A flexible gas sensor made of methyl salicylate and its preparation method

Abstract

This invention relates to the field of analytical detection technology, and more particularly to a flexible methyl salicylate gas sensor and its preparation method. The preparation method involves prepolymerizing polypyrrole with methyl salicylate template molecules and methacrylic acid functional monomers in an organic solvent, followed by adding a crosslinking agent and an initiator to carry out a polymerization reaction to obtain a copolymer. After removing the methyl salicylate template molecules, a MIP-PPy material is obtained. The MIP-PPy material is then mixed with a dichloromethane solution of polyvinyl chloride and coated onto an electrode surface. This sensor can rapidly and accurately detect the content of methyl salicylate released by plants, achieving stable and reliable in-situ detection of methyl salicylate in plants. This technology allows for early detection of plant diseases and prevention of infection spread, thus preventing crop losses.

Description

Technical Field

[0001] This invention relates to the field of analytical detection technology, and in particular to a methyl salicylate flexible gas sensor and its preparation method. Background Technology

[0002] Methyl salicylate (MeSa) is a volatile organic compound (VOC) with an aromatic odor and a key biomarker for plant disease detection and plant life regulation. Studies have shown that when plants (such as tobacco and tomatoes) are infected with diseases, they release MeSa into the surrounding environment. This signal not only enhances the defense mechanisms of infected plants but also activates the disease resistance of neighboring healthy plants, serving as a biomarker for early diagnosis of plant diseases. Therefore, detecting the release of MeSa from plants can help identify plant diseases early and prevent the spread of infection, which is of great significance for reducing agricultural economic losses and ensuring food security.

[0003] Currently, MeSa determination is typically performed using traditional analytical techniques, such as gas chromatography (GC), high-performance liquid chromatography (HPLC), and ultraviolet-visible spectroscopy (UV-Vis). While these conventional methods can usually accurately determine MeSa, they require sophisticated large-scale instruments, skilled technicians, and complex pretreatment steps, which increases the cost of detection and may cause environmental pollution. Furthermore, traditional detection methods are not suitable for in-situ, on-site detection of MeSa.

[0004] Electrochemical sensors are low-cost, easy to operate, portable, highly accurate, and have a fast response time, and have been applied to the detection of metabolites in plants. However, because plant tissues are soft and often irregularly shaped, traditional rigid electrode sensors (such as glassy carbon electrodes and gold electrodes) cannot achieve effective adhesion to the plant surface.

[0005] Therefore, how to develop a flexible gas sensor capable of detecting methyl salicylate released by plants in situ has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical challenges, this invention provides a method for preparing a methyl salicylate flexible gas sensor, comprising:

[0007] A mixture of ferric chloride and sodium benzenesulfonate (BSNa) was prepared by dissolving them in water. Pyrrole was then added to the mixture and polymerized in situ to obtain polypyrrole (PPy).

[0008] The polypyrrole, methyl salicylate template molecules, and methacrylic acid (MAA) functional monomers were dissolved in an organic solvent for prepolymerization. Then, a crosslinking agent and an initiator were added to carry out a polymerization reaction to obtain a copolymer. After removing the methyl salicylate template molecules, the MIP-PPy material was obtained.

[0009] The MIP-PPy material is mixed with a dichloromethane solution of polyvinyl chloride to prepare a mixed solution, which is then coated onto the electrode surface to obtain the methyl salicylate flexible gas sensor.

[0010] In this invention, sodium benzenesulfonate is used as a dopant and ferric chloride as an oxidant to initiate the oxidative polymerization of pyrrole monomers at 0°C, forming a conductive material polypyrrole (PPy) with a three-dimensional porous structure. Subsequently, specific recognition sites for the target substance are constructed based on molecular imprinting (MIP) technology: MeSa is used as a template molecule and pre-assembled with the aforementioned PPy via hydrogen bonding with a functional monomer of methacrylic acid. A crosslinking agent and an initiator are added to carry out a polymerization reaction to form a MeSa molecularly imprinted PPy complex (MIP-PPy). This complex is dispersed in a polyvinyl chloride / dichloromethane solution and then coated onto the electrode surface to obtain a methyl salicylate flexible gas sensor.

[0011] In some embodiments, the concentration of ferric chloride in the mixture is 0.06~0.09 g / ml, preferably 0.06~0.07 g / ml.

