A cicada wing-Au-Ag flexible nano-SERS array material and its preparation method and application in aging status assessment of No. 45 transformer oil

Abstract

The present invention discloses a cicada wing-Au-Ag flexible nano-SERS array material, a preparation method thereof, and an application in the aging status assessment of No. 45 transformer oil, and relates to the field of Raman spectroscopy technology. The preparation method of the cicada wing-Au-Ag flexible nano-SERS array material comprises the following steps: using pretreated cicada wings as a substrate template, uniformly loading gold nanoparticles on its surface by electron beam evaporation; immersing the cicada wing-Au nanofilm in an AgNO3 solution, stirring and controlling the temperature, slowly adding a sodium citrate solution, and reacting to obtain a cicada wing-Au-Ag array; immersing the cicada wing-Au-Ag array in a PBS buffer solution of 4-mercapto-N-(4-mercaptophenyl)pyrrolidamide, incubating in the dark, and obtaining a cicada wing-Au-Ag flexible nano-SERS array material. The cicada wing-Au-Ag flexible SERS substrate prepared by the present invention can realize extraction-free high-sensitivity detection of furfural in No. 45 transformer oil.

Description

Technical Field

[0001] The present invention relates to the technical field of Raman spectroscopy, and in particular to a cicada wing-Au-Ag flexible nano SERS array material, a preparation method thereof, and an application thereof in aging status assessment of No. 45 transformer oil. Background Art

[0002] Furfural, as one of the key indicators of oil-paper insulation aging, plays a key role in assessing transformer aging. Furfural content testing is becoming an effective alternative to the degree of polymerization (DP) method.

[0003] Surface-enhanced Raman scattering (SERS) is a highly sensitive vibrational spectroscopy technique widely used for the detection of trace substances. By manipulating the microscopic morphology of precious metal nanostructures, SERS can effectively detect the vibrational spectral information of target molecules. In recent years, the use of SERS for the detection of furfural in mineral oil / transformer oil in substations has been gaining popularity. However, due to the complex Raman spectral information of No. 45 transformer oil, when the low-level furfural diffuses from the insulation paper into the No. 45 transformer oil, its signal is almost completely obscured by the Raman signal of the No. 45 transformer oil. Therefore, conventional Raman spectroscopy requires extraction of furfural from the No. 45 transformer oil before Raman detection. This not only results in low sensitivity for furfural detection, but also requires a cumbersome operation that limits the detection technique to laboratory applications.

[0004] However, traditional SERS substrate preparation processes are complex, and no extraction-free SERS substrate suitable for furfural in No. 45 transformer oil has yet been developed on the market. To address the issues of existing furfural detection methods, such as cumbersome procedures, high detection limits, and poor detection consistency, this application proposes an innovative solution, providing a new method for the rapid and highly sensitive detection of dissolved furfural in No. 45 transformer oil, with important theoretical significance and practical application value. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a cicada wing-Au-Ag flexible nano SERS array material and its preparation method and application in the aging status assessment of No. 45 transformer oil.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for preparing a cicada wing-Au-Ag flexible nano SERS array material comprises the following steps:

[0008] S1: Using the pre-treated cicada wings as the substrate template, gold nanoparticles are uniformly loaded on the surface by electron beam evaporation to form a cicada wing-Au nanofilm;

[0009] S2: Add PVP solution to AgNO3 solution, stir, then immerse cicada wing-Au nanofilm, stir, control the temperature at 80-95°C, then slowly add sodium citrate solution, react for 40-60 minutes, and obtain cicada wing-Au-Ag array after post-treatment;

[0010] S3: Immerse the cicada wing-Au-Ag array in PBS buffer of 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide, stir, incubate in a constant temperature shaker in the dark, and obtain the cicada wing-Au-Ag flexible nano SERS array material after post-treatment.

[0011] The thickness of the cicada wing-Au nanofilm in step S1 is 8-12 nm.

