A needle-shaped turing nanostructure sers substrate and a preparation method thereof

Abstract

The application discloses a needle-shaped Turing nanostructure SERS substrate and a preparation method thereof, and belongs to the field of nanotechnology and detection. The preparation of the needle-shaped Turing nanostructure SERS substrate is specifically as follows: a silver needle is used as a carrier, a Turing nanostructure with fractal topological characteristics is induced to form by electrochemical etching the surface, then, a layer of zeolite imidazole framework-8 material is induced to conformally grow as a shell layer by using the nano-curvature characteristics of the fractal structure, and a composite SERS enhancement platform with electromagnetic field hot spot gathering effect and molecular screening enrichment capacity is constructed. The platform has the advantages of high structural uniformity, scalable manufacturing, signal enhancement and molecular recognition synergy, and significantly improves the detection sensitivity and signal reproducibility, and is suitable for trace analysis in a complex sample system, such as related applications in the fields of food safety, environmental pollution monitoring and biomedicine.

Description

Technical Field

[0001] This invention relates to a needle-like Turing nanostructure SERS substrate and its preparation method, belonging to the field of nanotechnology and detection. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) is a highly sensitive spectroscopic detection technique with molecular fingerprinting capabilities, and it has been widely used in trace analysis, environmental monitoring, food safety, and biomedicine. However, traditional SERS substrates generally suffer from problems such as uneven hotspot distribution, poor selectivity, and poor signal reproducibility. Especially in complex matrices, non-specific adsorption can easily cause background interference, significantly reducing the accuracy and stability of detection and limiting its widespread application in practical scenarios.

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

[0004] For example, Chinese patent CN114994009A discloses a method for preparing and applying a surface-enhanced Raman scattering substrate based on Ag@ZIF-8 core-shell nanochains; specifically, it avoids in-situ synthesis of ZIF-8 using silver nanowires to obtain beaded Ag@ZIF-8 core-shell nanochain materials. Chinese patent CN110646400A discloses a PS / Ag / ZIF-8 composite surface-enhanced Raman scattering active substrate and its preparation method; specifically, it uses an ordered polystyrene array as a substrate, loads Ag nanoparticles onto the array surface using magnetron sputtering, and then grows a ZIF-8 thin film on top of the Ag nanoparticles.

[0005] While these methods have enhanced SERS signals to some extent, they still face numerous challenges, including uneven hotspot distribution, complex fabrication processes, poor repeatability, structural instability, uneven MOF loading, and poor interfacial bonding. Furthermore, most SERS substrates are planar structures or particle packs, making them unsuitable for diverse applications such as flexible penetration and in-situ micro-area detection. Summary of the Invention

[0006] [Technical Issues]

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

[0008] [Technical Solution]

[0009] To address the aforementioned issues, the present invention aims to provide a needle-like Turing nanostructure SERS substrate and its preparation method. The core of this method is the use of electrochemical etching technology. Electrochemical etching, as a technique based on potential-controlled ion migration, can construct Turing-shaped fractal structures on metal surfaces. These structures possess self-organized nanopatterns, high porosity, abundant nano-intervals and curvature, and combine optical field confinement capabilities with good mechanical stability, providing an ideal structural basis for efficient SERS enhancement.

[0010] By constructing a multi-scale rough structure with Turing fractal characteristics on the surface of a silver needle, a high-density, uniform SERS hotspot is self-assembled. A layer of ZIF-8 metal-organic framework (MOF) with nanopores is then in-situ coated onto the surface of this structure, endowing it with molecular screening and enrichment functions and further enhancing light field penetration. The resulting substrate is a silver needle-ZIF-8 composite structure with excellent optical performance, chemical stability, and interfacial functional regulation capabilities. It can achieve a synergistic effect of electromagnetic field enhancement and molecular selective enrichment, improving signal sensitivity, selectivity, and stability, meeting the needs of multi-scene, micro-area, and in-situ detection, and possessing significant research value and application prospects.

[0011] To achieve the above objectives, the following technical solution is provided:

[0012] The first objective of this invention is to provide a method for preparing a needle-like Turing nanostructure SERS substrate, the method comprising the following steps:

[0013] (1) The pure silver needle was subjected to ultrasonic pretreatment 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. Electrochemical etching was performed in the potential range of -0.2 to 0.4 V by cyclic voltammetry to obtain TN-Ag needle.

[0014] (2) Rinse the TN-Ag needle obtained in step (1) with ethanol several times, and then incubate it in zinc nitrate solution;

[0015] (3) Immerse the TN-Ag needles incubated in step (2) into the ZIF-8 mixed solution to ensure uniform ZIF-8 deposition, rinse them clean, and dry them under nitrogen flow to obtain 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.

