CnTs / ag / agnws / sio2 combined sers substrate, preparation method and pesticide detection method

Abstract

The application discloses a CNTs / Ag / AgNWS / SiO2 combined SERS substrate, which is formed by dropping a CNTs / Ag / AgNWS solution on a silica glass sheet and drying, wherein the mass percentage of each component in the CNTs / Ag / AgNWS solution is as follows: silver nanoparticles 26-60%, silver nanowires 30-55% and multi-walled carbon nanotubes 3-20%. The application successfully attaches Ag nanoparticles to multi-walled carbon nanotubes, and then makes silver nanowires staggered and superimposed on the multi-walled carbon nanotubes. The application adopts silver nanoparticles with strong electromagnetic enhancement capability, combines the silver nanoparticles with carbon nanotubes, and adds silver nanowires with different structural shapes, and further enhances the Raman signal by using the charge transfer of the semiconductor, so that the Raman signal can be greatly enhanced, and the detection limit can be improved, and a good effect can be obtained by using a simple structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pesticide residue analysis and detection, and particularly relates to a CNTs / Ag / AgNWS / SiO2 (multi-walled carbon nanotube surface combined with silver nanoparticles combined with silver nanowire silicon dioxide material composite substrate) combined SERS (surface enhanced Raman spectroscopy) substrate, a preparation method and a pesticide detection method. BACKGROUND

[0002] With the development of agricultural technology, in order to make crops grow smoothly, using pesticides to treat crops is a common method. However, as the crops mature, accidents caused by pesticide residues gradually increase, so it is necessary to detect the pesticide residues on the surface of the crops after they mature.

[0003] Nowadays, many pesticide detection methods have been proposed, such as traditional pesticide residue detection methods such as thin layer chromatography, gas chromatography, high performance liquid chromatography, supercritical fluid chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, high performance capillary electrophoresis, etc. Although stable and reliable, good repeatability, complex sample pretreatment, long detection time, and detection results lag, it is not suitable for on-site detection. Therefore, it is of great practical significance to study a rapid and efficient pesticide residue detection method. Surface enhanced Raman spectroscopy (SERS) technology has the advantages of high sensitivity, strong anti-interference, fluorescence quenching, etc., and the signal can be enhanced by 10 -5 -6 times, reaching the standard of practical application, so it has great advantages and application potential in rapid detection of pesticide residues in agricultural and sideline products.

[0004] Before analysis and testing by using a Raman spectrometer, a suitable Raman substrate is selected to detect and analyze the analyte through the surface enhanced Raman effect of the substrate. There are two important mechanisms of Raman spectroscopy, which are electromagnetic field enhancement (EM) and chemical enhancement (CM), and these two mechanisms are also the focus of the current research field of surface enhanced Raman spectroscopy. In the research field of the mechanism, more attention is paid to the preparation of the surface enhanced Raman substrate. Most of the existing substrate preparation processes are complex, the preparation conditions are single and require too high, it is not easy to mass-produce, the application is relatively single, and the cost is slightly high. Therefore, seeking a more economical and reliable high-activity SERS substrate preparation method is a general trend. SUMMARY

[0005] The purpose of the present application is to provide a CNTs / Ag / AgNWS / SiO2 combined SERS substrate, a preparation method and a pesticide detection method. The present application can realize large-area uniform construction of a SERS substrate with a complex structure at a low cost and simply.

[0006] ​To achieve the purpose, the application designs a CNTs / Ag / AgNWS / SiO2 combined SERS substrate, which is formed by dropping CNTs / Ag / AgNWS solution on a silica glass sheet, and drying, wherein the mass percentage of each component of CNTs / Ag / AgNWS in the CNTs / Ag / AgNWS solution is 26-60% of silver nanoparticles, 30-55% of silver nanowires and 3-20% of multi-walled carbon nanotubes. The above components and ratio can optimally improve the inspection sensitivity, stabilize the substrate structure and have better performance. The essence of silver nanoparticles and silver nanowires is related to silver, and silver is a noble metal, which greatly improves the Raman enhancement effect.

[0007] A preparation method of a CNTs / Ag / AgNWS / SiO2 combined SERS substrate, which comprises the following steps:

[0008] Step 1: adding AgNO3 standard solution in deionized water;

[0009] Step 2: adding multi-walled carbon nanotube dispersion solution in the solution obtained in step 1 to obtain a mixed solution, and mixing the multi-walled carbon nanotube dispersion solution and the silver nitrate solution with a dilution concentration;

[0010] Step 3: using oil bath to magnetically stir and heat the mixed solution, and using oil bath to ensure constant temperature, thereby reducing the influence of temperature fluctuation on chemical reaction;

[0011] Step 4: adding sodium citrate solution in the solution after magnetic stirring and heating in step 3, and taking out after continuing to heat and cooling to room temperature, wherein the strong reducing property of sodium citrate solution in high-temperature water reduces Ag ions in AgNO3 into Ag nanoparticles;

