Preparation method and application of surface-enhanced Raman substrate based on hybrid system

Abstract

The invention relates to the technical field of material detection, in particular to a preparation method and application of a surface-enhanced Raman substrate based on a hybrid system, and the preparation method comprises the following steps: preparing spherical and star-shaped gold nanoparticle solutions; preparing expanded graphite suspension liquid; centrifuging the spherical nano-gold particle solution, taking precipitates, standing the star-shaped nano-gold particle solution, taking precipitates, and mixing the two precipitates to prepare a spherical-star-shaped mixed nano-gold particle concentrated solution; the concentrated solution and the expanded graphite suspension are subjected to ultrasonic treatment and mixing, and a gold-graphite mixed solution is obtained; and dispensing the gold-graphite mixed solution on filter paper, and drying to obtain the surface-enhanced Raman substrate based on the spherical-star-shaped nanogold hybrid system. In conclusion, the SERS substrate disclosed by the invention is high in sensitivity, capable of working under various wavelengths, flexible and bendable, and capable of being attached to a complex surface to realize in-situ detection, and the Raman scattering effect is enhanced through the cooperation of the spherical-star-shaped nanogold hybrid system and the expanded graphite.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, and in particular to a method for preparing and applying a surface-enhanced Raman substrate based on a hybrid system. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) technology, with its rapid, non-destructive, ultrasensitive, and fingerprint-like characteristics, has shown great application potential in fields such as organic molecule detection, trace substance analysis, and agricultural and food safety monitoring (e.g., pesticide residue detection). Its core lies in amplifying the Raman scattering signal by several orders of magnitude through a special substrate. However, existing SERS substrates still face significant technical bottlenecks, limiting their practical application scope: Limitations of solid substrates: Traditional SERS substrates mostly use rigid materials such as silicon wafers, glass sheets, and electrodes, which cannot adhere to the surface of fruits and vegetables, irregular devices, and other complex-shaped objects. They are difficult to use for in-situ sampling and direct detection, and require indirect analysis through cumbersome steps such as sample extraction, which can easily lead to sample loss or contamination. They are especially unsuitable for rapid on-site testing scenarios such as agricultural product safety.

[0003] Existing limitations of flexible substrates: Although research has been conducted to develop flexible SERS substrates to address the aforementioned issues, significant shortcomings remain. For example, patent CN111999279A proposes a flexible substrate based on a microsphere array, but its fabrication requires a transfer step from a rigid substrate to a flexible substrate using the microsphere array. This process is cumbersome, prone to structural damage, and has poor repeatability. Patent CN111208113A uses a flexible thin-film substrate to prepare a nano-silver substrate in situ, but interference from the substrate peaks on the glass slide affects signal accuracy during detection.

[0004] Selectivity of excitation wavelength: Conventional SERS substrates have limited optical properties, with fixed surface plasmon resonance (SPR) peak positions, exhibiting enhanced responses only to specific wavelengths of laser light. However, for biomolecules, pesticides, and other detectable substances, some substances are better suited to longer wavelength lasers (such as 785 nm) due to their fluorescence properties. Traditional substrates cannot meet the requirements for multi-wavelength compatibility, thus limiting detection flexibility and applicability.

[0005] Therefore, developing a SERS substrate that combines high sensitivity, flexibility, multi-wavelength compatibility, and ease of fabrication is key to overcoming existing technological limitations and promoting the practical application of SERS technology in in-situ detection of complex surfaces. Summary of the Invention

[0006] To overcome the shortcomings mentioned above, the present invention aims to provide a technical solution that can solve the above problems.

[0007] This invention provides a method for preparing a surface-enhanced Raman spectroscopy substrate based on a hybrid system, characterized by comprising the following steps: S1, prepare a solution of spherical gold nanoparticles; S2, prepare a solution of star-shaped gold nanoparticles; S3, using pre-made expanded graphite, an expanded graphite suspension is prepared; S4. After centrifuging the spherical gold nanoparticle solution in S1, take the precipitate. After standing the star-shaped gold nanoparticle solution in S2, take the precipitate. Mix the two precipitates in a certain proportion to prepare a spherical-star mixed gold nanoparticle concentrate. S5, the spherical-star mixed gold nanoparticle concentrate in S4 and the expanded graphite suspension in S3 are ultrasonically mixed to obtain a gold-graphite mixture, and a dispersed mixed gold nanoparticle-expanded graphite composite structure is formed in the gold-graphite mixture. S6, the gold-graphite mixture from S5 is drop-coated onto filter paper and dried to obtain a surface-enhanced Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system. The mixed gold nanoparticle-expanded graphite composite structure is dispersed on the filter paper and interlocks with the loose microstructure of the filter paper to form an integral composite structure. The filter paper serves as the physical support and interlocking carrier for the expanded graphite particles and provides the substrate with a soft and flexible function.

[0008] Further: In step S1, a spherical gold nanoparticle solution is prepared by synthesis. Specifically, tetrachloroauric acid is dissolved in ultrapure water, then stirred and heated to the boiling point, and then a certain amount of sodium citrate solution is injected. After the reaction is completed, a spherical gold nanoparticle solution is formed.

[0009] Further: In step S2, a star-shaped gold nanoparticle solution is obtained using a seed growth method. Specifically, the spherical gold nanoparticle solution prepared in step S1 is added to a precursor mixture prepared from tetrachloroauric acid and hydrochloric acid and stirred. A certain amount of silver nitrate solution and a certain amount of pre-prepared ascorbic acid solution are added dropwise and stirred continuously. When the solution color changes from red to blue-green, a certain amount of hexadecyltrimethylammonium bromide is added as a stabilizer to obtain star-shaped gold nanoparticles with a star-shaped structure with sharp branches.

