Metal element doped luminescent carbon dots and preparation method and application thereof

Abstract

The application discloses a metal element doped luminescent carbon dot and a preparation method and application thereof. The metal element doped luminescent carbon dot comprises a carbon dot, metal cations loaded on the surface of the carbon dot and reduced metal cations dispersed in the core of the carbon dot. The reduced metal cations are prepared from the metal cations through photoinduction. The reduced metal cations form a coordination state energy level structure in the core of the carbon dot, the energy level structure produces an enhanced near-infrared two-region absorption spectrum band, and has an enhanced light-heat conversion performance in the two-region wave band. The prepared photoinduced metal element doped luminescent carbon dot has an increased particle size, enhanced fluorescent light emitting characteristics and excellent near-infrared two-region light-heat conversion characteristics, and can be used as a fluorescent imaging preparation and a photothermal preparation and applied to the fields of biological fluorescent imaging, photoacoustic imaging and photothermal therapy.

Description

Technical Field

[0001] This invention relates to the field of carbon nanomaterials technology, specifically to a metal element-doped luminescent carbon dot, its preparation method, and its application. Background Technology

[0002] Carbon nanomaterials have attracted widespread attention due to their non-toxic elemental properties and unique mechanical and optical properties. There is a great interest in promoting the application of carbon nanomaterials in biological applications. For example, carbon nanotubes and graphene nanoparticles are widely used in biofluorescence imaging and photothermal therapy due to their excellent absorption and emission as well as photostability. However, the unavoidable structural toxicity of these 1 / 2D carbon nanomaterials, with their potential risks of strong inflammatory cell infiltration, pulmonary edema, and granuloma formation, seriously hinders their clinical application.

[0003] Carbon dots (CDs) are a novel 0D carbon nanomaterial with a size of less than 10 nanometers. Unlike 0D fullerenes, carbon dots have good water solubility, excellent biocompatibility, and tunable optical properties. Numerous studies have shown that CDs have low or no cytotoxicity and can be excreted through the human kidney filtration system, making them promising candidates for biomedical applications. Existing methods for preparing carbon dots generally have the following problems: (1) The products are difficult to separate and the yield is low, making them difficult to utilize effectively. (2) The red light quantum efficiency of carbon dots is generally low, and there is a lack of effective means to control the absorption band in the near-infrared II region. Compared with the near-infrared I region (NIRI 700-1000 nm), the near-infrared II region (NIRI 1000-1700 nm) window exhibits excellent tissue penetration, lower tissue absorption, reduced thermal diffusion, and higher biocompatibility power (the allowable power of an 808 nm laser is 0.33 W / cm). 2 The permissible power for a 1064nm laser is 1W / cm². 2 However, there is currently a lack of effective strategies to tune the absorption band gap of CDs to NIRII. Theoretically, increasing the degree of conjugation can produce NIRII absorption, but it also leads to increased hydrophobicity of the material, thereby reducing the material's ability to be excreted in bulk. Summary of the Invention

[0004] To overcome the problems existing in the prior art, one objective of this invention is to provide a metal-doped luminescent carbon dot. A second objective is to provide a method for preparing the aforementioned metal-doped luminescent carbon dot. A third objective is to provide a carbon dot composite material. A fourth objective is to provide a fluorescence imaging formulation or photothermal formulation. A fifth objective is to provide applications of the fluorescence imaging formulation or photothermal formulation. This invention employs defect engineering to adjust the optical bandgap of the carbon dot, constructing the absorption bandgap in NIR II without altering the carbon dot material size and water solubility. The resulting metal-doped luminescent carbon dot exhibits extremely strong near-infrared II photothermal conversion capability while maintaining a high fluorescence quantum yield, thus solving the aforementioned technical problems.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention provides a metal element-doped luminescent carbon dot, comprising a carbon dot, a metal cation loaded on the surface of the carbon dot, and a reduced metal cation dispersed in the core of the carbon dot; wherein the reduced metal cation is obtained by photo-induced generation of the metal cation; and wherein the reduced metal cation forms a coordination state energy level structure in the core of the carbon dot.

