A method for enhancing the sensitivity of a surface-enhanced Raman scattering substrate

Abstract

This invention belongs to the field of trace detection technology, specifically relating to a method for enhancing the sensitivity of a surface-enhanced Raman scattering (SERS) substrate. A sensitizing substrate for SERS comprises: a silver-aluminum substrate having a silver nanostructure and an alumina coating layer on its surface; and gold nanoparticle clusters formed on the surface of the silver-aluminum substrate. This invention improves sensitivity by forming gold nanoparticle clusters on the surface of the silver-aluminum substrate, further reducing the detection limit of SERS and achieving ultra-trace detection. Furthermore, the preparation process of this sensitizing substrate is simple, low-cost, and easy to promote and mass-produce.

Description

Technical Field

[0001] This invention belongs to the field of trace detection technology, specifically relating to a method for enhancing the sensitivity of a surface-enhanced Raman scattering substrate. Background Technology

[0002] When noble metals with nanoscale rough surfaces adsorb certain samples or molecules, their Raman scattering signals can exhibit several, or even significant, surface-enhanced Raman scattering (SERS) effects. Silver (Ag) has a higher electric field and lower loss than gold (Au) by two orders of magnitude, along with unique surface plasmon properties, making it more widely used. To cover a wider spectral range and improve SERS enhancement performance, researchers have developed nanoparticles of various shapes, such as spheres, rods, cubes, pyramids, plates, lines, corals, and stars. However, due to the fixed shape, the surface roughness is somewhat limited, especially for shapes like plates, rods, and cubes, where there is still considerable room for improvement in Raman sensitivity. Furthermore, metallic silver is easily oxidized and sulfided, and its nanosurfaces are highly active, readily oxidizing or adsorbing various molecules present in the environment. Therefore, researchers have found that coating its surface with an ultrathin protective layer can prevent silver nanostructures from being adsorbed by oxidants. However, regardless of whether the coating is oxide, carbon material, dense gold film, or other materials forming a shell, it will lead to a decrease in the Raman sensitivity of the substrate, which is extremely detrimental to trace and ultra-trace detection. Therefore, how to use simple and efficient methods to further enhance its sensitivity without affecting its durability, so as to obtain better surface-enhanced Raman scattering performance, is a technical problem that urgently needs to be solved in the field of trace detection.

[0003] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0004] The purpose of this invention is to provide a surface-enhanced Raman scattering (SERS) sensitizing substrate and its preparation method. The sensitizing substrate is made on a silver-aluminum substrate by using a relatively simple method to increase the surface roughness of the substrate to form a high-density "hot spot", thereby making it exhibit stronger SERS enhancement.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A surface-enhanced Raman scattering (SERS) sensitizing substrate comprising:

[0007] Silver-aluminum substrates with silver nanostructures and an alumina coating surface; and

[0008] Gold nanoparticle clusters formed on the surface of the silver-aluminum substrate.

[0009] More specifically, the silver nanostructure is selected from at least one of nanorods, nanotubes, nanowires and nanoparticles; the gold nanoparticles are selected from at least one of gold triangles and gold nanospheres.

[0010] More specifically, the thickness of the alumina coating layer is 0.75-1.5 nm; the diameter of the gold nanoparticles is 80-150 nm.

[0011] More specifically, the method for forming the gold nanoparticle clusters is as follows: first, the silver-aluminum substrate is immersed in a modification solution containing a silane coupling agent, or the modification solution containing a silane coupling agent is dropped onto the silver-aluminum substrate; then, the silver-aluminum substrate modified with the silane coupling agent is immersed in a modification solution containing gold nanoparticles, or the modification solution containing gold nanoparticles is dropped onto the silver-aluminum substrate modified with the silane coupling agent.