[0010] Furthermore, in step S2, the growth parameters of the star-shaped gold nanoparticles are optimized by adjusting the concentrations of the silver nitrate solution and the ascorbic acid solution, as well as the molar ratio of tetrachloroauric acid to spherical gold nanoparticles.

[0011] Further: In step S3, the pre-preparation method of expanded graphite is as follows: acetic acid and nitric acid are stirred and mixed, a certain amount of flake graphite is added, stirring is continued, and a certain amount of potassium permanganate is added. After the reaction is fully completed, the resulting mixture is washed with water until neutral, and then dried and subjected to high-temperature expansion treatment to obtain expanded graphite.

[0012] Further: In step S3, the specific method for preparing the expanded graphite suspension is as follows: the pre-prepared expanded graphite is added to ultrapure water and treated with an ultrasonic instrument to make it uniformly dispersed in the water to form an expanded graphite suspension.

[0013] Furthermore, in step S4, the optical properties of the spherical-star mixed gold nanoparticle concentrate are adjusted by adjusting the volume ratio of the spherical gold nanoparticle precipitate and the star-shaped gold nanoparticle precipitate.

[0014] The present invention also provides an application of a surface-enhanced Raman substrate based on a hybrid system. According to the above-mentioned method for preparing a surface-enhanced Raman substrate based on a hybrid system, a Raman substrate is prepared, and the Raman substrate is used as a Raman molecular probe to perform qualitative or quantitative analysis or detection of the components of the sampled object.

[0015] Further: The liquid sampled object is tested, specifically by: dropping the liquid sampled object onto the above-mentioned Raman substrate, allowing it to air dry naturally, and then placing it in a Raman spectroscopy detection device for detection. During the Raman spectroscopy detection process, the laser needs to be focused on the dispersed black expanded graphite particles.

[0016] Further: The solid-state sampled object is tested, specifically by wiping the surface of the solid-state sampled object with the above-mentioned Raman substrate to take a sample, and then placing the Raman substrate after wiping and sampling into a Raman spectroscopy detection device for detection. During the Raman spectroscopy detection process, the laser needs to be focused on the dispersed black expanded graphite particles.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. Significantly improved detection sensitivity and stability: The sharp protrusions of star-shaped gold nanoparticles form numerous "hot spots," with a local electric field intensity 5-8 times that of spherical particles; the porous structure of expanded graphite increases surface roughness and provides more adsorption sites. These two elements synergistically enhance the Raman scattering effect, allowing for a minimum detection concentration of 10 for typical pesticides (such as Thiram). -6 It has a concentration of mol / L (0.24 ppm) and excellent signal stability.

[0018] 2. Achieving broad-spectrum response and multi-wavelength compatibility: By adjusting the mixing ratio of spherical and star-shaped gold nanoparticles (volume ratio 0:1, 1:4, 1:1, 4:1, 1:0), the SPR absorption peak of the system can be tuned in the range of 525~745nm. It exhibits good enhancement effects at commonly used excitation wavelengths such as 532nm, 633nm, and 785nm, overcoming the selective dependence of traditional substrates on excitation wavelength.

[0019] 3. Flexible and in-situ detection capabilities: Using filter paper as a substrate, the substrate has soft and flexible properties, which can be used to directly wipe irregular surfaces such as fruits and vegetables to achieve in-situ sampling without sample pretreatment, simplifying the operation process and avoiding sample loss, thus expanding the application scenarios in the detection of complex surfaces.

[0020] 4. Simple preparation and high practicality: The "direct drop coating of nano gold-expanded graphite composite liquid" process is adopted, which does not require complicated transfer steps. The preparation process is simple and highly reproducible. The substrate can be stably stored for more than one month in a dry environment away from light at room temperature. It is also lightweight and easy to carry, making it suitable for rapid on-site testing.

[0021] Therefore, the SERS substrate of this invention has high sensitivity, can operate at multiple wavelengths, and possesses flexible and bendable properties, enabling in-situ detection by conforming to complex surfaces. It enhances the Raman scattering effect through a spherical-star-shaped gold nanoparticle hybrid system and expanded graphite. Furthermore, it exhibits a significant Raman scattering enhancement effect at different excitation wavelengths, achieving multi-wavelength compatible detection.

