阅读说明：本技术 一种茶叶中农药检测方法及装置 (Detection method and device for pesticide in tea ) 是由 付兰克 李浩文 伍李云 张婷婷 周靖 毛桂林 于 2021-07-21 设计创作，主要内容包括：本发明公开了一种茶叶中农药检测方法以及装置,方法包括制备SERS基底；将SERS基底涂抹在预设的多孔载体的检测面,直至SERS基底固化,得到SERS涂层；对SERS涂层进行还原处理,得到包含银纳米颗粒的检测层,并将检测层与多孔载体作为检测组件；获取待检测的茶叶,并使用预设的提取剂对茶叶进行化合物提取,得到待测溶液；使待测溶液穿透检测组件的检测层；用一激光束照射反应后的检测组件,使得该检测组件散射激光束,产生散射光；收集散射光并根据散射光生成茶叶的检测拉曼光谱,并基于预设的参考拉曼光谱以及检测拉曼光谱,确定茶叶中是否存在目标农药及目标农药的含量。本发明提供的检测方法能够快速且精确地对茶叶中农药残余进行检测。(The invention discloses a method and a device for detecting pesticide in tea, wherein the method comprises the steps of preparing an SERS substrate; coating the SERS substrate on a detection surface of a preset porous carrier until the SERS substrate is solidified to obtain an SERS coating; reducing the SERS coating to obtain a detection layer containing silver nanoparticles, and taking the detection layer and the porous carrier as a detection assembly; obtaining tea to be detected, and extracting compounds of the tea by using a preset extracting agent to obtain a solution to be detected; enabling the solution to be detected to penetrate through a detection layer of the detection assembly; irradiating the reacted detection assembly with a laser beam to enable the detection assembly to scatter the laser beam and generate scattered light; collecting scattered light, generating a detection Raman spectrum of the tea according to the scattered light, and determining whether the target pesticide exists in the tea and the content of the target pesticide based on a preset reference Raman spectrum and the detection Raman spectrum. The detection method provided by the invention can be used for rapidly and accurately detecting pesticide residues in the tea.)

1. A method for detecting pesticides in tea leaves is characterized by comprising the following steps:

preparing a SERS substrate, wherein the SERS substrate comprises a condensate, a silver salt and ammonium hydroxide;

smearing the SERS substrate on a detection surface of a preset porous carrier until the SERS substrate is cured to obtain an SERS coating;

reducing the SERS coating to obtain a detection layer containing silver nanoparticles, and taking the detection layer and the porous carrier as a detection assembly;

obtaining tea to be detected, and extracting compounds of the tea by using a preset extracting agent to obtain a solution to be detected;

enabling the solution to be detected to penetrate through a detection layer of the detection assembly so that the solution to be detected is in contact with and reacts with the silver nanoparticles;

irradiating the reacted detection assembly with a laser beam to enable the detection assembly to scatter the laser beam and generate scattered light;

collecting the scattered light, generating a detection Raman spectrum of the tea according to the scattered light, and determining whether the target pesticide exists in the tea and the content of the target pesticide based on a preset reference Raman spectrum and the detection Raman spectrum.

2. The method for detecting agricultural chemicals in tea leaves according to claim 1, wherein the solidified substance includes ethyl silicate and methyltriethoxysilane.

3. The method for detecting the pesticide in the tea leaves according to claim 1, wherein the SERS substrate further comprises a silane coupling agent.

4. The method for detecting pesticides in tea leaves according to claim 3, wherein the volume ratio of the cured product to the silane coupling agent is 10: 1.

5. the method for detecting pesticides in tea leaves according to claim 3, wherein the silane coupling agent comprises 3-aminopropyltriethoxysilane.

6. The method for detecting the pesticide in the tea leaves as claimed in claim 1, wherein the SERS substrate further comprises a cationic surfactant.

7. The method for detecting pesticides in tea leaves according to claim 6, wherein the volume ratio of the cured product to the cationic surfactant is 10: 1.

8. the method for detecting the pesticide in the tea leaves as claimed in claim 6, wherein the cationic surfactant comprises cetyltrimethylammonium chloride.

9. The method for detecting pesticides in tea according to claim 6, wherein the porous carrier comprises a glass product; the method comprises the following steps of smearing the SERS substrate on a detection surface of a preset porous carrier until the SERS substrate is cured to obtain the SERS coating, and further comprises the following steps:

and pre-treating the detection surface of the glass product in the sequence of absolute ethyl alcohol, saturated potassium hydroxide and water washing.

