PDA@Zn-MOF ternary composite modified electrode modified by glutamate oxidase, preparation method and application thereof

Abstract

The present invention discloses a PDA@Zn-MOF ternary composite modified electrode modified with glutamate oxidase, its preparation method and application, belonging to the technical field of electrochemical biosensors. The preparation method of the modified electrode includes: mixing an aqueous solution of zinc nitrate and an aqueous solution of 2-methylimidazole, drying to obtain Zn-MOF powder, adding it to a PBS buffer solution containing dopamine hydrochloride, and modifying it onto a conductive electrode by a drop-coating method or a potentiostatic method, and then drop-coating a glutamate oxidase solution. By measuring the current response value of the glutamate solution through the chronoamperometry (i-t method) and comparing it with plant samples, the glutamate concentration in plant molecules can be detected. The biosensor of the present invention can online monitor the change of glutamate concentration in plants, and has the advantages of simple preparation, high sensitivity and fast response speed.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical biosensors, and particularly relates to a PDA@Zn-MOF ternary composite modified electrode modified with glutamate oxidase, and a preparation method and application thereof. Background Art

[0002] L-glutamic acid (L-Glu) is one of the amino acids required for protein synthesis, provides energy and substances for plant growth, and plays a very important role in plant growth, development, and adaptation to environmental stress. The quantitative analysis and detection of Glu contribute to the study of the conduction pathway and physiological process of Glu in plant metabolism, and have important application values in the fields of agriculture, food, medicine, etc. Compared with detection methods such as fluorescence analysis, microdialysis, capillary electrophoresis, and high-performance liquid chromatography, the electrochemical biosensor method has the characteristics of simple operation, fast response, low detection limit, and high sensitivity, and has received extensive attention from scholars.

[0003] When electrochemically detecting the glutamate concentration in plants, glutamate oxidase (GluOx) is often used to catalytically oxidize glutamate to generate electroactive substances such as α-ketoglutarate and hydrogen peroxide (H2O2), and then hydrogen peroxide is further electrolyzed to generate hydrogen ions and oxygen, so that the electrode can detect the change in the electrical signal to achieve the detection of the glutamate concentration. The reaction formula is as follows:

[0004]

[0005]

[0006] As a protein, GluOx is easily inactivated by external conditions such as temperature, pressure, and substrate solution, and the enzyme activity is significantly reduced. Therefore, immobilizing the enzyme on a carrier is a strategy to improve its stability. Metal-organic frameworks (MOFs) are a new type of porous crystalline material with excellent properties such as high porosity, excellent chemical stability, large specific surface area, and structural diversity. The highly ordered framework of MOF protects the enzyme, and its large specific surface area provides good conditions for the loading of the enzyme. Utilizing these inherent characteristics, MOF has been widely used as a potential support material for enzyme immobilization.

[0007] The patent application "Glutamate Oxidase Biosensor and Its Preparation Method and Application" discloses the development of a biosensor for detecting glutamate using Pt NPS, MXene-Ti3C2Tx solution, and glutamate oxidase as modification materials. This sensor can be used to detect the content of sodium glutamate (MSG) in food, and has the advantages of high sensitivity, simple preparation, and good anti-interference ability. However, this sensor has not been applied to detect glutamate in plants, and there are few related reports on the determination of glutamate in plants at present. Summary of the Invention

[0008] To solve the problems of poor stability of GluOx and insufficient conductivity of Zn-MOF, and to fill the gap in the determination of glutamate in plants, the purpose of the present invention is to provide a modified electrode based on a ternary complex of PDA@Zn-MOF modified with glutamate oxidase, its preparation method and application. The modified electrode based on the ternary complex of PDA@Zn-MOF modified with glutamate oxidase prepared according to the present invention has the advantages of high sensitivity, fast response speed, and simple preparation when detecting glutamate in plant molecules.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] The present invention provides a preparation method of a modified electrode based on a ternary complex of PDA@Zn-MOF modified with glutamate oxidase, including the following steps:

[0011] (1) Prepare a PDA@Zn-MOF mixed solution: Add an aqueous solution of Zn(NO3)2 to an aqueous solution of 2-methylimidazole, stir, centrifuge to collect the precipitate product, wash with deionized water and dry to obtain Zn-MOF powder. Add the obtained Zn-MOF powder to a PBS buffer solution containing dopamine hydrochloride, stir to obtain a PDA@Zn-MOF mixed solution.

