Imaging photothermal gold shell coated long afterglow nanomaterial and preparation and application thereof

Abstract

The application provides a kind of imaging photothermal gold shell coated long afterglow nanomaterial and its preparation and application.The nanomaterial includes Cr doped zinc-gallium-germanium oxide long afterglow nanometer core, mesoporous silica shell layer coated on the surface of the nanometer core and gold shell layer coated on the outer surface of the mesoporous silica shell layer.The preparation method includes: hydrothermal reaction and calcination to prepare long afterglow nanometer core;Under the condition of alkali, make tetraethyl orthosilicate (TEOS) hydrolysis and condensation to form mesoporous silica shell layer, remove template and carry out amination under cetyltrimethylammonium bromide (CTAB) template;Gold ions are adsorbed on the aminated surface and reduced to form gold seeds using borohydride, and gold shell layer is formed by promoting growth using hydroxylamine salt in a gold precursor solution containing carbonate.The obtained nanomaterial has near-infrared long afterglow luminescence capability, and generates photothermal heating under 808 nm laser irradiation, which can be used for bacterial imaging and photothermal treatment of bacterial samples.

Description

Technical Field

[0001] This invention relates to the field of nanoluminescent materials and bio-optical imaging technology, specifically to a core-shell structured nanomaterial that combines near-infrared long-persistence luminescence imaging and near-infrared photothermal conversion capabilities, its preparation method, and its application in microbial imaging and photothermal processing. Background Technology

[0002] Long-persistent luminescence nanoparticles (PLNPs) are phosphorescent luminescent materials that continue to emit light for a period of time after the external excitation source is removed. Compared with traditional fluorescence imaging, which requires continuous excitation light, PLNPs avoid continuous excitation during the signal acquisition phase, thereby reducing the influence of background autofluorescence and scattered light. This is beneficial for improving the imaging signal-to-noise ratio and reducing the photodamage that may be caused by continuous illumination. In recent years, Cr... 3+ Near-infrared luminescent long-afterglow nanomaterials such as zinc gallate and zinc gallium germanate are used in bioimaging research because their emission wavelengths are located in the near-infrared window and their penetration ability is relatively strong.

[0003] In life science detection and microbiology-related applications, probes with only single imaging capabilities often fail to meet the integrated "detection-processing" requirements. In existing technologies, to obtain functions beyond imaging (such as near-infrared photothermal processing), it is typically necessary to further introduce photothermal components, ligands, or multilayer composite structures onto the surface of long-afterglow nanomaterials. This multi-step surface modification or composite process often leads to the following problems: First, it increases the synthesis and purification process, making process parameters more sensitive and resulting in decreased structural controllability and batch consistency; second, multilayer surface modification may alter the microenvironment surrounding the luminescent center or introduce energy transfer / absorption losses, thus causing a decrease in afterglow intensity or duration; third, some composite methods suffer from uneven distribution of photothermal components, weak binding, or insufficient stability, affecting the reproducibility of near-infrared photothermal responses; fourth, in microbial imaging scenarios, relying on additional ligands for binding may further increase the complexity and cost of material construction, and place higher demands on stability and scalable preparation.

[0004] Therefore, there is an urgent need to provide a long-afterglow composite nanomaterial and its preparation method with a relatively simplified and controllable structural design and preparation process. This material can maintain near-infrared long-afterglow imaging performance as much as possible while introducing photothermal conversion capability that responds to near-infrared laser (808 nm), and be suitable for afterglow imaging and photothermal processing of microbial (e.g., bacterial) samples, thus providing a material basis for integrated "imaging-processing" applications. Summary of the Invention

[0005] To address the problems that existing long-persistence imaging probes often require multi-step surface modification during multifunctional integration, leading to complex preparation, reduced batch consistency, and potential degradation of afterglow luminescence performance, the technical problem to be solved by this invention is to provide a long-persistence composite nanomaterial with a relatively simplified and controllable structural design and preparation process, and its preparation method, so that the obtained material can introduce near-infrared photothermal heating capability while maintaining basically consistent afterglow attenuation behavior, and can be used for afterglow imaging and photothermal treatment of microbial samples such as bacteria.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a gold-coated long afterglow nanomaterial, comprising the following steps:

[0008] Preparation of long afterglow nanoparticles (PLNPs): Cr was prepared by hydrothermal reaction and calcination. 3+ Long afterglow nanoparticles (PLNPs) were obtained by doping zinc-gallium-germanium oxide nanoparticles.

