CN115184334B - Raman spectrum detection method based on colloidal silver gradient aggregation effect - Google Patents

Abstract

The invention discloses a Raman spectrum detection method based on a colloidal silver gradient aggregation effect, which comprises the following steps of: (1) Synthesizing reinforcing reagent silver nano particles, and synthesizing the silver nano particles by reducing silver nitrate by taking sodium citrate as a reducing agent. (2) Preparing standard samples of molecules to be detected with different concentrations as a liquid to be detected; placing a proper amount of silver nano particles and a liquid to be detected into a sample detection tank for uniform mixing, then adding a small amount of coagulating agent, keeping the sample tank still, avoiding uniform mixing of the coagulating agent in the sol, enabling the lower layer of the sol to naturally agglomerate while the upper layer of the sol still keeps a dispersion state, and enabling the sample to be layered, so that an obvious interface is generated; (3) And detecting the laser alignment sol layering interface by using a Raman spectrometer to obtain the Raman spectrum of the molecule to be detected. The method has excellent detection capability on molecules such as crystal violet, methylene blue, diquat and the like, and has the advantages of simplicity, convenience, rapidness, high sensitivity, low cost and the like.

Description

A Raman spectroscopy detection method based on colloidal silver gradient aggregation effect

Technical Field

The invention belongs to the field of Raman spectroscopy technology detection, and in particular relates to a Raman spectroscopy detection method based on the gradient aggregation effect of colloidal silver.

Background Art

Aromatic dye molecules such as crystal violet, rhodamine 6G, methylene blue, malachite green, etc. are a class of organic pollutants present in the environment. They have a wide range of applications and can be used as dyes in textiles. In addition, they are also favored in the aquaculture industry because of their bactericidal and antibacterial effects. However, when these dyes enter the body, they will produce harmful hidden dye molecules, such as hidden crystal violet and hidden malachite green, which are serious pollutants in water bodies and have high residues, high carcinogenicity, and high toxicity. In addition, in order to meet the needs of agricultural production, a large amount of pesticides are used in production activities, which brings serious harm to the environment and humans. Realizing rapid, real-time, and highly sensitive detection of different molecules such as pesticide residues, dyes, and drugs is very important for environmental pollution monitoring, aquatic food safety, and human health.

Surface enhanced Raman spectroscopy (SERS) is a molecular detection technology with excellent characteristics such as non-destructive detection, convenience, and fingerprint recognition. Using gold and silver nanoparticle colloids as an enhanced substrate to perform Raman detection on molecules is a convenient and fast method. However, in actual detection, it is difficult to achieve highly sensitive SERS detection. At present, the coagulation method for Raman detection mainly adds the enhanced substrate, the test liquid and the coagulation agent into the sample pool, mixes them and then performs detection. The type selection and amount of coagulation agent added will have a great impact on the detection results. Excessive coagulation agent addition will cause a large number of nanoparticles to aggregate, which will not only produce competitive adsorption of the molecules to be tested, but also reduce the molecular adsorption sites due to excessive aggregation, so that good detection sensitivity cannot be obtained. Therefore, it is crucial to detect the molecules to be tested under the optimal aggregation conditions to obtain the best signal. Developing new detection methods in the system of Raman detection by sol method is of great significance to improving the detection ability of molecules.

Summary of the invention

The purpose of the present invention is to provide a method for adding a coagulation agent to a silver nanoparticle sol, causing the silver particles to aggregate in a gradient along the distribution of the coagulation agent without mixing, causing the solution to be stratified after the silver particles are naturally coagulated, and obtaining a highly sensitive Raman spectroscopy detection method based on the gradient aggregation effect of colloidal silver by detecting at the stratification interface.

A method in which a coagulation agent is added to a mixed solution of silver nanoparticles and a test liquid to partially aggregate and stratify the silver particles, and the molecules to be tested are detected at the stratification interface.

