A lumi-nol-embedded iron-based metal-organic framework composite material, a preparation method and application thereof

Abstract

The application relates to a luminol-embedded iron-based metal organic framework composite material and a preparation method and application thereof, and belongs to the technical field. The application discloses a preparation method of a luminol-embedded iron-based metal organic framework composite material (luminol@Fe-DOBDC MOFs), mainly adopting 2,5-dihydroxyterephthalic acid (DOBDC) as an organic linking agent, and Fe in FeCl3.6H2O 3+ As a metal node, Fe-DOBDC MOFs (Fe 3+ And the electronic interaction between the carboxyl groups, the fluorescence of the ligand is significantly quenched, and the stirring reaction with luminol can obtain a fluorescent double-emission composite material, that is, the luminol-embedded iron-based metal organic framework composite material (luminol@Fe-DOBDC MOFs).

Description

Technical Field

[0001] This invention belongs to the technical field of iron-based metal-organic framework composite materials, and relates to an iron-based metal-organic framework composite material embedded with luminol, its preparation method and application. Background Technology

[0002] Ascorbic acid (AA, vitamin C) plays a vital role in maintaining normal bodily functions. It possesses strong reducing properties and the ability to scavenge free radicals, helping to prevent various diseases such as scurvy, Parkinson's disease, cardiovascular disease, and various forms of cancer. AA also helps the immune system protect the body from viral infections, thus playing a significant role in the prevention and treatment of colds. Market attention to AA is increasing. Since the human body cannot synthesize AA, it is used as a nutritional supplement in fruit juices, canned foods, jams, candies, dairy products, meat products, flour, and especially in various commercial beverages. Therefore, establishing a simple, sensitive, and accurate method to detect the AA content in beverage samples is crucial for guiding healthy eating.

[0003] To date, numerous methods have been used for the detection of acrylamide (AA), including electrochemical, colorimetric, titration, liquid chromatography, and fluorescence methods. Among these, fluorescence analysis techniques are widely adopted due to their low cost, high sensitivity, rapid response, and real-time detection capabilities. Various fluorescent probes (including metal-organic frameworks (MOFs), carbon quantum dots, polypyridine / graphene quantum dots, gold nanoclusters, two-photon nanoparticles, infinitely coordinated polymer (ICP) nanoparticles, and upconversion nanoparticles) have been prepared and used for AA detection. However, some fluorescent probes are complex to prepare, contain toxic metal ions or organic reagents, and many materials are time-consuming and expensive to synthesize, making them unsuitable for rapid analysis. More importantly, these fluorescence techniques used for AA detection primarily employ single-fluorescence emission modes (fluorescence "enhancement" or "quenching"), which are susceptible to interference from instrument voltage variations and autofluorescence in practical detection. Fortunately, ratiometric fluorescence effectively overcomes these interferences by measuring the ratio of the intensities of two fluorescence emission peaks at different wavelengths. It provides built-in self-calibration, eliminates independent factors of various analytes, and improves the signal-to-noise ratio. Therefore, developing novel fluorescence platforms with proportional fluorescence signal output, high sensitivity, and selectivity is essential for the detection of AA.

[0004] Metal-organic frameworks (MOFs) are a class of porous crystalline materials self-assembled from metal cations or clusters and suitable organic ligands, attracting significant attention across various fields. Due to the diversity of metal ions and bridging ligands, they are designed to synthesize materials with varying sizes, structural features, and physicochemical properties. Recently, MOFs have made remarkable progress in applications such as gas storage and separation, catalysts, magnetic materials research, cell imaging, proton conduction, and chemiluminescence sensing. Among these applications, fluorescence sensing methods have been widely used. Various MOFs have been used as fluorescent probes for the detection of ammonia (AA). However, the number of MOF-based fluorescent probes for AA detection is limited, mainly focusing on lanthanide MOFs, which are expensive and scarce. Transition metal MOFs, on the other hand, are abundant and economical, but most exhibit only a single fluorescence emission peak and are susceptible to environmental interference, limiting their practical application. Different construction strategies have been employed to prepare fluorescent dual-emission MOFs. The most common method is to encapsulate fluorescent guest substances into MOFs to construct host-guest dual-emission MOFs. Li and his colleagues developed a proportional fluorescent probe (UiO-66-NH2@PB) for the visual and fluorescence determination of cationic surfactants by encapsulating the fluorescent dye Food Red 104 into zirconium-based MOFs (UiO-66-NH2). Wang and his colleagues... 2 Zirconium-based MOFs UiO-(OH)2@RhB were prepared for use in Al 3+ Ion ratio fluorescence sensing.

[0005] Therefore, it is urgent and meaningful to explore simple, green and rapid methods to prepare host-guest dual-emission MOFs for AA detection. Summary of the Invention

[0006] In view of this, one objective of the present invention is to provide a method for preparing a luminol-embedded iron-based metal-organic framework composite material; a second objective of the present invention is to provide a luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs); and a third objective of the present invention is to provide an application of the luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs) in the detection of fluorescence enhancement ratio of ascorbic acid (AA).

