阅读说明：本技术 一种碳量子点及其制备方法和应用 (Carbon quantum dot and preparation method and application thereof ) 是由 李力 董文飞 梅茜 葛明锋 常智敏 从瑛哥 张艳 于 2021-08-10 设计创作，主要内容包括：本发明涉及碳纳米材料技术领域,具体提供了一种碳量子点及其制备方法和应用,其原料包括碳源和稀土化合物,所述碳源包括苯二胺与有机酸,研究发现通过采用苯二胺与有机酸的混合物为碳源,搭配稀土元素的掺杂使用,使得到的碳量子点的荧光波长明显延长,从而可以降低生物组织的背景荧光,同时可以增加组织穿透性。(The invention relates to the technical field of carbon nano materials, and particularly provides a carbon quantum dot and a preparation method and application thereof.)

1. The carbon quantum dot is characterized in that raw materials comprise a carbon source and a rare earth compound, wherein the carbon source comprises phenylenediamine and an organic acid.

2. The carbon quantum dot of claim 1, wherein the rare earth compound is present in an amount of 5 to 50% by mass, preferably 10 to 30% by mass, based on the mass of the carbon source.

3. The carbon quantum dot according to claim 1 or 2, wherein the organic acid is at least one selected from the group consisting of citric acid, ascorbic acid, malic acid, tartaric acid, succinic acid, lactic acid, salicylic acid, and caffeic acid, and preferably malic acid.

4. The carbon quantum dot of any one of claims 1-3, wherein the phenylenediamine is selected from the group consisting of para-phenylenediamine and/or ortho-phenylenediamine; and/or the rare earth compound is selected from at least one of gadolinium chloride, erbium chloride and yttrium chloride; and/or, in the carbon source, the mass ratio of the phenylenediamine to the organic acid is 2-3.5: 1.

5. the carbon quantum dot according to any one of claims 1 to 4, wherein the carbon quantum dot further satisfies at least one of the following A-C:

A. the fluorescence emission wavelength of the carbon quantum dots is 592-650nm, preferably 605-630 nm;

B. the infrared spectrogram of the carbon quantum dot is 3343cm^-1，3214cm^-1，1612cm^-1，831cm^-1And 700cm^-1Has an absorption peak;

C. the particle size of the carbon quantum dots is 4-8 nm; and/or a lattice spacing of 0.23 nm.

6. A preparation method of a carbon quantum dot comprises the following steps: mixing a carbon source and a rare earth compound into water, and carrying out hydrothermal reaction to obtain carbon quantum dots; the carbon source is a mixture comprising phenylenediamine and an organic acid.

7. The method for preparing a carbon quantum dot as claimed in claim 6, wherein the temperature of the hydrothermal reaction is 140 ℃ to 200 ℃, preferably 160 ℃.

8. The method for preparing the carbon quantum dot according to claim 6 or 7, further comprising a step of modifying the carbon quantum dot with ethylene glycol bis (2-aminoethyl ether) tetraacetic acid after the hydrothermal reaction.

9. The method for producing a carbon quantum dot according to claim 8, wherein the mass ratio of ethylene glycol bis (2-aminoethyl ether) tetraacetic acid to phenylenediamine is 1:2 to 2:1, preferably 1:1.5 to 1.5: 1.

10. Use of the carbon quantum dot according to any one of claims 1 to 5 or the carbon quantum dot prepared by the preparation method according to any one of claims 6 to 9 as a probe for detecting metal ions; preferably, the metal ion is one of aluminum ion, ferric ion, ferrous ion, magnesium ion, lead ion, cobalt ion, copper ion and manganese ion.

11. A method for detecting a metal ion, characterized in that the carbon quantum dot according to any one of claims 1 to 5 or the carbon quantum dot produced by the production method according to any one of claims 6 to 9 is detected.

12. A kit or a test strip comprising the carbon quantum dot according to any one of claims 1 to 5 or the carbon quantum dot produced by the production method according to any one of claims 6 to 9.

Technical Field

The invention relates to the technical field of carbon nano materials, in particular to a carbon quantum dot and a preparation method and application thereof.