To achieve the above object, the technical solution of the present invention is as follows:

Step 1, preparation of silver nanoparticle sol

Add 75 mL of ultrapure water and 10-30 mL of sodium citrate with a mass fraction of 1-2% into a conical flask, stir and heat to 70° C., then add 1.5-2.5 mL of silver nitrate with a mass fraction of 1% and 2 mL of sodium borohydride with a mass fraction of 0.1-1%, and continue to stir evenly to obtain a seed solution of silver nanoparticles;

The second step growth of silver nanoparticles: 2 mL of 1-2% sodium citrate is added to 75 mL of ultrapure water, stirred and heated to 110° C., and then 10-20 mL of seed solution and 1.5-2.5 mL of 1% silver nitrate are added, and after fully stirring, 2 mL of 1-2% sodium citrate and 1.5-2.5 mL of 1% silver nitrate solution are added and the reaction is continued for 30 minutes to obtain silver nanoparticles grown in the second step;

2 mL of 1-2% sodium citrate was added to 80 mL of ultrapure water, and the mixture was heated to 110° C. with stirring, and then 10-20 mL of the silver nanoparticles grown in the second step and 1.5-2.5 mL of 1% silver nitrate were added, and the reaction was continued for 30 minutes to obtain a silver nanoparticle sol;

Step 2, prepare standard solutions of the molecules to be tested with different concentrations as test solutions:

Take 250-500uL of silver nanoparticle sol and 1-2mL of the standard solution of the molecule to be tested, add them into the detection cell and mix them evenly, then add 25-100uL of a coagulant solution with a concentration of 1-1.5mol/L, keep the sample cell still to prevent the coagulant from mixing in the solution, so that the lower layer of the sol naturally agglomerates while the upper layer remains dispersed, the sample shows a stratified phenomenon, and a clear interface is produced. Use a portable Raman spectrometer to detect at the stratified interface of the sample to obtain the final test result.

The coagulation agent is sodium chloride, sodium bromide, sodium iodide or magnesium sulfate, potassium chloride, potassium bromide, potassium iodide, magnesium chloride, magnesium bromide, magnesium iodide, calcium chloride, calcium bromide, and aluminum sulfate.

The amount of silver nanoparticle sol added in step 2 is 500uL.

In step 2, the amount of the standard solution of the molecule to be tested added is 2 mL.

The amount of the coagulation agent added in step 2 is 100uL.

The concentration of the coagulant in step 2 is 1.5 mol/L.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention first adds silver nanoparticle sol and a standard solution of a molecule to be tested into a sample pool and mixes them, then adds a small amount of coagulation agent, and keeps the sample pool still to prevent the coagulation agent from mixing with the silver colloid and the solution to be tested. The coagulation agent naturally sinks to the bottom of the sample pool, causing the silver particles at the bottom to aggregate and darken in color; while the silver particles at the top remain dispersed and present the original light yellow color. Therefore, the silver particles in the sample pool are partially aggregated, and the lower aggregated area and the upper non-aggregated area present an obvious interface due to different colors. The sample is detected by a portable Raman detector, and detection signals of different intensities are obtained at different positions of the sample detection pool. When the laser is aligned at the interface of the sol stratification, the best detection signal can be obtained. Compared with adding a large amount of coagulation agent to cause the solution to aggregate as a whole, the detection sensitivity of the molecule is increased. The obvious interface generated is conducive to locating the best detection position for detection. The method has simple process, low cost, short time consumption, high repeatability, and greatly improves the sensitivity of molecular detection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an optical photograph showing the coagulation of silver sol by adding different amounts of coagulation agents into a mixed solution of silver nanoparticle sol and a molecule to be tested;

FIG2a is a schematic diagram of Raman detection when 100uL of sodium chloride is added to a mixed solution of silver nanoparticle sol and a molecule to be detected;

FIG2 b is a Raman spectrum detected by focusing the laser at different positions of the solution when 100 uL of sodium chloride is added to the mixed solution of silver nanoparticle sol and crystal violet;

FIG3 is a Raman spectrum detected when different volumes of sodium chloride are added to a mixed solution of silver nanoparticle sol and crystal violet molecules;

FIG4 is a Raman spectrum detected when 100uL of sodium chloride is added to a mixed solution of silver nanoparticle sol and crystal violet of different concentrations;

FIG5 is a Raman spectrum detected when 100uL of sodium iodide is added to a mixed solution of silver nanoparticle sol and crystal violet of different concentrations;

