Silver particle-gold nanograting flexible substrate, and preparation method and use thereof

Abstract

The application belongs to the field of biochemical test, and particularly relates to a silver particle gold nanometer grating flexible substrate and a preparation method and application thereof. The polycarbonate layer in DVD or CD is used as a stamping mold, a three-dimensional periodic nanometer grating structure is prepared by stamping on a polyvinyl chloride (PVC) film, a gold layer is plated on the PVC, silver nanoparticles are uniformly decorated on the surface of the gold nanometer grating by using an interface self-assembly method, and the flexible substrate is prepared. The research results show that the electromagnetic field of the substrate is greatly enhanced, the uniform distribution of the silver nanoparticles and the periodic grating structure of the substrate enable the substrate to generate high-density and uniformly-distributed surface enhanced Raman scattering (SERS) hot spots, and the sensitivity and accuracy of detection are greatly improved. The application has the advantages of simple process, low cost and suitability for large-scale preparation, and provides a feasible idea for large-area preparation of a SERS substrate with high sensitivity, uniform signal and good stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biochemical tests, and particularly relates to a silver particle-gold nanometer grating flexible substrate and a preparation method thereof, and application of the silver particle-gold nanometer grating flexible substrate in rapid detection of trace organic pollutants. BACKGROUND

[0002] Surface Enhanced Raman Scattering (SERS) can be widely applied in food safety supervision, environmental monitoring, biological sensing and other fields as a non-destructive, rapid and efficient spectral analysis technology due to its high sensitivity, short detection time and fingerprint information identification. It is known that the significant enhancement of SERS signal mainly comes from the local surface plasmon resonance (LSPR) effect of noble metal nanostructures to produce electromagnetic field enhancement. In particular, when the gap between two or more adjacent noble metal nanoparticles is less than 10 nm, the electric field of the noble metal particles is coupled, and a very strong coupling electric field (referred to as SERS "hot spot") is generated at the gap. When the molecules to be detected are in the SERS "hot spot" area, the Raman signal can be amplified by more than 10 6 orders of magnitude, and the sensitivity can even reach the level of single molecule detection. However, the uneven distribution of hot spots in the SERS substrate makes the reproducibility of the Raman signal poor in actual detection. In order to improve the sensitivity and accuracy of actual detection, the substrate is required to produce high-density and uniformly distributed "hot spots".

[0003] In recent years, three-dimensional (3D) SERS substrates have attracted widespread attention because they can provide a larger "hot spot" range. At the same time, in order to further improve the uniformity, periodic structures have been introduced on the basis of three-dimensional SERS substrates, which lays a foundation for preparing SERS substrates with high sensitivity and signal uniformity. So far, a variety of methods have been used for the standardized manufacturing of three-dimensional periodic structures on SERS substrates, such as electron beam lithography, reactive ion etching and laser interference lithography. However, this high-precision etching technology requires expensive equipment, has a complex process, a long cycle and a high preparation cost, and is difficult to realize the large-scale preparation of SERS substrates. In addition, due to the limitation of etching precision, the gap between the obtained nanostructure units is large, which further limits the SERS activity of the three-dimensional periodic structure array. Therefore, it is still a challenge to explore an efficient and low-cost strategy to obtain a three-dimensional SERS substrate with high sensitivity.

[0004] Studies have shown that noble metal nanoparticles are decorated on three-dimensional periodic structures, and high-density and uniform hot spots can be obtained by using the electromagnetic field coupling effect between nanoparticles and the substrate. At present, researchers have developed a variety of nanoparticle modification methods, such as drop coating, spin coating and the like. However, the nanoparticles modified by these methods are randomly distributed, and are prone to aggregation and falling off, thereby leading to poor uniformity of the SERS signal. Although coupling agents such as biphenyl-4,4'-dithiol (BFDT), DNA chains and the like are used as coupling agents to achieve uniform anchoring of nanoparticles. However, these coupling agents are located in the gap between the nanoparticles and the substrate (SERS hot spot area), and the SERS signal of the coupling agents itself will seriously interfere with the detection signal of the target analyte. In summary, it is of great significance for the wide application of SERS detection technology to develop a simple and rapid preparation method of three-dimensional periodic structures and to explore a method of uniformly modifying nanoparticles without the aid of coupling agents. SUMMARY

