Dual-emission ratio type fluorescence sensing probe based on lanthanide MOFs as well as preparation method and application of dual-emission ratio type fluorescence sensing probe

Abstract

The invention belongs to the technical field of fluorescence sensors, and particularly relates to a dual-emission ratio type fluorescence sensing probe based on lanthanide MOFs as well as a preparation method and application of the dual-emission ratio type fluorescence sensing probe. The preparation method of the fluorescent sensing probe comprises the following steps: dissolving 3-hydroxy-2-naphthoic acid (HNA) in water, and adjusting the pH value to be alkaline to obtain a sodium 3-hydroxy-2-naphthoate solution; dissolving europium nitrate hexahydrate in methanol to obtain a europium nitrate solution; the preparation method comprises the following steps: mixing a 3-hydroxy-2-sodium naphthoate solution and a europium nitrate solution, transferring the mixture into a reaction kettle, carrying out a hydrothermal reaction, and after the reaction is finished, washing and drying to obtain lanthanide series MOFs; and dispersing lanthanide series MOFs in water to obtain a dual-emission ratio type fluorescence sensing probe solution. According to the present invention, the operation is simple, the Eu-MOFs fluorescence sensing probe is synthesized by using the 3-hydroxy-2-naphthoic acid as the organic ligand, such that the ACQ effect of the 3-hydroxy-2-naphthoic acid is overcome, and the fluorescence property of the 3-hydroxy-2-naphthoic acid is significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorescence sensors, and in particular relates to a dual-emission ratiometric fluorescence sensing probe based on lanthanide MOFs, and a preparation method and application thereof. Background Art

[0002] Tetracycline (TC), a broad-spectrum antibiotic, is widely used in animal husbandry, aquaculture, and for the prevention and treatment of human diseases due to its excellent antimicrobial activity and low cost. However, excessive use of TC leads to its residues in animal-derived foods and aquatic environments. Entering the human body through the food chain, it can induce health risks such as antibiotic resistance, allergic reactions, and liver and kidney damage. Therefore, the development of efficient, sensitive TC detection technologies that are suitable for complex matrices is of great significance for ensuring food safety and ecological security.

[0003] Currently, conventional methods for detecting TC include high-performance liquid chromatography, capillary electrophoresis chromatography, liquid chromatography-mass spectrometry, and enzyme-linked immunosorbent assay (ELISA). Although these methods exhibit excellent accuracy and sensitivity, the detection process is time-consuming and requires expensive and complex instrumentation and specialized technicians, severely limiting their universal application in monitoring TC. In contrast, fluorescence sensing technology has attracted considerable attention in recent decades due to its advantages such as low cost, high sensitivity, rapid response, and good selectivity. Lanthanide metal-organic frameworks (Ln-MOFs) have demonstrated significant advantages in the field of fluorescence sensing due to their unique luminescence properties (such as large Stokes shift, high quantum yield, and long fluorescence lifetime). In recent years, they have become an important research target for the detection of environmental pollutants. Therefore, it is necessary to construct a high-performance lanthanide MOFs fluorescence sensor to provide a feasible solution for the highly sensitive and visual detection of TC, which has important scientific value and application prospects in the field of food safety. Summary of the Invention

[0004] The purpose of the present invention is to provide a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs and its preparation method and application.

[0005] The implementation process of the present invention is as follows:

[0006] A method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs comprises the following steps:

[0007] (1) Preparation of lanthanide MOFs

[0008] 3-hydroxy-2-naphthoic acid (HNA) is dissolved in water and the pH is adjusted to alkaline with NaOH to obtain a sodium 3-hydroxy-2-naphthoate solution; europium nitrate hexahydrate is dissolved in methanol to obtain a europium nitrate solution; the sodium 3-hydroxy-2-naphthoate solution and the europium nitrate solution are mixed and transferred to a reactor for hydrothermal reaction. After the reaction is completed, the mixture is washed and dried to obtain lanthanide MOFs, namely Eu-HNA;

[0009] (2) Preparation of dual-emission ratiometric fluorescent sensing probe solution

[0010] The Eu-HNA obtained in step (1) is dispersed in water to obtain a dual-emission ratiometric fluorescent sensing probe solution.

[0011] Furthermore, in step (1), the pH of the solution is adjusted to 10-12 by NaOH.

[0012] Furthermore, in step (1), the molar ratio of the 3-hydroxy-2-naphthoic acid to the europium nitrate hexahydrate is 0.49:(0.16-0.65).

[0013] Furthermore, the molar volume ratio of the 3-hydroxy-2-naphthoic acid to the water is 0.49 mmol: (10-50) mL; and the volume ratio of the water to methanol is (10:50)-(50:10).

[0014] Furthermore, in step (1), the temperature of the hydrothermal reaction is 70-90° C., and the reaction time is 36-60 h.

[0015] Furthermore, in step (2), the concentration of the dual emission ratiometric fluorescent sensor probe solution is 1 mg·mL -1 .

[0016] The dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs is obtained by the above preparation method.

[0017] Application of the above-mentioned lanthanide MOFs-based dual-emission ratiometric fluorescent sensing probe in tetracycline detection.

