A photonic crystal-isolating-photonic element superlattice composite superstructure, and a preparation method and application thereof

Abstract

The application discloses a photonic crystal-plasmonic superlattice composite superstructure and a preparation method and application thereof, and belongs to the technical field of nanomaterials, and the method comprises the following steps: (1) self-assembling monodisperse silica nanogel particles in a medium to form a liquid colloidal crystal, coating the liquid colloidal crystal on a substrate surface, and evaporating a solvent to form a three-dimensional array of silica photonic crystals; (2) sequentially modifying gold nanoparticles by using mercapto polystyrene and 1,8-octanedithiol, and then making the gold nanoparticles form a film at a liquid interface to obtain a gold nanometer superlattice ordered two-dimensional monolayer film; and (3) transferring the gold nanometer superlattice ordered two-dimensional monolayer film to the three-dimensional array of silica photonic crystals to prepare the photonic crystal-plasmonic superlattice composite superstructure. When the photonic crystal-plasmonic superlattice composite superstructure is used as a SERS substrate, the photonic crystal light bandgap characteristics and the plasmonic localized plasmonic near-field coupling characteristics can be fully utilized, the interaction between light and matter can be synergistically enhanced, and the Raman enhancement effect can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of surface-enhanced Raman scattering spectral detection elements, in particular to a photonic crystal-plasmonic superlattice composite superstructure and a preparation method and application thereof. BACKGROUND

[0002] Surface-enhanced Raman scattering (SERS) technology is a high-sensitivity spectral analysis technology that can detect molecules at low or extremely low concentrations and is widely used in biomedical, food science and environmental analysis. SERS effect is mainly achieved through two mechanisms: electromagnetic enhancement (EM) and chemical enhancement (CM), of which the electromagnetic enhancement mechanism is the main contributor. The electromagnetic enhancement mechanism is mainly due to the localized surface plasmon resonance (LSPR) effect of noble metal nanostructures. When the excitation light at a specific wavelength is irradiated on the surface of the noble metal nanostructure, due to the LSPR effect, the light is focused on the edge, tip or gap of the nano material, thereby producing a strong electromagnetic field enhancement, which can further amplify the signal of the molecules in the field.

[0003] Photonic crystals are a class of materials with periodic dielectric constant distribution, which have unique optical bandgap characteristics and can significantly affect the propagation of light. The slow light effect of photonic crystals can significantly prolong the propagation path of light in the material, thereby enhancing the interaction between light and matter. Silicon dioxide photonic crystals have been applied in the design of SERS substrates to improve detection sensitivity and selectivity. By combining noble metal nanostructures with photonic crystals, the SERS effect can be further enhanced, and the detection sensitivity can be improved.

[0004] A preparation method of a surface-enhanced Raman scattering sensor device based on photonic crystal band edge effect is disclosed in Chinese patent document CN107132212A. The invention uses an amino modification liquid containing 3-aminopropyl triethoxysilane to perform an amino modification reaction on monodisperse SiO2 microspheres to obtain amino-modified SiO2 microspheres; gold nanoparticles solution is prepared by sodium citrate reduction method; an amino-modified SiO2 microsphere-ethanol suspension is prepared, and a glass slide is vertically inserted into the suspension to obtain a regular arrangement of SiO2 opal structure photonic crystals on the glass slide; gold nanoparticle solution is added to the surface of the photonic crystal in a cycle to obtain a surface-enhanced Raman scattering sensor device based on the opal structure photonic crystal. The invention uses the periodic ordered structure of the photonic crystal to achieve the ordered distribution of gold nanoparticles, and the obtained sensor device has high sensitivity.

[0005] The Chinese patent document with the publication number CN103257134A discloses a preparation method of a capillary-based surface enhanced Raman scattering substrate, which comprises the following steps: preparing a three-dimensional porous ordered SiO2 inverse opal photonic crystal in a capillary; and loading gold nanoparticles in the three-dimensional porous ordered SiO2 inverse opal structure by in-situ reduction or electrostatic adsorption. The capillary is used as the substrate, so that the analyte is limited to flow in the pipe, and the initiative of the analyte to contact the SERS hot spot is increased.

