Fluorescent sensor based on porphyrin nanoparticles / blue carbon dots and its preparation and application in Cr 3+ Application in detection

Abstract

The present invention discloses a fluorescence sensor based on porphyrin nanoparticles / blue carbon dots, which comprises a ratio fluorescence probe prepared by porphyrin nanoparticles and blue carbon dots, and is used for Cr 3+ The probe uses blue carbon dots (BCDs) as internal standards and porphyrin nanoparticles as Cr 3+ Sensing reagent. Porphyrin nanoparticles formed by block copolymers can effectively react with Cr 3+ The combination forms a metal complex, resulting in ligand-metal charge transfer, which causes a significant color change of the probe from red to blue. The fluorescent sensor is connected to a mobile phone to form a smartphone sensing platform. By identifying the RGB value of the fluorescent probe solution in the syringe, the Cr in the soil is detected. 3+ Visual detection. The present invention makes full use of porphyrin nanoparticles and Cr 3+ The formation of metal complexes leads to fluorescence quenching, and a blue internal standard carbon dot is designed to quickly detect Cr in soil. 3+ The fluorescent sensor device provides a convenient way to achieve in situ quantitative detection of heavy metals in soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorescence sensors and is a fluorescence sensor based on porphyrin nanoparticles / blue carbon dots and its preparation and application in Cr 3+ Specifically, it relates to a quenching fluorescence sensor based on porphyrin nanoparticles / blue carbon dots as fluorescent probes and a method for detecting Cr in actual soil. 3+ Perform a highly sensitive fluorescence visualization detection method. Background Art

[0002] With the development and utilization of earth resources (such as electroplating, leather making, textile manufacturing and metal mining), chromium pollution in soil is becoming increasingly serious. Chromium in soil can enter the human body through skin contact, inhalation, oral administration and other exposure methods, and hide in proteins or deposit in cells. Recent studies have shown that Cr 3+ Excessive accumulation of Cr will affect the normal function of organs such as the lungs, brain, liver, and kidneys, posing a significant risk to human health. 3+ If the content of Cr is too high, it will affect the body's antioxidant system. It is easy to suffer from some chronic oxidative diseases, such as diabetes, hypertension, etc., and it will also cause abnormal proliferation of tumors. Therefore, it is necessary to 3+ According to the FAO / WHO 2001 regulations, the permissible limit of chromium in soil is 20 mg / kg.

[0003] Traditional methods for detecting chromium in soil generally rely on large-scale instrumentation, such as atomic absorption spectroscopy and inductively coupled plasma mass spectrometry. Other methods include laser-induced breakdown spectroscopy (LIBS) and portable X-ray fluorescence (XRF). However, with the urgent need to protect the environment, the development of sensitive, rapid, and real-time / on-site methods for heavy metal ion detection remains a pressing challenge.

[0004] In the existing technology, commonly used rapid detection methods include fluorescence, colorimetry, etc. In recent years, some electrochemical and chemical spectroscopy methods have also been used for the rapid detection of chromium in soil. The colorimetric method uses the color change of light visible to the naked eye, while the electrochemical method mainly detects the changes in the target material quickly through the change of the intensity of the electrical signal. The fluorescence method shows changes in intensity and color, and the two confirm each other. Therefore, this method has been widely studied. At the same time, the fluorescence method also has the advantages of low cost, fast response speed, and strong portability. This provides the possibility for fluorescent detection of heavy metals. However, in the field of rapid detection of heavy metals in soil, due to the complexity and variability of the soil matrix and other metal-salt-organic complexes, this is not conducive to the rapid detection of Cr. 3+The rapid detection of Cr in soil requires both high selectivity and high sensitivity. In addition, the monochromatic fluorescence response strategy in soil detection is easily interfered by various factors such as background fluorescence, concentration fluctuations, instrument efficiency and excitation conditions, which in turn leads to technical problems such as reduced detection sensitivity and low detection selectivity. Therefore, there is an urgent need to develop a high-sensitivity fluorescence detection method to achieve the detection of Cr in soil. 3+ Convenient, fast and sensitive detection. Summary of the Invention

[0005] The purpose of the embodiment of the present invention is to provide a fluorescence sensor based on porphyrin nanoparticles / blue carbon dots and its preparation and application in Cr 3+ In the application of detection, a quenching fluorescence sensor with porphyrin nanoparticles / blue carbon dots as fluorescent probes is used to solve the technical problems of rapid detection of heavy metals in soil proposed in the above background technology. Due to the complexity and variability of the soil matrix and other metal-salt-organic complexes, the detection of heavy metals is easily interfered by multiple factors, which in turn causes reduced detection sensitivity and low detection selectivity.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0007] A fluorescent sensor based on porphyrin nanoparticles / blue carbon dots, characterized in that it comprises a ratiometric fluorescent probe prepared from porphyrin nanoparticles and blue carbon dots, which is used for Cr 3+ The ratio fluorescence probe is a quenching fluorescence sensor. It uses the ratio fluorescence strategy to prepare an ultra-sensitive fluorescent probe for Cr 3+ A ratiometric fluorescent probe was prepared by using porphyrin nanoparticles with sensitive response and inert blue carbon dots. A portable fluorescent sensing device was prepared based on the ratiometric fluorescent probe for real-time / on-site detection of Cr in soil. 3+ Sensitive detection.

[0008] Another purpose of the present invention is to prepare a porphyrin nanoparticle / blue carbon dot ratiometric fluorescent probe.

[0009] As a preferred embodiment of the above technical solution, the preparation method of the porphyrin nanoparticle / blue carbon dot ratio fluorescent probe comprises the following steps:

[0010] S1. Preparation of porphyrin nanoparticles: Utilizing the self-assembly principle of block copolymers, 5-15 mL of an aqueous solution containing an appropriate amount of polyoxyethylene polyoxypropylene ether triblock copolymer is slowly added to a 0.04-0.06 mg / mL porphyrin THF solution. After stirring for 0.5-2 hours, the solvent is removed by rotary evaporation to obtain a solid porphyrin nanoparticle. The solid is then dissolved in ethanol and the resulting solution is stored at 3-5°C for later use. The amount of polyoxyethylene polyoxypropylene ether triblock copolymer added is such that the concentration of the polyoxyethylene polyoxypropylene ether triblock copolymer in the final solution is 0.05-0.1%;

[0011] S2. Preparation of blue carbon dots: 10-30 mL of pulp-free lemon juice was mixed with 5-20 mL of water to form a transparent solution. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 150-200°C for 10-15 hours. After the reaction was complete, the reactor was naturally cooled to room temperature. The resulting blue carbon dot solution was dialyzed against deionized water for 15-30 hours and then freeze-dried. The resulting substance was prepared into a 0.5-2 mg / mL aqueous solution and stored in a refrigerator at 3-5°C until ready for use.

