Preparation method of Eu-MOF based ratiometric fluorescence sensor and application of Eu-MOF based ratiometric fluorescence sensor in portable detection of natamycin

Abstract

The invention belongs to the technical field of analysis and detection, and discloses a preparation method of an Eu-MOF based ratiometric fluorescence sensor and application of the Eu-MOF based ratiometric fluorescence sensor in portable detection of natamycin. The preparation method comprises the following steps: (1) dispersing 2, 5-dihydroxyterephthalic acid, pyromellitic acid and ZrCl4 in deionized water, then adding acetic acid, heating to react for a period of time, and then cooling to obtain a suspension; (2) transferring the obtained suspension into another reaction container, adding deionized water, continuously reacting, cooling after the reaction is completed, sequentially centrifuging with water, DMF (Dimethyl Formamide) and ethanol, and finally performing vacuum drying overnight to obtain an off-white solid UiO-66 (OH) 2 / (COOH) 2; and (3) dispersing EuCl3. 6H2O and the obtained UiO-66 (OH) 2 / (COOH) 2 in deionized water, carrying out heating reaction, cooling after the reaction is completed, centrifuging the obtained product, washing with water and ethanol, and finally, carrying out vacuum drying on the generated precipitate overnight to obtain an off-white solid Eu-coated UiO-66 (OH) 2 / (COOH) 2. The obtained Eu (at) UiO-66 (OH) 2 / (COOH) 2 has the advantages of high sensitivity, high selectivity, ratio fluorescence response and the like on NAT.

Description

Technical Field

[0001] The invention relates to the technical field of analysis and detection, and in particular to a preparation method of a Eu-MOF-based ratio fluorescence sensor and an application of a portable detection system for natamycin. Background Art

[0002] Natamycin (NAT), also known as natamycin, is a macrolide polyene antifungal drug fermented from Streptomyces natamycin, which can specifically inhibit the growth of molds and yeasts. As a microbial preservative, NAT has many advantages such as high efficiency, long-lasting antibacterial effect, and a wide antibacterial spectrum. Therefore, countries such as the United States and China have successively approved the use of NAT as a food preservative. In the food industry, NAT is widely used as an additive in juice, yogurt, cheese, ham, sausage, and beer. However, due to the excessive use of NAT in the production process, it will cause environmental pollution and pose a threat to human health, leading to symptoms such as nausea, diarrhea, and anorexia, and will also damage the immune system function. In addition, it may also lead to the increase of antibiotic-resistant bacteria. Therefore, Chinese food standards and regulations stipulate that the amount of NAT added to foods such as cheese, pastries, and sausages shall not exceed 0.3g / kg; the amount of NAT added to alcoholic beverages shall not exceed 0.01g / L.

[0003] In view of 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 detection method for NAT to protect food safety and the ecological environment. Traditional detection methods based on high performance liquid chromatography (HPLC) technology, such as HPLC-UV, LC-MS / MS and HPLC-diode array detector, have the disadvantages of low sensitivity, complex pretreatment, long time consumption and complicated operation. Although emerging technologies such as capillary electrophoresis, electrochemistry and immunochromatography have been explored, the further application of these methods is also limited due to their high cost, complex pretreatment process and complex instruments. Therefore, there is an urgent need for a method for on-site detection of NAT without instruments, which is convenient, visual, rapid, portable, easy to operate, highly selective and highly sensitive.