Background

Calcium ion (Ca)²⁺) Is an indispensable ion in all physiological activities of the body. Ca²⁺Plays an indispensable role in cell maintenance and biological functions, and also plays an important role in the action mechanism of certain hormones, all of which are composed of Ca²⁺Expressed. Ca²⁺Differentiation, proliferation, migration, growth and apoptosis, which are the second messengers to control. The influencing factors of Alzheimer's disease, Parkinson's disease and Huntington's disease may be related to intracellular Ca²⁺Concentration anomaly changes are closely related. In the study of cancer cells, it was gradually demonstrated that the occurrence and metastasis of tumors also correlated with Ca in cancer cells²⁺Aberrant regulation of levels is closely related. Thus, for Ca²⁺The high sensitivity and rapid detection of (A) is becoming an increasingly targeted category of research.

At present, Ca is available²⁺The detection method comprises atomic absorption spectrometry, calorimetry, inductively coupled plasma, nuclear magnetic resonance and ion selective electrode method. Unfortunately, these methods typically require expensive equipment and cumbersome samples. Because of the importance of intracellular calcium level detection, simple, economical and efficient Ca is developed²⁺A detection method is necessary.

Currently, most of light emitted by carbon quantum dots is blue fluorescence, for example, in the applicant's earlier patent CN11096450A, a carbon dot fluorescent probe for calcium ion detection and a preparation method thereof are disclosed, the wavelength is short (about 450 nm), and the autofluorescence of biological tissues is mostly blue light, so that the carbon quantum dots are not favorable for distinguishing target signals from background signals when applied to biological imaging; in addition, the blue light has poor penetrability to tissues, so that the optical imaging of deep tissues in the body is limited, and the application of the carbon quantum dots in biology is further limited.

Therefore, in order to meet the practical requirements of popularization and application of the carbon quantum dots, a preparation method capable of prolonging the fluorescence emission wavelength of the carbon quantum dots is urgently needed.

Disclosure of Invention

Therefore, the technical problem to be solved by the present invention is to overcome the drawbacks of the prior art, thereby providing a carbon quantum dot having a significantly extended fluorescence wavelength.

Therefore, the invention provides a carbon quantum dot, the raw materials of which comprise a carbon source and a rare earth compound, wherein the carbon source comprises phenylenediamine and an organic acid.

Further, the mass of the rare earth compound is 5 to 50%, preferably 10 to 30%, most preferably 15% of the total mass of the carbon source.

Further, the organic acid is at least one selected from citric acid, ascorbic acid, malic acid, tartaric acid, succinic acid, lactic acid, salicylic acid and caffeic acid, and is preferably malic acid.

Further, the phenylenediamine is selected from p-phenylenediamine and/or o-phenylenediamine.

Further, the rare earth compound is selected from at least one of gadolinium chloride, erbium chloride and yttrium chloride.

Further, the mass ratio of the phenylenediamine to the organic acid is 2-3.5: 1.

further, the fluorescence emission wavelength of the carbon quantum dot is 592-650nm, preferably 605-630 nm.

Further, the infrared spectrogram of the carbon quantum dots is 3343cm^-1，3214cm^-1，1612cm^-1，831cm^-1And 700cm^-1Has an absorption peak.

Further, the particle size of the carbon quantum dots is 4-8 nm. Further, the lattice spacing was 0.23 nm.

The invention also provides a preparation method of the carbon quantum dots, which comprises the following steps: dissolving a carbon source and a rare earth compound in water, and carrying out hydrothermal reaction to obtain carbon quantum dots; the carbon source is a mixture comprising phenylenediamine and an organic acid.

Further, the temperature of the hydrothermal reaction is 140-200 ℃, preferably 160 ℃.

Further, the hydrothermal reaction is followed by a step of modifying the carbon quantum dots with ethylene glycol bis (2-aminoethyl ether) tetraacetic acid.

Further, the mass ratio of ethylene glycol bis (2-aminoethyl ether) tetraacetic acid (EGTA) to phenylenediamine is 1:2 to 2:1, preferably 1:1.5-1.5: 1.

further, the temperature of the modification step is 60-120 ℃ for at least 1 hour.

In some preferred schemes, stirring is carried out under stirring, then ultrasonic treatment is carried out, and then the mixture is placed at 60-120 ℃ for modification, wherein the modification time is 3-8 h.

Further, the method also comprises a purification treatment step after the hydrothermal reaction or the modification step.

Further, the purification step is to filter the solution obtained from the hydrothermal reaction or the solution obtained from the modification step by primary filtration and then centrifuge to remove large particle precipitates, then filter the solution by a micron-sized filter membrane to obtain a clear solution, dialyze the solution (for example, dialyze for 12 hours), collect the solution in a dialysis bag, and dry the solution to obtain the purified carbon quantum dots.