[0009] Preparation of mesoporous silica-coated long afterglow nanoparticles MPLNPs: Under surfactant template and alkaline conditions, silicon source is hydrolyzed and polycondensed to form a mesoporous silica shell on the surface of the PLNPs. Subsequently, the surface of the mesoporous silica shell is subjected to amination treatment to obtain amination-coated mesoporous silica shell-coated long afterglow nanomaterials MPLNPs-NH2.

[0010] Preparation of gold-coated long afterglow nanomaterials MPLNPs@Au: Gold ions are adsorbed on the surface of MPLNPs-NH2 and reduced by a reducing agent to form gold seed particles. Subsequently, the gold seed particles are induced to grow in a gold precursor solution containing carbonate to form a gold shell layer, thus obtaining gold-coated long afterglow nanomaterials MPLNPs@Au.

[0011] In some embodiments, the reducing agent in step (3) is sodium borohydride, and the growth-promoting reducing agent is hydroxylamine hydrochloride; the carbonate-containing gold precursor solution is provided by a K-gold solution formed by the reaction of potassium carbonate and chloroauric acid.

[0012] The main intermediates in the above preparation process and the structural evolution from PLNPs to MPLNPs@Au are shown in the figure below. Figure 1 As shown.

[0013] This invention also provides a gold-coated long-afterglow nanomaterial, comprising: a long-afterglow nanocore, a mesoporous silica shell coating the surface of the long-afterglow nanocore, and a gold shell coating the outer surface of the mesoporous silica shell; wherein the long-afterglow nanocore is Cr 3+ Doped zinc-gallium-germanium oxide nanoparticles.

[0014] In some embodiments, the thickness of the mesoporous silica shell is 5–50 nm, and the thickness of the gold shell is 1–20 nm.

[0015] The present invention also provides the use of the above-mentioned nanomaterials in the preparation of imaging reagents for bacterial imaging, and in the preparation of formulations for photothermal heating treatment of bacterial samples, wherein the photothermal heating treatment is heating the bacterial sample under 808 nm laser irradiation.

[0016] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0017] By constructing a core-shell structure of "long-afterglow nanocore / mesoporous silica shell / gold shell", the material is endowed with near-infrared photothermal heating capability while maintaining its long-afterglow luminescence characteristics, providing a material basis for the integration of long-afterglow luminescence imaging and photothermal processing; Examples 4-6 and Figures 2-4 , Figures 6-9 This provides support for the aforementioned structural construction and performance.

[0018] By forming gold seeds on the surface of aminated mesoporous silicon shells and promoting their growth in a K-gold growth system to form a gold shell layer, the controllability and repeatability of the shell formation process are improved, thereby reducing the risk of structural inhomogeneity and batch-to-batch variation caused by multi-step composite processes; Examples 3-4 and Figure 2 It provides structural evidence for the formation of gold seeds and the growth of gold shells.

[0019] Examples show that the MPLNPs@Au exhibits a temperature rise response under 808 nm laser irradiation (see Example 5 and...). Figure 3 , Figure 9 Furthermore, the long afterglow decay curves before and after the gold shell coating are basically consistent (see Example 6 and...). Figure 4 ); combined with bacterial incubation imaging examples (see Example 7 and ); Figure 5 The nanomaterials can be used for bacterial imaging and photothermal heating of bacterial samples. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the gold shell coating process on the surface of long-afterglow nanomaterials, in which... Figure 1 (a) represents long afterglow nanoparticles (PLNPs). Figure 1 (b) MPLNPs-NH2, a long afterglow nanoparticle coated with and aminated from mesoporous silica. Figure 1 (c) MPLNPs-Au, a long afterglow nanoparticle with gold seed modification on its surface. Figure 1 (d) is the gold-coated long afterglow nanomaterial MPLNPs@Au;

