Synthesis method of a magnetic affinity adsorbent with size exclusion effect

Abstract

The present invention belongs to the technical field of functionalized nanomaterials, specifically a method for synthesizing a magnetic affinity adsorbent with a size exclusion effect. The present invention performs structural optimization on the basis of a 3D ordered macroporous ZIF-8 material, specifically comprising: aminoating the surface of the ZIF-8 material and modifying ferroferric oxide magnetic microspheres; further coating polydopamine of a suitable thickness to increase the biocompatibility of the material surface, significantly increasing the chemical stability of the material surface, and utilizing the abundant active hydroxyl groups on the PDA surface as affinity ligand immobilization sites to overcome the deficiency of the lack of active modification groups on the surface of the existing macroporous ZIF-8 material; the prepared material has excellent properties such as good chemical stability, highly ordered macroporous structure, biocompatible outer surface, high load and high activity fixed with affinity ligands, and can be used as an ideal macroporous size exclusion magnetic adsorbent in the pre-treatment of complex samples.

Description

Technical Field

[0001] The invention belongs to the technical field of functionalized nanomaterials, and particularly relates to a method for synthesizing a magnetic affinity adsorbent with a size exclusion effect. Background Art

[0002] The analysis of biological samples often involves the selective extraction of specific substances from biological samples such as tissues and body fluids. Even if these complex biological matrices can be initially ground and centrifuged to remove large pieces of tissue and cells, the resulting supernatant still contains a large number of substances such as vesicles and cell fragments that are difficult to remove by centrifugation, which greatly interferes with subsequent extraction and analysis operations. In addition, biological samples often contain physiologically active substances such as antibodies, enzymes, cytokines, and nucleic acids that are of great analytical significance. The extraction of these substances must rely on specific affinity ligands, and traditional solid-phase extraction based on hydrophobic / hydrophilic / ion exchange interactions makes it difficult to effectively extract specific physiologically active substances in biological samples.

[0003] In order to solve the existing problems in the analysis of biological samples, magnetic confinement medium solid phase extraction technology based on affinity ligands has been widely used in the pretreatment of biological samples in recent years. This technology is based on the principle of classical magnetic solid phase extraction method, using a magnetic material with a porous structure as an adsorbent, and fixing a specific affinity ligand that interacts with the target to be extracted on the surface of the adsorbent, thereby achieving selective extraction of the target in a complex sample matrix, while interfering substances in the matrix that are larger than the pore size of the adsorbent are removed by size exclusion. Taking into account the difference between the molecular size of the target active substance to be extracted (such as antibodies, enzymes, nucleic acids, etc. 2-20nm) and the size of the interfering substances in the biological matrix (such as vesicles 30-150nm, cell debris 300-500nm), fixed pore size porous materials with a pore size of 50-300nm are widely used as magnetic affinity adsorbents with size exclusion.

[0004] 3D ordered macroporous ZIF-8 materials are a "star" porous material that has attracted much attention in recent years. They are prepared by growing classic ZIF-8 crystals on ordered polystyrene microsphere templates and then dissolving and removing the microsphere templates, resulting in 3D ordered macroporous ZIF-8 materials with pore diameters similar to those of the template spheres. Compared with traditional porous materials, 3D ordered macroporous ZIF-8 materials have advantages such as large specific surface area, high porosity, ordered macropore distribution, highly uniform pore size distribution, and adjustable pore size within 50-800 nm. However, this "star" porous material remains difficult to use directly as a magnetic solid-phase extraction adsorbent. The main reasons are: ① The existing 3D ordered macroporous ZIF-8 materials are non-magnetic and can only be separated from the sample system by centrifugation, which is a cumbersome operation; ② All ZIF-8 materials have extremely strong nonspecific adsorption on the surface. If used as solid-phase extraction adsorbents, they will adsorb irrelevant impurities in the sample, resulting in reduced extraction selectivity; ③ The acid-resistant nature of ZIF-8 materials (they dissolve after being placed in a pH = 6.0 solution for 10 minutes) also limits their application scenarios as adsorbents; ④ Methylimidazole and zinc ions are mainly distributed on the surface of ZIF-8 materials, and they lack active groups such as amino, carbonyl, and hydroxyl groups that can be used to fix affinity ligands. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for synthesizing a magnetic affinity adsorbent with size exclusion effect, so as to overcome the various shortcomings of the 3D ordered macroporous ZIF-8 material in the prior art and enable it to be directly used as a magnetic solid phase extraction adsorbent.