[0012] The present invention also provides a method for preparing the sensitizing substrate, comprising the following steps:

[0013] A modification solution containing a silane coupling agent was prepared using raw materials, and the modification solution containing the silane coupling agent was used to modify a silver-aluminum substrate with a silver nanostructure surface; and

[0014] A gold nanoparticle-containing modification solution was prepared using raw materials, and the gold nanoparticle-containing modification solution was used to modify a silver-aluminum substrate modified with a silane coupling agent.

[0015] More specifically, the silane coupling agent is at least one of KH550, KH560 and KH590; the concentration of the silane coupling agent is 10-100 mM.

[0016] More specifically, the solvent of the modified liquid is water or alcohol, and the alcohol is methanol or ethanol.

[0017] More specifically, the modification time for the silane coupling agent-containing modification solution is 30-60 min; the modification time for the gold nanoparticle-containing modification solution is 12-24 h.

[0018] The present invention also provides a method for surface-enhanced Raman scattering, comprising the following steps:

[0019] The test solution is added dropwise onto the sensitizing substrate, or the sensitizing substrate is immersed in the test solution; and

[0020] The detection was performed using a Raman spectrometer.

[0021] More specifically, the wavelength of the Raman spectrometer is 532nm, 633nm, 785nm or 1064nm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention improves sensitivity by forming gold nanoparticle clusters on the surface of a silver-aluminum substrate, further reducing the detection limit of surface-enhanced Raman scattering, and achieving ultra-trace detection. Moreover, the preparation process of this sensitized substrate is simple, low-cost, and easy to promote and mass-produce. Attached Figure Description

[0024] Figure 1 Flowchart for the preparation of the sensitized substrate;

[0025] Figure 2 This is a flowchart of the surface-enhanced Raman scattering method;

[0026] Figure 3 This is a scanning electron microscope image of a common silver-aluminum substrate;

[0027] Figure 4 Scanning electron microscope image of a sensitized silver-aluminum substrate;

[0028] Figure 5 Raman spectra of methylene blue were detected on a standard silver-aluminum substrate.

[0029] Figure 6 To detect the Raman spectrum of methylene blue on a sensitized substrate. Detailed Implementation

[0030] The technical solution of this invention patent will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0031] Raman spectroscopy is a molecular-specific fingerprint spectroscopy technique that utilizes surface-enhanced Raman scattering (SERS) to identify and detect trace substances. The SERS mechanism is primarily based on two types of enhancement: physical and chemical. Physical enhancement mainly results from the enhancement of the local electromagnetic field caused by surface plasmon resonance. The type, size, and shape of the metal, as well as the frequency of the incident light, all affect physical enhancement. Silver and gold are the best SERS materials, exhibiting excellent plasmon responses in the visible and near-infrared bands, increasing Raman signal intensity by 5-6 orders of magnitude. Under specific conditions, they can even achieve single-molecule detection (enhancement factor 10¹⁴-10¹⁵). Furthermore, their small slit width and favorable spectral shape make them an ultrasensitive analytical tool, widely used in analytical chemistry, especially in trace detection.

[0032] To address the drawbacks of silver blank substrates being prone to oxidation and adsorption of impurity molecules, many researchers have begun to coat the surface of silver nanostructures with an ultrathin protective layer, thereby allowing silver to maintain its metallic activity in oxidizing environments. The disadvantages are that the coating process is relatively complex, and the coating layer often leads to a decrease in Raman sensitivity (by about an order of magnitude).

[0033] Therefore, while improving the stability and high-temperature resistance of the substrate has reduced its sensitivity, how to further improve its sensitivity to obtain better SERS performance is a technical problem that urgently needs to be solved in the field of trace detection.

[0034] Example 1

[0035] This embodiment provides a sensitizing substrate for a silver-aluminum-based surface-enhanced Raman scattering substrate. The substrate comprises: a silver-aluminum substrate having a silver nanostructure and an alumina coating layer on its surface, and a cluster of gold nanoparticles formed on the surface of the silver-aluminum substrate. The silver substrate is a substrate with a silver nanostructure surface, including but not limited to silver self-supporting substrates or other substrates with silver nanostructure surfaces. For example, it can be a pure silver substrate or other types of substrates; any substrate with a silver nanostructure surface can be used, and this embodiment does not limit this.

