Cyclodextrin polymer microcapsules for controlled release of silver nanoparticles by gelation

Abstract

The present invention belongs to the field of preparation of polysaccharide antibacterial agents, and discloses a cyclodextrin polymer microcapsule capable of controlling the release of silver nanoparticles through gelation. The preparation method is as follows: First, a porous crystal of cyclodextrin metal-organic framework with uniformly dispersed silver nanoparticles inside is synthesized in one step by a strategy of synergistic nucleation growth to induce multi-core encapsulation, and then a cyclodextrin polymer microcapsule capable of controlling the release of silver nanoparticles through gelation is obtained by cross-linking. The synthesis strategy of the present invention not only confines all silver nanoparticles within the pore channels of the cyclodextrin skeleton of the porous crystal, avoiding the problem of silver nanoparticles being loaded on the surface of the cyclodextrin polymer microcapsule, but also the size of the silver nanoparticles is small and the distribution is uniform. The microcapsule prepared by the present invention undergoes gelation when encountering water, and can achieve the controlled release of silver nanoparticles, and has good application potential in the fields of antibacterial, catalysis and pollutant detection, etc.

Description

Technical Field

[0001] The invention belongs to the field of preparation of polysaccharide antibacterial agents, and in particular relates to a cyclodextrin polymer microcapsule capable of controlled release of silver nanoparticles through gelation. Background Art

[0002] Silver nanoparticles (AgNPs) have shown broad application prospects in biomedicine, catalysis and sensing due to their unique optical, electrical and antibacterial properties. However, the problems of aggregation tendency, poor stability and uncontrollable release in practical applications have seriously restricted their large-scale application. In terms of antibacterial, the use of silver nanoparticles alone also has problems such as reduced antibacterial effect due to easy aggregation, or easy to be quickly cleared and unable to play a long-term role, and possible toxicity to host cells. To solve these challenges, the construction of efficient loading strategies has become the current research focus. Polymer microcapsules, as a functional material with high biocompatibility, shell structure, high specific surface area and adjustable physicochemical properties, provide an ideal carrier for the efficient loading of AgNPs. In antibacterial applications, compared with the direct use of silver nanoparticles (AgNPs), polymer microcapsules loaded with AgNPs can accurately control the release rate of AgNPs or silver ions through their carrier characteristics, avoiding excessive local concentration caused by one-time release, while maintaining long-term effective antibacterial concentration. In addition, the shell structure of polymer microcapsules can reduce the direct contact between AgNPs and host cells, significantly reduce cytotoxicity, and prevent AgNPs from aggregation, oxidation, or inactivation in body fluids or complex environments.

[0003] Polymer microcapsules can be prepared by first synthesizing a metal organic framework (MOF), and then preparing polymer microcapsules through a chemical cross-linking strategy. Based on this, polymer microcapsules embedded with AgNPs can be achieved through the path of "first constructing a composite MOF, then cross-linking and converting". This template method not only simplifies the preparation process of traditional microcapsules, but also can use the confinement effect of MOF to accurately control the loading sites and dispersion state of AgNPs, thereby significantly improving the controllability and repeatability of material preparation. In this process, AgNPs are precisely confined inside the MOF pores rather than on the surface, which becomes a key factor in determining the performance of the material. At present, the strategies for MOF loading AgNPs mainly include two categories: one is to first synthesize the MOF skeleton, and then grow silver nanoparticles using the MOF skeleton as a carrier; the other is to first synthesize silver nanoparticles, and then encapsulate the pre-synthesized silver nanoparticles in a metal organic framework. For example, the Shailendra Shakya group ( Small 2019, 15, 1901065.), and the research group of Chen Lei from the First Affiliated Hospital of Sun Yat-sen University (CN112778772A) synthesized cyclodextrin metal-organic frameworks embedded with silver nanoparticles by first synthesizing the MOF framework and then growing silver nanoparticles on the MOF framework as a carrier. Although this strategy is expected to prevent the aggregation of silver nanoparticles and limit their growth, it sometimes inevitably forms some silver nanoparticles on the surface of the cyclodextrin metal-organic framework. Therefore, this strategy still faces the challenge of non-specific deposition of AgNPs on the MOF surface. The second strategy for loading AgNPs on MOF has problems such as a complex preparation process and the structure of MOF being easily damaged during the encapsulation of silver nanoparticles.

