Electrochemical sensor and preparation method thereof

Abstract

The invention belongs to the technical field of electrochemical sensors, and relates to an electrochemical sensor which comprises a substrate, a working electrode, a counter electrode and a reference electrode, the working electrode, the counter electrode and the reference electrode are arranged on the substrate, and the working electrode, the counter electrode and the reference electrode form a three-electrode system; the working electrode comprises a base electrode, and a carboxylated multi-walled carbon nanotube modification layer and a gold nanoparticle modification layer which are sequentially arranged on the base electrode. The invention also relates to a preparation method of the electrochemical sensor. According to the technical scheme provided by the invention, the caffeine content in the electronic cigarette liquid can be rapidly detected.

Description

Technical Field

[0001] The present application relates to the technical field of electrochemical sensors, and more specifically, to an electrochemical sensor and a preparation method of an electrochemical sensor. Background Art

[0002] Caffeine, with the chemical formula C8H 10 N4O2, is a naturally occurring alkaloid and belongs to the N-methyl derivative of xanthine. It exists in many plant products such as coffee and cocoa beans, tea leaves, kola nuts or guarana berries, etc. It has special physiological effects on the human body. At moderate doses, caffeine has positive effects on attention, physical strength and mental performance. In addition, it can also reduce drowsiness and fatigue.

[0003] However, there are also relevant standards for the use of caffeine in e-liquids. For example, the national standard for e-cigarettes GB41700-2022 lists the requirements for allowable additives in e-liquids in Appendix A. Although caffeine is not explicitly mentioned as an allowable additive, coffee extract (containing caffeine) is an allowable additive, and its maximum usage amount should not exceed 50 mg / g; the French standard Afnor XP D90-300-2:2021 stipulates that except for nicotine, any pharmacological molecule such as caffeine is not allowed to be added; the EU Directive Directive2014 / 40 / EU requires the prohibition of adding caffeine to e-liquids. Therefore, the detection of caffeine content in e-liquids is very necessary.

[0004] Traditional caffeine detection methods mainly include chromatography, chromatography-mass spectrometry, electrochemical analysis, etc. Chromatography and chromatography-mass spectrometry have certain limitations in terms of equipment cost and detection cost. Summary of the Invention

[0005] The technical problem to be solved by the embodiments of the present application is that traditional caffeine detection methods are limited by equipment cost and detection cost, and it is impossible to simply, quickly, low-cost and highly sensitively detect the caffeine content in e-liquids.

[0006] To solve the above technical problem, the embodiments of the present application provide an electrochemical sensor, and adopt the following technical solutions:

[0007] An electrochemical sensor includes a substrate, and a working electrode, a counter electrode and a reference electrode disposed on the substrate. The working electrode, the counter electrode and the reference electrode form a three-electrode system;

[0008] The working electrode includes a base electrode, and a carboxylated multi-walled carbon nanotube modification layer and a gold nanoparticle modification layer sequentially disposed on the base electrode.

[0009] Further, the material of the substrate is selected from at least one of polyethylene terephthalate, polyvinyl chloride or ceramic; and / or

[0010] The counter electrode is selected from platinum electrodes; and / or

[0011] The reference electrode is selected from silver-silver chloride electrodes; and / or

[0012] The base electrode is selected from carbon electrodes; and / or

[0013] The material of the carboxylated multi-walled carbon nanotube modification layer includes an N,N-dimethylformamide dispersion of carboxylated multi-walled carbon nanotubes.

[0014] To solve the above technical problems, the embodiments of the present application also provide a preparation method of an electrochemical sensor, adopting the following technical solutions:

[0015] A preparation method of an electrochemical sensor, comprising the following steps:

[0016] Provide a substrate;

[0017] Prepare a base electrode, a counter electrode and a reference electrode on the substrate by screen printing;

[0018] Provide a carboxylated multi-walled carbon nanotube coating solution, coat the carboxylated multi-walled carbon nanotube coating solution on the base electrode, and obtain a carboxylated multi-walled carbon nanotube modification layer after drying;

[0019] Place the substrate in a chloroauric acid solution for electrodeposition treatment to form a gold nanoparticle modification layer on the carboxylated multi-walled carbon nanotube modification layer, and obtain a working electrode. Among them, the working electrode, the counter electrode and the reference electrode form a three-electrode system to obtain an electrochemical sensor.

