Preparation method of AgNCs (ZIF) (PDA)-based fluorescent sensor
By combining AgNCs@ZIF@PDA composite material with gradient modulus hydrogel, the problems of fluorescence quenching and interface adaptability of fluorescence sensors in flexible matrices are solved, achieving highly sensitive and stable detection of 2,4-D pesticides, which is suitable for rapid on-site detection of food safety.
Patent Information
- Application Number
- CN202511918849.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-18
- Publication Date
- 2026-05-19
AI Technical Summary
Existing fluorescent sensors suffer from low energy transfer efficiency due to the tendency of fluorescent indicators to aggregate and quench in flexible matrices. Furthermore, the sensor interface is poorly adapted to plant epidermal morphology, making it impossible to achieve high sensitivity and in-situ real-time monitoring.
A sensor combining AgNCs@ZIF@PDA double-shell composite material with gradient modulus hydrogel was constructed. The AgNCs were encapsulated by the ZIF framework to improve fluorescence intensity and stability, while the PDA shell enabled efficient energy transfer. The gradient modulus hydrogel was used to form a conformal adhesion interface, and combined with smartphone image analysis, rapid and sensitive detection was achieved.
It achieves highly sensitive and stable detection of 2,4-D pesticides, with a linear response in the range of 23.3-333.3 ng/mL, making it suitable for rapid on-site detection of food safety.
Smart Images
Figure CN122063087A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of smart agriculture and sensor technology, specifically relating to a fluorescence sensor (PWS) based on a double-shell AgNCs@ZIF@PDA composite material and a gradient modulus hydrogel. This sensor achieves highly sensitive, in-situ, real-time monitoring of 2,4-D pesticide residues on plant surfaces by establishing a conformal, adhesive plant-sensor interface. Background Technology
[0002] 2,4-D pesticides are widely used in modern agriculture due to their effectiveness and low cost. However, even at low concentrations, they can pose a serious threat to human health. To ensure food safety, many countries and regions have established strict maximum residue limits (MRLs), but pesticide violations still occur frequently. Therefore, establishing reliable and highly sensitive methods for detecting 2,4-D pesticide residues is of great significance for food safety monitoring and poisoning risk assessment. Traditional detection techniques (such as gas chromatography and mass spectrometry) offer high accuracy, but they rely on complex instruments, specialized operation, and long detection cycles, making them unsuitable for rapid on-site detection. Therefore, developing portable, rapid, and sensitive 2,4-D pesticide detection strategies has become an urgent problem to be solved.
[0003] In recent years, fluorescent sensors (PWS) based on flexible electronics and micro / nano fabrication technologies have shown great potential. They can monitor plant physiological parameters and convert them into readable signals, enabling in-situ real-time analysis. However, the development of existing fluorescent PWS faces two major challenges: first, fluorescent indicators tend to aggregate in flexible matrices, leading to fluorescence quenching and low energy transfer efficiency, which limits detection sensitivity; second, there is a significant mechanical adaptation problem between the sensor interface and the plant epidermal morphology, resulting in small contact area, signal attenuation, and noise interference.
[0004] Based on this, this invention designs a silver nanocluster@zeolite imidazole salt framework@polydopamine (AgNCs@ZIF@PDA) fluorescence sensor for sensitive and stable detection of 2,4-D pesticides. This method acquires fluorescence response signals via a smartphone and uses image analysis software to quantify the results. It allows for on-site detection without complex instruments, offering significant advantages such as portability, speed, and high sensitivity. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of existing fluorescent sensors, such as low energy transfer efficiency, poor interface dynamic adaptability, and inability to monitor pesticide degradation dynamics in real time and in situ, and to provide a method for preparing a fluorescent sensor based on AgNCs@ZIF@PDA composite material.
