Needle-like graphic nano-structure SERS substrate and preparation method thereof

Abstract

The invention discloses an SERS (Surface Enhanced Raman Scattering) substrate with a needle-like diagram nanostructure and a preparation method of the SERS substrate, and belongs to the field of nanotechnology and detection. The preparation method of the needle-like Turing nano-structure SERS substrate comprises the following steps: by taking a silver needle as a carrier, carrying out electrochemical etching on the surface of the silver needle to induce to form a Turing nano-structure with fractal topological characteristics, and then inducing to conformally grow a layer of zeolite imidazole framework-8 material as a shell layer by utilizing the nano curvature characteristics of the fractal structure, so as to prepare the needle-like Turing nano-structure SERS substrate. And a composite SERS enhanced platform with an electromagnetic field hot spot aggregation effect and a molecular screening and enriching capability is constructed. The platform has the advantages of high structural uniformity, expandability in manufacturing, synergy of signal enhancement and molecular recognition and the like, remarkably improves the detection sensitivity and the signal reproducibility, and is suitable for trace analysis in a complex sample system, such as related application in the fields of food safety, environmental pollution monitoring, biomedicine and the like.

Description

Technical Field

[0001] The invention relates to a needle-shaped Turing nanostructured SERS substrate and a preparation method thereof, and belongs to the field of nanotechnology and detection. Background Art

[0002] Surface-enhanced Raman scattering (SERS) is a spectroscopic detection technique with high sensitivity and molecular fingerprint recognition capabilities. It has been widely used in trace analysis, environmental monitoring, food safety, and biomedicine. However, traditional SERS substrates generally suffer from uneven hotspot distribution, poor selectivity, and poor signal reproducibility. In particular, nonspecific adsorption in complex matrices can easily cause background interference, significantly reducing detection accuracy and stability, limiting its widespread application in practical scenarios.

[0003] To improve SERS performance, common enhancement strategies currently include self-assembly of metal nanoparticles, template-assisted array structure construction, and the composite of functional materials such as metal organic frameworks (MOFs) on metal surfaces.

[0004] For example, Chinese patent CN114994009A discloses a method for preparing a surface-enhanced Raman scattering substrate based on Ag@ZIF-8 core-shell nanochains and its application. Specifically, the method avoids in-situ synthesis of ZIF-8 on silver nanowires, resulting in a beaded Ag@ZIF-8 core-shell nanochain material. Chinese patent CN110646400A discloses a PS / Ag / ZIF-8 composite structure surface-enhanced Raman scattering active substrate and its preparation method. Specifically, the substrate is an ordered polystyrene array, Ag nanoparticles are loaded onto the array surface via magnetron sputtering, and a ZIF-8 film is then grown on top of the Ag nanoparticles.

[0005] While these methods have enhanced the SERS signal to a certain extent, they still face numerous challenges, including uneven hotspot distribution, complex preparation processes, poor reproducibility, structural instability, uneven MOF loading, or poor interfacial bonding. Furthermore, most SERS substrates are planar structures or particle stacks, making them difficult to adapt to diverse application requirements such as flexible penetration and micro-area in-situ detection. Summary of the Invention

[0006] [Technical Issues]

[0007] Existing SERS substrates have problems such as poor enhancement effect, uneven enhancement, unstable Raman signal intensity, and poor reproducibility.

[0008] [Technical solution]

[0009] To address the above-mentioned issues, the present invention aims to provide a needle-like Turing nanostructured SERS substrate and a method for preparing the same. The core of this method is the use of electrochemical etching technology. As a technical means of regulating ion migration based on electric potential, electrochemical etching can construct Turing-shaped fractal structures on metal surfaces. Such structures have self-organized nanopatterns, high porosity, abundant nanogaps and curvatures, and both light field confinement capabilities and good mechanical stability, providing an ideal structural foundation for efficient SERS enhancement.