[0012] S3. Preparation of ratiometric fluorescent probe: 1900-1990 μL of the porphyrin nanoparticle solution prepared in S1 was added to 10-100 μL of the blue carbon dot solution prepared in S2, mixed thoroughly, and reacted for 1-3 minutes to obtain a ratiometric fluorescent probe.

[0013] This ratiometric fluorescent probe uses blue carbon dots (BCDs) as an internal standard and porphyrin nanoparticles as Cr 3+ Sensing reagent. Porphyrin nanoparticles formed by block copolymers can effectively react with Cr 3+ The binding forms a metal complex, leading to ligand-metal charge transfer (LMCT), which results in a significant color change of the probe from red to blue. Based on the responsive probe solution, a syringe-binding fluorescent sensor was prepared by 3D printing. The fluorescent sensor was connected to a mobile phone to form a smartphone sensing platform. By identifying the RGB value of the fluorescent probe solution in the syringe, the Cr in the soil was detected. 3+ Visual detection. The present invention makes full use of porphyrin nanoparticles and Cr 3+ The formation of metal complexes leads to fluorescence quenching, and a blue internal standard carbon dot is designed to quickly detect Cr in soil. 3+ The fluorescent sensor device provides a convenient way to achieve in situ quantitative detection of heavy metals in soil.

[0014] Another object of the present invention is to provide an application of a fluorescence sensor, wherein the fluorescence sensor is used to visually detect Cr in soil. 3+ application.

[0015] Preferably, in the application of the fluorescence sensor, the overall fluorescence color of the ratio fluorescence probe is red, and the Cr 3+ The blue fluorescence in the ratiometric fluorescent probe remains unchanged, while the red fluorescence is gradually quenched, showing a series of fluorescence changes from red to blue. A series of photos from red to blue are taken under ultraviolet light with a smartphone to achieve Cr 3+ Visual detection.

[0016] Preferably, the application of the fluorescent sensor is to prepare a variety of Cr 3+ The fluorescence intensity of the standard solution with the concentration of Cr was detected under 350-365nm ultraviolet light to establish the fluorescence intensity ratio I674 / I458 and Cr 3+ The concentration standard curve and linear equation were used to determine the concentration of Cr in the sample. The fluorescence intensity ratio I674 / I458 of the sample was tested and the Cr content in the sample was obtained according to the standard curve and linear equation. 3+ concentration, thereby achieving quantitative detection.

[0017] Preferably, the application of the fluorescence sensor is to use the fluorescence sensor as a detection reagent and to build a detection platform in combination with a smart phone to detect Cr in soil. 3+ .

[0018] Preferably, the intelligent sensing platform includes a platform body, a syringe 6, a miniature ultraviolet lamp 5 and a smart phone 7. A mobile phone clamp 2 for fixing the smart phone 7 is provided on one side of the platform body, a syringe clamp 3 for fixing the syringe 6 is provided on the upper part of the other side, and a fixing clamp 9 for fixing the miniature ultraviolet lamp 5 is provided on the lower part. A viewfinder 1 is provided on the syringe clamp 3, and the viewfinder 1 is used for taking pictures with the camera of the smart phone 7. An irradiation hole 4 for irradiation by the miniature ultraviolet lamp 5 is provided on the syringe clamp 3, and the syringe 6 is used to load a ratio fluorescent probe solution.

[0019] As a preferred embodiment of the above technical solution, specifically, a fluorescent sensing device adapted for a syringe is synthesized by 3D printing, a syringe 6 can be placed on the device, and the fluorescent color is obtained by a smart phone 7 to establish an intelligent sensing platform, which includes a mobile phone clip 2, a viewfinder 1, a syringe clip 3, an irradiation hole 4, a miniature ultraviolet lamp 5 and a smart phone 7; the application method of the intelligent sensing platform is that during detection, a syringe containing a ratio fluorescent probe solution is used to absorb the soil digestion solution, and after the reaction is completed, a photo from red to blue is taken with a smart phone under 350-365nm ultraviolet light, and the ratio of the intensity of B and R in the fluorescent photo is obtained by a color recognition APP, and the RGB value (B / R value) is compared with the Cr 3+ The linear relationship between the concentration of Cr 3+ The actual concentration can be detected quantitatively.

[0020] It should be noted that the present invention uses a fluorescent sensor to detect Cr 3+ The principle is based on the fluorescence quenching strategy. Specifically, the porphyrin nanoparticles formed by the block copolymer can effectively bind to Cr 3+ The combination forms a metal complex, resulting in ligand-metal charge transfer (LMCT), which quenches the red fluorescence of the porphyrin nanoparticles. The entire fluorescence signal response can be completed within 45-75 seconds. By establishing the fluorescence intensity and Cr 3+ The relationship between the concentration of Cr 3+ Quantitative detection of .

[0021] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0022] 1. Detection of Cr by the ratiometric fluorescent probe of the present invention 3+ Compared with other single-color fluorescence detection, it shows richer color changes, effectively avoids the instability problem of single-color fluorescence intensity, and realizes visual detection.

[0023] 2. The response time of the fluorescence sensor of the present invention is about 60s, which realizes rapid detection.

[0024] 3. The fluorescence spectrometer of the present invention is used to measure the Cr 3+ The detection limit was 17.63 nM, which was much lower than that of Cr in soil. 3+ The allowed limit.

[0025] 4. The fluorescent sensor of the present invention is compact, portable, and can quickly absorb the target object for detection, breaking the limitations of time and space.