10. The device for detecting the pesticide in the tea is characterized by comprising a Raman spectrum analyzer and a plurality of detection assemblies according to claims 1-9;

the detection assembly is used for obtaining a solution to be detected and enabling the solution to be detected to penetrate through a detection layer of the detection assembly so as to enable the solution to be detected to be in contact with the silver nanoparticles;

the Raman spectrometer comprises an emission component, a receiving component and an analysis component;

wherein the emitting component is used for emitting a laser beam to the detecting component;

the receiving assembly is used for collecting scattered light scattered by the detection assembly aiming at the laser beam and generating a detection Raman spectrum corresponding to the solution to be detected;

the analysis component is used for determining pesticide information corresponding to the tea leaves according to a preset reference Raman spectrum and the detection Raman spectrum.

Technical Field

The invention relates to the technical field of chemical detection, in particular to a method and a device for detecting pesticides in tea.

Background

Tea is second only to water in the world and is the most consumed beverage. There are over 20000 different kinds of tea in the world, and the tea leaves are classified into various kinds, and the six kinds of tea are classified into green tea, yellow tea, black tea, white tea and oolong tea. With the expansion of tea production scale, the problem of pesticide abuse in the tea cultivation process becomes more and more serious. The pesticides contained in the cultivated tea leaves pose a risk to both the farmer and the ultimate consumer. If pesticide residues in the tea leaves are found in the quality inspection process, the pesticide residues also affect the tea leaves. Therefore, controlling the content of pesticides in the tea cultivation process is extremely important. Therefore, in the tea cultivation process, cultivation personnel need to strictly control the using amount of pesticides and timely and effectively detect the amount of residual pesticides in the tea so as to quickly adjust the cultivation scheme and reduce pesticide residues as much as possible. At present, strict regulations are carried out on the residual quantity of pesticides in tea in various countries, and the residual quantity is generally set to be 30-0.05 mg/kg (or 30 parts per million to 50 parts per billion).

To date, over 700 known compounds have been isolated or identified in tea leaves, which are themselves rich in chemical components such as alkaloids, pigments, polyphenols. The content standard of quality detection is extremely low, so that certain difficulty is brought to the current tea residue. Existing detection schemes include Gas Chromatography (GC), High Performance Liquid Chromatography (HPLC), HPLC-tandem mass spectrometry (HPLC), and Enzyme-linked Immunosorbent Assay (ELISA), Near Infrared (NIR), Fourier Transform Infrared (FT-IR), as well as other electrochemical methods. However, the above scheme has accurate measurement, such as GC and HPLC, complex instrument and long measurement time; the measurement is fast, for example near infrared, and the measurement accuracy is poor. Therefore, the existing detection scheme aiming at the pesticide residue in the tea leaves still needs to be improved.

Disclosure of Invention

The invention aims to solve the technical problems that the existing detection method for pesticide residues in tea leaves has defects in portability and accuracy, and provides a method for detecting pesticide residues in tea leaves aiming at the defects of the prior art.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a method for detecting pesticides in tea leaves comprises the following steps:

preparing a SERS substrate, wherein the SERS substrate comprises a condensate, a silver salt and ammonium hydroxide;

smearing the SERS substrate on a detection surface of a preset porous carrier until the SERS substrate is cured to obtain an SERS coating;

reducing the SERS coating to obtain a detection layer containing silver nanoparticles, and taking the detection layer and the porous carrier as a detection assembly;

obtaining tea to be detected, and extracting compounds of the tea by using a preset extracting agent to obtain a solution to be detected;

enabling the solution to be detected to penetrate through a detection layer of the detection assembly so that the solution to be detected is in contact with and reacts with the silver nanoparticles;

irradiating the reacted detection assembly with a laser beam to enable the detection assembly to scatter the laser beam and generate scattered light;

collecting the scattered light, generating a detection Raman spectrum of the tea according to the scattered light, and determining whether the target pesticide exists in the tea and the content of the target pesticide based on a preset reference Raman spectrum and the detection Raman spectrum.

The method for detecting the pesticide in the tea leaves is characterized in that the condensate comprises ethyl silicate and methyl triethoxysilane.

According to the method for detecting the pesticide in the tea, the SERS substrate further comprises a silane coupling agent.

The method for detecting the pesticide in the tea leaves is characterized in that the volume ratio of the condensate to the silane coupling agent is 10: 1.

the method for detecting the pesticide in the tea leaves is characterized in that the silane coupling agent comprises 3-aminopropyl triethoxysilane.

The method for detecting the pesticide in the tea leaves is characterized in that the SERS substrate further comprises a cationic surfactant.

The method for detecting the pesticide in the tea leaves is characterized in that the volume ratio of the condensate to the cationic surfactant is 10: 1.

the method for detecting the pesticide in the tea leaves is characterized in that the cationic surfactant comprises hexadecyl trimethyl ammonium chloride.

