CN111019650A

CN111019650A - Synthesis method and application of red fluorescent carbon dots

Info

Publication number: CN111019650A
Application number: CN201911299043.3A
Authority: CN
Inventors: 金建成; 颜稔
Original assignee: Zhongyuan University of Technology
Current assignee: Zhongyuan University of Technology
Priority date: 2019-12-17
Filing date: 2019-12-17
Publication date: 2020-04-17
Anticipated expiration: 2039-12-17
Also published as: CN111019650B

Abstract

The invention belongs to the technical field of nanometer, relates to a preparation method of a carbon nanometer material, and particularly relates to a synthesis method and application of red fluorescent carbon dots. Namely, the Polythiophene (PTH) is directly oxidized and stripped by nitric acid, and the red fluorescent carbon dot with good fluorescence property is prepared. The method is a one-step method, and the carbon dots with long-wavelength fluorescence emission can be obtained by uniformly mixing PTh and nitric acid and then heating for a period of time. The carbon dots synthesized by the method have the advantages of good optical property, low toxicity and good biocompatibility, and can be applied to the biomedical fields of cell imaging and the like. The position of the fluorescence peak of the carbon dot can be regulated and controlled by simply changing the content of the nitric acid, the fluorescence peak of the carbon dot can be red-shifted from 575 nm to 595 nm, and the fluorescence emission peak of the obtained red fluorescence carbon dot is not changed along with the change of the excitation wavelength.

Description

Synthesis method and application of red fluorescent carbon dots

Technical Field

The invention belongs to the technical field of nanometer, relates to a preparation method of a carbon nanometer material, and particularly relates to a synthesis method and application of red fluorescent carbon dots.

Background

Carbon dots (C-dots) are typically fluorescent carbon nanoparticles with a size between 1-10 nm. In 2004, Xu et al discovered such fluorescent carbon nanoparticles for the first time when using gel electrophoresis to purify and separate single-walled carbon nanotubes prepared from arc discharge soot. Then, the C-dots becomes a star material due to the characteristics of ultra-small particle size, excellent fluorescence property, low preparation cost, abundant and easily obtained synthetic raw materials, simple synthetic method, easy functional modification and the like. They can be prepared by methods such as arc discharge, laser ablation, electrochemical synthesis, acid oxidation, microwave-assisted synthesis, pyrolysis/solvothermal method, hydrothermal method and the like. Compared with semiconductor quantum dots and organic dyes, C-dots have the characteristics of photobleaching resistance, photoscintillation resistance, good water solubility, no toxic or side effect, easiness in preparation and the like, have unique advantages in the field of biomedical application, are widely applied to aspects of biological imaging, biosensing, drug transportation and the like, and also arouse the interest of researchers. However, most of the reported synthesized C-dots fluoresce blue and green. When biological imaging is carried out, the biological sample has strong autofluorescence and background light scattering in a short wavelength region, and long-wavelength fluorescence can penetrate to a deeper part of the biological sample, so that the biological sample has higher imaging contrast. Therefore, there is a need to develop long wavelength emitted fluorescent C-dots that improve their practical operability for use in biological imaging. Patent CN201711399203.2 discloses a method for preparing red fluorescent carbon dot powder, which comprises using 1, 2, 4-benzenetriamine and polyethylene glycol as raw materials, obtaining red carbon dot solution through heating reaction, mixing the carbon dot solution with silica gel powder, and spin-drying on a rotary evaporator to obtain the red fluorescent carbon dot powder. The scheme has the advantage that the problem of quenching of carbon point fluorescence can be effectively overcome. The emission wavelength is 400nm to 520nm, and the wavelength of the carbon dots varies with the emission wavelength, which is not suitable for use in biological imaging.

Disclosure of Invention

The invention provides a synthesis method and application of a red fluorescent carbon dot, and solves the technical problems that the existing red fluorescent carbon dot can change along with the change of emission wavelength and fluorescence is unstable during imaging.

The technical scheme of the invention is realized as follows:

a method for synthesizing red fluorescent carbon dots comprises the following steps: adding a stripping agent into the carbon source, uniformly mixing, reacting under a certain condition, and oxidizing and stripping the carbon source to obtain the red fluorescent carbon dots.

The carbon source is polythiophene, and the stripping agent is concentrated nitric acid.

The ratio of the mass of the carbon source (mg) to the volume of the stripping agent (mL) is 20: (2-15).

The reaction condition is that the temperature is heated to 40-100 ℃, and the condensation reflux is carried out for 20 min-24 h.

The synthesis method of the red fluorescent carbon dots comprises the following steps: adding concentrated nitric acid into polythiophene, uniformly mixing, heating to 40-100 ℃, condensing and refluxing for 20 min-24 h to obtain a red fluorescent carbon dot suspension, and purifying to obtain the red fluorescent carbon dots.

