UCNPs@ZIF@PDA composite material and its preparation method and application

Abstract

The present application provides a UCNPs@ZIF@PDA composite material, its preparation method and application in 2,4-D detection, belonging to the field of biosensor technology. The present invention uses the above conversion, ZIF and DA as raw materials to synthesize a composite material. The composite material has great application prospects in the detection of the pesticide 2,4-D. When 2,4-D is present, the recovery effect of ALP on UCNPs@ZIF@PDA is weakened, thereby affecting the fluorescence intensity of the composite material. The present application further constructs an on-site detection sensor based on UCNPs@ZIF@PDA and a sensor based on UCNPs@ZIF@PDA fluorescent hydrogel. It has the advantages of low cost and simple operation, can perform on-site detection of 2.4-D, and provides a new perspective for portable monitoring of food safety and human health.

Description

Technical Field

[0001] The present invention relates to the technical field of biosensors, and in particular to a UCNPs@ZIF@PDA composite material, a preparation method thereof, and an application thereof in 2,4-D detection. Background Art

[0002] With the development of modern agriculture, herbicides have been widely used. Due to their carcinogenic, mutagenic, and mobile properties, they have led to surface water contamination and potential groundwater toxicity, garnering significant attention from environmental authorities. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a selective herbicide containing a phenoxyacetic acid group. Its weak aromatic acid properties make 2,4-D chemically similar to indoleacetic acid, making it a plant growth regulator and a synthetic plant hormone. Due to its low cost and good selectivity, 2,4-D is widely used to control broadleaf weeds in agriculture and forestry. However, 2,4-D has relatively high water solubility, genotoxicity, and endocrine-disrupting properties. Consequently, it is frequently detected in many natural water bodies and fruits and vegetables in various regions of the world, posing a direct health threat to organisms. Therefore, practical methods with high selectivity and sensitivity are urgently needed to monitor 2,4-D to ensure human health and food safety.

[0003] In modern analytical techniques, screen-printed electrodes have found applications in biomedicine, industry, and sensing due to their excellent material properties, fast response, and simple operation. Leveraging these advantages, Lin et al.'s research group used screen-printed electrodes modified with Prussian blue / reduced graphene oxide nanocomposites to detect organophosphorus pesticides. Due to their low cost, portability, disposable nature, ease of modification, and good biocompatibility, paper-based analytical methods have continued to advance in portable pesticide detection. Yang's research group developed a fluorescent paper-based assay for organophosphorus pesticides using gold nanoclusters as a fluorescent signal, based on the inhibitory effect of pesticides on tyrosinase. While these pesticide detection methods offer advantages such as miniaturization, ease of operation, and low cost, simplifying operations to a certain extent and opening up new perspectives for on-site pesticide detection, they also have limitations. For example, the luminescence or coloration of the designed systems is mostly blue or green, which cannot shield against interference from the biological matrix. Therefore, the search for highly stable near-infrared luminescent materials and the combined use of methods are warranted to achieve portable detection applications. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite material based on UCNPs@ZIF@PDA, a fluorescent hydrogel on-site detection sensor and a preparation method thereof, which can detect the content of 2,4-D simply and highly selectively.

[0005] A UCNPs@ZIF@PDA composite material has a core-shell structure, wherein the core is rare earth upconversion nanoparticles UCNPs, the inner shell is UCNPs@ZIF etched by DA dopamine to form a spherical shape, and the outer shell is a PDA coating.

[0006] Furthermore, the UCNPs are one of fluorides, oxides, sulfur-containing compounds, oxyfluorides, and halides.

[0007] Furthermore, the rare earth upconversion nanoparticles include one or more of NaYF4:Yb,Tm, NaYF4:Yb,Tm@NaYF4, NaYF4:Yb,Tm@NaYF4:Nd,Yb, NaYF4:Yb,Tm,Er@NaGdF4, NaYF4:Yb,Tm@NaGdF4, NaYF4:Yb,Tm,Er@NaYF4, NaYF4:Yb,Tm,ErNaYF4:Yb,Tm,Er@NaYF4:Nd,Yb.