[0006] This invention constructs a novel sensor combining AgNCs@ZIF@PDA double-shell composite material with hydrogel. Firstly, through Zn²... + Coordination with 2-methylimidazole encapsulates AgNCs exhibiting aggregation-induced emission (AIE) within a ZIF framework, forming an AgNCs@ZIF core. This structure significantly enhances fluorescence intensity and stability through spatial confinement. Subsequently, following a coordination-dissociation-polymerization mechanism, AgNCs@ZIF triggers rapid interfacial polymerization of dopamine, forming a PDA shell with adjustable thickness within 10 minutes at room temperature, ultimately yielding a double-shell AgNCs@ZIF@PDA composite material. This AgNCs@ZIF@PDA composite material is then embedded in a gradient modulus hydrogel disk. The hydrogel, through its polyacrylamide / nanoclay dual-network structure and the interpenetration of starch chains, achieves rapid in-situ gelation (30 minutes) and excellent mechanical properties.
[0007] The sensor's detection mechanism is based on a cascade reaction triggered by 2,4-D pesticide: 2,4-D inhibits ALP activity, preventing ALP from catalyzing the hydrolysis of AAP to ascorbic acid, thus hindering the decomposition of the PDA shell and ultimately suppressing fluorescence signal recovery. Higher pesticide concentrations result in weaker fluorescence recovery. To achieve rapid signal readout in point-of-care detection, this study converts the fluorescence response into a visually identifiable color change signal. Smartphones can capture true color images of samples containing the analyte. ImageJ software was used to analyze the color signal after exposure to 2,4-D. An image fitting algorithm was employed to obtain a linear quantitative relationship between the color signal and the 2,4-D concentration, enabling accurate calculation of the 2,4-D pesticide concentration in the sample.
[0008] The method for fabricating an AgNCs@ZIF@PDA fluorescence sensor according to the present invention comprises the following steps: A. Synthesis of AgNCs@ZIF@PDA composite material 0.1 mM PTLT and 0.1 mM AgNO3 were dissolved in 3 mL of N,N-dimethylacetamide to form a clear solution. Then, 1 mL of CH3CN was added, and the mixture was allowed to stand at room temperature for two days to obtain solid AgNCs. The synthesis of AgNCs@ZIF was as follows: 1 mL of Zn(Ac)2·6H2O (173 mM) and 3 mL of 2-methylimidazole (865 mM) were added to 1 mL of AgNCs (0.2 mg / mL) solution, and the reaction was carried out at room temperature for approximately 30 minutes. The AgNCs@ZIF product was collected by centrifugation and washed three times with methanol to remove unreacted ions and 2-methylimidazole. The synthesis of AgNCs@ZIF@PDA was as follows: 1 mL of DA (0.5 mM) was added to 500 μL of AgNCs@ZIF solution and reacted for 8–13 minutes. After the reaction was completed, the mixture was immediately centrifuged (6000 rpm, 12 minutes) and washed three times with deionized water to obtain the AgNCs@ZIF@PDA composite material (0.2 mg / mL).
[0009] B. Detection procedure for 2,4-D pesticide fluorescence detection 40 µL of 2,4-D standard solutions of different concentrations or the test sample were mixed with alkaline phosphatase (ALP, 1.0 U / mL) solution and incubated at 37 °C for approximately 1 hour. Subsequently, 20 µL of L-ascorbic acid-2-phosphate (AAP, 5 mM, dissolved in 10 mM, pH 8.5 Tris-HCl buffer) was added to the mixture, and incubation continued at 37 °C in the dark for 30 minutes. 50 µL of the above reaction solution was dropped onto the surface of the prepared AgNCs@ZIF@PDA hydrogel disk sensor. The solution rapidly covered and diffused throughout the hydrogel via capillary action. In a dark room, the sensor was excited using a fixed-configuration 365 nm UV light source, and fluorescence images were acquired using a smartphone at a fixed distance and parameters. Finally, the image was processed using ImageJ software to decompose the color signal into red (R), green (G), and blue (B) channels, and the Euclidean distance (ED) values of the images before and after the reaction were calculated. Quantitative analysis was performed based on the ED values and the standard curve of 2,4-D concentration.
