Preparation method and application of flexible strain sensor based on SERS (Surface Enhanced Raman Scattering) technology

Abstract

The invention discloses a preparation method and application of a flexible strain sensor based on an SERS (Surface Enhanced Raman Scattering) technology, and belongs to the field of optical strain sensing. The invention aims to solve the technical problems that the current mainstream optical strain sensing technology is limited in measuring range, the precision and the measuring range are difficult to consider at the same time, and the large strain detection requirements of flexible structures such as low-altitude aircrafts are difficult to adapt. According to the flexible strain sensor based on the SERS technology, a compact 4-MBA-Au NPs single-layer film is formed through a three-phase interface self-assembly method, and the compact 4-MBA-Au NPs single-layer film is successfully transferred to the adhesive surface of a VHB adhesive tape with ultrahigh flexibility and elasticity; the prepared sensor can realize 0-24% wide-range strain detection, the measurement precision is + / -2% FS, the limitation of the existing optical sensing technology on the detection range is broken through, and due to the excellent adhesion of the VHB adhesive tape, the sensor can be easily integrated on the surface of a material to be detected, and the sensor has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of optical strain sensing, specifically relating to a method for fabricating and applying a flexible strain sensor based on SERS technology. Background Technology

[0002] At the forefront of low-altitude aircraft technology, deformable materials are the core driving force for achieving aerodynamic adaptation and structural intelligence. These materials endow adaptive wings, smart skins, and other structures with crucial deformation capabilities. However, during service, these materials must repeatedly withstand large-amplitude cyclic loads, making them highly susceptible to fatigue damage and even sudden failure, posing serious safety hazards. Therefore, developing reliable large-strain detection technology to accurately perceive and assess the strain state of materials has become a key link in risk warning and safety assurance, and is a pressing technological challenge that needs to be overcome. An ideal detection technology needs to possess both a wide measurement range to characterize large deformations and high precision to capture early damage signals from minute strains. This is crucial for reliable fatigue life prediction and health warning. However, existing mainstream optical strain sensing methods have significant limitations in simultaneously meeting these wide measurement range and high precision requirements. The measurement range of FBG sensors is typically limited by the fiber material itself, generally not exceeding ±1500 με, corresponding to a strain of approximately ±0.15%. If the strain exceeds this range, it may cause fiber damage. Digital image correlation (DIC) is highly dependent on the texture features of the measured surface. Insufficient surface texture or substandard quality directly affects the accuracy of strain measurements. Furthermore, traditional Raman spectroscopy strain sensing methods are typically based on the characteristic peak shift effects of low-dimensional materials (such as graphene), limiting their effective strain measurement range (usually less than 2%) and making them unsuitable for large strain measurements. Therefore, overcoming the limitations of existing optical sensing technologies in simultaneously achieving wide-range and high-precision measurements, and developing novel large-strain detection technologies adapted to the flexible structures of low-altitude aircraft, can provide crucial data support for their structural health management and maintenance. Simultaneously, large-strain detection solutions also have significant pioneering and supporting implications for the development of next-generation variant aircraft. Summary of the Invention

[0003] The purpose of this invention is to address the technical challenges of current mainstream optical strain sensing technologies, such as limited measurement range, difficulty in balancing accuracy and range, and inability to meet the large strain detection requirements of flexible structures like low-altitude aircraft. This invention provides a method for fabricating a flexible strain sensor based on SERS technology and its applications. The invention constructs the SERS signal characteristic parameter H... ε The linear functional relationship between the strain ε and the strain ε was determined by detecting the 1588 cm⁻¹ region in the SERS spectrum. -1 With 1076cm -1 The bimodal intensity ratio of H εThis method quantitatively detects strain by varying the intensity ratio. It extends the effective strain measurement range to 24%, significantly exceeding the level of existing optical technologies, providing a new solution for large strain measurement and significantly improving its practicality. The invention employs a bimodal intensity ratio detection strategy, using a 1588cm² intensity ratio as the basis for measurement. -1 With 1076cm -1 The intensity ratio H of the characteristic peaks ε As a core sensing parameter, it can effectively suppress common system errors, overcome the inherent defect that single characteristic peak signals are easily affected by system noise, and significantly improve the measurement reliability and data accuracy of this SERS strain sensing method.