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

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

[0019] In one embodiment, the scan 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 scan cycles in the electrochemical etching process of step (1) is 9 to 17; preferably 13 scan 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, thereby obtaining the 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 objective of this invention is to provide a needle-like Turing nanostructure SERS substrate TN-Ag / ZIF-8 needle obtained by the preparation method described above.

[0027] In one embodiment, the TN-Ag / ZIF-8 needle exhibits a typical layered structure, with a Turing-shaped silver needle (TN-Ag) as the core and a ZIF-8 shell uniformly covering the outer layer.

[0028] Furthermore, the surface of the silver needle was electrochemically etched to form a multi-shaped nano-gap network, exhibiting a highly self-organized striped or spotted pattern, which is a typical Turing pattern structure; this pattern has high-density nano-curvature and multi-level pores, which is conducive to the formation of localized surface plasmon resonance (LSPR) hotspots.

[0029] The ZIF-8 shell is conformally grown on the TN-Ag surface through self-assembly to form a continuous and dense MOF coating, maintaining the overall morphology of the needle-like structure. Its nanoscale porous structure not only provides molecular screening and enrichment capabilities, but also further enhances the ability to locally confine and modulate light transmission through its high refractive index.

[0030] Overall, the TN-Ag / ZIF-8 needle combines a highly regular Turing morphology, a three-dimensional fractal structure, and a functional MOF shell coating, achieving an organic combination of plasma enhancement and molecular recognition in its structure. It is an ideal SERS platform with multi-scale enhancement capabilities.

[0031] The third objective of this invention is to provide an application of the aforementioned needle-like Turing nanostructure SERS substrate TN-Ag / ZIF-8 needle in the field of detection technology.

[0032] Beneficial effects:

[0033] This invention describes the fabrication of a needle-like Turing nanostructure SERS using silver needles as a carrier. Electrochemical etching is employed to induce the formation of a Turing nanostructure with fractal topological characteristics on the needle's surface, resulting in high-density nanoscale concave-convex features and self-similar pore morphology. Subsequently, utilizing the nano-curvature characteristics of this fractal structure, a zeolite imidazole framework-8 (ZIF-8) material is conformally grown as a shell, constructing a composite SERS enhancement platform with electromagnetic field hotspot aggregation effects and molecular screening enrichment capabilities. This platform offers advantages such as high structural uniformity, scalable fabrication, and synergistic signal enhancement and molecular recognition, significantly improving detection sensitivity and signal reproducibility. It is suitable for trace analysis in complex sample systems and can be widely applied 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) This 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 using an electrochemical etching method, achieving high-density, regularly distributed plasma-enhanced hotspots. This structure forms a stable and uniform localized surface plasmon resonance (LSPR) field under Raman excitation. Compared with unetched silver needles, the SERS signal of the substrate of this invention is stronger, and the uniformity of hotspot distribution is significantly improved, significantly outperforming most commercially available SERS substrates;

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

[0037] (3) This invention also solves the problems of complex and difficult-to-scale preparation of traditional SERS substrates. This invention adopts an electrochemical etching process that does not require templates or complex precursors. It only needs to control the reaction kinetics by electrode potential to spontaneously form Turing nanostructures on the surface of silver needles. The whole process is short (<10 minutes), highly repeatable, and simple, making it suitable for multi-needle sites 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 strength and 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 framework structure realizes the enhancement effect of uniform spatial distribution, while having good light collection ability and ease of operation; the multi-scale design realizes the structure-function synergistic optimization: it performs well in terms of electromagnetic enhancement, chemical selectivity, optical penetration and interface stability. Attached Figure Description

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

[0040] Figure 2 The following are characterization results of the TN-Ag / ZIF-8 needle prepared in Example 1 of this 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 the TN-Ag / ZIF-8 needle; (d) XPS spectra of Ag 3d before and after etching; (e) XRD patterns of different substrates; (f) Anti-reflection performance diagrams of different substrates.

[0041] Figure 3 Here are the 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 the TN-Ag needle; (c) Fractal structure diagram obtained from (b); (d) Fractal dimension data diagram.

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

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

[0044] Figure 6 The silver needle prepared for Example 1 was scanned for 13 cycles at a rate of 30 mV / s in the range of -0.2 V to +0.4 V. The graphs are as follows: (a) Current and voltage relationship during the cyclic voltammetry process; (b) Charge and time relationship during the cyclic voltammetry process; (c) Current and time relationship during the cyclic voltammetry process; (d) Voltage and time relationship during the cyclic voltammetry process.