[0012] (2) Modify the conductive electrode with the PDA@Zn-MOF mixed solution obtained in step (1) by drop coating or potentiostatic method, and dry to obtain an electrode modified with Zn-MOF and PDA.

[0013] (3) Drop coat the glutamate oxidase solution on the electrode modified with Zn-MOF and PDA obtained in step (2), and air dry at low temperature to obtain a modified electrode based on a ternary complex of PDA@Zn-MOF modified with glutamate oxidase.

[0014] Further, in step (1), the concentration of the aqueous solution of Zn(NO3)2 is 0.078 - 0.082 mol / L, and the concentration of the aqueous solution of 2-methylimidazole is 0.05 - 0.07 mol / L.

[0015] Further, in step (1), the rotation speed of the centrifugation is 6000 - 8000 rpm / min, and the centrifugation time is 10 - 30 min.

[0016] Further, in the PBS buffer solution containing dopamine hydrochloride in step (1), the concentration of dopamine hydrochloride is 2.0 - 2.4 mg / mL.

[0017] Further, the pH of the PBS buffer solution containing dopamine hydrochloride in step (1) is 7.5 - 8.5.

[0018] Further, in step (2), the obtained PDA@Zn - MOF mixed solution is used to modify the conductive electrode by the drop - coating method, and 1.3 - 1.9 μL of the PDA@Zn - MOF solution is drop - coated per square millimeter of the electrode.

[0019] Further, in step (2), the obtained PDA@Zn - MOF mixed solution is used to modify the conductive electrode by the potentiostatic method, the deposition voltage is 1.0 - 2.0 V, and the deposition time is 100 - 200 s.

[0020] Further, in step (2), the conductive electrode includes one or more of a graphite electrode, a glassy carbon electrode, and a carbon paste electrode.

[0021] Further, the drying method in step (2) is to dry under an infrared lamp.

[0022] Further, before the conductive electrode is modified with Zn - MOF and PDA in step (2), the conductive electrode is sequentially dried, polished, and ultrasonically treated.

[0023] Further, the polishing method is to polish with an aqueous slurry of alumina powder with a particle size of 0.1 μm on a polishing cloth.

[0024] Further, the ultrasonic treatment is sequentially carried out in ultrapure water and acetone.

[0025] Further, in step (3), the glutamate oxidase solution is drop - coated on the obtained electrode modified with Zn - MOF and PDA, and 0.6 - 1.3 μL of the glutamate oxidase solution is drop - coated per square millimeter of the electrode.

[0026] Further, the temperature for low - temperature air - drying in step (3) is 2 - 6 °C.

[0027] The present invention provides a modified electrode based on a ternary complex of PDA@Zn - MOF modified with glutamate oxidase prepared by the described preparation method.

[0028] Furthermore, for the modified electrode of the PDA@Zn-MOF ternary complex modified with glutamate oxidase, the carrier is the Zn-MOF material, the modifying substance is polydopamine (PDA), and the catalytically active substance is glutamate oxidase (GluOx).

[0029] The present invention also provides an application of the modified electrode of the PDA@Zn-MOF ternary complex modified with glutamate oxidase in detecting glutamate in plants.

[0030] Furthermore, in a glutamate solution with a certain concentration, the modified electrode of the PDA@Zn-MOF ternary complex modified with glutamate oxidase prepared by the present invention serves as the working electrode, the platinum electrode serves as the counter electrode, and the Ag / AgCl electrode serves as the reference electrode to form a three-electrode system, and the glutamate solution is detected by the chronoamperometry (i-t method).