[0008] Furthermore, DA dopamine monomer was anchored on the surface of UCNPs@ZIF through a polymerization process to obtain a core-shell structured UCNPs@ZIF@PDA composite material.

[0009] Furthermore, the expression of UCNPs: NaErF4:0.5%Tm 3+ , LiErF4:0.5%Tm 3+ @LiYF4, NaErF4@NaLuF4@NaYF4: 20%Yb, 2%Er@NaLuF4.

[0010] Further, the chemical expression of the composite material is: UCNPs@NaYF4@ZIF@PDA.

[0011] One aspect of the present application is to provide a fluorescent hydrogel, characterized in that it is prepared from the UCNPs@ZIF@PDA composite material according to claim 1.

[0012] One aspect of the present application is to provide a sensor prepared by UCNPs@ZIF@PDA composite material.

[0013] One aspect of the present application is to provide an application of a UCNPs@ZIF@PDA composite material, characterized in that the composite material is used to detect 2,4-D.

[0014] One aspect of the present application is to provide a method for preparing a UCNPs@ZIF@PDA composite material, the preparation method comprising:

[0015] Core-shell upconversion nanoparticles were prepared. The oleic acid ligands on the surface of the upconversion nanoparticles were replaced with polymer ligands using the ligand exchange method, so that the upconversion nanoparticles were converted from the oil phase to the water phase. The upconversion nanoparticles modified with the polymer ligands were coated with the ZIF shell using the static method. Finally, an appropriate amount of DA was added to the aqueous solution of UNCPs@ZIF, and DA formed a PDA shell under the catalytic action of ZIF.

[0016] Furthermore, the polymer ligand includes polyvinyl pyrrolidone, polyvinyl alcohol, polymolybdic acid, etc.

[0017] The mechanism of the present invention is as follows:

[0018] Preparation of uniformly sized and well-dispersed NaErF4:0.5% Tm oil phase in cyclohexane by chloride solvothermal method 3+ @NaYF4 core-shell upconversion nanoparticles (UCNPs) were characterized by transmission electron microscopy and X-ray diffraction analysis. A ligand exchange method was used to replace the oleic acid ligands on the surface of the upconversion nanoparticles with polymer ligands (such as polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), or polymolybdic acid), enabling conversion from an oil phase to an aqueous phase. This facilitates subsequent coating with a ZIF shell in methanol. The PVP-modified upconversion nanoparticles were then coated with a ZIF shell using a static method. Finally, an appropriate amount of DA was added to the aqueous solution of the UNCPs@ZIF, where it formed a PDA shell under the catalytic action of the ZIF. PDA, acting as an effective fluorescence quencher, effectively quenched the upconversion fluorescence. The strong reducing activity of ascorbic acid (AA), produced by the reaction of trisodium L-ascorbic acid-2-phosphate (AAP) with alkaline phosphatase (ALP), restored the degraded PDA structure to upconversion luminescence. Furthermore, the inhibitory effect of 2,4-D on ALP was exploited to enable pesticide detection. By optimizing the amount of added DA, the formation of PDA was regulated, and the sensitivity of the final composite material to 2,4-D was further controlled to achieve a relatively low detection limit (see Figure 5 ), and based on this, it is possible to monitor 2,4-D pesticides in actual samples. Based on this principle, hydrogels are further combined to achieve portable detection of 2,4-D. The practical application of hydrogel sheets was verified through dynamic degradation experiments of 2,4-D in tomatoes. The present invention has the advantages of low background interference, low cost, and portability, providing a new perspective for portable monitoring of food, environment, and public safety based on near-infrared nanoprobes. The present invention has the following characteristics:

[0019] (1) The enzyme-mimicking activity of ZIF was utilized and used as a growth platform for DA to achieve the combination of UCNPs@ZIF composite material and PDA.

[0020] (2) The UCNPs@ZIF@PDA composite material was encapsulated into a hydrogel sheet to construct a fluorescent hydrogel sensor.