[0022] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the fabrication process of the surface-enhanced Raman substrate described in this invention; Figure 2 (a), (b), and (c) are the UV-Vis absorption spectra of concentrated spherical-star mixed gold nanoparticles with different volume ratios at different times, where (a) corresponds to the AuNS-P(1-4) system, (b) corresponds to the AuNS-P(1-1) system, and (c) corresponds to the AuNS-P(4-1) system. Figure 3 To detect 10 spherical-star hybrid gold nanoparticle substrates with different proportions at an excitation wavelength of 532 nm -5 Raman spectra comparison of mol / L staining agent Rhodamine 6G (R6G); Figure 4 To detect 10 spherical-star hybrid gold nanoparticle substrates with different proportions at an excitation wavelength of 633 nm -5 Raman spectra comparison of mol / L staining agent R6G; Figure 5 To detect 10 spherical-star hybrid gold nanoparticle substrates with different proportions at an excitation wavelength of 785 nm -5 Raman spectra comparison of mol / L staining agent R6G; Figure 6 Figure 6 Raman spectroscopy was performed on substrates treated at different temperatures (20℃, 50℃, 80℃, 100℃). -5 1308 cm⁻¹ of mol / L staining agent R6G -1 Characteristic peak intensity comparison chart; Figure 7 To detect 10 Raman spectroscopy samples after storing the substrate in air at room temperature for different times (2 hours to 1 month). -5 1308 cm⁻¹ of mol / L staining agent R6G -1 Characteristic peak intensity variation graph; Figure 8 (a) Raman spectra of different concentrations of thiram on the surface of pear; Figure 8 (b) is the linear relationship curve between Raman peak intensity and thiram concentration; Figure 9 (a) Raman spectra of dimethyl sulfoxide (DMSO) at different volume concentrations; Figure 9 (b) is the curve showing the relationship between Raman peak intensity and DMSO volume concentration; Figure 10 This is a schematic diagram of the structure and stability of the Raman substrate described in this invention, including the morphology of the spherical-star hybrid gold nanoparticles, the composite structure with expanded graphite, the intercalation state of the filter paper carrier, and the time stability and laser response characteristics of the substrate. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0026] Please see Figures 1 to 10 In this embodiment of the invention, a method for preparing a surface-enhanced Raman substrate based on a hybrid system includes the following steps: S1, prepare a solution of spherical gold nanoparticles; S2, prepare a solution of star-shaped gold nanoparticles; S3, using pre-made expanded graphite, an expanded graphite suspension is prepared; S4. After centrifuging the spherical gold nanoparticle solution in S1, take the precipitate. After standing the star-shaped gold nanoparticle solution in S2, take the precipitate. Mix the two precipitates in a certain proportion to prepare a spherical-star mixed gold nanoparticle concentrate. S5, the spherical-star mixed gold nanoparticle concentrate in S4 and the expanded graphite suspension in S3 are ultrasonically mixed to obtain a gold-graphite mixture, in which a dispersed mixed gold nanoparticle-expanded graphite composite structure is formed. S6, the gold-graphite mixture in S5 is drop-coated onto filter paper and dried to obtain a surface-enhanced Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system. The mixed gold nanoparticle-expanded graphite composite structure is dispersed on the filter paper and interlocks with the loose microstructure of the filter paper to form an overall composite structure. The filter paper mainly serves as the physical support and interlocking carrier for the expanded graphite particles, providing the substrate with a soft and flexible function.

[0027] Specifically, commonly used spherical gold nanoparticles have the advantages of uniform morphology and strong controllability in synthesis, but their local surface plasmon resonance (LSPR) peaks are singular and their electric field enhancement is limited. Compared with spherical nanoparticles, the sharp protrusions distributed on the surface of star-shaped gold nanoparticles can form a significant electromagnetic field gradient, and their local electric field strength can reach 5 to 8 times that of spheres. This "lightning rod effect" provides more effective hot spots for SERS detection, resulting in a significant SERS enhancement effect.

[0028] It should be noted that the 'hybrid system' mentioned in this invention is a composite system formed by spherical gold nanoparticles, star-shaped gold nanoparticles, expanded graphite, and filter paper through a specific process. The spherical gold nanoparticles have uniform morphology and controllable synthesis; the sharp protrusions on the surface of the star-shaped gold nanoparticles can form a significant electromagnetic field gradient, enhancing the local electric field. The optical properties of the two components, when mixed in a specific ratio, can be controlled by adjusting the mixing volume ratio, laying the foundation for broadband SERS detection. Expanded graphite has a porous structure, allowing the mixed gold nanoparticles to accumulate on its surface, increasing the surface roughness of the gold nanoparticles on the filter paper and further enhancing the Raman scattering effect. The filter paper, as a flexible carrier, provides physical support and embedding for the expanded graphite particles, giving the substrate a flexible and bendable characteristic. Through the synergistic effect between the components, this hybrid system achieves advantages such as high sensitivity, broadband response, good flexibility, and repeatability, overcoming the performance limitations of single materials in surface-enhanced Raman detection.

[0029] Secondly, the 'precipitate' mentioned in this invention refers to the aggregate of gold nanoparticles formed at the bottom of the container after the gold nanoparticle solution is centrifuged (for spherical gold nanoparticles) or left to stand (for star-shaped gold nanoparticles). By removing the supernatant and retaining the bottom precipitate, the gold nanoparticles can be enriched, laying the foundation for the subsequent preparation of a high-concentration gold-graphite mixture. Specifically, after centrifugation of the spherical gold nanoparticle solution (e.g., at a speed of 8000~10000 rpm for 10~15 minutes), the gold nanoparticles settle due to centrifugal force, forming a precipitate. The star-shaped gold nanoparticle solution, due to its larger particle diameter and faster settling rate, naturally settles to form a precipitate after standing (e.g., at room temperature for 4~6 hours).

[0030] The 'spherical-star hybrid gold nanoparticle concentrate' described in this invention refers to a high-concentration gold nanoparticle dispersion system formed by mixing spherical and star-shaped gold nanoparticle precipitates in a specific volume ratio, adding a small amount of ultrapure water (or the supernatant of the original reaction solution of the spherical / star-shaped gold nanoparticle solution), and then redispersing. Its concentration is significantly higher than the original gold nanoparticle solution. By adjusting the mixing ratio of the two precipitates (e.g., a volume ratio of 1:4 to 4:1), the optical properties of the system (such as the position of surface plasmon resonance peaks) can be tunable, providing a suitable optical response basis for broadband Raman detection.

[0031] like Figure 1As shown, preferably, in step S5, the specific method for the flexible Raman substrate is as follows: the concentrated solution of spherical-star hybrid gold nanoparticles prepared in step S4 is ultrasonically mixed with the expanded graphite suspension in step S3 to obtain a gold-graphite mixture, in which a dispersed mixed gold nanoparticle-expanded graphite composite structure is formed. In step S6, the gold-graphite mixture is drop-coated onto filter paper, and after drying, a high-performance broadband response flexible surface-enhanced Raman substrate based on the spherical-star hybrid gold nanoparticle system is obtained.

