Eu / Ce-MOFs ratio fluorescence sensor, hydrogel sensor and preparation method and application of Eu / Ce-MOFs ratio fluorescence sensor

Abstract

The invention belongs to the technical field of fluorescent probes, and discloses an Eu / Ce-MOFs ratio fluorescent sensor, a hydrogel sensor and a preparation method and application of the Eu / Ce-MOFs ratio fluorescent sensor and the hydrogel sensor. The Eu-MOF and the Ce-MOF are subjected to a hydrothermal reaction, and the Eu / Ce-MOF ratio fluorescence sensor is obtained. The sensor has excellent stability and relatively high detection accuracy, and the detection limits of TC, OTC and DOX are respectively 73.0 nmol / L, 51.7 nmol / L and 54.9 nmol / L. The sensor has been successfully applied to detection of TC, OTC and DOX in pork and milk samples, and the recovery rate is 89.3%-112.9%. Besides, the invention further develops a visual sensing platform based on hydrogel, the TCs detection precision is remarkably improved through combination of smartphone imaging and a machine learning algorithm, and a reliable and intelligent solution is provided for on-site rapid detection of TCs.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorescent probes, and in particular relates to a fluorescent sensor. Background Art

[0002] Tetracycline antibiotics (TCs), including tetracycline (TC), oxytetracycline (OTC), and doxycycline hydrochloride (DOX), are widely used in livestock and aquaculture due to their broad-spectrum antimicrobial properties. These drugs are not only used to prevent and treat bacterial infections but also as growth promoters, improving animal performance and thus significantly enhancing the economic benefits of the aquaculture industry. However, overuse of these antibiotics in aquaculture can lead to excessive drug residues in animal-derived foods, posing multiple health risks to humans. Studies have shown that long-term consumption of foods containing tetracycline residues can trigger allergic reactions, promote the spread of antibiotic-resistant genes, and lead to liver damage. Consequently, the European Union has established maximum residue limits (MRLs) of 200 μg / kg for TCs in eggs and 100 μg / kg for TCs in milk. In recent decades, various analytical methods have been developed for the detection of TCs, including high-performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA), and electrochemical methods. Despite the excellent accuracy and sensitivity of these analytical methods, their practical application remains limited by their time-consuming analytical procedures, complex and tedious procedures, the need for specialized personnel, and the reliance on expensive precision instruments. These factors significantly restrict the promotion and application of these methods in routine testing. Therefore, a more efficient and simpler method for detecting TCs is urgently needed. To overcome these limitations, colorimetry, fluorescence (FL) sensing, and other rapid detection methods have been developed. FL sensing has attracted significant attention in antibiotic analysis due to its rapid reaction speed, low equipment cost, simple operation, and ease of visual observation. Furthermore, advances in nanotechnology have promoted the development of nanomaterials, and thus spurred the development of FL sensors. Common fluorescent materials include carbon dots (CDs), metal nanoclusters, and metal-organic frameworks (MOFs). Among these nanomaterials, MOFs have become promising candidates for constructing FL sensors due to their excellent thermal stability, structural tunability, and abundant surface active sites.

[0003] Prior art such as CN 114805826 A discloses a Eu 3+ Functionalized MOF fluorescent probe, preparation method thereof and application in detecting tetracycline drugs, Eu 3+The UiO-66-(COOH)2 / p-CBA was introduced. Despite the design of the MOF material, its effectiveness in detecting tetracyclines, such as its sensitivity, remains poor. Therefore, it is crucial to develop a convenient, rapid, sensitive, and intelligent detection method to monitor tetracycline contamination risks. Summary of the Invention

[0004] In response to the above technical problems, the present invention proposes a Eu / Ce-MOFs ratio fluorescence sensor, a hydrogel sensor, and a preparation method and application thereof.

[0005] To achieve the above object, the technical solution of the present invention is implemented as follows:

[0006] A method for preparing a Eu / Ce-MOFs ratio fluorescence sensor, comprising the following steps:

[0007] (1) dissolving 1,2,4,5-pyromellitic acid (H4btec) and 2,6-pyridinedicarboxylic acid (DPA) in a mixed solvent of DMF and water to obtain a mixed solution; adding an aqueous europium salt solution to the mixed solution, and performing a hydrothermal reaction to obtain Eu-MOF powder;

[0008] (2) dissolving 2-aminoterephthalic acid (BDC-NH2) in DMF, adding a cerium salt aqueous solution, and stirring to obtain Ce-MOF powder;

[0009] (3) Eu-MOF powder and Ce-MOF powder are added to DMF and mixed, and then subjected to hydrothermal reaction to obtain Eu / Ce-MOFs, namely Eu / Ce-MOFs fluorescence sensor.

[0010] In the above step (1), the molar ratio of 1,2,4,5-pyromellitic acid, 2,6-pyridinedicarboxylic acid and europium salt is 1:(5-12):(5-12); the europium salt is europium nitrate (Eu(NO3)3·6H2O) or europium chloride (EuCl3·6H2O).

[0011] Furthermore, the europium salt is europium nitrate.

[0012] In the above step (2), the molar ratio of 2-aminoterephthalic acid to cerium salt is 1:(2-10); the stirring temperature is 20-60° C., and the stirring time is 1-4 hours; and the cerium salt is cerium chloride (CeCl 3 · 7H 2 O) or cerium nitrate (Ce(NO 3 ) 3 · 6H 2 O).

[0013] Furthermore, the above-mentioned cerium salt is cerium chloride.

[0014] The mass ratio of Eu-MOF to Ce-MOF in the above step (3) is (10-15):1.

[0015] The temperature of the hydrothermal reaction in the above steps (1) and (3) is 100-150° C., wherein the time of the hydrothermal reaction in step (1) is 12-36 hours; and the time of the hydrothermal reaction in step (3) is 8-16 hours.

[0016] Eu / Ce-MOFs ratio fluorescence sensor prepared using the above preparation method.

[0017] The above-mentioned Eu / Ce-MOFs ratiometric fluorescence sensor is used in the detection of tetracycline antibiotics for non-disease diagnosis purposes.

[0018] Furthermore, the tetracycline antibiotic is any one of tetracycline (TC), oxytetracycline (OTC) and doxycycline hydrochloride (DOX).

[0019] In the application of tetracycline antibiotic detection for non-disease diagnosis purposes, the specific application is as follows: 0.5 mL of TC, OTC or DOX solution of the test concentration is added to 0.5 mL of Leu / Ce-MOFs solution (concentration of 5 μg / mL, pH = 8.0), incubated for 3 minutes, and the fluorescence intensity values at 426 nm and 617 nm are recorded with an excitation wavelength of 270 nm, and the F 617 / F 427 When the tetracycline antibiotic is tetracycline, the F 617 / F 427 Substitute the linear equation of fluorescence intensity ratio and TC concentration into y = 2.89694 + 0.01x (R 2 =0.999), the concentration of tetracycline in the test solution can be obtained; when the tetracycline antibiotic is oxytetracycline, F 617 / F 427 Substitute the linear equation of fluorescence intensity ratio and OTC concentration into y = 2.88349 + 0.00845x (R 2 =0.995), the concentration of oxytetracycline in the test solution can be obtained; when the tetracycline antibiotic is doxycycline hydrochloride, F 617 / F 427 Substitute the linear equation of fluorescence intensity ratio and DOX concentration into y = 2.77684 + 0.0162x (R 2 =0.997), the concentration of doxycycline hydrochloride in the test solution can be obtained.

[0020] A hydrogel sensor comprises a PVA hydrogel matrix and the above-mentioned Eu / Ce-MOFs ratio fluorescence sensor.