[0006] Although the above-mentioned invention has combined the photonic crystal and the noble metal nanostructure for the preparation of the SERS substrate, the upper noble metal nanoparticles are mostly in a disordered dispersion or accumulation structure, and the coupling efficiency of the photonic crystal and the noble metal nanostructure is low, the structural stability is easily lost in long-term use, and the SERS enhancement effect is not ideal. SUMMARY

[0007] In order to solve the above-mentioned problems in the prior art, the present application provides a preparation method of a photonic crystal-plasmonic superlattice composite superstructure, which effectively couples a three-dimensional array of silica photonic crystals and a two-dimensional monolayer film of gold nano-superlattice, utilizes the synergistic effect of the two to enhance the interaction between light and matter, so as to obtain better coupling effect and electromagnetic enhancement characteristics, and improve the SERS performance.

[0008] The specific technical solutions are as follows:

[0009] The preparation method of the photonic crystal-plasmonic superlattice composite superstructure comprises the following steps:

[0010] (1) self-assembling monodisperse silica nanogel particles with a particle size of 100-400 nm in a medium to form a liquid colloidal crystal, coating the liquid colloidal crystal on the surface of a substrate, and volatilizing the solvent to form a three-dimensional array of silica photonic crystals;

[0011] (2) preparing gold nanoparticles with a particle size of 10-60 nm, modifying the gold nanoparticles with mercaptobenzene and 1,8-octanedithiol in sequence, and forming a two-dimensional monolayer film of gold nano-superlattice at a liquid interface;

[0012] (3) transferring the two-dimensional monolayer film of gold nano-superlattice to the three-dimensional array of silica photonic crystals to couple the double-layer ordered structure, and obtaining the photonic crystal-plasmonic superlattice composite superstructure.

[0013] The application prepares a multi-level ordered superstructure film by effectively coupling a gold nanometer superlattice ordered two-dimensional monolayer film with a silica photonic crystal three-dimensional array. The gold nanometer superlattice ordered two-dimensional monolayer film has a significant near-field plasmonic coupling characteristic compared with monodisperse or disordered gold nanoparticles to enhance electromagnetic field intensity. Further, the reflection bandgap wavelength of the lower silica photonic crystal three-dimensional array is adjusted to match the wavelength band edge of the upper superlattice plasmonic structure, so that the photonic crystal bandgap characteristic and the localized surface plasmon resonance are further coupled to fully utilize the synergistic effect of both to enhance the interaction of light and matter, thereby obtaining a better coupling effect and electromagnetic enhancement characteristic, and further applied to a SERS substrate to improve the Raman enhancement performance.

[0014] The light bandgap wavelength of the lower silica photonic crystal three-dimensional array can be adjusted to match the main LSPR peak of the upper gold nanometer superlattice ordered two-dimensional monolayer film, and the final composite multi-level ordered superstructure can fully utilize the synergistic effect of both.

[0015] Preferably, in step (1), the monodisperse silica nanogel particles are prepared by a seed growth method. First, silica nanoseeds are synthesized using tetraethyl orthosilicate as a raw material and arginine as a catalyst. Then, the silica nanoseeds are further grown by using ammonia to catalyze the hydrolysis reaction of tetraethyl orthosilicate to obtain monodisperse silica nanogel particles. By changing the amount of seeds, monodisperse silica nanogel particles with different particle sizes can be prepared.

[0016] Specifically, in step (1), the medium includes at least one of ethanol, ethylene glycol, diethylene glycol, propylene carbonate, dimethylformamide, and dimethyl sulfoxide; and the volume fraction of the monodisperse silica nanogel particles in the medium is 15% to 40%.

[0017] The substrate includes, but is not limited to, a silicon wafer, glass, polyimide, polyethylene terephthalate, polydimethylsiloxane, ceramic, or a metal substrate.

[0018] Preferably, the solvent is volatilized by heating to form the silica photonic crystal three-dimensional array, and the heating condition is 30 to 100°C for 1.5 to 2 hours.