[0018] A method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe comprises the following steps:

[0019] (1) A dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution (sodium citrate aqueous solution), and tetracycline solutions of varying concentrations were mixed to prepare a series of detection standard solutions with varying tetracycline concentrations;

[0020] (2) Place the test standard solution in a fluorescence detector and record the fluorescence spectra of the series of test standard solutions in the range of 400-750 nm at an excitation wavelength of 395 nm.617 / F 510 The relationship between the concentration of tetracycline and the concentration of tetracycline was used to draw the standard curve of tetracycline detection;

[0021] (3) mixing a dual-emission ratiometric fluorescent sensor probe solution, a Tris-HCl buffer, a CitNa solution, and a sample of unknown tetracycline concentration to prepare a test sample;

[0022] (4) Place the sample to be tested in a fluorescence detector, record the fluorescence spectrum of the sample in the range of 400 to 750 nm at an excitation wavelength of 395 nm, and calculate the tetracycline concentration in the sample based on the standard curve in step (2).

[0023] A method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe is based on the application of fluorescent sensor test paper derived from lanthanide MOFs. A detection device based on the test paper is constructed for portable detection of tetracycline, comprising the following steps:

[0024] (1) A dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution, and a tetracycline solution with gradient concentrations were mixed to prepare a series of detection standard solutions with different tetracycline concentrations;

[0025] (2) The cut filter paper pieces are immersed in a series of detection standard solutions with different tetracycline concentrations, and after shaking and incubation, the filter paper pieces are taken out and dried to obtain portable detection strips;

[0026] (3) placing the portable test strip prepared in step (2) under a 365 nm ultraviolet lamp and photographing the test strip color change images caused by different concentrations of tetracycline, quickly and quantitatively converting the color information into digital information R / G value using RGB color recognition software ColorMax, and drawing a standard curve based on the relationship between R / G value and TC concentration;

[0027] (4) Mixing the dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution, and the sample to be tested to prepare the sample to be tested, immersing the cut filter paper in the sample to be tested, and after shaking and incubating, taking out and drying the filter paper to obtain the test paper;

[0028] (5) Place the test paper under a 365nm ultraviolet lamp and take a photo to capture the color image of the test paper caused by tetracycline. Use the RGB color recognition software ColorMax to quickly and quantitatively convert the color information into digital information R / G value, and calculate the tetracycline concentration in the sample based on the standard curve in step (3).

[0029] The design concept of the dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs described in the present invention is as follows:

[0030] Europium-based MOFs (Eu-MOFs) 3+ The unique antenna effect between TC and Eu enables efficient energy transfer: TC molecules, as photosensitizers, can transfer the absorbed energy to Eu in a directionally controlled manner. 3+ ions, significantly enhancing their characteristic luminescence intensity. This feature provides an ideal way to build a highly sensitive and selective TC detection platform. 3+ The dual emission characteristics of luminescence can be used to establish a self-calibration ratio fluorescence sensing model by monitoring the ratio change of the two luminescence intensities induced by TC. This dual signal output mechanism not only effectively overcomes the defect that single wavelength detection is susceptible to environmental interference, but also realizes the visual identification and monitoring of TC through the change of fluorescence color, laying a technical foundation for the development of portable on-site detection equipment. Therefore, the key to constructing a high-performance Eu-MOFs-based TC ratio fluorescence sensor is to rationally screen the best luminescent materials with excellent emission performance and emission spectrum consistent with Eu. 3+ Organic ligands with non-overlapping characteristic emissions. By rationally screening organic ligands and precisely controlling the luminescence properties of Eu-MOFs, ratiometric fluorescent probes based on Eu-MOFs can be effectively constructed.

[0031] Positive effects of the present invention:

[0032] (1) The present invention is simple to operate. It uses 3-hydroxy-2-naphthoic acid as an organic ligand to synthesize Eu-MOFs to obtain a ratiometric fluorescent probe. It not only overcomes the ACQ effect of 3-hydroxy-2-naphthoic acid, but also significantly improves the fluorescence performance of 3-hydroxy-2-naphthoic acid, increasing its fluorescence intensity by 1.72 times. In addition, the probe is mainly based on the emission of 3-hydroxy-2-naphthoic acid (510nm). When the ratiometric fluorescent probe reacts with TC, the β-diketone structure in the TC molecule significantly improves the fluorescence intensity of Eu through the antenna effect. 3+ The characteristic red emission (617 nm) of TC was obtained, and the inner filter effect between TC and 3-hydroxy-2-naphthoic acid caused the fluorescence intensity of the ligand to decrease, thus constructing a ratiometric fluorescence response system.

[0033] (2) This paper successfully developed a TC analysis method based on ratiometric fluorescence detection. By simultaneously recording the different fluorescence emission signals of two channels and utilizing their unique response pattern of one increase and one decrease, high sensitivity and high specificity of TC detection were achieved over a wide linear range.