[0021] Beneficial effects

[0022] In the present invention, a fluorescent hydrogel based on UCNPs@ZIF@PDA is used to achieve background-free on-site detection of 2,4-D pesticides. Upconversion has the characteristics of near-infrared excitation and red light emission, which can effectively avoid the interference of autofluorescence and background fluorescence in biological matrix samples. The closed zeolitic imidazolate framework structure (ZIF) unit provides physical protection from external interference, further improving its stability, fluorescence behavior or sensing performance. Dopamine (DA) can be rapidly aggregated and cross-linked on the ZIF unit within 10 minutes to form core-shell UCNPs@ZIF@PDA particles with adjustable shell (i.e., polydopamine, PDA) thickness. The functionalized hydrogel has stimulus-responsive properties and strong loading capacity, which is conducive to the manufacture of sensor devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0024] Figure 1 : Transmission electron microscopy image of UCNPs obtained in Example.

[0025] Figure 2 : Transmission electron microscopy image of UCNPs@ZIF obtained in Example.

[0026] Figure 3 : TEM image of UCNPs@ZIF@PDA obtained in Example.

[0027] Figure 4 : SEM image of UCNPs@ZIF@PDA hydrogel obtained in Example.

[0028] Figure 5 : Graph showing the effect of different DA concentrations on 2,4-D detection obtained in Example.

[0029] Figure 6 : Standard curve of Euclidean distance (ED) value and 2,4-D concentration obtained in Example.

[0030] Figure 7 : ED value and selection,interference graph obtained in the embodiment.

[0031] Figure 8 : Degradation diagram obtained in Example.

[0032] Figure 9 : 2,4-D plant detection diagram obtained in Example. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0034] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0035] Example 1

[0036] Preparation of UCNPs

[0037] First, 0.37980 g of ErCl₃·6H₂O and 0.00192 mg of TmCl₃·6H₂O were added to a 50 mL round three-necked flask. Subsequently, 6 mL of oleic acid and 15 mL of 1-octadecene were added. To remove oxygen from the reaction system, argon was bubbled into the flask while stirring at moderate speed for 30 minutes. While stirring, the solution was heated to 160°C at a rate of 10–15°C / min and then maintained under argon for 20 minutes until a pale pink oleic acid diol ester precursor was formed. The reaction system was then allowed to cool naturally to room temperature under the presence of argon. A methanol solution containing 0.1 g of sodium hydroxide and 0.148 g of NH₄F was added dropwise to the mixture until complete dissolution. The resulting mixture was then heated to 75°C and held for 50 minutes to remove the methanol. In subsequent experiments, argon was recirculated for 60 minutes to remove the methanol and any oxygen and water vapor introduced during the reaction. The system was heated to 300°C at a rate of 20°C / min and held for 90 minutes. Finally, the product was precipitated with acetone and centrifuged at 7500 rpm for 6 minutes. The product was dissolved in cyclohexane and washed three times with ethanol and cyclohexane before further use. 0.15168 g of YCl3·6H2O was added to a 100 mL flask containing 6 mL of oleic acid and 15 mL of 1-octadecene, and stirred under a nitrogen flow for 30 minutes. After heating to 150°C, heating was continued for 45 minutes until complete dissolution. After cooling, a methanol solution containing 0.05 g of sodium hydroxide and 0.074 g of NH4F was added dropwise to the solution and heated at 70°C for 30 minutes. Under nitrogen protection, 2 mL of UCNP cores was added dropwise and heated at 80°C for 30 minutes to completely remove the methanol. Argon was then passed through the flask for 60 minutes to remove impurities and water vapor. Finally, the reaction system was heated to 300°C and allowed to stand for 60 minutes. The obtained core-shell UCNPs were washed with a mixture of cyclohexane and ethanol (1:3) and then dispersed into 4 mL of cyclohexane solution. Figure 1 .

[0038] Preparation of UCNPs@ZIF@PDA

[0039] UCNPS was dispersed in 10 mL (0.1 M) of dilute HCl solution, ultrasonicated for 1 h, then washed three times with distilled water and dispersed in 5 mL of ethanol. Under vigorous stirring, 5 mL of ethanol containing 0.3 g of PVP (molecular weight 40,000) was dripped into the solution. After stirring for 24 h, PVP-coated UCNPs were obtained. Finally, the product (UCNPs-PVP) was collected from the solution by centrifugation, washed with ethanol to remove excess PVP molecules, and the product was dispersed in 1 mL of methanol. Subsequently, 20 μL of UCNPs methanol solution was added to a mixed solution of 5 mL of Zn(NO3)·H2O (50 mM) and 5 mL of 2-methylimidazole (50 mM), and allowed to stand at room temperature for 4 hours to prepare UCNPs@ZIF. Its transmission electron microscopy characterization is shown in Figure 2 .