The technical scheme of the invention has the following advantages:

1. according to the preparation method of the carbon quantum dot, researches show that the mixture of phenylenediamine and organic acid is used as a carbon source, and rare earth elements are doped for use, so that the fluorescence wavelength of the obtained carbon quantum dot is obviously prolonged, the background fluorescence of biological tissues can be reduced, and the tissue penetrability can be improved.

2. In a preferred embodiment, the mass of the rare earth compound is controlled to be 10-30% of the total mass of the carbon source and the rare earth compound, and the rare earth doping with the content can avoid the interference of surplus metal ions on the surface modification of EGTA in the process of modifying the carbon quantum dots by the EGTA under the condition of ensuring that the fluorescence wavelength is prolonged, so that the probe can detect calcium ions more sensitively, the detection sensitivity is obviously improved, and the fluorescence quantum yield is also obviously improved.

3. In a preferred embodiment, the mass ratio of ethylene glycol bis (2-aminoethyl ether) tetraacetic acid to phenylenediamine is controlled to be 1:1.5-1.5:1, so that EGTA with the most surface modification on the finally prepared carbon dots can be prepared, and a probe can efficiently recognize calcium ions.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a Transmission Electron Microscope (TEM) photograph and a particle size distribution diagram of carbon quantum dots obtained in example 1, the abscissa of the particle size distribution diagram being the particle size (nm) and the ordinate being the distribution percentage (%);

fig. 2 is an absorption spectrum and a fluorescence spectrum of a carbon quantum dot prepared in example 1 of the present invention, where three curves are an absorption curve, an excitation curve, and an emission curve from left to right in this order, the abscissa is a wavelength (nm), and the ordinate is an intensity (a.u.);

FIG. 3 is an infrared spectrum of a carbon quantum dot obtained in example 1 of the present invention;

FIG. 4 is the result of detection of copper ions in example 4, wherein (A) is a fluorescence intensity curve of calcium ion solutions of different concentrations; the fluorescence curves of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 150, 200, 250, 300, 350 and 400 mu M calcium ion solutions in sequence from top to bottom, wherein (B) is a linear relation;

FIG. 5 is the result of the test strip of example 5, wherein (A) is the fluorescence intensity curve of calcium ion solutions with different concentrations, from top to bottom, 5, 10, 100, 400 μ M; (B) is the color development result of the test strip corresponding to the calcium ion solution with different concentrations under 365 nm;

fig. 6 is a result of an experiment of selectivity of the carbon quantum dot of the present invention to different metal ions in experimental example 5.

Detailed Description

The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.

The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The reagents or instruments used are not indicated by manufacturers, and are all conventional reagent products which can be obtained commercially.

Example 1

The embodiment provides a preparation method of a carbon quantum dot, which comprises the following steps:

(1) 30mg of p-phenylenediamine solid, 10mg of malic acid and 5.9mg of yttrium chloride solid were weighed out and mixed into 30mL of ultrapure water, and subjected to ultrasonic agitation. The solution was then transferred to a 50mL reaction kettle lined with Teflon and allowed to react in an oven at 160 ℃ for 6 hours.

(2) After the reaction was completed, after the solution was cooled to room temperature, 30mg of ethylene glycol bis (2-aminoethyl ether) tetraacetic acid was added to the resulting solution, and stirring was continued and the ultrasonic operation was performed again. Likewise, the solution was transferred to a 50mL volume Teflon lined reactor and the reaction was continued in an oven at 80 ℃ for 5 hours.

(3) After the reaction is finished, cooling the solution to room temperature, primarily filtering the solution by using filter paper, transferring the solution into a centrifugal machine, centrifuging the solution at 10000 r/min to remove large-particle precipitates, and filtering the solution by using a 0.22 mu m water-phase filter membrane to obtain a clear solution. Then dialyzing the solution for 12 hours by using a dialysis bag (with the molecular weight cut-off of 3500Da), and changing water every four hours to remove unreacted raw material micromolecules; and finally, collecting the solution in the dialysis bag, and freeze-drying to obtain the purified carbon quantum dots.

And (3) performing performance test on the carbon quantum dots:

fig. 1 is a Transmission Electron Microscope (TEM) photograph of the carbon quantum dots prepared in this example. As can be seen from the figure, most of the nanoparticles are spherical, the particle size distribution is uniform, the size is mainly distributed in the range of 4-8nm, and the average particle size is 5 nm. HR-TEM images show that the lattice spacing is 0.23nm, which is consistent with the surface of the graphite structure, and the single nanoparticles are also layered.