[0012] In some embodiments, the concentration of sodium benzenesulfonate in the mixture is 0.01~0.05 g / ml, preferably 0.01~0.03 g / ml, and more preferably 0.018~0.02 g / ml.

[0013] In some embodiments, a mixture is prepared by dissolving ferric chloride and sodium benzenesulfonate in water at 0°C.

[0014] In some embodiments, the volume ratio of pyrrole to the mixture is (0.5~2.5) ml:150 ml; preferably (0.8~1.2) ml:150 ml.

[0015] In some implementations, the conditions for the in-situ polymerization include: the in-situ polymerization time is 3 to 12 hours (preferably 9 hours).

[0016] In some embodiments, the organic solvent in the prepolymerization reaction system is a mixture of methanol and acetonitrile (preferably in a volume ratio of 1:1).

[0017] In some embodiments, in the prepolymerization reaction system, the concentration of the polypyrrole is 2-4 mg / ml (preferably 2 mg / ml); the concentration of the methyl salicylate template molecule is 1-3 mM (preferably 1 mM); and the concentration of the methacrylic acid functional monomer is 3-10 mM (preferably 3 mM).

[0018] In some embodiments, the prepolymerization step includes: refrigerating at 2°C to 6°C for 6 to 24 hours (preferably 24 hours).

[0019] In some embodiments, the crosslinking agent is ethylene glycol dimethacrylate (EGDMA); and / or, the initiator is benzoyl peroxide (BPO).

[0020] In some embodiments, the concentration of the crosslinking agent in the polymerization reaction system is 1-5 mM (preferably 3.5 mM), and the concentration of the initiator is 0.1-3 mM (preferably 1.5 mM).

[0021] In some embodiments, the polymerization reaction is carried out at a temperature of 60-80°C (preferably 60°C).

[0022] In some embodiments, the polymerization reaction takes 3 to 9 hours (preferably 3 hours).

[0023] In some implementations, MIP-PPy materials are prepared by washing with ethanol to remove methyl salicylate template molecules.

[0024] In some embodiments, the concentration of the MIP-PPy material in the mixed solution is 3 to 10 mg / ml (preferably 5 mg / ml); and / or, the concentration of the dichloromethane solution of polyvinyl chloride is 0.5 to 1.5 mg / ml.

[0025] In some embodiments, the electrode is a LIG / PDMS electrode.

[0026] Preferably, the LIG / PDMS electrode preparation steps include: preparing laser-induced graphene on polyimide tape using laser direct writing technology, further transferring it onto polydimethylsiloxane, coating a reference electrode with Ag / AgCl slurry, and encapsulating the wires and passivation region to obtain the LIG / PDMS electrode.

[0027] Preferably, before coating with the mixed solution, the LIG / PDMS electrode is placed in a phosphate buffer solution (preferably 0.1 mol / L, pH=7.2-7.4) and activated by a constant potential method (preferably 1.7V) for 100-300s (preferably 180s) to remove impurities from the electrode surface.

[0028] Furthermore, the present invention provides a methyl salicylate flexible gas sensor, which is prepared by the aforementioned method.

[0029] The methyl salicylate flexible gas sensor includes a flexible substrate, a three-electrode system (working electrode, counter electrode, and reference electrode) located on the surface of the flexible substrate, an encapsulation layer located on the three-electrode system, and a material layer modified on the surface of the working electrode.

[0030] Furthermore, the present invention provides the application of the aforementioned methyl salicylate flexible gas sensor in the detection of methyl salicylate; preferably, its application in in situ in vivo detection of methyl salicylate released by plants.

[0031] Furthermore, the present invention provides a method for in-situ in vivo detection of methyl salicylate released by plants, comprising: attaching the methyl salicylate flexible gas sensor to the surface of the plant in a sealed gas chamber, and then connecting it to an electrochemical workstation for detection.

[0032] In the specific implementation process, the plant can be any plant that releases methyl salicylate, including but not limited to fruits, vegetables, flowers, and crops.

[0033] In the specific implementation process, the detection sites of the plant body include, but are not limited to, the stems, leaves, fruits, and other tissues of the plant.