[0012] Step 5: centrifuging the sample cooled to room temperature in step 4, and dispersing the centrifuged product in deionized water for storage at room temperature, wherein the Ag nanoparticles in the substrate are obtained, and the centrifuged product is the silver nanoparticles reduced by sodium citrate;

[0013] Step 6: preparing a new portion of deionized water, adding AgNO3 standard solution in the deionized water and performing ultrasonic oscillation cleaning;

[0014] Step 7: adding D(+) glucose powder in the deionized water and performing ultrasonic oscillation cleaning;

[0015] Step 8: adding polyvinylpyrrolidone (PVP) powder in the deionized water and performing ultrasonic oscillation cleaning;

[0016] Step 9: Add the NaCl standard solution into the deionized water and perform ultrasonic oscillation cleaning;

[0017] Step 10: Place the solution after ultrasonic oscillation cleaning in step 6 on a magnetic stirrer, add a magnetic stirrer in a beaker, and add the solution after ultrasonic oscillation cleaning in step 7 to perform magnetic stirring;

[0018] Step 11: Add the solution after ultrasonic oscillation cleaning in step 8 to the solution after magnetic stirring in step 10, and continue to perform magnetic stirring;

[0019] Step 12: Add the solution after ultrasonic oscillation cleaning in step 9 to the solution after magnetic stirring in step 11, and continue to perform magnetic stirring, so as to realize the full mixing of the solutions in the above three steps;

[0020] Step 13: Add the solution after magnetic stirring in step 12 to a reaction kettle (stainless steel autoclave lined with polytetrafluoroethylene), and perform heating in a drying box. The stainless steel autoclave lined with polytetrafluoroethylene is stable at room temperature and normal pressure, has no true melting point, and is insoluble in any solvent;

[0021] Step 14: After the heating in step 13 is completed, take out the reaction kettle and place it in a safe place. Cool the reaction kettle to room temperature in air without assistance (i.e., natural cooling). After cooling, move the liquid in the reaction kettle to a centrifuge tube;

[0022] Step 15: Perform centrifugation on the liquid in the centrifuge tube, remove the liquid above the centrifuge tube with a rubber bulb dropper, and collect the remaining fluffy off-white precipitate. Add the fluffy off-white precipitate to deionized water. The fluffy off-white precipitate is silver nanowires and impurities;

[0023] Step 16: Perform ultrasonic oscillation on the deionized water containing the precipitate obtained in step 15 to obtain a gray suspension. At this time, the suspension contains silver nanowires in the substrate;

[0024] Step 17: Take out the standby solution in step 5 with a rubber bulb dropper and add it to a test tube. Then add the suspension obtained in step 16 to the test tube, and perform ultrasonic oscillation on the mixed solution using an ultrasonic cleaning instrument. Prepare a CNTs / Ag / AgNWs solution and seal it. At this time, Ag nanoparticles are attached to the multi-walled carbon nanotubes, and silver nanowires are randomly stacked on the multi-walled carbon nanotubes. The mass percentage of each component in the CNTs / Ag / AgNWs solution is 26-60% for silver nanoparticles, 30-55% for silver nanowires, and 3-20% for multi-walled carbon nanotubes;

[0025] Step 18: Drop the CNTs / Ag / AgNWs solution obtained in Step 17 onto a silica glass slide and let it dry to obtain a SERS substrate with CNTs / Ag / AgNWs bound to SiO2.

[0026] In the above technical solution, the deionized water used in each step is prepared separately.

[0027] In step 1 of the above technical solution, AgNO3 standard solution is added to deionized water and stirred to dilute the 0.01–1 mol / L AgNO3 to 0.001–0.01 mol / L. The volume ratio of deionized water to AgNO3 standard solution is 57–95:3–5. Only by diluting silver nitrate to this concentration can silver nanoparticles with suitable effect and size be obtained during the subsequent reduction of silver nanoparticles with sodium citrate.

[0028] In step 2 of the above technical solution, the volume ratio of the solution obtained in step 1 to the multi-walled carbon nanotube dispersion solution is 60–100: 0.1–0.6. Within this range, the multi-walled carbon nanotube dispersion solution can be thoroughly mixed with the diluted silver nitrate solution.

[0029] In step 3 of the above technical solution, the mixed solution obtained in step 2 is stirred for 15-25 minutes using a magnetic stirrer with a rotation speed of 100-300 r / min, and heated to 80-105℃. This allows the carbon nanotube dispersion and AgNO3 solution to mix thoroughly, preparing for the subsequent attachment of more Ag nanoparticles onto the multi-walled carbon nanotubes. The mixture is then transferred to a constant-temperature oil bath heater, using oil bath heating to ensure constant temperature conditions and reduce the impact of temperature fluctuations on the chemical reaction. This operation ensures that most silver nanoparticles are ultimately adsorbed onto the multi-walled carbon nanotubes.

