Preparation method and application of electrospun nanofiber membrane-based flexible SERS (Surface Enhanced Raman Scattering) substrate

Abstract

The invention discloses a preparation method and application of an electrospun nanofiber membrane-based flexible SERS (Surface Enhanced Raman Scattering) substrate, and belongs to the field of preparation of SERS substrates. The preparation method comprises the following steps: firstly, preparing a polymer nanofiber membrane by adopting an electrostatic spinning method, and then depositing noble metal nanoparticles on the surface of the electrospinning polymer nanofiber membrane by adopting a magnetron sputtering technology, so as to obtain the noble metal nanoparticle and polymer nanofiber membrane flexible SERS (Surface Enhanced Raman Scattering) substrate. According to the present invention, the problems that the SERS substrate cannot be accurately controlled and cannot be continuously produced are solved, the preparation method has advantages of simpleness, high efficiency, no pollution, low cost and large-scale manufacturing compared with the existing preparation method, the substrate has characteristics of large specific surface area, high density hot spot distribution, good stability and adjustable size structure, and the trace detection of the pesticide residue on the irregular surface can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of surface-enhanced Raman scattering substrate preparation and detection, and relates to a method for preparing and applying an electrospun nanofiber membrane-based flexible SERS substrate. Background Technology

[0002] Thiram is a commonly used organosulfur pesticide. It is widely used for seed treatment and pest control in crops such as grains, vegetables, and fruits. However, studies have shown that long-term consumption of food with excessive thiram residues may lead to liver and kidney damage, affect the nervous system, and even pose a carcinogenic risk. Currently, most countries and regions have established strict maximum residue limits (MRLs) for thiram in various agricultural products. According to China's National Food Safety Standard for Maximum Residue Limits of Pesticides in Food (GB 2763-2021), the MRL for thiram in cereal crops is 0.2 mg / kg, and the MRL for some fruits and vegetables is as low as 0.05 mg / kg. Therefore, developing a simple, rapid, and highly sensitive method for detecting thiram residues in agricultural products is of great significance.

[0003] Surface-enhanced Raman scattering (SERS), as an emerging spectroscopic technique, has attracted widespread attention due to its outstanding advantages such as ultra-high sensitivity, ease of operation, rapid response, low cost, small sample requirements, and portable detection without pretreatment. This technique utilizes the localized surface plasmon resonance effect of noble metal nanostructures to significantly enhance the Raman signal of adsorbed molecules, thereby achieving trace-level detection. SERS technology has been applied in various fields, including pesticide residue monitoring, environmental pollutant detection, food safety analysis, art authentication, disease diagnosis, and biomedical research.

[0004] Polymer-based SERS substrates have attracted much attention due to their advantages such as being lightweight, flexible, and portable. These substrates can conform to the irregular surfaces of various real-world samples, enabling in-situ detection. Among them, polymer-based SERS substrates prepared using electrospinning technology have become a current research hotspot. First, electrospun polymer nanofibers can form a three-dimensional network structure with a large specific surface area, providing abundant deposition sites for plasma nanoparticles and target analytes. Second, the three-dimensional porous structure of the spun membrane facilitates the diffusion of target molecules from multiple directions to the "hotspot" region, thereby improving the probability of molecule capture and detection. In addition, the high tunability of electrospun polymer nanofibers allows SERS substrates to adapt to different detection scenarios and analytical needs. However, currently reported electrospun polymer-based SERS substrates still face many challenges, such as complex preparation processes, long production cycles, severe environmental pollution, and difficulty in achieving large-scale production. Therefore, it is of great significance to develop a simple, efficient, environmentally friendly, and scalable method for preparing electrospun polymer nanofiber-based SERS substrates.