[0004] Therefore, developing a simple loading strategy to achieve efficient confinement and uniform distribution of AgNPs inside the pores of MOF is of great significance for improving the performance and application potential of polymer microcapsule composites. Summary of the Invention

[0005] Based on the problems existing in the above-mentioned prior art, the present invention has developed a preparation method for cyclodextrin polymer microcapsules that can control the release of silver nanoparticles through gelation, aiming to achieve efficient confinement and uniform distribution of AgNPs inside the pores of the cyclodextrin framework of porous crystals based on a new loading strategy, and expand the application fields of silver nanocomposites.

[0006] To achieve the purpose, the present invention adopts the following technical solutions:

[0007] A preparation method for cyclodextrin polymer microcapsules that can control the release of silver nanoparticles through gelation, characterized in that: first, through the strategy of cooperative nucleation growth to induce multinuclear encapsulation, a porous crystal of cyclodextrin metal-organic framework with uniformly dispersed silver nanoparticles inside is synthesized in one step, and then a cyclodextrin polymer microcapsule that can control the release of silver nanoparticles through gelation is obtained by crosslinking. The specific steps are as follows:

[0008] Step 1: Through the strategy of cooperative nucleation growth to induce multinuclear encapsulation, a porous crystal of cyclodextrin metal-organic framework with uniformly dispersed silver nanoparticles inside is synthesized in one step. The specific steps are as follows:

[0009] Mix cyclodextrin and potassium salt and add water to stir until fully dissolved, then add methanol, place it in an oil bath at 40 - 55 °C and heat for 5 - 30 minutes, then stop heating and quickly add a methanol solution of silver precursor, react for 5 - 10 minutes, and obtain a porous crystal of cyclodextrin metal-organic framework with uniformly dispersed silver nanoparticles inside, denoted as CD-MOF@Ag NP.

[0010] Step 2: Prepare a cyclodextrin polymer microcapsule that can control the release of silver nanoparticles through gelation

[0011] The CD-MOF@Ag NPs prepared in Step 1 were added to an organic solvent, and a cross-linking agent was added to carry out a cross-linking reaction. The product was collected by centrifugation, separated and purified, and then dried under vacuum to obtain a cyclodextrin polymer microcapsule capable of controlled release of silver nanoparticles through gelation, denoted as CL-CD-MOF@Ag NP microcapsule.

[0012] Further, in Step 1, the potassium salt is at least one of anhydrous potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, anhydrous potassium bicarbonate, and anhydrous potassium carbonate; the cyclodextrin is at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin; and the silver precursor is one of silver nitrate, silver acetate, and silver sulfate.

[0013] Further: in Step 1, the potassium salt and cyclodextrin are fed in a molar ratio of 1-50:1, and the dosage ratio of the potassium salt, water, methanol, and the methanol solution of the silver precursor is 1.6 mmol: 5-10 mL: 3-5 mL: 1-2.5 mL, and the concentration of the methanol solution of the silver precursor is 1-50 mM.

[0014] Further, in Step 2, the organic solvent is one of methanol, ethanol, acetone, acetonitrile, isopropanol, chloroform, and carbon tetrachloride.

[0015] Further, in Step 2, the cross-linking agent is an epoxy cross-linking agent (such as ethylene glycol diglycidyl ether), an isocyanate cross-linking agent (such as isocyanate), or an acyl chloride cross-linking agent (such as 1,7-heptanedicarbonyl chloride).

[0016] Further, in Step 2, the CD-MOF@Ag NPs and the cross-linking agent are fed in a mass ratio of 1: 1-60, and the dosage ratio of the CD-MOF@Ag NPs and the organic solvent is 100-200 mg: 5-10 mL.

[0017] Further, in Step 2, the reaction temperature of the cross-linking reaction is 30-100 °C, and the reaction time is 0.5-7 days.

