Upconversion fluorescent nanoprobe, preparation method and application thereof

Abstract

The present application belongs to the field of pollutant detection, and particularly relates to an upconversion fluorescent nanoprobe, a preparation method, and an application thereof; the upconversion fluorescent nanoprobe provided by the present application can be excited by a light source with a wavelength of 980 nm, has no background fluorescence interference, and has a higher signal-to-noise ratio, which can improve the sensitivity and anti-interference ability of the fluorescent probe; and the upconversion fluorescent nanoprobe provided by the present application also has the ability to specifically detect permanganate (MnO4 ‑ ) and dichromate (Cr2O7 2‑ ) and other oxidizing ions, thus solving the problem that the existing fluorescent probes cannot meet the requirements of permanganate (MnO4 ‑ ) and dichromate (Cr2O7 2‑ ) Technical issues regarding testing requirements.

Description

Technical Field

[0001] The present application belongs to the field of pollutant detection, and in particular relates to an upconversion fluorescent nanoprobe and its preparation method and application. Background Art

[0002] Permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) is widely used in industrial fields such as material synthesis, surface treatment and medicine. For example, in the field of material synthesis, permanganate and dichromate can be used as oxidants to synthesize metal oxides, organic compounds and other materials. In the field of surface treatment, permanganate and dichromate are often used for metal surface treatment such as cleaning, rust removal and anti-corrosion to increase the corrosion resistance and mechanical properties of the material and extend its service life. In the field of medicine, it can be used to prepare the synthesis of pharmaceutical intermediates and prepare drugs. For example, benzyl alcohol can be oxidized to benzoic acid, and cyclohexanol can be oxidized to cyclohexanone, which can be used as one of the intermediates for the preparation of drugs such as aspirin. Aliphatic alcohols can also be oxidized to the corresponding carboxylic acid intermediates for use in the preparation of drugs.

[0003] But because permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) is widely used in the industrial field, which may lead to its discharge into the environment, thereby destroying the ecological balance of water bodies, causing toxic effects on aquatic organisms, and even adversely affecting human drinking water and food safety; therefore, it is necessary to effectively detect it to ensure that it is within a safe range and will not cause potential harm to human health; permanganate (MnO4 - ) can be detected by spectrophotometry and titration, but these methods take a long time to detect and are not suitable for rapid and real-time detection. In addition, the sensitivity and accuracy of the detection are not high. Electrochemical and chromatographic methods are not suitable for the detection of dichromate (Cr2O7 2- ) detection can achieve good sensitivity and accuracy, but it requires professional equipment and complex operations, is time-consuming, and is not conducive to rapid and real-time detection needs.

[0004] Fluorescent probes have the advantages of being simple and fast, and are widely used in the determination of metal ions and pesticide residues in industrial wastewater. However, the composition of industrial wastewater is complex and contains a variety of pollutants. Different pollutants may affect the detection of fluorescent probes. Therefore, fluorescent probes need good selectivity. And because permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) plasma has oxidizing properties. When the permanganate (MnO4 - ) and dichromate (Cr2O7 2-) and other oxidizing ions, the fluorescent probe must have good stability. However, the current performance of fluorescent probes is poor and cannot meet the detection requirements of oxidizing ions in industrial wastewater. Summary of the Invention

[0005] In view of this, the present application provides an up-conversion fluorescent nanoprobe and its preparation method and application, which is used to solve the problem that the existing fluorescent probes cannot meet the requirements of permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) Technical issues regarding testing requirements.

[0006] In a first aspect, the present application provides an upconversion fluorescent nanoprobe comprising a core nanoparticle NaYF4: Eu, an inner shell NaYbF4: Gd / Tm, an intermediate shell NaYbF4, an outer shell NaLuF4 and a silica layer;

[0007] The inner shell layer NaYbF4: Gd / Tm covers the core nanoparticle NaYF4: Eu;

[0008] The intermediate shell NaYbF4 covers the inner shell NaYbF4: Gd / Tm;

[0009] The outer shell NaLuF4 covers the intermediate shell NaYbF4;

[0010] The silicon dioxide layer covers the outer shell NaLuF4.

[0011] Preferably, the particle size of the upconversion fluorescent nanoprobe is 20-60 nm.

[0012] Preferably, in the core nanoparticles NaYF4:Eu, the molar ratio of Y:Eu is 70-95 mol%:5-30 mol%;

[0013] In the inner shell NaYbF4: Gd / Tm, the molar ratio of Yb:Gd:Tm is 38-79.5 mol%:20-60 mol%:0.5-2 mol%.

[0014] Further preferably, in the core nanoparticles NaYF4:Eu, the molar ratio of Y:Eu is 80 mol%:20 mol%;

[0015] In the inner shell NaYbF4: Gd / Tm, the molar ratio of Yb:Gd:Tm is 60 mol%:39 mol%:1 mol%.