[0006] The present invention provides a method for synthesizing a magnetic affinity adsorbent having a size exclusion effect, and the specific steps are as follows:

[0007] (1) Synthesis of 3D ordered macroporous ZIF-8 material (MZIF-8): First, monodisperse polystyrene microspheres of a specific diameter (50-800 nm) are prepared into an ordered polystyrene microsphere template by centrifugation or filtration; the dried ordered polystyrene microsphere template is immersed in a ZIF-8 precursor ion solution (such as a divalent zinc ion solution or a methylimidazole solution), and a dual solvent system is applied to complete in situ crystallization. ZIF-8 crystals grow in the voids of the polystyrene microsphere template; then, an organic solvent is used to wash away the polystyrene microspheres to obtain a 3D ordered macroporous ZIF-8 material;

[0008] (2) Synthesis of amino-modified magnetic ferroferric oxide microspheres, denoted as Fe3O4-NH2: Ferric chloride, 1,6-hexanediamine, and anhydrous sodium acetate were weighed in a round-bottom flask and dissolved in ethylene glycol. The mixture was transferred to a high-pressure reactor and heated at high temperature for reaction. After the reaction was completed, the Fe3O4-NH2 microspheres were washed with an appropriate solvent.

[0009] (3) Synthesis of magnetic macroporous ZIF-8 material, denoted as magMZIF-8: 50-200 mg of the product MZIF-8 material synthesized in step (1) and 10-40 mL of aminopropyl silanization reagent are uniformly dispersed in 20-100 mL of anhydrous ethanol, and stirred at 30-80°C for 2-24 hours to achieve amino modification of the surface of the MZIF-8 material; the resulting product is then washed with an appropriate neutral solvent to remove the unreacted silanization reagent and collected by centrifugation; the collected precipitate is dispersed in a 0.1-2.0% glutaraldehyde aqueous solution and reacted at 4-30°C for 5-30 minutes; the unreacted glutaraldehyde is washed with an appropriate neutral solvent and the product is collected by centrifugation; the resulting product and 5-50 mg of Fe3O4-NH2 microspheres synthesized in step (2) are co-dispersed in a pH 7.0-8.0 mol / L sieve. 8-9 alkaline solution, reacting at 4-30°C for 1-48 hours, then separating the product magMZIF-8 by applying a magnetic field, washing with an appropriate neutral solvent and drying;

[0010] (4) Synthesis of polydopamine-coated magnetic macroporous ZIF-8 material, denoted as magMZIF-8@PDA: The product magMZIF-8 synthesized in step (3) was uniformly dispersed in 50-200 mL of an alkaline solution with a pH of 8-9, and an aqueous solution of dopamine hydrochloride with a concentration of 8-20 mg / mL was slowly added under stirring. The mixture was reacted at 4-30°C for 2-24 hours, and then the product magMZIF-8@PDA was separated by applying a magnetic field, washed with an appropriate neutral solvent, and then dried;

[0011] (5) Synthesis of a magnetic macroporous ZIF-8 material coated with polydopamine modified with a specific ligand, denoted as magMZIF-8@PDA-Ligand: The product magMZIF-8@PDA synthesized in step (4) was dispersed in an alkaline solution of pH 8 to 9, and then an affinity ligand with an amino group in the structure (such as avidin, enzyme, antibody and other proteins, or aptamer, mRNA and other nucleic acids) was added, and the reaction was carried out at 4 to 50 ° C for 1 to 48 hours to ensure that the ligand was fixed on the surface of the magMZIF-8@PDA material. The obtained product was gently washed with an appropriate buffered salt solution compatible with the ligand, and the product magMZIF-8@PDA-Ligand was separated by applying a magnetic field and stored in an environment compatible with the ligand at 4 to 30 ° C.

[0012] Further:

[0013] In step (3), the amino groups on the surface of the MZIF-8 material are activated with a glutaraldehyde aqueous solution, the glutaraldehyde concentration is 0.1-2.0%, and the reaction time is 5-30 minutes.