[0010] By constructing a multi-scale rough structure with Turing fractal characteristics on the surface of the silver needle, the self-assembly construction of high-density uniform SERS hotspots is achieved; a layer of ZIF-8 metal-organic framework material (MOF) with nanopores is in situ coated on the surface of the structure to give it molecular screening and enrichment functions, and further enhance the light field penetration; the overall substrate formed is a silver needle-ZIF-8 composite structure with excellent optical properties, chemical stability and interface function regulation capabilities; it can achieve a synergistic effect of electromagnetic field enhancement and molecular selective enrichment, improve signal sensitivity, selectivity and stability, meet the needs of multi-scenario, micro-area, and in-situ detection, and has important research value and application prospects.

[0011] In order to achieve the above objectives, the technical solutions provided are as follows:

[0012] The first object of the present invention is to provide a method for preparing a needle-shaped Turing nanostructured SERS substrate, the preparation method comprising the following steps:

[0013] (1) Pure silver needles were ultrasonically pretreated to remove surface contaminants; then, the silver needles were used as working electrodes, and Ag / AgCl electrodes and platinum electrodes were used as reference electrodes and auxiliary electrodes, respectively. Electrochemical etching was performed in the potential range of -0.2 to 0.4 V by cyclic voltammetry to obtain TN-Ag needles;

[0014] (2) rinsing the TN-Ag needles obtained in step (1) with ethanol several times and then incubating them in a zinc nitrate solution;

[0015] (3) Immerse the TN-Ag needles after incubation in step (2) in a ZIF-8 mixed solution to ensure uniform ZIF-8 deposition, rinse them clean, and dry them under a nitrogen flow to obtain the needle-shaped Turing nanostructure SERS substrate TN-Ag / ZIF-8 needles.

[0016] In one embodiment, the pretreatment in step (1) refers to immersing the pure silver needle in ethanol, acetone and water in sequence and performing ultrasonic treatment on each of them.

[0017] In one embodiment, the size of the pure silver needle in step (1) is 0.5-0.8 mm in diameter and 100-120 mm in length.

[0018] In one embodiment, a 0.1-0.5 mol / L hydrochloric acid solution is used as the electrolyte during the electrochemical etching process in step (1).

[0019] In one embodiment, the scanning rate during the electrochemical etching process in step (1) is 20 to 40 mV / S, preferably 30 mV / S.

[0020] In one embodiment, the number of scanning cycles during the electrochemical etching process in step (1) is 9 to 17, preferably 13 scanning cycles.

[0021] In one embodiment, the incubation time in step (2) is 5 to 10 minutes.

[0022] In one embodiment, the concentration of the zinc nitrate solution in step (2) is 2 to 6 mmol / L.

[0023] In one embodiment, the ZIF-8 mixed solution in step (3) is prepared by allowing a methanol solution containing 4 mmol / L zinc nitrate and 16 mmol / L 2-methylimidazole to stand to promote the formation of ZIF-8 crystals to obtain a ZIF-8 mixed solution.

[0024] In one embodiment, the immersion time in step (3) is 5 to 25 minutes, preferably 15 minutes.

[0025] In one embodiment, the rinsing in step (3) is performed using methanol.

[0026] The second object of the present invention is to provide a needle-shaped Turing nanostructured SERS substrate TN-Ag / ZIF-8 needle obtained by the above-mentioned preparation method.

[0027] In one embodiment, the TN-Ag / ZIF-8 needles exhibit a typical layered structure, consisting of a Turing-shaped silver needle (TN-Ag) as the core and a ZIF-8 shell uniformly coated on the outer layer;

[0028] Furthermore, electrochemical etching formed a fractal nanogap network on the surface of the silver needles, presenting a highly self-organized striped or spotted pattern, a typical Turing pattern structure. This pattern has a high density of nanocurvature and multi-level pores, which is conducive to the formation of localized surface plasmon resonance (LSPR) hotspots.

[0029] The ZIF-8 shell grows conformally on the TN-Ag surface by self-assembly, forming a continuous and dense MOF coating that maintains the overall morphology of the needle-like structure. Its nanoscale pore structure not only provides molecular screening and enrichment capabilities, but also further enhances the local confinement and transmission regulation capabilities of light through its higher refractive index.

[0030] Overall, the TN-Ag / ZIF-8 needles have a highly regular Turing morphology, a three-dimensional fractal structure, and a functional MOF shell coating, which achieves an organic combination of plasmon enhancement and molecular recognition in structure, and is an ideal SERS platform with multi-scale enhancement capabilities.