[0026] 5. In addition, fluorescent photo information can be obtained by using a smartphone, and Cr can be obtained through the corresponding linear relationship. 3+ To a certain extent, this method avoids the complex operation of large instruments and enables real-time / on-site visual quantitative detection of soil heavy metals using fluorescent nanosensors, making the detection process portable, rapid, and low-cost.

[0027] 6. The ratiometric fluorescent probe based on porphyrin nanoparticles and blue carbon dots prepared by the present invention detects Cr through the ligand-metal charge transfer principle. 3+ It has good selectivity and sensitivity, can effectively avoid interference from other impurities, and has a fast response. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention.

[0029] Figure 1 This is a transmission electron microscope image of porphyrin nanoparticles according to an embodiment of the present invention.

[0030] Figure 2 TEM image (A) and particle size distribution diagram (B) of blue carbon dots according to an embodiment of the present invention.

[0031] Figure 3 These are the different excitation and emission wavelengths of the porphyrin nanoparticles according to the embodiments of the present invention.

[0032] Figure 4 These are the different excitation and emission wavelengths of the blue carbon dots according to the embodiment of the present invention.

[0033] Figure 5 This is a stability experiment of blue carbon dots (A), porphyrin nanoparticles (B), and ratiometric fluorescent probe (C) according to an embodiment of the present invention.

[0034] Figure 6 This is a temperature optimization experiment of the ratiometric fluorescent probe according to an embodiment of the present invention.

[0035] Figure 7 Different concentrations of Cr are added to the embodiment of the present invention. 3+ Fluorescence spectra of BCDs

A

B

[0036] Figure 8 Different concentrations of Cr were added to the samples of the present invention. 3+ After irradiation, the fluorescence intensity changes of the ratiometric sensing system constructed with porphyrin nanoparticles and BCDs (A: I674 / I458 = 2:1, B: I674 / I458 = 3:1, C: I674 / I458 = 4:1) with different initial fluorescence intensities were observed. The inset is the corresponding photograph taken under 365 nm UV light.

[0037] Figure 9 The ratio fluorescence probe of the present invention is Cr 3+ Reaction kinetics experiments.

[0038] Figure 10 Different concentrations of Cr were added to the samples of Example (A) of the present invention. 3+ The fluorescence response of the ratio fluorescent probe. The corresponding fluorescence images were taken under 365nm ultraviolet radiation. (B) The ratio I674 / I458 and Cr 3+ Linear relationship plot of concentration (0-50 μM).

[0039] Figure 11The selectivity and anti-interference ability of the ratiometric fluorescent probe in the embodiment of the present invention.

[0040] Figure 12 This is the construction of an intelligent sensing platform based on ratiometric fluorescent probes in the embodiment of the present invention. (B) Fluorescence color changes with Cr 3+ (C) Platform and Cr 3+ Linear relationship plot of concentration (0-50 μM).

[0041] Figure 13 It is a component of the intelligent sensing platform of the embodiment of the present invention.

[0042] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0043] 1. Viewfinder; 2. Mobile phone clip; 3. Syringe clip; 4. Irradiation hole; 5. Micro UV lamp; 6. Syringe; 7. Smart phone; 8. Smart sensor device; 9. Fixing clip.

[0044] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0045] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the following embodiments will help those skilled in the art to further understand the embodiments of the present invention, but do not limit the embodiments of the present invention in any form. It should be pointed out that for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the embodiments of the present invention. These all fall within the scope of protection of the embodiments of the present invention.

[0046] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0047] First of all, it should be noted that among the traditional methods for detecting chromium in soil, large instruments such as atomic absorption spectroscopy and inductively coupled plasma mass spectrometry are the most common. Other methods include laser induced breakdown spectroscopy (LIBS) and portable X-ray fluorescence (XRF). However, with the urgent need to protect the environment, the development of sensitive, rapid, real-time / on-site heavy metal ion detection methods is one of the challenges that need to be solved. In addition, the monochromatic fluorescence response strategy in soil detection is easily interfered by multiple factors such as background fluorescence, concentration fluctuations, instrument efficiency and excitation conditions. Therefore, there is an urgent need to develop a high-sensitivity fluorescence detection method to achieve the detection of Cr in soil. 3+ Convenient, fast and sensitive visual inspection.

[0048] Therefore, in order to solve the problems in the prior art, the present invention provides a fluorescence sensor based on porphyrin nanoparticles / blue carbon dots, which includes a ratiometric fluorescent probe prepared from porphyrin nanoparticles and blue carbon dots, that is, an ultra-sensitive fluorescent probe prepared by a ratiometric fluorescence strategy for Cr 3+ Visual detection of Cr 3+ Visual detection of Cr in soil. The ratio fluorescence probe is a quenching type fluorescence sensor, which is prepared by using porphyrin nanoparticles with sensitive response and inert blue carbon dots. A portable fluorescence sensing device is prepared based on the ratio fluorescence probe for real-time / on-site detection of Cr in soil. 3+ Sensitive detection.

[0049] It should be noted that rapid detection of Cr in soil 3+ The core of the proposed method is a ratiometric fluorescence system that uses blue carbon dots (BCDs) as internal standards and porphyrin nanoparticles as Cr 3+ Sensing reagent. Porphyrin nanoparticles formed by block copolymers can effectively react with Cr 3+ The binding forms a metal complex, resulting in ligand-metal charge transfer (LMCT), which will cause a significant color change of the probe from red to blue. The Cr in soil is detected by the degree of fluorescence quenching of porphyrin nanoparticles in a ratiometric fluorescence system. 3+ content.

[0050] An embodiment of the present invention further provides a method for preparing a fluorescence sensor, which includes preparing a porphyrin nanoparticle / blue carbon dot ratio fluorescence probe.