[0014] In step (4), in an alkaline solution of pH 8 to 9, a dopamine hydrochloride monomer at a concentration of 8 to 20 mg / mL is polymerized on the surface of the magMZIF-8 material to form a polydopamine coating layer, wherein the thickness of the polydopamine layer does not exceed one-third of the macropore diameter of the MZIF-8 material synthesized in step (1).

[0015] In steps (3) and (4), a pH-neutral solvent (pH=7.0±0.5) is used to clean the material.

[0016] In step (5), the amino group reacts with the hydroxyl group on the surface of the polydopamine layer in an alkaline solution at pH 8 to 9, so that the ligand with the amino group is covalently fixed to the surface of the magMZIF-8@PDA material.

[0017] The synthesis method of the magnetic affinity adsorbent with size exclusion provided by the present invention is based on the structural optimization of the 3D ordered macroporous ZIF-8 material, specifically comprising:

[0018] The surface of the 3D ordered macroporous ZIF-8 material is amino-treated, and aminoferric oxide microspheres are then fixed to the surface through glutaraldehyde cross-linking. This allows the material to be magnetically modified while maintaining its original structure. This overcomes the limitation of existing 3D ordered macroporous ZIF-8 materials, which have no magnetism and can only be separated by centrifugation.

[0019] Coating polydopamine on the surface of the magnetic macroporous ZIF-8 material increases the biocompatibility of the material surface, overcoming the problem of excessive nonspecific adsorption on the surface of existing classic ZIF-8 materials when processing biological samples. At the same time, the presence of the dopamine coating significantly increases the chemical stability of the material surface, overcoming the acid resistance of existing ZIF-8 materials.

[0020] The abundant active hydroxyl groups on the surface of PDA are used as affinity ligand immobilization sites to overcome the deficiency of the existing macroporous ZIF-8 material in lacking active modification groups on the surface.

[0021] Optimize appropriate conditions to ensure the appropriate thickness of the polydopamine layer of the material, maintain the integrity of the macroporous structure, and avoid the problem of the pore structure being covered due to the excessive thickness of the coating layer in conventional polymer coating methods.

[0022] The material finally prepared by the present invention has excellent properties such as good chemical stability, highly ordered macroporous structure, biocompatible outer surface, high loading capacity and high activity of fixed affinity ligands, and can be used as an ideal macroporous size exclusion magnetic adsorbent in the pretreatment of complex samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1Schematic diagram of the synthesis route of magMZIF-8@PDA-FcRn in Example 1.

[0024] Figure 2 Scanning electron micrographs of the materials at various stages of the preparation process in Example 1. A is a polystyrene microsphere template; B is a 3D ordered macroporous ZIF-8 material (MZIF-8); C is a magnetic macroporous ZIF-8 material (magMZIF-8); D is a polydopamine-coated magnetic macroporous ZIF-8 material (magMZIF-8@PDA); and E is magMZIF-8@PDA after acid treatment.

[0025] Figure 3 The following are electron micrographs of the materials at various stages of the preparation process in Example 1. A is a 3D ordered macroporous ZIF-8 material (MZIF-8); B is a magnetic macroporous ZIF-8 material (magMZIF-8); C is a polydopamine-coated magnetic macroporous ZIF-8 material (magMZIF-8@PDA); and D is magMZIF-8@PDA after acid treatment.

[0026] Figure 4 The infrared absorption spectra of the materials at various stages of the preparation process in Example 1 are shown. Among them: a is a classic non-macroporous ZIF-8 material; b is a 3D ordered macroporous ZIF-8 material (MZIF-8); c is a magnetic macroporous ZIF-8 material (magMZIF-8); d is a polydopamine-coated magnetic macroporous ZIF-8 material (magMZIF-8@PDA).

[0027] Figure 5 The following are X-ray diffraction patterns of the materials at various stages of the preparation process in Example 1. C-ZIF-8 is a classic non-macroporous ZIF-8 material; MZIF-8 is a 3D ordered macroporous ZIF-8 material; magMZIF-8 is a magnetic macroporous ZIF-8 material; and magMZIF-8@PDA is a polydopamine-coated magnetic macroporous ZIF-8 material.

