Preparation method and application of multicolor carbon quantum dots based on surface ligand functionalization

Abstract

The invention discloses a preparation method of multicolor carbon quantum dots based on surface ligand functionalization, and belongs to the technical field of nanotechnology. Firstly, sky blue luminous carbon quantum dots are synthesized on the basis of citric acid, multicolor carbon quantum dots are prepared through the steps of filtration, dialysis purification, surface modification and the like, and effective regulation and control of emission within the range of 300-1000 nm are achieved through a series of surface ligand functionalization strategies. The wavelength regulation method provided by the invention is simple and effective in system, and the synthesis method is simple and convenient. The fluorescence quantum yield of the prepared carbon quantum dots is high, and the highest fluorescence quantum yield can reach 79%; the cost and the toxicity are low, and the light-emitting wavelength can be regulated and controlled to the whole visible spectrum and the near-infrared band.

Description

Technical Field

[0001] The present invention belongs to the field of nanotechnology and relates to a preparation method and application of multi-color carbon quantum dots with high fluorescence quantum yield based on surface ligand functionalization. Background Art

[0002] Carbon quantum dots (CQDs) with a nanometer size of less than 10 nm have attracted great interest due to their extraordinary optical and physicochemical properties, which are attractive in fields such as sensing, bioimaging, photomedicine, catalysis, information encryption, and optoelectronic devices. One of the most attractive properties of carbon quantum dots is their tunable photoluminescence. The vast majority of CDs only emit strong blue or green light in the short wavelength region (420-530 nm). Due to the unclear chemical structure of carbon quantum dots and the corresponding luminescence mechanism, there are controversies and even contradictions. The development of multicolor luminescent carbon quantum dot systems is still in its early stages, which seriously limits the application of CDs in various fields. Therefore, it is still a great challenge to clarify the relationship between carbon quantum dot structure and luminescence properties and to design synthetic strategies for carbon quantum dots with tunable luminescence (especially long-wavelength fluorescence). Summary of the Invention

[0003] In order to address the shortcomings of the existing technology, the purpose of the present invention is to provide a preparation method of multi-color carbon quantum dots based on surface ligand functionalization and its application in cell imaging. The carbon quantum dots have high fluorescence quantum yield, low cost and toxicity, and the emission wavelength can be adjusted to the entire visible spectrum and near-infrared band.

[0004] As used in the present invention, the term "Carbon Quantum Dots" (CQDs), also known as carbon dots or carbon nanodots, is a class of zero-dimensional carbon nanomaterials with significant fluorescent properties. It is an ultrafine, dispersed, quasi-spherical carbon nanoparticle with a size of less than 10 nm.

[0005] The present invention provides a method for preparing multicolor carbon quantum dots based on surface ligand functionalization, comprising the following steps:

[0006] (1) Anhydrous citric acid is placed in a crucible and heated to react to obtain carbon quantum dots.

[0007] In step (1), the mass of the citric acid is 0.18-0.24 g; preferably, 0.2 g.

[0008] In step (1), the reaction time is 10-50 min; preferably, 20 min.

[0009] In step (1), the reaction temperature is 200-240°C; preferably, 200°C.

[0010] (2) Dispersing the carbon quantum dots obtained in step (1) into a first solvent and filtering to obtain a carbon quantum dot solution.

[0011] In step (2), the first solvent is one or more of ethanol, methanol, etc.; preferably, it is ethanol.

[0012] In step (2), the filter head has a specification of 0.22-0.45 μm; preferably, 0.22 μm.

[0013] (3) The carbon quantum dot solution obtained in step (2) is dialyzed and purified in a second solvent using a dialysis bag, and the purified carbon quantum dots are recorded as T-CQDs.

[0014] In step (3), the molecular weight of the dialysis bag is 100-500 Da; preferably, it is 500 Da.

[0015] In step (3), the second solvent is one or more of ethanol, methanol, etc.; preferably, it is ethanol.

[0016] In step (3), the dialysis time is 24-48 hours; preferably, 48 hours.