[0005] Magnetron sputtering, as an efficient, low-temperature, environmentally friendly, and controllable advanced coating technology, can be combined with electrospun polymer nanofiber technology to prepare high-performance, uniform, and flexible SERS substrates. This effectively overcomes the contamination problems and poor reproducibility associated with chemical reduction methods for preparing electrospun polymer-based SERS substrates. Furthermore, this method is highly suitable for large-scale production. The use of magnetron sputtering technology for the rapid and large-scale preparation of flexible SERS substrates based on electrospun nanofiber films is of great significance. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for preparing a flexible SERS substrate based on electrospun nanofiber membranes. First, a polymer nanofiber membrane is prepared using electrospinning. Then, noble metal nanoparticles are deposited on the surface of the electrospun polymer nanofiber membrane using magnetron sputtering technology, resulting in a noble metal nanoparticle@polymer nanofiber membrane flexible SERS substrate. This method is simple, efficient, low-cost, and can be manufactured on a large scale continuously. The prepared flexible SERS substrate based on electrospun nanofiber membranes possesses a large specific surface area, high-density hotspot distribution, good stability, and adjustable size structure, enabling the detection of trace pesticide residues on irregular surfaces.

[0007] The objective of this invention is achieved through the following technical solutions:

[0008] The first aspect of this invention provides a method for preparing an electrospun nanofiber membrane-based flexible SERS substrate, comprising the following steps:

[0009] (1) Preparation of electrospun polymer nanofiber membranes: Polymer powder was dissolved in an acetone / DMF mixed solution (volume ratio 1:2) and magnetically stirred for 12 hours until homogeneous to obtain a polymer spinning solution of a certain concentration. The prepared solution was injected into a 5 mL plastic syringe and placed in an electrospinning system for processing. During the spinning process, the ambient humidity and temperature were maintained at 30% and 25 °C, respectively, and the electrospinning process parameters, including extrusion speed, spinning voltage, roller speed, and distance between the needle and the receiver, were controlled. After electrospinning, the collected electrospun polymer nanofiber membranes were placed in a 60 °C vacuum oven for drying for 24 h.

[0010] (2) Preparation of flexible SERS substrate: Noble metal nanoparticles were deposited on electrospun polymer nanofiber membranes using radio frequency magnetron sputtering. First, the electrospun nanofiber membranes were cut into 10×10 cm pieces. 2 The dimensions were determined and fixed to the substrate support. Then, a precious metal target was inserted, and the sputtering chamber was evacuated to 1.0 × 10⁻⁶. -4Pa, and argon gas is introduced. After the RF power supply is turned on, a stable glow discharge is generated in the cavity. During sputtering, the cavity pressure, sputtering power, and argon gas flow rate are maintained at certain values.

[0011] Preferably, the polymer powder in step (1) is cellulose acetate, polyacrylonitrile, nylon 6, 6, and polylactic acid; the concentration of the polymer spinning solution is 1-10 wt.

[0012] Preferably, in step (1), the electrospinning parameters include a spinning solution extrusion speed of 1-5 ml / h; a spinning voltage of 10-20 kV; a roller rotation speed of 100-500 rpm / min; a sputtering time of 1-3 min; and a needle-to-receiver distance of 1-5 cm.

[0013] Preferably, the precious metal target material in step (2) is gold, silver and copper.

[0014] Preferably, in step (2), the cavity pressure in the magnetron sputtering parameters is 0.1-1.0 Pa, the sputtering power is 50-200 W, and the argon flow rate is 50-150 sccm.

[0015] The second aspect of the present invention provides an electrospun nanofiber membrane-based flexible SERS substrate prepared by the method described above. The method for preparing the electrospun nanofiber membrane-based flexible SERS substrate is characterized by comprising a supporting substrate and noble metal nanoparticles for modifying the substrate. The electrospun nanofiber membrane exhibits a fibrous morphology, and the SERS substrate exhibits a three-dimensional interwoven porous structure. The fiber diameter is 200±100 nm, and the diameter of the noble metal nanoparticles is 25±10 nm.

[0016] The third aspect of this invention provides the application of the aforementioned electrospun nanofiber membrane-based flexible SERS substrate in the identification and detection of 4-mercaptobenzoic acid.

[0017] The fourth aspect of this invention provides the application of the aforementioned electrospun nanofiber membrane-based flexible SERS substrate in the identification and detection of the pesticide thiram.

