An electrochemical gas sensor for detecting limonene and a method for preparing the same

Abstract

The application relates to the technical field of analytical detection, in particular to an electrochemical gas sensor for detecting limonene and a preparation method thereof. The preparation method is as follows: multi-walled carbon nanotubes are dispersed in a ZnO nanoparticle solution, and then a composite material modified electrode is prepared by coating the multi-walled carbon nanotubes on the surface of the electrode; then, limonene template molecules and acrylamide functional monomers are dispersed in an alcohol solvent, and a polymer solution is prepared by polymerization under the action of a crosslinking agent and an initiator; finally, the polymer solution is coated on the surface of the composite material modified electrode, and the electrochemical gas sensor is prepared after eluting the template molecules. The sensor can sensitively and accurately detect the content of limonene gas released by plants, realizes stable and accurate detection of limonene in a complex environment with high specificity and high sensitivity, and provides important theoretical basis and technical support for cultivating high-quality crops and helps the innovative development of the field of crop breeding.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of analytical detection technology, and particularly relates to an electrochemical gas sensor for detecting ocimene and a preparation method thereof. BACKGROUND

[0002] OCimene (OCM) is one of the important flavor substances in plants, and widely exists in crops such as kumquat, mango, hops, blackcurrant flower bud, mint, pepper, thyme and lavender. The content of OCM is closely related to the variety, maturity and quality of the crops. By detecting the content of OCM, the quality of the crops can be quickly and accurately evaluated, which provides a scientific basis for the grading, pricing and marketing of the crops after maturity. In addition, OCM has certain medicinal value, such as antiviral and antibacterial, and can be used for the development of food additives. Detecting the content of OCM helps to control the amount of food additives. Therefore, accurately detecting the content of OCM has important significance for crop breeding and food safety.

[0003] The common detection methods of OCM include gas chromatography-mass spectrometry, high performance liquid chromatography and spectrophotometry. However, these analytical detection methods are usually complex and time-consuming, and depend on large-scale instruments and professional technicians, which are high in cost and difficult to realize rapid and convenient detection. In contrast, electrochemical sensors have significant application potential in the detection of plant volatile gases due to their high sensitivity, real-time performance, anti-interference performance and economy.

[0004] Therefore, it is a technical problem to be solved in the field to develop an electrochemical gas sensor capable of in-situ and in-vivo detection of ocimene released by plants. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a preparation method of an electrochemical gas sensor for detecting ocimene, comprising: dispersing multi-walled carbon nanotubes in a ZnO nanoparticle solution to obtain a MWCNT-ZnO mixed solution, and coating the MWCNT-ZnO mixed solution on the surface of an electrode to obtain a composite material modified electrode.

[0006] Dispersing ocimene template molecules (OCM) and acrylamide (AM) functional monomers in an alcohol solvent to obtain a template-monomer solution; mixing the template-monomer solution with a crosslinking agent and an initiator to perform a polymerization reaction, and obtaining a molecularly imprinted polymer solution;

[0007] Coating the molecularly imprinted polymer solution on the surface of the composite material modified electrode, and eluting the template molecules to obtain the electrochemical gas sensor.

[0008] The application increases the ability of the sensor to adsorb the limonene gas molecules by the MWCNT-ZnO composite material modified electrode, and combines the carbon nanomaterial-MWCNT to improve the sensitivity of the electrochemical sensor, and cooperates with the molecular imprinting technology to improve the anti-interference ability of the electrochemical sensor.

[0009] In some embodiments, the mass-volume ratio of the multi-walled carbon nanotube to the ZnO nanoparticle solution is (0.5-2) mg:(0.5-5) ml; preferably (1-3) mg:1 ml, and more preferably 2 mg:1 ml.

[0010] In some embodiments, the mass percentage of the ZnO nanoparticles in the ZnO nanoparticle solution is (15-25) wt.%, preferably (18-22) wt.%.

[0011] In some embodiments, the electrode is an interdigital electrode (IDE electrode).

[0012] In some embodiments, the concentration of the limonene template molecule in the template-monomer solution is 1-5 mM (preferably 5 mM).

[0013] In some embodiments, the concentration of the acrylamide functional monomer in the template-monomer solution is 1-5 mM (preferably 1 mM).