[0031] Furthermore, the concentration of the glutamate solution is 100 - 110 μM.

[0032] Furthermore, the parameter settings of the chronoamperometry (i-t method) of the electrochemical workstation are as follows: the stirring speed is 100 - 500 rpm / min, the pulse width is 50 - 150 s, the rest time is 10 - 20 s, the number of step times is 10 - 50 times, and the initial voltage is 0.2 - 0.4 V.

[0033] Furthermore, by measuring the current response value of the glutamate solution through the chronoamperometry (i-t method) and comparing it with the plant sample, the glutamate concentration in the plant molecules can be detected. The biosensor of the present invention can online monitor the change of glutamate concentration in plants, and has the advantages of simple preparation, high sensitivity, fast response speed, and low detection limit.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] (1) The preparation method of the modified electrode of the PDA@Zn-MOF ternary complex modified with glutamate oxidase prepared by the present invention by the drop-coating method or the potentiostatic method is simple and low in cost.

[0036] (2) The modified electrode of the PDA@Zn-MOF ternary complex modified with glutamate oxidase prepared by the present invention has a large specific surface area, good conductivity, and high stability, and can sensitively detect the glutamate concentration in plant molecules.

[0037] (3) Due to the relatively low conductivity and dispersibility of MOF materials themselves, it is necessary to find other active substances to modify them. Dopamine (DA) can self-polymerize to form polydopamine (PDA) in an alkaline environment. PDA has hydrophilicity, and the dispersibility of MOF can be increased through simple stirring, which is beneficial to exposing the active surface of MOF and reducing its electrochemical impedance. In addition, ligand exchange between PDA and the MOF surface is conducive to electron migration during the reaction, thereby increasing its conductivity. At the same time, PDA can also effectively capture GluOx to maintain its activity and stability. The present invention provides a stable and effective method for detecting glutamate in plant molecules. Description of the Drawings

[0038] Figure 1 Scanning electron microscope image of the PDA@Zn-MOF ternary composite modified electrode modified with glutamate oxidase prepared in Example 1 of the present invention.

[0039] Figure 2 i-t graph when detecting glutamate solution with the PDA@Zn-MOF ternary composite modified electrode modified with glutamate oxidase prepared in Example 1 of the present invention. Detailed Embodiments

[0040] The specific embodiments described herein are only for explaining the present invention and are not used to limit the present invention. In addition, the technical features involved in the following described specific embodiments can be combined with each other as long as they do not conflict with each other.

[0041] Example 1:

[0042] Step 1) Add an aqueous solution of Zn(NO3)2 (4 mL, 0.078 mol / L) to an aqueous solution of 2-methylimidazole (8 mL, 0.05 mol / L), stir magnetically for 30 min, centrifuge for 10 min (6000 rpm / min) to collect the precipitate product, wash with deionized water and dry to obtain Zn-MOF powder. Add the obtained Zn-MOF powder (120 mg) to 10 mL of PBS buffer solution (pH = 7.5) containing dopamine hydrochloride (2.0 mg / mL), and stir magnetically for 12 h to obtain a PDA@Zn-MOF solution.

[0043] Step 2) Pre-treat the graphite electrode by drying, polishing and ultrasonic treatment in sequence. Using the drop-coating method, drop 4 μL of the PDA@ZN-MOF solution obtained in Step 1 onto a 3.14 square millimeter graphite electrode, and then dry it under an infrared lamp to obtain an electrode modified with Zn-MOF and PDA.

[0044] Step 3) Drop 2 μL of glutamate oxidase solution (2 mg / mL, with water as the solvent) onto the 3.14 square millimeter Zn-MOF and PDA modified electrode obtained in Step 2), and dry it at a low temperature of 6 °C to obtain a PDA@Zn-MOF ternary composite modified electrode based on glutamate oxidase modification (GluOx@PDA@Zn-MOF modified electrode).

