CN116482073A - CNTs/Ag/AgNWS/SiO 2 Combined SERS substrate, preparation method and pesticide detection method - Google Patents

Abstract

The invention discloses a SERS substrate combined with CNTs/Ag/AgNWS/ _SiO2 , which is formed by dropping a CNTs/Ag/AgNWS solution onto a silica glass sheet and drying it. The mass percentages of each component of the CNTs/Ag/AgNWS in the CNTs/Ag/AgNWS solution are 26-60% of silver nanoparticles, 30-55% of silver nanowires and 3-20% of multi-walled carbon nanotubes. The invention allows the Ag nanoparticles to be successfully attached to the multi-wall carbon nanotubes, and then the silver nanowires are scattered and superimposed on the multi-wall carbon nanotubes. Silver nanoparticles with strong electromagnetic enhancement ability are used, combined with carbon nanotubes, and silver nanowires with different structural shapes are added, and the charge transfer of semiconductors is used to further enhance the Raman signal, which can greatly enhance the Raman signal, and finally achieve the purpose of improving the detection limit, and obtain better results with a simple structure.

Description

CNTs/Ag/AgNWS/SiO2 Combined SERS Substrate, Preparation Method and Pesticide Detection method

technical field

The invention relates to the technical field of analysis and detection of pesticide residues, in particular to a CNTs/Ag/AgNWS/ _SiO2 (multi-walled carbon nanotube surface combined with silver nanoparticles combined with silver nanowire silica material composite substrate) combined SERS (surface-enhanced Raman spectroscopy) substrate, preparation method and pesticide detection method.

Background technique

With the development of agricultural technology, in order to make the crops grow smoothly, it is a common method to use pesticides to treat the crops. However, after 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.

Nowadays, many pesticide detection methods have been proposed, 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 and other traditional pesticide residue detection methods. Therefore, it is of great practical significance to study rapid and efficient pesticide residue detection methods. Surface-enhanced Raman spectroscopy (SERS) technology has the advantages of high sensitivity, strong anti-interference, and quenching of fluorescence, and surface-enhanced Raman spectroscopy can generally increase the signal by 10 ^-5 to 10 ^-6 times, which meets the standards for practical applications. Therefore, it has great advantages and application potential in the rapid detection of pesticide residues in agricultural and sideline products.

Before using a Raman spectrometer for analysis and testing, it is necessary to select a suitable Raman substrate and detect analytes through the surface-enhanced Raman effect of the substrate. There are two important mechanisms in Raman spectroscopy, namely electromagnetic field enhancement (EM) and chemical enhancement (CM). These two mechanisms are also the key areas of surface-enhanced Raman spectroscopy research. In the field of mechanism research, more attention is paid to the preparation of surface-enhanced Raman substrates. Most of the existing substrate preparation processes are complex, the preparation conditions are single and the requirements are too high, it is not easy to mass-produce, the application is relatively simple, and the cost is slightly high. Therefore, it is a general trend to seek more economical and reliable preparation methods for high-activity SERS substrates.

Contents of the invention

The purpose of the present invention is to provide a CNTs/Ag/AgNWS/SiO ₂ combined SERS substrate, preparation method and pesticide detection method. The present invention can realize the large-area and uniform construction of the SERS substrate with complex structure at low cost and relatively simple.

In order to achieve this goal, the present invention designs a CNTs/Ag/AgNWS/ _SiO combined SERS substrate. The CNTs/Ag/AgNWS/ _SiO combined SERS substrate is formed by dropping a CNTs/Ag/AgNWS solution onto a silica glass sheet and drying it. The mass percentages of each component of CNTs/Ag/AgNWS in the CNTs/Ag/AgNWS solution are silver nanoparticles 26-60% and silver nanowires 30-55% and multi-walled carbon nanotubes 3-20%. The above ingredients and ratio can optimize the inspection sensitivity, stabilize the substrate structure, and improve performance. Silver nanoparticles and silver nanowires are essentially related to silver, and silver is a noble metal, which greatly improves the Raman enhancement effect.