[0005] One of the purposes of the present application is to provide a method combining nanoimprinting and interfacial self-assembly technology, using a low-cost DVD or CD disc as a template to prepare a silver particle@gold nanometer grating flexible substrate. The substrate is simple to prepare, low in price, high in sensitivity, good in stability and flexibility, and provides a new idea for realizing on-site rapid detection of trace organic matter.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a preparation method of a silver particle@gold nanometer grating flexible substrate, comprising the following steps:

[0007] S1, taking silver nanoparticles with a particle size of 50-200 nm, dispersing them into a mixed solvent of n-hexane and ethanol to form a uniform silver nanoparticle colloidal suspension;

[0008] S2, peeling off the polycarbonate layer in the digital video disc (DVD) or CD, and cleaning it to serve as a polycarbonate layer template;

[0009] covering the polycarbonate layer template onto a PVC film, and using a nanoimprinting process to copy the three-dimensional periodic structure in the polycarbonate layer template to the surface of the PVC film at a temperature of 100-150 DEG C under a pressure of 300-500 N cm -2 to form a three-dimensional periodic arrangement of nanometer grating structures on the surface of the PVC film;

[0010] plasma sputtering a 10-30 nm thick gold film on the surface of the PVC film where the nanometer grating structure is located to form a gold nanometer grating;

[0011] S3, hydrophilic treatment is conducted on the surface of the gold nanometer grating, deionized water is added dropwise on the surface of the gold nanometer grating to form a water film, and the silver nanoparticle colloidal suspension is slowly added dropwise on the surface of the water film, under the self-assembly effect of the liquid phase interface, the silver particles are uniformly modified on the surface of the gold nanometer grating, and the silver particle@gold grating flexible substrate is prepared after natural drying at room temperature.

[0012] Preferably, the silver nanoparticles are prepared by the following method: 50 mL of ethylene glycol is placed in a 100 ml conical flask, then 0.6 g of silver nitrate and 1.2 g of polyvinylpyrrolidone (PVP) are added, and stirring is conducted until complete dissolution; then, the conical flask is placed in 160 °C silicon oil, and constant temperature reaction is conducted under stirring for 2 h, and then natural cooling is conducted to room temperature; the reaction product is cleaned by ultrasonic cleaning with distilled water and anhydrous ethanol alternately for 4-5 times, and centrifugal separation is conducted, and the silver nanoparticles are prepared.

[0013] As a further improvement of the preparation method of the Ag-NPs@gold nanometer grating flexible substrate, the following is provided:

[0014] Preferably, the PVP is PVP-K29, and the molecular weight is 8000-700000.

[0015] Preferably, in step S1, the n-hexane and ethanol are mixed in a volume ratio of 1:1 to form a mixed solvent.

[0016] Preferably, in step S1, the concentration of the silver nanoparticles in the colloidal suspension is 1-3 mg / mL.

[0017] Preferably, in step S2, a current of 10-30 mA is used for plasma sputtering on the surface of the nanometer grating structure in the PVC film for 2-4 min.

[0018] Preferably, in the three-dimensionally periodically arranged nanometer grating structure, the width W of the nanometer groove is 300 nm, the depth h of the nanometer groove is 90 nm, and the period P of the nanometer grating is 730 nm.

[0019] Preferably, in step S3, the thickness of the water film is 2-3 mm.

[0020] Preferably, in step S3, the thickness of the water film is 2-3 mm.

[0021] The second object of the present application is to provide an Ag-NPs@gold nanometer grating flexible substrate prepared by the above preparation method.

[0022] The second object of the present application is to provide the use of the above Ag-NPs@gold nanometer grating flexible substrate in rapid detection of trace organic pollutants.

[0023] The beneficial effects of the present application compared with the prior art are as follows:

[0024] 1) The present application relates to a simple, low-cost, green preparation method of silver nanoparticle-gold nanograting flexible substrate. The present application uses low-cost digital video disc (DVD or CD), peels off the polycarbonate layer in DVD or CD as a template, uses nanoimprint method to construct three-dimensional (three-dimensional) periodic nanograting structure on the surface of flexible and transparent polyvinyl chloride (PVC) sheet; then a thin gold (Au) layer is deposited on the PVC film by plasma sputtering, and a gold nanograting structure is obtained; finally, without the need for coupling agent, due to the fact that n-hexane is not soluble in water and is more volatile, the floating Ag-NPs are self-assembled into a monolayer at the air / solution interface, and the silver nanoparticles (Ag-NPs) are uniformly and closely arranged in a monolayer on the surface of the three-dimensional periodic gold nanograting by using the interfacial self-assembly method, and then the Ag-NPs-gold nanograting flexible substrate is constructed.