[0032] Specifically, at room temperature, the concentrated solution of spherical-star hybrid gold nanoparticles prepared in step S4 is added to the expanded graphite suspension prepared in step S3 and ultrasonically mixed for 5 minutes. The ultrasonically mixed solution is then dropped onto a 1 cm × 1 cm filter paper and dried in air overnight to obtain a high-performance, broadband-response flexible surface-enhanced Raman substrate based on the spherical-star hybrid gold nanoparticle system.

[0033] Secondly, in this invention, 'ultrasonic treatment' specifically refers to the operation of dispersing solid particles using an ultrasonic instrument (power, for example, 300~500W, frequency, for example, 40kHz). Its purpose is to break up particle agglomeration through cavitation effect and achieve uniform dispersion. 'Stirring', on the other hand, refers to the operation of mixing solution components uniformly through mechanical stirring (speed, for example, 500~800rpm). Therefore, the two have different functions and cannot be substituted for each other.

[0034] Furthermore, the high-performance, broadband-response flexible surface-enhanced Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system prepared by the method of this invention is easy to store. It only needs to be stored in a room-temperature, light-protected, and dry environment. When needed, the high-performance flexible SERS substrate material can be taken out and used directly. It is understood that the filter paper is a common filtering tool found in chemical laboratories, typically circular in shape and mostly made of cotton fibers. Because it is made of fibers, its surface has countless small pores that allow liquid particles to pass through, while larger solid particles cannot. This property allows for a certain degree of separation between mixed liquid and solid substances.

[0035] like Figure 1 As shown, preferably, in step S1, the Frens method is used to synthesize a solution of spherical gold nanoparticles. Specifically, tetrachloroauric acid (HAuCl4) is dissolved in ultrapure water, then stirred and heated to the boiling point, and then a certain amount of sodium citrate solution is quickly injected. After the reaction is completed, a solution of gold nanoparticles is formed.

[0036] In step S2, a large-diameter star-shaped gold nanoparticle solution is obtained using a seed growth method. Specifically, a certain amount of the spherical gold nanoparticle solution prepared in step S1 is added to a certain amount of a precursor mixture prepared by mixing tetrachloroauric acid (HAuCl4) and hydrochloric acid (HCl). The solution is stirred, and then a certain amount of silver nitrate (AgNO3) and a certain amount of ascorbic acid solution are added dropwise while stirring continuously. When the solution color rapidly changes from red to blue-green, a certain amount of hexadecyltrimethylammonium bromide is added as a stabilizer to obtain star-shaped gold nanoparticles with a sharply branched star structure.

[0037] Specifically, the Turkevich-Frens method can be used to synthesize solutions of gold nanoparticles. HAuCl4 is dissolved in ultrapure water and heated to boiling point with stirring in a round-bottom flask. A small amount of sodium citrate solution is rapidly added, causing a color change. After the reaction is complete, a solution of spherical gold nanoparticles (AuNPs) is produced. For example, 0.00449 g of HAuCl4 is dissolved in 150 ml of ultrapure water and heated to boiling point with stirring in a round-bottom flask. 6.25 mL of sodium citrate solution is rapidly added, causing a color change, and gold nanoparticles are produced after the reaction is complete. The Turkevich-Frens method is currently the most commonly used method for preparing gold nanoparticles and allows for control over particle size. This method was first developed by Turkevich in 1951 and improved by Frens in 1973. The particle size can be controlled by adjusting the ratio of sodium citrate to chloroauric acid.

[0038] Secondly, to obtain large-diameter star-shaped gold nanoparticles, a seed growth method can be used. A certain amount of tetrachloroauric acid (HAuCl4) and hydrochloric acid (HCl) are mixed in a beaker, and a certain amount of a previously prepared spherical gold nanoparticle solution is added. The solution is stirred, and then a certain amount of silver nitrate (AgNO3) and a certain amount of ascorbic acid solution are simultaneously added dropwise while continuing to stir. When the solution color rapidly changes from red to blue-green, a certain amount of hexadecyltrimethylammonium bromide is added to the beaker as a stabilizer, ultimately yielding a solution of gold nanoparticles (AuNSs) with a sharply branched star structure.

[0039] Specifically, for example, 3.75–6.75 mL of a 1 mM chloroauric acid (HAuCl4) solution and 15 μL of a 1 M hydrochloric acid (HCl) solution are mixed in a beaker to form a precursor mixture, and then 150 μL of a previously prepared solution of spherical gold nanoparticles with a diameter of approximately 20 nm is added. The mixture in the beaker is continuously stirred at a moderate stirring speed (700 rpm) at room temperature. Simultaneously, 300 μL of 0.02–0.08 mM silver nitrate and 75 μL of 50–200 mM ascorbic acid (AA) are added dropwise, while the mixture in the beaker is still stirred at 700 rpm throughout this process.

[0040] When the solution color rapidly changes from red to blue-green, the reaction is complete. At this point, add 2.7 ml of 1 mM hexadecyltrimethylammonium bromide (CTAB) to the beaker. CTAB is a cationic surfactant that can bind to and modify gold nanoparticles during their formation. CTAB modification creates a steric hindrance layer on the surface of the gold nanoparticles, hindering interparticle interactions and thus improving their stability in solution.

[0041] By systematically optimizing the precursor ratio, it was determined that when the molar ratio of HAuCl4 to the spherical gold nanoparticle solution prepared in step S1 is 30:1, the AgNO3 solution is 0.06 mM, and the ascorbic acid concentration is 100 mM, a star-shaped structure with sharp branches can be stably generated.