[0021] Figure 2Transmission electron microscopy (TEM) images of PLNPs, PLNPs@MSN, MPLNPs-Au, and MPLNPs@Au, among which... Figure 2 (a) represents PLNPs. Figure 2 (b) is PLNPs@MSN. Figure 2 (c) represents MPLNPs-Au. Figure 2 (d) represents MPLNPs@Au;

[0022] Figure 3 The photothermal heating curve and corresponding photothermal imaging image of MPLNPs@Au under 808 nm laser irradiation are shown.

[0023] Figure 4 Comparison of afterglow decay curves of PLNPs and MPLNPs@Au (collected 2 min after pre-excitation by 650 nm LED light source);

[0024] Figure 5 This is a laser confocal microscopy image of Escherichia coli after incubation with MPLNPs@Au, in which... Figure 5 (a) is a superimposed image of the bright field and the red emission signal. Figure 5 (b) is an overlay of the DAPI staining signal (blue) and the red luminescence signal (including local magnification);

[0025] Figure 6 Statistical diagrams of particle size distribution of PLNPs, mesoporous silica-coated long afterglow nanoparticles, and MPLNPs@Au. Figure 6 (a)~ Figure 6 (c));

[0026] Figure 7 EDS elemental surface scan and EDS energy spectrum of MPLNPs@Au ( Figure 7 (a)~ Figure 7 (b));

[0027] Figure 8 UV-Vis-NIR absorption and emission spectra of MPLNPs@Au Figure 8 (a)~ Figure 8 (b));

[0028] Figure 9 The photothermal cycling stability curve of MPLNPs@Au under 808 nm laser irradiation;

[0029] Figure 10 The pore size distribution curves (BET test) of PLNPs@MSN. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments. It should be understood that the embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Unless otherwise stated, all reagents used are commercially available reagents conventional in the art, and the water used is deionized water or ultrapure water.

[0031] The separation and purification of the product described in the embodiments can be carried out by centrifugation, a method commonly used in the art, and the product can be washed several times with deionized water and / or ethanol to remove unreacted substances and free reagents, followed by drying to obtain a solid product; the centrifugation conditions and number of washings can be selected within the conventional range in the art according to the particle size and dispersion system.

[0032] Explanation of terms and abbreviations

[0033] In this specification, PLNPs represents long-afterglow nanoparticles; PLNPs@MSN represents long-afterglow nanoparticles coated with mesoporous silica (which can also be abbreviated as MPLNPs for consistency with the annotations in the attached figures); MPLNPs-NH2 represents aminated PLNPs@MSN; MPLNPs-Au represents MPLNPs-NH2 with gold seed modification on the surface; and MPLNPs@Au represents long-afterglow nanomaterials coated with a gold shell. K-gold solution represents a gold precursor solution formed by the reaction of carbonate and chloroauric acid and then aged.

[0034] The "long-afterglow luminescence imaging" described in this specification refers to imaging using luminescence signals generated by long-afterglow nanomaterials. This includes both afterglow imaging formed by collecting afterglow signals after excitation has stopped and under conditions of no continuous excitation light irradiation, and luminescence imaging formed by collecting luminescence signals under excitation conditions of instruments such as microscopes / confocal microscopes.

[0035] In some embodiments, the chemical composition of the long afterglow nanoparticles is Zn. a Ga b Ge c O4:Cr, where a is 1.1–1.3, b is 1.5–1.7, c is 0.1–0.3, and the mole fraction of Cr relative to (a+b+c) is 0.05–1.0 mol.

[0036] In some embodiments, the hydrothermal reaction temperature is 200–240°C and the reaction time is 20–30 h; the calcination temperature is 750–850°C and the holding time is 0.5–2 h.

