WO2023060873A1

WO2023060873A1 - Rare-earth-element-doped carbon quantum dot ratio fluorescent probe, preparation method therefor and application thereof

Info

Publication number: WO2023060873A1
Application number: PCT/CN2022/089272
Authority: WO
Inventors: 李伟娜; 桑雨欣; 王娟; 牛永盛
Original assignee: 青岛农业大学
Priority date: 2021-10-12
Filing date: 2022-04-26
Publication date: 2023-04-20
Also published as: CN113861971B; CN113861971A

Abstract

The present invention belongs to the technical field of fluorescent nano-materials and environment monitoring, and disclosed are a rare-earth-element-doped carbon quantum dot ratio fluorescent probe, a preparation method therefor and an application thereof. The rare-earth-element-doped carbon quantum dot ratio fluorescent probe is obtained by using citric acid as a carbon source and melamine as a nitrogen source, adding a passivator formaldehyde and rare earth compound Eu(NO3)3·6H2O, uniformly mixing same in ultrapure water, carrying out a high-temperature reaction, then dialyzing same to remove small molecules, and drying. In the present invention, the rare-earth-element-doped carbon quantum dot ratio fluorescent probe is prepared by means of a one-step hydrothermal method. Europium ions are doped into carbon quantum dots in a hydrothermal reaction, the fluorescence of the carbon quantum dots may be maintained, and the carbon quantum dots may be specifically combined with tetracycline molecules. The described novel fluorescent probe has excellent physical and chemical stability, and the ratio fluorescence detection of target molecules may be achieved without complex carbon quantum dot modification.

Description

Rare earth element doped carbon quantum dot ratio fluorescent probe, its preparation method and application

technical field

The invention belongs to the technical field of fluorescent nanomaterials and environmental detection, and specifically relates to a rare earth element-doped carbon quantum dot ratio fluorescent probe, a preparation method and an application thereof.

Background technique

Tetracycline (TC), an important commonly used antibiotic, is widely used in animal husbandry, aquaculture and individualized therapy because of its low cost, high antibacterial activity, good oral absorption, and low toxicity. Unfortunately, due to the overuse of TC products, there have been some serious adverse effects on food safety, environmental protection and human health. Currently, there are a large number of analytical strategies for the detection of tetracyclines, such as liquid chromatography-mass spectrometry (LC-MS), high-performance liquid chromatography (HPLC), capillary electrophoresis (CE), chemiluminescence, and electrochemical analysis, which can accurately detect tetracyclines. However, there are shortcomings such as strict requirements for instruments, time-consuming, cumbersome steps, and professional skills. In recent years, fluorescence sensors or fluorescence analysis techniques have been successfully applied to the determination of TC due to their advantages of simple operation, fast response, low detection limit, less sample consumption, good selectivity, and low analysis cost. Notably, europium-based fluorescent sensing platforms exhibit highly enhanced fluorescence when combined with TC, which has attracted much attention in recent years. This can be attributed to the fact that TC can combine with europium ions (Eu ³⁺ ) to form a europium-tetracycline complex (Eu ³⁺ -TC), and transfer the energy absorbed by tetracycline to Eu ³⁺ , making Eu The characteristic fluorescence of ³⁺ is greatly enhanced, which is called "antenna effect". In addition, the fluorescence of Eu ³⁺ has unique spectral properties, including large Stokes shift, long fluorescence lifetime, and sharp linear emission region. However, the fluorescence intensity of the Eu ^{3+ -TC} complex is weak due to the quenching effect caused by the vibrational modes of Eu ³⁺ coordinated water molecules. Furthermore, these europium-based sensor platforms are limited in practical applications due to poor stability in humid environments and under UV light.