[0012] In step S2, the concentration of the AgNO3 solution is 0.05-2 mM, the concentration of the sodium citrate solution is 0.5-2 w / v%, and the concentration of the PVP solution is 0.1-0.4 wt%.

[0013] The volume ratio of the AgNO3 solution, sodium citrate solution and PVP solution is 4:(0.8-1.2):(0.8-1.2).

[0014] In step S3, the concentration of 4-mercapto-N-(4-mercaptophenyl)pyrrolidineamide in the PBS buffer of 4-mercapto-N-(4-mercaptophenyl)pyrrolidineamide is 0.1-0.15 mM, and the pH of the PBS buffer is 7.4.

[0015] The pre-processing steps of the cicada wings in step S1 are:

[0016] Cut cicada wings into 1×1 cm squares with sterile scissors and place them in beakers of acetone, anhydrous ethanol, and deionized water for ultrasonic cleaning. Transfer the cleaned cicada wings to a glass Petri dish and place it in a sterile vacuum drying oven. The vacuum chamber is evacuated to remove water molecules and gases adsorbed on the surface.

[0017] In step S1, the cicada wings are the hind wings of an adult cicada.

[0018] In step S1, the parameters of electron beam evaporation are: the target material is 99.999% high-purity gold, the evaporation deposition rate is 0.1-0.3Å / s, and the sample stage rotation speed is 5-10 rpm.

[0019] The present invention also provides a cicada wing-Au-Ag flexible nano SERS array material, which is prepared by the above-mentioned preparation method.

[0020] The present invention also provides an application of a cicada wing-Au-Ag flexible nano SERS array material in the aging state evaluation of No. 45 transformer oil.

[0021] Due to the adoption of the above technical solution, the beneficial effects of the present invention include:

[0022] (1) Cicada wings are a low-cost, green, and biodegradable biomaterial. Their nanoscale array structure, when attached with precious metals, can generate localized surface plasmon resonance (LSPR). This not only promotes the amplification of SERS signals, but also ensures good uniformity of the molecules adsorbed on their surfaces, thus helping to obtain stable SERS signals. The surface of cicada wings modified with precious metal nanoparticles was functionalized by coupling with 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide. The incubation time was short (only 40-60 minutes), and the resulting SERS array had high detection sensitivity.

[0023] (2) The present invention solves the problem of poor consistency of traditional SERS substrates. Natural cicada wings are used as templates. Their excellent array structure provides a stable space gap for the subsequent attachment of gold and silver nanoparticles, forming a SERS substrate with good consistency and uniform Raman "hot spots". The particle size of the synthesized silver nanoparticles can be controlled at 10 nm (±2 nm).

[0024] (3) The cicada wing-Au-Ag flexible SERS substrate prepared by the present invention can realize extraction-free high-sensitivity detection of furfural in No. 45 transformer oil, and the minimum detection limit (LOD) reaches 0.01 mg / L, which meets the detection requirements of furfural when the transformer insulation paper is slightly aged. In addition, the consistency index of the substrate was systematically evaluated: the relative standard deviation (RSD) was 3.54%, which showed good consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the preparation flow chart of cicada wing-Au-Ag flexible nano SERS array material.

[0026] Figure 2 This is a scanning electron microscope photograph of the cicada wing-Au-Ag flexible nano SERS array material prepared in Example 3, wherein: Figure 2 The scale bar in (a) is 500 nm. Figure 2 The scale bar in (b) is 300 nm. Figure 2 The scale bar in (c) is 200 nm. Figure 2 The scale bar in (d) is 100 nm.

[0027] Figure 3 This is the SERS spectrum of the cicada wing-Au-Ag flexible nano SERS array material used for trace detection of furfural in No. 45 transformer oil.

[0028] Figure 4When the cicada wing-Au-Ag flexible nano SERS array material was used to detect 1 mg / L furfural in 45# transformer oil, the furfural was located at 1658 cm -1 The corresponding Raman intensity histogram within the wavenumber range.

