CN112903769A - Toluidine blue modified metal organic framework electrode and preparation method and application thereof - Google Patents
Toluidine blue modified metal organic framework electrode and preparation method and application thereof Download PDFInfo
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- G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
- G01N33/74—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving hormones or other non-cytokine intercellular protein regulatory factors such as growth factors, including receptors to hormones and growth factors
Abstract
The toluidine blue modified metal organic frame electrode has an electrochemical signal molecule toluidine blue modified metal organic frame structure on the surface, has good electrochemical performance, and is prepared by a one-step in-situ electrodeposition method. The method is applied to electrochemical immunosensing, the method is simple, the cost is low, the detection limit is as low as 1.2 pg/mL when the IAA concentration is detected, and the linear range of the electrochemical response intensity and the IAA concentration is 20 pg/mL-20 ng/mL.
Description
Technical Field
The invention relates to an electrode and a preparation method and application thereof, in particular to a metal organic framework electrode and a preparation method and application thereof.
Background
The metal organic frame materials (MOFs for short) are also called porous coordination polymers, and are a new generation of crystal materials. The material is a periodic solid material with a complex network structure, which is formed by self-assembly of organic bridging ligands and metal ions or metal clusters through coordination bonds, hydrogen bonds, static electricity and the like. The metal organic framework material has the advantages of adjustable structure, easy modification, large specific surface area, and various physical and chemical properties such as topological structure, magnetism, catalysis, fluorescence and the like, can be widely applied to the fields of selective catalysis, gas adsorption and separation, biochemical sensing, drug delivery, immobilized active small molecules, molecular sieves, photoelectric materials and the like, and has huge application prospects.
Toluidine blue (abbreviated as TB) is a phenothiazine dye and has good reversible electron transfer capacity. TB is widely used in redox probes of electrochemical sensors because of its good chemical stability and high electrical conductivity. However, the media compounds are susceptible to leakage during the encapsulation process. Therefore, it is required to design a porous material that can effectively prevent the leakage of a medium to improve the stability of the electrochemical immunosensor.
Indole-3-acetic acid (hereinafter, IAA) is mainly produced in apical (shoot) cells and young leaves of plants, and plants can synthesize indole-3-acetic acid through various independent biosynthetic pathways. IAA is important for the regulation of various physiological processes of plants, including plant growth, cell division, enhancement, apoptosis and specific gene expression, and plays an important role in the stress and adaptation of plants to the external environment under stress. Therefore, accurate quantitative analysis of IAA in plants is essential.
In recent years, in the aspect of detection of the phytohormone indoleacetic acid, the electrochemical immunoassay method is a hot spot for detecting the phytohormone rapidly due to the advantages of simple and rapid operation and the like. There are many methods for detecting IAA using electrochemical sensing.
CN109521072A discloses a method for detecting indoleacetic acid and salicylic acid and an electrochemical sensor used by the same, wherein IAA and salicylic acid are detected electrochemically by using a graphene hydrogel modified electrode. CN102253223A discloses an electrochemical immunosensing method for detecting phytohormone beta-3-indoleacetic acid, which adopts an immuno-electrode modified by a gold electrode to detect IAA electrochemically. However, the electrochemical immunosensor has higher detection lower limit on IAA and higher raw material price.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects in the prior art and provide a toluidine blue modified metal organic framework electrode and a preparation method and application thereof, when the toluidine blue modified metal organic framework electrode is applied to detecting IAA, the phytohormone auxin with the level as low as 1.2 pg/mL can be detected, the linear range of the electrochemical response intensity and the IAA concentration is 20 pg/mL-20 ng/mL, the detection method is simple, and the cost is low.
The technical scheme adopted by the invention for solving the technical problems is as follows: the surface of the toluidine blue modified metal-organic framework electrode is provided with a metal-organic framework structure modified by electrochemical signal molecules; the electrochemical signal molecule is toluidine blue.
Preferably, the substrate of the toluidine blue modified metal organic framework electrode is a glassy carbon electrode, a carbon paste electrode, a carbon fiber electrode or an ITO conductive glass electrode, and the radius of the substrate is 1-5 mm (more preferably 2-3 mm).