[0034] (3) Compared with the single-signal fluorescence detection method, the present invention can observe the system fluorescence emission change from green to red emission as the TC concentration changes under UV light. Furthermore, by introducing a smartphone-based paper-based detection platform, visual quantitative detection of TC can be achieved with only a portable UV lamp, providing innovative ideas for the development of portable TC on-site detection devices, with significant application potential in environmental monitoring and food safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the XRD pattern of the lanthanide MOFs prepared in Example 1;

[0036] Figure 2 This is the SEM image of the lanthanide MOFs prepared in Example 1;

[0037] Figure 3 This is the XPS graph of the lanthanide MOFs prepared in Example 1;

[0038] Figure 4 is the fluorescence emission spectrum of HNA at different ratios (DMF / H2O);

[0039] Figure 5 is the fluorescence emission spectra of HNA and Eu-HNA prepared in Example 1;

[0040] Figure 6 Optimization of detection conditions for the dual-emission ratiometric fluorescent sensor probe, where (A) is the CitNa effect exploration diagram, (B) is the addition sequence exploration diagram, (C) is the pH exploration diagram, and (D) is the CitNa dosage exploration diagram;

[0041] Figure 7 The selectivity diagram of the dual-emission ratiometric fluorescent sensing probe, where (A) is a metal ion and (B) is a non-metal ion;

[0042] Figure 8 The fluorescence spectra of a series of detection standard solutions with different TC concentrations;

[0043] Figure 9 is the CIE diagram of the fluorescence spectrum at different TC concentrations;

[0044] Figure 10 It is the standard curve of low concentration range;

[0045] Figure 11 is the standard curve of the high concentration range;

[0046] Figure 12 This is the test data table for adding different TC concentrations to milk samples;

[0047] Figure 13 It is a portable test strip diagram;

[0048] Figure 14 Demonstration chart and standard curve for TC detection based on smartphone visualization platform;

[0049] Figure 15 This is a data table showing the detection of TC in milk samples using a smartphone-based sensing method. DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to the embodiments.

[0051] The dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs described in the present invention not only achieves highly sensitive and selective detection of tetracycline, but more importantly, as the TC concentration changes, the probe exhibits a visible fluorescence emission color change (gradually from green to red) under ultraviolet light. This provides a solution for the development of portable on-site rapid detection equipment for tetracycline, which is conducive to its practical application and promotion.

[0052] In a first aspect, the present invention provides a method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs, comprising the following steps:

[0053] (1) Preparation of lanthanide MOFs

[0054] Dissolve 0.49 mmol of 3-hydroxy-2-naphthoic acid in 10-50 mL of water and pass through 0.1 mol·L -1 The pH of the solution is adjusted to 10-12 with NaOH to obtain a sodium 3-hydroxy-2-naphthoate solution; 0.16-0.65 mmol of europium nitrate hexahydrate is dissolved in 10-50 mL of methanol to obtain a europium nitrate solution; the sodium 3-hydroxy-2-naphthoate solution and the europium nitrate solution are mixed and transferred to a reactor, and a hydrothermal reaction is carried out at 70-90°C for 36-60 hours. After the reaction is completed, the mixture is washed and dried to obtain lanthanide MOFs, namely Eu-HNA;

[0055] (2) Preparation of dual-emission ratiometric fluorescent sensing probe solution

[0056] The Eu-HNA obtained in step (1) was dispersed in water to obtain a concentration of 1 mg·mL -1 A dual-emission ratiometric fluorescent sensing probe solution.

[0057] In a second aspect, the present invention provides a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs.

[0058] In a third aspect, the present invention provides an application of a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs in the detection of tetracycline.

[0059] In a fourth aspect, the present invention provides a method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe, comprising the following steps:

[0060] (1) A dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution, and a tetracycline solution with gradient concentrations were mixed to prepare a series of detection standard solutions with different tetracycline concentrations;

[0061] (2) Place the test standard solution in a fluorescence detector and record the fluorescence spectra of the series of test standard solutions in the range of 400-750 nm at an excitation wavelength of 395 nm. 617 / F 510 The relationship between the concentration of tetracycline and the concentration of tetracycline was used to draw the standard curve of tetracycline detection;

[0062] (3) mixing a dual-emission ratiometric fluorescent sensor probe solution, a Tris-HCl buffer, a CitNa solution, and a sample of unknown tetracycline concentration to prepare a test sample;

[0063] (4) Place the sample to be tested in a fluorescence detector, record the fluorescence spectrum of the sample in the range of 400 to 750 nm at an excitation wavelength of 395 nm, and calculate the tetracycline concentration in the sample based on the standard curve in step (2).

[0064] In a fifth aspect, the present invention further provides a method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe, which is an application of a fluorescent sensor test paper derived from lanthanide MOFs. A detection device based on the test paper is constructed for portable detection of tetracycline, comprising the following steps:

[0065] (1) A dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution, and a tetracycline solution with gradient concentrations were mixed to prepare a series of detection standard solutions with different tetracycline concentrations;

[0066] (2) The cut filter paper pieces are immersed in a series of detection standard solutions with different tetracycline concentrations, and after shaking and incubation, the filter paper pieces are taken out and dried to obtain portable detection strips;

[0067] (3) placing the portable test strip prepared in step (2) under a 365 nm ultraviolet lamp and photographing the test strip color change images caused by different concentrations of tetracycline, quickly and quantitatively converting the color information into digital information R / G value using RGB color recognition software ColorMax, and drawing a standard curve based on the relationship between R / G value and TC concentration;

[0068] (4) Mixing the dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution, and the sample to be tested to prepare the sample to be tested. Immersing the cut filter paper in the sample to be tested, incubating with shaking, and then removing and drying the filter paper to obtain the test paper;

[0069] (5) Place the test paper under a 365nm ultraviolet lamp and take a photo to capture the color image of the test paper caused by tetracycline. Use the RGB color recognition software ColorMax to quickly and quantitatively convert the color information into digital information R / G value, and calculate the tetracycline concentration in the sample based on the standard curve in step (3).