[0045] In a 100 μM glutamate solution (with water as the solvent), the GluOx@PDA@Zn-MOF modified electrode prepared in Example 1 is used as the working electrode, a platinum electrode is used as the counter electrode, and an Ag / AgCl electrode is used as the reference electrode to form a three-electrode system. The glutamate solution is detected by chronoamperometry (i-t method). The parameters of the electrochemical workstation for chronoamperometry (i-t method) are set as follows: the stirring speed is 100 rpm / min, the pulse width is 50 s, the rest time is 10 s, the number of step times is 10 times, and the initial voltage is 0.2 V.

[0046] Example 2:

[0047] Step 1) Add an aqueous solution of Zn(NO3)2 (4 mL, 0.080 mol / L) to an aqueous solution of 2-methylimidazole (8 mL, 0.06 mol / L), stir magnetically for 30 min, centrifuge for 20 min (7000 rpm / min) to collect the precipitate product, wash it with deionized water and dry it to obtain Zn-MOF powder. Add the obtained Zn-MOF powder (140 mg) to 10 mL of PBS buffer solution containing dopamine hydrochloride (2.2 mg / mL) (pH = 8.0), and stir magnetically for 12 h to obtain a PDA@Zn-MOF solution.

[0048] Step 2) Pre-treat the glassy carbon electrode by drying, polishing and ultrasonic treatment in sequence. Using the drop-coating method, drop 5 μL of the PDA@Zn-MOF solution obtained in Step 1 onto the 3.14 square millimeter glassy carbon electrode, and then dry it under an infrared lamp to obtain a Zn-MOF and PDA modified electrode.

[0049] Step 3) Drop 3 μL of glutamate oxidase solution (2 mg / mL, with water as the solvent) onto the 3.14 square millimeter Zn-MOF and PDA modified electrode obtained in Step 2), and dry it at a low temperature of 4 °C to obtain a PDA@Zn-MOF ternary composite modified electrode based on glutamate oxidase modification (GluOx@PDA@Zn-MOF modified electrode).

[0050] In a 105 μM glutamic acid solution (with water as the solvent), the GluOx@PDA@Zn-MOF modified electrode prepared in Example 2 was used as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode to form a three-electrode system. The glutamic acid solution was detected by chronoamperometry (i-t method). The parameters of the chronoamperometry (i-t method) of the electrochemical workstation were set as follows: the stirring speed was 300 rpm / min, the pulse width was 100 s, the rest time was 15 s, the number of step times was 30 times, and the initial voltage was 0.3 V.

[0051] Example 3:

[0052] Step 1) An aqueous solution of Zn(NO3)2 (4 mL, 0.082 mol / L) was added to an aqueous solution of 2-methylimidazole (8 mL, 0.07 mol / L), and magnetic stirring was carried out for 30 min. The precipitate product was collected by centrifugation for 30 min (8000 rpm / min), washed with deionized water and dried to obtain Zn-MOF powder. The obtained Zn-MOF powder (160 mg) was added to 10 mL of PBS buffer solution (pH = 8.5) containing dopamine hydrochloride (2.4 mg / mL), and magnetic stirring was carried out for 12 h to obtain a PDA@Zn-MOF solution.

[0053] Step 2) The carbon paste electrode was successively subjected to drying, polishing and ultrasonic pretreatment. By the drop-coating method, 6 μL of the PDA@Zn-MOF solution obtained in Step 1 was drop-coated onto a 3.14 square millimeter carbon paste electrode, and then dried under an infrared lamp to obtain an electrode modified with Zn-MOF and PDA.

[0054] Step 3) 4 μL of glutamic acid oxidase solution (2 mg / mL, with water as the solvent) was drop-coated onto the 3.14 square millimeter Zn-MOF and PDA modified electrode obtained in Step 2, and dried at a low temperature of 2 °C to obtain a PDA@Zn-MOF ternary complex modified electrode based on glutamic acid oxidase modification (GluOx@PDA@Zn-MOF modified electrode).