[0004] Fluorescent sensors are gaining increasing attention not only because of their visualization, high selectivity, and high sensitivity, but also because their synthesis is very simple, and sometimes a large amount of products can be obtained by a one-pot method. Metal-organic frameworks (MOFs), a type of porous crystalline material known for its diverse structures and special physical and chemical properties (including optical, electrical, and magnetic properties), have been shown to be a promising fluorescent probe. They have remarkable structural stability, large specific surface area, tunable structural features, and rich fluorescent ligands. In recent years, some MOFs have been reported for the detection of certain metal ions, amino acids, and pesticides. However, single-emission fluorescence detection based on MOFs often faces challenges such as environmental interference and difficulty in distinguishing intensity changes. Therefore, there are very limited reports on fluorescent probes specifically used for the detection of NAT. Among various MOFs, lanthanide-functionalized metal-organic frameworks (Ln-MOFs) stand out due to their excellent dual-emission detection capabilities of luminescence and fluorescence. By adopting a dual-emission strategy, background interference can be effectively reduced through self-calibration, thereby achieving accurate ratiometric detection. In addition, compared with the single fluorescence technology, the fluorescence color change of the dual-emission probe is obvious, which is easy to distinguish, reduces visual fatigue, and has a better visual detection effect. Therefore, the development of the dual-emission Ln-MOF fluorescent probe makes it possible to detect NAT on-site without equipment. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and provide a method for preparing a Eu-MOF-based ratio fluorescence sensor and its application in portable detection of natamycin. 3+ By adding the free carboxyl group of blue fluorescent UiO-66(OH)2 / (COOH)2, a UiO-66 type dual luminescent MOFs material Eu@UiO-66(OH)2 / (COOH)2 was designed and synthesized by post-synthesis modification (PSM) method. When exposed to NAT environment, the blue emission of Eu@UiO-66(OH)2 / (COOH)2 synthesized by the present invention was significantly enhanced, while Eu 3+ The emission of α-H2O decreases sharply, resulting in a clear shift in fluorescence color from purple-red to blue.

[0006] To achieve the purpose of the present invention, the preparation method of the Eu-MOF-based ratio fluorescence sensor of the present invention comprises the following steps:

[0007] (1) 2,5-dihydroxyterephthalic acid, pyromellitic acid and ZrCl4 are dispersed in deionized water, and then acetic acid is added, heated for a period of time and then cooled to obtain a suspension;

[0008] (2) The suspension obtained in step (1) was transferred into another reaction vessel, and deionized water was added to continue the reaction. After the reaction was completed, the suspension was cooled, centrifuged with water, DMF, and ethanol in sequence, and finally vacuum dried overnight to obtain an off-white solid UiO-66(OH)2 / (COOH)2;

[0009] (3) Dispersing EuCl3·6H2O and the UiO-66(OH)2 / (COOH)2 obtained in step (2) in deionized water, heating for reaction, cooling after the reaction is completed, centrifuging the obtained product, washing with water and ethanol, and finally, vacuum drying the generated precipitate overnight to obtain an off-white solid Eu@UiO-66(OH)2 / (COOH)2.

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

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

[0012] Furthermore, in some embodiments of the present invention, 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.

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

[0014] Furthermore, in some embodiments of the present invention, the reaction period 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, in step (2), the mixture is centrifuged twice with water, DMF and ethanol in sequence.

[0018] Furthermore, in some embodiments of the present invention, 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.

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

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

[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) The present invention adds 2,5-dihydroxyterephthalic acid and Eu 3+ With two different luminescent components, a dual-emission fluorescent probe Eu@UiO-66(OH)2 / (COOH)2 was rationally designed and successfully synthesized. Eu@UiO-66(OH)2 / (COOH)2 was used as a ratiometric fluorescent sensor for NAT, with a distinct purple-red to blue color change, good selectivity, strong anti-interference, low detection limit (0.15μM, significantly lower than the national standard), and fast response speed (less than 1 minute).

[0024] (2) The Eu@UiO-66(OH)2 / (COOH)2 synthesized by the present invention, a UiO-66-type dual-luminescent MOFs material, has the advantages of high sensitivity, high selectivity and ratio fluorescence response to NAT. The Eu@UiO-66(OH)2 / (COOH)2 of the present invention has been successfully used to detect NAT in complex real samples such as beer and wastewater, and a satisfactory recovery rate has been achieved. Using the RGB values ​​obtained by a smartphone, the fluorescence color response of Eu@UiO-66(OH)2 / (COOH)2 can realize instrument-free quantitative detection of NAT in these real samples. Therefore, the probe shows great potential in portable, visual on-site quantitative detection of NAT in complex real samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the emission spectra of Eu@UiO-66(OH)2 / (COOH)2 at different DHTA / (PMA+DHTA) ratios;

[0026] Figure 2The fluorescence curves of Eu@UiO-66(OH)2 / (COOH)2 in the presence of different concentrations of NAT when the ratio of DHTA / (PMA+DHTA) is (a) 10%, (b) 20%, (c) 30%, (d) 40%, (e) 50%. The inset is the fluorescence photos of DMF solutions of Eu@UiO-66(OH)2 / (COOH)2 and NAT@Eu@UiO-66(OH)2 / (COOH)2 taken under UV light (302nm);