0.1-0.75mL of concentrated nitric acid is added to each mg of polythiophene.

The purification steps are as follows: adding water into the prepared red fluorescent carbon dot suspension for washing, stirring, standing, centrifuging, collecting precipitate, adding 0.1M NaOH solution into the precipitate to make the pH value of the precipitate neutral, centrifuging again, collecting precipitate, dispersing the precipitate into a mixed solution of N, N-dimethylformamide and water in a volume ratio of 1:4, dialyzing, and separating by silica gel column chromatography.

The synthesized red fluorescent carbon dots are applied to the preparation of biological imaging reagents.

The invention has the following beneficial effects:

(1) the invention provides a method for simply and rapidly synthesizing red fluorescent carbon dots, namely preparing the red fluorescent carbon dots by stripping PTh with nitric acid. Few cases exist about the synthesis of the red fluorescent carbon dots, and the traditional synthesis of the red fluorescent carbon dots is mainly a hydrothermal method or a later-stage polymer coating method. The hydrothermal method has high energy consumption, and the types of carbon sources which can be selected are very limited when the red fluorescent carbon dots are prepared. The polymer coating method is complicated in steps and needs to be dried by distillation for many times. The synthesis method of the invention utilizes nitric acid to directly oxidize and strip PTH, and the reaction is carried out for a period of time at a lower temperature, thus obtaining the red fluorescent carbon dots. The method is simple to operate and rapid to prepare, and the red fluorescent carbon dots can be obtained within 20 min.

(2) The reactants of the synthesis method are very simple, only PTH and nitric acid are needed, the reaction temperature of the synthesis method is very mild, the preparation of the red fluorescent carbon dots can be realized only by a simple heating device and a condensation reflux device, and the cost of synthesizing the carbon dots can be greatly reduced.

(3) The reaction time of the synthesis method is extremely short, the red fluorescent carbon dots can be prepared within 20 min, and the fluorescence emission peak of the red fluorescent carbon dots prepared by the synthesis method does not change along with the change of the excitation wavelength and is different from the carbon dots with the fluorescence emission peak changing along with the change of the excitation wavelength.

(4) The method successfully utilizes the oxidative shearing action of nitric acid to break a part of a pi electron conjugated system of the PTh, and prepares the red fluorescent carbon dots through the oxidative action of the nitric acid, and the fluorescence emission wavelength of the prepared carbon dots can be effectively adjusted between 575 and 595 nm.

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, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a fluorescence spectrum of a carbon spot of example 1.

FIG. 2 is a fluorescence spectrum of a carbon spot of example 2.

FIG. 3 is a fluorescence spectrum of a carbon spot of example 3.

FIG. 4 is a fluorescence spectrum of the carbon spot of example 4.

FIG. 5 is a fluorescence spectrum of the carbon spot of example 5.

Figure 6 is an image of the application of carbon dots to a cell.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

The method for synthesizing the red fluorescent carbon dots comprises the following steps:

20 mg of PTh and 15 mL of concentrated nitric acid are uniformly mixed, stirred for reaction at 40 ℃, and condensed and refluxed for 24 hours to obtain a tan carbon dot solution, wherein the fluorescence emission peak of the carbon dot is 595 nm, and the fluorescence excitation peak is 430 nm.

The excitation wavelengths are respectively selected to be 365 nm, 385 nm, 405 nm, 425 nm, 445 nm and 465 nm for excitation, and the result is shown in figure 1, and the position of the fluorescence emission peak of the carbon dot is not changed along with the change of the excitation wavelength, which is the reason that the carbon nuclear structure in the carbon dot is relatively complete.

Example 2

20 mg of PTh and 15 mL of concentrated nitric acid are uniformly mixed, stirred for reaction at 60 ℃, and condensed and refluxed for 24 hours to obtain a brownish red carbon dot solution, wherein the fluorescence emission peak of the carbon dot is located at 590 nm.

Samples were taken at intervals, and the results of the progress of the reaction were observed by spectrometry. And selecting samples which are reacted for 20 min, 40min, 1h, 2 h, 4h, 8h, 12 h and 24h to determine the fluorescence spectra, and referring to fig. 2, the fluorescence emission peak of the carbon point can not be shifted along with the reaction time, but the fluorescence intensity can be correspondingly increased. This is because the reaction is more complete with increasing reaction time, but the temperature is relatively low and is not sufficient to cause a large change in the structure of the carbon dots.

Example 3

20 mg of PTh and 15 mL of concentrated nitric acid are uniformly mixed, stirred for reaction at 80 ℃, and condensed and refluxed for 8 hours to obtain a brown yellow carbon dot solution, wherein the fluorescence emission peak of the carbon dot is 585 nm.

