A beta-CD / ZIF-8@ST-based high-adhesion and responsive release nano-pesticide system and a preparation method thereof

Abstract

The application discloses a kind of high adhesion and response release nano pesticide system based on β-CD / ZIF-8@ST.The pesticide system is a kind of nano carrier of special structure of twisted king block, which can improve the rain scouring resistance of carrier on plant leaf.The nano drug delivery system is formed with β-cyclodextrin, zeolite imidazole framework-8 (ZIF-8) and mesoporous silica nanoparticles as the carrier of insecticide, and is formed by tannic acid encapsulation after adsorbing insecticide.The nano pesticide system has good pH / amylase dual response release performance, and can promote the release of loaded pesticide molecules under acidic conditions.Through the construction of special morphology, the nano pesticide system has good leaf adhesion, reduces pesticide droplet sliding loss.The nano pesticide system has good biocompatibility and shielding ultraviolet ability.In terms of biological activity, it shows higher insecticidal effect on cruciferous plant third instar plutella xylostella than commercially available insecticide.

Description

Technical Field

[0001] This invention belongs to the field of nanotechnology application and development technology in agriculture, specifically involving a highly adhesive and responsive release nanopesticide system based on β-CDZIF-8@ST and its preparation method. It is a nanopesticide delivery system formed by encapsulating a kingpin-like structure of β-cyclodextrin, zeolite imidazole backbone-8 (ZIF-8) and mesoporous silica nanoparticles with tannic acid. Background Technology

[0002] In modern agriculture, pesticides play a vital role in controlling pests, diseases, and weeds, and in increasing crop yields. However, during the application of most conventional pesticides in the field, significant amounts of their active ingredients are lost due to rainwater runoff, leaching, volatilization, and degradation, posing a threat to the ecological environment and human health.

[0003] Preventing pesticide loss and improving pesticide utilization remain crucial issues in agriculture. Therefore, developing an efficient and environmentally friendly intelligent pesticide delivery system is of significant practical importance. Nanopesticide formulations can be classified into nano-dispersible formulations, carrier-coated formulations, and metal and oxide nanoparticles. Carrier-coated pesticides use nanomaterials as carriers, loading pesticides through adsorption, coupling, and other methods. The pore size can be adjusted to load various pesticides, storing and protecting the active ingredients. Furthermore, multifunctional surface modification can achieve stimulus-responsive controlled release of pesticides. Therefore, carrier-coated pesticides possess high dispersibility and solubility, good biodegradability, and stability, making them one of the key research directions for future nanopesticide research.

[0004] The low surface energy and hydrophobic waxy layer on leaf surfaces make it difficult for pesticide droplets to wet and deposit on plant leaves. Currently, improving the retention of pesticide carriers on leaf surfaces mainly relies on the carrier morphology or modifying the carrier surface with affinity groups. For example, pesticide carriers with topological morphologies complementary to the micro / nanostructure of leaves are designed. Various topological effect supports, such as cap-shaped carriers, pointed silica nanoparticles, and rod-shaped cellulose nanocrystals, have been developed to extend pesticide retention time through interactions with the micro / nanostructure of leaves. In addition to complementary topological morphologies, enhancing the non-covalent interaction between the carrier and the leaf wax is an effective way to improve pesticide retention. A series of adhesive materials, such as tannic acid (TA), polydopamine, and chitosan, are used to regulate the adhesive properties of pesticide carriers. It is evident that both surface functionalization modification of adhesive groups and the topological effects of pesticide carriers can enhance pesticide retention on leaves. To date, few studies have considered both of these effects simultaneously. Therefore, it is imperative to construct novel pesticide carriers with topological morphology and high leaf surface affinity to improve the bioavailability of pesticides.

[0005] Controlled-release pesticides refer to pesticides whose active ingredients are loaded onto a carrier, allowing for slow release through concentration diffusion. This prolongs the pesticide's action time, reduces the number of sprays, and improves pesticide utilization. Environmentally responsive controlled-release pesticides are even more intelligent, capable of releasing active ingredients in response to external stimuli such as pH, light, temperature, and enzymes. However, this generally requires surface modification of the loading system. If controlled release of pesticides under diverse environmental conditions can be achieved, even if nanopesticides accumulate in crops, the biocompatible nanocarrier will eventually degrade. Therefore, developing multi-responsive nanopesticide systems has significant potential applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide a highly adhesive and responsive release nanopesticide system based on β-CDZIF-8@ST. The system is formed by a kingpin-like topology of β-cyclodextrin, ZIF-8 and mesoporous silica nanoparticles, and encapsulated with tannic acid. This nanoparticle-loaded system has dual pH / digestive enzyme responsive release performance.

[0007] The present invention also provides a method for preparing the above-mentioned highly adhesive and responsive release nanopesticide system based on β-CDZIF-8@ST.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST, comprising the following steps: 1) One-pot preparation of ZIF-8 carrier doped with β-cyclodextrin: The metal ligand was mixed with an aqueous solution containing 2-methylimidazole, hexadecyltrimethylammonium bromide (CTAB) and β-cyclodextrin, and allowed to stand at room temperature for 2-4 hours. After centrifugation, washing and drying, the ZIF-8 carrier doped with β-cyclodextrin was obtained, denoted as β-CD / ZIF-8. 2) A selective occupation strategy was employed to achieve controllable site-specific growth of mesoporous silica (SiO2) on ZIF-8 nanoparticles. A sol-gel method was used to prepare a kingpin-like topological structure nanocarrier. Specifically, the β-CD / ZIF-8 obtained in step 1) was dissolved in a mixed solution composed of surfactant, urea, and deionized water. An organic solvent containing tetraethyl silicate was added, and the mixture was heated to 60-80℃ with stirring for 16-20 h. After centrifugation, washing, and drying, a kingpin-like structure nanocarrier, denoted as β-CD / ZIF-8@S, was obtained. 3) Disperse the β-CD / ZIF-8@S obtained in step 2) in an aqueous solution of the insecticide imidacloprid (IMI), stir in the dark at room temperature for 24-48 h, centrifuge and dry to obtain a nano-pesticide system loaded with insecticide β-cyclodextrin, ZIF-8 and mesoporous silica (β-CD / ZIF-8@S), denoted as IMI@β-CD / ZIF-8@S. In this step, the drug imidacloprid is loaded into the pores and surface of mesoporous silica and MOF material ZIF-8 by adsorption. 4) Disperse the IMI@β-CD / ZIF-8@S obtained in step 3) in water, add a tannic acid alkaline solution with pH 7-9, and stir the reaction at room temperature for 3-10 min. Through the polyhydroxyl and galloyl groups of tannic acid, it can be deeply cross-linked on the surface of mesoporous silica nanoparticles through hydrogen bonds, coordination bonds, hydrophobicity and electrostatic interactions. After centrifugation and washing, a nano-pesticide system with high loading rate of tannic acid is obtained, denoted as IMI@β-CD / ZIF-8@ST.