[0004] A method for fabricating a flexible strain sensor based on SERS technology comprises the following steps: Step 1: Preparing an aqueous solution of gold nanoparticles using the sodium citrate reduction method, centrifuging, and then resuspending the precipitate in anhydrous ethanol to obtain an Au NPs ethanol solution; Step 2: Adding an ethanol solution of 4-mercaptobenzoic acid and the Au NPs ethanol solution to anhydrous ethanol, sonicating, stirring, centrifuging, and then resuspending the precipitate in anhydrous ethanol to obtain a 4-MBA-Au NPs ethanol solution; Step 3: Forming a dense 4-MBA-Au NPs monolayer film from the 4-MBA-Au NPs ethanol solution using a three-phase interface self-assembly method; Step 4: Transferring the 4-MBA-Au NPs monolayer film to the paperless adhesive side of a hydrophilically treated VHB tape, and then allowing it to air dry to obtain a flexible strain sensor based on SERS technology. This flexible strain sensor is suitable for strain detection of deformable materials.

[0005] The principle of this invention: This invention addresses the technical bottleneck of balancing range and accuracy in large-strain optical detection. Based on SERS technology, it achieves high-performance detection capabilities by simultaneously improving both. The core advantage of SERS technology lies in its exceptional signal sensitivity, stemming from the highly localized "electromagnetic hotspots" generated by the localized surface plasmon resonance effect of noble metal nanostructures. Its key mechanism is that the intensity of this electromagnetic field enhancement effect is extremely sensitive to the spacing between nanoparticles: the smaller the distance between particles, the more significant the electromagnetic field enhancement, and the stronger the SERS signal; conversely, the larger the distance between particles, the weaker the electromagnetic field enhancement, and the sharper the signal drop. This characteristic allows subtle changes in the spacing between nanoparticles at the microscale to be sensitively captured by Raman detectors and accurately reflected through differences in SERS signal intensity. By integrating an array of SERS-active nanostructures onto a flexible substrate, when the flexible structure undergoes macroscopic strain and deformation, the distance between nanoparticles changes accordingly, effectively modulating the SERS signal intensity. Based on this principle, the SERS signal parameter H is precisely established. εA quantitative mapping relationship between strain and macroscopic strain ε was established, and a method for fabricating a flexible strain sensor was proposed and implemented. The key lies in the ordered structural design of the nano-sensitive units and their coordinated deformation with a flexible substrate (VHB tape). The sensor fabricated in this way achieves high linearity and high precision response over an extremely wide strain range (from micro-strain to large strain), overcoming the technical challenge of achieving both wide range and high precision in the health monitoring of flexible structures of low-altitude aircraft.

[0006] The beneficial effects of this invention are as follows: First, this invention fabricates a flexible strain sensor based on SERS technology, providing a novel method for wide-range, high-precision strain sensing based on SERS technology; this method constructs the characteristic parameter H of the SERS signal. ε The linear functional relationship between strain ε and strain enables wide-range strain detection from 0% to 24%, with a measurement accuracy of ±2%·FS, breaking through the limitations of existing optical sensing technologies in terms of detection range; secondly, this invention employs a bimodal intensity ratio H ε The detection strategy effectively improves the reliability and accuracy of the measurement; this method uses 1588cm -1 With 1076cm -1 Using the intensity ratio of characteristic peaks as the core sensing parameter, this strategy can effectively suppress interference from common system errors such as laser power fluctuations and noise, significantly improving the signal-to-noise ratio of the sensing signal and the stability of the detection results. Thirdly, this invention designs and fabricates a highly integrated and stable flexible strain sensor based on SERS technology. A dense 4-MBA-Au NPs monolayer (a 4-mercaptobenzoic acid-modified gold nanoparticle monolayer) is formed through a three-phase interface self-assembly method and successfully transferred to the adhesive surface of a highly flexible VHB tape. Thanks to the excellent adhesion of the VHB tape, the resulting sensor is easily integrated onto the surface of the material to be measured, showing promising application prospects. Attached Figure Description