[0040] The UCNPs@ZIF product was collected by centrifugation and washed three times with methanol to remove unreacted ions and 2-methylimidazole. 100 μL DA (5 mM) and 50 μL UCNPs@ZIF were added and reacted for 10 minutes at 37°C to synthesize UCNPs@ZIF@PDA. The transmission electron microscopy characterization is shown in Figure 3 .

[0041] Example 2

[0042] Effects of different DA concentrations on 2,4-D detection

[0043] A 10 ppm 2,4-D standard (50 μL) and 0.08 U / mL ALP (50 μL) were mixed and reacted at 37°C for 1 hour. Then, 5 mM AAP (25 μL) dissolved in 10 mM Tris-HCl buffer (100 μL, pH = 8.5) was added and incubated at 37°C for 25 minutes. Then, 100 μL UCNPs and 50 μL of DA solutions of different concentrations (ranging from 2 mM to 50 mM) were added and reacted at 37°C for 10 minutes. A linear relationship between DA concentration and pesticide inhibition efficiency (IE) was obtained, as shown in Figure 2. Figure 5 Finally, 5 mM DA was selected as the condition for pesticide detection.

[0044] Example 3

[0045] A preparation method based on UCNPs@ZIF@PDA fluorescent hydrogel and its application in 2,4-D, comprising the following steps:

[0046] (1) To make hydrogel sheets, we made a mold cast with a quartz slide. The mold contains two rows of holes with a diameter of 7 mm and a depth of 0.9 mm. Bovine serum albumin (BSA, content of 3.0%-10.0%), sodium alginate (content of 1.0%-5.0%) and glutaraldehyde (content of 0.5%-5.0%) were added to deionized water (pH = 7) for a double cross-linking reaction. UCNPs@ZIF@PDA was encapsulated into the hydrogel and shaped in the holes of the mold, and then immersed in CaCl2 (10mM) solution for 3 minutes. The hydrogel sheet was manually removed from the mold with tweezers and stored in deionized water. The obtained sodium alginate hydrogel sheet was stored at 4°C for future use. The SEM image of its UCNPs@ZIF@PDA hydrogel is shown in Figure 2. Figure 4 shown.

[0047] (2) These hydrogel discs were then assembled on glass slides (76.2 mm × 25.4 mm), and they were ready for testing. Different concentrations of 2,4-D standard (25 μL) and 25 μL ALP (4.0 U / mL-40 U / mL) were mixed and reacted at 37°C for 1 hour, and then 50 mM AAP (25 μL) dissolved in 10 mM Tris-HCl buffer (50 μL, pH = 8.5) was added and incubated at 37°C for 25 minutes. 30 μL of the reaction solution was dropped on the gel slice. Through capillary action, the liquid diffused to the entire gel disc. After that, fluorescence images at different 2,4-D concentrations were obtained under a 980 nm laser. After collecting the images, the data information on the hydrogel slices was analyzed using the commercial software ImageJ. The relationship between the logarithmic concentration of 2,4-D and the ED value was established, and the relationship diagram obtained is shown in the figure below. Figure 6 shown.

[0048] Example 4

[0049] A preparation method based on UCNPs@ZIF@PDA fluorescent hydrogel was used to detect 2,4-D in different samples to explore its practicality.

[0050] The specific samples were apple, pear juice and tap water. The sample pretreatment process was as follows: apples and pears purchased from a local supermarket were crushed to obtain apple and pear juice. Apple juice and pear juice were diluted 10 times for further use. Tap water was obtained directly from the pipeline. In the recovery study, a certain amount of 2,4-D standard (0.2, 2, 20 mg / mL) was added to the sample before application. The detection was carried out according to the method of Example 4 (2). As shown in Table 1, the recovery rate was 100.441%-112.960%, and the relative standard deviation was 1.317%-7.128%, which was within the allowable range, indicating that the detection strategy has potential applicability in actual samples.