[0009] Specifically, in step 1), the metal ligand can be zinc nitrate, zinc acetate, zinc hydroxide, or zinc sulfite, etc. More preferably, the molar ratio of the metal ligand to 2-methylimidazole can be 1:9-12, etc. The mass ratio of the metal ligand to hexadecyltrimethylammonium bromide can be 160-170:1, etc.; the mass ratio of the metal ligand to β-cyclodextrin can be 1-3:1, etc.

[0010] Specifically, in step 2), the surfactant can be hexadecyltrimethylammonium bromide, etc., and the mass ratio of β-CD / ZIF-8 to the surfactant can be 1:0.8-1.2, etc. More preferably, the mass ratio of β-CD / ZIF-8 to urea can be 1:0.6-0.8; and the mass-volume ratio of β-CD / ZIF-8 to tetraethyl silicate can be 1g:0.6-1.6ml.

[0011] Further, in step 2), the organic solvent can be a mixed solution of cyclohexane and isopropanol, preferably with a volume ratio of cyclohexane to isopropanol of 30-35:1. The nanocarrier β-CD / ZIF-8@S prepared in step 2) has a 16-faceted regular structure, an average diameter of 439 nm, and an average SiO2 thickness of less than 100 nm, approximately 60 nm. Specifically, in step 3), the mass ratio of β-CD / ZIF-8@S to the insecticide imidacloprid can be 1:0.5-3. The insecticide molecule size is smaller than the pore size of the mesoporous silica nanoparticles and the pore size of ZIF-8.

[0012] Specifically, in step 4), the mass ratio of IMI@β-CD / ZIF-8@S to tannic acid can be 1:0.4-0.9. The pH can be adjusted using alkaline substances such as sodium hydroxide or potassium hydroxide to obtain a tannic acid alkaline solution with a pH of 7-9.

[0013] This invention provides a highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST prepared by the above method.

[0014] The principle of this invention is as follows: This invention adopts the idea of ​​learning from nature, considering that the "long-handled" stones on the coast—accropode stones—are a type of protective block for breakwaters, usually placed on the outer layer of breakwaters to protect them by reducing the impact of waves. Based on this inspiration, a nanopesticide carrier with a structure similar to accropode stones is envisioned. The surface topology enhances interfacial interactions, which may effectively improve resistance to rainwater erosion, thereby achieving high retention on leaves. Metal-organic frameworks (MOFs) ZIF-8 have been widely studied in drug delivery applications due to their ease of preparation, high porosity, low cytotoxicity, and pH-responsive biodegradability. Utilizing the differences in binding energy and coordination number of different crystal faces of β-cyclodextrin-doped ZIF-8, six mesoporous silica nanofoot-like structures were selectively grown on six {100} faces of the β-CD / ZIF-8 nanocarrier surface, resulting in a precisely controllable accropode-type surface topology. This topology reduces the runoff behavior of traditional pesticide droplets and improves the persistence of pesticide deposition on leaf surfaces.

[0015] The zeolite imidazole ester framework material (ZIF-8) used in this invention to construct the topological structure possesses excellent biocompatibility and exhibits good stability under physiological conditions, while disintegrating under acidic conditions, demonstrating responsiveness to weakly acidic environments. Tannic acid (TA), a common natural plant polyphenol, has good adhesion and pH-responsive controlled-release properties, with acidic environments further facilitating drug release. Simultaneously, the β-cyclodextrin contained in the system can be hydrolyzed by amylase. Therefore, this drug-loaded system exhibits excellent pH / digestive enzyme dual-responsive release performance. This enables pH-responsive release of pesticide components, exhibiting sustained-release characteristics, prolonging release time, and extending the pesticide's action time. Encapsulating the nano-drug-loaded system with tannic acid avoids direct contact between the pesticide and operators, reducing potential toxicity to operators. The drug-loaded system does not require the addition of toxic solvents during release, making it environmentally friendly and reducing pollution to the ecological environment.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The nanopesticide system prepared in this invention utilizes both the surface functionalization modification of adhesive groups and the topological effect of the pesticide carrier to enhance pesticide retention on leaves. Tests show that, compared with existing similar mesoporous silica nanopesticide systems, the wettability and leaf adhesion performance of the nanopesticide system of this invention are greatly improved.

[0017] 2) The nano-pesticide system prepared by this invention has both pH and amylase dual response release properties, which can promote the release of loaded pesticide molecules under acidic conditions.

[0018] 3) The nano-pesticide system of this invention possesses excellent biocompatibility and UV shielding capabilities, effectively preventing the photodegradation of the insecticide imidacloprid (IMI) by ultraviolet light. Through the construction of a special morphology, the nano-pesticide system exhibits good leaf adhesion properties, reducing pesticide droplet slippage and loss. In terms of biological activity, it demonstrates a higher insecticidal effect against the third instar diamondback moth on cruciferous plants than commercially available insecticides.

