Preparation method of Eu-MOF-based ratio fluorescent sensor and application of portable detection of natamycin

Abstract

This invention belongs to the field of analytical detection technology and discloses a method for preparing an Eu-MOF-based ratio fluorescence sensor and its application in portable detection of natamycin. The preparation method includes the following steps: (1) 2,5-dihydroxyterephthalic acid, pyromellitic acid and ZrCl4 are dispersed in deionized water, then acetic acid is added, the mixture is heated for a period of time and then cooled to obtain a suspension; (2) The obtained suspension is transferred to another reaction vessel, deionized water is added, the reaction continues, the mixture is cooled after the reaction is completed, and the mixture is centrifuged with water, DMF and ethanol in sequence, and finally vacuum dried overnight to obtain a grayish-white solid UiO-66(OH)2 / (COOH)2; (3) EuCl3·6H2O is dispersed with the obtained UiO-66(OH)2 / (COOH)2 in deionized water, the mixture is heated to react, the mixture is cooled after the reaction is completed, the obtained product is centrifuged and washed with water and ethanol, and finally the precipitate is vacuum dried overnight to obtain a grayish-white solid Eu@UiO-66(OH)2 / (COOH)2. The obtained Eu@UiO-66(OH)2 / (COOH)2 exhibits advantages such as high sensitivity, high selectivity, and ratiometric fluorescence response to NAT.

Description

Technical Field

[0001] This invention relates to the field of analytical detection technology, specifically to a method for preparing an Eu-MOF-based ratio fluorescence sensor and its application in portable detection of natamycin. Background Technology

[0002] Natamycin (NAT), also known as natamycin, is a macrolide polyene antifungal drug derived from the fermentation of *Streptomyces natamycin*. It specifically inhibits the growth of molds and yeasts. As a microbial preservative, NAT has many advantages, including high efficacy, long-lasting antibacterial action, and a broad antibacterial spectrum. Therefore, countries such as the United States and China have approved its use as a food preservative. In the food industry, NAT is widely used as an additive in fruit juices, yogurt, cheese, ham, sausages, and beer. However, excessive NAT during production can cause environmental pollution and pose a threat to human health, leading to symptoms such as nausea, diarrhea, and loss of appetite, while also impairing the immune system. Furthermore, it may lead to an increase in antibiotic-resistant bacteria. Therefore, Chinese food standards and regulations stipulate that the amount of NAT added to cheese, pastries, sausages, and other foods must not exceed 0.3 g / kg; and the amount added to alcoholic beverages must not exceed 0.01 g / L.

[0003] Given the application value and safety risks of NAT in the food industry, it is necessary to establish a rapid, accurate, convenient, and economical on-site NAT detection method to protect food safety and the ecological environment. Traditional detection methods based on high-performance liquid chromatography (HPLC), such as HPLC-UV, LC-MS / MS, and HPLC-diode array detectors, suffer from drawbacks such as low sensitivity, complex pretreatment, long processing time, and complex operation. Although emerging technologies such as capillary electrophoresis, electrochemistry, and immunochromatography have been explored, their further application is limited due to high cost, complex pretreatment processes, and complex instrumentation. Therefore, there is an urgent need for an instrument-free on-site NAT detection method that is convenient, visual, rapid, portable, easy to operate, highly selective, and highly sensitive.

[0004] Currently, fluorescent sensors are receiving increasing attention, not only because of their visualization, high selectivity, and high sensitivity, but also because their synthesis process is very simple, sometimes requiring only a one-pot method to obtain large quantities of products. Metal-organic frameworks (MOFs) are porous crystalline materials renowned for their diverse structures and unique physical and chemical properties (including optical, electrical, and magnetic properties), and have proven to be promising fluorescent probes. They possess a wealth of properties, including significant structural stability, large specific surface area, tunable structural features, and fluorescent ligands. In recent years, some MOFs have been reported for the detection of certain metal ions, amino acids, and pesticides. However, MOF-based single-emission fluorescence detection often faces challenges such as environmental interference and difficulty in distinguishing intensity changes. Therefore, reports on fluorescent probes specifically for detecting NATs are very limited. Among various MOFs, lanthanide-functionalized metal-organic frameworks (Ln-MOFs) stand out due to their superior dual-emission detection capabilities of luminescence and fluorescence. By employing a dual-emission strategy, background interference can be effectively reduced through self-calibration, thereby achieving accurate ratiometric detection. Furthermore, compared to single-fluorescence techniques, dual-emission probes exhibit more pronounced fluorescence color changes, making them easier to distinguish, reducing visual fatigue, and resulting in better visual detection. Therefore, the development of dual-emission Ln-MOF fluorescent probes makes on-site NAT detection without the need for specialized equipment possible. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a method for preparing an Eu-MOF-based ratiometric fluorescence sensor and its application in portable detection of natamycin. This invention utilizes the red luminescent component Eu... 3+ Eu@UiO-66(OH)2 / (COOH)2, a UiO-66 type dual-emission MOF material, was designed and synthesized by adding the free carboxyl group of the blue fluorescent UiO-66(OH)2 / (COOH)2 via post-synthetic modification (PSM). When exposed to a NAT environment, the blue emission of the synthesized Eu@UiO-66(OH)2 / (COOH)2 was significantly enhanced, while the Eu@UiO-66(OH)2 / (COOH)2 showed a significantly enhanced blue emission. 3+ The emission of fluorescence drops sharply, causing the fluorescence color to change significantly from purplish-red to blue.

