CN113884475A - Tetracycline detection method based on europium-doped carbon quantum dot ratio fluorescent probe - Google Patents
Tetracycline detection method based on europium-doped carbon quantum dot ratio fluorescent probe Download PDFInfo
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- G01N21/64—Fluorescence; Phosphorescence
- G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
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- G01N21/64—Fluorescence; Phosphorescence
- G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
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Abstract
The invention discloses a tetracycline detection method based on a europium-doped carbon quantum dot ratiometric fluorescent probe, and belongs to the technical field of tetracycline detection. The tetracycline detection method based on the europium-doped carbon quantum dot ratiometric fluorescent probe is characterized in that the fluorescence intensity change I of a sample to be detected and Eu-CDs mixed solution is detected according to the characteristic that tetracycline can enable the europium-doped carbon quantum dot ratiometric fluorescent probe to generate obvious color change from blue to brown yellow to light purple to light rose red to light pink to final red620/I468Comparing with a standard curve to obtain the tetracycline content in the sample to be detected; in addition, the paper-based sensor containing the europium-doped carbon quantum dot ratio fluorescent probe is prepared, the intelligent mobile phone is used as a signal reader, the carrying is convenient, the site detection of tetracycline in a resource-limited environment can be realized, and the detection method is simple, sensitive and efficient.
Description
Technical Field
The invention belongs to the technical field of tetracycline detection, and particularly relates to a tetracycline detection method based on a europium-doped carbon quantum dot ratiometric fluorescent probe.
Background
Tetracycline (TC) is an important common antibiotic, and is widely applied to animal husbandry, aquaculture and individual treatment due to low cost, high antibacterial activity, good oral absorption and low toxicity. Unfortunately, there have been some serious adverse effects on food safety, environmental protection and human health due to the excessive use of TC products. At present, a large number of analysis strategies for detecting tetracycline exist, such as liquid chromatography-mass spectrometry (LC-MS), High Performance Liquid Chromatography (HPLC), Capillary Electrophoresis (CE), chemiluminescence and electrochemical analysis, and tetracycline can be accurately detected. However, the method has the defects of strict instrument requirements, time consumption, complicated step operation, requirement of professional skills and the like. In recent years, fluorescence sensors or fluorescence analysis techniques have been successfully used for measuring TC because of their advantages of simple operation, fast response speed, low detection limit, small sample amount, good selectivity, low analysis cost, and the like. Notably, europium-based fluorescence sensing platforms exhibit highly enhanced fluorescence when combined with TCs, and have attracted considerable attention in recent years. This can be attributed to the fact that TC can react with europium ions (Eu)3+) Combine to form a europium-tetracycline complex (Eu)3+-TC) and transfers the energy absorbed by the tetracycline to Eu3+Make Eu to be3+The characteristic fluorescence of (a) is greatly enhanced, which is referred to as "antenna effect". Further, Eu3+Has unique spectral characteristics including large Stokes shift, long fluorescence lifetime and sharp linear emission region. However, europium-bound tetracycline has a weak fluorescence intensity due to quenching effects caused by vibrational modes of coordinated water molecules. Furthermore, these europium-based sensor platforms have limited practical applications due to poor stability in humid environments and ultraviolet light.
Disclosure of Invention
One of the purposes of the invention is to provide a tetracycline detection method based on a europium-doped carbon quantum dot ratiometric fluorescent probe, which comprises the following steps:
(1) preparing the europium-doped carbon quantum dot ratio fluorescent probe into an aqueous solution, namely an Eu-CDs solution;
(2) taking the Eu-CDs solution prepared in the step (1), adding different amounts of tetracycline into the Eu-CDs solution, preparing the Eu-CDs solution into standard solutions with different tetracycline concentration gradients, and uniformly mixing the standard solutions;
(3) recording fluorescence intensities of 468nm and 620nm positions of standard solutions with different tetracycline concentration gradients by adopting a fluorescence spectrometry under the excitation of 380 nm;
(4) arranging and drawing the experimental data obtained in the step (3) by I620/I468The strength ratio of (A) to (B) is taken as the ordinate and the tetracycline concentration is taken as the abscissa to obtain the tetracycline concentration and I620/I468A linear equation of intensity ratio;
(5) mixing a sample solution to be detected with the Eu-CDs solution prepared in the step (1); fluorescence intensities at 468nm and 620nm of the solution to be measured are obtained by fluorescence spectrometry under the excitation of 380nm, and I is calculated620/I468And (5) substituting the linear equation obtained in the step (4) to calculate and obtain the content of the tetracycline in the sample solution to be detected.