[0016] The second aspect of the present application provides a method for preparing an upconversion fluorescent nanoprobe, which can be used to prepare the upconversion fluorescent nanoprobe described in the first aspect. The preparation method comprises the following steps:

[0017] Step S1, adding ammonium fluoride and sodium hydroxide to a precursor reaction solution containing a yttrium / europium-oleic acid complex to perform a core co-precipitation reaction to obtain core nanoparticles NaYF4:Eu;

[0018] Step S2, adding core nanoparticles NaYF4:Eu, ammonium fluoride, and sodium hydroxide to a precursor reaction solution containing a gadolinium / ytterbium / thulium-oleic acid complex to carry out an inner shell co-precipitation reaction to prepare a core-shell structured NaYF4:Eu@NaYbF4:Gd / Tm;

[0019] Step S3, adding NaYF4: Eu@NaYbF4: Gd / Tm, ammonium fluoride, and sodium hydroxide to the precursor reaction solution containing the ytterbium-oleic acid complex to carry out an intermediate shell co-precipitation reaction to prepare NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4 with a core-shell-shell structure;

[0020] Step S4, adding NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4, ammonium fluoride, and sodium hydroxide to the precursor reaction solution containing the lutetium-oleic acid complex to carry out an outer shell co-precipitation reaction to prepare a core-shell-shell-shell structure of NaYF4:Eu@NaYbF4: Gd / Tm@NaYbF4@NaLuF4;

[0021] Step S5: depositing nano-silica on the surface of NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4@NaLuF4 by the Stöber method to obtain an upconversion fluorescent nanoprobe coated with silica.

[0022] Preferably, in step S1, the method for preparing the precursor reaction solution of the yttrium / europium-oleic acid complex comprises: conducting a coordination reaction between yttrium salt, europium salt, oleic acid and 1-octadecene to prepare the precursor reaction solution of the yttrium / europium-oleic acid complex;

[0023] In step S2, the method for preparing a precursor reaction solution of the gadolinium / ytterbium / thulium-oleic acid complex comprises: conducting a coordination reaction between gadolinium salt, ytterbium salt, thulium salt, oleic acid, and 1-octadecene to prepare a precursor reaction solution of the gadolinium / ytterbium / thulium-oleic acid complex;

[0024] In step S3, the method for preparing the precursor reaction solution of the ytterbium-oleic acid complex comprises: performing a coordination reaction on ytterbium salt, oleic acid and 1-octadecene to prepare the precursor reaction solution of the ytterbium-oleic acid complex;

[0025] In step S4, the method for preparing the precursor reaction solution of the lutetium-oleic acid complex comprises: conducting a coordination reaction between lutetium salt, oleic acid and 1-octadecene to prepare the precursor reaction solution of the lutetium-oleic acid complex.

[0026] Preferably, in steps S1 to S4, the coordination reaction is carried out at a temperature of 150 to 180° C. and for a time of 20 to 40 minutes.

[0027] Preferably, in step S1, the process of the nuclear coprecipitation reaction is: heating to 40-60°C for reaction for 20-40 min, heating to 100-120°C for reaction for 20-30 min, removing methanol, vacuuming for 5-15 min, then heating to 250-300°C, and reacting under argon atmosphere for 0.5-1.5 h;

[0028] In step S2, the inner shell co-precipitation reaction process is as follows: heating to 40-60 ° C for reaction for 20-40 min, heating to 100-120 ° C for reaction for 20-30 min, removing methanol, vacuuming for 5-15 min, then heating to 250-300 ° C, and reacting under argon atmosphere for 0.5-1.5 h;

[0029] In step S3, the process of the intermediate shell co-precipitation reaction is: heating to 40-60°C for reaction for 20-40 min, heating to 100-120°C for reaction for 20-30 min, removing methanol, vacuuming for 5-15 min, then heating to 250-300°C, and reacting under argon atmosphere for 0.5-1.5 h;

[0030] In step S4, the outer shell co-precipitation reaction process is: heating to 40-60 ° C for reaction for 20-40 min, heating to 100-120 ° C for reaction for 20-30 min, removing methanol, vacuuming for 5-15 min, then heating to 250-300 ° C, and reacting under argon atmosphere for 0.5-1.5 h.

[0031] Preferably, in step S5, the process of the Stober method includes:

[0032] 2 g of surfactant CO-520 and 80 μL of ammonia water were added to 70 mg of core-shell-shell-shell structured NaYF4:Eu@NaYbF4: Gd / Tm@NaYbF4@NaLuF4, and then 40 μL of tetraethyl silicate was added after stirring and ultrasonication. After the reaction, the upconversion fluorescent nanoprobe was obtained by washing.

[0033] The third aspect of the present application provides an application of an upconversion fluorescent nanoprobe in detecting oxidative ions.

