Ratio-fluorescent probes based on lanthanide metal ions and carbon quantum dots and their applications

Abstract

This invention discloses a ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots and its applications. The ratiometric fluorescent probe comprises carbon quantum dots, a lanthanide metal ion solution, and a non-luminescent rare earth ion solution or a ferric ion solution. The ratio of carbon quantum dots, lanthanide metal ion solution, and non-luminescent rare earth ion solution is 0.1 mg–0.6 mg : 4 μL–35 μL : 10 μL–35 μL, and the ratio of carbon quantum dots, lanthanide metal ion solution, and ferric ion solution is 0.1 mg–0.6 mg : 10 μL–35 μL : 15 μL–25 μL. This ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots has advantages such as a wide detection range, high detection sensitivity, strong anti-interference ability, fast response speed, and low cost. It can be widely used in the detection of target substances in environmental, medical, and food fields, demonstrating high practical value and promising application prospects.

Description

Technical Field

[0001] This invention belongs to the fields of fluorescent nanomaterials and analytical chemistry, and relates to a ratiometric fluorescent probe and its application, specifically a ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots and its application. Background Technology

[0002] Fluorescence technology has attracted much attention due to its inherent advantages such as high sensitivity, low consumption, and portability. Currently, most traditional fluorescent probes rely on changes in the emission intensity of a single wavelength to detect target pollutants. However, this single wavelength change is greatly affected by external conditions such as the concentration of the fluorescent probe, resulting in relatively poor detection accuracy, detection range, and anti-interference ability, hindering its widespread application. To achieve higher accuracy and stronger anti-interference performance, it is necessary to develop a ratiometric fluorescent probe based on two wavelengths. Existing ratiometric fluorescent probes based on lanthanide metal ions and carbon quantum dots mainly involve doping lanthanide metal ions into carbon quantum dots or constructing ratiometric fluorescent probes by combining lanthanide metal complexes with carbon quantum dots. However, they still suffer from the following drawbacks: narrow detection range, poor detection sensitivity, poor anti-interference ability, long response time, and high cost. These shortcomings greatly limit the widespread application of fluorescence technology. Therefore, obtaining a ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots with a wide detection range, high detection sensitivity, strong anti-interference ability, fast response speed, and low cost is of great significance for expanding its application in environmental pollutant detection and medical biomaterials. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots with wide detection range, high detection sensitivity, strong anti-interference ability, fast response speed and low cost, and its application.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots, the ratiometric fluorescent probe comprising carbon quantum dots, a lanthanide metal ion solution, and a non-luminescent rare earth ion solution; the ratio of the carbon quantum dots, the lanthanide metal ion solution, and the non-luminescent rare earth ion solution is 0.1 mg~0.6 mg : 4 μL~35 μL : 10 μL~35 μL.

[0006] The above-mentioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved in that the ratio of carbon quantum dots, lanthanide metal ion solution and non-luminescent rare earth ion solution is 0.1 mg~0.5 mg : 15 μL~30 μL : 14 μL~25 μL.

[0007] The above-mentioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved in that the ratio of carbon quantum dots, lanthanide metal ion solution and non-luminescent rare earth ion solution is 0.2mg~0.5mg∶4μL~32μL∶14μL~26μL.

[0008] The aforementioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved in that the initial concentration of the lanthanide metal ion solution is 0.5 mol / L to 2 mol / L; and the lanthanide metal ion in the lanthanide metal ion solution is Tb. 3+ Eu 3+ At least one of them.

[0009] The above-mentioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved by the following steps in the preparation method of the carbon quantum dots:

[0010] S1. Dissolve citric acid and L-histidine in ultrapure water and sonicate to obtain a mixed solution;

[0011] S2. The mixed solution obtained in S1 is subjected to a hydrothermal reaction, centrifuged, and the supernatant is collected for dialysis and freeze-dried to obtain carbon quantum dots.

[0012] In a further improvement of the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots, in step S1, the mass ratio of citric acid to L-histidine is 1 to 6:1; the mass-to-volume ratio of citric acid to ultrapure water is 0.05 g to 0.15 g: 1 mL; and the sonication time is 10 min to 20 min.

[0013] The above-mentioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved in the following aspects: in S2, the hydrothermal reaction temperature is 150℃~200℃; the hydrothermal reaction time is 210min~290min; the centrifugation speed is 10000rpm~12000rpm; the centrifugation time is 22min~36min; the dialysis bag used in the dialysis process has a specification of 500Da~2000Da; and the dialysis time is 30h~50h.

[0014] The aforementioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved in that the initial concentration of the non-luminescent rare earth ion solution is 0.5 mol / L to 1 mol / L; and the non-luminescent rare earth ion in the non-luminescent rare earth ion solution is Y2. 3+ Gd 3+ At least one of them.

[0015] As a general technical concept, the present invention also provides a ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots, the ratiometric fluorescent probe comprising carbon quantum dots, a lanthanide metal ion solution and a ferric ion solution; the ratio of the carbon quantum dots, the lanthanide metal ion solution and the ferric ion solution is 0.1 mg to 0.6 mg: 10 μL to 35 μL: 15 μL to 25 μL.

[0016] The aforementioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved in that the initial concentration of the lanthanide metal ion solution is 0.5 mol / L to 2 mol / L; and the lanthanide metal ion in the lanthanide metal ion solution is Tb. 3+ Eu 3+ At least one of them.

[0017] The above-mentioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved by the following steps in the preparation method of the carbon quantum dots:

[0018] S1. Dissolve citric acid and L-histidine in ultrapure water and sonicate to obtain a mixed solution;

[0019] S2. The mixed solution obtained in S1 is subjected to a hydrothermal reaction, centrifuged, and the supernatant is collected for dialysis and freeze-dried to obtain carbon quantum dots.

[0020] In a further improvement of the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots, in step S1, the mass ratio of citric acid to L-histidine is 1 to 6:1; the mass-to-volume ratio of citric acid to ultrapure water is 0.05 g to 0.15 g: 1 mL; and the sonication time is 10 min to 20 min.

[0021] The above-mentioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved in the following aspects: in S2, the hydrothermal reaction temperature is 150℃~200℃; the hydrothermal reaction time is 210min~290min; the centrifugation speed is 10000rpm~12000rpm; the centrifugation time is 22min~36min; the dialysis bag used in the dialysis process has a specification of 500Da~2000Da; and the dialysis time is 30h~50h.

[0022] The aforementioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is further improved in that the initial concentration of the ferric ion solution is 0.5 mol / L to 1 mol / L.

[0023] As a general technical concept, the present invention also provides an application of the above-mentioned ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots in the detection of target substances in the environmental, medical and food fields.

[0024] In the above-described application, a further improvement is made, wherein the target substance includes ascorbic acid and Fe. 3+ Or a Lewis hard base; said Lewis hard base is PO3. 2- F - ,ClO - or NO2 - .