In the above tetracycline detection method based on the europium-doped carbon quantum dot rate fluorescent probe, the europium-doped carbon quantum dot rate fluorescent probe is prepared by the following method:
dissolving 8.0-12 mmol of citric acid and 0.2-0.3 mmol of melamine in water, and adding 0-1000 mu L of formaldehyde solution and 300-800 mg of Eu (NO)3)3·6H2O; fully mixing the solution, and reacting for 5-10 h at 180-220 ℃; cooling to room temperature after the reaction is finished, filtering and dialyzing the obtained solution, and removing small molecules with the molecular weight of less than 1000 Da; drying to obtain the europium-doped carbon quantum dot ratiometric fluorescent probe powder.
In a specific embodiment, the concentration of the formaldehyde solution is 8 mmol/L.
In a specific embodiment, the citric acid is used in an amount of 10 mmol; the dosage of the melamine is 0.25 mmol; the Eu (NO)3)3·6H2The dosage of O is 500 mg; the quantum yield is highest when the dosage of the formaldehyde solution is 560 mu L.
In a specific embodiment, in the step (1), the step (c) is carried outThe concentration of the Eu-CDs solution is 60 mug. mL-1。
In a specific embodiment, the mixing ratio of the sample solution to be tested and the Eu-CDs solution in the step (5) is 1: 1.
In a specific embodiment, the concentration of the standard solution of the tetracycline having different concentration gradients is in the range of 0-100. mu.M.
In a specific embodiment, the dialysis is performed by filtering with a 0.22 μm filter membrane, dialyzing the filtrate in ultrapure water for 24h with a dialysis bag with a cut-off molecular weight of 1000Da, and refreshing the water every 6 hours to remove small molecules.
The invention also aims to provide a paper-based sensor for detecting tetracycline, which is characterized in that filter paper is immersed in an aqueous solution of a europium-doped carbon quantum dot ratiometric fluorescent probe; after incubation culture is carried out for a period of time at room temperature, drying to obtain the paper-based sensor for detecting tetracycline;
the europium-doped carbon quantum dot ratiometric fluorescent probe is prepared by the following method:
dissolving 8.0-12 mmol of citric acid and 0.2-0.3 mmol of melamine in water, and adding 0-1000 mu L of formaldehyde solution and 300-800 mg of Eu (NO)3)3·6H2O; fully mixing the solution, and reacting for 5-10 h at 180-220 ℃; cooling to room temperature after the reaction is finished, filtering and dialyzing the obtained solution, and removing small molecules with the molecular weight of less than 1000 Da; drying to obtain the europium-doped carbon quantum dot ratiometric fluorescent probe powder.
In a specific embodiment, the concentration of the aqueous solution of the europium-doped carbon quantum dot ratiometric fluorescent probe is 60 mug. multidot.mL-1。
The filter paper can be cut into different shapes according to requirements, and the shape of the filter paper does not influence the detection result; in a specific embodiment, the filter paper is cut into a circular shape with a diameter of 6 mm.
In a specific embodiment, the room temperature incubation is room temperature incubation for 10 min.
The invention also aims to provide application of the paper-based sensor for detecting tetracycline in a tetracycline detection method of a smart phone as a signal reader.
The fourth purpose of the invention is to provide a tetracycline detection method using a smart phone as a signal reader, which comprises the following steps:
(1) adding tetracycline standard solutions with different concentrations to the surface of the paper-based sensor;
(2) downloading and installing a color scanning application program on the smart phone;
(3) recording the fluorescence color of the paper-based sensor in the step (1) under a 365nm ultraviolet lamp by using a color scanning application program on the smart phone, and digitizing and outputting the fluorescence color of the paper-based sensor to obtain an RG B value; taking R/B as a vertical coordinate and the concentration of tetracycline as a horizontal coordinate to obtain a linear equation of the concentration of tetracycline and R/B;
(4) adding a sample solution to be detected to the surface of the paper-based sensor;
(5) recording the fluorescence color of the paper-based sensor in the step (4) under a 365nm ultraviolet lamp by using a color scanning application program on the smart phone, and digitizing and outputting the fluorescence color of the paper-based sensor to obtain an RG B value; calculating R/B; and (4) substituting the numerical value of the R/B into the linear equation obtained in the step (3), and calculating to obtain the content of the tetracycline in the sample solution to be detected.