[0051] In an embodiment of the present invention, the preparation of the porphyrin nanoparticle / blue carbon dot ratio fluorescent probe comprises the following steps:

[0052] S1. Preparation of porphyrin nanoparticles: Utilizing the self-assembly principle of block copolymers, 5-15 mL of an aqueous solution containing an appropriate amount of polyoxyethylene polyoxypropylene ether triblock copolymer is slowly added to a 0.04-0.06 mg / mL porphyrin THF solution. After stirring for 0.5-2 hours, the solvent is removed by rotary evaporation to obtain a solid porphyrin nanoparticle. The solid is then dissolved in ethanol and the resulting solution is stored at 3-5°C for later use. The amount of polyoxyethylene polyoxypropylene ether triblock copolymer added is such that the concentration of the polyoxyethylene polyoxypropylene ether triblock copolymer in the final solution is 0.05-0.1%;

[0053] S2. Preparation of blue carbon dots: 10-30 mL of pulp-free lemon juice was mixed with 5-20 mL of water to form a transparent solution. The mixture was then transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 150-200°C for 10-15 hours. After the reaction was complete, the reactor was naturally cooled to room temperature. The resulting blue carbon dot solution was dialyzed against deionized water for 15-30 hours and then freeze-dried. The resulting substance was prepared into a 0.5-2 mg / mL aqueous solution and stored in a refrigerator at 3-5°C until ready for use.

[0054] S3. Preparation of ratiometric fluorescent probe: 1900-1990 μL of the porphyrin nanoparticle solution prepared in S1 was added to 10-100 μL of the blue carbon dot solution prepared in S2, mixed thoroughly, and reacted for 1-3 minutes to obtain a ratiometric fluorescent probe.

[0055] The probe uses blue carbon dots (BCDs) as internal standards and porphyrin nanoparticles as Cr 3+ Sensing reagent. Porphyrin nanoparticles formed by block copolymers can effectively react with Cr 3+ The binding forms a metal complex, leading to ligand-metal charge transfer (LMCT), which results in a significant color change of the probe from red to blue. Based on the responsive probe solution, a syringe-binding fluorescent sensor was prepared by 3D printing. The fluorescent sensor was connected to a mobile phone to form a smartphone sensing platform. By identifying the RGB value of the fluorescent probe solution in the syringe, the Cr in the soil was detected. 3+ Visual detection. The present invention makes full use of porphyrin nanoparticles and Cr 3+ The formation of metal complexes leads to fluorescence quenching, and a blue internal standard carbon dot is designed to quickly detect Cr in soil. 3+ The fluorescent sensor device provides a convenient way to achieve in situ quantitative detection of heavy metals in soil.

[0056] The embodiment of the present invention also provides an application of a fluorescence sensor, which can be used to visually detect Cr in soil. 3 + Application.

[0057] Further preferably, the overall fluorescence color of the ratio fluorescent probe is red, and the Cr 3+ The blue fluorescence in the ratiometric fluorescent probe remains unchanged, while the red fluorescence is gradually quenched, showing a series of fluorescence changes from red to blue. A series of photos from red to blue are taken under ultraviolet light with a smartphone to achieve Cr 3+ Visual detection.

[0058] Further preferably, in the application, the preparation of various Cr 3+The fluorescence intensity of the standard solution with the concentration of Cr was detected under 350-365nm ultraviolet light to establish the fluorescence intensity ratio I674 / I458 and Cr 3+ The standard curve and linear equation of the concentration (0-50μM) were used to measure the fluorescence intensity ratio I674 / I458 of the sample. The Cr content in the sample was obtained according to the standard curve and linear equation. 3+ concentration, thereby achieving quantitative detection.

[0059] More preferably, the fluorescent sensor is used as a detection reagent and combined with a smart phone to build a detection platform for detecting Cr in soil. 3+ .

[0060] Preferably, the intelligent sensing platform includes a platform body, a syringe 6, a miniature ultraviolet lamp 5 and a smart phone 7. A mobile phone clamp 2 for fixing the smart phone 7 is provided on one side of the platform body, a syringe clamp 3 for fixing the syringe 6 is provided on the upper part of the other side, and a fixing clamp 9 for fixing the miniature ultraviolet lamp 5 is provided on the lower part. A viewfinder 1 is provided on the syringe clamp 3, and the viewfinder 1 is used for taking pictures with the camera of the smart phone 7. An irradiation hole 4 for irradiation by the miniature ultraviolet lamp 5 is provided on the syringe clamp 3, and the syringe 6 is used to load a ratio fluorescent probe solution.

[0061] As a preferred embodiment of the above technical solution, specifically, a fluorescent sensing device adapted for a syringe is synthesized through 3D printing, the syringe can be placed on the device, and the fluorescent color is obtained through a smartphone to establish an intelligent sensing platform, which includes a mobile phone clip 2, a viewfinder 1, a syringe clip 3, an irradiation hole 4, a miniature ultraviolet lamp 5 and a smartphone 7. The application method of the intelligent sensing platform is that during detection, a syringe containing 1990-2000 μL ratio fluorescent probe solution is used to absorb 0-10 μL of soil digestion solution. After the reaction is completed, a smartphone is used to take a photo from red to blue under 350-365nm ultraviolet light, and the ratio of the intensity of B and R in the fluorescent photo is obtained through a color recognition APP, and the RGB value is compared with the Cr 3+ The linear relationship between the concentration of Cr 3+ The actual concentration can be detected quantitatively.

[0062] It should be noted that the present invention uses a fluorescent sensor to detect Cr 3+ The principle is based on the fluorescence quenching strategy. Specifically, the porphyrin nanoparticles formed by the block copolymer can effectively bind to Cr 3+ The combination forms a metal complex, resulting in ligand-metal charge transfer (LMCT), which quenches the red fluorescence of the porphyrin nanoparticles. The entire fluorescence signal response can be completed within 45-75 seconds. By establishing the fluorescence intensity and Cr 3+ The relationship between the concentration of Cr3+ Quantitative detection of .

[0063] Among them, the ratio fluorescence probe has a red overall fluorescence color due to the adjustment of the optimal ratio. 3+ The blue fluorescence of the ratio fluorescence probe remains unchanged, while the red fluorescence is gradually quenched, showing a series of fluorescence changes from red to blue under ultraviolet light, thus realizing the detection of Cr 3+ Visual detection.

[0064] Moreover, the quantitative detection of the smartphone detection platform is to obtain the ratio of the intensity of B and R in the fluorescence photo through the color recognition APP, and compare the RGB value (B / R value) with the Cr 3+ The linear relationship between the concentration of Cr 3+ actual concentration.

[0065] It should be noted that the fluorescent sensor is 3+ The initial fluorescence intensity at the concentration of 0 was I674 / I458=(2-5):1, which had a better detection effect, and the detection effect was optimal when I674 / I458=3:1.