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] (1) To address the shortcomings of traditional fluorescent probes, such as narrow detection range, poor detection sensitivity, poor anti-interference ability, and high cost, and the deficiencies of ratiometric fluorescent probes, such as high detection limit, long response speed, and the resulting difficulty in widely using them to detect target substances in environmental, medical, and food fields, this invention proposes a ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots. This probe is constructed from carbon quantum dots, a lanthanide metal ion solution, and a non-luminescent rare earth ion solution or a trivalent iron ion solution. Specifically, the carbon quantum dots used in this invention emit blue fluorescence and, as a novel zero-dimensional carbon-based material, possess excellent properties such as easy preparation and surface modification, high water solubility, low or non-toxicity, biocompatibility, and unique optical and chemical stability. Furthermore, the carbon quantum dots themselves have abundant surface groups (amino and carboxyl groups), which can interact with lanthanide metal ions through an "antenna effect." At this time, the abundant functional groups on the surface of the carbon quantum dots can coordinate with the lanthanide metal ions, enhancing their ff transition and quenching the blue fluorescence of the carbon quantum dots. Simultaneously, when a target substance is introduced into the system, the target substance can strengthen the interaction between the carbon quantum dots and lanthanide. The Dexter energy transfer between lanthanide and ferric ions leads to a further weakening of the blue fluorescence of carbon quantum dots and an enhancement of the characteristic fluorescence of lanthanide ions. Furthermore, by introducing non-luminescent rare-earth ions as signal amplifiers, the Dexter energy transfer between carbon quantum dots and lanthanide ions can be further strengthened. This allows for accurate detection of the target substance based on the ratio of their fluorescence intensity changes, combined with a linear equation relating the fluorescence intensity ratio to the target substance concentration. Alternatively, the introduction of the target substance can disrupt the structure of carbon quantum dots, quenching the characteristic fluorescence of both lanthanide and carbon quantum dots. Furthermore, the introduction of non-luminescent rare-earth ions increases the luminescence intensity of lanthanide ions, thereby increasing the linear range for ferric iron detection. This allows for accurate detection of the target substance based on the ratio of their fluorescence intensity changes, combined with a linear equation relating the fluorescence intensity ratio to the target substance concentration. Alternatively, the introduction of ferric ions disrupts the structure of both carbon quantum dots and lanthanide ions, weakening their characteristic fluorescence. When the system contains the target substance, this target substance will release Fe... 3+ Reduced to Fe2+ This invention restores the characteristic fluorescence of carbon quantum dots and lanthanide metal ions, allowing for accurate detection of target substances based on the ratio of their fluorescence intensity changes and a linear equation relating the fluorescence intensity ratio to the target substance concentration. Compared to conventional ratiometric fluorescent probes, this invention, based on lanthanide metal ions and carbon quantum dots, offers advantages such as a wide detection range, high detection sensitivity, strong anti-interference capability, fast response speed, and low cost. It can be widely used in the detection of target substances in environmental, medical, and food fields, demonstrating high practical value and promising application prospects.

[0027] (2) In this invention, the carbon quantum dots are prepared by the following method: using citric acid and L-histidine as raw materials, carbon quantum dots with surface groups (amino and carboxyl groups) can be prepared through hydrothermal reaction. At the same time, the drying method used is freeze drying, which helps to protect the surface groups of carbon quantum dots from oxidation or damage. However, conventional drying methods are usually vacuum drying, which easily damages the surface groups of carbon quantum dots. Moreover, carbon quantum dots prepared by vacuum drying are oily, which is not conducive to the reaction between carbon quantum dots and lanthanide metal ions, thus easily resulting in poor luminescence intensity and hindering accurate measurement. More importantly, the preparation method of this invention improves the response time, reduces the detection limit, increases the linear range of detection, and ensures that the probe has excellent selectivity by finely adjusting the morphology of the material (carbon quantum dots), the type and ratio of surface groups.

[0028] (3) In this invention, the ratiometric fluorescent probe constructed from carbon quantum dots, lanthanide metal ion solutions, and non-luminescent rare earth ion solutions for detecting phosphates in the environmental or medical fields has the following advantages: (a) It has a wide detection range for phosphates, such as the ability to accurately detect phosphate solutions with concentrations from 0.01 μmol / L to 50 μmol / L; (b) It has a low detection limit for phosphates, with a lower detection limit of 0.16 μmol / L; (c) It has low detection cost; (d) It has good selectivity and strong anti-interference ability, and can avoid various interfering ions (such as K+). + Na + Mg 2+ NO3 - SO4 2- CO3 2- CH3COO - SO3 2- (f) Fast response speed; after mixing the sample to be tested with the ratiometric fluorescent probe, it can be directly detected. Simultaneously, before using this ratiometric fluorescent probe to detect phosphates in the environmental or medical fields, it also includes: pretreatment of the phosphate solution to be tested with ascorbic acid solution, using the redox effect of ascorbic acid to remove interfering ions in the system, thereby avoiding interfering ions (such as Fe...).3+ This reduces interference with phosphate detection, thus improving detection accuracy.

[0029] (4) In this invention, the ratiometric fluorescent probe constructed from carbon quantum dots, lanthanide metal ion solutions, and non-luminescent rare earth ion solutions has the following advantages when detecting ferric ions in the environmental or medical fields: (a) It has a wide detection range for ferric ions, such as being able to accurately detect ferric ion solutions with a concentration ≤500 μmol / L; (b) It has a low detection limit for ferric ions, with a lower detection limit of 0.3 μM; (c) It has low detection cost; (d) It has good selectivity and strong anti-interference ability, and can avoid various interfering ions (such as K+). + Na + Mg 2+ NO3 - SO4 2- CO3 2- CH3COO - SO3 2- (f) The response speed is fast. After mixing the sample to be tested with the ratiometric fluorescent probe, it can be directly detected.

[0030] (5) In this invention, the ratiometric fluorescent probe constructed from carbon quantum dots, lanthanide metal ion solutions, and ferric ion solutions has the following advantages when detecting ascorbic acid in environmental or medical fields: (a) It has a wide detection range for ascorbic acid, such as being able to accurately detect ascorbic acid solutions with a concentration ≤300 μmol / L; (b) It has a low detection limit for ascorbic acid, with a lower detection limit of 1.67 μM; (c) It has low detection cost; (d) It has good selectivity and strong anti-interference ability, and can avoid various interfering ions (such as K+). + Na + Mg 2+ NO3 - SO4 2- CO3 2- CH3COO - SO3 2- (f) The response speed is fast. After mixing the sample to be tested with the ratiometric fluorescent probe, it can be directly detected. Attached Figure Description

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0032] Figure 1 The images shown are scanning electron microscope (SEM) image (a) and high-resolution transmission electron microscope (HRTEM) image (b) of carbon quantum dots (CQDs) prepared in Example 1 of this invention.

[0033] Figure 2 This is the fluorescence spectrum of carbon quantum dots (CQDs) prepared in Example 1 of the present invention.

