Long-persistent nanoparticles, nanoprobes, dual-probe system and detection method

Abstract

This invention belongs to the field of luminescent materials technology, and discloses long-afterglow nanoparticles, nanoprobes, a dual-probe system, and a detection method. The long-afterglow nanoparticles have the general chemical formula Li. x Zn 1‑x Ga2O4:Cr³⁺, where x ranges from 0.1 to 0.5. The long afterglow nanoparticles provided by this invention, through Li… + Partial replacement of Zn 2+ An innovative doping strategy was developed, successfully solving the problem of hydrothermal synthesis of ZnGa2O4:Cr 3+ The industry challenge of poor luminescent performance of PLNPs. Li + The doping effectively optimized the lattice structure and the concentration and depth of electron traps, resulting in a breakthrough enhancement in the afterglow intensity and average lifetime of the material in the near-infrared window. A nanoprobe was obtained by modifying the surface of long-afterglow nanoparticles with a hydroxyethyl deacetylated chitosan layer, exhibiting a unique pH-responsive charge-transfer capability. This probe was used for the detection of polystyrene nanoplastics, demonstrating a low detection limit and a wide linear range.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of luminescent materials, in particular to persistent luminescence nanoparticles, nanoprobes, double-probe systems and detection methods. BACKGROUND

[0002] Persistent Luminescence Nanoparticles (PLNPs) are a kind of functional materials that can continue to emit light after stopping excitation. The luminescence is due to the storage and slow release of excitation energy by the defect energy level inside the material. With its unique advantages such as in-situ excitation-free and no background fluorescence interference, PLNPs have shown great application potential in the fields of biological imaging, disease diagnosis, environmental monitoring, anti-counterfeiting encryption, etc. Among them, the PLNPs of zinc gallate doped with trivalent chromium ions (ZnGa2O4:Cr 3+ ) have become one of the current research hotspots due to their excellent near-infrared persistent luminescence performance and good biocompatibility.

[0003] At present, the methods for synthesizing ZnGa2O4:Cr 3+ PLNPs mainly include high-temperature solid-phase method and hydrothermal method. Although the high-temperature solid-phase method can prepare materials with high luminescent brightness, it usually has high energy consumption, harsh reaction conditions, and is prone to cause particle agglomeration, uneven size and uncontrollable morphology, which restricts its subsequent biological application. In comparison, the hydrothermal method has mild reaction conditions, controllable morphology and good crystallinity, and is more suitable for synthesizing uniformly dispersed nanoscale PLNPs. However, the ZnGa2O4:Cr 3+ PLNPs synthesized by the hydrothermal method generally have weak luminescent intensity and short afterglow lifetime, and their performance is usually inferior to that of samples prepared by the high-temperature solid-phase method, which greatly limits their application in high-sensitivity detection fields. The root cause lies in the fact that the defect structure, concentration and depth of electron traps of the crystals synthesized by the hydrothermal method cannot be optimized and controlled. Therefore, it is a technical problem to be solved in the field to develop a new type of ZnGa2O4:Cr 3+ PLNPs material that can be prepared by a mild hydrothermal method and has high-intensity and long-lifetime luminescence performance, and to expand its application in high-sensitivity detection.

[0004] On the other hand, the pollution of nanoscale plastic particles (Nanoplastics, NPs) in the environment is increasingly serious, especially polystyrene nanoplastics (PS NPs), which pose a potential threat to the ecological system and human health. However, it is still a great challenge to detect trace amounts of PS NPs in the environment quickly, highly sensitively and highly specifically. Traditional methods such as chromatography and mass spectrometry have problems such as complex pretreatment, expensive equipment and difficulty in on-site detection. Although the antibody-based immunoassay has specificity, the antibody is high in cost, poor in stability, and susceptible to interference from complex environmental matrices.

[0005] In recent years, although some studies have attempted to use functional nanomaterials for pollutant detection, when they are used for PS NP detection, the following problems are still generally faced: (1) the detection sensitivity is insufficient, and it is difficult to achieve pg mL -1 level trace detection; (2) poor specificity, which cannot effectively distinguish PS from other types of nano-plastics (such as PP, PE, PVC, etc.); (3) the detection process is complex, is easily disturbed by environmental matrix, and has poor recovery rate and stability in actual samples.

[0006] In view of this, the present application is proposed. SUMMARY

[0007] The present application aims to at least solve any one of the above technical problems, and provides long afterglow nanoparticles, nanoprobes, a double-probe system and a detection method.

[0008] To achieve the above-mentioned purpose, the first technical solution adopted by the present application is:

[0009] Long afterglow nanoparticles, whose chemical formula is Li x Zn 1-x Ga2O4:Cr³⁺, wherein the value of x ranges from 0.1 to 0.5.

[0010] Preferably, the value of x is 0.3 or 0.5.

[0011] Preferably, the preparation method is as follows: dissolving zinc source, gallium source, lithium source and chromium source in water, adjusting the pH of the solution to alkaline, and then separating the long afterglow nanoparticles after hydrothermal reaction.

[0012] Preferably, the temperature of the hydrothermal reaction is 200-220°C, and the reaction time is 18-24 hours.

[0013] The second technical solution adopted by the present application is:

[0014] Nanoprobes, comprising the long afterglow nanoparticles of the first technical solution and a hydroxyethyl deacetylated chitin layer modified on the surface thereof, i.e. PLNPs@GCS probes.

[0015] Preferably, the mass ratio of long afterglow nanoparticles to hydroxyethyl deacetylated chitin raw material is 1: (1-10).

[0016] The third technical solution adopted by the present application is:

[0017] A double-probe system for detecting polystyrene nano-plastics, comprising the nanoprobes of the second technical solution; and Fe3O4@Au-PSBP probes, which are coupled by gold-coated magnetite magnetic balls and polystyrene-specific polypeptides.

[0018] Preferably, the PLNPs@GCS probe and the Fe3O4@Au-PSBP probe form a complex through electrostatic interaction and polystyrene nano plastic bridging.