The preparation method of the toluidine blue modified metal organic framework electrode comprises the following steps:
(1) dissolving metal salt and supporting electrolyte in distilled water to obtain an aqueous solution, adding an ethanol solution of trimesic acid into the aqueous solution, uniformly mixing, adding a toluidine blue aqueous solution, and stirring to obtain an electrodeposition solution;
(2) and (2) polishing a substrate, washing, performing ultrasonic treatment, performing surface acid treatment, washing, performing electrochemical cleaning, washing, drying, performing electrodeposition in the electrodeposition solution obtained in the step (1), and cleaning with secondary distilled water to obtain the toluidine blue modified metal organic framework electrode.
Preferably, in step (1), the metal salt is a zinc salt (more preferably zinc nitrate, zinc acetate or zinc chloride), a copper salt or an iron salt.
Preferably, in the step (1), the supporting electrolyte is at least one of potassium nitrate, sodium chloride and potassium sulfate.
Preferably, in the step (1), the molar ratio of the metal salt to the cation of the supporting electrolyte is 3-10: 1.
Preferably, in step (1), the concentration of the metal salt in the aqueous solution is 0.001 g/mL-1.8 g/mL (more preferably 0.01 mg/mL-0.5 g/mL, and still more preferably 0.05 g/mL-0.2 g/mL).
Preferably, in the step (1), the concentration of the ethanol solution of trimesic acid is 0.001 g/mL-3.5 g/mL (more preferably 0.01 g/mL-0.5 g/mL, and still more preferably 0.02 g/mL-0.1 g/mL).
Preferably, in the step (1), the molar ratio of the metal salt to trimesic acid is 1-2: 1.
Preferably, in the step (1), the aqueous toluidine blue solution is prepared by dissolving toluidine blue in 0.1-0.5 mol/L nitric acid, and the concentration of the toluidine blue is 0.02-0.05 mol/L.
Preferably, in the step (1), the molar ratio of the metal salt to the toluidine blue is 100-400: 1; the stirring is carried out at room temperature, the stirring speed is 350-500 r/min, and the stirring time is 2.5-3.5 h.
Preferably, in the step (2), the polishing is performed in the alumina suspension of 0.2-1.0 μm and 0.02-0.1 μm in sequence.
Preferably, in the step (2), the rinsing is performed with ultrapure water.
Preferably, in the step (2), the ultrasonic treatment is performed in ultrapure water, ethanol and ultrapure water for 2-5 min respectively.
Preferably, in the step (2), the acid treatment is dropwise adding a sulfuric acid washing solution and keeping for 10-30 s.
Preferably, in the step (2), the blow-drying is performed by using nitrogen.
Preferably, in the step (2), the electrochemical cleaning step is: in 5-20 mL of 0.2-0.5 mol/L H2SO4And (3) circulating volt-ampere scanning between-1.0V and 1.0V at the speed of 0.1-0.5V/s until the obtained curve does not change.
Preferably, in the step (2), the electrodeposition is carried out by using a two-electrode system.
Preferably, in the step (2), the electrodeposition adopts a three-electrode system: the counter electrode is a graphite electrode, and the reference electrode is a saturated calomel electrode; the time for electrodeposition is 30-7200 s, preferably 300-1500 s; and in the deposition process, the potential of the electrode relative to the saturated calomel electrode is-2.0V to-0.5V.
The invention relates to an application of a toluidine blue modified metal organic framework electrode in electrochemical immunosensing.
Preferably, it is used for the detection of plant hormones, in particular for the detection of auxins.
Preferably, when a working curve is drawn and a sample to be tested is tested, the toluidine blue modified metal organic frame electrode after immune modification is used as a working electrode, a graphite electrode is used as a counter electrode, a saturated calomel electrode is used as a reference electrode to form a three-electrode system, and the electrolyte is phosphate buffer solution (hereinafter referred to as PBS) with the pH value of 6.86.