[0042] In step S2, the synthesis and growth parameters of the star-shaped gold nanoparticles are systematically screened and optimized by adjusting the concentration of silver nitrate, the molar ratio of tetrachloroauric acid and the spherical gold nanoparticles prepared in step S1, and the concentration of ascorbic acid, to determine the optimal ratio.

[0043] Specifically, to improve the detection performance of the flexible surface-enhanced Raman substrate in the hybrid system, the synthesis and growth parameters of star-shaped gold nanoparticles can be systematically optimized to achieve optimal performance in SERS detection. Among these, the control of silver nitrate concentration is particularly crucial. Silver nitrate selectively adsorbs onto specific crystal faces of gold seeds, inhibiting uniform growth and promoting the formation of anisotropic branched structures, thereby generating more "hot spot" regions to enhance the local electric field. The molar ratio of tetrachloroauric acid to the spherical gold nanoparticles prepared in step S1 directly affects the deposition rate and total amount of gold nanoparticles. Ascorbic acid, as a reducing agent, affects the reduction kinetics of the gold nanoparticles. Through systematic screening of the above parameters, the star-shaped gold nanoparticles achieve optimal performance in surface-enhanced Raman detection.

[0044] like Figure 1As shown, preferably, in step S3, the pre-preparation method of expanded graphite is as follows: acetic acid (CH3COOH) and nitric acid (HNO3) are stirred and mixed, a certain amount of flake graphite is added, and stirring is continued. A certain amount of potassium permanganate (KMnO4) is also added. After the reaction is complete, the resulting mixture is washed until neutral, and then dried and expanded at high temperature to obtain expanded graphite. In step S3, the specific method for preparing the expanded graphite suspension is as follows: the pre-prepared expanded graphite is added to ultrapure water and treated using an ultrasonic instrument to uniformly disperse it in the water, forming an expanded graphite suspension.

[0045] Specifically, at room temperature, acetic acid (CH3COOH) is gradually added to nitric acid (HNO3) while stirring, followed by the slow addition of a certain amount of crystalline flake graphite to the mixed solution. Subsequently, a small amount of potassium permanganate (KMnO4) is added to the homogeneous system formed by the above solution, allowing the reaction to proceed under continuous stirring. After the reaction is complete, the resulting mixture is washed until neutral and then dried at 60°C. Finally, the dried object is calcined using a spray gun, and expanded graphite is generated after high-temperature calcination.

[0046] For example, at ambient temperature, 2.5 mL of acetic acid (CH3COOH) was gradually added to 10 mL of nitric acid (HNO3) while stirring, followed by the slow addition of 5.0 g of crystalline flake graphite to the mixture. Then, 2.5 g of potassium permanganate (KMnO4) was introduced into the homogeneous system formed by the above solution. The reaction was carried out for 40 minutes with continuous stirring. The resulting mixture was washed with water until neutral and then dried at 60°C. Finally, it was heated at high temperature with a spray gun for 15 seconds to produce the corresponding expanded graphite.

[0047] like Figure 1 and Figure 2 As shown, preferably, in step S4, the specific method for preparing the spherical-star-shaped mixed gold nanoparticle concentrate is as follows: The synthesized spherical gold nanoparticle solution (AuNPs) is placed in a centrifuge tube and centrifuged. After centrifugation, the supernatant is removed and the precipitate is collected. The synthesized star-shaped gold nanoparticle solution (AuNSs) is allowed to settle, the supernatant is removed, and the precipitate is collected. The precipitate concentrates of spherical and star-shaped gold nanoparticles are mixed in different volume ratios to obtain the spherical-star-shaped mixed gold nanoparticle concentrate.

[0048] The underlying principle is as follows: the experimentally prepared AuNPs and AuNSs exhibit surface plasmon resonance (SPR) absorption peaks at 525 nm and 745 nm, respectively, in the UV-Vis absorption spectrum. When these two nanostructures are mixed, the concentrated solution of spherical-star hybrid gold nanoparticles exhibits tunable localized surface plasmon resonance (LSPR) characteristics, and the SPR peaks can be adjusted within the range of 525–745 nm under different mixing ratios (e.g., ...). Figure 2 (As shown).

[0049] Specifically, when the volume ratio of AuNSs to AuNPs is 1:4 (AuNS-P(1-4)), the absorption spectrum is dominated by a broad peak of AuNSs (690 nm); while when the volume ratio is 1:1 (AuNS-P(1-1)), the absorption spectrum is dominated by a broad peak of AuNPs (580 nm). At a volume ratio of AuNSs to AuNPs of 4:1 (AuNS-P(4-1)), the absorption spectrum shows double peaks at 540 nm and 675 nm, indicating that plasmon coupling occurs between the two types of particles.

[0050] Meanwhile, due to the aggregation between nanoparticles, the absorbance of the dispersed solution system decreases over time. For example... Figure 2 As shown in Figure ac, quantitative analysis revealed significant differences in the aggregation rates of different systems, in the following order: AuNS-P(1-4) > AuNS-P(1-1) > AuNS-P(4-1) > AuNSs > AuNPs. Although rapid aggregation led to a decrease in absorbance, the nano-gap formed by moderate aggregation could generate SERS hotspots. The broad-spectrum SPR coverage of these hotspots highly matched common Raman laser wavelengths (532 nm, 633 nm, and 785 nm), laying a solid foundation for achieving SERS detection across the entire wavelength range. This also enables this spherical-star-shaped gold nanoparticle hybrid system to play a role in broad-spectrum SERS detection, especially in complex detection scenarios requiring coverage of multiple laser wavelengths.

[0051] like Figure 1 As shown, preferably, in step S4, the optical properties of the spherical-star mixed gold nanoparticle concentrate are adjusted by adjusting the volume ratio of spherical gold nanoparticle precipitate to star-shaped gold nanoparticle precipitate.