[0036] It should be noted that the silver nanostructure can be a pure silver nanostructure or a composite nanostructure containing silver, that is, a composite nanostructure containing other elements besides silver; in addition, the surface of the substrate can contain only silver nanostructures or can include composite nanostructures containing silver, as long as the structure of the substrate surface includes silver-containing nanostructures, the embodiments disclosed herein do not limit this.

[0037] In the embodiments of this disclosure, the silver nanostructure includes at least one of nanorods, nanotubes, nanowires, and nanoparticles. The silver nanostructure includes, but is not limited to, nanorods, nanotubes, nanowires, nanoparticles, and various complex morphologies prepared by physical or chemical methods. The embodiments of this disclosure do not limit this.

[0038] In the embodiments of this disclosure, the thickness of the alumina coating layer is 0.75-1.5 nm.

[0039] In the embodiments of this disclosure, the diameter of the gold nanoparticles is 80-150 nm.

[0040] In the embodiments of this disclosure, the gold nanoparticle clusters are formed by immersing the silver-aluminum substrate with a silver nanostructure surface in a modification solution containing a silane coupling agent, or by dropping the modification solution containing a silane coupling agent onto the silver-aluminum substrate with a silver nanostructure surface; and then immersing the silver-aluminum substrate modified with the silane coupling agent in a gold sol modification solution, or by dropping the gold sol modification solution onto the silver-aluminum substrate modified with the silane coupling agent.

[0041] In the embodiments of this disclosure, the silane coupling agent includes at least one of KH550, KH560, and KH590. Silane coupling agents are a class of organosilicon compounds that simultaneously contain two groups with different chemical properties in their molecules. Their classic products can be represented by the general formula YSiX3. In this formula, Y is a non-hydrolyzable group (also an organic group, which can be epoxy, methacryloyloxy, mercapto, amino, alkyl, isocyanate, and vinyl), which can chemically react with polymers or form hydrogen bonds, thereby forming a strong bond with the polymer; X is a hydrolyzable group (including methoxy, ethoxy, halogen, etc.), which can react with hydroxyl-containing inorganic materials. Due to this special structure, silane coupling agents can act at the interface between inorganic materials (such as glass, metal, or minerals) and organic materials (such as organic polymers, coatings, or adhesives), binding or coupling two completely different materials. Therefore, silane coupling agents play a very good connecting role for silver nanostructures and gold nanoparticles, forming a rough nanostructure of the substrate. This structure provides more hot spots and greatly improves detection sensitivity.

[0042] Example 2 Preparation method of sensitized substrate

[0043] Figure 1 The flowchart illustrating the preparation of the sensitized substrate in Example 1 is shown.

[0044] The embodiments of this disclosure provide a method for preparing the above-described surface-enhanced Raman scattering sensitizing substrate, comprising the following steps:

[0045] Step S1: Prepare a modified solution containing a silane coupling agent using the raw materials;

[0046] Step S2: Modify the silver-aluminum substrate with a silver nanostructure surface using the modification solution.

[0047] Step S3: Prepare gold sol modification solution using raw materials;

[0048] Step S4: Modify the silver-aluminum substrate with a silver nanostructure surface that has been modified with the modified silane coupling agent using the modification solution.

[0049] In the embodiments of this disclosure, the raw materials include at least one of KH550, KH560, and KH590 corresponding to the silane coupling agent, and the embodiments of this disclosure do not limit this.

[0050] In the embodiments of this disclosure, the concentration of the silane coupling agent in the modified solution is 10-100 mM.

[0051] In the embodiments of this disclosure, the solvent of the modification solution is water or alcohol. After the substrate is prepared, it needs to be dried before use.

[0052] In the embodiments of this disclosure, the alcohol is methanol or ethanol.