[0029] Figure 5 This is the average distribution diagram of the cicada wing-Au-Ag flexible nano SERS array material. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0031] Example 1 Preparation of 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoyl:

[0032] Under nitrogen protection and in an ice bath, 4-mercaptopyridine-2-carboxylic acid (1.0 mmol, 155 mg) was dissolved in 10 mL of anhydrous DMF. EDC·HCl (1.2 mmol, 230 mg) and NHS (1.2 mmol, 138 mg) were added sequentially. After stirring and activation for 30 minutes, the mixture was warmed to room temperature and the reaction was continued for 2 hours. Subsequently, a solution of 4-aminothiophenol (1.1 mmol, 139 mg) in 5 mL of DMF was slowly added dropwise over 5 minutes. Triethylamine (2.0 mmol, 280 μL) was then added. After stirring at room temperature (25°C) in the dark for 12 hours, the pH was adjusted to neutral with 0.25 M HCl, and the crude product was precipitated in an ice-water bath. The crude product was filtered and purified by silica gel column chromatography (DCM / methanol = 20:1 → 10:1 gradient elution) to obtain a white solid product, 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoyl. Its H NMR spectrum data are as follows: 1 H NMR (500 MHz, DMSO- d 6) δ 9.12 (s, 1H), 8.64 (d, J = 4.2 Hz, 1H), 7.74(d, J = 2.1 Hz, 1H), 7.54 – 7.48 (m, 2H), 7.40 – 7.34 (m, 2H), 7.25 (dd, J =4.2, 2.2 Hz, 1H), 4.77 (s, 1H), 4.14 (s, 1H). The reaction equation for the preparation of 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoyl is as follows:

[0033]

[0034] Example 2 Preparation of cicada wing-Au-Ag flexible nano SERS array material:

[0035] S1: Using pre-treated 1×1 cm cicada wings as the base template, the template was evaporated by electron beam (vacuum degree 2×10 -6 Torr, the target material is 99.999% high-purity gold, the evaporation deposition rate is 0.1Å / s, and the sample stage rotation speed is 10 rpm) on its surface to uniformly load gold nanoparticles to form a cicada wing-Au nanofilm with a thickness of 8nm;

[0036] S2: Add 8 ml of 0.1 wt% PVP solution to 40 ml of 0.5 mM AgNO3 solution and stir. Then immerse the cicada wing-Au nanofilm in the solution and stir. Control the temperature at 80°C. Then slowly add 8 ml of 2 w / v% sodium citrate solution dropwise for 8 minutes. After reaction for 60 minutes, remove the cicada wings and rinse them with 15 ml of ice water. Blow dry with nitrogen and vacuum dry (40°C, 2 hours) to obtain the cicada wing-Au-Ag array.

[0037] S3: Immerse the cicada wing-Au-Ag array in 35 ml of 0.1 mM 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide PBS buffer (pH = 7.4), stir, and incubate in a 25°C constant temperature shaker at 200 rpm in the dark for 40 minutes. Remove the cicada wings and rinse them with 15 ml of anhydrous ethanol and 15 ml of deionized water in sequence. Blow dry with nitrogen and then vacuum dry (25°C, 1 hour) to obtain the cicada wing-Au-Ag flexible nano SERS array material.

[0038] Example 3 Preparation of cicada wing-Au-Ag flexible nano SERS array material:

[0039] S1: Using pre-treated 1×1 cm cicada wings as the base template, the template was evaporated by electron beam (vacuum degree 1×10 -6 Torr, the target material is 99.999% high-purity gold, the evaporation deposition rate is 0.2 Å / s, and the sample stage rotation speed is 8 rpm) to uniformly load gold nanoparticles on its surface to form a cicada wing-Au nanofilm with a thickness of 10 nm;

[0040] S2: Add 10 ml of 0.25 wt% PVP solution to 40 ml of 1 mM AgNO3 solution and stir. Then immerse the cicada wing-Au nanofilm in the solution and stir. Control the temperature at 90°C. Then slowly add 10 ml of 1 w / v% sodium citrate solution dropwise for 10 minutes. After reacting for 50 minutes, remove the cicada wings and rinse them with 15 ml of ice water. Blow dry with nitrogen and vacuum dry (40°C, 2 hours) to obtain the cicada wing-Au-Ag array.

