Preparation and use of a controlled release carrier for pesticides

Abstract

The application relates to the technical field of pesticide controlled release, in particular to a preparation and application of a pesticide controlled release carrier, which comprises the following raw materials: a natural polymer matrix, a temperature-sensitive material, a light-heat material, an acid solvent, an alkali solvent and a pesticide. Chitosan (CS) is used as a natural polymer material which is widely sourced, non-toxic and naturally degradable, the spherical gel has the advantages of simple preparation, controllable particle size and rich surface chemical bonds, and is widely applied to drug adsorption and delivery. The introduction of nanoparticles can endow the polymer hydrogel with unique functional characteristics. Diamond nanodiamond (DND) is a nanoscale carbon allotrope which is composed of a sp3 carbon diamond core and a reconstructed sp2 carbon surface layer, can absorb light in the ultraviolet, visible and near-infrared regions in the form of phonon scattering / lattice vibration and convert it into heat, and has excellent photo-thermal performance. Poly-N-isopropyl acrylamide (PNIPAm) is a temperature-sensitive material which is in a sol state at room temperature and is converted into a gel state when close to body temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pesticide controlled release, in particular to a pesticide controlled release carrier and its application. BACKGROUND

[0002] The global population continues to grow, and it is estimated that by 2050 the entire agricultural product will need to feed billions of people. The use of pesticides can increase crop yields, but the actual utilization rate is not higher than 0.1%, and pesticides are prone to loss into the air, water and soil, posing a threat to human health and the environment. The emergence of natural polymer pesticide intelligent controlled release systems can enable the carrier to respond to environmental stimuli (such as pH, temperature, etc.), extend the pesticide application period, reduce the amount of pesticide used, and thus improve the utilization efficiency of pesticides. Poly-N-isopropyl acrylamide (PNIPAm) is a temperature-sensitive polymer material. Due to the presence of hydrophilic amide groups (-CONH-) and hydrophobic isopropyl groups (-CH(CH3)2) in the macromolecular chain, PNIPAm exhibits opposite temperature sensitivity: PNIPAm solution is in sol state at room temperature and is converted into gel state near body temperature. Therefore, heat stimulation can be applied to change the hydrophilic and hydrophobic properties of PNIPAm to regulate drug release. In recent years, such thermosensitive polymer materials have been widely used in drug controlled release, chemical sensors and biochemical separation fields.

[0003] However, in practical applications, long-term control of medium temperature is not feasible. Among the externally applied stimuli, light is an attractive trigger source due to its high spatiotemporal controllability, non-invasiveness and remote operation convenience. Therefore, a large number of research works have been carried out to develop on-demand drug release systems with photo-thermal response. In such systems, the selection of a suitable photo-thermal reagent to absorb and convert light energy into heat energy is a key consideration. Compared with PDA and nanometer magnetite particles, carbon-based material DND is a more ideal choice for photo-thermal absorbers. First, it can mechanically strengthen the gel network structure and adjust the elasticity of the gel, and at the same time, it has excellent biocompatibility. In addition, the excellent thermal conductivity of DND is beneficial to temperature-responsive gel microspheres, because faster heat conduction can promote faster response of the composite material. Most importantly, DND has high light absorption in the full wave band, which lays the foundation for its light responsiveness.

[0004] In this paper, a kind of light-heat response type semi-interpenetrating network structure composite microspheres material CS / PNIPAm / DND is designed and prepared by using DND as light-heat material. As the main component of the light-heat response system, CS, PNIPAm and DND play different roles in the system. Specifically, CS acts as an elastic skeleton in the intelligent response system, providing excellent mechanical properties to the intelligent response system, DND has excellent light-heat performance, can absorb sunlight, and the temperature change caused by light can be sensed by temperature sensitive material PNIPAm and induced to occur structural transformation, thereby adjusting the release of drugs. Therefore, when the prepared intelligent response composite microspheres are tested as drug release carriers, they can be controlled by light-heat to achieve on-demand drug release. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present application is to provide a preparation and application of a pesticide controlled release carrier. A CS / PNIPAm / DND composite microsphere is designed and prepared by using widely available and environmentally friendly natural polymer chitosan as the carrier, poly (N-isopropyl acrylamide) (PNIPAm) as the temperature-sensitive material, and nano-diamond (DND) as the light-heat material, and the plant growth hormone indole butyric acid (IBA) is loaded. The preparation method is simple, the carbon-based light-heat material can maximize the utilization of solar energy, and the presence of light-heat material and temperature-sensitive material makes the composite microspheres sensitive to light and temperature, which is beneficial to the controlled release of light and temperature sensitive pesticides and can effectively improve the utilization rate of pesticides.