[0034] In the specific implementation process, the concentration of methyl salicylate can be obtained by establishing a standard curve.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] This invention provides an electrochemical flexible gas sensor for in-situ detection of methyl salicylate released from plants. This sensor can rapidly and accurately detect the content of methyl salicylate released by plants, achieving stable and reliable in-situ detection of methyl salicylate in plants. Compared with traditional rigid electrochemical sensors, the flexible electrode has superior adhesion, can adapt to irregular surfaces of plant tissues, and possesses high sensitivity, high specificity, and high stability. This technology enables early detection of plant diseases and prevention of infection spread, thus preventing crop losses. Furthermore, the flexible gas sensor for methyl salicylate of this invention has low manufacturing cost and simple process. By combining it with smart agriculture applications, it also supports unmanned, intelligent in-situ dynamic monitoring, providing a highly efficient and convenient solution for detecting methyl salicylate in modern agriculture. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention.

[0038] Figure 2 This is the standard curve of Example 1 and the comparative sensor.

[0039] Figure 3 These are the selective test results and in-situ detection results of the sensor in Example 1; where A is the selective test result and B is the in-situ detection result of MeSa release from citrus. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. In the embodiments provided in this specification, unless specific techniques or conditions are specified, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels. The electrochemical workstation in the following embodiments is an IVIUM portable electrochemical workstation (pocketSTAT).

[0041] Example 1

[0042] This embodiment provides a flexible methyl salicylate gas sensor, and the process flow diagram is shown below. Figure 1 As shown, the preparation method is as follows:

[0043] 1. Apply polyimide tape to a 6×6 cm area. 2 On a polytetrafluoroethylene (PTFE) plate, electrode patterns, including working electrodes, counter electrodes, and reference electrodes, are designed using CAD. The exported electrode patterns are then loaded into the software of the laser printing system. The printing power is 53%, and the printing depth is 10 μm. The PI tape is then patterned.

[0044] 2. Liquid polydimethylsiloxane (PDMS) was coated onto a polytetrafluoroethylene (PTFE) plate using a spin coater at a speed of 100 rpm for 90 s. The plate was then placed in a vacuum drying oven at 100°C and heated under vacuum for 12 hours. The PI film was then peeled off from the PDMS to obtain the LIG / PDMS electrode.

[0045] 3. Apply an appropriate amount of PDMS to the non-working area of ​​the electrode and heat to cure it to avoid short circuits. Finally, apply Ag / AgCl silver paste to the exposed reference electrode and heat to cure it.

[0046] 4. Place the LIG / PDMS electrode in phosphate buffer (0.1 mol / L, pH=7.2-7.4) and activate it at 1.7V for 180s using a constant potential method to remove impurities from the electrode surface.

[0047] 5. Under magnetic stirring, FeCl3 (9.75 g) as an oxidant and sodium benzenesulfonate (BSNa, 2.854 g) as a dopant were dissolved in 150 ml of deionized water and dissolved at approximately 0°C for 30 min. 1 ml of pyrrole (Py) monomer was slowly added to the above mixture using a syringe, and in-situ polymerization was carried out for 9 h. Afterward, the PPy was filtered and dried.

[0048] 6. Dissolve 50 mg PPy, 3.8 mg MeSa (template molecule), and 6.5 mg MAA (functional monomer) in 25 ml of methanol and acetonitrile (1:1, v / v), mix thoroughly, and refrigerate at 4 °C for 24 h for prepolymerization. Then, add 17.3 mg ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent and 9.1 mg benzoyl peroxide (BPO) as an initiator to synthesize the copolymer. The polymerization process is carried out at 60 °C for 3 h. After the copolymer precipitates, the MeSa template is eluted with ethanol for 1 h and then dried to obtain MIP-PPy.

[0049] 7. Add 5 mg of MIP-Ppy to 1 mL of polyvinyl chloride / dichloromethane solution (polyvinyl chloride concentration is 1 mg / mL), sonicate for 10 minutes to mix, then use a pipette to transfer 10 μL of the mixed solution onto the working area of ​​the sensor and completely cover the three electrodes. Dry under an infrared lamp to obtain the methyl salicylate flexible gas sensor MIP-PPy (PMAA).