The method for detecting the pesticide in the tea leaves is characterized in that the porous carrier comprises a glass product; the method comprises the following steps of smearing the SERS substrate on a detection surface of a preset porous carrier until the SERS substrate is cured to obtain the SERS coating, and further comprises the following steps:

and pre-treating the detection surface of the glass product in the sequence of absolute ethyl alcohol, saturated potassium hydroxide and water washing.

A detection device for pesticides in tea leaves specifically comprises a Raman spectrum analyzer and a plurality of detection assemblies;

the detection assembly is used for obtaining a solution to be detected and enabling the solution to be detected to penetrate through a detection layer of the detection assembly so as to enable the solution to be detected to be in contact with the silver nanoparticles;

the Raman spectrometer comprises an emission component, a receiving component and an analysis component;

wherein the emitting component is used for emitting a laser beam to the detecting component;

the receiving assembly is used for collecting scattered light scattered by the detection assembly aiming at the laser beam and generating a detection Raman spectrum corresponding to the solution to be detected;

the analysis component is used for determining pesticide information corresponding to the tea leaves according to a preset reference Raman spectrum and the detection Raman spectrum.

Has the advantages that: compared with the prior art, the invention provides a method and a device for detecting the pesticide in the tea, the method comprises the steps of firstly preparing an SERS (Surface-Enhanced Raman Scattering) substrate containing silver salt, ammonium hydroxide and a condensate, wherein the condensate possibly helps the silver salt in the SERS substrate to be reduced and then limited in a porous carrier distributed with the SERS substrate, and the ammonium hydroxide can reduce the reduction rate of the silver salt and increase the size of the finally formed silver nanoparticles. When the pesticides in the tea are required to be detected, firstly, extracting compounds from the tea to obtain a solution to be detected, then, enabling the solution to be detected to be in contact with the silver nanoparticles, finally, based on the surface enhanced Raman spectroscopy, emitting laser to a detection assembly composed of a detection layer and a porous carrier, collecting reflected scattered light, and manufacturing a detection Raman spectrum. And finally, referring to a preset reference Raman spectrum of the pesticide to be detected, and analyzing and detecting the Raman spectrum so as to detect the existence and the content of the pesticide. According to the scheme, the rapid detection of the pesticide with extremely low content can be realized only by one Raman spectrometer and the detection assembly, and the conditions such as environment, temperature and the like are relatively loose, so that the use is simple and convenient. And the reaction between the solution to be detected and the detection layer in the detection assembly can be realized only in a few minutes, so the scheme has the characteristic of high detection speed.

Drawings

Fig. 1 is a flow chart of the method for detecting the pesticide in the tea provided by the invention.

FIG. 2 is a Raman spectrum obtained by detecting pesticide with a detection component made of cured substances of different components in the method for detecting pesticide in tea provided by the invention

FIG. 3 is a Raman spectrum of carbaryl, endosulfan, dimethoate, disulfoton and malathion in black tea in the method for detecting pesticides in tea provided by the invention.

Fig. 4 is a raman spectrum of DDT in black tea in the method for detecting pesticides in tea provided by the present invention.

Fig. 5 is a raman spectrum obtained after detecting carbofuran of three samples in the method for detecting pesticides in tea provided by the present invention.

FIG. 6 is a Raman spectrum obtained after detection of organophosphorus pesticides O-formate of three samples in the method for detecting pesticides in tea provided by the invention.

Fig. 7 is a raman spectrum obtained by detecting three types of pesticides by using a detection assembly made of a cured material of pure TMOS in the method for detecting pesticides in tea leaves according to the present invention.

Fig. 8 is a raman spectrum for detecting mixed pesticides by using the detection assembly provided by the present invention in the detection method for pesticides in tea provided by the present invention.

Detailed Description

The invention provides a method and a device for detecting pesticide in tea, and in order to make the purpose, technical scheme and effect of the invention clearer and clearer, the invention is further described in detail by referring to the attached drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or wirelessly coupled. As used herein, the term "and/or" includes all or any element and all combinations of one or more of the associated listed items.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The inventor finds that the existing detection of pesticide residue in tea leaves is insufficient in portability and accuracy.