[0025] Among them, the silver nanoparticles (Ag-NPs) can be synthesized in liquid phase in an oil bath environment with ethylene glycol as a solvent and a reducing agent.

[0026] The results of finite difference time domain simulation (FDTD) show that under the excitation of 532 nm light, when the Ag-NPs are placed on the three-dimensional periodic gold nanograting, the electromagnetic field of the substrate is greatly enhanced due to the extremely strong coupling electric field generated at the gap between adjacent Ag-NPs and the gap between the Au layer and the Ag-NPs. At the same time, the three-dimensional nanostructure increases the "hot spot" density of the substrate, and the uniform distribution of the monolayer Ag-NPs plus the periodic grating structure of the substrate makes the substrate capable of producing high-density and uniformly distributed SERS "hot spots", which can greatly improve the sensitivity and accuracy of the determination. The present application has the advantages of simple process, low cost, and suitability for large-scale preparation, and provides a feasible approach for large-area preparation of SERS substrates with high sensitivity, uniform signal, good stability and reproducibility. It is expected to realize large-scale preparation of high-sensitivity SERS substrates, and further promote the practical application of SERS technology for on-site and rapid detection.

[0027] 2) The present application uses low-cost, recyclable DVD (or CD) and PVC film as raw materials, combines nanoimprint lithography and interfacial self-assembly technology, and prepares a three-dimensional SERS substrate with periodic structure. The entire preparation process avoids the use of coupling agents and expensive instruments, has a simple process, good reproducibility, and can be mass-produced, providing a reliable way for economically and effectively manufacturing SERS substrates for environmental detection. Moreover, the polycarbonate layer template can be reused.

[0028] 3) The Ag-NPs@gold nanograting flexible substrate prepared by this invention exhibits good stability and flexibility, can be bent at will while maintaining SERS performance, and can be easily cut into various shapes as needed, demonstrating the great potential of this substrate in practical applications. Application of surface-enhanced Raman scattering (SERS) sensing performance in rapid trace detection of organic pollutants.

[0029] 4) The hot spots between the gold nanograting structure and Ag-NPs, as well as between adjacent Ag-NPs, significantly enhance the SERS activity of the substrate. Furthermore, the construction of the three-dimensional periodic nanostructure increases the hot spot density while further enhancing the electromagnetic enhancement induced by localized interstitial plasma. On the other hand, the uniform distribution of monolayer Ag-NPs on the periodic structure ensures the uniformity of the SERS signal. This provides a new approach for advancing SERS technology in the rapid detection of trace organic pollutants. Attached Figure Description

[0030] Figure 1 This is a process flow diagram for preparing the Ag-NPs@Au grating flexible substrate according to the present invention.

[0031] Figure 2 The images represent the characterization of the substrate morphology; Figures (a)-(c) are SEM images, cross-sectional height images, and AFM morphology images of a DVD disc, respectively; Figures (d)-(f) are SEM images, cross-sectional height images, and AFM morphology images of a gold nanograting thin film, respectively; Figures (g)-(i) are SEM images, cross-sectional height images, and AFM morphology images of an Ag-NPs @ gold nanograting flexible substrate, respectively.

[0032] Figure 3 Figure (a) shows the XRD spectra of different substrates, and Figure (b) shows the UV-Vis spectra of different substrates.

[0033] Figure 4 Figure (a) shows the SEM image of Ag-NPs and its particle size distribution statistics; Figure (b) shows the SEM image of Ag-NPs after assembly and its gap size distribution statistics; Figure (c) shows the SEM image of monolayer Ag-NPs self-assembled on a planar substrate; Figure (d) shows the SEM image of silver nanoparticles drop-coated on a three-dimensional periodic substrate.

[0034] Figure 5 The electromagnetic field distribution images of the substrate were obtained by FDTD simulation. Figures (a)-(c) show the electromagnetic field intensity distribution of the monolayer Ag-NPs film, Ag-NPs@Au layer, and Ag-NPs@gold nanograting flexible substrate under 532 nm excitation light, respectively.

