Sandwich structure up-conversion nano-particles, preparation method thereof, nano-probe and application

Abstract

The invention discloses an up-conversion nanoparticle with a sandwich structure, a preparation method of the up-conversion nanoparticle, a nanoprobe and application, and relates to the technical field of up-conversion nanomaterials, and the up-conversion nanoparticle with the sandwich structure takes NaYbF4: Gd < 3 + > as an inner core, NaYbF4: Er < 3 + > as an inner shell layer and NaYF4 as an outer shell layer. Through a core-inner shell-outer shell structure design and an energy enrichment strategy, double improvement of LRET efficiency and quantum yield is realized, and the synthesized sandwich structure up-conversion nanoparticles are subjected to hydrophilic modification and are loaded with hydroxyl cobalt oxide, so that the nanoprobe which can be applied to high-sensitivity detection of ascorbic acid is prepared.

Description

Technical Field

[0001] The invention relates to the technical field of upconversion nanomaterials, and in particular to a sandwich structure upconversion nanoparticle and a preparation method thereof, a nanoprobe and application thereof. Background Art

[0002] Lanthanide-doped upconversion nanoparticles (UCNPs) convert near-infrared low-energy photons into high-energy photons through a multi-level energy upconversion transfer pathway. They have the advantages of large anti-Stokes shift, high photostability, narrow-band emission, and no background fluorescence. As a result, nanoprobes based on UCNPs have received increasing attention and have shown broad application prospects in the fields of biological imaging, food safety testing, and environmental monitoring.

[0003] Most upconversion nanoprobes are constructed based on the luminescence resonance energy transfer (LRET) process, in which UCNPs act as energy donors and specific target recognition groups act as energy acceptors. The LRET process is a distance-dependent physical process, and its efficiency (E) is inversely proportional to the sixth power of the donor-acceptor distance (r) (E∝r -6 ). Typically, the maximum distance for an effective LRET process is 10 nm. However, the diameter of UCNPs is usually tens of nanometers, and the luminescent ions are uniformly doped. Therefore, only the luminescent ions close to the surface of UCNPs can be effectively quenched, resulting in the inability to quench the luminescent ions in the core region. Unquenched luminescent ions will produce significant background signals, reducing the sensitivity of upconversion nanoprobes. Sandwich structured upconversion nanoparticles (SWUCNPs) confine the luminescent ions to the inner shell, shortening the distance to the energy acceptor and enhancing the LRET efficiency. However, limiting the luminescent layer to a thickness of 2~4 nm will reduce the upconversion luminescence (UCL) intensity of SWUCNPs and affect the sensitivity of the nanoprobe. Therefore, solving the contradiction between high quantum yield and LRET efficiency is the key to developing ultrasensitive upconversion nanoprobes. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an upconversion nanoprobe and a preparation method thereof. Through the core-inner shell-outer shell structure design and the energy enrichment strategy, the dual improvement of LRET efficiency and quantum yield is achieved. The synthesized sandwich structure upconversion nanoparticles are hydrophilically modified and loaded with cobalt hydroxide oxide to obtain an upconversion nanoprobe that can be used for high-sensitivity detection of ascorbic acid.

[0005] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions: The first object of the present invention is to provide a sandwich structure upconversion nanoparticle, wherein the sandwich structure upconversion nanoparticle is composed of NaYbF 4 :Gd 3+ For the kernel, NaYbF4 :Er 3+ is the inner shell, NaYF 4 For the outer shell.

[0006] In the present invention, the luminescent activator Er 3+ The inner shell is confined to shorten the distance between the luminescent layer and the energy acceptor, thus improving the LRET efficiency. In addition, the inner shell is made of NaYbF 4 As a matrix, it not only improves the absorption efficiency of 980 nm excitation light, but also promotes the transfer of energy from the core to the luminescent ions. In addition, NaYbF 4 :Gd 3+ The inner core acts as an energy-rich region, enhancing the absorption of 980 nm excitation light.