[0006] To achieve the objectives of this invention, the preparation method of the Eu-MOF-based ratiometric fluorescence sensor of this invention includes the following steps:

[0007] (1) Disperse 2,5-dihydroxyterephthalic acid, pyromellitic acid and ZrCl4 in deionized water, then add acetic acid, heat and react for a period of time, and then cool to obtain a suspension;

[0008] (2) Transfer the suspension obtained in step (1) to another reaction vessel, add deionized water, continue the reaction, cool after the reaction is completed, centrifuge with water, DMF and ethanol in sequence, and finally vacuum dry overnight to obtain grayish-white solid UiO-66(OH)2 / (COOH)2.

[0009] (3) Disperse EuCl3·6H2O and the UiO-66(OH)2 / (COOH)2 obtained in step (2) in deionized water, heat the reaction, cool after the reaction is completed, centrifuge the product and wash it with water and ethanol. Finally, vacuum dry the precipitate overnight to obtain grayish-white solid Eu@UiO-66(OH)2 / (COOH)2.

[0010] Furthermore, in some embodiments of the present invention, the molar ratio of 2,5-dihydroxyterephthalic acid and pyromellitic acid in step (1) is 0.8-1.2:3.8-9.2, for example 0.8-1.2:3.8-4.2, or 0.8-1.2:8.8-9.2.

[0011] Furthermore, in some embodiments of the present invention, the molar ratio of 2,5-dihydroxyterephthalic acid and ZrCl4 in step (1) is 0.8-1.2:4.5-5.5.

[0012] Furthermore, in some embodiments of the present invention, the molar volume ratio of 2,5-dihydroxyterephthalic acid, deionized water, and acetic acid in step (1) is 0.8-1.2 mmol: 45-55 mL: 4-6 mL.

[0013] Furthermore, in some embodiments of the present invention, the heating in step (1) is to 95-105°C.

[0014] Furthermore, in some embodiments of the present invention, the reaction time in step (1) is 20-28 hours.

[0015] Furthermore, in some embodiments of the present invention, the amount of deionized water used in step (2) is 1.5-2.5 times the amount of deionized water used in step (1).

[0016] Furthermore, in some embodiments of the present invention, the reaction time in step (2) is 10-15 hours.

[0017] Furthermore, in some embodiments of the present invention, step (2) involves centrifugation twice in sequence with water, DMF, and ethanol.

[0018] Furthermore, in some embodiments of the present invention, the mass ratio of UiO-66(OH)2 / (COOH)2 to EuCl3·6H2O in step (3) is 0.8-1.2:1.8-2.2.

[0019] Furthermore, in some embodiments of the present invention, the heating reaction in step (3) is a reaction at 75-85°C; preferably, the reaction time is 20-30 hours.

[0020] Furthermore, in some embodiments of the present invention, the centrifugation rate in steps (2) and (3) is 8000 r / min; preferably, the centrifugation time is 4-6 minutes each time.

[0021] Furthermore, in some embodiments of the present invention, the vacuum drying in steps (2) and (3) is carried out at 75-85°C.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] (1) This invention involves the addition of 2,5-dihydroxyterephthalic acid and Eu 3+ A dual-emission fluorescent probe, Eu@UiO-66(OH)2 / (COOH)2, was successfully designed and synthesized using two different luminescent components. Eu@UiO-66(OH)2 / (COOH)2 was used as a ratiometric fluorescence sensor for NAT, exhibiting a distinct color change from purplish-red to blue, good selectivity, strong anti-interference ability, low detection limit (0.15 μM, significantly lower than the national standard), and fast response speed (less than 1 minute).