[0034] Preferably, the oxidizing ion is selected from permanganate and / or dichromate.

[0035] Preferably, the application is specifically: application in detecting oxidative ions in water pollution.

[0036] Preferably, the application process comprises the steps of:

[0037] Step 1: mixing the upconversion fluorescent nanoprobe with a concentration gradient of an oxidizing ion standard solution and performing fluorescence detection to establish a linear relationship between the concentration gradient of the oxidizing ion standard solution and the emission intensity of the upconversion fluorescent nanoprobe;

[0038] Step 2: mixing the up-conversion fluorescent nanoprobe and the oxidizing ion sample to be detected, and then performing fluorescence detection to obtain the emission intensity of the oxidizing ion sample to be detected;

[0039] Step 3: Substitute the emission intensity of the upconversion fluorescent nanoprobe into the linear relationship between the concentration gradient of the oxidizing ion standard solution and the emission intensity of the upconversion fluorescent nanoprobe to calculate the concentration of the oxidizing ion in the oxidizing ion sample to be detected.

[0040] In summary, the present application provides an upconversion fluorescent nanoprobe and its preparation method and application.

[0041] The upconversion fluorescent nanoprobe provided in this application can be excited by low-energy near-infrared light, has no background fluorescence interference and has a higher signal-to-noise ratio, which can improve the sensitivity and anti-interference ability of the fluorescent probe. In addition, the upconversion fluorescent nanoprobe provided in this application can selectively detect permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) and other oxidizing ions with good specificity; at the same time, the chemical stability and dispersibility of the fluorescent probe in water are improved by silica coating, which is beneficial for the detection of permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) and other oxidizing ions, thus solving the problem that the existing fluorescent probes cannot meet the requirements of permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) Technical issues regarding testing requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0043] Figure 1 This is a diagram showing the structure and performance test results of UCNPs provided in Example 1 of the present application;

[0044] Figure 2 This is a diagram showing the structure and performance test results of UCNPs@SiO2 provided in Example 1 of the present application;

[0045] Figure 3 For different ions and permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) UV absorption spectra before and after adding UCNPs@SiO2;

[0046] Figure 4 Detection of different concentrations of permanganate (MnO4 - ) result graph;

[0047] Figure 5 Detection of different concentrations of dichromate (Cr2O7 2- ) result graph;

[0048] Figure 6 UCNPs@SiO2 selectively detect different ions and permanganate (MnO4 - ) and different ions and dichromate (Cr2O7 2- ) upconversion fluorescence intensity comparison chart. DETAILED DESCRIPTION

[0049] The present application provides an upconversion fluorescent nanoprobe and its preparation method and application, which is used to solve the problem that existing fluorescent probes cannot meet the requirements of permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) Technical issues regarding testing requirements.

[0050] The following will clearly and completely describe the technical solution of this application in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0051] Since the current fluorescent probes cannot meet the requirements of permanganate (MnO4 - ) and dichromate (Cr2O7 2-) and other oxidizing ion detection requirements, the present application provides an upconversion fluorescent nanoprobe, which is composed of a core nanoparticle NaYF4: Eu, an inner shell NaYbF4: Gd / Tm, an intermediate shell NaYbF4, an outer shell NaLuF4 and a silica layer; the structure is that the inner shell NaYbF4: Gd / Tm covers the core nanoparticle NaYF4: Eu; the intermediate shell NaYbF4 covers the inner shell NaYbF4: Gd / Tm; the outer shell NaLuF4 covers the intermediate shell NaYbF4; and the silica layer covers the outer shell NaLuF4.

[0052] The present application provides an upconversion fluorescent nanoprobe that can be excited by 980nm low-energy near-infrared light, thereby having no background fluorescence interference and having a higher signal-to-noise ratio, which can improve the sensitivity and anti-interference ability of the fluorescent probe in industrial wastewater; and - , Br - , CH3COO - , HCO3 - , CO3 2- , NO3 - , SO4 2- , H2PO4 - , HPO4 2- , PO4 3- and MnO4 - After mixing with upconversion fluorescent nanoprobes, or Cl - , Br - , CH3COO - ,NO3 - , SO4 2- , SCN - ,H2PO4 - , HPO4 2- , PO4 3- and Cr2O7 2- After mixing with the upconversion fluorescent nanoprobe, the upconversion fluorescence intensity of the upconversion fluorescent nanoprobe did not change significantly, indicating that the upconversion fluorescent nanoprobe provided by the present application can selectively detect permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) and other oxidizing ions, with good specificity; and the up-conversion fluorescent nanoprobe provided by the present application is also coated with silica, which improves the chemical stability and photostability of the fluorescent probe and also makes it have good water solubility and dispersibility, so that it is suitable for the detection of oxidizing ions in water, thereby overcoming the problem that the current fluorescent probe cannot meet the requirements of permanganate (MnO4 - ) and dichromate (Cr2O72- ) and other defects in the requirements for oxidizing ion detection.

