A divalent lanthanide metal labeled yellow-green fluorescent plastic microsphere, a preparation method and application thereof

Abstract

The application discloses a kind of divalent lanthanide series metal marked yellow-green fluorescent plastic microspheres and its preparation method and application, it is related to high molecular polymer preparation technical field.The preparation method of plastic microspheres of the application is as follows: under argon atmosphere, prepare nitrogen heterocyclic ligand N8;Under nitrogen atmosphere, drop the mixed solution of nitrogen heterocyclic ligand N8 and methanol into the mixed solution of EuBr2 and methanol to prepare Eu-N8 by reaction;Eu-N8 is dissolved in solvent containing polyvinylpyrrolidone, first embedding treatment is carried out by hydrothermal method, and PVP@Eu-N8 is obtained;PVP@Eu-N8 is added in the process of synthesizing polystyrene micro-nano plastic to carry out second hydrothermal coating treatment, and the plastic microspheres are obtained.The plastic microspheres prepared by the method of the application have uniform and consistent particle size, high-brightness yellow-green fluorescence, high stability, and can be directly added to various environmental samples to realize fluorescent tracing and quantitative detection of microplastics.

Description

Technical Field

[0001] This invention relates to the field of polymer preparation technology, and in particular to a yellow-green fluorescent plastic microsphere labeled with a divalent lanthanide metal, its preparation method, and its application. Background Technology

[0002] Microplastics, as an emerging pollutant, are complex in structure, diverse in type, and widely distributed, yet in-depth research on them remains lacking. Detection methods for microplastics are insufficient. Some researchers have proposed using metal-labeled plastic microspheres, determining the amount of microplastics by measuring the metal content after digestion. Existing studies primarily use palladium and trivalent europium as coatings. Europium-labeled microspheres exhibit red fluorescence, while palladium-labeled microspheres cannot be traced for their migration pathways using fluorescence. Commercially available lanthanide-labeled microspheres mainly exhibit red fluorescence, similar to the autoluminescence of organisms such as chlorophyll, which is unfavorable for observing their migration and transformation processes within organisms. Divalent europium also possesses fluorescent properties, making it a potential candidate for labeling plastic microspheres. However, the fluorescent complexes of divalent europium are easily oxidized to trivalent europium in air, altering their fluorescent properties. Furthermore, the addition of oxidizing initiators during the synthesis of plastic microspheres can also lead to the oxidation of divalent europium to trivalent europium, resulting in the loss of its fluorescent properties. Simultaneously, the metal-binding stability in divalent europium-labeled plastic microspheres is a critical issue that needs to be addressed. Improper preparation methods can lead to metal leakage from the microspheres, hindering long-term use. Summary of the Invention

[0003] To address the above shortcomings, this invention provides a method for preparing divalent lanthanide-labeled yellow-green fluorescent plastic microspheres and their applications. The plastic microspheres prepared by this method have uniform particle size, exhibit high-brightness yellow-green fluorescence, and high stability. They can be directly added to various environmental samples for fluorescent tracer and quantitative detection of microplastics. The specific technical solution is as follows:

[0004] A method for preparing divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres includes the following steps:

[0005] (1) The nitrogen heterocyclic ligand N8 was prepared under an argon atmosphere; the nitrogen heterocyclic ligand N8 is the abbreviation of 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexadecane;

[0006] (2) Under a nitrogen atmosphere, a mixture of nitrogen heterocyclic ligand N8 and methanol was slowly added dropwise to the mixture of EuBr2 and methanol to carry out the reaction. After removing the methanol, the mixture was purified by sublimation under reduced pressure to obtain Eu-N8.

[0007] (3) The Eu-N8 was dissolved in a solvent containing polyvinylpyrrolidone and subjected to a first encapsulation treatment by hydrothermal method to obtain PVP@Eu-N8;

[0008] (4) PVP@Eu-N8 is added during the synthesis of polystyrene micro-nanoplastics for a second hydrothermal coating treatment to obtain the yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metals.