[0031] The third object of the present invention is to provide an application of the needle-shaped Turing nanostructured SERS substrate TN-Ag / ZIF-8 needle described above in the field of detection technology.

[0032] Beneficial effects:

[0033] The preparation of the needle-shaped Turing nanostructure SERS of the present invention uses silver needles as carriers, and induces the formation of Turing nanostructures with fractal topological characteristics on their surface through electrochemical etching, thereby obtaining high-density nanoscale concave-convex features and self-similar pore morphology; then, utilizing the nano-curvature characteristics of the fractal structure, a layer of zeolite imidazole framework-8 material (ZIF-8) is induced to conformally grow as a shell layer, constructing a composite SERS enhancement platform with electromagnetic field hotspot aggregation effect and molecular screening and enrichment capabilities. This platform has the advantages of high structural uniformity, scalable manufacturing, and synergistic signal enhancement and molecular recognition, significantly improving detection sensitivity and signal reproducibility, and is suitable for trace analysis in complex sample systems; for example, it can be widely used in fields such as food safety, environmental pollution monitoring, and biomedicine;

[0034] Compared with the prior art, the present invention has the following significant technical effects and advantages:

[0035] (1) The present invention solves the problems of uneven hotspot distribution and poor signal reproducibility in traditional SERS substrates. A nanostructure with self-organized Turing fractal characteristics is constructed on the surface of silver needles by electrochemical etching, achieving high-density, regularly distributed plasma-enhanced hotspots. This structure forms a stable and uniform localized surface plasmon resonance (LSPR) field under Raman light excitation. Compared with unetched silver needles, the SERS signal of the substrate of the present invention is strong, and the uniformity of the hotspot distribution is significantly improved, which is significantly better than most commercially available SERS substrates;

[0036] (2) The present invention solves the problem of poor selectivity and strong interference of SERS substrates in complex sample environments. The present invention constructs a composite SERS substrate with molecular screening and enrichment capabilities by in situ growing a ZIF-8 shell on the surface of the Turing nanostructure. The ZIF-8 shell has a pore size of approximately 1.6 nm, which can effectively block the nonspecific adsorption of large molecular interfering substances while enriching small molecular target analytes, thereby significantly enhancing detection selectivity;

[0037] (3) The present invention also solves the problem of complex preparation and difficulty in scalability of traditional SERS substrates. The present invention adopts an electrochemical etching process that does not require templates and complex precursor regulation. It only needs to regulate the reaction kinetics through electrode potential to spontaneously form Turing nanostructures on the surface of silver needles. The entire process is short (<10 minutes), highly repeatable, and simple in process, making it suitable for multi-needle position and batch consistent preparation.

[0038] (4) The synergistic effect of various technical features has brought about a breakthrough in overall performance: the multi-scale roughness brought by the Turing structure effectively improves the local electromagnetic field intensity, and also provides highly active sites for MOF nucleation; the uniform conformal coating of ZIF-8 further enhances the selective enrichment ability of target molecules and suppresses background signals; the needle-like three-dimensional skeleton structure achieves a spatially uniform enhancement effect, while having good light collection ability and operational convenience; the multi-scale design realizes structure-function synergistic optimization: it performs well in electromagnetic enhancement, chemical selectivity, optical penetration and interface stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the layered architecture of the Turing structure silver needle and ZIF-8 shell of the present invention;

[0040] Figure 2 Figure 1 is a characterization result diagram of the TN-Ag / ZIF-8 needle prepared in Example 1 of the present invention; (a1) SEM image of the Ag needle tip before etching; (a2) SEM image of the Ag needle body before etching; (a3) ​​SEM image of the Ag needle tip after etching; (a4) SEM image of the Ag needle body after etching; (b1) SEM image of TN-Ag before ZIF-8 loading; (b2) SEM image of the TN-Ag / ZIF-8 structure after ZIF-8 loading; (c) EDS elemental spectrum of TN-Ag / ZIF-8 needle; (d) XPS spectrum of Ag 3d before and after etching; (e) XRD patterns of different substrates; (f) Anti-reflection performance diagram of different substrates;