[0035] Figure 6Figure (a) shows the SERS spectra of Ag-NPs@gold nanograting flexible substrates at different concentrations of R6G; Figure (b) shows the SERS spectra of substrates using 10... -7 Using R6G of M concentration as a probe molecule, SERS spectra were obtained on different substrates, including Au@PVC grating substrate (curve I), monolayer Ag-NPs film (curve II), Ag-NPs@Au layer (curve III), and Ag-NPs@gold nanograting flexible substrate (curve IV); Figure (c) is the SEM image of Ag-NPs@gold nanograting flexible substrate; Figure (d) is the SEM image of 10 -7 Using R6G at concentration M as a probe molecule, 613 cm⁻¹ -1 Figure (e) shows the mapping spectrum at the location; Figure (f) shows the relative standard deviation of the spectrum in the 50 μm × 50 μm region of the Ag-NPs@gold nanograting flexible substrate; Figure (f) shows the Raman spectra collected from 25 random points on five samples from different batches.

[0036] Figure 7 Figure (a) shows the SERS spectra of CV probe molecules at different concentration ranges; Figure (b) shows the SERS spectra at 1619 cm⁻¹. -1 The linear fitting curve of characteristic peak intensity versus logarithm of CV concentration; Figure (c) shows optical photographs of the substrate in a bent state and cut into different shapes; Figure (d) shows the characteristic peak intensity versus logarithm of CV concentration. -5 M CV is the probe molecule, and the Raman spectra of Ag-NPs @ gold nanograting flexible substrate in the initial and bent states are shown; Figure (e) shows the Raman spectra of 10 CV as the probe molecule. -7 MR6G is the probe molecule. SERS spectra of Ag-NPs stored on a flexible gold nanograting substrate for different times are shown in Figure (f). Figure (f) shows the Raman signal at 613 cm⁻¹ for different storage times. -1 The curve at that location.

[0037] Figure 8 The graph shows a comparison of the SERS performance of substrates prepared by changing different experimental parameters in Examples 1-3. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0039] Example 1

[0040] This embodiment provides a method for fabricating a flexible Ag-NPs@gold nanograting substrate, which specifically includes the following steps:

[0041] 1. Synthesis of silver nanoparticles

[0042] Silver nanoparticles were prepared in an oil bath environment using ethylene glycol as both solvent and reducing agent. First, 50 mL of ethylene glycol was placed in a 100 mL Erlenmeyer flask, followed by the addition of 0.6 g of silver nitrate and 1.2 g of PVP (PVP-K29, molecular weight 58,000), and stirred at room temperature until completely dissolved. Then, the Erlenmeyer flask was placed in silicone oil at 160 °C and reacted under stirring for 2 h, followed by natural cooling to room temperature. Next, the reaction product was ultrasonically washed 4-5 times alternately with distilled water and anhydrous ethanol, and centrifuged to obtain silver nanoparticles (Ag-NPs). The washed Ag-NPs were dispersed in a 1:1 mixture of hexane and ethanol to form a homogeneous colloidal suspension with a concentration of 2 mg / mL.

[0043] 2. Fabrication of the metal grating substrate

[0044] First, the polycarbonate layer of the DVD was peeled off and ultrasonically cleaned in ethanol to remove the dye coating on the surface. Then, it was subjected to treatment at 120 °C and 400 N / cm². -2 Under pressure, the three-dimensional periodic grating structure of the DVD template was replicated onto a PVC film using nanoimprinting technology. Finally, a 20 nm thick Au film, namely the gold nanograting, was deposited on the nanoimprinted PVC plate by plasma sputtering at a current of 20 mA for 3 min.

[0045] 3. Fabrication of Ag-NPs@gold nanograting flexible substrate

[0046] First, a 2.5 mm thick deionized water film was coated onto the surface of the Au grating. Then, the prepared Ag-NPs colloidal suspension was slowly dropped onto the edge using a micropipette. Since hexane is insoluble in water and more volatile, the floating Ag-NPs self-assembled into a monolayer at the air / solution interface. After drying at room temperature, Ag-NPs@gold nanograting flexible substrate 1 was obtained.

[0047] Example 2

[0048] This embodiment provides a method for preparing Ag-NPs@gold nanograting flexible substrate. The specific steps are the same as in Embodiment 1, except that in step 2, a nanoimprinting process is used at 100 °C to copy the three-dimensional periodic structure of the polycarbonate layer template in DVD to the surface of PVC film, thereby obtaining a three-dimensional periodic nanograting structure on the surface of PVC film.