The detection of metal ions has attracted extensive attention due to the toxic effects caused by excessive accumulation of metal ions in humans and animals. Of all metals, aluminum is one of the most widely used in modern day life and in many industries. Acid rain and human activities will significantly increase the content of free aluminum ions in the soil, causing environmental pollution to crop production. Aluminum containers, packaging materials, electrical and electronic equipment can lead to Al ³⁺ contamination in drinking water and food. In addition, Al ³⁺ can enter organisms through the respiratory tract, digestive tract, and skin, causing damage to the nervous system and causing various diseases, such as microcytic hypochromic anemia, gastrointestinal diseases, liver and kidney damage, memory loss, etc. The average Al ³⁺ intake of the human body is 3-10 mg per day, and the maximum weekly aluminum intake is 7 mg/kg body weight. Atomic absorption spectrometry, atomic and emission spectrometry, high performance liquid chromatography, electrochemical methods, and inductively coupled plasma mass spectrometry are the most widely used methods for routine Al ³⁺ detection. These methods usually require complicated sample preparation and expensive precision instruments, which make them unsuitable for rapid on-site detection of Al ions. Therefore, efficient, fast, and easy visual on-site detection of Al ³⁺ is still a great challenge.

Contents of the invention

One of the purposes of the present invention is to provide a method for preparing a rare earth element-doped carbon quantum dot ratio fluorescent probe. In order to achieve this purpose, the following steps are specifically adopted:

The raw material is citric acid as the carbon source, melamine as the nitrogen source, and the rare earth compound Eu(NO ₃ ) ₃ 6H ₂ O is added, and the three are mixed evenly in ultra-pure water, and the high-temperature reaction is carried out. After the reaction is completed, it is cooled to room temperature. The resulting solution is dialyzed with ultrapure water to remove small molecules; the remaining solution is dried by evaporation to obtain rare earth element-doped carbon quantum dot ratio fluorescent probe powder.

Preferably, the high temperature reaction is 180-220°C, and the reaction is 5-10 hours;

Preferably, the dosage of the citric acid is 8-12 mmol; the dosage of the melamine is 0.2-0.3 mmol; the dosage of the rare earth compound Eu(NO ₃ ) ₃ ·6H ₂ O is 300-800 mg.

In several specific embodiments, the raw material of the preparation method of the rare earth element-doped carbon quantum dot ratio fluorescent probe also contains formaldehyde, the addition amount of the formaldehyde solution is 0-1000 μL, and the concentration of the formaldehyde solution is 8 mmol /L.

In a specific embodiment, when the amount of the rare earth compound Eu(NO ₃ ) ₃ ·6H ₂ O is 500 mg, the fluorescence intensity is the strongest.

In a specific example, the dosage of citric acid is 10mmol; the dosage of melamine is 0.25mmol; the dosage of the rare earth compound Eu(NO ₃ ) ₃ ·6H ₂ O is 500mg; Highest yield.

The above statement about the amount of raw materials is only the amount used in laboratory operations, rather than an absolute limit on the amount used. Those skilled in the art should understand that in actual production, the amount used can be adjusted according to the above ratio according to the scale of production.

In a specific embodiment, the dialysis is first filtered with a 0.22 μm filter membrane, and the filtrate is dialyzed in ultrapure water for 24 hours using a dialysis bag with a cut-off molecular weight of 1000 Da, and the water is renewed every 6 hours to remove small molecules .

The second object of the present invention is to provide the rare earth element doped carbon quantum dot ratio fluorescent probe prepared by the above method, and the above rare earth element doped carbon quantum dot ratio fluorescent probe can be used for the detection of tetracycline and/or aluminum ions and the detection of tetracycline and/or Or the preparation of aluminum ion detection products.