[0052] Specifically, to achieve compatible detection across common excitation wavelengths such as 532 nm, 633 nm, and 785 nm, a suitable ratio of spherical-star hybrid gold nanoparticle concentrate is essential for the excellent optical properties and structural stability of this flexible substrate. The experimentally prepared spherical and star-shaped gold nanoparticles exhibit surface plasmon resonance (SPR) absorption peaks at 525 nm and 745 nm, respectively, in the UV-Vis absorption spectrum. When these two nanostructures are mixed, the spherical-star hybrid gold nanoparticle concentrate exhibits tunable localized surface plasmon resonance (LSPR) characteristics, allowing the SPR to be adjusted within the 525–745 nm range, thus providing the possibility of broadband SERS detection.

[0053] Furthermore, the high-performance flexible Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system and possessing broad-spectrum response characteristics, prepared using the method of this invention, can be used for SERS sensing detection simply by wiping the surface of the object to be tested. Spectra of relevant components can be rapidly acquired using commercial SERS equipment for qualitative or quantitative identification. Experimental tests showed that the SERS substrate prepared by the method of this invention exhibited excellent SERS signal enhancement. In specific experiments, different drugs were used to simulate drug residues in different environments, and tests were conducted. The results showed that the SERS substrate prepared by the method of this invention had a detection limit of 10 for two drugs, thiamethoxam and dimethyl sulfoxide. -6 mol / L and 1% (volume / volume).

[0054] Finally, the preparation method of this invention also has the advantages of simple process, convenient operation, strong repeatability, easy storage and portability, good uniformity, good flexibility, low cost, and high thermal stability. The prepared flexible SERS substrate can be rapidly sampled by directly wiping the surface of the target object, enabling the detection of pesticide residues on the surface of fruits and vegetables. In addition, the SERS substrate exhibits a significant enhancement effect under different excitation wavelengths, which provides a theoretical reference for the design of multi-wavelength compatible flexible SERS substrates through "nanostructure synergistic optimization".

[0055] The present invention also provides an application of a surface-enhanced Raman substrate based on a hybrid system. The Raman substrate prepared by the above preparation method is used as a Raman molecular probe. Depending on the state of the sampled object (liquid or solid), the corresponding detection method is used to perform qualitative or quantitative analysis or detection of the components of the sampled object.

[0056] The detection method for liquid collection objects is as follows: the liquid collection object is drop-coated onto the above-mentioned Raman substrate, and after it is allowed to air dry naturally, it is placed in a Raman spectroscopy detection device for detection. During the Raman spectroscopy detection process, the laser needs to be focused on the dispersed black expanded graphite particles.

[0057] The detection method for solid-state sampling objects is as follows: the surface of the solid-state sampling object is wiped with the above-mentioned Raman substrate to take a sample, and the Raman substrate after wiping and sampling is placed in a Raman spectroscopy detection device for detection. During the Raman spectroscopy detection process, the laser needs to be focused on the dispersed black expanded graphite particles.

[0058] Specifically, the high-performance flexible SERS substrate prepared by the above method can be used as a Raman molecular probe. Commercial SERS equipment can be used to acquire spectra for qualitative and quantitative detection and analysis of the components of the target object. For example, Rhodamine 6G (R6G) staining agent can be used as a Raman detection target to evaluate the SERS enhancement effect. An unknown concentration of R6G solution is added dropwise to the above-prepared flexible surface-enhanced Raman substrate material, and then allowed to air dry naturally.

[0059] Raman spectroscopy was performed using a Raman spectrometer equipped with 532nm, 633nm, and 785nm excitation lasers. Calculated parameters were selected, including laser power, spectral acquisition time, and spectral range. After automatically acquiring spectral information, qualitative analysis of the components was performed based on the positions of characteristic peaks, and quantitative detection was achieved according to the correlation between spectral intensity and concentration, thereby determining the type and content of the target components in the sample.

[0060] The high-performance flexible SERS substrate provided by this invention is particularly suitable for the detection of pesticide residues on fruits and vegetables. It only requires wiping the surface of fruits and vegetables with the substrate to collect samples, and then using a Raman spectrometer to perform Raman measurements and evaluations on the wiped substrate.

[0061] Experiment 1 like Figures 3-5 As shown, flexible SERS substrates prepared using different mixing ratios of spherical and star-shaped gold nanoparticles were used to detect the staining agent R6G at excitation wavelengths of 532 nm, 633 nm, and 785 nm, respectively, and corresponding comparative experiments were conducted.

[0062] Specifically, in the specific operational steps of the above preparation method, Raman substrates with a volume ratio of AuNSs to AuNPs of 1:4 (AuNS-P(1-4)), a volume ratio of AuNSs to AuNPs of 1:1 (AuNS-P(1-1)), a volume ratio of AuNSs to AuNPs of 4:1 (AuNS-P(4-1)), a pure AuNSs Raman substrate, and a pure AuNPs Raman substrate are prepared respectively, and used to detect a fixed concentration (10 -5 The staining agent R6G solution (mol / L) was detected at excitation wavelengths of 532 nm, 633 nm, and 785 nm. The detection results are as follows: Figures 3-5 As shown, the high-performance broadband-response flexible surface-enhanced Raman substrate based on the spherical-star-shaped gold nanoparticle hybrid system prepared by the method of the present invention exhibits a broadband response at excitation wavelengths of 532 nm, 633 nm, and 785 nm. Compared with pure spherical gold nanoparticle solutions or pure star-shaped gold nanoparticle solutions, it has an enhancement effect to varying degrees. In particular, the AuNS-P(4-1) system has the highest matching degree between its SPR peak position and common excitation wavelengths (532 nm, 633 nm, 785 nm), and its broadband response performance is the best.