[0009] Further, in step (1), the method for preparing the nitrogen heterocyclic ligand N8 is as follows:

[0010] Step A: Under an argon atmosphere, first add 10-15 mL of triethylamine and 200-250 mL of isopropanol to a three-necked flask and lower the temperature to -78 to -70°C; then add 5-10 mL of tris(2-aminoethyl)amine, and while stirring, add 7-8 mL of glyoxal solution dropwise at a rate of 0.08-0.16 mL / min. React for 16-24 h, and dry under reduced pressure to remove isopropanol; next, add 250-300 mL of chloroform and stir for 1-2 h, then filter to remove yellow solid impurities; finally, remove chloroform from the solution under reduced pressure to obtain the intermediate product.

[0011] Step B: Dissolve the intermediate product in 200-300 mL of dichloroethane, add 30-42 g of sodium triacetoxyborohydride at room temperature and react for 3-4 h. Remove dichloroethane under reduced pressure. Extract the product with dichloromethane 2-3 times, combine the extracts, dry under reduced pressure to remove dichloromethane, add water to the obtained product with stirring until completely dissolved, heat under nitrogen atmosphere to remove half of the aqueous solution, cool with ice water to recrystallize the product, filter to remove the liquid, and obtain a white solid. After drying the white solid under reduced pressure, obtain the nitrogen heterocyclic ligand N8.

[0012] Further, in step (2), the mixture of EuBr2 and methanol is prepared by mixing 0.1-0.3 mol of EuBr2 with 20-40 mL of methanol; the mixture of nitrogen heterocyclic ligand N8 and methanol is prepared by dissolving 0.1-0.2 mol of nitrogen heterocyclic ligand N8 in 20-30 mL of methanol.

[0013] Furthermore, in step (2), the dropping rate of the mixture of nitrogen heterocyclic ligand N8 and methanol is 1-4 mL / min.

[0014] Further, in step (2), the pressure for decompression is 10. -5 Pa, temperature is 150-250℃.

[0015] Furthermore, in step (3), the temperature of the first embedding treatment is 65-85℃ and the time is 1-3h.

[0016] Furthermore, in step (3), the mass of the polyvinylpyrrolidone is greater than or equal to the mass of Eu-N8.

[0017] Further, the specific method of step (4) is as follows: First, add 40-50 mL of ethanol aqueous solution or water with a volume concentration of 50-60% to a three-necked flask as a dispersion medium, then add Tris-HCl solution to adjust the pH to 7-8, then introduce nitrogen gas and heat to 65-85℃, then add 0.5-2.5 mL of styrene, 100 μL-500 μL of divinylbenzene and / or 0.5-2.5 mL of acrylonitrile, then add 0.05-0.1 g of potassium persulfate dissolved in 5-10 mL of water and react for 20-60 min, then add 5-10 mL of PVP@Eu-N8 to the reaction system and continue the reaction for 12-24 h to obtain the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres.

[0018] The present invention also provides a yellow-green fluorescent plastic microsphere labeled with a divalent lanthanide metal prepared by the above preparation method.

[0019] This invention also provides an application of the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres prepared by the above method in the detection of micro-nano plastics.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. The divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres synthesized in this invention encapsulate divalent europium in a core-shell structure, preventing it from being oxidized by free radicals in the environment. They exhibit stable yellow-green fluorescence, and the fluorescence intensity of the finished product remains unchanged after several months of storage, indicating that the encapsulated divalent europium is not oxidized and the binding is stable.

[0022] 2. The divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres synthesized in this invention differ from the red fluorescence of commercially available lanthanide metal-labeled plastic microspheres. They are a novel type of metal-labeled fluorescent plastic microspheres, possessing both fluorescence properties and metal labeling functions. They can be used to track their migration behavior in the environment using fluorescence microscopy and can also be used for quantitative detection based on metal labeling, demonstrating significant commercial application value.

[0023] 3. The lanthanide metals in the divalent lanthanide-labeled yellow-green fluorescent plastic microspheres prepared by this invention are stably bound. Long-term stability experiments show that the metal leakage from the synthesized yellow-green fluorescent plastic microspheres is about 0.01 μg / L per week, which is negligible compared to the amount of coating. This proves that the lanthanide metals coated on the fluorescent plastic microspheres prepared by this method will hardly leak from the plastic microspheres, and can be used for quantitative analysis of migration and fate of micro- and nano-plastics in complex environments. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0025] Figure 1 A scanning electron microscope image of the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres prepared in Example 3;

[0026] Figure 2 Excitation and emission spectra of the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres prepared in Example 1;

[0027] Figure 3 The graph shows the fluorescence intensity variation of the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres prepared in Example 1.