[0045] Figure 7 SEM images of TN-Ag were 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 18000x magnification; (b) SEM image at 50000x magnification.

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

[0048] Figure 10Figure 1 shows the SERS performance and enhancement mechanism of the TN-Ag / ZIF-8 substrate; (a1) Raman intensity at different scan cycles; (a2) Raman intensity at different scan rates; (a3) ​​Raman intensity of ZIF-8 at different growth times; (b) Comparison of SERS intensity of 4-MBA on different substrates; (c) Schematic diagram of photo-molecular synergistic SERS enhancement; (d) N2 adsorption-desorption isotherm of synthesized ZIF-8 powder, with pore size distribution shown in the inset; (e) Absorbance changes and calculated number of adsorbed molecules after immersing different substrates in 4-MBA solution; (f1) Simulated electromagnetic field distribution of the TN-Ag structure and (f2) Simulated electromagnetic field distribution of the TN-Ag / ZIF-8 structure. Detailed Implementation

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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. The specific embodiments described below further illustrate the present invention.

[0050] Example 1

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

[0052] (1) Take a commercially available pure silver needle (0.6 mm in diameter and 105 mm in length) and immerse it in ethanol, acetone and water in sequence, and perform ultrasonic treatment for 10 minutes each to remove surface contaminants.

[0053] (2) The Ag needle cleaned in step (1) was transferred to a 0.1 mol / L hydrochloric acid solution as the working electrode, while the Ag / AgCl electrode and the platinum sheet electrode were used as the reference electrode and the auxiliary electrode, respectively. Electrochemical etching was performed by cyclic voltammetry in a potential range of -0.2 to 0.4 V, and TN-Ag needles were obtained at a scan rate of 30 mV / S for 13 scan cycles.

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

[0055] (4) Rinse the TN-Ag needle obtained in step (2) thoroughly with ethanol several times, and then incubate it in 4 mmol / L zinc nitrate solution for 5 minutes;

[0056] (5) Then, use a clamp to vertically immerse the TN-Ag needle into the ZIF-8 mixed solution for 15 minutes to ensure uniform ZIF-8 deposition; finally, rinse the TN-Ag / ZIF-8 needle three times with methanol and dry it under nitrogen flow to obtain the final product.

[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 immersion time in the ZIF-8 mixed solution in step (5) was adjusted to 5, 10, 20 and 25 minutes respectively; TN-Ag / ZIF-8 needles with different ZIF-8 growth times were obtained respectively.

[0063] Comparative Example 1 (Silver not etched)

[0064] Commercially available pure silver needles (0.6 mm in diameter and 105 mm in length) were sequentially immersed in ethanol, acetone, and water, and subjected to ultrasonic treatment for 10 minutes to remove surface contaminants.

[0065] Comparative Example 2 (Silver without etching and ZIF-8 growth)

[0066] (1) Take a commercially available pure silver needle (0.6 mm in diameter and 105 mm in length) and immerse it in ethanol, acetone and water in sequence, and perform ultrasonic treatment for 10 minutes to remove surface contaminants.

[0067] (2) Prepare a methanol solution (total volume: 100 mL) containing 4 mmol / L zinc nitrate and 16 mmol / L 2-methylimidazole, and let it 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, use a clamp to vertically immerse the Ag needle into the ZIF-8 mixed solution for 15 minutes to ensure uniform ZIF-8 deposition; finally, rinse the TN-Ag / ZIF-8 needle three times with methanol and dry it under nitrogen flow to obtain the final product.

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

[0071] (1) Take a commercially available pure silver needle (0.6 mm in diameter and 105 mm in length) and immerse it in ethanol, acetone and water in sequence, and perform 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 the working electrode, while the Ag / AgCl electrode and the platinum sheet electrode were used as the reference electrode and the auxiliary electrode, respectively. Electrochemical etching was performed by cyclic voltammetry in a potential range of -0.2 to 0.4 V. The optimal TN-Ag needle was obtained at a scan rate of 30 mV / S for 13 scan cycles.

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

[0074] (4) Then, use a clamp to vertically immerse the TN-Ag needle into the ZIF-8 mixed solution for 15 minutes to ensure uniform ZIF-8 deposition; finally, rinse the TN-Ag / ZIF-8 needle three times with methanol and dry it under nitrogen flow to obtain the final product.