[0010] C. Construction of AgNCs@ZIF@PDA fluorescence sensor After the sensor reacts with 2,4-D, the light source, sample, and smartphone are kept in a fixed configuration to consistently capture true-color images in the presence of the analyte. An image digitization algorithm is applied to extract accurate data. ImageJ software is used to decompose the color signal into its three basic channels (RGB: red, green, and blue) and obtain the corresponding RGB values. A linear relationship between the ED algorithm intensity and the 2,4-D concentration is quantitatively analyzed using a fitting program, and a linear curve is constructed. In actual testing, the portable device is used to acquire images of the sensor in samples with unknown 2,4-D concentrations. The ED signal is extracted using the same method, and by substituting it into the aforementioned standard curve, the concentration of 2,4-D in the actual sample can be calculated.
[0011] D. Actual sample testing: To evaluate the practical applicability of this fluorescence sensor, real-world samples including apple juice, paddy field water, and tap water were tested. Paddy field water and tap water were filtered through a 0.22-micron membrane to remove particulate matter, and then concentrations of 1.0, 5.0, and 50.0 ng / mL were added, respectively. -1 2,4-D pesticide. A phosphate buffer (pH 8.0) was prepared by dissolving 11.9 g of anhydrous potassium dihydrogen phosphate and 3.2 g of potassium phosphate in 1000 mL of distilled water. Representative samples were washed to remove surface contaminants and cut into approximately 1 cm square pieces. The same concentrations (1.0, 5.0, and 50.0 ng / mL) of phosphate buffer were added. -1 After adding 2,4-D, 5 mL of buffer solution was added. The mixture was shaken for about 10 minutes, and the resulting extract was collected for analysis. 25 μL of the diluted solution was added dropwise to the sensor prepared in step B. The sensor image was acquired using the self-made portable device described in step C to obtain the corresponding ED. Substituting this into step C, the concentration of 2,4-D in the actual sample solution could be calculated. Then, the concentration was compared with the added amount to verify the feasibility of the device of the present invention.
[0012] The mechanism of this invention is as follows: The core mechanism of this invention lies in constructing a sensing system that utilizes a signaling unit and an adaptor interface in synergy. The double-shell AgNCs@ZIF@PDA composite material serves as the signaling unit. The inner ZIF layer enhances and stabilizes the fluorescence of AIEgen AgNCs through spatial confinement, while the outer PDA layer acts as a highly efficient fluorescence quencher and enzyme response unit. The gradient modulus hydrogel serves as the adaptor interface, penetrating and locking onto the plant epidermal trichomes through a sol-gel phase transition, forming a stable, conformal adhesion contact. During detection, 2,4-D pesticides inhibit alkaline phosphatase (ALP) activity, blocking the cascade reaction that catalyzes the decomposition of the PDA shell, thereby regulating the "recovery-inhibition" state of the fluorescence signal. Finally, smartphone imaging and RGB algorithms convert the fluorescence changes into pesticide concentration information, enabling in-situ, sensitive monitoring of pesticide residues on plant surfaces.
[0013] The sensing method developed in this invention can sensitively and stably acquire 2,4-D residue information. Based on the high affinity of ALP and the effective protective effect of ZIF, this fluorescent sensor can detect residues in the range of 23.3-333.3 ng / mL. -1 The study demonstrated a good linear relationship within the 2,4-D pesticide range. By using smartphones to collect data and ImageJ software to analyze color information, the study achieved accurate quantitative detection of 2,4-D, providing a new approach for rapid on-site detection of 2,4-D pesticides and also providing a basis for precise on-site monitoring of food safety.