[0006] In order to achieve the above purpose, the technical scheme is adopted.

[0007] The present application provides a preparation and application of a pesticide controlled release carrier, which comprises the following raw materials: a natural polymer matrix, a temperature-sensitive material, a light-heat material, an acid solvent, a base solvent and a pesticide.

[0008] Preferably, the natural polymer matrix is chitosan.

[0009] Preferably, the temperature-sensitive material is poly (N-isopropyl acrylamide).

[0010] Preferably, the light-heat material is nano-diamond.

[0011] Preferably, the acid solvent is acetic acid solution.

[0012] Preferably, the base solvent is sodium hydroxide solution.

[0013] Preferably, the pesticide is indole butyric acid.

[0014] Preferably, the concentration of the acetic acid solution is 2% (v / v), and the concentration of the sodium hydroxide solution is 2 mol / L.

[0015] (ii) Preparation of a pesticide controlled release carrier and its application, comprising the following steps:

[0016] Step 1, N-isopropyl acrylamide (NIPAm) monomer is added to deionized water, and stirred under nitrogen protection until it is completely dissolved;

[0017] Step 2, potassium persulfate (KPS) and N, N, N', N'-tetramethyl ethylenediamine (TEMED) are added to the NIPAm solution;

[0018] Step 3, N2 is passed into the above mixture for a period of time, and then it is placed at room temperature and dried to obtain PNIPAm;

[0019] Step 4, acetic acid solution is prepared;

[0020] Step 5, CS is dissolved in the acetic acid solution;

[0021] Step 6, a certain amount of PNIPAm and DND are sequentially added to the chitosan acetic acid solution and stirred uniformly;

[0022] Step 7, the above mixed solution is dropped into NaOH solution, solidified, filtered with a metal mesh screen to obtain CS / PNIPAm / DND microspheres;

[0023] Step 8, drug loading is performed by embedding method, and the mixed solution in step 6 is uniformly blended with IBA before the microspheres are formed.

[0024] Preferably, in step 3, the N2 passing time is 10 min~30 min.

[0025] Preferably, in step 4, the concentration of the acetic acid solution is 2% (v / v).

[0026] Preferably, in step 6, the concentration of the DND is 2 mg / mL; and the mass ratio of PNIPAm to CS is 1:4~1:2.

[0027] Preferably, in step 7, the concentration of the NaOH solution is 2 mol / L; and the solidification time is 30 min~180 min.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] In the present application, CS is a widely available, non-toxic, naturally degradable natural polymer material, and its spherical gel has the advantages of simple preparation, controllable particle size, and rich surface chemical bonds, and is widely used in drug adsorption and delivery. The introduction of nanoparticles can endow the polymer hydrogel with unique functional properties. Diamond nanoparticles (DND) are a kind of nanoscale carbon allotropes, which have sp 3Carbon-diamond core and reconstructed sp 2 The carbon surface layer has excellent photothermal properties, which can absorb light in the ultraviolet, visible and near-infrared regions in the form of phonon scattering / lattice vibration and convert it into heat. Poly-N-isopropylacrylamide (PNIPAm) is a temperature-sensitive material that is in a sol state at room temperature and is converted into a gel state near body temperature. Therefore, the temperature change caused by the photothermal material can be sensed by the temperature-sensitive material, which changes the hydrophilicity of PNIPAm and adjusts the drug release.

[0030] In the present application, after the introduction of PNIPAm, the light transmittance of the CS / PNIPAm solution changes obviously with temperature, and the CS / PNIPAm solution has excellent temperature-sensitive properties of PNIPAm.