[0053] As a preference, since the particle size and composition of the upconversion nanoparticles will affect their fluorescence emission spectrum, the present application also adjusts the composition and dosage of the core nanoparticles, the inner shell NaYbF4:Gd / Tm, the middle shell NaYbF4, and the outer shell NaLuF4 in the upconversion fluorescent nanoprobe to obtain a fluorescence emission spectrum with a better anti-Stokes luminescence effect, which satisfies the requirements of permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) ion detection requirements.

[0054] The upconversion fluorescent nanoprobe provided in this application will be specifically described below with reference to the embodiments and experimental examples.

[0055] Example 1

[0056] Example 1 of the present application provides a method for preparing an upconversion fluorescent nanoprobe, which includes the steps of preparing a precursor reaction solution of a rare earth-oleic acid complex, a coprecipitation reaction, and a silica coating step.

[0057] The steps of preparing the precursor reaction solution of the rare earth-oleic acid complex include:

[0058] Preparation of yttrium / europium-oleic acid complex precursor reaction solution: Yttrium acetate (0.32 mmol), europium acetate (0.08 mmol), oleic acid (4 mL) and 1-octadecene (6 mL) were added to a two-necked flask, heated to 160 °C in a heating mantle and reacted for 30 min. Water in the reaction system was removed and the reaction system was cooled to room temperature to obtain a yttrium / europium-oleic acid complex precursor reaction solution.

[0059] Preparation of a precursor reaction solution of a gadolinium / ytterbium / thulium-oleic acid complex: Ytterbium acetate (0.24 mmol), gadolinium acetate (0.156 mmol), thulium acetate (0.004 mmol), oleic acid (4 mL), and 1-octadecene (6 mL) were added to a two-necked flask. The mixture was heated to 160°C in a heating mantle and reacted for 30 min. Water was removed from the reaction system, and the mixture was cooled to room temperature to obtain a precursor reaction solution of a gadolinium / ytterbium / thulium-oleic acid complex.

[0060] Preparation of ytterbium-oleic acid complex precursor reaction solution: Ytterbium acetate (0.4 mmol), oleic acid (4 mL) and 1-octadecene (6 mL) were added to a two-necked flask, heated to 160 °C in a heating mantle and reacted for 30 min. Water was removed from the reaction system and the reaction mixture was cooled to room temperature to obtain the ytterbium-oleic acid complex precursor reaction solution.

[0061] Preparation of lutetium-oleic acid complex precursor reaction solution: Lutetium acetate (0.4 mmol), oleic acid (4 mL), and 1-octadecene (6 mL) were added to a two-necked flask and heated to 160 °C in a heating mantle for 30 min. Water was removed from the reaction system and the mixture was cooled to room temperature to obtain a lutetium-oleic acid complex precursor reaction solution.

[0062] The steps of the coprecipitation reaction include:

[0063] NH4F (1.52 mmol) and NaOH (1 mmol) were added to the prepared yttrium / europium-oleic acid complex precursor reaction solution, and the mixture was heated to 50°C for 30 min. The temperature was then raised to 110°C to remove methanol. After evacuation for 10 min, the temperature was raised to 300°C and the reaction was carried out under an argon atmosphere for 1 h to obtain an oleic acid-coated core nanoparticle reaction solution. The core nanoparticles were composed of NaYF4:Eu (Y:Eu=80 mol%:20 mol%), which were then washed and dispersed in cyclohexane.

[0064] To the prepared gadolinium / ytterbium / thulium-oleic acid complex precursor reaction solution, oleic acid-coated core nanoparticles in cyclohexane, NH4F (1.52 mmol) and NaOH (1 mmol) were added, and the mixture was heated to 50°C for 30 min; the temperature was raised to 110°C to remove methanol; after vacuuming for 10 min, the temperature was raised to 300°C and reacted under argon atmosphere for 1 h to obtain oleic acid-coated core-shell nanoparticles. The core-shell nanoparticles had a composition of NaYF4: Eu @NaYbF4: Gd / Tm (Yb: Gd:Tm=60 mol%:39mol%:1 mol%), which were washed and dispersed in cyclohexane.

[0065] To the prepared ytterbium-oleic acid complex precursor reaction solution, core-shell nanoparticle cyclohexane solution, NH4F (1.52 mmol) and NaOH (1 mmol) were added, and the mixture was heated to 50℃ for reaction for 30 min; the temperature was raised to 110℃ to remove methanol; after vacuuming for 10 min, the temperature was raised to 300℃ and reacted under argon atmosphere for 1 h to obtain oleic acid-coated core-shell-shell nanoparticle reaction solution. The core-shell-shell nanoparticles consisted of NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4, which were washed and dispersed in cyclohexane.

