High sensitivity silver nanoparticle array sers substrate and method of making same

Abstract

The application belongs to the technical field of surface enhanced Raman scattering (SERS) substrate preparation, and particularly relates to a high-sensitivity conical silver nanoparticle array SERS substrate and a preparation method thereof. The substrate comprises a silicon substrate, a PS microsphere array and a silver film layer composed of silver nanoparticles. The PS microsphere array is distributed in a hexagonal close-packed manner on the surface of the silicon substrate, and adjacent PS microspheres form a periodic gap region. The silver film layer uniformly covers the curved surface of the PS microspheres and the surface of the silicon substrate in the gap region. The silver film in the gap region is spatially constrained to form a conical silver nanoparticle array. The application can significantly improve the hotspot intensity and the enhancement factor of the SERS substrate, surpassing the traditional planar structure. The application realizes precise and flexible regulation of the nanostructure morphology, adapts to different excitation wavelengths and detection requirements, has a simple preparation process, low cost and can be prepared in a large area and uniformly. In addition, the application can also ensure the high repeatability and uniformity of the SERS signal.

Description

Technical Field

[0001] This invention belongs to the field of surface-enhanced Raman scattering (SERS) substrate preparation technology, specifically a high-sensitivity conical silver nanoparticle array SERS substrate and its preparation method. Background Technology

[0002] There is a planar silver film SERS substrate using PS microspheres as templates, which is realized by three parts: a silicon wafer substrate, a single-layer PS microsphere array, and a planar deposited silver film.

[0003] The substrate uses a silicon wafer as a support, on which a monolayer hexagonal close-packed PS microsphere array is self-assembled. Subsequently, a silver film is directly deposited on the surface of the PS microspheres and in the inter-microsphere regions. The silver film is continuously distributed in a planar manner on both the curved surface of the microspheres and in the inter-microsphere regions, without forming a protruding three-dimensional nanostructure. The local electromagnetic field enhancement generated by the plasmon effect on the silver film surface amplifies the Raman signal of the molecules adsorbed on the silver film surface. The microsphere array only serves as a template to provide a periodic structure, and the inter-microsphere regions only serve as silver film attachment areas and do not participate in structural shaping.

[0004] Because this scheme uses planar silver film deposition and does not utilize the gap space constraint effect, the gap region cannot form a three-dimensional protrusion structure, which leads to the inability to form longitudinal electromagnetic field coupling. It can only rely on the planar silver film to generate weak enhancement, ultimately resulting in low sensitivity, uncontrollable morphology, and unstable signal.

[0005] Traditional thinking has been limited to "planar deposition + planar structure", failing to realize that gap space constraints can form conical three-dimensional structures. If three-dimensional structures are forcibly made, complex processes such as photolithography and etching are often required, which are costly and difficult to fabricate on a large scale. The simple self-assembly route has long been unable to break through the controllable molding of three-dimensional structures. Summary of the Invention

[0006] The purpose of this invention is to address the problems of insufficient hot spots, poor uniformity, complex preparation, and uncontrollable structural morphology in existing SERS substrates. This invention provides a high-sensitivity conical silver nanoparticle array SERS substrate and its preparation method, aiming to achieve at least one of the following objectives: 1. Significantly improves the hot spot strength and enhancement factor of SERS substrates, surpassing traditional planar structures; 2. To achieve precise and flexible control of nanostructure morphology, adapting to different excitation wavelengths and detection requirements; 3. The preparation process is simple and inexpensive, and it can be used to prepare uniformly over a large area; 4. Ensure high repeatability and uniformity of SERS signals.

[0007] To achieve the above-mentioned objectives, the specific technical solution of this invention is as follows: A high-sensitivity conical silver nanoparticle array (SERS) substrate comprises a silicon wafer substrate, a PS microsphere array, and a silver film layer composed of silver nanoparticles. The PS microsphere array is hexagonally close-packed on the surface of the silicon wafer substrate, and adjacent PS microspheres form periodic gap regions. The silver film layer uniformly coats the curved surface of the PS microspheres and the silicon wafer surface in the gap regions. The silver film in the gap regions is spatially constrained, forming a conical silver nanoparticle array.