[0020] Further, the carboxylated multi-walled carbon nanotube coating solution is prepared by the following steps:

[0021] Provide multi-walled carbon nanotube materials, disperse the multi-walled carbon nanotube materials in nitric acid, carry out reflux oxidation treatment, and then carry out water washing and drying treatment;

[0022] Disperse the multi-walled carbon nanotube materials after water washing and drying treatment in a hydrogen peroxide solution, carry out ultrasonic treatment, and then carry out water washing and drying treatment to obtain carboxylated multi-walled carbon nanotube materials;

[0023] Disperse the carboxylated multi-walled carbon nanotube materials in an N,N-dimethylformamide solution and carry out ultrasonic treatment to obtain a carboxylated multi-walled carbon nanotube coating solution.

[0024] Further, the temperature of the reflux oxidation treatment is 130°C to 150°C; and / or

[0025] The duration of the reflux oxidation treatment is 5 h to 10 h.

[0026] Furthermore, the water washing and drying treatment specifically includes the following steps:

[0027] Wash the treated multi-walled carbon nanotube material with water until it is neutral;

[0028] Perform a drying treatment on the multi-walled carbon nanotube material after the water washing is completed. Among them, the temperature of the drying treatment is 60°C to 80°C; and / or, the duration of the drying treatment is 12 h to 24 h.

[0029] Furthermore, the mass fraction of the nitric acid is 60% to 80%; and / or

[0030] The concentration of the hydrogen peroxide solution is 10% to 30%; and / or

[0031] The concentration of the carboxylated multi-walled carbon nanotube coating solution is 0.2 mg / mL to 1.2 mg / mL.

[0032] Furthermore, the temperature of the ultrasonic treatment is 20°C to 30°C; and / or

[0033] The duration of the ultrasonic treatment is 3 h to 5 h.

[0034] Furthermore, the coating volume of the carboxylated multi-walled carbon nanotube coating solution is 1 μL to 5 μL.

[0035] Furthermore, the method adopted for the electrodeposition treatment is the potentiostatic deposition method. Among them, the deposition potential is -0.25 V, and the deposition duration is 50 s to 150 s.

[0036] Compared with the prior art, the embodiments of the present application mainly have the following beneficial effects:

[0037] The electrochemical sensor provided by the present application has a carboxylated multi-walled carbon nanotube modification layer provided on the base electrode. It has good electrical conductivity and a large specific surface area, can improve the electrical conductivity of the working electrode, can transfer the electrons generated by the reaction well, and realizes the detection of caffeine in e-cigarette oil with a fast reaction speed; at the same time, the setting of the carboxylated multi-walled carbon nanotube modification layer is beneficial to the loading and binding of gold nanoparticles. By setting the gold nanoparticle layer, its good electrical conductivity and large specific surface area can further improve the electrical conductivity of the working electrode and the reaction speed; in addition, gold nanoparticles have a certain catalytic oxidation ability, can catalytically oxidize caffeine in e-cigarette oil, and realize the improvement of the detection sensitivity of the electrochemical sensor to caffeine.

[0038] The electrochemical sensor provided by this application can be used for the detection of caffeine in e-cigarette oil, and has a wide detection range and a low detection limit (in the range of 5 μmol / L to 200 μmol / L, the response current of the catalytic oxidation reaction of this electrochemical sensor has a linear relationship with the change in caffeine concentration, and the linear relationship is: Y = 0.1374X + 7.7051, and the correlation coefficient is R 2 = 0.9943, and the detection limit is 1 μmol / L (S / N = 3)). The reaction is carried out at room temperature, with stable performance and good application prospects. Brief Description of the Drawings

[0039] In order to more clearly illustrate the solutions of this application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1 is a schematic structural diagram of the electrochemical sensor of this application;

[0041] Figure 2 is a flowchart of the preparation method of the electrochemical sensor of this application;

[0042] Figure 3 is about Figure 2 a flowchart of a specific implementation manner of step S300;

[0043] Figure 4 is a linear sweep voltammogram of the electrochemical sensor of Example 1 of this application in PBS solution with and without caffeine;

[0044] Figure 5 is a linear sweep voltammogram of the electrochemical sensor of Example 3 of this application in PBS solution with different caffeine contents;

[0045] Figure 6 is a linear relationship diagram between the response current generated by the electrochemical sensor of Example 3 of this application to PBS solutions with different caffeine concentrations and the corresponding caffeine concentrations.