The invention utilizes a one-step electrochemical deposition method to construct a metal organic frame electrode with toluidine blue as an electrochemical signal molecule; in the electrodeposition reaction liquid, metal salt is used as a cation source, trimesic acid is used as an organic ligand, and toluidine blue is used as an electrochemical signal probe molecule. During the electrodeposition process, a negative potential is applied to the working electrode, and OH can be generated-So that the carboxyl of the trimesic acid ligand is deprotonated, and the cation and the trimesic acid ligand grow a metal organic framework structure on the surface of the electrode. Due to the electrostatic attraction between the negatively charged trimesic acid ligand and the positively charged toluidine blue ion, the per-structure is formed in the metal organic frameworkIn the process, toluidine blue electrochemical signal molecules in the electrolyte are wrapped in crystals of the metal organic framework, and the toluidine blue modified metal organic framework electrode can be obtained by one-step in-situ electrodeposition.
The invention has the beneficial effects that: (1) the surface of the toluidine blue modified metal organic framework electrode has a metal organic framework structure modified by electrochemical signal molecules, has good electrochemical performance, and can be applied to electrochemical immunosensing; (2) the toluidine blue modified metal organic framework electrode is obtained by adopting a one-step in-situ electrodeposition method, and the preparation method is simple, convenient and easy to operate; (3) the toluidine blue modified metal organic framework electrode is applied to electrochemical immunosensing, can detect the phytohormone auxin as low as 1.2 pg/mL, has the linear range of electrochemical response intensity and IAA concentration of 20 pg/mL-20 ng/mL, and has the advantages of simple method and low cost.
Drawings
FIG. 1 is a graph of electrochemical response signals of a toluidine blue modified metal organic framework electrode prepared in example 1 of the present invention for detecting IAA after immune modification;
FIG. 2 is a standard curve diagram of detection of IAA after immune modification of toluidine blue modified metal organic framework electrode prepared in example 1 of the present invention;
fig. 3 is an electrochemical response curve obtained by detecting the toluidine blue modified metal-organic framework electrode prepared in example 2 of the present invention under the condition that the IAA concentration is 0 after the immunological modification;
fig. 4 is an electrochemical response curve obtained by detecting the toluidine blue modified metal-organic framework electrode prepared in example 3 of the present invention under the condition that the IAA concentration is 0 after the immunological modification;
fig. 5 is an electrochemical response curve obtained by detecting the toluidine blue modified metal-organic framework electrode prepared in example 4 of the present invention under the condition that the IAA concentration is 0 after the immunological modification.
Detailed Description
The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples. The method is a conventional method without particular description. The starting materials are commercially available from the open literature unless otherwise specified.
Example 1
0.266 g of zinc nitrate hexahydrate (0.0009 mol) was dissolved in 3 mL of distilled water to give a 0.089 g/mol aqueous zinc nitrate solution, and 0.0303 g of potassium nitrate (0.0003 mol) was added as a supporting electrolyte. 0.105 g of trimesic acid (0.0005 mol) is dissolved in 3 mL of ethanol, the obtained 0.035 g/mL ethanol solution of trimesic acid is added into the zinc nitrate aqueous solution and mixed evenly, 300 mu L of 0.025 mol/L toluidine blue aqueous solution is added, and the mixture is stirred at the speed of 400 r/min for 3 hours at room temperature to obtain the electrodeposition solution. The toluidine blue aqueous solution is prepared by dissolving toluidine blue in 0.1mol/L nitric acid.
Grinding and polishing a glassy carbon electrode (GCE for short) with the radius of 3mm in 0.5 and 0.05 mu m of alumina suspension successively, cleaning the surface of the electrode by using ultrapure water, and performing ultrasonic treatment in the ultrapure water, ethanol and the ultrapure water for 3 min respectively to remove alumina powder remaining on the surface of the electrode; dropwise adding concentrated sulfuric acid pickling solution on the surface of the electrode, keeping for 15 s, and washing with ultrapure water; using an electrochemical clean to completely remove contaminants at 10 mL of 0.50 mol/L H2SO4Cyclic voltammetry scanning at a speed of 0.1V/s at-1.0V to 1.0V until the obtained curve does not change any more; after rinsing with ultrapure water, nitrogen was blown dry. The electrode was placed in the bath and electrodeposited at-1.3V for 300 s (vs. saturated calomel electrode). And then washing with secondary distilled water to obtain the toluidine blue modified metal organic framework electrode (TB @ MOFs/GCE for short).