[0007] Preferably, the metal cation is a sodium ion or a lithium ion.

[0008] Preferably, the carbon dots have a particle size of 2-6 nm.

[0009] The second aspect of this invention provides a method for preparing the metal element-doped luminescent carbon dots described in the first aspect, comprising the following steps:

[0010] S1. A carbon source, a nitrogen source, and a metal carbonate are mixed in an organic solvent and subjected to a solvothermal reaction to obtain carbon dots with metal cations on their surface; the carbon source has reducing properties.

[0011] S2. Light-induced carbon dots containing metal cations on their surface are prepared by irradiating them with strong light to obtain metal element-doped luminescent carbon dots.

[0012] Preferably, the carbon source is selected from citric acid, oxalic acid, or ascorbic acid.

[0013] Preferably, the nitrogen source is urea or ethylenediamine.

[0014] Preferably, the metal carbonate is one or more of sodium carbonate, sodium bicarbonate, lithium carbonate, and lithium bicarbonate.

[0015] Preferably, the organic solvent is formic acid.

[0016] Preferably, the mass ratio of the carbon source to the nitrogen source is 1:(1-6).

[0017] More preferably, the mass ratio of citric acid to urea is 1:(1-6). Even more preferably, the mass ratio of citric acid to urea is 1:(2-3).

[0018] Preferably, the ratio of the total mass of the carbon source and nitrogen source to the volume of the organic solvent is (0.05-0.5) g: 1 mL.

[0019] More preferably, the ratio of the total mass of citric acid and urea to the volume of formic acid is (0.05-0.5) g: 1 mL. Even more preferably, the ratio of the total mass of citric acid and urea to the volume of formic acid is 0.1 g / mL, 0.2 g / mL, 0.3 g / mL, or 0.4 g / mL.

[0020] Preferably, the molar ratio of the metal carbonate to the organic solvent is 1:(5-40).

[0021] More preferably, the molar ratio of sodium carbonate to formic acid is 1:(5-40). Even more preferably, the molar ratio of sodium carbonate to formic acid is 1:10, 1:15, 1:20, 1:25, 1:30, or 1:35.

[0022] Preferably, in step S1, the temperature of the solvothermal reaction is 160-200℃.

[0023] More preferably, in step S1, the temperature of the solvothermal reaction is 180-190°C.

[0024] Preferably, in step S1, the solvothermal reaction takes 2-6 hours.

[0025] More preferably, in step S1, the solvothermal reaction takes 2-4 hours.

[0026] Preferably, step S1 further includes the following steps: centrifugation after the solvothermal reaction, and drying the obtained solid to obtain red light emitting carbon dots encapsulated by metal cations.

[0027] More preferably, the centrifugal separation specifically involves adding an organic solvent that promotes the precipitation of carbon dots and is miscible with water to the system after the solvothermal reaction, followed by centrifugation to precipitate the solid. Further preferably, the organic solvent is selected from anhydrous ethanol, anhydrous methanol, etc., and can be one or more types. Further preferably, the ratio of the amount of organic solvent to the volume of the solution after the reaction is 1-4:1 (e.g., 1:1, 2:1, 3:1, 4:1, etc.), and an excess of organic solvent is preferable (e.g., a volume ratio of 2-3:1) to ensure thorough separation of the solid product.

[0028] More preferably, the centrifugation process is performed multiple times, with the number of centrifugations being 2-4 times, such as 2, 3, or 4 times. Specifically, the centrifugation speed is preferably 6000-12000 rpm, more preferably 8000 rpm. After centrifugation, the supernatant solution is removed, and the lower precipitate is freeze-dried to obtain highly efficient red light emitting carbon dots.

[0029] More preferably, freeze drying is used.

[0030] Preferably, in step S2, the light induction time is 1-60 min.

[0031] More preferably, in step S2, the light induction time is 2-10 minutes. Even more preferably, in step S2, the light induction time is 4-6 minutes.

[0032] Preferably, in step S2, the light-induced light intensity is 0.1-5 W / cm². 2 .