[0024] (2) The Eu@UiO-66(OH)2 / (COOH)2 dual-luminescent MOF material synthesized in this invention exhibits advantages such as high sensitivity, high selectivity, and ratiometric fluorescence response to NAT. The Eu@UiO-66(OH)2 / (COOH)2 of this invention has been successfully used to detect NAT in complex real-world samples such as beer and wastewater, achieving satisfactory recoveries. Utilizing the RGB values ​​obtained from a smartphone, the fluorescence color response of Eu@UiO-66(OH)2 / (COOH)2 enables instrument-free quantitative detection of NAT in these real-world samples. Therefore, this probe shows great potential for portable, visualized, on-site quantitative detection of NAT in complex real-world samples. Attached Figure Description

[0025] Figure 1 The emission spectra of Eu@UiO-66(OH)2 / (COOH)2 under different DHTA / (PMA+DHTA) ratios are shown.

[0026] Figure 2The fluorescence curves of Eu@UiO-66(OH)2 / (COOH)2 in the presence of different concentrations of NAT are shown in the figures for DHTA / (PMA+DHTA) ratios of (a) 10%, (b) 20%, (c) 30%, (d) 40%, and (e) 50%. The inset shows fluorescence photographs of DMF solutions of Eu@UiO-66(OH)2 / (COOH)2 and NAT@Eu@UiO-66(OH)2 / (COOH)2 taken under a UV lamp (302 nm).

[0027] Figure 3 The CIE chromaticity coordinates of Eu@UiO-66(OH)2 / (COOH)2 and NAT@Eu@UiO-66(OH)2 / (COOH)2 at DHTA / (PMA+DHTA) ratios of (a) 10%, (b) 20%, (c) 30%, (d) 40%, and (e) 50%.

[0028] Figure 4 (a) P-XRD patterns of UiO-66 (simulated), UiO-66(OH)2 / (COOH)2 and Eu@UiO-66(OH)2 / (COOH)2; (b) FTIR of UiO-66(OH)2 / (COOH)2 and Eu@UiO-66(OH)2 / (COOH)2; (c) XPS spectra of UiO-66(OH)2 / (COOH)2 and Eu@UiO-66(OH)2 / (COOH)2; (d) O1s binding energies in UiO-66(OH)2 / (COOH)2 and Eu@UiO-66(OH)2 / (COOH)2.

[0029] Figure 5 The fluorescence spectra and photographs of Eu@UiO-66(OH)2 / (COOH)2 (a) in solid state and (b) in DMF obtained in Example 1 of this invention are shown.

[0030] Figure 6 The following are the fluorescence spectra of Eu@UiO-66(OH)2 / (COOH)2 obtained in Example 1 of this invention: (a) fluorescence spectrum in DMF for seven days; (b) fluorescence intensity in DMF for seven days; (c) photobleaching characteristics under ultraviolet light (310 nm).

[0031] Figure 7 The time-resolved fluorescence response of Eu@UiO-66(OH)2 / (COOH)2 to NAT (50 μM) obtained in Example 1 of this invention;

[0032] Figure 8(a) Emission spectra of Eu@UiO-66(OH)2 / (COOH)2 obtained in Example 1 of the present invention under different concentrations of NAT (0-120 μM); (b) I 439 / I 614 Linear relationship with NAT (0-100 μM) concentration (slit: 10 nm, 10 nm; Ex: 280 nm). Inset: Fluorescence photograph under 302 nm excitation; (c) CIE chromaticity coordinates of Eu@UiO-66(OH)2 / (COOH)2 obtained in Example 1 of the present invention in the presence of different concentrations of NAT;

[0033] Figure 9 This is a schematic diagram of a portable smartphone detecting NAT in this invention;

[0034] Figure 10 (a) The color changes of different concentrations of NAT and the Eu@UiO-66(OH)2 / (COOH)2 suspension obtained in Example 1 of this invention on a titration plate under a 302nm UV lamp; (b) The linear relationship between different concentrations of NAT and B / R.

[0035] Figure 11 (a) The operation procedure for performing colorimetric tests on actual samples using a smartphone; (b) Reading the RGB values ​​of NAT in beer and wastewater samples using a smartphone;

[0036] Figure 12 (a) The relative fluorescence intensity of Eu@UiO-66(OH)2 / (COOH)2 in response to NAT in the real sample; (b) The RGB values ​​of the response of Eu@UiO-66(OH)2 / (COOH)2 to NAT in the real sample, obtained by using a smartphone. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and not intended to limit the invention.