FIG6 is a Raman spectrum detected when 100uL of sodium bromide is added to a mixed solution of silver nanoparticle sol and crystal violet of different concentrations;

FIG7 is a Raman spectrum detected when 100 uL of magnesium sulfate is added to a mixed solution of silver nanoparticle sol and crystal violet of different concentrations;

FIG8 is a Raman spectrum detected when 100uL of sodium chloride is added to a mixed solution of silver nanoparticle sol and different concentrations of rhodamine 6G;

FIG9 is a Raman spectrum of a mixed solution of silver nanoparticle sol and methylene blue of different concentrations when 100 uL of sodium chloride is added;

FIG. 10 is a Raman spectrum detected when 100 uL of sodium chloride is added to a mixed solution of silver nanoparticle sol and malachite green of different concentrations.

FIG. 11 is a Raman spectrum detected when 100 uL of sodium chloride is added to a mixed solution of silver nanoparticle sol and diquat of different concentrations.

FIG. 12 is a Raman spectrum detected when 100 uL of sodium chloride is added to a mixed solution of silver nanoparticle sol and different concentrations of thiabendazole.

DETAILED DESCRIPTION

The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

Preparation of silver nanoparticle sol

Add 75 mL of ultrapure water and 10-30 mL of sodium citrate with a mass fraction of 1-2% into a conical flask, stir and heat to 70° C., then add 1.5-2.5 mL of silver nitrate with a mass fraction of 1% and 2 mL of sodium borohydride with a mass fraction of 0.1-1%, and continue to stir evenly to obtain a seed solution of silver nanoparticles;

The second step growth of silver nanoparticles: 2 mL of 1-2% sodium citrate is added to 75 mL of ultrapure water, stirred and heated to 110° C., and then 10-20 mL of seed solution and 1.5-2.5 mL of 1% silver nitrate are added, and after fully stirring, 2 mL of 1-2% sodium citrate and 1.5-2.5 mL of 1% silver nitrate solution are added and the reaction is continued for 30 minutes to obtain silver nanoparticles grown in the second step;

2 mL of 1-2% sodium citrate was added to 80 mL of ultrapure water, and the mixture was heated to 110° C. with stirring. Then, 10-20 mL of the silver nanoparticles grown in the second step and 1.5-2.5 mL of 1% silver nitrate were added. The reaction was continued for 30 minutes to obtain a silver nanoparticle sol.

Figure 1 is an optical photograph of the silver nanoparticle sol in the sample pool after being induced to aggregate by different volumes of coagulants. After adding the silver nanoparticle sol and the sample to be tested into the sample pool and mixing them evenly, after adding the coagulant, the solution is kept still so that the coagulant is not mixed with the test solution and coagulation occurs naturally. When the amount of coagulant added exceeds 100uL, all the sols in the sample pool aggregate and the overall color of the sol becomes darker. When the amount of coagulant added does not exceed 100uL, only the lower part of the sol aggregates. The aggregated part becomes darker in color and forms a clear interface with the non-aggregated part.

Figure 2a is a schematic diagram of Raman detection after adding 100uL of coagulation agent to the mixed solution of silver nanoparticle sol and the test liquid. The laser is aimed at the layered interface for detection.

Embodiment 1:

Step 1, preparation of silver nanoparticle sol

Add 75 mL of ultrapure water and 20 mL of 1% sodium citrate in a conical flask, stir and heat to 70°C, then add 1.7 mL of 1% silver nitrate and 2 mL of 1% sodium borohydride, continue stirring to obtain a silver nanoparticle seed solution;

The second growth of silver nanoparticles: 2 mL of 1% sodium citrate was added to 75 mL of ultrapure water, stirred and heated to 110° C., and then 10 mL of seed solution and 1.7 mL of 1% silver nitrate were added. After fully stirring, 2 mL of 1% sodium citrate and 1.7 mL of 1% silver nitrate solution were added and the reaction was continued for 30 minutes to obtain silver nanoparticles grown in the second step.