In order to solve the above problems, in an embodiment of the present invention, a SERS substrate is prepared, wherein the SERS substrate includes a cured product, a silver salt, and ammonium hydroxide; smearing the SERS substrate on a detection surface of a preset porous carrier until the SERS substrate is cured to obtain an SERS coating; reducing the SERS coating to obtain a detection layer containing silver nanoparticles, and taking the detection layer and the porous carrier as a detection assembly; obtaining tea to be detected, and extracting compounds of the tea by using a preset extracting agent to obtain a solution to be detected; enabling the solution to be detected to penetrate through a detection layer of the detection assembly so that the solution to be detected is in contact with and reacts with the silver nanoparticles; irradiating the reacted detection assembly with a laser beam to enable the detection assembly to scatter the laser beam and generate scattered light; collecting the scattered light, generating a detection Raman spectrum of the tea according to the scattered light, and determining whether the target pesticide exists in the tea and the content of the target pesticide based on a preset reference Raman spectrum and the detection Raman spectrum.

For example, the embodiment of the invention can be applied to the scenes of quality inspection after tea production, sampling detection of tea in a certain area before picking the tea, periodic detection of pesticide residues in the tea and the like.

It should be noted that the above application scenarios are only presented to facilitate understanding of the present invention, and the embodiments of the present invention are not limited in any way in this respect. Rather, embodiments of the present invention may be applied to any scenario where applicable.

The invention will be further explained by the description of the embodiments with reference to the drawings.

As shown in fig. 1, the present embodiment provides a method for detecting pesticide in tea, which may include the following steps:

s10, preparing a SERS substrate, wherein the SERS substrate comprises a condensate, a silver salt and ammonium hydroxide.

Specifically, before detecting pesticide residues in tea leaves, a SERS substrate comprising a silver salt solution is prepared.

The silver salt is reduced during subsequent processing to form silver nanoparticles. Compared with gold nanoparticles, silver nanoparticles are more active in detection of pesticides containing organic phosphates and carbamates and easier to detect, so that the silver nanoparticles are used as metal nanoparticles for SERS detection.

The SERS substrate further comprises a cured substance, wherein the cured substance is a compound which can be cured under a certain condition, so that silver nanoparticles generated by a subsequent reduction reaction are fixed in holes formed by curing and holes of a porous carrier for bearing the SERS substrate. As the cured product, a material capable of undergoing a sol-gel reaction, i.e., a gel material, can be used. The gel is provided with a plurality of holes which are communicated with each other, so that the gel can fix the silver nanoparticles on one hand and can enable substances needing to be detected to penetrate through the gel to be contacted with the silver nanoparticles on the other hand. In this example, the substance to be detected is tea extract. The selection of the gel material as the cured product can be made in consideration of various factors such as stability of the gel, cost, size of the formed pores, and the like.

The size of the nanoparticles also affects the sensitivity of detection of different compounds. The silver salt, AgNO3, which is most commonly used, is used to produce nanoparticles with the size of 10-20 nm, and on one hand, the nanoparticles with the size are easy to lose from a porous carrier and holes formed after a cured substance is cured, on the other hand, the nanoparticles are difficult to contact with pesticides, and the sensitivity is lower under 785nm light-emitting excitation. In order to form silver nanoparticles on a larger scale, the composition of the SERS substrate is improved in this embodiment, and ammonium hydroxide is further included in SERS.

Ammonium hydroxide (NH)₃OH) is used to increase the stability of the silver ions in the silver salt. In solution, ammonium ionsThe ion reacts with silver ion to form a complex of complex amine ([ Ag (NH) ]₃)₂](OH) or i.e. [ Ag (NH) ]₃)₂]+). In the complexed amine complex, silver ions are in complexed form and therefore can maintain an oxidation state charge of + 1. This form of covalent coordination is very stable and is more difficult to reduce than the silver ions in common silver salts, so the reduction speed is slower and the fractal of the nanoparticles is larger in the process of forming silver nanoparticles. The more fractal nano particles are more difficult to release into a glass vial due to the fact that the silver nano particles formed subsequently are difficult to release, loss caused by small size of the nano particles is reduced, detection sensitivity is improved, and sensitivity of pesticide detection can be improved. In addition, the alkaline solution environment can initiate the base-catalyzed gel curing process during the preparation of the SERS substrate. In this embodiment, the size of the finally formed silver nanoparticles is 100 to 200 nm. The silver nanoparticles of this size can be firmly stabilized in the pores, and also increase the probability of contact with the pesticide ingredient, and exhibit higher sensitivity at 785nm excitation light.

When mixing the silver salt, ammonium hydroxide and the cured product, a certain amount of water is added as a solvent. Taking TMOS as an example of a cured product, 1-2 volumes of 0.1-1.0 mol/L silver nitrate and 28% NH₃And (5) mixing OH (aq) with 1 volume of TMOS for 1-5 minutes to obtain the SERS substrate. Wherein the optimum concentration of the nitrate is 1 mol/L.

Further, the size of the hole to be formed subsequently can be adjusted by adjusting the components of the cured product and the ratio of each component. This example describes cured products of TMOS and Methyltrimethoxysilane (MTMS).

