Nano composite material film, preparation method thereof and in-situ imaging method of plant tissue metabolite

Abstract

The invention provides a nanocomposite film, a preparation method thereof and an in-situ imaging method of plant tissue metabolites, and relates to the technical field of mass spectrometric detection. The preparation method of the composite material film comprises the following steps: adding a chloroauric acid solution into a MoS2 dispersion liquid, and stirring and reacting in a dark place to obtain a dispersion liquid of Au and MoS2; mixing the dispersion liquid of the graphene oxide with the Au-coated MoS2 / GO, and doping to obtain Au-coated MoS2 / GO suspension liquid; and filtering the suspension by using a microfiltration membrane, and drying to obtain the nano composite material film. The in-situ imaging method comprises the following steps: pressing a plant tissue on the nanocomposite film; and MALDI-MSI is adopted to carry out scanning analysis and imaging. The nano composite material film has the advantages of high sensitivity, high stability, high flexibility, low background interference and flexible size adjustability, can obtain high-quality mass spectrum imaging data in different types of tissues of plants, and has no obvious spatial dislocation.

Description

Technical Field

[0001] The present invention relates to the technical field of mass spectrometry detection, and in particular to a flexible nanocomposite film and a preparation method thereof, and an in-situ imaging method for plant tissue metabolites. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Laser desorption / ionization (LDI)-mass spectrometry imaging (MSI), an emerging in situ molecular imaging technique using small organic molecules as a matrix, offers the advantages of being label-free, high spatial resolution, high throughput, and broad molecular coverage. It overcomes the challenges of traditional metabolomics and is increasingly being used in botany. However, some plant tissues are difficult to prepare frozen sections for LDI-MSI due to their inherent biological properties, such as the high water content of succulent organs, the lignified fibrous structure of mature roots, and the fragile anatomical features and thick epidermis of leaves.

[0004] Molybdenum disulfide (MoS2), as an effective substrate for laser desorption ionization mass spectrometry, has been proven to be useful for high-speed detection and imaging of small molecule compounds in positive and negative ion modes. Heterostructures containing noble metal nanoparticles can significantly improve the desorption / ionization efficiency of the analytes. Therefore, the development of composite material matrices suitable for positive and negative ion modes to overcome the limitations of single materials and to give play to the synergistic effects between materials is an important research direction. The current plant tissue imaging technology based on flexible substrates combined with mass spectrometry imaging has technical bottlenecks that only allow single ion mode analysis and are applicable to limited types of plant tissue samples, which greatly restricts the detection and visualization analysis of more valuable plant molecules. Summary of the Invention

[0005] Based on the current state of the art, the present invention aims to provide a nanocomposite film, a method for preparing it, and a method for in situ imaging of plant tissue metabolites. Based on a flexible nanocomposite film composed of gold nanoparticles loaded with molybdenum disulfide and doped with graphene oxide (Au@MoS2 / GO) as a substrate, combined with tissue imprinting and LDI-MSI techniques, this method enables in situ, positive and negative ion dual-mode visualization of metabolites in fresh plant tissues, including roots, fruit, nodules, and leaves. This method, which eliminates the need for sectioning and matrix spraying, is suitable for plant samples where tissue sections are difficult to prepare, and offers high sensitivity, high spatial resolution, and flexibility.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] In a first aspect, a method for preparing a nanocomposite film comprises the following steps:

[0008] S1. Add chloroauric acid solution to MoS2 dispersion, stir and react for 30-40 minutes in the dark to obtain Au@MoS2 dispersion;

[0009] S2, mixing the graphene oxide dispersion with the Au@MoS2 dispersion so that the mass ratio of graphene oxide to Au@MoS2 is (2-3): (7-8), and obtaining the Au@MoS2 / GO suspension by doping;

[0010] S3. After filtering the Au@MoS2 / GO suspension using a microporous filter membrane, the microporous filter membrane is dried in the dark to obtain the nanocomposite film.

[0011] In a second aspect, the nanocomposite film is prepared by the above-mentioned method for preparing the nanocomposite film.