[0046] Reference Signs:

[0047] 1, substrate; 2, working electrode; 3, counter electrode; 4, reference electrode. Detailed Description of the Specific Embodiments

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion. The terms "first", "second", etc. in the specification and claims of this application or the above drawings are used to distinguish different objects and not to describe a specific order.

[0049] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0050] Please refer to Figure 1 As shown, an electrochemical sensor provided by an embodiment of this application includes: a substrate 1, a working electrode 2, a counter electrode 3, and a reference electrode 4.

[0051] The working electrode 2, the counter electrode 3, and the reference electrode 4 are all disposed on the substrate 1, and the counter electrode and the reference electrode form a three-electrode system.

[0052] In some embodiments, the working electrode 2 includes a base electrode (not shown in the figure) and a carboxylated multi-walled carbon nanotube modified layer (not shown in the figure) and a gold nanoparticle modified layer (not shown in the figure) sequentially disposed on the base electrode.

[0053] The working electrode 2 of the electrochemical sensor provided by the embodiment of this application has a carboxylated multi-walled carbon nanotube modified layer disposed on the base electrode. It has good conductivity and a large specific surface area, can improve the conductivity of the working electrode 2, can transfer the electrons generated by the reaction well, and realizes the detection of caffeine in e-cigarette oil with a fast reaction speed; at the same time, the setting of the carboxylated multi-walled carbon nanotube modified layer is beneficial to the loading and binding of gold nanoparticles. By setting the gold nanoparticle layer, its good conductivity and large specific surface area can further improve the conductivity and reaction speed of the working electrode 2; in addition, gold nanoparticles have a certain catalytic oxidation ability, can catalytically oxidize caffeine in e-cigarette oil, and realize the improvement of the detection sensitivity of the electrochemical sensor to caffeine.

[0054] In some embodiments, the material of the substrate is selected from at least one of polyethylene terephthalate (PET), polyvinyl chloride (PVC), or ceramics. In this embodiment, the substrate is a PET substrate.

[0055] In some embodiments, the base electrode is a carbon electrode, and the material of the carboxylated multi-walled carbon nanotube modification layer includes an N,N-dimethylformamide dispersion of carboxylated multi-walled carbon nanotubes.

[0056] In some embodiments, the counter electrode 3 is selected from a platinum electrode.

[0057] In some embodiments, the reference electrode 4 is selected from a silver-silver chloride electrode.

[0058] In this embodiment, the base electrode, the counter electrode 3, and the reference electrode 4 can be printed on the surface of the substrate by screen printing. With screen printing electrodes, there is no need for cumbersome grinding and polishing pretreatment, reducing the manufacturing cost and difficulty of the electrochemical sensor. In addition, since the working electrode area is small, the reagents used in detection can be reduced, lowering the detection cost.

[0059] Please refer to Figure 2 As shown, based on the above electrochemical sensor, an embodiment of the present application further provides a preparation method for an electrochemical sensor, including the following steps:

[0060] Step S100, providing a substrate;

[0061] Step S200, preparing a base electrode, a counter electrode, and a reference electrode on the substrate by screen printing;

[0062] Step S300, providing a carboxylated multi-walled carbon nanotube coating solution, coating the carboxylated multi-walled carbon nanotube coating solution on the base electrode, and drying to obtain a carboxylated multi-walled carbon nanotube modification layer;

[0063] Step S400, placing the substrate in a chloroauric acid solution for electrodeposition treatment to form a gold nanoparticle modification layer on the carboxylated multi-walled carbon nanotube modification layer to obtain a working electrode.

[0064] In this embodiment, the working electrode, the counter electrode, and the reference electrode form a three-electrode system to obtain an electrochemical sensor.

[0065] The electrochemical sensor prepared by the preparation method of the electrochemical sensor provided by the embodiment of the present application can be used for the detection of caffeine in e-cigarette oil, has a specific cavity, and has a wide detection range and a low detection limit. The reaction is carried out at room temperature, with stable performance and good application prospects.