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] 1. A method for preparing a luminol-embedded iron-based metal-organic framework composite material, the preparation method comprising the following steps:

[0009] (1) Preparation of Fe-DOBDC MOFs: A solution of N,N-dimethylformamide (DMF) containing 2,5-dihydroxyterephthalic acid (DOBDC) was added to a solution of N,N-dimethylformamide (DMF) containing ferric chloride hexahydrate (FeCl3·6H2O). After stirring and mixing, the mixture was transferred to an autoclave and heated at 100–200 °C for 8–20 h. After naturally cooling to room temperature, a black suspension was obtained. After centrifugation, excess ligands, luminol, and Fe were repeatedly washed to remove the suspension. 3+ Fe-DOBDC MOFs can then be obtained;

[0010] (2) Preparation of luminol@Fe-DOBDC MOFs: The Fe-DOBDC MOFs were dispersed in water and mixed with luminol. The mixture was stirred at room temperature until a black precipitate was obtained. The supernatant was removed by centrifugation, and the black dispersion was obtained as the luminol@Fe-DOBDC MOFs.

[0011] Preferably, in step (1), the molar ratio of 2,5-dihydroxyterephthalic acid (DOBDC) and ferric chloride hexahydrate (FeCl3·6H2O) is 2:1 to 1:2.

[0012] Preferably, in step (1), the lining of the autoclave is stainless steel Teflon.

[0013] Preferably, in step (1), the washing process uses N,N-dimethylformamide (DMF) and ultrapure water as washing solvents in sequence.

[0014] Preferably, in step (1), the rotation speed of the centrifuge is 10,000 to 12,000 rpm and the time is 5 to 10 min.

[0015] Preferably, in step (2), the final concentration of luminol after addition is 0.1 to 0.5 mM.

[0016] Preferably, in step (2), the centrifugation speed is 10000-12000 rpm and the time is 5-10 min.

[0017] 2. The luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs) prepared according to the above preparation method.

[0018] 3. Application of the above-mentioned luminol-embedded iron-based metal-organic framework composites (luminol@Fe-DOBDC MOFs) in the detection of fluorescence enhancement ratio of ascorbic acid (AA).

[0019] The beneficial effects of this invention are as follows: This invention discloses a method for preparing luminol-embedded iron-based metal-organic framework composite materials (luminol@Fe-DOBDC MOFs), mainly using 2,5-dihydroxyterephthalic acid (DOBDC) as an organic linker and Fe from ferric chloride hexahydrate (FeCl3·6H2O). 3+ As a metallic node, Fe-DOBDC MOFs (Fe) were obtained by reaction in an autoclave. 3+ The electron interaction between the ligand and the carboxylic acid group significantly quenches the fluorescence of the ligand. Continued stirring with luminol yields a fluorescent dual-emission composite material, namely, a luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs). When ascorbic acid (AA) is added to the luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs) prepared in this invention, the ascorbic acid (AA) reacts with Fe... 3+ Complexation leads to Fe 3+ With reduced content, the fluorescence intensity of luminol@Fe-DOBDC MOFs at 540 nm was significantly improved when the excitation wavelength was 365 nm, while the fluorescence intensity at 430 nm changed slightly. During this process, the fluorescence intensity of the ligand served as a sensitive signal, and the fluorescence intensity of luminol served as a reference signal for self-calibration in AA detection. Therefore, the luminol@Fe-DOBDC MOFs embedded with luminol prepared in this invention provides a highly efficient, accurate, and rapid (within approximately 2–3 minutes) dual-emission fluorescence platform for detecting the fluorescence enhancement ratio of ascorbic acid (AA).

[0020] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0022] Figure 1 This is a flowchart of the preparation of Fe-DOBDC MOFs (A) and luminol-embedded iron-based metal-organic framework composites (luminol@Fe-DOBDC MOFs) (B) in Example 1;

[0023] Figure 2SEM (A) and TEM (B) images of the luminol@Fe-DOBDC MOFs embedded with luminol prepared in Example 1;

[0024] Figure 3 EDS elemental analysis diagram of the luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs) prepared in Example 1;

[0025] Figure 4 The images show the fluorescence excitation and emission spectra of the luminol@Fe-DOBDC MOFs prepared in Example 1 at different excitation wavelengths from 345 nm to 380 nm. In the illustrations, a is a photograph of luminol@Fe-DOBDC MOFs under visible light and b is a photograph of luminol@Fe-DOBDC MOFs under a 365 nm ultraviolet lamp.

[0026] Figure 5 SEM (A) and TEM (B) images of 50 μL luminol@Fe-DOBDC MOFs solution after adding 20 μM ascorbic acid (AA) solution;

[0027] Figure 6 The fluorescence emission spectra of luminol@Fe-DOBDC MOFs before and after adding 20 μM ascorbic acid (AA) solution to 50 μL of luminol@Fe-DOBDC MOFs solution are shown in the inset. In the inset, a is a photo of luminol@Fe-DOBDC MOFs without AA and b is a fluorescence photo of luminol@Fe-DOBDC MOFs with AA added.