[0019] Preferably, the gold nanoparticles are prepared by a seed growth method. Chloroauric acid, sodium borohydride, and cetyltrimethylammonium bromide (CTAB) are used as raw materials to prepare a nanogold seed solution. Then, the nanogold seed solution, ascorbic acid, cetyltrimethylammonium chloride (CTAC), and chloroauric acid are used as raw materials to further grow the nanogold seed to prepare a gold nanoparticle solution.

[0020] The mercaptan polystyrene and 1,8-octanedithiol can be connected to the gold nanoparticles through gold-sulfur bonds to graft and modify the gold nanoparticles at a molecular level.

[0021] Preferably, the average molecular weight of the mercaptan polystyrene PSSH is 5000-20000 g / mol; the mercaptan polystyrene is modified by using a mercaptan polystyrene solution with a concentration of 10 -6 ~10 -4 mol / L to react with the gold nanoparticle solution.

[0022] Preferably, the 1,8-octanedithiol is modified by using a 1,8-octanedithiol solution with a concentration of 5.0*10 -6 ~1.5*10 -5 mol / L to react with the gold nanoparticle solution modified by the mercaptan polystyrene.

[0023] Further, the gold nanoparticle modified by the mercaptan polystyrene and the 1,8-octanedithiol is dispersed in toluene, and then is transferred to a diethylene glycol subphase, and after the toluene is completely volatilized, a gold nanoparticle superlattice monolayer film is obtained on the diethylene glycol interface.

[0024] The application further provides a preparation method of the photonic crystal-plasmonic superlattice composite superstructure.

[0025] The photonic crystal-plasmonic superlattice composite superstructure comprises, from bottom to top, a substrate, a three-dimensional array of silica photonic crystals and a two-dimensional monolayer film of gold nanoparticle superlattice.

[0026] The application further provides a SERS substrate comprising the photonic crystal-plasmonic superlattice composite superstructure, which can enhance the Raman signal and improve the detection sensitivity when applied to the SERS substrate.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] (1) The photonic crystal-plasmonic superlattice composite superstructure is prepared by simple chemical synthesis and physical deposition, without the need for complex equipment and expensive reagents. (2) The traditional preparation method of the composite superstructure usually needs expensive equipment such as electron beam lithography (EBL) and focused ion beam etching (FIB), but the method of the application only needs basic laboratory equipment, reduces the preparation cost, is low in energy consumption and low in equipment requirement. (3) The particle size of the silica nanogel and the photonic crystal light band gap wavelength can be accurately controlled by adjusting the seed amount and the reaction conditions, and the superstructure substrate can be customized according to different detection requirements. (4) The surface local plasmon resonance effect of the gold nanoparticle superlattice can be accurately controlled by adjusting the gold nanoparticle superlattice spacing, and the electromagnetic field enhancement effect can be further optimized.

[0029] (2) The slow light effect of the silica photonic crystal significantly prolongs the propagation path of light in the material, enhances the interaction between light and matter, and thus improves the intensity of the SERS signal. The LSPR effect and near-field coupling characteristics of the gold nanoparticle superlattice produce strong electromagnetic field enhancement at a specific wavelength, further improving the sensitivity of the SERS signal. The synergistic enhancement of the two effects enables the multi-level ordered superstructure of the application to maximize the interaction between light and matter, thereby enhancing the electromagnetic field strength and achieving significant Raman enhancement effect.

[0030] (3) The preparation method of the application has high controllability and stability, ensuring the repeatability of the SERS substrate between batches and samples and improving the consistency of the detection results. The gold nanoparticle superlattice ordered two-dimensional monolayer film is fixed on the surface of the silica photonic crystal three-dimensional array by physical transfer, ensuring the structural stability of the SERS substrate, which can maintain good performance even after long-term use. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The figure is a schematic diagram for the preparation of the photonic crystal-plasmonic superlattice composite superstructure.