[0012] In a third aspect, a method for in situ imaging of plant tissue metabolites comprises the steps of:

[0013] S4, fixing the nanocomposite film on a substrate, pressing a plant tissue onto the nanocomposite film to transfer the juice in the plant tissue to the nanocomposite film in situ, and removing the plant tissue;

[0014] S5. After vacuum drying the nanocomposite film and substrate, LDI-MSI is used for scanning analysis and imaging.

[0015] The beneficial effects of the present invention are as follows:

[0016] 1. This invention fabricates a nanocomposite composed of gold nanoparticle-modified MoS2 and GO-doped nanocomposites through a layer-by-layer self-assembly method, resulting in the Au@MoS2 / GO material. This material exhibits a larger surface area, providing numerous adsorption sites for analytes. Its high hydrophobicity significantly reduces analyte delocalization, thereby reducing bias in MSI detection. Leveraging the properties of MoS2, this composite material can be used for "bipolar" detection in both positive and negative ion modes, expanding the molecular detection coverage and throughput of plant metabolites.

[0017] 2. The nanocomposite film provided by the present invention can be used as an imaging substrate for LDI-MSI, exhibiting high sensitivity, high stability, high flexibility, low background interference, and flexible size adjustability, making it suitable for both positive and negative ion mode analysis. This overcomes the technical bottleneck of conventional matrix-assisted LDI-MSI, which is difficult to use with fresh plant tissues due to their inherent biological properties. It can obtain high-throughput detection of metabolic compounds in different types of plant tissues, and the high-quality mass spectrometry imaging data obtained is free of significant spatial dislocation. It can directly visualize the distribution of metabolites in plant tissues, expanding the application scope of MSI. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0019] Figure 1 The preparation and characterization results of the Au@MoS2 / GO nanocomposite and nanofilm in Example 1 of the present invention are shown. (a) is a picture of the aqueous dispersion of GO, MoS2, and Au@MoS2 / GO nanocomposites; (b) is a transmission electron microscopy (TEM) image of GO, MoS2, and Au@MoS2 / GO nanomaterials; (c) is a flow chart of the preparation and LDI-MSI analysis of the Au@MoS2 / GO flexible nanofilm; (d) is an image of the Au@MoS2 / GO flexible nanofilm and the actual film cut and pasted onto an ITO glass surface; (e) is a scanning electron microscopy image of the surface and cross-section of the Au@MoS2 / GO flexible nanofilm; and (f) is a static water contact angle test image of the Au@MoS2 / GO flexible nanofilm surface.

[0020] Figure 2 The results of imaging stability tests of different types of small molecule metabolites using the Au@MoS2 / GO flexible nanofilm as an LDI-MSI imaging substrate in Example 1 of the present invention are shown. (a) shows the mass spectrometry images of abscisic acid, gibberellin GA3, baicalin, and wogonin standards in positive ion mode; (b) shows the mass spectrometry images of caffeic acid, citric acid, baicalin, and wogonin standards in negative ion mode.

[0021] Figure 3 It is a monochromatic mass spectrum image and overlay of the region-specific distribution ions in the ginseng main root imprint in Example 1 of the present invention.

[0022] Figure 4The following are the visualization results of metabolites in fresh plant tissue imprints using the Au@MoS2 / GO membrane combined with LDI-MSI in Example 2 of the present invention. (a) shows the mass spectrometry image of representative metabolites in ginseng roots; (b) shows the mass spectrometry image of representative metabolites in Scutellaria baicalensis nodules; (c) shows the mass spectrometry image of representative metabolites in hawthorn fruit; and (d) shows the mass spectrometry image of representative metabolites in Artemisia annua leaves. DETAILED DESCRIPTION

[0023] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0024] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0025] A method for preparing a nanocomposite film comprises the following steps:

[0026] S1. Add chloroauric acid solution to MoS2 dispersion, stir and react for 30-40 minutes in the dark to obtain Au@MoS2 dispersion;

[0027] S2, mixing the graphene oxide dispersion with the Au@MoS2 dispersion so that the mass ratio of graphene oxide to Au@MoS2 is (2-3): (7-8), and obtaining the Au@MoS2 / GO suspension by doping;

[0028] S3. After filtering the Au@MoS2 / GO suspension using a microporous filter membrane, the microporous filter membrane is dried in the dark to obtain the nanocomposite film.