2 mL of 1% sodium citrate was added to 80 mL of ultrapure water, and the mixture was heated to 110° C. with stirring, and then 10 mL of the silver nanoparticles grown in the second step and 1.7 mL of 1% silver nitrate were added, and the reaction was continued for 30 minutes to obtain a silver nanoparticle sol;

Step 2, prepare standard solutions of the molecules to be tested with different concentrations as test solutions:

Prepare a 0.01 mol/L crystal violet standard solution, dilute the solution to obtain a 10 ^-8 mol/L standard test solution. Take 500uL of silver nanoparticle sol and 2mL of standard test solution and add them to the detection cell to mix well, then add 100uL of 1.5mol/L coagulation agent sodium chloride, do not mix the sample, keep the sample cell still to allow the sol to aggregate naturally, the lower part of the sol aggregates, and a clear interface is formed with the unaggregated part of the upper layer. Focus the laser at different positions of the solution, starting from the bottom and moving upward, and detect every 1mm. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

In Example 1, after 100 uL of sodium chloride was added to the sample to produce stratification, the Raman spectra detected at different positions of the solution are shown in FIG2b . When the laser is focused at the interface, the optimal detection signal is obtained.

Example 2

Step 1, preparation of silver nanoparticle sol

Add 75 mL of ultrapure water and 10 mL of 2% sodium citrate in a conical flask, stir and heat to 70°C, then add 1.5 mL of 1% silver nitrate and 2 mL of 0.5% sodium borohydride, and continue to stir to obtain a seed solution of silver nanoparticles;

The second growth of silver nanoparticles: 2 mL of 2% sodium citrate was added to 75 mL of ultrapure water, stirred and heated to 110° C., and then 15 mL of seed solution and 1.5 mL of 1% silver nitrate were added. After fully stirring, 2 mL of 2% sodium citrate and 1.5 mL of 1% silver nitrate solution were added and the reaction was continued for 30 minutes to obtain silver nanoparticles grown in the second step.

2 mL of 2% sodium citrate was added to 80 mL of ultrapure water, and the mixture was heated to 110° C. with stirring, and then 15 mL of the silver nanoparticles grown in the second step and 1.5 mL of 1% silver nitrate were added, and the reaction was continued for 30 minutes to obtain a silver nanoparticle sol;

Step 2, prepare standard solutions of the molecules to be tested with different concentrations as test solutions:

Prepare a 0.01 mol/L crystal violet standard solution, and dilute the solution in sequence to obtain a standard test solution of 10 ^-7 mol/L-10 ^-16 mol/L. Take 500uL of silver nanoparticle colloid and put it into the sample detection pool, add 2mL of crystal violet test solution with a concentration of 10 ^-8 mol/L and mix well. Then add 500uL, 400uL, 300uL, 200uL, 100uL, 75uL, 50uL, and 25uL of a sodium chloride solution with a concentration of 1.5mol/L respectively, without mixing the sample, so that the sol naturally aggregates. When the volume of sodium chloride exceeds 100uL, the silver nanoparticles aggregate as a whole, the color changes to dark gray, and the solution is detected using a portable Raman spectrometer; when the volume of sodium chloride does not exceed 100uL, the lower part of the sol aggregates, and a clear interface is formed with the unaggregated part of the upper layer, and the laser is focused on the interface for detection. The Raman spectrometer power was 300 mW, the laser wavelength was 785 nm, and the integration time was 20 s.

In Example 2, the Raman spectra of the sample detected when different volumes of sodium chloride were added are shown in FIG. 3 . When the volume of the coagulation agent is 100 uL, the optimal detection signal is obtained.

Example 3

Step 1, preparation of silver nanoparticle sol

Add 75 mL of ultrapure water and 15 mL of 1.5% sodium citrate in a conical flask, stir and heat to 70° C., then add 2.3 mL of 1% silver nitrate and 2 mL of 0.8% sodium borohydride, and continue to stir to obtain a seed solution of silver nanoparticles;

The second growth of silver nanoparticles: 2 mL of 1.5% sodium citrate was added to 75 mL of ultrapure water, stirred and heated to 110° C., and then 13 mL of seed solution and 2.3 mL of 1% silver nitrate were added. After fully stirring, 2 mL of 1.5% sodium citrate and 2.3 mL of 1% silver nitrate solution were added and the reaction was continued for 30 minutes to obtain silver nanoparticles grown in the second step.