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

[0028] Figure 4 (a) P-XRD patterns of UiO-66 (simulation), 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) Binding energy of O1s in UiO-66(OH)2 / (COOH)2 and Eu@UiO-66(OH)2 / (COOH)2;

[0029] Figure 5 The fluorescence spectra and photos of Eu@UiO-66(OH)2 / (COOH)2 (a) in solid state and (b) in DMF obtained in Example 1 of the present invention;

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

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

[0032] Figure 8(a) The emission spectra of Eu@UiO-66(OH)2 / (COOH)2 obtained in Example 1 of the present invention at 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 photo 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] Fig. 9 It is a schematic diagram of the portable smart phone detecting NAT in the present invention;

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

[0035] Fig.11 (a) The operation process of smartphone color reading test on actual samples; (b) Reading RGB values ​​of NAT in beer and wastewater samples by smartphone;

[0036] Fig.12 (a) Relative fluorescence intensity of Eu@UiO-66(OH)2 / (COOH)2 in response to NAT in real samples; (b) RGB values ​​of Eu@UiO-66(OH)2 / (COOH)2 in response to NAT in real samples by using a smartphone. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be understood through the practice of the present invention. It should be understood that the following description is only used to explain the present invention and is not intended to limit the present invention.

[0038] As used herein, the terms "comprises," "including," "having," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0039] The conjunction "consisting of excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed-ended so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0040] When amount, concentration or other value or parameter is expressed as range, preferred range or a series of upper preferred value and lower preferred value limit range, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0041] Singular forms include plural references unless the context clearly indicates otherwise. "Optional" or "either" means that the subsequently described event or incident may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0042] Approximate terms in the specification and claims are used to modify quantities, indicating that the present invention is not limited to the specific quantity, but also includes acceptable and modified parts close to the quantity without causing changes in the relevant basic functions. Accordingly, the use of "about", "approximately", etc. to modify a numerical value means that the present invention is not limited to the exact numerical value. In some examples, the approximate terms may correspond to the accuracy of the instrument for measuring the numerical value. In the specification and claims of this application, range limitations can be combined and / or interchanged, and if not otherwise stated, these ranges include all subranges contained therein.

[0043] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0044] In addition, the descriptions of the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" described below mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to 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 the present invention were of analytical grade. ZrCl4 (>98%) and EuCl3·6H2O (99.9%) were provided 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 on a Bruker-D8 Advanced instrument using CuKα radiation. X-ray photoelectron spectroscopy (XPS) was obtained by THS-103. Fourier transform infrared spectroscopy (FTIR) results were recorded by Thermofisher Nicolet iS10 using KBr particles in the range of 4000–400 cm -1 Inductively coupled plasma mass spectra (ICP-MS) were recorded by an Agilent 7700ce mass spectrometer (Agilent Technologies). Fluorescence spectra were recorded on a Hitachi F-7000 fluorescence spectrometer using a xenon lamp. Fluorescence lifetime decay was measured on an Edinburgh FLS980 spectrophotometer. Ultraviolet-visible absorption spectra (UV-vis) data were collected on an INESA N4S spectrophotometer using a deuterium lamp.

[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, and then 5 mL of acetic acid was added and reacted at 100 ° C for 24 hours. After cooling, the above suspension was transferred to a 250 mL round-bottom flask, and 100 mL of deionized water was added, and the reaction continued for 12 hours. After cooling, centrifuged twice with water, DMF, and ethanol at 8000 r / min, each for 5 minutes. Finally, vacuum dried at 80 ° C overnight to obtain an off-white solid UiO-66 (OH) 2 / (COOH) 2. In addition, the molar ratio of the ligand (DHTA / PMA = 1:9, 3:7, 2:3, 1:1) was changed, and four other analogs were synthesized according to the above method.

[0049] A 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 at 80°C overnight to obtain an off-white solid Eu@UiO-66(OH)2 / (COOH)2. 3+ Four other similarly synthesized UiO-66(OH)2 / (COOH)2 analogs (with different molar ratios of DHTA / PMA) were functionalized.