[0049] Finally, Ag-NPs@gold nanograting flexible substrate 2 was prepared.

[0050] Example 3

[0051] This embodiment provides a method for preparing Ag-NPs@gold nanograting flexible substrate. The specific steps are the same as in Embodiment 1, except that in step 2, a 10 nm thick Au film is plasma sputtered on the surface of the grating structure on the PVC film for 3 min at a current of 10 mA to form a gold nanograting.

[0052] Finally, Ag-NPs@gold nanograting flexible substrate was prepared.

[0053] Comparative Example 1

[0054] This comparative example provides a method for preparing a flexible Ag-NPs nanograting substrate. The specific steps are the same as in Example 1, except that in step 2, a three-dimensional periodic grating structure of a DVD template is copied onto a PVC film using nanoimprinting technology, without plasma sputtering. Then, a 2.5 mm thick deionized water film is coated onto the surface of the PVC film. Subsequently, the prepared Ag-NPs colloidal suspension is slowly dripped onto the edge using a micropipette. Since hexane is insoluble in water and more volatile, the floating Ag-NPs self-assemble into a monolayer at the air / solution interface. Finally, after drying at room temperature, a monolayer Ag-NPs film is obtained.

[0055] Comparative Example 2

[0056] This comparative example provides a method for preparing a flexible substrate with Ag-NPs nanogratings. The specific steps are the same as in Example 1, except that: a PVC film is taken and, without imprinting, plasma sputtered at 20 mA for 3 min to deposit a 20 nm thick Au film on the unimprinted PVC plate. Subsequently, a 2.5 mm thick deionized water film is coated on the surface of the Au film. Then, the prepared Ag-NPs colloidal suspension is slowly dropped onto the edge area using a micropipette. Since hexane is insoluble in water and more volatile, the floating Ag-NPs self-assemble into a monolayer at the air / solution interface. Finally, after drying at room temperature, an Ag-NPs@Au layer is obtained.

[0057] The process of preparing the entire Ag-NPs@gold nanograting flexible substrate and the self-assembly process in the above embodiment are shown in Figure 1.

[0058] (1) Characterization of Ag-NPs@gold nanograting flexible substrate

[0059] The samples were characterized using techniques such as scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV), and atomic force microscopy (AFM).

[0060] Figure 2The morphological features of the three-dimensional periodic structure during the fabrication process are shown; Figures (a)-(c) are SEM images, cross-sectional height, and AFM morphology images of DVD discs, respectively; Figures (d)-(f) are SEM images, cross-sectional height, and AFM morphology images of gold nanograting films, respectively; Figures (g)-(i) are SEM images, cross-sectional height, and AFM morphology images of Ag-NPs@gold nanograting flexible substrates, respectively.

[0061] Depend on Figure 2 It can be seen that the surface of the DVD polycarbonate layer has a typical nanograting structure with a period P of 730 nm, as shown in the SEM characterization results. Figure 2 (a) The magnified SEM image shows that the stripe boundaries of the nanograting are clear and the groove width W is 300 nm. Figure 2 The AFM image in (b) provides a clearer view of the fringe structure of the nanograting, and the corresponding cross-sectional height distribution shows that the groove depth h is 90 nm. After nanoimprinting on a PVC board using a DVD polycarbonate layer as a template, a three-dimensional periodic nanograting structure was successfully constructed on the PVC film, exhibiting a period and height similar to the DVD template, as shown in the image. Figure 2 As shown in (d)-(f), this demonstrates that the three-dimensional periodic structure has been successfully transferred from the DVD template to the PVC film surface. Ag-NPs were then assembled on the surface of the gold nanograting using liquid-phase interface self-assembly technology, thus constructing an Ag-NPs@gold nanograting flexible substrate. Figure 2 (g) SEM results show that, without the addition of any coupling agent, Ag-NPs can be uniformly modified onto the surface of gold nanogratings via interfacial self-assembly. The assembled Ag-NPs are uniformly and orderly arranged over a large area; SEM magnification image ( Figure 2 (g) Illustration shows that the assembled Ag-NPs are a monolayer structure, with the Ag-NPs closely packed on the surface of the gold nanograting; Figure 2 (i) shows that the flexible substrate of gold nanograting after assembling Ag-NPs still maintains a good three-dimensional periodic structure, which further proves that the assembled monolayer Ag-NPs are arranged in a regular and orderly manner.