A kind of CNTs/Ag/AgNWS/ _SiO The preparation method of the SERS base that combines, it comprises the steps:

Step 1: Add AgNO ₃ standard solution in deionized water;

Step 2: adding the multi-walled carbon nanotube dispersion solution to the solution obtained in step 1 and mixing to obtain a mixed solution, allowing the multi-walled carbon nanotube dispersion solution and the diluted silver nitrate to be fully mixed;

Step 3: Use the oil bath method to magnetically stir and heat the above mixed solution, and use the oil bath method to ensure a constant temperature condition, thereby reducing the influence of temperature fluctuation factors on the chemical reaction;

Step 4: Add sodium citrate solution to the solution after magnetic stirring and heating in step 3, continue heating, take it out and cool it to room temperature, the strong reducibility of sodium citrate solution in high temperature water reduces Ag ions in AgNo ₃ to Ag nanoparticles;

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, the Ag nanoparticles in the substrate are obtained, and the centrifuged product is silver nanoparticles reduced by sodium citrate;

Step 6: Prepare a new portion of deionized water, and add AgNO ₃ standard solution in the deionized water, and perform ultrasonic cleaning;

Step 7: Add D(+) glucose powder to deionized water, and perform ultrasonic cleaning;

Step 8: adding polyvinylpyrrolidone (PVP) powder into deionized water, and cleaning with ultrasonic oscillation;

Step 9: Add NaCl standard solution in deionized water, and perform ultrasonic cleaning;

Step 10: Put the solution cleaned by ultrasonic oscillation in step 6 on a magnetic stirrer, add a magnetic stirrer in the beaker, and add the solution cleaned by ultrasonic oscillation in step 7 for magnetic stirring;

Step 11: Add the solution cleaned by ultrasonic oscillation in step 8 to the solution after magnetic stirring in step 10, and continue magnetic stirring;

Step 12: Add the solution cleaned by ultrasonic oscillation in step 9 to the solution after magnetic stirring in step 11, and continue magnetic stirring to realize the full mixing of each solution in the above three steps;

Step 13: Add the solution after magnetic stirring in step 12 into a reaction kettle (a stainless steel autoclave lined with polytetrafluoroethylene), and heat in a drying oven. The stainless steel autoclave lined with polytetrafluoroethylene is stable at normal temperature and pressure, has no true melting point, and is insoluble in any solvent;

Step 14: After the heating in step 13, take out the reactor and place it in a safe place. Without assistance, cool the reactor to room temperature in the air (i.e. natural cooling). After cooling, move the liquid in the reactor to a centrifuge tube;

Step 15: Centrifuge the liquid in the reaction kettle in a centrifuge tube, remove the upper liquid in the centrifuge tube with a plastic dropper, collect the remaining fluffy off-white precipitate, and add it to deionized water. The fluffy off-white precipitate is silver nanowires and impurities;

Step 16: ultrasonically oscillating the deionized water containing the precipitate obtained in step 15 to obtain a gray suspension, in which there are silver nanowires in the substrate;

Step 17: Take out the spare solution in step 5 with a rubber dropper and add it to the test tube, then add the suspension obtained in step 16 to the test tube, and use an ultrasonic cleaner to ultrasonically oscillate the mixed solution to 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 stacked on the multi-walled carbon nanotubes. The mass percentage of each component of the 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;

Step 18: Drop the CNTs/Ag/AgNWs solution obtained in Step 17 onto a silica glass slide to dry, and finally obtain a CNTs/Ag/AgNWs SiO ₂ bonded SERS substrate.

In the above technical scheme, the deionized water in each step is deionized water prepared separately.

In step 1 of the above technical solution, add _AgNO3 standard solution into deionized water, stir, dilute 0.01-1mol/L _AgNO3 to 0.001-0.01mol/L, and the volume ratio of ionized water to _AgNO3 standard solution is 57-95:3-5. Only when the silver nitrate is diluted to this concentration, silver nanoparticles with appropriate effect and size can be obtained when sodium citrate reduces the silver nanoparticles.

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 the range, the multi-walled carbon nanotube dispersion solution can be fully mixed with the diluted silver nitrate solution.

In step 3 of the above technical solution, use a magnetic stirrer with a rotating speed of 100-300r/min to stir the mixed solution obtained in step 2 for 15-25 minutes, and heat the mixed solution to 80-105°C, so that the carbon nanotube dispersion solution and the AgNo ₃ solution can be fully mixed to prepare for the subsequent attachment of more Ag nanoparticles on the multi-walled carbon nanotubes. Then move the mixture into a constant temperature oil bath heater, and use oil bath heating to ensure constant temperature conditions and reduce the influence of temperature fluctuation factors on chemical reactions . This operation ensures that most silver nanoparticles can be adsorbed on the multi-walled carbon nanotubes in the end.