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

[0051] Example 2

[0052] Luminescent sensing experiment: The suspension obtained by dispersing Eu@UiO-66(OH)2 / (COOH)2 in DMF is used to detect the analyte. Usually, the powder (30 mg) of Eu@UiO-66(OH)2 / (COOH)2 is dispersed in 40 mL of DMF and ultrasonicated for 20 minutes. Then, 2 mL of Eu@UiO-66(OH)2 / (COOH)2 suspension is taken, 20 μL of analyte (10 mM) is added, and the fluorescence spectrum is tested. The excitation wavelength is set to 280 nm, and the slit width is 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 random discharge of NAT pharmaceutical factory wastewater can affect the ecological environment. The present invention studies 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. In addition, the effect of interfering substances on Eu@UiO-66(OH)2 / (COOH)2 was also studied, because some other components present in beer and wastewater may affect the luminescence properties of Eu@UiO-66(OH)2 / (COOH)2, such as 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), metal ions (Ca), 2+ , K + Mg 2+ 、Na + 、Zn 2+ ), vitamins (vitamin B5 (VB5), vitamin H (VH)) and antibacterial drugs (ampramycin (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 analytes with a concentration of 10 mM were transferred into 2 mL of the probe suspension. The fluorescence spectra of these mixtures were then measured, and it was found that among all the tested drugs, only NAT caused a significant change in the ratio fluorescence of the Eu@UiO-66(OH)2 / (COOH)2 suspension, and the remaining drugs did not cause a significant change in the fluorescence intensity of the probe suspension, indicating that the probe has good selectivity for NAT, and further research has found that the probe of the present invention has good anti-interference performance.

[0056] like Figure 1As shown in the figure, the fluorescence and detection performance of Eu@UiO-66(OH)2 / (COOH)2 can be adjusted by adjusting the ratio of DHTA / (PMA+DHTA). When the ratio is 20%, Eu@UiO-66(OH)2 / (COOH)2 can achieve dual emission at 439nm and 614nm under 280nm 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 in the figure, when the ratio of DHTA / (PMA+DHTA) 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 ratio of DHTA / PMA is adjusted to 10% and 20%, Eu@UiO-66(OH)2 / (COOH)2 achieves a color change from purple to blue. When the ratio is 20%, adding 1μM NAT will cause I 439 / I 614 The value of I increases by 2.6%, and when the ratio is 10%, I 439 / I 614 The value increased by 2.1%. In addition, the color change of Eu@UiO-66(OH)2 / (COOH)2 synthesized with different ligand ratios before and after adding NAT was also verified by the CIE chromaticity diagram ( Figure 3 ). The results show that when a 20% ratio is selected for NAT detection, 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 spectrum of the UiO-66 single crystal structure, which indicates that the synthesis of MOFs is successful. The Fourier transform infrared spectrum (FTIR) of the synthesized MOFs is shown in Figure 4 (b). At 1583 and 1390 cm -1 There are two characteristic absorption peaks at 1704cm, which are the asymmetric and symmetric stretching vibration peaks of carboxylate. -1 The characteristic absorption peak of free carboxyl groups is shown at 1704 cm -1 The peak at becomes relatively weak, indicating that the free carboxyl group and Eu 3+The X-ray photoelectron spectroscopy (XPS) further confirmed that Eu 3+ Combination with free carboxyl groups. Figure 4 As shown in (c), it can be clearly observed that Eu in Eu@UiO-66(OH)2 / (COOH)2 3+ The binding energy of Eu@UiO-66(OH)2 / (COOH)2 is 1135.38 eV, which proves that 3+ In addition, from Figure 4 (d) It can be seen that the binding energy of O 1s changes from 531.83 eV to 531.58 eV, which indicates that Eu in Eu@UiO-66(OH)2 / (COOH)2 3+ Successfully coordinated to the free carboxyl group. 3+ The amount of Zr was calculated by inductively coupled plasma mass spectrometry (ICP-MS). 4+ With Eu 3+ The molar ratio is 1.315:1.