[0037] In some embodiments, the mass ratio of PLNPs to hexadecyltrimethylammonium bromide is 1:(2-6); tetraethyl orthosilicate is added in stages for hydrolysis and polycondensation.

[0038] In some embodiments, the amination treatment may employ an aminosilane coupling agent (e.g., 3-aminopropyltriethoxysilane) and react at 50–80°C for 6–24 h to introduce amino groups onto the surface of the mesoporous silica shell.

[0039] In some embodiments, the chloroauric acid solution has a mass fraction of 0.5–2 wt%; the sodium borohydride concentration for forming gold seeds is 1–20 mM; the potassium carbonate concentration in the K-gold solution is 0.05–1 mg / mL; and the hydroxylamine hydrochloride concentration for promoting growth is 1–20 mM.

[0040] In some embodiments, the thickness of the mesoporous silica shell can be controlled by adjusting the amount of silicon source added, the number of feedings, the reaction temperature and the reaction time, and can be controlled within the range of 5 to 50 nm; the thickness of the gold shell can be controlled by adjusting the composition and concentration of the gold precursor solution, the amount of reducing agent added and the growth-promoting reaction time, and can be controlled within the range of 1 to 20 nm.

[0041] Example 1: Preparation of long afterglow nanoparticles (PLNPs)

[0042] (1) Preparation of precursor solution: Ge 4+ Precursor solution: Weigh 1.0459 g GeO2, add 30 mL of ultrapure water, slowly add 350 μL of concentrated ammonia solution until the solution becomes clear, and then dilute to 50 mL to obtain 0.2 mol / L GeO2. 4+ Precursor solution; Zn 2+ Precursor solution: Weigh 14.875 g Zn(NO3)2·6H2O, and dilute to 100 mL with ultrapure water to obtain 0.5 mol / L Zn 2+ Precursor solution; Ga 3+ Precursor solution: Weigh 2.348 g Ga₂O₃ and dispense it into two reaction vessels. Add 9 mL of concentrated nitric acid and 10 mL of ultrapure water to each vessel, and react at 150 °C for 24 h until the solution becomes clear. Combine the clear solutions and bring the volume to 50 mL to obtain 0.5 mol / L Ga₂O₃. 3+ Precursor solution; Cr 3+ Precursor solution: Weigh 1 g Cr(NO3)3·9H2O, and dilute to 25 mL with ultrapure water to obtain 0.1 mol / L Cr 3+ Precursor solution, stored away from light. (2) Preparation of PLNPs: Take 1 mL of Ge 4+ Precursor solution (0.2 mmol), 2.4 mL Zn 2+ Precursor solution (1.2 mmol), 3.2 mL Ga 3+ Precursor solution (1.6 mmol) with 75 μL Cr3+ The precursor solution (0.0075 mmol) was mixed and thoroughly stirred under vigorous stirring. The pH of the mixed solution was adjusted to approximately 8.0 with ammonia and measured using a pH meter. Stirring was continued at room temperature for 1 h to form the precursor solution. The precursor solution was transferred to a high-pressure reactor and reacted at 220 °C for 24 h. After the reaction, the supernatant was removed, the precipitate was collected, centrifuged, washed, and vacuum dried. The dried product was calcined in a muffle furnace at 800 °C for 1 h, cooled, and ground to obtain long-afterglow nanoparticles (PLNPs) (Zn). 1.2 Ga 1.6 Ge 0.2 O4:Cr).