[0007] The second object of the present invention is to provide a method for preparing sandwich structure upconversion nanoparticles, comprising the following steps: (1) Ytterbium salt, gadolinium salt, ligand, NH 4 F, NaOH reaction, NaYbF 4 :Gd 3+ Nanoparticles; (2) Ytterbium salt, erbium salt and ligand, NH 4 F, NaOH reaction, in NaYbF 4 :Gd 3+ Nanoparticles coated with β-NaYbF 4 :Er 3+ , and obtain NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ Nanoparticles; (3) Yttrium salt and ligand, NH 4 F, NaOH reaction, in NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ Nanoparticles coated with NaYF 4 , and obtain NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 Nanoparticles.

[0008] Furthermore, the ytterbium salt includes but is not limited to at least one of ytterbium chloride, sulfate, nitrate, and oleate; the gadolinium salt includes but is not limited to at least one of gadolinium chloride, sulfate, nitrate, and oleate; the erbium salt includes but is not limited to at least one of erbium chloride, sulfate, nitrate, and oleate; the yttrium salt includes but is not limited to at least one of yttrium chloride, sulfate, nitrate, and oleate.

[0009] Furthermore, the ligand is oleic acid, but is not limited thereto.

[0010] Furthermore, the preparation process of the sandwich structure upconversion nanoparticles is carried out in a protective atmosphere, such as argon.

[0011] Furthermore, the sandwich structure upconversion nanoparticles are treated with acid to remove surface ligands and to modify hydrophilic molecules on the surface, thereby obtaining hydrophilic sandwich structure upconversion nanoparticles, which is beneficial for the subsequent preparation of aqueous phase highly sensitive nanoprobes for detecting ascorbic acid in serum.

[0012] In a specific embodiment, the acid can be selected from dilute hydrochloric acid with a pH of 0.8 to 1.2.

[0013] In a specific embodiment, the hydrophilic molecule is polyacrylic acid, but is not limited thereto.

[0014] The third object of the present invention is to provide applications of the sandwich structure upconversion nanoparticles in chemical and biological sensing, cell imaging, drug delivery, biomedical detection and diagnosis, food safety and quality control, environmental monitoring, optoelectronic devices and energy.

[0015] The fourth object of the present invention is to provide a nanoprobe, which comprises the sandwich structure upconversion nanoparticles and cobalt oxyhydroxide.

[0016] Furthermore, the cobalt oxyhydroxide is a cobalt oxyhydroxide nanosheet. Furthermore, the cobalt oxyhydroxide nanosheet is formed by reacting a cobalt salt with an oxidant under alkaline conditions. The cobalt salt includes but is not limited to at least one of cobalt chloride and cobalt nitrate; the oxidant is sodium hypochlorite, but is not limited thereto.

[0017] The fifth object of the present invention is to provide application of the nanoprobe in ascorbic acid detection.

[0018] When ascorbic acid is added to the nanoprobe solution of the present invention, CoOOH undergoes a redox reaction with ascorbic acid, and CoOOH is reduced to Co 2+. CoOOH itself acts as a luminescence quencher, and its absorption spectrum overlaps with the green emission spectrum (540 nm) of SWUCNPs, which will quench the green emission. As the concentration of ascorbic acid increases, CoOOH is continuously reduced, the quenching effect on green emission weakens, the luminescence intensity of the solution at 540 nm continues to increase, and the upconversion emission at 655 nm is not affected. Therefore, the fluorescence modality detection of ascorbic acid can be achieved based on the response to the ascorbic acid concentration according to the ratio of the upconversion green emission and red emission intensities. At the same time, since the optical properties of the solution, such as the color, will also change after CoOOH is reduced, the change in the color of the solution can be detected by naked eye observation or colorimetry, thereby realizing colorimetric and naked eye visualization detection of ascorbic acid.

[0019] In this paper, the red fluorescence at 655 nm is used as the reference signal. SWUCNPs show two main emission peaks (540 nm and 655 nm) under 980 nm excitation, which is due to the fact that Er 3+ Two excited states ( 4 S 3 / 2 , 4 F 9 / 2 ) to the ground state ( 4 I 15 / 2 ). After the introduction of ascorbic acid, CoOOH is reduced, and the quenching effect on the green emission at 540 nm is changed, while the red emission at 655 nm is not affected. Therefore, the nanoprobe of the present invention has the advantages of self-calibration and anti-interference, and can achieve more accurate and reliable ascorbic acid detection.