[0031] In the present application, the release of the CS / PNIPAm / DND microspheres to the pesticide IBA has temperature and light sensitivity. When the temperature is lower than the LCST, the cumulative release rate of IBA at 20°C is 14.6%, and after the temperature is increased to 25°C, the cumulative release rate of IBA increases slightly to 18.4%. However, at 40°C, the cumulative release rate increases significantly to 40.4%. When the system is given intermittent light, the drug release rate shows an "on-off" trend with the light on and off. BRIEF DESCRIPTION OF DRAWINGS

[0032] The present application will be further described in detail below in combination with the drawings and specific examples.

[0033] Figure 1 The figure is for the determination of the LCST of CS / PNIPAm;

[0034] Figure 2 The figure is the SEM-EDS graph of the sample, wherein figure (a, d) is the CS microsphere; figure (b, e) is the CS / PNIPAm microsphere; figure (f) is PNIPAm; figure (c, g) is the SEM graph of the CS / PNIPAm / DND microsphere; figure (h) is the picture of the microsphere; figure (i) and (j) are the EDS graphs of CS / PNIPAm and CS / PNIPAm / DND, respectively;

[0035] Figure 3 The figure is the infrared spectrum graph;

[0036] Figure 4 The figure is the TGA graph of the sample;

[0037] Figure 5 The figure is the Zeta potential graph of the sample;

[0038] Figure 6Figure is the photothermal performance diagram of the sample; wherein, figure (a) is the UV-visible diffuse reflectance spectrum of CS / PNIPAm, DND and CS / PNIPAm / DND; figure (b) is the temperature change of water, DND and CS / PNIPAm / DND aqueous solution (2 mg / mL) under light; figures (c-d) are the temperature change of CS, CS / PNIPAm and CS / PNIPAm / DND microspheres at different times and the corresponding infrared thermal imaging diagram; figure (e) is the temperature change curve of CS / PNIPAm / DND microspheres under different light intensities; figure (f) is the photothermal stability of CS / PNIPAm / DND aqueous solution;

[0039] Figure 7 Figure is the release curve of IBA in deionized water at different temperatures (20, 25 and 40℃) and the release model fitting at different temperatures; wherein, (b) first-order model; (c) Korsmeyer-Peppas model; (d) Higchi model;

[0040] Figure 8 Figure is (a) the IBA release of CS / PNIPAm / DND composite microspheres (2.0 mg / mL DND) under intermittent light and no light, (b) the corresponding temperature change diagram;

[0041] Figure 9 Figure is the growth diagram of pea seeds under different light and different concentration treatments. Embodiment

[0042] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application.

[0043] The present application uses natural polymer chitosan as a carrier, PNIPAm as a temperature-sensitive material, and DND as a photothermal material to prepare a pesticide controlled release carrier by alkali gel method, and investigates the influence of temperature and light on the release performance of pesticides, and finally uses it for pea growth experiment. The specific content is as follows:

[0044] A preparation method of a pesticide controlled release carrier, comprising the following steps: Example

[0045] Step 1, 0.4 g of CS is dissolved in 20 mL of 2% (v / v) acetic acid solution, and a certain amount of PNIPAm and 0.04 g of DND are added in sequence to prepare a suspension with a DND content of 2 mg / mL;

[0046] Step 5, after the suspension in step 4 was stirred thoroughly and left to stand to remove the air bubbles, it was dropped into 2 mol / L NaOH solution with a syringe to form gel beads, which were cured at room temperature;

[0047] Step 6, the microspheres were then filtered with a metal mesh, washed with deionized water to obtain CS / PNIPAm / DND microspheres. Example

[0048] Step 1, 0.24 g of N-isopropyl acrylamide (NIPAm) monomer was weighed into 5 mL of deionized water and stirred under nitrogen protection until it was completely dissolved;

[0049] Step 2, 5 mg of potassium persulfate (KPS) and 5 μL of N, N, N', N'-tetramethyl ethylenediamine (TEMED) were added to step 1, and N2 was passed for 10 min;

[0050] Step 3, the linear homopolymer in step 2 was left to stand at room temperature for 24 h and dried to obtain PNIPAm;

[0051] Step 4, 0.4 g of CS was dissolved in 20 mL of 2% (v / v) acetic acid solution, and a certain amount of PNIPAm was added;

[0052] Step 5, after the suspension in step 4 was stirred thoroughly and left to stand to remove the air bubbles, it was dropped into 2 mol / L NaOH solution with a syringe to form gel beads, which were cured at room temperature;

[0053] Step 6, the microspheres were then filtered with a metal mesh, washed with deionized water to obtain CS / PNIPAm / DND microspheres.