[0028] Figure 6 A classic adsorbent and the adsorbent of the present invention were used to extract antibody molecules from cell fermentation broth. Nanoparticle tracking analysis of the resulting eluate yielded a particle size distribution. A is a classic magnetic solid-phase extraction adsorbent for immobilizing FcRn; B is magMZIF-8@PDA-FcRn.

[0029] Figure 7 The hysteresis curve of the magMZIF-8@PDA-FcRn material in the embodiment (A) and the magnetic response performance of the material in the cell fermentation broth (HCCF) matrix (B). DETAILED DESCRIPTION

[0030] The present invention is further described below through embodiments with reference to the accompanying drawings.

[0031] Example 1. Preparation of magMZIF-8@PDA-FcRn and its use as a magnetic affinity adsorbent with size exclusion to extract IgG molecules with high FcRn affinity from cell fermentation broth.

[0032] 1.1. Preparation of magMZIF-8@PDA-FcRn. magMZIF-8@PDA-FcRn is a polydopamine-coated magnetic macroporous ZIF-8 material with fixed FcRn as an affinity ligand. The preparation process is shown in Figure 1 shown.

[0033] (1) Synthesis of 3D ordered macroporous ZIF-8 material (MZIF-8): A monodisperse polystyrene microsphere dispersion (10 mg / mL) with a diameter of 300 nm was ultrasonically treated for 20 minutes until uniform dispersion, and then centrifuged at 2500 rpm for 24 hours to obtain an ordered polystyrene microsphere template. After discarding the supernatant, the precipitate was dried at 60°C under normal pressure for 24 hours. 8.15 g of zinc nitrate hexahydrate and 6.75 g of methylimidazole were weighed and dissolved in 45 mL of methanol to obtain a ZIF-8 precursor ion solution. The dried ordered polystyrene microsphere template was then immersed in the ZIF-8 precursor ion solution, placed at room temperature for 1 hour, and then placed in a reduced pressure environment for 10 minutes to ensure that the precursor ion solution fully entered the voids of the polystyrene microsphere template. The resulting product was dried at 50°C for 3 hours until the methanol evaporated completely. The product was then immersed in 50 mL of a 1:1 methanol:ammonia mixture and allowed to stand at room temperature for 24 hours to allow ZIF-8 crystals to grow on polystyrene microplates. After the reaction, the product was washed several times with N,N-dimethylformamide to remove the polystyrene microsphere template. The product was then dried at 70°C to obtain a white powder, representing the MZIF-8 material.

[0034] (2) Synthesis of amino-modified magnetic ferroferric oxide microspheres (Fe3O4-NH2): 2 g of ferric chloride hexahydrate, 7.2 g of 1,6-hexanediamine, and 8 g of anhydrous sodium acetate were weighed in a round-bottom flask and 60 mL of ethylene glycol was added. The mixture was stirred thoroughly until dissolved and then transferred to an autoclave for heating at 200°C for 6 hours. After the reaction, the product was washed several times with anhydrous ethanol and dried under reduced pressure at 50°C to obtain a black powder, which was Fe3O4-NH2 microspheres. The powder was ground before each use to reduce microsphere agglomeration.

[0035] (3) Synthesis of magnetic macroporous ZIF-8 material (magMZIF-8): 120 mg of the MZIF-8 material synthesized in step (1) and 20 mL of 3-aminopropyltrimethoxysilane (APTS) were added to 40 mL of anhydrous ethanol and ultrasonically treated for 20 minutes until uniformly dispersed. The reaction was stirred at 60°C for 7 hours to achieve amino modification of the surface of the MZIF-8 material. The resulting product was then repeatedly washed with anhydrous ethanol to remove free 3-aminopropyltrimethoxysilane in the system. The washed material was collected by centrifugation and dispersed in 40 mL of 0.5% glutaraldehyde aqueous solution. After reacting at room temperature for 20 minutes, the supernatant was immediately centrifuged to remove unreacted glutaraldehyde. The resulting material was then washed with anhydrous ethanol several times and the product was collected by centrifugation. The obtained product and 20 mg of Fe3O4-NH2 microspheres synthesized in step (2) were co-dispersed in 100 mL of 10 mM Tris solution (pH 8.5). After reacting at room temperature for 24 hours, the product was separated by applying a magnetic field, repeatedly washed with deionized water and anhydrous ethanol, and then dried under reduced pressure at 40°C to obtain a gray powder as magMZIF-8 material.