Immune modification: dropping 3.0 muL of 0.25 mg/mL chitosan (CS for short) on a MOFs modified glass carbon electrode (TB @ MOFs/GCE), dropping 6 muL of 2.5% glutaraldehyde (GA for short) for reaction for 2h after drying to obtain a GA-CS/TB @ MOFs/GCE electrode, and dropping 6.0 muL of PBS containing 0.1% indole-3-acetic acid antibody (anti-IAA for short) on the GA-CS/TB @ MOFs/GCE electrode; and preserving at 4 ℃ for 12h to ensure the saturation adsorption of the anti-IAA on the surface of the electrode to obtain the anti-IAA/GA-CS/TB @ MOFs/GCE modified electrode. After the electrode is sequentially washed by PBS solution and dried by blowing, 6.0 mu L of PBS solution containing 3% bovine serum albumin is dripped on the electrode, and the temperature is kept for 1 h at 4 ℃ to seal the nonspecific adsorption sites, so that the immune modified toluidine blue modified metal-organic framework electrode (also called BSA/anti-IAA/GA-CS/TB @ MOFs/GCE modified electrode according to the composition) is obtained. When not in use, the electrodes were stored in PBS at 4 ℃.
Drawing a standard working curve: on a prepared BSA/anti-IAA/GA-CS/TB @ MOFs/GCE modified electrode, 6.0 mu L of PBS containing IAA with the concentration of 20 pg/mL, 50 pg/mL, 100 pg/mL, 200 pg/mL, 500 pg/mL, 1 ng/mL, 2 ng/mL, 5 ng/mL, 10 ng/mL and 20 ng/mL is respectively dripped, the temperature is incubated for 1 h at 37 ℃, and the surface of the electrode is washed by PBS solution, so that IAA/BSA/anti-IAA/GA-CS/TB @ MOFs/GCE modified electrodes with different IAA concentrations are obtained. A three-electrode system (the working electrode is an IAA/BSA/anti-IAA/GA-CS/TB @ MOFs/GCE modified electrode, the counter electrode is a graphite electrode, the reference electrode is a saturated calomel electrode, and the electrolyte is PBS with the pH value of 6.86) is adopted, and a square wave voltammetry method is adopted for detection, so that an electrochemical response signal on the working electrode is obtained. And drawing a standard working curve by taking the logarithm of the IAA concentration as an abscissa and the electrochemical response relative current as an ordinate.
Electrochemical immunodetection of the sample: dropwise adding a 6.0 mu L sample onto a BSA/anti-IAA/GA-CS/TB @ MOFs/GCE modified electrode, incubating for 1 h at 37 ℃, and washing the surface of the electrode by using a PBS solution to obtain the IAA/BSA/anti-IAA/GA-CS/TB @ MOFs/GCE modified electrode of the sample. The method comprises the steps of detecting by adopting a three-electrode system (an IAA/BSA/anti-IAA/GA-CS/TB @ MOFs/GCE modified electrode is used as a working electrode, a graphite electrode is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, and PBS with the pH value of 6.86 is used as electrolyte), obtaining an electrochemical response signal by adopting a square wave voltammetry, and calculating the concentration according to a standard working curve, thereby indirectly realizing the quantitative analysis of the target analyte IAA in a sample.
The toluidine blue modified metal organic framework electrode obtained in the embodiment is subjected to immune modification and then is used as a working electrode, an electrochemical response signal curve for detecting IAA is shown in figure 1, it can be seen from the figure that when no IAA is contained, the maximum peak current (i.e. absolute current, current after baseline subtraction) is 6.001 muA, and the electrochemical signal is strong, which indicates that the electrochemical signal of the obtained electrode is good; as IAA concentration increases, the electrochemical response also decreases.
Preparing a plurality of IAA standard solutions with extremely low concentration, testing a working curve in an extremely low concentration interval according to a method for drawing a standard working curve, and measuring the detection limit to be 1.2 pg/mL under the condition that the signal-to-noise ratio is set to be 3.