[0033] More preferably, in step S2, the light-induced light intensity is 0.8-2 W / cm². 2 .

[0034] Preferably, in step S2, the intense light is a laser with a wavelength of 530-980nm.

[0035] More preferably, in step S2, the wavelength of the laser is 730-980nm.

[0036] Preferably, step S2 further includes the following steps: dissolving carbon dots in water and using a laser with a wavelength of 530-980 nm to induce light irradiation within the absorption spectrum band of the carbon dot aqueous solution.

[0037] Preferably, step S2 further includes the following steps: after laser induction, deionized water is dialyzed for purification, and the resulting liquid is lyophilized.

[0038] More preferably, the molecular weight cutoff of the dialysis bag used for dialysis purification is 500-5000 Da.

[0039] More preferably, the dialysis time is 12-72 hours.

[0040] A third aspect of the present invention provides a carbon dot composite material comprising the metal element-doped luminescent carbon dots described in the first aspect and biomolecules; the biomolecules comprising amino acids, polypeptides or proteins.

[0041] Preferably, the mass ratio of the metal element-doped luminescent carbon dots to biomolecules is 1:(10-100).

[0042] The fourth aspect of the present invention provides a fluorescence imaging formulation or a photothermal formulation, wherein the raw materials for preparation include the metal element-doped luminescent carbon dots described in the first aspect, or the carbon dot composite material described in the third aspect.

[0043] The fifth aspect of the present invention provides the use of the fluorescent imaging formulation or photothermal formulation described in the fourth aspect in biofluorescence imaging, photoacoustic imaging, or in the preparation of photothermal therapeutic drugs.

[0044] The beneficial effects of this invention are:

[0045] 1) This invention provides a metal-doped luminescent carbon dot. The surface metal cations of the carbon dot migrate to the carbon-based core of the carbon dot via a photoinduced reduction reaction, forming a coordination state energy level structure with the core carbon. This energy level structure generates an enhanced near-infrared II absorption band and exhibits enhanced photothermal conversion performance in the II band. The prepared photoinduced metal-doped luminescent carbon dot composite formulation with protein, peptide, or amino acid molecules has increased particle size, enhanced fluorescence and luminescence properties, and maintains excellent near-infrared II photothermal conversion characteristics. It can be used as a fluorescence imaging formulation and a photothermal formulation in fields such as biofluorescence imaging, photoacoustic imaging, and photothermal therapy.

[0046] 2) The luminescent carbon dots prepared by this invention have efficient aqueous red light and near-infrared II photothermal effects. In addition, the aqueous solution of the carbon dot composite material can also be injected into mice via intravenous injection, achieving long-term retention in mouse tumors, thereby achieving the effect of therapeutic guidance. Furthermore, through the treatment of near-infrared II laser, effective near-infrared II photothermal therapy can be achieved. Attached Figure Description

[0047] Figure 1 The images are transmission electron microscopy (TEM) and atomic force microscopy (AFM) images of carbon dots; where (a) is a TEM image of CDs; (b) is a TEM image of ir-CDs; (c) is an AFM image of CDs; and (d) is an AFM image of ir-CDs.

[0048] Figure 2 A comparison of the infrared spectra of CDs and ir-CDs;

[0049] Figure 3 Comparison of XPS spectra of CDs and ir-CDs; where (a) is the full XPS spectrum; (b) is the fine spectrum of sodium; (c) is the N1s spectrum; and (d) is the C1s spectrum.

[0050] Figure 4The optical properties of CDs and ir-CDs are characterized; (a) and (b) are the changes in absorption and fluorescence of CDs during laser irradiation treatment, respectively; (c) and (d) are the three-dimensional fluorescence spectra of CDs and ir-CDs, respectively.

[0051] Figure 5 The absorption spectrum (a), emission spectrum (b), and fluorescence lifetime spectrum (c) of CDs, ir-CDs, and BSA-ir-CDs in dimethyl sulfoxide solution are shown.