[0051] Table 1. Detection of 2,4-D in real samples based on UCNPs@ZIF@PDA fluorescent hydrogel

[0052]

[0053]

[0054] Example 5

[0055] A method for preparing UCNPs@ZIF@PDA fluorescent hydrogel was developed. By adding a negative control, the selectivity and anti-interference ability of the hydrogel sheet for 2,4-D recognition were studied, and its adaptability in the environment was explored.

[0056] The test method is to use chlorpyrifos, malathion, fipronil, isocarbophos, imidacloprid, carbaryl, anthracene, toluine, tyrosine, ovalbumin, trypsin, BSA, Zn 2+ 、Ba 2+ 、Na + , K + The negative control was tested according to the method of 4(2). The results showed that even if these substances were present, ED did not fluctuate significantly, indicating that these coexisting compounds did not affect the recognition of the hydrogel sheet (e.g. Figure 7 shown).

[0057] Example 6

[0058] Monitoring of 2,4-D Degradation Residues in Tomato Seedlings

[0059] 50 mL of 2,4-D solution (100 μg / mL) was sprayed on the plant. After spraying the pesticide, the tomato plants were harvested on the 1st, 3rd, 6th, 7th, 8th, 9th and 14th day. After collecting 0.5 g of sample, the sample was added to 1 mL of ethanol and ultrasonicated for 10 minutes and centrifuged at 1000 rpm for 5 minutes. The detection was carried out according to the method of 4 (2). The results showed that after the initial spraying, a high level of 2,4-D residue (19.6 μg / mL) was detected in the tomato leaves (as shown in Figure 4(2)). Figure 8 Over the next 6 days, the fluorescence color of the hydrogel sheet changed from dark red to light red over time, indicating that 2,4-D was gradually degraded. The degradation of 2,4-D followed pseudo-first-order kinetics, with the equation y = 57.64e -1.089x +0.212, half-life (T 1 / 2 During the 14-day follow-up measurement, the pesticide on the tomato leaves was basically degraded after 6 days after spraying 2,4-D.

[0060] Example 7

[0061] The plant-wearable sensor based on UCNPS@ZIF@PDA can realize 2,4-D on-site monitoring in a non-invasive manner on hairy plants.

[0062] Based on the method of 4(2), the gel sheets were attached to different parts of different plants such as peppers, lettuce, and carrots, and they showed obvious responses to the presence or absence of 2,4-D. This experiment shows that the plant surface does not affect the signal response of the hydrogel sheet to the target pesticide (e.g. Figure 9 shown).

[0063] In this specification, the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the embodiments described later, the description is relatively simple, and the relevant parts can be referred to the partial description of the previous embodiments.

[0064] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A UCNPs@ZIF@PDA composite material, characterized in that: The UCNPs@ZIF@PDA composite material is a core-shell structure, wherein the core is rare earth upconversion nanoparticles UCNPs, the inner shell is UCNPs@ZIF etched by DA dopamine to form a spherical shape, and the outer shell is a PDA coating; Expression of UCNPs: NaErF4:0.5%Tm 3+ 、LiErF4:0.5%Tm 3+ @LiYF4.

2. The method for preparing a composite material according to claim 1, wherein: The preparation method comprises: Rare earth upconversion nanoparticles were prepared, and the oleic acid ligands on the surface of the upconversion nanoparticles were replaced with polymer ligands using a ligand exchange method, so that the upconversion nanoparticles were converted from an oil phase to a water phase; The upconversion nanoparticles modified with polymer ligands were coated with ZIF shells by the static method. Finally, an appropriate amount of DA was added to the aqueous solution of UNCPs@ZIF, and DA formed a PDA shell under the catalysis of ZIF.

3. A fluorescent hydrogel, characterized in that: The UCNPs@ZIF@PDA composite material according to claim 1 is prepared.

4. A sensor, characterized in that: The UCNPs@ZIF@PDA composite material according to claim 1 is encapsulated into a hydrogel sheet.

5. An application of the UCNPs@ZIF@PDA composite material according to claim 1, characterized in that: The composite material is used for detecting 2,4-dichlorophenoxyacetic acid.

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