[0014] In some embodiments, the crosslinking agent is ethylene glycol dimethacrylate (EGDMA).

[0015] In some embodiments, the initiator is benzoyl peroxide (AIBN).

[0016] In some embodiments, the concentration of the crosslinking agent in the polymerization system is 1-5 mM (preferably 3 mM).

[0017] In some embodiments, the concentration of the initiator in the polymerization system is 0.05-0.5 mM (preferably 0.5 mM).

[0018] In some embodiments, the reaction temperature of the polymerization reaction is 55-65°C (preferably 58-62°C).

[0019] Preferably, the reaction time of the polymerization reaction is 30-60 minutes (preferably 60 minutes).

[0020] In some embodiments, the electrochemical gas sensor is prepared after eluting the template molecule with a mixture of ethanol and water.

[0021] Preferably, the volume ratio of the ethanol and water is (2-4):1, preferably 3:1.

[0022] In some embodiments, the electrode is sonicated with ethanol before use to remove impurities on the surface of the electrode.

[0023] Further, the present application provides an electrochemical gas sensor for detecting limonene prepared by the preparation method.

[0024] Further, the present application provides the electrochemical gas sensor for detecting limonene in the detection of limonene; preferably in situ in vivo detection of limonene released by plants.

[0025] In the specific implementation process, the plant is any plant releasing limonene, including but not limited to fruits, vegetables, flowers, crops, etc.

[0026] Further, the present application provides a method for in situ in vivo detection of limonene released by a plant body, comprising: placing the electrochemical gas sensor in a gas chamber and attaching it to the surface of the plant body, and then connecting an electrochemical workstation for detection.

[0027] In the specific implementation process, the part of the plant body includes but is not limited to the stem, leaf, fruit, etc. of the plant.

[0028] In the specific implementation process, the concentration of limonene can be obtained by establishing a standard curve.

[0029] In the specific implementation process, after connecting the electrochemical workstation, i-t scanning (potential 1V, sampling interval 0.1s) is used for detection.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] The present application provides an electrochemical sensor capable of in situ in vivo detection of limonene released by plants, which can sensitively and accurately detect the content of limonene gas released by plants, and realize stable and accurate detection of limonene in a complex environment with high specificity and high sensitivity. Through this technology, important theoretical basis and technical support are provided for the cultivation of high-quality crops, and innovation and development are promoted in the field of crop breeding.

[0032] In addition, the present application not only has faster detection speed, but also has low manufacturing cost and simple process. When combined with the application scene of smart agriculture, this technology can support real-time dynamic monitoring of unmanned and intelligentization, thereby providing efficient and convenient solutions for modern agriculture. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is the process flow chart of embodiment 1 of the present application.

[0034] Figure 2 is the selectivity test result graph of the sensor of embodiment 1 of the present application.

[0035] Figure 3 is the linear curve of the sensor of Example 1 and the comparative sensor of the present application.

[0036] Figure 4 is a schematic diagram of in-situ detection of release of ocimene from plants by the sensor of Example 1 of the present application; wherein (a) is a schematic diagram of connection of the sensor; and (b) is a schematic diagram of a cross-section of the gas chamber. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. In the embodiments provided in the present specification, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased through a regular channel. The chemical workstations used in the following examples are EmStat4R mini electrochemical workstations. The MWCNT and ZnO nanoparticles used in the following examples are purchased from Jiangsu Xianfeng Nanometer Material Technology Co., Ltd., and the part numbers are 100294 and 102110, respectively. The OCM, AM, EGDMA and AIBN are purchased from Sigma-Aldrich (America), and the part numbers are W353977, A9099-25G, 335681 and 8.01641, respectively.

[0038] Example 1

[0039] The present embodiment provides an electrochemical gas sensor for detecting ocimene, and the preparation flowchart is shown in Figure 1 The preparation method is as follows:

[0040] (1) The IDE electrode is purchased from Changchun Beirun Electronics Technology Co., Ltd., and the specification is 10*5*0.635 mm. The IDE electrode is ultrasonically treated with ethanol for 5 minutes, and then dried with nitrogen to remove impurities on the surface of the electrode.