[0052] Figure 6 The image shows the cytotoxicity test results of BSA-ir-CDs (a); the fluorescence images of CDs, ir-CDs, and BSA-ir-CDs after the same incubation time (b).

[0053] Figure 7 The images show in vitro photothermal experiments of CDs, ir-CDs, and BSA-ir-CDs (a)(b) and cell photothermal killing (c).

[0054] Figure 8 A control group (a) of BSA-ir-CDs before and after injection into mice and a metabolic diagram (b) of BSA-ir-CDs at different times in mice;

[0055] Figure 9 Figures show the results of a photothermal therapy experiment on mouse tumors using BSA-ir-CDs carbon dot materials; (a) shows the tumor retention after injection via the tail vein; (b) shows tumor sections before and after photothermal treatment; (c) shows changes in tumor volume; and (d) shows the therapeutic effect and growth of the tumor in the mice. Detailed Implementation

[0056] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from conventional commercial channels or prepared and isolated through simple synthesis; unless otherwise specified, the processes employed are conventional processes in the art.

[0057] Example 1

[0058] 1. Preparation of red-emitting carbon dots encapsulated by metal cations

[0059] Dissolve 2g of citric acid and 4g of urea in 30mL of formic acid, then add 4g of sodium carbonate and mix well. Place the liquid in a 50mL polytetrafluoroethylene high-pressure reactor and heat to react at 180℃ for 3 hours using an oven. After the reaction, add 60mL of ethanol to the solution, centrifuge at 8000 rpm, transfer the upper layer, take the lower precipitate, centrifuge 3 times, and freeze-dry the lower precipitate to obtain a purplish-black solid powder, namely red light emitting carbon dots encapsulated by metal cations, denoted as CDs.

[0060] 2. Preparation of photoinduced metal element doped luminescent carbon dots

[0061] The carbon dots prepared in step 1 were dissolved in water and induced using an 808 nm laser with an induction power of 1 W / cm. 2 The induction time was 5 min, then the solution was collected and purified by dialysis in a 500 Da dialysis bag for 12 h, with deionized water replaced every 4 hours. The solution was freeze-dried to obtain a black solid powder, namely near-infrared II photothermal carbon dots, denoted as ir-CDs.

[0062] 3. Preparation of carbon dot composite materials

[0063] Bovine serum albumin and the carbon dots from step 2 were mixed at a mass ratio of 1:100 at room temperature and then uniformly mixed by ultrasonic technology. The mixture was then dripped onto a support membrane using a syringe and naturally dried to obtain a carbon dot composite material, denoted as BSA-ir-CDs.

[0064] Examples 2-6

[0065] The preparation methods of Examples 2-6 are the same as those of Example 1, except that the dialysis times are 24h, 36h, 48h, 60h, and 72h, respectively.

[0066] Examples 7-11

[0067] The preparation methods of Examples 7-11 are the same as those of Example 1, except that the molecular weights of the dialysis bags are 1000 Da, 2000 Da, 3000 Da, 4000 Da, and 5000 Da, respectively.

[0068] Examples 12-17

[0069] The preparation methods of Examples 12-17 are the same as those of Example 1, except that the laser wavelengths are 530nm, 589nm, 630nm, 655nm, 730nm, and 980nm, respectively.

[0070] Examples 18-30

[0071] The preparation methods of Examples 18-30 are the same as those of Example 1, except that the laser power is 0.8 W / cm². 2 0.9w / cm 2 1.0w / cm 2 1.1w / cm 2 1.2w / cm 2 1.3w / cm 2 1.4w / cm 2 1.5w / cm 2 1.6w / cm 2 1.7w / cm 2 1.8w / cm 2 1.9w / cm 2 2.0w / cm 2 .

[0072] Examples 31-32

[0073] The preparation methods of Examples 31-32 are the same as those of Example 1, except that carbon dots are mixed with peptides and amino acids respectively.