In the step 4 of the above technical solution, adding a sodium citrate solution with a mass fraction of 0.5-1%, the volume ratio of the mixed solution in the step 2 to the sodium citrate solution is 95-200: 2-6; within this range, the sodium citrate can play its own characteristics well, and can fully reduce a large number of silver nanoparticles;

In the step 4, continue heating at 80-105°C for 35-50 minutes, seal the beaker with plastic wrap during the heating period, take it out after heating and cool it to room temperature, at this time, the strong reducibility of the sodium citrate solution in high-temperature water reduces the Ag ions in the _AgNO to Ag nanoparticles.

In step 5 of the above technical solution, the centrifugation process is to use a centrifuge to centrifuge at a speed of 4000-4800r/min for 80-100 minutes, and the centrifuged product is dispersed in 3-6mL of deionized water. Selecting centrifugation can greatly shorten the separation time;

In step 6, add AgNO ₃ standard solution to deionized water, perform ultrasonic oscillation for 1-5 minutes, dilute 0.1-1 mol/L AgNO ₃ to 0.01-0.03 mol/L, and the volume ratio of deionized water to AgNO ₃ standard solution is 10-30:2-6.

In step 7 of the above technical solution, the mass range of D(+) glucose powder is 0.05-0.2g, the range of deionized water is 3-6ml, and ultrasonic vibration is performed for 1-5 minutes to fully dissolve the D(+) glucose powder into deionized water;

In step 8, the mass range of polyvinylpyrrolidone powder is 0.5-2g, the range of deionized water is 3-6ml, and ultrasonic vibration is performed for 1-5 minutes to fully dissolve the polyvinylpyrrolidone powder into deionized water;

In step 9, add NaCl standard solution to deionized water, perform ultrasonic oscillation for 1 to 5 minutes, dilute 0.1 to 1 mol/L NaCl to 0.01 to 0.06 mol/L, and the volume ratio of deionized water to NaCl standard solution is 10 to 30:0.1 to 1, so that the NaCl solution and deionized water can be fully mixed.

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

In steps 11 and 12, add D(+) glucose solution, polyvinylpyrrolidone solution and NaCl standard solution to the AgNo ₃ solution, wherein the volume ratio of D(+) glucose solution to AgNo ₃ solution is 3-5:15-30, the volume ratio of polyvinylpyrrolidone solution to AgNo ₃ solution is 3-5:15-30, and the volume ratio of NaCl standard solution to AgNo ₃ solution is 10-30:15-30, so that the added solutions mix well;

D(+) glucose solution specifications: analytically pure, purity >99.5%;

PVP (polyvinylpyrrolidone) solution is a polyvinylpyrrolidone solution with a mass fraction of 2 to 5%, and the relative molecular mass is 40000;

The concentration of the NaCl solution ranges from 0.01 to 1 mol/L.

In step 13, the heating temperature range is 140-180°C, and the heating time is 20-24h;

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 2300-3000r/min, and the centrifugation time is 50-70 minutes;

The volume ratio of the standby solution in step 5 added to the test tube in step 17 and the suspension obtained in step 16 is 1:1.

A method of using the above-mentioned CNTs/Ag/AgNWS/ _SiO combined SERS substrate for pesticide spectral detection, characterized in that: the detection method is to drop the probe molecule rhodamine and pesticides on the CNTs/Ag/AgNWS/ _SiO combined SERS substrate, then leave it to wait for natural drying, and perform Raman detection after drying to obtain the Raman test chart of the pesticide, the pesticide is thiram or diquat.

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

1. Structural innovation: Ag nanoparticles are successfully attached to multi-walled carbon nanotubes, and then silver nanowires are scattered and superimposed on the multi-walled carbon nanotubes. Silver nanoparticles with strong electromagnetic enhancement ability are used, combined with carbon nanotubes, and silver nanowires with different structural shapes are added, and the charge transfer of semiconductors is used to further enhance the Raman signal, which can greatly enhance the Raman signal, and finally achieve the purpose of improving the detection limit, and obtain better results with a simple structure.

2. The preparation requirements are not high: the preparation process can be completed at room temperature, the operation is relatively simple, the time required is not long, the cost is low, and it is easy to reproduce.

3. Good substrate performance: in practical application, it can detect thiram at a lower concentration, with strong uniformity and stability.