[0070] Example 1

[0071] A method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs comprises the following steps:

[0072] (1) Preparation of lanthanide MOFs

[0073] 0.49mmol 3-hydroxy-2-naphthoic acid was dissolved in 20mL water and passed through 0.1mol·L -1 The pH of the solution was adjusted to 11 with NaOH to obtain a sodium 3-hydroxy-2-naphthoate solution; 0.33 mmol of europium nitrate hexahydrate was dissolved in 40 mL of methanol to obtain a europium nitrate solution; the 3-hydroxy-2-naphthoic acid solution and the europium nitrate solution were mixed and stirred for 10 minutes, then transferred to a reactor and heated to 80°C for a hydrothermal reaction for 48 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the product was then centrifuged and washed, and finally dried in an oven at 60°C overnight to obtain lanthanide MOFs as a yellow powder, namely Eu-HNA;

[0074] (2) Preparation of dual-emission ratiometric fluorescent sensing probe solution

[0075] Disperse 10 mg of Eu-HNA obtained in step (1) in 10 mL of water to obtain a concentration of 1 mg mL -1 The uniformly dispersed dual-emission ratiometric fluorescent sensor probe solution was recorded as Eu-HNA (1 mg mL -1 The ratio probe solution mainly exhibits the characteristic emission peak of HNA ligand at 510 nm, while Eu 3+ No characteristic emission signal is observed.

[0076] Example 2

[0077] A method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs comprises the following steps:

[0078] (1) Preparation of lanthanide MOFs

[0079] 0.49mmol 3-hydroxy-2-naphthoic acid was dissolved in 10mL water and passed through 0.1mol·L -1 The pH of the solution was adjusted to 10 with NaOH to obtain a sodium 3-hydroxy-2-naphthoate solution; 0.16 mmol of europium nitrate hexahydrate was dissolved in 50 mL of methanol to obtain a europium nitrate solution; the sodium 3-hydroxy-2-naphthoate solution and the europium nitrate solution were mixed and stirred for 10 minutes, then transferred to a reactor and heated to 70°C for a hydrothermal reaction for 60 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the product was then centrifuged and washed, and finally dried in an oven at 50°C overnight to obtain lanthanide MOFs as a yellow powder, namely Eu-HNA;

[0080] (2) Preparation of dual-emission ratiometric fluorescent sensing probe solution

[0081] Disperse 10 mg of Eu-HNA obtained in step (1) in 10 mL of water to obtain a concentration of 1 mg mL -1 The ratio probe solution mainly presents the characteristic emission peak of HNA ligand at 510nm, while Eu 3+ No characteristic emission signal is observed.

[0082] Example 3

[0083] A method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs comprises the following steps:

[0084] (1) Preparation of lanthanide MOFs

[0085] 0.49mmol 3-hydroxy-2-naphthoic acid was dissolved in 50mL water and passed through 0.1mol·L -1 The pH of the solution was adjusted to 12 with NaOH to obtain a sodium 3-hydroxy-2-naphthoate solution; 0.65 mmol of europium nitrate hexahydrate was dissolved in 10 mL of methanol to obtain a europium nitrate solution; the sodium 3-hydroxy-2-naphthoate solution and the europium nitrate solution were mixed and stirred for 10 minutes, then transferred to a reactor and heated to 90°C for a hydrothermal reaction for 36 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the product was then centrifuged and washed, and finally dried in an oven at 65°C overnight to obtain lanthanide MOFs as a yellow powder, namely Eu-HNA;

[0086] (2) Preparation of dual-emission ratiometric fluorescent sensing probe solution

[0087] Disperse 10 mg of Eu-HNA obtained in step (1) in 10 mL of water to obtain a concentration of 1 mg mL -1 The ratio probe solution mainly presents the characteristic emission peak of HNA ligand at 510nm, while Eu3+ No characteristic emission signal is observed.

[0088] Example 4

[0089] A method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs comprises the following steps:

[0090] (1) Preparation of lanthanide MOFs

[0091] 0.49mmol 3-hydroxy-2-naphthoic acid was dissolved in 30mL water and passed through 0.1mol·L -1 The pH of the solution was adjusted to 11 with NaOH to obtain a sodium 3-hydroxy-2-naphthoate solution; 0.45 mmol of europium nitrate hexahydrate was dissolved in 40 mL of methanol to obtain a europium nitrate solution; the sodium 3-hydroxy-2-naphthoate solution and the europium nitrate solution were mixed and stirred for 10 minutes, then transferred to a reactor and heated to 80°C for a hydrothermal reaction for 60 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the product was then centrifuged and washed, and finally dried in an oven at 60°C overnight to obtain lanthanide MOFs as a yellow powder, namely Eu-HNA;

[0092] (2) Preparation of dual-emission ratiometric fluorescent sensing probe solution

[0093] Disperse 10 mg of Eu-HNA obtained in step (1) in 10 mL of water to obtain a concentration of 1 mg mL -1 The ratio probe solution mainly presents the characteristic emission peak of HNA ligand at 510nm, while Eu 3+ No characteristic emission signal is observed.