[0038] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0039] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0040] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0041] The singular form includes the plural objects of discussion unless the context clearly indicates otherwise. "Optional" or "any one" means that the matter or event described thereafter may or may not occur, and the description includes both the possibility that the event occurs and the possibility that the event does not occur.

[0042] Approximate terms used in the specification and claims to modify quantities indicate that the invention is not limited to that specific quantity, but also includes acceptable modifications close to that quantity that do not alter the relevant essential function. Correspondingly, the use of "about," "approximately," etc., to modify a numerical value means that the invention is not limited to that precise value. In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this application's specification and claims, scope definitions can be combined and / or interchanged, unless otherwise stated, these scopes include all subscopes contained therein.

[0043] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0044] Furthermore, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., described below refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms are not necessarily directed at the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0045] All chemicals used in this invention are of analytical grade. ZrCl4 (>98%) and EuCl3·6H2O (99.9%) were supplied by China Jiuding Chemical Reagent Co., Ltd. All other chemicals were purchased from Aladdin. Wastewater was taken from a biopharmaceutical industrial park in Wuhan, Hubei Province, and beer was purchased from a local supermarket in Wuhan.

[0046] Powder X-ray diffraction (P-XRD) was performed using CuKα radiation on a Bruker-D8 Advanced instrument. X-ray photoelectron spectroscopy (XPS) was obtained using a THS-103. Fourier transform infrared spectroscopy (FTIR) results were recorded using KBr particles on a Thermofisher Nicolet iS10, ranging from 4000 to 400 cm⁻¹. -1 Inductively coupled plasma mass spectrometry (ICP-MS) was performed using an Agilent 7700ce mass spectrometer (Agilent Technologies). Fluorescence spectra were recorded using a xenon lamp on a Hitachi F-7000 fluorescence spectrometer. Fluorescence lifetime decay was measured on an Edinburgh FLS980 spectrophotometer. Ultraviolet-visible absorption spectroscopy (UV-vis) data were collected using a deuterium lamp on an INESA N4S spectrophotometer.

[0047] Example 1

[0048] First, 2,5-dihydroxyterephthalic acid (DHTA, 198.13 mg, 1 mmol), pyromellitic acid (PMA, 1016.6 mg, 4 mmol), and ZrCl4 (1165.2 mg, 5 mmol) were dispersed in 50 mL of deionized water, followed by the addition of 5 mL of acetic acid. The reaction was carried out at 100 °C for 24 hours. After cooling, the suspension was transferred to a 250 mL round-bottom flask, and another 100 mL of deionized water was added. The reaction was continued for 12 hours. After cooling, the mixture was centrifuged twice each at 8000 rpm with water, DMF, and ethanol for 5 min each time. Finally, the mixture was vacuum dried overnight at 80 °C to obtain a grayish-white solid UiO-66(OH)2 / (COOH)2. Furthermore, by varying the molar ratio of the ligands (DHTA / PMA = 1:9, 3:7, 2:3, 1:1), four other analogues were synthesized using the same method.

[0049] One portion of the synthesized UiO-66(OH)2 / (COOH)2 (500 mg) and EuCl3·6H2O (1000 mg) were dispersed in 40 mL of deionized water and reacted at 80 °C for 24 hours. After cooling, the solid product was centrifuged at 8000 r / min for 5 minutes and washed with water and ethanol. Finally, the resulting precipitate was vacuum dried overnight at 80 °C to obtain a grayish-white solid Eu@UiO-66(OH)2 / (COOH)2. Following the above method, the same method was used with Eu... 3+ Four other synthesized UiO-66(OH)2 / (COOH)2 analogs (with different molar ratios of DHTA / PMA) were functionalized.

[0050] Unless otherwise specified, "Eu@UiO-66(OH)2 / (COOH)2 obtained in Example 1 of this invention" in the experiments of this invention refers to Eu@UiO-66(OH)2 / (COOH)2 prepared by DHTA / PMA molar ratio of 1:4.