Description of drawings

Figure 1 is a flow chart for the preparation of CNTs/Ag/AgNWS/SiO ₂ SERS substrate;

Figure 2 is a TEM image of the CNTs/Ag/AgNWS/SiO ₂ SERS substrate;

Figure 3 is a physical picture of the CNTs/Ag/AgNWS/SiO ₂ SERS substrate;

Figure 4 is a Raman test diagram of the CNTs/Ag/AgNWS/SiO ₂ SERS substrate using the probe molecule rhodamine;

Figure 5 is the stability Raman test diagram of CNTs/Ag/AgNWS/SiO ₂ SERS substrate;

Figure 6 is the uniformity Raman test diagram of CNTs/Ag/AgNWS/SiO ₂ SERS substrate;

Figure 7 is a Raman test chart of the CNTs/Ag/AgNWS/SiO ₂ SERS substrate using the pesticide thiram;

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

Example 1

A CNTs/Ag/AgNWS/ _SiO2 combined SERS substrate, the CNTs/Ag/AgNWS solution is dropped on a silica glass sheet, and after drying, a CNTs/Ag/AgNWS/ _SiO2 combined SERS substrate is formed, and the mass percentage of each component in the CNTs/Ag/AgNWS solution is 46% of silver nanoparticles, 46% of silver nanowires and 8% of multi-walled carbon nanotubes;

The preparation method of the SERS substrate _combined with CNTs/Ag/AgNWS/SiO, as shown in Figure 1, includes the following steps:

Step 1: Add 5ml of AgNo ₃ standard solution into 95ml of deionized water and stir for 10 minutes, the solution is colorless at this time;

Step 2: Add 0.5 ml of multi-walled carbon nanotube dispersion solution to the above colorless solution, mix it, and stir for 5 minutes, at this time, the solution changes from colorless to black;

Step 3: Using an oil bath with a rotational speed of 200r/min to magnetically stir the above black solution and heat it to 95°C;

Step 4: After heating to 95°C, add 2mL of sodium citrate solution with a mass fraction of 1% to the black solution, keep the temperature at 95°C and heat and stir for 40 minutes, take it out and cool to room temperature after 40 minutes;

Step 5: Centrifuge the black solution sample cooled to room temperature, the centrifugation speed is 4500r/min, and the centrifugation time is 90 minutes. After the centrifugation, the centrifuged product is dispersed in 5mL deionized water and stored at room temperature for later use;

Step 6: In a 100mL beaker, add 12mL of deionized water, measure 3mL of _AgNO3 standard solution with a concentration of 0.1mol/L from the test tube, add it to the beaker filled with the above-mentioned ionized water, stir for 10 minutes, and then ultrasonically oscillate for 2 minutes to prepare a _AgNO3 solution with a concentration of 0.02mol/L. At this time, the solution is colorless;

Step 7: Weigh 0.12g of D(+) glucose with an electronic balance, add it to 5ml of deionized water, and ultrasonically oscillate for 2 minutes, then seal it for later use;

Step 8: Weigh 1g of PVP powder with an electronic balance, add it to 5ml of deionized water, then ultrasonically oscillate for 2 minutes and seal it for later use;

Step 9: Take 0.6 mL of NaCl standard solution with a concentration of 1 mol/L in a test tube, add it to 14.4 mL of deionized water, and oscillate ultrasonically for 2 minutes to prepare a NaCl solution with a concentration of 0.04 mol/L, and seal it for later use;

Step 10: Put the _AgNO3 solution prepared in step 6 on a magnetic stirrer, add a magnetic stirrer in the beaker, then add the glucose solution into the _AgNO3 solution, and continue stirring at a speed of 120r/min for 10 minutes;

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

Step 12: Add the NaCl solution prepared in step 9 to the solution in step 11, and continue to stir for 10 minutes to make the solution completely uniformly mixed, and the solution in the beaker is a cloudy hydrosol;

Step 13: Add the hydrosol solution prepared in step 12 into a stainless steel autoclave lined with polytetrafluoroethylene with a capacity of 50 mL, and continue heating in a drying oven at 160° C. for 22 hours;

Step 14: Take out the stainless steel autoclave after heating and place it in a safe place. Cool the autoclave to room temperature in the air without assistance, and transfer the liquid in the Teflon liner to a centrifuge tube after cooling;

Step 15: Centrifuge the solution in step 14 in a centrifuge at a speed of 2500r/min for 60 minutes, remove the upper liquid in the centrifuge tube with a rubber dropper, collect the remaining fluffy off-white precipitate, add it to 5mL deionized water, and the volume ratio of deionized water to the mixed solution obtained in step 14 is 5:40;