[0066] In some embodiments, in step S200, a base electrode, a counter electrode, and a reference electrode are prepared on the substrate by a screen printing process, which specifically includes the following steps:

[0067] Provide carbon paste and print it onto the substrate by a screen printing process to form a carbon electrode as the base electrode;

[0068] Provide conductive platinum paste and print it onto the substrate by a screen printing process to form a platinum electrode as the counter electrode;

[0069] Provide silver-silver chloride paste and print it onto the substrate by a screen printing process to form a silver-silver chloride electrode as the reference electrode.

[0070] Please refer to Figure 3 As shown, in some embodiments, the carboxylated multi-walled carbon nanotube coating solution in step S300 is prepared through the following steps:

[0071] In step S301, provide multi-walled carbon nanotube material, disperse the multi-walled carbon nanotube material in nitric acid, perform reflux oxidation treatment, and then perform water washing and drying treatment.

[0072] In some embodiments, the mass fraction of the nitric acid is 60% - 80%. Specifically, the mass fraction of the nitric acid can be any value among 60%, 70%, 80% or the range formed between any two values.

[0073] In some embodiments, the temperature of the reflux oxidation treatment is 130°C - 150°C. Specifically, the temperature of the reflux oxidation treatment can be set to any value among 130°C, 140°C, 150°C or the range formed between any two values.

[0074] In some embodiments, the duration of the reflux oxidation treatment is 5h - 10h. Specifically, the duration of the reflux oxidation treatment can be set to any value among 5h, 6h, 7h, 8h, 9h, 10h or the range formed between any two values.

[0075] In the embodiments of the present application, by selecting the mass fraction within the above range, it is convenient to perform preliminary carboxylation treatment on the multi-walled carbon nanotube material; at the same time, through the reflux oxidation treatment, the carboxylation treatment degree of the nitric acid on the multi-walled carbon nanotube material is improved.

[0076] In some embodiments, the water washing and drying treatment specifically includes the following steps:

[0077] Wash the multi-walled carbon nanotube material after the reflux oxidation treatment until it is neutral;

[0078] Perform drying treatment on the multi-walled carbon nanotube material that has completed water washing.

[0079] In some embodiments, the temperature of the drying treatment is 60°C to 80°C. Specifically, the temperature of the drying treatment can be set to any value among 60°C, 70°C, and 80°C or the range formed between any two values.

[0080] In some embodiments, the duration of the drying treatment is 12 h to 24 h. Specifically, the duration of the drying treatment can be set to any value among 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, and 24 h or the range formed between any two values.

[0081] Step S302: Disperse the multi-walled carbon nanotube material after water washing and drying treatment in a hydrogen peroxide solution, perform ultrasonic treatment, and then perform water washing and drying treatment to obtain a carboxylated multi-walled carbon nanotube material.

[0082] In some embodiments, the concentration of the hydrogen peroxide solution is 10% to 30%. Specifically, the mass fraction of the hydrogen peroxide solution can be any value among 10%, 20%, and 30% or the range formed between any two values.

[0083] In some embodiments, the temperature of the ultrasonic treatment is 20°C to 30°C. Specifically, the temperature of the ultrasonic treatment can be set to any value among 20°C, 25°C, and 30°C or the range formed between any two values.

[0084] The duration of the ultrasonic treatment is 3 h to 5 h. Specifically, the duration of the ultrasonic treatment can be set to any value among 3 h, 4 h, and 5 h or the range formed between any two values.

[0085] In the embodiment of the present application, the multi-walled carbon nanotube material subjected to preliminary carboxylation treatment with nitric acid is further oxidized with hydrogen peroxide, so as to oxidize the carboxyl groups of the multi-walled carbon nanotube material into carboxyl groups, thereby further improving the carboxylation of the multi-walled carbon nanotube material.

[0086] Step S303: Disperse the carboxylated multi-walled carbon nanotube material in an N,N-dimethylformamide solution and perform ultrasonic treatment to obtain a carboxylated multi-walled carbon nanotube coating solution.

[0087] In some embodiments, the concentration of the carboxylated multi-walled carbon nanotube coating solution obtained after step S303 is 0.2 mg / mL to 1.2 mg / mL.