The above expression of the amount of the raw materials is only the amount used in the laboratory operation, and is not an absolute limitation of the amount thereof, and it will be understood by those skilled in the art that in the actual production, the amount may be adjusted in the above-mentioned ratio according to the production scale.
The method for detecting tetracycline is suitable for substrate samples such as aqueous solution and the like, such as water bodies and milk; the solid sample can be prepared in the form of an aqueous solution, or can be detected after removing water-insoluble components by filtration.
In the steps (1) and (4), the addition amount of the tetracycline standard solution or the sample solution to be detected with different concentrations on the paper-based sensor can be adjusted according to the size of the test paper sheet used for preparing the paper-based sensor; in a specific embodiment of the invention, the size of the test paper sheet is a disk with a diameter of 6mm, and the addition amount of the tetracycline standard solution or the sample solution to be tested with different concentrations on the test paper sheet is 200. mu.L/sheet.
The preparation of the europium-doped carbon quantum dot and the tetracycline detection principle thereof provided by the invention are as follows: europium ions are doped into the lattice structure of the carbon quantum dots to serve as specific identification units of TC. Without tetracycline addition, europium-doped carbon quantum dots fluoresce blue (λ em ═ 420 nm). After binding to tetracycline, based on Internal Filtration Effect (IFE) and Eu3+-antenna effect of TC, gradual quenching of blue fluorescence of carbon quantum dots, gradual enhancement of characteristic red fluorescence of europium-doped elements (λ em ═ 620nm), resulting in a ratiometric fluorescence signal change based on tetracycline content. Accordingly, the detection system gradually changed in color from blue to tan to light purple to light rose red to light pink to final red under the uv lamp.
The technical scheme of the invention has the advantages that:
the europium-doped carbon quantum dot ratiometric fluorescent probe is prepared by a one-step hydrothermal method. Europium ions are doped into the carbon quantum dots, so that the blue fluorescence of the carbon quantum dots can be kept, the red fluorescence of the europium ions can be enhanced by the specific combination of the europium ions and tetracycline molecules, and a ratio fluorescence signal and obvious gradual change of color are generated. The novel fluorescent probe has excellent physical and chemical stability, does not need complex carbon quantum dot modification, can realize ratio fluorescence detection on target molecules through a single carbon quantum dot, and can observe the obvious change of the color of the carbon quantum dot from blue to brown yellow to light purple to light rose red to light pink to final red gradually by naked eyes under an ultraviolet lamp.
In addition, a portable paper-based sensor without instruments and a POCT platform assisted by a smart phone are developed and used for on-site visual detection of tetracycline. The developed paper-based sensor has the characteristics of easy carrying, low cost, high selectivity and high sensitivity, and can directly and easily read out a detection signal by naked eyes. The smart phone has the characteristics of portability and easiness in operation as a simple answer analyzer. When the concentration of TC exceeds a certain level, a direct visual color change alerts the user, and further cell phone-assisted image processing can provide a quantitative analysis of tetracycline concentration. Provides a powerful method for qualitative identification and semi-quantitative analysis of tetracycline in sites and resource-poor areas. Shows great potential application in food safety monitoring. Not only provides a new strategy for the ratio fluorescence and visual sensing of tetracycline, but also provides new insights for developing an efficient ratio fluorescence and visual sensing platform, which is promising for many other field tests in the future.
Drawings
FIG. 1 TEM analysis and HRTEM image of europium doped carbon quantum dot ratiometric fluorescent probe;
FIG. 2 is an X-ray photoelectron spectroscopy (XPS) chart of Eu-CDs;
FIG. 3 the effect of europium doping concentration on the fluorescence spectrum of the Eu-CDs-TC complex;
FIG. 4 is a fluorescence spectrum of the effect of different concentrations of TC on the fluorescence intensity of Eu-CDs;
FIG. 5 is a linear equation for detecting tetracycline by using europium-doped carbon quantum dot ratiometric fluorescent probes;
FIG. 6 the specificity of europium doped carbon quantum dot ratiometric fluorescent probes for tetracycline;
FIG. 7 is a linear equation for detecting tetracycline based on europium-doped carbon quantum ratio fluorescent probes in combination with smart phones and paper-based sensors.