FIG. 2 is a graph of UV-VIS absorption spectrum and a fluorescence emission spectrum of the carbon quantum dot prepared in this example, from which it can be seen that the UV-VIS absorption wavelength of the carbon dot is 200-800nm, the maximum absorption peak is located at 236nm, and shoulder peaks exist at 280nm and 530 nm; under excitation light with 490nm wavelength (optimal excitation wavelength), the carbon quantum dot has an optimal emission peak, and the fluorescence emission peak is located at 630nm (fluorescence emission wavelength). The carbon quantum dot is used for detecting calcium ions, and the fluorescence of the carbon quantum dot is weakened by the influence of the calcium ions, so that the good red fluorescence performance of the carbon quantum dot can be used as a detection signal of the calcium ions.

FIG. 3 is an infrared spectrum of the carbon quantum dots prepared in this example, and it can be seen from the analysis of the intensity of the transmission peak that the tensile vibration of-OH is 3343cm^-1And 3214cm^-1The peak appears, and the peak related to N-H is located at 1612cm^-1Because the surface of the yttrium-mediated nano particle is rich in hydroxyl, amino and other groups, the carbon nano particle has good water solubility. The stretching vibration of the aromatic ring skeleton and the methyl C-H is respectively 1500cm^-1And 1380cm^-1The peak composition at (c). At 831cm^-1And 700cm^-1The peaks are 1, 4-disubstituted benzene and chloride respectively.

Example 2

The embodiment provides a preparation method of a carbon quantum dot, which comprises the following steps:

(1) 30mg of p-phenylenediamine solid, 10mg of malic acid and 5.9mg of yttrium chloride solid were weighed out and mixed into 30mL of ultrapure water, and subjected to ultrasonic agitation. The solution was then transferred to a 50mL reaction kettle lined with Teflon and allowed to react in an oven at 160 ℃ for 6 hours.

(2) After the reaction is finished, cooling the solution to room temperature, primarily filtering the solution by using filter paper, transferring the solution into a centrifugal machine, centrifuging the solution at 10000 r/min to remove large-particle precipitates, and filtering the solution by using a 0.22 mu m water-phase filter membrane to obtain a clear solution. Then dialyzing the solution for 12 hours by using a dialysis bag (with the molecular weight cut-off of 3500Da), and changing water every four hours to remove unreacted raw material micromolecules; and finally, collecting the solution in the dialysis bag, and freeze-drying to obtain the purified carbon quantum dots.

The carbon quantum dots are prepared into 0.01mg/ml carbon quantum dot solution by adopting ultrapure water (solvent), and the carbon quantum dots have the optimal emission peak under the excitation light with the wavelength of 490nm by observing with a fluorescence spectrophotometer, wherein the fluorescence emission peak is positioned at 630 nm.

Example 3

The embodiment provides a preparation method of a carbon quantum dot, which comprises the following steps:

(1) 30mg of p-phenylenediamine solid, 10mg of malic acid and 5.9mg of gadolinium chloride solid were weighed out and mixed into 30mL of ultrapure water, and the mixture was subjected to ultrasonic agitation. The solution was then transferred to a 50mL reaction kettle lined with Teflon and allowed to react in an oven at 160 ℃ for 6 hours.

(2) After the reaction was completed, after the solution was cooled to room temperature, 30mg of ethylene glycol bis (2-aminoethyl ether) tetraacetic acid was added to the resulting solution, and stirring was continued and the ultrasonic operation was performed again. Likewise, the solution was transferred to a 50mL volume Teflon lined reactor and the reaction was continued in an oven at 80 ℃ for 5 hours.

(3) After the reaction is finished, cooling the solution to room temperature, primarily filtering the solution by using filter paper, transferring the solution into a centrifugal machine, centrifuging the solution at 10000 r/min to remove large-particle precipitates, and filtering the solution by using a 0.22 mu m water-phase filter membrane to obtain a clear solution. Then dialyzing the solution for 12 hours by using a dialysis bag (with the molecular weight cut-off of 3500Da), and changing water every four hours to remove unreacted raw material micromolecules; and finally, collecting the solution in the dialysis bag, and freeze-drying to obtain the purified carbon quantum dots.

The carbon quantum dots are prepared into 0.01mg/ml carbon quantum dot solution by adopting ultrapure water (solvent), and the carbon quantum dots have the optimal emission peak under the excitation light with the wavelength of 475nm by observing with a fluorescence spectrophotometer, wherein the fluorescence emission peak is positioned at 610 nm.