[0043] Example 2: Preparation of mesoporous silica coating and amination (MPLNPs-NH2)

[0044] 40 mg of PLNPs solid powder and 160 mg of cetyltrimethylammonium bromide (CTAB) were weighed and added to 45 mL of ultrapure water for ultrasonic dispersion. 650 μL of NaOH aqueous solution (1 mol / L) was added to the dispersion, and the mixture was stirred in a 70°C water bath for 0.5 h. 160 μL of tetraethyl orthosilicate (TEOS) was slowly added under continuous stirring. After reacting for 1 h, another 160 μL of TEOS was added, and stirring continued for another 1.5 h to obtain PLNPs@MSN. Subsequently, the CTAB template agent was removed by washing with ethanol and centrifugation at least four times to obtain mesoporous silica-coated long-afterglow nanoparticles. BET analysis of the PLNPs@MSN showed a mesoporous pore size peak of approximately 4 nm (see [link to BET analysis]). Figure 10 Take 10 mg of the above product and sonicate it into 10 mL of anhydrous ethanol. Add 1 mL of 3-aminopropyltriethoxysilane (APTES) and heat and stir for 4 h. After washing with ethanol, centrifuge 3 times and dry, the aminated product MPLNPs-NH2 is obtained.

[0045] Example 3: Preparation of gold-coated long afterglow nanomaterials MPLNPs@Au

[0046] Gold-shell structures were prepared using a seed growth method. 1 mL of MPLNPs-NH2 ethanol dispersion (1 mg / mL) was added to 100 μL of chloroauric acid solution (1 wt%), and the mixture was stirred at 50 °C for 4 h. After centrifugation and washing, the precipitate was redispersed in 2 mL of ethanol. 40 μL of NaBH4 solution (10 mM) was added dropwise as a reducing agent under vigorous stirring. After approximately 5 min, the solution turned brownish-red, yielding MPLNPs-Au with gold seed modification. A K-gold solution was prepared: 10 mg of K2CO3 was dissolved in 40 mL of ultrapure water and stirred for 10 min. 600 μL of chloroauric acid solution was added, and stirring continued for 30 min. The resulting solution was stored in the dark and aged overnight. 50 μL of MPLNPs-Au dispersion was added to 3 mL of K-gold solution, followed by the addition of 40 μL of NH2OH·HCl solution (10 mM) and reaction, yielding gold-shell-coated long-afterglow nanomaterials MPLNPs@Au.

[0047] Example 4: Structural Characterization

[0048] The morphology and core-shell structure of PLNPs, PLNPs@MSN, MPLNPs-Au, and MPLNPs@Au were characterized using transmission electron microscopy (TEM). Figure 2 As shown in (a), PLNPs exhibit a nanoparticle morphology; Figure 2 As shown in (b), a silica coating layer is formed on the surface of the PLNPs (labeled as MPLNPs in the attached figure); as Figure 2 As shown in (c), gold seed particles are formed on the surface of the silica coating layer; as Figure 2 As shown in (d), the gold seed further grows to form an outer gold shell structure. Furthermore, at least 50 particles were randomly selected for particle size analysis, and the results are as follows... Figure 6 As shown, the average particle size of PLNPs is 16.3 ± 3.5 nm, the average particle size of the mesoporous silica-coated particles is 113.8 ± 23.3 nm, and the average particle size of MPLNPs@Au is 121.5 ± 30.3 nm. Furthermore, the elemental composition and distribution of MPLNPs@Au were verified using EDS elemental surface scanning and energy dispersive spectroscopy, with results as follows. Figure 7 As shown, Au coexists with signals from elements such as Si, Zn, Ga, and Ge, supporting the gold-shell coating structure. The optical properties of the material were characterized using UV-Vis-NIR absorption and emission spectroscopy, with results as follows: Figure 8 As shown, the material exhibits absorption in the visible-near infrared band and emission signals in the 650–850 nm band, with a peak around 700 nm.

[0049] In some implementations, energy dispersive spectroscopy (EDS) or elemental surface scanning can be used to further verify the distribution of outer gold elements, and X-ray diffraction (XRD) can be used to characterize the crystal phase of the long afterglow nanonucleus.