[0036] (4) Synthesis of polydopamine-coated magnetic macroporous ZIF-8 material (magMZIF-8@PDA): The product magMZIF-8 synthesized in step (3) was added to 20 mL of anhydrous ethanol and ultrasonicated for 20 minutes until uniformly dispersed. Subsequently, 65 mL of 10 mM Tris solution (pH 8.5) was added, and 35 mL of a 12.5 mg / mL dopamine hydrochloride aqueous solution was slowly added dropwise to the system under stirring. After reacting at room temperature for 6 hours, the product was separated by applying a magnetic field, and the material was repeatedly washed with anhydrous ethanol. After drying under reduced pressure at 40°C, a black powder was obtained, which is the magMZIF-8@PDA material.

[0037] (5) Synthesis of FcRn-modified polydopamine-coated magnetic macroporous ZIF-8 material (magMZIF-8@PDA-FcRn): 120 mg of the product magMZIF-8@PDA synthesized in step (4) was weighed and dispersed in 20 mL of 10 mM Tris solution (pH 8.5). 8 mL of 2 mg / mL streptavidin (SA) solution was then added and incubated at 15°C with slow shaking for 24 h. Streptavidin was covalently immobilized on the polydopamine surface as a primary ligand. The product was separated by applying a magnetic field and the resulting material was repeatedly washed with phosphate buffer (pH = 7.2). The resulting streptavidin-immobilized material (magMZIF-8@PDA-SA) was then added to 6 mL of a 0.5 mg / mL C-terminally biotin-labeled FcRn solution (stabilized by 5% trehalose, 5% mannitol, and 0.01% Tween-80 in 20 mM phosphate buffer, pH 7.2). After incubation at 4°C with gentle shaking for 24 hours, FcRn, acting as a secondary ligand, was immobilized on the entire surface of the material through the specific affinity between streptavidin and biotin. The product was separated using a magnetic field and repeatedly washed with phosphate buffer (pH 7.2). The resulting magMZIF-8@PDA-FcRn material was dispersed at 20 mg / mL in 20 mM phosphate-Tween buffer (pH 7.2) to form a suspension and stored at 2-8°C until ready for use.

[0038] 1.2 Characterization of the prepared magMZIF-8@PDA-FcRn material

[0039] The surface morphology of the synthesized material was characterized at the nanoscale using a ZEIS Gemini 300 field-emission scanning electron microscope at an accelerating voltage of 3 kV. The sample was attached to a conductive adhesive and then gold-sprayed. The skeletal morphology of the synthesized material was characterized at the nanoscale using a Tecnai G2 F20 S-Twin field-emission transmission electron microscope at an operating voltage of 150 kV. The sample was dispersed in anhydrous ethanol, dropped onto a copper grid, and then dried. Fourier transform infrared spectroscopy was used to qualitatively analyze the characteristic chemical bonds in the material to confirm the successful synthesis of the material. The sample was pressed into a potassium bromide pellet and the spectrum was scanned. The crystal structure of the material was characterized using a Bruker D2 PHASER X-ray polycrystal diffractometer. The magnetic hysteresis curve of the sample was recorded at room temperature using a LakeShore 7404 vibrating sample magnetometer.

[0040] 1.3. Performance of magMZIF-8@PDA-FcRn as a magnetic affinity adsorbent with size exclusion and comparison with the performance of a classical solid-phase extraction adsorbent with a non-porous structure immobilizing FcRn