[0008] Furthermore, in the aforementioned high-sensitivity conical silver nanoparticle array SERS substrate, the diameter of the PS microspheres is 800 nm-2 μm, the gap width between the PS microspheres is 20-80 nm, the thickness of the silver film layer is 10-50 nm, the cone height of the conical silver nanoparticle array is 10-50 nm, the cone base diameter is consistent with the gap width between the PS microspheres, and the period of the conical silver nanoparticle array is the same as the period of the PS microsphere array (each pair of adjacent microspheres corresponds to one gap, which also corresponds to one conical silver particle; the periodic arrangement of the PS microspheres is the same as the periodic arrangement of the conical silver particles in the gaps, and the conical array is a "gap replica" of the microsphere array).

[0009] As a preferred embodiment of this application, the method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate described above includes the following steps: (1) Silicon wafer pretreatment: The single crystal silicon wafer is ultrasonically cleaned with acetone, ethanol and ultrapure water in sequence and then dried; then treated with oxygen plasma; this step can improve the surface hydrophilicity and provide a good interface for the uniform spreading of PS microsphere array.

[0010] (2) PS microsphere array self-assembly: The gas-liquid interface micro-propulsion injection method is used to mix PS microspheres with ethanol to prepare a dispersion; the dispersion is slowly injected into the surface of ultrapure water. In an environment with a certain temperature and humidity, the PS microspheres self-assemble at the gas-liquid interface to form a large-area single-layer hexagonal close-packed array; then the array is transferred to the silicon wafer after the pretreatment in step (1) and dried naturally to form a periodic gap region with a certain gap width between the microspheres. (3) Silver film deposition and cone array formation: Silver film deposition is carried out by magnetron sputtering, that is, the silver film composed of silver nanoparticles is uniformly covered on the surface of the silicon wafer within the curved surface and gaps of the PS microspheres; due to the spatial constraint effect of the gap width of the PS microspheres, the silver film in the gap area naturally forms a cone-shaped array of silver nanoparticles with a certain cone height and cone bottom diameter. (4) Drying and shaping: After the deposition in step (3) is completed, the obtained sample is naturally evaporated and dried at room temperature to obtain a high-sensitivity conical silver nanoparticle array SERS substrate.

[0011] As a preferred embodiment of this application, in step (1) of the method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate, the ultrasonic cleaning time with acetone, ethanol and ultrapure water is 10±2 min respectively; after cleaning, it is dried with nitrogen gas; and the oxygen plasma treatment time is 40 s.

[0012] As a preferred embodiment of this application, in step (2) of the method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate, the volume ratio of PS microspheres to ethanol is 1:1 to 1:2 (more preferably 1:1.5); the concentration of the dispersion is 1wt% to 3wt% (more preferably 2wt%); the temperature at which the PS microspheres self-assemble at the gas-liquid interface is 25 to 35°C (more preferably 30°C), the humidity is 40 to 60% (more preferably 50%), and the self-assembly time is 3 to 8 minutes (more preferably 5 minutes).

[0013] As a preferred embodiment of this application, in step (3) of the method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate, the sputtering conditions for silver film deposition by magnetron sputtering are: sputtering power 60~90W (more preferably 80W), argon flow rate 12~18sccm (more preferably 15sccm), and vacuum degree approximately 3×10⁻⁶. -5 ~8×10 -5 Pa (more preferably, a vacuum degree of 5 × 10 Pa) -5 Pa), deposition rate 0.1-0.5 nm / s.

[0014] As a preferred embodiment of this application, in the method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate, it is necessary to establish a matching relationship between the silver film thickness and the PS gap width, wherein the silver film thickness is ≤ 0.6 to 1.2 times the PS gap width.

[0015] This invention also protects a high-sensitivity conical silver nanoparticle array SERS substrate prepared by any of the methods described above.

[0016] Furthermore, this invention also protects the application of the high-sensitivity conical silver nanoparticle array SERS substrate described above in improving the electromagnetic field strength and hotspot density of the SERS substrate.

[0017] Alternatively, the three-dimensional conical silver nanoparticle array formed by the spatial constraint of the silver film in the interstitial region can enhance the performance of SERS substrates, such as in the trace SERS detection of pesticide residues, environmental pollutants, and small biological molecules.

[0018] Compared with existing technologies, the beneficial effects of this invention are: (1) The three-dimensional conical structure realizes multi-dimensional field coupling in the horizontal and vertical directions, and the electromagnetic field enhancement effect is significantly better than that of ordinary planar structure, and the hot spot intensity is greatly improved.

[0019] (2) The height of the conical array can be precisely controlled by adjusting the gap width of the PS microspheres, which can flexibly adapt to different excitation wavelengths and detection requirements.

