Near-infrared II-region fluorescence emission carbon dot as well as preparation and application thereof

Abstract

The invention discloses a near-infrared II-region fluorescence emission carbon dot as well as preparation and application thereof. The preparation method of the near-infrared II-region fluorescence emission carbon dots, provided by the invention, comprises the following steps: (1) dissolving small organic molecules containing amino groups and small organic molecules containing boric acid groups in an acid-containing ethanol solution to obtain a carbon dot precursor solution; (2) carrying out volumetric thermal reaction on the carbon dot precursor solution obtained in the step (1) to obtain a carbon dot crude product; and (3) carrying out centrifugation, dialysis and freeze drying treatment on the carbon dot crude product obtained in the step (2) to obtain the near-infrared II-region fluorescence emission carbon dot. Compared with the prior art, the preparation method has the advantages that small organic molecules are used as a carbon source, boron and nitrogen elements are co-doped, and a benzene ring-containing conjugated structure in a precursor molecule is beneficial to forming a regular and ordered sp2 conjugated structure in the carbon dot in a reaction process and is beneficial to red shift of a fluorescence emission wave band, so that near-infrared II-region fluorescence emission of the carbon dot is realized.

Description

Technical Field

[0001] The present invention relates to the field of biotechnology, and particularly to a carbon dot with fluorescence emission in the second near-infrared region and its preparation and application. Background Art

[0002] Compared with traditional fluorescence imaging, fluorescence imaging technology in the second near-infrared region (900 - 1800 nm) can achieve deeper tissue penetration (5 - 20 mm), higher spatial resolution, and more sensitive detection, and has broader application prospects in the fields of tumor imaging and optical therapy. Since the pioneering research on the use of single-walled carbon nanotubes for in vivo NIR-II FI, more and more NIR-II fluorescent chromophores have been developed, including rare-earth doped nanoparticles, inorganic quantum dots, and gold nanoclusters. These nanomaterials have good optical and chemical properties, but there are potential chronic toxicities. Due to the quantum size effect, carbon dots can exhibit significant photoluminescence properties, with advantages such as tunable fluorescence emission spectra, easy modification, good biocompatibility, and biodegradability. In particular, in contrast to inorganic chromophores, carbon dots can effectively avoid the risks brought by foreign metal elements, promoting in vivo bioimaging and potential clinical practice.

[0003] For example, Chinese Patent No. CN117568025A discloses a preparation method of near-infrared carbon dots based on Bauhinia racemosa and its application in the field of bioimaging. The near-infrared carbon dots of Bauhinia racemosa are prepared by using the branches and leaves of Bauhinia racemosa as a carbon source through a one-step solvothermal method; these carbon dots are independent of excitation, and the quantum efficiency is 27.22% under 409 nm excitation, with good fluorescence properties. However, the fluorescence emission wavelength of these carbon dots is in the first near-infrared region of 600 - 800 nm, and the depth and accuracy of fluorescence tissue imaging are still insufficient. Summary of the Invention

[0004] In view of this, the present invention provides a carbon dot with fluorescence emission in the second near-infrared region and its preparation and application. The preparation method of the carbon dot with fluorescence emission in the second near-infrared region provided by the present invention includes the following steps:

[0005] (1) Dissolve an organic small molecule containing an amino group and an organic small molecule containing a boronic acid group in an acid-containing ethanol solution to obtain a carbon dot precursor solution;

[0006] (2) Subject the carbon dot precursor solution in step (1) to a volume thermal reaction to obtain a crude carbon dot product;

[0007] (3) Subject the crude carbon dot product in step (2) to centrifugation, dialysis, and freeze-drying treatments to obtain the carbon dot with fluorescence emission in the second near-infrared region.

[0008] Optionally, in the step (1), the organic small molecule containing an amino group is an amine containing a benzene ring, and is selected from at least one of 1,2-diaminonaphthalene, 2,3-diaminonaphthalene or 1,8-diaminonaphthalene; the organic small molecule containing a boronic acid group is selected from at least one of benzeneboronic acid, 1,4-benzenediboronic acid or 3-aminobenzeneboronic acid.

