Cellulose-Eu-MOF composite material and preparation method and application thereof

Abstract

The invention discloses a cellulose-Eu-MOF composite material as well as a preparation method and application thereof. The preparation method of the cellulose-Eu-MOF composite material comprises the following steps: mixing a lotus root silk cellulose fiber suspension with an Eu < 3 + > salt solution and a ligand solution to form a composite suspension, then standing and culturing the composite suspension, and growing an Eu-based ligand compound in situ in the lotus root silk cellulose solution to obtain the LCNF-Eu-MOF composite material. The probe can be used for fluorescence detection and diagnosis of a biomarker AA of DED. The LCNF-Eu-MOF film-based fluorescence sensor shows high sensitivity and fluorescence quenching effect on AA, and the detection limit is as low as 4.63 [mu] M; meanwhile, the LCNF-MOF composite film also has the advantages of high selectivity, recoverability, easiness in visual detection and the like, so that the LCNF-MOF composite film can be used as an instant fluorescent platform of DED biomarkers, and a sustainable material is potentially converted into a practical clinical tool.

Description

Technical Field

[0001] This invention belongs to the field of biodetection technology, specifically relating to a cellulose-Eu-MOF composite material, its preparation method, and its application. Background Technology

[0002] Dry eye disease (DED) is one of the most common eye diseases in modern society, mainly caused by insufficient tear secretion or rapid tear evaporation. As early as 2019, there were over 340 million DED patients worldwide, and delayed diagnosis can significantly impact patients' quality of life. With advancements in science and technology, the widespread use of electronic devices, and prolonged close-range visual tasks on smartphones and computers, the incidence of DED has increased significantly, and the importance of early diagnosis of DED is widely recognized.

[0003] However, in the field of dry eye diagnosis technology, existing visualization diagnostic technologies have many problems that urgently need to be solved: On the one hand, traditional diagnostic methods mostly rely on large-scale testing equipment, which has the disadvantages of poor portability, complex operation, and high testing costs, making it difficult to meet the needs of primary healthcare scenarios or immediate diagnosis; on the other hand, existing fluorescence sensors often use non-degradable synthetic materials, which do not conform to the current green and sustainable development concept, and some sensors have problems such as high detection limits, narrow detection range, and insufficient fluorescence stability, which cannot accurately cover the detection range of target substances (such as ascorbic acid, AA) required in dry eye diagnosis, affecting the accuracy and reliability of diagnostic results. Therefore, providing a convenient and efficient DED diagnostic device has become an urgent problem to be solved in the early diagnosis of dry eye.

[0004] Ascorbic acid (AA) is an important water-soluble antioxidant with a significant ability to alleviate tissue damage induced by oxidative stress. High concentrations of AA can effectively counteract the damage caused by oxidative stress in DED. Early diagnosis of DED can be made by detecting the level of ascorbic acid, thus AA can serve as a biomarker for the early diagnosis of DED.

[0005] Current methods for monitoring ammonia (AA) levels mainly include fluorescence, electrochemical, and colorimetric methods. However, the latter two methods still face challenges such as expensive instruments, complex operation, and susceptibility to interference. Fluorescence methods, on the other hand, overcome traditional limitations due to their simplicity, visual readout, and high sensitivity, making them highly suitable for point-of-care testing (POCT). With advancements in fluorescence sensing technology, significant breakthroughs have been achieved in sensor design based on various fluorescent materials, such as quantum dots (QDs), metal-organic frameworks (MOFs), upconversion nanocrystals, and nanozymes. Therefore, developing photosensitive materials with excellent luminescence properties, ease of fabrication, superior mechanical properties, and high sensitivity is crucial for improving AA fluorescence sensing and opening new possibilities in the POCT field. Chinese invention patent CN 118594621A discloses a MOF-confined metal oxide nanozyme, its preparation method, and its application in ascorbic acid detection. The MOF-confined metal oxide nanozyme can generate an emission signal by catalyzing the chemiluminescent reaction of H2O2 oxidizing luminol. The quenching effect of AA on chemiluminescence is used to achieve highly sensitive and specific detection of ascorbic acid. However, this MOF-confined metal oxide nanozyme has a significant response to the pH of the sample, and its use in the detection of AA in samples such as tears has a significant impact on the detection results.