[0019] The fourth technical solution adopted by the present application is:

[0020] The method for detecting polystyrene nano plastic is characterized in that the double-probe system of the third technical solution is used for detection, and the method comprises the following steps:

[0021] The sample to be detected is contacted with the PLNPs@GCS probe and the Fe3O4@Au-PSBP probe to form a complex bridged by polystyrene nano plastic, and the unreacted free probe is removed;

[0022] The complex is treated under conditions suitable for dissociation of the PLNPs@GCS probe, and the Fe3O4@Au-PSBP probe is removed by magnetic separation;

[0023] The afterglow luminescence signal of the separated PLNPs@GCS probe is detected, and the content of polystyrene nano plastic in the sample is determined according to the signal intensity.

[0024] Preferably, the method for determining the content of polystyrene nano plastic in the sample according to the signal intensity is: comparing the measured afterglow luminescence signal intensity with a standard curve of polystyrene nano plastic concentration and afterglow luminescence signal intensity established in advance to determine.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] The long-afterglow nano particles provided by the present application are synthesized by doping Li + partly replace Zn 2+ The innovative doping strategy successfully solves the industry problem of poor luminescence performance of ZnGa2O4:Cr 3+ PLNPs. The doping of Li + effectively optimizes the crystal lattice structure and the concentration and depth of electron traps, so that the afterglow intensity and average lifetime of the material in the near-infrared window (~700 nm) are greatly enhanced; by accurately adjusting the doping ratio x, the luminescence intensity or afterglow time of the material can be optimized to meet the needs of different application scenarios. At the same time, the material has excellent chargeability and can be repeatedly activated by ultraviolet light or LED red light to realize a repeatable decay cycle, which is extremely practical; the material can be synthesized by one-step hydrothermal method, avoiding the high energy consumption and particle agglomeration problems of high-temperature solid-phase method, and realizing low-temperature, green and controllable synthesis of small-size, high-crystallinity and high-performance PLNPs.

[0027] The PLNPs@GCS probe provided by the application is modified with a hydroxyethyl deacetylated chitin (GCS) layer on the surface of the long afterglow nanoparticle, and the probe has a unique pH response charge conversion capability, is positively charged on the surface under acidic conditions, can be combined with PS NPs with negative charge with high efficiency, and is negatively charged on the surface under alkaline conditions, can be effectively dissociated from the Fe3O4@Au-PSBP-PS complex with negative charge all the time, and this characteristic is the core of realizing high sensitivity and low background detection; the GCS shell not only provides good water solubility and dispersion stability for the PLNPs, but also lays a foundation for subsequent potential in-vivo application due to its natural biocompatibility; the surface modification process does not damage the excellent long afterglow performance of the PLNPs core, so that the PLNPs core becomes a stable, reliable and self-fluorescent signal reporting unit.

[0028] The "magnetic separation probe (Fe3O4@Au-PSBP) + signal probe (PLNPs@GCS)" double-probe system provided by the application is used for detecting PS NPs, based on the highly specific target recognition capability of the PSBP polypeptide to PS NPs, can effectively distinguish PS from other common nano-plastics (such as PP, PE, PET, PVC, etc.), and ensures the specificity of detection from the source; the Fe3O4 magnetic core makes the separation operation in the whole detection process fast, simple, efficient, easy to realize automation, and can effectively enrich the target, and reduce the matrix interference; PS NPs act as a "bridge" to convert the concentration information into the number of complex that can be magnetically separated, and then amplify and output the afterglow signal of the dissociated PLNPs@GCS, so as to realize the sensitive conversion from the recognition event to the optical signal.

[0029] The method for detecting polystyrene nano-plastics provided by the application makes full use of the advantages of long afterglow luminescence without background interference and the double-probe signal amplification mechanism, and the detection limit of PS NPs is as low as 0.033 pg mL -1 , the linear range is wide (0.01 pg mL -1 - 800 pg mL -1 ), far exceeding the existing detection technology; the method can also effectively exclude the interference of complex environmental matrix, and has excellent spiked recovery rate (92.59% - 104.70%) and small relative standard deviation (RSD) in actual sample detection, and has good repeatability; the method does not need large and expensive instruments, the detection process can be completed in a short time, and the probe can be repeatedly charged and used, which significantly reduces the cost of single detection, and provides a powerful practical tool for large-scale environmental screening and daily monitoring of PS NPs. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Fig. 1 is a schematic diagram of the synthesis process of the Fe3O4@Au-PSBP magnetic separation probe according to the application; Figs. 2 (a) and (b) are Li x Zn1-x Ga2O4:Cr 3+ TEM images, particle size distribution (n=200) of Li

[0031] Figure 2 (a), (b) are Li x Zn 1-x Ga2O4:Cr 3+ XRD patterns, relative intensity of 311 crystal plane crystallinity (100% for x=0) of Li

[0032] Figure 3 (a), (b) are Li x Zn 1-x Ga2O4:Cr 3+ (x=0-0.5), (c) is Li x Zn 1-x Ga2O4:Cr 3+ (x=0.3) afterglow emission spectrum; (d) is Li x Zn 1-x Ga2O4:Cr 3+ (x=0-0.5) afterglow decay curve;

[0033] Figure 4 (a), (b), (c), (d), (e), (f) are Li x Zn 1-x Ga2O4:Cr 3+ (x=0-0.5) re-excitation afterglow decay curve;

[0034] Figure 5 (a) is the afterglow emission spectrum of Li2Ga2O4:Cr; (b) is the transmission electron microscope image of Li2Ga2O4:Cr;

[0035] Figure 6 (a) is the diffuse reflectance spectrum of Li x Zn 1-x Ga2O4:Cr 3+ (x=0-0.5), (b), (c), (d), (e), (f), (g) are Kubelka-Munk plots of Li x Zn 1-x Ga2O4:Cr 3+ (x=0-0.5) when x=0, x=0.1, x=0.2, x=0.3, x=0.4, x=0.5, respectively.