[0074] Characterization of carbon dot materials

[0075] The morphologies of the raw carbon dots (CDs) and photoinduced metal element-doped luminescent carbon dots (ir-CDs) obtained in Example 1 were tested by transmission electron microscopy (TEM) and atomic force microscopy (AFM), and the results are as follows. Figure 1 As shown. Figure 1 It can be seen that the carbon dots are uniformly distributed, and the high-resolution transmission electron microscope (HRTEM) image shows 0.21 nm lattice stripes, which are attributed to the (100) crystal plane of graphene; the AFM image shows that the height of the carbon dots is between 2 and 6 nm.

[0076] Infrared spectroscopy and X-ray electron spectroscopy were performed on the CDs and ir-CDs of Example 1, and the results are as follows: Figure 2 and Figure 3 As shown, (a) is the XPS full spectrum; (b) is the fine spectrum of sodium; (c) is the N1s spectrum; and (d) is the C1s spectrum. From the fine spectrum of sodium... Figure 3 As can be seen from b, sodium changed from +1 to between 0 and +1, indicating a certain degree of reduction. It is speculated that sodium may have entered the carbon-based core of the carbon dots and formed new coordination structures with them. From... Figure 3 c and d show that before and after laser induction, the carbonyl and pyridine nitrogen groups on the carbon dot surface increase, while the hydroxyl groups decrease to a certain extent.

[0077] Carbon dot material performance testing

[0078] 1. The optical properties of the CDs from Example 1 were characterized. During the laser processing, the raw carbon dots... Figure 4 a and Figure 4 b shows that the absorption in the 900-1400nm range gradually increases, while the fluorescence weakens to some extent. Figure 4 c and Figure 4 d represents the three-dimensional fluorescence spectra of CDs and ir-CDs, respectively, which also confirms the fluorescence attenuation.

[0079] 2. To address the fluorescence attenuation observed in ir-CDs, BSA-ir-CDs were prepared by coating the carbon dot surface with bovine serum albumin, thus reducing surface energy dissipation of the carbon dots. Figure 5 The absorption (a), emission (b), and fluorescence lifetime spectra (c) of CDs, ir-CDs, and BSA-ir-CDs in dimethyl sulfoxide solution are shown. BSA-ir-CDs exhibit a significant enhancement in fluorescence compared to CDs and ir-CDs. Figure 5 c shows that the fluorescence lifetime has also increased from 18 ns to about 30 ns.

[0080] 3. Toxicity tests were performed on the carbon nanocomposite material obtained in Example 3. Cytotoxicity tests: CCK-8 assays were performed using 4T1 (breast adenocarcinoma cell line), ID8 (mouse ovarian surface epithelial cells), and MDA-MB-231 (human breast cancer cells) to evaluate the cytotoxicity of BSA-ir-CDs. First, approximately 5000 cells were seeded into 96-well plates and incubated for 12 hours. Then, the culture medium was replaced with 100 μL of fresh medium containing different concentrations of ir-Na-CD. After 48 hours of incubation, the cells were treated with the CCK-8 reagent for 3 hours, and then the absorbance at 450 nm was measured using a Tecan microplate reader (ThermoScientific). The results are as follows: Figure 6 As shown in a, ir-Na-CD at a concentration of 1 mg / mL is almost non-toxic.

[0081] Cell imaging: 4T1 cells were seeded into 6-well plates and incubated for 24 hours. Cells were then analyzed using CDs, ir-CDs, and BSA-ir-CDs (500 μg / mL). -1 4T1 cells were treated for 0.5 h and 2 h. Afterward, the culture medium was removed, and the cells were washed three times with PBS before fluorescence imaging. Live cells were observed using an Olympus IX73 inverted microscope equipped with a 40× objective lens, an excitation wavelength of 587 nm, and an LP filter of 610 nm. Cell fluorescence patterns of CDs, ir-CDs, and BSA-ir-CDs materials at the same incubation time were compared. Figure 6 b) BSA-ir-CDs exhibit better fluorescence imaging performance within the same incubation time.