[0034] Figure 3 This is the fluorescence spectrum of the ratiometric fluorescent probe in the presence of phosphate in Example 1 of the present invention.

[0035] Figure 4 This is a graph showing the linear relationship between the fluorescence spectrum of the ratiometric fluorescent probe and the phosphate concentration in Example 1 of the present invention.

[0036] Figure 5 The fluorescence spectrum of the ratiometric fluorescent probe used to detect phosphate in Example 4 of this invention is shown in the presence of different interfering ions.

[0037] Figure 6 The fluorescence spectra of the ratiometric fluorescent probe used to detect ferric ions in Example 4 of this invention are shown in the presence of different interfering ions.

[0038] Figure 7 The fluorescence spectrum of the ratiometric fluorescent probe used to detect ferric ions in Example 8 of this invention is shown in the presence of different interfering ions. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0040] Unless otherwise specified, all materials and instruments used in the following embodiments are commercially available. The processes and equipment used are conventional, and all data obtained are averages from at least three repeated experiments.

[0041] Example 1

[0042] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is composed of carbon quantum dots, a lanthanide metal ion solution, and a non-luminescent rare earth ion solution, wherein the ratio of carbon quantum dots, lanthanide metal ion solution, and non-luminescent rare earth ion solution is 0.40 mg: 20 μL: 20 μL.

[0043] In this embodiment, the lanthanide metal ion solution is a 1 mol / L Eu(NO3)3 solution, and the non-luminescent rare earth ion solution is a 1 mol / L Y(NO3)3 solution.

[0044] In this embodiment, the carbon quantum dots (CQDs) used are prepared by the following method, including the following steps:

[0045] 2g of citric acid and 0.7g of L-histidine were dissolved in 20mL of ultrapure water and sonicated for 15min to obtain a mixed solution. The mixed solution was placed in a Teflon autoclave and heated to 180℃ for 240min. The product (pale yellow solution) was then centrifuged at 10000rpm for 24min, and the brown supernatant was collected. The supernatant was dialyzed using a 500Da dialysis bag for 48h to remove small molecules and further purify the carbon quantum dots (CQDs). The obtained CQDs were then freeze-dried to obtain carbon quantum dot powder. The fluorescence intensity of the dialysate (CQDs before freeze-drying) was 420 (slit width 5, photomultiplier tube voltage 500). The fluorescence intensity of the carbon quantum dot powder was 690.

[0046] Figure 1 These are scanning electron microscope (SEM) images (a) and high-resolution transmission electron microscope (HRTEM) images (b) of the carbon quantum dots (CQDs) prepared in Example 1 of this invention. Figure 1 As shown in 'a', CQDs are uniformly distributed near-spherical nanoparticles. HRTEM image ( Figure 1 b) shows that the CQDs have clear lattice fringes with a lattice spacing of about 0.26 nm, which is consistent with the (100) plane of graphite carbon.

[0047] Figure 2 This is the fluorescence spectrum of carbon quantum dots (CQDs) prepared in Example 1 of this invention. Figure 2 It is known that the optimal excitation wavelength for CQDs is 320 nm. Under 320 nm ultraviolet light excitation, carbon quantum dots exhibit the strongest fluorescence intensity at 420 nm, which appears as blue.

[0048] An application of the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots in the detection of phosphate in the environmental field according to Embodiment 1 of the present invention, specifically, utilizes the phosphate in the solution of the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots in Embodiment 1, including the following steps:

[0049] (1) 20 mL of the phosphate solution to be tested was mixed with 10 μL of 0.1 mol / L ascorbic acid solution for pretreatment. Pretreatment with ascorbic acid can remove interfering ions (such as Fe) from the phosphate solution to be tested. 3+ This allows us to avoid their interference with the detection results and obtain a mixed solution A.

[0050] (2) Mix 0.40 mg of carbon quantum dots, 20 μL of lanthanide metal ion solution (the solution is a 1 mol / L Eu(NO3)3 solution), 20 μL of non-luminescent rare earth ion solution (the solution is a 1 mol / L Y(NO3)3 solution) with mixed solution A, and adjust the pH value to 4 with 0.5 mol / L NaOH solution to obtain mixed solution B.

[0051] (3) The fluorescence intensity of mixed solution B was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of mixed solution B at 420 nm and 630 nm was obtained. 630 / I 420 ), at this time I 630 / I 420 It is 0.8473.

[0052] (4) Based on the fluorescence intensity ratio of mixed solution B at 420 nm and 630 nm, and combined with the linear equation of fluorescence intensity ratio and phosphate concentration, the concentration of phosphate in the phosphate solution to be tested is obtained.

[0053] In this embodiment, the linear equation between the fluorescence intensity ratio and the phosphate concentration was constructed by the following method: specifically, the ratiometric fluorescent probe constructed in Example 1 was used to detect standard phosphate solutions of different concentrations, including the following steps:

[0054] (a) Standard phosphate solutions of different concentrations (phosphate concentrations of 0.01–50 μmol / L) were mixed with 10 μL and 0.1 mol / L ascorbic acid solutions for pretreatment.

[0055] (b) 0.40 mg of carbon quantum dots prepared in Example 1, 20 μL of 1 mol / L Eu(NO3)3 solution and 20 μL of 1 mol / L LY(NO3)3 solution were mixed with pretreated standard phosphate solutions of different concentrations, and the pH was adjusted to 4 with 0.5 mol / L NaOH solution.

[0056] (c) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (b) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, this involves using fluorescence spectroscopy to record the emission spectra of standard solutions with different phosphate concentration gradients under excitation at 320 nm, such as... Figure 3 As shown, add Eu 3+ The blue characteristic fluorescence of CQDs at 420 nm weakens, while the fluorescence at 630 nm hardly increases. The addition of Y... 3+ A slight increase in fluorescence was observed at 630 nm. With increasing phosphate concentration, the fluorescence at 420 nm continued to decrease, while the fluorescence at 630 nm increased slightly. 3+ The characteristic red fluorescence increased significantly.

[0057] (d) Plotting the concentration of the standard phosphate solution on the x-axis and the ratio of fluorescence intensity at 420 nm and 630 nm for the mixed solutions of different concentrations obtained in step (c) on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the phosphate concentration, as follows: Figure 4 As shown, the linear relationship is y = 0.2797x + 0.6243, where y is the fluorescence intensity ratio at 420 nm and 630 nm (IL). 630 / I 420 ), where x is the phosphate concentration, and the linear correlation coefficient is R. 2 =0.9921, detection limit is 0.12μM.

[0058] Calculations show that the concentration of phosphate in the test solution in Example 1 of this invention is 0.80 μM, which has the advantages of good stability and high repeatability.