[0041] Figure 3 SEM cross-sectional images of the TN-Ag needle in Example 1; (a) SEM cross-sectional image of the TN-Ag needle; (b) low-magnification SEM image of TN-Ag; (c) fractal structure image converted from (b); (d) fractal dimension data graph;

[0042] Figure 4 SEM images of TN-Ag / ZIF-8 needles prepared in Example 1; (a) SEM image at ×3000 magnification; (b) SEM image at ×6000 magnification; (c) SEM image at ×20000 magnification; (d) SEM image at ×50000 magnification;

[0043] Figure 5 Raman spectra of different substrates; (a) Bulk Raman spectra of 4-MBA powder; (b) SERS spectra of 4-MBA collected from TN-Ag substrates prepared with different scanning rates; (c) SERS spectra of 4-MBA collected from TN-Ag substrates prepared with different scanning cycles; (d) SERS spectra of 4-MBA on TN-Ag / ZIF-8 substrates with different ZIF-8 growth times;

[0044] Figure 6 Data of the silver needle prepared in Example 1 scanned over 13 cycles at a rate of 30 mV / s in the range of -0.2 V to +0.4 V; (a) Current vs. voltage during cyclic voltammetry; (b) Charge vs. time during cyclic voltammetry; (c) Current vs. time during cyclic voltammetry; (d) Voltage vs. time during cyclic voltammetry;

[0045] Figure 7 SEM images of TN-Ag obtained at different scan rates; (a) SEM image of TN-Ag at a scan rate of 20 mV / s; (b) SEM image of TN-Ag at a scan rate of 25 mV / s; (c) SEM image of TN-Ag at a scan rate of 30 mV / s; (d) SEM image of TN-Ag at a scan rate of 40 mV / s;

[0046] Figure 8 SEM images of TN-Ag / ZIF-8 were obtained for Comparative Example 3; (a) SEM image at ×18000 magnification; (b) SEM image at ×50000 magnification;

[0047] Figure 9 SEM images of ZIF-8 grown on TN-Ag for 0, 5, 15, and 25 minutes; (a) SEM image of original TN-Ag; (b) SEM image of TN-Ag / ZIF-8 grown on ZIF-8 for 5 minutes; (c) SEM image of TN-Ag / ZIF-8 grown on ZIF-8 for 15 minutes; (d) SEM image of TN-Ag / ZIF-8 grown on ZIF-8 for 25 minutes;

[0048] Figure 10Figure 3 is a diagram of the SERS performance and enhancement mechanism of TN-Ag / ZIF-8 substrate; (a1) Raman intensity at different scanning periods; (a2) Raman intensity at scanning rate; (a3) ​​Raman intensity at different growth times of ZIF-8; (b) Comparison of SERS intensity of 4-MBA on different substrates; (c) Schematic diagram of light-molecule synergistic SERS enhancement; (d) N2 adsorption-desorption isotherm of synthesized ZIF-8 powder, with pore size distribution as shown in the inset; (e) Absorbance changes after immersing different substrates in 4-MBA solution and the calculated number of adsorbed molecules; (f1) Simulated electromagnetic field distribution of TN-Ag structure and (f2) Simulated electromagnetic field distribution of TN-Ag / ZIF-8 structure. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. The following specific embodiments further describe the present invention.

[0050] Example 1

[0051] Preparation of TN-Ag / ZIF-8 needles includes the following steps:

[0052] (1) Commercially available pure silver needles (0.6 mm in diameter and 105 mm in length) were immersed in ethanol, acetone, and water, respectively, and ultrasonically treated for 10 minutes each to remove surface contaminants.

[0053] (2) transferring the Ag needle cleaned in step (1) into a 0.1 mol / L hydrochloric acid solution as a working electrode, while an Ag / AgCl electrode and a platinum sheet electrode were used as a reference electrode and an auxiliary electrode, respectively; electrochemical etching was performed by cyclic voltammetry in a potential range of -0.2 to 0.4 V, at a scan rate of 30 mV / s and 13 scan cycles to obtain a TN-Ag needle;

[0054] (3) preparing a methanol solution containing 4 mmol / L zinc nitrate and 16 mmol / L 2-methylimidazole (total volume: 100 mL) and allowing it to stand for 10 minutes to promote the formation of ZIF-8 crystals to obtain a ZIF-8 mixed solution;

[0055] (4) The TN-Ag needles obtained in step (2) were rinsed thoroughly with ethanol several times and then incubated in a 4 mmol / L zinc nitrate solution for 5 minutes;

[0056] (5) Subsequently, the TN-Ag needle was vertically immersed in the ZIF-8 mixed solution using a fixture for 15 min to ensure uniform ZIF-8 deposition; finally, the TN-Ag / ZIF-8 needle was rinsed three times with methanol and dried under a nitrogen flow.

