A raman enhancer, its preparation method and application
By preparing dopamine carbon dot modified gold nanoparticle Raman enhancer, the problems of poor stability of Raman enhancer and detection in tobacco samples were solved, achieving highly sensitive and rapid detection of imidacloprid, meeting the relevant residue limit requirements.
Patent Information
- Application Number
- CN202210202689.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-03-02
- Publication Date
- 2026-02-24
- Estimated Expiration
- 2042-03-02
AI Technical Summary
There are few existing methods for preparing Raman enhancers, and the number of targets that can generate Raman signal enhancement is limited. Gold nanoparticles prepared by conventional methods have poor stability, are not easy to preserve, and are prone to aggregation. Furthermore, the complexity of the tobacco system poses a challenge to the rapid SERS detection of imidacloprid residues.
Dopamine carbon dots were used as reducing agents and stabilizers, combined with the reduction of chloroauric acid by trisodium citrate, to prepare dopamine carbon dot modified gold nanoparticles for rapid detection of imidacloprid in tobacco by surface-enhanced Raman scattering.
It achieves highly sensitive detection of imidacloprid, with a detection limit of 0.08 mg/L and a detection sensitivity of 0.5 mg/kg, meeting the relevant limit detection requirements. Furthermore, the dopamine carbon dot modified gold nanomaterials do not agglomerate after being refrigerated for more than six months, maintaining good stability.
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Figure CN114563392B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a Raman enhancer, its preparation method, and its application, belonging to the field of chemical analysis and detection technology. Background Technology
[0002] Imidacloprid is a novel imidazoline ketone fungicide with high activity against downy mildew, an oomycete disease of crops such as grapes, vegetables, and tobacco. It also has control effects against other pathogens such as ascomycetes and Alternaria. Imidacloprid is a new type of imidazoline pesticide widely used for the control of downy mildew, blight, and pear black spot diseases in various crops. While imidazoloprid has relatively low toxicity, strict limits on its residues are imposed by various countries. For example, the EU recommends a maximum residue level (MRL) of 2 mg / kg for imidazoloprid in parsley. -1 The United States recommends a minimum limit (MRL) of 1.5 mg / kg for imidacloprid in scallions. -1 The Collaborating Centre for Tobacco Scientific Research (CORESTA) recommends a minimum concentration (MRL) of 3.0 mg / kg for imidacloprid in tobacco. -1 The maximum residue limits for imidacloprid vary among different types of plants in my country's food standards, with the lowest being 0.02 mg / kg in potatoes. -1 The highest residue limit was 40 mg / kg in celery. -1 The residue limits for imidacloprid pesticides in tobacco are currently being established. Domestic reports indicate residues in tobacco. To address the needs of agricultural product trade import / export and quality and safety supervision, establishing a simple, accurate, and highly sensitive detection method for analyzing imidacloprid residues in natural products is urgent and of significant practical importance.
[0003] Currently, the main methods for detecting imidacloprid residues include gas chromatography, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry. Chromatographic methods have high requirements for the operating environment, are complex and time-consuming in the analysis process, have expensive equipment, and require the participation of professional personnel, which limits their use in real-time monitoring.
[0004] Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical tool with an irreplaceable role in the identification of substance composition and molecular structure analysis. SERS technology uses surface-roughened metals such as gold, silver, and copper as active substrates, allowing analyte molecules to adsorb onto or come very close to the surface of the noble metal nanostructures on the active substrate, resulting in a significant enhancement of the Raman scattering signal. The active substrate is often referred to as a Raman enhancer. SERS offers advantages such as no sample preparation required, short measurement time, and high sensitivity and accuracy, making it suitable for rapid and online detection, and it holds promise as a new method for the analysis of pesticides such as imidacloprid.