[0051] Example 2

[0052] Luminescence sensing experiment: The suspension obtained by dispersing Eu@UiO-66(OH)2 / (COOH)2 in DMF was used to detect the analyte. Typically, 30 mg of Eu@UiO-66(OH)2 / (COOH)2 powder was dispersed in 40 mL of DMF and sonicated for 20 minutes. Then, 2 mL of the Eu@UiO-66(OH)2 / (COOH)2 suspension was taken, and 20 μL of the analyte (10 mM) was added. The fluorescence spectrum was then measured. The excitation wavelength was set to 280 nm, and the slit width was 10 nm / 10 nm.

[0053] Sensing performance of Eu@UiO-66(OH)2 / (COOH)2

[0054] NAT has been widely used as a preservative. However, excessive use of NAT can harm health, and the indiscriminate discharge of NAT-treated pharmaceutical wastewater can negatively impact the ecological environment. This invention investigates the effect of Eu@UiO-66(OH)2 / (COOH)2 on the detection of NAT and further applies it to the detection of wastewater samples from beer and pharmaceutical industrial parks. Furthermore, the effects of interfering substances on Eu@UiO-66(OH)2 / (COOH)2 were investigated, as other components present in beer and wastewater may affect the luminescence properties of Eu@UiO-66(OH)2 / (COOH)2. These include several common amino acids (phenylalanine (L-Phe), glycine (Gly), glutamic acid (L-Glu), methionine (L-Met), arginine (L-Arg), tyrosine (L-Tyr), leucine (L-Leu), proline (L-Pro), serine (L-Ser), threonine (L-Thr), isoleucine (L-Ile), histidine (L-His)), glutathione (GSH), and metal ions (Ca). 2+ K + Mg 2+ Na + Zn 2+ Vitamins (vitamin B5 (VB5), vitamin H (VH)) and antibacterial drugs (ampramin (Apra), butoconazole nitrate (BN), florfenicol (FF), erythromycin (ERY), thiamphenicol (TAP), kanamycin sulfate (KS), neomycin sulfate (NS), clindamycin phosphate (CP), cephalexin (CPX), tobramycin (TOB), butenafine hydrochloride (BTH), ractopamine hydrochloride (RAC)).

[0055] 20 μL of the above analyte at a concentration of 10 mM was transferred into 2 mL of probe suspension. The fluorescence spectra of these mixtures were then measured. The results showed that among all tested reagents, only NAT caused a significant change in the ratio fluorescence of the Eu@UiO-66(OH)2 / (COOH)2 suspension; the other reagents did not cause significant changes in the fluorescence intensity of the probe suspension. This indicates that the probe has good selectivity for NAT, and further research revealed that the probe of this invention has good anti-interference performance.

[0056] like Figure 1As shown, the fluorescence and detection performance of Eu@UiO-66(OH)2 / (COOH)2 can be adjusted by regulating the ratio of DHTA / (PMA+DHTA). When the ratio is 20%, Eu@UiO-66(OH)2 / (COOH)2 achieves dual emission at 439 nm and 614 nm under 280 nm excitation. The NAT response performance of Eu@UiO-66(OH)2 / (COOH)2 prepared with different ratios of DHTA / PMA was tested.

[0057] The results are as follows Figure 2 As shown, when the DHTA / (PMA+DHTA) ratio is 30%, 40%, and 50%, the fluorescence of Eu@UiO-66(OH)2 / (COOH)2 is relatively weak, and the color change is not obvious after adding NAT. When the DHTA / PMA ratio is adjusted to 10% and 20%, Eu@UiO-66(OH)2 / (COOH)2 achieves a color change from purplish-red to blue. When the ratio is 20%, adding 1 μM NAT will cause I... 439 / I 614 The value increased by 2.6%, while when the proportion was 10%, I 439 / I 614 The value increased by 2.1%. Furthermore, the color changes of Eu@UiO-66(OH)2 / (COOH)2 synthesized with different ligand ratios before and after the addition of NAT were also verified by the CIE chromaticity diagram. Figure 3 The results show that when NAT detection is performed at a ratio of 20%, the color changes significantly and the detection limit decreases.