[0006] Lanthanide MOFs (Ln-MOFs) are hybrids composed of organic ligands and lanthanide metal ions. Due to their unique "antenna effect" and excellent optical properties, they have attracted great attention in the field of fluorescence sensing. However, MOFs are usually obtained in the form of rigid powders, which hinders their practical application. Chinese invention patent CN120209342A discloses a europium-based metal-organic framework and its preparation method and application. Europium salt, H4BTA-2OH, and ascorbic acid are added to a binary solution, and the solution is subjected to ultrasonic treatment, heating, and post-treatment in sequence to prepare a europium-based metal-organic framework. The framework was then used to detect the anthrax biomarker 2,6-pyridinedicarboxylic acid (DPA), showing excellent detection sensitivity.

[0007] Based on the above analysis, this invention provides a sustainable cellulose-Eu-MOF composite film on the basis of the prior art, and uses it for the detection of AA and the early diagnosis of dry eye syndrome. Summary of the Invention

[0008] The main objective of this invention is to provide a cellulose-Eu-MOF composite material, its preparation method, and its application, in order to overcome the shortcomings of the prior art.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a cellulose-Eu-MOF composite material, comprising mixing a lotus root fiber cellulose fiber suspension with Eu... 3+ The salt solution and ligand solution are mixed to form a composite suspension. The Eu-based ligand compound is grown in situ in the solution of lotus root cellulose fibers to obtain the cellulose-Eu-MOF composite material.

[0010] In some specific embodiments, the ligand solution is an H3BTC ethanol solution.

[0011] In some specific embodiments, Eu 3+ The molar ratio of H3BTC to H3BTC is 0.01~0.03:0.06~0.09.

[0012] In some specific embodiments, the mass fraction of the lotus root cellulose fiber suspension in the cellulose-Eu-MOF composite material is 0.1~0.5%; for example, the mass fraction of the lotus root cellulose fiber suspension is 0.22%.

[0013] As a preferred embodiment, the method for preparing lotus root cellulose fiber includes: cutting lotus root into small pieces, soaking them in 95% ethanol and 1% HCl in sequence, treating the insoluble matter with alkaline solution, centrifuging, and collecting the precipitate; then, bleaching the cellulose in H2O2 by stirring, further washing and centrifuging, and dispersing it in water to obtain a lotus root cellulose suspension.

[0014] As a second aspect of the invention, the present invention provides a cellulose-Eu-MOF composite material, which is prepared by the preparation method described above.

[0015] As a third aspect of the invention, the present invention provides a cellulose-Eu-MOF composite film, comprising the cellulose-Eu-MOF composite material as described above, which is obtained by drying at 35 °C for 5-7 days.

[0016] As a fourth aspect of the invention, the present invention provides the use of the cellulose-Eu-MOF composite material as described above in the fluorescence detection of ascorbic acid.

[0017] In cellulose-Eu-MOF composites or cellulose-Eu-MOF composite films, when the loading of Eu-MOF is less than 50 wt%, it can be used for the qualitative detection of ascorbic acid.

[0018] Preferably, the loading of the Eu-MOF is 42~45wt%.

[0019] When the loading of Eu-MOF is higher than 50 wt%, it can be used for the quantitative detection of ascorbic acid.

[0020] Preferably, the loading of the Eu-MOF is 50~85wt%.

[0021] As a fifth aspect of the invention, the present invention provides a fluorescence sensor comprising at least the cellulose-Eu-MOF composite material or the cellulose-Eu-MOF composite film as described above.

[0022] As a sixth aspect of the invention, the present invention provides a method for fluorescence detection of ascorbic acid, comprising using the cellulose-Eu-MOF composite material as described above, and specifically including the following steps: S1. Prepare an ascorbic acid standard solution, then add the standard solution to the cellulose-Eu-MOF composite material as described in claim 7 for reaction, dry to form a cellulose-Eu-MOF composite film, and then use an enzyme-linked immunosorbent assay (ELISA) reader for fluorescence detection to obtain a linear curve of the concentration of cellulose-Eu-MOF-AA. S2. The sample to be tested is added to the cellulose-Eu-MOF composite material, dried, and then subjected to fluorescence detection. Based on the linear concentration curve of cellulose-Eu-MOF-AA in S1, the content of ascorbic acid in the sample to be tested is quantitatively analyzed.