[0032] Figure 2 a is the scanning electron microscope image of the silica photonic crystal three-dimensional array in Example 1; b is the reflection spectrum of the silica photonic crystal in Example 1, and the inset is a real object diagram; c is the scanning electron microscope image of the gold nanoparticle superlattice ordered two-dimensional monolayer film in Example 1; d is the absorption spectrum of the gold nanoparticle superlattice ordered two-dimensional monolayer film in Example 1; e is the scanning electron microscope image of the photonic crystal-plasmonic superlattice composite superstructure SERS substrate in Example 1.

[0033] Figure 3 a is the reflection spectrum of the silica photonic crystal in Example 4, and the inset is a real object diagram; b is the reflection spectrum of the photonic crystal-plasmonic superlattice composite superstructure SERS substrate in Example 4.

[0034] Figure 4 a is the Raman spectrum of methylene blue molecules of M in Example 4; b is the Raman intensity column chart of methylene blue molecules of M at 1622 cm -5 -1 DETAILED DESCRIPTION

[0035] ​​In order to make the objects, characteristics and advantages of the present application more apparent, specific embodiments will be described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in many different ways from what is described herein, and should not be construed as being limited to the embodiments set forth herein below. The technical features of various embodiments of the present application can be combined with each other as long as there is no conflict.

[0036] The operation methods not specified in the following examples are generally carried out according to the conventional conditions or the conditions recommended by the manufacturers. The contents not described in detail in the specification belong to the prior art known to those skilled in the art. The experimental materials used in the following examples can be purchased from the conventional biochemical reagent companies, unless otherwise specified.

[0037] In the examples, the preparation flow chart of the photonic crystal-plasmonic superlattice composite superstructure is shown in Figure 1

[0038] Example 1

[0039] (1) Preparation of monodisperse silica nanocolloidal particles:

[0040] S1: 0.087 g of L-arginine was dissolved in 87 mL of water, and after stirring for 10 min, 5.55 mL of tetraethyl orthosilicate was added, and the temperature was raised to 70°C, and hydrolysis was carried out for 24 h to obtain a silica nanoparticle solution with a particle size of about 20 nm as a seed solution.

[0041] S2: 200 μL of the seed solution was added to 14 mL of water, and added to a solution of 200 mL of ethanol and 8 mL of ammonia water, and after thoroughly stirring and mixing, 16 mL of tetraethyl orthosilicate was injected at a rate of 4 mL / h using a syringe pump, and magnetic stirring was carried out for 12 h, and the final monodisperse silica nanocolloidal particles with a particle size of 200 nm were obtained by washing with anhydrous ethanol three times (8000 rpm, 5 min).

[0042] (2) Assembly of silica photonic crystals:

[0043] The prepared silica nanocolloidal particles were uniformly dispersed in propylene carbonate, and a liquid colloidal crystal with a volume fraction of 30% was obtained by volatile-induced self-assembly, and then coated on a silicon wafer substrate, and then heated, and the heating conditions were 60°C, 0.5 h, to form a three-dimensional array of silica photonic crystals.

[0044] (3) Preparation of gold nanoparticles:

[0045] ​S1 : A freshly prepared NaBH4 solution (600 μΐ, 0.010 mol / L) was quickly injected into a mixed solution of CTAB (9.9 mL, 0.10 mol / L) and HAuCl4(0.0250 mol / L). After stirring at 300 r / min for 3 h, the reaction mixture was placed in a water bath at 30 °C for 3 h to obtain a gold nanoparticle seed solution.

[0046] S2: 500 μΐ of gold nanoparticle seed solution (gold seeds stabilized with CTAB) was mixed with ascorbic acid AA (15.0 mL, 0.10 mol / L) and CTAC (20.0 mL, 0.20 mol / L) and stirred at 600 r / min for 1 min, then HAuCl4(20 mL, 0.000050 mol / L) was injected. After continuous stirring for 15 min (300 rpm), 15 mL of the solution after the first growth was collected, purified by centrifugation (16000 r / min x 20 min) and the gold nanoparticles were redispersed in a CTAC (2.5 mL, 0.020 mol / L) solution.