[0041] (2) 2 mg of MWCNT is weighed and placed in 1 ml of 20wt.% ZnO NPs dispersion solution, and ultrasonically treated for 2 hours to make it uniformly dispersed, to obtain a MWCNT-ZnO mixed solution, and 10 μL of the solution is dropped and coated on the working area of the IDE electrode sensor and completely covers the surface of the three-electrode, and dried to obtain MWCNT-ZnO / IDE.

[0042] OCM (final concentration 5 mM) and AM (final concentration 1 mM) were added into ethanol and sonicated for 60 min to obtain the template-monomer solution. AIBN (final concentration 0.5 mM) and EGDMA (final concentration 3 mM) were added into the prepared template-monomer solution and sonicated for 60 min at 60 °C to promote the polymerization reaction. After the completion of the polymerization reaction, 100 μL of the liquid was pipetted into the working area of MWCNT-ZnO / IDE and dried in a drying oven. After drying, the electrode was properly washed with a mixture of ethanol and water (3: 1 v / v) to remove the template molecule OCM. After drying again in a drying oven, the electrochemical gas sensor MIP / MWCNT-ZnO / IDE for detecting ocimene was obtained.

[0043] Example 2

[0044] The detection performance of the electrochemical gas sensor prepared in Example 1 was tested in this example, and the steps were as follows:

[0045] (1) 100 ppm OCM standard gas was used as the gas source, and high-purity nitrogen was used as the carrier gas. A double-channel mass flow controller was used to control the OCM gas concentration flowing into the gas chamber by adjusting the flow rates of OCM and high-purity nitrogen. The sensor was placed in a 20 ml sealed gas chamber, and the i-t method was used to test the sensor response in 0, 5, 10, 20, 30, 40, 50, 75, 100 ppm OCM gas at 1 V potential and draw the standard curve. The definition of sensor response is the change in resistance (AR) of the sensor exposed to the target gas divided by the initial resistance (R0) of the sensor in air, and then taking its absolute value. The linear equation of the sensor is shown in Figure 3 , the detection range of the sensor is 5-100 ppm, and the detection limit is 0.25 ppm (S / N=3).

[0046] (2) 100 ppm of 3-carene, β-caryophyllene, β-myrcene, geraniol and linalool were used to verify the interference of the electrochemical gas sensor prepared in Example 1. The selectivity test results are shown in Figure 2 , the electrochemical gas sensor prepared in Example 1 only showed high response to OCM.

[0047] (3) A simple gas chamber with a length, width and height of 12*7*5 mm and a wall thickness of 1 mm was printed using a 3D printer, and the sensor was attached to the gas chamber as shown in Figure 4 (b). Subsequently, the sensor was connected to an electrochemical workstation for i-t scanning (potential 1 V, sampling interval 0.1 s). After testing in clean air for 100 s, the sensor with the gas chamber was fixed on the surface of a mango fruit for 100 s testing, as shown in Figure 4(a) shown. The obtained response signal was calculated by bringing in the standard curve to calculate the concentration of OCM released by the measured fruit, and the test results are shown in Table 1.

[0048] Table 1 OCM content detection results in mango fruit (ppm)

[0049]

[0050] (4) Comparison with traditional detection methods

[0051] Gas chromatography (GC) was used as a control. The chromatographic column was DB-5 ms, 30 m in length, 0.25 μm in film thickness, and 0.25 mm in inner diameter. The temperature program was as follows: 50°C for 2 min, heated to 250°C at a rate of 15°C / min, and held for 8 min. The injection port temperature was 220°C, the FID detector temperature was 260°C, the split ratio was 10:1, and the injection amount was 1 mL. The GC standard curve was plotted with OCM concentration as the abscissa and peak area as the ordinate. After collecting the surrounding gas of the same mango fruit sample in (3), 0.25 mL of gas was extracted with a gas-tight syringe and injected directly through the GC injection port. The test results are shown in Table 2, which shows that the detection results of the sensor of the present application are very close to those of the GC method, indicating that the electrochemical gas sensor for detecting ocimene of the present application is accurate and reliable.

[0052] Table 2 GC detection results of OCM content in mango fruit (ppm)

[0053]

[0054] Comparative Example 1

[0055] This comparative example provides an electrochemical gas sensor for detecting ocimene, and the only difference between the preparation method and Example 1 is that MWCNT is replaced with an equal amount of graphene (GO).