[0018] This invention discloses a method for preparing a flexible SERS substrate based on electrospun nanofiber membranes. By combining electrospinning with magnetron sputtering—a rapid, low-cost, and large-scale continuous production technology—a composite SERS substrate with a three-dimensional interwoven nanofiber structure was successfully fabricated. This innovative design exhibits three synergistic advantages: First, the three-dimensional porous network structure of the electrospun fiber membrane provides a high specific surface area loading platform for nanoparticles, allowing target molecules to diffuse from multiple directions to the "hot spot" region, significantly improving signal capture efficiency. Second, by adjusting sputtering parameters (such as power, time, and gas pressure), uniform deposition of noble metal nanoparticles on the fiber surface can be achieved, avoiding the agglomeration phenomenon common in chemical methods and forming uniformly distributed "hot spots." Third, magnetron sputtering is a physical vapor deposition process, eliminating the need for reducing agents, stabilizers, and other chemical reagents, thus avoiding solution contamination, byproduct residues, and subsequent cleaning difficulties associated with traditional chemical reduction methods, meeting the requirements of green manufacturing.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The electrospun nanofiber membrane-based flexible SERS substrate prepared by the present invention has a three-dimensional porous high-density hot spot area. The three-dimensional porous network structure of the electrospun polymer fiber membrane provides a high specific surface area loading platform for nanoparticles. Target molecules can diffuse to the "hot spot" region from multiple directions, significantly improving the signal capture efficiency.

[0021] (2) The electrospun nanofiber membrane-based flexible SERS substrate prepared by the present invention can detect harmful substances on irregular surfaces. The polymer fiber membrane itself is flexible and thin, and it still maintains good flexibility after sputtering. It can fit irregular surfaces (such as fruit peels, skin, etc.) and is suitable for in-situ and on-site detection.

[0022] (3) The present invention uses magnetron sputtering technology to deposit noble metal nanoparticles, which has the advantages of being simple, fast, pollution-free, low cost and large scale. Magnetron sputtering is a physical vapor deposition, which does not require the use of reducing agents, stabilizers and other chemical reagents, thus avoiding the solution pollution, by-product residues and subsequent cleaning problems caused by traditional chemical reduction methods, and meeting the requirements of rapid, large-scale and green preparation.

[0023] (4) The electrospun nanofiber membrane-based flexible SERS substrate prepared by the present invention can precisely and controllably adjust the hot spot distribution. By adjusting the sputtering parameters (such as power, time, and gas pressure), the uniform deposition of noble metal nanoparticles on the fiber surface can be achieved, avoiding the agglomeration phenomenon commonly seen in chemical methods, and forming uniformly distributed "hot spots". Attached Figure Description

[0024] Figure 1Scanning electron microscope images of the electrospun nanofiber membrane-based flexible SERS substrates prepared for Example 1 and Comparative Example 1, where e is Example 1, and a, b, c, d and f are Comparative Example 1.

[0025] Figure 2 The UV-Vis absorption spectra of the electrospun nanofiber membrane-based flexible SERS substrates prepared in Example 1 and Comparative Example 1 are shown.

[0026] Figure 3 X-ray diffraction curves of the electrospun nanofiber membrane-based flexible SERS substrates prepared in Example 1 and Comparative Example 1.

[0027] Figure 4 The detection spectra of different concentrations of 4-MBA molecules on the electrospun nanofiber membrane-based flexible SERS substrate prepared in Example 1.

[0028] Figure 5 The electrospun nanofiber membrane-based flexible SERS substrate prepared in Example 1 is paired with 10 -3 Two-dimensional Raman intensity spectrum of M4-MBA molecule.

[0029] Figure 6 The detection spectra of different concentrations of thiophanate-methyl bimolecules on the electrospun nanofiber membrane-based flexible SERS substrate prepared in Example 1. Detailed Implementation

[0030] The present invention will be further described below with reference to specific examples and accompanying drawings. In the specific embodiments of the present invention, unless otherwise specified, the methods described are conventional methods in the art.

[0031] Example 1

[0032] A method for preparing and applying an electrospun nanofiber membrane-based flexible SERS substrate, the steps of which are as follows:

[0033] (1) Preparation of electrospun polymer nanofiber membrane: Cellulose acetate polymer powder was dissolved in an acetone / DMF mixed solution (volume ratio 1:2) and magnetically stirred for 12 hours until homogeneous to obtain a 10 wt% cellulose acetate polymer spinning solution. The prepared solution was injected into a 5 mL plastic syringe and placed in an electrospinning system for processing. During the spinning process, the ambient humidity and temperature were maintained at 30% and 25 °C, respectively, the extrusion speed was 1.0 mL / h, the spinning voltage was 20 kV, the sputtering time was 3 min, the roller speed was 300 rpm, and the distance between the needle and the receiver was 5 cm. After electrospinning, the collected electrospun polymer nanofiber membrane was placed in a 60 °C vacuum oven for drying for 24 h.