[0017] (4) the T-CQDs obtained in step (3) were subjected to amide coupling reaction with o-phenylenediamine, 1,2,4-triaminobenzene and 1,2,4,5-tetraaminobenzene under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and 1-hydroxybenzotriazole (HOBt), respectively, to obtain the corresponding carbon quantum dots, which were respectively recorded as CQD1-1, CQD1-2 and CQD1-3;

[0018] or,

[0019] The T-CQDs obtained in step (3) are subjected to amide coupling reaction with 4-iodo-o-phenylenediamine, 4-bromo-o-phenylenediamine, 4-chloro-o-phenylenediamine and 4-fluoro-o-phenylenediamine under the catalysis of EDC and HOBt, respectively, to obtain corresponding carbon quantum dots, which are respectively recorded as CQD2-1, CQD2-2, CQD2-3 and CQD2-4;

[0020] or,

[0021] The T-CQDs obtained in step (3) were subjected to amide coupling reaction with 3,4,5,6-tetrafluorobenzene-1,2-diamine, 4,5-fluoro-o-phenylenediamine, 3-fluoro-1,2-phenylenediamine, 3,4,5-trifluoro-1,2-diaminobenzene and 4-fluoro-1,2-phenylenediamine under the catalysis of EDC and HOBt, respectively, to obtain corresponding carbon quantum dots, which were respectively recorded as CQD3-1, CQD3-2, CQD3-3, CQD3-4 and CQD2-4;

[0022] or,

[0023] The T-CQDs obtained in step (3) were subjected to amide coupling reaction with 1,4-diaminonaphthalene, 4-fluoro-1-aminonaphthalene and 2,6-diaminoanthracene under the catalysis of EDC and HOBt, respectively, to obtain the corresponding carbon quantum dots, which were recorded as CQD4-1, CQD4-2 and CQD4-3.

[0024] In step (4), the mass ratio of the carbon quantum dots to the o-phenylenediamine, the 1,2,4-triaminobenzene and the 1,2,4,5-tetraaminobenzene is 10:(32-38), preferably 10:36.

[0025] In step (4), the mass ratio of the T-CQDs to the catalyst EDC is 10:(50-70); preferably, 10:50.

[0026] In step (4), the mass ratio of the T-CQDs to the catalyst HOBt is 10:(30-50); preferably, 10:40.

[0027] In step (4), the mass ratio of the carbon quantum dots to the 4-iodo-o-phenylenediamine, the 4-bromo-o-phenylenediamine, the 4-chloro-o-phenylenediamine and the 4-fluoro-o-phenylenediamine is 10:(55-60); preferably, 10:60.

[0028] In step (4), the mass ratio of the carbon quantum dots to the 3,4,5,6-tetrafluorobenzene-1,2-diamine, the 4,5-fluoro-o-phenylenediamine, the 3-fluoro-1,2-phenylenediamine, the 3,4,5-trifluoro-1,2-diaminobenzene and the 4-fluoro-1,2-phenylenediamine is 10:(45-48); preferably, 10:48.

[0029] In step (4), the mass ratio of the carbon quantum dots to the 1,4-diaminonaphthalene, the 4-fluoro-1-aminonaphthalene and the 2,6-diaminoanthracene is 10:(72-78); preferably, 10:75.

[0030] In step (4), the temperature of the amide coupling reaction is 25-35°C; preferably, 25°C.

[0031] In step (4), the amide coupling reaction time is 24-36 hours; preferably, 36 hours.

[0032] The present invention also provides multicolor carbon quantum dots prepared according to the above method, the surface modified ligand small molecule structure is clear, the modification method is simple, the fluorescence wavelength control range is 300nm-1000nm, and the quantum yield control range is 18%-79%.

[0033] The present invention also provides a method for preparing the multicolor carbon quantum dots based on surface ligand functionalization, and the application of the multicolor carbon quantum dots based on surface ligand functionalization prepared according to the method in cell imaging.

[0034] In a specific embodiment, the method for preparing multicolor carbon quantum dots based on surface ligand functionalization of the present invention comprises the following steps:

[0035] (a) 0.2 g of anhydrous citric acid was placed in a crucible and heated at 200 °C for 20 min to obtain carbon quantum dots.

[0036] (b) dispersing the carbon quantum dots obtained in step (a) into a first solvent and filtering the solvent with a 0.22 μm filter to obtain a carbon quantum dot solution.