[0063] Experiment 2 like Figure 6 As shown, corresponding comparative experiments were conducted using Raman substrates treated at different temperatures.

[0064] Specifically, in the specific operational steps of the above preparation method, in step S6, filter paper coated with a gold-graphite mixture is placed in a drying oven, and the drying oven is set to three temperatures: room temperature (20℃), 50℃, and 80℃, and stored for 30 minutes respectively. Then, it is used to determine the fixed concentration (10... -5 The detection results of the staining agent R6G solution (mol / L) are as follows: Figure 6 As shown, this result indicates that the high-performance broadband response flexible surface-enhanced Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system prepared by the method of the present invention has good high-temperature resistance.

[0065] Experiment 3 like Figure 7 As shown, the Raman substrates prepared using the above method were stored in room temperature air for different numbers of days, and corresponding comparative experiments were conducted.

[0066] Specifically, in the specific operational steps of the above preparation method, in step S6, filter paper coated with a gold-graphite mixture is stored in room temperature air away from light. After 2 hours, 10 hours, 24 hours, 54 hours, 7 days, and 1 month, it is used to determine the fixed concentration (10...-5 The detection results of the staining agent R6G solution (mol / L) are as follows: Figure 7 As shown, this result indicates that the high-performance broadband response flexible surface-enhanced Raman substrate based on the spherical-star-shaped gold nanoparticle hybrid system prepared by the method of the present invention has reached a relatively stable state after initial adjustment.

[0067] Experiment 4 like Figure 8 As shown, the Raman substrate prepared by the above method was used to detect the pesticide residue concentration of thiram on a solid object.

[0068] Specifically, in the specific operational steps of the above preparation method, in step S6, a high-performance, broadband-response flexible surface-enhanced Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system is prepared. A sample is taken from the surface of a pear with a known concentration of thiram pesticide residue. The sampled high-performance, broadband-response flexible SERS substrate based on the spherical-star-shaped gold nanoparticle hybrid system is then analyzed using a Raman spectroscopy detection device. The Raman spectral intensities for different thiram pesticide residue concentrations are shown below. Figure 8 As shown in Figure a, the relationship between the Raman spectral intensity and the exponential coefficient of the thiram pesticide residue concentration is as follows: Figure 8 As shown in b. This result indicates that the high-performance flexible surface-reinforced Raman substrate prepared by the method of this invention has a good detection effect on thiram pesticide residues, and can qualitatively and quantitatively detect the concentration of thiram pesticide residues, with a minimum detection concentration as low as 10. -6 mol / L (0.24 ppm).

[0069] Experiment 5 like Figure 9 As shown, the Raman substrate prepared by the above method was used to perform a dimethyl sulfoxide (DMSO) volume concentration detection experiment on a liquid object.

[0070] To further validate its practical applications, this substrate was used for the semi-quantitative detection of dimethyl sulfoxide (DMSO) in food packaging materials. DMSO is commonly used as a processing aid in plastic packaging production, and residues may migrate into food during storage, especially at high temperatures. This rapid and sensitive method allows for the direct detection of DMSO residues on packaging surfaces via swabs, providing a simple and reliable solution for food safety monitoring. Furthermore, as a commonly used solvent in chemical synthesis and biopharmaceutical fields, DMSO residue monitoring is of great significance for industrial cleanliness validation and laboratory safety.

[0071] Specifically, in the specific operational steps of the above preparation method, in step S6, a high-performance, broadband-response flexible surface-enhanced Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system is prepared. A dimethyl sulfoxide (DMSO) solution of known volume concentration is taken and then dropped onto the high-performance flexible SERS substrate based on the spherical-star-shaped gold nanoparticle hybrid system prepared by the above method. After it air-dries naturally, it is placed in a Raman spectroscopy detection device for detection. The Raman spectral intensities at different concentrations are as follows: Figure 9 As shown in Figure a, the relationship between the Raman spectral intensity and the exponential coefficient of the volume concentration (1~100%) of the dimethyl sulfoxide (DMSO) solution is as follows: Figure 9 As shown in b. This result indicates that the high-performance flexible surface-enhanced Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system prepared by the method of the present invention has good detection performance for dimethyl sulfoxide (DMSO) solution, and can qualitatively and quantitatively detect the volume concentration of dimethyl sulfoxide (DMSO), with the lowest detectable volume concentration reaching 1%.

[0072] This invention achieves a targeted breakthrough in the bottlenecks of existing SERS substrate technology through the synergistic design of a spherical-star-shaped gold nanoparticle hybrid system with expanded graphite and filter paper substrates. The main beneficial effects are as follows: 1. By preparing star-shaped gold nanoparticle solutions using spherical gold nanoparticle solutions as seeds, the sharp protrusions on their surfaces create more "hot spot" regions, enhancing the local electric field and thus further improving the Raman scattering enhancement effect and detection performance. The "lightning rod effect" formed by the sharp protrusions on the star-shaped gold nanoparticle surface increases the "hot spot" region, strengthens the local electric field, and improves detection sensitivity.

[0073] 2. Furthermore, by adding a mixed expanded graphite suspension to the concentrated solution of spherical-star-shaped mixed gold nanoparticles, the mixed gold nanoparticles can be enriched on the surface of the expanded graphite, thereby further increasing the surface roughness of the gold nanoparticles on the filter paper, and thus improving the Raman scattering enhancement effect and improving its detection performance. The porous structure of expanded graphite can enrich the mixed gold nanoparticles, increase the surface roughness of the substrate, and synergistically enhance the Raman signal with the gold nanoparticle 'hot spots'.