Step 16: Use an ultrasonic cleaner to ultrasonically oscillate the solution in Step 15 for 10 minutes to obtain a gray suspension, which is stored for later use;

Step 17: Take out 3mL of the CNTs/AgNPs solution obtained in Step 5 with a plastic dropper and add it to a centrifuge tube, then add 3mL of the AgNWS solution obtained in Step 16, and then use an ultrasonic cleaner to ultrasonically oscillate the mixed solution for 20 minutes to mix the two solutions evenly, then seal the prepared CNTs/Ag/AgNWs, and refrigerate at 4°C for later use;

Step 18: Apply the CNTs/Ag/AgNWs suspension onto the cleaned glass sheet, and place it in an environment of 4 degrees Celsius after air-drying for later use. Figure 2 is a TEM image of the CNTs/Ag/AgNWs SERS substrate. It can be seen from the figure that the silver nanoparticles are adsorbed on the multi-walled carbon nanotubes, and the silver nanowires are stacked on the multi-walled carbon nanotubes. This shows that the preparation of the substrate structure is completely feasible and the effect is good;

Step 19: Place the CNTs/Ag/AgNWs/SiO ₂ combined SERS substrate in step 18 for 1 day, 7 days, 15 days, 30 days and 45 days, respectively, and then detect rhodamine at a concentration of 10 ^-8 mol/L on the 1st day, 7 days, 15 days, 30 days and 45 days. The results are shown in Figure 5. It can be seen that the substrate can still detect rhodamine well when it is placed for a long time of 45 days, which proves that the substrate has good stability;

Step 20: Perform Raman detection on the SERS substrate combined with CNTs/Ag/AgNWs/ _SiO2 in step 18, and randomly select 5 test points, as shown in Figure 6. It can be seen from the figure that the signals of the 5 randomly selected points are good, and the substrate has good uniformity.

Example 2:

A CNTs/Ag/AgNWS/SiO2 combined SERS substrate, the CNTs/Ag/AgNWS solution is dropped on a silica glass sheet, and after drying, a CNTs/Ag/AgNWS/SiO2 combined SERS substrate is formed, and the mass percentages of each component in the CNTs/Ag/AgNWS solution are 45% of silver nanoparticles, 45% of silver nanowires and 10% of multi-walled carbon nanotubes;

The preparation method of the SERS substrate _combined with CNTs/Ag/AgNWS/SiO, as shown in Figure 1, includes the following steps:

Step 1: Add 4ml of AgNo ₃ standard solution into 90ml of deionized water and stir for 10 minutes, the solution is colorless at this time;

Step 2: Add 0.4 ml of multi-walled carbon nanotube dispersion solution to the above colorless solution, mix it, and stir for 5 minutes, at this time, the solution changes from colorless to black;

Step 3: Using an oil bath with a rotational speed of 300r/min to magnetically stir the above black solution and heat it to 100°C;

Step 4: After heating to 100°C, add 5 mL of sodium citrate solution with a mass fraction of 0.5% to the black solution, keep the temperature at 100°C and heat and stir for 45 minutes, take it out and cool to room temperature after 45 minutes;

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

Step 6: In a 100mL beaker, add 16mL of deionized water, measure 4mL of _AgNO3 standard solution with a concentration of 0.1mol/L from the test tube, add it to the beaker containing the above-mentioned ionized water, stir for 10 minutes, and then ultrasonically oscillate for 2 minutes to prepare a _AgNO3 solution with a concentration of 0.02mol/L. At this time, the solution is colorless;

Step 7: Weigh 0.2g of D(+) glucose with an electronic balance, add it to 3ml of deionized water, and ultrasonically oscillate for 2 minutes, then seal it for later use;

Step 8: Weigh 1.5g of PVP powder with an electronic balance, add it to 3ml of deionized water, then ultrasonically oscillate for 2 minutes and seal it for later use;

Step 9: Take 1 mL of NaCl standard solution with a concentration of 1 mol/L in a test tube, add it to 24 mL of deionized water, and oscillate ultrasonically for 2 minutes to prepare a NaCl solution with a concentration of 0.04 mol/L, and seal it for later use;

Step 10: Put the _AgNO3 solution prepared in step 6 on a magnetic stirrer, add a magnetic stirrer in the beaker, then add the glucose solution into the _AgNO3 solution, and continue stirring at a speed of 150r/min for 10 minutes;

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

Step 12: Add the NaCl solution prepared in step 9 to the solution in step 11, and continue to stir for 10 minutes to make the solution completely uniformly mixed, and the solution in the beaker is a cloudy hydrosol;