[0034] (2) Preparation of flexible SERS substrate based on electrospun nanofiber membrane: Gold nanoparticles were deposited on electrospun cellulose acetate nanofiber membranes using radio frequency magnetron sputtering. First, the electrospun nanofiber membranes were cut into 10×10 cm pieces. 2 The dimensions were determined and fixed to the substrate support. Then, a gold target was inserted, and the sputtering chamber was evacuated to 1.0 × 10⁻⁶. -4 The pressure was set to Pa, and argon gas was introduced. After the RF power supply was turned on, a stable glow discharge was generated in the cavity. During sputtering, the chamber pressure, applied power, and argon gas flow rate were maintained at 0.1 Pa, 100 W, and 110 sccm, respectively.

[0035] The morphology of the SERS substrate was characterized using scanning electron microscopy, such as... Figure 1 As shown, the surface of pure cellulose acetate is relatively smooth. As the sputtering time increases, gold nanoparticles gradually appear on the substrate surface. However, further increasing the sputtering time will cause the gold nanoparticles to agglomerate, and the agglomeration of particles will reduce the area of ​​the hot spot region.

[0036] The structure of the SERS substrate was characterized using ultraviolet-visible absorption spectroscopy, such as... Figure 2 As shown, the pure CA-NF film did not exhibit a significant absorption feature in the UV-Vis spectrum. In contrast, all AuNPs@CA-NF substrates showed a significant characteristic peak at 525 nm, which corresponds to the localized surface plasmon resonance (LSPR) peak of the gold nanoparticles.

[0037] The chemical structure of the SERS substrate was characterized using X-ray diffraction, such as... Figure 3 As shown, the XRD pattern of the original cellulose acetate nanofiber membrane shows three characteristic peaks at 2θ = 16.8°, 23.1°, and 39.7°, corresponding to the (110), (002), and (004) crystal planes of cellulose type I, respectively. In addition to the above cellulose acetate diffraction peaks, all AuNPs@CA-NF substrates exhibit four significant characteristic peaks at 2θ = 38.2°, 44.6°, 64.4°, and 77.6°, which are attributed to the (111), (200), (220), and (311) crystal planes of face-centered cubic gold nanoparticles (JCPDS card number 04-0784).

[0038] Comparative Example 1

[0039] A method for preparing an electrospun nanofiber membrane-based flexible SERS substrate differs from Example 1 only in step (2), where the sputtering time is 1, 2, and 4 min.

[0040] Figure 1In the diagram, a and b represent pure electrospun acetate nanofibers, while c, d, and f represent gold nanoparticles@electrospun acetate nanofiber composites sputtered for 1, 2, and 4 min, respectively. As the sputtering time changes, the surface of pure electrospun acetate nanofibers becomes smooth and flat. After sputtering with gold nanoparticles, the surface becomes rougher, and the number of nanoparticles increases. However, if the sputtering time is too long, the nanoparticles may aggregate.

[0041] Application Example 1

[0042] The electrospun nanofiber membrane-based flexible SERS substrate from Example 1 was used for the identification and detection of 4-MBA molecules, and the steps are as follows:

[0043] The SERS substrate was cut into multiple 10×10 mm pieces. 2 Small substrates were immersed in 4-MBA ethanol solutions of different concentrations for 1.0 h to ensure full contact between the substrates and crystal violet. The substrates were then removed and identified using a microconfocal Raman spectrometer with a laser power of 5 mW, an integration time of 10 s, a total of 3 integrations, and an objective magnification of 10x.

[0044] Raman spectra of different concentrations of 4-MBA detected by the SERS substrate are as follows: Figure 4 As shown, the substrate can achieve a detection efficiency of 10 for 4-MBA. -11 M. Furthermore, 4-MBA is at 1085 cm. -1 The Raman intensity at a given location exhibits a good linear relationship with the logarithm of the concentration, and its R0... 2 The value reached 0.91, indicating that the prepared SERS substrate has high detection sensitivity and quantitative detection capability.