[0005] Sol-type Raman enhancers can be prepared on a large scale and have cost advantages, making them key products for the widespread application of SERS. In existing technologies, the preparation of gold nanoparticle sols with particle sizes smaller than 10 nm typically involves a chemical reduction method in an aqueous or oil phase, where a strong reducing agent (sodium borohydride, ascorbic acid, etc., with sodium borohydride usually prepared using trisodium citrate solution) reacts with chloroauric acid. However, as the nanoparticle size decreases, the dispersibility deteriorates. Simultaneously, as the nanoparticle size decreases, the specific surface area increases, surface activity rises, and the stability of the nanoparticle sol solution decreases, making it prone to aggregation, resulting in a significant reduction in the Raman effect.
[0006] Therefore, due to the limited number of methods for preparing sol-based Raman enhancers, the limited number of targets capable of generating Raman signal enhancement, and the poor stability and tendency to aggregate in laboratory-produced products, the preparation of Raman enhancers is a bottleneck restricting the application of SERS. The targets refer to precious metals capable of generating enhancement hotspots, such as gold, silver, and copper. Furthermore, the inherent complexity of the tobacco system itself poses a challenge to the rapid SERS detection of imidacloprid residues in tobacco samples. Summary of the Invention
[0007] To address the current limitations of Raman spectroscopy enhancement agent preparation methods, the limited number of targets capable of generating Raman signal enhancement, the poor stability of gold nanoparticles prepared by conventional methods (making them difficult to preserve and prone to aggregation), and the lack of reports and challenges in rapid SERS detection of imidacloprid residues in tobacco samples due to the complexity of the tobacco system, this invention provides a method for preparing a Raman spectroscopy enhancement agent in its first aspect. The second aspect of this invention provides a Raman spectroscopy enhancement agent. The third aspect of this invention provides an application of the Raman spectroscopy enhancement agent.
[0008] The technical solution of the present invention:
[0009] A method for preparing Raman enhancers, using dopamine carbon dots as reducing agents and stabilizers, employs a modified trisodium citrate reduction of chloroauric acid method to prepare dopamine carbon dot modified gold nanoparticles.
[0010] Specifically, the preparation method includes the following steps:
[0011] Step 1: Synthesis of dopamine carbon dots: Dopamine and citric acid are dissolved in water and mixed evenly to obtain a mixed solution. After hydrothermal reaction, the solution is cooled to obtain a brown solution. The brown solution is filtered, centrifuged, and the supernatant is dried under vacuum to obtain the dopamine carbon dots.
[0012] Step 2: Preparation of dopamine carbon dot modified gold nanoparticles: Dissolve the dopamine carbon dots and trisodium citrate in water, heat in an oil bath, add chloroauric acid to obtain a mixture, stir in the dark, cool to room temperature, centrifuge, and the supernatant is the dopamine carbon dot modified gold nanoparticles.
[0013] In step one, the hydrothermal temperature is 180-200℃, and the hydrothermal time is 8-10 hours. In step one, the concentration of dopamine in the mixed solution is 1.0-2.0 g / 20 mL, and the concentration of citric acid in the mixed solution is 0.5-1.0 g / 20 mL.
[0014] In step two, the oil bath heating temperature is 90-100℃, and the stirring time in the dark is 50-60 minutes. In step two, the concentration of the dopamine carbon dots in water is 12-15 mg / 40 mL, the concentration of the trisodium citrate in water is 20-25 mg / 40 mL, and the concentration of the chloroauric acid in the mixture is 10-15 mg / mL.
[0015] A Raman enhancer is a dopamine carbon dot modified gold nanoparticle obtained by the above preparation method.
[0016] An application of a Raman enhancer for rapid detection of imidacloprid in tobacco using surface-enhanced Raman scattering includes the following steps:
[0017] Step 1: Preparation of dopamine carbon dot modified gold nanoparticle Raman enhancer: Using dopamine carbon dots as reducing agent and stabilizer, the dopamine carbon dot modified gold nanoparticle Raman enhancer is prepared by a modified trisodium citrate reduction method for chloroauric acid.
[0018] Step 2: Establish a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak for surface-enhanced Raman scattering spectroscopy (SERS) of imidacloprid: Mix imidacloprid standard solutions of different concentrations with the dopamine carbon dot modified gold nanoparticle Raman enhancer, and use a portable Raman spectrometer to perform Raman spectroscopy on the area to be detected. Determine the highest characteristic peak of imidacloprid as the quantitative characteristic peak for surface-enhanced Raman scattering spectroscopy, and establish a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak.