[0059] An application of the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots in the detection of ferric ions in the medical field according to Embodiment 1 of the present invention specifically involves using the ratiometric fluorescent probe solution based on lanthanide metal ions and carbon quantum dots from Embodiment 1 to detect ferric ions, including the following steps:

[0060] (1) Mix 20 mL of the ferric ion solution to be tested with 0.40 mg of carbon quantum dots, 20 μ L of lanthanide metal ion solution (which is a 1 mol / L Eu(NO3)3 solution) and 20 μ L of non-luminescent rare earth ion solution (which is a 1 mol / L Y(NO3)3 solution), and adjust the pH to 10 with 0.5 mol / L NaOH solution to obtain mixed solution A.

[0061] (2) The fluorescence intensity of mixed solution A was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of mixed solution A at 420 nm and 630 nm was obtained. 630 / I 420 ), at this time I 630 / I 420 It is 1.894.

[0062] (3) Based on the fluorescence intensity ratio of mixed solution A at 420 nm and 630 nm, and combined with the linear equation of fluorescence intensity ratio and ferric ion concentration, the concentration of ferric ions in the solution to be tested is obtained.

[0063] In this embodiment, the linear equation between the fluorescence intensity ratio and the concentration of ferric ions was constructed by the following method: specifically, the ratiometric fluorescent probe constructed in Example 1 was used to detect standard ferric ion solutions of different concentrations, including the following steps:

[0064] (a) 20 mL of standard ferric ion solutions of different concentrations (0–500 μmol / L) were mixed with 0.40 mg of carbon quantum dots prepared in Example 1, 20 μL of 1 mol / L Eu(NO3)3 solution and 20 μL of 1 mol / L LY(NO3)3 solution, and the pH was adjusted to 7 with 0.5 mol / L NaOH solution.

[0065] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ferric ions under excitation at 320 nm.

[0066] (c) Using the concentration of ferric ions in the standard ferric ion solution as the abscissa and the ratio of fluorescence intensity at 420 nm and 630 nm of the mixed solutions of different concentrations obtained in step (b) as the ordinate, a linear equation was constructed between the fluorescence intensity ratio and the concentration of ferric ions. The linear relationship is y = -0.0035x + 1.929, where y is the ratio of fluorescence intensity at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ferric ions, and the linear correlation coefficient is R. 2 =0.9947, detection limit is 0.30μM.

[0067] The calculation results show that the concentration of ferric ions in the ferric ion solution to be tested in Example 1 of this invention is 10 μM.

[0068] Comparative Example 1

[0069] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 1, except that in Comparative Example 1, the ratio of carbon quantum dots, lanthanide metal ion solution and non-luminescent rare earth ion solution is 0.46 mg: 13 μL: 29 μL.

[0070] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 1 and the phosphate concentration includes the following steps:

[0071] (a) 20 mL of standard phosphate solutions of different concentrations (phosphate concentration of 0.01 to 50 μmol / L) were mixed with 10 μL and 0.1 mol / L ascorbic acid solutions for pretreatment.

[0072] (b) 0.46 mg of carbon quantum dots prepared in Example 1, 13 μL of 1 mol / L Eu(NO3)3 solution and 29 μL of 1 mol / L LY(NO3)3 solution were mixed with pretreated standard phosphate solutions of different concentrations, and the pH was adjusted to 7 with 0.5 mol / L NaOH solution.

[0073] (c) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (b) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different phosphate concentration gradients under excitation at 320 nm. The results showed that the sensitivity of this ratiometric fluorescent probe to phosphate was reduced: I 1 630 -I 0 630 =8(I 0 630 I represents the fluorescence intensity at 630 nm without the addition of phosphate. 1 630 (This refers to the fluorescence intensity at 630 nm when 1 μmol of phosphate is added.) This indicates that extreme pH values ​​can affect CQDs and Eu. 3+ The Dexter energy transfer between them.

[0074] (d) Plotting the concentration of the standard phosphate solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (c) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the phosphate concentration. The linear relationship is y = 0.0015x + 0.5149, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the phosphate concentration, and the linear correlation coefficient is R. 2 =0.9265, detection limit is 52μM.

[0075] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 1 and the concentration of ferric ions includes the following steps:

[0076] (a) 20 mL of standard ferric ion solutions of different concentrations (0–500 μmol / L) were mixed with 0.46 mg of carbon quantum dots prepared in Example 1, 13 μL of 1 mol / L Eu(NO3)3 solution and 29 μL of 1 mol / L LY(NO3)3 solution, and the pH was adjusted to 3 with 0.5 mol / L NaOH solution.

[0077] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ferric ions under excitation at 320 nm.

[0078] (c) Plotting the concentration of the standard ferric ion solution on the x-axis and the ratio of fluorescence intensity at 420 nm and 630 nm of the mixed solutions of different concentrations obtained in step (b) on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the concentration of ferric ions. The linear relationship is y = -0.0008x + 1.950, where y is the ratio of fluorescence intensity at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ferric ions, and the linear correlation coefficient is R. 2 =0.8456, detection limit is 36μM.

[0079] Comparative Example 2

[0080] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 1, except that in Comparative Example 2, the ratio of carbon quantum dots, lanthanide metal ion solution and non-luminescent rare earth ion solution is 0.88 mg: 17 μL: 24 μL.

[0081] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 2 and the phosphate concentration includes the following steps:

[0082] (a) 20 mL of standard phosphate solutions of different concentrations (phosphate concentration of 0.01 to 50 μmol / L) were mixed with 10 μL and 0.1 mol / L ascorbic acid solutions for pretreatment.

[0083] (b) 0.88 mg of carbon quantum dots prepared in Example 1, 17 μL of 1 mol / L Eu(NO3)3 solution and 24 μL of 1 mol / L LY(NO3)3 solution were mixed with pretreated standard phosphate solutions of different concentrations, and the pH was adjusted to 4 with 0.5 mol / L NaOH solution.

[0084] (c) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (b) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different phosphate concentration gradients under excitation at 320 nm. The results showed that the fluorescence of this ratiometric fluorescent probe was significantly weakened at both 420 nm and 630 nm. This indicates that inappropriate CQD concentrations not only affect their own fluorescence intensity through the fluorescence internal filtering effect, but also affect the fluorescence intensity of CQDs and Eu. 3+ Antenna effect.

[0085] (d) Plotting the concentration of the standard phosphate solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (c) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the phosphate concentration. The linear relationship is y = 0.0008x + 0.2105, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the phosphate concentration, and the linear correlation coefficient is R. 2 =0.8412, detection limit is 79μM.

[0086] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 2 and the concentration of ferric ions includes the following steps:

[0087] (a) 20 mL of standard ferric ion solutions of different concentrations (0–500 μmol / L) were mixed with 0.88 mg of carbon quantum dots prepared in Example 1, 17 μL of 1 mol / L Eu(NO3)3 solution and 24 μL of 1 mol / L LY(NO3)3 solution, and the pH was adjusted to 4 with 0.5 mol / L NaOH solution.

[0088] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ferric ions under excitation at 320 nm.

[0089] (c) Plotting the concentration of the standard ferric ion solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (b) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the ferric ion concentration. The linear relationship is y = -0.0005x + 1.980, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ferric ions, and the linear correlation coefficient is R. 2=0.8560, detection limit is 66μM.