[0028] Figure 7 Images showing the addition of blank solution (Control), ascorbic acid (AA, 20 μM), cysteine ​​(Cys, 50 μM), oxalic acid (OA, 50 μM), dopamine (DA, 50 μM), citric acid (CA, 50 μM), and glutathione (GSH, 50 μM) to a 50 μL mixed solution of luminol@Fe-DOBDC MOFs and 1,10-phenanthroline (2 mg / mL).

[0029] Figure 8The solutions included luminol@Fe-DOBDC MOFs, a mixed solution of luminol@Fe-DOBDC MOFs + AA (100 μM), a mixed solution of luminol@Fe-DOBDC MOFs + AA (100 μM) + 1,10-phenanthroline (2 mg / mL), and 1,10-phenanthroline (2 mg / mL) + Fe 2+ UV-Vis absorption spectrum of a 100 μM mixed solution;

[0030] Figure 9 The fluorescence intensity (A) of luminol@Fe-DOBDC MOFs obtained at different temperatures at 540 nm before and after the addition of AA, and the fluorescence intensity of different Fe atoms are shown. 3+ The ratio of the amount of substance of DOBDC to Fe 3+ The fluorescence intensity of luminol@Fe-DOBDC MOFs obtained by reaction under AA before and after addition (B), the fluorescence intensity of luminol@Fe-DOBDC MOFs obtained by reaction under different luminol concentrations before and after addition of AA at 540 nm (C), and the fluorescence intensity of luminol@Fe-DOBDC MOFs in luminol@Fe-DOBDC MOFs solution before and after addition of AA under different pH conditions (D).

[0031] Figure 10 The graph shows the change in fluorescence intensity of luminol@Fe-DOBDC MOFs solution (50 μL) before and after the addition of AA (20 μM) as a function of A addition time;

[0032] Figure 11 Performance analysis of fluorescence enhancement and ratio detection of AA at different concentrations was conducted. A shows the image under UV light after adding 0.2–30 M ascorbic acid (AA) to luminol@Fe-DOBDC MOFs solution (50 μL); B shows the change in fluorescence intensity with ascorbic acid (AA) concentration; and C shows the linear relationship between ascorbic acid (AA) concentration and fluorescence intensity of luminol@Fe-DOBDC MOFs solution.

[0033] Figure 12 To add ascorbic acid (AA, 20 μM) and different metal ions (Mg) to a luminol@Fe-DOBDC MOFs solution (50 μL), 2+ Ca 2+ Zn 2+ Cu 2+ Pb 2+ Fe 2+ Co 2+The changes in fluorescence intensity were observed after various amino acids (Glc, Glu, Pro, Ala, Gly, Ser, His, Arg, Val, Tyr, all at 100 M concentration) and other reducing substances (Cys, DA, GSH, CA, OA, all at 50 M concentration). Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0035] Example 1

[0036] A luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs) specifically includes the following steps:

[0037] (1) Preparation of Fe-DOBDC MOFs: 5 mL of N,N-dimethylformamide (DMF) solution containing 0.77 mmol 2,5-dihydroxyterephthalic acid (DOBDC) was added to 5 mL of N,N-dimethylformamide (DMF) solution containing 0.77 mmol ferric chloride hexahydrate (FeCl3·6H2O). After stirring for 20 min, the mixture was transferred to an autoclave (lined with stainless steel Teflon) and heated at 150 °C for 12 h. After naturally cooling to room temperature, a black suspension was obtained. The suspension was centrifuged at 10,000–12,000 rpm for 5–10 min and washed three times (using N,N-dimethylformamide (DMF) and ultrapure water as washing solvents, respectively) to remove excess ligands, luminol, and Fe. 3+ Fe-DOBDC MOFs can then be obtained (the process is as follows). Figure 1 (As shown in A);

[0038] (2) Preparation of luminol-embedded iron-based metal-organic framework composites (luminol@Fe-DOBDC MOFs): The Fe-DOBDC MOFs prepared above were dispersed in water and mixed with luminol (the final concentration of luminol after addition was 0.25 mM). The mixture was stirred at room temperature for 2 h until a black precipitate was obtained. The supernatant was removed by centrifugation at 10000-12000 rpm for 5-10 min, and the black dispersion was obtained, which is the luminol-embedded iron-based metal-organic framework composite (luminol@Fe-DOBDC MOFs) (the process is as follows). Figure 1 (As shown in B), store at 4℃ for later use.

[0039] Performance Characterization

[0040] The luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDCMOFs) prepared in Example 1 was dissolved in 4 mL of deionized water to obtain a water-soluble luminol@Fe-DOBDC MOFs solution for later use. In the following tests, 20 μL of luminol@Fe-DOBDC MOFs solution was used each time.

[0041] Dissolve ascorbic acid (AA) in deionized water to form a 1 mM ascorbic acid (AA) solution for later use.