[0041] S3: Immerse the cicada wing-Au-Ag array in 35 ml of 0.12 mM 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide PBS buffer (pH = 7.4), stir, and incubate in a 25°C constant temperature shaker at 200 rpm in the dark for 50 min. Remove the cicada wings and rinse them with 15 ml of anhydrous ethanol and 15 ml of deionized water in sequence. Blow dry with nitrogen and then vacuum dry (25°C, 1 h) to obtain the cicada wing-Au-Ag flexible nano SERS array material.

[0042] Example 4 Preparation of cicada wing-Au-Ag flexible nano SERS array material:

[0043] S1: Using the pre-treated 1×1 cm cicada wings as the base template, the evaporation was performed by electron beam evaporation (the vacuum degree was less than 2×10 - 6 Torr, the target material is 99.999% high-purity gold, the evaporation deposition rate is 0.3 Å / s, and the sample stage rotation speed is 5 rpm) on its surface to uniformly load gold nanoparticles to form a cicada wing-Au nanofilm with a thickness of 12 nm;

[0044] S2: Add 12 ml of 0.4 wt% PVP solution to 40 ml of 2 mM AgNO3 solution and stir. Then immerse the cicada wing-Au nanofilm in the solution and stir. Control the temperature at 95°C. Then slowly add 12 ml of 0.5 w / v% sodium citrate solution dropwise for 10 minutes. After reacting for 40 minutes, remove the cicada wings and rinse them with 15 ml of ice water. Blow dry with nitrogen and vacuum dry (40°C, 2 hours) to obtain the cicada wing-Au-Ag array.

[0045] S3: Immerse the cicada wing-Au-Ag array in 30 ml of 0.15 mM 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide PBS buffer (pH = 7.4), stir, and incubate in a 25°C constant temperature shaker at 250 rpm in the dark for 60 min. Remove the cicada wings and rinse them with 15 ml of anhydrous ethanol and 15 ml of deionized water in sequence. Blow dry with nitrogen and then vacuum dry (25°C, 1 h) to obtain the cicada wing-Au-Ag flexible nano SERS array material.

[0046] The pretreatment steps of cicada wings in Example 2-4 are:

[0047] The hind wings of adult cicadas were cut into 1×1 cm squares with sterile scissors and ultrasonically cleaned in 50 ml acetone, 50 ml anhydrous ethanol and 50 ml deionized water at 25°C for 5 min. The cleaned cicada wings were transferred to a glass culture dish and placed in a sterile vacuum drying oven for vacuum drying (30°C, -0.095 MPa, 2 h) to remove water molecules and gases adsorbed on the surface.

[0048] Comparative Example 1 Preparation of Cicada Wing-Au-Ag Flexible Nano SERS Array Material:

[0049] The preparation method of the SERS array in this comparative example is basically the same as that in Example 3, except that the 35 ml 0.12 mM 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide PBS buffer in step S3 is replaced with 35 ml 0.12 mM 4-aminothiophenol PBS buffer.

[0050] Comparative Example 2 Preparation of Cicada Wing-Au-Ag Flexible Nano SERS Array Material:

[0051] The preparation method of the SERS array in this comparative example is basically the same as that in Example 3, except that the 35 ml of 0.12 mM 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide PBS buffer in step S3 is replaced with 35 ml of 0.12 mM 3-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide PBS buffer.

[0052] The preparation method of 3-mercapto-N-(4-mercaptophenyl)pyrrolidineamide is basically the same as that in Example 1, except that 1.0 mmol of 4-mercaptopyridine-2-carboxylic acid is replaced by an equal molar amount of 3-mercaptopyridine-2-carboxylic acid.

