CN115044370A

CN115044370A - Hetero-element-doped red light carbon dot for detecting various metal ions and preparation method and application thereof

Info

Publication number: CN115044370A
Application number: CN202210641580.7A
Authority: CN
Inventors: 徐晖; 尤昕; 郑丽婷; 林碧玉; 曾红亮; 王艺伟
Original assignee: Fujian Agriculture and Forestry University
Current assignee: Fujian Agriculture and Forestry University
Priority date: 2022-06-08
Filing date: 2022-06-08
Publication date: 2022-09-13

Abstract

The invention discloses a hetero-element-doped red-light carbon dot for detecting zinc ions and manganese ions, and a preparation method and application thereof, and solves the problems of complicated steps, low quantum yield and selectivity, single metal ion identification and large interference of inherent blue autofluorescence in a biological matrix during actual sample detection in the conventional carbon dot synthesis process. The hetero-element doped red light carbon dot is prepared by taking lotus plumule as a carbon source, reduced glutathione and o-phenylenediamine as precursors and formamide as a solvent through a solvothermal method in one step. The preparation process of the carbon dots is simple, and the carbon dots can be synthesized by only one step; the red light area has strong luminescence and higher quantum yield; the zinc ion and manganese ion anti-interference material has characteristic response to zinc ions and manganese ions and strong anti-interference capability to non-target metal ions. The mixed element doped red light carbon dot has the advantages of good selectivity, high sensitivity and low detection limit, is suitable for detecting heavy metal ions, and can carry out quantitative analysis on zinc ions and manganese ions in a macroalgae sample.

Description

Hetero-element-doped red light carbon dot for detecting various metal ions and preparation method and application thereof

Technical Field

The invention belongs to the technical field of nano detection, and particularly relates to a hetero-element doped red light carbon dot for detecting zinc ions and manganese ions, and a preparation method and application thereof.

Background

Zinc is the second major transition metal element and also the second major micronutrient for human body. Zinc has multiple functions, and plays various important roles in various reaction processes of a human body, such as gene transcription, brain activity, immune function, antibiosis and anticancer. Imbalanced zinc intake can cause a number of health problems such as prostate cancer, skin disorders, wilson's disease, excessive sexual maturation, loss of blood brain barrier function, cerebral ischemia blood brain barrier, type two diabetes, and the like. In addition, excessive zinc in the natural environment can reduce the microbial activity of soil, and produce phytotoxic effects. Manganese is one of the third most abundant transition metal elements and trace elements essential to human body on earth, and also has important influence on various physiological and biochemical processes of human body. Manganese participates in synthesis and activation of various enzymes of a human body, and not only can activate hundreds of enzymes, but also can activate components of active centers such as arginase, coenzyme, pyruvate carboxylase and the like. Therefore, the manganese has important functions of promoting the growth and development of human bodies, regulating endocrine systems, promoting bone hematopoiesis, enhancing the regeneration capacity of tissue wounds, accelerating the synthesis of proteins and vitamins, improving immunity, resisting cancer, resisting aging and the like. However, intake of high concentrations of manganese also tends to cause manganese poisoning, resulting in diseases such as arteriosclerosis, cerebral hemorrhage, and cardiac infarction. Therefore, the method is particularly important for monitoring and quantifying the content of zinc ions and manganese ions in environmental resources. Especially for human bodies, the intake of zinc ions and manganese ions needs to be strictly controlled, and the health of human bodies is affected by too much or too little zinc ions and manganese ions, so that a method capable of accurately and quickly detecting zinc and manganese is required to be established.

At present, many analysis methods such as atomic absorption spectrometry, inductively coupled plasma mass spectrometry, electrochemical analysis, etc. have been applied to the detection of zinc ions and manganese ions. However, these methods also have the disadvantages of expensive required instruments and equipment, complex operation flow, long analysis time, poor selectivity, high detection limit and the like in the actual detection process. In recent years, carbon dots have become widely researched nano materials due to the characteristics of photoluminescence, high light stability, low toxicity, good biocompatibility and the like, are often used as fluorescent probes for rapidly detecting various metal ions, and have the advantages of simple and convenient operation, high analysis speed, low detection cost, good selectivity, high sensitivity and the like.

To date, there have been many studies to detect zinc ions or manganese ions alone using synthetic carbon dots. However, most of the carbon dots synthesized at present have strong luminescence in the blue-green region or weak luminescence in the red region, and the quantum yield is low. The interference from the inherent blue autofluorescence in the biological matrix requires avoidance of the blue region in the actual sample detection. The fluorescent biological probe prepared by the red light carbon dots can effectively avoid autofluorescence interference and has strong penetrability to tissues. Therefore, it is very important and urgent to prepare red carbon dots and use the red carbon dots for the detection of zinc ions and manganese ions.