[0020] The beneficial effects of the present invention are: 1. Compared with the traditional sandwich structure of NaYF 4 @NaYF 4 :Yb 3+ , Er 3+ @NaYF 4 In comparison, the UCL intensities of the SWUCNPs described in the present invention at 540 nm and 655 nm are increased by 56 times and 117 times, respectively, achieving the synergistic optimization of high LRET efficiency and high UCL intensity.

[0021] 2. The luminescent center of the SWUCNPs described in the present invention is confined to the inner shell layer, and combined with the outer shell layer to inhibit quenching, the LRET efficiency and quantum yield can be improved. 2 The quantum yield under the excitation conditions reaches 9.50%, far exceeding that of NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4(0.14%).

[0022] 3. The nanoprobe described in the present invention exhibits an ultra-low detection limit (LOD=38 nM) in ascorbic acid detection, which is an order of magnitude higher in sensitivity than similar probes, and has excellent selectivity and anti-interference capabilities.

[0023] 4. The structural design of SWUCNPs described in the present invention can be extended to other rare earth doped systems, and is suitable for fields such as biosensing and environmental monitoring, and maintains stable luminescence performance in a wide pH range (5-9) and during long-term storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the present invention using a layer-by-layer growth strategy to synthesize SWUCNPs (A) and the design strategy of SWUCNPs to achieve high LRET efficiency and high quantum yield (B); Figure 2 The structural characterization diagrams and UCL spectra of upconversion nanoparticles with different structures in the present invention are shown in Figure 1. 4 :Gd 3+ TEM image of nanoparticles; (B) NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ TEM image of nanoparticles; (C) NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 TEM image of nanoparticles; (D) NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 HAADF image of nanoparticles and line scan distribution of Yb, Gd, and Y elements; (E) NaYbF 4 :Gd 3+ Nanoparticles, NaYbF 4 :Gd 3 + @NaYbF 4 :Er 3+ Nanoparticles and NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 XRD pattern of nanoparticles; (F)NaYbF 4 :Gd 3+Nanoparticles, NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ Nanoparticles and NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 UCL spectra of nanoparticles; Figure 3 In Example 2, different Yb 3+ NaYbF prepared at doping ratios (20%, 40%, 60%, 80%) 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 TEM image (A), XRD pattern (B), UCL spectrum (C), and UCL intensity at 540 nm and 655 nm (D) of the nanoparticles; Figure 4 NaYF prepared in Comparative Example 1 4 Nanoparticles, NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ Nanoparticles, NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 TEM image and particle size distribution of nanoparticles (A) and NaYbF prepared in Example 1 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 Comparison of UCL spectra (B) and absorption spectra (C) of nanoparticles; Figure 5 NaYbF prepared in Example 1 and Comparative Examples 1 to 4 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 Nanoparticles, NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 Nanoparticles, NaYbF 4 :Gd3+ ,Er 3+ @NaYF 4 Nanoparticles, NaYbF 4 :Gd 3+ ,Er 3 + @NaYbF 4 Nanoparticles and NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 Quantum yield of nanoparticles at different power densities; Figure 6 The principle of the nanoprobe for detecting AA and the effects of ascorbic acid concentration and the type of interfering substances on the UCL intensity of the nanoprobe; (A) schematic diagram of the principle of the nanoprobe for detecting AA; (B) UCL spectra of the nanoprobe at different AA concentrations (0-20 μM); (C) UCL intensity ratio of the nanoprobe at 540 nm (F / F 0 ) and AA concentration; (D) UCL spectrum of the nanoprobe after adding 20 μM AA and different interferents; (E) Selectivity and anti-interference ability of the nanoprobe in the presence of interferents; Figure 7 The sensing ability of nanoprobe a, nanoprobe b, and nanoprobe c to AA is studied; (A) UCL spectra of nanoprobe a at different AA concentrations; (B) UCL intensity ratio of nanoprobe a at 540 nm (F / F 0 ) and AA concentration; (C) UCL spectra of nanoprobe b at different AA concentrations; (D) UCL intensity ratio of nanoprobe b at 540 nm (F / F 0 ) and AA concentration; (E) UCL spectra of the three nanoprobes after adding different concentrations of AA; (F) Signal contrast of the three nanoprobes detecting AA; (G) Detection limits of the three nanoprobes detecting AA. DETAILED DESCRIPTION

[0025] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments and diagrams.