[0066] The technical effects of the fluorescence sensor according to the embodiment of the present invention are further described below by listing specific embodiments. Example 1:

[0067] 1. Preparation of porphyrin nanoparticles

[0068] Before the experiment, all glassware was soaked in aqua regia for two hours, then rinsed with pure water and dried. Utilizing the self-assembly principle of block copolymers, 10 mL of an aqueous solution containing an appropriate amount of polyoxyethylene polyoxypropylene ether triblock copolymer was slowly added to a 0.05 mg / mL porphyrin THF solution. After stirring for one hour, the solvent was removed by rotary evaporation to obtain solid porphyrin nanoparticles. The resulting solution was then dissolved in ethanol and stored at 4°C until further use. The amount of polyoxyethylene polyoxypropylene ether triblock copolymer added was such that the final concentration of the polyoxyethylene polyoxypropylene ether triblock copolymer in the solution was 0.075%.

[0069] 2. Preparation of blue carbon dots

[0070] Mix 20 mL of pulp-free lemon juice with 10 mL of water to form a clear solution. The mixture is then transferred to a 50 mL Teflon-lined stainless steel autoclave and heated at 150-200°C for 10-15 hours. After the reaction is complete, the reactor is cooled naturally to room temperature. The blue carbon dot solution is dialyzed against deionized water for 15-30 hours to remove small molecules. The dialyzed blue carbon dots are freeze-dried, and the resulting carbon dot powder is prepared into a 1 mg / mL aqueous solution and stored in a refrigerator at 4°C until ready for use.

[0071] 3. Preparation of ratiometric fluorescent probe solution

[0072] A ratiometric fluorescent probe was prepared by adding 1950 μL of the porphyrin nanoparticle solution to 50 μL of the blue carbon dot solution, mixing thoroughly, and reacting for 2 minutes. Simultaneously, optimization experiments (e.g., component response, temperature, kinetics, photostability, component ratio), as well as selectivity and anti-interference tests, were performed to obtain the optimal ratiometric fluorescent probe solution.

[0073] 4. Construction of fluorescence sensor

[0074] 1998 μL of the prepared ratio probe solution is placed into syringe 6 from the top (preferably, the syringe is a micro syringe, which can be disposable to avoid sample interference). When testing is to be performed, 2 μL of soil digestion solution is drawn from the syringe needle for testing.

[0075] 5. Construction of intelligent sensing platform

[0076] A fluorescent sensing device adapted for a syringe was designed and synthesized using 3D printing technology. The syringe can be placed on the device, which consists of a mobile phone clip 2, a viewfinder 1, a syringe clip 3, an irradiation hole 4, and a miniature ultraviolet lamp 5. By connecting the designed device to a smartphone 7, a simple smartphone sensing platform can be made. The platform can conveniently store and analyze data. In particular, the color recognition application on the smartphone can convert the color information of the fluorescent image into data information (RGB value), thereby completing quantitative detection. As mentioned above, the optimized nanofluorescent probe (initial fluorescence intensity ratio is 3 / 1) can detect Cr in a series of gradient ranges of 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 5.0, 10.0, 20.0, and 50.0µM. 3 + We used a designed smartphone sensing platform to capture fluorescence images of the target probe's response under UV light. After the reaction was complete, a series of images were taken with the smartphone under 365nm UV light, ranging from red to blue. A color recognition app was used to obtain the corresponding RGB values ​​for further statistical analysis. All corresponding tests were repeated three times.

[0077] It should be noted that the platform designed in the present invention is a 3D printing device designed for the fluorescence sensing device of the syringe 6 (syringe clamp 3, irradiation hole 4, position of the viewfinder 1, etc.), based on the position of the mobile phone and the syringe.

[0078] 6. Practical application of intelligent sensing platform

[0079] 2 μL of soil digestion solution was absorbed into a syringe containing 1998 μL of proportional fluorescent probe solution, which ultimately diluted the actual sample nearly 1000 times. 3+ The limited concentration of Cr will also be reduced by 1000 times, which is within the detectable range of the sensor. In the actual sample detection process, the digestion liquid of 10 soil samples was delivered to the syringe of the designed ratio fluorescence sensor, and 10 samples were collected by smartphone after 4 minutes. Subsequently, the data analyzed by the smartphone color recognition was compared with the data detected by atomic absorption (AAS). This sensing platform is able to accurately detect Cr in soil. 3+ , with high feasibility and applicability. Therefore, the designed ratio fluorescence sensing platform can quickly and conveniently detect Cr in soil 3+ , which is expected to become a portable heavy metal detection device.

[0080] The various materials of Example 1 of the present invention were characterized and obtained Figures 1-12 , the specific description is as follows:

[0081] Figure 1 Transmission electron microscopy image of porphyrin nanoparticles.

[0082] Figure 2 Transmission electron microscopy image (A) and particle size distribution diagram (B) of blue carbon dots.

[0083] Figure 3 Figure 1 shows the different excitation and emission wavelengths of porphyrin nanoparticles: (A) Excitation spectrum of porphyrin nanoparticles. (B) Different fluorescence emission spectra of porphyrin nanoparticles at excitation wavelengths of 330nm-395nm. (C) Fluorescence intensity of porphyrin nanoparticles at 674nm under different excitation wavelengths.

[0084] Figure 4 Figure 2 shows the different excitation and emission wavelengths of blue carbon dots: (A) Excitation spectrum of blue carbon dots. (B) Different fluorescence emission spectra of blue carbon dots at excitation wavelengths of 330 nm to 395 nm. (C) Fluorescence intensity of blue carbon dots at 458 nm at different excitation wavelengths.

[0085] Figure 5 Stability experiments of blue carbon dots (A), porphyrin nanoparticles (B), and ratiometric fluorescent probes (C).

[0086] Figure 6 Temperature optimization experiment of the ratiometric fluorescent probe of the present invention: (A) In the temperature range of 20-40℃, Cr-free 3+ Fluorescence spectrum of the colorimetric fluorescent probe; (B) Addition of 10µM Cr 3+ Fluorescence spectrum of the colorimetric fluorescent probe at temperatures between 20°C and 40°C; (C) Temperature-dependent colorimetric fluorescent probe for detecting Cr 3+ The effect of (I674 / I458) was the addition of 10µM Cr 3+ The fluorescence intensity ratio of (I674 / I458) 0 is when no Cr is added. 3+ of.