[0019] 4) The raw materials involved in the nano-pesticide system of this invention are cheap and readily available, with a high drug loading rate and high insecticidal activity efficiency. Attached Figure Description

[0020] Figure 1 SEM images of β-CD / ZIF-8 (a), β-CD / ZIF-8@S (b, inset: photograph of “accropode” stone); TEM images of β-CD / ZIF-8@S (c) and IMI@β-CD / ZIF-8@ST (d); Figure 2 These are the nitrogen adsorption-desorption isotherms for ZIF-8, β-CD / ZIF-8, β-CD / ZIF-8@S and IMI@β-CD / ZIF-8@ST; Figure 3 are the zeta potential diagrams of ZIF-8, β-CD, β-CD / ZIF-8, β-CD / ZIF-8@S and IMI@β-CD / ZIF-8@ST; Figure 4 The thermogravimetric analysis (TGA) curves for β-CD, ZIF-8, β-CD / ZIF-8, β-CD / ZIF-8@S, and β-CD / ZIF-8@ST are shown below. Figure 5 These are the release curves of the IMI@β-CD / ZIF-8@ST nanopesticide system at different pH values ​​and in the presence of α-amylase; Figure 6 It includes IMI@MS, IMI@β-CD / ZIF-8, IMI@β-CD / ZIF-8@S, and commercially available IMI insecticides (IMI). WGDynamic contact angle of IMI@β-CD / ZIF-8@ST solution on cucumber leaves; Figure 7 It includes IMI@MS, MI@β-CD / ZIF-8, IMI@β-CD / ZIF-8@S, and commercially available IMI insecticides (IMI). WG The retention (LHC) of IMI@β-CD / ZIF-8@ST solution on cucumber leaves; Figure 8 The images show scans of different samples on the leaf surface before and after simulated rain (a) and the adhesion rate of each sample on the leaf surface after different simulated rain showers (b). Figure 9 It is the raw material for IMI pesticide and commercially available IMI insecticide (IMI). WG Photostability curves of different samples of IMI@β-CD / ZIF-8@S and IMI@β-CD / ZIF-8@ST after ultraviolet irradiation; Figure 10 The cell viability of HepG2 cells after co-incubation with different concentrations of IMI@β-CD / ZIF-8@ST samples for 24 h; Figure 11 The images show the germination rate and root length of IMI@β-CD / ZIF-8@ST treated seeds (a) and corresponding digital photographs of cucumber seed germination at different concentrations (b). In the figures, concentrations a to f are 0, 25, 50, 100, 200, and 400 μg / mL, respectively. Figure 12 Confocal imaging of different parts (leaves, stems, roots) of tobacco plants 24 h after foliar spraying (a, c) and root spraying (b, d) of FITC (a, b) and IMI@β-CD / ZIF-8@ST / FITC (c, d); Figure 13 Different doses of IMI, IMI WG Insecticidal effects of IMI@β-CD / ZIF-8@ST on diamondback moth larvae; Figure 14 It's IMI, IMI WG The insecticidal effects of IMI@β-CD / ZIF-8@ST on diamondback moth under different UV irradiation times; Figure 15 Is IMI@β-CD / ZIF-8@ST(1), IMI WG (2) and IMI (3) are photographs of leaf damage after 0, 20, 40, 80 and 120 min of UV irradiation. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, all raw materials used in the following examples are commercially available products that can be directly purchased or prepared using conventional methods in the art. Room temperature refers to 25±5℃.

[0023] Example 1: Preparation of ZIF-8 support doped with β-cyclodextrin 1 1.5 g of zinc acetate dihydrate (Zn(CH3COO)2·2H2O) was uniformly dissolved in 25 mL of deionized water. Then, the mixture was added dropwise to 25 mL of an aqueous solution containing 5.6 g of 2-methylimidazole, 9.0 mg of hexadecyltrimethylammonium bromide (CTAB), and 0.75 g of β-cyclodextrin (β-CD). The reaction mixture was stirred for 2 min and allowed to stand at room temperature for 2 h, resulting in precipitation. The precipitate was centrifuged, washed with deionized water, and dried at 60 °C overnight (12 h) to obtain the final precipitate (β-CD / ZIF-8).

[0024] Example 2: Preparation of ZIF-8 support doped with β-cyclodextrin 1.5 g of zinc acetate dihydrate (Zn(CH3COO)2·2H2O) was uniformly dissolved in 25 mL of deionized water. Then, the mixture was added dropwise to 25 mL of an aqueous solution containing 5.6 g of 2-methylimidazole, 9.0 mg of hexadecyltrimethylammonium bromide (CTAB), and 0.5 g of β-cyclodextrin (β-CD). The reaction mixture was stirred for 2 min and allowed to stand at room temperature for 2 h, resulting in precipitation. The precipitate was centrifuged, washed with deionized water, and dried overnight at 60 °C to obtain the final precipitate (β-CD / ZIF-8).

[0025] Example 3: Preparation of ZIF-8 support doped with β-cyclodextrin 1.5 g of zinc acetate dihydrate (Zn(CH3COO)2·2H2O) was uniformly dissolved in 25 mL of deionized water. Then, the mixture was added dropwise to 25 mL of an aqueous solution containing 5.6 g of 2-methylimidazole, 9.0 mg of hexadecyltrimethylammonium bromide (CTAB), and 1.0 g of β-cyclodextrin (β-CD). The reaction mixture was stirred for 2 min and allowed to stand at room temperature for 2 h, resulting in precipitation. The precipitate was centrifuged, washed with deionized water, and dried overnight at 60 °C to obtain the final precipitate (β-CD / ZIF-8).