[0030] In step 4 of the above technical solution, a sodium citrate solution with a mass fraction of 0.5-1% is added. The volume ratio of the mixed solution in step 2 to the sodium citrate solution is 95-200:2-6. Within this range, sodium citrate can effectively exert its own properties and fully reduce a large number of silver nanoparticles.

[0031] In step 4, continue heating at 80-105℃ for 35-50 minutes. During heating, seal the beaker with plastic wrap. After heating, remove it and cool it to room temperature. At this time, the strong reducing power of sodium citrate solution in high-temperature water reduces the Ag ions in AgNO3 into Ag nanoparticles.

[0032] In step 5 of the above technical solution, the centrifugation process involves centrifuging at a speed of 4000-4800 r / min for 80-100 minutes using a centrifuge. The centrifuged product is then dispersed in 3-6 mL of deionized water. Selecting centrifugation can greatly shorten the separation time.

[0033] In step 6, AgNO3 standard solution is added to deionized water and ultrasonically vibrated for 1 to 5 minutes to dilute 0.1 to 1 mol / L AgNO3 to 0.01 to 0.03 mol / L. The volume ratio of deionized water to AgNO3 standard solution is 10 to 30: 2 to 6.

[0034] In step 7 of the above technical solution, the mass range of D(+) glucose powder is 0.05-0.2g, the deionized water range is 3-6ml, and ultrasonic oscillation is performed for 1-5 minutes to allow the D(+) glucose powder to be fully dissolved in the deionized water;

[0035] In step 8, the mass range of polyvinylpyrrolidone powder is 0.5-2g, the deionized water range is 3-6ml, and the mixture is ultrasonically vibrated for 1-5 minutes to allow the polyvinylpyrrolidone powder to be fully dissolved in the deionized water.

[0036] In step 9, add NaCl standard solution to deionized water and sonicate for 1 to 5 minutes to dilute 0.1 to 1 mol / L NaCl to 0.01 to 0.06 mol / L. The volume ratio of deionized water to NaCl standard solution is 10 to 30: 0.1 to 1 to ensure that the NaCl solution and deionized water are fully mixed.

[0037] In step 10 of the above technical solution, the magnetic stirring speed range is 100-150 r / min;

[0038] In steps 11 and 12, D(+) glucose solution, polyvinylpyrrolidone solution, and NaCl standard solution are added to the AgNo3 solution. The volume ratio of D(+) glucose solution to AgNo3 solution is 3-5:15-30, the volume ratio of polyvinylpyrrolidone solution to AgNo3 solution is 3-5:15-30, and the volume ratio of NaCl standard solution to AgNo3 solution is 10-30:15-30, to ensure that the added solutions are thoroughly mixed.

[0039] D(+) glucose solution specifications: analytical grade, purity >99.5%;

[0040] The PVP (polyvinylpyrrolidone) solution is a polyvinylpyrrolidone solution with a mass fraction of 2-5% and a relative molecular mass of 40,000.

[0041] The concentration range of NaCl solution is 0.01–1 mol / L.

[0042] In step 13, the heating temperature range is 140–180℃, and the heating time is 20–24 hours;

[0043] In steps 15 and 16, the volume ratio of deionized water to the mixed solution obtained in step 14 is 2-6:40-60, the centrifuge speed is 2300-3000 r / min, and the centrifugation time is 50-70 minutes.

[0044] The volume ratio of the prepared solution from step 5 to the suspension obtained in step 16 added to the test tube in step 17 is 1:1.

[0045] A method for pesticide spectral detection using the above-mentioned CNTs / Ag / AgNWS / SiO2 combined SERS substrate is characterized by the following: the detection method involves dropping the probe molecule rhodamine and the pesticide onto the CNTs / Ag / AgNWS / SiO2 combined SERS substrate, then allowing it to stand and air dry naturally, and finally performing Raman detection to obtain the Raman test pattern of the pesticide, wherein the pesticide is thiram or diquat.

[0046] Compared with the prior art, the present invention improves the structure and preparation, and has the following technical effects:

[0047] 1. Structural Innovation: Ag nanoparticles were successfully attached to multi-walled carbon nanotubes, and then silver nanowires were stacked onto the multi-walled carbon nanotubes in a staggered manner. Silver nanoparticles with strong electromagnetic enhancement capabilities were used and combined with carbon nanotubes, and silver nanowires of different structural shapes were added. The charge transfer of semiconductors was utilized to further enhance the Raman signal, which greatly enhances the Raman signal and ultimately improves the detection limit. Good results were achieved with a simple structure.

[0048] 2. Low preparation requirements: The preparation process can be completed at room temperature, the operation is relatively simple, the time required is short, the cost is low, and it is easy to replicate.