[0023] Preferably, the detection limit for ascorbic acid is 4.63 μM.

[0024] Preferably, the sample to be tested includes any one of food or medicine.

[0025] As a seventh aspect of the invention, the present invention provides the use of a cellulose-Eu-MOF composite material as described above, or a cellulose-Eu-MOF composite film, in detecting the content of ascorbic acid in tears.

[0026] As an eighth aspect of the invention, the present invention provides a diagnostic device for dry eye syndrome, comprising at least the cellulose-Eu-MOF composite material or the cellulose-Eu-MOF composite film as described above.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention prepares an LCNF-MOF composite film by in-situ integration of Eu-MOF and lotus root cellulose fiber (LCNF) for the fluorescence detection of AA, a biomarker for the diagnosis of DED. The LCNF-MOF film-based fluorescence sensor exhibits high sensitivity and significant fluorescence quenching effect for AA, with a detection limit as low as 4.63 μM. At the same time, it also has the advantages of high selectivity, recyclability and easy visualization detection, thus making the LCNF-MOF composite film a real-time fluorescence platform for DED biomarkers, potentially transforming sustainable materials into practical clinical tools.

[0028] (2) The LCNF-MOF composite film provided by the present invention uses lotus root silk cellulose fiber as raw material, which solves the technical problems of non-environmentally friendly materials, complex process and poor detection performance in the detection of dry eye biomarkers in the prior art. At the same time, it also lays a scientific foundation for the development of sustainable and portable visual diagnostic sensors, and combines green environmental protection with high-performance detection in the field of early diagnosis of dry eye.

[0029] (3) The present invention directly synthesizes LCNF-MOF composite films through a one-step synthesis method. Compared with traditional hot solvent method, liquid phase epitaxy and other MOF material preparation methods, it does not require strict control of material growth temperature or the addition of a large amount of organic matter, which greatly saves preparation time and operating costs. At the same time, it effectively avoids the problem of increased difficulty in cleaning MOF precipitates due to excessive organic matter participating in the reaction, significantly improving the efficiency of material preparation and the feasibility of practical application. The simple preparation characteristics of this material also lay the foundation for the large-scale production and low-cost application of subsequent diagnostic devices, avoiding the problem of difficult popularization of diagnostic technology due to complex material preparation and high cost.

[0030] (4) The present invention incorporates MOFs into a cellulose-based polymer matrix to form a composite film, which effectively combines the advantages of MOFs and cellulose, thereby greatly expanding the application range of cellulose-Eu-MOF composite films in portable light-emitting devices.

[0031] (5) By integrating sustainable cellulose materials with easily synthesized Ln-MOF, this invention successfully prepared a functionalized fluorescent composite film, which not only solved the core technical problems of non-environmentally friendly materials, complex processes and poor detection performance in existing dry eye diagnosis technology, but also laid a scientific foundation for the development of sustainable and portable visual diagnostic sensors, filling the technical gap in the field of combining green environmental protection and high-performance detection. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram illustrating the preparation principle of the LCNF-MOF composite film provided in Example 1 of the present invention.

[0034] Figure 2The linear fitting curve of the LCNF-MOF composite film provided in Example 1 of the present invention under low concentration of ascorbic acid (0~2mM).

[0035] Figure 3 The exponential fitting curve of the LCNF-MOF composite film provided in Example 1 of the present invention under high concentration of ascorbic acid (0 mM-40 mM).

[0036] Figure 4 This is a comparison diagram showing the effect of different pH values ​​on the LCNF-MOF composite film provided in Example 1 of the present invention.

[0037] Figure 5 This is a comparison diagram of the effects of different anti-interference substances on the LCNF-MOF composite film provided in Example 1 of the present invention.

[0038] Figure 6 The image shows the test results of the reusability of the LCNF-MOF composite film for detecting ascorbic acid provided in Example 1 of this invention.