[0028] Figure 4 The content of microplastics in Arabidopsis thaliana was detected after the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres prepared in Example 3 were introduced into Arabidopsis thaliana plants as micro-nanoplastics pollutants.

[0029] Figure 5 The divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres prepared in Example 3 were used as a model of micro / nano plastic pollutants. After entering the plant root system, they exhibited yellow-green fluorescent properties. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0031] Example 1

[0032] The preparation method of the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres in this embodiment is as follows:

[0033] (1) Under an argon atmosphere, 12 mL of triethylamine and 250 mL of isopropanol were added to a 1 L three-necked flask. The mixture was cooled to -78°C, and 5 mL of tris(2-aminoethyl)amine was added. 7.5 mL of glyoxal solution was added dropwise at a rate of 0.08 mL / min using a syringe peristaltic pump while stirring with a stirrer. The reaction was allowed to proceed for 24 h. Isopropanol was removed by drying under reduced pressure at 40°C. 300 mL of chloroform was added and stirred for 2 h. The mixture was then filtered to remove yellow solid impurities. The chloroform in the solution was removed under reduced pressure to obtain the intermediate product.

[0034] The intermediate product was dissolved in 200 mL of dichloroethane, and 42 g of sodium triacetoxyborohydride was added at room temperature and reacted for 4 h. The dichloroethane was removed under reduced pressure. The product was extracted twice with 300 mL of dichloromethane, and the extracts were combined and dried under reduced pressure to remove the dichloromethane. Water was added to the obtained product with stirring until it was completely dissolved. Half of the aqueous solution was removed under reduced pressure under a nitrogen atmosphere. The product was recrystallized by cooling with ice water, and the liquid was removed by filtration to obtain a white solid. The white solid was dried under reduced pressure to obtain the nitrogen heterocyclic ligand.

[0035] (2) In a nitrogen atmosphere, add 0.1 mol EuBr2 and 20 mL methanol to a 100 mL flask, dissolve 0.1 mol of nitrogen heterocyclic ligand in 20 mL methanol, slowly add nitrogen heterocyclic ligand solution to the flask, remove methanol to obtain Eu-N8, and purify Eu-N8 by sublimation under reduced pressure to obtain pure Eu-N8.

[0036] (3) Add 0.1g Eu-N8 and 0.1g polyvinylpyrrolidone to a solution containing 10ml of water, and perform encapsulation treatment by hydrothermal method under magnetic stirring. Heat the solution to 70℃, react for 1h, and dry under reduced pressure to obtain PVP@Eu-N8 powder.

[0037] (4) Add 20 mL of water and 25 mL of alcohol to a three-necked flask, then add 5 mL of 1 mol / L Tris-HCl solution to adjust the pH to approximately 7. After purging with nitrogen and heating to 70 °C, add 1 mL of styrene and 100 μL of the crosslinking agent divinylbenzene. Then add 0.05 g of potassium persulfate solution dissolved in 5 mL of water and react for 30 min until the solution becomes translucent. Add 5 mL of PVP@Eu-N8 solution to the reaction system and continue the reaction for 24 h to obtain a light yellow suspension of divalent lanthanide-labeled yellow-green fluorescent plastic microspheres. The particle size of the nanoplastic microspheres synthesized in this example was measured to be 200 nm using a potentiometric particle size analyzer.

[0038] Figure 2 The excitation and emission spectra of the plastic microspheres prepared in this embodiment are shown. The excitation and emission spectra of the plastic microspheres prepared in other embodiments are basically the same as those in this embodiment. Figure 2 It can be seen that the plastic microspheres prepared in this embodiment have an excitation wavelength of 386nm and an emission wavelength of 567nm.

[0039] Figure 3 The fluorescence intensity of the plastic microspheres prepared in this embodiment was measured at 567 nm after being in an air atmosphere for 4 hours at an excitation wavelength of 386 nm. The graph shows that the fluorescence intensity remained basically unchanged, indicating that the plastic microspheres prepared in this embodiment are tightly coated with divalent europium, preventing them from being easily oxidized. The fluorescent plastic microspheres prepared by this method have air stability.