[0029] In the above method, chloroauric acid is reduced to gold nanoparticles in MoS2 and anchored on the MoS2 surface to form gold nanoparticle-modified MoS2, which is then doped with graphene oxide to form Au@MoS2 / GO. This nanocomposite material has a larger specific surface area and can adsorb and enrich metabolites in plant tissues; Au@MoS2 / GO is then composited on a microporous filter membrane by filtration to obtain a nanocomposite film in a simple manner.

[0030] Optionally, in S1, the MoS2 dispersion is a dispersion of few-layer MoS2 nanosheets, and the few-layer MoS2 nanosheets have 1 to 10 layers, and have the characteristics of excellent efficiency in "light-to-heat" conversion, excellent surface adsorption and hydrophobicity, high specific surface area and excellent flexibility.

[0031] Optionally, in S1, the method for preparing the dispersion of the few-layer MoS2 nanosheets includes: dispersing the few-layer MoS2 nanosheet powder in an ethanol aqueous solution with a volume concentration of 60%, and ultrasonically treating it for 30 to 40 minutes to achieve uniform dispersion.

[0032] Optionally, in S1, the molar concentration of the chloroauric acid solution is 0.1-0.2 M, the mass concentration of the MoS2 dispersion is 1-2 mg / mL, and the volume ratio of the chloroauric acid solution and the MoS2 dispersion is (0.078-0.156):(10-20). The relatively small amount of gold nanoparticle loading can effectively prevent the agglomeration of gold nanoparticles, thereby avoiding the generation of Au adduct ion peaks and causing background interference.

[0033] Optionally, in S1, the addition method is slow dropwise addition for 8 to 10 minutes, and then during the stirring process, chloroauric acid is reduced to nanogold and embedded in the MoS2 nanosheets.

[0034] Optionally, in S2, the method for preparing the graphene oxide dispersion includes: adding graphene oxide powder to water and ultrasonicating it for 1 to 1.5 hours at a power of 400 to 600 W to disperse it into a single layer of nanosheets.

[0035] Optionally, in S2, the mass concentration of the graphene oxide dispersion is 4 to 6 mg / mL.

[0036] Optionally, in S2, the doping method includes: ultrasonic treatment for 10 to 12 minutes, with an ultrasonic treatment power of 400 to 600 W, to obtain an Au@MoS2 / GO composite material; wherein, the MoS2 nanosheets loaded with gold nanoparticles are stacked with GO.

[0037] Optionally, in S3, the microporous filter membrane is a hydrophilic mixed cellulose microporous filter membrane with a pore size of 0.45 to 2.0 μm to adapt to the Au@MoS2 / GO aqueous dispersion.

[0038] Optionally, in S3, the filtration method is vacuum filtration, and the mass / area ratio of the Au@MoS2 / GO suspension and the microporous filter membrane is 2.29-3.06 mg / cm 2 , so that Au@MoS2 / GO is loaded into the microporous filter membrane.

[0039] Optionally, in S3, the drying method includes: using a vacuum pump in combination with a Buchner funnel to perform vacuum-assisted filtration, and the drying time is 5 to 6 hours.

[0040] A method for in situ imaging of plant tissue metabolites, comprising the steps of:

[0041] S4, fixing the nanocomposite film on a substrate, pressing fresh plant tissue on the nanocomposite film to transfer juice in the fresh plant tissue to the nanocomposite film in situ, and removing the plant tissue;

[0042] S5. After vacuum drying the nanocomposite film and substrate, LDI-MSI is used for scanning analysis and imaging.

[0043] In the above process, the endogenous metabolites of fresh plant tissue are transferred to the nanocomposite film along with the juice during the pressing process, and the relative spatial position remains unchanged, realizing in situ imaging during the detection process.