[0039] Figure 7 The image shows a comparison of simulated healthy human body tears and tears from a DED patient with the LCNF-MOF composite film provided in Example 1 of this invention.

[0040] Figure 8 This is a fluorescence image of commercially available cellulose nanocrystals combined with Eu-MOF, provided in Comparative Example 1 of this invention.

[0041] Figure 9 This is a fluorescence image of lotus root fiber cellulose bound to Eu-MOF in Example 1 of the present invention.

[0042] Figure 10 This is a micrograph of Comparative Example 1 of the present invention, which combines commercial cellulose nanocrystals with Eu-MOF.

[0043] Figure 11 This is a micrograph of lotus root fiber cellulose combined with Eu-MOF in Example 1 of the present invention.

[0044] Figure 12 The effect of the composite film prepared in Example 5 of this invention on the detection of different concentrations of ascorbic acid was investigated.

[0045] Figure 13 This is a SEM image of the LCNF-MOF composite film prepared in Example 1 of the present invention.

[0046] Figure 14 The LCNF-MOF composite film prepared in Example 1 of the present invention can achieve bending and folding behavior. Detailed Implementation

[0047] The invention will be more fully understood through the following detailed description, read in conjunction with the accompanying drawings. Detailed embodiments of the invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary and the invention can be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as intended to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0048] This invention proposes a simplified solution-mixed synthesis method for cellulose and Eu-MOF composite materials. Specifically, it employs a one-step synthesis method that combines a ligand pre-dispersion strategy (using ethanol to dissolve H3BTC) with dynamic coordination of metal ions to directly obtain LCNF-MOF composite films, overcoming the technical limitations of traditional MOF synthesis which requires multiple reaction steps. Compared to traditional hot solvent methods and liquid phase epitaxy methods for MOF material preparation, this method eliminates the need for strict control of material growth temperature and the addition of large amounts of organic matter. It only requires mixing a specific concentration of metal ion aqueous solution with a cellulose dispersion, then adding a ligand ion ethanol solution dropwise, and stirring for 2 hours with a magnetic stirrer to allow the mixed solution to fully react and for Eu-MOF to grow completely, thus obtaining a mixed dispersion of cellulose and Eu-MOF. This process significantly reduces preparation time and operating costs, while effectively avoiding the increased difficulty in cleaning MOF precipitates caused by excessive organic matter participating in the reaction, significantly improving the efficiency of material preparation and the feasibility of practical applications. The ease of preparation of this material lays the foundation for the large-scale production and low-cost application of subsequent diagnostic devices, avoiding the problem of diagnostic technology being difficult to popularize due to the complexity and high cost of material preparation.

[0049] Cellulose is an abundant natural polymer compound found in plants and is one of the most abundant renewable resources on Earth. Its inherent functionality, mechanical strength, sustainability, and excellent processability make it an ideal platform for fluorescence sensors. Cellulose acts as a robust scaffold for Ln-MOFs, enabling the resulting composite materials to exhibit superior performance, particularly in portable luminescent devices.

[0050] Furthermore, this invention first breaks through the limitations of traditional materials by selecting natural lotus root fiber cellulose as the base material. This material is not only widely available and biocompatible, but also has good dispersibility, which can solve the problems of non-degradability and poor environmental friendliness of synthetic materials. Secondly, in terms of preparation process, the complex high-temperature and high-pressure synthesis process is abandoned, and a simple solution synthesis method at room temperature (one-step synthesis method) is adopted to realize the in-situ growth of Eu-MOF crystals in cellulose solution, effectively reducing preparation costs and simplifying operation steps, solving the problems of cumbersome and energy-intensive preparation processes of traditional MOF-based composite materials. Furthermore, through systematic characterization of the optical properties, mechanical properties and morphology of the composite film, it is found that it has a significant fluorescence quenching effect on ascorbic acid (AA), and the quenching mechanism is elucidated. Finally, it is constructed into a fluorescence sensor that can be seen with the naked eye. The detection limit of this sensor is as low as 4.63 μM, which can completely cover the detection range of AA in the diagnosis of dry eye disease, solving the problems of high detection limit, insufficient detection accuracy and poor visualization effect of existing sensors. Compared with cellulose from other sources, lotus root fiber cellulose fiber (LCNF) has the advantages of short growth cycle, easy processing and high cellulose purity.