[0087] Figure 7 To add different concentrations of Cr 3+ Fluorescence spectra of BCDs (A) and porphyrin nanoparticles (B) (λex = 365 nm). 3+ The increase in concentration did not affect the blue fluorescence of BCDs, but the red fluorescence of porphyrin nanoparticles was gradually quenched.

[0088] Figure 8 To add different concentrations of Cr 3+ Fluorescence intensity changes of the ratiometric sensing system constructed with porphyrin nanoparticles and BCDs (A: I674 / I458 = 2:1, B: I674 / I458 = 3:1, C: I674 / I458 = 4:1) with different initial fluorescence intensities. The inset is the corresponding photograph taken under 365 nm UV light.

[0089] Figure 9 The ratio fluorescence probe of Example 1 of the present invention is Cr 3+ The reaction kinetics experiments showed that the designed ratiometric fluorescent probe can effectively detect Cr 3+ The response is completed in about 60 seconds.

[0090] Figure 10 Add different concentrations of Cr to Example 1 3+ The fluorescence response of the ratio fluorescent probe (A) is taken under 365nm ultraviolet radiation. 3+ Linear relationship graph of concentration (0-50 μM) (B).

[0091] Figure 11 This is a test of the selectivity and anti-interference ability of the ratiometric fluorescent probe of Example 1 of the present invention.

[0092] Figure 12 The present invention (A) Construction of intelligent sensing platform based on ratiometric fluorescence probe. (B) Fluorescence color changes with Cr 3+ (C) Platform and Cr 3+Linear relationship plot of concentration (0-50 μM).

[0093] To further characterize the material, the fluorescent sensor obtained in Example 1 of the present invention was used to construct an intelligent sensing platform to test soil in parts of China. The test results of Example 1 of the present invention were obtained, as shown in Table 1.

[0094] Table 1

[0095] Area Found (µM) Standard (µM) Recovery (%) RSD (%) Jiangsu 0.243±0.006 0.275±0.003 88.4 1.2 Hainan 0.153±0.003 0.147±0.002 104.1 3.0 Qinghai 0.251±0.005 0.245±0.001 102.4 2.4 Gansu 0.233±0.007 0.257±0.001 90.7 1.5 Shaanxi 0.221±0.004 0.230±0.002 96.1 4.0 Shanxi 0.218±0.005 0.239±0.001 91.2 3.6 Shangdong 0.254±0.007 0.286±0.002 88.8 3.0 Henan 0.241±0.002 0.234±0.002 103.0 3.2 Inner Mongolia 0.133±0.004 0.121±0.001 109.9 2.5 Ningxia 0.207±0.002 0.221±0.002 93.7 1.6

[0096] It should be noted that the soil tested in this embodiment of the present invention has been acidified and digested, and the soil digestion solution is tested. The selection of soil from various regions serves only to demonstrate the universality of the fluorescent sensor designed by this invention and the intelligent sensing platform constructed, and to verify its accuracy by comparing the test results with those of a traditional large-scale instrument (atomic absorption spectrometer). Example 2:

[0097] 1. Preparation of porphyrin nanoparticles

[0098] Before the experiment, all glassware was soaked in aqua regia for two hours, then rinsed with pure water and dried. To a 0.04 mg / mL porphyrin THF solution, 5 mL of an aqueous solution containing an appropriate amount of polyoxyethylene polyoxypropylene ether triblock copolymer was slowly added. After stirring for 0.5 hours, the solvent was removed by rotary evaporation to obtain solid porphyrin nanoparticles. The resulting solution was then dissolved in ethanol and stored at 4°C until further use. The amount of polyoxyethylene polyoxypropylene ether triblock copolymer added was such that the final concentration of the polyoxyethylene polyoxypropylene ether triblock copolymer in the solution was 0.05%.

[0099] 2. Preparation of blue carbon dots

[0100] Mix 10 mL of pulp-free lemon juice with 5 mL of water to form a clear solution. The mixture was then transferred to a 50 mL Teflon-lined stainless steel autoclave and heated at 150°C for 10 h. After the reaction was complete, the reactor was cooled naturally to room temperature. The blue carbon dot solution was dialyzed against deionized water for 15 hours to remove small molecules. The dialyzed blue carbon dots were freeze-dried, and the resulting carbon dot powder was prepared into a 0.5 mg / mL aqueous solution and stored in a refrigerator at 4°C until ready for use.

[0101] 3. Preparation of ratiometric fluorescent probe solution

[0102] A ratiometric fluorescent probe was prepared by adding 1900 μL of the porphyrin nanoparticle solution to 100 μL of the blue carbon dot solution, mixing thoroughly, and reacting for 1 minute. Simultaneously, optimization experiments (e.g., component response, temperature, kinetics, photostability, component ratio), as well as selectivity and anti-interference tests, were performed to obtain the optimal ratiometric fluorescent probe solution.

[0103] 4. Construction of fluorescence sensor

[0104] Place 1990 μL of the prepared ratio probe solution into a micro syringe from the top (the micro syringe can be disposable to avoid sample interference). When testing, draw 10 μL of soil digestion solution from the syringe needle for testing.

[0105] 5. Construction of intelligent sensing platform

[0106] A fluorescent sensing device adapted for a syringe was designed and synthesized using 3D printing technology. The syringe can be placed on the device, which consists of a mobile phone clip 2, a viewfinder 1, a syringe clip 3, an irradiation hole 4, and a miniature ultraviolet lamp 5. By connecting the designed device to a smartphone 7, a simple smartphone sensing platform can be created. This platform can conveniently store and analyze data. In particular, the color recognition application on the smartphone can convert the color information of the fluorescent image into data information (RGB value), thereby completing quantitative detection. As mentioned above, the optimized nanofluorescent probe (fluorescence intensity ratio of 2 / 1) can detect Cr in a series of gradient ranges of 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 5.0, 10.0, 20.0, and 50.0µM. 3+ We used a designed smartphone sensing platform to capture fluorescence images of the target probe's response under UV light. After the reaction was complete, a series of images were taken with the smartphone under 365nm UV light, ranging from red to blue. A color recognition app was used to obtain the corresponding RGB values ​​for further statistical analysis. All corresponding tests were repeated three times.