[0020] (3) PS template self-assembly can realize large-area preparation, with simple process and low cost.

[0021] (4) The structure has a uniform period, good SERS signal repeatability, and high detection sensitivity.

[0022] (5) It can be used for trace SERS detection of pesticide residues, environmental pollutants and biological small molecules. Attached Figure Description

[0023] Figure 1 A schematic diagram of the SERS substrate structure of a cone-shaped silver nanoparticle array; Among them, 1-a silver film layer composed of silver nanoparticles, 2-PS microsphere array, 3-silicon substrate (Si substrate). Figure 2 A schematic diagram of the fabrication process for a sensitive cone-shaped silver nanoparticle array SERS substrate; Figure 3 The concentration gradient spectra of the four substances are shown. Figure 4 Figure 1 shows the test results of SERS substrate signal repeatability and long-term stability. Among them, (a) a stacked three-dimensional Raman spectrum of 10 random points on the same substrate; (b) a statistical bar chart of the corresponding characteristic peak signal intensity; (c) three-dimensional Raman spectra of the same batch of substrates stored in the dark for 30 days at different time points; (d) statistical analysis of the characteristic peak intensity of storage stability; (e) a stacked three-dimensional SERS spectrum of 10 independently prepared batches of substrates; and (f) a statistical bar chart of the reproducibility of characteristic peak signals of multiple batches of substrates. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] In this invention, some conventional operating equipment, devices and components have been omitted or only briefly described.

[0028] Unless otherwise specified in the examples, the conditions shall be performed according to the standard conditions or the conditions recommended by the manufacturer.

[0029] In this application, any percentage not marked indicates its weight percentage content.

[0030] In this application, all unspecified proportional relationships refer to mass ratios.

[0031] Any steps or apparatus not described in detail are prior art or have no substantial impact on the effectiveness of this application.

[0032] Example 1: like Figure 1 As shown, the high-sensitivity conical silver nanoparticle array SERS substrate in this embodiment includes, from bottom to top: a silicon wafer substrate (monocrystalline silicon wafer) 3, a PS microsphere array (single-layer hexagonal close-packed distribution) 2 arranged on its surface, and a silver film layer 1 composed of silver nanoparticles covering the curved surface and gap region (adjacent PS microspheres in the PS microsphere array form a periodic gap region) of the silicon wafer surface; the silver film in the gap region is spatially constrained, forming a three-dimensional conical silver nanoparticle array.

[0033] In the PS microsphere array 2, the diameter of the PS microspheres is approximately 800 nm, and the gap width between adjacent PS microspheres is approximately 20 nm; the thickness of the silver film layer 1 is 30 nm. The height of the cone-shaped silver nanoparticles formed in the gap region is approximately 20 nm, and the diameter of the cone base is consistent with the gap width (approximately 20 nm). The entire array period is the same as the PS microsphere period.

[0034] like Figure 2 As shown, the specific fabrication steps of a high-sensitivity conical silver nanoparticle array SERS substrate are as follows: (1) Silicon wafer pretreatment: The single crystal silicon wafer was ultrasonically cleaned with acetone, ethanol and ultrapure water for 10 minutes each, and then dried with nitrogen; then treated with oxygen plasma for 40 seconds to improve the surface hydrophilicity and provide a good interface for the uniform spreading of PS microsphere array.

[0035] (2) Self-assembly of PS microsphere array: Using a gas-liquid interface micro-propulsion injection method, PS microspheres with a diameter of 800 nm were mixed with ethanol at a volume ratio of 1:1.5 to prepare a dispersion with a mass fraction of approximately 2 wt%. The prepared dispersion was slowly injected into the surface of ultrapure water. In an environment with a temperature of 30 °C and a humidity of 50%, the PS microspheres self-assembled at the gas-liquid interface for 5 minutes to form a large-area monolayer hexagonal close-packed array. The formed monolayer hexagonal close-packed array was then transferred to the silicon wafer pretreated in step (1) and allowed to dry naturally. Periodic gap regions with a gap width of approximately 20 nm were formed between the microspheres.

[0036] (3) Silver film deposition and cone array formation: Silver film deposition was performed using magnetron sputtering. The sputtering conditions were: sputtering power 80W, argon flow rate 15sccm, and vacuum degree approximately 5×10⁻⁶. -5 At a deposition rate of 0.3 nm / s, the silver film thickness was 30 nm. The silver film uniformly covered the silicon wafer surface within the curved surface and gaps of the PS microspheres. Due to the spatial constraint effect of the gap width (approximately 20 nm) of the PS microspheres, the silver film in the gap region naturally formed an array of conical silver nanoparticles with a cone height of approximately 20 nm and a cone base diameter of approximately 20 nm. Since the conical structure and the silver film layer on the curved surface of the PS microspheres constitute a multi-level plasmon coupling system, a strong local electromagnetic field enhancement is generated.