Samples were taken at intervals, and the progress of the reaction was observed by spectrometry. And selecting samples which are reacted for 20 min, 40min, 1h, 2 h, 4h, 8h, 12 h and 24h to determine the fluorescence spectra, and referring to fig. 3, the fluorescence emission peak of the carbon point can not shift along with the reaction time, but the fluorescence intensity can increase and finally tends to be stable. This is because the reaction rate increases with an increase in the reaction temperature, but the structure of the carbon dots has not yet changed greatly.

Example 4

dispersing 20 mg of PTh in 2mL of water by shaking, adding 15 mL of concentrated nitric acid, stirring and mixing uniformly, stirring and reacting at 100 ℃, sampling at intervals, performing spectral determination, and observing the reaction process.

The fluorescence spectrum of the sample is measured by selecting the samples which are reacted for 20 min, 40min, 1h, 2 h, 4h, 6 h, 8h, 12 h, 24h and 48 h, as shown in figure 4, the fluorescence emission peak of the prepared carbon dot is gradually blue-shifted from 595 nm to 575 nm along with the prolonging of the reaction time, which is the reason that the stripping effect of nitric acid is stronger under the condition of 100 ℃, and the size of the carbon dot is gradually reduced along with the proceeding of the reaction.

Example 5

20 mg of PTh is shaken and dispersed in 15 mL of concentrated nitric acid, 0 mL, 2mL, 5mL and 8 mL of water are respectively added, the mixture is stirred and mixed uniformly, the mixture is stirred and reacted for 24 hours at the temperature of 100 ℃, a solution of a carbon dot is obtained, and the fluorescence spectrum of the solution is measured, and the result is shown in figure 5. The more the water is added, the lower the concentration of nitric acid is, the more red-shifted the fluorescence emission peak of carbon point from 575 nm to 595 nm. This is because the stripping action of nitric acid decreases with decreasing concentration, and pi-electron conjugation of the obtained carbon dots gradually increases.

Examples of the effects of the invention

Washing the carbon dot solution prepared in the example 1 with water, stirring, standing, centrifuging to collect precipitate, adding 0.1M NaOH solution into the precipitate to make the pH value of the precipitate neutral, centrifuging again to collect precipitate, dispersing the precipitate into a mixed solution of N, N-dimethylformamide and water in a volume ratio of 1:4, dialyzing, and separating by silica gel column chromatography to obtain red fluorescent carbon dots.

The purified carbon dots are applied to cell imaging, and the steps are as follows:

inoculating human cervical cancer cells into a culture dish, and culturing at 37 ℃ to make the cells adhere to the wall. Diluting the carbon dots to 50 mug/mL by using a fresh culture medium, replacing the culture medium containing the carbon dots to continuously culture for 16 h, then cleaning the carbon dots for 3 times by using sterile phosphate buffer solution, observing the imaging of the carbon dots on human cervical carcinoma cells by using a laser confocal microscope, wherein the result is shown in figure 6.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A method for synthesizing red fluorescent carbon dots is characterized by comprising the following steps: adding a stripping agent into the carbon source, uniformly mixing, reacting under a certain condition, and oxidizing and stripping the carbon source to obtain the red fluorescent carbon dots.

2. The method of claim 1, wherein: the carbon source is polythiophene, and the stripping agent is concentrated nitric acid.

3. The method of claim 2, wherein: the mass-volume ratio of the carbon source to the stripping agent is 20: (2-15).

4. The method of claim 3, wherein: the reaction condition is that the temperature is heated to 40-100 ℃, and the condensation reflux is carried out for 20 min-24 h.

5. The method for synthesizing a red fluorescent carbon dot as claimed in claim 4, comprising the steps of: adding concentrated nitric acid into polythiophene, uniformly mixing, heating to 40-100 ℃, condensing and refluxing for 20 min-24 h to obtain a red fluorescent carbon dot suspension, and purifying to obtain the red fluorescent carbon dots.

6. The method of claim 5, wherein: 0.1-0.75mL of concentrated nitric acid is added to each mg of polythiophene.

7. The method for synthesizing a red fluorescent carbon dot as claimed in claim 5, wherein the purification step is: adding water into the prepared red fluorescent carbon dot suspension for washing, stirring, standing, centrifuging, collecting precipitate, adding 0.1M NaOH solution into the precipitate to make the pH value of the precipitate neutral, centrifuging again, collecting precipitate, dispersing the precipitate into a mixed solution of N, N-dimethylformamide and water in a volume ratio of 1:4, dialyzing, and separating by silica gel column chromatography.

8. Use of a red fluorescent carbon dot synthesized according to any one of claims 1 to 7 for the preparation of a biological imaging agent.