[0041] (1) magMZIF-8@PDA-FcRn material or other classic solid-phase extraction adsorbents that immobilize FcRn are used to extract antibody molecules from cell fermentation broth: The extraction parameters are designed based on the pH-dependent binding between FcRn and antibodies. Specific parameters: The magnetic solid-phase extraction adsorbent is dispersed in a buffer solution to form a suspension system. When used, the amount of material added is controlled by adding an appropriate volume of suspension to an empty tube, and a magnetic field is applied to remove the supernatant of the suspension. The pH of the cell fermentation broth sample is adjusted to 6.0 with a glycine hydrochloride solution. 20 mg of magnetic solid-phase extraction adsorbent is added to 2 mL of the fermentation broth sample, and the mixture is incubated at 37°C with slow shaking for 20 minutes to allow the antibody molecules to bind to the affinity ligand FcRn of the magnetic solid-phase extraction adsorbent. A magnetic field is then applied to remove the supernatant of the cell fermentation broth. The nonspecific adsorption on the surface of the material was removed by washing with a phosphate buffer at pH 6.0, and then the antibody molecules bound to the surface of the magnetic solid phase extraction adsorbent were eluted using 120 μL of a phosphate buffer at pH 7.2 (under this condition, the affinity ligand FcRn has no affinity for the antibody molecules).

[0042] (2) Analysis of particle size in the eluate: The obtained eluate was injected into the Malvern Panalytical NanoSight 300 nanoparticle tracking analysis system to analyze the particle content and particle size distribution therein.

[0043] Figure 2 Scanning electron micrographs of the materials at various stages of the preparation process in Example 1. A is a polystyrene microsphere template; B is a 3D ordered macroporous ZIF-8 material (MZIF-8); C is a magnetic macroporous ZIF-8 material (magMZIF-8); D is a polydopamine-coated magnetic macroporous ZIF-8 material (magMZIF-8@PDA); and E is magMZIF-8@PDA after acid treatment.

[0044] After coupling with the FcRn protein, the presence of buffer salts and surfactants made drying difficult and affected the electron microscope's focus, making it impossible to capture images of the FcRn protein. This demonstrates that the magMZIF-8@PDA material prepared in this example possesses a regularly ordered macroporous structure with pores approximately 200 nm in diameter, and the material structure remains intact after acid treatment.

[0045] Figure 3 The following are electron micrographs of the materials at various stages of the preparation process in Example 1. A is a 3D ordered macroporous ZIF-8 material (MZIF-8); B is a magnetic macroporous ZIF-8 material (magMZIF-8); C is a polydopamine-coated magnetic macroporous ZIF-8 material (magMZIF-8@PDA); and D is magMZIF-8@PDA after acid treatment.

[0046] After coupling to the FcRn protein, the presence of buffer salts and surfactants made drying difficult and affected electron microscope focus, making it impossible to capture images of the FcRn-coupled material. This demonstrates that the magMZIF-8@PDA material prepared in this example possesses a regularly ordered macroporous structure with a polydopamine coating approximately 20 nm thick. The material structure remains intact after acid treatment.

[0047] Figure 4 The infrared absorption spectra of the materials at various stages of the preparation process in Example 1 are shown. Among them: a is a classic non-macroporous ZIF-8 material; b is a 3D ordered macroporous ZIF-8 material (MZIF-8); c is a magnetic macroporous ZIF-8 material (magMZIF-8); d is a polydopamine-coated magnetic macroporous ZIF-8 material (magMZIF-8@PDA).

[0048] Figure 5 The following are X-ray diffraction patterns of the materials at various stages of the preparation process in Example 1. C-ZIF-8 is a classic non-macroporous ZIF-8 material; MZIF-8 is a 3D ordered macroporous ZIF-8 material; magMZIF-8 is a magnetic macroporous ZIF-8 material; and magMZIF-8@PDA is a polydopamine-coated magnetic macroporous ZIF-8 material.

[0049] Figure 6 Nanoparticle tracking analysis was performed on the eluates obtained by extracting antibody molecules from cell fermentation broth using a conventional adsorbent and the adsorbent of the present invention. A represents a conventional magnetic solid-phase extraction adsorbent immobilizing FcRn; B represents magMZIF-8@PDA-FcRn. The comparison shows that the use of magMZIF-8@PDA-FcRn as a magnetic solid-phase extraction adsorbent significantly reduces the number of impurity particles larger than 300 nm in the eluate, demonstrating the material's excellent size exclusion efficiency.