[0059] The emission spectra of Eu@UiO-66(OH)2 / (COOH)2 in both solid state and DMF show that Eu 3+ The narrow-band emission characteristic of the ion confirms that Eu 3+ The successful packaging of ions in the framework. Figure 5 As shown in (a), Eu was observed at wavelengths of 590, 614, 653, and 700 nm. 3+ The unique emission 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. 3+ In addition to the main emission at 614 nm, Eu@UiO-66(OH)2 / (COOH)2 shows a broad emission peak near 439 nm, which is the characteristic fluorescence of the ligand 2,5-dihydroxyterephthalic acid, and its intensity is relatively low. Therefore, the DMF suspension of Eu@UiO-66(OH)2 / (COOH)2 shows red fluorescence under ultraviolet light (302 nm). In addition, the fluorescence stability of Eu@UiO-66(OH)2 / (COOH)2 in DMF at room temperature was also studied.

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

[0061] For an excellent sensor, fast response is also a key criterion. Therefore, the present invention studies the response time of Eu@UiO-66(OH)2 / (COOH)2 to NAT. Figure 7 As shown in the figure, the intensity ratio of the emission peaks at 439 nm and 614 nm increased significantly within 1 min. The results showed that Eu@UiO-66(OH)2 / (COOH)2 can be used as a fast and convenient probe to detect NAT.

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

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

[0064] I0 represents the fluorescence intensity of the highest peak 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 0.15μM (≈0.10mg / kg), which is much lower than the maximum allowable amount of 0.01g / L in beer (0.3g / kg in cheese) specified by the Chinese standard. Therefore, this probe has great potential for quantitative detection of NAT in actual samples.

[0065] Mobile phone detection

[0066] There are some disadvantages of using fluorescence instruments to detect NAT, such as large size and high cost, which limits on-site real-time monitoring. To address this problem, the present invention uses 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, the Eu@UiO-66(OH)2 / (COOH)2 suspension containing different concentrations of analytes was dropped into the titration plate. Photos were taken using a smartphone camera under 302nm UV light without background correction. The RGB values ​​of the photo images were then recorded ( Fig. 9 ).like Fig.10 (a) and Fig.10 As shown in (b), the color of the Eu@UiO-66(OH)2 / (COOH)2 suspension changes from purple to blue with the increase of NAT concentration. 2 =0.9922) showed a strong linear correlation, and the LOD was 3.33 μM (≈2.22 mg / kg), which was much lower than the standard value.

[0068] Example 3

[0069] Actual sample analysis:

[0070] Beer was purchased from a supermarket in Wuhan, Hubei Province. First, the carbon dioxide in the beer was removed by ultrasound. A mixture of 20 mL of beer and 60 mL of methanol was centrifuged at 8000 r / min for 10 minutes, and then filtered with 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 with a 0.22 μm filter membrane to obtain a beer test sample. NAT beer solution (10 mM) was prepared using the beer test sample, and then different volumes of NAT beer solution were drawn and added to 2 mL of 0.75 mg / mL Eu@UiO-66(OH)2 / (COOH)2 (prepared in Example 1 of the present invention) suspension, so that the concentrations of NAT were 5, 14, 16 and 35 μM, respectively. 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. In the first step, 40 mL of wastewater was filtered with a 0.45 μm filter membrane to remove insoluble impurities. In the second step, the filtrate was purified with octadecylsilane (ODS) and ethylenediamine-N-propylsilane (PSA), and then centrifuged at 8000 r / min for 10 minutes to collect the supernatant. In the third step, after evaporation and drying in a vacuum, the residue was dissolved in 40 mL of DMF and filtered through a 0.22 μm filter membrane to obtain a 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 the present invention) suspension to make the NAT concentrations of 5, 14, 16 and 35 μM, respectively. Finally, the fluorescence data of the mixture 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 Fig.12 As shown in (a), the recovery rates in beer ranged from 91.4% to 104.7%, with RSD values ​​less than 3.65% (n = 3); the recovery rates in wastewater ranged from 90.4% to 107.4%, with RSD values ​​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 can provide in-depth understanding of the actual situation, ensuring accuracy and convenience. On-site testing through visual observation and recording of color changes makes the whole process quick and convenient. In view of the excellent performance of Eu@UiO-66(OH)2 / (COOH)2 in NAT detection, the precision and accuracy of the auxiliary RGB values ​​of smartphones were also evaluated ( Fig.11 ). As shown in Table 2 and Fig.12As shown in (b), the recovery rates of beer ranged from 92.7% to 108.4%, with RSD values ​​lower than 3.87% (n=3); the recovery rates of wastewater ranged from 91.3% to 105.8%, with RSD values ​​lower than 4.43% (n=3). The results showed that NAT can be quantitatively detected using smartphone-assisted RGB values. This work provides a portable method for on-site instrument-free detection of NAT in real samples.