[0047] S3: CTAC (20 mL, 0.10 mol / L) and gold nanoparticles (750 μΐ, purified and dispersed in 0.020 mol / L CTAC) were mixed and sonicated for 10 min. Then the mixture was stirred (400 r / min) in a water bath at 30 °C, then AA (1.3 mL, 0.010 mol / L) was added and stirred for 1 min, then HAuCl4(50 mL, 0.00050 mol / L) was injected into it at a concentration of 20 mL / h using a syringe pump. Finally, the mixture was stirred (400 r / min) at 30 °C for another 5 min, then the final gold nanoparticle solution (containing Au NP@CTAC, the concentration of the gold nanoparticle solution was 7.69 x 10 -10 mol / L, and the particle size was 30 nm) was obtained by refrigeration.

[0048] (4) Modification of gold nanoparticles:

[0049] S1 : 10 ml of the gold nanoparticle solution obtained in the above step was centrifuged twice to remove excess CTAC. After the second centrifugation, the volume of the solution was reduced to <100 μΐ, then the concentrated solution was added dropwise to a vigorously stirred (1000 rpm) THF solution (2 ml, 5.0 x 10 -6mol / L) (PSSH average molecular weight of 12000 g / mol, PSSH: gold nanoparticle molar ratio of 1300:1). The resulting mixture was stirred at 300 rpm for at least 24 hours to allow PSSH to completely replace CTAC, yielding mercaptopolystyrene-modified gold nanoparticles (Au NP@PSSH). The Au NP@PSSH solution was centrifuged, the supernatant removed, and the volume of the solution reduced to <100 μL.

[0050] S2: The Au NP@PSSH solution was centrifuged, the supernatant was removed, and the volume of the solution was reduced to <100 μL. The concentrated Au NP@PSSH solution was then added dropwise to the 1,8-octanedithiol OCT solution (THF, 2 mL, 1.0 × 10 -5 mol / L) (the molar ratio of 1,8-octanedithiol to gold nanoparticles in Au NP@PSSH was 2600:1). The resulting mixture was further mixed for at least 24 hours to allow sufficient interaction between OCT and the residual active sites on the gold nanoparticles, resulting in a gold nanoparticle solution modified with both mercaptopolystyrene and 1,8-octanedithiol ligands.

[0051] (5) Preparation of ordered two-dimensional monolayers of gold nanosuperlattices:

[0052] S1: The dual-ligand-modified gold nanoparticle solution was centrifuged three times, concentrated, and redispersed in 1 mL of toluene under ultrasonication. Equal volumes of water and ethanol were then added to form a 1:1:1 mixture with the toluene solution. The upper toluene layer was extracted and the washing and extraction process was repeated to obtain Au NP@PSSH@OCT.

[0053] S2: The Au NP@PSSH@OCT in 1 mL of toluene was slowly transferred into a polytetrafluoroethylene test tube (~2 cm inner diameter, maximum volume of 30.0 mL) containing 20 mL of diethylene glycol (DEG). The mouth of the test tube was covered with a glass Petri dish to control the evaporation rate of toluene. After the toluene evaporated, an ordered two-dimensional monolayer of gold nanosuperlattice was formed on the surface of the DEG phase.

[0054] (6) Construction of photonic crystal-plasmon superlattice composite superstructure:

[0055] The prepared gold nano-superlattice ordered two-dimensional single-layer film is transferred to the surface of the silicon dioxide photonic crystal three-dimensional array in step (2), so that the double-layer ordered structure is coupled to prepare the photonic crystal-plasmon superlattice composite superstructure.

[0056] like Figure 2 As shown in a in Figure 1, the three-dimensional array of silicon dioxide photonic crystals has a long-range ordered structure. Figure 2Figure 1 shows the SEM image of the gold nanometer superlattice ordered two- dimensional monolayer film, which is assembled by the 30 nm diameter double-ligand modified gold nanoparticles. The gold nanoparticles are uniform in size and present regular hexagonal close-packed structure, which verifies the formation of the superlattice ordered array. Figure 2 Figure 1c is the SEM image of the gold nanometer superlattice ordered two- dimensional monolayer film, which is assembled by the 30 nm diameter double-ligand modified gold nanoparticles. The gold nanoparticles are uniform in size and present regular hexagonal close-packed structure, which verifies the formation of the superlattice ordered array. Figure 2 Figure 1d shows the absorption spectrum of the gold nanometer superlattice ordered two-dimensional monolayer film assembled by the 30 nm diameter double-ligand modified gold nanoparticles. The absorption peak is at 658 nm and the absorbance is 1.003. Figure 2 Figure 1e shows that the upper layer of gold nanoparticles and the lower layer of silica both maintain highly ordered structure, and the gold nanoparticles are uniformly distributed on the surface of the silica photonic crystal array and present mulberry-like multi-level ordered composite structure.