[0018] The CL-CD-MOF@Ag NP microcapsules prepared by the method of the present invention have silver nanoparticles uniformly embedded in the crosslinked cyclodextrin metal-organic framework, forming a microcapsule structure; when the CL-CD-MOF@Ag NP microcapsules encounter water, they gelate, expand in volume, and then trigger the controlled release of silver nanoparticles. And the controlled release of silver nanoparticles exhibits a two-stage release characteristic, specifically: when the CL-CD-MOF@Ag NP microcapsules gelate upon encountering water, the volume will expand by more than 4 times, first triggering the release of silver nanoparticles with a particle size not greater than 5 nm, which can basically reach complete release within 2 h; at this time, most silver nanoparticles with a particle size greater than 5 nm still remain in the cyclodextrin polymer microcapsules and can maintain a stable and continuous release of about 3% / h within 2 - 24 h, thus realizing the two-stage release characteristic of "rapid onset - long-term maintenance".

[0019] The cyclodextrin polymer microcapsules prepared by the present invention that can control the release of silver nanoparticles through gelation exhibit various application potentials: they have good antibacterial performance against Escherichia coli and can be used to prepare antibacterial agents; they can be used as catalysts to catalytically reduce nitroarenes and turn harmful nitroarenes into useful substances; they can be used as SERS substrates to detect organic pollutants.

[0020] The beneficial effects of the present invention are reflected in:

[0021] 1. The present invention provides a preparation method of cyclodextrin polymer microcapsules that can control the release of silver nanoparticles through gelation. The raw materials used are inexpensive, abundant in reserves, and the production conditions are safe and simple, with obvious cost advantages.

[0022] 2. The cyclodextrin polymer microcapsules prepared by the present invention that can control the release of silver nanoparticles through gelation have the advantages of high selectivity, high activity, high stability, good adsorption performance, excellent dispersibility, excellent adhesion, and biocompatibility, and have good potential in the fields of antibacterial, catalysis, and detection of pollutants.

[0023] 3. The present invention develops a new synthesis strategy, namely the strategy of synergistic nucleation growth-induced multinuclear encapsulation, to synthesize in one step the porous crystals of cyclodextrin metal-organic framework with uniformly dispersed silver nanoparticles inside, and then obtain cyclodextrin polymer microcapsules that can control the release of silver nanoparticles through gelation by crosslinking. This strategy not only confines all silver nanoparticles within the pore channels of the cyclodextrin skeleton of the porous crystals, avoiding the problem of silver nanoparticles being loaded on the surface of cyclodextrin polymer microcapsules, but also the silver nanoparticles are small in size and uniformly distributed. Brief Description of the Drawings

[0024] Figure 1 It is the scanning electron microscope image of CD-MOF@Ag NP prepared in Example 1 of the present invention.

[0025] Figure 2 Mapping image of Ag element in CD-MOF@Ag NP prepared in Example 1 of the present invention.

[0026] Figure 3 XRD image of CD-MOF@Ag NP prepared in Example 1 of the present invention.

[0027] Figure 4 XRD image of CL-CD-MOF@Ag NP microcapsules prepared in Example 1 of the present invention.

[0028] Figure 5 Fourier transform infrared spectrum of CL-CD-MOF@Ag NP microcapsules prepared in Example 1 of the present invention and the raw material of cyclodextrin γ-CD used.

[0029] Figure 6 Transmission electron microscope image of CL-CD-MOF@Ag NP microcapsules prepared in Example 1 of the present invention.

[0030] Figure 7 Transmission electron microscope image of CL-CD-MOF@Ag NP microcapsules after gelation prepared in Example 1 of the present invention.

[0031] Figure 8 Release curve of silver nanoparticles in CL-CD-MOF@Ag NP microcapsules in Example 3 of the present invention.

[0032] Figure 9 Bacterial colony photos of Escherichia coli exposed to different concentrations of CL-CD-MOF@Ag NP microcapsules in Example 4 of the present invention.

[0033] Figure 10 Histogram of the number of bacterial colonies of Escherichia coli exposed to different concentrations of CL-CD-MOF@Ag NP microcapsules in Example 4 of the present invention.

[0034] Figure 11 Time-killing curve of CL-CD-MOF@Ag NP microcapsules against Escherichia coli in Example 4 of the present invention.