[0044] Optionally, in S4, the fresh plant tissue is cut into thin slices with a thickness of less than 5 mm and then transferred in situ, which is suitable for plant tissues with larger thickness, including: plant tissues of ginseng roots, hawthorn fruits and Scutellaria baicalensis nodules; or the plant tissue is spread out and then transferred in situ, which is suitable for plant tissues with smaller thickness, including plant tissues of Artemisia annua leaves.

[0045] Optionally, in S4, the substrate is ITO glass with a square resistance of less than 6Ω, and the fixing method is to use conductive copper foil double-sided tape for bonding.

[0046] Optionally, in S4, a vise is used for pressing, and the pressing time is 15 to 30 seconds; the pressing force is 5 to 30 N and is evenly distributed on the plant tissue; and the pressing direction is perpendicular to the nanocomposite film.

[0047] Optionally, in S5, the LDI-MSI analysis mode is selected as positive ion mode or negative ion mode, and the laser energy is set to 80-90%.

[0048] Example 1

[0049] Preparation of Au@MoS2 / GO film and imaging effect and stability analysis of plant metabolites as LDI-MSI substrate.

[0050] The preparation method comprises:

[0051] S1. Prepare 0.1 M HAuCl4·3H2O chloroauric acid solution with deionized water. Disperse MoS2 nanosheet powder in 60% ethanol aqueous solution by volume and ultrasonicate (400W) for 30 min to obtain 1 mg·mL HAuCl4·3H2O solution.-1 MoS2 dispersion, such as Figure 1 As shown in the liquid in the MoS2 bottle in (a); the chloroauric acid solution was slowly added dropwise to the MoS2 dispersion, and the addition process was completed after 8 minutes. Then, stirring was continued in the dark for 30 minutes. With the successful reduction of HAuCl4 in MoS2, the color of the solution gradually changed from gray to gray-brown, indicating the formation of gold nanoparticles, and a dispersion of Au@MoS2 nanocomposite material was obtained.

[0052] S2. Graphene oxide (GO) powder was ultrasonically treated in water (400W) for 1 h to prepare a mass concentration of 4 mg mL -1 According to the mass ratio of graphene oxide to Au@MoS2 of 2:8, the graphene oxide dispersion and the Au@MoS2 dispersion were directly mixed and ultrasonically treated (400W) for 10min to obtain Au@MoS2 / GO suspension, such as Figure 1 The liquid in the Au@MoS2 / GO bottle is shown in (a).

[0053] S3, such as Figure 1 As shown in (c), a hydrophilic mixed cellulose microporous filter membrane with a diameter of 50 mm and a pore size of 1.5 μm was laid in a suction funnel. 30 mL of Au@MoS2 / GO suspension (concentration of 1.5 mg / mL) was ultrasonically treated (400 W) for 15 min and then transferred to a suction funnel for vacuum filtration. The mass / area ratio of the Au@MoS2 / GO suspension and the microporous filter membrane was converted to 2.29 mg / cm 2 , and then dried at room temperature and normal pressure in the dark (25°C, 4h) to obtain a nanocomposite film (Au@MoS2 / GO film).

[0054] Figure 1 (b) shows a few-layer MoS2 sheet (MoS2 in the figure), a single-layer GO sheet (GO in the figure), and spherical gold nanoparticles anchored on the MoS2 surface (Au@MoS2 / GO in the figure) detected by transmission electron microscopy (TEM); compared with MoS2 or GO, the Au@MoS2 / GO nanocomposite has a larger specific surface area, which is crucial for the adsorption and enrichment of analytes in LDI-MS; high-resolution transmission electron microscopy (HRTEM) observed a clear planar lattice spacing of The lattice fringes are 1.01 nm, corresponding to the (111), (100) and (001) crystal plane reflections of Au, MoS2 and GO, respectively, further indicating that the Au@MoS2 / GO composite material was successfully prepared.

[0055] The prepared nanocomposite film Figure 1As shown in (d), it has the characteristics of thin thickness, large area and extremely high flexibility, making it extremely easy to store and use.