[0057] Example 2

[0058] The difference between this example and Example 1 is that, in the preparation of monodisperse silica nanogel particles, the amount of seed solution added is 150 μL, and monodisperse silica nanogel particles with a particle size of 233 nm are prepared, and a three-dimensional array of silica photonic crystals is obtained by assembly. Other parameters and conditions are the same as those of Example 1, and the reflection peak of the prepared silica photonic crystal is at 487 nm. After being combined with the gold nanometer superlattice ordered two-dimensional monolayer film, the photonic crystal-plasmonic superlattice composite superstructure can be prepared.

[0059] Example 3

[0060] The difference between this example and Example 1 is that, in the preparation of monodisperse silica nanogel particles, the amount of seed solution added is 100 μL, and monodisperse silica nanogel particles with a particle size of 255 nm are prepared, and a three-dimensional array of silica photonic crystals is obtained by assembly. Other parameters and conditions are the same as those of Example 1, and the reflection peak of the prepared silica photonic crystal is at 527 nm. After being combined with the gold nanometer superlattice ordered two-dimensional monolayer film, the photonic crystal-plasmonic superlattice composite superstructure can be prepared.

[0061] Example 4

[0062] The difference between this example and Example 1 is that, in the preparation of monodisperse silica nanogel particles, the amount of seed solution added is 50 μL, and monodisperse silica nanogel particles with a particle size of 300 nm are prepared, and a three-dimensional array of silica photonic crystals is obtained by assembly. Other parameters and conditions are the same as those of Example 1, and the reflection peak of the prepared silica photonic crystal is at 623 nm, as shown inFigure 3 As shown in a. After being combined with the ordered two-dimensional monolayer of gold nano superlattice, the photonic crystal-plasmon superlattice composite superstructure can be prepared. The reflection spectrum of the composite superstructure is shown in FIG. Figure 3 As shown in b.

[0063] Application Example 1

[0064] The photonic crystal-plasmon superlattice composite superstructure prepared in Example 4 was used as a SERS substrate to verify its Raman enhancement effect. Figure 4 As shown in a, a three-dimensional array of silicon dioxide photonic crystals, a two-dimensional monolayer of gold nano-superlattice ordered, and a composite superstructure of photonic crystal-plasmon superlattice prepared under the same parameter conditions were used as SERS substrates to detect 10 -5 The Raman spectrum of the methylene blue molecule was used to evaluate the SERS enhancement performance of the composite superstructure. The Raman spectrum signal obtained can clearly identify the characteristic peak of the methylene blue molecule (1395cm -1 and 1622cm -1 Compared with the single silicon dioxide photonic crystal three-dimensional array substrate and the gold nano-superlattice ordered two-dimensional monolayer film substrate, the Raman signal of the photonic crystal-plasmon superlattice composite superstructure has a significant enhancement. Figure 4 Middle b shows different substrate detection 10 -5 The methylene blue molecule M is at 1622 cm -1 The Raman intensity histogram at is shown. The results show that the Raman intensity of the 3D silica photonic crystal array substrate is only 9.67, while the Raman characteristic peak intensity of the gold nanosuperlattice ordered 2D monolayer substrate is 4468.41 due to the electromagnetic field enhancement provided by the plasmonic nanoparticles. The Raman intensity of the photonic crystal-plasmonic superlattice composite superstructure is as high as 14508.67, which is 3.25 times that of the gold nanosuperlattice ordered 2D monolayer substrate and 1500 times that of the 3D silica photonic crystal array substrate. This verifies the excellent effect of the photonic crystal-plasmonic superlattice composite superstructure in enhancing Raman spectroscopy.