[0036] Figure 7 (a), (b) are Li + Zn 3+ TSL spectra of PLNPs, luminescence mechanism diagram;

[0037] Figure 8 (a), (b), (c) are TEM images, particle size distribution diagrams, and energy spectrum element distribution diagrams of PLNPs@GCS in Example 2, respectively;

[0038] Figure 9 (a), (b) are zeta potential characterization diagrams and infrared characterization diagrams of PLNPs, PLNPs-OH, PLNPs-NH2 and PLNPs@GCS in Example 2, respectively; (c) is a zeta potential change diagram of PLNP@GCS under different pH conditions; (d) is a thermogravimetric analysis diagram of PLNPs and PLNPs@GCS;

[0039] Figure 10 (a) is a photoluminescence spectrum of Fe3O4@Au-PSBP, PLNPs@GCS and Fe3O4@Au-PSBP-PLNPs@GCS complex in Example 4; (b), (c), (d) are influence diagrams of PLNPs@GCS dosage, detection time, and composite probe separation time on detection signal, respectively;

[0040] Figure 11 (a) is a change of afterglow luminescence signal in the system solution after magnetic separation with PS NPs in Example 4; (b) is a relationship diagram of change value of afterglow luminescence intensity in the solution after magnetic separation and PS NPs concentration; (c) is the selectivity of PS NPs detection. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be clearly and completely described below. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased in the market.

[0042] The first embodiment of the present application provides long afterglow nanoparticles, whose chemical general formula is Li x Zn 1-x Ga2O4:Cr³⁺, wherein the value range of x is 0.1-0.5.

[0043] The present application creatively introduces Li + Zn 3+ PLNPs, Li+ doped with a part of zinc ions Zn 2+ and precisely control the Zn / Li ratio x, synthesize Li x Zn 1-x Ga2O4:Cr³⁺ has excellent long-time near-infrared (NIR) luminescence performance, maintains the original nanoscale size advantage (<40 nm), increases new traps and deepens the intrinsic trap depth, significantly optimizes the defect structure and luminescence performance of the material, and improves the afterglow luminescence (PL) intensity and lifetime of ZnGa2O4:Cr 3+ The long afterglow nanoparticle PLNPs have a cubic spinel structure, the crystallinity of the 311 crystal face increases with the increase of x, and reaches the maximum value when x=0.3; the long afterglow nanoparticle PLNPs have a near-infrared afterglow emission peak at 700 nm, and can be repeatedly activated by ultraviolet light or red light.

[0044] In some preferred embodiments, the value of x is 0.3 or 0.5.

[0045] The long afterglow nanoparticle preparation method used in the application is a commonly used hydrothermal synthesis method, and the preparation method is as follows: dissolving zinc source, gallium source, lithium source and chromium source in water, adjusting the pH of the solution to alkaline, and then separating the nanoparticles after hydrothermal reaction. The specific parameters are not limited, and the skilled person in the art can select appropriate parameters according to the adaptability of the raw materials.

[0046] As an example, Zn 2+ , Ga 3+ , Li + , Cr 3+ are mixed under vigorous stirring, the pH value is adjusted to 8-9, the obtained turbid solution is stirred vigorously at room temperature for 1 h-2 h, hydrothermal reaction is carried out at 200°C-220 °C for 18 h-24 h, and the nanoparticles are collected by centrifugation and washed. The zinc source, gallium source, lithium source and chromium source used can be zinc nitrate hexahydrate, gallium nitrate, lithium nitrate and chromium nitrate, respectively.

[0047] The second embodiment of the application provides a nanoprobe, which comprises the long afterglow nanoparticle of the first embodiment and a hydroxyethyl deacetylated chitin layer modified on the surface of the long afterglow nanoparticle, i.e. a PLNPs@GCS probe.

[0048] After the PLNPs are modified by GCS, the obtained PLNPs@GCS probe has a clear core-shell structure, the thickness of the GCS shell layer on the surface is about 2 nm, and the particle size is about 23 nm. The pH-responsive charge conversion ability is endowed to the PLNPs@GCS probe by the GCS surface modification, the protonation of the free amino groups in the GCS skeleton is enhanced in an acidic environment, the probe is positively charged, can be combined with PS NPs which are negatively charged with high efficiency, and the surface of the probe is negatively charged in an alkaline environment.

[0049] The preparation method of the PLNPs@GCS probe is not particularly limited, and GCS can be loaded on the surface of the PLNPs, and those skilled in the art can select a suitable preparation method according to the modification component and the modification object. For example, the surface of the PLNPs is sequentially modified by hydroxylation, amination, and amide reaction of GCS. The grafting amount of GCS is directly related to the pH-responsive charge conversion ability of the PLNPs@GCS probe, and therefore the grafting amount of GCS can be adaptively adjusted by those skilled in the art according to the required response pH of the raw material amount of PLNPs and GCS. For example, the mass ratio of PLNPs to GCS raw material is 1: (1-10), and at this time, the grafting amount of hydroxyethyl chitosan on the surface of the nanoprobe is about 0.047 mg GCS per 1 mg PLNPs.

[0050] As a specific example: 1) hydroxylation modification: uniformly disperse the PLNPs in a NaOH solution, and vigorously stir for 10 h-16 h to obtain a hydroxylated long afterglow nanomaterial (PLNPs-OH), centrifuge, wash, and vacuum dry; 2) amination modification: uniformly disperse the PLNPs-OH in an anhydrous ethanol solution, dropwise add 3-aminopropyltriethoxysilane under magnetic stirring, stir the mixture at 60°C for 12 h-14 h, centrifuge to collect the obtained amino-functionalized long afterglow nanomaterial (PLNPs-NH2), and wash and dry; 3) amide reaction modification of GCS: uniformly mix a PBS solution of the PLNPs, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC), and N-hydroxysuccinimide (NHS), pre-activate under electromagnetic stirring at room temperature for 2 h-4 h, then add GCS, adjust the pH value of the reaction system to 7.5-8.5, stir the reaction at 60°C for 10 h-14 h, centrifuge, wash, and then disperse the precipitate in a PBS solution (pH 5.5 and pH 7.4), and store at 4°C for use.

[0051] The third embodiment of the present application provides a double-probe system for detecting polystyrene nano-plastic, which comprises the nanoprobe of the second embodiment; and a Fe3O4@Au-PSBP probe coupled by a gold shell-wrapped ferrite magnetic ball and a polystyrene-specific polypeptide.