[0062] Compared to the original PVC sheet, the XRD pattern of the substrate after sputtering gold ( Figure 3(a) shows the characteristic peaks of the gold (111) crystal plane (PDF#03-065-8601). Since the cubic structure and lattice constant of gold and silver are similar, the diffraction peaks are similar to each other. The XRD pattern of the Ag-NPs@gold nanograting flexible substrate shows four peaks, which are related to the (311), (220), (200) and (111) crystal planes of Ag-NPs, respectively (PDF#01-087-0597). Subsequently, the substrate was tested with UV-Vis spectra to select a suitable excitation wavelength for SERS detection. The results are shown in Figure 3(b). No obvious absorption bands were found on the original PVC sheet and the PVC sheet with the gold layer. At the same time, an LSPR band of 400 nm to 600 nm was found on the Ag-NPs@Au grating flexible substrate. This absorption peak indicates that the electromagnetic enhancement effect can be better excited when the wavelength of the laser is 532 nm. In addition, as Figure 4 As shown in (a), the average particle size of Ag-NPs is 90 nm. The average gap between adjacent Ag-NPs on the Ag-NPs@gold nanograting flexible substrate obtained by interfacial self-assembly is 3.6 nm. Figure 4 (b) This is expected to provide an effective SERS hotspot for the detection of target molecules.

[0063] (2) FDTD simulation and electromagnetic enhancement mechanism

[0064] In contrast, Ag-NPs were modified onto the surface of an Au planar substrate using the same interfacial self-assembly method to prepare Ag-NPs@Au layer substrates. Figure 4 As shown in (c), the flat monolayer Ag-NPs are uniformly distributed on the Au film surface, indicating that the method of interfacial self-assembly modification of Ag-NPs proposed in this invention has good universality.

[0065] In contrast, Ag-NPs were modified onto the surface of a gold nanograting using a conventional drop-coating method. The results showed that the Ag-NPs were randomly distributed on the grating surface and tended to aggregate. Figure 4 (d)).

[0066] The SERS properties of the substrate were investigated using a Renishaw inVia Reflex laser Raman spectrometer. Rhodamine 6G (R6G) and crystal violet (CV) were used as detector molecules. The excitation wavelength was 532 nm, the integration time was 5 s, and the powers were 0.05 mW and 0.1 mW, respectively. Mapping and Raman signals were measured under the same testing conditions. X-ray diffraction (XRD) patterns were obtained using a Philips X'pert-PRO XRD instrument.

[0067] Raman enhancement is mainly attributed to local electric field enhancement, and the optical hotspots induced by the substrate structure have always been a hot topic in SERS research. To further elucidate the electromagnetic field enhancement induced by the nano-gap between adjacent Ag-NPs and Au grating structures, finite element modeling was performed based on the observed microstructure using model parameters, and a series of numerical simulations were conducted under 532 nm excitation. The simulation results in Figure 5 show the electric field distribution of monolayer Ag-NPs film, Ag-NPs@Au layer, and Ag-NPs@gold nanograting flexible substrate. The electric field distribution is compared with that of monolayer Ag-NPs film (…). Figure 5 Compared to (a), the addition of the Au planar mirror structure increases the electric field of Ag-NPs ( Figure 5 (b) shows a significant enhancement. The large electromagnetic field exists not only in the gaps between adjacent Ag-NPs but also between the Au layer and the Ag-NPs. Clearly, these nano-gap gaps provide numerous SERS hotspots for subsequent detection. On the other hand, as Metiu first theoretically proposed, the electromagnetic enhancement caused by localized surface plasmon excitation can be further amplified through this mirror-nanoparticle (NPOM) structure. This mirror structure has proven highly effective in improving the SERS performance of the substrate. It is also important to note that the enhancement of the electromagnetic field intensity is related to the geometry of the fabricated structure. Due to the presence of the three-dimensional periodic structure, the electric field on the Ag-NPs@gold nanograting surface is greatly enhanced (Fig. 5(c)). It has been reported that the composite structure of metal particles and metal gratings leads to effective coupling between surface plasmons (SPPs) generated by the grating and localized surface plasmons (LSPs) excited by the metal nanoparticles. As a dual-resonance SERS system, this structure can provide a higher electric field intensity. Based on the relationship between the enhancement factor and the fourth power of the electric field strength, finite-difference time-domain (FDTD) simulation results show that better SERS performance can be obtained on Ag-NPs@gold nanograting flexible substrates by changing the substrate structure. This will be verified in subsequent SERS tests.