[0055] In an 110 μM glutamic acid solution (with water as the solvent), the GluOx@PDA@Zn-MOF modified electrode prepared in Example 3 was used as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode to form a three-electrode system. The glutamic acid solution was detected by chronoamperometry (i-t method). The parameters of the chronoamperometry (i-t method) of the electrochemical workstation were set as follows: the stirring speed was 500 rpm / min, the pulse width was 150 s, the rest time was 20 s, the number of step times was 50 times, and the initial voltage was 0.4 V.

[0056] Example 4:

[0057] Step 1) Add an aqueous solution of Zn(NO3)2 (4 mL, 0.078 mol / L) to an aqueous solution of 2-methylimidazole (8 mL, 0.05 mol / L), stir magnetically for 30 min, centrifuge for 10 min (6000 rpm / min) to collect the precipitate product, wash with deionized water and dry to obtain Zn-MOF powder. Add the obtained Zn-MOF powder (120 mg) to 10 mL of PBS buffer solution (pH = 7.5) containing dopamine hydrochloride (2.0 mg / mL), and stir magnetically for 12 h to obtain a PDA@Zn-MOF solution.

[0058] Step 2) Pre-treat the graphite electrode by drying, polishing and ultrasonic treatment in sequence. Using the graphite electrode as the working electrode, the counter electrode is a platinum electrode, and the reference electrode is an Ag / AgCl electrode to form a three-electrode system. Immerse the three electrodes into the PDA@Zn-MOF solution obtained in Step 1), and deposit PDA and Zn-MOF on the graphite electrode by the potentiostatic method. Set the parameters of the electrochemical workstation: the deposition voltage is 1.0 V, the deposition time is 100 s, and then dry it under an infrared lamp to obtain an electrode modified with Zn-MOF and PDA.

[0059] Step 3) Drop 2 μL of glutamate oxidase solution (2 mg / mL, with water as the solvent) onto the 3.14 square millimeter Zn-MOF and PDA modified electrode obtained in Step 2), and air-dry it at a low temperature of 6 °C to obtain a PDA@Zn-MOF ternary composite modified electrode based on glutamate oxidase modification (GluOx@PDA@Zn-MOF modified electrode).

[0060] In a 100 μM glutamate solution (with water as the solvent), use the GluOx@PDA@Zn-MOF modified electrode prepared in Example 4 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode system, and detect the glutamate solution by the chronoamperometry (i-t method). The parameters of the chronoamperometry (i-t method) of the electrochemical workstation are set as follows: the stirring speed is 100 rpm / min, the pulse width is 50 s, the rest time is 10 s, the number of steps is 10 times, and the initial voltage is 0.2 V.

[0061] Example 5:

[0062] Step 1) Add an aqueous solution of Zn(NO3)2 (4 mL, 0.080 mol / L) to an aqueous solution of 2-methylimidazole (8 mL, 0.06 mol / L), stir magnetically for 30 min, centrifuge for 20 min (7000 rpm / min) to collect the precipitate product, wash with deionized water and dry to obtain Zn-MOF powder. Add the obtained Zn-MOF powder (140 mg) to 10 mL of PBS buffer solution (pH = 8.0) containing dopamine hydrochloride (2.2 mg / mL), and stir magnetically for 12 h to obtain a PDA@Zn-MOF solution.

[0063] Step 2) Pre-treat the glassy carbon electrode by drying, polishing and ultrasonic treatment in sequence. Using the glassy carbon electrode as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode system. Immerse the three electrodes into the PDA@Zn-MOF solution obtained in Step 1), and deposit PDA and Zn-MOF on the glassy carbon electrode by the potentiostatic method. Set the parameters of the electrochemical workstation: the deposition potential is 1.5 V, the deposition time is 150 s, and then dry it under an infrared lamp to obtain an electrode modified with Zn-MOF and PDA.