[0094] Example 5

[0095] A method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe comprises the following steps:

[0096] (1) Add 60 μL Eu-HNA (1 mg mL -1 )、600μL Tris-HCl buffer (pH=8), 40μL CitNa solution (1.0mmol·L -1 ) and 300 μL of different gradient concentrations (0.2~100 μmol·L -1 ) TC solution was mixed evenly to prepare a series of detection standard solutions with different tetracycline concentrations;

[0097] (2) Place the test standard solution in a fluorescence detector and record the fluorescence spectra of the series of test standard solutions in the range of 400-750 nm at an excitation wavelength of 395 nm.617 / F 510 The relationship between the concentration of tetracycline and the concentration of tetracycline was used to draw the standard curve of tetracycline detection;

[0098] (3) Add 60 μL Eu-HNA (1 mg mL -1 )、600μL Tris-HCl buffer (pH=8), 40μL CitNa solution (1.0mmol·L -1 ) and 300 μL of a sample with unknown tetracycline concentration were mixed evenly to prepare a sample to be tested;

[0099] (4) Place the sample to be tested in a fluorescence detector, record the fluorescence spectrum of the sample in the range of 400 to 750 nm at an excitation wavelength of 395 nm, and calculate the tetracycline concentration in the sample based on the standard curve in step (2).

[0100] Example 6 Application of Lanthanide MOFs-derived Fluorescent Sensing Test Paper

[0101] A method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe comprises the following steps:

[0102] (1) Add 60 μL Eu-HNA (1 mg mL -1 )、600μL Tris-HCl buffer (pH=8), 40μL CitNa solution (1.0mmol·L -1 ) and 300 μL of different gradient concentrations (0.2~100 μmol·L -1 ) TC solution was mixed evenly to prepare a series of detection standard solutions with different tetracycline concentrations;

[0103] (2) dipping the cut filter paper pieces into the series of detection standard solutions with different tetracycline concentrations prepared in step (1), shaking and incubating them, and then taking out and drying the filter paper pieces to obtain portable detection test strips;

[0104] (3) placing the portable test strip prepared in step (2) under a 365 nm ultraviolet lamp and photographing the test strip color change images caused by different concentrations of tetracycline, quickly and quantitatively converting the color information into digital information R / G value using RGB color recognition software ColorMax, and drawing a standard curve based on the relationship between R / G value and TC concentration;

[0105] (4) Add 60 μL Eu-HNA (1 mg mL -1 )、600μL Tris-HCl buffer (pH=8), 40μL CitNa solution (1.0mmol·L -1) and 300 μL of the sample to be tested were mixed evenly to prepare the sample to be tested, the cut filter paper was immersed in the sample to be tested, and after shaking incubation, the filter paper was taken out and dried to obtain the test paper;

[0106] (5) Place the test paper under a 365nm ultraviolet lamp and take a photo to capture the color image of the test paper caused by tetracycline. Use the RGB color recognition software ColorMax to quickly and quantitatively convert the color information into digital information R / G value, and calculate the tetracycline concentration in the sample based on the standard curve in step (3).

[0107] Performance testing:

[0108] (1) The structure, morphology and bonding information of the lanthanide MOFs prepared in Example 1 were investigated

[0109] like Figure 1 The XRD results show that the diffraction peak of the synthesized Eu-HNA is highly consistent with the simulated diffraction peak (CCDC: 885839), confirming the successful synthesis of Eu-HNA crystals. Figure 2 The SEM observation of Eu-HNA showed that the morphology was a long rod-like structure. XPS was used to characterize the element types in Eu-HNA, such as its full spectrum. Figure 3 As shown, HNA has only two groups of peaks, O1s and C1s, while Eu-HNA contains three elements, Eu, O and C, and has four peaks, Eu3d, O1s, C1s and Eu4d, indicating that Eu is successfully combined with HNA.

[0110] (2) Fluorescence performance test of organic ligand HNA and lanthanide MOFs

[0111] The HNA powder was ultrasonically dispersed in 1 mL of DMF / water mixtures with different ratios (the volume fraction of DMF was 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%) to test the fluorescence performance. Figure 4 As shown in the figure, the fluorescence signal of HNA gradually increases with the increase of the DMF ratio in the mixed solution. It is worth noting that due to the strong hydrophobicity of HNA molecules in the aqueous phase, they easily form high aggregation states in aqueous solution, resulting in significant fluorescence quenching. This phenomenon fully confirms the aggregation-induced quenching property of HNA.