[0053] In the embodiments of this disclosure, the step of modifying the silver-aluminum substrate with a silver nanostructure surface using the modifying solution includes the following modification methods: immersing the silver-aluminum substrate with a silver nanostructure surface in a modifying solution containing a silane coupling agent, or dropwise adding the modifying solution containing a silane coupling agent onto the silver-aluminum substrate with a silver nanostructure surface; then immersing the silane-coupled silver-aluminum substrate in a gold sol modifying solution, or dropwise adding the gold sol modifying solution onto the silane-coupled silver-aluminum substrate. Any method that allows the modifying solution to contact and react with the substrate surface to form gold nanoparticle clusters can be used, and the embodiments of this disclosure are not limited to this.

[0054] In the embodiments of this disclosure, in the step of modifying the silver-aluminum substrate with a silver nanostructure surface using the silane coupling agent modification solution, the modification time is 30-60 min; in the step of modifying the silver-aluminum substrate with a silver nanostructure surface modified with the silane coupling agent using the gold sol modification solution, the modification time is 12-24 h.

[0055] It should be noted that the following factors were considered when designing the modification time: If the modification time is too short, there is insufficient time to form sufficiently dense gold nanoparticle clusters, thus failing to enhance surface-enhanced Raman scattering (SERS) sensitivity. If the modification time is too long, the gold nanoparticle clusters become too dense, which is detrimental to SERS. Modification times of 30-60 min and 12-24 h correspond to sufficiently dense gold nanoparticle clusters, which exhibit a good effect on enhancing SERS sensitivity.

[0056] Example 3 Surface-enhanced Raman scattering method

[0057] Figure 2 The flowchart of a surface-enhanced Raman scattering method is illustrated schematically.

[0058] A surface-enhanced Raman scattering method includes the following steps:

[0059] Step S1: Add the test solution to the sensitizing substrate of Example 1, or immerse the sensitizing substrate of Example 1 in the test solution;

[0060] Step S2: Detection using a Raman spectrometer.

[0061] In the embodiments of this disclosure, the wavelength of the Raman spectrometer used for detection includes 532 nm, 633 nm, 785 nm and 1064 nm.

[0062] The embodiments of this disclosure modify a silver-aluminum substrate with a silver nanostructure surface to form gold nanoparticle clusters, thereby enhancing the surface-enhanced Raman scattering (SERS) effect. When the substrate is used for detection, the surface gold nanoparticle clusters act as "hot spots," significantly improving the sensitivity of the substrate for SERS and laying the material basis for quantitative detection of SERS. Furthermore, it has the advantages of simple preparation process, strong practicality, and the ability to perform quantitative detection.

[0063] Example 4

[0064] To verify the Raman enhancement effect of the sensitized silver-aluminum substrate, methylene blue (MB) was used as the detector molecule for detection and evaluation.

[0065] A standard silver-aluminum substrate was immersed in a 100 mM KH590 ethanol solution, ensuring the solution level covered the substrate surface. After immersion for 30 minutes, the substrate was removed, rinsed with anhydrous ethanol, and then the surface solution was gently blown away with a syringe. The substrate was then allowed to air dry for approximately 10 minutes before proceeding to the next modification step. The modified silver-aluminum SERS substrate was then immersed in a gold sol with a particle size of 80 nm. After 24 hours, the substrate was removed, rinsed with anhydrous ethanol, and then the surface solution was gently blown away with a syringe. The surface solution was prepared and allowed to air dry naturally. Then, a 5*5mm sensitizing substrate was immersed in MB standard solutions with concentrations of 1ppb (μg / L), 10ppb (μg / L), 100ppb (μg / L), and 1ppm (μg / L), respectively, for 30 min, 30 min, 10 min, and 3 min. After immersion, the substrate was removed and gently dried with a bulb syringe. Residual solution was absorbed with filter paper, and the substrate was then placed on a Raman spectrometer for detection. The same procedure was followed for ordinary silver-aluminum substrates. Test parameters: integration time 1s, integration times 1, laser power 100mW, laser wavelength 785nm.