The principle of the preparation of rare earth element-doped carbon quantum dots and its detection of tetracycline and cascade recognition of aluminum ions provided by the present invention is: doping europium ions into the lattice structure of carbon quantum dots as a specific recognition unit of TC. When no tetracycline is added, europium-doped carbon quantum dots emit blue fluorescence (λem=420nm). After combining with tetracycline, based on the internal filter effect (IFE) and the "antenna effect" of Eu ³⁺ -TC, the blue fluorescence of carbon quantum dots is gradually quenched, and the characteristic red fluorescence of doped europium is gradually enhanced (λem=620nm) , yielding a ratiometric fluorescence signal change based on tetracycline content. Correspondingly, the color of the detection system under UV light gradually changed from blue to brown-yellow to light purple to light rose red to light pink to the final red, and a significant change occurred. The present invention is further applied to the cascade recognition of Al ³⁺ , since tetracycline compounds (TCs) can form chelates with multivalent cations Al ³⁺ . After the interaction between europium-doped carbon quantum dots and TC, further adding Al ³⁺ , the fluorescence of europium-doped carbon quantum dots at about 468nm gradually recovered, and the red fluorescence of Eu ³⁺ -TC complexes at 620nm gradually disappeared, realizing Al ³⁺ The ratiometric fluorescent cascade is identified, accompanied by a dramatic change in color from red to pink to blue.

The advantage of technical scheme of the present invention:

Rare earth element-doped carbon quantum dot ratio fluorescent probe was prepared by one-step hydrothermal method. Europium ions were doped into carbon quantum dots, which can not only maintain the blue fluorescence of carbon quantum dots, but also specifically bind to tetracycline molecules. Enhances the red fluorescence of europium ions. The composite system can further interact with Al ³⁺ , and both produce ratiometric fluorescence signals and significant gradients of color in the cascade recognition of both tetracycline and Al ³⁺ . This new type of fluorescent probe has excellent physical and chemical stability, does not require complicated carbon quantum dot modification, and can achieve ratiometric fluorescence detection of multiple target molecules through a single carbon quantum dot. The significant color change of the system with the change of the concentration of the analyte can be clearly observed.

In addition, an instrument-free portable paper-based sensor and a smartphone-assisted POCT platform were developed for the on-site visual detection of tetracycline and Al ³⁺ . The developed paper-based sensor has the characteristics of easy portability, low cost, high selectivity and high sensitivity, and can directly and easily read out the detection signal with the naked eye. As a simple answer analyzer, a smartphone is portable and easy to operate. When the concentration of TC and Al ³⁺ exceeds a certain level, the direct color change visible to the naked eye warns the user, and further mobile phone-assisted image processing can provide quantitative analysis of tetracycline and Al ³⁺ concentration. Provides a robust method for the qualitative identification and semi-quantitative analysis of tetracyclines and Al ³⁺ in field and resource-poor areas. It shows great potential application in food safety monitoring. Not only provides a new strategy for the ratiometric fluorescence and vision sensing of tetracycline and Al ³⁺ , but also provides new insights into the development of efficient ratiometric fluorescence and vision sensing platform, which is promising for many other On-site testing.

Description of drawings

Figure 1 Transmission electron microscope analysis diagram and HRTEM diagram of rare earth element-doped carbon quantum dot ratio fluorescent probe;

X-ray photoelectron spectroscopy (XPS) diagram of Fig. 2Eu-CDs;

The influence of Fig. 3 europium doping concentration on the fluorescence spectrum of Eu-CDs-TC complex;

Fig. 4 Fluorescence spectra of the effect of different concentrations of TC on the fluorescence intensity of Eu-CDs;

Figure 5 The linear equation for the detection of tetracycline by the rare earth element-doped carbon quantum dot ratio fluorescent probe;

Figure 6 The specificity of the rare earth element-doped carbon quantum dot ratio fluorescent probe to tetracycline;

Fig. 7 Fluorescence spectra of different concentrations of Al ³⁺ on the fluorescence intensity of Eu-CDs-TC;

Figure 8 The linear equation for the detection of Al ³⁺ by the rare earth element-doped carbon quantum dot ratio fluorescent probe;

Figure 9 Selectivity of Eu-CDs-TC complex to Al ³⁺ cascade recognition;

Figure 10 is based on the linear equation of europium-doped carbon quantum dot ratio fluorescent probe combined with smart phone and paper-based sensor to detect tetracycline;

Figure 11 The linear equation for the detection of Al ³⁺ based on europium-doped carbon quantum dot ratiometric fluorescent probes combined with smartphones and paper-based sensors.