Step 13: Add the hydrosol solution prepared in step 12 into a stainless steel autoclave lined with polytetrafluoroethylene with a capacity of 50 mL, and continue heating in a drying oven at 140° C. for 20 hours;

Step 14: Take out the stainless steel autoclave after heating and place it in a safe place. Cool the autoclave to room temperature in the air without assistance, and transfer the liquid in the Teflon liner to a centrifuge tube after cooling;

Step 15: Centrifuge the solution in step 14 in a centrifuge at a speed of 3000r/min for 50 minutes, remove the upper liquid in the centrifuge tube with a rubber dropper, collect the remaining fluffy off-white precipitate, add it to 3mL deionized water, and the volume ratio of deionized water to the mixed solution obtained in step 14 is 3:51;

Step 16: Use an ultrasonic cleaner to ultrasonically oscillate the solution in Step 15 for 10 minutes to obtain a gray suspension, which is stored for later use;

Step 17: Take out 2 mL of the CNTs/AgNPs solution obtained in Step 5 with a rubber dropper and add it to a centrifuge tube, then add 2 mL of the suspension (AgNWS solution) obtained in Step 16, and then use an ultrasonic cleaner to ultrasonically oscillate the mixed solution for 20 minutes to mix the two solutions evenly, then seal the prepared CNTs/Ag/AgNWs, and refrigerate at 4 °C for later use;

Step 18: Drop-coat the CNTs/Ag/AgNWs solution on the cleaned glass sheet, and place it in an environment of 4°C after air-drying for later use;

Step 19: Place the CNTs/Ag/AgNWs/SiO ₂ combined SERS substrate in step 18 for 1 day, 7 days, 15 days, 30 days and 45 days, respectively, and then detect rhodamine at a concentration of 10 ^-8 mol/L on the 1st day, 7 days, 15 days, 30 days and 45 days. The results are shown in Figure 5. It can be seen that the substrate can still detect rhodamine well when it is placed for a long time of 45 days, which proves that the substrate has good stability;

Step 20: Perform Raman detection on the SERS substrate combined with CNTs/Ag/AgNWs/ _SiO2 in step 18, and randomly select 5 test points, as shown in Figure 6. It can be seen from the figure that the signals of the 5 randomly selected points are good, and the substrate has good uniformity.

Test case 1:

A rhodamine solution was prepared, and 0.0479 g of rhodamine red solid powder was weighed with an electronic balance and added to 100 mL of deionized water to obtain a 10 ^-3 mol/L R6G mother solution. Use a test tube to measure 1mL of ^10-3 mol/L R6G mother liquor into a centrifuge tube, then add deionized water to make it volume up to 10mL to obtain a ^10-4 mol/L R6G solution (i.e. 1ml R6G+9ml deionized water dilution), and so on to dilute to ^10-12 mol/L.

Rhodamine solutions of different concentrations were dropped onto the silica glass sheet of Example 1, and then allowed to stand for natural drying, and Raman detection was performed after natural drying. Figure 4 is the Raman test graph of the CNTs/Ag/AgNWs/ _SiO2- bound SERS substrate obtained in Example 1 using different concentrations of the probe molecule rhodamine. It can be seen from Figure 4 that the probe molecule rhodamine can still be detected at a low concentration of ^10-12 mol/L, which shows that the detection performance of the substrate is good.

Test case 2:

Configure thiram solution:

10mg/L thiram bis-ethanol solution: Weigh 0.01g thiram bis-ethanol powder with an electronic balance, add it to 100mL ethanol, and ultrasonically oscillate for 2min to prepare 10mg/L thiram bis-ethanol solution;

5mg/L thiram diethyl alcohol solution: take 5mL from the 10mg/L thiram diethyl alcohol solution with a rubber dropper, add 5mL ethanol to form a 5mg/L thiram diethyl alcohol solution;

1mg/L thiram bis-ethanol solution: Take out 1mL from the 10mg/L thiram bis-ethanol solution with a rubber dropper, add 9mL ethanol to form a 1mg/L thiram bis-ethanol solution;

0.1mg/L thiram bis-ethanol solution: Take out 1mL from the 1mg/L thiram bis-ethanol solution with a rubber dropper, add 9mL ethanol to form a 0.1mg/L thiram bis-ethanol solution.

0.01mg/L thiram bis-ethanol solution: Take out 1mL from the 0.1mg/L thiram bis-ethanol solution with a rubber dropper, add 9mL ethanol to form a 0.01mg/L thiram bis-ethanol solution.