[0014] Compared with existing technologies, the present invention has the following characteristics: (1) By constructing a double-shell AgNCs@ZIF@PDA composite material with a heterogeneous interface, this invention cleverly utilizes the spatial confinement effect of the ZIF framework and the efficient energy transfer characteristics of the PDA shell, fundamentally solving the quenching problem caused by the aggregation of fluorophores in traditional fluorescence sensors, and significantly improving fluorescence lifetime, stability and energy transfer efficiency.
[0015] (2) A gradient modulus hydrogel interface was designed. By utilizing its sol-gel phase transition and capillary action, topological interlocking and conformal adhesion to complex plant epidermis (such as trichomes) were achieved, fundamentally solving the problem of dynamic adaptability between the sensor and the plant interface.
[0016] (3) This invention combines AgNCs@ZIF@PDA with smartphone fluorescence analysis technology to achieve instrument-free, rapid and visual detection. It shows obvious response to 2,4-D pesticides and has a low detection limit, making it suitable for on-site quantitative analysis and food safety monitoring. Attached Figure Description
[0017] Figure 1This diagram illustrates the synthesis of AgNCs@ZIF@PDA composite material with hydrogel and its application in a 2,4-D fluorescence sensor. Figure 2 Analysis of AgNCs@ZIF composite material; (a) Transmission electron microscope (TEM) image of AgNCs@ZIF prepared in Example 1; (b) Fluorescence enhancement pattern of the material; Figure 3 Analysis of AgNCs@ZIF@PDA composite material; (a) TEM image of AgNCs@ZIF@PDA; (b) Energy dispersive spectroscopy (EDS) distribution of the material; Figure 4 For the study of hydrogel performance; (a) is a scanning electron microscope (SEM) image of the hydrogel cross section; (b) is a SEM image of the hydrogel applied to tomato leaves; (c) is the ultraviolet-visible transmission spectrum of the hydrogel disk. Figure 5 The study focuses on the performance of the hydrogel disk sensing platform; (a) shows the linear relationship between the quantitative response of ED and the concentration of 2,4-D; (b) compares the performance indicators of the ED algorithm with other color processing methods. Figure 6 For the selectivity of hydrogel disks; Figure 7 To use a hydrogel disk sensor for in-situ monitoring of 2,4-D degradation kinetics in leaves; Detailed Implementation Example 1: Schematic diagram of the synthesis of AgNCs@ZIF@PDA composite material and hydrogel, and its application in a 2,4-D fluorescence sensor. By preparing AgNCs@ZIF composites with aggregation-induced emission (AIE) effect, dopamine polymerization was subsequently initiated within 10 minutes at room temperature to construct a double-shell AgNCs@ZIF@PDA composite. Further, a gradient modulus hydrogel disk based on this material was designed, which formed a topological interlocking network through capillary action and in-situ polymerization. A cascade reaction sensing mechanism based on 2,4-D pesticide triggering and alkaline phosphatase mediated was constructed for in-situ detection of 2,4-D pesticides in plants.
[0018] Example 2: Synthesis and Characterization of AgNCs@ZIF Materials First, 1 mL of AIEgen silver nanoclusters (AgNCs) solution was mixed with 1 mL of zinc acetate solution (173 mM) and 3 mL of 2-methylimidazole solution (865 mM), and the mixture was stirred at room temperature for 30 minutes. After the reaction was completed, the precipitate was collected by centrifugation (6000 rpm, 10 minutes) and washed three times with methanol to obtain the AgNCs@ZIF composite material.
[0019] The morphology of the product was characterized by transmission electron microscopy (TEM), and the results are as follows: Figure 2 As shown in (a), the material exhibits a uniform rhombic dodecahedral structure. Fluorescence spectroscopy analysis ( Figure 2 (b) shows that the fluorescence intensity of AgNCs@ZIF is significantly enhanced compared with that of free AgNCs, demonstrating the effective spatial confinement effect of ZIF encapsulation.