[0007] Figure 1 In Figure a, the SEM morphology of the 4-MBA-Au NPs monolayer film prepared in Example 1 is shown; in Figure b, the particle size distribution of 4-MBA-Au NPs is shown; in Figure c, the UV-Vis absorption spectrum of 4-MBA-Au NPs is shown; and in Figure d, the Raman spectrum of 4-MBA-Au NPs is shown. Figure 2 The images show a comparison of the flexible strain sensor based on SERS technology prepared in Example 1 before and after strain; where a is a schematic diagram with a strain of 24%, b is a schematic diagram without strain, and c is a comparison of Raman spectra before and after strain. Figure 3 The strain ε and the corresponding bimodal intensity ratio H of the flexible strain sensor based on SERS technology in Example 1 are used to apply this method. ε The scatter distribution and the fitted function curve. Detailed Implementation

[0008] Specific Implementation Method 1: This implementation method is a fabrication method for a flexible strain sensor based on SERS technology, specifically completed according to the following steps: Step 1: Prepare an aqueous solution of gold nanoparticles using the sodium citrate reduction method, centrifuge, and then resuspend the precipitate obtained by centrifugation in anhydrous ethanol to obtain an Au NPs ethanol solution; Step 2: Add the ethanol solution of 4-mercaptobenzoic acid and the Au NPs ethanol solution to anhydrous ethanol, sonicate, stir, centrifuge, and then resuspend the precipitate obtained by centrifugation in anhydrous ethanol to obtain a 4-MBA-Au NPs ethanol solution; Step 3: Form a dense 4-MBA-Au NPs monolayer film from the 4-MBA-Au NPs ethanol solution using the three-phase interface self-assembly method; Step 4: Transfer the 4-MBA-Au NPs monolayer film to one paperless adhesive side of a VHB tape that has been hydrophilically treated, and then allow it to dry naturally to obtain a flexible strain sensor based on SERS technology.

[0009] The 4-mercaptobenzoic acid used in this embodiment is abbreviated as 4-MBA. Its molecular structure is that the para-hydrogen atoms of the benzene ring are replaced by thiol groups (-SH) and carboxyl groups (-COOH), respectively. 4-MBA-Au NPs achieve stable bonding by forming Au-S bonds between the thiol groups (-SH) of 4-MBA and the Au atoms on the surface of gold nanoparticles. The distances between the functional groups of the 4-MBA molecule and the Au atoms, from closest to farthest, are thiol group, benzene ring, and carboxyl group. In this embodiment, the 4-MBA molecule serves as a Raman probe molecule, exhibiting characteristic fingerprint peaks. The densely packed gold nanoparticles in the 4-MBA-Au NPs monolayer film generate SERS enhancement through the localized surface plasmon resonance (LSPR) effect, significantly amplifying the Raman spectrum of the 4-MBA molecule. VHB tape, with its excellent adhesion, flexibility, and high elasticity, simplifies the sensor integration process. In this embodiment, the Raman spectrum of the 4-MBA molecule can reflect the vibrational characteristics of its functional groups, with the 523 cm⁻¹ peak being the most prominent. -1 The characteristic peak is attributed to the out-of-plane bending vibration of the benzene ring, 1076 cm⁻¹. -1 The characteristic peak is attributed to C–S stretching vibration, 1178 cm⁻¹ -1 The characteristic peak is attributed to C–H bending vibration, 1588 cm⁻¹ -1 The characteristic peaks are attributed to the C=C skeletal stretching vibrations of the benzene ring. In this embodiment, the densely packed gold nanoparticles can effectively excite the LSPR effect. The strong local electric field formed by interparticle plasmon coupling significantly enhances the SERS signal of the 4-MBA probe molecules adsorbed on the particle surface. This enhancement mechanism directly affects the molecular vibrational modes of 4-MBA, causing significant changes in the signals of its characteristic Raman peaks, providing a strong signal basis for subsequent qualitative and quantitative detection based on SERS spectroscopy.