[0051] The technical solution of the present invention will be described in detail below through specific embodiments.

[0052] Example 1

[0053] This embodiment provides a method for preparing LCNF-MOF composite films, see reference. Figure 1 This is a schematic diagram illustrating the principle of preparing the LCNF-MOF composite film in this embodiment. Lotus root cellulose fibers are prepared using lotus root as raw material, and then the lotus root cellulose fibers are combined with Eu... 3+ After being mixed with H3BTC, a composite suspension is formed. The composite suspension is then allowed to stand and be cultured. Eu-based ligand compounds grow in situ on the surface of lotus root cellulose fibers. After drying, the LCNF-MOF composite film is obtained.

[0054] The specific steps include: Step 1: Purification of cellulose fiber from lotus root fibers.

[0055] Lotus root was cut into small pieces and soaked in 95% ethanol and 1% HCl at room temperature for 12 h, respectively. Then it was thoroughly washed with deionized water. The insoluble residue was then treated with 5% NaOH at 70 ℃ for 6 h. The mixture was diluted with water, centrifuged three times at 9000 rpm, and the precipitate was collected. Subsequently, the cellulose was bleached in 5% H2O2 for 12 h. The mixture was further washed and centrifuged (9000 rpm, three cycles) to disperse the bleached fiber in water, resulting in a lotus root fiber cellulose suspension with a mass fraction of 0.22 wt%.

[0056] Step 2: Preparation of LCNF-MOF composite membrane.

[0057] Eu(NO3)3 6H2O (10.704 mg) and H3BTC (16.38 mg) were dissolved in 2.4 mL of H2O and 6 mL of 99% ethanol, respectively, to form metal ion solution and ligand solution, respectively.

[0058] The cellulose suspension of lotus root slices was mixed with a metal ion solution and stirred for 2 h. Then, a ligand solution was added and the mixture was stirred for another 2 h to carry out the reaction. After the reaction was completed, the precipitate was washed with water and redispersed in water to obtain a 0.22 wt% composite suspension.

[0059] 10 mL of the composite suspension (0.22 wt%) was poured into a culture dish with a diameter of 35 mm and dried at 35 °C for 5-7 days to obtain the LCNF-MOF composite film.

[0060] See Figure 9 This is a fluorescence photograph of the lotus root fiber cellulose combined with Eu-MOF in Example 1 of the present invention. Under ultraviolet light irradiation, the LCNF-MOF composite film emits red fluorescence.

[0061] Examples 2-5

[0062] The only difference between Examples 2-5 and Example 1 is that Eu(NO3)3 is decreased in each case. The mass of 6H2O and H3BTC (Eu(NO3)3) The ratio of 6H2O and H3BTC remains unchanged, which is equivalent to reducing the content of Eu-MOF by 4 times, 6 times, 8 times and 16 times respectively, while maintaining the total solid content in the film at 0.22wt%. Then, composite films with different Eu-MOF contents are obtained by using the same method as in Example 1.

[0063] With a constant total solids content of 0.22 wt%, the Eu-MOF ratio decreased synchronously with the decrease in feed, and the fluorescence intensity decreased accordingly, resulting in a weakened quenching response to AA; conversely, the higher the Eu-MOF content, the more significant the detection sensitivity.

[0064] Meanwhile, as the Eu-MOF decreases, the proportion of cellulose in lotus root fibers gradually increases, resulting in a more uniform film formation and a smoother surface.

[0065] In other words, under the same solid content conditions, the higher the Eu-MOF loading in the film, the more significant the detection sensitivity. However, at this time, the cellulose content in the film decreases, and the quality of the resulting composite film decreases.

[0066] Based on the above analysis, the present invention further verified the effect of Eu-MOF loading in the thin film on ascorbic acid detection.

[0067] The present invention also used thermogravimetric analysis to analyze the loading of Eu-MOF in the films provided in Examples 1-5, and the results are shown in Table 1. 3+ With increasing addition, the loading of Eu-MOF in the film gradually increases.

