Application of rhodamine skeleton-based fluorescent probe in detection of salicylic acid

Abstract

The invention discloses application of a rhodamine skeleton-based fluorescent probe. Specifically, the rhodamine skeleton-based fluorescent probe 1-5 can be used for rapidly and quantitatively detecting the content of salicylic acid on the surfaces of fruits and vegetables, agricultural and sideline products and water. Through experiments, the invention develops a portable, simple and efficient spraying method, and the probes 1-5 are utilized to detect the residual SA in various fruit and vegetable foods. A portable, simple, accurate and quantitative detection sensing platform for on-site detection of SA content can be established by combining the portability of the test paper with the RGB value analysis function of a smart phone, or quantitative and qualitative detection of SA in soil and water can be realized through soil surface analysis and water adding standard recovery experiment.

Description

Technical Field

[0001] The invention relates to the technical field of rapid food detection, and in particular to an application of a rhodamine skeleton-based fluorescent probe in detecting salicylic acid. Background Art

[0002] The increasing attention paid to food safety has prompted people to focus on natural and safe antimicrobial agents to control pathogenic microorganisms in fruits and vegetables before and after harvest. Salicylic acid (SA), naturally extracted from willow bark, is widely used in food processing and preservation as a safe compound with high application value potential. However, SA can also cause unknown side effects such as urticaria, angioedema, ototoxicity, and central nervous system diseases in sensitive individuals. Worse, many studies have found that SA residues can contaminate waterways, farmland soil, and food, posing high risks to human health, the environment, and food safety; long-term contact and ingestion of SA can cause liver and kidney damage, dizziness, nausea, protein denaturation, and even mucosal bleeding or necrosis. According to EU standards (EC1223 / 2009), the salicylic acid content in cosmetics shall not exceed 0.5%, and my country requires that the salicylic acid concentration in cosmetics be less than 2%. In addition, salicylic acid can be used as a preservative, with a concentration between 0.09% and 2%. Excessive SA in human serum (>3-4×10 -4 g / mL) may be toxic. To date, few methods have been developed to detect SA on the surface of fruits and vegetables, as well as in soil and water. Therefore, simple and efficient methods and tools are urgently needed to visualize and quantitatively detect SA with high sensitivity and selectivity.

[0003] Traditional techniques for detecting SA include high performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS), gas chromatography-mass spectrometry (GC-MS), surface plasmon resonance, chromatography, mass spectrometry, and electrochemical analysis. These methods require expensive and bulky instruments, high operating costs, specialized personnel, cumbersome pretreatment, low selectivity, and a large number of solvent-treated sample tests. To the best of our knowledge, none of these methods can achieve visualization and portable detection of SA.

[0004] So far, fluorescent probe-based methods have been popular due to their low cost-effectiveness, simple operation, portability and fast response speed. In particular, fluorescent probes based on the rhodamine skeleton are ideal for detecting analytes due to their excellent photophysical properties, including high molar absorption coefficient, excellent photostability, biocompatibility, excellent fluorescence quantum yield and excellent water solubility. Therefore, the rhodamine skeleton was modified to introduce heterocyclic benzimidazole functional groups with improved optical properties and provide hydrogen donors (NH groups in the ring and pyridine nitrogen), which helped to achieve selective binding, thereby obtaining high-performance fluorescent probes for detecting SA. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of time-consuming and cumbersome analysis and pretreatment of samples, high equipment cost, complicated operation and large amount of solvent treatment samples in existing SA detection methods. The present invention discloses a simple and fast-responding fluorescent probe to detect SA on the surface of fruits and vegetables, soil surface and water. The method has high sensitivity and selectivity, and can realize visual detection of SA by irradiating with ultraviolet light (365nm) through a smart phone, and has good application prospects.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of the present invention is a method for detecting the surface analysis of food, fruits and vegetables, comprising the following steps:

[0008] (1) Several types of food and vegetable samples were purchased from a local supermarket, including cabbage, lettuce, jujube, and tangerine.