[0052] The amino acid sequence of the polystyrene-specific polypeptide PSBP is CHWGMWSY, cysteine-histidine-tryptophan-glycine-methionine-tryptophan-serine-tyrosine.

[0053] In the dual-probe system, the potential of Fe3O4@Au-PSBP is negative and does not change with pH, the potential of PLNPs@GCS is positive under acidic conditions and is negative under alkaline conditions, and the system can be converted between electrostatic adsorption and electrostatic repulsion according to the change in pH. Based on this characteristic, Fe3O4@Au-PSBP serves as a magnetic separation probe, and PLNPs@GCS serves as a pH-responsive signal probe. The two can form a complex through electrostatic interaction and the bridging of polystyrene nanoplastics. Based on the high specificity of the PSBP polypeptide for PS NPs, the system can effectively distinguish PS from other common nanoplastics, thereby ensuring the specificity of the detection from the source. The Fe3O4 magnetic core makes the separation operation in the entire detection process fast, simple, efficient, easy to automate, and can effectively enrich the target and reduce matrix interference. PS NPs serve as a "bridge" to convert the concentration information into the number of magnetically separable complexes, and then amplify and output the afterglow signal of the dissociated PLNPs@GCS, thereby realizing the sensitive conversion from the recognition event to the optical signal.

[0054] The preparation method of the Fe3O4@Au-PSBP probe is a method commonly used in the art, and PSBP can be used to modify the gold-coated magnetite. As a specific example, after dissolving PSBP in dimethyl sulfoxide (DMSO), Fe3O4@Au is mixed for 12-24 hours, and then the unreacted peptide is discarded by magnetic separation, and the Fe3O4@Au-PSBP probe is collected and washed.

[0055] The fourth embodiment of the present application provides a method for detecting polystyrene nanoplastics, which uses the dual-probe system of the third embodiment for detection, and includes the following steps:

[0056] The sample to be tested is contacted with the PLNPs@GCS probe and the Fe3O4@Au-PSBP probe to form a complex bridged by polystyrene nanoplastics, and the unreacted free probe is removed.

[0057] The complex is treated under conditions suitable for dissociation of the PLNPs@GCS probe, and the Fe3O4@Au-PSBP probe is removed by magnetic separation;

[0058] The afterglow luminescence signal of the separated PLNPs@GCS probe is detected, and the content of polystyrene nanoplastics in the sample is determined according to the signal intensity.

[0059] The detection method utilizes the negative charge of PS NPs and the pH-responsive charge conversion characteristics of PLNPs@GCS probes as switches to control the "opening" and "closing" of the signal. The main principle is "double probe complexation-dissociation-detection". In the initial state, the black Fe3O4@Au-PSBP is combined with the luminescent PLNPs@GCS, resulting in light shielding and signal closure. The number of captured PS NPs determines how much negative charge Fe3O4@Au-PSBP can capture after capture, thereby attracting more positively charged PLNPs@GCS through electrostatic adsorption, and removing the unquenched PLNPs@GCS probes by magnetic separation. When the pH is switched to alkaline, the PLNPs@GCS reverses from positive to negative, and the attracted PLNPs@GCS probes are released for detection by electrostatic repulsion. The higher the concentration of PS NPs in the sample, the more negative charge Fe3O4@Au-PSBP can capture after capturing PS, which can attract more positively charged PLNPs@GCS. Therefore, the more PLNPs@GCS is released after pH switching, and the stronger the afterglow signal detected. −1 -800 pg mL −1 , the detection limit is as low as 0.033 pg mL −1 .

[0060] As some preferred embodiments, during the detection process, the amount of PLNPs@GCS is 300 μL-700 μL, and the amount of Fe3O4@Au-PSBP is 150 μL-250 μL; the detection time, i.e., the time for Fe3O4@Au-PSBP probe to capture PS and contact with PLNPs@GCS, is generally controlled to be 20 min-90 min; the separation time, i.e., the time for PLNPs@GCS to dissociate from the combination of Fe3O4@Au-PSBP and PS, is generally controlled to be 30 min-70 min.

[0061] Due to the "fingerprint" characteristic peak of Cr 3+ luminescent center at about 700 nm, in order to obtain the strongest luminescent signal and avoid background interference as much as possible, the afterglow luminescent signal intensity of the PLNPs@GCS at 700 nm wavelength is detected.

[0062] In some preferred embodiments, the measured afterglow luminescent signal intensity is compared with the standard curve of PS NPs concentration and afterglow luminescent signal intensity established in advance to determine the content of polystyrene nanoplastics in the sample.

[0063] A number of specific embodiments are provided below to illustrate long persistent nanoparticles, nanoprobes, dual-probe systems and detection methods in detail, and to characterize the corresponding performance.

[0064] Some reagents used in the following examples are as follows:

[0065] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 99.99%), gallium nitrate (Ga(NO3)3, 99.99%), chromium nitrate (Cr(NO3)2·9H2O, 99.99%), lithium nitrate (LiNO3, 99.99%), Ethyldimethylaminopropyl carbodiimide (EDC), N-Hydroxysuccinimide (NHS), Glycol chitosan (GCS) were purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd. (Shanghai, China); 3-Aminopropyltriethoxysilane (APTES) was purchased from Sangon Biotech (Shanghai) Co., Ltd. (Shanghai, China); ultrapure water was purchased from Wahaha Group Co., Ltd. (Hangzhou, China); Ga(NO3)3solution (0.5 mol L −1 ), Zn(NO3)2solution (0.5 mol L −1 ), LiNO3solution (1 mol L −1 ), and Cr(NO3)2solution (0.01 mol L −1 ) were used as precursor solutions.

[0066] Example 1. Preparation and characterization of long persistent nanoparticles

[0067] 1.1 Preparation of long persistent nanoparticles: According to the general chemical formula Li x Zn 1-x Ga2O4:Cr 3+ , the amounts of each raw material were determined, Zn(NO3)2·6H2O, Ga(NO3)3, Cr(NO3)2·9H2O, and LiNO3 were mixed uniformly under vigorous stirring, the pH value was adjusted to 8-9, the resulting turbid solution was stirred vigorously at room temperature for 1 h-2 h, and reacted at 200 °C-220 °C for 18 h-24 h. The prepared nanoparticles were collected by centrifugation, washed twice with ultrapure water, and finally washed with anhydrous ethanol. The ratio x of Zn 2+ and Li + precursor solutions was adjusted according to the above method, and PLNPs with different Li ion doping concentrations were similarly synthesized.