[0010] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the preparation method of the Au NPs ethanol solution in step one is as follows: chloroauric acid aqueous solution, silver nitrate aqueous solution, sodium citrate aqueous solution, and Tris aqueous solution are mixed evenly, then injected into hot water, and reacted at 100℃ for 0.5h~1h to obtain an aqueous solution of gold nanoparticles. Other steps are the same as in Specific Implementation Method One.

[0011] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the concentration of the chloroauric acid aqueous solution is 50 mg / mL; the concentration of the silver nitrate aqueous solution is 2 mg / mL; the concentration of the sodium citrate aqueous solution is 60 mg / mL to 200 mg / mL; and the concentration of the Tris aqueous solution is 2 mol / L. Other steps are the same as in Specific Implementation Method One or Two.

[0012] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the volume ratio of the chloroauric acid aqueous solution, silver nitrate aqueous solution, sodium citrate aqueous solution, Tris aqueous solution, and hot water is 400 μL:85 μL:200 μL:400 μL:200 mL; the centrifugation speed is 2000 r / min to 5000 r / min, and the centrifugation time is 5 min to 15 min. Other steps are the same as in Specific Implementation Methods One to Three.

[0013] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the concentration of the 4-mercaptobenzoic acid ethanol solution in step two is 50 mg / mL; in step two, 40 μL of the 4-mercaptobenzoic acid ethanol solution and 1 mL of Au NPs ethanol solution are added to 200 mL of anhydrous ethanol, sonicated for 1 hour, stirred for 1 hour, and then centrifuged at 2000 r / min to 5000 r / min for 5 min to 15 min. The precipitate obtained after centrifugation is then resuspended in 1 mL of anhydrous ethanol to obtain a 4-MBA-Au NPs ethanol solution. Other steps are the same as in Specific Implementation Methods One to Four.

[0014] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the specific operation of the three-phase interface self-assembly method described in step three is as follows: Dichloromethane, 4-MBA-Au NPs ethanol solution, and water are added sequentially to a centrifuge tube. The centrifuge tube is then placed in a vortex mixer and vortexed at speed 10 for 10 seconds. Next, n-hexane is added. 4-MBA-Au NPs spontaneously assemble into a film at the water-n-hexane interface, and the n-hexane is removed, forming a dense 4-MBA-Au NPs monolayer film. The volume ratio of dichloromethane, 4-MBA-Au NPs ethanol solution, water, and n-hexane is 10 mL:100 μL:15 mL:5 mL. Other steps are the same as in Specific Implementation Methods One to Five.

[0015] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that: the hydrophilic treatment method in step four involves peeling off the release paper from one side of the VHB tape, placing it in a plasma cleaner, and introducing oxygen to modify the surface of the VHB tape to remove impurities and enhance surface wettability and adhesion; the power of the plasma cleaner is 50mW~200mW, and the surface modification time is 30s~300s; in step four, the 4-MBA-Au NPs monolayer film is transferred to the paperless adhesive side of the hydrophilicated VHB tape using a dip-coating method; the VHB tape in step four is 3M VHB4910 acrylic foam tape, a double-sided tape with a thickness of 1mm and a cut size of 20mm×5mm. Other steps are the same as in Specific Implementation Methods One through Six.

[0016] Specific implementation method eight: This implementation method is a flexible strain sensor suitable for strain detection of deformable materials.