[0054] Step 7, the drug loading method adopts the embedding method, and the specific operation is to uniformly mix with the solution before step 6. Example

[0055] Step 1, 0.24 g of N-isopropyl acrylamide (NIPAm) monomer was weighed into 5 mL of deionized water and stirred under nitrogen protection until it was completely dissolved;

[0056] Step 2, 5 mg of potassium persulfate (KPS) and 5 μL of N, N, N', N'-tetramethyl ethylenediamine (TEMED) were added to step 1, and N2 was passed for 10 min;

[0057] Step 3, the linear homopolymer in step 2 was left to stand at room temperature for 24 h and dried to obtain PNIPAm;

[0058] Step 4, 0.4 g CS was dissolved in 20 mL 2% (v / v) acetic acid solution, and a certain amount of PNIPAm and 0.04 g DND were added to prepare a suspension with a DND content of 2 mg / mL;

[0059] Step 5, after the suspension in Step 4 was fully stirred and left to remove air bubbles, it was dropped into a 2 mol / L NaOH solution using a syringe to form gel beads, which were cured at room temperature;

[0060] Step 6, the microspheres were then filtered with a metal mesh and washed with deionized water to obtain CS / PNIPAm / DND microspheres;

[0061] Step 7, the drug loading method used an embedding method, which was specifically uniformly mixed with the solution before Step 6.

[0062] The activated adsorbents of dredged sediment prepared in Examples 1, 2, and 3 and the dried samples of the originally collected dredged sediment were characterized and analyzed for performance, as follows:

[0063] Thermal stimuli can change the optical transmittance by changing the balance of hydrophilicity and hydrophobicity. Therefore, according to the change in transmittance with the temperature of the polymer solution, the low critical solution temperature was studied using ultraviolet-visible spectroscopy, and a graph of temperature versus transmittance percentage was plotted, with the inflection point being the LCST.

[0064] As can be seen from Figure 1 , as the temperature increased from 20 to 35℃, the CS solution remained transparent, with a transmittance of more than 90%. However, the CS / PNIPAm solution changed from a clear solution state to a turbid state as the temperature increased. This is because the PNIPAm chains in the composite contract dramatically as the temperature increases, making the solution opaque. This indicates that the LCST of CS / PNIPAm is ~33℃.

[0065] The surface morphology of the pesticide controlled-release carrier obtained in Example 1 was observed using a cold field scanning electron microscope, and the results are shown in Figure 2 .

[0066] As can be seen from Figure 2 (h), the size of the three types of microspheres prepared was 3-4 mm. Among them, the CS and CS / PNIPAm microspheres were similar in color, appearing white. After adding DND, the color of the CS / PNIPAm / DND microspheres changed to black, and after drying, the microspheres showed obvious volume shrinkage, with a size of 1-2 mm. To further observe the differences in the morphology of the microspheres, SEM was used to observe the samples at a higher magnification, as shown in Figure 2(a-c), it can be seen that the surfaces of CS, CS / PNIPAm and CS / PNIPAm / DND samples all present irregular shape. The cross-sections of the samples were tested and it was found that the cross-section of pure CS microspheres is relatively smooth Figure 2 (d), after the addition of the temperature-sensitive material PNIPAm, the cross-section has flaky wrinkles Figure 2 (e), which is due to the lamellar structure of PNIPAm Figure 1 . CS / PNIPAm / DND has a similar cross-sectional morphology as CS / PNIPAm Figure 2 (g), through the EDS test of CS / PNIPAm and CS / PNIPAm / DND, it was found that the carbon content increased from 52.5% to 61.3%, which proved the successful compounding of DND and CS / PNIPAm.