[0035] Figure 12 UV-Vis spectrum of the reaction solution of CL-CD-MOF@Ag NP microcapsules catalyzing 4-nitrophenol changing with time in Example 5 of the present invention.

[0036] Figure 13 Detection limit graph of CL-CD-MOF@Ag NP microcapsules as SERS substrate for R6G in Example 6 of the present invention.

[0037] Figure 14 SERS spectra of bisphenol A and bisphenol AF using the CL-CD-MOF@Ag NP microcapsules as SERS substrates in Example 6 of the present invention.

[0038] Figure 15 Schematic diagram of the release of silver nanoparticles from the CL-CD-MOF@Ag NP microcapsules prepared in the present invention after gelation. Detailed implementation manners

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Example 1

[0041] In this example, cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles through gelation were synthesized according to the following steps:

[0042] Step 1: Mix 0.1 mmol of γ-CD and 1.6 mmol of anhydrous potassium carbonate, add 6 mL of deionized water, stir until fully dissolved, then add 5 mL of methanol, place in an oil bath at 50 °C for 5 minutes, then stop heating and quickly add 1 mL of a 10 mM methanol solution of silver nitrate, react for 10 minutes to obtain a porous crystal of cyclodextrin metal-organic framework with uniformly dispersed silver nanoparticles inside, denoted as CD-MOF@Ag NP.

[0043] Step 2: Add 200 mg of the product prepared in Step 1, denoted as CD-MOF@Ag NP, to 10 mL of ethanol, add 5 g of ethylene glycol diglycidyl ether as a crosslinking agent, place in an oven at 50 °C and heat for 5 days, centrifuge to collect the product, filter the product by suction, wash with ethanol, and dry in vacuo at 40 °C for 12 hours to obtain cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles through gelation, denoted as CL-CD-MOF@Ag NP microcapsules.

[0044] The scanning electron microscope image of the CD-MOF@Ag NP obtained in this example is as Figure 1 shown. It can be seen from the figure that basically no silver nanoparticles are loaded on the surface of the cyclodextrin skeleton of the porous crystal.

[0045] The Mapping image of the Ag element in the CD-MOF@Ag NP obtained in this example is as Figure 2 shown. It can be seen from the figure that the silver nanoparticles are loaded inside the pores of the cyclodextrin skeleton of the porous crystal rather than on the surface.

[0046] The XRD pattern of the CD-MOF@Ag NP obtained in this example is as Figure 3As shown, by comparing the PDF card of silver nanoparticles and the signal peaks of the simulated CD-MOF, it can be seen that the CD-MOF@Ag NP was successfully prepared, and it can also be seen that the synthesized silver nanoparticles are of small size.

[0047] The XRD pattern of the CL-CD-MOF@Ag NP microcapsules obtained in this example is as Figure 4 shown. It can be seen from the figure that the synthesized silver nanoparticles are of small size.

[0048] The Fourier transform infrared spectra of the CL-CD-MOF@Ag NP microcapsules obtained in this example and the cyclodextrin γ-CD raw material used are as Figure 5 shown. It can be seen from the figure that the C-O-C stretching vibration (1020 - 1150 cm -1 ) of the cyclodextrin monomer is a sharp peak, and this sharp peak becomes broader and duller with the occurrence of the cross-linking reaction, proving the successful preparation of the cyclodextrin polymer microcapsules.

[0049] The transmission electron micrograph of the CL-CD-MOF@Ag NP microcapsules obtained in this example is as Figure 6 shown. It can be seen from the figure that basically no silver nanoparticles are loaded on the surface of the microcapsules.

[0050] Disperse 20 mg of the CL-CD-MOF@Ag NP microcapsules obtained in this example in 1 mL of deionized water to form gelled microcapsules, and then directly characterize their morphology by transmission electron microscopy. Figure 7 is the transmission electron micrograph of the gelled microcapsules. Comparing Figure 6 and Figure 7 it can be seen that the CL-CD-MOF@Ag NP microcapsules obtained in this example gel upon contact with water, can rapidly trigger the release of silver nanoparticles with a particle size less than 5 nm, while most silver nanoparticles with a particle size greater than 5 nm are retained in the microcapsules. At the same time, it can be seen that in the product synthesized in this example based on the strategy of synergistic nucleation growth-induced multinuclear encapsulation, the silver nanoparticles are uniform in size and small in particle size.