[0090] Comparative Example 3

[0091] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 1, except that in Comparative Example 3, the ratio of carbon quantum dots, lanthanide metal ion solution (which is a 1 mol / L Eu(NO3)3 solution) and non-luminescent rare earth ion solution (which is a 1 mol / L Y(NO3)3 solution) is 0.31 mg: 56 μL: 18 μL.

[0092] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 3 and the phosphate concentration includes the following steps:

[0093] (a) 20 mL of standard phosphate solutions of different concentrations (phosphate concentration of 0.01 to 50 μmol / L) were mixed with 10 μL and 0.1 mol / L ascorbic acid solutions for pretreatment.

[0094] (b) 0.31 mg of carbon quantum dots prepared in Example 1, 56 μL of 1 mol / L Eu(NO3)3 solution and 18 μL of 1 mol / L LY(NO3)3 solution were mixed with pretreated standard phosphate solutions of different concentrations, and the pH was adjusted to 5 with 0.5 mol / L NaOH solution.

[0095] (c) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (b) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different phosphate concentration gradients under excitation at 320 nm. The results showed that the linear range of this ratiometric fluorescent probe for phosphate was significantly reduced, indicating that inappropriate Eu... 3+ Concentration affects the detection range of phosphate.

[0096] (d) Plotting the concentration of the standard phosphate solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (c) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the phosphate concentration. The linear relationship is y = 0.0028x + 0.5149, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the phosphate concentration, and the linear correlation coefficient is R. 2 =0.8597, detection limit is 48μM.

[0097] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 3 and the concentration of ferric ions includes the following steps:

[0098] (a) 20 mL of standard ferric ion solutions of different concentrations (0–500 μmol / L) were mixed with 0.31 mg of carbon quantum dots prepared in Example 1, 56 μL of 1 mol / L Eu(NO3)3 solution and 18 μL of 1 mol / L LY(NO3)3 solution, respectively, and the pH was adjusted to 5 with 0.5 mol / L NaOH solution.

[0099] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ferric ions under excitation at 320 nm.

[0100] (c) Plotting the concentration of the standard ferric ion solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (b) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the ferric ion concentration. The linear relationship is y = -0.0002x + 1.840, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ferric ions, and the linear correlation coefficient is R. 2 =0.9921, detection limit is 52μM.

[0101] Comparative Example 4

[0102] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 1, except that in Comparative Example 4, the ratio of carbon quantum dots, lanthanide metal ion solution (which is a 1 mol / L Eu(NO3)3 solution) and non-luminescent rare earth ion solution (which is a 1 mol / L Y(NO3)3 solution) is 0.47 mg: 21 μL: 90 μL.

[0103] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 4 and the phosphate concentration includes the following steps:

[0104] (a) 20 mL of standard phosphate solutions of different concentrations (phosphate concentration of 0.01 to 50 μmol / L) were mixed with 10 μL and 0.1 mol / L ascorbic acid solutions for pretreatment.

[0105] (b) 0.47 mg of carbon quantum dots prepared in Example 1, 21 μL of 1 mol / L Eu(NO3)3 solution and 90 μL of 1 mol / L LY(NO3)3 solution were mixed with pretreated standard phosphate solutions of different concentrations, and the pH was adjusted to 4 with 0.5 mol / L NaOH solution.

[0106] (c) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (b) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different phosphate concentration gradients under excitation at 320 nm. The results showed that the linear range of this ratiometric fluorescent probe for phosphate was significantly reduced, indicating that an inappropriate Y... 3+ Concentration effect of Eu 3+ The fluorescence intensity affects the detection limit.

[0107] (d) Plotting the concentration of the standard phosphate solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (c) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the phosphate concentration. The linear relationship is y = 0.0210x + 0.6547, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the phosphate concentration, and the linear correlation coefficient is R. 2 =0.9751, detection limit is 16μM.

[0108] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 4 and the concentration of ferric ions includes the following steps:

[0109] (a) 20 mL of standard ferric ion solutions of different concentrations (0–500 μmol / L) were mixed with 0.47 mg of carbon quantum dots prepared in Example 1, 21 μL of 1 mol / L Eu(NO3)3 solution and 90 μL of 1 mol / L LY(NO3)3 solution, and the pH was adjusted to 4 with 0.5 mol / L NaOH solution.

[0110] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ferric ions under excitation at 320 nm.

[0111] (c) Plotting the concentration of the standard ferric ion solution on the x-axis and the ratio of fluorescence intensity at 420 nm and 630 nm for the mixed solutions of different concentrations obtained in step (b) on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the concentration of ferric ions. The linear relationship is y = -0.0003x + 1.765, where y is the ratio of fluorescence intensity at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ferric ions, and the linear correlation coefficient is R. 2 =0.784, detection limit is 62μM.

[0112] Example 2

[0113] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is composed of carbon quantum dots, a lanthanide metal ion solution, and a non-luminescent rare earth ion solution, wherein the ratio of carbon quantum dots, lanthanide metal ion solution, and non-luminescent rare earth ion solution is 0.39 mg: 26 μL: 21 μL.

[0114] In this embodiment, the lanthanide metal ion solution is a 1 mol / L Eu(NO3)3 solution, and the non-luminescent rare earth ion solution is a 1 mol / L Y(NO3)3 solution.

[0115] In this embodiment, the carbon quantum dots (CQDs) used are prepared by the following method, including the following steps:

[0116] Dissolve 1.9 g of citric acid and 0.8 g of L-histidine in 18 mL of ultrapure water and sonicate for 15 min. Place the mixture in a Teflon autoclave and heat at 180 °C for 3 h. Then centrifuge the product (pale yellow solution) at 10,000 rpm for 26 min. Collect the brown supernatant and dialyze it using a 1000 Da dialysis bag for 48 h to remove small molecules and further purify the CQDs. Freeze-dry the obtained CQDs to obtain a powder. The fluorescence intensity of the dialysate was 415 (slit width 5, photomultiplier tube voltage 500).

[0117] Example 3

[0118] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 2, except that in Example 3, the ratio of carbon quantum dots, lanthanide metal ion solution and non-luminescent rare earth ion solution is 0.37 mg: 24 μL: 18 μL.

[0119] Example 4

[0120] Investigating the specificity of ratio fluorescent probes

[0121] The ratiometric fluorescent probe from Example 1 was mixed with 5 μmol / L phosphate (pi) and 100 times the concentration (500 μmol / L, F) - 10 times that of 50 μmol / L) containing interfering ions (K + Na + Mg 2+ ,Fe 3+ ,Fe 2+ Cu 2+ Zn 2+ ,Mn 2+ N i2+ Al 3+ Cl - NO3 - SO4 2- CO3 2- CH3COO - SO3 2- NO2 - ,Br - ,F - S2O8 4- The solutions were mixed, and their fluorescence intensities were detected. The results are as follows: Figure 5 As shown, Figure 5 In this context, solution a is a cation solution, and solution b is an anion solution. Figure 5 It can be seen that when using ratiometric fluorescent probes for detection, only phosphate has a quenching effect on fluorescence at 420 nm and produces a strong fluorescence peak at 630 nm, indicating that the ratiometric fluorescent probe has good selectivity and anti-interference ability for phosphate.