[0082] 4. CDs, ir-CDs, and BSA-ir-CDs materials all possess certain photothermal properties. A photothermal test was conducted for comparison: 1 mL of each of the CDs, ir-CDs, and BSA-ir-CDs aqueous solutions (500 μg / mL) was added. -1 The sample was introduced into a quartz cuvette and then treated with a 1064nm laser at 1W·cm⁻¹. -2 Irradiation was performed at a power density of 10 nm for 10 minutes, using pure water as a negative control. A thermocouple probe connected to a digital thermometer was inserted perpendicularly into the BSA-ir-CDs aqueous solution along the optical path. The digital thermometer recorded the temperature of the BSA-ir-CDs aqueous solution at 10-second intervals. The temperature change of the BSA-ir-CDs aqueous solution over time was monitored under 1064 nm laser irradiation until the solution reached room temperature. Figure 7 As shown, cell killing assays were performed: 4T1 cells were seeded into 6-well plates and incubated for 24 hours. Cells were then killed using CDs, ir-CDs, and BSA-ir-CDs (500 μg / mL). -1 4T1 cells were treated with a 1064nm laser at 1W·cm⁻¹. -2 Cells were irradiated at a high power density for 10 minutes, with PBS used as a control group. For cell viability assays after laser exposure, a live / dead cell double staining kit was used for co-staining, and confocal fluorescence microscopy was used to monitor live and dead cells. The double staining kit contained calcein acetoxymethyl ester and propidium iodide; the former stained live cells only as green fluorescence, and the latter stained dead cells only as red fluorescence. Compared to CDs, ir-CDs and BSA-ir-CDs exhibited better in vitro photothermal conversion capabilities and superior cell-killing effects. It was also verified that BSA-ir-CDs achieved a significant enhancement in fluorescence without affecting the near-infrared II photothermal performance map.

[0083] 5. In vivo biodistribution imaging of ir-CDs was performed using Balb / c mice aged 6 to 8 weeks. Mice were intravenously (tail vein) injected with 100 μL of a BSA-ir-CDs aqueous solution (500 μg / mL) at different time points (0 h, 1 h, 3 h, 6 h, 12 h, 24 h, and 48 h). -1 Mice were then sacrificed to obtain organ imaging. A ChemDoc™ MP imaging system (Bio-Rad Laboratories, Inc.) was used to capture images using a 650 / 670 nm emission filter under 589 nm excitation. Throughout the experiment, no animals showed any signs of acute toxicological effects. The in vivo metabolic profile of the carbon dot composite material in Example 3 is shown below. Figure 8 As shown.

[0084] from Figure 8As shown in a and b, the photoinduced metal element-doped luminescent carbon dot composite material exhibits virtually no cytotoxicity at 500 ppm. The carbon dots injected into mice rapidly spread throughout their bodies and were metabolized and excreted through the kidneys. This demonstrates the biocompatibility of the composite material.

[0085] 6. A photothermal therapy experiment was conducted on mouse tumors using carbon dot material BSA-ir-CDs. Specific steps included: 5 × 10⁴ T₁ cells per mouse (5 × 10⁴ cells per mouse). 5 A tumor-bearing mouse model was established by subcutaneous injection into the upper back region of female BALB / c mice. Once the tumor volume reached ~80 mm... 3 Mice were randomly divided into five groups (n=5 per group), and each group was injected intratumorally with 100 μL PBS or BSA-ir-CDs (5000 μg·mL). -1 The groups were as follows: G1 (PBS: no irradiation), G2 (PBS: 1064nm laser), G3 (BSA-ir-CDs: intravenous injection + no irradiation), G4 (BSA-ir-CDs: intratumoral injection + no irradiation), G5 (BSA-ir-CDs: intravenous injection + 1064nm laser), and G6 (intratumoral injection + 1064nm laser). Mice were anesthetized with isoflurane during the procedure. Tumor volume was recorded every two days and calculated using the formula: V = ([tumor length] × [tumor width]²) / 2. Mice were euthanized on day 16 after the initial treatment, and the tumors were dissected to compare tumor size among the groups.