[0056] The nanocomposite film was fixed to the indium tin oxide (ITO) glass surface using double-sided copper foil tape, and then the molecules on the film surface were directly analyzed and imaged; the results are shown in Figure 2. Figure 1 As shown in (e), the surface of the Au@MoS2 / GO film presents a densely packed and defect-free structure, and the cross-sectional microstructure of the film shows that Au@MoS2 and GO are stacked together.

[0057] The effective surface area of the membrane is approximately 11.9 cm 2 , providing a large number of adsorption sites for the analyte; the static water contact angle test results are as follows Figure 1 As shown in (f), the contact angle is 126.87°, indicating that the high hydrophobicity of the film surface significantly reduces the delocalization of the analyte, thereby reducing the bias of MSI detection.

[0058] The imaging effect stability test process includes:

[0059] The standard solutions of two plant hormones (abscisic acid and gibberellin GA3) and two flavonoid glycosides (baicalin and wogonin) were mixed as the detection standard in positive ion mode; the standard solutions of two phenolic acids (caffeic acid and citric acid) and two flavonoids (baicalein and wogonin) were prepared as the detection standard in negative ion mode: the nanocomposite film was prepared into a circular film with a diameter of 3mm by a puncher and fixed on the ITO glass surface by double-sided copper foil tape, and 1.5μL of the mixed standard solution (including the detection standard in positive ion mode and the detection standard in negative ion mode) was dropped onto the surface of the Au@MoS2 / GO film, and MSI analysis was performed at a spatial resolution of 150μm. Figure 2 (a) and Figure 2 As shown in (b), the Au@MoS2 / GO film as an LDI-MSI substrate can produce high-quality images in both positive and negative ion modes, making it an imaging substrate suitable for dual-mode visualization analysis. Clear images of abscisic acid, gibberellin GA3, baicalin, and wogonin are displayed in the positive ion mode, while the uniform distribution of caffeic acid, citric acid, baicalein, and wogonin is shown in the negative ion mode. This demonstrates that the Au@MoS2 / GO film substrate provides a stable mass spectrometry signal, which is crucial for the effective detection of molecules in fresh plants.

[0060] Example 2

[0061] In situ visualization analysis of metabolites in fresh ginseng roots, Scutellaria baicalensis root nodules, Hawthorn fruit, and Artemisia annua leaf tissues, including the following steps:

[0062] S4. Use conductive copper foil double-sided tape to fix the nanocomposite film cut to a set size on an ITO slide (square resistance <6Ω) with a size of 25mm×75mm. Use tweezers to place the plant tissue on the surface of the nanocomposite film and press it with a vise to transfer the juice in the tissue to the nanocomposite film in situ.

[0063] The plant tissues of ginseng root, hawthorn fruit and scutellaria nodule were cut into thin slices with a thickness of 5 mm and pressed, with the cut sections kept relatively parallel, and the pressing time was 30 seconds; the pressing force of ginseng root and scutellaria nodule was 10N and evenly distributed on the plant tissue; the pressing force of hawthorn fruit was 5N and evenly distributed on the plant tissue; the Artemisia annua leaves were flattened and directly pressed for 15 seconds; the pressing force was 10N and evenly distributed on the plant tissue; the vise was able to control the pressing direction to be perpendicular to the surface of the nanocomposite film.

[0064] S5. After vacuum drying the nanocomposite film and substrate, LDI-MSI is used for scanning analysis and imaging, wherein the laser energy is set to 85%.

[0065] The results of LDI-MSI analysis of the blot of ginseng taproot are shown in Figure 2. Figure 3 As shown in the figure, single-color ion maps (m / z 102.1 map and m / z 139.0 map) and superimposed ion maps (Overlay map) with representative distribution characteristics were extracted, and it was found that the metabolite transfer was relatively complete, and the representative ions were specifically distributed in the response tissue area. No significant spatial dislocation of the analytes was observed, which proved the accuracy of this method in in situ transfer and imaging molecules.