[0040] Example 2

[0041] The preparation method of the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres in this embodiment is as follows:

[0042] (1) Under an argon atmosphere, 12 mL of triethylamine and 250 mL of isopropanol were added to a 1 L three-necked flask. The mixture was cooled to -78°C, and 5 mL of tris(2-aminoethyl)amine was added. 7.5 mL of glyoxal solution was added dropwise at a rate of 0.10 mL / min using a syringe peristaltic pump while stirring with a paddle. The reaction was allowed to proceed for 24 h. Isopropanol was removed by drying under reduced pressure at 40°C. 300 mL of chloroform was added and stirred for 2 h. The mixture was then filtered to remove yellow solid impurities. The chloroform in the solution was removed under reduced pressure to obtain the intermediate product.

[0043] The intermediate product was dissolved in 300 mL of dichloroethane, and 42 g of sodium triacetoxyborohydride was added at room temperature and reacted for 4 h. The dichloroethane was removed under reduced pressure. The product was extracted three times with 300 mL of dichloromethane, and the extracts were combined and dried under reduced pressure to remove the dichloromethane. Water was added to the obtained product with stirring until it was completely dissolved. Half of the aqueous solution was removed under reduced pressure under a nitrogen atmosphere. The product was recrystallized by cooling with ice water, and the liquid was removed by filtration to obtain a white solid. The white solid was dried under reduced pressure to obtain the nitrogen heterocyclic ligand.

[0044] (2) In a nitrogen atmosphere, add 0.1 mol EuBr2 and 20 mL methanol to a 100 mL flask, dissolve 0.1 mol of nitrogen heterocyclic ligand in 20 mL methanol, gradually add nitrogen heterocyclic ligand solution to the flask, remove methanol to obtain Eu-N8, and purify Eu-N8 by sublimation under reduced pressure to obtain pure Eu-N8.

[0045] (3) Add 0.3g Eu-N8 and 0.5g polyvinylpyrrolidone to a solution containing 50ml of water, and perform encapsulation treatment by hydrothermal method under magnetic stirring. Heat the solution to 70℃, react for 3h, and dry under reduced pressure to obtain PVP@Eu-N8 powder.

[0046] (4) Add 20 mL of water and 25 mL of alcohol to a three-necked flask, then add 5 mL of 1 mol / L Tris-HCl solution to adjust the pH to approximately 7. After purging with nitrogen and heating to 70 °C, add 0.5 mL of styrene, 0.5 mL of acrylonitrile, and 100 μL of the crosslinking agent divinylbenzene. Then add 0.05 g of potassium persulfate solution dissolved in 5 mL of water and react for 30 min until the solution becomes translucent. Add 5 mL of PVP@Eu-N8 solution to the reaction system and continue the reaction for 24 h to obtain a light yellow suspension of yellow-green fluorescent plastic microspheres labeled with divalent lanthanides. The particle size of the nanoplastic microspheres synthesized in this example was measured to be 240 nm using a potentiometric particle size analyzer. Compared with Example 1, the plastic microspheres synthesized in this example have higher fluorescence intensity and heat resistance.

[0047] Example 3

[0048] (1) Under an argon atmosphere, 12 mL of triethylamine and 250 mL of isopropanol were added to a 1 L three-necked flask. The mixture was cooled to -78°C, and 5 mL of tris(2-aminoethyl)amine was added. 7.5 mL of glyoxal solution was added dropwise at a rate of 0.12 mL / min using a syringe peristaltic pump while stirring with a stirrer. The reaction was allowed to proceed for 24 h. Isopropanol was removed by drying under reduced pressure at 40°C. 300 mL of chloroform was added and stirred for 2 h. The mixture was then filtered to remove yellow solid impurities. The chloroform in the solution was removed under reduced pressure to obtain the intermediate product.

[0049] The intermediate product was dissolved in 250 mL of dichloroethane, and 42 g of sodium triacetoxyborohydride was added at room temperature and reacted for 4 h. The dichloroethane was removed under reduced pressure. The product was extracted three times with 300 mL of dichloromethane, and the extracts were combined and dried under reduced pressure to remove the dichloromethane. Water was added to the obtained product with stirring until it was completely dissolved. Half of the aqueous solution was removed under reduced pressure under a nitrogen atmosphere. The product was recrystallized by cooling with ice water, and the liquid was removed by filtration to obtain a white solid. The white solid was dried under reduced pressure to obtain the nitrogen heterocyclic ligand.