[0068] (3) SERS performance characterization of Ag-NPs@gold nanograting flexible substrate

[0069] First, Rhodamine 6G (R6G) solutions of different concentrations were used as probe molecules to evaluate the SERS activity of the constructed Ag-NPs@gold nanograting flexible substrate. As shown in Figure 6(a), even when the concentration was reduced to 10... -13 The characteristic peaks of the M,Ag-NPs@gold nanograting flexible substrate can still be clearly distinguished, indicating that the SERS substrate has high SERS sensitivity.

[0070] To further investigate the source of this high sensitivity, the gold nanograting prepared in step 2 of Example 1, the monolayer Ag-NPs film prepared in Comparative Example 1, the Ag-NPs@Au layer prepared in Comparative Example 2, and the Ag-NPs@gold nanograting flexible substrate 1 prepared in step 3 of Example 1 were used. -7 MR6G was used as a probe molecule to collect Raman spectra of the above-mentioned substrates (Figure 6(b) curves I-IV, Au@PVC grating substrate (curve I), monolayer Ag-NPs film (curve II), Ag-NPs@Au layer (curve III), Ag-NPs@gold nanograting flexible substrate (curve IV)). The results show that no Raman signal of R6G was detected on the gold nanograting substrate alone, indicating that the SERS activity of the gold nanograting is low (curve I); while the monolayer Ag-NPs film constructed on the PVC surface using liquid-phase interface self-assembly technology showed a strong SERS signal, indicating that the Ag-NPs on the film surface can provide a high density of SERS hotspots (curve II). When the monolayer Ag-NPs were assembled onto the flat Au layer surface, its SERS signal intensity was further improved (curve III). For this Ag-NPs@Au layer substrate, in addition to the SERS hotspots provided between Ag-NPs, SERS hotspots are also generated between Ag-NPs and the Au film. Furthermore, the specular reflection of the Au film promotes the absorption of incident light, and the electromagnetic enhancement caused by local surface plasmon excitation can be further amplified through this mirror-nanoparticle structure, resulting in a stronger electric field enhancement. When a monolayer of Ag-NPs is assembled onto the surface of a three-dimensional periodic gold nanograting, the SERS signal intensity is significantly improved. Compared to other substrates, the Ag-NPs@Au nanograting flexible substrate exhibits higher SERS sensitivity (curve IV). Corresponding to the numerical simulation results, in actual detection, the SERS activity of the Ag-NPs@gold nanograting flexible substrate is significantly improved with the presence of the three-dimensional periodic structure. This further demonstrates that the dynamic interaction between LSPs and SPPs is beneficial to improving the SERS sensitivity of the substrate.

[0071] In practical applications of rapid on-site detection, SERS substrates need to possess good signal repeatability. Our Raman spectroscopy obtained from a 50 μm × 50 μm region confirms the excellent uniformity of the Ag-NPs@gold nanograting flexible substrate. -7 Using R6G at concentration M as a probe molecule, 613 cm⁻¹ -1 The mapping spectrum at the location shows relatively uniform color, indicating that the substrate has a large area of ​​signal uniformity during detection. Furthermore, the relative standard deviation (RSD) of the intensity, calculated compared to the average relative peak intensity, is 12.2%. Figure 6(c) This further demonstrates that the prepared SERS substrate possesses good signal uniformity. On the other hand, SERS sensitivity tests were performed on different batches of substrates prepared using the same method and parameters to evaluate the reproducibility of the substrate's SERS performance. As shown in Figure 6(d), the SERS spectra of 25 random points extracted from five different batches of samples were similar to each other, indicating that good signal reproducibility exists between different batches of substrates using this simple preparation method. Therefore, this substrate provides a reliable guarantee for the uniformity and reproducibility of Raman signals in practical detection.