[0045] SERS substrate pairs 10 -3 The two-dimensional Raman intensity spectrum of M 4-MBA is as follows: Figure 5 As shown, high-density SERS hotspots are clearly and uniformly distributed on the surface of the cellulose acetate nanofiber membrane. This uniformity confirms the excellent signal reproducibility of the AuNPs@CA-NF substrate.

[0046] Application Example 2

[0047] The electrospun nanofiber membrane-based flexible SERS substrate from Example 1 was used for the identification and detection of the pesticide thiram bimolecule. The steps are as follows:

[0048] The SERS substrate was cut into multiple 10×10 mm pieces. 2Small substrates were immersed in different concentrations of thiram diethanol solution for 1.0 h to ensure full contact between the substrate and thiram. The substrates were then removed and identified under a microconfocal Raman spectrometer with a laser power of 10 mW, an integration time of 10 s, a total of 3 integrations, and an objective magnification of 10x.

[0049] Raman spectra of different concentrations of thiamethoxam detected by the SERS substrate are as follows: Figure 6 As shown, the substrate can achieve a detection efficiency of 10 for thiamethoxam. -8 M. Furthermore, Fu Mei Shuang is 1386 cm tall. -1 The Raman intensity at a given location exhibits a good linear relationship with the logarithm of the concentration, and its R0... 2 The value reached 0.91, indicating that the prepared electrospun polymer SERS substrate has high detection sensitivity and quantitative analysis capability.

[0050] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing and applying an electrospun nanofiber membrane-based flexible SERS substrate, characterized in that, Includes the following steps: (1) Preparation of electrospun polymer nanofiber membrane: The polymer powder was dissolved in an acetone / DMF mixed solution (volume ratio 1:2) and magnetically stirred for 12 hours until homogeneous to obtain a polymer spinning solution of a certain concentration; the prepared solution was injected into a 5 mL plastic syringe and placed in an electrospinning system for processing; during the spinning process, the ambient humidity and temperature were maintained at 30% and 25 °C, respectively, and the electrospinning process parameters, including extrusion speed, spinning voltage, roller speed, sputtering time, and distance between needle and receiver, were controlled; after electrospinning was completed, the collected electrospun polymer nanofiber membrane was placed in a 60 °C vacuum oven for drying for 24 h; (2) Preparation of flexible SERS substrate: Noble metal nanoparticles were deposited on electrospun polymer nanofiber membranes using radio frequency magnetron sputtering technology; firstly, the electrospun nanofiber membranes were cut into 10×10 cm pieces. 2 The dimensions were determined and fixed onto the substrate support; then, a precious metal target was inserted, and the sputtering chamber was evacuated to 1.0 × 10⁻⁶. -4 Pa, and argon gas is introduced; After the RF power supply is turned on, a stable glow discharge is generated inside the cavity; during the sputtering process, the cavity pressure, sputtering power and argon flow rate are maintained at certain values.

2. The preparation method according to claim 1, characterized in that, The polymer powder mentioned in step (1) is cellulose acetate, polyacrylonitrile, nylon 6, 6, and polylactic acid; the concentration of the polymer spinning solution is 1-10 wt.

3. The preparation method according to claim 1, characterized in that, In step (1), the electrospinning parameters include a spinning solution extrusion speed of 1-5 ml / h, a spinning voltage of 10-20 kV, a roller rotation speed of 100-500 rpm / min, and a needle-to-receiver distance of 1-5 cm.

4. The preparation method according to claim 1, characterized in that, The precious metal target material mentioned in step (2) is gold, silver and copper.

5. The preparation method according to claim 1, characterized in that, In step (2), the magnetron sputtering parameters include a cavity pressure of 0.1-1.0 Pa, a sputtering power of 50-200 W, a sputtering time of 1-3 min, and an argon flow rate of 50-150 sccm.

6. The SERS substrate prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The substrate includes noble metal nanoparticles that support and modify the substrate. The electrospun nanofiber membrane exhibits a fibrous morphology, and the SERS substrate exhibits a three-dimensional interwoven porous structure. The fiber diameter is 200±100 nm, and the diameter of the noble metal nanoparticles is 25±10 nm.

7. The application of the SERS substrate as described in claim 6 in the identification and detection of 4-mercaptobenzoic acid (4-MBA).

8. The application of the SERS substrate as described in claim 6 in the identification and detection of the pesticide thiram.

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