[0037] (4) Drying and shaping: After deposition, the sample is naturally evaporated and dried at room temperature to obtain a high-sensitivity cone-shaped silver nanoparticle array SERS substrate.

[0038] Example 2: like Figure 1 As shown, the high-sensitivity conical silver nanoparticle array SERS substrate in this embodiment includes, from bottom to top: a silicon wafer substrate (monocrystalline silicon wafer) 3, a PS microsphere array (single-layer hexagonal close-packed distribution) 2 arranged on its surface, and a silver film layer 1 composed of silver nanoparticles covering the curved surface and gap region (adjacent PS microspheres in the PS microsphere array form a periodic gap region) of the silicon wafer surface. The silver film in the gap region is spatially constrained, forming a three-dimensional conical silver nanoparticle array.

[0039] In the PS microsphere array 2, the diameter of the PS microspheres is approximately 800 nm, and the gap width between adjacent PS microspheres is approximately 20 nm; the thickness of the silver film layer 1 is 30 nm. The height of the cone-shaped silver nanoparticles formed in the gap region is approximately 20 nm, and the diameter of the cone base is consistent with the gap width (approximately 20 nm). The entire array period is the same as the PS microsphere period.

[0040] like Figure 2 As shown, the specific fabrication steps of a high-sensitivity conical silver nanoparticle array SERS substrate are as follows: (1) Silicon wafer pretreatment: The single crystal silicon wafer was ultrasonically cleaned with acetone, ethanol and ultrapure water for 10 minutes each, and then dried with nitrogen; then treated with oxygen plasma for 40 seconds to improve the surface hydrophilicity and provide a good interface for the uniform spreading of PS microsphere array.

[0041] (2) Self-assembly of PS microsphere array: Using a gas-liquid interface micro-propulsion injection method, PS microspheres with a diameter of 800 nm were mixed with ethanol at a volume ratio of 1:1.5 to prepare a dispersion with a mass fraction of approximately 2 wt%. The prepared dispersion was slowly injected into the surface of ultrapure water. In an environment with a temperature of 30 °C and a humidity of 60%, the PS microspheres self-assembled at the gas-liquid interface for 5 minutes to form a large-area monolayer hexagonal close-packed array. The formed monolayer hexagonal close-packed array was then transferred to the silicon wafer pretreated in step (1) and allowed to dry naturally. (Due to the increase in humidity, the capillary force between the microspheres weakened,) and a periodic gap region with a gap width of approximately 60 nm was formed between the microspheres.

[0042] (3) Silver film deposition and cone array formation: Silver film deposition was performed using magnetron sputtering. The sputtering conditions were: sputtering power 80W, argon flow rate 15sccm, and vacuum degree approximately 5×10⁻⁶. -5 At a deposition rate of 0.3 nm / s, the silver film thickness was 40 nm. The silver film uniformly covered the silicon wafer surface within the curved surface and gaps of the PS microspheres. Due to the spatial constraint effect of the gap width (approximately 20 nm) of the PS microspheres, the silver film in the gap region naturally formed a cone-shaped array of silver nanoparticles with a cone height of approximately 60 nm (one of the highest cone height structures reported so far in the PS template method) and a cone base diameter of approximately 20 nm. Since the cone structure and the silver film layer on the curved surface of the PS microspheres constitute a multi-level plasmon coupling system, a strong local electromagnetic field enhancement is generated.

[0043] (4) Drying and shaping: After deposition, the sample is naturally evaporated and dried at room temperature to obtain a high-sensitivity cone-shaped silver nanoparticle array SERS substrate.

[0044] Performance testing: Adapted to 785nm near-infrared excitation wavelength, the detection limit for the biological small molecule glucose reaches 1×10⁻⁶. - 9 mol / L, suitable for non-destructive testing of biological fluids.