As shown in fig. 2, a standard graph of electrochemical response versus current is plotted on the ordinate, with the logarithm of the IAA concentration being plotted on the abscissa. The electrochemical response relative current is a current relative value obtained by taking the maximum peak current obtained when the IAA concentration is 0 as a zero point. The corresponding IAA concentration range is 20 pg/mL-20 ng/mL, and the standard equation is deltai = 0.6212
-0.0428, wherein ΔiIn order to electrochemically respond to the relative current flow,
logarithmic of IAA concentration, correlation coefficient R2And = 0.9969, which indicates the linear correlation between the fitting result and the actual measurement result, and indicates that the linear correlation is good when the toluidine blue-modified metal organic framework electrode obtained in this embodiment is used as a working electrode to detect a mixed solution containing 20 pg/mL to 20 ng/mL IAA after immune modification.
Example 2
0.5 g of zinc nitrate hexahydrate (0.0017 mol) was dissolved in 5 mL of distilled water to give a 0.1 g/mol aqueous zinc nitrate solution, and 0.0303 g of potassium nitrate (0.0003 mol) was added as a supporting electrolyte. 0.2 g of trimesic acid (0.0010 mol) is dissolved in 5 mL of ethanol, the obtained 0.04 g/mL of trimesic acid ethanol solution is added into a zinc nitrate aqueous solution and uniformly mixed, 500 mu L of 0.02 mol/L toluidine blue aqueous solution is added, and the mixture is stirred at the room temperature at the speed of 350 r/min for 3.5 h to obtain the electrodeposition solution. The toluidine blue aqueous solution is prepared by dissolving toluidine blue in 0.5mol/L nitric acid.
Grinding and polishing a Glassy Carbon Electrode (GCE) with the radius of 2mm in alumina suspension of 1.0 mu m and 0.05 mu m in sequence, cleaning the surface of the electrode by using ultrapure water, and respectively performing ultrasonic treatment in ultrapure water, ethanol and ultrapure water for 2 min to obtain a productRemoving the alumina powder remained on the surface of the electrode; dropwise adding concentrated sulfuric acid pickling solution on the surface of the electrode, keeping the solution for 30 s, and washing the solution with ultrapure water; the contaminants were thoroughly removed by electrochemical cleaning at 5 mL of 0.5mol/L H2SO4Scanning to be stable at a scanning cyclic voltammetry of-1.0V to 1.0V and 0.3V/s; after rinsing with ultrapure water, nitrogen was blown dry. The electrode was placed in the bath and electrodeposited at-2V for 500 s (vs. saturated calomel electrode). And then washing with secondary distilled water to obtain the toluidine blue modified metal organic framework electrode (TB @ MOFs/GCE).
Immune modification: the same as in example 1.
The immune modified electrode without IAA is subjected to electrochemical detection in PBS solution to test the electrochemical performance of the obtained electrode. The detection method is the same as the electrochemical immunoassay of the sample in example 1. As can be seen from fig. 3, when the IAA concentration is 0, the maximum peak current (i.e., the absolute current, the current after deducting the baseline) is 5.612 μ a, and the electrochemical signal is strong, which indicates that the obtained electrode has good electrochemical performance.
Example 3
0.8 g of zinc nitrate hexahydrate (0.0027 mol) was dissolved in 5 mL of distilled water to give a 0.16 g/mol aqueous zinc nitrate solution, and 0.0606 g of potassium nitrate (0.0006 mol) was added as a supporting electrolyte. 0.5 g of trimesic acid (0.0024 mol) is dissolved in 5 mL of ethanol, the obtained 0.1 g/mL of trimesic acid ethanol solution is added into zinc nitrate aqueous solution and mixed evenly, 600 mu L of 0.025 mol/L toluidine blue aqueous solution is added, and the mixture is stirred at the room temperature at the speed of 500 r/min for 2.5 h to obtain the electrodeposition solution. The toluidine blue aqueous solution is prepared by dissolving toluidine blue in 0.2mol/L nitric acid.