[0037] (c) The carbon quantum dot solution in step (b) was dialyzed and purified in a second solvent using a dialysis bag with a molecular weight of 500 Da for 48 h, and the purified carbon quantum dots were recorded as T-CQDs.

[0038] (d) 10 mg of the T-CQDs obtained in step (c) were subjected to amide coupling reaction with 36 mg of o-phenylenediamine at 25° C. under the catalysis of 50 mg of EDC and 40 mg of HOBt for 36 h to obtain carbon quantum dots CQD1-1.

[0039] (e) The carbon quantum dots obtained in step (d) were dialyzed and purified in ethanol using a dialysis bag with a molecular weight of 500 Da for 48 h to obtain green light carbon quantum dots CQD1-1 with high fluorescence quantum yield.

[0040] The present invention also provides a series of carbon quantum dots CQD1-1, CQD1-2, CQD1-3, CQD2-1, CQD2-2, CQD2-3, CQD2-4, CQD3-1, CQD3-2, CQD3-3, CQD3-4, CQD4-1, CQD4-2 and CQD4-3 prepared by the above method, and the luminescence wavelength covers the range of 300nm-1000nm.

[0041] The present invention also provides the use of the multicolor carbon quantum dots described above in cell imaging; wherein the cells are Hela cells.

[0042] The present invention has the following beneficial effects: First, sky-blue carbon quantum dots are synthesized based on citric acid, and then a series of surface ligand functionalization strategies are proposed to control the emission wavelength of the carbon quantum dots. The synthesis method is simple and convenient. The carbon quantum dots emit light in the wavelength range of 300nm-1000nm, and the quantum yield can be adjusted within the range of 18%-79%. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments disclosed in the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments disclosed in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 1 is a transmission electron micrograph of T-CQDs prepared in Example 1 of the present invention and a corresponding particle size distribution diagram.

[0045] Figure 2 1 is the infrared spectrum of the multicolor carbon quantum dots prepared in Example 1 of the present invention before and after modification.

[0046] Figure 3 This is a photograph of the multi-color carbon quantum dots prepared in Example 1 of the present invention under the excitation of a 365nm ultraviolet lamp.

[0047] Figure 4 is the fluorescence quantum yield of the multicolor carbon quantum dots prepared in Example 1 of the present invention.

[0048] Figure 5 These are the ultraviolet-visible absorption and fluorescence spectra of the multicolor carbon quantum dots prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0049] The present invention is further described in detail with reference to the following specific examples and accompanying drawings. The processes, conditions, experimental methods, etc. for implementing the present invention, except for those specifically mentioned below, are common knowledge and common common sense in the art and are not particularly limited by the present invention.

[0050] Obviously, the described embodiments are only some of the embodiments disclosed herein, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the disclosure, application, or use of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments disclosed herein without inventive effort are intended to fall within the scope of protection of this disclosure.

[0051] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0052] The present invention discloses a method for preparing multi-color carbon quantum dots based on surface ligand functionalization, which belongs to the field of nanotechnology. First, sky-blue luminescent carbon quantum dots were synthesized based on citric acid, and multi-color carbon quantum dots were prepared through filtration, dialysis purification, surface modification and other steps. Through a series of surface ligand functionalization strategies, effective regulation of emission in the range of 300nm-1000nm was achieved. The wavelength control method proposed in the present invention is simple and effective, and the synthesis method is simple and convenient. The carbon quantum dots prepared by the present invention have a high fluorescence quantum yield, which can reach up to 79%; the cost and toxicity are low, and the luminescent wavelength can be controlled to the entire visible spectrum and the near-infrared band.

[0053] Example 1 Preparation of multicolor carbon quantum dots based on surface ligand functionalization

[0054] 0.2g of anhydrous citric acid was placed in a crucible and heated at 200°C for 20 minutes to obtain carbon quantum dots. The obtained carbon quantum dots were dispersed in ethanol and filtered with a filter to obtain a carbon quantum dot solution. The carbon quantum dot solution was dialyzed against ethanol using a dialysis bag to purify the purified carbon quantum dots, which were designated T-CQDs. 10mg of the purified T-CQDs were then subjected to an amide coupling reaction with 36mg of o-phenylenediamine at 25°C in the presence of 50mg of EDC and 40mg of HOBt for 36 hours to obtain carbon quantum dots CQD1-1.