[0026] The abbreviations in the present invention are shown in Table 1.

[0027] Table 1

[0028] The doping concentration in the present invention is calculated based on the feed ratio of the rare earth chloride raw material added when synthesizing the up-conversion nanoparticles.

[0029] Example 1

[0030] (1)NaYbF 4 :Gd 3+ Preparation of nanoparticles Weigh 1 mmol YbCl 3 6H 2 O, 0.1 mmol GdCl 3 6H 2 O was mixed with 30 mL OA and 75 mL ODE, heated to 160 °C and stirred for 1 h, and then cooled to room temperature and 50 mL of 0.74 g NH 4 F and 0.5 g of NaOH in methanol were heated to 40 °C and stirred for 50 min, then heated to 100 °C in a vacuum and kept warm for 20 min, and then heated to 300 °C in an argon atmosphere and kept warm for 1 h. After cooling to room temperature, 5 mL of the reaction mixture was taken and washed three times with ethanol and cyclohexane to obtain NaYbF 4 :Gd 3 + Nanoparticles, spare.

[0031] (2)NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ Preparation of nanoparticles 1 mmol YbCl 3 6H 2 O, 0.1 mmol ErCl 3 6H 2 O was mixed with 6 mL OA and 15 mL ODE, heated to 160°C in an argon-filled environment and stirred until the solution became transparent, then cooled to room temperature; NaYbF prepared in step (1) was added under stirring. 4 :Gd 3+ nanoparticles, and 15 mL of 0.148 g NH 4 F and 0.1 g of NaOH in methanol were heated to 50 °C and stirred for 40 min, then heated to 100 °C in a vacuum and kept warm for 20 min, then heated to 300 °C in an argon atmosphere and kept warm for 1 h, cooled to room temperature, and the product was precipitated with ethanol and washed three times with ethanol to obtain NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ Nanoparticles, spare.

[0032] (3)NaYbF 4 :Gd3+ @NaYbF 4 :Er 3+ @NaYF 4 Preparation of nanoparticles 1 mmol YCl 3 6H 2 O was mixed with 6 mL OA and 15 mL ODE, heated to 160°C in an argon-filled environment and stirred until the solution became transparent, then cooled to room temperature; NaYbF prepared in step (2) was added under stirring. 4 :Gd 3+ @NaYbF 4 :Er 3+ nanoparticles, and 15 mL of 0.148 g NH 4 A methanol solution of F and 0.1 g NaOH was heated to 50 °C and stirred for 40 min, then heated to 100 °C in a vacuum and kept warm for 20 min, then heated to 300 °C in an argon atmosphere and kept warm for 1 h, cooled to room temperature, and the product was precipitated with ethanol and washed three times with ethanol to obtain NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 Nanoparticles, spare.

[0033] from Figure 2 (A)~2(C) It can be seen that the inner core is of regular shape, and as the shell grows, the particle gradually becomes larger and maintains a relatively uniform spherical shape. The thickness of the inner shell and outer shell are about 3.5nm and 1nm, respectively.

[0034] from Figure 2 (D) It can be seen that Gd 3+ Mainly distributed in the kernel, Yb 3+ Distributed in the core and inner shell, Y 3+ Distributed in the outer shell.

[0035] from Figure 2 (E) It can be seen that the diffraction peaks of the three nanoparticles prepared in this example are similar to those of β-NaYbF 4 The crystal standard peaks (JCPDS No. 27-1427) are consistent, indicating that the present invention has successfully synthesized these three nanoparticles.