[0045] Comparative Example 1: The excessively rapid silver film deposition rate prevented the formation of a cone-shaped structure. like Figure 1As shown, the high-sensitivity conical silver nanoparticle array SERS substrate in this embodiment includes, from bottom to top: a silicon wafer substrate (monocrystalline silicon wafer) 3, a PS microsphere array (single-layer hexagonal close-packed distribution) 2 arranged on its surface, and a silver film layer 1 composed of silver nanoparticles covering the curved surface and gap region (adjacent PS microspheres in the PS microsphere array form a periodic gap region) of the silicon wafer surface. The silver film in the gap region is spatially constrained, forming a three-dimensional conical silver nanoparticle array.

[0046] In the PS microsphere array 2, the diameter of the PS microspheres is approximately 800 nm, and the gap width between adjacent PS microspheres is approximately 20 nm; the thickness of the silver film layer 1 is 30 nm. The height of the cone-shaped silver nanoparticles formed in the gap region is approximately 20 nm, and the diameter of the cone base is consistent with the gap width (approximately 20 nm). The entire array period is the same as the PS microsphere period.

[0047] like Figure 2 As shown, the specific fabrication steps of a high-sensitivity conical silver nanoparticle array SERS substrate are as follows: (1) Silicon wafer pretreatment: The single crystal silicon wafer was ultrasonically cleaned with acetone, ethanol and ultrapure water for 10 minutes each, and then dried with nitrogen; then treated with oxygen plasma for 40 seconds to improve the surface hydrophilicity and provide a good interface for the uniform spreading of PS microsphere array.

[0048] (2) Self-assembly of PS microsphere array: Using a gas-liquid interface micro-propulsion injection method, PS microspheres with a diameter of 800 nm were mixed with ethanol at a volume ratio of 1:1.5 to prepare a dispersion with a mass fraction of approximately 2 wt%. The prepared dispersion was slowly injected into the surface of ultrapure water. In an environment with a temperature of 30 °C and a humidity of 50%, the PS microspheres self-assembled at the gas-liquid interface for 5 minutes to form a large-area monolayer hexagonal close-packed array. The formed monolayer hexagonal close-packed array was then transferred to the silicon wafer pretreated in step (1) and allowed to dry naturally. Periodic gap regions with a gap width of approximately 20 nm were formed between the microspheres.

[0049] (3) Silver film deposition and cone array formation: Silver film deposition was performed using magnetron sputtering. The sputtering conditions were: sputtering power 80W, argon flow rate 15sccm, and vacuum degree approximately 5×10⁻⁶. -5 In this step, to improve the preparation efficiency, the magnetron sputtering deposition rate is increased to 1 nm / s, and the thickness of the deposited silver film is 30 nm.

[0050] The results showed that the silver film in the interstitial region was stacked in a planar shape and did not form a conical structure, which was not significantly different from the traditional planar silver film substrate.

[0051] The above results indicate that when magnetron sputtering deposition is performed, if the deposition rate is too fast, the diffusion time of silver atoms on the substrate surface is insufficient, preventing them from directionally aggregating and forming a cone shape within the limited space of the interstitial region. Instead, they can only grow along the surface plane. In this invention, after repeated adjustments, it was found that the deposition rate needs to be strictly controlled within the range of 0.1-0.5 nm / s to ensure that silver atoms have sufficient diffusion time to self-assemble into a cone structure under the constraint of the interstitial space.

[0052] Comparative Example 2: Excessive silver film thickness caused the gaps to be filled, resulting in the loss of the cone-shaped structure. like Figure 1 As shown, the high-sensitivity conical silver nanoparticle array SERS substrate in this embodiment includes, from bottom to top: a silicon wafer substrate (monocrystalline silicon wafer) 3, a PS microsphere array (single-layer hexagonal close-packed distribution) 2 arranged on its surface, and a silver film layer 1 composed of silver nanoparticles covering the curved surface and gap region (adjacent PS microspheres in the PS microsphere array form a periodic gap region) of the silicon wafer surface. The silver film in the gap region is spatially constrained, forming a three-dimensional conical silver nanoparticle array.

[0053] In the PS microsphere array 2, the diameter of the PS microspheres is approximately 800 nm, and the gap width between adjacent PS microspheres is approximately 20 nm; the thickness of the silver film layer 1 is 30 nm. The height of the cone-shaped silver nanoparticles formed in the gap region is approximately 20 nm, and the diameter of the cone base is consistent with the gap width (approximately 20 nm). The entire array period is the same as the PS microsphere period.