Detailed Description
Terms used in the present invention have generally meanings as commonly understood by one of ordinary skill in the art, unless otherwise specified.
The present invention will be described in further detail with reference to the following data in conjunction with specific examples. The following examples are intended to illustrate the invention and are not intended to limit the scope of the invention in any way.
Example 1
A preparation method of a europium-doped carbon quantum dot ratiometric fluorescent probe comprises the following steps:
1920mg (10.0mmol) of citric acid and 31.5mg (0.25mmol) of melamine are weighed out and dissolved in 10mL of ultrapure water, and 560. mu.L of formaldehyde solution (formaldehyde concentration 8.0 mmol-L) and 500mg Eu (NO)3)3·6H2O (99.99%). The solution was mixed well, transferred to a 25mL stainless steel autoclave lined with polytetrafluoroethylene, reacted at a temperature of 220 ℃ for 10 hours, cooled to room temperature, and after the resulting dark yellow solution was filtered through a 0.22 μm filter membrane and further dialyzed with a dialysis bag (molecular weight cut off 1000Da) in ultrapure water for 24 hours, and the water was refreshed every 6 hours to remove small molecules. Subsequently, the solution in the bag was dialyzed by evaporation and dried at 80 ℃ to obtain powder of europium-doped carbon quantum dot ratiometric fluorescent probe with a quantum yield of 10.81%.
FIG. 1 is a Transmission Electron Microscope (TEM) image and a High Resolution Transmission Electron Microscope (HRTEM) image of the europium-doped carbon quantum dot ratiometric fluorescent probe (Eu-CDs) prepared by the above method. As can be seen from a in FIG. 1, Eu-CDs are uniformly distributed approximately spherical nanoparticles, and the particle size distribution histogram of Eu-CDs shows that the particle size distribution is 1.0-3.0nm, and the average particle size is 2.0 nm. HRTEM images (b in FIG. 1) show that Eu-CDs have sharp lattice fringes with a lattice spacing of about 0.20nm, which is consistent with the (100) plane of graphitic carbon.
In order to further confirm the elemental composition and chemical bonds of Eu-CDs, X-ray photoelectron spectroscopy (XPS) measurements were performed. FIG. 2 is an XPS plot of Eu-CDs, wherein a is an XPS survey scan spectrum of Eu-CDs, b is an XPS spectrum of C1s, C is an XPS spectrum of N1s, d is an XPS spectrum of O1s, and e is an XPS spectrum of Eu3 d;
as can be seen from fig. 2, the XPS full scan spectrum shows four distinct peaks at 281.08,398.08,537.08 and 1131.08eV, due to C1s, N1s, O1s and Eu3d, with element contents of 60.11%, 2.99%, 33.03% and 3.87%, respectively. The high Eu content confirms successful doping of Eu in CDs (a in fig. 2). In high resolution spectra (fig. 2b-e), the C1s band can be deconvoluted at 284.7,285.7 and 288.4eV into three peaks, corresponding to C-C/C ═ C, C-N/C-O and C ═ O groups, respectively; in the N1s spectrum, the peaks at 399.9 and 401.5eV correspond to the N-C and N-H groups; the O1s band is 531.2, 532.0 and 532.9eV, and can be deconvoluted into three peaks, which are respectively assigned to C ═ O and C — OH groups. Eu3d is attributed to 3d at 1134.0 and 1164.0eV, respectively5/2And 3d3/2Photoemission of the structure. High resolution Eu3d spectrum is composed of four peaksRespectively is Eu3+(1165.0 and 1135.4eV) and Eu2+(1155.0 and 1125.5 eV).
Example 2
A preparation method of a europium-doped carbon quantum dot ratiometric fluorescent probe comprises the following steps:
1536mg (8.0mmol) of citric acid and 25.2mg (0.2mmol) of melamine are weighed out and dissolved in 10mL of ultrapure water, and 300mg of Eu (NO) is added3)3·6H2O (99.99%). The solution was mixed well, transferred to a 25mL stainless steel autoclave lined with polytetrafluoroethylene, reacted at a temperature of 220 ℃ for 10 hours, cooled to room temperature, and after the resulting dark yellow solution was filtered through a 0.22 μm filter membrane and further dialyzed with a dialysis bag (molecular weight cut off 1000Da) in ultrapure water for 24 hours, and the water was refreshed every 6 hours to remove small molecules. Subsequently, the solution in the bag was dialyzed by evaporation and dried at 80 ℃ to obtain powder of europium-doped carbon quantum dot ratiometric fluorescent probe with a quantum yield of 7.50%.