[0057] Example 2

[0058] The difference from Example 1 is that the scanning rate of the working electrode in step (2) is adjusted to 20, 25, 35, and 40 mV / S, respectively; TN-Ag needles with different etching degrees are obtained respectively.

[0059] Example 3

[0060] The difference from Example 1 is that the scanning cycles of the working electrode in step (2) are adjusted to 9, 11, 15, and 17 times respectively; TN-Ag needles with different etching degrees are obtained respectively.

[0061] Example 4

[0062] The difference from Example 1 is that the time of immersing in the ZIF-8 mixed solution in step (5) is adjusted to 5, 10, 20, and 25 minutes, respectively; TN-Ag / ZIF-8 needles with different ZIF-8 growth times are obtained.

[0063] Comparative Example 1 (Silver not etched)

[0064] A commercial pure silver needle (0.6 mm in diameter, 105 mm in length) was immersed in ethanol, acetone, and water in sequence and subjected to ultrasonic treatment for 10 minutes to remove surface contaminants.

[0065] Comparative Example 2 (Silver not etched and ZIF-8 grown)

[0066] (1) Commercially available pure silver needles (0.6 mm in diameter and 105 mm in length) were immersed in ethanol, acetone, and water, followed by ultrasonic treatment for 10 minutes to remove surface contaminants.

[0067] (2) preparing a methanol solution containing 4 mmol / L zinc nitrate and 16 mmol / L 2-methylimidazole (total volume: 100 mL) and allowing it to stand for 10 minutes to promote the formation of ZIF-8 crystals to obtain a ZIF-8 mixed solution;

[0068] (3) Rinse the silver needles thoroughly with ethanol several times and then incubate them in 4 mmol / L zinc nitrate solution for 5 minutes;

[0069] (4) Then, a fixture was used to vertically immerse the Ag needle into the ZIF-8 mixed solution for 15 min to ensure uniform ZIF-8 deposition; finally, the TN-Ag / ZIF-8 needle was rinsed three times with methanol and dried under a nitrogen flow.

[0070] Comparative Example 3 (without ZIF-8 incubation)

[0071] (1) Commercially available pure silver needles (0.6 mm in diameter and 105 mm in length) were immersed in ethanol, acetone, and water, followed by ultrasonic treatment for 10 minutes to remove surface contaminants.

[0072] (2) The Ag needle cleaned in step (1) was transferred to a 0.1 mol / L hydrochloric acid solution as a working electrode, while an Ag / AgCl electrode and a platinum electrode were used as a reference electrode and an auxiliary electrode, respectively; electrochemical etching was performed by cyclic voltammetry in a potential range of -0.2 to 0.4 V, at a scan rate of 30 mV / s and 13 scan cycles to obtain an optimal TN-Ag needle;

[0073] (3) preparing a methanol solution containing 4 mmol / L zinc nitrate and 16 mmol / L 2-methylimidazole (total volume: 100 mL) and allowing it to stand for 10 minutes to promote the formation of ZIF-8 crystals to obtain a ZIF-8 mixed solution;

[0074] (4) Subsequently, the TN-Ag needle was vertically immersed in the ZIF-8 mixed solution using a fixture for 15 min to ensure uniform ZIF-8 deposition; finally, the TN-Ag / ZIF-8 needle was rinsed three times with methanol and dried under a nitrogen flow.