[0019] Step 3: Surface-enhanced Raman scattering spectroscopy determination of imidacloprid in tobacco leaf samples: The tobacco leaves are pretreated to obtain the sample solution to be tested. The sample solution to be tested is mixed with the dopamine carbon dot modified gold nano Raman enhancer. The portable Raman spectrometer is used to perform Raman spectroscopy detection on the area to be tested. Based on the peak area of the quantitative characteristic peak and the linear relationship established in Step 2, the concentration of imidacloprid in the tobacco sample is calculated.
[0020] The specific steps for pretreating the tobacco leaves to obtain the test sample liquid in step three are as follows: using acetonitrile as the extractant, the tobacco powder of the tobacco leaf sample is extracted by ultrasonic extraction, filtered, and the filtrate is concentrated to dryness by rotary evaporation to obtain residue. The residue is dissolved in acetonitrile a second time and the volume is adjusted to obtain the test sample liquid.
[0021] The volume of the imidacloprid standard solution is 200 μL, and the concentration is 0.08-2.85 μg / mL; the volume of the dopamine carbon dot modified gold nanoparticle Raman enhancer is 50-100 μL.
[0022] Beneficial technical effects of the present invention:
[0023] 1. Based on the initial synthesis of dopamine carbon dots, this invention introduces dopamine carbon dots into the synthesis process of gold nanoparticle Raman enhancers for the first time, acting as a reducing agent and stabilizer. Combined with trisodium citrate as a reducing agent, chloroauric acid is reduced, thus proposing a novel method for synthesizing gold nanoparticle Raman enhancers. This method utilizes the groups on the carbon dot surface, such as hydroxyl groups (-OH), and the reducing properties of dopamine itself, the raw material for carbon dot preparation. Combined with trisodium citrate, which acts as a buffer system and reducing agent, chloroauric acid is reduced. The resulting gold nanoparticles exhibit significant Raman enhancement effects and significantly enhanced stability. They do not agglomerate after more than six months of refrigerated storage and can also be stored at room temperature for short periods without affecting the enhancement effect.
[0024] 2. The Raman enhancer of this invention, when used for the detection of imidacloprid residues in tobacco, utilizes dopamine-modified gold nanomaterials as Raman enhancers. This enhances the interaction between imidacloprid and the carbon dots on the gold nanoparticle surface, achieving both electromagnetic and chemical enhancement effects. This results in highly sensitive detection of imidacloprid, with a detection limit of 0.08 mg / L. Furthermore, the Raman enhancement effect of the dopamine-modified gold nanomaterials reduces interference from coexisting substances in tobacco, ensuring that these substances do not interfere with the determination. The SERS detection sensitivity for imidacloprid in tobacco samples reaches 0.5 mg / kg, and the maximum residue limit (MRL) for imidacloprid in tobacco is 3 mg / kg, fully meeting the relevant limit detection requirements. This surface-enhanced Raman scattering method for rapid detection of imidacloprid in tobacco is characterized by high specificity, simple operation, speed, and low instrument cost. Attached Figure Description
[0025] Figure 1 (a) is an electron micrograph of the dopamine carbon dots prepared in Example 1. Figure 1 (b) is an electron microscope image of the dopamine carbon dot modified gold nanoparticle Raman enhancer prepared in Example 1;
[0026] Figure 2 SERS spectra of methanol, AuNPs, imidacloprid solution, and AuNPs + imidacloprid standards at different concentrations;
[0027] 1-Methanol, methanol is the solvent for imidacloprid standard; 2-Dopamine carbon dot modified gold nanoparticles, i.e., AuNPs; 3-Imidacloprid solution; 4-AuNPs + 0.71 μg / mL imidacloprid solution; 5-AuNPs + 0.93 μg / mL imidacloprid solution; 6-AuNPs + 1.14 μg / mL imidacloprid solution.
[0028] Figure 3 The above are SERS spectra of different concentrations of imidacloprid in Example 2 of this invention.