[0122] The ratiometric fluorescent probe from Example 1 was mixed with 50 μmol / LFe 3+ And 10 times the concentration (500 μmol / L) of interfering ions (K + Na + Mg 2+ ,Fe 2+ Cu 2+ Zn 2+ ,Mn 2+ Ni 2+ Al 3+ Cl - NO3 - SO4 2- CO3 2- CH3COO - SO3 2- NO2 - ,Br - ,F -S2O8 4- PO3 2- The mixtures were analyzed, and their fluorescence intensities were measured. The results are as follows: Figure 6 As shown, Figure 6 In this context, solution a is a cation solution, and solution b is an anion solution. Figure 6 It can be seen that when using ratiometric fluorescent probes for detection, only ferric ions have a quenching effect on the fluorescence at 420 nm, and a strong fluorescence peak is generated at 630 nm, indicating that the ratiometric fluorescent probe has good selectivity and anti-interference ability for ferric ions.

[0123] Example 5

[0124] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is composed of carbon quantum dots, lanthanide metal ion solution and ferric ion solution, wherein the ratio of carbon quantum dots, lanthanide metal ion solution and ferric ion solution is 0.40 mg: 20 μL: 20 μL.

[0125] In this embodiment, the lanthanide metal ion solution is a 1 mol / L Eu(NO3)3 solution, and the ferric ion solution is a 0.5 mol / L Fe(NO3)3 solution.

[0126] In this embodiment, the carbon quantum dots (CQDs) used were prepared by the method in Example 1.

[0127] An application of the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots in the detection of ascorbic acid in the medical field, as described in Example 5 of the present invention, specifically involves utilizing ascorbic acid in the solution of the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots in Example 5, including the following steps:

[0128] (1) Mix 20 mL of the ascorbic acid solution to be tested with 0.40 mg of carbon quantum dots, 20 μ L of lanthanide metal ion solution (which is a 1 mol / L Eu(NO3)3 solution) and 20 μ L of ferric ion solution (which is a 0.5 mol / L Fe(NO3)3 solution), and adjust the pH to 7 with 0.5 mol / L NaOH solution to obtain mixed solution A.

[0129] (2) The fluorescence intensity of mixed solution A was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of mixed solution A at 420 nm and 630 nm was obtained. 630 / I 420 ), at this time I 630 / I 420 It is 0.41.

[0130] (3) Based on the fluorescence intensity ratio of mixed solution A at 420 nm and 630 nm, and combined with the linear equation of fluorescence intensity ratio and ascorbic acid concentration, the concentration of ascorbic acid in the ascorbic acid solution to be tested is obtained.

[0131] In this embodiment, the linear equation between the fluorescence intensity ratio and the ascorbic acid concentration was constructed by the following method: specifically, the ratiometric fluorescent probe constructed in Example 5 was used to detect standard ascorbic acid solutions of different concentrations, including the following steps:

[0132] (a) 20 mL of standard ascorbic acid solutions of different concentrations (0–300 μmol / L) were mixed with 0.40 mg of carbon quantum dots prepared in Example 1, 20 μL of 1 mol / L Eu(NO3)3 solution and 20 μL of 0.5 mol / L Fe(NO3)3 solution, respectively, and the pH was adjusted to 7 with 0.5 mol / L NaOH solution.

[0133] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ascorbic acid under excitation at 320 nm. The results showed that the addition of Eu... 3+ The blue characteristic fluorescence of CQDs at 420 nm weakens, while the fluorescence at 630 nm hardly increases. The addition of Fe... 3+ CQDs and Eu 3+ The characteristic fluorescence peaks of Fe were quenched to varying degrees; with increasing ascorbic acid concentration, Fe... 3+ Reduced to Fe 2+ Fluorescence recovery.

[0134] (c) Using the concentration of ascorbic acid in the standard ascorbic acid solution as the x-axis and the ratio of fluorescence intensity at 420 nm and 630 nm of the mixed solutions of different concentrations obtained in step (b) as the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the ascorbic acid concentration. The linear relationship is y = 0.0055x + 0.3553, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ascorbic acid, and the linear correlation coefficient is R. 2 =0.9963, detection limit is 2.51μM.

[0135] The calculation results show that the concentration of ascorbic acid in the ascorbic acid solution to be tested in Example 5 of the present invention is 9.96 μM.

[0136] Comparative Example 5

[0137] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 5, except that in Comparative Example 5, the ratio of carbon quantum dots, lanthanide metal ion solution and ferric ion solution is 0.46 mg: 13 μL: 29 μL.

[0138] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 5 and the ascorbic acid concentration includes the following steps:

[0139] (a) 20 mL of standard ascorbic acid solutions of different concentrations (0–300 μmol / L) were mixed with 0.46 mg of carbon quantum dots prepared in Example 1, 13 μL of 1 mol / L Eu(NO3)3 solution and 29 μL of 0.5 mol / L Fe(NO3)3 solution, respectively, and the pH was adjusted to 7 with 0.5 mol / L NaOH solution.

[0140] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ascorbic acid under excitation at 320 nm.

[0141] (c) Plotting the concentration of the standard ascorbic acid solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (b) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the ascorbic acid concentration. The linear relationship is y = 0.0006x + 0.3547, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ascorbic acid, and the linear correlation coefficient is R. 2 =0.8416, detection limit is 46μM.

[0142] Comparative Example 6

[0143] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 5, except that in Comparative Example 6, the ratio of carbon quantum dots, lanthanide metal ion solution and ferric ion solution is 0.88 mg: 17 μL: 24 μL.

[0144] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 6 and the ascorbic acid concentration includes the following steps:

[0145] (a) 20 mL of standard ascorbic acid solutions of different concentrations (0–300 μmol / L) were mixed with 0.88 mg of carbon quantum dots prepared in Example 1, 17 μL of 1 mol / L Eu(NO3)3 solution and 24 μL of 0.5 mol / L Fe(NO3)3 solution, respectively, and the pH was adjusted to 4 with 0.5 mol / L NaOH solution.

[0146] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ascorbic acid under excitation at 320 nm.

[0147] (c) Plotting the concentration of the standard ascorbic acid solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (b) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the ascorbic acid concentration. The linear relationship is y = 0.0003x + 0.3298, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ascorbic acid, and the linear correlation coefficient is R. 2 =0.8416, detection limit is 51μM.

[0148] Comparative Example 7

[0149] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 5, except that in Comparative Example 7, the ratio of carbon quantum dots, lanthanide metal ion solution and ferric ion solution is 0.31 mg: 56 μL: 18 μL.