[0026] Example 4: Preparation of β-CD / ZIF-8@S nanocarrier with a twisted block structure 0.5 g of the β-CD / ZIF-8 prepared in Example 1 was dissolved in a mixed solution consisting of 15 mL of deionized water, 0.5 g of CTAB, and 0.3 g of urea. Then, 15 mL of cyclohexane, 0.46 mL of isopropanol, and 0.5 mL of tetraethyl orthosilicate (TEOS) were stirred to form a white solution. The two solutions were then mixed with magnetic stirring and heated to 70 °C for 16 h. After centrifugation, the solution was washed with ethanol and freeze-dried (at -25 to -30 °C for 24 h) to obtain the nanocarrier β-CD / ZIF-8@S.

[0027] Example 5: Preparation of the insecticide-loaded nanopesticide system IMI@β-CD / ZIF-8@S 50 mg of the nanocarrier β-CD / ZIF-8@S prepared in Example 4 was mixed and suspended in 100 mL (1 mg / mL) of imidacloprid IMI aqueous solution. The mixture was stirred in the dark at room temperature for 24 h. The free IMI was removed by centrifugation, and the mixture was dried at 60 °C overnight to obtain the nanopesticide system loaded with insecticide, denoted as IMI@β-CD / ZIF-8@S.

[0028] Example 6: Preparation of the tannic acid-blocked nanopesticide system IMI@β-CD / ZIF-8@ST 0.1 g of the IMI@β-CD / ZIF-8@S prepared in Example 5 was dispersed in 10 mL of water. Then, 2 mL of a tannic acid alkaline solution (24 mM, pH=8) was added to the above mixed suspension, and the mixture was stirred continuously at room temperature for 5 min. After the reaction was completed, the precipitate was collected by centrifugation and washed with water to obtain the tannic acid-blocked nanopesticide system, denoted as IMI@β-CD / ZIF-8@ST.

[0029] Meanwhile, as a comparison, the nanocarrier prepared in Example 4 was used to prepare a tannic acid-blocked nanosystem, denoted as β-CD / ZIF-8@ST, by referring to the method in Example 6.

[0030] Comparative Example 1: Preparation of IMI@MS 1) Preparation of MS nanocarriers 2.2 g CTAB and 1.1 mL triethanolamine were dissolved in a mixed solution consisting of 2 mL ethanol and 20 mL deionized water. The mixture was then heated to 80 °C with stirring, and 0.5 mL TEOS was slowly added dropwise. After reacting for 4 h, mesoporous spherical silica (MS) was obtained by centrifugation, washing, and drying overnight.

[0031] 2) Preparation of MS nanopesticide system loaded with insecticide 50 mg MS was dispersed in 100 mL (1 mg / mL) of imidacloprid (IMI) solution and stirred in the dark at room temperature for 24 h. Then it was centrifuged and dried at 60 °C overnight to obtain IMI@MS.

[0032] Comparative Example 2: Preparation of IMI@β-CD / ZIF-8 loaded with insecticide 50 mg of the β-CD / ZIF-8 prepared in Example 1 was dispersed in 100 mL (1 mg / mL) of imidacloprid (IMI) solution and stirred in the dark at room temperature for 24 h. The solution was then centrifuged and dried at 60 °C overnight to obtain IMI@β-CD / ZIF-8.

[0033] Comparative Example 3: Preparation of nanocarrier β-CD / ZIF-8@ST without insecticide IMI loading 0.1 g of the β-CD / ZIF-8@S prepared in Example 4 was dispersed in 10 mL of water. Then, 2 mL of a tannic acid alkaline solution (24 mM, pH=8) was added to the above mixed suspension, and the mixture was stirred continuously at room temperature for 5 min. After the reaction was completed, the precipitate was collected by centrifugation and washed with water to obtain the tannic acid-blocked nanocarrier, denoted as β-CD / ZIF-8@ST.

[0034] Test Example 1: Morphology, particle size and thermogravimetric analysis of the tannic acid-encapsulated nanopesticide system IMI@β-CD / ZIF-8@ST Figure 1 (a) is a SEM image of β-CD / ZIF-8, showing a regular structure with 16 cross-sections, clearly revealing 10 {110} and 6 {100} cross-sections, with particle sizes ranging from 250 to 300 nm. (b) is a SEM image of β-CD / ZIF-8@S, showing six non-crystalline SiO2 foot-like structures with distinct mesoporous channels selectively grown on the {100} surface of β-CD / ZIF-8. (c) is a TEM image of β-CD / ZIF-8@S, further confirming the kingpin-like structure. The synthesized nanocarriers have an average diameter of 439 nm and an average SiO2 thickness of approximately 60 nm. Six mesoporous silica nanofoot-like structures, exhibiting a kingpin-like structure, were selectively grown on the surface of the ZIF-8 nanocarriers. (d) is a TEM image of IMI@β-CD / ZIF-8@ST, indicating that tannic acid encapsulation has no significant effect on the shape.

[0035] Figure 2Nitrogen adsorption-desorption isotherms for samples ZIF-8, β-CD / ZIF-8, β-CD / ZIF-8@S, and IMI@β-CD / ZIF-8@ST are presented. The figures show that all four samples exhibit distinct type IV adsorption-desorption isotherms, indicating the presence of porous structures. The specific surface area and pore volume of ZIF-8 are 190.21 m². 2 / g and 0.19 cm 3 / g. The specific surface area and pore volume of the doped β-CD / ZIF-8 are significantly increased. Compared with β-CD / ZIF-8, the specific surface area and pore volume of β-CD / ZIF-8@S are slightly decreased, from 1097.98 m² / g. 2 / g and 0.84 cm 3 / g decreased to 1071.62 m 2 / g and 0.73 cm 3 / g. High specific surface area is beneficial for IMI loading. After loading IMI and encapsulating TA, the specific surface area of ​​IMI@β-CD / ZIF-8@ST is 968.54m². 2 / g) and pore volume (0.52 cm³) 3 The / g) further decreases due to the blocking effect of IMI and TA on the pores.