[0055] Figure 1 A is the transmission electron microscopy image of T-CQDs. From the results, it can be seen that the carbon quantum dots are evenly dispersed and the particle size is about 2.2±0.7nm ( Figure 1 B). In addition, the Fourier transform infrared spectroscopy data showed that the carbonyl peak position of the modified carbon quantum dots shifted from 1705 cm-1 of T-CQDs to -1 Move to 1710-1730cm -1 The modified carbon quantum dots showed the aromatic skeleton of the modified molecules, indicating the successful modification of carbon quantum dots ( Figure 2The photo of the successfully modified carbon quantum dots under 365nm ultraviolet light excitation is as follows. Figure 3 As shown. Figure 4 As shown in Figure 2, the quantum yield of functionalized carbon quantum dots is improved, with the highest quantum yield being 79%, corresponding to CQD3-1. The functionalized carbon quantum dots also show a red shift in the emission wavelength, as shown in Figure 2. Figure 5 As shown in Figure A, the control strategy of the first group is to change the number of amino groups, and the emission wavelengths of the functionalized carbon quantum dots obtained are 485nm, 505nm and 510nm, corresponding to CQD1-1, CQD1-2 and CQD1-3; the control strategy of the second group is to change the small molecule dipole moment, and the emission wavelengths of the functionalized carbon quantum dots obtained are 470nm, 530nm, 600nm and 650nm, corresponding to CQD2-1, CQD2-2, CQD2-3 and CQD2-4 ( Figure 5 B); The third group's control strategy is to change the symmetry of small molecules, and the emission wavelengths of the functionalized carbon quantum dots obtained are 370nm, 410nm, 540nm, 560nm and 650nm, corresponding to CQD3-1, CQD3-2, CQD3-3, CQD3-4 and CQD2-4 ( Figure 5 C); The fourth group's control strategy is to extend the conjugation, and the emission wavelengths of the functionalized carbon quantum dots obtained are 530nm, 750nm and 880nm, corresponding to CQD4-1, CQD4-2 and CQD4-3 ( Figure 5 D).

[0056] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0057] As used in the present invention, the term "comprising" is an open expression, that is, including the contents specified in the present invention, but not excluding other aspects.

[0058] As used herein, the term "about" when applied to a value means that some slight imprecision in the value is allowed in the calculation or measurement (approximately or reasonably close to the value by some method). If for some reason the imprecision specified by "about" is not understood in this conventional sense in the art, then "about" as used herein at least indicates the variation that may result from conventional methods of measuring or using such parameters.

[0059] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0060] Currently reported carbon quantum dots are often derived from direct microwave treatment or solvent thermal reaction of organic precursors, making it difficult to achieve controllable regulation of the emission wavelength of carbon quantum dots. In addition, the existing regulation methods have a narrow regulation range, which is difficult to meet the development needs of carbon quantum dots. The surface ligand modification strategy proposed in this invention is based on citric acid carbon quantum dots with carboxyl groups on the surface. By analyzing the relationship between the surface functional groups of carbon quantum dots and their luminescent properties, small molecules with different symmetry, dipole moment and degree of conjugation are introduced through the amide coupling reaction between carboxyl groups and amino groups to promote the charge transfer process of the carbon quantum dots themselves, successfully achieving the regulation of the wavelength of carbon quantum dots from 300nm to 1000nm.

[0061] The protection content of the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention and are protected by the appended claims.