[0058] The crystal structures of the synthesized UiO-66(OH)2 / (COOH)2 and Eu@UiO-66(OH)2 / (COOH)2 were characterized by powder X-ray diffraction (P-XRD). Figure 4 (a) shows that the P-XRD pattern of the material prepared in this experiment is basically consistent with the simulated pattern of the UiO-66 single crystal structure, indicating that the synthesis of MOFs was successful. The Fourier transform infrared (FTIR) spectra of the synthesized MOFs are shown below. Figure 4 (b). At 1583 and 1390 cm -1 There are two characteristic absorptions at this point, namely the asymmetric and symmetric stretching vibration peaks of the carboxylate. UiO-66(OH)2 / (COOH)2 shows a peak at 1704 cm⁻¹. -1 The characteristic absorption peak of the free carboxyl group was observed at 1704 cm⁻¹. However, Eu@UiO-66(OH)₂ / (COOH)₂ showed a peak at 1704 cm⁻¹. -1 The peak at that point becomes relatively weak, indicating that the free carboxyl group interacts with Eu. 3+Successful coordination. X-ray photoelectron spectroscopy (XPS) further confirmed Eu. 3+ The binding with free carboxyl groups. For example... Figure 4 As shown in (c), Eu in Eu@UiO-66(OH)2 / (COOH)2 can be clearly observed. 3+ The binding energy is 1135.38 eV, which proves that Eu in Eu@UiO-66(OH)2 / (COOH)2 3+ The existence of. Furthermore, from Figure 4 (d) It can be seen that the binding energy of O 1s changes from 531.83 eV to 531.58 eV, indicating that Eu@UiO-66(OH)2 / (COOH)2 contains Eu 3+ It was successfully coordinated to the free carboxyl group. To understand the effect of Eu doping... 3+ The quantity of Zr was also tested using inductively coupled plasma mass spectrometry (ICP-MS) to calculate the Zr content. 4+ With Eu 3+ The molar ratio is 1.315:1.

[0059] In both solid-state and DMF, the emission spectra of Eu@UiO-66(OH)2 / (COOH)2 show Eu 3+ The narrow-band emission characteristic of ions confirms Eu 3+ Successful encapsulation of ions within the framework. For example... Figure 5 As shown in (a), Eu was observed at wavelengths of 590, 614, 653, and 700 nm. 3+ The unique launch bands correspond to 5 D0→ 7 F J (J = 1, 2, 3 and 4) transitions. Figure 5 (b) shows the fluorescence spectrum of Eu@UiO-66(OH)2 / (COOH)2 in DMF. Besides Eu 3+ In addition to the main emission at 614 nm, Eu@UiO-66(OH)2 / (COOH)2 exhibits a broad emission peak near 439 nm, which is the characteristic fluorescence of the ligand 2,5-dihydroxyterephthalic acid, although its intensity is low. Therefore, the DMF suspension of Eu@UiO-66(OH)2 / (COOH)2 exhibits red fluorescence under ultraviolet light (302 nm). Furthermore, the fluorescence stability of Eu@UiO-66(OH)2 / (COOH)2 in DMF at room temperature was investigated.

[0060] like Figure 6As shown in (a) and (b), after 7 days of storage in DMF, the two emission peaks at 439 nm and 614 nm did not change significantly, indicating that Eu@UiO-66(OH)2 / (COOH)2 is quite stable in DMF at room temperature. Furthermore, the photobleaching properties of Eu@UiO-66(OH)2 / (COOH)2 were also tested. The results are as follows... Figure 6 As shown in (c), the peak intensity at 439 nm wavelength remained stable over 6 hours, while the peak intensity at 614 nm wavelength decreased slowly from 0 to 3 hours and remained stable after 3 hours. These results demonstrate that Eu@UiO-66(OH)2 / (COOH)2 has great potential as a fluorescence sensor.

[0061] For a high-performance sensor, fast response is also a key criterion. Therefore, this invention investigates the response time of Eu@UiO-66(OH)2 / (COOH)2 to NAT. Figure 7 As shown, the intensity ratio of the emission peaks at 439 nm and 614 nm increased significantly within 1 minute. The results indicate that Eu@UiO-66(OH)2 / (COOH)2 can serve as a rapid and convenient probe for detecting NAT.

[0062] like Figure 8 As shown in (a), with increasing NAT concentration, the fluorescence intensity of Eu@UiO-66(OH)2 / (COOH)2 at 439 nm gradually increases, while the fluorescence intensity at 614 nm gradually decreases. The color change from magenta to blue has been verified by CIE colorimetry. Figure 8 (c)). For example Figure 8 As shown in (b), within the concentration range of 0-100 μM, the intensity ratio of the emission peaks at 439 nm and 614 nm exhibits a good linear relationship with the NAT concentration, with a linear correlation coefficient of 0.9972. The limit of detection (LOD) is calculated according to the Stern-Volmer equation as follows:

[0063] I0 / I = 1 + Ksv[NAT]

[0064] I0 represents the peak fluorescence intensity of Eu@UiO-66(OH)2 / (COOH)2, I represents the fluorescence intensity after adding NAT, and the Ksv value is 0.0182. The calculated detection limit is 0.15 μM (≈0.10 mg / kg), which is far below the maximum allowable amount of NAT in beer (0.01 g / L) and cheese (0.3 g / kg) specified in Chinese standards. Therefore, this probe has great potential for the quantitative detection of NAT in real samples.