[0009] Optionally, in the step (1), the acid-containing ethanol solution is an anhydrous ethanol solution dissolved with hydrochloric acid or sulfuric acid, and the concentration of hydrochloric acid or sulfuric acid is 1 mol / L - 3 mol / L.

[0010] Optionally, in the step (1), in the carbon dot precursor solution, the concentration of the organic small molecule containing an amino group is 1 g / L to 10 g / L.

[0011] Optionally, in the step (1), in the carbon dot precursor solution, the concentration of the organic small molecule containing a boronic acid group is 1 g / L to 10 g / L.

[0012] Optionally, in the step (1), in the carbon dot precursor solution, the molar ratio of the organic small molecule containing an amino group to the organic small molecule containing a boronic acid group ranges from 1:1 to 1:3.

[0013] Optionally, in the step (2), the volumetric thermal reaction is carried out in a hydrothermal autoclave, the reaction temperature is 150 - 200 °C, and the reaction time is 6 - 20 h.

[0014] Optionally, in the step (3), the rotation speed of the centrifugation is 8000 - 15000 rpm; the dialysis time is 3 - 5 days, and the dialysis fluid is changed every 12 h; the temperature of the freeze-drying is -20 to -80 °C, and the drying time is 3 - 7 days.

[0015] The near-infrared II-region fluorescence-emitting carbon dots prepared by the method also belong to the protection scope of the present invention.

[0016] The application of the near-infrared II-region fluorescence-emitting carbon dots in fluorescence imaging also belongs to the protection scope of the present invention.

[0017] Beneficial effects:

[0018] The present invention uses an organic small molecule containing amino and boronic acid groups as a carbon source, and prepares carbon dots doped with boron and nitrogen elements in one step by a solvothermal method. The conjugated structure containing benzene rings in the precursor molecules helps to form a regular and ordered sp2 conjugated structure inside the carbon dots during the reaction process, while the doping of boron and nitrogen elements can effectively regulate the chemical composition and electron transition process of the carbon dots. At the structural and elemental composition levels, it is beneficial to the red shift of the fluorescence emission band, thereby realizing the fluorescence emission of carbon dots in the second near-infrared region. Compared with the prior art, the carbon dots of the present invention have the characteristics of easy availability of raw materials, simple preparation method, strong water solubility and easy dispersion, and high biocompatibility. In addition, the carbon dots of the present invention have a high fluorescence quantum yield and are easy to achieve efficient near-infrared fluorescence imaging of tissues. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For purposes of illustration and not limitation, the present invention will now be described in accordance with preferred embodiments of the present invention, particularly with reference to the accompanying drawings, in which:

[0020] Figure 1 is a transmission electron microscope photograph of the carbon dots prepared in Example 1 of the present invention.

[0021] Figure 2 is the X-ray photoelectron spectrum of the carbon dots prepared in Example 1 of the present invention.

[0022] Figure 3 is the high-resolution spectrum of the N1s peak in the X-ray photoelectron spectrum of the carbon dots prepared in Example 1 of the present invention.

[0023] Figure 4 is the near-infrared fluorescence emission spectrum of the carbon dots prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The technical solutions of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only illustrative and explanatory of the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection of the present invention.

[0025] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products, or can be prepared by known methods.

[0026] In the following embodiments, the size and morphology of the carbon dots are obtained by transmission electron microscopy. The fluorescence properties of the carbon dots are obtained by a near-infrared fluorescence emission spectrometer, the test light source is a laser, and the concentration is 1 mg / mL. The cytotoxicity of the carbon dots is characterized by the cell survival rate detected by the CCK-8 experiment.

[0027] The chemical reagents used in the experiments were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0028] Example 1: Preparation of Carbon Dots with Fluorescence Emission in the Second Near-Infrared Region

[0029] This example provides a kind of carbon dots with fluorescence emission in the second near-infrared region, and its preparation method includes the following steps:

[0030] (1) Prepare the carbon dot precursor solution: First, prepare an acidic ethanol solution, and the concentration of hydrochloric acid in the obtained acidic ethanol solution (prepared with hydrochloric acid) is 1 mol / L; then dissolve 1,2-diaminonaphthalene and phenylboronic acid in the acidic ethanol solution to obtain the carbon dot precursor solution, where the concentration of 1,2-diaminonaphthalene is 1 g / L, the concentration of phenylboronic acid is 1 g / L, and the molar ratio of 1,2-diaminonaphthalene to phenylboronic acid is 1:1.