Example 4

The embodiment provides a method for detecting the concentration of copper ions, which comprises the following steps:

(1) weighing the carbon quantum dots prepared in example 1, adding ultrapure water to prepare 18 parts of nanoparticle aqueous solution with the concentration of 0.01mg/mL, and respectively adding 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 150, 200, 250, 300, 350 and 400 mu M calcium ion solution into the solution system;

(2) under the condition of 490nm excitation light, the fluorescence intensity of the nanoparticle solution at 630nm is recorded, and the measured (F0/F) -1 is taken as the y-axis, the corresponding calcium ion concentration is taken as the x-axis, and a standard curve graph is drawn to obtain a linear regression equation.

As shown in FIG. 4, (F0/F) -1 is linear with calcium ion concentration in the range of 0-400 μ M of the experimental design, and the formula is (F0/F) -1 ═ 0.0012[ Ca [ ]²⁺]+0.04045, coefficient of correlation R²Reaches 0.995, wherein F0 and F are the fluorescence intensity of the nanoparticle solution in the absence of calcium ion solution and in the presence of calcium ion solution, [ Ca ]²⁺]Is the calcium ion concentration. The nano particles can be applied to the indication of the calcium ion concentration in the solution.

Example 5

The embodiment provides a test strip, and the preparation method comprises the steps of taking the carbon quantum dots in the embodiment 1, adding ultrapure water to prepare a solution with the concentration of 0.01mg/mL, infiltrating the test strip, and drying to obtain the test strip.

The embodiment also provides a method for detecting the concentration of calcium ions, which comprises the following steps: the test strip prepared in the embodiment is used for soaking calcium ion solutions (5, 10, 100 and 400 mu M) with different concentrations, the fluorescence intensity of the test strip is measured after drying, and the test strip is placed under a 365nm ultraviolet lamp for inspection.

The results are shown in FIG. 5, and it can be seen from FIG. 5A that the fluorescence intensity of the test strip added with 5. mu.M calcium ions is 2426(a.u.), and the fluorescence intensity gradually decreases to 1597(a.u.) with the increase of the calcium ion concentration, indicating that the fluorescence intensity of the solution decreases to 65.83% after the calcium ion solution is added. In FIG. 5B, the test paper becomes increasingly dark in fluorescence with increasing calcium ion concentration under a 365nm UV lamp. These changes can be discerned by the naked eye. Experimental results show that the calcium ion sensor is applied to the paper-based nano sensor, so that the calcium ion detection is more convenient.

Comparative example 1

The comparative example provides a preparation method of a carbon quantum dot, comprising the following steps:

(1) 30mg of p-phenylenediamine solid and 10mg of malic acid were weighed out and mixed into 30mL of ultrapure water, sonicated and stirred. The solution was then transferred to a 50mL reaction kettle lined with Teflon and allowed to react in an oven at 160 ℃ for 6 hours.

(2) After the reaction is finished, cooling the solution to room temperature, adding ethylene glycol bis (2-aminoethyl ether) tetraacetic acid with the same mass as p-phenylenediamine into the obtained solution, continuing stirring and carrying out ultrasonic operation again. Likewise, the solution was transferred to a 50mL volume Teflon lined reactor and the reaction was continued in an oven at 80 ℃ for 5 hours.

(3) After the reaction is finished, cooling the solution to room temperature, primarily filtering the solution by using filter paper, transferring the solution into a centrifugal machine, centrifuging the solution at 10000 r/min to remove large-particle precipitates, and filtering the solution by using a 0.22 mu m water-phase filter membrane to obtain a clear solution. Then dialyzing the solution for 12 hours by using a dialysis bag (with the molecular weight cut-off of 3500Da), and changing water every four hours to remove unreacted raw material micromolecules; and finally, collecting the solution in the dialysis bag, and freeze-drying to obtain the purified carbon quantum dots.

The carbon quantum dots are prepared into 0.01mg/ml carbon quantum dot solution by using ultrapure water as a solvent, and the carbon quantum dots have an optimal emission peak under excitation light with a wavelength of 475nm by observing with a fluorescence spectrophotometer, wherein the fluorescence emission peak is positioned at 572 nm.