[0056] The detection performance of the sensor was tested by the method in Example 2, and the sensor detection range was 10-75 ppm, the detection limit was 0.56 ppm (S / N=3), and the detection effect was not as good as Example 1. Figure 3

[0057] Comparative Example 2

[0058] This comparative example provides an electrochemical gas sensor for detecting ocimene, and the only difference between the preparation method and Example 1 is that the functional monomer AM is replaced with an equal amount of β-cyclodextrin (β-CD).

[0059] The detection performance of the sensor was tested by the method in Example 2, and the sensor detection range was 10-75 ppm, the detection limit was 0.56 ppm (S / N=3), and the detection effect was not as good as Example 1. Figure 3 ​As shown in the figure, the detection range of the sensor is 15~75ppm, and the detection limit is 0.85 ppm (S / N=3), and the detection effect is not as good as that of Example 1.

[0060] Comparative Example 3

[0061] The present comparative example provides an electrochemical gas sensor for detecting limonene, and the preparation method is only different from that of Example 1 in that: a non-imprinted polymer (NIP) is synthesized without adding OCM templates during the polymerization of the functional monomer AM.

[0062] The detection performance of the sensor is tested by the method in Example 2, and the results are shown in the figure. Figure 3 As shown in the figure, the detection range of the sensor is 10~75ppm, and the detection limit is 0.73ppm (S / N=3), and the detection sensitivity is significantly lower than that of Example 1.

[0063] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part 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 embodiments of the present application.

Claims

1. A method for preparing an electrochemical gas sensor for detecting limonene, characterized by, The method comprises the following steps: dispersing multi-walled carbon nanotubes in a ZnO nanoparticle solution to obtain a MWCNT-ZnO mixed solution, coating the MWCNT-ZnO mixed solution on the surface of an electrode to obtain a composite material modified electrode; dispersing a template molecule of a limonene and an acrylamide functional monomer in an alcohol solvent to obtain a template-monomer solution; mixing the template-monomer solution with a crosslinking agent and an initiator to perform a polymerization reaction to obtain a molecularly imprinted polymer solution; coating the molecularly imprinted polymer solution on the surface of the composite material modified electrode, and eluting the template molecule to obtain the electrochemical gas sensor.

2. The production method according to claim 1, characterized by, The mass-volume ratio of the multi-walled carbon nanotubes to the ZnO nanoparticle solution is (0.5-2) mg:(0.5-5) ml. And / or, the mass percentage of the ZnO nanoparticles in the ZnO nanoparticle solution is (15-25) wt.%.

3. The preparation method according to claim 1, characterized in that, The electrode is an IDE electrode.

4. The production method according to any one of claims 1 to 3, characterized by, In the template-monomer solution, the concentration of the limonene template molecule is 1-5 mM. And / or, in the template-monomer solution, the concentration of the acrylamide functional monomer is 1-5 mM.

5. The production method according to any one of claims 1 to 3, characterized by, The crosslinking agent is ethylene glycol dimethacrylate. And / or, the initiator is benzoyl peroxide. And / or, in the polymerization reaction system, the concentration of the crosslinking agent is 1-5 mM. And / or, in the polymerization reaction system, the concentration of the initiator is 0.05-0.5 mM. And / or, the reaction temperature of the polymerization reaction is 55-65 DEG C.

6. The production method according to any one of claims 1 to 3, characterized by, The template molecule is eluted by using a mixture of ethanol and water to obtain the electrochemical gas sensor.

7. The production method according to any one of claims 1 to 3, characterized by, Before use, the electrode is ultrasonically cleaned with ethanol to remove impurities on the surface of the electrode.

8. The electrochemical gas sensor for detecting limonene prepared by the method of any one of claims 1-7.

9. The electrochemical gas sensor for detecting limonene of claim 8 is used for detecting limonene.

10. The electrochemical gas sensor for detecting limonene of claim 8 is used for in-situ detection of limonene released by plants in vivo.

11. A method for detecting release of ocimene from a plant in situ in a living body, characterized by, The method comprises the following steps: placing the electrochemical gas sensor of claim 8 in a gas chamber and attaching it to the surface of a plant body, and then connecting an electrochemical workstation for detection.

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