[0064] Step 3) Drop 3 μL of glutamate oxidase solution (2 mg / mL, with water as the solvent) onto the Zn-MOF and PDA modified electrode of 3.14 square millimeters obtained in Step 2), and dry it at a low temperature of 4 °C to obtain a PDA@Zn-MOF ternary composite modified electrode based on glutamate oxidase modification (GluOx@PDA@Zn-MOF modified electrode).

[0065] In a 105 μM glutamate solution (with water as the solvent), use the GluOx@PDA@Zn-MOF modified electrode prepared in Example 5 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode system, and detect the glutamate solution by the chronoamperometry (i-t method). The parameters of the chronoamperometry (i-t method) of the electrochemical workstation are set as follows: the stirring speed is 300 rpm / min, the pulse width is 100 s, the rest time is 15 s, and the number of step times is 30 times.

[0066] Example 6:

[0067] Step 1) Add an aqueous solution of Zn(NO3)2 (4 mL, 0.082 mol / L) to an aqueous solution of 2-methylimidazole (8 mL, 0.07 mol / L), stir magnetically for 30 min, centrifuge for 30 min (8000 rpm / min) to collect the precipitate product, wash with deionized water and dry to obtain Zn-MOF powder. Add the obtained Zn-MOF powder (160 mg) to 10 mL of PBS buffer solution containing dopamine hydrochloride (2.4 mg / mL) (pH = 8.5), stir magnetically for 12 h to obtain a PDA@Zn-MOF solution.

[0068] Step 2) Pre-treat the carbon paste electrode by drying, polishing and ultrasonic treatment in sequence. Using the carbon paste electrode as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode to form a three-electrode system. Immerse the three electrodes into the PDA@Zn-MOF solution obtained in Step 1), and deposit PDA and Zn-MOF on the carbon paste electrode by the potentiostatic method. Set the parameters of the electrochemical workstation: the deposition potential is 2.0 V, the deposition time is 200 s, and then dry it under an infrared lamp to obtain an electrode modified with Zn-MOF and PDA.

[0069] Step 3) Drop 4 μL of glutamate oxidase solution (2 mg / mL, with water as the solvent) onto the 3.14 square millimeter Zn-MOF and PDA modified electrode obtained in Step 2), and dry it at a low temperature of 2 °C to obtain a glutamate oxidase-modified PDA@Zn-MOF ternary composite modified electrode (GluOx@PDA@Zn-MOF modified electrode).

[0070] In a 110 μM glutamate solution (with water as the solvent), using the GluOx@PDA@Zn-MOF modified electrode prepared in Example 6 as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode to form a three-electrode system, and detect the glutamate solution by the chronoamperometry (i-t method). The parameters of the chronoamperometry (i-t method) of the electrochemical workstation are set as follows: the stirring speed is 500 rpm / min, the pulse width is 100 s, the rest time is 20 s, the number of step times is 50 times, and the initial voltage is 0.4 V.

[0071] Figure 1 This is the scanning electron microscope image of the glutamate oxidase-modified PDA@Zn-MOF ternary composite modified electrode prepared in Example 1 of the present invention. From Figure 1 It can be seen that the glutamate oxidase-modified PDA@Zn-MOF ternary composite modified electrode prepared by the present invention has a regular crystal framework, and the dots in the figure are the modified glutamate oxidase.

[0072] Figure 2This is the i-t graph obtained when detecting glutamate solution using the modified electrode of the PDA@Zn-MOF ternary complex modified with glutamate oxidase prepared in Example 1 of the present invention. From Figure 2 it can be seen that no current response value was detected within 200 s after the start of the detection, because glutamate oxidase had not yet played a catalytic role. After 200 s, a current response was detected, and as time extended, the current response became stronger, because GluOx catalyzed glutamate to generate more hydrogen peroxide, so a stronger electrical signal was detected on the electrode. This shows that the modified electrode of the PDA@Zn-MOF ternary complex modified with glutamate oxidase prepared in the present invention can realize sensitive detection of glutamate in plants when used as a working electrode.