[0112] To explore the regulatory effect of metal coordination on the aggregation-induced quenching effect, we designed a comparative experiment: equimolar amounts of HNA powder and Eu-HNA prepared in Example 1 were dispersed in 1 mL of aqueous solution, and fluorescence spectra were measured at an excitation wavelength of 395 nm. The results are shown in Figure 2. Figure 5 The fluorescence intensity of Eu-HNA was 1.72 times that of pure HNA system, which was attributed to Eu3+ The metal-ligand coordination between the organic ligands effectively inhibits the intermolecular π-π stacking, thereby successfully overcoming its aggregation-induced quenching effect. In addition, Eu-HNA exhibits excellent ligand emission peaks and potential Eu 3+ The characteristic emission peak provides an ideal platform for constructing a self-calibrating ratiometric fluorescence sensor to detect TC.

[0113] (III) Optimization of detection conditions for dual-emission ratiometric fluorescence sensing probes

[0114] In order to improve the analytical performance of the detection system, the sample addition order, Tris-HCl buffer pH, CitNa dosage and other conditions were optimized. The Eu-HNA solution prepared in Example 1 was selected with a concentration of 1 mg·mL -1 A uniformly dispersed dual-emission ratiometric fluorescent sensing probe solution.

[0115] First, the role of CitNa was discussed. Figure 6 A The results show that when TC and Hris-HCl+TC were added to the dual-emission ratiometric fluorescent sensor probe solution in Example 1, the fluorescence signal of the dual-emission ratiometric fluorescent sensor probe solution did not change much, but the fluorescence signal at 620nm was significantly improved after the addition of CitNa. This is because CitNa replaced the water chelated with Eu-HNA, inhibiting the quenching effect caused by water molecules.

[0116] At the same time, the effect of the order of adding Tris-HCl, CitNa and TC on the fluorescence signal was observed. Figure 6 Figure B shows that the order of adding Tris-HCl and CitNa does not significantly affect the sensitivity of TC detection. However, when TC is added before Tris-HCl and CitNa, its fluorescence response signal is greatly weakened. Therefore, the recommended addition order during detection is "Eu-HNA probe solution → Tris-HCl → CitNa → TC."

[0117] Furthermore, the effect of the pH of Tris-HCl solution on the detection system was observed. Figure 6 The results showed that the best detection result was obtained when the pH of Tris-HCl solution was 8. Finally, the optimal dosage of CitNa was explored. Figure 6 D The results show that when the amount of CitNa added is 40 μL, Eu 3+ The fluorescence response is the strongest.

[0118] (IV) Selectivity investigation of dual-emission ratiometric fluorescence sensing probes

[0119] The Eu-HNA solution prepared in Example 1 was used with a concentration of 1 mg·mL -1A uniformly dispersed dual-emission ratiometric fluorescent sensing probe solution.

[0120] Prepare 50 μmol·L -1 Ca 2+ 、Co 2+ 、Fe 3+ , K + Mg 2+ 、Na + 、Ni 2+ 、Zn 2+ , vitamin C (AA), ciprofloxacin (CIP), glucose (Glu), glycine (Gly), glutathione (GSH), L-arginine (L-Arg), L-cysteine ​​(L-Cys), L-lysine (L-Lys), urea (UA) solution. Then 60 μL Eu-HNA (1 mg mL -1 )、600 μL Tris-HCl buffer (pH=8), 40 μL CitNa solution (1.0 mmol·L -1 ) and 300 μL of one of the above solutions to form a test solution. Each test solution was placed in a fluorescence detector, and the fluorescence spectrum was collected at an excitation wavelength of 395 nm. The peak graph was collected from the wavelength of 420 nm to 750 nm. Each set of data was measured three times.

[0121] The results are as follows Figure 7 As shown in the figure, many metal ions, amino acids and antibiotics did not produce obvious responses to the fluorescence signal of Eu-HNA. Only when the test sample contained TC, F 617 / F 510 The fluorescence ratio changed significantly, indicating that the detection system has good selectivity for TC.

[0122] (V) Detection of TC concentration in samples using the standard curve method

[0123] The Eu-HNA solution prepared in Example 1 was used with a concentration of 1 mg·mL -1 A uniformly dispersed dual-emission ratiometric fluorescent sensing probe solution.

[0124] A method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe comprises the following steps:

[0125] (1) Draw a standard curve

[0126] First, 60 μL of Eu-HNA (1 mg mL -1 )、600μL Tris-HCl buffer (pH=8), 40μL CitNa solution (1.0mmol·L -1) and 300 μL of different gradient concentrations (0.2 μmol·L -1 ,2μmol·L -1 ,4μmol·L -1 ,6μmol·L -1 ,8μmol·L -1 ,10μmol·L -1 ,20μmol·L -1 ,30μmol·L -1 ,40μmol·L -1 ,50μmol·L -1 ,60μmol·L -1 ,70μmol·L -1 ,80μmol·L -1 ,90μmol·L -1 ,100μmol·L -1 ) TC solution was mixed evenly to prepare a series of detection standard solutions with different tetracycline concentrations;

[0127] Then, a series of detection standard solutions with different tetracycline concentrations were placed in a fluorescence detector, and the fluorescence spectra of the series of detection standard solutions in the range of 400-750 nm were collected at an excitation wavelength of 395 nm. Each set of data was measured three times, and the fluorescence intensity ratio F was established. 617 / F 510 The relationship between the concentration of tetracycline and the concentration of tetracycline was used to draw the standard curve of tetracycline detection;