Claims

1. A method for preparing multicolor carbon quantum dots based on surface ligand functionalization, characterized in that: The method comprises the following steps: (1) Anhydrous citric acid is placed in a crucible and heated to react to obtain carbon quantum dots; (2) dispersing the carbon quantum dots obtained in step (1) into a first solvent and filtering the solvent with a filter to obtain a carbon quantum dot solution; (3) then dialysis-purifying the carbon quantum dot solution obtained in step (2) in a second solvent using a dialysis bag, and then obtaining purified carbon quantum dots, which are recorded as T-CQDs; (4) The T-CQDs obtained in step (3) were subjected to amide coupling reaction with o-phenylenediamine, 1,2,4-triaminobenzene and 1,2,4,5-tetraaminobenzene under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 1-hydroxybenzotriazole, respectively, to obtain the corresponding carbon quantum dots, which were respectively recorded as CQD1-1, CQD1-2 and CQD1-3; or, The T-CQDs obtained in step (3) were subjected to amide coupling reaction with 4-iodo-o-phenylenediamine, 4-bromo-o-phenylenediamine, 4-chloro-o-phenylenediamine and 4-fluoro-o-phenylenediamine under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 1-hydroxybenzotriazole to obtain corresponding carbon quantum dots, which were respectively recorded as CQD2-1, CQD2-2, CQD2-3 and CQD2-4; or, The T-CQDs obtained in step (3) are subjected to amide coupling reaction with 3,4,5,6-tetrafluorobenzene-1,2-diamine, 4,5-fluoro-o-phenylenediamine, 3-fluoro-1,2-phenylenediamine, 3,4,5-trifluoro-1,2-diaminobenzene and 4-fluoro-1,2-phenylenediamine under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 1-hydroxybenzotriazole to obtain corresponding carbon quantum dots, which are respectively recorded as CQD3-1, CQD3-2, CQD3-3, CQD3-4 and CQD2-4; or, The T-CQDs obtained in step (3) were subjected to amide coupling reaction with 1,4-diaminonaphthalene, 4-fluoro-1-aminonaphthalene and 2,6-diaminoanthracene under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 1-hydroxybenzotriazole to obtain the corresponding carbon quantum dots, which were respectively recorded as CQD4-1, CQD4-2 and CQD4-3.

2. The preparation method according to claim 1, wherein In the step (1), the mass of the citric acid is 0.18-0.24 g; the temperature of the heating reaction is 200-240° C.; and the time of the heating reaction is 10-50 min.

3. The preparation method according to claim 1, wherein In the step (2), the first solvent is one or both of ethanol and methanol; the filter head used has a specification of 0.22-0.45 μm.

4. The preparation method according to claim 1, wherein In the step (3), the molecular weight of the dialysis bag is 100-500 Da; the second solvent is one or both of ethanol and methanol; and the dialysis time is 24-48 h.

5. The method for preparing multicolor carbon quantum dots based on surface ligand functionalization according to claim 1, wherein: In the step (4), the mass ratio of the T-CQDs to the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide is 10:(50-70); and / or, The mass ratio of the T-CQDs to the 1-hydroxybenzotriazole is 10:(30-50).

6. The method for preparing multicolor carbon quantum dots based on surface ligand functionalization according to claim 1, wherein: In the step (4), The temperature of the amide coupling reaction is 25-35°C; and / or, The amide coupling reaction time is 24-36 hours.

7. The method for preparing multicolor carbon quantum dots based on surface ligand functionalization according to claim 1, characterized in that: In the step (4), The mass ratio of the T-CQDs to the o-phenylenediamine, the 1,2,4-triaminobenzene and the 1,2,4,5-tetraaminobenzene is 10:(32-38); or The mass ratio of the T-CQDs to the 4-iodo-o-phenylenediamine, the 4-bromo-o-phenylenediamine, the 4-chloro-o-phenylenediamine, and the 4-fluoro-o-phenylenediamine is 10:(55-60); or The mass ratio of the T-CQDs to the 3,4,5,6-tetrafluorobenzene-1,2-diamine, the 4,5-fluoro-o-phenylenediamine, the 3-fluoro-1,2-phenylenediamine, the 3,4,5-trifluoro-1,2-diaminobenzene and the 4-fluoro-1,2-phenylenediamine is 10:(45-48); or The mass ratio of the T-CQDs to the 1,4-diaminonaphthalene, 4-fluoro-1-aminonaphthalene and 2,6-diaminoanthracene is 10:(72-78).

8. Multicolor carbon quantum dots based on surface ligand functionalization prepared by the method according to any one of claims 1 to 7.

9. The multicolor carbon quantum dots according to claim 8, wherein The surface-modified ligand small molecule structure of the multicolor carbon quantum dots is clear, the fluorescence wavelength is adjustable in the range of 300nm-1000nm, and the quantum yield is adjustable in the range of 18%-79%.

10. The method for preparing multicolor carbon quantum dots based on surface ligand functionalization according to any one of claims 1 to 7, and the use of multicolor carbon quantum dots in cell imaging according to claim 8.

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