Example 3
A preparation method of a europium-doped carbon quantum dot ratiometric fluorescent probe comprises the following steps:
2304mg (12.0mmol) of citric acid and 37.8mg (0.3mmol) of melamine were weighed out and dissolved in 10mL of ultrapure water, and 1000. mu.L of a formaldehyde solution (formaldehyde concentration of 8.0mmol/L) and 800mg of Eu (NO) (NO concentration)3)3·6H2O (99.99%). The solution was mixed well, transferred to a 25mL stainless steel autoclave lined with polytetrafluoroethylene, reacted at a temperature of 220 ℃ for 10 hours, cooled to room temperature, and after the resulting dark yellow solution was filtered through a 0.22 μm filter membrane and further dialyzed with a dialysis bag (molecular weight cut off 1000Da) in ultrapure water for 24 hours, and the water was refreshed every 6 hours to remove small molecules. Subsequently, the solution in the bag was dialyzed by evaporation and dried at 80 ℃ to obtain powder of europium-doped carbon quantum dot ratiometric fluorescent probe with a quantum yield of 9.02%.
Example 4
Influence of europium doping concentration on fluorescence spectrum of Eu-CDs-TC complex
Based on the method of example 1, Eu (NO) is set3)3·6H2The O doping concentration is respectively 300mg, 500mg and 800mg, and different Eu (NO) is prepared3)3·6H2Eu-CDs with O doping concentration; and detecting the fluorescence spectrum after adding TC, wherein the result is shown in figure 3, and the fluorescence spectrum shows strong doping concentration dependence as can be seen from the fluorescence intensity curve and the fluorescence intensity photograph, and the fluorescence intensity enhancement amplitude of Eu-CDs-TC becomes larger as the Eu doping concentration is increased from 300mg to 500 mg; after the Eu doping concentration exceeds 500mg, the fluorescence intensity can be reduced due to newly generated defects and reduced surface passivation, and the fluorescence intensity enhancement amplitude of the Eu doping concentration of 800mg is lower than that of the Eu doping sample of 500mg instead; thus, 500mg of doped Eu-CDs produced the highest fluorescence intensity enhancement after interaction with TC compared to other doping concentrations. Therefore, the Eu doping concentration of 500mg is the optimum concentration.
Example 5
A method for detecting tetracycline comprises the following steps:
(1) the europium-doped carbon quantum dot ratiometric fluorescent probe prepared in example 1 was prepared to a concentration of 60. mu.g.mL-1The aqueous solution of (1) is Eu-CDs solution;
(2) taking the Eu-CDs solution prepared in the step (1), adding different amounts of tetracycline into the Eu-CDs solution, and preparing the Eu-CDs solution into standard solutions with tetracycline of different concentration gradients, wherein the concentration of the tetracycline is 0-100 mu M; mixing, and culturing at room temperature for 5 min;
(3) recording emission spectra of standard solutions with different concentration gradients of tetracycline under 380nm excitation by adopting a fluorescence spectrometry; the results are shown in FIG. 4; from FIG. 4, it can be seen that the fluorescence intensity of the Eu-CDs system at 468nm decreases significantly with increasing tetracycline concentration, while the fluorescence intensity at 620nm increases gradually. When the concentration of tetracycline is higher than 80. mu.M, F468In a quenched state, but F620No longer increasing and begins to decrease.
(4) The experimental data obtained are arranged and plotted as I620/I468The intensity ratio of (a) is taken as the ordinate, the TC concentration is taken as the abscissa, and a linear equation is obtained as shown in fig. 5, wherein the linear relation is that Y is 0.0630 x-0.242; linear correlation coefficient R2＝0.999。
(5) Mixing the solution of the sample to be tested with the Eu-CDs solution prepared in the step (1) according to the ratio of 1:1, and culturing for 5min at room temperature; fluorescence intensities at 468nm and 620nm of the solution to be measured are obtained by fluorescence spectrometry under the excitation of 380nm, and I is calculated620/I468And (4) comparing the standard curve obtained in the step (4) to calculate and obtain the content of the tetracycline in the sample solution to be detected.