[0075] Results Analysis

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

[0077] The microstructure of TN Ag / ZIF-8 needles was meticulously characterized using scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown:

[0078] like Figure 2 As shown in a1 to a4, the original silver needles, with an initial diameter of approximately 600 μm, underwent electrochemical etching, resulting in the formation of nanostructures on their surface. Figure 2 b1 and Figure 3 ab, the etching process produced a 3μm thick coral-like fractal fine structure ( Figure 3 cd calculates the fractal dimension D f ≈2.63), with dense 5-20 nm nanometer gaps, forming a Turing pattern architecture controlled by reaction-diffusion kinetics. Subsequently, a ZIF-8 shell is grown in situ on this fractal substrate, forming a uniform circular coating that encapsulates the etched silver surface while partially penetrating its porous network (≈2.63). Figure 2 b2 and Figure 4 ).

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

[0080] X-ray photoelectron spectroscopy (XPS) analysis of silver in the 3d region at 368.3 eV (Ag3d). 5 / 2 ) and 374.3eV (Ag3d 3 / 2 ()( Figure 2 d) indicates that the etching process preserved the metallic properties of silver, with no significant surface oxidation. X-ray diffraction (XRD) patterns determined the crystal 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 the main peak of cubic Ag (JCPDS 04-0783), confirming the metallic nature of the etched substrate. The ZIF-8 coating exhibits characteristic diffraction peaks at 7.6° (011), 13.0° (112), and 18.6° (222), although the crystallinity is significantly reduced compared to bulk ZIF-8 powder. This loss of crystallinity is likely due to lattice distortion resulting from the conformal growth of ZIF-8 on the curved fractal Ag surface, which suppresses the typical rhombic dodecahedral morphology of ZIF-8 crystals. Furthermore, the weak diffraction peaks observed in the TN-Ag pattern are attributed to the formation of trace AgCl (JCPDS 31-1238) during the etching process. Besides structural modification, the ZIF-8 coating plays a crucial role in optical modulation through its synergistic interaction with the Turing-patterned silver substrate. For example... Figure 2 As shown in f, compared to bare TN-Ag, the TN-Ag / ZIF-8 architecture exhibits a significant 30% reduction in reflectivity within the 370-800 nm range. In this hierarchical nanostructure, the multiple reflections within the pores of ZIF-8 and the plasmonic near-field confinement generated by fractal Ag synergistically prolong the interaction between photons and metal hotspots. This cooperative light-trapping effect amplifies electromagnetic field localization, thus providing a crucial foundation for 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) The effect of different Ag etching conditions (scan rate and scan cycle) on the signal intensity of TN-Ag / ZIF-8 pins as SERS substrate.

[0083] The signal response intensity of the SERS substrate TN-Ag needle prepared above was evaluated using 4-mercaptobenzoic acid (4-MBA) as a Raman probe; specifically, the SERS substrate TN-Ag needle was immersed in 10... -6 The substrate was immersed in a mol / L 4-MBA ethanol solution for 1 hour, and the solution volume was adjusted to completely submerge the etched area of ​​the substrate. After immersion, the substrate was rinsed three times with ultrapure water and ethanol to remove unabsorbed molecules. Then it was thoroughly dried 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 represents the signal intensity of 4-mercaptobenzoic acid (4-MBA) as a Raman probe; (The rest of the text appears to be a fragmented and incomplete expression, possibly due to OCR errors.) Figure 5 As shown in bc, different etching conditions have a significant impact on the signal intensity of the prepared TN-Ag needles. Cyclic voltammetric etching at 30 mV / s for 13 cycles yielded the TN-Ag substrate with the maximum SERS signal.

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

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

[0087] The signal response intensity of the SERS substrate TN-Ag / ZIF-8 needle prepared above was evaluated using 4-mercaptobenzoic acid (4-MBA) as a Raman probe; specifically, the TN-Ag / ZIF-8 needle was immersed in 10... -6 The substrate was immersed in a mol / L 4-MBA ethanol solution for 1 hour, and the solution volume was adjusted to completely submerge the etched area of ​​the substrate. After immersion, the substrate was rinsed three times with ultrapure water and ethanol to remove unabsorbed molecules. Then it was thoroughly dried 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 5As shown in d, the TN-Ag / ZIF-8 needles that obtained the optimal SERS signal were obtained when the ZIF-8 time was 15 minutes. Parallel optimization of the kinetics indicates that incubation is a prerequisite; directly immersing the etched substrate into the precursor solution without incubation will result in an agglomerated coating. Figure 8 According to the optimized scheme, the high curvature region of the fractal substrate guides the early ZIF-8 spherical nuclei, aligning its porous channels with LSPR hotspots. Figure 9 Time-dependent studies showed that the coating reached 91% of its maximum SERS strength within 10 minutes. Figure 5 d) demonstrates the rapid localization of analytes via fractal-guided MOF assembly. However, exceeding 15 minutes leads to ZIF-8 overgrowth, clogging the plasma cavity, isolating the analyte from hotspots, and diminishing the enhancement effect; this balance between fractal geometry and molecular sieves allows for spatial coordination of the analyte in the region of maximum electromagnetic field.