Grinding and polishing a Glassy Carbon Electrode (GCE) with the radius of 2mm in alumina suspension of 1.0 mu m and 0.03 mu m in sequence, cleaning the surface of the electrode by using ultrapure water, and performing ultrasonic treatment in the ultrapure water, ethanol and the ultrapure water for 5 min respectively to remove alumina powder remaining on the surface of the electrode; dropwise adding concentrated sulfuric acid pickling solution on the surface of the electrode, keeping for 20 s, and washing with ultrapure water; using an electrochemical clean to completely remove contaminants at 20 mL of 0.3 mol/L H2SO4In the range of-1.0V to 1.0V is scanned to be stable by scanning cyclic voltammetry of 0.5V/s; after rinsing with ultrapure water, nitrogen was blown dry. The electrode was placed in the bath and electrodeposited at-0.5V for 1500 s (vs. saturated calomel electrode). And then washing with secondary distilled water to obtain the toluidine blue modified metal organic framework electrode (TB @ MOFs/GCE).
Immune modification: the same as in example 1.
The immune modified electrode without IAA is subjected to electrochemical detection in PBS solution to test the electrochemical performance of the obtained electrode. The detection method is the same as the electrochemical immunoassay of the sample in example 1. As can be seen from fig. 4, when the IAA concentration is 0, the maximum peak current (i.e., the absolute current, the current after deducting the baseline) is 5.305 μ a, and the electrochemical signal is strong, which indicates that the obtained electrode has good electrochemical performance.
Example 4
0.4 g of zinc chloride (0.0029 mol) was dissolved in 5 mL of distilled water to give a 0.08 g/mol aqueous solution of zinc chloride, and 0.0303 g of potassium chloride (0.0003 mol) was added as a supporting electrolyte. 0.5 g of trimesic acid (0.0024 mol) is dissolved in 5 mL of ethanol, the obtained 0.1 g/mL of trimesic acid ethanol solution is added into a zinc nitrate aqueous solution and uniformly mixed, 150 mu L of 0.05 mol/L toluidine blue aqueous solution is added, and the mixture is stirred at the room temperature at the speed of 500 r/min for 2.5 h to obtain the electrodeposition solution. The toluidine blue aqueous solution is prepared by dissolving toluidine blue in 0.1mol/L nitric acid.
Grinding and polishing a Glassy Carbon Electrode (GCE) with the radius of 2.5mm in alumina suspension liquid of 0.5 mu m and 0.03 mu m in sequence, cleaning the surface of the electrode by using ultrapure water, and performing ultrasonic treatment in the ultrapure water, ethanol and the ultrapure water for 4 min respectively to remove alumina powder remaining on the surface of the electrode; dropwise adding concentrated sulfuric acid pickling solution on the surface of the electrode, keeping the solution for 10 s, and washing the solution with ultrapure water; the contaminants were thoroughly removed by electrochemical cleaning at 15 mL of 0.2mol/L H2SO4Scanning to be stable at a scanning cyclic voltammetry of-1.0V to 1.0V and 0.2V/s; after rinsing with ultrapure water, nitrogen was blown dry. The electrode was placed in the bath and 1200 s (vs. saturated calomel electrode) was electrodeposited at-1V. Then washing with secondary distilled water to obtain toluidine blue pigmentDecorated metal organic framework electrodes (TB @ MOFs/GCE).
Immune modification: the same as in example 1.
The immune modified electrode without IAA is subjected to electrochemical detection in PBS solution to test the electrochemical performance of the obtained electrode. The detection method is the same as the electrochemical immunoassay of the sample in example 1. As can be seen from fig. 5, when the IAA concentration is 0, the maximum peak current (i.e., the absolute current, the current after deducting the baseline) is 5.247 μ a, and the electrochemical signal is strong, which indicates that the obtained electrode has good electrochemical performance.
Claims (10)
1. The toluidine blue modified metal organic framework electrode is characterized in that the surface of the toluidine blue modified metal organic framework electrode is provided with a metal organic framework structure modified by electrochemical signal molecules; the electrochemical signal molecule is toluidine blue.