The method for detecting tetracycline has good stability and high repeatability, and the detection limit is 6.9 nM.
Specificity of europium-doped carbon quantum dot ratiometric fluorescent probe for tetracycline:
and (2) respectively mixing Tetracycline (Tetracycline) and analogues thereof (Oxytetracycline, Chlortetracycline, Erythromycin) solutions with the same concentration (100 mu M) with the same volume of the Eu-CDs solution prepared in the step (1), culturing for 5 minutes at room temperature, and recording an emission spectrum of the mixture under the excitation of 380nm by adopting a fluorescence spectrometry. As shown in FIG. 6, only tetracycline can cause fluorescence quenching of Eu-CDs at 468nm and generate a strong new fluorescence emission peak at 620 nm.
Example 6
A method for detecting tetracycline based on a europium-doped carbon quantum dot ratio fluorescent probe combined with a smart phone and a paper-based sensor comprises the following steps:
(1) the europium-doped carbon quantum dot ratiometric fluorescent probe prepared in example 1 was prepared to a concentration of 60. mu.g.mL-1An aqueous solution of (a);
(2) the filter paper was cut into a circular shape having a diameter of about 6mm, and then immersed in Eu-CDs (60. mu.g. mL) prepared in step (1)-1) In solution; incubating for 10min at room temperature, and drying in air at room temperature; obtaining a paper-based sensor for detecting tetracycline;
(3) adding TC aqueous solutions with different concentrations (0-150 mu M) to the surface of the circular paper-based sensor prepared in the step (2); the addition amount is 200 mu L/piece of paper-based sensor;
(4) the fluorescent color change of the circular paper-based sensor was observed with the naked eye under an ultraviolet lamp. By application ofThe shop downloads the acquired color scanning application program (APP) to digitize and output the fluorescence color of the paper-based sensor, and then the R GB value is acquired; the obtained experimental data (R/B) are arranged and plotted to obtain a linear equation (figure 7), and the linear relation is Y-0.049 x-0.219; linear correlation coefficient R2＝0.998。
(5) Adding a sample solution to be detected to the surface of the paper-based sensor prepared in the step (2); the addition amount is 200 mu L/piece of paper-based sensor; recording the fluorescence color of the paper-based sensor under an ultraviolet lamp by using a color scanning application program on the smart phone, and digitizing and outputting the fluorescence color of the paper-based sensor to obtain an RG value and a B value; calculating R/B; and (5) substituting the numerical value of the R/B into the linear equation obtained in the step (4), and calculating to obtain the content of the tetracycline in the sample solution to be detected.
The tetracycline detected by the method has good stability and high repeatability, and the detection limit is 13.2 nM.
In conclusion, the europium-doped carbon quantum dot ratiometric fluorescent probe synthesized by the invention not only provides a new strategy for TC ratiometric fluorescence and visual sensing, but also provides new insight for developing efficient ratiometric fluorescence and visual sensing platforms.
The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.
Claims (10)
1. A tetracycline detection method based on a europium-doped carbon quantum dot ratiometric fluorescent probe is characterized by comprising the following steps of:
(1) preparing the europium-doped carbon quantum dot ratio fluorescent probe into an aqueous solution, namely an Eu-CDs solution;
(2) taking the Eu-CDs solution prepared in the step (1), adding different amounts of tetracycline into the Eu-CDs solution, preparing the Eu-CDs solution into standard solutions with different tetracycline concentration gradients, and uniformly mixing the standard solutions;
(3) recording fluorescence intensities of 468nm and 620nm positions of standard solutions with different tetracycline concentration gradients by adopting a fluorescence spectrometry under the excitation of 380 nm;
(4) arranging and drawing the experimental data obtained in the step (3) by I620/I468The strength ratio of (A) to (B) is taken as the ordinate and the tetracycline concentration is taken as the abscissa to obtain the tetracycline concentration and I620/I468A linear equation of intensity ratio;
(5) mixing a sample solution to be detected with the Eu-CDs solution prepared in the step (1); fluorescence intensities at 468nm and 620nm of the solution to be measured are obtained by fluorescence spectrometry under the excitation of 380nm, and I is calculated620/I468And (5) substituting the linear equation obtained in the step (4) to calculate and obtain the content of the tetracycline in the sample solution to be detected.