[0050] (2) In a nitrogen atmosphere, add 0.1 mol EuBr2 and 20 mL methanol to a 100 mL flask, dissolve 0.1 mol of nitrogen heterocyclic ligand in 20 mL methanol, gradually add nitrogen heterocyclic ligand solution to the flask, remove methanol to obtain Eu-N8, and purify Eu-N8 by sublimation under reduced pressure to obtain pure Eu-N8.

[0051] (3) Add 0.3g Eu-N8 and 0.5g polyvinylpyrrolidone to a solution containing 50ml of water, and perform encapsulation treatment by hydrothermal method under magnetic stirring. Heat the solution to 70℃, react for 3h, and dry under reduced pressure to obtain PVP@Eu-N8 powder.

[0052] (4) Add 45 mL of water to a three-necked flask, then add 5 mL of 1 mol / L Tris-HCl solution to adjust the pH to approximately 7. After purging with nitrogen and heating to 70 °C, add 2.5 mL of styrene, 2.5 mL of acrylonitrile, and 500 μL of the crosslinking agent divinylbenzene. Then add 0.03 g of potassium persulfate solution dissolved in 5 mL of water and react for 20 min until the solution turns milky white. Prepare a 5 mL aqueous solution of 0.3 g PVP@Eu-N8 and add it to the reaction system. After reacting for 1 h, the solution turns light yellow. Continue reacting for 24 h to obtain a light yellow suspension of yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metals. The scanning electron microscope image of the plastic microspheres synthesized in this example is shown below. Figure 1 As shown, by Figure 1 It can be seen that the microspheres have a regular morphology and uniform particle size, with an average particle size of 52.78±7.142nm.

[0053] Example 4

[0054] To verify that divalent europium is tightly encapsulated in the core and shell without leakage, the suspension of nanoplastic microspheres synthesized in Example 3 was dialyzed for one week using a dialysis bag to remove impurities. The dialyzed suspension was used as the working solution for subsequent experiments or commercial applications. The working solution was dialyzed using a dialysis bag, and samples were taken weekly to detect the degree of europium leakage. The europium content in the samples was detected by inductively coupled plasma mass spectrometry (ICP-MS). After seven consecutive weeks of sampling, the weekly leakage was approximately 0.01 μg, which is negligible compared to the amount of encapsulation, indicating that the plastic microspheres synthesized by this method have good stability and that the encapsulated europium is almost non-leaking. Simultaneously, a certain amount of nanoplastic microspheres prepared in Example 3 was digested with mixed acid, and the Eu content was measured. The results showed that Eu accounted for 0.26% of the mass of the nanoplastic microspheres in Example 3.

[0055] Example 5

[0056] The nanoplastic microspheres synthesized in Example 3 were used as a pollutant model to study the microplastic pollution stress on plant growth. Specifically, after culturing Arabidopsis thaliana for 21 days, a nanoplastic suspension was added to the culture medium to prepare solutions of 10 mg / L, 1 mg / L, and 0.1 mg / L. The prepared solutions were then poured into the pots of Arabidopsis thaliana every 3 days for one month, for a total of 10 waterings. The stems, leaves, and roots of the stressed Arabidopsis thaliana plants were harvested, dried, weighed, and digested with mixed acid. The Eu content was detected by inductively coupled plasma mass spectrometry (ICP-MS). The mass of nanoplastic microspheres absorbed by Arabidopsis thaliana was calculated based on the specific gravity of Eu relative to the mass of the nanoplastic microspheres. The absorption capacity of Arabidopsis thaliana for different concentrations of nanoplastic suspensions was compared and analyzed. Figure 4 As shown, the content of plastic microspheres can be calculated by the content of coated Eu, indicating that the plastic microspheres of this invention can be used for quantitative detection of micro- and nano-plastics in complex environments. Furthermore, the yellow-green fluorescent plastic microspheres prepared using this method can be observed to accumulate within a plant (Arabidopsis thaliana) under a fluorescence microscope, as shown... Figure 5 As shown, the yellow-green fluorescent plastic microspheres prepared by this method can be detected by fluorescent labeling.

[0057] In summary, the plastic microspheres prepared by the method of the present invention have uniform particle size, high brightness yellow-green fluorescence, and high stability. They can be directly added to various environmental samples to achieve fluorescence tracing and quantitative detection of microplastics.