The test object in fig. 2 is a pesticide mixture containing carbaryl and endosulfan sulfate (volume ratio 1: 1) in an amount of 50ppb (50 ng/ml). SERS substrates with different formulas are adopted to manufacture a detection assembly, and the pesticide mixture is detected. (A) Pure TMOS, (B) volume ratio of TMOS to MTMS 5: 1, (C) the volume ratio of TMOS to MTMS is 1: 1. pure TMOS formulation showed p-carbarylThe preferential selective binding of endosulfan, while the potentiating effect on endosulfan is very small. The enhanced effect of endosulfan and carbaryl was greater after addition of MTMS to the TMOS formulation. This result shows the ability to detect multiple pesticides in a mixture simultaneously. The 1:1 formulation has universal sensitivity in detecting various pesticides in the mixture. For more experiments, the volume ratio of TMOS to MTMS was varied from 1: 1-1: 10, or both can be used as a cured material, and when the concentrations of the two are mixed, the ratio is exceeded, and the SERS substrate is difficult to attach on the porous carrier. Wherein the dashed line in the raman spectrum is an XY cursor for directing the peak of interest; the abscissa is the Raman shift (Raman shift) in cm^-1The ordinate is Relative light Intensity (Relative Intensity). The definitions of the horizontal and vertical axes are identical to those of fig. 2, which are not otherwise indicated in the following figures.

Further, the cured material selected in this embodiment includes TEOS (Tetraethyl Orthosilicate) and MTES (Methyltriethoxysilane).

In sol-gel reactions, the speed, extent and mechanism of reaction are influenced by a number of factors, such as the size of the alkyl ligands in the sol, the pH, the type of solvent and the concentration of the solvent, temperature, pressure, chemical structure and nature of the transition state. Each factor affects the characteristics and suitability of the final gel to be formed. For example, a cured product having an excessively high reaction rate cannot be uniformly adhered to the surface of the porous support.

In an acidic environment, the hydrolyzed product is a chain-shaped gel, while in an alkaline environment, the product containing the hydrolyzed TEOS is a gel with a three-dimensional network structure, so that the silver nanoparticles are easier to bind.

In addition, TEOS is less toxic, and in sol-gel reactions TEOS forms ethanol, whereas many gel materials, which form toxic substances, such as TMOS, form toxic methanol after hydrolysis.

MTES in the cured material can help the sol-gel reaction of TEOS, and MTES can be compatible with TEOS, so that the SERS substrate has smaller polarity and is more hydrophobic. Moreover, long chains formed by MTES in the sol-gel reaction make the polarity of the long chains lower than that of the commonly used MTMS, so that the SERS substrate has higher polarity and is helpful for extracting pesticides from a solution. In addition, the product of MTES in the sol-gel reaction is ethanol, which is less toxic.

Further, the porous carrier in this embodiment is a glass article, and the SERS substrate further includes a silane coupling agent. The silane coupling agent can improve the adhesion performance of the glass fiber and the resin, and can be added into a SERS substrate, and when the SERS substrate forms a coating on the surface of a glass vial, the adhesion between the coating and the glass vial can be increased. The silane coupling agent selected in this example is 3-Aminopropyltriethoxysilane (APTES). APTES has a pendant ammonium group (-NH)₂) The radical, in which the nitrogen is present in the form of a lone pair of electrons. Silver is positive and therefore able to interact with the ammonium groups and is more stable. Therefore, the addition of APTES also helps to fix the silver in the coating during the subsequent reduction process, further reducing the loss of silver. Gold is negative compared to silver, so if the metal in the metal salt used in the SERS substrate is gold, the gold nanoparticles cannot be significantly stabilized using lone pair electrons of the silane coupling agent. In this embodiment, the volume ratio of TEOS and MTES to APTES as a whole is 10: 1.

when the components of tea leaves are extracted, an organic solvent is often used as an extracting agent, and the combination of TEOS, MTES and APTES has strong compatibility with the organic solvent, especially ethanol, so that when an organic solvent such as ethanol is used as the extracting agent, a solution to be tested after the compound is extracted can more easily enter a coating formed by the SERS substrate provided in the embodiment.

Further, the SERS substrate further includes a cationic surfactant, the cationic surfactant serves as an organic template in this embodiment, and the cationic surfactant is assembled to generate a porous gel through an interface between an organic substance and an inorganic substance in a sol-gel reaction, so that the pore size of the finally formed coating can be adjusted.

The cationic surfactant selected in this embodiment is Cetyltrimethylammonium chloride (CTAC). The volume ratio of CTAC to APTES is 1:1, or TEOS and MTES as a whole in a volume ratio to CTAC of 10: 1, TEOS/MTES ═ 10: 1. in the SERS substrate of this example, the final concentration of CTAC is 10^ (-4) M.