[0042] 1. The relevant properties of the luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs) prepared in Example 1 were tested, as shown below:

[0043] Figure 2 SEM (A) and TEM (B) images of the luminol-embedded iron-based metal-organic framework composite (luminol@Fe-DOBDC MOFs) prepared in Example 1. Figure 2 It can be seen that the luminol@Fe-DOBDC MOFs are irregular spherical in shape with a diameter of 250-300 nm.

[0044] Figure 3 EDS elemental analysis diagram of the luminol@Fe-DOBDC MOFs embedded with luminol prepared in Example 1. Figure 3EDS elemental mapping images of Fe, N, C, and O confirmed the uniform distribution of these elements within luminol@Fe-DOBDC MOFs. Furthermore, the atomic percentages of Fe, N, C, and O in the synthesized fluorescent luminol@Fe-DOBDC MOFs were 2.72%, 0.32%, 85.73%, and 11.23%, respectively. These results clearly demonstrate that the method of this invention can indeed successfully prepare luminol@Fe-DOBDC MOFs.

[0045] Figure 4 The images show the fluorescence excitation and emission spectra of the luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs) prepared in Example 1 at different excitation wavelengths from 345 nm to 380 nm. In the illustrations, a is a photograph of the luminol@Fe-DOBDC MOFs solution under visible light, and b is a photograph of the luminol@Fe-DOBDC MOFs solution under a 365 nm UV lamp. Figure 4 As can be seen, luminol@Fe-DOBDC MOFs exhibit yellow-green fluorescence under a 365nm UV lamp. With increasing excitation wavelength from 345nm to 380nm, the fluorescence emission at 540nm and 430nm shows a typical bell-shaped curve, with the maximum intensity at the 365nm excitation wavelength. Specifically, the fluorescence intensity of luminol@Fe-DOBDC MOFs gradually increases with increasing excitation wavelength, reaching a peak at 365nm, and then gradually decreases. This behavior reflects potential electronic transitions occurring within the system. Simultaneously, luminol@Fe-DOBDC MOFs exhibit typical excitation-independent emission characteristics, suggesting that the prepared luminol@Fe-DOBDC MOFs may be single-photon emitters.

[0046] 2. The feasibility of using the luminol@Fe-DOBDC MOFs fluorescence "enhancement" ratio method to detect ascorbic acid (AA) is as follows:

[0047] After adding 20 μM ascorbic acid (AA) solution to 50 μL of luminol@Fe-DOBDC MOFs solution, the SEM and TEM images are shown below. Figure 5 As shown in Figures A and B. From... Figure 2 and Figure 5 The comparison shows that when ascorbic acid (AA) is added to luminol@Fe-DOBDC MOFs, their irregular spherical shape changes slightly.

[0048] Figure 6The fluorescence emission spectra of 50 μL luminol@Fe-DOBDC MOFs solution before and after the addition of 20 μM ascorbic acid (AA) solution are shown. In the inset, a is the fluorescence image of the luminol@Fe-DOBDC MOFs solution without AA, and b is the fluorescence image of the luminol@Fe-DOBDC MOFs solution with AA. Figure 6 It can be seen that when the excitation wavelength is 365 nm, luminol@Fe-DOBDC MOFs exhibit weak fluorescence emission at 430 nm and 540 nm, respectively; after the addition of ascorbic acid (AA) solution, the Fe contained in luminol@Fe-DOBDC MOFs... 3+ The redox reaction with ascorbic acid (AA) enhanced the fluorescence intensity, while Fe 3+ Reduced to Fe 2+ The yellow-green fluorescence intensity of luminol@Fe-DOBDC MOFs at 540 nm was enhanced by 119%, while the blue fluorescence intensity of luminol at 430 nm showed a slight change. Other reports suggest that Fe... 3+ The fluorescence quenching of the ligand 2,5-dihydroxyterephthalic acid (DOBDC) is due to the absorption of the excitation source energy by both and Fe. 3+ This is due to the electronic interactions between the Fe and the carboxylic acid group components; 3+ Reduced to Fe by AA 2+ After that, Fe 3+ The chelating ability of p-phenylcarboxylate is greatly reduced, thus the fluorescence intensity of luminol@Fe-DOBDC MOFs is enhanced in the presence of AA. Therefore, this demonstrates that the fluorescence "enhancement" and ratio strategy proposed using luminol@Fe-DOBDC MOFs can indeed detect AA.

[0049] To further explore the mechanism of fluorescence "enhancement" ratio detection of AA in luminol@Fe-DOBDC MOFs, the reaction of Fe with AA after its introduction into luminol@Fe-DOBDC MOFs was investigated using the reagent 1,10-phenanthroline. 3+ The price state. Figure 7 Images showing the addition of blank solution (Control), ascorbic acid (AA, 20 μM), cysteine ​​(Cys, 50 μM), oxalic acid (OA, 50 μM), dopamine (DA, 50 μM), citric acid (CA, 50 μM), and glutathione (GSH, 50 μM) to a 50 μL mixed solution of luminol@Fe-DOBDC MOFs and 1,10-phenanthroline (2 mg / mL). Figure 7It can be seen that after adding 1,10-phenanthroline to the mixture of luminol@Fe-DOBDC MOFs and AA, due to Fe 2+ The formation of the 1,10-phenanthroline orange-red complex, whose color changes from black to orange-red, is due to the formation of Fe. 3+ The redox reaction between AA and Fe was also investigated. Furthermore, other reducing agents (oxalic acid, dopamine, glutathione, citric acid, and cysteine) were used to verify its selectivity against ascorbic acid. The addition of only cysteine ​​resulted in a slight color change, consistent with other reported selectivity results. This is because AA reacts with Fe... 3+ Its reducing power is stronger than that of other reducing substances.