[0036] from Figure 2 (F) It can be seen that due to the absence of rare earth activator ions, NaYbF 4 :Gd 3+ The core has no upconversion luminescence. 4 :Er 3+After the inner shell layer, the core-shell UCNPs showed three main emission peaks (521, 540, and 655 nm), which originated from Er 3+ The three excited states (2H 11 / 2 、4S 3 / 2 and 4F 9 / 2 ) to the ground state (4I 15 / 2 ) transition. Further, by epitaxial growth of NaYF 4 After the protective shell, the up-conversion luminescence intensity is greatly improved.

[0037] Example 2 FWf 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 The synthesis method of the nanoparticles is the same as that of Example 1, except that the inner shell Yb 3+ The doping ratio of Yb in the inner shell of Example 1 is 20%, 40%, 60%, and 80%. 3+ The doping ratio is 98%. It should be noted that Yb 3+ The doping ratio refers to the Yb 3+ Relative to the doping levels of all rare earth metals (Yb and Er).

[0038] from Figure 3 (A) It can be seen that with the increase of Yb 3+ The crystal morphology of the particles remains consistent and the particle size is similar as the doping ratio changes, which indicates that the crystal growth process is affected by the template effect of the core.

[0039] from Figure 3 (B) It can be seen that all NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 The XRD patterns of the nanoparticles are consistent with the hexagonal β-NaYbF 4 The crystal standard peaks match, which indicates that the inner shells are different Yb 3+ The doping ratio does not change the basic structure of the crystal.

[0040] from Figure 3 (C) It can be seen that as the Yb 3+ With the increase of doping ratio, the UCL intensity of SWUCNPs increases, which indicates that the Yb 3+ The doping concentration has a great influence on the up-conversion luminescence. High concentration doping of sensitizing ions is conducive to improving the up-conversion luminescence intensity.

[0041] from Figure 3 (D) It can be seen that NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 The UCL intensity of the nanoparticles at 540 nm and 655 nm increases with the Yb 3+ The doping ratio increases with the increase of Yb 3+ The doping ratio enhances the absorption of the excitation light and can determine that 98% of the Yb in the inner shell 3+ The doping ratio is synthesized NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 Optimal doping ratio of nanoparticles.

[0042] Comparative Example 1 Prepare NaYF according to the method of Example 1 4 Nanoparticles, NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ Nanoparticles and NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 Nanoparticles.

[0043] from Figure 4 (A) It can be seen that the particle sizes of the three nanoparticles prepared in this comparative example are 20.4 nm, 27.7 nm and 29.7 nm, respectively.

[0044] from Figure 4 (B) It can be seen that NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 The UCL intensities of the nanoparticles at 540 nm and 655 nm are respectively NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 56 and 117 times that of nanoparticles.

[0045] from Figure 4 (C) It can be seen that NaYbF 4 :Gd 3+@NaYbF 4 :Er 3+ @NaYF 4 The absorption interface of the nanoparticles at an excitation wavelength of 980 nm is NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 5 times that of the nanoparticles, which indicates that NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 Nanoparticles have a stronger ability to absorb excitation light.

[0046] Comparative Example 2 Prepare a double-layer NaYbF 4 :Gd 3+ ,Er 3+ @NaYF 4 Nanoparticles.

[0047] Comparative Example 3 Prepare a double-layer NaYbF 4 :Gd 3+ ,Er 3+ @NaYbF 4 Nanoparticles.

[0048] Comparative Example 4 Prepare a double-layer NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 Nanoparticles.

[0049] The quantum yields of the nanoparticles prepared in Example 1 and Comparative Examples 1 to 4 at different power densities were tested by integrating sphere method. Figure 5 ).from Figure 5 It can be seen that NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 The quantum yield of the nanoparticles is higher than that of the other four nanoparticles at each power density, which fully proves that the NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 The advantages of nanoparticles in luminescence efficiency.

[0050] Example 3 (1)NaYbF 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 Acid treatment of nanoparticles 200 mg of NaYbF prepared in Example 1 was added 4 :Gd 3+ @NaYbF 4 :Er 3+ @NaYF 4 The nanoparticles were dispersed in 60 mL of dilute hydrochloric acid (pH = 1), ultrasonically treated for 1 h to accelerate the protonation and dissociation of the ligand OA, centrifuged, and washed twice with ultrapure water; the acid-treated SWUCNPs were dispersed in 20 mL of ultrapure water to obtain a hydrophilic SWUCNPs dispersion for later use.