[0029] Figure 4 This illustrates the linear relationship between different concentrations of imidacloprid and the intensity of the characteristic peak in Example 2 of the present invention.
[0030] Figure 5 The above are SERS spectra of tobacco extract with different concentrations of imidacloprid added in Example 2 of the present invention.
[0031] 1-Tobacco leaf extract, 2-Tobacco leaf extract + 0.1 mg / kg imidacloprid standard, 3-Tobacco leaf extract + 0.5 mg / kg imidacloprid standard, 4-Tobacco leaf extract + 1.0 mg / kg imidacloprid standard, 4-Tobacco leaf extract + 1.5 mg / kg imidacloprid standard. Detailed Implementation
[0032] To more clearly illustrate the technical solution of the present invention, specific embodiments and appendices will be used below. Figure 1-5 A detailed introduction will be provided.
[0033] A method for preparing dopamine carbon dot-modified gold nanoparticles Raman enhancers, using dopamine carbon dots as a reducing agent and stabilizer, and employing a modified trisodium citrate reduction of chloroauric acid method to prepare the dopamine carbon dot-modified gold nanoparticles, includes the following steps:
[0034] Step 1: Synthesis of dopamine carbon dots: Dopamine carbon dots are synthesized by hydrothermal method using dopamine as raw material and dopamine and citric acid as reducing agents.
[0035] Weigh 1.0-2.0g of dopamine and 0.5-1.0g of citric acid and dissolve them in 20mL of ultrapure water. Mix them evenly by ultrasonication to obtain a mixed solution. Transfer the mixed solution to a polytetrafluoroethylene-lined hydrothermal reactor and heat it at a constant temperature of 180-200℃ for 8-10 hours to carry out the hydrothermal reaction. After the reaction is completed, allow it to cool naturally to room temperature to obtain a brown solution. Remove large particulate impurities from the brown solution using a 0.22μm filter membrane, and then centrifuge it at high speed of 8000-10000rpm for 10-15min. Dry the supernatant under vacuum to obtain dopamine carbon dots.
[0036] Step 2: Preparation of dopamine carbon dot modified gold nanoparticles: Using the dopamine carbon dots and trisodium citrate as reducing agents and the dopamine carbon dots as stabilizers, the modified gold nanoparticles are prepared by reducing chloroauric acid using a modified trisodium citrate reduction method.
[0037] 12-15 mg of dopamine carbon dots and 20-25 mg of trisodium citrate were dissolved in 40 mL of ultrapure water, heated in an oil bath to 90-100 °C, and HAuCl4 was added to obtain a mixture. The concentration of HAuCl4 in the mixture was 10-15 mg / mL. The mixture was stirred in the dark for 50-60 min, cooled to room temperature, and centrifuged at 8000-10000 rpm for 10-15 min. The supernatant was the dopamine carbon dot modified gold nanoparticles.
[0038] A dopamine carbon dot modified gold nanoparticle Raman enhancer prepared by the above method is used for rapid detection of imidacloprid in tobacco by surface-enhanced Raman scattering.
[0039] Specifically, a method for rapid detection of imidacloprid in tobacco using surface-enhanced Raman scattering with dopamine carbon dots modified gold nanoparticles as a Raman enhancer includes the following steps:
[0040] Step 1: Preparation of dopamine carbon dot modified gold nanoparticle Raman enhancer;
[0041] (11) Synthesis of dopamine carbon dots: Dopamine carbon dots were synthesized by hydrothermal method using dopamine as raw material and dopamine and citric acid as reducing agents.
[0042] Weigh 1.0-2.0g of dopamine and 0.5-1.0g of citric acid, dissolve them in 20mL of ultrapure water, and ultrasonically mix them to obtain a mixed solution. Transfer the mixed solution to a polytetrafluoroethylene-lined hydrothermal reactor and heat it at a constant temperature of 180-200℃ for 8-10 hours to carry out the hydrothermal reaction. After the reaction is completed, allow it to cool naturally to room temperature to obtain a brown solution. Remove large particulate impurities from the brown solution using a 0.22μm filter membrane, then centrifuge it at high speed. Vacuum dry the supernatant to obtain dopamine carbon dots.