[0065] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for fabricating a photonic crystal-plasmonic superlattice composite superstructure, characterized in that, Comprise: (1) self-assemble monodisperse silica nanogel with a particle size of 100-400 nm in a medium to form a liquid colloidal crystal, coat the surface of a substrate with the liquid colloidal crystal, and evaporate the solvent to form a three-dimensional array of silica photonic crystal; (2) prepare gold nanoparticles with a particle size of 10-60 nm, modify the gold nanoparticles with mercaptan polystyrene and 1,8-octanedithiol in sequence, and form a film of the gold nanoparticle superlattice ordered two-dimensional monolayer at a liquid interface to obtain a gold nanoparticle superlattice ordered two-dimensional monolayer film; (3) transfer the gold nanoparticle superlattice ordered two-dimensional monolayer film to the three-dimensional array of silica photonic crystal to couple the double-layer ordered structure, and prepare the photonic crystal-plasmonic superlattice composite superstructure. In step (2), the gold nanoparticles modified with mercaptan polystyrene and 1,8-octanedithiol are dispersed in toluene, and then transferred to a diethylene glycol subphase. After the toluene is completely volatilized, the gold nanoparticle superlattice ordered two-dimensional monolayer film is obtained at the diethylene glycol interface.

2. The method for preparing a photonic crystal-plasmon superlattice composite superstructure according to claim 1, wherein: In step (1), the monodisperse silica nanogel is prepared by a seed growth method. First, silica nanoseeds are synthesized using tetraethyl orthosilicate as a raw material and arginine as a catalyst. Then, the silica nanoseeds are further grown by catalyzing the hydrolysis of tetraethyl orthosilicate with ammonia in the system to obtain monodisperse silica nanogel.

3. The method of claim 1, wherein the photonic crystal-plasmonic superlattice composite superstructure is prepared by the steps of: In step (1), the medium comprises at least one of ethanol, ethylene glycol, diethylene glycol, propylene carbonate, dimethylformamide, and dimethyl sulfoxide; and / or the substrate comprises a silicon wafer, glass, polyimide, polyethylene terephthalate, polydimethylsiloxane, ceramic, or metal substrate.

4. The method of claim 1, wherein the photonic crystal-plasmonic superlattice composite superstructure is prepared by the steps of: In step (1), the solvent is volatilized by heating to form the three-dimensional array of silica photonic crystal, and the heating conditions are 30-100°C for 1.5-2 h.

5. The method of claim 1, wherein the photonic crystal-plasmonic superlattice composite superstructure is prepared by the steps of: In step (2), the gold nanoparticles are prepared by a seed growth method; and mercaptan polystyrene and 1,8-octanedithiol are connected to the gold nanoparticles through gold-sulfur bonds.

6. The method of claim 1, wherein the photonic crystal-plasmonic superlattice composite superstructure is prepared by the steps of: In step (2), The average molecular weight of the mercaptan polystyrene PSSH is 5000-20000 g / mol; the mercaptan polystyrene is modified by reacting a mercaptan polystyrene solution with a gold nanoparticle solution, wherein the concentration of the mercaptan polystyrene solution is 10 -6 ~10 -4 mol / L. and / or, using a 1,8-octanedithiol solution with a concentration of 5.0 x 10 -6 1.5 x 10 -5 mol / L to react with the solution of the gold nanoparticles modified by mercapto polystyrene, to complete the modification of 1,8-octanedithiol.

7. The photonic crystal-plasmonic superlattice composite superstructure prepared by the method of any one of claims 1-6.

8. The photonic crystal-plasmonic superlattice composite superstructure of claim 7, wherein, The structure comprises, from bottom to top, a substrate, a three-dimensional array of silica photonic crystal, and a gold nanoparticle superlattice ordered two-dimensional monolayer film.

9. A SERS substrate, characterized in that, The photonic crystal-plasmonic superlattice composite superstructure of claim 7 or 8.

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