[0107] 6. Practical application of intelligent sensing platform

[0108] A syringe containing 1990 μL of the proportional fluorescent probe solution was used to absorb 10 μL of soil digestion solution (the soil was treated by acidification digestion), which ultimately diluted the actual sample by nearly 200 times. 3+The limited concentration of the soil sample will also be reduced by 200 times, which is within the detectable range of the sensor. In the actual sample detection process, the digestion liquid of 10 soil samples was transported to the syringe of the designed ratio of the fluorescence sensor, and 10 samples were collected by smartphone after 4 minutes. After the reaction was completed, a series of photos from red to blue were taken with a smartphone under 350nm ultraviolet light. The ratio of the intensity of B and R in the fluorescence photo was obtained by the color recognition APP, and the RGB value was compared with the Cr 3+ The linear relationship between the concentration of Cr 3+ The actual concentration can be detected quantitatively. Example 3:

[0109] 1. Preparation of porphyrin nanoparticles

[0110] Before the experiment, all glassware was soaked in aqua regia for two hours, then rinsed with pure water and dried. To a 0.06 mg / mL porphyrin THF solution, 15 mL of an aqueous solution containing an appropriate amount of polyoxyethylene polyoxypropylene ether triblock copolymer was slowly added. After stirring for 2 hours, the solvent was removed by rotary evaporation to obtain solid porphyrin nanoparticles. The resulting solution was then dissolved in ethanol and stored at 5°C until further use. The amount of polyoxyethylene polyoxypropylene ether triblock copolymer added was such that the final concentration of the polyoxyethylene polyoxypropylene ether triblock copolymer in the solution was 0.1%.

[0111] 2. Preparation of blue carbon dots

[0112] 30 mL of pulp-free lemon juice was mixed with 20 mL of water to form a clear solution. The mixture was then transferred to a 50 mL Teflon-lined stainless steel autoclave and heated at 200°C for 15 hours. After the reaction was complete, the reactor was cooled naturally to room temperature. The blue carbon dot solution was dialyzed against deionized water for 30 hours to remove small molecules. The dialyzed blue carbon dots were freeze-dried, and the resulting carbon dot powder was prepared into a 2 mg / mL aqueous solution and stored in a refrigerator at 5°C until ready for use.

[0113] 3. Preparation of ratiometric fluorescent probe solution

[0114] A ratiometric fluorescent probe was prepared by adding 1990 μL of the porphyrin nanoparticle solution to 10 μL of the blue carbon dot solution, mixing thoroughly, and reacting for 3 minutes. Simultaneously, optimization experiments (e.g., component response, temperature, kinetics, photostability, component ratio), as well as selectivity and anti-interference tests, were performed to obtain the optimal ratiometric fluorescent probe solution.

[0115] 4. Construction of fluorescence sensor

[0116] Place 1995 μL of the prepared ratio probe solution into a micro syringe from the top (the micro syringe can be disposable to avoid sample interference). When testing, draw 5 μL of soil digestion solution from the syringe needle for testing.

[0117] 5. Construction of intelligent sensing platform

[0118] A fluorescent sensing device adapted for a syringe was designed and synthesized using 3D printing technology. The syringe can be placed on the device, which consists of a mobile phone clip 2, a viewfinder 1, a syringe clip 3, an irradiation hole 4, and a miniature ultraviolet lamp 5. By connecting the designed device to a smartphone 7, a simple smartphone sensing platform can be manufactured. The platform can conveniently store and analyze data. In particular, the color recognition application on the smartphone 7 can convert the color information of the fluorescent image into data information (RGB value), thereby completing quantitative detection. As mentioned above, the optimized nanofluorescent probe (fluorescence intensity ratio of 4 / 1) can detect Cr in a series of gradient ranges of 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 5.0, 10.0, 20.0, and 50.0µM. 3+ We used a designed smartphone sensing platform to capture fluorescence images of the target probe's response under UV light. After the reaction was complete, a series of images from red to blue were taken using a smartphone under 365nm UV light. The corresponding RGB values ​​of these images were obtained using a color recognition app for further statistical analysis. All corresponding tests were repeated three times.

[0119] 6. Practical application of intelligent sensing platform

[0120] 5 μL of soil digestion solution was absorbed into a syringe containing 1995 μL of proportional fluorescent probe solution, which ultimately diluted the actual sample by nearly 400 times. 3+ The limiting concentration of chlorine would also be reduced by 400 times, which is within the sensor's detectable range. During the actual sample testing process, digested liquid from 10 soil samples was transferred to a syringe 6 of the designed fluorescence sensor. Four minutes later, the 10 samples were collected using a smartphone. The data analyzed by the smartphone's color recognition function was then compared with data from atomic absorption spectroscopy (AAS).

[0121] According to the above results, it can be seen that the beneficial effects of the embodiments of the present invention are as follows: the ratio fluorescence probe of the present invention detects Cr 3+ Compared with other single-color fluorescence detection, it shows richer color changes, effectively avoids the instability of single-color fluorescence intensity, and realizes visual detection; the response time of the fluorescence sensor of the present invention is completed within 60s, realizing rapid detection; the fluorescence spectrometer of the present invention is used to detect Cr 3+ The detection limit was 17.63 nM, which was much lower than that of Cr in soil.3+ The fluorescence sensor of the present invention is compact, portable, and can quickly absorb the target object for detection, breaking the limitations of time and space. In addition, the fluorescence photo information can be obtained by using a smart phone, and the Cr can be obtained through the corresponding linear relationship. 3+ The concentration content of soil heavy metals can be measured by the ratiometric fluorescent probe based on porphyrin nanoparticles and blue carbon dots prepared by the present invention. The ratiometric fluorescent probe detects Cr by the ligand-metal charge transfer principle. 3+ It has good selectivity and sensitivity, can effectively avoid interference from other impurities, and has a fast response.