[0036] Figure 3 This is a zeta potential graph for ZIF-8, β-CD, β-CD / ZIF-8, β-CD / ZIF-8@S, and IMI@β-CD / ZIF-8@ST. The graph shows that the zeta potentials of pure ZIF-8 and β-CD are +43.6 mV and -20.1 mV, respectively. After β-CD doping, the zeta potential of β-CD / ZIF-8 becomes positive (+9.5 mV). The zeta potential of β-CD / ZIF-8@S is -23.6 mV, due to the presence of silanol groups. After introducing IMI and TA, the zeta potential of β-CD / ZIF-8@ST drops to -34.8 mV, confirming the successful loading of the drug and the coating of the TA.

[0037] Figure 4The thermogravimetric analysis (TGA) curves for β-CD, ZIF-8, β-CD / ZIF-8, β-CD / ZIF-8@S, and β-CD / ZIF-8@ST are shown in the figures. As can be seen, all samples exhibit continuous weight loss up to 800℃, with weight loss below 100℃ attributed to water evaporation. For the β-CD curve, rapid weight loss mainly occurs in the 130–200℃ range, which is related to the thermal degradation of β-CD. ZIF-8 exhibits three weight loss stages. The first stage (150–200℃) reflects the desorption of solvent molecules and water from the cavities or surface of ZIF-8. A relatively long plateau occurs in the 210–400℃ range, indicating good thermal stability of ZIF-8. Weight loss above 430℃ is caused by the carbonization of organic ligands and the decomposition of the ZIF-8 skeleton. Compared to ZIF-8, β-CD / ZIF-8 exhibits superior thermal stability in the 200–600℃ range. In contrast, both β-CD / ZIF-8@S and β-CD / ZIF-8@ST exhibited a gradual and slow weight loss within 500℃. The total weight loss of β-CD / ZIF-8, β-CD / ZIF-8@S, and β-CD / ZIF-8@ST were 42.9%, 68.7%, and 73.7%, respectively.

[0038] The above Figure 2 , 3 The results in sections 4 and 4 fully demonstrate the successful loading of imidacloprid and the successful modification of tannic acid.

[0039] Test Example 2: Controlled Release Experiment of Tannic Acid-Encapsulated Nanopesticide System IMI@β-CD / ZIF-8@ST The release behavior of IMI@β-CD / ZIF-8@ST under different pH values ​​(pH = 4, 7, 9) and in the presence of α-amylase was investigated using dialysis. In simple terms, 5 mL of IMI@β-CD / ZIF-8@ST suspension (1 mg / mL) was placed in a dialysis bag and then in 45 mL of PBS solution under different environmental conditions (pH 4, 7, 9, and pH 7 with the addition of α-amylase, i.e., 40 mg of α-amylase was added to 100 mL of pH=7 PBS buffer). The release system was then maintained in a shaker at 100 rpm in a 25°C incubator. At specified time intervals of 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 24 h, 36 h, 48 h, 60 h, and 72 h, 2 mL of sample suspension was taken for analysis, and an equal volume of fresh PBS solution under different environmental conditions was added. The collected supernatant was monitored by UV-Vis spectroscopy at 270 nm, and the cumulative release of IMI was further calculated. Each experiment was repeated three times.

[0040] Figure 5The released pesticide curves of the IMI@β-CD / ZIF-8@ST nanopesticide system under α-amylase and different pH conditions are shown. The release rate of IMI varies under different pH conditions. At pH 4, the cumulative release of IMI within 72 hours is 82.7%, while at pH 7 and 9, the cumulative release is only 49.9% and 37.7%, respectively, indicating a clear pH dependence. IMI is released faster under acidic conditions. This may be due to the Zn content in ZIF-8. 2+ The Zn-N coordination bond between the 2-methylimidazolium (2-mim) organic ligand and the 2-methylimidazolium (2-mim) cleaves under acidic conditions, leading to crystal structure disintegration and IMI release. Compared to the absence of α-amylase, the cumulative release rate of IMI after 72 hours was significantly higher (65.9%), indicating that α-amylase disrupts the 1-4 glycosidic bond of β-CD. α-Amylase is widely distributed in the salivary glands and midgut of insects and promotes the rapid release of IMI.

[0041] Test Example 3: Determine the static contact angle to evaluate the wettability of the sample on the leaf.

[0042] After washing, cucumber leaves were firmly fixed onto a glass slide. Then, 5 μL of different samples (IMI@MS, IMI@β-CD / ZIF-8, IMI@β-CD / ZIF-8@S, and commercially available IMI insecticide) were dropped onto the leaf surface. WG A suspension of IMI@β-CD / ZIF-8@ST was prepared. After 10 seconds, the droplet size was recorded using a contact angle meter. Deionized water treatment served as a blank control.

[0043] Figure 6 This graph shows the change in contact angle values ​​of the samples on cucumber leaves over time: The surface of cucumber leaves is hydrophobic, and the contact angle of water on the leaf surface is 96.4°. The contact angle of IMI@β-CD / ZIF-8@S decreases to 78.9°, indicating an increase in the contact area between the Twisted King block structure carrier and the leaf surface. Commercially available IMI insecticide. WG The contact angle reached 75.7°, which is attributed to the presence of a large amount of surfactant in commercial formulations. Further modification with tannic acid (TA) significantly reduced the contact angle of IMI@β-CD / ZIF-8@ST to 69.6°. The smaller contact angle may be due to hydrogen bonding between the polyphenol groups on the carrier and the wax components of the leaf epidermis, enhancing wettability. Experimental results indicate that the suspension of the IMI@β-CD / ZIF-8@ST nanopesticide system prepared in this invention exhibits good wettability on hydrophobic leaf surfaces.