[0065] Mobile phone testing

[0066] Using fluorescence instruments to detect NAT has several drawbacks, such as large size and high cost, limiting real-time on-site monitoring. To address this issue, this invention employs a portable smartphone to perform detection by analyzing the B / R value of the fluorescence image. This process involves downloading and installing a free RGB color value application on the smartphone.

[0067] Then, suspensions of Eu@UiO-66(OH)2 / (COOH)2 containing different concentrations of analytes were added dropwise to a titration plate. Photos were taken using a smartphone camera under a 302nm UV lamp, without background correction. The RGB values ​​of the photographs were then recorded. Figure 9 ).like Figure 10 (a) and Figure 10 As shown in (b), the color of the Eu@UiO-66(OH)2 / (COOH)2 suspension changed from purplish-red to blue with increasing NAT concentration. The B / R value is related to the NAT concentration (0-70 μM, R...). 2 =0.9922) showed a strong linear correlation, with an LOD of 3.33 μM (≈2.22 mg / kg), which was far below the standard value.

[0068] Example 3

[0069] Actual sample analysis:

[0070] The beer was purchased from a supermarket in Wuhan, Hubei Province. First, carbon dioxide was removed from the beer using an ultrasonic method. A mixture of 20 mL beer and 60 mL methanol was centrifuged at 8000 rpm for 10 minutes, then filtered through a 0.22 μm filter membrane to remove insoluble matter. The resulting liquid was evaporated to dryness, dissolved in 20 mL of DMF, and filtered again through a 0.22 μm filter membrane to obtain the beer test sample. A NAT beer solution (10 mM) was prepared using the beer test sample. Different volumes of the NAT beer solution were then added to 2 mL of a 0.75 mg / mL Eu@UiO-66(OH)2 / (COOH)2 suspension (prepared in Example 1 of this invention), resulting in NAT concentrations of 5, 14, 16, and 35 μM. Finally, the fluorescence data of the mixture at 439 nm and 614 nm were recorded and analyzed.

[0071] Wastewater was collected from a biopharmaceutical industrial park in Wuhan, Hubei Province. First, 40 mL of wastewater was filtered through a 0.45 μm membrane to remove insoluble impurities. Second, the filtrate was purified with octadecylsilane (ODS) and ethylenediamine-N-propylsilane (PSA), then centrifuged at 8000 rpm for 10 minutes, and the supernatant was collected. Third, after evaporation and drying under vacuum, the residue was dissolved in 40 mL of DMF and filtered through a 0.22 μm membrane to obtain the wastewater test sample. Then, a 10 mM NAT solution was prepared using the wastewater test sample. Different volumes of NAT solution were added to 2 mL of 0.75 mg / mL Eu@UiO-66(OH)2 / (COOH)2 (prepared in Example 1 of this invention) suspension to achieve NAT concentrations of 5, 14, 16, and 35 μM. Finally, the fluorescence data of the mixtures at 439 nm and 614 nm were recorded and analyzed.

[0072] Table 1. Quantification of NAT in beer and wastewater samples.

[0073]

[0074]

[0075] As shown in Table 1 and Figure 12 As shown in (a), the recoveries in beer ranged from 91.4% to 104.7%, with an RSD of less than 3.65% (n=3); the recoveries in wastewater ranged from 90.4% to 107.4%, with an RSD of less than 2.93% (n=3). These results indicate that the probe Eu@UiO-66(OH)2 / (COOH)2 can quantify NAT in real samples.

[0076] Table 2. Quantification of NAT in beer and wastewater samples using smartphone-assisted RGB values.

[0077]

[0078]

[0079] On-site testing provides a deep understanding of the actual situation, ensuring accuracy and convenience. The entire process is quick and convenient, involving visual observation and recording of color changes during on-site testing. Given the superior performance of Eu@UiO-66(OH)2 / (COOH)2 in NAT detection, this invention also evaluates the precision and accuracy of smartphone-assisted RGB values. Figure 11 As shown in Table 2 and Figure 12As shown in (b), the recovery rates for beer ranged from 92.7% to 108.4%, with RSD values ​​below 3.87% (n=3); the recovery rates for wastewater ranged from 91.3% to 105.8%, with RSD values ​​below 4.43% (n=3). These results demonstrate that NAT can be quantitatively detected using smartphone-assisted RGB values. This work provides a portable method for the on-site, instrument-free detection of NAT in real samples.