[0068] 1.2 Effect of Li ion doping on morphology and crystal structure: To systematically investigate the effect of Li + doping on the nanoparticles, the size and crystal structure of the nanoparticles were studied by transmission electron microscopy (TEM) and x-ray powder diffraction (XRD), and the results are shown in Figures 1-2 . It should be noted that x in the general formula represents the degree of Li + substitution for Zn 2+ , i.e., the amount of Li + in the precursor solution.

[0069] As can be seen from Figure 1 , in the absence of Li + (x = 0), the obtained ZnGa2O4:Cr 3+ PLNPs are spherical, and with the addition of Li + , the obtained Li x Zn 1-x Ga2O4:Cr 3+ PLNPs gradually become rhombohedral, and doping has no obvious effect on the size of the PLNPs. As can be seen from Figure 2 (a), the prepared Li x Zn 1-x Ga2O4:Cr 3+ (x = 0-0.5) nanocrystals have a highly crystalline typical cubic spinel structure (JCPDS 86-0413), i.e. Figure 2 , the PDF #86-0413 sample in (a) is consistent with the cubic spinel structure regardless of the Li + ion doping concentration. As can be seen from Figure 2 (b), with the increase of the amount of Li + ion doping, the crystallinity of the 311 crystal plane gradually increases and reaches a maximum at x = 0.3. The elemental composition of the synthesized Li x Zn 1-x Ga2O4:Cr 3+ was characterized by ICP-MS, and the results are shown in Table 1. As can be seen from Table 1, the content of Li element increases with the increase of the addition amount, and the content of Zn element gradually decreases, which confirms the successful doping of Li element.

[0070] Table 1: ICP-MS elemental quantification (x = 0-0.5)

[0071] .

[0072] 1.3 Effect of Li ion doping on optical properties: The excitation spectrum, emission spectrum and decay spectrum were measured by a fluorescence spectrophotometer to study the effect of Li +Doping effect on persistent luminescence, the specific method as follows. (1) Li x Zn 1- x Ga2O4:Cr 3+ Nanoparticle afterglow emission spectrum measurement: under phosphorescence mode, Li x Zn 1-x Ga2O4:Cr 3+ The solid powder gets the emission spectrum. (2) Excitation spectrum: using fluorescence spectrophotometer, fixing the characteristic emission peak of 700 nm, measuring Li x Zn 1-x Ga2O4:Cr 3+ The solid powder gets the excitation spectrum. (3) Afterglow decay image: in the imaging experiment, using UV lamp (254 nm) as light source, placing 50 mg of Li x Zn 1-x Ga2O4:Cr 3+ (x=0.3) nanoparticles in 96-well plate, irradiating PLNPs for a fixed time, after light irradiation, placing the 96-well plate in IVIS imaging system to collect decay image, then analyzing the persistent luminescence of each sample by radiation intensity. (4) Afterglow decay curve: the sample is excited by 254 nm UV lamp for 5 min before measurement, recording the decay curve after 15 s of excitation stop, and normalizing the curve with the strongest PL intensity as 1. The PLNPs lifetime is fitted by multi-exponential decay fitting method, and is fitted by three-exponential decay fitting method (ExpDec3): I( T )=I0+A1exp(−t / τ1)+A2exp(−t / τ2)+A3exp(−t / τ3). Where I0 is the initial afterglow intensity, I( T ) is the afterglow intensity at time t; A1, A2 and A3 are constants; τ1, τ2 and τ3 are the lifetimes of three different decay processes. (5) Re-excitation afterglow decay curve: the sample is excited by 254 nm UV lamp for 5 min before measurement (i.e. the first decay curve), then activated by red LED lamp for 2 min every 1000 s, and the re-excitation afterglow decay curve is recorded after 15 s of excitation stop. The results are shown in Figures 3-4 , Tables 2-3.

[0073] From Figure 3 (a) it can be seen that the PL of Li ion doped PLNPs has enhanced luminescence intensity, and the maximum luminescence intensity from x=0 to x=0.5 is respectively: 1650, 2299, 2627, 2906, 1951 and 2790, which reaches the maximum at x=0.3; from Figure 3 (b) it can be seen that the excitation peak has a slight red shift; from Figure 3(c) It can be seen that the PL can last for 6 h after the excitation light is stopped, and can be repeatedly excited by red LED light; from Figure 3 (d) It can be seen that the Li-ion doped PLNPs show slower decay in the PL decay curve, and the maximum luminescence lifetime is x=0.5, while x=0.3 is only second to x=0.5. From Table 2 and Table 3, it can be seen that the best average lifetime of the Li-ion doped PLNPs is 30% longer than that of the PLNPs without Li-ion doping (τ av (x=0.5)=36.07 s, τ av (x=0)=8.84 s).

[0074] From Figure 4 it can be seen that the Li x Zn 1-x Ga2O4:Cr 3+ (x=0-0.5) shows excellent chargeability under the condition of UV (254 nm) and visible light (650 nm red LED light) re-excitation, and has a repeatable decay cycle. Figure 5 It can be seen that the applicant tried to adjust the Li-ion doping ratio to 100%, that is, completely replace the Zn ions, but the particle size of Li2Ga2O4:Cr obtained is about 1.8 μM, and has no photoluminescence property. In summary, the appropriate doping of Li ions can effectively improve the PL intensity and lifetime of ZnGa2O4:Cr 3+ . x Zn 1-x Ga2O4:Cr 3+ has excellent long-time NIR luminescence performance.

[0075] Table 2: Decay parameters of the afterglow decay curve fitting

[0076]

[0077] Table 3: Average afterglow lifetime of Li x Zn 1-x Ga2O4:Cr 3+

[0078] .