[0054] like Figure 2 As shown, the specific fabrication steps of a high-sensitivity conical silver nanoparticle array SERS substrate are as follows: (1) Silicon wafer pretreatment: The single crystal silicon wafer was ultrasonically cleaned with acetone, ethanol and ultrapure water for 10 minutes each, and then dried with nitrogen; then treated with oxygen plasma for 40 seconds to improve the surface hydrophilicity and provide a good interface for the uniform spreading of PS microsphere array.

[0055] (2) Self-assembly of PS microsphere array: Using a gas-liquid interface micro-propulsion injection method, PS microspheres with a diameter of 800 nm were mixed with ethanol at a volume ratio of 1:1.5 to prepare a dispersion with a mass fraction of approximately 2 wt%. The prepared dispersion was slowly injected into the surface of ultrapure water. In an environment with a temperature of 30 °C and a humidity of 50%, the PS microspheres self-assembled at the gas-liquid interface for 5 minutes to form a large-area monolayer hexagonal close-packed array. The formed monolayer hexagonal close-packed array was then transferred to the silicon wafer pretreated in step (1) and allowed to dry naturally. Periodic gap regions with a gap width of approximately 20 nm were formed between the microspheres.

[0056] (3) Silver film deposition and cone array formation: Silver film deposition was performed using magnetron sputtering. The sputtering conditions were: sputtering power 80W, argon flow rate 15sccm, and vacuum degree approximately 5×10⁻⁶. -5 At a deposition rate of 0.3 nm / s, the silver film thickness was adjusted to 60 nm. The silver film uniformly covered the silicon wafer surface within the curved surface and gaps of the PS microspheres. Due to the spatial constraint effect of the PS microsphere gap width (approximately 20 nm), the silver film within the gap region naturally formed an array of conical silver nanoparticles with a cone height of approximately 20 nm and a cone base diameter of approximately 20 nm. Because the conical structure and the silver film layer on the curved surface of the PS microspheres constitute a multi-level plasmon coupling system, a strong local electromagnetic field enhancement is generated.

[0057] (4) Drying and shaping: After deposition, the sample is naturally evaporated and dried at room temperature to obtain a high-sensitivity cone-shaped silver nanoparticle array SERS substrate.

[0058] The results showed that the gaps between the PS microspheres were completely filled by the silver film, forming a continuous planar silver film. The conical structure completely disappeared, and the SERS enhancement effect was comparable to that of ordinary planar silver film substrates.

[0059] The above results indicate that when the thickness of the silver film exceeds the gap width of the PS microspheres, the silver film will cover the entire gap area, making it impossible to form a conical growth under spatial constraints.

[0060] Therefore, a matching relationship is established between the silver film thickness and the PS gap width: the silver film thickness should be ≤ 1.2 times the PS gap width. For example, a 20nm gap corresponds to a silver film thickness ≤ 24nm, and a 40nm gap corresponds to a silver film thickness ≤ 48nm, ensuring the formation of the tapered structure.

[0061] Test: Measurement using the substrate prepared in Example 1 Test method: 1. Sample blank background of the substrate before testing. The ordered nanostructured SERS substrate synthesized and self-assembled in Example 1 was cut to a size suitable for the sample stage of a portable Raman spectrometer. A clean, analyte-free blank substrate is flattened and fixed onto the Raman sample stage, ensuring that the nanostructure surface of the substrate is facing upwards, without wrinkles or fingerprint contamination. Turn on the portable Raman spectrometer and set the uniform acquisition parameters; Six to eight non-overlapping test points were randomly selected on the surface of a blank substrate. A set of Raman spectra was independently collected at each point as the substrate background signal. Save all blank background spectra for subsequent baseline subtraction of the sample to be tested, and eliminate interference from carbon and silicon substrate impurities.

[0062] 2. Sample preparation of e-cigarette liquid to be tested Using a calibrated 10 μL pipette, accurately aspirate 10 μL of the e-cigarette oil sample to be tested. With the pipette tip suspended vertically and aligned with the center of the nano-active region of the substrate, slowly and evenly add the liquid to ensure that the droplet completely covers the plasma-active region of the substrate without overflowing the edge of the substrate. After the sample is dropped, the substrate is placed in a dust-free, light-proof, room-temperature, and well-ventilated environment to air dry naturally, avoiding dust and direct airflow on the sample throughout the process; wait for the droplets to completely evaporate and for a uniform adsorption film of the target molecules to form on the substrate surface (without visible liquid film or localized agglomerated liquid spots). The entire air-drying process is conducted in the dark to prevent photodegradation of nicotine and cooling agent molecules.