[0050] Example 2

[0051] This embodiment tests the detection performance of the flexible gas sensor prepared in Example 1, and the steps are as follows:

[0052] (1) Using 100ppm MeSa standard gas as the gas source and high-purity nitrogen as the carrier gas, a dual-channel mass flow controller was used to control the concentration of MeSa gas flowing into the gas chamber by adjusting the flow rates of MeSa and high-purity nitrogen. The sensor of Example 1 was placed in a 20ml sealed gas chamber, and the response of the sensor in 1ppm, 10ppm, 20ppm, 30ppm, 40ppm, 50ppm, 60ppm, 70ppm, 80ppm, 90ppm and 100ppm MeSa gas was tested at a potential of 1V using the it method, and a standard curve was plotted. The sensor response was defined as the change in resistance of the sensor exposed to the target gas (ΔR) divided by the initial resistance of the sensor in the air (R0), and then the absolute value was taken.

[0053] The results are as follows Figure 2 As shown, the linear equation is y = 0.25x + 15.73, the detection range is 1~100 ppm, the detection limit is 0.025 ppm (S / N = 3), and the correlation coefficient is 0.977.

[0054] (2) Interference verification was performed on the sensor of Example 1 using 100 ppm of methyl salicylate, methyl jasmonate, ethyl acetate, ethanol, and toluene.

[0055] The results are as follows Figure 3 As shown in Figure A, the sensor in Example 1 only exhibits a high response to MeSa.

[0056] (3) In-situ detection of MeSa release from plants

[0057] The flexible sensor from Example 1 was connected to an electrochemical workstation for an it scan (potential 1V, sampling interval 0.1 s). After testing in clean air for 100 s, the sensor was attached to the surface of a citrus fruit and placed in the 150 mL sample chamber of the gas sensing system for 5 minutes, followed by a 100 s test. The resistance curve is shown below. Figure 3 As shown in B. The obtained response signal was used to calculate the concentration of MeSa released by the tested plant by substituting it into a standard curve.

[0058] Simultaneously, gas chromatography-mass spectrometry (GC-MS) was used to test the same fruit sample as a control. The citrus fruit was placed in the 150 mL sample chamber of the gas sensing system for 5 minutes to generate sufficient headspace gas. The headspace gas in the sample chamber was then purged into a gas sampling bag with high-purity nitrogen. An aged solid-phase microextraction head was inserted into the gas sampling bag for adsorption for 30 minutes, followed by desorption at the GC-MS inlet for 10 minutes. The conditions for gas chromatography-mass spectrometry are as follows:

[0059] (1) Chromatographic column: capillary column with polyethylene glycol as stationary phase (30 mm × 0.32 mm × 0.25 μm); injector temperature 250 ℃; carrier gas (helium) flow rate 1 mL∙min −1 Initial temperature 120 ℃, hold for 3 min, 10 ℃∙min −1 The temperature was programmed to rise to 200 °C and held for 2 min; the injection split ratio was 1:20.

[0060] (2) Mass spectrometry conditions: transfer line temperature 210 ℃; ion source 210 ℃; mass-to-charge ratio scan range 35–500 m / z; solvent delay set to 3 min.

[0061] The same fruit sample was tested 6 times, and the results are shown in Table 1. The results show that the RSD of the test result of Example 1 is 7.43%, the consistency of the results is good and close to the concentration detected by gas chromatography-mass spectrometry, indicating that the detection results of the sensor in Example 1 are accurate and reliable.

[0062] Table 1. Test results of MeSa in fruit samples

[0063]

[0064] Comparative Example 1

[0065] This comparative example provides a flexible gas sensor for detecting methyl salicylate. The only difference in preparation method from Example 1 is that PPy is replaced with an equal amount of polyaniline (PANI), and the flexible gas sensor MIP-PANI (PMAA) is finally obtained.

[0066] The sensor's detection performance was tested using the method described in Example 2, such as... Figure 2 As shown, the sensor's detection range is 20~70ppm, and its detection performance is not as good as that of Example 1.

[0067] Comparative Example 2

[0068] This comparative example provides a flexible gas sensor for detecting methyl salicylate. The preparation method differs from that in Example 1 only in that the functional monomer MAA is replaced with an equal amount of methyl methacrylate (MMA), and the flexible gas sensor MIP-PPy (PMMA) is finally obtained.

[0069] The sensor's detection performance was tested using the method described in Example 2, such as... Figure 2 As shown, the detection range of this sensor is 10~80 ppm, and the detection effect is not as good as that of Example 1.