[0050] Figure 8 The solutions included luminol@Fe-DOBDC MOFs, a mixed solution of luminol@Fe-DOBDC MOFs + AA (100 μM), a mixed solution of luminol@Fe-DOBDC MOFs + AA (100 μM) + 1,10-phenanthroline (2 mg / mL), and 1,10-phenanthroline (2 mg / mL) + Fe 2+ The UV-Vis absorption spectrum of a mixed solution (concentration 100 μM). Figure 8 It can be seen that the addition of 1,10-phenanthroline to luminol@Fe-DOBDC MOFs and AA resulted in a maximum absorption peak at 510 nm, similar to that of Fe. 2+ Absorption in the presence of 1,10-phenanthroline; the obvious absorption peak at 510 nm can be attributed to Fe. 2+ Formation of an orange-red complex with 1,10-phenanthroline. The enediol group of AA is oxidized to form an ortho-diketone group of dehydroascorbic acid (DHAA), while Fe... 3+ Simultaneously reduced to Fe 2+ Therefore, it is speculated that Fe 3+ Reduced to Fe by AA 2+ The redox interaction is the reason for the "enhanced" fluorescence.

[0051]

[0052] 3. Optimization of conditions for ascorbic acid (AA) detection using the luminol@Fe-DOBDC MOF fluorescence "enhancement" ratio method is detailed below:

[0053] To achieve sensitive detection of AA, the synthesis temperature of Fe-DOBDC MOFs, Fe... 3+ The ratio of the amount of substance of DOBDC to Fe 3+The concentration of luminol added during the synthesis of luminol@Fe-DOBDC MOFs, the pH value of the solution during AA detection, and the reaction time were investigated. Considering the slight change in fluorescence at 430 nm, the fluorescence intensity at 540 nm was explored to evaluate and optimize the experimental conditions.

[0054] Figure 9 The fluorescence intensity (A) of luminol@Fe-DOBDC MOFs obtained at different synthesis temperatures at 540 nm before and after the addition of AA, and the fluorescence intensity of different Fe atoms are shown. 3+ The ratio of the amount of substance of DOBDC to Fe 3+ The fluorescence intensity at 540 nm of luminol@Fe-DOBDC MOFs synthesized under different luminol concentrations before and after the addition of AA (B); the fluorescence intensity at 540 nm of luminol@Fe-DOBDC MOFs synthesized under different luminol concentrations before and after the addition of AA (C); and the fluorescence intensity at 540 nm of the solutions obtained from the reaction before and after the addition of AA to the luminol@Fe-DOBDC MOFs solution under different pH conditions (D). Figure 9 As can be seen from Figure A, before reaching 150℃ in the autoclave, regardless of the presence or absence of AA, the fluorescence intensity at 540nm increases with increasing synthesis temperature; the fluorescence intensity reaches its maximum at 150℃, and then decreases. Therefore, luminol@Fe-DOBDC MOFs for AA detection can be prepared by reacting in an autoclave within the temperature range of 100–200℃. Furthermore, to achieve the maximum and stable fluorescence enhancement effect, 150℃ is chosen as the optimal condition for AA detection. Figure 9 As can be seen from B, in Fe 3+ luminol@Fe-DOBDCMOFs for detecting AA can be prepared in the range of 2:1 to 1:2 / DOBDC, while Fe 3+ The fluorescence enhancement effect is strongest when the ratio of DOBDC is 1:1. Figure 9 As shown in Figure C, within the specified range, the fluorescence intensity of the prepared luminol@Fe-DOBDC MOFs gradually increased after adding luminol at concentrations of 0.5–8.0 mM. In the presence of AA, the strongest fluorescence enhancement effect was observed at 1 mM luminol, indicating that luminol@Fe-DOBDC MOFs for AA detection can be prepared by adding luminol at concentrations of 0.5–8.0 mM. Figure 9As shown in Figure D, in the detection of AA, the fluorescence intensity of luminol@Fe-DOBDC MOFs showed a slight change in the solution pH range of 3.6–4.6, and then increased sequentially with increasing pH from 4.6 to 5.6. This may be due to Fe 3+ The fluorescence is enhanced through self-hydrolysis in weakly acidic or alkaline environments. Therefore, luminol@Fe-DOBDCMOFs can be used to detect AA in a pH range of 3.6–5.6. To achieve the maximum and stable fluorescence enhancement, pH=4.0 was chosen as the optimal condition for AA detection.