[0128] like Figure 8 As shown, as the TC concentration increased from 0.2 μmol·L -1 Increased to 100 μmol·L -1 , Eu 3+ The characteristic emission peak at 617nm is significantly enhanced, while the emission peak of HNA at 510nm is gradually weakened. Based on the dual signal amplification mechanism, the fluorescence intensity ratio (F 617 / F 510 ) showed an obvious concentration-dependent enhancement and maintained a good linear relationship with the TC concentration. It is worth noting that the sensor showed two linear relationships, such as Figure 10 and Figure 11 , low concentration range (0.2~10μmol·L -1 ) is consistent with y=0.0294x+0.0811(R 2 =0.997), high concentration range (10-100 μmol·L -1 ) meets y=0.0550x-0.186(R 2 =0.996). According to the formula LOD=3σ / k, the detection limit was calculated to be 56 nmol·L -1 . Figure 9 The CIE diagram of the fluorescence spectrum at different TC concentrations shows that with the increase of TC concentration, the fluorescence emission color of the probe changes from green to red, which provides the necessary conditions for TC visual monitoring and establishes a reliable platform for TC detection in practical applications.

[0129] (2) Taking milk sample testing as an example

[0130] First, milk was pretreated according to GB / T 22900-2008, and the TC concentrations (0 μmol·L -1 ,20μmol·L -1 ,40μmol·L -1 ,80μmol·L -1 ) of milk solution samples for actual sample testing;

[0131] Then, 60 μL Eu-HNA (1 mg mL -1 )、600μL Tris-HCl buffer (pH=8), 40μL CitNa solution (1.0mmol·L -1 ) and 300 μL of pretreated milk sample solutions with different TC contents were mixed evenly to prepare the test samples;

[0132] Finally, the sample to be tested was placed in a fluorescence detector and the fluorescence spectrum of the sample was recorded in the range of 400-750 nm under an excitation wavelength of 395 nm. When the amount of TC added was 0, there was no absorption peak in this wavelength range, indicating that no TC was detected in the milk sample. -1 ,40μmol·L -1 and 80 μmol·L -1 of solution.

[0133] Figure 12 The results showed that the recoveries of spiked milk samples with different TC contents ranged from 94.94% to 101.07%, with relative standard deviations (RSDs) ranging from 0.2% to 2.6%. This result indicates that Eu-HNA has high precision and accuracy for TC detection and has potential practical application value.

[0134] (6) Detecting TC based on smartphone visualization platform

[0135] The Eu-HNA solution prepared in Example 1 was used with a concentration of 1 mg·mL -1 A uniformly dispersed dual-emission ratiometric fluorescent sensor probe solution was prepared. The TC concentration in the sample was detected using a portable test strip method.

[0136] A method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe comprises the following steps:

[0137] (1) Preparation of portable test strips

[0138] (1.1) Add 60 μL of Eu-HNA (1 mg mL -1 )、600μL Tris-HCl buffer (pH=8), 40μL CitNa solution (1.0mmol·L -1 ) and 300 μL of different concentrations (0.2 μmol·L -1 , 4 μmol·L -1 , 10 μmol·L -1 , 20 μmol·L -1 , 40 μmol·L -1 , 60 μmol·L -1 , 80 μmol·L -1 , 100 μmol·L -1 ) TC solution was mixed evenly to prepare a series of detection standard solutions with different tetracycline concentrations;

[0139] (1.2) Immerse the cut filter paper pieces in a series of different tetracycline concentration detection standard solutions, shake and incubate for 1 minute, remove and dry the filter paper pieces to obtain portable detection strips;

[0140] (2) Draw a standard curve based on the relationship between R / G value and TC concentration

[0141] The portable test strip prepared in step (1) is placed under a 365nm ultraviolet lamp and photographed to capture images of the test strip color changes caused by different concentrations of tetracycline, and the color information is quickly and quantitatively converted into digital information R / G value using RGB color recognition software ColorMax, and a standard curve is drawn based on the relationship between R / G value and TC concentration;

[0142] like Figure 13 and Figure 14 The results showed that the paper-based sensor has a high sensitivity and low energy consumption in the range of 0.2 to 100 μmol·L -1 The fluorescence of the image was significantly transformed from green to red within the concentration range, and the detection results were visually intuitive. The image RGB values ​​were further analyzed using a smartphone selection program, and it was found that the R / G ratio had a good linear relationship with the TC concentration within the corresponding range (y = 0.0292x + 0.482, R 2 =0.997), with a detection limit of 598 nM. This method is simple and portable, and through rapid conversion of light color to numerical value, it provides an efficient solution for on-site real-time monitoring of TC.