[0053] Comparative Example 3 Preparation of Cicada Wing-Au-Ag Flexible Nano SERS Array Material:

[0054] The preparation method of the SERS array in this comparative example is basically the same as that in Example 3, except that the 35 ml of 0.12 mM 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide PBS buffer in step S3 is replaced with 35 ml of 0.12 mM 6-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide PBS buffer.

[0055] The preparation method of 3-mercapto-N-(4-mercaptophenyl)pyrrolidineamide is basically the same as that in Example 1, except that 1.0 mmol of 4-mercaptopyridine-2-carboxylic acid is replaced by an equal molar amount of 6-mercaptopyridine-3-carboxylic acid.

[0056] Application Examples

[0057] Application of cicada wing-Au-Ag flexible nano-SERS array material in aging status assessment of No. 45 transformer oil:

[0058] (1) Preparation of standard solution: Furfural was added to No. 45 transformer oil and ultrasonicated for 20 min to prepare 0.01 mg / L, 0.1 mg / L, and 1 mg / L standard solutions respectively;

[0059] (2) The cicada wing-Au-Ag flexible nano-SERS array materials prepared in Examples 2-4 and Comparative Examples 1-3 were respectively transferred into a 1 mg / L standard solution and incubated in a constant temperature box at 60°C for 20 min to obtain test samples. The samples were marked as Example 2, Example 3-1, Example 4, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively;

[0060] The cicada wing-Au-Ag flexible nano SERS array material prepared in Example 3 was respectively transferred into 0.01 and 0.1 mg / L standard solutions and incubated in a constant temperature box at 60°C for 20 min to obtain test samples, which were labeled as Example 3-0.01 and Example 3-0.1, respectively.

[0061] (3) Raman spectroscopy was performed using an ATR-3000 portable Raman spectrometer (excitation light wavelength of 532 nm, laser power of 30 mW, integration time of 1 s, integration times of 10 times, slit width of 10 μm, and 1200 nm grating) to obtain furfural signal information.

[0062] Figure 1 Flowchart for preparing cicada wing-Au-Ag flexible nano SERS array material for Examples 2-4 of the present application.

[0063] Figure 2 is a scanning electron microscope photograph of the cicada wing-Au-Ag flexible nano SERS array material prepared in Example 3, wherein: Figure 2 The scale bar in (a) is 500 nm. Figure 2 The scale bar in (b) is 300 nm. Figure 2 The scale bar in (c) is 200 nm. Figure 2 The scale bar in (d) is 100 nm; Figure 2 Four SEM images at different magnifications show that the surface of cicada wings is covered with an average height of about 100 nm ( Figure 2 (b) is a SEM photo taken at a 45° tilt. The overall height of the "hills" on the surface of the cicada wing is about 100 nm). The ordered microscopic array structure, namely the nanohills, has a structural feature of being narrow at the top and wide at the bottom, with a diameter of about 100 nm at the widest point. The nanogaps between arrays are between 30-100 nm. This tightly arranged nanoarray structure with a specific size has an ultra-large specific surface area, which is more conducive to the attachment of precious metal nanomaterials and increases the distribution range of the substrate's Raman active sites. Secondly, the natural nanogaps formed between the hills can provide effective enrichment space for the molecules to be tested, making the adsorption of molecules on its surface more stable and uniform. Figure 2(bd) It can be seen that AgNPs with a particle size of about 10 nm (small particles on the surface of the small hill (appearing in a plush state), with a size of about 10 nm) are in situ grown on the cicada wing-Au surface. It can be observed from the figure that AgNPs with uniform particle size are evenly and densely attached to the cicada wing-Au surface, forming a highly ordered and tightly packed nanostructure. These evenly distributed AgNPs are conducive to a strong synergistic effect with the cicada wing-Au substrate, which greatly enhances the local electromagnetic field and thus improves the SERS activity.