[0075] Result Analysis

[0076] 1. Morphology and structural characterization of TN-Ag / ZIF-8 needles

[0077] The microstructure of TN Ag / ZIF-8 needles was characterized in detail using scanning electron microscopy (SEM). Figure 2 As shown:

[0078] like Figure 2 As shown in a1 to a4, the original silver needle with an initial diameter of about 600 μm was electrochemically etched to form a nanostructure on the surface. Figure 2 b1 and Figure 3 ab, The etching process produces a 3 μm thick coral-like fractal fine structure ( Figure 3 cd calculates the fractal dimension D f ≈2.63), with dense 5-20 nm nanogaps, forming a Turing pattern architecture controlled by reaction-diffusion dynamics. Subsequently, the ZIF-8 shell grew in situ on this fractal substrate, forming a uniform circular coating that encapsulated the etched silver surface while partially penetrating its porous network ( Figure 2 b2 and Figure 4 ).

[0079] Furthermore, energy dispersive X-ray spectroscopy (EDS) showed the same profiles of C, N, Zn, and O elements on the Ag substrate ( Figure 2 c), confirming the uniform distribution of ZIF-8.

[0080] The X-ray photoelectron spectroscopy (XPS) analysis of silver 3d region is at 368.3eV (Ag3d 5 / 2 ) and 374.3eV(Ag3d 3 / 2 )( Figure 2 d), indicating that the etching process retains the metallic properties of silver and there is no obvious surface oxidation. The X-ray diffraction (XRD) pattern determines the crystalline phase composition of the TN-Ag / ZIF-8 structure ( Figure 2 e). The main peaks at 38.1°(111), 44.3°(200), 64.4°(220), and 77.5°(311) match those of cubic Ag (JCPDS 04-0783), confirming the metallic nature of the etched substrate. The ZIF-8 coating shows characteristic diffraction peaks at 7.6°(011), 13.0°(112), and 18.6°(222), although the crystallinity is significantly reduced compared to the bulk ZIF-8 powder. This loss of crystallinity is likely due to lattice distortion caused by conformal growth of ZIF-8 on the curved fractal Ag surface, which suppresses the typical rhombic dodecahedral morphology of ZIF-8 crystals. In addition, the weak diffraction peaks observed in the TN-Ag pattern are attributed to the formation of trace amounts of AgCl (JCPDS 31-1238) during the etching process. In addition to structural modification, the ZIF-8 coating plays a key role in optical modulation through synergistic interaction with the Turing-patterned silver substrate. Figure 2 As shown in Figure 5, the reflectivity of the TN-Ag / ZIF-8 architecture in the 370-800nm ​​range is significantly reduced by 30% compared to bare TN-Ag. In this hierarchical nanostructure, multiple reflections within the pores of ZIF-8 and the plasmonic near-field confinement generated by the fractal Ag work together to prolong the interaction of photons with the metal hotspots. This cooperative light-trapping effect amplifies the electromagnetic field localization, thus providing a key foundation for the subsequent SERS performance.

[0081] 2. Effects of different Ag etching conditions and ZIF-8 growth time on the signal intensity of TN-Ag / ZIF-8 as a SERS substrate

[0082] (1) Effect of different Ag etching conditions (scanning rate and scanning cycle) on the signal intensity of TN-Ag / ZIF-8 needles as SERS substrate.

[0083] The signal response intensity of the SERS substrate TN-Ag needle prepared above was evaluated by using 4-mercaptobenzoic acid (4-MBA) as a Raman probe; specifically, the SERS substrate TN-Ag needle was immersed in 10 -6 The etched area of ​​the substrate was completely immersed in a 4-mol / L 4-MBA ethanol solution for 1 h. The solution volume was adjusted to completely immerse the etched area of ​​the substrate. After immersion, the substrate was rinsed three times with ultrapure water and ethanol, respectively, to remove unabsorbed molecules; and then dried thoroughly under a nitrogen flow. Subsequently, the SERS spectra of the probe molecules adsorbed on the substrate were recorded.

[0084] The results are as follows Figure 5 As shown, Figure 5 a is the signal intensity of 4-mercaptobenzoic acid (4-MBA) as a Raman probe; Figure 5 bc It can be seen that different etching conditions have a significant impact on the signal intensity of the prepared TN-Ag needles. The TN-Ag substrate with the maximum SERS signal was obtained by performing 13 cycles of cyclic voltammetry etching at 30mV / s.