[0051] (2) Preparation of nanoprobes: Add 20 mL of PAA aqueous solution (4 mg / mL) to the hydrophilic SWUCNPs dispersion prepared in step (1), stir overnight, and wash three times with ultrapure water and ethanol respectively; disperse the PAA-modified SWUCNPs in 20 mL of ultrapure water (10 mg / mL) for later use.

[0052] 1000 μL of PAA-modified SWUCNP aqueous solution and different volumes of CoCl 2 The aqueous solution (10 mmol / L, 0-2000 μL) was added to a 10 mL centrifuge tube, followed by 1000 μL of NaOH aqueous solution (0.8 mol / L) and 1000 μL of NaClO aqueous solution (2 mol / L), and ultrasonic treatment was performed for 10 min. 2+ Under alkaline conditions, it was oxidized by NaClO to generate CoOOH, which was modified on the surface of negatively charged SWUCNPs. Finally, the prepared nanoprobes were dispersed in 5 mL of deionized water.

[0053] Example 4 Performance test of nanoprobe detection of AA: AA solutions of different concentrations were added into a solution system containing the nanoprobe, wherein the system contained 0.5 mL of the nanoprobe solution prepared in Example 2 and 1.5 mL of a HEPES buffer solution (10 mM).

[0054] from Figure 6B shows that with the increase of AA concentration, the UCL intensity can be observed to recover gradually. Taking the emission at 540 nm as the sensing signal, the UCL intensity ratio (F / F 0 , F 0 and F represent the relationship between the UCL intensity of the nanoprobe at 540 nm before and after adding AA) and the AA concentration, as shown in Figure 6 As shown in C, the results show that in the range of 0~20 μM, the UCL intensity and AA concentration show a good linear relationship (R 2 =0.997), with a limit of detection (LOD) as low as 38 nM.

[0055] 1.5 mL of HEPES buffer solution (10 mM), 20 μM AA and different interfering substance solutions (prepared with ultrapure water, with a concentration of 50 μM) were added to 0.5 mL of the nanoprobe solution prepared in Example 2, and the UCL spectrum was measured.

[0056] from Figure 6 D and 6E, it can be seen that the presence of interferents has no significant effect on the UCL intensity of the nanoprobe, which proves that the nanoprobe described in the present invention has high selectivity and anti-interference ability.

[0057] Example 5 According to the method of Example 3, the NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 Nanoparticle preparation Nanoprobe a.

[0058] According to the method of Example 3, the NaYF 4 @NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 Nanoparticle preparation Nanoprobe b.

[0059] The nanoprobe prepared in Example 3 was named nanoprobe c.

[0060] The sensing ability of nanoprobe a, nanoprobe b and nanoprobe c to AA was studied.

[0061] from Figure 7 A and 7B show that for nanoprobe a, due to the core Er 3+ The inability to effectively quench the luminescence results in a high background emission. When detecting AA, although there is a linear response in the range of 0-20 μM, the signal contrast is low, only 4.2. Figure 7C and 7D show that the background luminescence of nanoprobe b is low, with a linear range of 0~22 μM, but the reduction of its luminescence center and excitation light absorption limits its sensitivity. Figure 7 E~7G shows that high Yb 3+ The doped nanoprobe c showed a significant luminescence change from dark to bright when detecting AA, with a signal contrast of 24.5 and a detection limit as low as 38 nM, which is much lower than the other two nanoprobes, showing the highest sensitivity.

[0062] Example 6 In order to verify the feasibility and reliability of the nanoprobe of the present invention in detecting AA in actual samples, human serum, lemon, watermelon, grape and other samples were selected, the human serum samples were from healthy volunteers, and the fruit samples were from the juice squeezed and filtered.

[0063] The sample was diluted 10 times with HEPES buffer (10 mM), and the AA content was detected using the nanoprobe prepared in Example 3 at different spiked concentrations (0, 30, 60 μM). The recovery rate was calculated and the results are shown in Table 1.