[0021] The preparation method of the above-mentioned hydrogel sensor adopts the freeze-thaw method, and the specific steps are as follows: PVA is completely dissolved in deionized water, and the Eu / Ce-MOFs ratio fluorescence sensor is added. After freeze-thaw cycles, the hydrogel sensor is obtained.

[0022] The hydrogel sensor is used in the visual detection of tetracycline drugs for non-disease diagnosis purposes.

[0023] The above application includes collecting images of the hydrogel sensor when detecting tetracycline antibiotics (tetracycline (TC), oxytetracycline (OTC) and doxycycline hydrochloride (DOX)), using the RGB value of the image of the hydrogel sensor as a feature vector, modeling the feature vector, and using the modeled data model to obtain the concentration of tetracycline antibiotics through the color of the hydrogel sensor.

[0024] Furthermore, the application of this method in visual detection of tetracyclines for non-disease diagnosis purposes is described in the following steps: For intelligent image analysis, a machine learning-based strategy for FL image recognition and RGB (red, green, and blue) value prediction was designed and proposed. Predictive modeling was performed using a SVM algorithm implemented in Python. The proposed method consists of two main components: image acquisition and data processing. First, FL images were captured using a smartphone equipped with a high-definition camera. To ensure data comprehensiveness, 900 FL images were systematically collected, encompassing various lighting angles and viewing angles. The entire dataset was divided into a training set (70%) and a test set (30%). Subsequently, the RGB values of composite hydrogels containing different TCs concentrations were accurately extracted from the images as feature vectors. Finally, the SVM data model was trained and the model accuracy was tested, achieving a 95% confidence level.

[0025] The beneficial effects produced by the present invention are:

[0026] (1) The present invention proposes a heterogeneous structure of Eu / Ce-MOFs, which has an overall irregular nanosheet morphology and a regular rod-like morphology. In addition, the presence of microporous structures in the Eu / Ce-MOFs demonstrates excellent porosity and good adsorption properties, providing ample active sites for highly sensitive sensors.

[0027] (2) The present invention synthesized a dual-emission ratiometric FL sensor Eu / Ce-MOFs for real-time intelligent detection of TCs. Due to the influence of the inner filter effect (IFE), the red fluorescence of Eu / Ce-MOFs weakened with the increase of TCs concentration. The sensor showed excellent sensitivity and specificity for TCs, and the LODs of TC, OTC, and DOX were 73.0, 51.7, and 54.9 nmol / L, respectively. The sensor achieved good recovery and accuracy in the practical application of TCs residue analysis in pork and milk samples. Specifically, it was applied to the detection of TC, OTC, and DOX in pork and milk samples with a recovery of 89.3% to 112.9%.

[0028] (3) This paper develops a Eu / Ce-MOFs-based hydrogel sensing platform, providing a more direct method for visual and quantitative detection of TCs. Specifically, by combining FL color photography under UV irradiation with a machine learning algorithm, an intelligent detection platform was established that can rapidly and efficiently analyze RGB values and accurately determine TC concentrations. The proposed intelligent TC detection method provides a valuable reference for the design and optimization of future FL detection systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 (a) Schematic diagram of the synthesis of Eu / Ce-MOFs; (b) Schematic diagram of the detection of TC, OTC, and DOX by Eu / Ce-MOFs; (c) Schematic diagram of hydrogel visualization and machine learning-based analysis.

[0031] Figure 2 SEM images of (a) Eu-MOF, (b) Ce-MOF and (c) Eu / Ce-MOFs; (d) EDS spectrum of Eu / Ce-MOFs; (e) XRD analysis patterns of Eu-MOF, Ce-MOF and Eu / Ce-MOFs; (f) N2 adsorption isotherms of Eu / Ce-MOFs; (g) FT-IR spectrum of Eu / Ce-MOFs; (h) Full XPS spectra of Eu-MOF, Ce-MOF and Eu / Ce-MOFs; High-resolution XPS spectra of (i) Eu 3d and (j) Ce 3d of Eu-MOF, Ce-MOF and Eu / Ce-MOFs.

[0032] Figure 3 EDS spectra of (a) Eu-MOF and (b) Ce-MOF.

[0033] Figure 4 Transmission electron microscopy image of Eu / Ce-MOFs.

[0034] Figure 5 Transmission electron microscope energy spectrum of Eu / Ce-MOFs.

[0035] Figure 6 Barrett-Joyner-Halenda pore size distribution diagram of Eu / Ce-MOFs.

[0036] Figure 7 High-resolution XPS spectra of (a) C 1s, (d) N 1s, and (g) O 1s of Eu-MOF; high-resolution XPS spectra of (b) C 1s, (e) N 1s, and (h) O 1s of Ce-MOF; high-resolution XPS spectra of (c) C 1s, (f) N 1s, and (i) O 1s of Eu / Ce-MOFs.

[0037] Figure 8 (a) UV-visible absorption and fluorescence emission spectra of Eu / Ce-MOFs (λex = 270 nm) and the UV-visible absorption and fluorescence emission spectra of Eu / Ce-MOFs under sunlight and UV 254 nm lamp; (b) Fluorescence spectra of Eu / Ce-MOFs and raw material solution (insert: Ce-MOF, Eu-MOF and Eu / Ce-MOFs under sunlight and UV 254 (c) Effect of NaCl concentration on the fluorescence intensity of Eu / Ce-MOFs; (d) Reproducibility of fluorescence intensity of Eu / Ce-MOFs; (e) Fluorescence stability of Eu / Ce-MOFs within 7 days; (f) Anti-photobleaching property of Eu / Ce-MOFs under continuous irradiation of xenon lamp at 617 nm and 427 nm; (g) FL emission spectra of Eu / Ce-MOFs at different excitation wavelengths; (h) Fluorescence spectrum of Eu / Ce-MOFs as a function of pH; (i) Fluorescence intensity ratio (F) of the sensor after adding TC, OTC and DOX. 617 / F 427 ) changes over time.

[0038] Figure 9 (a) Fluorescence images of Eu / Ce-MOFs dispersed in water, ethanol, methanol, acetonitrile, and DMF under sunlight and (b) 254 nm UV light.

[0039] Figure 10 (a) F of Eu / Ce-MOFs 617 / F 427(a) Changes of the pH value with the pH value and (b) XRD spectra of Eu / Ce-MOFs under different pH conditions.

[0040] Figure 11 Under 254nm ultraviolet light irradiation, the fluorescence color of Eu / Ce-MOFs changes in the pH range of 2 to 12.

[0041] Figure 12 (a) XRD spectra of Eu / Ce-MOFs before and after the addition of TCs; (b) UV-visible absorption spectrum of TCs and fluorescence spectrum of Eu / Ce-MOFs; (c) FL decay curves of Eu / Ce-MOFs before and after the introduction of TCs; fluorescence spectra of Eu / Ce-MOFs at different concentrations of (d) TC, (e) OTC and (f) DOX; F 617 / F 427 Linear relationships with (g) TC, (h) OTC, and (i) DOX concentrations.

[0042] Figure 13 UV-visible spectra of (a) TC, (b) OTC, (c) DOX, Eu / Ce-MOFs, and Eu / Ce-MOFs coexisting with TC, OTC, and DOX, respectively.

[0043] Figure 14 FT-IR spectra of Eu / Ce-MOFs after the addition of TC, OTC, and DOX.

[0044] Figure 15 (a) XPS spectra of TC and Eu / Ce-MOFs mixture and their high-resolution XPS spectra of (b) C 1s, (c) N 1s, (d) O 1s, (e) Eu3d, and (f) Ce 3d.