[0088] In some embodiments, in the step of coating the carboxylated multi-walled carbon nanotube coating solution on the base electrode in the step S300, the coating volume of the carboxylated multi-walled carbon nanotube coating solution is 1 μL to 5 μL. Specifically, the coating volume of the carboxylated multi-walled carbon nanotube coating solution can be set to any value among 1 μL, 2 μL, 3 μL, 4 μL, 5 μL or a range formed between any two values.

[0089] In some embodiments, in the step of the step S400, the method adopted for the electrodeposition treatment is a potentiostatic deposition method.

[0090] In this embodiment, the deposition potential in the potentiostatic deposition method is -0.25 V, and the deposition duration is 50 s to 150 s.

[0091] The electrochemical sensor prepared by the preparation method of the electrochemical sensor provided by the embodiments of the present application can be used for the detection of caffeine in e-cigarette oil, and has a wide detection range and a low detection limit (in the range of a concentration of 5 μmol / L to 200 μmol / L, the response current of the catalytic oxidation reaction of this electrochemical sensor has a linear relationship with the change in caffeine concentration, and the linear relationship is: Y = 0.1374X + 7.7051, and the correlation coefficient is R 2 = 0.9943, and the detection limit is 1 μmol / L (S / N = 3)). The reaction is carried out at room temperature, the performance is stable, and it has good application prospects.

[0092] The present application will be specifically described below through specific embodiments. The following embodiments are only partial embodiments of the present application and do not limit the present application.

[0093] Example 1

[0094] Step (1), providing a substrate;

[0095] Step (2), respectively forming a base electrode, a counter electrode and a reference electrode on the corresponding area of the substrate through a screen printing process;

[0096] Step (3), taking 3 μL of the carboxylated carbon nanotube coating solution and coating it on the base electrode to form a carboxylated multi-walled carbon nanotube modification layer;

[0097] Among them, the carboxylated carbon nanotube coating is prepared through the following steps:

[0098] Disperse 1.0 g of multi-walled carbon nanotube material in 200 mL of nitric acid with a mass fraction of 68%, carry out reflux treatment at 140 °C for 7 h, wash it with distilled water to neutrality after cooling to room temperature, and carry out drying treatment at 60 °C for 16 h to obtain a crude product of carboxylated multi-walled carbon nanotube material;

[0099] Take 0.1 g of the crude carboxylated multi-walled carbon nanotube material and disperse it in a 20% hydrogen peroxide solution. After ultrasonic treatment at room temperature for 4 h, perform drying treatment at 60 °C for 16 h to obtain the carboxylated multi-walled carbon nanotube material;

[0100] Disperse the carboxylated multi-walled carbon nanotube material in N,N-dimethylformamide and perform ultrasonic treatment at room temperature for 3 h to obtain a carboxylated multi-walled carbon nanotube coating with a concentration of 0.6 mg / mL;

[0101] Step (4): Place the substrate in 5 mL of a 5 mmol / L chloroauric acid solution for electro-deposition treatment for 100 s to form a gold nanoparticle modification layer on the carboxylated multi-walled carbon nanotube modification layer, thereby obtaining a working electrode, wherein the constant potential of the electro-deposition treatment is -0.25 V.

[0102] The working electrode, the counter electrode, and the reference electrode form a three-electrode system to obtain an electrochemical sensor.

[0103] Example 2

[0104] The difference between this example and Example 1 is only that in step (4), the concentration of the chloroauric acid solution is 10 mmol / L.

[0105] Example 3

[0106] The difference between this example and Example 1 is only that in step (4), the concentration of the chloroauric acid solution is 15 mmol / L.

[0107] Example 4

[0108] The difference between this example and Example 1 is only that in step (4), the concentration of the chloroauric acid solution is 20 mmol / L.

[0109] Example 5

[0110] The difference between this example and Example 1 is only that in step (4), the concentration of the chloroauric acid solution is 25 mmol / L.

[0111] Performance test:

[0112] Configuration of the test solution: Prepare 5 mL of a PBS solution with a concentration of 0.1 mol / L and a pH of 7, and add 5 μL of 1.5 mmol / L caffeine to form a test solution with a caffeine concentration of 150 μmol / L. Before the electrochemical experiment, the test solution is deoxygenated by passing N2.