[0044] Test Example 4: Retention Capacity (LHC) of Sample Aqueous Suspension on Leaf Surface Leaf residual chlorophyll (LHC) is another important indicator for pesticide evaluation. The amount of chlorophyll on the leaf surface was determined using a micro-weighing and immersion method. Fresh cucumber leaves were cut into quadrilaterals with a diameter of 2 cm (S is the leaf surface area), and these quadrilaterals were immersed in different samples (IMI@MS, IMI@β-CD / ZIF-8, and commercially available IMI insecticide) using tweezers. WG The leaves were immersed in a suspension (100 μg / mL) of IMI@β-CD / ZIF-8@S and IMI@β-CD / ZIF-8@ST for 20 seconds. The leaves were then quickly removed until no more droplets remained, and finally weighed using an electronic analytical balance (W represents the weight loss of the leaves after immersion and during the initial immersion period). Each test was analyzed three times. LHC was calculated per unit area of ​​leaf as the ratio of W to S.

[0045] Figure 7 The retention amount of the sample suspension on cucumber leaves: water was used as a control, and water, IMI@MS, IMI@β-CD / ZIF-8, and commercially available IMI insecticide were also tested. WG The retention rates of IMI@β-CD / ZIF-8@S and IMI@β-CD / ZIF-8@ST on fresh cucumber leaves were 7.05, 10.89, 12.61, 15.74, 16.95 and 22.16 mg / cm³, respectively. 2 It is worth noting that, although IMI in test 3... WG The contact angle is smaller than that of IMI@β-CD / ZIF-8@S, but the LHC of IMI@β-CD / ZIF-8@S is greater than that of IMI. WG This indicates that the torsion block structure forms a topological effect with the blade surface, resulting in a high LHC. The unique structure allows it to effectively adhere to the blade surface without slipping. The introduction of TA further increases the LHC of IMI@β-CD / ZIF-8@ST (22.16 mg / cm³). 2 This enhancement of LHC may be due to the fact that polyphenol groups can form strong hydrogen bonds with the epidermal wax on the leaf, thereby promoting the adhesion and retention of the carrier on the leaf surface.

[0046] Test Example 5: Study on the rain resistance of the sample Excellent rain resistance directly affects pesticide accumulation on leaves. The adhesion of the nanocarrier to leaves was further evaluated through simulated rain washout tests. Simply put, 1 mL of a 10 mg / mL nanocarrier was used... −1 The IMI@β-CD / ZIF-8@ST suspension was sprayed onto cucumber leaves and allowed to air dry. To simulate rain washing, 10 mL of deionized water was diluted with 0.2 mL of water and sprayed onto cucumber leaves. −1The solution was sprayed evenly onto the treated leaves at a rate of 10 cm, with each leaf tilted at a 60° angle. This washing process was repeated five times. After washing, the leaves were chopped and soaked in 10 ml of water. The leaves were then ultrasonically cleaned for 1 hour to remove any remaining IMI. Finally, the IMI concentration was measured using a UV-Vis spectrophotometer, and the adhesion rate was calculated. WG IMI@spherical mesoporous silica (IMI@MS) and IMI@β-CD / ZIF-8@S were compared using equal amounts of IMI. Simultaneously, the distribution of samples on cucumber leaves after washing experiments (0, 3, and 5 washes) was further observed using scanning electron microscopy. All experiments were performed in triplicate.

[0047] Figure 8 The images show SEM images (a) simulating the adhesion of samples to the leaf surface before and after rainwater washing, and (b) showing the adhesion rate of each sample to the leaf surface before and after washing. Figure 8 As shown in Figure a, due to the size effect at the nanoscale, the three samples extensively covered the leaf surface before rinsing and formed a dispersed distribution according to the leaf texture. After rinsing with water, compared with the IMI@MS and IMI@β-CD / ZIF-8@S treatment groups, a large number of nanoparticles remained on the leaves of the IMI@β-CD / ZIF-8@ST treatment group. It was also observed that the IMI@β-CD / ZIF-8@ST nanocarriers were even distributed in the protruding structures on the leaf surface.

[0048] exist Figure 8 As shown in Figure b, after five simulated rain washes, IMI@MS, IMI@β-CD / ZIF-8@S, and IMI WG The residue rates of the groups were 19.6%, 42.3%, and 38.9%, respectively. Under the same conditions, the residue rate of IMI@β-CD / ZIF-8@ST was still approximately 71.2%. The unique twisted block shape allows the nanocarrier to adhere firmly to the folds of the leaf surface, effectively resisting rain erosion and preventing slippage. Simultaneously, the strong hydrogen bonding between the polyphenolic groups of tannic acid in the carrier and the waxy components on the leaf also contributes to improved adhesion. This dual synergistic effect enhances the adhesion of nanoparticles to plant leaves, significantly reducing pesticide loss.

[0049] Test Example 6: Photostability of the Nanopesticide System IMI@β-CD / ZIF-8@ST Many pesticides are prone to photolysis under ultraviolet radiation, leading to loss of activity. Therefore, improving their photostability is crucial in practical applications. Samples of IMI technical grade pesticide and IMII... WGIMI@β-CD / ZIF-8@S and IMI@β-CD / ZIF-8@ST were diluted with distilled water to a concentration of 200 mg / L. Then, 50 mL of each suspension was placed in a quartz tube and stirred continuously. The quartz tube was then exposed at a distance of 80 cm under a 300 W UV lamp (365 nm wavelength). The distance between the quartz conical flask and the UV lamp was 80 cm. After predetermined time intervals, 2 mL of solution was drawn from each tube and analyzed using UV-vis, measuring its absorbance. The cumulative residual rate (CRR) is the ratio of the absorbance of the sample after irradiation to the absorbance before irradiation. All experiments were performed in triplicate.

[0050] Figure 9 It is the residual rate of IMI in the system after the sample is irradiated with ultraviolet light: pure IMI and IMI WG The degradation was rapid under radiation, with cumulative residue rates of only 18.3% and 26.4% after 300 min, respectively. Encapsulating IMI in a nanocarrier significantly improved its stability. Under the same UV irradiation conditions, the cumulative residue rates of IMI@β-CD / ZIF-8@S and IMI@β-CD / ZIF-8@ST were 53.3% and 88.9%, respectively. This comparison clearly demonstrates that the β-CD / ZIF-8@ST nanocarrier (i.e., the system without drug-loaded IMI) can significantly block UV radiation and prevent IMI degradation.