[0066] In the prepared lutetium-oleic acid complex precursor reaction solution, core-shell-shell nanoparticle cyclohexane solution, NH4F (1.52 mmol) and NaOH (1 mmol) were added, and the mixture was heated to 50°C for reaction for 30 min; the temperature was raised to 110°C to remove methanol; after vacuuming for 10 min, the temperature was raised to 300°C and reacted under argon atmosphere for 1 h to obtain oleic acid-coated core-shell-shell-shell nanoparticle reaction solution. The core-shell-shell-shell nanoparticle composition is NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4@NaLuF4, denoted as UCNPs, which are dispersed in cyclohexane (4 mL).

[0067] The silica coating process involved taking 1.4 mL of a cyclohexane dispersion of UCNPs, adding 8.6 mL of cyclohexane and 0.4 g of the surfactant CO-520, stirring at 300 rpm for 10 minutes, then adding 1.6 g of CO-520 and 80 μL of ammonia water, sonicating for 30 minutes, and finally adding 40 μL of tetraethyl silicate, stirring, and reacting for 48 hours. After the reaction, the mixture was washed multiple times with a mixture of acetone, water, and anhydrous ethanol and then dispersed in water to obtain an upconversion fluorescent nanoprobe, designated UCNPs@SiO2 (1.0 mg / mL).

[0068] The process of dispersing the product prepared in the coprecipitation reaction in cyclohexane includes: transferring the product to a centrifuge tube, adding anhydrous ethanol (4 mL, 99.55%), suspending and shaking evenly, centrifuging at 7500 rpm for 6 min, and removing the supernatant liquid; adding cyclohexane (4 mL, 99.5%), adding anhydrous ethanol (8 mL, 99.5%), suspending and shaking evenly, centrifuging at 7500 rpm for 6 min, and removing the supernatant liquid; adding cyclohexane (4 mL, 99.5%), anhydrous ethanol (4 mL, 99.5%), and methanol (4 mL, 99.5%), suspending and shaking evenly, centrifuging at 7500 rpm for 6 min, removing the supernatant liquid, dispersing it in cyclohexane (99.5%), and sealing and storing at low temperature.

[0069] Experimental Example 1

[0070] Experimental Example 1 of this application conducts structural and performance tests on the UCNPs and upconversion fluorescent nanoprobes (UCNPs@SiO2) provided in Example 1. The test results are as follows: Figure 1-3 shown.

[0071] The instruments used for structural testing include a Japanese HT7700 transmission electron microscope (TEM), operating at 100 kV; a high-resolution transmission electron microscope (HRTEM, FEI TALOS F200S, Czech Republic), operating at 200 kV; and an X-ray diffractometer (XRD, Malvern Panalytical DY 735, UK), with a scanning rate of 5 min. -1 , 2θ range of 10-90°; American Thermo-Filsher-Nicolet 6700 Fourier transform infrared spectrometer, scanning range of 4000~500 cm -1 , with a resolution of 2 cm -1 The number of scans was 32; the Zeta potential was measured using a British ZetasizerNANOZS nanoparticle size and Zeta potential analyzer.

[0072] The instruments used for performance testing include a PerkinElmer Lambda 950 UV-Vis-NIR spectrophotometer (USA), with a scanning wavelength range of 200-800 nm, and an Ocean Optics USB-2000+ fluorescence spectrometer, using a 980 nm infrared semiconductor laser as the excitation light source.

[0073] Among them, the structure and performance test of UCNPs provided in Example 1 are as follows Figure 1 As shown in the figure, the transmission electron microscopy (TEM) and element distribution (EDS) test results are shown in the figure. Figure 1 As shown in a~j; from Figure 1 As can be seen from Figure a, the average diameter of UCNPs is 39.5 nm. Figure 1 Figures b, ch, and i show the types and distribution of rare earth elements in UCNPs. UCNPs contain rare earth elements such as Y, Eu, Yb, Gd, Tm, and Lu. 3+ and Eu 3+ Distributed in the core particles, Gd 3+ 、Tm 3+ Distributed in the inner shell, Yb 3+ Distributed in the inner shell and the middle shell, Lu 3+ Distributed in the outer shell, this shows that the fluorescent nanoprobes provided in this application are composed of NaYF4: Eu, NaYbF4: Gd / Tm, NaYbF4 and NaLuF4 from the inside out; Figure 1From the transmission electron microscopy image of a single UCNPs shown in Figure j, it can be seen that the lattice fringe spacing d of the UCNPs is 0.520 nm, corresponding to the (100) plane of the hexagonal phase structure, indicating that the prepared UCNPs have a good crystal structure; the X-ray diffraction test results of the UCNPs provided in Example 1 (Figure k) show that the prepared UCNPs have a hexagonal phase crystal structure; the upconversion fluorescence emission spectrum under 980 nm semiconductor laser excitation (Figure l) shows that compared with the single-shell nanoparticles NaYF4: Eu@NaYbF4: Gd / Tm or the double-shell nanoparticles NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4, NaYF4: Eu@NaYbF4: Gd / Tm@NaLuF4, the core-shell-shell-shell nanoparticles UCNPs NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4@NaLuF4 provided in Example 1 of the present application have the strongest upconversion fluorescence.