[0064] like Figure 3 As shown, in Examples 2-4 of the present application, when the furfural concentration was 1 mg / L, the furfural was located at 1658 cm -1 The characteristic peak intensity at 1658 cm -1 There is still an obvious characteristic peak at the wave number 1658 cm -1 The Raman signal corresponding to furfural can still be observed nearby, with a furfural signal intensity of approximately 2642.45 au and a corresponding noise signal of approximately 818.30 au. The signal-to-noise ratio is approximately 3.23, satisfying the 3x signal-to-noise ratio relationship, indicating that this signal is valid. However, when an array obtained by coupling cicada wings with Au-Ag using other compounds is used to detect furfural in No. 45 transformer oil, the intensity of the characteristic peak is much lower than that of this application.

[0065] Figure 4 When 1 mg / L furfural in 45# transformer oil was detected at different positions on the cicada wing-Au-Ag array, furfural was located at 1658 cm -1 The Raman intensity histogram corresponding to the wave number range. During the test, the cicada wing-Au-Ag substrate (1×1cm) was placed according to Figure 5 The pattern is divided into 16 areas, and then 8 areas are selected ( Figure 5 8 numbered regions), one group of furfural signals was tested in each region, and the furfural signal at 1658 cm -1 The signal strength at the wave number is plotted into a bar graph by plotting the signal strength measured in 8 areas, such as Figure 4 As shown, it can be seen that the signal reproducibility of furfural is good, and its relative standard deviation is RSD=3.54%.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. However, any equivalent changes, modifications and evolutions made by ordinary technicians in this field without departing from the scope of the technical solution of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a cicada wing-Au-Ag flexible nano SERS array material, characterized in that: The following steps are involved: S1: Using the pre-treated cicada wings as the substrate template, gold nanoparticles are uniformly loaded on the surface by electron beam evaporation to form a cicada wing-Au nanofilm; S2: Add PVP solution to AgNO3 solution, stir, then immerse cicada wing-Au nanofilm, stir, control the temperature at 80-95°C, then slowly add sodium citrate solution, react for 40-60 minutes, and obtain cicada wing-Au-Ag array after post-treatment; S3: Immerse the cicada wing-Au-Ag array in PBS buffer containing 4-mercapto-N-(4-mercaptophenyl)pyrrolidinoamide, stir, and incubate in a constant temperature shaker in the dark. After post-treatment, a cicada wing-Au-Ag flexible nano-SERS array material is prepared. The thickness of the cicada wing-Au nanofilm in step S1 is 8-12 nm; In step S2, the concentration of the AgNO3 solution is 0.5-2 mM, the concentration of the sodium citrate solution is 0.5-2 w / v%, and the concentration of the PVP solution is 0.1-0.4 wt%; the volume ratio of the AgNO3 solution, the sodium citrate solution, and the PVP solution is 4:(0.8-1.2):(0.8-1.2).

2. The preparation method according to claim 1, characterized in that In step S3, the concentration of 4-mercapto-N-(4-mercaptophenyl)pyrrolidineamide in the PBS buffer of 4-mercapto-N-(4-mercaptophenyl)pyrrolidineamide is 0.1-0.15 mM, and the pH of the PBS buffer is 7.

4.

3. The preparation method according to claim 1, characterized in that In step S1, the pretreatment steps of the cicada wings are: Cut cicada wings into 1×1 cm squares with sterile scissors and place them in beakers of acetone, anhydrous ethanol, and deionized water for ultrasonic cleaning. Transfer the cleaned cicada wings to a glass Petri dish and place it in a sterile vacuum drying oven. The vacuum chamber is evacuated to remove water molecules and gases adsorbed on the surface.

4. The preparation method according to claim 1, characterized in that In step S1, the cicada wings are the hind wings of an adult cicada.

5. The preparation method according to claim 1, characterized in that In step S1, the parameters of electron beam evaporation are as follows: the target material is 99.999% high-purity gold, the evaporation deposition rate is 0.1–0.3 Å / s, and the sample stage rotation speed is 5–10 rpm.

6. A cicada wing-Au-Ag flexible nano SERS array material, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 5.

7. An application of the cicada wing-Au-Ag flexible nano SERS array material according to claim 6 in the aging status assessment of No. 45 transformer oil.

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