[0050] Figure 7 Figures 1 and 2 show the hysteresis curve of the magMZIF-8@PDA-FcRn material in the examples (A) and its magnetic response in the complex matrix of cell fermentation broth (B). This indicates that the magMZIF-8@PDA-FcRn material prepared in the examples has excellent magnetic responsiveness and is suitable for use as a magnetic solid-phase extraction adsorbent.

Claims

1. A method for synthesizing a magnetic affinity adsorbent having a size exclusion effect, characterized in that: The specific steps are: (1) Synthesis of 3D ordered macroporous ZIF-8 material, denoted as MZIF-8: First, monodisperse polystyrene microspheres with a diameter of 50-800 nm are prepared into ordered polystyrene microsphere templates by centrifugation or filtration; the dried ordered polystyrene microsphere templates are immersed in a ZIF-8 precursor ion solution to complete in situ crystallization, and ZIF-8 crystals grow in the voids of the polystyrene microsphere templates; then, the polystyrene microspheres are washed away with an organic solvent to obtain a 3D ordered macroporous ZIF-8 material; (2) Synthesis of amino-modified magnetic ferroferric oxide microspheres, denoted as Fe3O4-NH2: Ferric chloride, 1,6-hexanediamine, and anhydrous sodium acetate were weighed in a round-bottom flask and dissolved in ethylene glycol. The mixture was transferred to a high-pressure reactor and heated at high temperature for reaction. After the reaction was completed, the Fe3O4-NH2 microspheres were washed with a solvent. (3) Synthesis of magnetic macroporous ZIF-8 material, denoted as magMZIF-8: 50-200 mg of the product MZIF-8 material synthesized in step (1) and 10-40 mL of aminopropyl silanization reagent are uniformly dispersed in 20-100 mL of anhydrous ethanol, and stirred at 30-80 ° C for 2-24 hours to achieve amino modification of the surface of the MZIF-8 material; the resulting product is then washed with a neutral solvent to remove the unreacted silanization reagent and collected by centrifugation; the collected precipitate is dispersed in a 0.1-2.0% glutaraldehyde aqueous solution and reacted at 4-30 ° C for 5-30 minutes; the unreacted glutaraldehyde is washed with a neutral solvent and the product is collected by centrifugation; the resulting product and 5-50 mg of Fe3O4-NH2 microspheres synthesized in step (2) are co-dispersed in a pH 7.0-8.0 mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L mol / L 8-9 alkaline solution, react at 4-30 ° C for 1-48 hours, then separate the product magMZIF-8 by applying a magnetic field, wash with a neutral solvent and dry; (4) Synthesis of polydopamine-coated magnetic macroporous ZIF-8 material, denoted as magMZIF-8@PDA: The product magMZIF-8 synthesized in step (3) was uniformly dispersed in 50-200 mL of an alkaline solution with a pH of 8-9, and an aqueous solution of dopamine hydrochloride with a concentration of 8-20 mg / mL was added under stirring. The mixture was reacted at 4-30 °C for 2-24 hours, and then the product magMZIF-8@PDA was separated by applying a magnetic field, washed with a neutral solvent, and dried. (5) Synthesis of a polydopamine-coated magnetic macroporous ZIF-8 material modified with a specific ligand, designated as magMZIF-8@PDA-Ligand: The product magMZIF-8@PDA synthesized in step (4) was dispersed in an alkaline solution with a pH of 8 to 9, and then an affinity ligand with an amino group in the structure was added. The reaction was carried out at 4 to 50 °C for 1 to 48 hours to ensure that the ligand was fixed on the surface of the magMZIF-8@PDA material. The obtained product was washed with a buffered salt solution compatible with the ligand, and the product magMZIF-8@PDA-Ligand was separated by applying a magnetic field and stored in an environment compatible with the ligand at 4 to 30 °C.

2. The synthesis method according to claim 1, wherein In step (4), the thickness of the polydopamine coating layer does not exceed one-third of the macropore diameter of the MZIF-8 material synthesized in step (1).

3. The synthesis method according to claim 1, wherein The affinity ligand with amino group in step (5) is avidin, enzyme or antibody protein, or aptamer, mRNA nucleic acid.

4. A magnetic affinity adsorbent with size exclusion effect obtained by the synthesis method according to any one of claims 1 to 3.

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