2. The toluidine blue-modified metal-organic framework electrode according to claim 1, wherein the substrate of the electrode is a glassy carbon electrode, a carbon paste electrode, a carbon fiber electrode or an ITO conductive glass electrode, and the radius of the substrate is 1-5 mm, preferably 2-3 mm.
3. The preparation method of the toluidine blue modified metal organic framework electrode is characterized by comprising the following steps:
(1) dissolving metal salt and supporting electrolyte in distilled water to obtain an aqueous solution, adding an ethanol solution of trimesic acid into the aqueous solution, uniformly mixing, adding a toluidine blue aqueous solution, and stirring to obtain an electrodeposition solution;
(2) and (2) polishing a substrate, washing, performing ultrasonic treatment, performing surface acid treatment, washing, performing electrochemical cleaning, washing, drying, performing electrodeposition in the electrodeposition solution obtained in the step (1), and cleaning with secondary distilled water to obtain the toluidine blue modified metal organic framework electrode.
4. The method for preparing a toluidine blue-modified metal-organic framework electrode according to claim 3, wherein in the step (1), the metal salt is zinc salt, copper salt or iron salt; the zinc salt is preferably zinc nitrate, zinc acetate or zinc chloride; the supporting electrolyte is at least one of potassium nitrate, sodium chloride and potassium sulfate; the molar ratio of the metal salt to cations of the supporting electrolyte is 3-10: 1; the concentration of the metal salt in the aqueous solution is 0.001 g/mL-1.8 g/mL, preferably 0.01 mg/mL-0.5 g/mL, and more preferably 0.05 g/mL-0.2 g/mL.
5. The method for preparing a toluidine blue-modified metal-organic framework electrode according to claim 3 or 4, wherein in step (1), the concentration of the ethanol solution of trimesic acid is 0.001 g/mL to 3.5 g/mL, preferably 0.01 g/mL to 0.5 g/mL, more preferably 0.02 g/mL to 0.1 g/mL; the molar ratio of the metal salt to trimesic acid is 1-2: 1; the aqueous solution of toluidine blue is prepared by dissolving toluidine blue in 0.1-0.5 mol/L nitric acid, and the concentration of the toluidine blue is 0.02-0.05 mol/L; the molar ratio of the metal salt to the toluidine blue is 100-400: 1; the stirring is carried out at room temperature, the stirring speed is 350-500 r/min, and the stirring time is 2.5-3.5 h.
6. The method for preparing a toluidine blue-modified metal organic framework electrode according to any one of claims 3 to 5, wherein in the step (2), the grinding and polishing are sequentially performed in an alumina suspension of 0.2 to 1.0 μm and 0.02 to 0.1 μm; the rinsing is carried out by adopting ultrapure water; the ultrasonic treatment is carried out for 2-5 min in ultrapure water, ethanol and ultrapure water respectively in sequence; the acid treatment is dropwise adding a sulfuric acid washing solution and keeping for 10-30 s; the blow-drying is performed by using nitrogen.
7. The method for preparing a toluidine blue-modified metal-organic framework electrode according to any one of claims 3 to 6, wherein in the step (2), the step of electrochemically cleaning comprises: in 5-20 mL of 0.2-0.5 mol/L H2SO4in-1.0V to 1.0V, cyclic voltammetry scanning is carried out at a speed of 0.1-0.5V/s until the obtained curve is not changed any more; the electrodeposition adopts a two-electrode or three-electrode system;in the three-electrode system, the counter electrode is a graphite electrode, and the reference electrode is a saturated calomel electrode; the time for electrodeposition is 30-7200 s, preferably 300-1500 s; and in the deposition process, the potential of the electrode relative to the saturated calomel electrode is-2.0V to-0.5V.
8. The toluidine blue modified metal organic framework electrode is applied to electrochemical immunosensing.
9. Use according to claim 8, for the detection of plant hormones, in particular for the detection of auxins.
10. The application of claim 8 or 9, wherein when a working curve is drawn and a sample to be tested is tested, the toluidine blue modified metal organic framework electrode after immune modification is used as a working electrode, a graphite electrode is used as a counter electrode, a saturated calomel electrode is used as a reference electrode to form a three-electrode system, and an electrolyte is a phosphoric acid buffer solution with the pH value of 6.86.
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