[0043] (12) Preparation of gold nanoparticles modified with dopamine carbon dots: using the dopamine carbon dots and trisodium citrate as reducing agents and the dopamine carbon dots as stabilizers, the modified gold nanoparticles modified with dopamine carbon dots are prepared by reducing chloroauric acid using a modified trisodium citrate reduction method.
[0044] Weigh 12-15 mg of dopamine carbon dots and 20-25 mg of trisodium citrate, dissolve them in 40 mL of ultrapure water, heat in an oil bath to 100 °C, add HAuCl4, the concentration of HAuCl4 in the mixture is 10-15 mg / mL, stir in the dark for 60 min, cool to room temperature, centrifuge at high speed, and the supernatant is dopamine carbon dots modified gold nanoparticles.
[0045] Step 2: Establish a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak for surface-enhanced Raman scattering (SERS) detection of imidacloprid: Mix imidacloprid standard solutions of different concentrations with the dopamine carbon dot modified gold nanoparticle Raman enhancer, and perform Raman spectroscopy detection on the area to be detected using a portable Raman spectrometer. Determine the Raman peak position of imidacloprid based on its molecular structure and density functional theory (DFT) calculations. Then, select the highest characteristic peak of imidacloprid as the quantitative characteristic peak for SERS detection of imidacloprid, and establish a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak.
[0046] (21) SERS detection of imidacloprid: Take 200 μL of imidacloprid standard solution of different concentrations and mix it with 50-100 μL of dopamine carbon dot modified gold nano Raman enhancer. Use a portable Raman spectrometer to detect the area to be detected by Raman spectroscopy.
[0047] (22) Determination of wavenumber for SERS detection of imidacloprid and SERS analysis of standard: The Raman peak position of imidacloprid was determined based on the molecular structure of imidacloprid and the density functional theory (DFT) calculation. Then, the highest characteristic peak of imidacloprid was selected as the quantitative characteristic peak of imidacloprid detected by surface-enhanced Raman scattering spectroscopy, and a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak was established.
[0048] Step 3: SERS determination of imidacloprid in tobacco leaf samples: The tobacco leaves are pretreated to obtain the sample solution to be tested. The sample solution to be tested is mixed with dopamine carbon dot modified gold nano Raman enhancer. The portable Raman spectrometer is used to detect the Raman spectrum of the area to be tested. The concentration of imidacloprid in tobacco is calculated based on the peak area of the characteristic peak.
[0049] (31) Pretreatment of tobacco leaf samples: Acetonitrile was used as the extractant to extract the tobacco powder of the tobacco leaf samples by ultrasonic extraction, and the filtrate was concentrated to dryness by rotary evaporation to obtain the residue. The residue was dissolved in acetonitrile for a second time and the volume was adjusted to obtain the sample solution to be tested. The tobacco powder of the tobacco leaf samples can be cigarette samples.
[0050] (32) If the residue of imidacloprid pesticide in the sample solution to be tested is higher than or equal to 0.5 mg / kg, the sample solution to be tested is mixed with dopamine carbon dot modified gold nano Raman enhancer, and the Raman spectrum of the area to be tested is detected using a portable Raman instrument. The concentration of imidacloprid in tobacco is calculated based on the peak area of the quantitative characteristic peak.
[0051] (33) If the residue of imidacloprid pesticide in the sample solution is less than 0.5 mg / kg, it can be verified by the sample spike recovery rate and precision test.