Experimental example 1

The carbon quantum dots were prepared by the method of example 1 using different carbon sources in table 1 below, and the other materials and process conditions were kept the same as in example 1, and the influence of different carbon sources on the carbon quantum dots was examined. The prepared carbon quantum dots were prepared into a 0.01mg/ml carbon quantum dot solution using ultrapure water as a solvent, and the results of observation with a fluorescence spectrophotometer are shown in Table 1.

TABLE 1 carbon sources and results of the experiments

As can be seen from the above table, the carbon quantum dots obtained by using p-phenylenediamine or o-phenylenediamine in combination with an organic acid as a carbon source have longer fluorescence wavelength, wherein malic acid is preferably used in combination with phenylenediamine.

Experimental example 2

The rare earth compounds are added according to the dosage in the following table 2, the carbon quantum dots are prepared according to the method of the example 1, other materials and process conditions are consistent with those of the example 1, and the influence of the addition of different rare earth on the carbon quantum dots is examined. The prepared carbon quantum dots are prepared into 0.01mg/ml carbon quantum dot solution by using ultrapure water as a solvent, and the solution is observed by a fluorescence spectrophotometer. The fluorescence quantum yield of the carbon quantum dots was measured directly by the Edinburgh FLS980 fluorescence spectrometer.

The results are shown in Table 2.

TABLE 2 amount of rare earth compound and experimental results

As can be seen from the table above, the mass of the rare earth compound in the carbon source is too large or too small in percentage, which affects the fluorescence emission wavelength and fluorescence quantum yield, and the carbon quantum dots obtained in the range of 10% -30% have better emission wavelength and fluorescence quantum yield.

Experimental example 3

Hydrothermal reactions were carried out at the temperatures shown in Table 3 below, and the other materials and process conditions were kept the same as in example 1, and the influence of different temperatures on the carbon quantum dots was examined. The prepared carbon quantum dots were prepared as a 0.01mg/ml carbon quantum dot solution using ultrapure water as a solvent, and the results of observation with a fluorescence spectrophotometer are shown in Table 3.

TABLE 3 hydrothermal reaction temperature and Experimental results

Reaction temperature	Optimum excitation wavelength (nm)	Fluorescence emission wavelength (nm)
			140℃	490	615
180℃	490	625
			200℃	490	611

As can be seen from the above table, the temperature of the hydrothermal reaction also affects the fluorescence emission wavelength of the carbon quantum dots, and in order to obtain a longer fluorescence wavelength, the temperature of the hydrothermal reaction is preferably controlled to be about 180 ℃.

Experimental example 4

Ethylene glycol bis (2-aminoethyl ether) tetraacetic acid was added in the amounts shown in Table 4 below, carbon quantum dots were prepared according to the method of example 1, the other materials and process conditions were the same as those in example 1, and the influence of the addition amount of ethylene glycol bis (2-aminoethyl ether) tetraacetic acid on the carbon quantum dots was examined. The prepared carbon quantum dots are prepared into 0.01mg/ml carbon quantum dot solution by using ultrapure water as a solvent, and the solution is observed by a fluorescence spectrophotometer.

The sensitivity of calcium ion is calculated according to a formula after a standard curve is made.

The results are shown in Table 4.

TABLE 4 amount of rare earth compound used and experimental results

As can be seen from the table above, the sensitivity of the detection method can be obviously improved by controlling the mass ratio of the ethylene glycol bis (2-aminoethyl ether) tetraacetic acid to the phenylenediamine to be 1.5:1-1: 1.5.

Experimental example 5

The carbon quantum dots prepared in example 1 were weighed, ultrapure water was added to prepare 11 parts of nanoparticle aqueous solution with a concentration of 0.01mg/mL, calcium ion solution, potassium ion solution, sodium ion solution, aluminum ion solution, iron ion solution, ferrous ion solution, magnesium ion solution, lead ion solution, cobalt ion solution, copper ion solution, and manganese ion solution each having a concentration of 200 μ M were added to the solution system, and the fluorescence intensity was measured.

The results are shown in FIG. 6, comparing Ca with other ions²⁺And Fe³⁺The influence on the fluorescence intensity of the carbon dots is the most significant. As for the mechanism of fluorescence decay of calcium ions, as described above, EGTA has a significantly better affinity for calcium ions than other interfering ions, resulting in the aggregation of carbon dots and the fluorescent layer. However, in live cell calcium ion detection, relatively low Fe³⁺The effect of the content is negligible. Therefore, in future living cell experiments, the carbon dots can play a relatively superior role in the fluorescence characteristic of the calcium ion selective reaction.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.