Then switch to different concentrations of thiram solution and let it stand at room temperature for later use.

Thiram solutions of different concentrations were dropped onto the silica glass sheet of Example 1, and then left to wait for natural drying, and Raman detection was performed after natural drying. Figure 7 is the Raman test chart of the SERS substrate combined with CNTs/Ag/AgNWs/SiO ₂ using different concentrations of the pesticide thiram. It can be seen from Figure 7 that the pesticide thiram can still be detected at a low concentration of 0.01 mg/L. It can be seen that the substrate has good detection performance and sensitivity, and is suitable for the detection of pesticide thiram residues.

The content not described in detail in this specification belongs to the prior art known to those skilled in the art.

Claims (10)

1. CNTs/Ag/AgNWS/SiO ₂ A bonded SERS substrate characterized by: the CNTs/Ag/AgNWS/SiO ₂ The combined SERS substrate is formed by dripping CNTs/Ag/AgNWS solution on a silicon dioxide 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 nano particles, 30-55% of silver nano wires and 3-20% of multi-wall carbon nano tubes.

2. CNTs/Ag/AgNWS/SiO ₂ The preparation method of the combined SERS substrate is characterized by comprising the following steps of:

step 1: adding AgNO into deionized water ₃ A standard solution;

step 2: adding the multiwall carbon nanotube dispersion solution into the solution obtained in the step 1, and mixing to obtain a mixed solution;

step 3: magnetically stirring and heating the mixed solution by using an oil bath mode;

step 4: adding sodium citrate solution into the solution obtained after the magnetic stirring and heating in the step 3, continuously heating, taking out the solution, and cooling to room temperature;

step 5: centrifuging the sample cooled to room temperature in the step 4, dispersing the centrifuged product in deionized water, and storing the product in room temperature for standby, thereby obtaining Ag nano particles in a substrate;

step 6: preparing a part of deionized water again, and adding AgNO into the deionized water ₃ Standard solution, and carrying out ultrasonic oscillation cleaning;

step 7: d (+) glucose powder is added into deionized water, and ultrasonic oscillation cleaning is carried out;

step 8: adding polyvinylpyrrolidone powder into deionized water, and performing ultrasonic oscillation cleaning;

step 9: adding NaCl standard solution into deionized water, and performing ultrasonic oscillation cleaning;

step 10: placing the solution subjected to ultrasonic vibration cleaning in the step 6 on a magnetic stirrer, adding a magnetic stirrer into a beaker, and adding the solution subjected to ultrasonic vibration cleaning in the step 7 to perform magnetic stirring;

step 11: adding the solution subjected to ultrasonic vibration cleaning in the step 8 into the solution subjected to magnetic stirring in the step 10, and continuing magnetic stirring;

step 12: adding the solution subjected to ultrasonic vibration cleaning in the step 9 into the solution subjected to magnetic stirring in the step 11, and continuing magnetic stirring;

step 13: adding the solution magnetically stirred in the step 12 into a reaction kettle, and heating;

step 14: step 13, taking out the reaction kettle after heating, cooling the reaction kettle to room temperature, and transferring liquid in the reaction kettle to a centrifuge tube after cooling;

step 15: centrifuging the liquid in the reaction kettle in a centrifuge tube, collecting precipitate, and adding the precipitate into deionized water;

step 16: carrying out ultrasonic oscillation on the deionized water containing the precipitate obtained in the step 15 to obtain a suspension;

step 17: adding the standby solution in the step 5 into a test tube, then adding the suspension obtained in the step 16 into the test tube, and carrying out ultrasonic oscillation to prepare CNTs/Ag/AgNWs solution;

step 18: dropping the CNTs/Ag/AgNWS solution obtained in the step 17 onto a silica glass sheet, and airing to obtain CNTs/Ag/AgNWS SiO ₂ A bound SERS substrate.

3. The CNTs/Ag/AgNWS/SiO according to claim 2 ₂ The preparation method of the combined SERS substrate is characterized by comprising the following steps of: in step 1, agNO is added into deionized water ₃ Stirring the standard solution, and stirring the AgNO with the concentration of 0.01-1 mol/L ₃ Diluting to 0.001-0.01 mol/L, and mixing ionized water and AgNO ₃ The volume ratio of the standard solution is 57-95:3-5.