[0052] Example 1
[0053] A method for preparing a dopamine carbon dot modified gold nanoparticle Raman enhancer includes the following steps:
[0054] Step 1: Synthesis of Dopamine Carbon Dots: Weigh 1.0 g of dopamine and 0.7 g of citric acid and dissolve them in 20 mL of ultrapure water. Mix thoroughly by ultrasonication to obtain a homogeneous solution. Transfer the solution to a polytetrafluoroethylene-lined hydrothermal reactor and heat at 200 °C for 10 hours to carry out the hydrothermal reaction. After the reaction is complete, allow it to cool naturally to room temperature to obtain a brown solution. Remove large particulate impurities from the brown solution using a 0.22 μm filter membrane, then centrifuge at 8000-10000 rpm for 10-15 min. Vacuum dry the supernatant to obtain dopamine carbon dots. The electron micrograph is shown below. Figure 1 As shown in (a);
[0055] Step 2: Preparation of Dopamine Carbon Dot Modified Gold Nanoparticles: Dissolve 13 mg of dopamine carbon dots and 22 mg of trisodium citrate in 40 mL of ultrapure water. Heat in an oil bath to 100 °C, add HAuCl4 to obtain a mixture. The concentration of HAuCl4 in the mixture is 11 mg / mL. Stir in the dark for 60 min, cool to room temperature, and centrifuge at 8000-10000 rpm for 10-15 min. The supernatant is the dopamine carbon dot modified gold nanoparticle Raman enhancer. Its electron micrograph is shown below. Figure 1 As shown in (b).
[0056] In step two, the two reducing agents, dopamine carbon dots and citric acid, are first mixed and heated in an oil bath to disperse them evenly and form a relatively stable system. Then, chloroauric acid is added dropwise to further improve the stability of the gold nanoparticles.
[0057] like Figure 1 As shown in (a), the dopamine carbon dots are uniformly dispersed, with a diameter of 2-6 nm. Figure 1As shown in (b), the dopamine carbon dot-modified gold nanoparticle Raman enhancer exhibits an amorphous edge structure with a size of 45±5 nm. The formation of this amorphous edge structure is likely due to nitrogen atom doping in dopamine. The sharp angles of the edge structure of the dopamine carbon dot-modified gold nanoparticles, compared to spherical shapes, lead to more significant plasmon resonance, resulting in better Raman enhancement. The presence of oxygen-containing groups on the dopamine carbon dots increases their interaction with the gold nanoparticles. The presence of dopamine carbon dots around the gold nanoparticles promotes better uniform dispersion, prevents aggregation, and significantly increases the stability of the gold nanoparticles.
[0058] Example 2
[0059] A method for rapid detection of imidacloprid in tobacco by surface-enhanced Raman scattering using dopamine carbon dot-modified gold nanoparticle Raman enhancer as described in Example 1 includes the following steps:
[0060] Step 1: Prepare dopamine carbon dot modified gold nanoparticle Raman enhancer according to the method in Example 1;
[0061] Step 2: Establish a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak for imidacloprid detection using surface-enhanced Raman scattering spectroscopy:
[0062] (21) SERS detection of imidacloprid: 200 μL of imidacloprid standard solutions of different concentrations (2.850 mg / L, 1.428 mg / L, 0.714 mg / L, 0.535 mg / L, 0.140 mg / L, and 0.08 mg / L) were mixed with 50-100 μL of dopamine carbon dot modified gold nanoparticle Raman enhancer. Raman spectroscopy of the target area was performed using a portable Raman spectrometer under conditions of 785 nm excitation light, 500 mW laser power, and a scanning time of 10 seconds. The obtained SERS spectra are shown below. Figure 3 As shown, the curve still has obvious Raman peaks at a concentration as low as 0.08 mg / L. Therefore, the detection concentration of imidacloprid standard solution by this method reaches 0.08 mg / L.
[0063] (22) Determination of wavenumber for SERS detection of imidacloprid and SERS analysis of standard: The Raman peak position of imidacloprid was determined based on the molecular structure of imidacloprid and the density functional theory (DFT) calculation. Then, the highest characteristic peak of imidacloprid was selected as the quantitative characteristic peak of imidacloprid detected by surface-enhanced Raman scattering spectroscopy, and a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak was established.