[0050] Example 5: Photothermal Performance Test

[0051] MPLNPs@Au was prepared into an aqueous dispersion with a concentration of 200 μg / mL. One mL of the sample was placed in a plastic centrifuge tube and centrifuged under an 808 nm laser (power density 1.5 W / cm²). 2 After irradiation for 4 minutes, the temperature rises and tends to stabilize, with a temperature difference ΔT of approximately 16℃ (see...). Figure 3 Temperature was recorded using a thermal imager. Furthermore, multiple on / off laser cycle tests were performed on the same sample, and the temperature-time curves are shown below. Figure 9 As shown, this indicates that the material has a certain degree of photothermal cycling stability.

[0052] Example 6: Afterglow Luminescence Performance Test

[0053] PLNPs and MPLNPs@Au were pre-excited for 2 min using a 650 nm LED light source. After excitation was stopped, afterglow decay curves were acquired at a wavelength of 700 nm. Figure 4 As shown, the afterglow decay curves of the materials before and after gold coating basically overlap, and the t of PLNPs 1 / 2 Approximately 1.3 s, t of MPLNPs@Au 1 / 2 The time was approximately 1.4 s, indicating that the gold coating did not significantly weaken the long-afterglow luminescence performance. 1 / 2 Depend on Figure 4 The afterglow attenuation curves were calculated, and both were collected under the same conditions.

[0054] Example 7: Bacterial Imaging Example

[0055] Escherichia coli (E. coli) was used as a model bacterium. E. coli was incubated with MPLNPs@Au dispersion for 30 min, followed by centrifugation and washing. The bacteria were then stained with DAPI. Bright-field images, the DAPI channel (blue), and the red luminescent channel of the nanomaterials were acquired using laser confocal microscopy in fluorescence imaging mode and then superimposed. Figure 5 As shown in (a), a red luminescent signal can be observed at the bacterial outline shown in the bright-field image; as Figure 5 As shown in (b), the DAPI staining signal and the red emission signal show a spatial correspondence. These results demonstrate that the MPLNPs@Au can bind to Escherichia coli and be used for bacterial imaging.

[0056] In one application embodiment, when the MPLNPs@Au is used as an imaging reagent for bacterial imaging, it can be incubated with the bacterial sample to be tested and unbound nanomaterials can be washed away. Subsequently, the luminescence signal is acquired and imaged using a fluorescence microscope or a laser confocal microscope. If afterglow imaging is required, the MPLNPs@Au can be pre-excited with a visible light or near-infrared light source (e.g., pre-excited with a 650 nm LED for 2 min). After excitation is stopped, the afterglow luminescence signal is acquired and imaged under conditions without continuous excitation light irradiation.

[0057] In one application embodiment, when the MPLNPs@Au is used as a photothermal treatment agent for photothermal heating of bacterial samples, it can be mixed with the bacterial samples and the system can be heated under 808 nm laser irradiation; the irradiation time and power density can be selected within the conventional range in the art according to the required temperature rise (e.g., power density 1.5 W / cm²). 2 , irradiation for 4 minutes).

[0058] The present invention has been described above with reference to specific embodiments, but the present invention is not limited to the above embodiments. Those skilled in the art can make reasonable changes or equivalent substitutions to the types and amounts of raw materials, reaction conditions, shell thickness, and testing conditions without departing from the concept and principle of the present invention, and all such changes should fall within the protection scope of the present invention.