Claims

1. Preparation method of a PDA@Zn-MOF ternary composite modified electrode modified with glutamate oxidase, characterized in that It includes the following steps: (1) Prepare the PDA@Zn-MOF mixed solution: Add an aqueous solution of Zn(NO3)2 to an aqueous solution of 2-methylimidazole, stir, centrifuge to collect the precipitate product, wash it with water and dry it to obtain Zn-MOF powder. Add the obtained Zn-MOF powder to a PBS buffer solution containing dopamine hydrochloride, stir to obtain the PDA@Zn-MOF mixed solution; the concentration of the aqueous solution of Zn(NO3)2 is 0.078 - 0.082 mol / L, and the concentration of the aqueous solution of 2-methylimidazole is 0.05 - 0.07 mol / L; the concentration of dopamine hydrochloride in the PBS buffer solution containing dopamine hydrochloride is 2.0 - 2.4 mg / mL. (2) Modify the conductive electrode with the PDA@Zn-MOF mixed solution obtained in step (1) by the drop-coating method or the potentiostatic method, and dry it to obtain an electrode modified with Zn-MOF and PDA. (3) Drop-coat the glutamate oxidase solution on the electrode modified with Zn-MOF and PDA obtained in step (2), and air-dry it to obtain a ternary composite modified electrode based on glutamate oxidase-modified PDA@Zn-MOF.

2. The preparation method of the PDA@Zn-MOF ternary composite modified electrode modified based on glutamate oxidase according to claim 1, wherein, In step (1), the pH of the PBS buffer solution containing dopamine hydrochloride is 7.5 - 8.

5.

3. The preparation method of the PDA@Zn-MOF ternary composite modified electrode based on glutamate oxidase modification according to claim 1, wherein In step (1), the rotation speed of the centrifugation is 6000 - 8000 rpm / min, and the centrifugation time is 10 - 30 min.

4. The preparation method of the PDA@Zn-MOF ternary composite modified electrode modified based on glutamate oxidase according to claim 1, characterized in that, In step (2), when modifying the conductive electrode with the drop-coating method using the obtained PDA@Zn-MOF solution, 1.3 - 1.9 μL of the PDA@Zn-MOF solution is drop-coated per square millimeter of the electrode.

5. The preparation method of the PDA@Zn-MOF ternary composite modified electrode modified based on glutamate oxidase according to claim 1, characterized in that, In step (2), when modifying the conductive electrode with the potentiostatic method using the obtained PDA@Zn-MOF mixed solution, the deposition voltage is 1.0 - 2.0 V, and the deposition time is 100 - 200 s.

6. The preparation method of the PDA@Zn-MOF ternary composite modified electrode modified based on glutamate oxidase according to claim 1, characterized in that, The conductive electrode in step (2) is one of a graphite electrode, a glassy carbon electrode, and a carbon paste electrode; the drying method in step (2) is to dry it under an infrared lamp.

7. The preparation method of the PDA@Zn-MOF ternary composite modified electrode modified based on glutamate oxidase according to claim 1, wherein, In step (3), when drop-coating the glutamate oxidase solution on the electrode modified with Zn-MOF and PDA obtained, 0.6 - 1.3 μL of the glutamate oxidase solution is drop-coated per square millimeter of the electrode; the air-drying temperature is 2 - 6 °C.

8. A ternary composite modified electrode based on glutamate oxidase-modified PDA@Zn-MOF prepared by the preparation method according to any one of claims 1 - 7.

9. Use of the PDA@Zn-MOF ternary composite modified electrode modified based on glutamate oxidase in detecting glutamate in plants, characterized in that, The application is to detect the glutamate solution by the chronoamperometry method. The parameter settings of the chronoamperometry method of the electrochemical workstation are: the stirring speed is 100 - 500 rpm / min, the pulse width is 50 - 150 s, the rest time is 10 - 20 s, the number of step times is 10 - 50 times, and the initial voltage is 0.2 - 0.4 V.

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