4. The CNTs/Ag/AgNWS/SiO according to claim 2 ₂ The preparation method of the combined SERS substrate is characterized by comprising the following steps of: the volume ratio of the solution obtained in the step 1 to the multiwall carbon nanotube dispersion solution is 60-100: 0.1 to 0.6.

5. The CNTs/Ag/AgNWS/SiO according to claim 2 ₂ The preparation method of the combined SERS substrate is characterized by comprising the following steps of: in the step 3, the mixed solution obtained in the step 2 is stirred for 15 to 25 minutes by using a magnetic stirrer with the rotating speed of 100 to 300r/min, the mixed solution is heated to 80 to 105 ℃, and then the mixture is transferred into a constant-temperature oil bath heater, and the constant-temperature condition is ensured by an oil bath heating method.

6. The CNTs/Ag/AgNWS/SiO according to claim 2 ₂ The preparation method of the combined SERS substrate is characterized by comprising the following steps of: in the step 4, adding sodium citrate solution with the mass fraction of 0.5-1%, wherein the volume ratio of the mixed solution in the step 2 to the sodium citrate solution is 95-200: 2 to 6;

in the step 4, heating is continued for 35-50 minutes at 80-105 ℃, the beaker is sealed by using a preservative film during heating, and the beaker is taken out and cooled to room temperature after heating.

7. The CNTs/Ag/AgNWS/SiO according to claim 2 ₂ The preparation method of the combined SERS substrate is characterized by comprising the following steps of: in the step 5, the centrifugal treatment process is that a centrifugal machine is utilized to centrifuge for 80 to 100 minutes at the rotating speed of 4000 to 4800r/min, and the product after centrifugation is dispersed in 3 to 6mL of deionized waterIn (a) and (b);

in step 6, agNO is added into deionized water ₃ Standard solution is subjected to ultrasonic oscillation for 1 to 5 minutes, and AgNO with the concentration of 0.1 to 1mol/L is added ₃ Diluting to 0.01-0.03 mol/L, deionized water and AgNO ₃ The volume ratio of the standard solution is 10-30: 2 to 6.

8. The CNTs/Ag/AgNWS/SiO according to claim 2 ₂ The preparation method of the combined SERS substrate is characterized by comprising the following steps of: in the step 7, the mass range of the D (+) glucose powder is 0.05-0.2 g, the deionized water range is 3-6 ml, and the ultrasonic oscillation is carried out for 1-5 minutes;

in the step 8, the mass range of polyvinylpyrrolidone powder is 0.5-2 g, the deionized water range is 3-6 ml, and ultrasonic oscillation is carried out for 1-5 minutes;

in the step 9, adding NaCl standard solution into deionized water, carrying out ultrasonic oscillation for 1-5 minutes, diluting 0.1-1 mol/L NaCl to 0.01-0.06 mol/L, wherein the volume ratio of the deionized water to the NaCl standard solution is 10-30: 0.1 to 1.

9. The CNTs/Ag/AgNWS/SiO according to claim 2 ₂ The preparation method of the combined SERS substrate is characterized by comprising the following steps of: in the step 10, the magnetic stirring rotating speed range is 100-150 r/min;

in steps 11 and 12, in AgNo ₃ Adding a D (+) glucose solution, a polyvinylpyrrolidone solution and a NaCl standard solution into the solution, wherein the D (+) glucose solution and AgNo ₃ The volume ratio of the solution is 3-5: 15-30 parts of polyvinylpyrrolidone solution and AgNo ₃ The volume ratio of the solution is 3-5: 15-30, naCl standard solution and AgNo ₃ The volume ratio of the solution is 10-30: 15-30;

in the step 13, the heating temperature is 140-180 ℃ and the heating time is 20-24 hours;

in the steps 15 and 16, the volume ratio of the deionized water to the mixed solution obtained in the step 14 is 2-6: 40-60, the rotation speed of the centrifugal machine is 2300-3000 r/min, and the centrifugation time is 50-70 minutes;

in step 17, the volume ratio of the standby solution in step 5 to the suspension obtained in step 16, which is added into the test tube, is 1:1.

10. a CNTs/Ag/AgNWS/SiO as claimed in claim 1 ₂ The method for detecting the pesticide spectrum by the combined SERS substrate is characterized by comprising the following steps of: the detection mode is to drop probe molecule rhodamine and pesticide to CNTs/Ag/AgNWS/SiO ₂ And standing and airing the pesticide on the combined SERS substrate, and carrying out Raman detection after airing to obtain a Raman test chart of the pesticide.