[0067] FTIR spectra reflect the reaction between DND / YS-CS composites, such as Figure 3 . Due to the presence of sodium hydroxide residue on the surface of the microspheres, peaks at 1448 and 866 cm -1 appeared in the spectra of CS, CS / PNIPAm and CS / PNIPAm / DND, which are characteristic peaks of sodium hydroxide. The peak near 3382 cm -1 of CS is the stretching vibration of -OH and the stretching vibration of N-H of -NH2. The peaks at 1652 and 1409 cm -1 are the bending vibration of -NH2 and -OH, respectively, while 906 cm -1 corresponds to the stretching vibration of C-O on the skeleton. The asymmetric stretching of -CH3 of PNIPAm, the stretching of secondary amide C=O and the deformation vibration of secondary amide N-H were observed at 2971, 1652 and 1540 cm -1 , respectively, which is consistent with the previous research results of PNIPAm. The absorption peaks of CS / PNIPAm are consistent with the characteristic peaks of the two monomers, indicating that the CS / PNIPAm microspheres are composed of CS and PNIPAm. The characteristic peaks of DND were observed at 3421, 1637 and 1049 cm -1 , which are the stretching vibration absorption peaks of -OH, C-O and graphite C-C, respectively. The stretching vibration peak of -OH was observed to move slightly from 3455 cm -1 in CS / PNIPAm to 3465 cm -1 in CS / PNIPAm / DND, confirming that hydrogen bonding is the main interaction between DND and CS / PNIPAm. These results strongly prove the successful synthesis of the composite material.

[0068] The thermal stability of the samples was studied by TGA, as shown in Figure 4It can be seen that DND has good thermal stability, with only a slight mass loss of about 10% at 500°C; in the high temperature range of 500-750°C, the mass loss is obvious due to the oxidation of carbon rings. The decomposition of PNIPAm undergoes two processes: the first process occurs between 170°C and 340°C, due to the cleavage of the side chains and cross-linked parts of the PNIPAm polymer layer, resulting in a mass loss of about 5% of the composite microspheres; in the second process, from 340°C to 600°C, the mass loss of the composite microspheres is 54.5%, which is due to the destruction of the polymer skeleton at high temperature. In contrast, the CS / PNIPAm / DND composite has two obvious mass losses in the same temperature range. The second mass loss temperature range is consistent with DND (600-750°C), which can be determined to be from the oxidation of carbon rings. The mass loss in the temperature range of 200-500°C is mainly due to the oxidative decomposition of the polymer PNIPAm.

[0069] Zeta potential analysis was further used to evaluate the surface characteristics of CS / PNIPAm / DND, such as Figure 5 The average surface charge of CS is -18.03 mV, which is due to the residual NaOH neutralizing the -NH 3+ groups on the CS molecular chain, reducing the charge of CS to a negative value. However, the zeta potential value of CS / PNIPAm drops to -19.87 mV, lower than that of pure CS, indicating that the PNIPAm molecules containing negative functional groups have successfully combined with CS. The potential value of DND is 33.0 mV, and the zeta potential value of the composite after adding DND changes to -14.93 mV, proving the combination of CS / PNIPAm and DND.

[0070] The light absorption performance of DND, CS / PNIPAm and CS / PNIPAm / DND microspheres was reflected by ultraviolet-visible-near infrared diffuse reflectance spectroscopy, and the results are shown in Figure 6 (a). CS / PNIPAm has relatively low light absorption in the visible and infrared regions, while the photothermal material DND has high absorption in the full spectrum (250-2500 nm), indicating that it can be used as an efficient light absorber. After compounding DND with CS / PNIPAm, the CS / PNIPAm / DND composite microspheres also show high light absorption performance in the entire ultraviolet-visible-near infrared region, indicating that the introduction of DND can significantly improve the light absorption capacity of CS / PNIPAm / DND microspheres, laying a foundation for their responsive drug release.