[0113] Configuration of the control solution: Prepare 5 mL of a PBS solution with a concentration of 0.1 mol / L and a pH of 7 as the control solution.

[0114] At room temperature, the electrochemical sensors prepared in Example 1 were used to conduct electrochemical experiments on the test solution and the control solution respectively. During the test, differential pulse voltammetry was used, and the results were recorded as linear sweep voltammograms, as Figure 4 shown. Among them, the oxidation peak current measured by the electrochemical sensor prepared in Example 1 was 2.75×10 -5 A.

[0115] At room temperature, the electrochemical sensor prepared in Example 2 was used to conduct an electrochemical experiment on the test solution. During the test, differential pulse voltammetry was used. The oxidation peak current measured by the electrochemical sensor prepared in Example 2 was 2.80×10 -5 A.

[0116] At room temperature, the electrochemical sensor prepared in Example 3 was used to conduct an electrochemical experiment on the test solution. During the test, differential pulse voltammetry was used. The oxidation peak current measured by the electrochemical sensor prepared in Example 3 was 2.88×10 -5 A.

[0117] At room temperature, the electrochemical sensor prepared in Example 4 was used to conduct an electrochemical experiment on the test solution. During the test, differential pulse voltammetry was used. The oxidation peak current measured by the electrochemical sensor prepared in Example 4 was 2.87×10 -5 A.

[0118] At room temperature, the electrochemical sensor prepared in Example 5 was used to conduct an electrochemical experiment on the test solution. During the test, differential pulse voltammetry was used. The oxidation peak current measured by the electrochemical sensor prepared in Example 5 was 2.85×10 -5 A.

[0119] According to Figure 4 what is shown, it can be known that a peak current will be generated when the test solution contains caffeine. Therefore, the electrochemical sensor provided by the embodiments of the present application can accurately and quickly detect caffeine in e-cigarette oil.

[0120] In addition, the electrochemical sensors prepared in Examples 1 to 5 were used to conduct electrochemical experiments on the test solution with a caffeine concentration of 150 μmol / L. By comparing the oxidation peak currents obtained, it can be known that by changing the concentration of the chloroauric acid solution, the detection sensitivity of the electrochemical sensor to caffeine can be changed. When the concentration of the chloroauric acid solution is 15 mmol / L, the detection sensitivity of the electrochemical sensor to caffeine is the most sensitive. Moreover, further increasing the concentration of the chloroauric acid solution has little effect on the detection sensitivity of the electrochemical sensor. Therefore, it can be known that when the concentration of the chloroauric acid solution is 15 mmol / L, the detection sensitivity of the electrochemical sensor to caffeine is the most sensitive.

[0121] Based on the above performance tests, further experiments were carried out:

[0122] Using the electrochemical sensor prepared in Example 3, electrochemical experiments were carried out on test solutions with caffeine concentrations of 5 μmol / L, 60 μmol / L, 100 μmol / L, 150 μmol / L, 200 μmol / L and the control solution respectively. During the test, differential pulse voltammetry was used, and the linear sweep voltammogram was recorded, as Figure 5 shown; and the response current generated by the electrochemical sensor to PBS solutions with different caffeine concentrations was corresponded to the caffeine concentration, and the linear relationship diagram was recorded, as recorded Figure 6 shown.

[0123] According to Figure 5 it can be known that as the caffeine concentration in the PBS solution increases, the oxidation peak current measured by the electrochemical sensor is higher. According to Figure 6 it can be known that in the range of caffeine concentration from 5 μmol / L to 200 μmol / L, the response current of the catalytic oxidation reaction of the electrochemical sensor in this example has a linear relationship with the change of caffeine concentration, and the linear relationship is: Y = 0.1374X + 7.7051, and the correlation coefficient is R 2 = 0.9943, and the detection limit is 1.0 μmol / L (S / N = 3).

[0124] In summary, the electrochemical sensor provided by the embodiment of the present application can detect the caffeine concentration in e-cigarette oil under normal temperature conditions, and has a fast reaction speed, stable performance, and good application prospects.