Detailed ways

The terms used in the present invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art.

The present invention will be described in further detail below in conjunction with specific examples and with reference to data. The following examples are just to illustrate the present invention, but not to limit the scope of the present invention in any way.

Example 1

A preparation method of a rare earth element-doped carbon quantum dot ratio fluorescent probe, the steps are as follows:

Weigh 1920 mg (10.0 mmol) of citric acid and 31.5 mg (0.25 mmol) of melamine and dissolve them in 10 mL of ultrapure water, then add 560 μL of formaldehyde solution (formaldehyde concentration is 8.0 mmol/L) and 500 mg of Eu(NO ₃ ) ₃ 6H ₂ O (99.99%). Mix the solution thoroughly, transfer it to a 25mL polytetrafluoroethylene-lined stainless steel autoclave, and react at a temperature of 220°C for 10 hours. After cooling to room temperature, the resulting dark yellow solution is filtered through a 0.22 μm filter membrane and used with a dialysis bag (cut off Molecular weight of 1000 Da) was further dialyzed in ultrapure water for 24 hours, and the water was refreshed every 6 hours to remove small molecules. Subsequently, by evaporating the solution in the dialysis bag and drying at 80 °C, the powder of the rare earth element-doped carbon quantum dot ratio fluorescent probe was obtained with a quantum yield of 10.81%.

Figure 1 is a transmission electron microscope (TEM) image and a high resolution transmission electron microscope (HRTEM) image of rare earth element-doped carbon quantum dot ratio fluorescent probes (Eu-CDs) prepared by the above method. It can be seen from a in Figure 1 that Eu-CDs are nearly spherical nanoparticles with uniform distribution. The histogram of Eu-CDs particle size distribution shows that the particle size distribution is 1.0-3.0nm, and the average particle size is 2.0nm. The HRTEM image (b in Fig. 1) shows that the Eu-CDs have clear lattice fringes with a lattice spacing of about 0.20 nm, which is consistent with the (100) plane of graphitic carbon.

To further confirm the elemental composition and chemical bonds of Eu-CDs, X-ray photoelectron spectroscopy (XPS) measurements were performed. Figure 2 is the XPS diagram of Eu-CDs, where a is the full-scan XPS spectrum of Eu-CDs, b is the XPS spectrum of C1s, c is the XPS spectrum of N1s, d is the XPS spectrum of O1s, and e is the XPS spectrum of Eu3d ;

It can be seen from Figure 2 that the XPS full-scan spectrum shows four obvious peaks at 281.08, 398.08, 537.08 and 1131.08eV, which are attributed to C1s, N1s, O1s and Eu3d, and the element contents are 60.11%, 2.99%, 33.03% and 3.87%. The high content of Eu confirmed the successful doping of Eu in CDs (Fig. 2a). In the high-resolution spectra (Fig. 2b–e), the C1s band can be deconvoluted into three peaks at 284.7, 285.7 and 288.4 eV, corresponding to CC/C=C, CN/CO and C=O groups ; In the N1s spectrum, the peaks at 399.9 and 401.5eV correspond to NC and NH groups; the O1s band is at 531.2, 532.0 and 532.9eV, which can be deconvoluted into three peaks, which are respectively assigned to C=O and C-OH group. The photoemission of Eu3d at 1134.0 and 1164.0 eV is attributed to the 3d _5/2 and 3d _3/2 structures, respectively. The high-resolution Eu3d spectrum consists of four peaks, namely Eu ³⁺ (1165.0 and 1135.4eV) and Eu ²⁺ (1155.0 and 1125.5eV).