[0066] Scanning electron microscope image of a common silver-aluminum substrate is shown below. Figure 3 The scanning electron microscope image of the sensitized substrate is shown below. Figure 4 ;

[0067] Test results are as follows Figure 5-6 As shown, from Figure 6 It can be seen that the Raman spectrum (curves 5-8) of MB detected by the sensitized substrate at 1 ppm shows a significantly higher absolute intensity of the characteristic peak of MB than that of MB measured on the unmodified ordinary silver-aluminum substrate. Figure 5 (Curves 1-4). As the detection concentration decreases, the intensity of different characteristic peaks decreases. The peak intensity of the sensitized substrate is stronger than that of the ordinary silver-aluminum substrate, and the intensity change has a good linear relationship with the concentration. Under the conditions of this embodiment, the modified substrate can clearly detect MB molecules at concentrations below 0.01 ppm (Curve 7), demonstrating the characteristics of ultra-trace analysis.

[0068] As can be seen from the above embodiments, the preparation method provided by the present invention is simple, has a significant sensitizing effect, high sensitivity, and a remarkable surface enhancement effect on the substrate, enabling quantitative analysis of trace substances. It has high practicality and broad application prospects in food, environment, biology, and medicine.

[0069] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A surface-enhanced Raman scattering (SERS) sensitizing substrate, characterized in that, include: A silver-aluminum substrate with a silver nanostructure and an alumina coating surface; and Gold nanoparticle clusters are formed on the surface of the silver-aluminum substrate; wherein the method for forming the gold nanoparticle clusters is as follows: first, the silver-aluminum substrate is immersed in a modification solution containing a silane coupling agent, or the modification solution containing a silane coupling agent is dropped onto the silver-aluminum substrate; then, the silver-aluminum substrate modified with the silane coupling agent is immersed in a modification solution containing gold nanoparticles, or the modification solution containing gold nanoparticles is dropped onto the silver-aluminum substrate modified with the silane coupling agent.

2. The sensitizing substrate according to claim 1, characterized in that, The silver nanostructure is selected from at least one of nanorods, nanotubes, nanowires, and nanoparticles; The gold nanoparticles are selected from at least one of gold triangles and gold nanospheres.

3. The sensitizing substrate according to claim 1, characterized in that, The thickness of the alumina coating layer is 0.75-1.5 nm. The diameter of the gold nanoparticles is 80-150 nm.

4. The method for preparing the sensitizing substrate according to any one of claims 1-3, characterized in that, Includes the following steps: A modification solution containing a silane coupling agent was prepared using raw materials, and the modification solution containing the silane coupling agent was used to modify a silver-aluminum substrate with a silver nanostructure surface; and A gold nanoparticle-containing modification solution was prepared using raw materials, and the gold nanoparticle-containing modification solution was used to modify a silver-aluminum substrate modified with a silane coupling agent.

5. The preparation method according to claim 4, characterized in that, The silane coupling agent is at least one of KH550, KH560 and KH590; the concentration of the silane coupling agent is 10-100 mM.

6. The preparation method according to claim 4, characterized in that, The solvent for the modification solution is water or alcohol.

7. The preparation method according to claim 4, characterized in that, The modification time for the silane coupling agent-containing modification solution is 30-60 min; the modification time for the gold nanoparticle-containing modification solution is 12-24 h.

8. A method for surface-enhanced Raman scattering, characterized in that, Includes the following steps: The test solution is added dropwise onto the sensitizing substrate according to any one of claims 1-3, or the sensitizing substrate according to any one of claims 1-3 is immersed in the test solution; and The detection was performed using a Raman spectrometer.

9. The surface-enhanced Raman scattering method according to claim 8, characterized in that, The Raman spectrometer has wavelengths of 532 nm, 633 nm, 785 nm, or 1064 nm.

Images