[0125] Obviously, the above-described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The drawings show the preferred embodiments of the present application, but do not limit the patent scope of the present application. The present application can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of the present application more thorough and comprehensive. Although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing specific embodiments, or perform equivalent replacements on some of the technical features. Any equivalent structure directly or indirectly using the content of the specification and drawings of the present application in other related technical fields is similarly within the scope of the patent protection of the present application.

Claims

1. An electrochemical sensor, characterized in that, It includes a substrate, a working electrode, a counter electrode, and a reference electrode disposed on the substrate. The working electrode, the counter electrode, and the reference electrode form a three - electrode system; The working electrode includes a base electrode, and a carboxylated multi - walled carbon nanotube modified layer and a gold nanoparticle modified layer sequentially disposed on the base electrode.

2. The electrochemical sensor according to claim 1, wherein The material of the substrate is selected from at least one of polyethylene terephthalate, polyvinyl chloride, or ceramics; and / or The counter electrode is selected from platinum electrodes; and / or The reference electrode is selected from silver - silver chloride electrodes; and / or The base electrode is selected from carbon electrodes; and / or The material of the carboxylated multi - walled carbon nanotube modified layer includes an N,N - dimethylformamide dispersion of carboxylated multi - walled carbon nanotubes.

3. A preparation method of an electrochemical sensor, characterized in that, It includes the following steps: Provide a substrate; Prepare a base electrode, a counter electrode, and a reference electrode on the substrate by a screen - printing process; Provide a carboxylated multi - walled carbon nanotube coating solution, coat the carboxylated multi - walled carbon nanotube coating solution on the base electrode, and obtain a carboxylated multi - walled carbon nanotube modified layer after drying; Place the substrate in a chloroauric acid solution for electrodeposition treatment to form a gold nanoparticle modified layer on the carboxylated multi - walled carbon nanotube modified layer, obtaining a working electrode. Among them, the working electrode, the counter electrode, and the reference electrode form a three - electrode system to obtain an electrochemical sensor.

4. The method for preparing an electrochemical sensor according to claim 3, characterized in that, The carboxylated multi - walled carbon nanotube coating solution is prepared through the following steps: Provide multi - walled carbon nanotube material, disperse the multi - walled carbon nanotube material in nitric acid, perform reflux oxidation treatment, and then perform water washing and drying treatment; Disperse the multi - walled carbon nanotube material after water washing and drying treatment in a hydrogen peroxide solution, perform ultrasonic treatment, and then perform water washing and drying treatment to obtain carboxylated multi - walled carbon nanotube material; Disperse the carboxylated multi - walled carbon nanotube material in an N,N - dimethylformamide solution and perform ultrasonic treatment to obtain a carboxylated multi - walled carbon nanotube coating solution.

5. The preparation method of the electrochemical sensor according to claim 4, characterized in that, The temperature of the reflux oxidation treatment is 130°C - 150°C; and / or The duration of the reflux oxidation treatment is 5h - 10h.

6. The preparation method of the electrochemical sensor according to claim 4, characterized in that, The water washing and drying treatment specifically includes the following steps: Wash the treated multi - walled carbon nanotube material with water until it is neutral; Perform drying treatment on the multi - walled carbon nanotube material after water washing. Among them, the temperature of the drying treatment is 60°C - 80°C; and / or, the duration of the drying treatment is 12h - 24h.

7. The preparation method of the electrochemical sensor according to claim 4, characterized in that, The mass fraction of the nitric acid is 60% - 80%; and / or The concentration of the hydrogen peroxide solution is 10% - 30%; and / or The concentration of the carboxylated multi - walled carbon nanotube coating solution is 0.2mg / mL - 1.2mg / mL.

8. The preparation method of the electrochemical sensor according to claim 4, wherein, The temperature of the ultrasonic treatment is 20°C - 30°C; and / or The duration of the ultrasonic treatment is 3h - 5h.

9. The method for preparing the electrochemical sensor according to claim 3, wherein, The coating volume of the carboxylated multi - walled carbon nanotube coating solution is 1μL - 5μL.

10. The preparation method of the electrochemical sensor according to claim 3, characterized in that, The method used for the electrodeposition treatment is a constant - potential deposition method, where the deposition potential is - 0.25V and the deposition duration is 50s - 150s.

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