[0074] The structure and performance test results of UCNPs@SiO2 provided in Example 1 are as follows Figure 2 As shown, from Figure 2 From the TEM image shown in Figure a, it can be seen that the size of UCNPs coated with SiO2 is slightly larger than 40 nm, and the thickness of the SiO2 coating layer is about 2.6 nm;

[0075] The infrared spectra of UCNPs and UCNPs@SiO2 provided in Example 1 are shown in FIG. Figure 2 As shown in Figure b, it can be seen from Figure b that UCNPs have a high affinity to 3000-2800 cm -1 The CH stretching vibration absorption peak of oleic acid molecule appears at 1562-1463 cm -1 The C=O stretching vibration and CH bending vibration characteristic peaks at 1060 cm -1 The Si-O stretching vibration absorption peak appears at ; this indicates that the silica-coated upconversion fluorescent nanoprobe (UCNPs@SiO2) was prepared in this application, and the zeta potential of the prepared upconversion fluorescent nanoprobe (UCNPs@SiO2) was -12.9 mV, as shown in Figure c.

[0076] The upconversion fluorescence spectrum of UCNPs@SiO2 provided in Example 1 is shown in FIG. Figure 2 As shown in Figure d, it can be seen from Figure d that the addition of permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) will lead to a decrease in the upconversion emission intensity, which shows that the upconversion fluorescent nanoprobe (UCNPs@SiO2) provided in Example 1 has the ability to detect permanganate (MnO4 -) and dichromate (Cr2O7 2- ) and other oxidizing ions.

[0077] UV absorption spectra of different ions and permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) before and after adding upconversion fluorescent nanoprobe (UCNPs@SiO2) as shown in the following figure: Figure 3 shown; from Figure 3 As can be seen in Figure a, permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) have broad absorption in the range of 200~700nm and 200~500nm respectively; Figure 3 As can be seen in Figure b, when coexisting with the upconversion fluorescent nanoprobe (UCNPs@SiO2), permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) showed no significant change in the UV-visible absorption spectrum.

[0078] Experimental Example 2

[0079] Experimental Example 2 of this application tests the performance of the upconversion fluorescent nanoprobe (UCNPs@SiO2) provided in Example 1 to explore the performance of the upconversion fluorescent nanoprobe in detecting permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) when the sensitivity and other performance, the test results are as follows Figure 4-5 shown.

[0080] Among them, the detection of permanganate (MnO4 - ) process includes adding different concentrations of MnO4 - , and incubated with UCNPs@SiO2 nanoprobes at room temperature for 2 min, and the target substance MnO4 was detected based on the change of upconversion fluorescence intensity. - The concentration of 2477 was detected using an Ocean Optics USB-2000+ fluorescence spectrometer with a 980 nm near-infrared semiconductor laser as the excitation light source.

[0081] Detection of permanganate (MnO4 - ) results such as Figure 4 As shown, Figure 4 As shown in Figure b, with the increase of MnO4 - As the concentration (0~2000uM) gradually increased, the upconversion emission intensity of UCNPs@SiO2 nanoprobe at 344 nm and 361 nm gradually decreased; Figure 4 As shown in Figure c, when MnO4 -In the concentration range of 0.6~80 μM, the relative intensity of upconversion emission of UCNPs@SiO2 nanoprobe is similar to that of MnO4 - The concentration has a good linear relationship, and the linear equation is y = 0.0952 x + 0.0626; Figure 4 As shown in Figure d, when MnO4 - The upconversion emission relative intensity of UCNPs@SiO2 nanoprobes is significantly different from that of MnO4 in the concentration range of 100~2000 μM. - The concentration has a good linear relationship, and the linear equation is y = 0.4976 x - 0.7080; this shows that MnO4 - When the concentration is 0.6~2000μM, the upconversion fluorescence intensity of UCNPs@SiO2 nanoprobe is significantly affected by the MnO4 - The concentration of MnO4 has a linear response, that is, the concentration gradient of 0.6~2000 μM is used in this application. - After incubation with the nanoprobe, the upconversion fluorescence intensity can be correlated with the MnO4 - The linear relationship between the concentration of MnO4 - After the water sample to be tested is mixed and incubated with the fluorescent nanoprobe, the upconversion fluorescence intensity of the nanoprobe is substituted into the above linear relationship to obtain the MnO4 - concentration.