[0009] (2) The cabbages in the experimental groups were sprayed with 1 mM, 5 mM, and 10 mM SA solutions, respectively, while the control group was pretreated with water. Then, the cabbages were air-dried to simulate actual SA residues. Subsequently, the probe 1 solution (1 mm) was sprayed on the surface of the cabbages.

[0010] (3) In addition, taking jujube fruit as an example, the surface of the experimental group jujube fruit was sprayed with SA solution (1mM, 5mM, 10mM) for pretreatment, and the surface of the control group jujube fruit was treated with water. Subsequently, the fruits were air-dried. After the test paper was soaked in the solution of probe 1 (1mM), the test paper was tightly attached to the surface of the dry jujube fruit.

[0011] (4) Finally, the smartphone was used to capture photos of the sprays and paper strips under natural light and UV light (365 nm) in a dark environment.

[0012] (5) In the quantitative experiment of agricultural and sideline products (potatoes, yam bean and white radish), all agricultural products were purchased from local supermarkets. The samples were cut into small pieces (1 g each) and soaked in 5 mL of deionized distilled water or a certain amount of SA. Subsequently, the mixture was ultrasonically treated for 5 minutes, and the supernatant extracted from each sample was used as the test solution. Finally, six different concentrations of SA were added to the solution with probe 1 for spectral testing, and the spectral signal was recorded at a wavelength of 582 nm. Each experiment was performed in triplicate. The recovery rate was calculated using the following formula: Recovery rate (%) = measured c / specified c × 100%.

[0013] The second technical solution of the present invention is to prepare a fluorescent test paper sensor for portable, simple, accurate and quantitative on-site detection of SA content based on the assistance of a smartphone.

[0014] (1) First, the test paper was immersed in a solution of probe 1 (1 mM) for 1 minute and then dried at room temperature. Subsequently, the test paper was cut into multiple round strips and placed on a glass slide.

[0015] (2) Then, different concentrations of SA were dropped onto the test strips as the treatment group and water treatment as the control group. The droplets completely covered the surface of the test strips and then air-dried at room temperature.

[0016] (3) Finally, the fluorescence images of these paper strips were taken under natural light and dark environment UV light (365nm). By establishing a linear relationship between the RGB ratio (R / B) and SA concentration (R / B: red channel / blue channel, c: SA concentration), the fluorescence images were directly converted into the corresponding RGB channel values ​​to calculate the SA concentration.

[0017] The third technical solution of the present invention is a method for quantitatively detecting the recovery rate of SA in water and soil surface analysis experiments, comprising the following steps:

[0018] (1) Water samples were collected from tap water, Yuehu Lake and Huaxi River. Water samples were filtered through a 0.22 μm water membrane and stored at room temperature. Soil Two types of soil (sandy soil and silty soil) were collected from local farmland without any pretreatment.

[0019] (2) 1 g of soil sample was placed in a petri dish and divided into three groups: control group, water treatment group, and experimental group. In addition, the water treatment group was sprayed with probe 1 solution (1 mM) for imaging. In addition, the experimental group was sprayed with different concentrations of SA (concentrations were 1 mM, 5 mM, and 10 mM), and then the probe 1 solution (1 mM) was sprayed on the soil surface.

[0020] (3) Finally, the images were captured using a smartphone under natural light and UV light (365nm).

[0021] Based on the above technical scheme, the present invention has the following technical effects: Five rhodamine-based probes (1-5) are invented and synthesized as candidate probes for detecting SA. Probe 1 contains a 2-aminobenzimidazole molecule, which has extremely high sensitivity and selectivity to SA and has a distinct fluorescence "off-on" mode. After adding SA, the color of the solution can be observed to change from colorless to pink with the naked eye. Therefore, the RGB values ​​are extracted based on the color recognition application of the smartphone to capture and quantify the test paper and food samples. In order to demonstrate the practicality of the probe, we conducted soil surface analysis experiments and evaluated the qualitative and quantitative detection of SA in actual food samples through conventional spike recovery studies to verify the accuracy of the method. In summary, our work provides a fast, convenient, low-cost and reliable tool for visual quantitative detection of SA, which has great application potential in environmental and food safety monitoring. The advantages of the present invention are summarized as follows:

[0022] 1. Through experiments, we developed a portable, simple and efficient spraying method, using probes 1 to 6 to detect SA residues in various fruit and vegetable foods.