The effects of CTAC include:

1) promoting the formation of silver nanoparticles, providing more useable metal nanoparticles for SERS. In coatings comprising CTAC, silver nanoparticles are more easily bound. Therefore, the sensitivity of detection can be improved during detection.

2) CTAC helps to pre-concentrate more hydrophobic compounds, most pesticides are hydrophobic compounds. When the solution to be detected containing the pesticide enters the coating, the head amino group of the CTAC can interact with the silver nanoparticles, and the hydrophobic tail can interact with the pesticide molecules in the solution to be detected, so that the hydrophobic tail can more easily concentrate on the surface of the silver nanoparticles, and the detection sensitivity is improved. Existing electrolytes, such as lithium chloride, sodium chloride, nitrate, sulfate or citrate, often act as aggregants for silver or gold colloidal solutions. However, these aggregating agents form a hydrophilic surface on the metal nanoparticles, while hydrophobic compounds, such as pesticides, are more difficult to contact with the metal nanoparticles and therefore less sensitive to detection.

S20, smearing the SERS substrate on the detection surface of a preset porous carrier until the SERS substrate is cured to obtain the SERS coating.

Specifically, after the SERS substrate is prepared, the SERS substrate is coated on a detection surface of a prepared porous carrier, and the detection surface is directly contacted with a solution to be detected for detecting the solution to be detected. And then sealing the porous carrier at a certain temperature for a period of time, so that the SERS substrate is cured on the surface of the porous carrier or cured after gelation, and obtaining the SERS coating.

The material of the porous carrier may include ceramics, glass, etc. The shape of the porous carrier includes a bottle shape, a sheet shape, a test tube shape and the like. The material and shape of the porous carrier can be adjusted according to the requirements of users.

For convenience of explanation, the porous carrier used in this example is a glass vial, and the detection surface is mainly the inner wall of the glass vial. Since this example is based on SERS, the glass vial is colorless and transparent in order to ensure that the scattered light can be effectively detected.

Since the uniformity of the SERS substrate curing on the porous carrier directly affects the subsequent contact between the sample and the metal nanoparticles, in this embodiment, after the SERS substrate is added to the glass vial, the glass vial is rotated on a roller or a shaker at 200-25000rpm, and the slower the speed, the more uniform the thin coating finally formed. The method can save the SERS substrate, the volume of the glass vial adopted in the embodiment is 1-5mL, and only 50-500mL of glass vial is needed to cover the inner wall of the glass vial. In addition, the curing temperature adopted by the embodiment is 20-25 ℃, and the time can be adjusted according to the curing condition.

Further, since the main chemical components of the glass vial are silicon and oxygen, after the SERS coating is obtained, the glass vial may be pre-treated in advance in order to enhance the bonding of the coating to the surface of the glass vial.

The first pretreatment method of this embodiment is to pretreat the detection surface of the glass vial in advance in the order of absolute ethanol, saturated potassium hydroxide, and water washing, thereby hydroxylating the surface of the glass vial, so that the SERS substrate is more effectively bonded by the — Si-O-H bond on the surface of the glass vial.

The silane coupling agent can also realize surface modification on the detection surface of the glass vial. The second pretreatment of this example is to pre-treat the test surface of the vial with a silane coupling agent, such as 1% APTES dissolved in absolute ethanol, for an extended period of time, typically 24 hours being recommended, and then discard the absolute ethanol and 1% APTES and wash the vial.

S30, carrying out reduction treatment on the SERS coating to obtain a detection layer containing silver nanoparticles, and taking the detection layer and the porous carrier as a detection assembly.

After the SERS coating is formed, silver still exists in the SERS coating in the form of silver ions, in order to obtain silver nanoparticles, the SERS coating is subjected to reduction treatment by using a strong reducing agent, wherein the strong reducing agent adopted in the embodiment is sodium borohydride, the volume of the reducing agent is 1-5ml, and the concentration of the reducing agent is 0.01-0.03 mol/L. Besides sodium borohydride, other substances capable of reducing silver ions into silver nanoparticles can be used as the strong reducing agent, such as borohydride such as potassium borohydride.

And contacting the prepared sodium borohydride solution with the detection surface of the porous carrier. For example, when the porous carrier is a glass vial, sodium borohydride is poured into the glass vial. At this time, the sodium borohydride should be in complete contact with the SERS coating, e.g. for a sheet-like porous carrier, the sodium borohydride should completely cover the SERS coating; when the porous carrier is a glass vial, the volume of sodium borohydride should be comparable to or sufficient to completely fill the interior walls of the glass vial.