[0082] Among them, the detection of dichromate (Cr2O7 2- ) process includes adding different concentrations of Cr2O7 2- , and incubated with UCNPs@SiO2 nanoprobes at room temperature for 1 min, and the target substance Cr2O7 was detected according to the change of upconversion fluorescence intensity. 2- The concentration of 2477 was detected using an Ocean Optics USB-2000+ fluorescence spectrometer with a 980 nm near-infrared semiconductor laser as the excitation light source.

[0083] Detection of dichromate (Cr2O7 2- ) results such as Figure 5 As shown, Figure 5 As shown in Figure b, with the increase of Cr2O7 2- As the concentration (0~2000 μM) gradually increased, the upconversion emission intensity of UCNPs@SiO2 nanoprobe at 344 nm and 361 nm gradually decreased; Figure 5 As shown in Figure c, when Cr2O7 2- In the concentration range of 2~200 μM, the relative intensity of upconversion emission of UCNPs@SiO2 nanoprobe is similar to that of Cr2O7 2-The concentration has a good linear relationship, and the linear regression equation is y = 0.1472 x - 0.0394; Figure 5 As shown in Figure d, when Cr2O7 2- The upconversion emission intensity of UCNPs@SiO2 nanoprobes is relatively close to that of Cr2O7 in the concentration range of 500~2000 μM. 2- The concentration has a good linear relationship, and the linear regression equation is y = 0.6737 x - 1.4801; this shows that in Cr2O7 2- When the concentration is 2~2000 μM, the upconversion fluorescence intensity of UCNPs@SiO2 nanoprobe is affected by the Cr2O7 2- The concentration of Cr2O7 has a linear response; that is, the present application uses a concentration gradient of 2~2000 μM 2- After incubation with upconversion fluorescent nanoprobes, the upconversion fluorescence intensity can be correlated with the Cr2O7 2- The linear relationship between the concentration of Cr2O7 2- After the water sample to be tested and the nanoprobe are mixed and incubated, the upconversion fluorescence intensity of the nanoprobe is measured and substituted into the above linear relationship to obtain the Cr2O7 2- concentration.

[0084] from Figure 4-5 It can be seen that the upconversion fluorescent nanoprobe (UCNPs@SiO2) provided in this application can detect (0~2000 μM) concentrations of permanganate (MnO4 - ) and dichromate (Cr2O7 2- ), with good sensitivity.

[0085] Experimental Example 3

[0086] Experimental Example 3 of this application tests the performance of the upconversion fluorescent nanoprobe (UCNPs@SiO2) provided in Example 1 to explore the detection performance of the upconversion fluorescent nanoprobe in detecting permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) and other oxidative ions, the test results are as follows Figure 6 As shown;

[0087] Among them, the instruments used for performance testing include the Ocean Optics USB-2000+ fluorescence spectrometer, which uses a 980 nm near-infrared semiconductor laser as the excitation light source.

[0088] The performance test process includes: adding 800 μM Cl - , Br - , CH3COO - , HCO3 -, CO3 2- , NO3 - , SO4 2- ,H2PO4 - , HPO4 2- , PO4 3- and MnO4 - , respectively, and incubated with upconversion fluorescence nanoprobe (UCNPs@SiO2) at room temperature for 2 minutes, and then tested its upconversion fluorescence spectrum. The test results are as follows Figure 6 As shown in Figure a, it can be seen from Figure a that Cl - , Br - ,CH3COO - , HCO3 - , CO3 2- , NO3 - , SO4 2- , H2PO4 - , HPO4 2- , PO4 3- After incubation with upconversion fluorescent nanoprobe (UCNPs@SiO2), the fluorescence intensity did not undergo obvious quenching, while the addition of MnO4 - After incubation with the upconversion fluorescent nanoprobe (UCNPs@SiO2), the fluorescence intensity was greatly quenched.

[0089] The performance test process also includes: adding 2000 μM Cl - , Br - , CH3COO - ,NO3 - , SO4 2- , SCN - ,H2PO4 - , HPO4 2- , PO4 3- and Cr2O7 2- , respectively, and incubated with upconversion fluorescent nanoprobe (UCNPs@SiO2) at room temperature for 1 min, and then tested its upconversion fluorescence spectrum. The test results are as follows Figure 6 As shown in Figure b, it can be seen from Figure b that Cl - , Br - ,CH3COO - , NO3 - , SO4 2- , SCN - , H2PO4 - , HPO4 2- , PO4 3-After incubation with upconversion fluorescent nanoprobe (UCNPs@SiO2), the fluorescence intensity did not undergo obvious quenching, while the addition of Cr2O7 2- After incubation with the upconversion fluorescent nanoprobe (UCNPs@SiO2), the fluorescence intensity was greatly quenched.