[0051] Example 2

[0052] In this example, the water absorption rate of the CL-CD-MOF@Ag NP microcapsules during gelation was tested according to the following steps:

[0053] Disperse 200 mg of the CL-CD-MOF@Ag NP microcapsules prepared in Example 1 in deionized water (10 mL), let stand for 1 h, and then filter with a 0.45 μm filter paper. Collect and dry the solid with additional filter paper and weigh it. The water absorption rate of the CL-CD-MOF@Ag NP microcapsules was calculated using formula (1).

[0054]

[0055] where w d (mg) and w w (mg) are the initial mass of the CL-CD-MOF@Ag NP microcapsules (i.e., 200 mg) and the mass after hydrogelation, respectively.

[0056] After calculation, the water absorption rate of the CL-CD-MOF@Ag NP microcapsules is 598%. Therefore, when the CL-CD-MOF@Ag NP microcapsules encounter water and gelate, the volume expands by more than 4 times.

[0057] Example 3

[0058] In this example, the loading amount of silver nanoparticles and the release of silver nanoparticles in the CL-CD-MOF@Ag NP microcapsules were tested according to the following steps:

[0059] Suspend the CL-CD-MOF@Ag NP microcapsules (100 mg) in water (5 mL) using a dialysis bag (MWCO 1000). Clamp the dialysis bag at the end side and immerse it in 200 mL of water. Stir using a magnetic stirrer at 350 rpm. Take equal amounts of solution (3 mL) at 15 minutes, 30 minutes, 1 hour, 2 hours, 6 hours, 9 hours, 12 hours, and 1 day, and replace the same volume of solvent after each sampling. The samples were nitrated with nitric acid, and the loading amount of silver nanoparticles and the release of silver nanoparticles were determined by ICP-MS. After testing, the loading amount of silver nanoparticles in the CL-CD-MOF@Ag NP microcapsules (i.e., the ratio of the mass of silver nanoparticles in the microcapsules to the total mass of the microcapsules) was approximately 0.6%.

[0060] The release curve of silver nanoparticles in the CL-CD-MOF@Ag NP microcapsules is as Figure 8 shown. It can be seen from the figure that as time increases, the release amount of silver nanoparticles also gradually increases. At 2 h, the release amount basically reached 20%, indicating that the silver nanoparticles with a particle size not greater than 5 nm in the obtained microcapsules accounted for approximately 20% of the total loading amount. After 2 h, the silver nanoparticles with a particle size greater than 5 nm began to be stably released, maintaining a release rate of approximately 3% / h within 2 - 24 h.

[0061] Example 4

[0062] In this example, the antibacterial performance of the CL-CD-MOF@Ag NP microcapsules obtained in Example 1 was verified, and the specific steps are as follows:

[0063] Disperse the CL-CD-MOF@Ag NP microcapsules prepared in Example 1 uniformly in deionized water at a concentration of 1 mg / mL to obtain microgels.

[0064] Add 100 μL of LB broth medium to a 96-well plate, and then add 100 μL of the prepared microgel to the first row of the 96-well plate. Dilute to make the concentration of microcapsules in the well plate 16 μg / mL or 32 μg / mL. Finally, add 10 μL of the bacterial suspension of Escherichia coli (1×10 6 CFU mL -1 ), seal with a sealing film, and incubate at 37 °C for 16 h. At the same time, use the sample wells without added microgel as negative controls. After incubation, dilute the liquid in each well by the same multiple with LB broth medium. Then, use a pipette to aspirate 100 μL of the diluted mixture again and drop it onto the surface of the medium. Immediately use a spreader to spread it evenly on the surface of the medium, place it in a constant temperature incubator at 37 °C for 12 h, and observe. Use the colony counting method to evaluate the antibacterial performance of the microcapsules against Escherichia coli.