[0063] 3. Sample SERS spectral data acquisition The dried sample substrate was then fixed back onto the Raman stage, keeping the nano-active layer facing the laser beam path. Use the same instrument parameters as when acquiring a blank background, without changing the laser power, integration time, or wavenumber scan range; Within the active area of ​​the dropped sample, 6 to 8 independent test points are randomly selected, which are dispersed and non-overlapping. The test points are evenly distributed within the air-drying area of ​​the droplet, avoiding the drying and aggregation zone at the edge. Collect a complete Raman spectrum once for each location and save all original spectra. 4. Data Preprocessing Operations Baseline correction and background subtraction were performed on the spectra of all sample points and the previously collected baseline blank background spectra; at the same time, menthol, WS-3 and WS-23 were identified based on the characteristic Raman peaks of each cooling agent.

[0064] The specific results are shown in Table 1 and Table 2. Figure 3 and Figure 4 .

[0065] Table 1. Measurement limits and sensitivities of four substances

[0066] Table 2. Quantitative SERS and qualitative detection results of cooling agents in four commercially available e-cigarette liquid samples.

[0067] From Table 1, Table 2, Figure 3 and Figure 4 It can be known that: (1) The three-dimensional conical array on this substrate generates local electromagnetic field coupling in both the transverse and longitudinal directions, and the high-density three-dimensional hotspots significantly amplify the Raman scattering signal. This is evident from the concentration gradient spectrum (e.g., Figure 3As can be seen, trace amounts of four small molecules—nicotine, menthol, WS-3, and WS-23—can be identified. The detection limit for nicotine is as low as 0.001 mg / g, and it still exhibits a high signal-to-noise ratio characteristic peak at extremely low concentrations, directly demonstrating that the electromagnetic field enhancement effect of the three-dimensional structure is significantly superior to that of the traditional two-dimensional planar SERS substrate. As shown in Table 1, the improvement factor parameters indicate that, compared to the two-dimensional planar SERS substrate, the signal intensity of the analyte at the same concentration is increased by 10%. 4 ~10 5 times.

[0068] (2) The height of the substrate cone array is precisely controlled by the gaps between the PS template spheres, which can match the adsorption and electromagnetic resonance conditions of analytes of different sizes. For example Figure 3 All four types of molecules can be stably detected. This work simultaneously achieves trace detection of four types of organic small molecules with huge structural differences, namely nicotine, menthol, and two amide cooling agents. It proves that by adjusting the gap between PS microspheres and the cone height, it is possible to flexibly adapt to the detection needs of different molecular systems.

[0069] (3) Figure 4 (e) and (f) show the signal statistics for different preparation batches, with 10 independent batches of substrates at 854 cm⁻¹. -1 1000cm -1 The characteristic peak RSD is only 6.72% and 6.39%, and the signal fluctuations of multiple batches are extremely small.

[0070] (4) such as Figure 4 Single-point repeatability (a)(b): Ten test points were randomly selected from the same substrate, and the characteristic peak RSD was only 2.38% and 3.42%, respectively, with almost no signal fluctuation between the test points; Long-term storage stability (c)(d): After the substrate was stored in the dark for 30 days, the RSD of the signal at 30 time points was only 4.43% and 4.49%, respectively, indicating that the structure did not fail after long-term storage. Batch reproducibility (e)(f): RSD < 7% for 10 independently prepared substrates.

[0071] (5) The three-dimensional high-density hotspot structure of the substrate exhibits excellent SERS enhancement capabilities for a variety of small organic molecules. Concentration gradient experiments confirm that, for example... Figure 3 This substrate can achieve ultra-low detection limits for amide small molecules; as shown in Table 2, it can simultaneously screen multiple components in complex matrix samples of e-cigarette oil. After expansion, it can be widely used for rapid trace detection of pesticide residues, environmental organic pollutants, and biological small molecules.

[0072] Based on the above embodiments and process verification, the key parameters of this solution can be flexibly adjusted within the following ranges, with the core principle being to ensure the self-forming of the conical silver structure under gap constraints: (1) PS microspheres and gap control: The diameter can be selected from 800nm ​​to 2μm. By adjusting the self-assembly temperature and humidity, ethanol-water mixing ratio, and dispersion concentration, the gap can be precisely controlled at 20-80nm. The cone height is positively correlated with the gap width.

[0073] (2) Silver film deposition: Magnetron sputtering or vacuum thermal evaporation can be used. The deposition rate must be controlled at 0.1-0.5 nm / s (optimal 0.2-0.3 nm / s). If the rate is too fast, a cone-shaped structure cannot be formed.