After the reduction treatment, the porous carrier should be cleaned for many times to avoid the influence of the residual strong reducing agent on the aggregation of the reduced silver particles, thereby influencing the particle size of the finally formed silver nanoparticles.

After being reduced by the strong reducing agent, silver ions are converted into metal silver and are mutually aggregated to form a plurality of silver nanoparticles, and the silver nanoparticles can be restrained in holes in the porous carrier and holes in the detection layer due to the size of the silver nanoparticles. And taking the SERS coating containing the silver nanoparticles as a detection layer to obtain the detection assembly containing the metal nanoparticles.

Further, in order to avoid sodium borohydride residue, after sodium borohydride reduction is adopted, redundant sodium borohydride is washed away by water for 2 times, then diluted nitric acid with 70% is used for neutralization, and finally diluted hydrochloric acid is used for washing, so that the SERS gel containing silver nanoparticles is obtained.

S40, obtaining tea leaves to be detected, and performing compound extraction on the tea leaves by using a preset extraction agent to obtain a solution to be detected.

Specifically, since tea leaves themselves are solid, it is necessary to extract components from tea leaves first, and dissolve the residues of tea leaves in a solution to obtain a solution to be tested. The compound of tea can be extracted by chemical method, boiling method, wave irradiation extraction method, etc. However, the above scheme has certain requirements on extraction conditions, and the extraction in this embodiment is performed by using an extractant, which is simpler and faster. In a first embodiment of this example, the extraction agent is ethanol and water, and the volume ratio of ethanol to water is 1: 1. and (3) extracting the compound at an ambient temperature (4-40 ℃).

Certain pesticides, such as carbaryl, have greater solubility and stability in ethanol than in water. Most pesticides have certain hydrophobicity, and water can promote hydrolysis and degradation of the pesticides. However, even though these pesticides have a higher solubility in ethanol, they are relatively only slightly soluble in ethanol, and most pesticides have a higher solubility in acetonitrile (MeCN), such as bis-p-chlorophenyltrichloroethane (DDT). In a second embodiment of this example, the extracting agents are ethanol, water and MeCN, wherein the volume ratio of ethanol, water and MeCN is 1: 1:1, extracting the compound at the ambient temperature (4-40 ℃).

Although pesticides have higher solubility in MeCN, other compounds in tea, such as caffeine, also have higher solubility in MeCN. Therefore, the volume ratio of ethanol, water and MeCN can be adjusted to reduce the content of compounds that do not need to be detected, depending on the composition of the pesticide to be detected.

Although other extractants can extract pesticide components in tea leaves, many organic solvents destroy the activity of the SERS detection layer and the detection layer falls off to influence the detection efficiency, and EtOH and MeCN do not influence the detection layer of the embodiment, so that the extractants are the optimal extractants.

And S50, enabling the solution to be detected to penetrate through the detection layer of the detection assembly, so that the solution to be detected is in contact with the silver nanoparticles.

And finally, adding the treatment liquid to the detection surface of the detection assembly, and enabling the treatment liquid to penetrate through a detection layer in the detection assembly so as to enable the solution to be detected to be in contact with the metal nanoparticles.

And the solution to be detected can penetrate through the detection layer of the detection assembly by means of gravity, external force generated by shaking and the like. For example, a sheet-shaped porous carrier, a solution to be tested of mixed water is dripped on the surface of the detection layer, and the solution to be tested permeates the detection layer and contacts with the silver nanoparticles under the action of gravity. For example, where the porous support is a glass vial, the solution to be tested is added to the glass vial and then shaken for a period of time to allow the solution to be tested to passively pass through the detection layer and contact the silver nanoparticles. In the present embodiment, a glass vial is preferably used as the porous carrier, and the shaking time is 1 to 5 minutes. Because the solution to be detected can be solidified in a low-temperature environment, and the stability of the components of the detection layer can be influenced by overhigh temperature, the reaction temperature is recommended to be 4-40 ℃, and the reaction can be completed at normal temperature.

S60, irradiating the reacted detecting component with a laser beam, so that the detecting component scatters the laser beam to generate scattered light.

Specifically, a laser beam is emitted to a detection assembly, wherein the solution to be detected is in full contact with the silver nanoparticles, and the substances in the detection assembly generate Raman scattering.

S70, collecting the scattered light, generating a detection Raman spectrum of the tea according to the scattered light, and determining whether the target pesticide exists in the tea and the content of the target pesticide based on a preset reference Raman spectrum and the detection Raman spectrum.