The invention takes lotus plumule as a carbon source, reduced glutathione and o-phenylenediamine as precursors and formamide as a solvent to synthesize a red light carbon dot which has double emission and does not depend on excitation in one step. The red-light carbon dots are used as fluorescent probes, and the surface functional groups can be used for specifically binding metal ions by adjusting the content of N, S atoms without additional chemical modification, so that the fluorescent characteristics of the red-light carbon dots are changed to realize quantitative detection of zinc ions and manganese ions, the preparation cost is low, the operation is simple, the sensitivity is high, the time is saved, and the energy consumption is high in applicability. The method established by the invention can be used for estimating the content of Mn and Zn elements in the macroalgae, and provides a basis for macroalgae diet guidance and safety and health evaluation to support the industrial value of the algae.

Disclosure of Invention

The invention aims to provide a preparation method and application of a hetero-element-doped red-light carbon dot for detecting zinc ions and manganese ions, which are used for solving the problems of complicated steps, low quantum yield and selectivity, single metal ion identification and large interference of inherent blue autofluorescence in a biological matrix during actual sample detection in the conventional carbon dot synthesis process. The mixed element doped red light carbon dot can react with Mn through the surface oxygen-containing and nitrogen-containing groups ²⁺ And Zn ²⁺ Coordination occurs to form electron-hole recombination, and fluorescence is specifically quenched; meanwhile, the mercapto group on the surface of the carbon dot can capture Zn ²⁺ The electron donating ability of the thiol group is enhanced by intramolecular charge transfer, thereby causing the fluorescence to undergo blue shift.

In order to achieve the purpose, the technical scheme of the invention is as follows:

firstly, 0.1 g of lotus plumule, 0.6804 g of reduced glutathione and 0.6106 g of o-phenylenediamine are dissolved in 20 mL of formamide, and then the mixture is transferred into a polytetrafluoroethylene reaction kettle and reacts for 2 hours at 160 ℃. After the reaction product was cooled to room temperature, it was centrifuged at 1000 rpm for 20 min in a centrifuge, and the supernatant was collected and diluted 5-fold with deionized water. The obtained solution is dialyzed for one week by a 1000 Da molecular weight dialysis bag, filtered by a 0.22 mu m micropore filter, and finally freeze-dried to obtain dark green mixed element doped red light carbon dot powder.

The hetero-element doped red light carbon point has large Stokes shift which is larger than 200 nm, wherein the content of carbon element is 56.56%, the content of oxygen element is 24.67%, the content of nitrogen element is 16.12%, and the content of sulfur element is 2.65%; the surface of the material is connected with a plurality of electron-donating polar groups, including carboxyl, hydroxyl, amino, pyridine, pyrrole, sulfydryl and the like.

The mixed element doped red light carbon dots are used for detecting heavy metal ions, and can realize the rapid detection of zinc ions and manganese ions. The prepared red carbon dot has non-excitation dependency, can emit light in a visible light red area, effectively avoids blue autofluorescence interference, has two emission peaks at 442 nm and 680 nm, and has good fluorescence stability. In a system with zinc ions or manganese ions and other various metal ions coexisting, the red light carbon dots can be used as fluorescent probes to realize high-sensitivity and high-selectivity identification, the detection limit of the red light carbon dots on the zinc ions is 19.1 nmol/L, and the detection limit of the manganese ions is 0.23 nmol/L.

The method for synthesizing the red light carbon dots has the advantages of simple operation, quick response and high sensitivity, can qualitatively and quantitatively detect the zinc ions and the manganese ions without chemically modifying a detection probe, and has good application prospect. The analysis and detection results of the red light carbon dots on Fujian macroalgae (kelp, laver and products thereof) show that the kelp, the laver and the products thereof all contain rich Mn and Zn elements, and the Mn and Zn element content in the laver is higher than that of the kelp, so that the kelp and the laver can be used as a preferable food for supplementing Mn and Zn. The method established by the invention can be used for estimating the content of Mn and Zn elements in the macroalgae, and provides a basis for macroalgae diet guidance and safety and health evaluation to support the industrial value of the algae.

Has the advantages that:

1. the carbon source used in the invention is economical and easily available, the preparation process is simple and quick, no toxic or side effect exists, and the target carbon point can be synthesized by only one step.