[0049] 3. Excellent substrate performance: In practical applications, it can detect low concentrations of thiram pesticides and has strong uniformity and stability. Attached Figure Description

[0050] Figure 1 Flowchart for the fabrication of CNTs / Ag / AgNWS / SiO2 SERS substrate;

[0051] Figure 2 TEM image of a CNTs / Ag / AgNWS / SiO2 SERS substrate;

[0052] Figure 3 Physical image of CNTs / Ag / AgNWS / SiO2 SERS substrate;

[0053] Figure 4 Raman spectroscopy pattern of rhodamine probe molecule used on CNTs / Ag / AgNWS / SiO2 SERS substrate;

[0054] Figure 5 Raman spectroscopy results for the stability of the CNTs / Ag / AgNWS / SiO2 SERS substrate;

[0055] Figure 6 Raman spectroscopy results for the uniformity of the CNTs / Ag / AgNWS / SiO2 SERS substrate;

[0056] Figure 7 Raman spectroscopy results for CNTs / Ag / AgNWS / SiO2 SERS substrates using the pesticide thiram; Detailed Implementation

[0057] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0058] Example 1

[0059] A CNTs / Ag / AgNWS / SiO2-bonded SERS substrate is formed by dropping a CNTs / Ag / AgNWS solution onto a silica glass slide and drying it. The CNTs / Ag / AgNWS solution contains silver nanoparticles (46%), silver nanowires (46%), and multi-walled carbon nanotubes (8%) by mass percentage.

[0060] Methods for preparing SERS substrates combining CNTs / Ag / AgNWS / SiO2, such as Figure 1 As shown, it includes the following steps:

[0061] Step 1: Add 5 ml of AgNO3 standard solution to 95 ml of deionized water and stir for 10 minutes. At this time, the solution is colorless.

[0062] Step 2: Add 0.5 ml of multi-walled carbon nanotube dispersion solution to the above colorless solution, mix them, and stir for 5 minutes. At this time, the solution changes from colorless to black.

[0063] Step 3: Use an oil bath at 200 r / min to magnetically stir the above black solution and heat it to 95°C;

[0064] Step 4: After heating to 95°C, add 2 mL of 1% sodium citrate solution to the black solution, maintain the temperature at 95°C and heat and stir for 40 minutes. After 40 minutes, remove it and cool it to room temperature.

[0065] Step 5: Centrifuge the black solution sample that has been cooled to room temperature at a speed of 4500 r / min for 90 minutes. After centrifugation, disperse the centrifuged product in 5 mL of deionized water and store it at room temperature for later use.

[0066] Step 6: Add 12 mL of deionized water to a 100 mL beaker. Measure 3 mL of 0.1 mol / L AgNO3 standard solution from a test tube and add it to the beaker containing the deionized water. Stir for 10 minutes, then sonicate for 2 minutes to prepare a 0.02 mol / L AgNO3 solution. At this point, the solution is colorless.

[0067] Step 7: Weigh 0.12g of D(+) glucose using an electronic balance, add it to 5ml of deionized water, and sonicate for 2 minutes before sealing and storing.

[0068] Step 8: Weigh 1g of PVP powder using an electronic balance, add it to 5ml of deionized water, then sonicate for 2 minutes and seal for later use.

[0069] Step 9: Measure 0.6 mL of 1 mol / L NaCl standard solution into a test tube, add it to 14.4 mL of deionized water, and sonicate for 2 minutes to prepare a 0.04 mol / L NaCl solution. Seal and store for later use.

[0070] Step 10: Place the AgNO3 solution prepared in step 6 on a magnetic stirrer, add a magnetic stir bar to the beaker, then add the glucose solution to the AgNO3 solution, and stir continuously at 120 r / min for 10 minutes;

[0071] Step 11: Add the PVP solution prepared in step 8 to the solution in step 10, and continue stirring for 20 minutes to ensure that the solution is mixed evenly;

[0072] Step 12: Add the NaCl solution prepared in step 9 to the solution in step 11, and continue stirring for 10 minutes to make the solution completely and uniformly mixed. At this time, the solution in the beaker is a turbid hydrosol.

[0073] Step 13: Add the hydrosol solution prepared in step 12 into a stainless steel autoclave with a capacity of 50 mL PTFE liner, and heat it continuously in a drying oven at 160°C for 22 hours.

[0074] Step 14: After heating is complete, remove the stainless steel autoclave and place it in a safe location. Cool the autoclave to room temperature in the air without any assistance. After cooling, transfer the liquid in the polytetrafluoroethylene liner to a centrifuge tube.

[0075] Step 15: Centrifuge the solution from Step 14 at 2500 r / min for 60 minutes. Remove the liquid at the top of the centrifuge tube with a dropper and collect the remaining fluffy grayish-white precipitate. Add the precipitate to 5 mL of deionized water. The volume ratio of deionized water to the mixed solution obtained in Step 14 is 5:40.

[0076] Step 16: Use an ultrasonic cleaner to ultrasonically vibrate the solution from step 15 for 10 minutes to obtain a gray suspension, which is then stored for later use.