[0020] Example 3: Synthesis and Characterization of AgNCs@ZIF Materials Synthesis and Characterization of AgNCs@ZIF@PDA Material: Based on Example 1, 1 mL of dopamine (DA, 0.5 mM) aqueous solution was added to 500 μL of AgNCs@ZIF dispersion, and the reaction was carried out at room temperature for 10 minutes. After centrifugation (6000 rpm, 12 minutes), the precipitate was collected to obtain the final product AgNCs@ZIF@PDA.
[0021] TEM images ( Figure 3 (a) clearly shows that the material has a complete core-shell structure. Energy dispersive spectroscopy (EDS) elemental distribution map ( Figure 3 (b) further confirmed that elements such as S, Zn, N, and O are uniformly distributed in the composite material, proving the successful coating of PDA and the successful preparation of the composite material.
[0022] Example 4: Preparation and Performance Evaluation of Gradient Modulus Hydrogel Disks A pregel solution was prepared by mixing 100 μL of AgNCs@ZIF@PDA dispersion with AP solution, acrylamide solution, BIS solution, and KPS solution. 50 μL of this solution was then dropped onto a substrate and allowed to stand at room temperature for 30 minutes to complete gelation, forming a hydrogel disc.
[0023] Scanning electron microscopy (SEM) shows the cross-section of the hydrogel ( Figure 4 (a) has a three-dimensional interconnected porous structure. When applied to the surface of tomato leaves, SEM images ( Figure 4 (b) indicates that the hydrogel can seamlessly adhere to the leaf epidermis and penetrate the interstitial spaces, forming a conformal adhesion interface. Ultraviolet-visible transmission spectrum ( Figure 4 (c) shows that the hydrogel has high transmittance (>90%) in the key wavelength band of photosynthesis (450-720 nm), ensuring that it has minimal impact on plant physiological activities.
[0024] Example 5: Study on 2,4-D detection performance Different concentrations of 2,4-D standard solutions were detected using the detection procedure described in step B. Fluorescence images were acquired using a smartphone, and the Euclidean distance (ED) value was calculated. Figure 5 As shown in (a), the ED value corresponds to the 2,4-D concentration in the range of 23.3–333.33 ng / mL. - ¹ It exhibits a good linear relationship within the range (y=2.10x+2.81, R²=0.98). The ED algorithm of this invention is compared with other common RGB processing algorithms (…). Figure 5 (b) shows that the ED algorithm has advantages in detection limit and R. 2 It has significant advantages in all aspects, verifying its superiority as a quantitative analysis method.
[0025] Example 6: Selectivity and Anti-interference To evaluate the specificity of the sensor, its sensitivity to high concentrations (1000 ng / mL) was tested. - ¹) Responses to common interfering substances (such as other types of pesticides, metal ions, and biomolecules). Results are as follows: Figure 6 As shown in (a), only the target compound 2,4-D (100 ng / mL) was present. - ¹) It can elicit a significant signal response, while the signal changes caused by other interfering objects are negligible, demonstrating the sensor's high selectivity and anti-interference performance.
[0026] Example 7: In-situ monitoring of pesticide degradation kinetics The hydrogel sensor was attached to the surface of tomato leaves sprayed with 2,4-D and allowed to degrade naturally for 10 days. Fluorescence images were collected daily at set times, and ED values were quantified. Results are as follows: Figure 7 As shown in (a), the ED value decreases systematically over time, clearly depicting the residual degradation kinetics of 2,4-D on the leaf surface. Data analysis and calculations show that the half-life of 2,4-D under these conditions is 1.51 days, successfully demonstrating the powerful ability of this sensor to monitor pesticide degradation behavior in real time and in situ.