[0074] 3. Furthermore, a concentrated solution of spherical-star hybrid gold nanoparticles was obtained by mixing spherical and star-shaped gold nanoparticles in a specific ratio. The optical properties of this concentrated solution can be controlled by adjusting the mixing volume ratio of the two spherical and star-shaped gold nanoparticles, laying the foundation for broadband SERS detection. By controlling the mixing ratio of spherical and star-shaped gold nanoparticles, a broadband SPR response can be achieved, adapting to multi-wavelength excitation and laying the foundation for broadband SERS detection.

[0075] 4. Overcoming the defects of existing flexible substrates: This invention eliminates the need for substrate transfer, reducing the risk of structural damage; it also avoids interference from substrate peaks on the glass slide, resulting in a purer detection signal.

[0076] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a surface-enhanced Raman spectroscopy substrate based on a hybrid system, characterized in that, Includes the following steps: S1, prepare a solution of spherical gold nanoparticles; S2, prepare a solution of star-shaped gold nanoparticles; S3, using pre-made expanded graphite, an expanded graphite suspension is prepared; S4. After centrifuging the spherical gold nanoparticle solution in S1, take the precipitate. After standing the star-shaped gold nanoparticle solution in S2, take the precipitate. Mix the two precipitates in a certain proportion to prepare a spherical-star mixed gold nanoparticle concentrate. S5, the spherical-star mixed gold nanoparticle concentrate in S4 and the expanded graphite suspension in S3 are ultrasonically mixed to obtain a gold-graphite mixture, and a dispersed mixed gold nanoparticle-expanded graphite composite structure is formed in the gold-graphite mixture. S6, the gold-graphite mixture from S5 is drop-coated onto filter paper and dried to obtain a surface-enhanced Raman substrate based on a spherical-star-shaped gold nanoparticle hybrid system. The mixed gold nanoparticle-expanded graphite composite structure is dispersed on the filter paper and interlocks with the loose microstructure of the filter paper to form an integral composite structure. The filter paper serves as the physical support and interlocking carrier for the expanded graphite particles and provides the substrate with a soft and flexible function.

2. The method for preparing a surface-enhanced Raman substrate based on a hybrid system according to claim 1, characterized in that, In step S1, a spherical gold nanoparticle solution is prepared by synthesis. Specifically, tetrachloroauric acid is dissolved in ultrapure water, then stirred and heated to the boiling point, and then a certain amount of sodium citrate solution is injected. After the reaction is completed, a spherical gold nanoparticle solution is formed.

3. The method for preparing a surface-enhanced Raman substrate based on a hybrid system according to claim 1, characterized in that, In step S2, a star-shaped gold nanoparticle solution is obtained by seed growth method. Specifically, the spherical gold nanoparticle solution prepared in step S1 is added to the precursor mixture prepared by tetrachloroauric acid and hydrochloric acid and stirred. A certain amount of silver nitrate solution and a certain amount of pre-prepared ascorbic acid solution are added dropwise and stirred continuously. When the solution color changes from red to blue-green, a certain amount of hexadecyltrimethylammonium bromide is added as a stabilizer to obtain star-shaped gold nanoparticles with a star-shaped structure with sharp branches.

4. The method for preparing a surface-enhanced Raman substrate based on a hybrid system according to claim 3, characterized in that, In step S2, the growth parameters of the star-shaped gold nanoparticles are optimized by adjusting the concentrations of silver nitrate solution and ascorbic acid solution, as well as the molar ratio of tetrachloroauric acid to spherical gold nanoparticles.

5. The method for preparing a surface-enhanced Raman substrate based on a hybrid system according to claim 1, characterized in that, In step S3, the pre-preparation method of expanded graphite is as follows: acetic acid and nitric acid are stirred and mixed, a certain amount of flake graphite is added, stirring is continued, and a certain amount of potassium permanganate is added. After the reaction is fully completed, the resulting mixture is washed with water until neutral, and then dried and subjected to high-temperature expansion treatment to obtain expanded graphite.

6. The method for preparing a surface-enhanced Raman substrate based on a hybrid system according to claim 5, characterized in that, In step S3, the specific method for preparing the expanded graphite suspension is as follows: pre-prepared expanded graphite is added to ultrapure water and treated with an ultrasonic instrument to make it uniformly dispersed in the water to form an expanded graphite suspension.

7. The method for preparing a surface-enhanced Raman substrate based on a hybrid system according to claim 1, characterized in that, In step S4, the optical properties of the spherical-star mixed gold nanoparticle concentrate are adjusted by adjusting the volume ratio of spherical gold nanoparticle precipitate to star-shaped gold nanoparticle precipitate.

8. An application of a surface-enhanced Raman substrate based on a hybrid system, characterized in that, According to any one of claims 1-7, a method for preparing a surface-enhanced Raman substrate based on a hybrid system is provided, wherein a Raman substrate is prepared and the Raman substrate is used as a Raman molecular probe to perform qualitative or quantitative analysis or detection of the components of the sampled object.

9. The application of a surface-enhanced Raman substrate based on a hybrid system according to claim 8, characterized in that, The liquid sample is tested by dripping it onto the Raman substrate and allowing it to air dry naturally before placing it in a Raman spectroscopy detection device. During the Raman spectroscopy detection process, the laser needs to be focused onto the dispersed black expanded graphite particles.

10. The application of a surface-enhanced Raman substrate based on a hybrid system according to claim 8, characterized in that, The solid-state sampled object is tested by wiping its surface with the Raman substrate described above. The sampled Raman substrate is then placed in a Raman spectroscopy detection device for testing. During the Raman spectroscopy detection process, the laser needs to be focused onto the dispersed black expanded graphite particles.

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