[0058] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing yellow-green fluorescent plastic microspheres labeled with divalent lanthanide metals, characterized in that, Includes the following steps: (1) The nitrogen heterocyclic ligand N8 was prepared under an argon atmosphere, wherein the nitrogen heterocyclic ligand N8 is an abbreviation for 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexadecane; (2) Under a nitrogen atmosphere, a mixture of nitrogen heterocyclic ligand N8 and methanol was slowly added dropwise to the mixture of EuBr2 and methanol to carry out the reaction. After removing the methanol, the mixture was purified by sublimation under reduced pressure to obtain Eu-N8. (3) The Eu-N8 is dissolved in a solvent containing polyvinylpyrrolidone and subjected to a first encapsulation treatment by hydrothermal method. The temperature of the first encapsulation treatment is 65-85℃ and the time is 1-3h to obtain PVP@Eu-N8. The mass of the added polyvinylpyrrolidone is greater than or equal to the mass of Eu-N8; (4) PVP@Eu-N8 is added during the synthesis of polystyrene micro-nanoplastics for a second hydrothermal coating treatment to obtain the divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres. The specific method is as follows: First, add 40-50 mL of 50-60% ethanol aqueous solution or water as a dispersion medium to a three-necked flask, and adjust the pH to 7-8 with Tris-HCl solution; then, purge with nitrogen and heat to 65-80℃, and add 1-2.5 mL of styrene, 100 μL-500 μL of divinylbenzene and / or 0.5-2.5 mL of acrylonitrile; then, add 0.05-0.1 g of potassium persulfate dissolved in 5-10 mL of water and react for 20-60 min; finally, prepare 5 mL of 0.3 g of PVP@Eu-N8 aqueous solution and add it to the reaction system to continue the reaction for 12-24 h to obtain the final product.

2. The method for preparing divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres according to claim 1, characterized in that, In step (1), the method for preparing the nitrogen heterocyclic ligand N8 is as follows: Step A: Under an argon atmosphere, first add 10-15 mL of triethylamine and 200-250 mL of isopropanol to a three-necked flask and lower the temperature to -78 to -70°C; then add 5-10 mL of tris(2-aminoethyl)amine, and while stirring, add 7-8 mL of glyoxal solution dropwise at a rate of 0.08-0.16 mL / min. React for 16-24 h, and dry under reduced pressure to remove isopropanol; next, add 250-300 mL of chloroform and stir for 1-2 h, then filter to remove yellow solid impurities; finally, remove chloroform from the solution under reduced pressure to obtain the intermediate product. Step B: Dissolve the intermediate product in 200-300 mL of dichloroethane, add 30-42 g of sodium triacetoxyborohydride at room temperature and react for 3-4 h. Remove dichloroethane under reduced pressure. Extract the product with dichloromethane 2-3 times. Combine the extracts and dry under reduced pressure to remove dichloromethane. Add water to the obtained product with stirring until completely dissolved. Heat under nitrogen atmosphere to remove half of the aqueous solution. Cool with ice water to recrystallize the product. Filter to remove the liquid and obtain a white solid. Dry the white solid under reduced pressure to obtain the nitrogen heterocyclic ligand N8.

3. The method for preparing divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres according to claim 1, characterized in that, In step (2), the mixture of EuBr2 and methanol is prepared by mixing 0.1-0.3 mol of EuBr2 with 20-40 mL of methanol; the mixture of nitrogen heterocyclic ligand N8 and methanol is prepared by dissolving 0.1-0.2 mol of nitrogen heterocyclic ligand N8 in 20-30 mL of methanol.

4. The method for preparing divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres according to claim 1, characterized in that, In step (2), the dropping rate of the mixture of nitrogen heterocyclic ligand N8 and methanol is 1-4 mL / min.

5. The method for preparing divalent lanthanide metal-labeled yellow-green fluorescent plastic microspheres according to claim 1, characterized in that, In step (2), the pressure for decompression is 10. -5 Pa, temperature is 150-250℃.

6. A yellow-green fluorescent plastic microsphere labeled with a divalent lanthanide metal, prepared by the preparation method according to any one of claims 1 to 5.

7. The application of a yellow-green fluorescent plastic microsphere labeled with a divalent lanthanide metal as described in claim 6 in the detection of micro / nanoplastics.

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