[0023] 2. By combining the portability of the test paper with the RGB value analysis function of the smartphone, a portable, simple, accurate and quantitative on-site detection sensing platform for SA content is established.

[0024] 3. Quantitative and qualitative detection of SA in soil and water was achieved through soil surface analysis and water spike recovery experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is an experimental diagram showing the sensitivity enhancement factor of the fluorescence spectra of probes 1-5 to SA.

[0026] Figure 2 The experimental process and results of the residual analysis of salicylic acid on the surface of cabbage and lettuce. (a) The procedure of testing paper strips in actual food analysis. (b) Using a smartphone to capture photos of jujube and sugar orange SA test strips under natural light and 365nm UV light and analyze them. (c) The average G / B ratio of jujube and sugar orange SA test strips under 365nm UV light.

[0027] Figure 3 Figure 2 shows the application of the test paper sensor on the surface of fruits. (a) Imaging process of food analysis using probe 1 (1 mM). (b) Photos of food samples (cabbage and lettuce) under natural light and ultraviolet light (365 nm). (c) Average G / B ratio of food samples under ultraviolet light (365 nm).

[0028] Figure 4 To combine the portability of the test paper with the RGB value analysis function of a smartphone, a portable, simple, accurate, and quantitative on-site detection sensing platform for SA content was established. (a) Preparation and testing procedures of the probe 1 paper strip. (b) Schematic diagram of SA quantification based on mobile phone signal processing. (c) Photographs of the test paper (probe 1, 1 mM) exposed to different concentrations of SA (0 mM; 1 mM; 2 mM; 4 mM; 6 mM; 8 mM and 10 mM) using natural light with a white background and UV light (365 nm) with a black background. (d) Plot of the relationship between the G / B value and SA concentration in the range of 0-10 mM.

[0029] Figure 5 Qualitative detection diagram for soil surface analysis. a) Schematic diagram of probe 1 detecting SA in soil imaging. (b) Soil surface analysis after spraying different concentrations of SA (1 mM, 5 mM and 10 mM) and probe 1 (1 mM). DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0031] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0032] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0033] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0034] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0035] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0036] Example 1

[0037] The synthesis method of probes 1 to 5 comprises the following steps:

[0038] (1) Rhodamine B: 1 mmol, HOBt 1.2 mmol, EDCI: 1.2 mmol and 10 mL of anhydrous acetonitrile were stirred in a 50 mL flask for 4 h, and then 1.5 mmol of 2-aminobenzimidazole or 2-amino-1-methylbenzimidazole or (1H-benzimidazole-2-methylene)amine or 2-aminobenzoxazole or 2-aminobenzothiazole was added to the mixture, and the color gradually changed from red to purple. The mixture was reacted at room temperature for 5 h;

[0039] (2) The reaction progress was tracked by thin layer silica gel plate until the substrate disappeared, then the reaction solvent was evaporated under reduced pressure, and the resulting mixture was separated and purified by silica gel column chromatography, eluent v / v: ethyl acetate / petroleum ether = 1:6, to obtain probes 1 to 6 respectively; the reaction equation is shown below:

[0040]

[0041] The physicochemical properties, nuclear magnetic resonance and high-resolution mass spectra of the synthesized probes 1 to 5 are shown in Table 1.

[0042] Table 1. Physicochemical properties, NMR and high-resolution mass spectrometry data of target probes

[0043]

[0044]

[0045] Probe 1 to probe 5 for SA spectrum performance test:

[0046] We evaluated the fluorescence spectra of probes 1 to 5 for SA sensitivity enhancement experiments, such as Figure 1 As shown in the figure, under the same test conditions, the fluorescence intensity of probe 1 was significantly enhanced by 88.4 times, and the fluorescence intensity of probe 2, probe 3, probe 4 and probe 5 was enhanced by 15.9 times, 12.1 times, 62.5 times and 52.8 times, respectively. In summary, the experiment clearly shows that probe 1 has the best sensitivity enhancement factor for SA. Therefore, in subsequent studies, we prefer probe 1 as the probe for SA detection.