[0143] (3) Taking milk sample testing as an example

[0144] First, milk was pretreated according to GB / T 22900-2008, and the milk with different TC contents (0 μmol·L -1 ,10μmol·L -1 ,30μmol·L -1 ,50μmol·L -1 ) of milk solution samples for actual sample testing;

[0145] Then, 60 μL Eu-HNA (1 mg mL -1 )、600μL Tris-HCl buffer (pH=8), 40μL CitNa solution (1.0mmol·L -1 ) and 300 μL of pretreated milk sample solutions with different TC contents were mixed evenly to prepare test samples; the cut filter paper was immersed in the test sample, and after shaking incubation, the filter paper was taken out and dried to obtain the test paper;

[0146] (4) Place the test paper under a 365nm ultraviolet lamp and take a photo to capture the color image of the test paper caused by tetracycline. Use the RGB color recognition software ColorMax to quickly and quantitatively convert the color information into digital information R / G value, and calculate the tetracycline concentration in the sample based on the standard curve in step (2). Figure 15 As shown, the portable test strip method had recoveries ranging from 94.38% to 97.86%, with a relative standard deviation (RSD) of less than 5.3%, demonstrating the reliability of this method for detecting tetracycline in real-world samples. Therefore, the smartphone-based sensing platform makes this method suitable for on-site monitoring of tetracycline, even in resource-limited areas.

[0147] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the contents disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of the present application and include common knowledge or customary techniques in the art that are not disclosed in this application. The description and examples are to be considered merely as exemplary, and the present application is not limited to the precise structures described above and shown in the drawings, and various modifications and variations may be made without departing from the scope thereof.

Claims

1. A method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs, characterized in that: The steps include: (1) Preparation of lanthanide MOFs 3-hydroxy-2-naphthoic acid is dissolved in water and the pH is adjusted to alkaline with NaOH to obtain a sodium 3-hydroxy-2-naphthoate solution; europium nitrate hexahydrate is dissolved in methanol to obtain a europium nitrate solution; the sodium 3-hydroxy-2-naphthoate solution and the europium nitrate solution are mixed and transferred to a reactor for hydrothermal reaction. After the reaction is completed, the mixture is washed and dried to obtain lanthanide MOFs, namely Eu-HNA; (2) Preparation of dual-emission ratiometric fluorescent sensing probe solution The Eu-HNA obtained in step (1) is dispersed in water to obtain a dual-emission ratiometric fluorescent sensing probe solution.

2. The method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs according to claim 1, characterized in that: In step (1), the pH of the solution is adjusted to 10-12 by NaOH.

3. The method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs according to claim 1, characterized in that: In step (1), the molar ratio of the 3-hydroxy-2-naphthoic acid to the europium nitrate hexahydrate is 0.49:(0.16-0.65).

4. The method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs according to claim 1, characterized in that: The molar volume ratio of the 3-hydroxy-2-naphthoic acid to the water is 0.49 mmol: (10-50) mL; the volume ratio of the water to methanol is (10:50)-(50:10).

5. The method for preparing a dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs according to claim 1, characterized in that: In step (1), the temperature of the hydrothermal reaction is 70 to 90° C., and the reaction time is 36 to 60 hours.

6. A dual-emission ratiometric fluorescent sensing probe based on lanthanide MOFs obtained by the preparation method of claim 1.

7. Use of the lanthanide MOFs-based dual-emission ratiometric fluorescent sensor probe according to claim 6 in the detection of tetracycline.

8. A method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe, characterized in that: The steps include: (1) A dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution, and a tetracycline solution with gradient concentrations were mixed to prepare a series of detection standard solutions with different tetracycline concentrations; (2) Place the test standard solution in a fluorescence detector and record the fluorescence spectra of the series of test standard solutions in the range of 400-750 nm at an excitation wavelength of 395 nm. 617 / F 510 The relationship between the concentration of tetracycline and the concentration of tetracycline was used to draw the standard curve of tetracycline detection; (3) mixing a dual-emission ratiometric fluorescent sensor probe solution, a Tris-HCl buffer, a CitNa solution, and a sample of unknown tetracycline concentration to prepare a test sample; (4) Place the sample to be tested in a fluorescence detector, record the fluorescence spectrum of the sample in the range of 400 to 750 nm at an excitation wavelength of 395 nm, and calculate the tetracycline concentration in the sample based on the standard curve in step (2).

9. A method for detecting tetracycline using a dual-emission ratiometric fluorescent sensor probe, characterized in that: The steps include: (1) A dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution, and a tetracycline solution with gradient concentrations were mixed to prepare a series of detection standard solutions with different tetracycline concentrations; (2) The cut filter paper pieces are immersed in a series of detection standard solutions with different tetracycline concentrations, and after shaking and incubation, the filter paper pieces are taken out and dried to obtain portable detection strips; (3) placing the portable test strip prepared in step (2) under a 365 nm ultraviolet lamp and photographing the test strip color change images caused by different concentrations of tetracycline, quickly and quantitatively converting the color information into digital information R / G value using RGB color recognition software ColorMax, and drawing a standard curve based on the relationship between R / G value and TC concentration; (4) Mixing the dual-emission ratiometric fluorescent sensor probe solution, Tris-HCl buffer, CitNa solution, and the sample to be tested to prepare the sample to be tested, immersing the cut filter paper in the sample to be tested, and after shaking and incubating, taking out and drying the filter paper to obtain the test paper; (5) Place the test paper under a 365nm ultraviolet lamp and take a photo to capture the color image of the test paper caused by tetracycline. Use the RGB color recognition software ColorMax to quickly and quantitatively convert the color information into digital information R / G value, and calculate the tetracycline concentration in the sample based on the standard curve in step (3).

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