[0077] Step 17: Use a dropper to take 3 mL of the CNTs / AgNPs solution obtained in Step 5 and add it to a centrifuge tube. Then add 3 mL of the AgNWS solution obtained in Step 16. After that, use an ultrasonic cleaner to sonicate the mixed solution for 20 minutes to mix the two solutions evenly. Then seal the prepared CNTs / Ag / AgNWs and refrigerate it at 4°C for later use.

[0078] Step 18: Apply the CNTs / Ag / AgNWs suspension onto the cleaned glass slide, allow it to air dry naturally, and then seal it at 4 degrees Celsius for later use. Figure 2 The image shows a TEM image of the CNTs / Ag / AgNWs SERS substrate. As can be seen from the image, silver nanoparticles are adsorbed onto multi-walled carbon nanotubes, and silver nanowires are stacked on the multi-walled carbon nanotubes in a staggered manner. This indicates that the preparation of this substrate structure is completely feasible and has good results. Figure 3 This is a photo of the base after it has dried.

[0079] Step 19: Place the SERS substrate with CNTs / Ag / AgNWs / SiO2 bound in Step 18 for 1 day, 7 days, 15 days, 30 days, and 45 days, respectively. Then, detect 10 at days 1, 7, 15, 30, and 45. -8 The results for rhodamine at a concentration of mol / L are as follows: Figure 5 As shown, rhodamine can still be detected well even after the substrate has been placed for a relatively long time (45 days), which proves that the substrate has good stability.

[0080] Step 20: Perform Raman spectroscopy on the SERS substrate with CNTs / Ag / AgNWs / SiO2 bound in Step 18, randomly selecting 5 test points, such as... Figure 6 As shown in the figure, the signals at the five randomly selected points are good, indicating that the substrate has good uniformity.

[0081] Example 2:

[0082] A CNTs / Ag / AgNWS / SiO2-bonded SERS substrate is formed by dropping a CNTs / Ag / AgNWS solution onto a silica glass slide and drying it. The CNTs / Ag / AgNWS solution contains silver nanoparticles (45%), silver nanowires (45%), and multi-walled carbon nanotubes (10%) by mass percentage.

[0083] Methods for preparing SERS substrates combining CNTs / Ag / AgNWS / SiO2, such as Figure 1 As shown, it includes the following steps:

[0084] Step 1: Add 4 ml of AgNO3 standard solution to 90 ml of deionized water and stir for 10 minutes. At this time, the solution is colorless.

[0085] Step 2: Add 0.4 ml of multi-walled carbon nanotube dispersion solution to the above colorless solution, mix them, and stir for 5 minutes. At this time, the solution changes from colorless to black.

[0086] Step 3: Use an oil bath at 300 r / min to magnetically stir the above black solution and heat it to 100°C;

[0087] Step 4: After heating to 100℃, add 5mL of 0.5% sodium citrate solution to the black solution, maintain the temperature at 100℃ and heat and stir for 45 minutes. After 45 minutes, remove it and cool it to room temperature.

[0088] Step 5: Centrifuge the black solution sample cooled to room temperature at a speed of 4800 r / min for 95 minutes. After centrifugation, disperse the product in 6 mL of deionized water and store it at room temperature for later use.

[0089] Step 6: Add 16 mL of deionized water to a 100 mL beaker. Measure 4 mL of 0.1 mol / L AgNO3 standard solution from a test tube and add it to the beaker containing the deionized water. Stir for 10 minutes, then sonicate for 2 minutes to prepare a 0.02 mol / L AgNO3 solution. At this point, the solution is colorless.

[0090] Step 7: Weigh 0.2g of D(+) glucose using an electronic balance, add it to 3ml of deionized water, and sonicate for 2 minutes before sealing and storing.

[0091] Step 8: Weigh 1.5g of PVP powder using an electronic balance, add it to 3ml of deionized water, then sonicate for 2 minutes and seal for later use.

[0092] Step 9: Measure 1 mL of 1 mol / L NaCl standard solution into a test tube, add it to 24 mL of deionized water, and sonicate for 2 minutes to prepare a 0.04 mol / L NaCl solution. Seal and store for later use.

[0093] Step 10: Place the AgNO3 solution prepared in step 6 on a magnetic stirrer, add a magnetic stir bar to the beaker, and then add the glucose solution to the AgNO3 solution. Stir continuously for 10 minutes at a speed of 150 r / min.

[0094] Step 11: Add the PVP solution prepared in step 8 to the solution in step 10, and continue stirring for 20 minutes to ensure that the solution is mixed evenly;

[0095] Step 12: Add the NaCl solution prepared in step 9 to the solution in step 11, and continue stirring for 10 minutes to make the solution completely and uniformly mixed. At this time, the solution in the beaker is a turbid hydrosol.

[0096] Step 13: Add the hydrosol solution prepared in step 12 into a stainless steel autoclave with a capacity of 50 mL PTFE liner, and heat it continuously in a drying oven at 140°C for 20 hours.