[0066] Further LDI-MSI analysis of three components of ginseng root (Panax ginseng) tissue (including rhizome, main root and lateral root) was performed. Figure 4 As shown in (a), the five ginsenosides are mainly distributed in the phloem of the main root and lateral roots, and are distributed in all regions of the rhizome; the contents of ginsenoside-Rg1 / Rf, ginsenoside-Re / Rd and ginsenoside-Rb1 in the rhizome and lateral roots are significantly higher than those in the main root, the content of ginsenoside-Ro is higher in the main root, and the content of ginsenoside-Rc / Rb2 / Rb3 is relatively uniform in all tissues; in addition, glucose is detected to be widely distributed in the three tissue parts, which may be related to the localization of saponin synthesis or accumulation sites; the above experimental results demonstrate the applicability of this method in fresh plant samples and show the potential for application in more plant tissue types.

[0067] Furthermore, in situ analysis was performed on the longitudinal sections of Scutellaria baicalensis nodules and roots with high fibrosis and low water content, and a total of 8 representative ions with distribution characteristics were screened out, including 4 amino acids, 1 organic acid, 1 choline, and 2 flavonoids. Figure 4 As shown in (b), amino acid, choline, baicalein and wogonin are distributed in the root cortex and nodule area, while aminobutyric acid and cysteine are enriched in the nodule area. The distribution of proline and valine is significantly different from that of other metabolites, and they are mainly enriched in the roots. These results provide a basis for explaining the metabolic differences between the roots and nodules of Scutellaria baicalensis.

[0068] Hawthorn (Crataegus pinnatifida) fruit is rich in endogenous metabolites, such as organic acids and phenolic acids. These endogenous molecules are continuously synthesized and degraded during fruit development, resulting in changes in their spatial distribution and content, which is of great significance for the nutritional value and quality control of the fruit. The high-resolution metabolite mass spectrometry imaging data obtained by in situ analysis are shown in (c) in Figure 4: maleic acid, succinic acid, citric acid, caffeic acid, and dihydroxybenzoic acid are co-localized throughout the fruit and are relatively evenly distributed; while the other three organic acids (malic acid, coumaric acid, and tartaric acid) are only present in the outer peel and inner peel. The applicability of the method of this example to different tissue samples of juice-rich fruit samples is verified. These results confirm that this method can serve as an ideal strategy for metabolite detection and imaging in fragile and water-rich plant tissues in the future.

[0069] Medicinal leaves, such as Artemisia annua leaves, contain a wide variety of metabolites with important biological activities. These metabolites are synthesized and metabolized in different regions and cell types of the leaves. However, due to the rich structure, waxy texture, and thin layer of tissue in the plant epidermis, it is impossible to completely slice the leaf surface, making it difficult to obtain spatial information of its metabolites. The high-resolution MSI images of endogenous metabolites obtained in this example are shown in Figure 2. Figure 4 As shown in (d) in the figure: artemisinin and its derivatives (artemisinin A, artemisinin B and dihydroartemisinic acid) are all distributed in the leaf veins and leaves, and the other four metabolites also have similar positioning, including dihydroxybenzoic acid, dihydrocarvone and luteolin; it was further found that feruloylquinic acid is more concentrated in the leaf veins; these results further demonstrate the important application value of this method, and the research results provide direct evidence for exploring the biosynthetic pathway and extraction of natural products in Artemisia annua.

[0070] This example demonstrates that this method can perform direct visual analysis of metabolites in plant tissue samples of different textures, can achieve a wide range of natural product detection, and can obtain true metabolite distribution information in plant tissues with high sensitivity and spatial resolution. It is a reliable and highly applicable molecular imaging tool.

[0071] The above demonstrates that, based on the excellent efficiency of Au@MoS2 / GO flexible nanofilms in light-to-heat conversion, their excellent surface adsorption and hydrophobicity, high specific surface area, and exceptional flexibility, combined with plant tissue imprinting technology for molecular transfer, and leveraging the advantages of LDI-MSI for in situ analysis, rapidity, and the absence of pre-labeling, a novel mass spectrometry imaging method has been established to analyze the spatial distribution of metabolites in fresh plant samples. This provides a new strategy to supplement the shortcomings of current conventional LDI-MSI technology and expand the application range of mass spectrometry imaging technology.