[0017] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One through Eight in that the strain detection method is as follows: Step 1: Install a flexible strain sensor based on SERS technology onto an electric tensile stage, record the initial gauge length before tensile testing as L0 (in mm), and then use a Raman spectrometer to detect the Raman spectrum of the sensor on the surface of the deformable material in the initial state; Step 2: Perform a quasi-static tensile test on the deformable material containing the sensor on the surface using an electric tensile stage. The test adopts a graded loading mode, applying tensile strain step by step with a displacement control step size of 50 μm, and record the gauge length after tensile testing of the deformable material containing the sensor on the surface as L0. ε The unit is mm, according to the formula Calculate the strain ε until the strain reaches 24%, and simultaneously detect the Raman spectra of the deformable material surface sensor under different tensile strains during this process; Step 3, SERS spectral data processing: ① Process the obtained Raman spectra under each tensile strain, and extract the 1588 cm⁻¹ data for each tensile strain. -1 and 1076cm -1 ② Calculate the fitting intensity of the characteristic peak at 1588 cm⁻¹ under various strains. -1 With 1076cm -1 The intensity ratio of the double peak of the characteristic peak to H ε , Step 3① involves data processing including Raman spectrum smoothing, baseline correction, and Raman peak fitting. After fitting, the 1588 cm⁻¹ peak is extracted. -1 and 1076cm -1 Characteristic peak intensity information; Step 4: Construct strain ε and bipeak intensity ratio H εFunctional relationship: with strain ε as the abscissa, the bimodal intensity ratio H ε Plot the calibration curve with the vertical axis as the ordinate; perform function fitting on the curve to obtain the fitted linear function H. ε =0.797+0.159ε, coefficient of determination R 2 =0.999; Step 5: Peel off the release paper on the other side of the SERS-based flexible strain sensor and attach it to the surface of the deformable test material. Apply strain to the test material, detect the Raman spectrum of the sensor on the surface of the test material, and process the data. Extract the 1588cm⁻¹ spectrum. -1 and 1076cm -1 The fitted intensity of the characteristic peaks and the bimodal intensity ratio H were calculated. ε Then substitute H ε The strain occurring on the surface of the material under test can be calculated from ε = 0.797 + 0.159. Other steps are the same as in specific implementation methods one through eight.

[0018] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the deformable test material mentioned in step five includes carbon fiber composite material, thermoplastic polyurethane film, polydimethylsiloxane film, 3MW8751 film, 3MW8607 film, and silicone film. Other steps are the same as in Specific Implementation Methods One to Nine.

[0019] The beneficial effects of the present invention are verified using the following embodiments: Example 1: A method for preparing a flexible strain sensor based on SERS technology, specifically comprising the following steps: Step 1: Mixing 400 μL of chloroauric acid aqueous solution (50 mg / mL), 85 μL of silver nitrate aqueous solution (2 mg / mL), 200 μL of sodium citrate aqueous solution (100 mg / mL), and 400 μL of Tris aqueous solution (2 mol / L) thoroughly, then injecting the mixture into 200 mL of hot water at 100°C, reacting at 100°C for 1 h to obtain an aqueous solution of gold nanoparticles, centrifuging at 3000 r / min for 6 min, removing the supernatant, and resuspending the precipitate obtained by centrifugation in 200 mL of anhydrous ethanol to obtain an Au NPs ethanol solution; Step 2: Adding 40 μL of 4-mercaptobenzoic acid ethanol solution and 1 mL of Au NPs ethanol solution to 200 mL of hot water at 100°C for 1 h to obtain an aqueous solution of gold nanoparticles, then centrifuging at 3000 r / min for 6 min, removing the supernatant, and resuspending the precipitate obtained by centrifugation in 200 mL of anhydrous ethanol to obtain an Au NPs ethanol solution; In 1 mL of anhydrous ethanol, the 4-MBA-Au NPs were sonicated for 1 h, stirred for 1 h, and then centrifuged at 3000 r / min for 6 min. The precipitate was then resuspended in 1 mL of anhydrous ethanol to obtain a 4-MBA-Au NPs ethanol solution. The concentration of the 4-mercaptobenzoic acid ethanol solution in step two was 50 mg / mL. In step three, 10 mL of dichloromethane, 100 μL of 4-MBA-Au NPs ethanol solution, and 15 mL of water were added sequentially to a 40 mL centrifuge tube. The centrifuge tube was then placed in a vortex mixer and vortexed at speed 10 for 10 s. Then, 5 mL of n-hexane was added. The 4-MBA-Au NPs spontaneously assembled into a film at the water-n-hexane interface, and the n-hexane was absorbed to form a dense 4-MBA-Au molecule. NPs monolayer film; Step 4: Peel off the release paper from one side of the VHB tape, then place it in a plasma cleaner and introduce oxygen to modify the surface of the VHB tape to remove impurities and enhance surface wettability and adhesion; The plasma cleaner has a power of 200mW and the surface modification time is 300s, resulting in a hydrophilic VHB tape; Transfer the 4-MBA-Au NPs monolayer film to the paperless adhesive side of the hydrophilic VHB tape using a lift-up method, and then let it air dry to obtain a flexible strain sensor based on SERS technology; The VHB tape mentioned in Step 4 is 3MVHB4910 acrylic foam tape, which is double-sided, 1mm thick, and cut to a size of 20mm×5mm.