[0055] Under the optimal reaction conditions described above, kinetic behavior is also an important factor in AA detection. Figure 10 The graph shows the change in fluorescence intensity of luminol@Fe-DOBDC MOFs (50 μL) before and after the addition of AA (20 μM) with reaction time. Figure 10 It can be seen that the fluorescence of luminol@Fe-DOBDC MOFs is stable between 10 and 200 s with an excitation wavelength of 365 nm and an emission wavelength of 540 nm. After the addition of AA, the fluorescence intensity rapidly increases, reaching a stable high fluorescence intensity at 150 s. This indicates that Fe in luminol@Fe-DOBDC MOFs... 3+ Reduced to Fe by AA 2+ It is a rapid redox interaction. Therefore, this fluorescence "enhancement" platform for AA detection has the advantage of a rapid response within approximately 2–3 minutes (150 seconds).

[0056] 4. The sensitivity of the luminol@Fe-DOBDC MOFs fluorescence "enhancement" ratio method for detecting ascorbic acid (AA) conditions is shown below:

[0057] Under the above optimized conditions (temperature range of 150℃ in the autoclave, Fe...), 3+ The performance of fluorescence enhancement and ratio detection of AA was analyzed using different concentrations of AA (DOBDC ratio 1:1, luminol concentration 1.0 mM, pH = 4.0, and reaction time 150 s after AA addition). The results are as follows: Figure 11 As shown, A is an image under UV light after adding 0.2–30 M ascorbic acid (AA) to a luminol@Fe-DOBDC MOFs solution (50 μL); B shows the change in fluorescence intensity with ascorbic acid (AA) concentration; and C shows the linear relationship between ascorbic acid (AA) concentration and fluorescence intensity of the luminol@Fe-DOBDC MOFs solution. Figure 11As can be seen from Figure A, under a 365nm ultraviolet lamp, the yellow-green fluorescence becomes more pronounced with increasing AA concentration; from... Figure 11 As can be seen from B, with the increase of AA concentration from 0.2 to 30 M, the fluorescence intensity at 540 nm gradually increases, while the fluorescence intensity at 430 nm remains relatively unchanged, reaching a plateau at 30 M; from Figure 11 As can be seen from C, the concentration of ascorbic acid (AA) and the fluorescence intensity of luminol@Fe-DOBDC MOFs solution show a good linear relationship, and the linear fitting equation is I. 540 nm / I 430 nm =1.303 + 0.047c AA (where c) AA The concentration of ascorbic acid (AA) is expressed in methanogens (M), with a correlation coefficient (r) of 0.995. Simultaneously, from... Figure 11 It can be seen that the limit of detection (LOD) for AA detection using luminol@Fe-DOBDC MOFs is calculated to be 70 nM (the formula for calculating LOD is LOD = 3σ / k, where σ is the standard deviation of the control sample and k is the fluorescence ratio (IL). 540 nm / I 430 nm The absolute value of the slope between the concentration of AA and the concentration of AA is shown in Table 1. This demonstrates that, compared to other reported methods for AA detection (as shown in Table 1), the method for detecting AA using luminol@Fe-DOBDC MOFs in this invention exhibits higher sensitivity, a low LOD of 70 nM, and a linear range of 0.2–30 M.

[0058] Table 1. Comparison of different methods for detecting AA

[0059]

[0060]