[0031] (2) Take the carbon dot precursor solution obtained in step (1) and put it into a hydrothermal autoclave with a volume of 100 mL. The dosage of the carbon dot precursor solution is 1 / 3 of the volume of the hydrothermal autoclave, react in the hydrothermal autoclave for 12 h, the reaction temperature is 150 °C, and a hydrothermal product, that is, the crude carbon dots, is obtained after the reaction.

[0032] (3) Centrifuge the crude carbon dots obtained in step (2) at a speed of 10000 rpm, dialyze for 7 days, and the cut-off molecular weight of the dialysis bag (produced by Union Carbide Corporation, USA) used is 1000, and freeze-dry (Toshiba) at -80 °C for 7 days to obtain carbon dots.

[0033] Detect the carbon dots prepared in this example:

[0034] 1. Size and Morphology of Carbon Dots

[0035] The size and morphology of the carbon dots are all obtained by a transmission electron microscope (FEI Tecnai F20, Thermo Fisher Scientific).

[0036] The particle size of the carbon dots is 2.72 ± 0.53 nm, and they are evenly dispersed, as Figure 1 shown.

[0037] 2. Fluorescent Properties of Carbon Dots

[0038] The fluorescent properties of the carbon dots are all obtained by a near-infrared fluorescence emission spectrometer (FLS1000, Edinburgh Instruments), the test light source is a laser, and the concentration is 1 mg / mL.

[0039] Result: The X-ray photoelectron spectroscopy spectrum of the carbon dots is as Figure 2 shown, and it contains characteristic peaks of B1s at 195.2 eV, C1s at 284.1 eV, N1s at 399.2 eV, and O1s at 530.1 eV. The peaks of N 1s at 398.5, 399.2, 400.1, and 401.5 eV are respectively attributed to B-N bonds, pyridine N, pyrrole N, and graphitic N (Figure 3 )。The fluorescence of the carbon dots was further studied by near-infrared fluorescence spectroscopy at multiple excitation wavelengths, and the spectra showed fluorescence emission related to the characteristic excitation of the carbon dots. The carbon dots had the best near-infrared II-region fluorescence emission at 1230 nm under 808 nm light excitation ( Figure 4 ). The complex fluorescence emission behavior was related to the core formed by the conjugated structure of the precursor molecules' benzene rings in the carbon dots and the influence of boron and nitrogen element doping in the conjugated structure on the band gap and quantum size effect.

[0040] Example 2. Preparation of carbon dots with near-infrared II-region fluorescence emission

[0041] The specific method and steps for preparing the carbon dots with near-infrared II-region fluorescence emission in this example were the same as those in Example 1, except that: in step (2), the reaction temperature in the hydrothermal autoclave was 160 °C and the reaction time was 12 h.

[0042] Example 3. Preparation of carbon dots with near-infrared II-region fluorescence emission

[0043] The specific method and steps for preparing the carbon dots with near-infrared II-region fluorescence emission in this example were the same as those in Example 1, except that: in step (2), the reaction temperature in the hydrothermal autoclave was 180 °C and the time was 12 h.

[0044] Example 4. Preparation of carbon dots with near-infrared II-region fluorescence emission

[0045] The specific method and steps for preparing the carbon dots with near-infrared II-region fluorescence emission in this example were the same as those in Example 1, except that: in step (2), the reaction temperature in the hydrothermal autoclave was 200 °C and the time was 8 h.

[0046] Example 5. Preparation of carbon dots with near-infrared II-region fluorescence emission

[0047] The specific method and steps were the same as those in Example 1, except that: in step (2), the reaction temperature in the hydrothermal autoclave was 200 °C and the time was 4 h.

[0048] The carbon dots prepared in Examples 1 to 5 were detected.

[0049] (1) Particle size of the carbon dots: The detection method was the same as that in Example 1.

[0050] (2) Fluorescence emission peak position of the carbon dots: The detection method was the same as that in Example 1.