[0068] Table 1. Eu-MOF loading in Examples 1-5

[0069] See Figure 12 To investigate the effect of the composite film prepared in Example 5 on the detection of different concentrations of ascorbic acid, after a 16-fold reduction, the composite film still responded to ascorbic acid, but the relationship between ascorbic acid concentration and light intensity was not positively correlated. This may be because Eu-MOF has fewer active sites. When the concentration of ascorbic acid to be measured is high, the active sites are insufficient to effectively bind with too much ascorbic acid, and the change in light intensity ratio will decrease sharply or even stop, and the linear relationship will break.

[0070] The detection results of the composite film in Example 4 using the above method are the same as those in Example 5, indicating that the detection sensitivity of ascorbic acid is related to the amount of Eu-MOF loaded in the composite film.

[0071] Furthermore, in Examples 1-3, when different concentrations of ascorbic acid were tested, the relationship between the ascorbic acid concentration and the light intensity value was positively correlated.

[0072] Clearly, in Eu-MOF composite films, qualitative detection can be performed when the Eu-MOF loading is below 50 wt%, while quantitative detection can be performed when the loading is above 50 wt%.

[0073] Ascorbic acid detection

[0074] The detection of ascorbic acid using LCNF-MOF composite films includes the following steps: 100 μL of the LCNF-MOF composite solution from Example 1 was added to an ELISA plate and dried at 35 °C for 2–3 days. Then, different concentrations of ascorbic acid AA (0–40 mM, see details) were added. Figure 2 Each sample was 20 μL in volume and dried at 35°C for 12 h. The composite film containing ascorbic acid was then placed in an ELISA reader, and the fluorescence spectra corresponding to different ascorbic acid concentrations were recorded. Each concentration was measured at least 3 times to reduce experimental error.

[0075] See each Figure 2 and Figure 3 The figures are the linear fitting curves of the LCNF-MOF composite film provided in Example 1 of the present invention for detecting low concentrations of ascorbic acid (0~2 mM) and the exponential fitting curves for high concentrations of ascorbic acid (0 mM-40 mM).

[0076] Under low concentrations of ascorbic acid (0–2 mM), the ratio of its light intensity to its concentration follows a linear relationship with the Stun-Volmo equation (I0 / I = 1 + K). SV [C], I0 and I represent the fluorescence intensity before and after the addition of AA solution, respectively, and K... SV It is the Stern-Volmer quenching constant ( ¹), [C] is the concentration of AA). For example... Figure 2 Under the linear conditions shown, the acquired fluorescence spectrum can more easily, quickly, and accurately read the concentration of ascorbic acid, demonstrating excellent detection performance.

[0077] like Figure 3 As shown, under high concentrations of ascorbic acid (0 mM-40 mM), the relationship between light intensity and concentration is not linear. The ratio of light intensity values ​​(y) to ascorbic acid concentration (x) forms an exponential relationship, as shown in the following formula: y = y0 + A exp(R0 x).

[0078] Different detection limits can be calculated using the formula LOD = 3σ / k, where σ is the standard deviation of the blank measurement and k is the slope of the calibration curve. Based on the formula, the theoretical detection limit for ascorbic acid in Example 5 can be calculated to be 4.63 μM.

[0079] Obviously, the technical solution of the present invention can be used to detect ascorbic acid, and the test samples include, but are not limited to, food and pharmaceuticals.

[0080] Feasibility of diagnosing dry eye syndrome

[0081] The feasibility of detecting ascorbic acid content in tears for the diagnosis of dry eye was analyzed, including an evaluation by detecting ascorbic acid content in tears. Specifically, 100 µL of the LCNF-MOF dispersion prepared in Example 1 was deposited into each well of an ELISA plate and dried at 35 °C for 1-2 days.

[0082] To better reflect real-world applications and further verify the feasibility of detecting ascorbic acid for diagnosing dry eye, this embodiment analyzes the effects of pH value and interfering substances in tears on the fluorescence of LCNF-MOF composite films.

[0083] First, this embodiment analyzed the effect of pH value (pH = 6-9) in tears on fluorescence, see reference. Figure 4 The fluorescence of the LCNF-MOF composite film is almost unaffected in the pH range of 6-9.