[0080] In summary, this invention achieves its goal by adding 2,5-dihydroxyterephthalic acid and Eu. 3+ A dual-emission fluorescent probe, Eu@UiO-66(OH)2 / (COOH)2, was successfully synthesized by rationally designing two different luminescent components. Eu@UiO-66(OH)2 / (COOH)2 was used as a ratiometric fluorescence sensor for NAT, exhibiting a distinct color change from purplish-red to blue, good selectivity, strong anti-interference ability, low detection limit (0.15 μM, significantly lower than the national standard), and fast response speed (less than 1 minute). Furthermore, Eu@UiO-66(OH)2 / (COOH)2 has been successfully used to detect NAT in complex real-world samples such as beer and wastewater, achieving satisfactory recoveries. Using RGB values ​​obtained from a smartphone, the fluorescence color response of Eu@UiO-66(OH)2 / (COOH)2 enables instrument-free quantitative detection of NAT in these real-world samples. Therefore, this probe shows great potential for portable, visualized, on-site quantitative detection of NAT in complex real-world samples.

[0081] Those skilled in the art will readily understand that the above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An application of an Eu-MOF-based ratiometric fluorescence sensor, characterized in that, The application involves using the Eu-MOF-based ratiometric fluorescence sensor to detect natamycin. The preparation method of the Eu-MOF-based ratiometric fluorescence sensor includes the following steps: (1) 2,5-dihydroxyterephthalic acid, pyromellitic acid and ZrCl4 were dispersed in deionized water, and then acetic acid was added. After heating and reacting for a period of time, the mixture was cooled to obtain a suspension. (2) Transfer the suspension obtained in step (1) to another reaction vessel, add deionized water, continue the reaction, cool after the reaction is completed, centrifuge with water, DMF and ethanol in sequence, and finally vacuum dry overnight to obtain grayish-white solid UiO-66(OH)2 / (COOH)2. (3) Disperse EuCl3·6H2O and the UiO-66(OH)2 / (COOH)2 obtained in step (2) in deionized water, heat the reaction, cool after the reaction is completed, centrifuge the product and wash it with water and ethanol. Finally, vacuum dry the precipitate overnight to obtain the grayish-white solid Eu@UiO-66(OH)2 / (COOH)2, which is the Eu-MOF-based ratio fluorescence sensor.

2. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, In step (1), the molar ratio of 2,5-dihydroxyterephthalic acid to pyromellitic acid is 0.8-1.2:3.8-9.

2.

3. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, In step (1), the molar ratio of 2,5-dihydroxyterephthalic acid to pyromellitic acid is 0.8-1.2:3.8-4.

2.

4. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, In step (1), the molar ratio of 2,5-dihydroxyterephthalic acid to pyromellitic acid is 0.8-1.2:8.8-9.

2.

5. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, In step (1), the molar ratio of 2,5-dihydroxyterephthalic acid to ZrCl4 is 0.8-1.2:4.5-5.

5.

6. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, In step (1), the molar volume ratio of 2,5-dihydroxyterephthalic acid, deionized water, and acetic acid is 0.8-1.2 mmol: 45-55 mL: 4-6 mL.

7. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, In step (1), the heating is performed at 95-105℃.

8. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, The reaction time in step (1) is 20-28 hours.

9. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, The amount of deionized water used in step (2) is 1.5-2.5 times that used in step (1).

10. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, The reaction time in step (2) is 10-15 hours.

11. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, In step (2), centrifugation is performed twice in sequence using water, DMF, and ethanol.

12. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, In step (3), the mass ratio of UiO-66(OH)2 / (COOH)2 to EuCl3·6H2O is 0.8-1.2:1.8-2.

2.

13. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, The heating reaction in step (3) is a reaction that is heated to 75-85℃.

14. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, The reaction time for the heating reaction in step (3) is 20-30 hours.

15. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, The centrifugation rate in steps (2) and (3) is 8000 r / min.

16. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, The centrifugation time in steps (2) and (3) is 4-6 minutes each time.

17. The application of the Eu-MOF-based ratiometric fluorescence sensor according to claim 1, characterized in that, The vacuum drying in steps (2) and (3) is carried out at 75-85 °C.

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