[0080] In summary, the present invention adds 2,5-dihydroxyterephthalic acid and Eu 3+ Two different luminescent components were rationally designed and successfully synthesized as a dual-emission fluorescent probe Eu@UiO-66(OH)2 / (COOH)2. Eu@UiO-66(OH)2 / (COOH)2 was used as a ratiometric fluorescent sensor for NAT, with a distinct purple-red to blue color change, good selectivity, strong anti-interference, low detection limit (0.15 μM, significantly lower than the national standard), and fast response speed (less than 1 minute). In addition, Eu@UiO-66(OH)2 / (COOH)2 has been successfully used to detect NAT in complex real samples such as beer and wastewater, with satisfactory recovery rates. Using the RGB values ​​obtained by a smartphone, the fluorescence color response of Eu@UiO-66(OH)2 / (COOH)2 enables instrument-free quantitative detection of NAT in these real samples. Therefore, this probe shows great potential in portable, visual on-site quantitative detection of NAT in complex real samples.

[0081] Those skilled in the art will easily understand that the above descriptions are merely embodiments of the present invention and are 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 in the protection scope of the present invention.

Claims

1. A method for preparing a Eu-MOF-based ratio fluorescence sensor, characterized in that: The preparation method comprises the following steps: (1) 2,5-dihydroxyterephthalic acid, pyromellitic acid and ZrCl4 are dispersed in deionized water, and then acetic acid is added, heated for a period of time and then cooled to obtain a suspension; (2) The suspension obtained in step (1) was transferred into another reaction vessel, and deionized water was added to continue the reaction. After the reaction was completed, the suspension was cooled, centrifuged with water, DMF, and ethanol in sequence, and finally vacuum dried overnight to obtain an off-white solid UiO-66(OH)2 / (COOH)2; (3) Dispersing EuCl3·6H2O and the UiO-66(OH)2 / (COOH)2 obtained in step (2) in deionized water, heating for reaction, cooling after the reaction is completed, centrifuging the obtained product and washing with water and ethanol, and finally, vacuum drying the generated precipitate overnight to obtain an off-white solid Eu@UiO-66(OH)2 / (COOH)2, which is the Eu-MOF-based ratio fluorescence sensor.

2. The method for preparing the Eu-MOF-based ratio fluorescence sensor according to claim 1, characterized in that: In the step (1), the molar ratio of 2,5-dihydroxyterephthalic acid to pyromellitic acid is 0.8-1.2:3.8-9.2, such as 0.8-1.2:3.8-4.2, and also such as 0.8-1.2:8.8-9.

2.

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

5.

4. The method for preparing the Eu-MOF-based ratio fluorescence sensor according to claim 1, characterized in that: In the 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; preferably, the heating in the step (1) is heated to 95-105° C.; preferably, the reaction period in the step (1) is 20-28 hours.

5. The method for preparing the Eu-MOF-based ratio fluorescence sensor according to claim 1, characterized in that: The amount of deionized water used in step (2) is 1.5-2.5 times the amount of deionized water used in step (1).

6. The method for preparing the Eu-MOF-based ratio fluorescence sensor according to claim 1, characterized in that: The reaction time in step (2) is 10-15 hours; preferably, in step (2), water, DMF and ethanol are used for centrifugation twice in sequence.

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

2.

8. The method for preparing the Eu-MOF-based ratio fluorescence sensor according to claim 1, characterized in that: The heating reaction in step (3) is carried out by heating to 75-85° C.; preferably, the reaction time is 20-30 hours.

9. The method for preparing the Eu-MOF-based ratio fluorescence sensor according to claim 1, characterized in that: The centrifugal speed in steps (2) and (3) is 8000 r / min; preferably, each centrifugal time is 4-6 minutes; preferably, the vacuum drying in steps (2) and (3) is carried out at 75-85°C.

10. Use of the Eu-MOF-based ratio fluorescence sensor obtained according to any one of claims 1 to 9, characterized in that: The application is to use the Eu-MOF-based ratio fluorescence sensor to detect natamycin.

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