[0045] Figure 16 Fluorescence color of Eu / Ce-MOFs changes with increasing concentrations of (a) TC, (b) OTC, and (c) DOX under 254 nm UV light (0–500 μmol / L).

[0046] Figure 17 Color parameters of Eu / Ce-MOFs on the CIE chromaticity coordinate diagram after adding different concentrations of (a) TC, (b) OTC, and (c) DOX.

[0047] Figure 18(a) Selectivity of Eu / Ce-MOFs for different interfering antibiotics; (b) Detection performance of TC, (c) OTC, and (d) DOX in the coexistence of other antibiotics; (e) Anti-interference ability of Eu / Ce-MOFs for TCs analysis; Anti-interference ability of Eu / Ce-MOFs for the analysis of (f) TC, (g) OTC, and (h) DOX in actual samples.

[0048] Figure 19 (a) SEM image of PVA hydrogel; (b) SEM image of Eu / Ce-MOFs hydrogel; (c) energy spectrum of Eu / Ce-MOFs hydrogel.

[0049] Figure 20 (a) XPS spectrum of PVA hydrogel and its (b) O 1s and (c) C 1s high-resolution XPS spectra.

[0050] Figure 21 (a) XPS spectrum of Eu / Ce-MOFs hydrogel and its high-resolution XPS spectra of (b) C1s, (c) N1s, (d) O1s, (e) Eu 3d, and (f) Ce 3d.

[0051] Figure 22 (a) Photos of hydrogels containing different concentrations (μmol / L) of TC, OTC, and DOX under sunlight and 254 nm UV light; (b) Flowchart of TCs detection assisted by the SVM algorithm. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0053] Example 1

[0054] A preparation method of a Eu / Ce-MOFs ratio fluorescence sensor in this embodiment, the synthesis schematic diagram is shown as follows Figure 1 As shown in a, the steps are as follows:

[0055] (1) Preparation of Eu-MOF (powder): 0.4461 g of Eu(NO3)3·6H2O was dissolved in 5 mL of water to prepare solution A. 0.0254 g of H4btec and 0.1671 g of DPA were dissolved in 15 mL of a mixed solvent of N,N-diethylformamide (DMF) and water (DMF:water = 1:1) to prepare solution B. After solution A and solution B were thoroughly mixed and stirred for 30 minutes, the resulting solution was placed in a stainless steel autoclave lined with polytetrafluoroethylene and heated hydrothermally at 120°C for 24 hours. After cooling to ambient temperature, the precipitate was washed three times with DMF and anhydrous ethanol. Finally, the precipitate was dried in a vacuum drying oven at 50°C overnight.

[0056] (2) Preparation of Ce-MOF (powder): First, 0.0931 g of CeCl₃·7H₂O was mixed with 5 mL of water. Then, 0.0091 g of BDC-NH₂ was added to 15 mL of DMF, stirred, and placed on a magnetic stirrer at 40°C and 600 rpm for two hours. The precipitate was washed three times with DMF and anhydrous ethanol, and finally dried in a vacuum drying oven at 50°C overnight.

[0057] (3) Preparation of Eu / Ce-MOFs: 50 mg of the prepared Eu-MOF powder and 4 mg of Ce-MOF powder were dissolved in 8 mL of DMF and stirred at 600 r / min on a magnetic stirrer for 30 min. The resulting solution was then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heated continuously at 120°C for 12 h. After cooling to room temperature, the solution was washed three times with DMF and three times with anhydrous ethanol. The supernatant was discarded, and the precipitate was dried in a vacuum drying oven at 50°C overnight to obtain Eu / Ce-MOFs, i.e., the Eu / Ce-MOFs ratiometric fluorescence sensor.

[0058] The SEM image of Eu-MOF shows obvious irregular nanosheet morphology ( Figure 2 a), and EDS analysis showed the presence of C, N, O, and Eu elements in Eu-MOF ( Figure 3 a). SEM image of Ce-MOF shows regular rod-like morphology ( Figure 2 b), and its EDS shows the presence of C, N, O and Ce elements in Ce-MOF ( Figure 3 b). The SEM image of Eu / Ce-MOFs shows the overall morphology of Eu / Ce-MOFs with heterogeneous structure ( Figure 2 c). Transmission electron microscopy (TEM) image of Eu / Ce-MOFs ( Figure 4 ) is consistent with the SEM image results; in addition, EDS analysis confirmed the presence of C, N, O, Eu and Ce elements in the entire heterogeneous material ( Figure 2 d and Figure 5 ), and the changes in the percentage of element content further verified the successful synthesis of Eu / Ce-MOFs with heterogeneous structure (Table 1). Figure 2 e is the X-ray diffraction spectra (XRD) of Eu-MOF, Ce-MOF and Eu / Ce-MOFs. In the range of 5°-90°, the diffraction peaks of Eu / Ce-MOFs (blue curve) are located near 16.72°, 23.88°, 29.17°, 33.83°, 41.68°, 45.08°, 48.48° and 51.57°. Among them, the sharp and prominent diffraction peaks near 16.72° and 33.83° correspond to the (111) and (320) lattice planes. After the reaction of Eu-MOF with Ce-MOF, the characteristic peaks of Ce-MOF are still clearly visible in Eu / Ce-MOFs, while the diffraction peaks of Eu-MOF near 9.98° and 27.29° disappear in Eu / Ce-MOFs. These data provide strong support for the successful synthesis of Eu / Ce-MOFs.

[0059] Table 1 Changes in the percentage content of different elements in Eu-MOF, Ce-MOF and Eu / Ce-MOFs

[0060]

[0061] like Figure 2 As shown in Fig. 5, the N2 adsorption-desorption isotherm of Eu / Ce-MOFs is consistent with the type III temperature curve, and the BET specific surface area of Eu / Ce-MOFs is 30.78 m 2 g -1 In addition, the average pore size of Eu / Ce-MOFs was 1.36 nm ( Figure 6 ), confirming the presence of microporous structures in Eu / Ce-MOFs. A large number of microporous structures exhibit excellent porous properties and good adsorption properties, providing sufficient active sites for highly sensitive sensors. The surface functional groups of Eu / Ce-MOFs were identified using Fourier transform infrared spectroscopy (FT-IR). Figure 2 g). For DPA, 1708 cm -1 and 1298cm -1 The absorption peaks at 1575 cm correspond to the stretching vibrations of C=O and CO in the carboxyl group. -1 , 1461cm -1 and 1265cm -1 The three different absorption peaks at 918cm belong to the stretching vibrations of CN, C=C and C=N in the pyridine ring. -1 The characteristic peak observed atO =C-OH) is caused by the out-of-plane bending vibration. In the FT-IR of H4btec, the wavelength range is 2500-2700 cm -1 The absorption peak at 1690-1730 cm is the stretching vibration of the -OH group. -1 The absorption peaks at 1380-1404 cm are the symmetric stretching vibrations of C=O. However, these characteristic peaks disappeared in Eu-MOF, and the symmetric stretching vibrations of O=CO (1380-1404 cm) were observed in Eu-MOF. -1 ) and asymmetric (1583-1620cm -1 ) stretching vibration. Considering the strong affinity between lanthanide metals and oxygen, this is due to the coordination of lanthanide metals with oxygen on the hydroxyl group, indicating that the carboxylic acid oxygen in H4btec is successfully coordinated with Eu. In addition, by comparing with DPA FT-IR, it is found that the CO of Eu-MOF is from 1298 cm -1 Move to 1288cm -1 , further proved that the carboxyl oxygen atom in the ligand and Eu 3+ At the same time, 1390cm -1 The absorption peaks near the 3+ 1683cm in BDC-NH2 -1 The absorption peak at 1587-1620cm is the C=O stretching vibration of the carboxyl group. -1 and 1380-1406cm -1 The characteristic bands at 3400 cm correspond to the asymmetric and symmetric stretching vibrations of the carboxyl group. -1 The broad peak at is caused by the -OH stretching vibration of water. From the above analysis, it can be seen that there are a large number of carboxyl and hydroxyl functional groups in Eu / Ce-MOFs, and the presence of hydroxyl groups is beneficial to enhancing the stability and hydrophilicity of the material.