[0150] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 7 and the ascorbic acid concentration includes the following steps:

[0151] (a) 20 mL of standard ascorbic acid solutions of different concentrations (0–300 μmol / L) were mixed with 0.31 mg of carbon quantum dots prepared in Example 1, 56 μL of 1 mol / L Eu(NO3)3 solution and 18 μL of 0.5 mol / L Fe(NO3)3 solution, respectively, and the pH was adjusted to 5 with 0.5 mol / L NaOH solution.

[0152] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ascorbic acid under excitation at 320 nm.

[0153] (c) Plotting the concentration of the standard ascorbic acid solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (b) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the ascorbic acid concentration. The linear relationship is y = 0.0008x + 0.3459, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I 630 / I 420 ), where x is the concentration of ascorbic acid, and the linear correlation coefficient is R. 2 =0.8743, detection limit is 39μM.

[0154] Comparative Example 8

[0155] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 5, except that in Comparative Example 8, the ratio of carbon quantum dots, lanthanide metal ion solution and ferric ion solution is 0.47 mg: 21 μL: 90 μL.

[0156] Constructing a linear equation between the fluorescence intensity ratio of the ratiometric fluorescent probes in Comparative Example 8 and the ascorbic acid concentration includes the following steps:

[0157] (a) 20 mL of standard ascorbic acid solutions of different concentrations (0–300 μmol / L) were mixed with 0.47 mg of carbon quantum dots prepared in Example 1, 21 μL of 1 mol / L Eu(NO3)3 solution and 90 μL of 0.5 mol / L Fe(NO3)3 solution, respectively, and the pH was adjusted to 4 with 0.5 mol / L NaOH solution.

[0158] (b) The fluorescence intensity of the mixed solutions of different concentrations obtained in step (a) was detected by fluorescence spectroscopy, and the fluorescence intensity ratio (Ig) of the mixed solutions of different concentrations at 420 nm and 630 nm was obtained. 630 / I 420 Specifically, fluorescence spectroscopy was used to record the emission spectra of standard solutions with different concentration gradients of ascorbic acid under excitation at 320 nm.

[0159] (c) Plotting the concentration of the standard ascorbic acid solution on the x-axis and the fluorescence intensity ratio of the mixed solutions of different concentrations obtained in step (b) at 420 nm and 630 nm on the y-axis, a linear equation was constructed between the fluorescence intensity ratio and the ascorbic acid concentration. The linear relationship is y = 0.0007x + 0.3124, where y is the fluorescence intensity ratio at 420 nm and 630 nm (I0). 630 / I 420 ), where x is the concentration of ascorbic acid, and the linear correlation coefficient is R. 2 =0.8654, detection limit is 42μM.

[0160] Example 6

[0161] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is composed of carbon quantum dots, lanthanide metal ion solution and ferric ion solution, wherein the ratio of carbon quantum dots, lanthanide metal ion solution and ferric ion solution is 0.39 mg: 26 μL: 21 μL.

[0162] In this embodiment, the lanthanide metal ion solution is a 1 mol / L Eu(NO3)3 solution, and the ferric ion solution is a 0.5 mol / L Fe(NO3)3 solution.

[0163] In this embodiment, the carbon quantum dots (CQDs) used were prepared by the method in Example 2.

[0164] Example 7

[0165] A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots is basically the same as the ratiometric fluorescent probe in Example 6, except that in Example 7, the ratio of carbon quantum dots, lanthanide metal ion solution and ferric ion solution is 0.37 mg: 24 μL: 18 μL.

[0166] Example 8

[0167] Investigating the specificity of ratio fluorescent probes

[0168] The ratiometric fluorescent probe from Example 5 was mixed with 50 μmol / L ascorbic acid and 10 times the concentration (500 μmol / L) of interfering ions (K). + Na + Mg 2+ ,Fe 2+ Cu 2+ Zn 2+ ,Mn 2+ N i2+ Al 3+ Cl - NO3 - SO4 2- CO32- CH3COO - SO3 2- ,PO3 2- NO2 - ,Br - ,F - S2O8 4- The mixtures were analyzed, and their fluorescence intensities were measured. The results are as follows: Figure 7 As shown, Figure 7 In this context, solution a is a cation solution, and solution b is an anion solution. Figure 7 It can be seen that when using ratiometric fluorescent probes for detection, only ascorbic acid has a quenching effect on fluorescence at 420 nm and produces a strong fluorescence peak at 630 nm, indicating that the ratiometric fluorescent probe has good selectivity and anti-interference ability against ascorbic acid.

[0169] In this invention, the effects of different preparation methods on the fluorescence intensity of carbon quantum dots were also investigated, specifically:

[0170] A method for preparing carbon quantum dots (CQDs) includes the following steps: 1.6 g of citric acid and 0.8 g of L-histidine are dissolved in 18 mL of ultrapure water and sonicated for 10 min. The mixed solution is placed in a Teflon autoclave and heated at 180 °C for 280 min. The product (pale yellow solution) is then centrifuged at 12000 rpm for 30 min. The brown supernatant is collected and dialyzed using a 500 Da dialysis bag for 48 h to remove small molecules and further purify the CQDs. The obtained CQDs are freeze-dried to obtain a powder, and the fluorescence intensity of the dialysate is 426 (slit width 5, photomultiplier tube voltage 500).

[0171] A method for preparing carbon quantum dots (CQDs) includes the following steps: 2.4 g of citric acid and 0.6 g of L-histidine are dissolved in 22 mL of ultrapure water and sonicated for 10 min. The mixed solution is placed in a Teflon autoclave and heated at 190 °C for 240 min. Then, the product (pale yellow solution) is centrifuged at 12000 rpm for 25 min. The brown supernatant is collected and dialyzed using a 500 Da dialysis bag for 48 h to remove small molecules and further purify the CQDs. The obtained CQDs are freeze-dried to obtain a powder, and the fluorescence intensity of the dialysate is 417 (slit width 5, photomultiplier tube voltage 500).

[0172] A method for preparing carbon quantum dots (CQDs) includes the following steps: 1.5 g of citric acid and 1.5 g of L-histidine are dissolved in 24 mL of ultrapure water and sonicated for 10 min. The mixed solution is placed in a Teflon autoclave and heated at 160 °C for 360 min. The product (pale yellow solution) is then centrifuged at 12000 rpm for 36 min. The brown supernatant is collected and dialyzed using a 2000 Da dialysis bag for 30 h to remove small molecules and further purify the CQDs. The obtained CQDs are freeze-dried to obtain a powder, and the fluorescence intensity of the dialysate is 405 (slit width 5, photomultiplier tube voltage 500).

[0173] A method for preparing carbon quantum dots (CQDs) includes the following steps: 1.8 g of citric acid and 1.8 g of L-histidine are dissolved in 23 mL of ultrapure water and sonicated for 10 min. The mixed solution is placed in a Teflon autoclave and heated at 160 °C for 340 min. Then, the product (pale yellow solution) is centrifuged at 11000 rpm for 32 min. The brown supernatant is collected and dialyzed using a 2000 Da dialysis bag for 30 h to remove small molecules and further purify the CQDs. The obtained CQDs are freeze-dried to obtain a powder, and the fluorescence intensity of the dialysate is 405 (slit width 5, photomultiplier tube voltage 500).