[0047] Example 2

[0048] Probe 1 was used to detect SA in cabbage and lettuce. As a widely used preservative and antimicrobial agent, the large-scale use and absorption of SA may bring side effects and potential health threats. Therefore, it is crucial to detect SA at millimolar concentrations in fruits and vegetables.

[0049] 1. Experimental methods:

[0050] (1) Several types of food and vegetable samples were purchased from a local supermarket, including cabbage, lettuce, jujube, and tangerine.

[0051] (2) The cabbages in the experimental groups were sprayed with 1 mM, 5 mM, and 10 mM SA solutions, respectively, while the control group was pretreated with water. Then, the cabbages were air-dried to simulate actual SA residues. Subsequently, the probe 1 solution (1 mM) was sprayed on the surface of the cabbages.

[0052] (3) Finally, photos of the sprays and paper strips were captured by a smartphone under natural light and UV light (365 nm) in a dark environment.

[0053] The results showed that probe 1 was used to detect SA in various real food samples. Figure 2 The preparation and imaging processes were revealed. Cabbage and lettuce were sprayed with SA (1mM, 5mM and 10mM), and then the probe 1 solution (1mM) was sprayed on the corresponding food surface. The colorless to red color can be clearly observed by the naked eye under natural light. At the same time, under a portable UV lamp with a wavelength of 365nm, they can quickly show a fluorescence transition from cyan to red even at a concentration of 1mM of SA, which proves the rapidity and sensitivity of SA detection. This study shows that probe 1 can be used as a direct and effective tool to conveniently detect SA on-site, thereby safeguarding human health.

[0054] Example 3

[0055] We further evaluated the applicability and practicality of probe 1 in fruits. Typically, millimolar concentrations of SA are directly applied to the surface of fruits in food storage. We used the prepared test paper sensing method to demonstrate its on-site detection capabilities. The preparation and detection procedures are shown in Figure 3 .

[0056] 1. Experimental methods:

[0057] (1) Taking jujube fruit as an example, the surface of the experimental group jujube fruit was sprayed with SA solution (1mM, 5mM, 10mM) for pretreatment, and the surface of the control group jujube fruit was treated with water. Subsequently, the fruits were air-dried. After the test paper was soaked in the solution of probe 1 (1mM), the test paper was tightly attached to the surface of the dry jujube fruit.

[0058] (2) Finally, the smartphone was used to capture photos of the sprays and paper strips under natural light and UV light (365 nm) in a dark environment.

[0059] The results showed that SA (1mM, 5mM and 10mM) was sprayed on the surface of jujube and sugar orange food to simulate the presence of SA residues, and then the prepared probe 1 (1mM) was loaded on the test paper and attached to the surface of these fruits. Figure 3As shown, the photos were taken under natural light and ultraviolet light (365nm). Under natural light, as the concentration of SA increases, the colorless test paper gradually turns pink. In addition, the color of the test paper also transitions from cyan fluorescence to pink fluorescence, and gradually deepens under ultraviolet light. This high-contrast color and fluorescence change does not require complex analytical instruments and is therefore more suitable for real-time, naked-eye quantitative detection of SA on the surface of food.

[0060] Example 4

[0061] To further investigate the feasibility and accuracy of probe 1 in complex systems, we selected real food samples such as potato, yam bean, and white radish for detection and standard recovery experimental evaluation.

[0062] Table 2. Determination of the recovery of SA in various actual agricultural and sideline products.

[0063]

[0064] Experimental methods:

[0065] (1) In the quantitative experiment of agricultural and sideline products (potatoes, yam bean and white radish), all agricultural products were purchased from local supermarkets. The samples were cut into small pieces (1 g each) and soaked in 5 mL of deionized distilled water or a certain amount of SA.