[0064] like Figure 2As shown in curves 4-6, the SERS spectra of dopamine-modified gold nanoparticle Raman enhancer + imidacloprid standard all show a value of 631 cm⁻¹. -1 698cm -1 1186cm -1 1356cm -1 1416cm -1 and 1578cm -1 Based on the molecular structure and density functional theory of imidacloprid, the characteristic SERS peaks at the peak position were determined to be Raman peaks of imidacloprid. At 1186 cm⁻¹ -1 The highest peak is located at 1186cm. -1 The characteristic peak at a certain position is used as the quantitative characteristic peak for SERS detection of imidacloprid; the peak intensity of this quantitative characteristic peak in the SERS spectrum of imidacloprid varies with the concentration of the standard solution (2.850, 1.428, 0.714, 0.535, 0.140 and 0.08 mg / L), as shown below. Figure 3 As shown, the linear regression equation between imidacloprid concentration and the peak area of the quantitative characteristic peak is: y = 27613.21x - 1041.63, R0 2 =0.9850; the linear equation shows a good linear relationship, which in turn proves that the selection of this quantitative characteristic peak is reasonable;
[0065] in addition, Figure 2 Curves 1 and 2 show that neither the solvent of imidacloprid standard—methanol—nor the dopamine carbon dot modified gold nanoparticles themselves produce the characteristic peaks of imidacloprid. Curve 3 shows that without the presence of dopamine carbon dot modified gold nanoparticles (Au NPs), almost no Raman characteristic peaks of imidacloprid were observed in imidacloprid alone, proving that the synthesized dopamine carbon dot modified gold nanoparticle Raman enhancer played a significant Raman signal enhancement effect.
[0066] Step 3: SERS determination of imidacloprid in tobacco leaf samples:
[0067] (31) Pretreatment of tobacco leaf samples: The tobacco leaf samples were dried at 40℃ for 15 hours, pulverized, passed through a 40-mesh sieve, and sealed for storage. 1g of tobacco powder was accurately weighed and placed in a 50mL Erlenmeyer flask. 20mL of acetonitrile was added, and the samples were extracted by ultrasonication at room temperature for 30 minutes. The mixture was filtered, and the filtrate was concentrated to dryness at 50℃ using a rotary evaporator. The residue was dissolved in acetonitrile and the volume was adjusted to 10mL to obtain the sample solution to be tested.
[0068] (32) Take 200 μL of the sample solution to be tested and mix it with 100 μL of dopamine carbon dot modified gold nano Raman enhancer. Use a portable Raman spectrometer to perform surface-enhanced Raman spectroscopy detection on the area to be tested. When the residue of imidacloprid pesticide in the positive sample is higher than or equal to 0.5 mg / kg, the residue of imidacloprid in the tobacco sample can be calculated based on the peak area of the quantitative characteristic peak of the sample to be tested and the standard curve fitted by the method in Example 2.
[0069] (33) Sample spike recovery and precision test and verification.
[0070] Specifically as follows: Figure 5 As shown, through spiked recovery and precision tests, i.e., after processing the tobacco leaf sample in step (31) to obtain the blank test sample solution, different concentrations of imidacloprid standard solution (0.1, 0.5, 1.0, 1.5 mg / kg) were added, and 100 μL of dopamine carbon dot modified gold nano Raman enhancer were mixed with each solution for SERS detection, resulting in curves 2-5. The results show that when the added imidacloprid concentration is 0.5 mg / kg, the 1186 cm⁻¹ curve is 1186 cm⁻¹. -1 The characteristic peaks were still identifiable. When the concentration was as low as 0.1 mg / kg, the obtained SRES spectrum was similar to that of the blank tobacco sample. In curve 1, the treated sample liquid / tobacco extract was mixed with 100 μL of dopamine carbon dot modified gold nanoparticle Raman enhancer, and blank surface-enhanced Raman scattering spectroscopy was performed. It was found that matrix interference reduced the recognition of imidacloprid SRES spectrum, and the imidacloprid Raman characteristic peaks were not significant. Therefore, the detection limit of imidacloprid in tobacco samples by this method is 0.5 mg / kg. When the imidacloprid pesticide residue in the sample is lower than 0.5 mg / kg, the detection result is not detected. The spiked recovery and precision test results show that the detection method of the present invention has good reproducibility. The detection limit of imidacloprid pesticide residue in tobacco is 0.5 mg / kg, the experimental reproducibility is good, and the detection rate is >90%.