[0062] In addition, the chemical structure and elemental composition of Eu-MOF, Ce-MOF, and Eu / Ce-MOFs were studied using XPS spectroscopy. The full spectrum of Eu-MOF showed the presence of C, O, N, and Eu elements. The full spectrum of Ce-MOF was dominated by C, O, N, and Ce elements, while the full spectrum of Eu / Ce-MOFs was dominated by C1s, O 1s, N 1s, Eu 3d, and Ce 3d peaks ( Figure 2 h), which provides evidence for the presence of C, O, N, Eu and Ce elements in Eu / Ce-MOFs, and the results are in good agreement with the element distribution measured by TEM. The elements of Eu-MOF, Ce-MOF and Eu / Ce-MOFs were analyzed by high-resolution scanning spectroscopy ( Figure 7Taking Eu / Ce-MOFs as an example, its high-resolution scanning spectrum was analyzed. The high-resolution XPS spectrum of C1s ( Figure 7 c) shows three peaks at 285.21, 286.54 and 288.78 eV, which are attributed to CC / C=C, COC and C=O, respectively. The N1s high-resolution XPS spectrum of Eu / Ce-MOFs is deconvoluted into two peaks ( Figure 7 f), which are attributed to NH (399.48 eV) and NC (401.79 eV), respectively. Figure 7 In Fig. 1, the O1s peaks of Eu / Ce-MOFs at 531.22 and 532.00 eV are attributed to the C=O and CO groups in the ligands. Figure 2 i shows the high-resolution scanning spectra of Eu-MOF and Eu / Ce-MOFs, where Eu 3d 3 / 2 and Eu 3d 5 / 2 The characteristic peaks are located at 1164.82, 1154.60, 1135.06 and 1125.14 eV respectively. The high-resolution XPS spectrum of Ce 3d ( Figure 2 j) shows that there are mixed valence states in Ce-MOF and Eu / Ce-MOFs. The two characteristic peaks at 882.31 and 902.80 eV belong to Ce 3d 5 / 2 , the characteristic peaks at 885.87 and 905.24 eV belong to Ce 3d 3 / 2 After the reaction of Eu-MOF and Ce-MOF, the two characteristic peaks of Eu 3d moved from 1124.55eV and 1134.83eV to 1125.14eV and 1135.06eV, indicating that Eu 3+ It may be coordinated with -COOH in the ligands used to synthesize Ce-MOF. In addition, the two characteristic peaks of Ce3d moved from 889.00eV and 903.71eV to 902.80eV and 905.24eV, indicating that Ce 3+ It may be coordinated with the ligands used to synthesize Eu-MOF. XPS characterization results confirmed the successful synthesis of heterogeneous Eu / Ce-MOFs.

[0063] Example 2

[0064] A preparation method of a Eu / Ce-MOFs ratio fluorescence sensor in this embodiment, the synthesis schematic diagram is shown as follows Figure 1 As shown in a, the steps are as follows:

[0065] (1) Preparation of Eu-MOF (powder): 0.5352 g of Eu(NO3)3·6H2O was dissolved in 5 mL of water to prepare solution A. 0.0254 g of H4btec and 0.0835 g of DPA were dissolved in 15 mL of a mixed solvent of N,N-diethylformamide (DMF) and water (DMF:water = 1:1) to prepare solution B. After solution A and solution B were thoroughly mixed and stirred for 30 minutes, the resulting solution was placed in a stainless steel autoclave lined with polytetrafluoroethylene and heated hydrothermally at 150°C for 12 hours. After cooling to ambient temperature, the precipitate was washed three times with DMF and anhydrous ethanol. Finally, the precipitate was dried in a vacuum drying oven at 50°C overnight.

[0066] (2) Preparation of Ce-MOF (powder): First, 0.1862 g of CeCl₃·7H₂O was mixed with 5 mL of water. Then, 0.0091 g of BDC-NH₂ was added to 15 mL of DMF, stirred, and placed on a magnetic stirrer at 60°C, 600 rpm, and stirred for one hour. The precipitate was washed three times with DMF and anhydrous ethanol, and finally dried in a vacuum drying oven at 50°C overnight.

[0067] (3) Preparation of Eu / Ce-MOFs: 50 mg of the prepared Eu-MOF powder and 5 mg of Ce-MOF powder were dissolved in 8 mL of DMF and stirred at 600 r / min on a magnetic stirrer for 30 min. The resulting solution was then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heated continuously at 100°C for 16 h. After cooling to room temperature, the solution was washed three times with DMF and three times with anhydrous ethanol. The supernatant was discarded, and the precipitate was dried in a vacuum drying oven at 50°C overnight to obtain Eu / Ce-MOFs, i.e., the Eu / Ce-MOFs ratiometric fluorescence sensor.

[0068] Example 3

[0069] A preparation method of a Eu / Ce-MOFs ratio fluorescence sensor in this embodiment, the synthesis schematic diagram is shown as follows Figure 1 As shown in a, the steps are as follows:

[0070] (1) Preparation of Eu-MOF (powder): 0.2231 g of Eu(NO3)3·6H2O was dissolved in 5 mL of water to prepare solution A. 0.0254 g of H4btec and 0.2005 g of DPA were dissolved in 15 mL of a mixed solvent of N,N-diethylformamide (DMF) and water (DMF:water = 1:1) to prepare solution B. After solution A and solution B were thoroughly mixed and stirred for 30 minutes, the resulting solution was placed in a stainless steel autoclave lined with polytetrafluoroethylene and heated hydrothermally at 100°C for 36 hours. After cooling to ambient temperature, the precipitate was washed three times with DMF and anhydrous ethanol. Finally, the precipitate was dried in a vacuum drying oven at 50°C overnight.

[0071] (2) Preparation of Ce-MOF (powder): First, 0.0372 g of CeCl₃·7H₂O was mixed with 5 mL of water. Then, 0.0091 g of BDC-NH₂ was added to 15 mL of DMF, stirred, and placed on a magnetic stirrer at 20°C and 600 rpm for four hours. The precipitate was washed three times with DMF and anhydrous ethanol, and finally dried in a vacuum drying oven at 50°C overnight.

[0072] (3) Preparation of Eu / Ce-MOFs: 30 mg of the prepared Eu-MOF powder and 2 mg of Ce-MOF powder were dissolved in 8 mL of DMF and stirred at 600 r / min on a magnetic stirrer for 30 min. The resulting solution was then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heated continuously at 150°C for 8 h. After cooling to room temperature, the solution was washed three times with DMF and three times with anhydrous ethanol. The supernatant was discarded, and the precipitate was dried in a vacuum drying oven at 50°C overnight to obtain Eu / Ce-MOFs, i.e., the Eu / Ce-MOFs ratiometric fluorescence sensor.