[0051] (3) Fluorescence lifetime (ns) of the carbon dots: Detected by a steady-state and transient fluorescence spectrometer (Edinburgh Instruments: FLS1000).

[0052] (4) Near-infrared fluorescence quantum yield (%) of the carbon dots: The absolute quantum yield was measured by a Hamamatsu quantum yield measurement system C9920-02G.

[0053] (5) Cell survival rate (%): The detection method is the same as that in Example 1.

[0054] The detection results are shown in Table 2.

[0055] Table 2

[0056]

[0057] The solvothermal reaction conditions have an obvious influence on the fluorescence emission characteristics of carbon dots. With the increase of reaction temperature (comparing Example 1, Example 2 and Example 3), and the increase of reaction time (Example 5 and Example 4), the nucleation of carbon dots becomes more complete, the particle size of carbon dots gradually increases, and the fluorescence emission peak position has a certain degree of red shift. At the same time, with the red shift of the emission wavelength, the non-radiative dissipation of energy increases, and the near-infrared fluorescence quantum yield of carbon dots shows a decreasing trend. The cell survival rate of all examples reaches more than 90%, indicating that the prepared carbon dots do not produce significant toxicity to cells and have good biocompatibility.

[0058] Example 6. Preparation of carbon dots with fluorescence emission in the second near-infrared region

[0059] The specific method and steps for preparing carbon dots with fluorescence emission in the second near-infrared region in this example are the same as those in Example 1, except that: in step (2), the reaction time in the hydrothermal autoclave is 6 h.

[0060] Example 7. Preparation of carbon dots with fluorescence emission in the second near-infrared region

[0061] The specific method and steps for preparing carbon dots with fluorescence emission in the second near-infrared region in this example are the same as those in Example 1, except that: in step (2), the reaction time in the hydrothermal autoclave is 10 h.

[0062] Example 8. Preparation of carbon dots with fluorescence emission in the second near-infrared region

[0063] The specific method and steps for preparing carbon dots with fluorescence emission in the second near-infrared region in this example are the same as those in Example 1, except that: in step (2), the reaction time in the hydrothermal autoclave is 16 h.

[0064] Example 9. Preparation of carbon dots with fluorescence emission in the second near-infrared region

[0065] The specific method and steps for preparing carbon dots with fluorescence emission in the second near-infrared region in this example are the same as those in Example 1, except that: in step (2), the reaction time in the hydrothermal autoclave is 20 h.

[0066] The carbon dots prepared in Examples 6 to 9 were detected, and the detection method was the same as that in Example 1.

[0067] The detection results are shown in Table 3.

[0068] Table 3

[0069]

[0070] Comparing Example 1 with Examples 6 - 9, at the same reaction precursor concentration, as the reaction time prolongs, the growth of carbon dots after nucleation becomes more sufficient, the particle size gradually increases, and the fluorescence emission peak shows a red - shift trend.

[0071] Example 10: Preparation of carbon dots with fluorescence emission in the second near - infrared region

[0072] The specific method and steps for preparing carbon dots with fluorescence emission in the second near - infrared region in this example are the same as those in Example 1, except that: in step (1), the concentration of 1,2 - diamino naphthalene is 2 g / L; the concentration of phenylboronic acid is 2 g / L.

[0073] Example 11: Preparation of carbon dots with fluorescence emission in the second near - infrared region

[0074] The specific method and steps for preparing carbon dots with fluorescence emission in the second near - infrared region in this example are the same as those in Example 1, except that: in step (1), the concentration of 1,2 - diamino naphthalene is 4 g / L; the concentration of phenylboronic acid is 4 g / L.

[0075] Example 12: Preparation of carbon dots with fluorescence emission in the second near - infrared region

[0076] The specific method and steps for preparing carbon dots with fluorescence emission in the second near - infrared region in this example are the same as those in Example 1, except that: in step (1), the concentration of 1,2 - diamino naphthalene is 6 g / L; the concentration of phenylboronic acid is 6 g / L.

[0077] Example 13: Preparation of carbon dots with fluorescence emission in the second near - infrared region

[0078] The specific method and steps for preparing carbon dots with fluorescence emission in the second near - infrared region in this example are the same as those in Example 1, except that: in step (1), the concentration of 1,2 - diamino naphthalene is 8 g / L; the concentration of phenylboronic acid is 8 g / L.