[0085] Electrochemical analysis showed that the oxidation peak was at 0.327 V (anode), the redeposition peak was at -0.127 V (cathode), and the charge peak (Q s ) reached a peak at 13 cycles ( Figure 6 ), indicating that the dynamic dissolution-redeposition equilibrium maximizes the effective surface area of ​​the silver electrode. The scan rate plays a crucial role in the morphology: slower rates produce larger nanoparticles due to limited electron transport, while faster rates lead to Ag + Insufficient reduction, thus affecting uniformity ( Figure 7 ).

[0086] (2) Effect of different ZIF-8 growth conditions on the signal intensity of TN-Ag / ZIF-8 needles as SERS substrates

[0087] The signal response intensity of the SERS substrate TN-Ag / ZIF-8 needle prepared above was evaluated by using 4-mercaptobenzoic acid (4-MBA) as a Raman probe; specifically, the TN-Ag / ZIF-8 needle was immersed in 10 -6 The etched area of ​​the substrate was completely immersed in a 4-mol / L 4-MBA ethanol solution for 1 h. The solution volume was adjusted to completely immerse the etched area of ​​the substrate. After immersion, the substrate was rinsed three times with ultrapure water and ethanol, respectively, to remove unabsorbed molecules; and then dried thoroughly under a nitrogen flow. Subsequently, the SERS spectra of the probe molecules adsorbed on the substrate were recorded.

[0088] The results are as follows Figure 5d shows that the best SERS signal of TN-Ag / ZIF-8 needles was obtained when the ZIF-8 time was 15 minutes. The parallel optimization of the kinetics showed that incubation is a prerequisite. Directly immersing the etched substrate in the precursor solution without incubation will produce an agglomerated coating ( Figure 8 According to the optimized scheme, the high curvature regions of the fractal substrate guided the early nucleation of ZIF-8 spheres, aligning their porous channels with the LSPR hotspots ( Figure 9 Time-dependent studies showed that the coating reached 91% of the maximum SERS intensity within 10 minutes ( Figure 5 d), demonstrating rapid localization of analytes via fractal-guided MOF assembly. However, exceeding 15 minutes leads to excessive growth of ZIF-8, which blocks the plasmonic cavity, isolates the analyte from the hotspot, and weakens the enhancement effect; this balance between fractal geometry and molecular sieving enables spatial coordination of the analyte in the region of maximum electromagnetic field.

[0089] 3. Analysis of SERS enhancement performance of TN-Ag / ZIF-8 needles

[0090] 4-Mercaptobenzoic acid (4-MBA) was used as a Raman probe to evaluate the signal response intensity of the SERS substrates prepared in the examples and comparative examples. Specifically, the SERS substrate was immersed in 10 -6 The substrate was immersed in a 4-mol / L 4-MBA ethanol solution for 1 hour. The solution volume was adjusted to completely immerse the etched area of ​​the substrate. After immersion, the substrate was rinsed three times with ultrapure water and ethanol to remove unabsorbed molecules. The substrate was then thoroughly dried under a nitrogen stream. Subsequently, the SERS spectra of the probe molecules adsorbed on the substrate were recorded.