[0079] 1.4 Mechanism study of the influence of Li-ion doping on optical properties

[0080] By diffuse reflectance spectroscopy combined with Tauc plotting method and Kubelka-Munk function conversion, the optical band gap (Eg) of Li x Zn 1-x Ga2O4:Cr 3+ (x=0-0.5) was estimated, and the results are as follows​Figure 6 As shown, the calculated values ​​of Eg are 4.12 eV (x=0), 4.42 eV (x=0.1), 4.12 eV (x=0.2), 3.96 eV (x=0.3), 3.91 eV (x=0.4), and 4.27 eV (x=0.5). Li + After ion doping, Li x Zn 1-x Ga2O4:Cr 3+ The band gaps (x=0.3 and x=0.4) are slightly narrower than the band gap (x=0), which means that under UV excitation, electrons are more likely to be excited from the valence band to the conduction band, thus enhancing the electron transition efficiency to some extent.

[0081] Thermoluminescence (TL) spectroscopy was further investigated to understand its mechanism. TL measurement is a common tool for studying the properties and distribution of electron traps in fluorescent materials. The results are as follows: Figure 7 As shown in (a), for undoped Li + ZnGa2O4:Cr 3+ PLNPs exhibit a pristine TL peak at approximately 338.2 K. However, in Li... + In doped PLNPs, the intensity of the original TL peak increases, indicating an increase in the concentration of intrinsic electron traps. Furthermore, the TL peak associated with intrinsic electron traps undergoes a slight shift upon mg doping (when x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, Li...). x Zn 1-x Ga2O4:Cr 3+ The TL peaks are at 338.2, 345.2, 339.2, 345.6, 345.2, and 351.4 K, respectively. Interestingly, Li... + When the doping concentrations are x=0.2 and x=0.3, new peaks appear at approximately 420 K and 410 K, respectively, with the peaks reaching their maximum at x=0.3. In the above PL decay curves, when x=0.5, Li... x Zn 1-x Ga2O4:Cr 3+ PL is the largest. (Reference) Figure 7 (b) shows the luminescence mechanism diagram, which is mainly because excessively low concentration and depth of electron traps can affect afterglow performance. Considering the key role of electron trap concentration and depth in the afterglow mechanism, the integral area under the TL intensity (299K to 450K) curves was further compared, and the results are shown in Table 4. This reflects the concentration in the shallow layer, where the concentration in the shallow layer is the highest at x=0.5, which corresponds to the longest afterglow decay time at x=0.5.

[0082] Table 4: Integral area under the TL intensity (299 K to 450 K) curve

[0083] .

[0084] From the above, it can be seen that when the Li content (x = 0.3) is moderate, the PL intensity reaches the highest; and when the Li content (x = 0.5) is further increased, the afterglow duration is significantly prolonged. This indicates that Li + doping effectively improves the luminescent performance of ZnGa2O4:Cr by regulating the electron trap concentration and depth. However, excessive Li + doping (x > 0.5) instead reduces the luminescent efficiency, highlighting the importance of precisely controlling the doping ratio. In addition, Li + doping has no obvious effect on the size of the PLNPs, and the doped material exhibits excellent chargeability, enabling repeatable decay cycles, providing stability assurance for its practical application. Thermoluminescence spectral analysis further reveals the mechanism of Li + doping: the original TL peak intensity increases with the increase of Li⁺ doping amount, indicating that the inherent electron trap concentration in the material is improved, thereby delaying the carrier release process and prolonging the afterglow time.

[0085] Example 2 Preparation and characterization of PLNPs@GCS probes

[0086] 2.1 Preparation of PLNPs@GCS probes: 1) Hydroxylation modification: 80 mg-120 mg of PLNPs was ultrasonically dispersed in 80 mL-120 mL of NaOH (5 mmolL −1 ) solution, and stirred vigorously for 10 h-16 h to obtain hydroxylated long afterglow nanomaterials (PLNPs-OH), which were centrifuged, washed with ultrapure water three times and vacuum dried;

[0087] 2) Amino modification: 80 mg-120 mg of PLNPs-OH was ultrasonically dispersed in anhydrous ethanol solution (80 mL-120 mL), and 3-aminopropyltriethoxysilane (300 μL-500 μL) was added dropwise under magnetic stirring at 60°C for 12-14 h. The obtained amino-functionalized long afterglow nanomaterials (PLNPs-NH2) were collected by centrifugation, washed with anhydrous ethanol, and dried under vacuum for later use;

[0088] 3) Amide reaction modification of GCS: 4 mg mL −1 -6 mg mL −1PLNPs PBS solution (pH 5.5-pH 6.5) were added 13 mg-18 mg EDC and 40 mg-50 mg NHS, respectively, and pre-activated for 2-4 h under electromagnetic stirring at room temperature, then 80 mg-120 mg GCS was added and the pH value of the reaction system was adjusted to 7.5-8.5 using NaOH solution (concentration of 1 mol L −1 ); the reaction solution was stirred at 60 ℃ for 10 h-14 h, then centrifuged, washed with ultrapure water, and the precipitate was redispersed in PBS solution (pH 5.5 and pH 7.4) and stored at 4 ℃ for use.

[0089] 2.2 Functional characterization of PLNPs@GCS probes

[0090] According to the preparation method of 1.1 and 2.1, the prepared PLNPs@GCS probes (x=0.3, GCS grafting amount of 0.047 mg GCS per 1 mg PLNPs) were characterized for functionalization. Figure 8 (a) Transmission electron microscopy showed that the PLNPs@GCS probes modified by GCS showed a clear core-shell structure, and the thickness of the GCS shell on the surface was about 2 nm. Figure 8 (b) The particle size distribution graph showed that the particle size increased from about 14 nm to about 23 nm. Figure 8 (c) The energy spectrum analysis element distribution graph showed that the HAADF was a high-angle annular dark field image, and the results showed that Zn, Ga and O elements were mainly enriched in the core region of PLNPs, while N and C elements were uniformly distributed in the entire nanostructure.