Claims
1. A method for fabricating an AgNCs@ZIF@PDA-based fluorescent sensor, characterized in that, The specific steps are as follows: A. Synthesis of AgNCs@ZIF@PDA composite material 0.1 mM PTLT and 0.1 mM AgNO3 were dissolved in 3 mL of N,N-dimethylacetamide to form a clear solution. Then, 1 mL of CH3CN was added, and the mixture was allowed to stand at room temperature for two days to obtain solid AgNCs. The synthesis method of AgNCs@ZIF was as follows: 1 mL of Zn(Ac)2·6H2O (173 mM) and 3 mL of 2-methylimidazole (865 mM) were added to 1 mL of AgNCs (0.2 mg / mL) solution, and the reaction was carried out at room temperature for 30 minutes. The AgNCs@ZIF product was collected by centrifugation and washed three times with methanol to remove unreacted ions and 2-methylimidazole. The synthesis method of AgNCs@ZIF@PDA is as follows: 1 mL of DA (0.5 mM) is added to 500 μL of AgNCs@ZIF solution and reacted for 8-13 minutes. After the reaction is completed, the mixture is immediately centrifuged (6000 rpm, 12 minutes), washed three times with deionized water, and the AgNCs@ZIF@PDA composite material (0.2 mg / mL) is obtained. B. Fabrication of the 2,4-D detection sensor: Under nitrogen protection, a 2% starch solution was gelled at 90°C for approximately 4 hours. A nano-clay aqueous suspension with a concentration of 125 mg / mL was prepared by adding nano-clay to deionized water and sonicating for approximately 8-13 minutes. In a 1.5 mL test tube, the following were added sequentially: 100 μL AP solution, 100 μL AgNCs@ZIF@PDA, 600 μL 333.3 mg / mL acrylamide solution (dissolved using the nano-clay aqueous suspension), 100 μL BIS solution, 100 μL KPS solution, and 5 μL TEMED. The mixture was rapidly vortexed to homogenize, and then 50 μL of the pre-gelled solution was added dropwise to the target location. Gel formation was completed after approximately 30 minutes, resulting in a portable 2,4-D fluorescence sensor.
2. The preparation method according to claim 1, characterized in that... The precursors for preparing AgNCs@ZIF@PDA are R-4-phenylthiazoline-2-thione (PTLT), silver nitrate (AgNO3), dimethylimidazole (2-M), zinc acetate (Zn(Ac)2), and dopamine hydrochloride (DA).
3. The preparation method according to claim 1, characterized in that... The concentrations of R-4-phenylthiazoline-2-thione are 0.1 mM, silver nitrate is 0.1 mM, silver nitrate is 173 mM, dimethylimidazole is 865 mM, and dopamine hydrochloride is 0.5 mM.
4. The preparation method according to claim 1, characterized in that... The starch (AP) used had a concentration of 2%, the nano-clay had a concentration of 125 mg / mL, the acrylamide (AAm) had a concentration of 333 mg / mL, the potassium persulfate (KPS) had a concentration of 30 mg / mL, and the methylenebisacrylamide (BIS) had a concentration of 10 mg / mL.
5. The preparation method according to claim 1, characterized in that... The 2,4-D pesticide detection platform is constructed based on AgNCs@ZIF@PDA, and its signal output mode is fluorescence signal.
6. The application of the AgNCs@ZIF@PDA fluorescence sensor as described in claim 5 in 2,4-D detection, characterized in that: 40 μL of 2,4-D standard solutions of different concentrations were mixed with ALP (1.0 U / mL) and incubated at 37 °C for 1 hour. Then, 20 μL of AAP (5 mM) in Tris-HCl buffer (10 mM, pH 8.5) was added, and the mixture was incubated at 37 °C for 30 minutes. 50 μL of the reaction mixture was then dropped onto a hydrogel disc, and its concentration was quantitatively analyzed by fluorescence signal intensity.
7. The application of the AgNCs@ZIF@PDA-based fluorescence sensor as described in claim 1 in the detection of 2,4-D pesticides in food samples, characterized in that: The fluorescence images of the reaction system were acquired using a smartphone with a CMOS camera. The color signal was quantitatively analyzed using the ED algorithm, and the concentration of 2,4-D in the food sample was accurately quantified based on the standard curve.