[0061] The fluorescence method 1 in Table 1 above is derived from the reference "Gu, L.; Zhang, J.; Yang, G.; Tang, Y.; Zhang, X.; Huang, X.; Zhai, W.; Fodjo, EK; Kong, C., Green preparation of carbon quantum dots with wolfberry as on-off-on nanosensors for the detection of Fe 3+and l-ascorbic acid. Food Chem. 2021, 376, 131898-131904; Fluorescence method 2 is from reference "Wu, A.; Ding, H.; Zhang, W.; Rao, H.; Wang, L.; Chen, Y.; Lu, C.; Wang, X., A colorimetric and fluorescence turn-on probe for the detection of ascorbic acid in living cells and beverages. Food Chem. 2021, 363, 130325-130331"; Electrochemical method 1 is from reference "de Faria, LV; Lisboa, TP; de Farias, DM; Araujo, FM; Machado, MM; deSousa, RA; Matos, MAC; Munoz, RAA; Matos, RC, Direct analysis of ascorbicacid in food beverage samples by flow injection analysis using reduced graphene oxide sensor. Food Chem. 2020, 319, 126509-126514; Fluorescence method 3 is from reference "Li, X.;Wang, C.;Li, P.;Sun, X.;Shao, Z.;Xia, J.;Liu, Q.;Shen, F.;Fang, Y., Beer-derived nitrogen, phosphorus co-doped carbon quantum dots: highly selective on-off-on fluorescent probes for the detection of ascorbic acid in fruits. FoodChem. 2022, 409, 135243-135250"; Colorimetric method 1 is from reference "Wei, Z.;Li, H.;Liu, S.;Wang, W.;Chen, H.;Xiao, L.;Ren, C.;Chen, X.Carbon dots as fluorescent / colorimetric probes for real-time detection of hypochlorite and ascorbic acid in cells and body fluid. Anal. Chem. 2019, 91(24), 15477-15483. Fluorescence method 4 is derived from the reference "Guo, L.; Liu, Y.; Kong, R.; Chen, G.; Liu, Z.; Qu, F.; Xia, L.; Tan, W., A metal-organic framework as selectivity regulator for Fe. 3+and ascorbic acid detection. Anal. Chem. 2019, 91(19), 12453-12460”, Fluorescence method 5 is from reference “Meng, HM; Zhang, XB; Yang, C.; Kuai, H.; Mao, GJ; Gong, L.; Zhang, W.; Feng, S.; Chang, J., Efficient two-photonfluorescence nanoprobe for turn-on detection and imaging of ascorbic acid inliving cells and tissues. Anal. Chem. 2016, 88(11), 6057-6063”, Fluorescence method 6 is from reference “Zhao, P.; He, K.; Han, Y.; Zhang, Z.; Yu, M.; Wang, H.; Huang, Y.; Nie, Z.; Yao, S., Near-infrared dual-emission quantum dots-gold nanoclusters nanohybrid via co-template synthesis”. For ratiometric fluorescent detection and bioimaging of ascorbic acid in vitro and in vivo. Anal. Chem. 2015, 87(19), 9998-10005”, colorimetric method 2 is from reference “Luo, X.;Zhang, W.;Han, Y.;Chen, X.;Zhu, L.;Tang, W.;Wang, J.;Yue, T.;Li, Z., N, S co-doped carbon dots based fluorescent "on-off-on" sensor for determination of ascorbic acid in common fruits. Food Chem. 2018, 258, 214-221”, colorimetric method 3 is from reference “Peng, J.;Ling, J.;Zhang, X.-Q.;Zhang, L.-Y.;Cao, Q.-E.;Ding, Z.-T., A rapid, sensitive and selective colorimetric method for detection of ascorbic acid”. acid.Sens.Actuat.B:Chem.2015,221,708-716”, Fluorescence method 7 is from reference “Du,SZ; Sun,Z.; Qing,M.; Wang,L.; Tang,Q.; Zhou,J.; Luo,HQ; Li,NB,Infinitecoordination polymer nanoparticles used for fluorescence turn-on sensing of ascorbic acid.ACS Appl.Nano Mater.2021,4(7),6872-6880”, Fluorescence method 8 is from reference “Zeng,YN; Zheng,HQ; Gu,JF; Cao,GJ; Zhuang,WE; Lin,JD; Cao,R.; Lin,ZJ,Dual-emissive metal-organic framework as a fluorescent “switch”forratiometric sensing of hypochlorite and ascorbic acid”. acid.Inorg.Chem.2019,58(19),13360-13369”, Fluorescence method 9 is from reference “Zhang,J.-H.;Zhang,Z.-T.;Sheng,M.-S.;Xiao,H.-Y.;Zhang,F.;Meng,J.;Lai,M.-M.;Wu,X.-M.;Li,Y.,Luminescent carbonnanoclusters for sensitive detection of ascorbic acid and fluorescent printing.ACS Appl.Nano Mater.2022,5(4),5234-5243”.

[0062] 5. The selectivity of ascorbic acid (AA) under certain conditions was determined by the fluorescence "enhancement" ratio method of luminol@Fe-DOBDC MOFs, as detailed below:

[0063] Figure 12 To add ascorbic acid (AA, 20 μM) and different metal ions (Mg) to a luminol@Fe-DOBDC MOFs solution (50 μL), 2+ Ca 2+ Zn 2+ Cu 2+ Pb 2+ Fe 2+ Co2+ The changes in fluorescence intensity were observed after the addition of various amino acids (Glc, Glu, Pro, Ala, Gly, Ser, His, Arg, Val, Tyr, all at 100 M) and other reducing agents (Cys, DA, GSH, CA, OA, all at 50 M). Figure 12 It can be seen that adding oxalic acid (OA), dopamine (DA), glutathione (GSH), citric acid (CA), cysteine ​​(Cys), and other reducing agents to the luminol@Fe-DOBDC MOFs solution did not result in significant fluorescence changes. The addition of other metal ions (including Mg) also did not change fluorescence. 2+ Ca 2+ Zn 2+ Cu 2+ Pb 2+ F e2+ Co 2 + No significant fluorescence change was observed after adding ascorbic acid, along with various amino acids (including glucose (Glc), glutamic acid (Glu), proline (Pro), alanine (Ala), glycine (Gly), serine (Ser), histidine (His), arginine (Arg), and valine (Val)). However, the fluorescence was significantly enhanced after adding ascorbic acid. This indicates that this fluorescence "enhancement" ratio method has good selectivity for other interfering reducing substances, metal ions, and amino acids in the detection of AA, and is beneficial for determining the fluorescence "enhancement" ratio of AA in beverage samples.