[0091] From Figure 9 (a) potential characterization, the potential of unmodified PLNPs was-8.31 mV, and the potential of hydroxyl and amino modified PLNPs was-23.21 mV and 3.99 mV, respectively. The GCS shell was modified by amide reaction, and the potential was positive at pH=5.5, and the potential was negative at pH=7.4, which was due to the successful modification of GCS with charge conversion ability. In addition, the surface modification of PLNPs was further proved by Fourier transform infrared spectroscopy (FT-IR), from Figure 9 (b) FT-IR spectrum, it can be seen that PLNPs-NH2 appeared a new absorption peak Si−O−Si at 1001 cm −1 , which proved the successful modification of APTES, and after GCS functionalization, the absorption peak of- CO−NH− at 1636 cm −1 was observed, in addition, 2929 cm −1 and 2858 cm −1Symmetric and asymmetric stretching vibrations of C-H and GCS stretching vibrations at 1091 cm −1 all proved the successful modification of GCS. Further exploration of the pH-dependent effect of GCS surface modification on the surface charge of PLNPs@GCS showed that Figure 9 (c) confirmed that it endowed the material with the ability of pH-responsive charge conversion, and the enhanced protonation of free amino groups in the GCS skeleton in an acidic environment caused the charge conversion of PLNPs@GCS with pH changes. Figure 9 (d) The thermogravimetric analysis (TGA) curve showed that the weight loss below 200°C was mainly due to the desorption of water adsorbed by the material, while the weight loss in the range of 200°C to 800°C was mainly caused by the thermal decomposition of the GCS shell in PLNPs@GCS, with a weight loss rate of 4.5%. Accordingly, the grafting amount of GCS on the surface of PLNPs was calculated to be 0.047 mg / mg PLNPs (i.e. 0.047 mg of GCS was loaded per mg of PLNPs).

[0092] Example 3 Preparation of Fe3O4@Au-PSBP probe

[0093] PSBP was dissolved in dimethyl sulfoxide (DMSO) at a concentration of 2 mg mL −1 and stored as a stock solution at 4°C, and diluted with water to 0.4 mg mL −1 ; then, 2 mL of PSBP (0.4 mg mL −1 ) was mixed with 2 mL of Fe3O4@Au (1 mg mL −1 ) for 12-24 h, and after magnetic separation, the unreacted peptide was discarded by magnetic separation, and the Fe3O4@Au-PSBP probe was collected and washed.

[0094] Example 4 Method for detecting polystyrene nano-plastic and optimization

[0095] 4.1 The double-probe system composed of Fe3O4@Au-PSBP and PLNPs@GCS synthesized in Example 3 was used to detect PS NPs. The specific method is as follows:

[0096] Standard curve construction: 2 mL of PS solution with different concentrations (0.01, 50, 300, 400, 800 pg mL −1) and 400 μL PLNPs@GCS probe, incubate for 20-120 min on a shaker, then remove the PLNPs@GCS probe that is not electrostatically combined with the Fe3O4@Au-PSBP probe by magnetic separation, and add PBS with pH 7.4 to redissolve to 3 mL, and incubate for 20-80 min on a shaker. After incubation, separate the Fe3O4@Au-PSBP probe, and measure the PL intensity of the remaining PLNPs@GCS probe at 700 nm; construct a standard curve according to the change in PL intensity; and quantify the PS concentration in the actual sample according to the standard curve.

[0097] The sample processing method is as follows: 0.35 g of edible salt is added to ultrapure water to dissolve and make up to 10 mL, and 10 mL of bottled drinking water is taken for standby; after sample preparation, 1 mL of bottled drinking water and edible salt solution is taken respectively, and 1 mL of PS (0, 200, 400, 800 pg mL −1 ) solution of different concentrations is added. After mixing, 200 μL Fe3O4@Au-PSBP probe and 400 μL PLNPs@GCS probe are added, incubated for 60 min on a shaker, then remove the PLNPs@GCS probe that is not electrostatically combined with the Fe3O4@Au-PSB probe by magnetic separation, and add PBS with pH 7.4 to redissolve to 3 mL, and incubate for 40 min on a shaker. After incubation, separate the Fe3O4@Au-PSBP probe, and measure the PL intensity of the remaining PLNPs@GCS probe at 700 nm, quantify the PS concentration in the sample according to the standard curve, and calculate the recovery rate.

[0098] The following three solutions are configured and the persistent luminescence emission spectrum is measured in the phosphorescence mode of the fluorescence spectrophotometer: 1) 200 μL Fe3O4@Au-PSBP probe and PBS with pH 7.4 to 3 mL; 2) 400 μL PLNPs@GCS probe and PBS with pH 7.4 to 3 mL; 3) 200 μL Fe3O4@Au-PSBP probe and 400 μL PLNPs@GCS probe mixed and PBS with pH 7.4 to 3 mL. The results are shown in Figure 10 (a). The results show that when the Fe3O4@Au-PSBP probe and the PLNPs@GCS probe are combined to form a composite probe by electrostatic action, the black Fe3O4@Au-PSBP probe will produce a light shielding effect on the PLNPs@GCS probe, resulting in a significant decrease in the PL signal of the PLNPs@GCS probe Figure 10a). Therefore, after detecting PS NPs, two-step separation operation is needed: the first step is to remove the unbound excess PLNPs@GCS probes; the second step is to dissociate the Fe3O4@Au-PSBP-PLNPs@GCS complex to separate the PLNPs@GCS probes for signal detection.

[0099] 4.2 Optimization of detection method: To improve the detection efficiency, the experimental conditions need to be optimized. The amount of Fe3O4@Au-PSBP probe (1 mg mL −1 ) is fixed at 200 μL, and the concentration of PS NPs is 400 pg mL −1 , the effect of the concentration of PLNPs@GCS probe, detection time and separation time on the detection of PS NPs by Fe3O4@Au-PSBP and PLNPs@GCS dual probe system is explored. Figure 10 (b) It can be seen that the afterglow intensity (700 nm) of the system gradually increases with the increase of the amount of PLNPs@GCS probe in the range of 100 μL-400 μL, and tends to balance at 400 μL. Further increase of the amount has little effect on the final afterglow signal intensity. It is speculated that the Fe3O4@Au-PSBP-PLNPs@GCS complex has reached a saturated state at 400 μL, and the excess PLNPs@GCS probe cannot be effectively combined with the Fe3O4@Au-PSBP probe. Then the effect of detection time on the final afterglow signal detection of the system is investigated, and the results are shown in Figure 10 (c). The effect of detection time on the afterglow intensity of the system shows a trend of first increasing and then decreasing. When the detection time is less than 60 min, the afterglow intensity increases, and reaches the maximum at 60 min. When the detection time exceeds 60 min, the afterglow intensity begins to decrease gradually. This may be because the long detection time leads to the loss of probes, reducing the final detection signal intensity. After determining the amount of probe and detection time, in order to ensure that the PLNPs@GCS probe in the Fe3O4@Au-PSBP-PLNPs@GCS complex can be fully dissociated, the time for separating the PLNPs@GCS probe is also investigated, and the results are shown in Figure 10 (d). The 40 min with the highest afterglow intensity is selected.