2. The method for detecting tetracycline based on europium-doped carbon quantum dot ratiometric fluorescent probe of claim 1, wherein said europium-doped carbon quantum dot ratiometric fluorescent probe is prepared by the following method:
dissolving 8.0-12 mmol of citric acid and 0.2-0.3 mmol of melamine in water, and adding 0-1000 mu L of formaldehyde solution and 300-800 mg of Eu (NO)3)3·6H2O; fully mixing the solution, and reacting for 5-10 h at 180-220 ℃; cooling to room temperature after the reaction is finished, filtering and dialyzing the obtained solution, and removing small molecules with the molecular weight of less than 1000 Da; drying to obtain the europium-doped carbon quantum dot ratiometric fluorescent probe powder.
3. The method for detecting tetracycline based on europium-doped carbon quantum dot ratiometric fluorescent probe of claim 2, wherein the concentration of the formaldehyde solution is 8 mmol/L.
4. The method for detecting tetracycline based on europium-doped carbon quantum dot ratiometric fluorescent probe of claim 3, wherein the amount of citric acid is 10 mmol; the dosage of the melamine is 0.25mmol; the Eu (NO)3)3·6H2The dosage of O is 500 mg; the amount of the formaldehyde solution is 560. mu.L.
5. The method for detecting tetracycline based on europium-doped carbon quantum dot ratiometric fluorescent probe of claim 1, wherein the concentration of Eu-CDs solution in step (1) is 60 μ g-mL-1。
6. The method for detecting tetracycline based on europium-doped carbon quantum dot ratiometric fluorescent probe of claim 5, wherein the mixing ratio of the sample solution to be detected and the Eu-CDs solution in step (5) is 1: 1.
7. The method for detecting tetracycline based on europium-doped carbon quantum dot ratiometric fluorescent probe of any one of claims 1 to 6, wherein the concentration range of the standard solution of different concentration gradients of tetracycline is 0-100 μ M.
8. A paper-based sensor for detecting tetracycline is characterized in that filter paper is immersed in an aqueous solution of a europium-doped carbon quantum dot ratiometric fluorescent probe; after incubation culture is carried out for a period of time at room temperature, drying to obtain the paper-based sensor for detecting tetracycline;
the europium-doped carbon quantum dot ratiometric fluorescent probe is prepared by the following method:
dissolving 8.0-12 mmol of citric acid and 0.2-0.3 mmol of melamine in water, and adding 0-1000 mu L of formaldehyde solution and 300-800 mg of Eu (NO)3)3·6H2O; fully mixing the solution, and reacting for 5-10 h at 180-220 ℃; cooling to room temperature after the reaction is finished, filtering and dialyzing the obtained solution, and removing small molecules with the molecular weight of less than 1000 Da; drying to obtain the europium-doped carbon quantum dot ratiometric fluorescent probe powder.
9. The paper-based sensor for detecting tetracycline in claim 8, wherein the paper-based sensor is applied to a tetracycline detection method of a smart phone as a signal reader.
10. A tetracycline detection method using a smart phone as a signal reader is characterized by comprising the following steps:
(1) adding different concentrations of tetracycline standard solutions to the paper-based sensor surface of claim 8;
(2) downloading and installing a color scanning application program on the smart phone;
(3) recording the fluorescence color of the paper-based sensor in the step (1) under an ultraviolet lamp by using a color scanning application program on the smart phone, and digitizing and outputting the fluorescence color of the paper-based sensor to obtain an RG B value; taking R/B as a vertical coordinate and the concentration of tetracycline as a horizontal coordinate to obtain a linear equation of the concentration of tetracycline and R/B;
(4) adding a sample solution to be tested to the paper-based sensor surface of claim 8;
(5) recording the fluorescence color of the paper-based sensor in the step (4) under an ultraviolet lamp by using a color scanning application program on the smart phone, and digitizing and outputting the fluorescence color of the paper-based sensor to obtain an RG B value; calculating R/B; and (4) substituting the numerical value of the R/B into the linear equation obtained in the step (3), and calculating to obtain the content of the tetracycline in the sample solution to be detected.
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