[0097] Step 14: After heating is complete, remove the stainless steel autoclave and place it in a safe location. Cool the autoclave to room temperature in the air without any assistance. After cooling, transfer the liquid in the polytetrafluoroethylene liner to a centrifuge tube.

[0098] Step 15: Centrifuge the solution from Step 14 at 3000 r / min for 50 minutes. Use a dropper to remove the liquid at the top of the centrifuge tube and collect the remaining fluffy grayish-white precipitate. Add the precipitate to 3 mL of deionized water. The volume ratio of deionized water to the mixed solution obtained in Step 14 is 3:51.

[0099] Step 16: Use an ultrasonic cleaner to ultrasonically vibrate the solution from step 15 for 10 minutes to obtain a gray suspension, which is then stored for later use.

[0100] Step 17: Take 2 mL of the CNTs / AgNPs solution obtained in Step 5 using a dropper and add it to a centrifuge tube. Then add 2 mL of the suspension (AgNWS solution) obtained in Step 16. After that, use an ultrasonic cleaner to sonicate the mixed solution for 20 minutes to mix the two solutions evenly. Then seal the prepared CNTs / Ag / AgNWs and refrigerate it at 4°C for later use.

[0101] Step 18: Drop the CNTs / Ag / AgNWs solution onto the cleaned glass slide, let it air dry naturally, and then seal it for later use at 4°C.

[0102] Step 19: Place the SERS substrate with CNTs / Ag / AgNWs / SiO2 bound in Step 18 for 1 day, 7 days, 15 days, 30 days, and 45 days, respectively. Then, detect 10 at days 1, 7, 15, 30, and 45. -8 The results for rhodamine at a concentration of mol / L are as follows: Figure 5 As shown, rhodamine can still be detected well even after the substrate has been placed for a relatively long time (45 days), which proves that the substrate has good stability.

[0103] Step 20: Perform Raman spectroscopy on the SERS substrate with CNTs / Ag / AgNWs / SiO2 bound in Step 18, randomly selecting 5 test points, such as... Figure 6 As shown in the figure, the signals at the five randomly selected points are good, indicating that the substrate has good uniformity.

[0104] Test Example 1:

[0105] To prepare a rhodamine solution, 0.0479 g of rhodamine red solid powder was weighed using an electronic balance and added to 100 mL of deionized water, yielding 10... -3 1 mL of mol / L R6G stock solution. -3 A mol / L R6G stock solution was added to a centrifuge tube, followed by the addition of deionized water to bring the volume to 10 mL, yielding 10 mol / L. -4 Dilute the R6G solution to 1 mol / L (i.e., 1 ml R6G + 9 ml deionized water) and so on to a concentration of 10 mol / L. -12 mol / L.

[0106] Different concentrations of Rhodamine solutions were dropped onto the silica glass slide of Example 1, and then left to air dry naturally. After air drying, Raman spectroscopy was performed. Figure 4 Raman spectroscopy patterns of the CNTs / Ag / AgNWs / SiO2-bound SERS substrate obtained in Example 1 were obtained using different concentrations of the probe molecule rhodamine. Figure 4 It can be seen that the probe molecule rhodamine at a low concentration of 10 -12 It can still be detected at mol / L, indicating that the substrate has good detection performance.

[0107] Test Example 2:

[0108] Preparation of thiram solution:

[0109] 10 mg / L thiram diethanol solution: Weigh 0.01 g of thiram powder using an electronic balance, add it to 100 mL of ethanol, and sonicate for 2 min to prepare a 10 mg / L thiram diethanol solution;

[0110] 5 mg / L thiram diethanol solution: Take 5 mL of 10 mg / L thiram diethanol solution with a dropper and add 5 mL of ethanol to form a 5 mg / L thiram diethanol solution;

[0111] 1 mg / L thiram diethanol solution: Take 1 mL of 10 mg / L thiram diethanol solution with a dropper and add 9 mL of ethanol to form a 1 mg / L thiram diethanol solution;

[0112] 0.1 mg / L thiram diethanol solution: Take 1 mL of 1 mg / L thiram diethanol solution with a dropper and add 9 mL of ethanol to form a 0.1 mg / L thiram diethanol solution.

[0113] 0.01 mg / L thiram diethanol solution: Take 1 mL of 0.1 mg / L thiram diethanol solution with a dropper and add 9 mL of ethanol to form a 0.01 mg / L thiram diethanol solution.

[0114] Then, convert them into thiram solutions of different concentrations and let them stand at room temperature for later use.

[0115] Different concentrations of thiram solution were dropped onto the silica glass slide of Example 1, and then left to air dry naturally. After air drying, Raman spectroscopy was performed. Figure 7 Raman spectroscopy images of CNTs / Ag / AgNWs / SiO2-bound SERS substrates using different concentrations of the pesticide thiram were obtained by [the following text is missing from the original] Figure 7 It can be seen that the pesticide thiram can still be detected at a low concentration of 0.01 mg / L, indicating that the substrate has good detection performance and high sensitivity, making it suitable for the detection of thiram residues.