[0079] Example 14: Preparation of carbon dots with fluorescence emission in the second near - infrared region

[0080] The specific method and steps for preparing carbon dots with fluorescence emission in the second near - infrared region in this example are the same as those in Example 1, except that: in step (1), the concentration of 1,2 - diamino naphthalene is 10 g / L; the concentration of phenylboronic acid is 10 g / L.

[0081] Example 15: Preparation of carbon dots with fluorescence emission in the second near - infrared region

[0082] The specific method and steps for preparing carbon dots with fluorescence emission in the second near-infrared region in this example are the same as those in Example 1, except that: in step (1), the concentration of 1,2-diaminonaphthalene is 2 g / L; the concentration of phenylboronic acid is 4 g / L, and the molar ratio of 1,2-diaminonaphthalene to phenylboronic acid is 1:2.

[0083] Example 16. Preparation of carbon dots with fluorescence emission in the second near-infrared region

[0084] The specific method and steps for preparing carbon dots with fluorescence emission in the second near-infrared region in this example are the same as those in Example 1, except that: in step (1), the concentration of 1,2-diaminonaphthalene is 2 g / L; the concentration of phenylboronic acid is 6 g / L, and the molar ratio of 1,2-diaminonaphthalene to phenylboronic acid is 1:3.

[0085] The carbon dots prepared in Examples 10 to 16 were detected, and the detection method was the same as that in Example 1.

[0086] The detection results are shown in Table 4.

[0087] Table 4

[0088]

[0089] Comparing Example 1, Example 10, Example 11 and Example 12, at the same reaction temperature and time, the increase in the concentration of the carbon dot precursor is more conducive to the nucleation and growth of carbon dots. Therefore, the particle size of the carbon dots shows an increasing trend, and a larger particle size is conducive to the red shift of the fluorescence emission wavelength. However, a higher precursor concentration (Examples 13 and 14) causes the formation of precipitation, which is not conducive to the preparation of carbon dots. And increasing the concentration of phenylboronic acid in the precursor can also make the reaction more complete (Examples 1, 15 and 16), promoting the nucleation and growth of carbon dots.

[0090] Example 17. Preparation of carbon dots with fluorescence emission in the second near-infrared region

[0091] The specific method and steps for preparing carbon dots with fluorescence emission in the second near-infrared region in this example are the same as those in Example 1, except that: in step (1), the used 1,2-diaminonaphthalene is replaced with 2,3-diaminonaphthalene with an equal molar concentration.

[0092] Example 18. Preparation of carbon dots with fluorescence emission in the second near-infrared region

[0093] The specific method and steps for preparing carbon dots with fluorescence emission in the second near-infrared region in this example are the same as those in Example 1, except that: in step (1), the used 1,2-diaminonaphthalene is replaced with 1,8-diaminonaphthalene with an equal molar concentration.

[0094] Example 19. Preparation of carbon dots with fluorescence emission in the second near-infrared region

[0095] The specific method and steps for preparing carbon dots with near-infrared II region fluorescence emission in this example are the same as those in Example 1, except that: in step (1), the used phenylboronic acid is replaced with 1,4-benzenediboronic acid with an equimolar concentration.

[0096] Example 20. Preparation of carbon dots with near-infrared II region fluorescence emission

[0097] The specific method and steps for preparing carbon dots with near-infrared II region fluorescence emission in this example are the same as those in Example 1, except that: in step (1), the used phenylboronic acid is replaced with 3-aminophenylboronic acid with an equimolar concentration.

[0098] Perform the following performance tests on the carbon dots prepared in Example 1 and Examples 17 to 20.

[0099] DFT calculation of the energy difference (eV) between the LUMO and HOMO levels of carbon dots: By constructing a monolayer graphene-like structure conjugated with 24 benzene rings, and according to the positions of boron and nitrogen elements in the precursor molecule, element doping is carried out on the model of carbon dots. Select the functional / basis set as TD-PBE0-D3(BJ) / def2-TZVP, and use Gaussian 16 software to calculate the LUMO and HOMO levels.