[0073] Example 4

[0074] A preparation method of a Eu / Ce-MOFs ratio fluorescence sensor in this embodiment, the synthesis schematic diagram is shown as follows Figure 1 As shown in a, the steps are as follows:

[0075] (1) Preparation of Eu-MOF (powder): 0.3363 g of EuCl3·6H2O was dissolved in 5 mL of water to prepare solution A. 0.0254 g of H4btec and 0.1671 g of DPA were dissolved in 15 mL of a mixed solvent of N,N-diethylformamide (DMF) and water (DMF:water = 1:1) to prepare solution B. After solution A and solution B were thoroughly mixed and stirred for 30 minutes, the resulting solution was placed in a stainless steel autoclave lined with polytetrafluoroethylene and heated hydrothermally at 120°C for 24 hours. After cooling to ambient temperature, the precipitate was washed three times with DMF and anhydrous ethanol. Finally, the precipitate was dried in a vacuum drying oven at 50°C overnight.

[0076] (2) Preparation of Ce-MOF (powder): First, 0.1086 g of Ce(NO₃)₃·6H₂O was mixed with 5 mL of water. Then, 0.0091 g of BDC-NH₂ was added to 15 mL of DMF, stirred, and placed on a magnetic stirrer at 40°C and 600 rpm for two hours. The precipitate was washed three times with DMF and anhydrous ethanol, and finally dried in a vacuum drying oven at 50°C overnight.

[0077] (3) Preparation of Eu / Ce-MOFs: 50 mg of the prepared Eu-MOF powder and 4 mg of Ce-MOF powder were dissolved in 8 mL of DMF and stirred at 600 r / min on a magnetic stirrer for 30 min. The resulting solution was then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heated continuously at 120°C for 12 h. After cooling to room temperature, the solution was washed three times with DMF and three times with anhydrous ethanol. The supernatant was discarded, and the precipitate was dried in a vacuum drying oven at 50°C overnight to obtain Eu / Ce-MOFs, i.e., the Eu / Ce-MOFs ratiometric fluorescence sensor.

[0078] Example 5

[0079] The preparation method of the Eu / Ce-MOFs hydrogel sensor of this embodiment comprises the following steps:

[0080] First, 1.5 g of PVA-1799 was added to 10.5 g of deionized water. The solution was heated and stirred continuously at 95°C for 2 hours to completely dissolve the PVA. The solution was then sonicated for 15 minutes to remove air bubbles, resulting in a uniform, transparent PVA solution. Subsequently, the Eu / Ce-MOFs prepared in Example 1 were added to DMF to create a 3 mg / mL Eu / Ce-MOFs solution. 1 mL of the Eu / Ce-MOFs solution was added to the PVA gel solution and stirred at room temperature for 10 minutes before being allowed to stand at room temperature to remove air bubbles. The Eu / Ce-MOFs-containing PVA gel solution was transferred to a glass Petri dish and frozen at -20°C for 20 hours, followed by thawing at 25°C for 4 hours. After three freeze-thaw cycles, the Eu / Ce-MOFs-based hydrogel was obtained. Finally, the hydrogel was pressed using a circular pattern mold to produce circular hydrogel sensors with uniform shape and size.

[0081] As shown in SEM analysis ( Figure 19 As shown in (a, b), Eu / Ce-MOFs hydrogel has a more porous structure compared to pure polyvinyl alcohol (PVA) hydrogel. From the EDS mapping, it was observed that Eu / Ce-MOFs were uniformly dispersed in the hydrogel. In addition, the XPS analysis of PVA and Eu / Ce-MOFs hydrogels ( Figure 20 , 21) further confirmed that Eu / Ce-MOFs had been successfully dispersed in the hydrogel network.

[0082] Implementation effect examples

[0083] The optical properties, TCs detection conditions, TCs detection mechanism, and TCs detection performance of the Eu / Ce-MOFs ratiometric fluorescence sensor prepared in Example 1 of the present invention were explored. The specific steps are as follows:

[0084] (1) Optical performance

[0085] The optical properties of Eu / Ce-MOFs were analyzed by UV-visible absorption spectroscopy and fluorescence emission spectroscopy. The solutions were prepared as follows: the obtained Eu / Ce-MOFs were dissolved in DMF to prepare a 2.5 μg / mL solution for testing its fluorescence properties, UV-visible absorption spectrum and anti-photobleaching properties; H4btec, DPA, Eu-MOF, Ce-MOF and Eu / Ce-MOFs were dissolved in DMF to prepare a 2.5 μg / mL solution for testing its fluorescence properties under 270 nm excitation; 5 μg / mL Eu / Ce-MOFs (0.5 mL) were mixed with different concentrations (0, 0.1, 1, 10, 10 2 , 10 3μmol / L) of sodium chloride solution were mixed in equal volumes to detect the effect of ionic strength on the stability of Eu / Ce-MOFs; three batches of Eu / Ce-MOFs were prepared into 2.5μg / mL DMF-dissolved solutions to detect the reproducibility of Eu / Ce-MOFs; 2.5μg / mL Eu / Ce-MOFs solution was prepared, and the change in its fluorescence intensity under 270nm excitation was measured every 24 hours to study its storage stability; 5μg / mL Eu / Ce-MOFs (0.5mL) solution was mixed with equal volumes of buffer solutions of different pH values to study the effect of acid and base on the fluorescence intensity of Eu / Ce-MOFs; 5μg / mL Eu / Ce-MOFs (0.5mL) solution was mixed with equal volumes of 50μmol / L TC, OTC and DOX, respectively, and the fluctuation of fluorescence intensity was recorded within 15 minutes to determine the optimal incubation time. Figure 8 As shown in a, Eu / Ce-MOFs exhibits a clear UV absorption peak at 240 nm, which is caused by the π-π* transition of C=C. Figure 8 As shown in b, free DPA and H4btec ligands have almost no emission peaks under 270nm excitation. Ce-MOF exhibits a clear characteristic emission wavelength at 427nm, which is attributed to the BDC-NH2 ligand absorbing the excitation light and transferring the energy to Ce. 3+ At the same time, Eu-MOF exhibited characteristic emission wavelengths at 557nm, 581nm, 594nm, 617nm, and 695nm, which was attributed to Eu 3+ 5D0→7F J (J=0,1,2,3,4) transitions. The sharp emission peaks of Eu / Ce-MOFs at 427nm, 557nm, 581nm, 594nm, 617nm and 695nm include the characteristic emission peaks of Ce-MOF and Eu-MOF. Under 254nm ultraviolet light, the fluorescence colors of Ce-MOF, Eu-MOF and Eu / Ce-MOFs are blue, red and purple, respectively. Figure 8 b illustration). These phenomena further demonstrate the successful preparation of Eu / Ce-MOFs.

[0086] Furthermore, some important environmental factors (ionic strength, reproducibility, storage stability and resistance to photobleaching) were explored to study the stability of Eu / Ce-MOFs. 3 μmol / L, the FL intensity of Eu / Ce-MOFs remained basically unchanged ( Figure 8 c), indicating that Eu / Ce-MOFs have high salt tolerance. This is beneficial for FL sensing in aqueous environments. Three batches of Eu / Ce-MOFs were prepared and the fluorescence intensity was measured. Figure 8As shown in Figure d, the fluorescence intensities of the three batches of Eu / Ce-MOFs are basically consistent, proving that Eu / Ce-MOFs have high reproducibility. Figure 8 Figure e shows the change in FL intensity of Eu / Ce-MOFs over 7 days. It is clearly observed that the FL intensity of Eu / Ce-MOFs remains almost unchanged over the 7-day period, demonstrating the excellent storage stability of Eu / Ce-MOFs. After continuous irradiation at 270 nm for 20 minutes, the FL intensities of Eu / Ce-MOFs at 617 nm and 427 nm show little change, indicating that Eu / Ce-MOFs have good resistance to photobleaching. These results demonstrate that Eu / Ce-MOFs have excellent FL stability and can serve as an effective FL sensor for TCs residue analysis, with strong potential for practical application.