[0116] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A SERS substrate combining CNTs / Ag / AgNWS / SiO2, characterized in that: The CNTs / Ag / AgNWS / SiO2-bonded SERS substrate is formed by dropping a CNTs / Ag / AgNWS solution onto a silica glass slide and drying it. The mass percentage of each component of the CNTs / Ag / AgNWS in the CNTs / Ag / AgNWS solution is 26-60% silver nanoparticles, 30-55% silver nanowires, and 3-20% multi-walled carbon nanotubes. The preparation method of the CNTs / Ag / AgNWS solution is as follows: Step 1: Add AgNO3 standard solution to deionized water; Step 2: Add multi-walled carbon nanotube dispersion to the solution obtained in Step 1 and mix to obtain a mixed solution; Step 3: Use an oil bath to magnetically stir and heat the above mixture; Step 4: Add sodium citrate solution to the solution after magnetic stirring and heating in Step 3, continue heating, and then remove and cool to room temperature; Step 5: Centrifuge the sample cooled to room temperature in Step 4, then disperse the centrifuged product in deionized water and store it at room temperature for later use. At this time, Ag nanoparticles in the substrate are obtained. Step 6: Prepare a new batch of deionized water, add AgNO3 standard solution to the deionized water, and perform ultrasonic oscillation cleaning; Step 7: Add D(+) glucose powder to deionized water and perform ultrasonic oscillation cleaning; Step 8: Add polyvinylpyrrolidone powder to deionized water and perform ultrasonic oscillation cleaning; Step 9: Add NaCl standard solution to deionized water and perform ultrasonic oscillation cleaning; Step 10: Place the solution after ultrasonic cleaning in step 6 onto a magnetic stirrer, add a magnetic stir bar to the beaker, and add the solution after ultrasonic cleaning in step 7 for magnetic stirring. Step 11: Add the solution after ultrasonic oscillation cleaning in step 8 to the solution after magnetic stirring in step 10, and continue magnetic stirring; Step 12: Add the solution after ultrasonic oscillation cleaning in Step 9 to the solution after magnetic stirring in Step 11, and continue magnetic stirring; Step 13: Add the solution after magnetic stirring in step 12 to the reaction vessel and heat it; Step 14: After heating in Step 13 is complete, remove the reactor and cool it to room temperature. After cooling, transfer the liquid in the reactor to a centrifuge tube. Step 15: Centrifuge the liquid in the reactor in a centrifuge tube, collect the precipitate, and add it to deionized water; Step 16: The deionized water containing the precipitate obtained in Step 15 is subjected to ultrasonic vibration to obtain a suspension; Step 17: Add the prepared solution from step 5 to a test tube, then add the suspension obtained in step 16 to the test tube and perform ultrasonic oscillation to prepare the CNTs / Ag / AgNWs solution.

2. A method for preparing a SERS substrate combining CNTs / Ag / AgNWS / SiO2, characterized in that, It includes the following steps: Step 1: Add AgNO3 standard solution to deionized water; Step 2: Add multi-walled carbon nanotube dispersion to the solution obtained in Step 1 and mix to obtain a mixed solution; Step 3: Use an oil bath to magnetically stir and heat the above mixture; Step 4: Add sodium citrate solution to the solution after magnetic stirring and heating in Step 3, continue heating, and then remove and cool to room temperature; Step 5: Centrifuge the sample cooled to room temperature in Step 4, then disperse the centrifuged product in deionized water and store it at room temperature for later use. At this time, Ag nanoparticles in the substrate are obtained. Step 6: Prepare a new batch of deionized water, add AgNO3 standard solution to the deionized water, and perform ultrasonic oscillation cleaning; Step 7: Add D(+) glucose powder to deionized water and perform ultrasonic oscillation cleaning; Step 8: Add polyvinylpyrrolidone powder to deionized water and perform ultrasonic oscillation cleaning; Step 9: Add NaCl standard solution to deionized water and perform ultrasonic oscillation cleaning; Step 10: Place the solution after ultrasonic cleaning in step 6 onto a magnetic stirrer, add a magnetic stir bar to the beaker, and add the solution after ultrasonic cleaning in step 7 for magnetic stirring. Step 11: Add the solution after ultrasonic oscillation cleaning in step 8 to the solution after magnetic stirring in step 10, and continue magnetic stirring; Step 12: Add the solution after ultrasonic oscillation cleaning in Step 9 to the solution after magnetic stirring in Step 11, and continue magnetic stirring; Step 13: Add the solution after magnetic stirring in step 12 to the reaction vessel and heat it; Step 14: After heating in Step 13 is complete, remove the reactor and cool it to room temperature. After cooling, transfer the liquid in the reactor to a centrifuge tube. Step 15: Centrifuge the liquid in the reactor in a centrifuge tube, collect the precipitate, and add it to deionized water; Step 16: The deionized water containing the precipitate obtained in Step 15 is subjected to ultrasonic vibration to obtain a suspension; Step 17: Add the prepared solution from step 5 to a test tube, then add the suspension obtained in step 16 to the test tube and perform ultrasonic oscillation to prepare the CNTs / Ag / AgNWs solution. Step 18: Drop the CNTs / Ag / AgNWs solution obtained in Step 17 onto a silica glass slide and let it dry to obtain a SERS substrate with CNTs / Ag / AgNWs bound to SiO2.