2 mL of 1.5% sodium citrate was added to 80 mL of ultrapure water, and the mixture was heated to 110° C. with stirring, and then 13 mL of the silver nanoparticles grown in the second step and 2.3 mL of 1% silver nitrate were added, and the reaction was continued for 30 minutes to obtain a silver nanoparticle sol;

Step 2, prepare standard solutions of the molecules to be tested with different concentrations as test solutions:

Prepare a 0.01 mol/L crystal violet standard solution, and dilute the solution in sequence to obtain a 10 ^-8 mol/L-10 ^-16 mol/L standard test solution. Take 500uL of silver nanoparticle sol and put it into the sample detection cell, add 2mL of crystal violet test solution of different concentrations and mix them. Then add 100uL of 1.5mol/L sodium chloride solution as a coagulant. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layers for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of sodium chloride to the test samples of different concentrations in Example 3, the Raman spectra detected at the interface where the sol is delaminated are shown in FIG. 4 . In this example, a crystal violet signal of 10 ^-15 mol/L can be detected.

Example 4

Step 1, preparation of silver nanoparticle sol

Add 75 mL of ultrapure water and 25 mL of 1.8% sodium citrate in a conical flask, stir and heat at 70°C, then add 2.5 mL of 1% silver nitrate and 2 mL of 0.6% sodium borohydride, and continue to stir to obtain a silver nanoparticle seed solution;

The second growth of silver nanoparticles: 2 mL of 1.8% sodium citrate was added to 75 mL of ultrapure water, stirred and heated to 110° C., and then 18 mL of seed solution and 2.5 mL of 1% silver nitrate were added. After fully stirring, 2 mL of 1.8% sodium citrate and 2.5 mL of 1% silver nitrate solution were added and the reaction was continued for 30 minutes to obtain silver nanoparticles grown in the second step.

2 mL of 1.8% sodium citrate was added to 80 mL of ultrapure water, and the mixture was heated to 110° C. with stirring, and then 18 mL of the silver nanoparticles grown in the second step and 2.5 mL of 1% silver nitrate were added, and the reaction was continued for 30 minutes to obtain a silver nanoparticle sol;

Step 2, prepare standard solutions of the molecules to be tested with different concentrations as test solutions:

Prepare a 0.01 mol/L crystal violet standard solution, and dilute the solution in sequence to obtain a 10 ^-8 mol/L-10 ^-16 mol/L standard test solution. Take 500uL of silver nanoparticle sol and put it into the sample detection cell, add 2mL of crystal violet test solution of different concentrations and mix them. Then add 100uL of 1.5mol/L sodium iodide solution as a coagulation agent. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layers for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of sodium iodide to the test samples of different concentrations in Example 4, the Raman spectra detected at the interface where the sol is delaminated are shown in FIG5 . In this example, a crystal violet signal of 10 ^-13 mol/L can be detected.

Embodiment 5:

Step 1, preparation of silver nanoparticle sol

Add 75 mL of ultrapure water and 30 mL of 1.3% sodium citrate in a conical flask, stir and heat to 70°C, then add 2 mL of 1% silver nitrate and 2 mL of 0.1% sodium borohydride, and continue to stir to obtain a silver nanoparticle seed solution;

The second growth of silver nanoparticles: 2 mL of 1.3% sodium citrate was added to 75 mL of ultrapure water, stirred and heated to 110° C., and then 20 mL of seed solution and 2 mL of 1% silver nitrate were added. After fully stirring, 2 mL of 1.3% sodium citrate and 2 mL of 1% silver nitrate solution were added and the reaction was continued for 30 minutes to obtain silver nanoparticles grown in the second step.