[0020] Figure 1 Image a shows the SEM morphology of the 4-MBA-Au NPs monolayer film prepared in Example 1; image b shows the particle size distribution of the 4-MBA-Au NPs; image c shows the UV-Vis absorption spectrum of the 4-MBA-Au NPs; and image d shows the Raman spectrum of the 4-MBA-Au NPs. Figure 1It can be seen that the 4-MBA-Au NPs prepared in Example 1 have a regular morphology and uniform particle size, with a size of approximately 100 nm. Their surface plasmon resonance absorption peak is located at 563 nm. The 4-MBA-Au NPs molecules exhibit two typical Raman characteristic peaks, at 1076 cm⁻¹. -1 The C–S stretching vibration peak at 1588 cm⁻¹ is similar to that at 1588 cm⁻¹. -1 The peak of the C=C skeleton stretching vibration of the benzene ring is observed. In the SERS substrate prepared by self-assembly, gold nanoparticles are densely arranged and can form a continuous and uniform monolayer film structure.

[0021] Example 2: Testing the strain ε and bimodal intensity ratio H of the flexible strain sensor based on SERS technology prepared in Example 1. ε Functional relationship: Step 1: Install the SERS-based flexible strain sensor onto an electric tensile stage and record the initial gauge length before tensile testing as L0 (in mm, L0 = 10 mm). Then, use a Raman spectrometer to detect the Raman spectrum of the sensor on the deformable material surface in the initial state. Step 2: Perform a quasi-static tensile test on the deformable material with the sensor on its surface using an electric tensile stage. The test adopts a graded loading mode, applying tensile strain in 50 μm displacement control steps. Record the gauge length L of the deformable material with the sensor on its surface after tensile testing. ε The unit is mm, L ε The thicknesses are 10.05, 10.10, 10.15, ..., 12.40 mm respectively; according to the formula... Calculate the strain ε until the strain reaches 24%, and during this process, use a Raman spectrometer to simultaneously detect the Raman spectra of the deformable material surface sensor under different tensile strains; the Raman spectrometer mentioned in step two is equipped with a 785nm laser; the integration time of the Raman spectroscopy detection is 10 seconds; the electric tensile stage mentioned in step two can perform single-axis bidirectional position movement according to the instructions of the control system; Step three, SERS spectral data processing: ① Process the obtained Raman spectra under each tensile strain, and extract the 1588cm² data for each tensile strain. -1 and 1076cm -1 ② Calculate the fitting intensity of the characteristic peak at 1588 cm⁻¹ under various strains. -1 With 1076cm -1 The intensity ratio of the double peak of the characteristic peak to H ε , Step 3① involves data processing including Raman spectrum smoothing, baseline correction, and Raman peak fitting. After fitting, the 1588 cm⁻¹ peak is extracted. -1 and 1076cm -1 Characteristic peak intensity information; Step 4: Construct strain ε and bipeak intensity ratio H εFunctional relationship: with strain ε as the abscissa, the bimodal intensity ratio H ε Plot the calibration curve with the vertical axis as the ordinate; perform function fitting on the curve to obtain the fitted linear function H. ε =0.797+0.159ε, coefficient of determination R 2 =0.999.

[0022] Figure 2 The images show a comparison of the flexible strain sensor based on SERS technology prepared in Example 1 before and after strain; where a is a schematic diagram with a strain of 24%, b is a schematic diagram without strain, and c is a comparison of the Raman spectra before and after strain. Figure 2 It can be seen that when strain is applied to flexible materials, the dense arrangement of gold nanoparticles is disrupted, and the interparticle spacing changes with the degree of strain, which in turn causes a corresponding change in the intensity of the characteristic peaks in the SERS spectrum, ultimately leading to changes in the SERS characteristic parameter H. ε Things have changed.