[0071] 1) Experimental method: To test the photothermal performance of the composite microspheres, 3 mL of 2 mg / mL DND and CS / PNIPAm / DND suspensions were placed in a cuvette and irradiated for 10 min, and then the temperature change with time was compared with that of the same volume of water solution within 10 min of irradiation. In addition, a certain amount of CS, CS / PNIPAm and CS / PNIPAm / DND wet spheres were evenly covered on a 6 cm diameter petri dish, and then irradiated with a 100 mW / cm 2 of xenon lamp, while the sample temperature at each fixed time point was monitored with an infrared thermal imager. Finally, the temperature change of CS / PNIPAm / DND composite microspheres at different light intensities (50, 100, 150 mW / cm 2 ) for a fixed time and the photothermal stability of the composite material were discussed. Specifically as follows:

[0072] 2) Experimental results: To study the photothermal conversion performance of the composite microspheres, pure water, 2.0 mg / mL DND solution and CS / PNIPAm / DND solution were irradiated for 10 minutes, respectively. As shown in Figure 6 (b), after 10 minutes of irradiation, the temperature of pure water only rose from 23.6°C to 26.7°C, while the temperature of DND solution rose by 8.2°C under the same conditions. The temperature of CS / PNIPAm / DND aqueous solution was similar to that of DND, but slightly lower, which confirmed that the addition of DND to the CS / PNIPAm / DND system could effectively absorb light energy and convert it into heat energy.

[0073] From Figure 6 (c) and (d), it can be seen that the temperature of the microspheres tends to be stable after 10 minutes of exposure to light. Under the same irradiation conditions, the temperature of CS / PNIPAm / DND beads rose by 12.5°C, while the temperature of CS and CS / PNIPAm microspheres without DND only rose by 6.4 and 8.2°C, so CS / PNIPAm / DND has good light-heat conversion ability under irradiation. Next, the temperature change of CS / PNIPAm / DND solution under different irradiation intensities (50, 100, 150 mW / cm 2 ) was tested (as shown in Figure 6 (e)), and it was found that the temperature of CS / PNIPAm / DND solution rose with the increase of irradiation intensity. In addition, Figure 6 (f), the temperature change observed in 5 irradiation on / off cycles proves that CS / PNIPAm / DND has good photothermal stability.

[0074] Experimental method:

[0075] To realize the temperature-induced drug release, a certain amount of CS / PNIPAm / DND composite microspheres were placed in 15 mL water, and drug release experiments were carried out at different temperatures (20, 25 and 40°C). Finally, the absorbance of the release solution at 281 nm was measured by a UV-visible spectrophotometer, the IBA concentration was calculated according to the IBA standard curve, and the cumulative release rate (RP) of the drug was calculated

[0076] Experimental results:

[0077] From Figure 7 As can be seen from (a), the cumulative release rate of IBA of the composite microspheres increases with the increase of temperature. At 20°C, IBA is released slowly, and the cumulative release rate is 14.6% after 10 h. At 25°C, the cumulative release rate increases slightly to 18.4%. The low drug release rate is due to the presence of PNIPAm. When the external temperature is lower than the LCST (33°C) of PNIPAm, the PNIPAm chain is in a relaxed state, the composite sphere structure is loose, and IBA is slowly released into the solution with the invasion of water molecules. When the temperature rises to 40°C, the cumulative release rate reaches 40.4%. The cumulative release amount of the drug before and after the phase transition can be increased by about 20%. This is because when the temperature rises above the LCST of PNIPAm, the exposed hydrophobic methyl groups in PNIPAm will shrink to form a heat-sensitive chain. At the same time, the shrinkage of the temperature-sensitive material makes the surface of the composite microspheres more porous, promoting the free outflow of IBA molecules in the pores of the composite skeleton.