Example 2

Weigh 1536 mg (8.0 mmol) of citric acid and 25.2 mg (0.2 mmol) of melamine and dissolve them in 10 mL of ultrapure water, then add 300 mg of Eu(NO ₃ ) ₃ ·6H ₂ O (99.99%). Mix the solution thoroughly, transfer it to a 25mL polytetrafluoroethylene-lined stainless steel autoclave, and react at a temperature of 220°C for 10 hours. After cooling to room temperature, the resulting dark yellow solution is filtered through a 0.22 μm filter membrane and used with a dialysis bag (cut off Molecular weight of 1000 Da) was further dialyzed in ultrapure water for 24 hours, and the water was refreshed every 6 hours to remove small molecules. Subsequently, by evaporating the solution in the dialysis bag and drying at 80 °C, the powder of the rare earth element-doped carbon quantum dot ratio fluorescent probe was obtained with a quantum yield of 7.50%.

Example 3

Weigh 2304 mg (12.0 mmol) of citric acid and 37.8 mg (0.3 mmol) of melamine and dissolve them in 10 mL of ultrapure water, then add 1000 μL of formaldehyde solution (formaldehyde concentration is 8.0 mmol/L) and 800 mg of Eu(NO ₃ ) ₃ 6H ₂ O (99.99%). Mix the solution thoroughly, transfer it to a 25mL polytetrafluoroethylene-lined stainless steel autoclave, and react at a temperature of 220°C for 10 hours. After cooling to room temperature, the resulting dark yellow solution is filtered through a 0.22 μm filter membrane and used with a dialysis bag (cut off Molecular weight of 1000 Da) was further dialyzed in ultrapure water for 24 hours, and the water was refreshed every 6 hours to remove small molecules. Subsequently, by evaporating the solution in the dialysis bag and drying at 80 °C, the powder of the rare earth element-doped carbon quantum dot ratio fluorescent probe was obtained with a quantum yield of 9.02%.

Example 4

Effect of Europium Doping Concentration on the Fluorescence Spectrum of Eu-CDs-TC Composite

On the basis of _the method in Example 1, set the doping _{concentration} of Eu(NO ₃ ) ₃ ·6H ₂ O to 300 mg, 500 mg and 800 mg _respectively , and prepare Eu- CDs; and detect its fluorescence spectrum after adding TC, the results are shown in Figure 3, as can be seen from the fluorescence intensity curve and fluorescence intensity photos, the fluorescence spectrum shows a strong doping concentration dependence, with the Eu doping concentration Increased from 300mg to 500mg, the fluorescence intensity of Eu-CDs-TC increased greatly; after the Eu doping concentration exceeded 500mg, the fluorescence intensity decreased due to newly generated defects and reduced surface passivation, and the Eu doping concentration of 800mg The magnitude of fluorescence intensity enhancement was lower than that of 500mg Eu-doped samples; thus, compared with other doping concentrations, 500mg-doped Eu-CDs produced the highest fluorescence intensity enhancement after interacting with TC. Therefore, the Eu doping concentration of 500 mg is the optimum concentration.

Example 5

A method for detecting tetracycline, the steps are as follows:

(1) The rare earth element-doped carbon quantum dot ratio fluorescent probe prepared in Example 1 was prepared into an aqueous solution with a concentration of 60 μg·mL ⁻¹ , which was the Eu-CDs solution;

(2) Take the Eu-CDs solution prepared in step (1), add different amounts of tetracycline to it, and prepare it into a standard solution with different concentration gradients of tetracycline, wherein the concentration of tetracycline is 0-100 μ M; Cultivate for 5 minutes under the condition;

(3) Adopt fluorescence spectroscopy to record the emission spectrum of the standard solution of tetracycline different concentration gradients under the excitation of 380nm; The result is as shown in Figure 4; As can be seen from Figure 4, with the increase of tetracycline concentration, the Eu-CDs system is at 468nm The fluorescence intensity at 620nm decreased significantly, while that at 620nm gradually increased. When the tetracycline concentration was higher than 80 μM, F ₄₆₈ was in a quenched state, but F ₆₂₀ stopped increasing and began to decrease.