[0023] Figure 3 The strain ε and corresponding bimodal intensity ratio H of the flexible strain sensor based on SERS technology prepared in Example 1 ε The scatter distribution and fitted function curve; by Figure 3 It can be seen that: This invention constructs the SERS signal characteristic parameter H ε The linear functional relationship between H and strain ε ε =0.797+0.159ε, coefficient of determination R 2 =0.999; indicating a high goodness of fit. Quantitative strain detection can be achieved by detecting changes in the H value in the SERS spectrum. This method can achieve a wide strain detection range of 0-24%, with a measurement accuracy of ±2%·FS. It overcomes the bottleneck of limited measurement range commonly found in existing mainstream optical strain sensing methods, and overcomes the technical difficulties of limited measurement range and difficulty in balancing accuracy and range in current mainstream optical strain sensing technologies. This provides a detection method for flexible strain sensors based on SERS technology to meet the large strain detection needs of flexible structures such as low-altitude aircraft.

[0024] Example 3: Testing the strain of polydimethylsiloxane film (PDMS), specifically performed as follows: The release paper on the other side of the flexible strain sensor based on SERS technology prepared in Example 1 was peeled off and pasted onto the surface of the deformable test material. Strain was applied to the test material, the Raman spectrum of the sensor on the test material surface was detected and data processed, and the 1588 cm⁻¹ spectrum was extracted. -1 and 1076cm -1 The fitted intensity of the characteristic peaks and the bimodal intensity ratio H were calculated. ε Substitute the H obtained in Example 2 ε=0.797+0.159ε can be used to calculate the strain on the surface of the material under test; the deformable material under test is a polydimethylsiloxane film (PDMS) with a thickness of 0.1 mm.

[0025] Table 1 shows the tensile strain verification data of polydimethylsiloxane film (PDMS). The measured strain ε is the strain calculated in Example 3. Table 1 shows that the sensor of this invention has accurate measurement performance and has passed the tensile strain verification of PDMS material. Test data show that the error is less than ±2%·FS, which is within the sensor error range.

[0026]

Claims

1. A method for fabricating a flexible strain sensor based on SERS technology, characterized in that... The preparation method is specifically carried out according to the following steps: Step 1: Prepare an aqueous solution of gold nanoparticles using the sodium citrate reduction method, centrifuge, and then resuspend the precipitate obtained by centrifugation in anhydrous ethanol to obtain an Au NPs ethanol solution; Step 2: Add the ethanol solution of 4-mercaptobenzoic acid and the Au NPs ethanol solution to anhydrous ethanol, sonicate, stir, centrifuge, and then resuspend the precipitate obtained by centrifugation in anhydrous ethanol to obtain a 4-MBA-Au NPs ethanol solution; Step 3: Form a dense 4-MBA-Au NPs monolayer film from the 4-MBA-Au NPs ethanol solution using the three-phase interface self-assembly method; Step 4: Transfer the 4-MBA-Au NPs monolayer film to one paperless adhesive side of a hydrophilically treated VHB tape, and then allow it to dry naturally to obtain a flexible strain sensor based on SERS technology.

2. The method for fabricating a flexible strain sensor based on SERS technology according to claim 1, characterized in that... The preparation method of the gold nanoparticle aqueous solution in step one is as follows: chloroauric acid aqueous solution, silver nitrate aqueous solution, sodium citrate aqueous solution and Tris aqueous solution are mixed evenly, and then injected into hot water. The mixture is reacted at 100℃ for 0.5h~1h to obtain the gold nanoparticle aqueous solution.

3. The method for fabricating a flexible strain sensor based on SERS technology according to claim 2, characterized in that... The concentration of the chloroauric acid aqueous solution is 50 mg / mL, the concentration of the silver nitrate aqueous solution is 2 mg / mL, the concentration of the sodium citrate aqueous solution is 60 mg / mL to 200 mg / mL, and the concentration of the Tris aqueous solution is 2 mol / L.