[0064] The recovery rate is calculated by: Recovery rate = (AB) / C*100% Among them, A is the concentration measured by the nanoprobe after adding the standard concentration of AA, B is the AA concentration in the actual sample, and C is the added standard concentration of AA.

[0065] Table 1

[0066] As shown in Table 1, the average recovery rate of the nanoprobes of the present invention for detecting samples containing AA is between 95% and 103%, and the relative standard deviation (RSD) is between 1.2% and 5.1%.

[0067] In addition, the nanoprobe prepared in Example 3 was used to detect low concentrations of AA (0.15, 0.20, 0.25, 0.3 μM) and compared with the HPLC-MS / MS method. The results are shown in Table 2.

[0068] Table 2

[0069] As can be seen from Table 2, the detection results of the two methods are consistent, which shows that the nanoprobe of the present invention can sensitively and reliably detect AA in actual samples.

[0070] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A sandwich structure upconversion nanoparticle, characterized in that: The sandwich structure upconversion nanoparticles are composed of NaYbF4:Gd 3+ For the core, NaYbF4:Er 3+ is the inner shell and NaYF4 is the outer shell.

2. A method for preparing sandwich structure upconversion nanoparticles, characterized in that: The following steps are involved: (1) Reaction of ytterbium salt and gadolinium salt with ligand, NH4F and NaOH to obtain NaYbF4:Gd 3+ Nanoparticles; (2) Ytterbium salt and erbium salt react with ligand, NH4F and NaOH to form NaYbF4:Gd 3+ Nanoparticles coated with β-NaYbF4:Er 3+ , to obtain NaYbF4:Gd 3+ @NaYbF4:Er 3+ Nanoparticles; (3) The yttrium salt reacts with the ligand, NH4F, and NaOH to form NaYbF4:Gd 3+ @NaYbF4:Er 3+ The surface of the nanoparticles is coated with NaYF4 to obtain NaYbF4:Gd 3+ @NaYbF4:Er 3+ @NaYF4 nanoparticles.

3. The preparation method according to claim 2, characterized in that: The ytterbium salt is at least one of ytterbium chloride, sulfate, nitrate and oleate; The gadolinium salt is at least one of chloride, sulfate, nitrate and oleate of gadolinium; The erbium salt is at least one of erbium chloride, sulfate, nitrate and oleate; The yttrium salt is at least one of yttrium chloride, sulfate, nitrate and oleate; The ligand is oleic acid; The preparation process of the sandwich structure upconversion nanoparticles is carried out in a protective atmosphere.

4. The preparation method according to claim 2, characterized in that: The sandwich structure upconversion nanoparticles are treated with acid to remove surface ligands and to modify hydrophilic molecules on the surface.

5. The preparation method according to claim 4, characterized in that: The acid is dilute hydrochloric acid with a pH of 0.8 to 1.2; The hydrophilic molecule is polyacrylic acid.

6. Application of the sandwich structure upconversion nanoparticles according to claim 1 or the sandwich structure upconversion nanoparticles obtained by the preparation method according to any one of claims 2 to 5 in chemical and biological sensing, cell imaging, drug delivery, biomedical detection and diagnosis, food safety and quality control, environmental monitoring, optoelectronic devices and energy.

7. A nanoprobe, characterized in that: The nanoprobe comprises the sandwich structure upconversion nanoparticles according to claim 1 or the sandwich structure upconversion nanoparticles obtained by the preparation method according to any one of claims 2 to 5 and cobalt oxyhydroxide.

8. The nanoprobe according to claim 7, characterized in that: The cobalt oxyhydroxide is cobalt oxyhydroxide nanosheets.

9. The nanoprobe according to claim 8, characterized in that: The cobalt oxyhydroxide nanosheets are formed by reacting a cobalt salt with an oxidant under alkaline conditions; The cobalt salt is at least one of cobalt chloride and cobalt nitrate; The oxidant is sodium hypochlorite.

10. Use of the nanoprobe according to any one of claims 7 to 9 in the detection of ascorbic acid.

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