[0084] Secondly, interfering substances are added to the tear film, and then these substances are added separately to the composite film. The interfering substances include: Na... + Ions (170 mM), K + Ions (42 mM), Ca 2+ Ions (2 mM), Mg 2+ Ions (1.1 mM), pyruvate (0.2 mM), nitrite (115 μM), glucose (5 mM), glutamate (25.5 μM). Results are as follows: Figure 5 As shown, the aforementioned interfering substances have almost no effect on the fluorescence properties of the LCNF-MOF composite film, indicating that the LCNF-MOF composite film can have strong anti-interference ability and higher accuracy in the tear environment.

[0085] Third, this embodiment also evaluates the reversibility of the LCNF-MOF composite film by alternately exposing it to 1 mM AA (20 µL) and deionized water.

[0086] See Figure 6 The image shows the reusability test results of the LCNF-MOF composite film provided in Example 1. After five repeated alternating uses, the fluorescence performance of the LCNF-MOF composite film remained stable, indicating that it can be reused for the detection of ascorbic acid.

[0087] Furthermore, at the clinical level, the average concentration of amino acids (AA) in tears was 0.61 ± 0.59 mM, with 0.8 mM considered as the average level of AA in the tears of healthy individuals. The clinical concentration of AA fell within the linear detection range.

[0088] Based on the above analysis, this embodiment further verifies the following: Place 100 µL of LCNF-MOF dispersion in a petri dish and dry for 1 day to obtain a film with a diameter of about 1 cm. Prepare 20 µL of tears from healthy human subjects (0.8 mM ascorbic acid) and human subjects with dry eye syndrome (0.01 mM ascorbic acid) and add them to the film.

[0089] like Figure 7 The image shows a comparison of the LCNF-MOF composite film provided in Example 1 with simulated healthy human tears and tears from a DED patient. The results indicate that because the ascorbic acid concentration in the patient's tears is much lower than the average level in healthy human tears, the patient's tears have virtually no effect on the fluorescence of the film. In contrast, the ascorbic acid concentration in healthy human tears is higher and at the average level, thus having a greater impact on the film's fluorescence, resulting in fluorescence quenching. This allows for visual assessment of whether a person has dry eye syndrome.

[0090] Comparative Example 1

[0091] The only difference between this comparative example and Example 1 is that the lotus root cellulose is replaced with a commercially available cellulose nanocrystal aqueous dispersion of the same concentration (purchased from Zhejiang Yuewei New Material Technology Co., Ltd.), while the preparation method is the same.

[0092] Cellulose nanocrystals and Eu 3+ They can be grown in situ in a dispersion of cellulose nanocrystals and bonded together by chemical bonds to form a thin film, such as... Figure 8 The image shown is a fluorescence image of the comparative example of commercially available cellulose nanocrystals combined with Eu-MOF. Figure 9 Compared with the provided fluorescence images of lotus root fiber cellulose combined with Eu-MOF, the LCNF-MOF composite film emitted red fluorescence under ultraviolet light irradiation, while Comparative Example 1 did not emit fluorescence.

[0093] See Figure 10 The images shown are micrographs of commercial cellulose nanocrystals combined with Eu-MOF in this comparative example. Image a was taken under white light, and image b was taken under ultraviolet light. Under the optical microscope, it can be observed that although Eu can coordinate well with cellulose nanocrystals, most of them are crystals. This may be because the number and length of cellulose nanocrystals are insufficient to support the formation of a thin film.

[0094] See Figure 11 The images shown in Example 1 are micrographs of lotus root cellulose combined with Eu-MOF. Image a was taken under white light, and image b was taken under ultraviolet light. The lotus root cellulose used has a longer length and better film-forming properties, which enables it to encapsulate Eu-MOF. Therefore, the composite film of lotus root cellulose and Eu-MOF can achieve detection and film formation at the same mass fraction. Under the same conditions, commercial cellulose nanocrystals cannot achieve the same detection results for AA.