[0087] (2) Optimization of TCs detection conditions

[0088] To obtain the optimal detection conditions for TC, OTC, and DOX, the excitation wavelength, solvent type, solution pH, and incubation time of TCs in the sensor were studied in detail. Figure 8 As shown in Figure b, the FL emission peaks at 617 nm and 427 nm have a high sensitivity to the FL response of TCs, so the emission peaks at 617 nm and 427 nm are selected as the optimal detection wavelengths for quantitative analysis. In addition, when the excitation wavelength changes from 240 nm to 300 nm, the FL emission intensity of Eu / Ce-MOFs at 427 nm and 617 nm first increases and then decreases ( Figure 8 g). The maximum emission intensity at 617nm is obtained under an excitation wavelength of 270nm. However, at this excitation wavelength, the emission intensity at 427nm is relatively low. The maximum emission intensity at 427nm occurs under 260nm excitation, at which time the emission intensity at 617nm is relatively low. Since the peak intensity at 617nm is larger and the red change is more easily recognized by the naked eye, 270nm is determined to be the optimal excitation wavelength for the FL sensor. Different solvents also have a certain degree of influence on the performance of FL materials. The obtained Eu / Ce-MOFs powder was dispersed in different solvents, such as water, ethanol, methanol, acetonitrile and DMF. Under a 254nm ultraviolet lamp, the Eu / Ce-MOFs solution dispersed in water exhibited blue fluorescence ( Figure 9 b), this may be because water partially quenches the red fluorescence of Eu. Eu / Ce-MOFs exhibit red fluorescence in ethanol, methanol, acetonitrile and DMF, but its red fluorescence is more obvious and more stable in DMF. Eu / Ce-MOFs solutions in different solvents are all white and opaque solutions under sunlight ( Figure 9 a). Therefore, DMF was selected as the solvent for dispersing Eu / Ce-MOFs.

[0089] It can be clearly observed that the FL intensity at 427 nm does not change much in the pH range of 2-12, while the FL intensity at 617 nm first increases and then decreases with the increase of pH and reaches the maximum value at pH = 9 ( Figure 8 h). In addition, the FL intensity ratio at 617 nm and 427 nm first increases and then decreases with the increase of pH and reaches the maximum value at pH = 9 ( Figure 10 a). XRD was used to test the stability and durability of Eu / Ce-MOFs fluorescence sensor under different pH conditions. Figure 10 In b, Eu / Ce-MOFs did not undergo obvious structural changes in the pH range of 2-12, confirming the excellent stability of the Eu / Ce-MOFs fluorescence sensor. In addition, with the help of the excitation energy provided by the portable UV lamp, the effect of pH on the fluorescence characteristics of Eu / Ce-MOFs can be intuitively observed. Figure 11 As shown, under 254nm UV light, the fluorescence of Eu / Ce-MOFs brightens with increasing pH in the range of 2-9, then dims as the pH increases. Considering the detection environment, pH = 8 (0.05mol / L Tris-HCl buffer) was determined to be the optimal detection condition. The effect of incubation time on the performance of Eu / Ce-MOFs was also studied. Figure 8 i recorded the fluctuation of FL intensity within 15 min after adding TC, OTC and DOX into Eu / Ce-MOFs. 617 / F 427 A relatively stable state was reached 3 min after adding TC, OTC, and DOX. Once stabilized, the FL intensity remained essentially unchanged for a long period of time. Therefore, in subsequent experiments, TCs were detected with an incubation time of 3 min.

[0090] (3) Sensing mechanism for detecting TCs

[0091] The FL quenching observed during TCs detection may be due to multiple mechanisms, including (a) MOFs skeleton collapse; (b) fluorescence resonance energy transfer (FRET) and (c) inner filter effect (IFE). The fluorescence response of Eu / Ce-MOFs to TCs was studied using XRD, UV-vis, FT-IR, fluorescence lifetime and XPS. The XRD spectra of Eu / Ce-MOFs before and after the addition of TC, OTC and DOX remained consistent ( Figure 12 a), indicating that the framework structure of Eu / Ce-MOFs did not change during the TC detection process. Therefore, the FL quenching is not caused by the collapse of the Eu / Ce-MOFs framework. Figure 13It was observed that TC, OTC and DOX had similar characteristic peaks. When TC, OTC and DOX were mixed with Eu / Ce-MOFs, the UV absorption spectrum of the mixture was the sum of the spectra of TCs and Eu / Ce-MOFs and no new absorption peaks appeared, indicating that Eu / Ce-MOFs and TCs remained independent during the detection process and no new substances were formed during the fluorescence quenching process. It is worth noting that the characteristic peaks of TC, OTC and DOX were red-shifted, which may be due to the aggregation of TCs adsorbed on the surface of Eu / Ce-MOFs. In addition, the excitation spectrum of Eu / Ce-MOFs overlapped significantly with the broad-spectrum absorption bands of TC, OTC and DOX ( Figure 12 b), indicating that TCs can absorb the excitation energy of the Eu / Ce-MOFs sensor and quench its FL intensity. These results indicate that the quenching of Eu / Ce-MOFs by TCs may be caused by IFE or FRET. However, there is no obvious overlap between the absorption spectra of TC, OTC and DOX and the emission spectra of Eu / Ce-MOFs, which excludes the possibility of FRET. There is no obvious change in the FT-IR spectra in the presence or absence of TC, OTC and DOX ( Figure 14 ), indicating that there is no chemical reaction between Eu / Ce-MOFs and TCs. In addition, the FL lifetime of Eu / Ce-MOFs did not change significantly after the addition of TC, OTC, and DOX ( Figure 12 c), confirming that IFE is the main cause of fluorescence quenching.

[0092] Taking the reaction between TC and Eu / Ce-MOFs as an example, the changes in XPS spectra after the introduction of TC were studied. Figure 15 As shown in a, the XPS spectrum after adding TC retains the original five elements. In the high-resolution C1s spectrum ( Figure 15 b), the increase of C=C content confirms the existence of TC. The characteristic peak of NC moves from 401.79eV to 401.64eV ( Figure 15 c). In the O1s spectrum ( Figure 15 d), the peak position of CO shifts from 531.22eV to 531.09eV, while the peak position of C=O shifts from 532.00eV to 531.88eV. In the Eu3d spectrum ( Figure 15 e), Eu 3d 5 / 2 The peaks of Ce 3d 5 / 2 The peak value also shifted from 882.31eV to 883.1eV ( Figure 15 f) This may be due to the formation of complexes between TC and Eu or Ce. Combined with the above data, it is speculated that TCs can form complexes with Eu or Ce.3+ and Ce 3+ Forming a complex to inhibit the ligand energy from moving to Eu 3+ and Ce 3+ The transfer of β-catenin resulted in the quenching of fluorescence at 617 nm and 427 nm.

[0093] (4) Eu / Ce-MOFs ratiometric fluorescence detection of TCs

[0094] Photoluminescence detection experiments were performed in room temperature aqueous solution. First, Eu / Ce-MOFs powder was dissolved in 1 mL of DMF to prepare a 3.0 mg / mL Eu / Ce-MOFs solution, which was then diluted to 5 μg / mL with Tris-HCl buffer (0.05 mol / L, pH = 8.0). 0.5 mL of TC, OTC, or DOX solutions of varying concentrations were added to 0.5 mL of the Eu / Ce-MOFs solution. After incubation for 3 minutes, the fluorescence spectrum was recorded. In addition, the fluorescence intensity of the mixed solution (final concentration of Eu / Ce-MOFs was 2.5 μg / mL) after different types of antibiotics (gentamicin sulfate (GEN), neomycin (NEO), erythromycin (EM), kanamycin sulfate (KANA), florfenicol (FFC), streptomycin sulfate (STR), lincomycin (LIN), thiamphenicol (THI), and metronidazole (MTZ)) were mixed with the same volume of Eu / Ce-MOFs solution to investigate the selectivity of Eu / Ce-MOFs for TC, OTC, and DOX. At the same time, common cations, anions, and biomacromolecules were mixed with the same volume of Eu / Ce-MOFs solution (final concentration of Eu / Ce-MOFs in the mixed solution was 2.5 μg / mL) to investigate the anti-interference ability of Eu / Ce-MOFs in detecting TC, OTC, and DOX.