4. The method for fabricating a flexible strain sensor based on SERS technology according to claim 2, characterized in that... The volume ratio of the chloroauric acid aqueous solution, silver nitrate aqueous solution, sodium citrate aqueous solution, Tris aqueous solution, and hot water is 400μL:85μL:200μL:400μL:200mL.

5. The method for fabricating a flexible strain sensor based on SERS technology according to claim 1, characterized in that... The concentration of the ethanol solution of 4-mercaptobenzoic acid mentioned in step two is 50 mg / mL.

6. The method for fabricating a flexible strain sensor based on SERS technology according to claim 1, characterized in that... The specific operation of the three-phase interface self-assembly method described in step three is as follows: add dichloromethane, 4-MBA-Au NPs ethanol solution and water to the centrifuge tube in sequence, then place the centrifuge tube in a vortex shaker and vortex at speed 10 for 10 seconds, then add n-hexane. 4-MBA-Au NPs spontaneously assemble into a film at the water and n-hexane interface, absorb the n-hexane, and form a dense 4-MBA-Au NPs monolayer film.

7. The method for fabricating a flexible strain sensor based on SERS technology according to claim 1, characterized in that... In step four, the 4-MBA-Au NPs monolayer film is transferred to the paperless adhesive side of the hydrophilic VHB tape using a dip-coating method.

8. The application of the flexible strain sensor based on SERS technology prepared by the preparation method according to any one of claims 1 to 7, characterized in that... The flexible strain sensor is suitable for strain detection of deformable materials.

9. The application of the flexible strain sensor based on SERS technology according to claim 8, characterized in that... The strain detection method is as follows: Step 1: Install the SERS-based flexible strain sensor onto an electric tensile stage and record the initial gauge length before tensile testing as L0 (in mm). Then, use a Raman spectrometer to detect the Raman spectrum of the sensor on the deformable material surface in the initial state. Step 2: Perform a quasi-static tensile test on the deformable material with the sensor on its surface using an electric tensile stage. The test adopts a graded loading mode, applying tensile strain in 50 μm displacement control steps. Record the gauge length L of the deformable material with the sensor on its surface after tensile testing. ε The unit is mm, according to the formula Calculate the strain ε until the strain reaches 24%, and simultaneously detect the Raman spectra of the deformable material surface sensor under different tensile strains during this process; Step 3, SERS spectral data processing: ① Process the obtained Raman spectra under each tensile strain, and extract the 1588 cm⁻¹ data for each tensile strain. -1 and 1076cm -1 ② Calculate the fitting intensity of the characteristic peak at 1588 cm⁻¹ under various strains. -1 With 1076cm -1 The intensity ratio of the double peak of the characteristic peak to H ε , ; The data processing described in step 3① includes: Raman spectrum smoothing, baseline correction, and Raman peak fitting. After fitting, the 1588 cm⁻¹ peak is extracted. -1 and 1076cm -1 Characteristic peak intensity information; Step 4: Construct strain ε and bipeak intensity ratio H ε Functional relationship: with strain ε as the abscissa, the bimodal intensity ratio H ε Plot the calibration curve using the ordinate; perform function fitting on the curve to obtain the fitted linear function H. ε =0.797+0.159ε, coefficient of determination R 2 =0.999; Step 5: Peel off the release paper on the other side of the SERS-based flexible strain sensor and attach it to the surface of the deformable test material. Apply strain to the test material, detect the Raman spectrum of the sensor on the surface of the test material, and process the data. Extract the 1588cm⁻¹ spectrum. -1 and 1076cm -1 The fitted intensity of the characteristic peaks and the bimodal intensity ratio H were calculated. ε Then substitute H ε The strain occurring on the surface of the material under test can be calculated from ε = 0.797 + 0.

159.

10. The application of the flexible strain sensor based on SERS technology according to claim 9, characterized in that... The deformable test material mentioned in step five includes carbon fiber composite material, thermoplastic polyurethane film, polydimethylsiloxane film, 3MW8751 film, 3MW8607 film and silicone film.

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