[0100] 4.3 Evaluation of detection performance: Under the optimal detection conditions of 4.2, the standard curve of PS NPs is constructed according to the method of 4.1, and the analysis performance of the method is evaluated. From Figure 11(a) It can be seen that after magnetic separation, the intensity of afterglow luminescence increases with the increase of PS NP concentration; this indicates that the higher the concentration of PS NPs, the more negatively charged PS NPs are captured by the Fe3O4@Au-PSBP probe, thus increasing the negative charge density on its surface, and consequently loading more PLNPs@GCS probe through electrostatic interaction, resulting in a higher intensity of afterglow luminescence. Figure 11 (b) It can be seen that at a PS NPs concentration of 0.01 pg / mL −1 -800 pg mL −1 Within the specified range, the concentration of PS NPs shows a linear relationship with ΔPL (the change in afterglow luminescence intensity at 700 nm), and the linear relationship is Y = 35.465 + 1.214X (X: PS NPs concentration, Y: ΔPL), R 2 The limit of detection (3s) was 0.9896. −1 .

[0101] As can be seen, this invention can achieve highly sensitive detection of polystyrene nanoplastics, with a detection range of 0.01 pg / mL. −1 –800 pg mL −1 The detection limit is as low as 0.033 pg mL. −1 .

[0102] 4.4 Specificity test for PS NPs detection: The test method is as follows: prepare 400 pg mL of PBS with pH 5.5. −1 200 μL of Fe3O4@Au-PSBP probe and 400 μL of PLNPs@GCS probe were added to 2 mL of PS, polypropylene (PP), polyethylene (PE), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) solutions. The mixture was incubated on a shaker for 60 min. Then, unbound PLNPs@GCS probes were magnetically separated, and the remaining PLNPs@GCS probes were redissolved in PBS (pH 7.4) to a final volume of 3 mL. The mixture was incubated on a shaker for 40 min. After incubation, the Fe3O4@Au-PSBP probe was separated, and the PLNPs@GCS probes at 700 nm were measured.

[0103] The results are as follows Figure 11As shown in (c), the results indicate that the detection system exhibits a specific response to PS NPs in PBS buffer, while showing no significant response to other nanoplastics (PP, PE, PMMA, PET, PVC), confirming its high specificity for PS NPs. Subsequently, the spiked recovery rate was tested in bottled drinking water and saline solution, and the results are shown in Table 5. The recovery rate in bottled drinking water was 96.16%–104.70%, and the recovery rate in saline solution was 92.59%–103.46%. This method can effectively overcome the interference of food matrices and demonstrates good practical application value.

[0104] Table 5: Spike Recovery Rate

[0105] .

[0106] The embodiments described above illustrate only a portion of the implementation methods of the present invention, and not all of them. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A nanoprobe, characterized in that, The probe comprises long-afterglow nanoparticles and a hydroxyethyl deacetylated chitosan layer modified on their surface, namely PLNPs@GCS probe; the chemical formula of the long-afterglow nanoparticles is Li. x Zn 1-x Ga2O4:Cr³⁺, where x ranges from 0.1 to 0.

5.

2. The nanoprobe as described in claim 1, characterized in that, The value of x is 0.3 or 0.

5.

3. The nanoprobe as described in claim 1 or 2, characterized in that, The method for preparing the long afterglow nanoparticles is as follows: zinc source, gallium source, lithium source and chromium source are dissolved in water, the pH of the solution is adjusted to alkaline, and the long afterglow nanoparticles are obtained after hydrothermal reaction.

4. The nanoprobe as described in claim 3, characterized in that, The hydrothermal reaction is carried out at a temperature of 200 ℃-220 ℃ for 18-24 hours.

5. The nanoprobe as described in claim 1, characterized in that, The mass ratio of long afterglow nanoparticles to hydroxyethyl deacetylated chitosan raw material is 1:(1-10).

6. A dual-probe system, characterized in that, For detecting polystyrene nanoplastics, the nanoprobes according to any one of claims 1-5 are included; and the Fe3O4@Au-PSBP probe is composed of a gold-shelled magnetite sphere coupled with a polypeptide that specifically binds to polystyrene.

7. The dual-probe system as described in claim 6, characterized in that, PLNPs@GCS probes and Fe3O4@Au-PSBP probes form a composite through electrostatic interaction and bridging by polystyrene nanoplastics.

8. A method for detecting polystyrene nanoplastics, characterized in that, Detection using the dual-probe system as described in claim 6 or 7 includes the following steps: The sample to be tested is brought into contact with PLNPs@GCS probe and Fe3O4@Au-PSBP probe to form a composite bridged by polystyrene nanoplastics, and unreacted free probes are removed. The composite was treated under conditions suitable for the dissociation of the PLNPs@GCS probe, and the Fe3O4@Au-PSBP probe was removed by magnetic separation. The afterglow emission signal of the separated PLNPs@GCS probe was detected, and the content of polystyrene nanoplastics in the sample was determined based on the signal intensity.

9. The method for detecting polystyrene nanoplastics as described in claim 8, characterized in that, The method for determining the content of polystyrene nanoplastics in a sample based on signal intensity is as follows: the measured afterglow emission signal intensity is compared with a pre-established standard curve of polystyrene nanoplastic concentration and afterglow emission signal intensity.

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