[0095] Under the optimal conditions of pH = 8 and incubation time of 3 min, the detection performance of Eu / Ce-MOFs for TC, OTC and DOX FL was investigated. The schematic diagram of Eu / Ce-MOFs detecting TC, OTC and DOX is shown in Figure 2. Figure 1 b. The changes in fluorescence spectra after adding different concentrations of TC, OTC and DOX to the Eu / Ce-MOFs solution are shown in Figure 12 df. The increase in TC, OTC, and DOX concentrations resulted in a gradual decrease in the fluorescence intensity at 426 nm and 617 nm. A ratiometric fluorescence sensing model was established based on the relationship between the ratio of the two fluorescence intensities and the concentrations of TC, OTC, and DOX ( Figure 12 gi). Figure 12 gi showed that after adding TC, OTC and DOX, F 617 / F 427The FL intensity ratio of DOX increased with the continuous increase of TC, OTC and DOX concentrations. 617 / F 427 The ratio is the highest. When the concentration is 150μmol / L, the F 617 / F 426 The ratio is the highest. In the range of 0-150 μmol / L, it was observed that the fluorescence intensity ratio showed a good linear relationship with the concentration of TC and OTC. The linear equations were y=2.89694+0.01x(R 2 =0.999) and y = 2.88349 + 0.00845x (R 2 =0.995)( Figure 12 g, h). The limits of detection (LOD) of TC and OTC were 73.0 nmol / L and 51.7 nmol / L, respectively (S / N=3). Figure 12 As shown in Fig. 1, the FL intensity ratio (F 617 / F 427 ) showed a good linear relationship with DOX concentration, and the LOD was 54.9 nmol / L. As the concentration of TCs increased, the red color became darker under 254 nm UV light ( Figure 16 ac). In addition, Figure 17 The CIE chromaticity coordinates of Eu / Ce-MOFs for detecting TCs are presented, confirming that the red luminescence of Eu / Ce-MOFs under 254nm UV irradiation gradually dims with increasing concentrations of TC, OTC, and DOX. Compared with other TC detection methods, the Eu / Ce-MOFs ratiometric FL sensor in this application has a lower LOD and a wider linear response range. The rich color changes make Eu / Ce-MOFs a promising material for FL sensing applications.

[0096] Considering the specific response ability of FL sensor to TCs and the complexity of food mechanism, the effects of various potential interfering substances on FL sensor were tested, including antibiotics, carbohydrates, amino acids, metal ions, and anions. The detection method was consistent with that of TCs, only using equal amounts of substances instead of TCs. Figure 18 As shown in a, Eu / Ce-MOFs had no obvious response to other antibiotics. When TC, OTC and DOX coexisted with other antibiotics, there was no significant effect on the FL intensity ratio, indicating that the FL sensor has strong selectivity for TC, OTC and DOX ( Figure 18 Randomly select interfering substances, such as cations (Na + ,K + , Mg 2+ and Mn 2+ ), anion (Cl- ,I - , CO3 2- and CH3COO - ), amino acids (serine (Ser), glycine (Gly) and proline (Pro)) and sugars (glucose (Glu) and lactose (lactose)) to evaluate the response of the FL sensor. Interference tests showed that at a concentration of 10 μmol / L, the effect of interfering substances on the FL response of the FL sensor was negligible ( Figure 18 e). Figure 18 As shown in Figures f-h, even in the presence of these interfering substances, the presence of interfering substances has little effect on the normal detection of Eu / Ce-MOFs. Therefore, even under complex environmental conditions, Eu / Ce-MOFs exhibit high selectivity and anti-interference in the detection of TC, OTC, and DOX.

[0097] Application Examples

[0098] 1. Determination of TC, OTC and DOX in actual samples

[0099] Based on the results of the anti-interference experiments, the Eu / Ce-MOFs FL sensor has the potential to be used for evaluating TC, OTC, and DOX in real samples. Therefore, we further analyzed the analytical capabilities of Eu / Ce-MOFs for TC, OTC, and DOX in raw pork and fresh milk. First, these real samples were pretreated. The specific sample pretreatment process is as follows:

[0100] Raw pork: Add 2.0 g minced pork sample and 10 mL of 1% formic acid acetonitrile solution to a 50 mL centrifuge tube, vortex for 1 minute and ultrasonically vibrate for 30 minutes, then add 1 g NaCl and 4 g anhydrous MgSO4, vibrate for 5 minutes, and centrifuge for 10 minutes (10,000 rpm). Collect the supernatant and add 150 mg C 18 , 50 mg of N-propylethylenediamine adsorbent, and 900 mg of Na2SO4, vortex for 5 minutes, and then centrifuge for 5 minutes (10,000 rpm). Take 7 mL of the supernatant, blow it to near dryness with nitrogen at 40°C, add 7 mL of acetonitrile, vortex for 5 minutes, and ultrasonically vibrate for 10 minutes before collecting it through a 0.22 μm microporous nylon organic filter membrane.

[0101] Milk: Milk samples were pretreated according to existing methods. 20 mL of acetonitrile was added to 20 mL of milk and sonicated for 10 minutes to remove proteins and other organic molecules. The mixture was then centrifuged at 10,000 rpm for 10 minutes, and the supernatant was filtered through a 0.22 μm filter. Finally, the collected filtrate was diluted 50-fold with Tris-HCl buffer for further analysis.

[0102] 2 mL of TC, OTC, and DOX solutions of varying concentrations were then added to 2 mL of pretreated pork and milk samples, respectively, to create spiked pork and milk samples containing 0–150 μmol / L TC and OTC, and 0–100 μmol / L DOX. Each sample was prepared in triplicate and tested three times using the FL method to minimize the influence of random errors caused by equipment and environmental factors. Raw pork from different supermarkets and pure milk from different brands were used as blank samples to determine the initial levels of TC, OTC, and DOX. The results are shown in Table 2.

[0103] Table 2 Test results of different types of blank pork and milk samples

[0104]

[0105] ND: Not Detected

[0106] As can be seen from Table 3, TC, OTC, and DOX were not detected in the initial blank sample. Since TC, OTC, and DOX were not detected in the real samples, the standard addition method was used to simulate the real test conditions.

[0107] In addition, the reliability of the FL sensor measurement results was verified by conventional high performance liquid chromatography (HPLC) method. The specific chromatographic parameters are as follows: the chromatographic column is Agilent Eclipse Plus C 18 The column was 50 mm × 2.1 mm, 1.8 μm. The mobile phases for gradient elution were A (ammonium acetate (5 mmol / L), formic acid (0.1%, v / v), and methanol (2%, v / v)) and B (pure methanol). The gradient elution program is detailed in Table 3. The flow rate was 0.3 mL / min, and the column temperature was 35°C. The sample injection volume was 10.0 μL, and the UV-visible detector wavelength was 350 nm.