[0174] A method for preparing carbon quantum dots (CQDs) includes the following steps: 2g of citric acid is sonicated in 20mL of ultrapure water for 15min. The mixed solution is placed in a Teflon autoclave and heated at 180℃ for 240min. The product (pale yellow solution) is then centrifuged at 3000rpm for 10min. The brown supernatant is collected and dialyzed using a 2000Da dialysis bag for 10h to remove small molecules, further purifying the CQDs. The obtained CQDs are then freeze-dried to obtain a powder. The fluorescence intensity of the dialysate is 216 (slit width 5, photomultiplier tube voltage 500).

[0175] A method for preparing carbon quantum dots (CQDs) includes the following steps: 2.1 g of citric acid and 0.3 g of L-histidine are dissolved in 36 mL of ultrapure water and sonicated for 2 min. The mixed solution is placed in a Teflon autoclave and heated at 180 °C for 240 min. The product (pale yellow solution) is then centrifuged at 5000 rpm for 16 min. The brown supernatant is collected and dialyzed using a 2000 Da dialysis bag for 10 h to remove small molecules, further purifying the CQDs. The obtained CQDs are freeze-dried to obtain a powder, and the fluorescence intensity of the dialysate is 268 (slit width 5, photomultiplier tube voltage 500).

[0176] A method for preparing carbon quantum dots (CQDs) includes the following steps: 4 g of citric acid and 0.1 g of L-histidine are dissolved in 44 mL of ultrapure water and sonicated for 2 min. The mixed solution is placed in a Teflon autoclave and heated at 220 °C for 450 min. The product (pale yellow solution) is then centrifuged at 5000 rpm for 30 min. The brown supernatant is collected and dialyzed using a 2000 Da dialysis bag for 48 h to remove small molecules and further purify the CQDs. The obtained CQDs are freeze-dried to obtain a powder, and the fluorescence intensity of the dialysate is 163 (slit width 5, photomultiplier tube voltage 500).

[0177] A method for preparing carbon quantum dots (CQDs) includes the following steps: 5 g of citric acid and 1.6 g of L-histidine are dissolved in 50 mL of ultrapure water and sonicated for 2 min. The mixed solution is placed in a Teflon autoclave and heated at 140 °C for 100 min. Then, the product (pale yellow solution) is centrifuged at 10,000 rpm for 30 min. The brown supernatant is collected and dialyzed using a 500 Da dialysis bag for 48 h to remove small molecules and further purify the CQDs. The obtained CQDs are freeze-dried to obtain a powder, and the fluorescence intensity of the dialysate is 154 (slit width 5, photomultiplier tube voltage 500).

[0178] In summary, compared with conventional ratiometric fluorescent probes, the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots of this invention has the advantages of wide detection range, high detection sensitivity, strong anti-interference ability, and low cost. It can be widely used to detect target substances in the environmental or medical fields, has high application value, and good application prospects.

[0179] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above. Therefore, any simple modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention's technical solutions shall still fall within the protection scope of the present invention.

Claims

1. A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots, characterized in that, The ratiometric fluorescent probe comprises carbon quantum dots, a lanthanide metal ion solution, and a non-luminescent rare earth ion solution; the ratio of the carbon quantum dots, the lanthanide metal ion solution, and the non-luminescent rare earth ion solution is 0.1 mg–0.6 mg : 4 μL–35 μL : 10 μL–35 μL; the lanthanide metal ion in the lanthanide metal ion solution is Eu. 3+ The non-luminescent rare earth ion in the non-luminescent rare earth ion solution is Y. 3+ ; The method for preparing the carbon quantum dots includes the following steps: S1. Dissolve citric acid and L-histidine in ultrapure water and sonicate to obtain a mixed solution; S2. The mixed solution obtained in S1 is subjected to a hydrothermal reaction, centrifuged, and the supernatant is collected for dialysis and freeze-dried to obtain carbon quantum dots.

2. The ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots according to claim 1, characterized in that, The ratio of carbon quantum dots, lanthanide metal ion solution, and non-luminescent rare earth ion solution is 0.1 mg~0.5 mg : 15 μL~30 μL : 14 μL~25 μL.

3. The ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots according to claim 1, characterized in that, The ratio of carbon quantum dots, lanthanide metal ion solution, and non-luminescent rare earth ion solution is 0.2 mg to 0.5 mg: 4 μL to 32 μL: 14 μL to 26 μL.

4. A ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots, characterized in that, The ratiometric fluorescent probe comprises carbon quantum dots, a lanthanide metal ion solution, and a ferric ion solution; the ratio of the carbon quantum dots, the lanthanide metal ion solution, and the ferric ion solution is 0.1 mg–0.6 mg : 10 μL–35 μL : 15 μL–25 μL; the lanthanide metal ion in the lanthanide metal ion solution is Eu. 3+ ; The method for preparing the carbon quantum dots includes the following steps: S1. Dissolve citric acid and L-histidine in ultrapure water and sonicate to obtain a mixed solution; S2. The mixed solution obtained in S1 is subjected to a hydrothermal reaction, centrifuged, and the supernatant is collected for dialysis and freeze-dried to obtain carbon quantum dots.

5. The ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots according to any one of claims 1 to 4, characterized in that, The initial concentration of the lanthanide metal ion solution is 0.5 mol / L to 2 mol / L.

6. The ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots according to claim 5, characterized in that, In step S1, the mass ratio of citric acid to L-histidine is 1 to 6:1; the mass-to-volume ratio of citric acid to ultrapure water is 0.05 g to 0.15 g: 1 mL; and the ultrasonication time is 10 min to 20 min. In step S2, the hydrothermal reaction temperature is 150℃~200℃; the hydrothermal reaction time is 210 min~290 min; the centrifugation speed is 10000 rpm~12000 rpm; the centrifugation time is 22 min~36 min; the dialysis bag used in the dialysis process has a specification of 500 Da~2000 Da; and the dialysis time is 30 h~50 h.

7. The ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots according to any one of claims 1 to 3, characterized in that, The initial concentration of the non-luminescent rare earth ion solution is 0.5 mol / L to 1 mol / L.

8. The ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots according to claim 4, characterized in that, The initial concentration of the ferric ion solution is 0.5 mol / L to 1 mol / L.

9. The application of any one of claims 1 to 3, a ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots, in the detection of target substances in environmental, medical, and food fields; wherein the target substance is Fe. 3+ or PO3 2- .

10. The application of the ratiometric fluorescent probe based on lanthanide metal ions and carbon quantum dots as described in claim 4 in the detection of target substances in the environmental, medical, and food fields; wherein the target substance is ascorbic acid.

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