[0066] (2) Subsequently, the mixture was sonicated for 5 minutes, and the supernatant extracted from each sample was used as the test solution. Finally, six different concentrations of SA were added to the solution with probe 1 for spectral testing, and the spectral signal was recorded at a wavelength of 582 nm. Each experiment was repeated three times. The recovery rate was calculated using the following formula: Recovery rate (%) = measured c / specified c × 100%.

[0067] The results showed that the recoveries of SA (at concentrations of 6, 10, 14, 18, 22, and 26 μM) for the three food samples were 88.0% to 107.3%, 94.4-114.6%, and 93.0-112.3%, respectively, when introduced into the samples independently according to the fluorescent detection solution. These results indicate that probe 1 is an efficient and practical tool for the accurate detection of SA in actual food samples.

[0068] Example 5

[0069] Fabrication of fluorescent test strip / smartphone sensor platform. It is widely believed that a portable, simple, accurate, and quantitative device for on-site detection of SA content would be an ideal tool for consumers. With this in mind, we combined the portability of the test strip with the RGB analysis function of a smartphone and utilized this detection platform to detect SA.

[0070] 1. Experimental methods:

[0071] (1) First, the test paper was immersed in a solution of probe 1 (1 mM) for 1 minute and then dried at room temperature. Subsequently, the test paper was cut into multiple round strips and placed on a glass slide.

[0072] (2) Then, different concentrations of SA were dropped onto the test strips as the treatment group and water treatment as the control group. The droplets completely covered the surface of the test strips and then air-dried at room temperature.

[0073] (3) Finally, the fluorescence images of these paper strips were taken under natural light and dark environment UV light (365nm). By establishing a linear relationship between the RGB ratio (R / B) and SA concentration (R / B: red channel / blue channel, c: SA concentration), the fluorescence images were directly converted into the corresponding RGB channel values ​​to calculate the SA concentration.

[0074] The results show that Figure 4 As shown in the figure, under the irradiation of ultraviolet light (365nm), the probe 1 with a concentration of 1mM emits blue fluorescence on the test paper. As the concentration of SA gradually increases (1mM, 2mM, 4mM, 6mM, 8mM and 10mM), the test paper array changes from colorless to pink (exposed to natural light) and changes from cyan to pink under the irradiation of ultraviolet light (365nm), which can be identified by the naked eye. In the range of 1-10mM, the R / B ratio shows a good linear relationship with the SA concentration, and R 2 The value was 0.99. Therefore, these findings validated the great potential of the smartphone-assisted test strip sensor platform for practical detection of SA in daily life.

[0075] Example 5

[0076] Application to environmental soil and water samples. Given the widespread use of SA and its inadvertent release into the environment leading to water and soil contamination, the residue problem of SA may threaten human health.

[0077] Table 3. SA recoveries in various water samples using probe 1.

[0078]

[0079] 1. Experimental methods:

[0080] (1) Water samples were collected from tap water, Yuehu Lake and Huaxi River. Water samples were filtered through a 0.22 μm water membrane and stored at room temperature. Soil Two types of soil (sandy soil and silty soil) were collected from local farmland without any pretreatment.

[0081] (2) 1 g of soil sample was placed in a petri dish and divided into three groups: control group, water treatment group, and experimental group. In addition, the water treatment group was sprayed with probe 1 solution (1 mM) for imaging. In addition, the experimental group was sprayed with different concentrations of SA (concentrations were 1 mM, 5 mM, and 10 mM), and then the probe 1 solution (1 mM) was sprayed on the soil surface.

[0082] The results show that we conducted a conventional spike recovery experiment on water samples to accurately and quantitatively analyze SA. As shown in Table 3, we used probe 1 to analyze three water samples (tap water, lake water, and river water) treated with different concentrations of SA. The recovery rates ranged from 92.8% to 108.9%, and the RSD values ​​(1.2% to 4.8%) were within the acceptable range. The results show that probe 1 is suitable for quantitative detection of SA in various water samples. At the same time, in Figure 5 As shown, sandy soil and silty soil samples were sprayed with 1mM, 5mM and 10mM SA solutions, respectively, and then treated by spraying probe 1 solution (1mM). When these samples were exposed to natural light, the color contrast of the soil from the inherent earthy yellow (control group) to red (treated group) could be clearly observed by the naked eye. Under irradiation with a portable ultraviolet lamp at a wavelength of 365nm, the fluorescence color spontaneously transitioned rapidly from cyan (0mM SA) to red (treated with SA) and gradually deepened, indicating that probe 1 can be used to qualitatively detect SA at concentrations of 1mM to 10mM in soil samples.