[0074] (3) Silver film thickness matching: the thickness should be ≤ 1.2 times the gap width. If it is too thick, it will fill the gap and cause the cone to disappear. The usual choice is 10-50nm.

[0075] (4) PS microsphere retention: It is not recommended to remove them, otherwise a large number of conical silver particles will fall off; retaining PS can form multi-level plasmon coupling, which can improve the enhancement effect and structural stability.

[0076] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

[0077] This background section is provided to generally present the context of the invention. The work of the currently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither expressly nor impliedly acknowledged as prior art to the invention.

Claims

1. A high-sensitivity cone-shaped silver nanoparticle array SERS substrate, characterized in that: It includes a silicon wafer substrate, a PS microsphere array, and a silver film layer composed of silver nanoparticles; wherein, the PS microsphere array is hexagonally close-packed on the surface of the silicon wafer substrate, and adjacent PS microspheres form periodic gap regions; the silver film layer uniformly covers the curved surface of the PS microspheres and the silicon wafer surface in the gap regions, and the silver film in the gap regions is spatially constrained to form a conical silver nanoparticle array.

2. The high-sensitivity conical silver nanoparticle array SERS substrate according to claim 1, characterized in that: The diameter of the PS microspheres is 800nm-2μm, and the gap width between the PS microspheres is 20-80nm; the thickness of the silver film layer is 10-50nm; the cone height of the conical silver nanoparticle array is 10-50nm, and the diameter of the cone base is the same as the gap width between the PS microspheres; the period of the conical silver nanoparticle array is the same as the period of the PS microsphere array.

3. The method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Silicon wafer pretreatment: The monocrystalline silicon wafer is ultrasonically cleaned with acetone, ethanol and ultrapure water in sequence and then dried; then it is treated with oxygen plasma. (2) PS microsphere array self-assembly: The gas-liquid interface micro-propulsion injection method is used to mix PS microspheres with ethanol to prepare a dispersion; the dispersion is slowly injected into the surface of ultrapure water. In an environment with a certain temperature and humidity, the PS microspheres self-assemble at the gas-liquid interface to form a large-area single-layer hexagonal close-packed array; then the array is transferred to the silicon wafer after the pretreatment in step (1) and dried naturally to form a periodic gap region with a certain gap width between the microspheres. (3) Silver film deposition and cone array formation: Silver film deposition is carried out by magnetron sputtering, that is, the silver film composed of silver nanoparticles is uniformly covered on the surface of the silicon wafer within the curved surface and gaps of the PS microspheres; due to the spatial constraint effect of the gap width of the PS microspheres, the silver film in the gap area naturally forms a cone-shaped array of silver nanoparticles with a certain cone height and cone bottom diameter. (4) Drying and shaping: After the deposition in step (3) is completed, the obtained sample is naturally evaporated and dried at room temperature to obtain a high-sensitivity conical silver nanoparticle array SERS substrate.

4. The method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate as described in claim 3, characterized in that: In step (1), the ultrasonic cleaning time with acetone, ethanol and ultrapure water is 10±2 min respectively; after cleaning, it is dried with nitrogen gas; the oxygen plasma treatment time is 40 s.

5. The method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate as described in claim 3, characterized in that: In step (2), the volume ratio of PS microspheres to ethanol is 1:1 to 1:2; the concentration of the dispersion is 1wt% to 3wt%.

6. The method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate as described in claim 3, characterized in that: In step (2), the temperature of the PS microspheres during self-assembly at the gas-liquid interface is 25~35℃, the humidity is 40~60%, and the self-assembly time is 3~8 minutes.

7. The method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate as described in claim 3, characterized in that, In step (3), the sputtering conditions for silver film deposition by magnetron sputtering are: sputtering power 60~90W, argon flow rate 12~18sccm, and vacuum degree 3×10 -5 ~8×10 -5 Pa, deposition rate 0.1-0.5 nm / s.

8. The method for preparing a high-sensitivity conical silver nanoparticle array SERS substrate as described in claim 3, characterized in that: The thickness of the silver film is ≤ 0.6~1.2 times the width of the PS gap.

9. A high-sensitivity cone-shaped silver nanoparticle array SERS substrate prepared by the method according to any one of claims 3-8.

10. The application of the high-sensitivity conical silver nanoparticle array SERS substrate as described in claim 9 in improving the electromagnetic field strength and hotspot density of the SERS substrate.

Images