3. The method for preparing the CNTs / Ag / AgNWS / SiO2-bonded SERS substrate according to claim 2, characterized in that: In step 1, AgNO3 standard solution is added to deionized water and stirred to dilute 0.01-1 mol / L AgNO3 to 0.001-0.01 mol / L. The volume ratio of deionized water to AgNO3 standard solution is 57-95:3-5.

4. The method for preparing the CNTs / Ag / AgNWS / SiO2-bonded SERS substrate according to claim 2, characterized in that: The volume ratio of the solution obtained in step 1 to the multi-walled carbon nanotube dispersion solution is 60–100: 0.1–0.

6.

5. The method for preparing the CNTs / Ag / AgNWS / SiO2-bonded SERS substrate according to claim 2, characterized in that: In step 3, the mixture obtained in step 2 is stirred for 15 to 25 minutes using a magnetic stirrer with a speed of 100 to 300 r / min, and the mixture is heated to 80 to 105°C. Then the mixture is transferred to a constant temperature oil bath heater to ensure constant temperature conditions.

6. The method for preparing the CNTs / Ag / AgNWS / SiO2-bonded SERS substrate according to claim 2, characterized in that: In step 4, a sodium citrate solution with a mass fraction of 0.5-1% is added, and the volume ratio of the mixed solution in step 2 to the sodium citrate solution is 95-200:2-6. In step 4, continue heating at 80-105°C for 35-50 minutes. During heating, seal the beaker with plastic wrap. After heating, remove it and cool it to room temperature.

7. The method for preparing the CNTs / Ag / AgNWS / SiO2-bonded SERS substrate according to claim 2, characterized in that: In step 5, the centrifugation process involves centrifuging at 4000–4800 r / min for 80–100 minutes, and then dispersing the centrifuged product in 3–6 mL of deionized water. In step 6, AgNO3 standard solution is added to deionized water and ultrasonically vibrated for 1 to 5 minutes to dilute 0.1 to 1 mol / L AgNO3 to 0.01 to 0.03 mol / L. The volume ratio of deionized water to AgNO3 standard solution is 10 to 30: 2 to 6.

8. The method for preparing a SERS substrate combining CNTs / Ag / AgNWS / SiO2 according to claim 2, characterized in that: In step 7, the mass range of D(+) glucose powder is 0.05-0.2g, the deionized water range is 3-6ml, and the ultrasonic oscillation is performed for 1-5 minutes; In step 8, the mass range of polyvinylpyrrolidone powder is 0.5-2g, the mass range of deionized water is 3-6ml, and the ultrasonic oscillation is performed for 1-5 minutes; In step 9, add NaCl standard solution to deionized water and sonicate for 1 to 5 minutes to dilute 0.1 to 1 mol / L NaCl to 0.01 to 0.06 mol / L. The volume ratio of deionized water to NaCl standard solution is 10 to 30: 0.1 to 1.

9. The method for preparing a SERS substrate combining CNTs / Ag / AgNWS / SiO2 according to claim 2, characterized in that: In step 10, the magnetic stirring speed range is 100–150 r / min; In steps 11 and 12, D(+) glucose solution, polyvinylpyrrolidone solution, and NaCl standard solution are added to the AgNO3 solution. The volume ratio of D(+) glucose solution to AgNO3 solution is 3-5:15-30, the volume ratio of polyvinylpyrrolidone solution to AgNO3 solution is 3-5:15-30, and the volume ratio of NaCl standard solution to AgNO3 solution is 10-30:15-30. In step 13, the heating temperature range is 140–180℃, and the heating time is 20–24 hours; In steps 15 and 16, the volume ratio of deionized water to the mixed solution obtained in step 14 is 2-6:40-60, the centrifuge speed is 2300-3000 r / min, and the centrifugation time is 50-70 minutes. In step 17, the volume ratio of the prepared solution from step 5 to the suspension obtained in step 16 added to the test tube is 1:

1.

10. A method for dual-spectral detection of the pesticide thiram using a SERS substrate combining CNTs / Ag / AgNWS / SiO2 as described in claim 1, characterized in that: The detection method involves dropping the probe molecule rhodamine and the pesticide thiram onto a SERS substrate bound to CNTs / Ag / AgNWS / SiO2, allowing it to stand and dry, and then performing Raman detection to obtain the Raman spectrum of the pesticide thiram.

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