And collecting the Raman scattering, and converting photon energy of the scattered light into electric signal intensity through a detector to generate a detection Raman spectrum corresponding to the solution to be detected. Since the SERS substrate includes silver nanoparticles, raman scattering signals of molecules on the surface of the silver nanoparticles are stronger than conventional raman signals, compared to ordinary raman scattering.

Because different substances have specific shapes on the Raman spectrum, the shapes of the different substances on the Raman spectrum can be used as fingerprints of the substances, and the substance components of the solution to be detected can be qualitatively detected based on the prestored fingerprints of the pesticide to be detected. Meanwhile, if the raman spectrum of the pesticide is prepared in advance according to a known concentration, a raman spectrum of a standard amount of the pesticide can be prepared, thereby realizing quantitative measurement. The implementation pre-stores a reference Raman spectrum of the pesticide to be detected, wherein the spectrum not only contains the 'fingerprint' of the pesticide, but also contains light intensities corresponding to pesticide contents with different concentrations, so as to realize qualitative and quantitative detection of the pesticide.

In this example, SERS spectra of various pesticides, such as carbamates (e.g., carbaryl), organochlorines (e.g., endosulfan), organophosphates (e.g., ortho-carbamate, dimethylcarbamate, or chlorpyrifos), and DDT, are prepared in advance. Fig. 3 and 4 list SERS spectra of common pesticides, including Carbaryl (Carbaryl), Endosulfan (Endosulfan), Dimethoate (dimerate), phosophos (Fonofos), malathion (Methyl Parathion), and DDT.

The pesticide to be detected in fig. 5 is carbamate pesticide carbofuran, and a detection spectrum is formed by scattered light collected after a sample is irradiated by laser. The sample of curve a is the detection component provided in this example after the solution to be detected is extracted from black tea and reacted, curve B is a carbofuran solution with a certain concentration, and curve C is an aqueous solution soaked with black tea. All three were irradiated at 150mW, 785nm, i.e., light emission, for two seconds, 5 times (10 seconds in total). Wherein, the condensate in the SERS substrate of the detection assembly is TMOS.

The pesticide detected in fig. 6 is an organophosphorus pesticide O-formate, and a detection spectrum is formed by scattered light collected after a sample is irradiated with laser light. The sample of curve a is the detection assembly provided in this example after the solution to be detected is extracted from black tea and reacted, wherein the extraction time is 5 minutes. Curve B is a solution containing a concentration of O-formate. Curve C is the aqueous black tea solution that was not extracted. All three were irradiated at 150mW, 785nm, i.e., light emission, for two seconds, 5 times (10 seconds in total).

In other types of tea, such as green tea and black tea, the test results obtained were similar to those obtained in black tea.

As shown in fig. 7, (a) Carbaryl (carbamate) as a carbamate pesticide, (B) endosulfan as an organochlorine pesticide, and (C) a dimephate as a phosphate pesticide, respectively, were subjected to raman spectroscopy on a detection module fabricated on a SERS substrate of a pure TMOS formulation.

Due to different specificities of pesticides, in an actual cultivation process, cultivation personnel generally use a plurality of pesticides in a combined manner, and therefore it is worth verifying whether the detection assembly provided by the embodiment can effectively detect the components and the content of the pesticides when a mixture of a plurality of pesticides exists.

As shown in fig. 8, the detection module in the present embodiment was used to detect low concentrations of the pesticides (D) carbaryl, (E) a mixture of carbaryl and endosulfate (volume ratio 1: 1), and (F) a mixture of carbaryl, endosulfate and O-formate (volume ratio 1: 1: 1). The content of each component was 50 ppb. Therefore, the detection assembly adopted by the embodiment can detect multiple pesticides simultaneously, and can realize accurate detection even if the concentration is low.

Based on the detection method of pesticides in tea, the embodiment provides a detection device of pesticides in tea, wherein the detection device of pesticides in tea comprises the detection assembly and the raman spectrum analyzer.

The Raman spectrum analyzer comprises a transmitting component, a receiving component and an analyzing component. The emitting assembly may emit a laser beam to the detecting assembly such that the detecting assembly scatters the laser beam to generate scattered light, i.e., raman light. The receiving assembly is used for collecting the Raman light, converting photon energy of the Raman light into electric signal intensity and generating a detection Raman spectrum corresponding to a detection target in the detection assembly. Finally, the analysis component determines whether the pesticide is present in the detection raman spectrum and the content of the pesticide based on a reference raman spectrum of the pesticide desired to be detected.

In this embodiment, a commercially available conventional raman spectrum analyzer can be used as the raman spectrum analyzer, and the detection device provided in this embodiment can be obtained by specifically designing the porous carrier for these raman spectrum analyzers and by using the above-described manner for preparing the detection assembly. Since the manner of preparing the detecting element is described above, it is not described herein in detail.