2. The carbon dots emit in a visible light long wavelength region and have strong penetrability; and the fluorescence detection probe has larger Stokes shift (more than 200 nm), excitation and fluorescence emission spectrums can be well separated, the interference of inherent blue self-fluorescence in a biological matrix can be effectively avoided, and the self-quenching of the fluorescence is eliminated, so that the signal-to-noise ratio of the fluorescence detection is obviously improved.

3. The carbon point has characteristic response to zinc ions and manganese ions, can be obviously distinguished from other metal elements, and has low detection limit. The detection limit of zinc ions is 19.1 nmol/L, and the detection limit of manganese ions is 0.23 nmol/L.

4. The carbon dots are not easily influenced by ionic strength and ultraviolet lamp irradiation time, and have good fluorescence stability.

5. According to the invention, reduced glutathione and o-phenylenediamine are added to dope nitrogen and sulfur, the surface of the carbon dot synthesized by a hot solvent method contains a large amount of hydroxyl, and the nitrogen and the sulfur can be connected with the hydroxyl through sp3 hybridization, so that the luminescent property of the carbon dot can be improved, the quantum yield can be improved, and the fluorescence red shift of the carbon dot can be achieved by 13.64%.

6. The method is used for metal ion detection, is simple and easy to operate, and can be used for on-site rapid detection.

Drawings

FIG. 1 shows the UV-visible absorption spectrum (blue), excitation spectrum (red), and emission spectrum (black) of a red carbon dot;

FIG. 2 is a transmission electron micrograph (A, B) of red carbon dots and a distribution graph (C) of the particle size thereof;

FIG. 3 is a graph showing the fluorescence intensity of red-light carbon dots under different concentrations of NaCl (A) and under continuous irradiation of an ultraviolet lamp (B);

FIG. 4 is a schematic diagram of a process for synthesizing red carbon dots and detecting Mn ²⁺ And Zn ²⁺ The mechanism of application of (c);

FIG. 5 shows the addition of Mn to red (black) and red carbon dots ²⁺ (red) fluorescence spectrum;

FIG. 6 is a graph of red light carbon dots (black) and red light carbon dots with Zn added ²⁺ (red) fluorescence spectrum;

FIG. 7 is Zn ²⁺ A linear plot of fluorescence intensity at concentrations ranging from 1 ng/mL to 50 ng/mL;

FIG. 8 shows the detection of Zn by fluorescent probe ²⁺ Respectively adding interfering ions and Zn into the red light carbon dot solution ² ⁺ ；

FIG. 9 shows Mn ²⁺ A linear relationship graph of fluorescence intensity under different concentration ranges;

FIG. 10 shows the detection of Mn by fluorescent probe ²⁺ Respectively adding interfering ions and Mn into the red light carbon dot solution ² ⁺ 。

Detailed Description

The invention will be further illustrated with reference to the following specific examples.

Example 1, a method for preparing a hetero-element-doped red light carbon dot for detecting zinc ions and manganese ions:

The synthesized carbon dots showed characteristic absorption peaks at 270 nm, 395 nm, 420 nm, 640 nm and 680 nm, respectively (FIG. 1). Under single-wavelength excitation, the carbon dots are in the blue region (lambda) _Em = 442 nm) and red light region (λ) _Em = 680 nm) has two distinct emission peaks. When the excitation wavelength is increased from 360 nm to 430 nm, the fluorescence emission peak is not shifted, which indicates that the synthesized carbon dots have non-excitation dependence and the emission wavelength is independent of the excitation wavelength. And the carbon dots have excitation capability with different wavelengths, so the carbon dots have wide application prospect. Selection of Red fluorescence (. lamda.) in biological studies _Ex = 420 nm，λ _Em = 680 nm), interference of the biomolecule autofluorescence can be reduced, photodamage is minimized, and penetration into tissue is deeper. The red carbon dots prepared by the method can be used as fluorescent probes for detecting metal elements.

The red-light carbon dots have uniform particle size distribution, spherical shape, no obvious agglomeration (figure 2A), graphite-like structure (figure 2B) and average particle size of 5.46 +/-1.03 nm (figure 2C).

The red carbon dots have good fluorescence stability. The red fluorescence of the carbon dot depends on the pH value, and in an acidic solution, the fluorescence intensity of the carbon dot increases along with the increase of the pH value, while in an alkaline solution, the characteristic peak of the red fluorescence can be deconvoluted into two peaks of 650 nm and 680 nm. In addition, when the NaCl concentration reaches 1 mol/L, the fluorescence intensity of the red carbon dots is not obviously influencedThe red carbon dots are shown to have good stability in high ionic strength environments (fig. 3A). Irradiating under 365 nm ultraviolet lamp for 90 min, and passing through fluorescence spectrophotometer at lambda _Ex λ measurement at 420 nm = _Em Fluorescence intensity at = 680 nm, it was found that the fluorescence intensity decreased by about 15% (fig. 3B). The fluorescent intensity is only slightly reduced after the irradiation of a high-intensity ultraviolet lamp, which shows that the red carbon dots have better photobleaching resistance.