[0108] Table 3 Gradient elution procedures for TC, OTC, and DOX

[0109]

[0110] The reliability and reproducibility of the Eu / Ce-MOFs sensor for analyzing TC, OTC, and DOX in different real samples were determined by calculating the TC, OTC, and DOX recoveries. The results are shown in Table 4.

[0111] Table 4 Detection results of TC, OTC and DOX in pork and milk samples

[0112]

[0113]

[0114] ND: Not Detected

[0115] As shown in Table 4, the recoveries of TC, OTC, and DOX in pork and milk samples by this method ranged from 89.3% to 112.9%, with relative standard deviations (RSDs) ranging from 0.2% to 6.0%. These high recoveries and low RSDs demonstrate that the FL sensor can be used to detect TCs in real samples. Subsequently, pork and milk samples containing TC, OTC, and DOX were tested using the hydrogel-based FL sensor, demonstrating that the method is suitable for visual detection of TCs. Furthermore, the reliability and accuracy of the ratiometric FL sensor were verified by comparing HPLC data with fluorescence measurement results. These results demonstrate that the assay meets the requirements for practical application.

[0116] 2. Machine Learning-Assisted Intelligent Visualization Detection of Eu / Ce-MOFs Hydrogels

[0117] The abundant hydroxyl and carboxyl functional groups in the hydrogel can provide more adsorption sites to accumulate and adsorb TCs. In order to evaluate the ability of Eu / Ce-MOFs hydrogel to detect TCs and facilitate on-site detection of TCs, the hydrogel sensor prepared in Example 5 was immersed in an aqueous solution containing different concentrations of TC, OTC and DOX. The immersion process was carefully controlled at room temperature to ensure that the hydrogel was evenly exposed to the antibiotic solution. After soaking for 30 minutes, the hydrogel was placed in a culture dish, and the visual response of the hydrogel was detected under sunlight and ultraviolet light (254nm). The feasibility of visual sensing based on Eu / Ce-MOFs hydrogel was studied. Figure 22 As shown in a, the Eu / Ce-MOFs-based hydrogel has no obvious color change under natural light. Under 254nm ultraviolet light, the Eu / Ce-MOFs hydrogel exhibits red fluorescence. However, when the Eu / Ce-MOFs hydrogel is immersed in solutions of different concentrations of TC (0-150μmol / L), OTC (0-150μmol / L), and DOX (0-100μmol / L), the fluorescence shows varying degrees of quenching.

[0118] In order to establish an intelligent detection system and minimize the judgment errors of human vision, a smartphone-based FL imaging method was implemented. Figure 1c, specifically including: (1) using a smartphone camera to capture FL images, (2) transferring the images to a computer for processing, (3) using the SVM algorithm for image classification, feature extraction, and RGB value conversion, (4) building a model based on the relationship between the extracted RGB values and TCs concentrations, and (5) training and testing the model. Specifically, each image is annotated with the corresponding concentration value as the label for training the SVM model. Subsequently, the RGB values of the target area of the image are extracted as feature vectors. The RGB values are normalized to the range [0,1] using Equation 1 to improve model performance. The sklearn.svm.SVR model is initialized and trained according to Equations 2 and 3, and the penalty parameters and error tolerance are optimized.

[0119]

[0120] model = SVR(kernel = 'rbf', C = 1000, gamma = 0.01, epsilon = 0.01) (Equation 2)

[0121] model.fit(X_train,y_train) (Equation 3)

[0122] Among them, Confidence: confidence, which indicates the reliability of the predicted value. Distance: the distance from the sample to the decision boundary, which indicates the deviation between the predicted value and the actual value. max(Distances): the maximum value of all sample distances, used for normalization so that the confidence falls within the range of [0,1]. model: model. SVR is support vector regression, which is used to predict continuous values. kernel = 'rbf': indicates the kernel function type. C: regularization parameter, a regularization parameter that controls model complexity and error tolerance. A larger C will make the model focus more on reducing errors, which may lead to overfitting. A smaller C will allow more errors, which may lead to underfitting. Gamma: a parameter of the RBF kernel, which determines the range of influence of a single sample on the model. epsilon: fault tolerance, used to control the model's tolerance to errors. Model.fit(): indicates training the model. X_train: indicates the feature matrix of the training data. y_train: indicates the label of the training data. After model training, the system demonstrated reliable prediction ability on the test dataset, achieving a confidence level of 95% ( Figure 22 b).

[0123] This intelligent sensing platform uses a machine learning algorithm to rapidly convert visible FL changes into specific RGB values, enabling quantitative detection of TCs. This method represents a significant advancement in low-dose, high-throughput, real-time analysis, establishing an intelligent sensing platform for rapid on-site detection of TCs.

[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a Eu / Ce-MOFs ratio fluorescence sensor, characterized in that: Here are the steps: (1) Dissolving 1,2,4,5-pyromellitic acid and 2,6-pyridinedicarboxylic acid in a mixed solvent of DMF and water to obtain a mixed solution; adding an aqueous solution of europium salt to the mixed solution, and performing a hydrothermal reaction to obtain Eu-MOF powder; (2) Dissolve 2-aminoterephthalic acid in DMF, add cerium salt aqueous solution, and stir to obtain Ce-MOF powder; (3) The Eu-MOF powder prepared in step (1) and the Ce-MOF powder prepared in step (2) are added to DMF and mixed, and subjected to a hydrothermal reaction to obtain Eu / Ce-MOFs, i.e., a Eu / Ce-MOFs fluorescence sensor.

2. The method for preparing the Eu / Ce-MOFs ratio fluorescence sensor according to claim 1, characterized in that: In the step (1), the molar ratio of 1,2,4,5-pyromellitic acid, 2,6-pyridinedicarboxylic acid and europium salt is 1:(5-12):(5-12); the europium salt is europium nitrate or europium chloride.

3. The preparation method of the Eu / Ce-MOFs ratio fluorescence sensor according to claim 2, characterized in that: In step (2), the molar ratio of 2-aminoterephthalic acid to cerium salt is 1:2-10; the stirring temperature is 20-60° C., and the stirring time is 1-4 hours; and the cerium salt is cerium chloride or cerium nitrate.

4. The method for preparing the Eu / Ce-MOFs ratio fluorescence sensor according to claim 3, characterized in that: The mass ratio of Eu-MOF powder to Ce-MOF powder in step (3) is (10-15):1; the temperature of the hydrothermal reaction in steps (1) and (3) is 100-150° C., wherein the time of the hydrothermal reaction in step (1) is 12-36 h; and the time of the hydrothermal reaction in step (3) is 8-16 h.

5. A Eu / Ce-MOFs ratio fluorescence sensor prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the Eu / Ce-MOFs ratiometric fluorescence sensor according to claim 5 in the detection of tetracycline antibiotics for purposes other than disease diagnosis.

7. A hydrogel sensor, characterized in that: The hydrogel sensor comprises a PVA hydrogel matrix and the Eu / Ce-MOFs ratio fluorescence sensor according to claim 5.

8. The method for preparing the hydrogel sensor according to claim 7, characterized in that: The steps are as follows: PVA is completely dissolved in deionized water, Eu / Ce-MOFs ratio fluorescence sensor is added, and after freeze-thaw cycles, a hydrogel sensor is obtained.

9. Use of the hydrogel sensor according to claim 7 in visual detection of tetracycline drugs for purposes other than disease diagnosis.

10. The use according to claim 9, characterized in that The application collects fluorescence images of tetracycline antibiotics detected by a hydrogel sensor, then extracts the RGB values of the image as feature vectors and establishes a model, and uses the data model to obtain the concentration of tetracycline antibiotics through the fluorescence color of the hydrogel sensor.

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