[0070] Comparative Example 3

[0071] This comparative example provides a flexible gas sensor for detecting methyl salicylate. The only difference from Example 1 is that a non-imprinted polymer (NIP-PPy) was synthesized without adding a MeSa template when polymerizing the functional monomer PMAA, and the flexible gas sensor NIP-PPy (PMAA) was finally obtained.

[0072] The sensor's detection performance was tested using the method described in Example 2, such as... Figure 2 As shown, the detection range of this sensor is 10~90ppm, and the detection effect is not as good as that of Example 1.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a methyl salicylate flexible gas sensor, characterized in that, include: A mixture of ferric chloride and sodium benzenesulfonate was prepared by dissolving them in water. Pyrrole was then added to the mixture and polymerized in situ to obtain polypyrrole. The polypyrrole, methyl salicylate template molecules, and methacrylic acid functional monomers were dissolved in an organic solvent for prepolymerization. Then, a crosslinking agent and an initiator were added to carry out a polymerization reaction to obtain a copolymer. After removing the methyl salicylate template molecules, the MIP-PPy material was obtained. A mixed solution was prepared by mixing MIP-PPy material with a dichloromethane solution of polyvinyl chloride. The mixed solution was then coated onto the electrode surface to obtain the methyl salicylate flexible gas sensor. In the mixed solution, the concentration of the MIP-PPy material is 3~10 mg / ml; the concentration of the polyvinyl chloride dichloromethane solution is 0.5~1.5 mg / ml; The electrode is a LIG / PDMS electrode.

2. The preparation method according to claim 1, characterized in that, The concentration of ferric chloride in the mixture is 0.06~0.09 g / ml; And / or, in the mixture, the concentration of sodium benzenesulfonate is 0.01~0.05 g / ml; And / or, a mixture is prepared by dissolving ferric chloride and sodium benzenesulfonate in water at 0°C; And / or, the volume ratio of pyrrole to the mixture is (0.5~2.5) ml: 150 ml.

3. The preparation method according to claim 1 or 2, characterized in that, The conditions for in-situ polymerization include: the in-situ polymerization time is 3~12h.

4. The preparation method according to claim 1 or 2, characterized in that, In the prepolymerization reaction system, the organic solvent is a mixture of methanol and acetonitrile; And / or, in the prepolymerization reaction system, the concentration of the polypyrrole is 2-4 mg / ml; the concentration of the methyl salicylate template molecule is 1-3 mM; The concentration of the methacrylic acid functional monomer is 3~10mM; And / or, the prepolymerization step includes: refrigerating at 2°C to 6°C for 6 to 24 hours.

5. The preparation method according to claim 3, characterized in that, In the prepolymerization reaction system, the organic solvent is a mixture of methanol and acetonitrile; And / or, in the prepolymerization reaction system, the concentration of the polypyrrole is 2-4 mg / ml; the concentration of the methyl salicylate template molecule is 1-3 mM; The concentration of the methacrylic acid functional monomer is 3~10mM; And / or, the prepolymerization step includes: refrigerating at 2°C to 6°C for 6 to 24 hours.

6. The preparation method according to claim 1, 2, or 5, characterized in that, 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 1~5mM, and the concentration of the initiator is 0.1~3mM; And / or, the polymerization reaction is carried out at a temperature of 60~80°C.

7. The preparation method according to claim 3, characterized in that, 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 1~5mM, and the concentration of the initiator is 0.1~3mM; And / or, the polymerization reaction is carried out at a temperature of 60~80°C.

8. The preparation method according to claim 4, characterized in that, 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 1~5mM, and the concentration of the initiator is 0.1~3mM; And / or, the polymerization reaction is carried out at a temperature of 60~80°C.

9. The preparation method according to claim 1 or 2, characterized in that, The fabrication steps of the LIG / PDMS electrode include: preparing laser-induced graphene on polyimide tape using laser direct writing technology, further transferring it onto polydimethylsiloxane, coating a reference electrode with Ag / AgCl slurry, and encapsulating the wires and passivation region to obtain the LIG / PDMS electrode.

10. A flexible gas sensor made of methyl salicylate, characterized in that, It is prepared by any one of claims 1 to 9.

11. The application of the methyl salicylate flexible gas sensor of claim 10 in in-situ in vivo detection of methyl salicylate released by plants; the application includes: In a sealed gas chamber, the methyl salicylate flexible gas sensor as described in claim 10 is attached to the surface of a plant and then connected to an electrochemical workstation for detection.

Images