[0095] Furthermore, the fact that Eu-MOFs exist in the form of rigid powder hinders their practical application. Combining lotus root fiber cellulose with Eu-MOFs effectively solves this problem. Lotus root fiber cellulose can provide stable support for Eu-MOFs, such as... Figure 13 The image shown is a SEM image of the LCNF-MOF composite film provided in Embodiment 1 of the present invention. Eu-MOF is filled within the cellulose-formed network structure, preventing the Eu-MOF from easily detaching, thus giving Embodiment 1 its excellent flexibility. Figure 14 The LCNF-MOF composite film provided in Embodiment 1 of the present invention can achieve bending and folding behavior, which is an advantage that commercial cellulose nanocrystals cannot provide.

[0096] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims.

Claims

1. A method for preparing a cellulose-Eu-MOF composite material, comprising mixing a lotus root fiber cellulose fiber suspension with Eu... 3+ The salt solution and ligand solution are mixed to form a composite suspension. The composite suspension is then allowed to stand and be cultured. The Eu-based ligand compound is grown in situ in the lotus root fiber cellulose solution to obtain the cellulose-Eu-MOF composite material.

2. The preparation method according to claim 1, characterized in that, The ligand solution is an H3BTC ethanol solution; And / or, Eu 3+ The molar ratio of H3BTC to H3BTC is 0.01~0.03:0.06~0.09; And / or, in the cellulose-Eu-MOF composite material, the mass fraction of the lotus root fiber cellulose suspension is 0.1~0.5%.

3. The preparation method according to claim 1, characterized in that, The preparation method of lotus root cellulose fiber includes: cutting lotus root into small pieces, soaking them in 95% ethanol and 1% HCl in sequence, treating the insoluble matter with alkaline solution, centrifuging and collecting the precipitate; then, bleaching the cellulose in H2O2 by stirring, further washing and centrifuging, and dispersing it in water to obtain lotus root cellulose suspension.

4. A cellulose-Eu-MOF composite material, prepared by the preparation method according to any one of claims 1-3.

5. A cellulose-Eu-MOF composite film, comprising the cellulose-Eu-MOF composite material as described in claim 4, obtained by drying at 35 °C for 5-7 days.

6. The use of a cellulose-Eu-MOF composite material as described in claim 4 or a cellulose-Eu-MOF composite film as described in claim 5 in the fluorescence detection of ascorbic acid.

7. A fluorescence sensor for detecting ascorbic acid, comprising at least the cellulose-Eu-MOF composite material as described in claim 4, or the cellulose-Eu-MOF composite film as described in claim 5; In cellulose-Eu-MOF composite materials or cellulose-Eu-MOF composite films, when the loading of Eu-MOF is less than 50 wt%, it can be used for the qualitative detection of ascorbic acid; preferably, the loading of Eu-MOF is 42~45 wt%. When the loading of Eu-MOF is higher than 50 wt%, it can be used for the quantitative detection of ascorbic acid; preferably, the loading of Eu-MOF is 50~85 wt%.

8. A fluorescent detection method for ascorbic acid, characterized in that, This includes using the cellulose-Eu-MOF composite material as described in claim 7, specifically comprising the following steps: S1. Prepare an ascorbic acid standard solution, then add the standard solution to the cellulose-Eu-MOF composite material as described in claim 7 for reaction, dry to form a cellulose-Eu-MOF composite film, and then use an enzyme-linked immunosorbent assay (ELISA) reader for fluorescence detection to obtain a linear curve of the concentration of cellulose-Eu-MOF-AA. S2, the sample to be tested is added to the cellulose-Eu-MOF composite material, dried, and then subjected to fluorescence detection. Based on the linear concentration curve of cellulose-Eu-MOF-AA in S1, the content of ascorbic acid in the sample to be tested is quantitatively analyzed.

9. The fluorescence detection method for ascorbic acid according to claim 8, characterized in that, The detection limit for ascorbic acid is 4.63 μM; The sample to be tested includes any one of food or medicine.

10. The use of a cellulose-Eu-MOF composite material as described in claim 4, or a cellulose-Eu-MOF composite film as described in claim 5, in detecting the content of ascorbic acid in tears.

11. A diagnostic device for dry eye syndrome, comprising at least the cellulose-Eu-MOF composite material as described in claim 4, or the cellulose-Eu-MOF composite film as described in claim 5.

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