[0071] The foregoing has described in detail representative embodiments and test examples of the present invention. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention. Changes and combinations that are obvious to those skilled in the art are all within the protection scope of the present invention.
Claims
1. A method for preparing a Raman enhancer for rapid SERS detection of imidacloprid residues in tobacco samples, characterized in that... Dopamine carbon dots were used as reducing agents and stabilizers, and a modified trisodium citrate-chloroauric acid reduction method was employed to prepare dopamine carbon dot-modified gold nanoparticles. The specific steps included: Step 1: Synthesis of dopamine carbon dots: Dopamine and citric acid are dissolved in water and mixed evenly to obtain a mixed solution. After hydrothermal reaction, the solution is cooled to obtain a brown solution. The brown solution is filtered, centrifuged, and the supernatant is vacuum dried to obtain the dopamine carbon dots. The concentration of dopamine in the mixed solution is 1.0-2.0 g / 20 mL, the concentration of citric acid in the mixed solution is 0.5-1.0 g / 20 mL, the hydrothermal temperature is 180-200℃, and the hydrothermal time is 8-10 hours. Step 2: Preparation of dopamine carbon dots modified gold nanoparticles: Dissolve the dopamine carbon dots and trisodium citrate in water, heat in an oil bath, add chloroauric acid to obtain a mixture, stir in the dark, cool to room temperature, centrifuge, and the supernatant is the dopamine carbon dots modified gold nanoparticles. The concentration of the dopamine carbon dots in water is 12-15 mg / 40 mL, the concentration of the trisodium citrate in water is 20-25 mg / 40 mL, the concentration of the chloroauric acid in the mixture is 10-15 mg / mL, the oil bath heating temperature is 90-100℃, and the stirring time in the dark is 50-60 min.
2. A Raman enhancer, characterized in that... The dopamine carbon dot modified gold nanoparticles are obtained by the preparation method described in claim 1.
3. The application of the Raman enhancer according to claim 2, characterized in that... For rapid detection of imidacloprid in tobacco using surface-enhanced Raman scattering, the following steps are included: Step 1: Preparation of dopamine carbon dot modified gold nanoparticle Raman enhancer: Using dopamine carbon dots as reducing agent and stabilizer, the dopamine carbon dot modified gold nanoparticle Raman enhancer is prepared by a modified trisodium citrate reduction method for chloroauric acid. Step 2: Establish a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak for surface-enhanced Raman scattering spectroscopy (SERS) of imidacloprid: Mix imidacloprid standard solutions of different concentrations with the dopamine carbon dot modified gold nanoparticle Raman enhancer, and use a portable Raman spectrometer to perform Raman spectroscopy on the area to be detected. Determine the highest characteristic peak of imidacloprid as the quantitative characteristic peak for surface-enhanced Raman scattering spectroscopy, and establish a linear relationship between the concentration of imidacloprid and the peak area of the quantitative characteristic peak. Step 3: Surface-enhanced Raman scattering spectroscopy determination of imidacloprid in tobacco leaf samples: The tobacco leaves are pretreated to obtain the sample solution to be tested. The sample solution to be tested is mixed with the dopamine carbon dot modified gold nano Raman enhancer. The portable Raman spectrometer is used to perform Raman spectroscopy detection on the area to be tested. Based on the peak area of the quantitative characteristic peak and the linear relationship established in Step 2, the concentration of imidacloprid in the tobacco sample is calculated.
4. The application according to claim 3, characterized in that... The specific steps for pretreating the tobacco leaves to obtain the test sample liquid in step three are as follows: using acetonitrile as the extractant, the tobacco powder of the tobacco leaf sample is extracted by ultrasonic extraction, filtered, and the filtrate is concentrated to dryness by rotary evaporation to obtain residue. The residue is dissolved in acetonitrile a second time and the volume is adjusted to obtain the test sample liquid.
5. The application according to claim 3, characterized in that... The volume of the imidacloprid standard solution is 200 μL, and the concentration is 0.08-2.85 μg / mL; the volume of the dopamine carbon dot modified gold nano Raman enhancer is 50-100 μL.