[0091] The results are as follows Figure 10 a1 to a3 show the optimization results of TN-Ag / ZIF-8 needles. Subsequently, the TN-Ag / ZIF-8 needles prepared in Example 1 and the product obtained in the comparative example were used for SERS performance testing. Figure 10 b shows that TN-Ag / ZIF-8 can be - 6 The molL probe can also significantly amplify the signal at the molecular level, which is the result of the synergistic effect of its photochemical layering; however, the unetched Ag and Ag / ZIF-8 substrates only amplify the signal at 10 -2 mol / L probe molecules produce weak signals. Figure 10 c Schematic illustration of the proposed dual-scale enhancement mechanism of TN-Ag / ZIF-8, where the Turing-patterned Ag fractals and the porous framework of ZIF-8 synergistically amplify the signal through photomanipulation and molecular confinement. Finite-difference time-domain (FDTD) simulation under 785 nm excitation ( Figure 10f) confirmed that the TN-Ag architecture persists with a strong local electromagnetic field, which is caused by plasmon coupling within the fractal nanogaps. The ZIF-8 coating extends the LSPR region into the MOF shell, homogenizing the field distribution through its dielectric properties. Unlike traditional periodic nanostructures, the non-periodic but self-similar nature of the Turing nanoarchitecture makes the LSPR hotspots uniform over the extended area, thereby improving the stability and spatial coverage of Raman signal acquisition. A Fabry-Perot-like optical cavity is formed by the etched gaps, which contributes to the resonant confinement of localized surface plasmon resonance photons and increases light absorption. Importantly, the higher refractive index of ZIF-8 (compared to air) amplifies photon recycling: backscattered light from the Ag fractal undergoes secondary reflection at the MOF-air interface and re-excites the plasmon mode, synergistically enhancing the electromagnetic field and extending the field lifetime. The molecular enrichment capability of the ZIF-8 shell further complements this photon gain. The MOF shell has a 2433m 2 / g ultra-high surface area and 1.6nm selective pores ( Figure 10 d), while excluding larger interfering substances, 4-MBA is concentrated near the plasma hotspot. Adsorption experiments quantified this effect: the adsorption amount of TN-Ag / ZIF-8 was 1.89 times and 3.39 times that of TN-Ag and Ag / ZIF.8, respectively ( Figure 10 e, inset). This enhanced adsorption originates from the fractal TN-Ag, with the porous ZIF-8 acting as a multi-stage molecular concentrator. The dual-scale SERS amplification is attributed to photonic-chemical synergistic design: mesoscopic fractal plasmons compress light into nanogap-confined electromagnetic hotspots, enhancing photon capture efficiency; microscopic MOF engineering expands these domains through refractive index-guided recycling, while selectively enriching analytes in the photoactivated zone. This interfacial synergy connects electromagnetic amplification with molecular spatial targeting, achieving multi-stage signal enhancement.

[0092] The embodiments provided above are not intended to limit the scope of the present invention, nor are the steps described to limit their execution order. Any obvious improvements to the present invention made by those skilled in the art in combination with existing common knowledge shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a needle-shaped Turing nanostructured SERS substrate, characterized in that: The preparation method comprises the following steps: (1) Ultrasonic pretreatment of pure silver needles to remove surface contaminants; Then, it was used as the working electrode, and the Ag / AgCl electrode and platinum sheet electrode were used as the reference electrode and auxiliary electrode, respectively. TN-Ag needles were obtained by electrochemical etching in the potential range of -0.2 to 0.4 V by cyclic voltammetry. (2) rinsing the TN-Ag needles obtained in step (1) with ethanol several times and then incubating them in a zinc nitrate solution; (3) Immerse the TN-Ag needles after incubation in step (2) in a ZIF-8 mixed solution to ensure uniform ZIF-8 deposition, rinse them clean, and dry them under a nitrogen flow to obtain the needle-shaped Turing nanostructure SERS substrate TN-Ag / ZIF-8 needles.

2. The preparation method according to claim 1, characterized in that The scanning rate during the electrochemical etching process in step (1) is 20 to 40 mV / S.

3. The preparation method according to claim 1, characterized in that The number of scanning cycles during the electrochemical etching process in step (1) is 9 to 17 times.

4. The preparation method according to claim 1, characterized in that The incubation time in step (2) is 5 to 10 minutes.

5. The preparation method according to claim 1, characterized in that The concentration of the zinc nitrate solution in step (2) is 2-6 mmol / L.

6. The preparation method according to claim 1, characterized in that Preparation of the ZIF-8 mixed solution in step (3): a methanol solution containing 4 mmol / L zinc nitrate and 16 mmol / L 2-methylimidazole is allowed to stand to promote the formation of ZIF-8 crystals to obtain a ZIF-8 mixed solution.

7. The preparation method according to claim 1, characterized in that The immersion time in step (3) is 5 to 25 minutes.

8. The preparation method according to claim 1, characterized in that The scanning rate during the electrochemical etching process in step (1) is 30 mV / S, and the number of scanning cycles is 13 times.

9. The needle-shaped Turing nanostructured SERS substrate TN-Ag / ZIF-8 needle obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the needle-shaped Turing nanostructured SERS substrate TN-Ag / ZIF-8 needles according to claim 9 in the field of detection technology.

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