[0090] It can be seen from Experimental Example 3 that the upconversion fluorescent nanoprobe provided by this application can be used in Cl - , Br - ,CH3COO - , NO3 - , SO4 2- , SCN - , H2PO4 - , HPO4 2- , PO4 3- ,HCO3 - , CO3 2- , MnO4 - and Cr2O7 2- In the presence of plasma, selective detection of permanganate (MnO4 - ) and dichromate (Cr2O7 2- ) and other oxidizing ions with good specificity; at the same time, the upconversion fluorescent nanoprobe has excellent chemical stability and dispersibility in water.

[0091] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An upconversion fluorescent nanoprobe, characterized in that: It includes core nanoparticles NaYF4:Eu, inner shell NaYbF4:Gd / Tm, middle shell NaYbF4, outer shell NaLuF4 and silica layer; The inner shell NaYbF4: Gd / Tm covers the core nanoparticle NaYF4: Eu; The intermediate shell NaYbF4 covers the inner shell NaYbF4: Gd / Tm; The outer shell NaLuF4 covers the intermediate shell NaYbF4; The silicon dioxide layer covers the outer shell NaLuF4; In the core nanoparticles NaYF4:Eu, the molar ratio of Y:Eu is 70-95 mol%:5-30 mol%; In the inner shell NaYbF4: Gd / Tm, the molar ratio of Yb:Gd:Tm is 38-79.5 mol%:20-60 mol%:0.5-2 mol%.

2. The upconversion fluorescent nanoprobe according to claim 1, characterized in that: The particle size of the upconversion fluorescent nanoprobe is 20-60 nm.

3. The upconversion fluorescent nanoprobe according to claim 1, characterized in that: The thickness of the silicon dioxide layer in the upconversion fluorescent nanoprobe is 1-4 nm.

4. The method for preparing an upconversion fluorescent nanoprobe according to any one of claims 1 to 3, characterized in that: Step S1, adding ammonium fluoride and sodium hydroxide to a precursor reaction solution containing a yttrium / europium-oleic acid complex to perform a core co-precipitation reaction to obtain core nanoparticles NaYF4:Eu; Step S2, adding core nanoparticles NaYF4:Eu, ammonium fluoride, and sodium hydroxide to a precursor reaction solution containing a gadolinium / ytterbium / thulium-oleic acid complex to carry out an inner shell co-precipitation reaction to prepare a core-shell structure NaYF4:Eu@NaYbF4:Gd / Tm; Step S3, adding NaYF4: Eu@NaYbF4: Gd / Tm, ammonium fluoride, and sodium hydroxide to the precursor reaction solution containing the ytterbium-oleic acid complex to carry out an intermediate shell co-precipitation reaction to prepare NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4 with a core-shell-shell structure; Step S4, adding NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4, ammonium fluoride, and sodium hydroxide to the precursor reaction solution containing the lutetium-oleic acid complex to carry out an outer shell co-precipitation reaction to prepare NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4@NaLuF4 with a core-shell-shell-shell structure; Step S5: depositing nano-silica on the surface of NaYF4: Eu@NaYbF4: Gd / Tm@NaYbF4@NaLuF4 by the Stöber method to obtain an upconversion fluorescent nanoprobe coated with silica.

5. The method for preparing an upconversion fluorescent nanoprobe according to claim 4, characterized in that: In steps S1 to S4, a precursor reaction solution containing a yttrium / europium-oleic acid complex, a precursor reaction solution containing a gadolinium / ytterbium / thulium-oleic acid complex, a precursor reaction solution containing a ytterbium-oleic acid complex, and a precursor reaction solution containing a lutetium-oleic acid complex are obtained through coordination reactions; The coordination reaction temperature is 150-180° C., and the time is 20-40 min.

6. Use of an upconversion fluorescent nanoprobe according to any one of claims 1 to 3 in detecting oxidative ions, characterized in that: The oxidizing ion is selected from permanganate or dichromate.

7. The use according to claim 6, characterized in that The application is specifically: application in detecting oxidizing ions in water pollution.

8. The use according to claim 6, characterized in that The application process includes the steps of: Step 1: mixing the upconversion fluorescent nanoprobe with a concentration gradient of an oxidizing ion standard solution and performing fluorescence detection to establish a linear relationship between the concentration gradient of the oxidizing ion standard solution and the emission intensity of the upconversion fluorescent nanoprobe; Step 2: mixing the up-conversion fluorescent nanoprobe and the oxidizing ion sample to be detected, and then performing fluorescence detection to obtain the emission intensity of the oxidizing ion sample to be detected; Step 3: Substitute the emission intensity of the upconversion fluorescent nanoprobe into the linear relationship between the concentration gradient of the oxidizing ion standard solution and the emission intensity of the upconversion fluorescent nanoprobe to calculate the concentration of the oxidizing ion in the oxidizing ion sample to be detected.

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