(4) The obtained experimental data is arranged and plotted, with the intensity ratio of I ₆₂₀ /I ₄₆₈ as the ordinate, and the TC concentration as the abscissa, to obtain a linear equation as shown in Figure 5, and the linear relationship is Y=0.0630x-0.242 ; Linear correlation coefficient R ² =0.999.

(5) Mix the sample solution to be tested with the Eu-CDs solution prepared in step (1) at a ratio of 1:1, and incubate at room temperature for 5 minutes; use fluorescence spectroscopy to obtain the 468nm and Fluorescence intensity at 620nm, calculate the intensity ratio of I ₆₂₀ /I ₄₆₈ , and compare with the linear equation obtained in step (4), calculate and obtain the content of tetracycline in the sample solution to be tested.

The above method for detecting tetracycline has good stability and high repeatability, and the detection limit is 6.9nM.

Specificity of Rare Earth Doped Carbon Quantum Dots Ratio-Fluorescent Probes for Tetracycline:

Tetracycline (Tetracycline) and its analogs (Oxytetracycline Oxytetracycline, Chlortetracycline Chlortetracycline, Erythromycin Erythromycin) solution of the same concentration (100 μM) were mixed with the Eu-CDs solution prepared in step (1) of equal volume respectively, and After incubation at room temperature for 5 min, the emission spectrum of the mixture was recorded by fluorescence spectroscopy under excitation at 380 nm. As shown in Figure 6, only tetracycline can cause the fluorescence quenching of Eu-CDs at 420 nm and generate a strong new fluorescence emission peak at 620 nm.

Example 6

A method for detecting aluminum ions, the steps are as follows:

(1) Prepare the rare earth element-doped carbon quantum dot ratio fluorescent probe prepared in Example 1 into an aqueous solution with a concentration of 60 μg mL ^-1 , and then add tetracycline to prepare a concentration of tetracycline of 100 μM and a concentration of Eu-CDs of 60 μg·mL mL ^-1 mixed solution (Eu-CDs-TC complex);

(2) Take the mixed solution prepared in step (1), add different amounts of Al ³⁺ to it, and prepare it into a standard solution of Al ³⁺ with different concentration gradients (Al(ClO ₄ ) ₃ is used in the preparation of the standard solution 9H ₂ O), wherein the concentration of Al ³⁺ is 0-50 μM; after mixing evenly, incubate at room temperature for 5 minutes;

(3) adopt fluorescence spectrometry to record the emission spectrum of the Eu-CDs-TC-Al ³⁺ solution of Al ³⁺ different concentration gradients under the excitation of 380nm; The result is as shown in Figure 7; As can be seen from Figure 7: With the increase of Al ³⁺ concentration, the fluorescence emission of Eu-CDs-TC-Al ³⁺ increases at 468nm, and the fluorescence emission at 620nm decreases with the increase of Al ³⁺ content.

(4) The obtained experimental data is arranged and plotted, with the intensity ratio of I ₄₆₈ /I ₆₂₀ as the ordinate, and the Al concentration as the ^abscissa , to obtain a linear equation as shown in Figure 8, and the linear relationship is Y=0.160x -0.379; linear correlation coefficient R ² =0.996.

(5) Mix the sample solution to be tested with the Eu-CDs-TC complex solution prepared in step (1) at a ratio of 1:1, and incubate at room temperature for 5 minutes; use fluorescence spectroscopy under excitation at 380 nm to obtain the Fluorescence intensity at 468nm and 620nm of the solution, calculate the intensity ratio of I ₄₆₈ /I ₆₂₀ , and compare with the standard curve obtained in step (4), calculate the content of Al ³⁺ in the sample solution to be tested.