2 mL of 1.3% sodium citrate was added to 80 mL of ultrapure water, and the mixture was stirred and heated to 110° C., and then 20 mL of the silver nanoparticles grown in the second step and 2 mL of 1% silver nitrate were added, and the reaction was continued for 30 minutes to obtain a silver nanoparticle sol;

Prepare a 0.01 mol/L crystal violet standard solution, and dilute the solution in sequence to obtain a 10 ^-8 mol/L-10 ^-16 mol/L standard test solution. Take 400uL of silver nanoparticle sol and put it into the sample detection cell, and add 1.8mL of crystal violet test solution of different concentrations to mix. Then add 100uL of 1 mol/L coagulation agent sodium bromide solution. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layer for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of sodium bromide to the samples of different concentrations in Example 5, the Raman spectra detected at the interface where the sol is delaminated are shown in FIG6 . In this example, a crystal violet signal of 10 ^-15 mol/L can be detected.

Example 6

Step 1, preparing silver nanoparticle sol, the same as in Example 1;

Prepare 0.01mol/L crystal violet standard solution, dilute the solution in sequence to obtain ^10-8mol /L- ^10-16mol /L standard test solution. Take 500uL of silver nanoparticle sol and put it into the sample detection cell, add 2mL of crystal violet test solution of different concentrations and mix them. Then add 100uL of 1.5mol/L coagulation agent magnesium sulfate solution. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layer for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of magnesium sulfate to the test samples of different concentrations in Example 6, the Raman spectra detected at the interface where the sol is delaminated are shown in FIG. 7 . In this example, a crystal violet signal of 10 ^-15 mol/L can be detected.

Example 7

Step 1, preparing silver nanoparticle sol, the same as in Example 1;

Prepare 0.01mol/L Rhodamine 6G standard solution, dilute the solution in sequence to obtain ^10-8mol /L- ^10-16mol /L standard test solution. Take 500uL of silver nanoparticle sol and put it into the sample detection cell, add 2mL of Rhodamine 6G test solution of different concentrations and mix them. Then add 100uL of 1.5mol/L sodium chloride solution as a coagulant. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layer for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of sodium chloride to the test samples of different concentrations in Example 7, the Raman spectra detected at the interface where the sol is delaminated are shown in FIG8 . In this example, a 10 ^-14 mol/L rhodamine 6G signal can be detected.

Example 8

Step 1, preparing silver nanoparticle sol, the same as in Example 1;

Prepare a 0.01 mol/L methylene blue standard solution, and dilute the solution in sequence to obtain a 10 ^-8 mol/L-10 ^-16 mol/L standard test solution. Take 500uL of silver nanoparticle sol and put it into the sample detection cell, add 2mL of methylene blue test solution of different concentrations and mix them. Then add 100uL of 1.5mol/L sodium chloride solution as a coagulant. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layers for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of sodium chloride to the samples of different concentrations in Example 8, the Raman spectra detected at the interface where the sol is delaminated are shown in FIG9 . In this example, a methylene blue signal of 10 ^-15 mol/L can be detected.

Example 9

Step 1, preparing silver nanoparticle sol, the same as in Example 1;

Prepare a 0.01 mol/L malachite green standard solution, and dilute the solution in sequence to obtain a 10 ^-8 mol/L-10 ^-16 mol/L standard test solution. Take 500uL of silver nanoparticle sol and put it into the sample detection cell, add 2mL of malachite green test solution of different concentrations and mix them. Then add 100uL of 1.5mol/L sodium chloride solution as a coagulant. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layers for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of sodium chloride to the test samples of different concentrations in Example 9, the Raman spectra detected at the interface where the sol is delaminated are shown in FIG. 10 . In this example, a malachite green signal of 10 ^-14 mol/L can be detected.

Example 10

Step 1, preparing silver nanoparticle sol, the same as in Example 1;

Prepare a 0.01 mol/L diquat standard solution, and dilute the solution in sequence to obtain a 10 ^-8 mol/L-10 ^-13 mol/L standard test solution. Take 500uL of silver nanoparticle sol and put it into the sample detection cell, add 2mL of diquat test solution of different concentrations and mix them. Then add 100uL of 1.5mol/L sodium chloride solution as a coagulant. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layer for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of sodium chloride to the test samples of different concentrations in Example 10, the Raman spectra detected at the interface where the sol is delaminated are shown in FIG. 11 . In this example, a 10 ^-12 mol/L diquat signal can be detected.