[0078] To determine the temperature-responsive release mechanism of IBA in the CS / PNIPAm / DND composite microspheres, we analyzed the release data according to the most commonly used first-order model, Korsmeyer-Peppas and Higuchi model, and the correlation coefficient (R 2 ) was used as the main factor to select the best fitting model. As shown in Table 1, the R 2 of the Korsmeyer-Peppas model of the three samples is higher than that of the other two models, indicating that the Korsmeyer-Peppas model has a good fitting effect on the experimental data. In the Korsmeyer-Peppas model, the release index n is an important parameter for drug release of the drug-loaded microspheres. The release index of the Korsmeyer-Peppas model of the three samples is 0.43<n<0.89, which indicates that the release mode of the CS / PNIPAm / DND composite microspheres conforms to irregular diffusion, and the release of the drug is a synergistic effect of diffusion and matrix swelling. Since the composite microspheres have a cross-linked network structure, the release of IBA is also related to the relaxation of CS and PNIPAm chains.

[0079] Experimental method:

[0080] To determine the light-responsive drug release ability of CS / PNIPAm / DND composite microspheres, a certain amount of composite material was placed in 15 mL water, and intermittent irradiation was performed under a certain light intensity, then the release liquid was taken out, 3 mL of release liquid was removed every hour with a pipette, and immediately the same volume of deionized water was added for further irradiation. Finally, the absorbance of the release liquid at 281 nm was measured by UV-visible spectrophotometer, and the cumulative release rate of the drug was calculated according to the IBA standard curve.

[0081] Experimental results:

[0082] Compared with the temperature-based intelligent response release system, the photothermal effect has the greatest practical application potential because it can directly use clean and abundant natural sunlight as a trigger source. In this system, the excellent photothermal performance of DND endows the composite microspheres with photosensitivity. As shown in Figures 1 to 4 Without light, IBA is slowly released from the composite spheres by diffusion, and the cumulative release amount of IBA is only 17.73% in 8.5 hours. When the composite system is given intermittent light, the cumulative release amount of IBA from the composite microspheres can reach 30.43%. Specifically, under the initial 1 h of unlighted conditions, the medium temperature stabilizes at ~24℃, and IBA slowly diffuses into the solution (0-5.67%). Half an hour after turning on the light, the medium temperature rises to 33.8℃, and the release of IBA increases significantly (5.67-11.38%). When the light is turned off (1.5-2.5 h), the medium temperature falls back to 23.4℃, and the drug release slows down. The subsequent drug release trend is similar, and the drug release rate shows an "on-off" change trend with the light on and off.

[0083] Experimental method:

[0084] As a plant growth hormone, IBA plays a role by affecting the plant growth process and coordinating adventitious roots. In order to investigate the practical application effect of DND / CS-based semi-IPN composite material, this section applies CS / PNIPAm / DND drug-containing microspheres to the rooting and germination experiments of peas, and evaluates the ability of CS / PNIPAm / DND composite microspheres for intelligent light-controlled release of IBA for plant growth by measuring the length of pea sprouts and roots.

[0085] Experimental results:

[0086] First, the complete and uniform size of the pea seeds were selected, and then soaked in pure water or solutions containing CS / PNIPAm / DND composite microspheres with concentrations of 26, 260, and 520 mg / L for 9 h, respectively. Meanwhile, another group of composite microspheres with a concentration of 26 mg / L was selected to soak the peas in water. During the soaking process, two xenon lamp lightings were applied, each for 30 min. After soaking, the seeds were washed with distilled water several times and placed on the surface of a petri dish lined with wet filter paper. Each dish contained 10 pre-soaked pea seeds, and water was added as needed to keep the filter paper moist. The root length and shoot length of the seeds were measured after 0, 1, 3, 5, and 7 days, and the average values were recorded.

[0087] The growth activity of drug-containing CS / PNIPAm / DND microspheres on peas is shown in Figure 4 As can be seen, after 7 days of growth in natural conditions, the root length and shoot length of pea seeds treated with different concentrations of drug-containing microspheres (26, 260, and 520 mg / L) increased with increasing concentration of drug-containing microspheres. The root length increased from 2.04 to 2.86 cm, and the shoot length increased from 1.32 to 2.19 cm. When intermittent light was applied to pea seeds with a concentration of 26 mg / L, the root length and shoot length were significantly higher than those of pea seeds without light treatment. This is because light can promote the structural phase transition of temperature-sensitive materials inside the CS / PNIPAm / DND microspheres, promote the release of IBA, and thus promote seed germination and root growth.

