test the response of the single-molecule chain pH sensor based on graphene electrodes provided in this embodiment to solutions with pH values of 1, 2, 3, 4, and 7 respectively. The specific test process is the same as that in Example 1. As Figure 8 shown, the results show that the single-molecule chain pH sensor based on graphene electrodes provided in this embodiment can sense different pH values.

[0071] Example 3 Preparation of a single-molecule chain pH sensor based on graphene electrodes.

[0072] In this example, the monomer molecules that undergo polymerization reaction are replaced with 2-(3-methylpentan-2-yl)aniline monomer. Prepare 1 mL of an aqueous solution containing 0.002 M 2-(3-methylpentan-2-yl)aniline monomer and 0.001 M p-toluenesulfonic acid (p-TSA). Dropwise add hydrochloric acid to adjust the pH of the solution to about 1, and further disperse it evenly by ultrasonic treatment. Use this solution as the electrolyte. The remaining preparation process is the same as that in Example 1.

[0073] Test the response of the single-molecule chain pH sensor based on graphene electrode provided in this example to solutions with pH values of 2, 4, and 6 respectively. The specific test process is the same as that in Example 1. As Figure 9 shown, the results indicate that the single-molecule chain pH sensor based on graphene electrode provided in this example can sense different pH values.

[0074] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A single-molecule chain pH sensor based on a graphene electrode, characterized in that, It includes a graphene source electrode, a single-molecule chain, and a graphene drain electrode connected in sequence through an amide bond; Among them, the single-molecule chain includes a starting unit, a single-molecule polymer, and a termination unit connected in sequence; The starting unit and the ending unit are selected from or ; The single-molecule polymer is formed by electrochemically polymerizing monomer molecules, and the monomer molecules are selected from any one of the following structural formulas: 、 、 、 、 、 、 、 、 、 、 、 。 2. The single-molecule chain pH sensor based on a graphene electrode according to claim 1, characterized in that, The graphene source electrode and the graphene drain electrode are graphene dot electrodes.

3. The single-molecule chain pH sensor based on a graphene electrode according to claim 2, wherein The graphene dot electrode is a graphene dot electrode with a nanogap.

4. A preparation method of a single-molecule chain pH sensor, characterized in that, A method for preparing a single-molecule chain pH sensor based on a graphene electrode according to any one of claims 1 to 3, comprising the following steps: S100. Prepare a graphene electrode array on a substrate by using micro-nano processing technology; S200. Modify the graphene electrode array into a graphene drain electrode and a graphene source electrode with a carboxyl group at the end by using reactive ion etching; S300. Connect the starting unit and the termination unit to the carboxyl ends of the graphene source electrode and the graphene drain electrode respectively by using an amide condensation reaction; S400. Polymerize monomer molecules to form a single-molecule polymer through an electrochemical polymerization reaction. Utilize the potential difference between the graphene source electrode and the graphene drain electrode to connect the single-molecule polymer to the starting unit and the termination unit respectively under the action of electric field polarization, and obtain a single-molecule chain pH sensor based on a graphene electrode.

5. The preparation method of the single-molecule chain pH sensor according to claim 4, characterized in that, The process of step S300 is as follows: Add p-phenylenediamine or aniline, a graphene electrode array with a carboxyl group at the end, and a dehydrating agent into the reaction system. Under a nitrogen atmosphere, add pyridine, let it stand, and carry out an amide condensation reaction for 24 to 72 h. Rinse and dry to obtain a graphene source electrode and a graphene drain electrode respectively connected with the starting unit and the termination unit.

6. The preparation method of the single-molecule chain pH sensor according to claim 5, characterized in that, The dehydrating agent is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride.

7. The preparation method of the single-molecule chain pH sensor according to claim 4, characterized in that, In step S400, the potential difference is 0.5 to 1.5 V or -0.5 to -1.5 V.

8. The preparation method of the single-molecule chain pH sensor according to claim 4, characterized in that, The electrolyte introduced in step S400 is selected from at least one of tetrabutylammonium hexafluorophosphate solution and morpholineethanesulfonic acid solution.

9. The preparation method of the single-molecule chain pH sensor according to claim 8, characterized in that, In step S400, an electrolyte is introduced in 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.

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