Claims

1. An application of a rhodamine skeleton fluorescent probe in detecting salicylic acid, characterized in that: The synthesis method of the structures of rhodamine skeleton fluorescent probes 1 to 5 is as follows: Rhodamine skeleton fluorescent probes 1-5 can be used to quickly and quantitatively detect salicylic acid on the surface of fruits and vegetables, agricultural and sideline products, and water.

2. The use of a rhodamine skeleton-based fluorescent probe in detecting salicylic acid according to claim 1, characterized in that: The specific method of using rhodamine skeleton fluorescent probes 1 to 5 to quantitatively detect the surface of fruits and vegetables and agricultural and sideline products is as follows: (1) The vegetables in the experimental group were sprayed with 1 mM, 5 mM, and 10 mM salicylic acid solutions, respectively, while the vegetables in the control group were pretreated with water. The vegetables were air-dried to simulate actual salicylic acid residues, and 1 mM probe 1-6 solutions were sprayed on the surface of the vegetables; (2) The fruit surfaces of the experimental groups were sprayed with 1 mM, 5 mM, and 10 mM SA solutions for pretreatment, and the fruit surfaces of the control group were treated with water. The fruits were air-dried, and the test strips were soaked in 1 mM solutions of probes 1 to 5, and then the test strips were tightly attached to the dry fruit surface; (4) Finally, take photos of the spray and test strips with a smartphone under natural light and 365 nm UV light in a dark environment; (5) In the quantitative experiment of agricultural and sideline products, the samples were cut into small pieces, each weighing 1 g, and soaked in 5 mL of deionized distilled water or a certain amount of salicylic acid solution. The mixture was ultrasonically treated for 5 min, and the supernatant extracted from each sample was used as the test solution. Six different concentrations of salicylic acid were added to the solutions with probes 1 to 5 for spectral testing, and the spectral signals were recorded at a wavelength of 582 nm. Each experiment was performed in triplicate.

3. The use of a rhodamine skeleton-based fluorescent probe in detecting salicylic acid according to claim 1, characterized in that: The portable, simple, accurate and quantitative on-site detection method of SA content assisted by smartphone is as follows: immerse the test paper in 1 mM probe 1 solution for 1 minute and then dry it at room temperature; cut the test paper into multiple round strips and place them on a glass slide; drop salicylic acid of different concentrations on the test strips as the treatment group and water treatment as the control group; after the droplets completely cover the surface of the test paper and then air-dry it at room temperature, the fluorescence image of the paper strip is taken under natural light and 365 nm ultraviolet light in a dark environment; and by establishing a linear relationship between the RGB ratio and the salicylic acid concentration, the fluorescence image is directly converted into the corresponding RGB channel value to calculate the concentration of SA.

4. The use of a rhodamine skeleton-based fluorescent probe in detecting salicylic acid according to claim 1, characterized in that: The method for detecting salicylic acid in water using fluorescent probes 1 to 5 is as follows: the water sample is filtered through a 0.22 μm water membrane and stored at room temperature; 1 g of soil sample is placed in a culture dish and divided into three groups: a control group, a water treatment group, and an experimental group; the water treatment group is sprayed with 1 mM probe 1 solution for imaging; the experimental group is sprayed with salicylic acid of different concentrations of 1 mM, 5 mM, and 10 mM, and then 1 mM probe 1 solution is sprayed on the soil surface, and finally photos are taken under natural light and 365 nm ultraviolet light.

5. The use of a rhodamine skeleton-based fluorescent probe in detecting salicylic acid according to claims 2 to 4, characterized in that: Fluorescent probe 1 was used to detect salicylic acid content.

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