[0100] Table 5

[0101]

[0102] It can be seen from the results of DFT calculation that the positions of amino groups in the benzene ring conjugate structure (Examples 1, 17, 18, and 20) and the number of boric acid groups (Examples 1 and 19) in the conjugate structure can adjust the HOMO and LUMO levels of carbon dots, thereby affecting the fluorescence emission performance of carbon dots.

[0103] Example 21. Preparation of carbon dots with a precursor molecule without a benzene ring conjugate structure

[0104] The specific method and steps for preparing carbon dots in this example are the same as those in Example 1, except that: in step (1), the used phenylboronic acid is replaced with boric acid with an equimolar concentration, and 1,2-diaminonaphthalene is replaced with ethylenediamine with an equimolar concentration.

[0105] Table 6

[0106] Test item Example 1 Example 21 Peak position of fluorescence emission of carbon dots (nm) 1230 467

[0107] Comparing Example 1 with Example 21, the structure of the precursor molecule has a significant impact on the fluorescence emission performance of the prepared carbon dots. When the precursor molecule does not contain a benzene ring conjugate structure (Example 21), the carbon dots cannot produce near-infrared II region fluorescence.

[0108] The above specific embodiments do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations and alternatives can occur depending on design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing near-infrared II region fluorescent emission carbon dots, characterized in that: The steps include: (1) dissolving an organic small molecule containing an amino group and an organic small molecule containing a boric acid group in an acid-containing ethanol solution to obtain a carbon dot precursor solution; (2) subjecting the carbon dot precursor solution of step (1) to a volumetric thermal reaction to obtain a crude carbon dot product; (3) The crude carbon dot product of step (2) is treated by centrifugation, dialysis and freeze-drying to obtain the near-infrared II region fluorescent carbon dots.

2. The method for preparing near-infrared II region fluorescent emission carbon dots according to claim 1, characterized in that: In the step (1), The organic small molecule containing an amino group is an amine containing a benzene ring, which is selected from at least one of 1,2-diaminonaphthalene, 2,3-diaminonaphthalene or 1,8-diaminonaphthalene; The organic small molecule containing a boronic acid group is selected from at least one of phenylboronic acid, 1,4-phenyldiboronic acid or 3-aminophenylboronic acid.

3. The method for preparing near-infrared II region fluorescent emission carbon dots according to claim 1, characterized in that: In the step (1), the acid-containing ethanol solution is an anhydrous ethanol solution dissolved with hydrochloric acid or sulfuric acid, wherein the concentration of the hydrochloric acid or sulfuric acid is 1 mol / L-3 mol / L.

4. The method for preparing near-infrared II region fluorescent emission carbon dots according to claim 1 or 2, characterized in that: In the step (1), the concentration of the amino-containing organic small molecules in the carbon dot precursor solution is 1 g / L to 10 g / L.

5. The method for preparing near-infrared II region fluorescent emission carbon dots according to claim 1 or 2, characterized in that: In the step (1), the concentration of the organic small molecules containing boric acid groups in the carbon dot precursor solution is 1 g / L to 10 g / L.

6. The method for preparing near-infrared II region fluorescent emission carbon dots according to claim 1 or 2, characterized in that: In the step (1), in the carbon dot precursor solution, the molar ratio of the organic small molecule containing an amino group to the organic small molecule containing a boric acid group is in the range of 1:1-1:

3.

7. The method for preparing near-infrared II region fluorescent carbon dots according to claim 1, characterized in that: In the step (2), the volumetric heat reaction is carried out in a hydrothermal reactor at a temperature of 150 to 200° C. and a reaction time of 6 to 20 hours.

8. The method for preparing near-infrared II region fluorescent carbon dots according to claim 1, characterized in that: In the step (3), The centrifugal speed is 8000-15000rpm; The dialysis time is 3-5 days, and the frequency of dialysate replacement is once every 12 hours; The freeze-drying temperature is -20 to -80°C, and the drying time is 3 to 7 days.

9. Carbon dots emitting near-infrared II fluorescence prepared by the method according to any one of claims 1 to 8.

10. Use of the near-infrared II region fluorescence emission carbon dots as claimed in claim 9 in fluorescence imaging.

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