The above method for detecting Al ³⁺ has good stability and high repeatability; the detection limit is 28.6nM; the LOD of Al ³⁺ is calculated as: LOD=3Sb/s, where Sb represents the standard error of 10 consecutive scans of the blank sample, S represents the slope of the calibration curve.

Examination of the selectivity of Eu-CDs-TC complexes for Al ³⁺ cascade recognition and other metal ions (Ca ²⁺ , Ni ²⁺ , Co ²⁺ , Mg ²⁺ , Cd ²⁺ , Hg ²⁺ , Zn ²⁺ , Cu ²⁺ ) to Al ³⁺ interference:

Metal ion solutions with a concentration of 50 μM were added to the Eu-CDs-TC complex solution prepared in the above step (1), and the Eu-CDs-TC complex solution without metal ion solution was used as a blank control (Blank ). After incubation for 5 min, the emission spectrum of the mixture was recorded by fluorescence spectroscopy under excitation at 380 nm to study the selectivity of Eu-CDs-TC to Al ³⁺ . The results are shown in Fig. 9, only Al ³⁺ can cause the fluorescence recovery of the Eu-CDs-TC complex at 468 nm.

Example 7

A method for detecting tetracycline based on europium-doped carbon quantum dot ratio fluorescent probe combined with smart phone and paper-based sensor, the steps are as follows:

(1) The rare earth element-doped carbon quantum dot ratio fluorescent probe prepared in Example 1 was prepared into an aqueous solution with a concentration of 60 μg mL ⁻¹ ;

(2) Cut the filter paper into a circle with a diameter of about 6 mm, and then immerse it in the Eu-CDs (60 μg·mL ^-1 ) solution prepared in step (1); after incubating at room temperature for 10 min, dry it in the air at room temperature ; Obtain a paper-based sensor for detecting tetracycline;

(3) Add TC aqueous solutions of different concentrations (0-150 μM) to the surface of the circular paper-based sensor prepared in step (2); the amount added is 200 μL/sheet of paper-based sensor;

(4) Observe the fluorescence color change of the circular paper-based sensor with naked eyes under ultraviolet light. The color scanning application program (APP: colorimeter) obtained by downloading from the app store digitizes and outputs the fluorescent color of the paper-based sensor to obtain the RGB value; uses the obtained experimental data (R/B) to sort out the graph and obtain the linear equation (Fig. 10 ), the linear relationship is Y=0.049x-0.219; the linear correlation coefficient R ² =0.998.

(5) Add the sample solution to be tested to the surface of the paper-based sensor prepared in step (2); the addition amount is 200 μL/sheet of paper-based sensor; record the fluorescence of the paper-based sensor under ultraviolet light with the color scanning application program on the smartphone color, and digitalize and output the fluorescent color of the paper-based sensor to obtain the RGB value; calculate R/B; substitute the value of R/B into the linear equation obtained in step (4), and calculate the content of tetracycline in the sample solution to be tested .

The detection of tetracycline by the above method has good stability and high repeatability, and the detection limit is 13.2nM.

Example 8

A method based on europium-doped carbon quantum dot ratio fluorescent probe combined with smart phone and paper-based sensor to detect Al ³⁺ , the steps are as follows:

(1) Prepare the rare earth element-doped carbon quantum dot ratio fluorescent probe prepared in Example 1 into an aqueous solution with a concentration of 60 μg mL ^-1 ; then add tetracycline to prepare a tetracycline concentration of 100 μM and a Eu-CDs concentration of 60 μg·mL mL ^-1 mixed solution (Eu-CDs-TC complex);

(2) Cut the filter paper into a circle with a diameter of about 6 mm, and then immerse it in the Eu-CDs-TC complex solution prepared in step (1); after incubating at room temperature for 10 min, dry it in the air at room temperature; Paper-based sensor for detecting Al ³⁺ ;

(3) Add Al ³⁺ aqueous solutions of different concentrations (0-80 μM) to the surface of the circular paper-based sensor prepared in step (2); the amount added is 200 μL/sheet of paper-based sensor;

(4) Observe the fluorescence color change of the circular paper-based sensor with naked eyes under ultraviolet light. The color scanning application program (APP: colorimeter) obtained by downloading from the application store digitizes and outputs the fluorescence color of the paper-based sensor to obtain the RGB value; uses the obtained experimental data (B/R) to organize the drawing and obtain the linear equation (Fig. 11 ), the linear relationship is Y=0.1445x-0.1445; the linear correlation coefficient R ² =0.998.