Example 2 the method of claim 1, wherein the mixed element doped red carbon dots for detecting zinc ions and manganese ions can detect trace Zn ²⁺ And Mn ²⁺ ：

According to the synthesis and photoluminescence mechanism of the red carbon dots (figure 4), the red carbon dots have no excitation dependence, and have two emission peaks in a red spectral region, wherein the two emission peaks are respectively positioned at 442 nm and 680 nm. Mn when interfering ions are present in the solution system ²⁺ Can effectively quench the fluorescence peak of the red carbon spot at 680 nm (figure 5). Likewise, only Zn ²⁺ The fluorescence peak of the red carbon spot at 650 nm can be enhanced, and the fluorescence peak of the red carbon spot at 680 nm can be weakened (figure 6).

(1) The synthesized red light carbon dot solution is used as a fluorescence ratio probe applied to Zn ²⁺ The specific process of the detection is as follows:

detection of Zn Using Red light carbon dot solution as fluorescent Probe for assay ²⁺ The sensitivity of (1) is to add 980. mu.L HEPES buffer solution with concentration of 0.1M into 1 mL red light carbon dot solution, and then add Zn with different concentrations ²⁺ And (3) carrying out full mixing reaction on the ion standard solution at room temperature, wherein the detection final concentration is 0 ng/mL-50 ng/mL, and the acidity of the reaction system is controlled to be pH = 6.8. Finally, the fluorescence intensity of the sample solutions was measured at an excitation wavelength of 420 nm, respectively. From addition of different concentrations of Zn ²⁺ As can be seen from the graph (FIG. 7) showing the change in fluorescence intensity at a concentration of 1 to 50 ng/mL, as Zn changes ²⁺ As the addition amount was increased, the fluorescence intensity of the fluorescent probe at 650 nm gradually increased and the fluorescence reached the maximum when the addition amount reached 50 ng/mL. Zn at a fluorescence intensity of 650 nm ²⁺ The concentration of the compound has a good linear relation of y =15.852 in the range of 1-50 ng/mLx +144.7, correlation coefficient R ² Is 0.9984, the detection limit of the method is 1.25 ng/mL (equivalent to 19.1 nmol/L), and the detection sensitivity is high.

Detection of Zn Using Red light carbon dot solution as fluorescent ratiometric Probe ²⁺ It is necessary to examine Zn ²⁺ Selectivity of detection. Under the same condition, respectively adding interference ions with the final concentration of 20 ng/mL including Pb into the red light carbon dot solution ²⁺ 、Cd ²⁺ 、Zn ² ⁺ 、Co ²⁺ 、Cr ²⁺ 、Hg ²⁺ 、Cu ²⁺ 、As ⁵⁺ 、Bi ³⁺ 、Ca ²⁺ 、Ba ²⁺ 、Na ⁺ 、Al ³⁺ 、Fe ³⁺ 、Cl ^- 、I ^- The 16 metal solutions were further added with Zn to a final concentration of 10 ng/mL ²⁺ Separately recording the addition of Zn ²⁺ Fluorescence intensities before and after (FIG. 8). It was found that Zn was added ²⁺ The post-fluorescence is obviously enhanced, which shows that the fluorescent probe is directed to Zn ²⁺ Has high selectivity.

(2) The synthesized red-light carbon dot solution is used as a fluorescent probe to rapidly detect Mn based on a 'Signal-off' mode ² ⁺ The specific process is as follows:

detection of Mn for assay Using Red-emitting carbon dot solution as fluorescent Probe ²⁺ The sensitivity of (1) is to add 980. mu.L HEPES buffer solution with concentration of 0.1M into 1 mL red light carbon dot solution, and then add Mn with different concentrations ²⁺ And (3) carrying out full mixing reaction on the ion standard solution at room temperature, wherein the detection final concentration is 0 ng/mL-100 ng/mL, and the acidity of the reaction system is controlled to be pH = 6.8. Finally, the fluorescence intensity of the emission peak of the sample solution at 680 nm is measured at an excitation wavelength of 420 nm. From the addition of different concentrations of Mn ²⁺ As can be seen from the graph (FIG. 9) showing the change in fluorescence intensity at a concentration of 2 to 50 ng/mL, the change in fluorescence intensity with Mn ²⁺ The fluorescence intensity of the fluorescent probe at 680 nm is gradually reduced due to the increase of the addition amount, and the fluorescent probe has a good quenching effect. When Mn is present ²⁺ When the concentration is increased from 1 ng/mL to 100 ng/mL, the fluorescence intensity still shows a gradually decreasing trend until the Mn concentration is increased ²⁺ At concentrations above 90 ng/mL, the fluorescence intensity was completely quenched. Mn ²⁺ The concentration is 1-50 ngHas good linear relation y = -12.296x +725.44 in the range of mL and the correlation coefficient R thereof ² The detection limit of the method is 0.999, the detection limit of the method is 0.0127 ng/mL (equivalent to 0.23 nmol/L), and the detection sensitivity is high.