[0064] 6. The luminol@Fe-DOBDC MOFs fluorescence "enhancement" ratio method was used to detect ascorbic acid (AA) in beverage samples, as detailed below:

[0065] To evaluate the feasibility of the fluorescence "enhancement" ratio method for detecting amino acids (AA) in real beverage samples, three different commercial beverages (Pulse, Uni-President Fresh Orange Juice, and Minute Maid) were used to monitor AA concentration. All three beverage samples were purchased from supermarkets and required no further purification. To ensure that the AA concentration remained within the linear range in this work, the beverage samples were diluted 100-fold, 10-fold, and 5-fold, respectively. The AA detection results were cross-validated with the product instructions of the purchased beverages and a standard fluorescence method based on o-phenylenediamine (OPD) (Table 2). In short, due to the in-situ formation of fluorescent quinoline by OPD and AA under alkaline conditions, the mixed solution of OPD and AA exhibits blue fluorescence emission at approximately 425 nm. Based on this, a standard method for detecting AA in beverage samples based on OPD was established. The experimental results of the fluorescence "enhancement" ratio method proposed in this invention are basically consistent with those of the standard fluorescence method based on OPD. This indicates that the fluorescence "enhancement" ratio method proposed in this invention has high accuracy in detecting AA, further demonstrating the good potential application of this dual-emission platform based on luminol@Fe-DOBDC MOFs in the detection of AA in real beverages.

[0066] Table 2. AA detection results using the fluorescence "enhancement" ratio method and the OPD-based fluorescence method.

[0067]

[0068] In summary, this invention successfully prepared a luminol-embedded iron-based metal-organic framework composite material (luminol@Fe-DOBDC MOFs), mainly using 2,5-dihydroxyterephthalic acid (DOBDC) as an organic linker and Fe from ferric chloride hexahydrate (FeCl3·6H2O). 3+ As a metallic node, Fe-DOBDC MOFs (Fe) were obtained by reaction in an autoclave. 3+ (Due to the electronic interaction between the ligand and the carboxylic acid group, the fluorescence of the ligand is significantly quenched), and the reaction with luminol can be continued with stirring. Under single excitation at 365 nm, the dual-emission luminol@Fe-DOBDC MOFs prepared in this invention have two fluorescence emission peaks at 430 nm and 540 nm, which are 110 nm apart. Environmental interference can be eliminated by calibration with the built-in proportional signal. In addition, based on the Fe in luminol@Fe-DOBDC MOFs... 3+The luminol@Fe-DOBDC MOFs demonstrated high redox properties with amino acids (AA) and achieved fluorescence enhancement ratio detection of AA in commercial beverages within 2–3 min (150 s) using a fluorescence enhancement ratio method. It exhibited high sensitivity for AA detection in the 0.2–30 M range, with a LOD of 70 nM, and high selectivity for other reducing agents (such as Cys, DA, GSH, CA, and OA), amino acids, and metal ions. The detection results of AA in various commercial beverages using this method showed good agreement with standard OPD-based fluorescence methods. Therefore, the use of a MOF-based dual-emission platform offers significant potential for the detection of AA in real-world samples.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for the preparation of an embedded luminol iron metal-organic framework composite material for fluorescence-enhanced ratio detection of ascorbic acid, characterized by, The preparation method comprises the following steps: (1) Preparation of Fe-DOBDC MOFs: The N,N-dimethylformamide solution containing 2,5-dihydroxyterephthalic acid was added to the N,N-dimethylformamide solution containing iron chloride hexahydrate, and after stirring and mixing, it was moved into an autoclave, heated at 150-200°C for 12-20 h, and then naturally cooled to room temperature to obtain a black suspension. After rotary centrifugation, the excess ligand and Fe were removed by repeated washing 3+ , and Fe-DOBDC MOFs were obtained (2) preparing the luminol-embedded iron-based metal organic framework composite material: after dispersing the Fe-DOBDC MOFs in water, mixing with luminol, stirring at room temperature until a black precipitate is obtained, centrifuging to remove the supernatant, and obtaining a black dispersion, which is the luminol-embedded iron-based metal organic framework composite material.

2. The production method according to claim 1, characterized by, In step (1), the molar ratio of 2,5-dihydroxyterephthalic acid to ferric chloride hexahydrate is 2:1-1:

2.

3. The preparation method according to claim 1, characterized in that, In step (1), the inner lining of the autoclave is stainless steel Teflon.

4. The method of claim 1, wherein, In step (1), the washing is performed with N,N-dimethylformamide and ultrapure water as the washing solvents in sequence.

5. The preparation method according to claim 1, characterized in that, In step (1), the rotation speed of the centrifugation is 10,000-12,000 rpm, and the time is 5-10 min.

6. The method of claim 1, wherein, In step (2), the final concentration of luminol after addition is 0.1-0.5 mM.

7. The preparation method according to claim 1, characterized in that, In step (2), the rotation speed of the centrifugation is 10,000-12,000 rpm, and the time is 5-10 min.

8. The luminol-embedded iron-based metal organic framework composite material prepared by the preparation method according to any one of claims 1-7.

9. Application of the luminol-embedded iron-based metal organic framework composite material according to claim 8 in the fluorescence-enhanced ratio detection of ascorbic acid.

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