[0072] The practicality of Ag-NPs@gold nanograting flexible substrates was verified by testing simulated pollution solutions containing the toxic organic pollutant crystal violet (CV). Extensive use of CV can lead to environmental pollution, and ingestion can cause laryngitis and stomach ulcers. Figure 7 (a) shows the SERS spectra of CV probe molecules at different concentrations. Even when the concentration is reduced to 10... -8 M can also distinguish significant Raman signals. Additionally, at concentrations of 10... -4 Up to 10 -7 Within the M concentration range, 1619 cm -1 The peak intensity and the corresponding logarithm of the concentration at a given point showed a good linear relationship. Figure 7 (b) On the other hand, the flexibility and stability of the substrate are also crucial for practical testing in different environments. Figure 7 (c) demonstrates that the substrate exhibits good flexibility and can be freely cut into different shapes as needed. For example... Figure 7 As shown in (d), the Raman spectrum of the substrate in the bent state is basically consistent with that of the original substrate, which further reveals the potential of the Ag-NPs@gold nanograting flexible substrate in practical applications. Meanwhile, Figures 7 ((e)-(f)) show the SERS spectra of the substrate after storage for different times. The Ag-NPs@gold nanograting flexible substrate still maintains high SERS sensitivity after 3 months, demonstrating good storage stability. This further reveals the great potential of the Ag-NPs@gold nanograting flexible substrate in practical applications.

[0073] Figure 8 This is a comparison of the SERS performance of substrates prepared under different experimental parameters in Examples 1-3. Figure 8 It can be seen that the substrate prepared with the parameters in Example 1 exhibits better SERS activity.

[0074] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A method for preparing a flexible substrate with silver particles@gold nanogratings, characterized in that, Includes the following steps: S1. Take silver nanoparticles with a particle size of 50~200 nm and disperse them in a mixed solvent of n-hexane and ethanol in a volume ratio of 1:1 to form a uniform silver nanoparticle colloidal suspension. The concentration of silver nanoparticles in the colloidal suspension is 1~3 mg / mL. S2. Peel off the polycarbonate layer from the digital video disc (DVD) or CD, clean it, and use it as a template for the polycarbonate layer. A polycarbonate layer template is applied to a PVC film, and nanoimprinting is performed at 100-150 °C at a temperature of 300-500 N / cm. -2 Under pressure, the three-dimensional periodic structure in the polycarbonate layer template is copied to the surface of the PVC film, and a three-dimensional periodic nanograting structure is obtained on the surface of the PVC film. A gold nanograting is formed by plasma sputtering a 10-30 nm thick gold film onto the surface of the PVC film containing the nanograting structure. S3. The surface of the gold nanograting is hydrophilically treated, and deionized water is dropped onto the surface of the gold nanograting to form a water film. The colloidal suspension of silver nanoparticles is slowly dropped onto the surface of the water film. Under the self-assembly of the liquid phase interface, the silver particles are uniformly modified onto the surface of the gold nanograting. The substrate is then dried naturally at room temperature to obtain a flexible substrate of silver particles@gold nanograting. Steps S1 and S2 are not in any particular order.

2. The method for preparing a flexible substrate with silver particles@gold nanogratings according to claim 1, characterized in that, The silver nanoparticles were prepared as follows: 50 mL of ethylene glycol was placed in a 100 mL Erlenmeyer flask, followed by the addition of 0.6 g of silver nitrate and 1.2 g of polyvinylpyrrolidone (PVP), and stirred until completely dissolved. Then, the Erlenmeyer flask was placed in silicone oil at 160 °C and reacted at a constant temperature for 2 h under stirring, followed by natural cooling to room temperature. The reaction product was ultrasonically washed 4-5 times alternately with distilled water and anhydrous ethanol, and then separated by centrifugation to obtain the silver nanoparticles.

3. The method for preparing a flexible substrate with silver particles@gold nanogratings according to claim 2, characterized in that, The PVP is PVP-K29 with a molecular weight of 8,000-700,000.

4. The method for preparing a flexible substrate with silver particles@gold nanogratings according to claim 1, characterized in that, In step S2, a current of 10~30 mA is used to perform plasma sputtering on the surface of the nanograting structure in the PVC film for 2~4 min.

5. The method for preparing a flexible substrate with silver particles@gold nanogratings according to claim 1, characterized in that, In the three-dimensional periodically arranged nanograting structure, the width W of the nanogroove is 300 nm, the depth h of the nanogroove is 90 nm, and the period P of the nanograting is 730 nm.

6. The method for preparing a flexible substrate with silver particles@gold nanogratings according to claim 1, characterized in that, In step S3, the thickness of the water film is 2-3 mm.

7. A flexible substrate of silver particles@gold nanogratings prepared by the preparation method of any one of claims 1-6.

8. Use of the silver particle@gold nanograting flexible substrate of claim 7 in the rapid detection of trace organic pollutants.

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