[0051] Test Example 7: Biosafety Assessment of the Nanopesticide System IMI@β-CD / ZIF-8@ST - Determination of Cell Viability Before practical application, the toxicity of nanopesticides to crops and non-target organisms must be confirmed. The safety of the carrier material is assessed by measuring cell viability. Cell experiments were conducted using the MTT assay to evaluate the cytotoxicity of HepG2 cells. Simply put, HepG2 cells (9 × 10⁻⁶) 3 cells / cm 2 The culture medium was inoculated into 96-well plates. Then, 100 µL of fresh high-glucose medium (purchased from Solarbio) containing different concentrations (0, 12.5, 25, 50, 100, 200 μg / mL) of β-CD / ZIF-8@ST was added to each well. After incubation for 24 h, 10 µL of MTT solution (5 mg / mL) was added, and the plates were incubated at 37°C for another 4 h. The supernatant was discarded, and 100 μL of DMSO was added to each well. Finally, the absorbance was calculated at 490 nm using a microplate reader. Each treatment was performed in triplicate.

[0052] Figure 10The results showed the cell viability of HepG2 cells after co-incubation with samples of different concentrations for 24 h. Even when the carrier concentration reached 200 μg / mL after drug loading, the cells still had a high survival rate (88%), demonstrating that IMI@β-CD / ZIF-8@ST has good biosafety.

[0053] Test Example 8: Biosafety Assessment of Cucumber Seeds Using the Nanopesticide System IMI@β-CD / ZIF-8@ST - Determination of Seed Germination Rate The safety of IMI@β-CD / ZIF-8@ST was investigated by measuring seed germination rate. Different concentrations (25, 50, 100, 200, 400 μg / mL) of IMI@β-CD / ZIF-8@ST aqueous suspensions were prepared for seed germination experiments. Ten cucumber seeds were evenly placed in 5 ml of the corresponding aqueous suspension in a petri dish lined with filter paper. Deionized water served as a blank control. The petri dishes were incubated in a growth chamber for 5 days under the following conditions (25℃, 70% relative humidity, 16:8 light-dark cycle). Germination rate and root length were then calculated. Each experiment was performed three times.

[0054] Figure 11 The images show the germination rate and root length of seeds treated with the IMI@β-CD / ZIF-8@ST nanopesticide system (a) and corresponding digital photographs of cucumber seed germination (b). The figures show that the cucumber germination rate reached 90%, and the average root length exceeded 6 cm, indicating that the carrier had no effect on seed germination. Figure 11 a). Digital photographs of seed germination further support this view. Figure 11 (b) In summary, IMI@β-CD / ZIF-8@ST exhibits good biocompatibility as a pesticide carrier.

[0055] Test Example 9: Absorption and translocation of IMI@β-CD / ZIF-8@ST / FITC in different parts of the plant To evaluate whether the nanocarrier can be absorbed and transported by plants. Tobacco was used as the target plant in hydroponics, and tobacco roots and leaves were exposed to FITC-labeled IMI@β-CD / ZIF-8@ST. The preparation process is as follows.

[0056] IMI@β-CD / ZIF-8@ST (100 mg) was immersed in an ethanol solution (10 mL) containing FITC (5 mg). The hydroxyl groups in the tannic acid interacted with the isothiocyanate group in the FITC to label the tannin. After reacting overnight, FITC-labeled IMI@β-CD / ZIF-8@ST (denoted as IMI@β-CD / ZIF-8@ST / FITC) was obtained.

[0057] To verify the translocation of nanocarriers to other tissues via leaves, 5 mL of IMI@β-CD / ZIF-8@ST / FITC suspension (1 mg / mL) was uniformly sprayed onto tobacco leaves. Tobacco seedlings were transplanted into Hoagland nutrient solution (10 mL, 1 mg / mL) to promote root absorption and distribution. Hoagland nutrient solution was used as a control in the experimental plants. After treatment, the plants were cultured for 24 h under specific conditions (25°C, 70% humidity, 16 h / 8 h light / dark), and the distribution of IMI@β-CD / ZIF-8@ST / FITC in various tissues was detected using a 488 nm confocal laser scanning microscope (CLSM).

[0058] Figure 12 These are fluorescence visualization images of different parts of tobacco plants (leaves, stems, and roots) after 24 hours of foliar spraying and root application of FITC (a, b) and IMI@β-CD / ZIF-8@ST / FITC (c, d). The fluorescence signal was weaker on the leaves of FITC-treated plants 24 hours after spraying, while no fluorescence signal was detected on the stems and roots. Figure 12 a). For example Figure 12 As shown in b, for plants treated with FITC under root application conditions, fluorescence signals were observed only in the roots. The results indicate that FITC is absorbed by the plant but not translocated. In contrast, the FITC-labeled IMI@β-CD / ZIF-8@ST nanocarriers, whether applied to leaves or roots, were effectively absorbed by tobacco seedlings and subsequently transported to other tissues. Figure 12 c and Figure 12 d). It is evident that the nano-pesticide system IMI@β-CD / ZIF-8@ST can realize the transport and distribution of pesticides within plants, thereby improving the effective utilization rate of pesticides.

[0059] Test Example 10: Insecticidal Activity of the Nanopesticide System IMI@β-CD / ZIF-8@ST The purity of IMI and commercially available IMI particles (IMI) were determined using the leaf immersion method. WG The insecticidal activity of IMI@β-CD / ZIF-8@ST against the 3rd instar diamondback moth was investigated. IMI and IMI@β-CD / ZIF-8@ST were directly diluted with deionized water. WGIMI@β-CD / ZIF-8@ST solutions were used, with IMI concentrations of 250, 125, 62.5, 31.25, and 15.625 mg / L, respectively. Fresh cabbage leaves were cut into small pieces, soaked in the corresponding test suspensions for 10 minutes, and then air-dried. The treated leaves were transferred to petri dishes containing 10 third-instar diamondback moths, with each group repeated three times. The plants were incubated at 25°C, 70% relative humidity, and a 16 / 8 light / dark photoperiod for 48 h, and the mortality rate was recorded.