[0065] In this example, the photos of bacterial colonies of Escherichia coli exposed to different concentrations of CL-CD-MOF@Ag NP microcapsules are as Figure 9 shown, and the bar chart of the number of bacterial colonies is as Figure 10 shown. It can be seen from Figure 9 and Figure 10 that the CL-CD-MOF@Ag NP microcapsules synthesized in Example 1 have a good antibacterial effect on Escherichia coli, and the antibacterial effect is better with the increase of concentration.

[0066] In this example, the time-kill curve of CL-CD-MOF@Ag NP microcapsules against Escherichia coli is as Figure 11 shown. It can be seen from Figure 11 that the bactericidal effect of CL-CD-MOF@Ag NP microcapsules on Escherichia coli is significant in the first 2 hours. As time increases, the bactericidal effect is not so significant but there is still an antibacterial effect, which also proves that the CL-CD-MOF@AgNP microcapsules prepared in the present invention have the dual-stage release characteristics of "rapid onset - long-term maintenance".

[0067] Example 5

[0068] This example verifies the catalytic performance of CL-CD-MOF@Ag NP microcapsules in catalyzing 4-nitrophenol. The specific steps are as follows:

[0069] Take 1.5 mL of ultrapure water in a 10 mL small glass bottle, add 50 μL of a 4-nitrophenol aqueous solution with a concentration of 5 mM and 0.5 mL of a sodium borohydride aqueous solution with a concentration of 0.1 M. The solution is yellow. Take 10 mg of the CL-CD-MOF@Ag NP microcapsules prepared in Example 1 and add them to the small glass bottle. The color of the solution gradually fades until it becomes colorless and transparent. Use an ultraviolet spectrophotometer to measure the change in absorbance.

[0070] In this example, the UV-Vis spectral diagram of the reaction solution of CL-CD-MOF@Ag NP microcapsules catalyzing 4-nitrophenol over time is as Figure 12 shown. It can be seen from the figure that the microcapsules have a good effect on catalyzing 4-nitrophenol. At 20 min, 4-nitrophenol has completely changed to 4-aminophenol.

[0071] Example 6

[0072] In this example, the performance of CL-CD-MOF@Ag NP microcapsules as a SERS substrate for detecting organic pollutants was verified. The specific steps are as follows:

[0073] Select the CL-CD-MOF@Ag NP microcapsules prepared in Example 1 as the SERS substrate material, and adsorb R6G solutions with different concentrations (1.0×10 -6 M, 1.0×10 -7 M, 1.0×10 -8 M, 1.0×10 -9 M, 1.0×10 -10 M, 1.0×10 -11 M, 1.0×10 -12 M) respectively to determine the detection limit of R6G when using the microcapsules as the SERS substrate. The results are as Figure 13 shown. It can be seen from the figure that the detection limit of CL-CD-MOF@Ag NP microcapsules as the SERS substrate material for R6G is 1.0×10 -9 M, and R6G with concentrations of 1.0×10 -10 M, 1.0×10 -11 M, and 1.0×10 -12 M cannot be detected.

[0074] Take 5 mg of the CL-CD-MOF@Ag NP microcapsules prepared in Example 1 as the SERS substrate and add them to 5 mL of aqueous solutions of bisphenol A (BPA) and bisphenol AF (BPAF) with a concentration of 1.0×10 -6 M respectively, and stir for 1 h. Take 10 μL of the test solution and drop it onto a glass slide. After drying, it is used for Raman testing. The results are as Figure 14As shown. It can be seen from the figure that the Raman signal of the CL-CD-MOF@Ag NP microcapsules can still be detected when the concentrations of bisphenol A (BPA) and bisphenol AF (BPAF) are as low as 1.0×10 -6 M. This indicates that the CL-CD-MOF@Ag NP microcapsules have good sensitivity to the organic pollutants bisphenol A (BPA) and bisphenol AF (BPAF) as SERS substrates.