(5) Add the sample solution to be tested to the surface of the paper-based sensor prepared in step (2); the amount added is 200 μL/sheet of paper-based sensor; record the fluorescence of the paper-based sensor under ultraviolet light with the color scanning application program on the smartphone color, and digitize and output the fluorescent color of the paper-based sensor to obtain the RGB value; calculate B/R; substitute the value of B/R into the linear equation obtained in step (4) to calculate the Al ³⁺ in the sample solution to be tested content.

Using the above method to detect Al ³⁺ has good stability and high repeatability, and the detection limit is 160nM.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention to other forms. Any skilled person who is familiar with this profession may use the technical content disclosed above to change or remodel it into an equivalent change. Example. However, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

A preparation method of a rare earth element-doped carbon quantum dot ratio fluorescent probe, characterized in that the steps are as follows:

The raw material is citric acid as the carbon source, melamine as the nitrogen source, and the rare earth compound Eu(NO 3 ) 3 6H 2 O is added, and the three are mixed evenly in ultra-pure water, and the high-temperature reaction is carried out. After the reaction is completed, it is cooled to room temperature. The resulting solution is dialyzed with ultrapure water to remove small molecules; the remaining solution is dried by evaporation to obtain rare earth element-doped carbon quantum dot ratio fluorescent probe powder.
The preparation method of the rare earth element-doped carbon quantum dot ratio fluorescent probe according to claim 1, characterized in that the high temperature reaction is 180-220° C., and the reaction is 5-10 hours.
According to the preparation method of the rare earth element doped carbon quantum dot ratio fluorescent probe according to claim 1, it is characterized in that,

The dosage of the citric acid is 8-12mmol; the dosage of the melamine is 0.2-0.3mmol; the dosage of the rare earth compound Eu(NO 3 ) 3 ·6H 2 O is 300-800mg.
According to the preparation method of the rare earth element-doped carbon quantum dot ratio fluorescent probe according to claim 3, it is characterized in that, the raw material also contains formaldehyde solution, the addition amount of the formaldehyde solution is 0-1000 μ L, and the concentration of the formaldehyde solution is 8 mmol /L.
According to the preparation method of the described rare earth element doped carbon quantum dot ratio fluorescent probe of claim 4, it is characterized in that, the consumption of described citric acid is 10mmol; The consumption of described melamine is 0.25mmol; The consumption of described rare earth compound Eu(NO 3 ) The dosage of 3 ·6H 2 O is 500 mg; the dosage of the formaldehyde solution is 560 μL.
According to the preparation method of the rare earth element-doped carbon quantum dot ratio fluorescent probe according to any one of claims 1-6, it is characterized in that the dialysis is firstly filtered with a filter membrane of 0.22 μm, and the filtrate adopts a cut-off molecular weight of 1000Da The dialysis bag was dialyzed in ultrapure water for 24 hours, and the water was renewed every 6 hours to remove small molecules.
The rare earth element doped carbon quantum dot ratio fluorescent probe prepared by the method described in claim 6.
The application of the rare earth element-doped carbon quantum dot ratio fluorescent probe in the detection of tetracycline according to claim 7.
The application of the rare earth element-doped carbon quantum dot ratio fluorescent probe in the detection of aluminum ions according to claim 7.
The application of the rare earth element-doped carbon quantum dot ratio fluorescent probe in claim 7 in the preparation of products for detecting tetracycline and/or aluminum ions.