Embodiment 11

Step 1, preparing silver nanoparticle sol, the same as in Example 1;

Prepare a 0.01 mol/L thiabendazole standard solution, and dilute the solution in sequence to obtain a 10 ^-8 mol/L-10 ^-12 mol/L standard test solution. Take 500uL of silver nanoparticle sol and put it into the sample detection cell, add 2mL of different concentrations of thiabendazole test solution and mix them. Then add 100uL of 1.5mol/L sodium chloride solution as a coagulant. The lower part of the sol aggregates and forms a clear interface with the unaggregated part of the upper layer. The laser is focused on the interface of the layer for detection. The Raman spectrometer power is 300mW, the laser wavelength is 785nm, and the integration time is 20s.

After adding 100 uL of sodium chloride to the test samples of different concentrations in Example 11, the Raman spectra detected at the interface where the sol is stratified are shown in FIG. 12 . In this example, a 10 ^-11 mol/L thiazole signal can be detected.

Claims (6)

1. The Raman spectrum detection method based on the colloidal silver gradient aggregation effect is characterized by comprising the following steps of:

Step1, preparing silver nanoparticle sol

Adding 75mL of ultrapure water and 10-30 mL of sodium citrate with the mass fraction of 1-2% into a conical flask, stirring and heating to 70 ℃, adding 1.5-2.5 mL of silver nitrate with the mass fraction of 1% and 2mL of sodium borohydride with the mass fraction of 0.1-1%, and continuously and uniformly stirring to obtain a seed solution of silver nano particles;

Second step of silver nanoparticle growth: adding 2mL of sodium citrate with the mass fraction of 1-2% into 75mL of ultrapure water, stirring and heating to 110 ℃, adding 10-20 mL of seed solution and 1.5-2.5 mL of silver nitrate with the mass fraction of 1%, fully and uniformly stirring, adding 2mL of sodium citrate with the mass fraction of 1-2% and 1.5-2.5 mL of silver nitrate with the mass fraction of 1% for continuous reaction for 30 minutes, and obtaining silver nano particles growing in the second step;

Adding 2mL of sodium citrate with mass fraction of 1-2% into 80mL of ultrapure water, stirring and heating to 110 ℃, adding 10-20 mL of silver nanoparticles grown in the second step and 1.5-2.5 mL of silver nitrate with mass fraction of 1%, and continuing to react for 30 minutes to obtain silver nanoparticle sol;

step 2, preparing standard solutions of molecules to be detected with different concentrations as the solution to be detected:

Adding 250-500 uL of silver nanoparticle sol and 1-2 mL of molecular standard solution to be detected into a detection tank, uniformly mixing, then adding 25-100 uL of coagulant solution with the concentration of 1-1.5 mol/L, keeping the sample tank standing to avoid uniformly mixing the coagulant in the solution, enabling the lower layer of the sol to naturally agglomerate while the upper layer is kept in a dispersed state, enabling the sample to present a layering phenomenon, generating an obvious interface, and detecting at the layering interface of the sample by using a portable Raman spectrometer to obtain a final detection result.

2. The method for detecting raman spectra based on colloidal silver gradient aggregation effect according to claim 1, wherein the coagulating agent is sodium chloride, sodium bromide, sodium iodide, magnesium sulfate, potassium chloride, potassium bromide, potassium iodide, magnesium chloride, magnesium bromide, magnesium iodide, calcium chloride, calcium bromide, aluminum sulfate.

3. The method for detecting raman spectrum based on colloidal silver gradient aggregation effect according to claim 1, wherein the amount of silver nanoparticle sol added in the step 2 is 500uL.

4. The method for detecting raman spectra based on colloidal silver gradient aggregation effect according to claim 1, wherein the standard solution of the molecule to be detected in the step 2 is added in an amount of 2mL.

5. The method for detecting raman spectra based on colloidal silver gradient aggregation effect according to claim 1, wherein the adding amount of the coagulant in the step 2 is 100uL.

6. The method for detecting raman spectra based on colloidal silver gradient aggregation effect according to claim 1, wherein the concentration of the coagulant in the step 2 is 1.5mol/L.