[0086] Figure 9 Figures show the results of a photothermal therapy experiment on mouse tumors using BSA-ir-CDs carbon dot composite materials; (a) shows tumor retention after tail vein injection; (b) shows tumor sections before and after photothermal treatment; (c) shows changes in tumor volume; and (d) shows the therapeutic effect and tumor growth in mice. Figure 9 Comparing G3 and G5, it can be seen that the carbon dot composite material BSA-ir-CDs has enhanced photothermal conversion performance in the second-zone wavelength region, and can effectively treat mouse tumors under 1064nm laser. Comparing G5 and G6, it can be seen that the aqueous solution of carbon dot composite material BSA-ir-CDs can also be injected into mice via intravenous injection, achieving long-term retention in mouse tumors, thereby achieving the effect of therapeutic guidance. Furthermore, it can be effectively treated with near-infrared second-zone laser to achieve near-infrared second-zone photothermal therapy.

[0087] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A metal element-doped luminescent carbon dot, characterized in that, Includes carbon dots, metal cations loaded on the surface of the carbon dots, and reduced metal cations dispersed in the core of the carbon dots; The reduced metal cation is prepared by photoinduced reduction of the metal cation; The reduced metal cations form a coordination state energy level structure in the carbon dot core; The method for preparing the metal element-doped luminescent carbon dots includes the following steps: S1. A carbon source, a nitrogen source, and a metal carbonate are mixed in an organic solvent and subjected to a solvothermal reaction to obtain carbon dots with metal cations on their surface; the carbon source has reducing properties. S2. Light-induced carbon dots containing metal cations on their surface are prepared by irradiating them with strong light to obtain metal element-doped luminescent carbon dots. The carbon source is selected from citric acid; the nitrogen source is urea; the organic solvent is formic acid; the metal carbonate is one or more of sodium carbonate, sodium bicarbonate, lithium carbonate, and lithium bicarbonate; and the intense light is a laser with a wavelength of 655-980nm.

2. The metal element-doped luminescent carbon dot according to claim 1, characterized in that, The metal cation is sodium ion or lithium ion.

3. The method for preparing metal element-doped luminescent carbon dots according to claim 1 or 2, characterized in that, Includes the following steps: S1. A carbon source, a nitrogen source, and a metal carbonate are mixed in an organic solvent and subjected to a solvothermal reaction to obtain carbon dots with metal cations on their surface; the carbon source has reducing properties. S2. Light-induced carbon dots containing metal cations on their surface are prepared by irradiating them with strong light to obtain metal element-doped luminescent carbon dots.

4. The method for preparing metal element-doped luminescent carbon dots according to claim 3, characterized in that, In step S1, the dosage conditions are selected from one or more of the following: A) The mass ratio of the carbon source to the nitrogen source is 1:(1-6); B) The ratio of the total mass of the carbon source and nitrogen source to the volume of the organic solvent is (0.05-0.5) g: 1 mL; C) The molar ratio of the metal carbonate to the organic solvent is 1:(5-40).

5. The method for preparing metal element-doped luminescent carbon dots according to claim 3, characterized in that, In step S1, the temperature of the solvothermal reaction is 160-200℃; And / or, the solvothermal reaction time is 2-6 h.

6. The method for preparing metal element-doped luminescent carbon dots according to claim 3, characterized in that, In step S2, the light induction time is 1-60 min; And / or, the light-induced illumination intensity is 0.1-5 W / cm². 2 .

7. A carbon dot composite material, characterized in that, It includes the metal element-doped luminescent carbon dots and biomolecules as described in claim 1 or 2; the biomolecules include amino acids, polypeptides or proteins.

8. The carbon dot composite material according to claim 7, characterized in that, The mass ratio of the metal element-doped luminescent carbon dots to amino acids is 1:(10-100).

9. A fluorescence imaging formulation or photothermal formulation, characterized in that, The raw materials for preparation include the metal element-doped luminescent carbon dots as described in claim 1 or 2, or the carbon dot composite material as described in claim 7 or 8.

10. The use of the fluorescent imaging agent or photothermal agent of claim 9 in biofluorescence imaging, photoacoustic imaging, or in the preparation of photothermal therapeutic drugs.

Images