[0075] In summary, the present invention first synthesizes a porous crystal of cyclodextrin metal-organic framework with uniformly dispersed silver nanoparticles inside, and then obtains cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles through crosslinking. This strategy not only confines all silver nanoparticles within the pores of the cyclodextrin framework of the porous crystal, avoiding the problem of silver nanoparticles being loaded on the surface of the cyclodextrin polymer microcapsules, but also the silver nanoparticles are small in size and uniformly distributed. And as Figure 15 shown, the microcapsules prepared by the present invention undergo gelation and volume expansion when exposed to water, realizing the controlled release of silver nanoparticles.

[0076] The above are only exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation, characterized in that: Firstly, a cyclodextrin metal organic framework porous crystal with silver nanoparticles uniformly dispersed inside is synthesized in one step through a coordinated nucleation growth induced multi-core encapsulation strategy, and then a cyclodextrin polymer microcapsule capable of controlled release of silver nanoparticles by gelation is obtained through cross-linking, specifically comprising the following steps: Step 1: Synthesize porous crystals of cyclodextrin metal organic frameworks with silver nanoparticles uniformly dispersed inside in one step through the strategy of synergistic nucleation growth induced multi-core encapsulation. The specific steps are as follows: Cyclodextrin and potassium salt were mixed and stirred with water until fully dissolved, and then methanol was added, and the mixture was placed in a 40-55°C oil bath and heated for 5-30 minutes, and then the heating was stopped and the methanol solution of the silver precursor was quickly added, and the mixture was reacted for 5-10 minutes to obtain porous crystals of cyclodextrin metal organic framework with silver nanoparticles uniformly dispersed inside, which were recorded as CD-MOF@Ag NP. Step 2: Preparation of cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation The CD-MOF@Ag NP prepared in step 1 is added to an organic solvent, and a cross-linking agent is added to carry out a cross-linking reaction. The product is collected by centrifugation, and the product is separated, purified, and vacuum-dried to obtain cyclodextrin polymer microcapsules that can control the release of silver nanoparticles by gelation, which are recorded as CL-CD-MOF@Ag NP microcapsules.

2. The method for preparing cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation according to claim 1, characterized in that: In step 1, the potassium salt is at least one of anhydrous potassium phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, anhydrous potassium bicarbonate and anhydrous potassium carbonate, the cyclodextrin is at least one of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin, and the silver precursor is one of silver nitrate, silver acetate and silver sulfate.

3. The method for preparing cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation according to claim 1, characterized in that: In step 1, the potassium salt and cyclodextrin are added in a molar ratio of 1-50:1, the dosage ratio of potassium salt, water, methanol and methanol solution of silver precursor is 1.6 mmol: 5-10 mL: 3-5 mL: 1-2.5 mL, and the concentration of methanol solution of silver precursor is 1-50 mM.

4. The method for preparing cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation according to claim 1, characterized in that: In step 2, the organic solvent is one of methanol, ethanol, acetone, acetonitrile, isopropanol, chloroform and carbon tetrachloride, and the cross-linking agent is an epoxy cross-linking agent, an isocyanate cross-linking agent or an acyl chloride cross-linking agent.

5. The method for preparing cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation according to claim 1, characterized in that: In step 2, the CD-MOF@Ag NP and the cross-linking agent are added in a mass ratio of 1:1~60, and the amount ratio of CD-MOF@Ag NP to the organic solvent is 100~200 mg: 5~10 mL.

6. The method for preparing cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation according to claim 1, characterized in that: In step 2, the reaction temperature of the cross-linking reaction is 30-100° C., and the reaction time is 0.5-7 days.

7. A cyclodextrin polymer microcapsule capable of controlled release of silver nanoparticles by gelation, obtained by the preparation method according to any one of claims 1 to 6.

8. The cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation according to claim 7, characterized in that: The cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation are cross-linked cyclodextrin metal organic frameworks in which silver nanoparticles are uniformly embedded to form a microcapsule structure; the cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation undergo gelation and volume expansion when encountering water, thereby triggering the controlled release of the silver nanoparticles.

9. Use of the cyclodextrin polymer microcapsules capable of controlled release of silver nanoparticles by gelation as claimed in claim 7, characterized in that: Used to prepare antibacterial agents; or, used as a catalyst to catalyze the reduction of nitroaromatic hydrocarbons; or, used as a SERS substrate to detect organic pollutants.

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