[0088] In summary, among the factors affecting the drug release performance of CS / PNIPAm / DND microspheres, such as LCST, photo-thermal properties, etc., we can summarize that:

[0089] (1) The pre-prepared PNIPAm forms a semi-interpenetrating network structure with DND and CS. The presence of DND gives the system good photo-thermal properties, and PNIPAm provides temperature-sensitive properties for the intelligent release system. SEM, FTIR, Zeta potential, and TGA analysis results prove the successful synthesis of the material.

[0090] (2) The turbidity experiment shows that the LCST of CS / PNIPAm is ~33°C. When the system temperature is higher than 33°C, the opacity of CS / PNIPAm solution increases, and the PNIPAm molecular chain changes from random coil conformation to coiled globular.

[0091] (3) UV-Vis diffuse reflectance spectroscopy proves that DND gives CS / PNIPAm material the ability to absorb light in the full wave band, and CS / PNIPAm / DND composite microspheres retain the excellent light-thermal conversion ability of DND. The temperature change observed in 5 light on / off cycles proves that CS / PNIPAm / DND has good photo-thermal stability.

[0092] (4) The CS / PNIPAm / DND composite microspheres have obvious responsiveness to external environment (such as light, temperature). The IBA release mode at different temperatures conforms to the Korsmeyer-Peppas model. When the temperature is lower than the LCST, the cumulative release rate of IBA at 20°C is 14.6%, and after the temperature is raised to 25°C, the cumulative release rate of IBA slightly increases to 18.4%. While at 40°C, the cumulative release rate significantly increases to 40.4%. When the system is given intermittent light, the drug release rate presents an "on-off" trend with the light on and off. Therefore, by changing the external conditions such as light and temperature, the temperature of the polymer can be quickly raised above the LCST, the PNIPAm chain is contracted, and the release process of IBA is regulated.

[0093] (5) The IBA-loaded CS / PNIPAm / DND composite microspheres are used for pea growth, and the growth state of the peas after being given intermittent light shows that the CS / PNIPAm / DND has potential for practical application, and provides certain reference for the future development of green agriculture.

[0094] Although the present application has been described in detail in the general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present application. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of protection required by the present application.

Claims

1. A method for preparing a pesticide controlled release carrier, characterized by, The method comprises the following steps: Step 1, N-isopropyl acrylamide NIPAm monomer is added to deionized water, and stirring is carried out under nitrogen protection until it is completely dissolved; Step 2, potassium persulfate K2S2O8 and N, N, N', N'-tetramethyl ethylenediamine TEMED are added to the NIPAm solution; Step 3, N2 is passed into the above mixture for a period of time, and then the mixture is placed at room temperature and dried to obtain poly (N-isopropyl acrylamide) PNIPAm; Step 4, an acetic acid solution is prepared; Step 5, chitosan CS is dissolved in the acetic acid solution; Step 6, PNIPAm and DND are sequentially added to the chitosan acetic acid solution, and stirring is carried out until they are uniformly mixed; wherein the mass ratio of PNIPAm to CS is 1:4 to 1:2; the concentration of DND is 2 mg / mL; Step 7, the mixed solution is dropped into a NaOH solution to form gel beads, and the beads are solidified and filtered through a metal mesh screen to obtain CS / PNIPAm / DND microspheres; Step 8, a drug loading is carried out by using an embedding method, and the mixed solution in step 6 is uniformly mixed with IBA before the gel beads are formed.

2. The method of claim 1, wherein the pesticide controlled release carrier is prepared by the steps of: The pesticide is indole butyric acid.

3. The method for preparing a pesticide controlled release carrier according to claim 1, wherein the concentration of the acetic acid solution is 2% (v / v); and the concentration of the NaOH solution is 2 mol / L.

4. The method of claim 1, wherein the pesticide controlled release carrier is prepared by the steps of: The N2 time is 10 min to 30 min; and the solidification time is 30 min to 180 min.

5. Use of a pesticide controlled release carrier according to claim 1 in the controlled release of a medicament, characterized in that, The drug controlled release refers to a drug controlled release in agricultural planting.

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