[0089] 3. SERS enhancement performance analysis of TN-Ag / ZIF-8 pins

[0090] The signal response intensity of the SERS substrates prepared in the examples and comparative examples was evaluated using 4-mercaptobenzoic acid (4-MBA) as a Raman probe; specifically, the SERS substrates were immersed in 10... -6 The substrate was immersed in a mol / L 4-MBA ethanol solution for 1 hour, and the solution volume was adjusted to completely submerge the etched area of ​​the substrate. After immersion, the substrate was rinsed three times with ultrapure water and ethanol, respectively, to remove unabsorbed molecules. Then, it was 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 demonstrate the optimization results of the TN-Ag / ZIF-8 needle. Subsequently, the TN-Ag / ZIF-8 needle prepared in Example 1 and the product obtained in the comparative example were used for SERS performance testing. Figure 10 b demonstrated that TN-Ag / ZIF-8 even at 10 - 6 The probe can also significantly amplify the signal at the mol / L molecular level, which is a result of its photonic chemical layering synergy; however, the unetched Ag and Ag / ZIF-8 substrates only amplify the signal at 10 mol / L. -2 A weak signal was generated at a mol / L probe molecule concentration. Figure 10 c schematically illustrates the proposed dual-scale enhancement mechanism of TN-Ag / ZIF-8, in which the Turing-patterned Ag fractal and the porous framework of ZIF-8 synergistically amplify the signal through optical manipulation and molecular confinement. Finite-difference time-domain (FDTD) simulations under 785 nm excitation ( Figure 10f) Confirms the persistent strong local electromagnetic field in the TN-Ag architecture, caused by plasmonic coupling within the fractal nanogap. 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 aperiodic but self-similar nature of the Turing nanostructure allows for a uniform distribution of LSPR hotspots across the extended region, thereby improving the stability and spatial coverage of Raman signal acquisition. A Fabry-Perot-like optical cavity formed by etched voids contributes to the resonant confinement of localized surface plasmonic 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, re-exciting the plasmonic 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 2433 m... 2 The ultra-high surface area of ​​ / g and the selective pore size of 1.6nm ( Figure 10 d) While eliminating larger interfering substances, it concentrated 4-MBA near the plasma hotspot. Adsorption experiments quantified this effect: the adsorption capacity 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, illustration). This enhanced adsorption originates from fractal TN-Ag, with porous ZIF-8 acting as a multi-stage molecular concentrator. The dual-scale SERS amplification is attributed to the photonic chemical synergistic design: mesoscopic fractal plasma compresses light into nanogap-confined electromagnetic hotspots, improving photon capture efficiency; microscopic MOF engineering extends these domains through refractive index-guided recycling, while selectively enriching analytes in photoactivated regions; this interfacial synergy links 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 invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a needle-like Turing nanostructure SERS substrate, characterized in that, The preparation method includes the following: (1) The pure silver needles are subjected to ultrasonic pretreatment to remove surface contaminants; Then, using it as the working electrode, and the Ag / AgCl electrode and platinum sheet electrode as the reference electrode and auxiliary electrode, respectively, electrochemical etching was performed in the potential range of -0.2~0.4 V by cyclic voltammetry to obtain TN-Ag needles; The scanning rate during the electrochemical etching process is 20~40 mV / S, and the number of scanning cycles is 9~17. (2) Rinse the TN-Ag needle obtained in step (1) with ethanol several times, and then incubate it in zinc nitrate solution; (3) Immerse the TN-Ag needles incubated in step (2) into the ZIF-8 mixed solution to ensure uniform ZIF-8 deposition, rinse them clean, and dry them under nitrogen flow to obtain needle-shaped Turing nanostructure SERS substrate TN-Ag / ZIF-8 needles.

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

3. 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.

4. The preparation method according to claim 1, characterized in that, In step (3), the ZIF-8 mixed solution 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, thereby obtaining the ZIF-8 mixed solution.

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

6. The preparation method according to claim 1, characterized in that, In step (1), the electrochemical etching process has a scan rate of 30 mV / S and a scan cycle of 13 times.

7. The needle-like Turing nanostructure SERS substrate TN-Ag / ZIF-8 needles obtained by the preparation method according to any one of claims 1 to 6.

8. The application of the needle-like Turing nanostructure SERS substrate TN-Ag / ZIF-8 needle as described in claim 7 in the field of detection technology.

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