[0060] In the UV irradiation experiment, effective IMI concentrations of 250 mg L were respectively... −1 IMI, IMI WG The effects of IMI@β-CD / ZIF-8@ST suspension on leaves before and after UV irradiation were evaluated. After irradiation of the three sample solutions for 0, 20, 40, 80, 120, and 180 min, respectively, the leaves were immersed in the treated solutions for 10 min, then removed and dried. Insecticidal activity was determined using the above method, and the degree of damage caused by the diamondback moth to the leaves immersed in the three sample solutions at different UV irradiation times was photographed and recorded.

[0061] Figure 13 These are insecticidal activity curves of nano-loaded drug delivery systems at different concentrations. The corresponding median lethal concentration (LC50) was calculated using SPSS statistical software. 50 LC50 values ​​for IMI@β-CD / ZIF-8@ST against diamondback moth 50 The value was 30.32 mg / L, lower than IMI (44.54 mg / L) and IMI. WG LC50 of (34.85 mg / L) 50 Values ​​are detailed in Table 1. This indicates that IMI@β-CD / ZIF-8@ST has a higher insecticidal effect than commercially available pesticides. IMI@β-CD / ZIF-8@ST has excellent leaf wettability and good liquid retention, thus depositing more pesticide active ingredients on the fed leaves, thereby killing the diamondback moth.

[0062] Table 1. Results of toxicity tests of three samples against diamondback moth larvae. Figure 14 It shows IMI, IMI WG The mortality rates of diamondback moths were investigated using three samples: IMI@β-CD and ZIF-8@ST, under different UV irradiation times. After 120 min of irradiation, the mortality rates of IMI solution and IMI... WGThe insecticidal effect of the two methods decreased significantly, with mortality rates of 23.3% and 26.6%, respectively, indicating that IMI was rapidly decomposed under ultraviolet light. In contrast, the mortality rate of IMI@β-CD / ZIF-8@ST remained at 80% after the same period of irradiation. This demonstrates the resistance of the carrier to ultraviolet photodegradation, and IMI embedded in the β-CD / ZIF-8@ST carrier exhibits excellent photostability and insecticidal efficacy.

[0063] Figure 15 The following are given: IMI@β-CD / ZIF-8@ST(1), IMI WG Photographs of leaf damage after UV irradiation (2) and (3) at 0, 20, 40, 80, and 120 mins, as shown by IMI (3). Figure 15 As can be seen, the leaves treated with IMI@β-CD / ZIF-8@ST showed less damage at different time points, while those treated with IMI and IMI... WG The treated leaves showed severe erosion. This demonstrates that IMI@β-CD / ZIF-8@ST, when adhered to the leaves, enhances both insecticidal and leaf-protecting effects.

Claims

1. A method for preparing a highly adhesive and responsively releasing nanopesticide system based on β-CD / ZIF-8@ST, characterized in that, Includes the following steps: 1) The metal ligand was mixed with an aqueous solution containing 2-methylimidazole, hexadecyltrimethylammonium bromide and β-cyclodextrin, and allowed to stand at room temperature for 2-4 hours. After centrifugation, washing and drying, the β-CD / ZIF-8 carrier doped with β-cyclodextrin was obtained. 2) Dissolve the β-CD / ZIF-8 obtained in step 1) in a mixed solution composed of surfactant, urea and deionized water, add an organic solvent containing tetraethyl silicate, and then heat to 60-80℃ for 16-20h with stirring. After centrifugation, washing and drying, the nanocarrier β-CD / ZIF-8@S with a twisted block structure is obtained. 3) Disperse the β-CD / ZIF-8@S obtained in step 2) in an aqueous solution of the insecticide imidacloprid IMI, stir in the dark at room temperature for 24-48 h, centrifuge and dry to obtain the β-CD / ZIF-8@S nano-pesticide system IMI@β-CD / ZIF-8@S loaded with insecticide; 4) Disperse the IMI@β-CD / ZIF-8@S obtained in step 3) in water, add a tannic acid alkaline solution with pH 7-9, stir and react at room temperature for 3-10 min, centrifuge and wash to obtain the product; In step 1), the metal ligand is zinc nitrate or zinc acetate; In step 2), the surfactant is hexadecyltrimethylammonium bromide, and the mass ratio of β-CD / ZIF-8 to the surfactant is 1:0.8-1.

2.

2. The preparation method of the highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST as described in claim 1, characterized in that, In step 1), the molar ratio of the metal ligand to 2-methylimidazole is 1:9-12.

3. The preparation method of the highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST as described in claim 1, characterized in that, In step 1), the mass ratio of the metal ligand to hexadecyltrimethylammonium bromide is 160-170:1; the mass ratio of the metal ligand to β-cyclodextrin is 1-3:

1.

4. The preparation method of the highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST as described in claim 1, characterized in that, In step 2), the mass ratio of β-CD / ZIF-8 to urea is 1:0.6-0.8; the mass-volume ratio of β-CD / ZIF-8 to tetraethyl silicate is 1g:0.6-1.6ml.

5. The preparation method of the highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST as described in claim 1, characterized in that, In step 2), the organic solvent is a mixed solution of cyclohexane and isopropanol.

6. The preparation method of the highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST as described in claim 1, characterized in that, In step 3), the mass ratio of β-CD / ZIF-8@S to the insecticide imidacloprid is 1:0.5-3.

7. The preparation method of the highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST as described in claim 1, characterized in that, In step 4), the mass ratio of IMI@β-CD / ZIF-8@S to tannic acid is 1:0.4-0.

9.

8. A highly adhesive and responsive release nanopesticide system based on β-CD / ZIF-8@ST prepared by any one of claims 1 to 7.

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