Claims

1. A method for preparing a long afterglow nanomaterial with a gold shell coating, characterized in that, Includes the following steps: S1) Preparation of long afterglow nanoparticles (PLNPs): Ge-containing nanoparticles... 4+ Precursor solutions, containing Zn 2+ Precursor solutions, Ga-containing 3+ Precursor solutions and Cr-containing 3+ The precursor solutions were mixed, the pH was adjusted to 7.5–9.5 and stirred to obtain a precursor solution; the precursor solution was placed in a closed reaction vessel for hydrothermal reaction to obtain a hydrothermal product; the hydrothermal product was washed, dried, calcined and ground to obtain near-infrared luminescent long-afterglow nanoparticles (PLNPs); the chemical composition of the long-afterglow nanoparticles (PLNPs) was Zn. a Ga b Ge c O4:Cr, where a is 1.1–1.3, b is 1.5–1.7, c is 0.1–0.3, and the mole fraction of Cr relative to (a+b+c) is 0.05–1.0 mol%; S2) Preparation of mesoporous silica-coated and amination-treated long afterglow nanoparticles: The PLNPs and hexadecyltrimethylammonium bromide were dispersed in water, and an alkali was added to form an alkaline reaction system. Tetraethyl orthosilicate was added at 40-80°C to perform hydrolysis and polycondensation to form a mesoporous silica shell on the surface of the PLNPs, resulting in PLNPs@MSN. After washing the PLNPs@MSN to remove the template agent, it was amination-treated to obtain MPLNPs-NH2. S3) Preparation of gold-coated long afterglow nanomaterials MPLNPs@Au: MPLNPs-NH2 is dispersed in an alcohol solvent and contacted with chloroauric acid to adsorb gold ions onto its surface. Borohydride is added to reduce and form surface gold seeds to obtain MPLNPs-Au. MPLNPs-Au is added to a K-gold solution containing chloroauric acid and carbonate, and hydroxylamine hydrochloride is added as a reducing agent to grow the gold seeds to form a gold shell layer, thus obtaining MPLNPs@Au.

2. The preparation method according to claim 1, characterized in that, The hydrothermal reaction temperature in step S1 is 200–240°C and the reaction time is 20–30 h; the calcination temperature is 750–850°C and the holding time is 0.5–2 h.

3. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of PLNPs to hexadecyltrimethylammonium bromide is 1:(2-6), and tetraethyl orthosilicate is added in portions for hydrolysis and polycondensation, with each addition being 200-1200 μL / 100 mg PLNPs. The template agent is removed by washing with ethanol and centrifuging at least 4 times.

4. The preparation method according to claim 1, characterized in that, The amination treatment in step S2 is as follows: PLNPs@MSN are dispersed in an alcohol solvent, an aminosilane coupling agent is added, and the mixture is reacted at 50-80°C for 6-24 h to introduce amino groups onto the surface of the mesoporous silica shell.

5. The preparation method according to claim 1, characterized in that, In step S3, the chloroauric acid solution has a mass fraction of 0.5–2 wt%, the borohydride is sodium borohydride with a concentration of 1–20 mM, the K-gold solution contains potassium carbonate with a concentration of 0.05–1 mg / mL, the K-gold solution is aged under light-protected conditions for 8–24 h, and the hydroxylamine hydrochloride has a concentration of 1–20 mM.

6. The nanomaterial prepared by the method according to any one of claims 1-5, characterized in that, include: Long-afterglow nanonucleus, a mesoporous silica shell coating the surface of the long-afterglow nanonucleus, and a gold shell coating the outer surface of the mesoporous silica shell. The long-afterglow nanonucleus is a Cr-doped zinc-gallium-germanium oxide nanoparticle, and the chemical composition of the long-afterglow nanonucleus is Zn. a Ga b Ge c O4:Cr, wherein a is 1.1–1.3, b is 1.5–1.7, c is 0.1–0.3, and the molar fraction of Cr relative to (a+b+c) is 0.05–1.0 mol%, and the thickness of the mesoporous silica shell is 5–50 nm.

7. The nanomaterial according to claim 6, characterized in that, The thickness of the gold shell layer is 1–20 nm.

8. The nanomaterial according to claim 6 or 7, characterized in that, The average particle size of the long-afterglow nanonucleus is 10–30 nm, and the average particle size of the long-afterglow nanomaterial coated with the gold shell is 80–200 nm.

9. Use of the nanomaterial according to any one of claims 6 to 8 in the preparation of imaging reagents for bacterial imaging and / or formulations for photothermal treatment of bacterial samples, wherein the photothermal treatment is a heating treatment of the bacterial sample under 808 nm laser irradiation, and the bacterial imaging includes: The nanomaterials are first pre-excited using visible light or near-infrared light sources. After excitation is stopped, the afterglow emission signal is collected and imaged under conditions of no continuous excitation light irradiation.

Images