Detection of Mn using red light carbon dot solution as fluorescent probe ²⁺ It is necessary to examine Mn ²⁺ Selectivity of detection. Under the same condition, interference ions with the final concentration of 20 ng/mL including Pb are respectively added into the red light carbon dot solution ²⁺ 、Cd ²⁺ 、Zn ²⁺ 、Co ²⁺ 、Cr ²⁺ 、Hg ²⁺ 、Cu ²⁺ 、As ⁵⁺ 、Bi ³⁺ 、Ca ²⁺ 、Ba ²⁺ 、Na ⁺ 、Al ³⁺ 、Fe ³⁺ 、Cl ^- 、I ^- The 16 metal solutions were then added with Mn to a final concentration of 10 ng/mL ²⁺ Separately recording the addition of Mn ²⁺ Fluorescence intensities before and after (FIG. 10). The addition of Mn was found ²⁺ The late fluorescence has obvious quenching phenomenon, which shows that the fluorescent probe is used for Mn ²⁺ Has high selectivity.

Example 3, the synthetic red carbon dots were used for analytical testing of practical samples of Fujian macroalgae:

firstly, 0.4 g of actual samples which are washed and dried are respectively taken, ground into powder and subjected to microwave digestion together with concentrated nitric acid. Zn in algae real sample is detected by the method of example 2 by using the red light carbon dots as fluorescent probes ²⁺ And Mn ²⁺ Detection is carried out, and the result is compared with the accuracy of a national standard detection method (flame atomic absorption spectrometry). The method is found to have little difference with the results obtained by the national standard method, has higher accuracy and can be used as a new method for detecting zinc ions and manganese ions. Method for detecting Zn in Fujian macroalgae (kelp, laver and products thereof) based on established fluorescent probe ²⁺ And Mn ²⁺ And (5) carrying out quantitative detection. The results show that the kelp, the laver and the products thereof all contain rich Mn and Zn elements, and people can meet the self nutritional requirements by eating the kelp and the laver at ordinary times. Meanwhile, researches find that the contents of Mn and Zn elements in the laver are higher than those of the kelp, and the laver can be used as a preferable food for supplementing Mn and Zn elements. WhileThe method established by the invention can be used for estimating the content of Mn and Zn elements in the macroalgae, and provides a basis for macroalgae diet guidance and safety and health evaluation to support the industrial value of the algae.

The above description is only a few embodiments of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims

1. A preparation method of a red light carbon dot doped with hetero elements for detecting zinc ions and manganese ions is characterized by comprising the following steps:

dissolving lotus plumule, reduced glutathione and o-phenylenediamine in formamide, transferring the formamide into a polytetrafluoroethylene reaction kettle, reacting at 160 ℃ for 2 hours, cooling a reaction product to room temperature, centrifuging, collecting supernatant, diluting with deionized water, dialyzing the obtained solution with a 1000 Da molecular weight dialysis bag, filtering through a 0.22 mu m microporous filter, and finally freeze-drying to obtain dark green mixed element doped red light carbon dot powder.

2. The preparation method of claim 1, wherein the mass ratio of the lotus plumule, the reduced glutathione and the o-phenylenediamine is 1:6.804: 6.106.

3. The preparation method of any one of claims 1 to 2, wherein the heteroelement-doped red carbon dots for detecting zinc ions and manganese ions have a large Stokes shift of more than 200 nm.

4. The red-light doped heteroelement carbon dot for detecting zinc ions and manganese ions according to claim 1, wherein the content of carbon in the red-light doped heteroelement carbon dot is 56.56%, the content of oxygen is 24.67%, the content of nitrogen is 16.12%, and the content of sulfur is 2.65%; the surface of the material is connected with a plurality of electron-donating polar groups including carboxyl, hydroxyl, amino, pyridine, pyrrole and sulfydryl.

5. Use of the heteroelement-doped red-light carbon dot of any one of claims 1 to 4 in heavy metal ion detection.