[0122] The above describes in detail the preferred embodiments of the present invention, and describes the basic principles, main features and advantages of the present invention. However, those skilled in the art should understand that the embodiments of the present invention are not limited to the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Within the scope of knowledge possessed by ordinary technicians in this field, various changes can be made without departing from the purpose of the embodiments of the present invention. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived from this are still within the scope of protection of the embodiments of the present invention.

Claims

1. A fluorescent sensor based on porphyrin nanoparticles / blue carbon dots, characterized in that: Contains a ratiometric fluorescent probe made of porphyrin nanoparticles and blue carbon dots for Cr 3+ Visual detection; the preparation method of the fluorescent sensor comprises the following steps: S1. Preparation of porphyrin nanoparticles: Utilizing the self-assembly principle of block copolymers, 5-15 mL of an aqueous solution containing an appropriate amount of polyoxyethylene polyoxypropylene ether triblock copolymer is slowly added to a 0.04-0.06 mg / mL porphyrin THF solution. After stirring for 0.5-2 hours, the solvent is removed by rotary evaporation to obtain a solid porphyrin nanoparticle. The solid is then dissolved in ethanol and the resulting solution is stored at 3-5°C for later use. The amount of polyoxyethylene polyoxypropylene ether triblock copolymer added is such that the concentration of the polyoxyethylene polyoxypropylene ether triblock copolymer in the final solution is 0.05-0.1%; S2. Preparation of blue carbon dots: 10-30 mL of pulp-free lemon juice was mixed with 5-20 mL of water to form a clear solution. The clear solution was then transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 150-200°C for 10-15 hours. After the reaction was complete, the reactor was naturally cooled to room temperature. The resulting blue carbon dot solution was dialyzed against deionized water for 15-30 hours and then freeze-dried. The resulting substance was prepared into a 0.5-2 mg / mL aqueous solution and stored in a refrigerator at 3-5°C until ready for use. S3. Preparation of ratiometric fluorescent probe: 1900-1990 μL of the porphyrin nanoparticle solution prepared in S1 was added to 10-100 μL of the blue carbon dot solution prepared in S2, mixed thoroughly, and reacted for 1-3 minutes to obtain a ratiometric fluorescent probe.

2. The method for preparing the fluorescence sensor according to claim 1, wherein: The method comprises preparing a porphyrin nanoparticle / blue carbon dot ratiometric fluorescent probe, comprising the following steps: S1. Preparation of porphyrin nanoparticles: Utilizing the self-assembly principle of block copolymers, 5-15 mL of an aqueous solution containing an appropriate amount of polyoxyethylene polyoxypropylene ether triblock copolymer is slowly added to a 0.04-0.06 mg / mL porphyrin THF solution. After stirring for 0.5-2 hours, the solvent is removed by rotary evaporation to obtain a solid porphyrin nanoparticle. The solid is then dissolved in ethanol and the resulting solution is stored at 3-5°C for later use. The amount of polyoxyethylene polyoxypropylene ether triblock copolymer added is such that the concentration of the polyoxyethylene polyoxypropylene ether triblock copolymer in the final solution is 0.05-0.1%; S2. Preparation of blue carbon dots: 10-30 mL of pulp-free lemon juice was mixed with 5-20 mL of water to form a clear solution. The clear solution was then transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 150-200°C for 10-15 hours. After the reaction was complete, the reactor was naturally cooled to room temperature. The resulting blue carbon dot solution was dialyzed against deionized water for 15-30 hours and then freeze-dried. The resulting substance was prepared into a 0.5-2 mg / mL aqueous solution and stored in a refrigerator at 3-5°C until ready for use. S3. Preparation of ratiometric fluorescent probe: 1900-1990 μL of the porphyrin nanoparticle solution prepared in S1 was added to 10-100 μL of the blue carbon dot solution prepared in S2, mixed thoroughly, and reacted for 1-3 minutes to obtain a ratiometric fluorescent probe.

3. Use of the fluorescent sensor according to claim 1 or the fluorescent sensor prepared by the preparation method according to claim 2 in visual detection of Cr3+ in soil.

4. The use according to claim 3, characterized in that The overall fluorescence color of the ratio fluorescent probe is red, and the Cr 3+ The blue fluorescence in the ratiometric fluorescent probe remains unchanged, while the red fluorescence is gradually quenched, showing a series of fluorescence changes from red to blue. A series of photos from red to blue are taken under ultraviolet light with a smartphone to achieve Cr 3+ Visual detection.

5. The use according to claim 3, characterized in that Formulated with various Cr 3+ The fluorescence intensity of the standard solution was measured under 350-365 nm ultraviolet light to establish the fluorescence intensity ratio I674 / I458 and Cr 3+ Concentration standard curve and linear equation; The fluorescence intensity ratio I674 / I458 of the sample was detected, and the Cr content in the sample was obtained according to the standard curve and linear equation. 3+ concentration, thereby achieving quantitative detection.

6. The use according to claim 3, 4 or 5, characterized in that: The fluorescence sensor is used as a detection reagent and combined with a smart phone to build a detection platform for detecting Cr in soil. 3+ .

7. The use according to claim 6, characterized in that: The detection platform constructed by the smartphone comprises a platform body, a syringe (6), a micro-ultraviolet lamp (5) and a smartphone (7); a mobile phone clamp (2) for fixing the smartphone (7) is provided on one side of the platform body; a syringe clamp (3) for fixing the syringe (6) is provided on the upper part of the other side; and a fixing clamp (9) for fixing the micro-ultraviolet lamp (5) is provided on the lower part; a viewfinder (1) is provided on the syringe clamp (3); the viewfinder (1) is used for the camera of the smartphone (7) to take pictures; an irradiation hole (4) for irradiation by the micro-ultraviolet lamp (5) is provided on the syringe clamp (3); and the syringe (6) is used to load a ratio fluorescent probe solution.

8. The use according to claim 6, characterized in that: The application method of the detection platform built by the smartphone is as follows: during the detection, a syringe containing a ratio fluorescence probe solution is used to absorb the soil digestion solution. After the reaction is completed, a smartphone is used to take a photo from red to blue under 350-365nm ultraviolet light. The ratio of the intensity of B and R in the fluorescence photo is obtained through the color recognition app, and the RGB value is compared with the Cr 3+ The linear relationship between the concentration of Cr 3+ The actual concentration can be detected quantitatively.

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