[0072] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing a nanocomposite film, characterized in that: The following steps are involved: S1. Add chloroauric acid solution to MoS2 dispersion, stir and react for 30-40 minutes in the dark to obtain Au@MoS2 dispersion; S2, mixing the graphene oxide dispersion with the Au@MoS2 dispersion so that the mass ratio of graphene oxide to Au@MoS2 is (2-3): (7-8), and obtaining the Au@MoS2 / GO suspension by doping; S3. After filtering the Au@MoS2 / GO suspension using a microporous filter membrane, the microporous filter membrane is dried in the dark to obtain the nanocomposite film.

2. The method for preparing a nanocomposite film according to claim 1, wherein: In S1, the MoS2 dispersion is a dispersion of few-layer MoS2 nanosheets, and the number of layers of the few-layer MoS2 nanosheets is 1 to 10; Alternatively, the method for preparing the dispersion of the few-layer MoS2 nanosheets comprises: dispersing the few-layer MoS2 nanosheet powder in an ethanol aqueous solution with a volume concentration of 60%, and ultrasonically treating the solution for 30 to 40 minutes.

3. The method for preparing a nanocomposite film according to claim 1, wherein: In S1, the molar concentration of the chloroauric acid solution is 0.1-0.2 M, the mass concentration of the MoS2 dispersion is 1-2 mg / mL, and the volume ratio of the chloroauric acid solution to the MoS2 dispersion is (0.078-0.156): (10-20); Alternatively, in S1, the adding method is slow dropwise addition, and the adding time is 8 to 10 minutes.

4. The method for preparing a nanocomposite film according to claim 1, wherein: In S2, the method for preparing a dispersion of graphene oxide includes: adding graphene oxide powder to water and sonicating for 1 to 1.5 hours; Alternatively, in S2, the mass concentration of the graphene oxide dispersion is 4 to 6 mg / mL; Alternatively, in S2, the doping method includes: ultrasonic treatment for 10 to 12 minutes.

5. The method for preparing a nanocomposite film according to claim 1, wherein: In S3, the microporous filter membrane is a hydrophilic mixed cellulose microporous filter membrane with a pore size of 1.5 to 2.0 μm; Alternatively, in S3, the filtration method is vacuum filtration, and the mass / area ratio of the Au@MoS2 / GO suspension and the microporous filter membrane is 2.29-3.06 mg / cm 2 ; Alternatively, in S3, the drying method includes: using a vacuum pump in conjunction with a Buchner funnel to perform vacuum-assisted filtration, and the drying time is 5 to 6 hours.

6. A nanocomposite film prepared by the preparation method according to any one of claims 1 to 5.

7. A method for in situ imaging of plant tissue metabolites, characterized in that: Including steps: S4. Fixing the nanocomposite film according to claim 6 on a substrate, pressing a plant tissue onto the nanocomposite film to transfer the juice in the plant tissue to the nanocomposite film in situ, and removing the plant tissue; S5. After vacuum drying the nanocomposite film and substrate, MALDI-MSI is used for scanning analysis and imaging.

8. The in situ imaging method of plant tissue metabolites according to claim 7, wherein: In S4, the plant tissue is cut into slices with a thickness of less than 5 mm and then transferred in situ, or the plant tissue is spread out and then transferred in situ.

9. The in situ imaging method of plant tissue metabolites according to claim 7, wherein: In S4, the substrate is ITO glass, and the fixing method is bonding using a conductive copper foil double-sided tape; Alternatively, in S4, the pressing time is 15 to 30 seconds; the pressing force is 5 to 30 N and is evenly distributed on the plant tissue; and the pressing direction is perpendicular to the nanocomposite film.

10. The in situ imaging method of plant tissue metabolites according to claim 7, wherein: In S5, the MALDI-MSI analysis mode was selected as positive ion mode or negative ion mode, and the laser energy was set to 80-90%.

Images