Near-infrared second-region response nitrogen-doped carbon dots N-CDs and preparation method and application thereof

Abstract

The invention belongs to the technical field of nano photo-thermal materials, and provides nitrogen-doped carbon dots N-CDs responding to a near-infrared second region as well as a preparation method and application of the nitrogen-doped carbon dots N-CDs in order to solve the problems that an existing carbon dot material is poor in response to the near-infrared second region, too short in fluorescence emission wavelength and the like. The preparation method comprises the following steps: by taking citric acid and biuret as substrates, adding N, N-dimethylformamide (DMF) to carry out solvothermal reaction, generating a red product, dispersing the red product in a sodium hydroxide solution, carrying out ultrasonic treatment, centrifuging to obtain a black precipitate, and washing with hydrochloric acid and deionized water in sequence to obtain the near-infrared second-region response black nitrogen-doped carbon dots N-CDs. The fluorescence emission of the N-CDs has obvious red shift, and the light conversion capability of the N-CDs in a near-infrared second region (1060 nm) is enhanced. The technology is simple in preparation process, low in cost and short in reaction time. The quantum dot has the advantages of wide photoresponse range, high quantum efficiency and the like, can be applied to the field of photothermal diagnosis and treatment, and particularly can be applied to photothermal diagnosis and treatment, biological imaging and catalytic antibiosis of tumor cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of nano-photothermal materials, and specifically relates to nitrogen-doped carbon dots N-CDs responding to the second near-infrared region, and a preparation method and application thereof, especially in photothermal diagnosis and treatment, bio-imaging and catalytic antibacterial applications. Background Art

[0002] The incidence and mortality of malignant tumors are showing a continuous upward trend. Cancer has seriously endangered human health and life. In recent years, related technologies such as photothermal diagnosis and fluorescence imaging have begun to gain more attention due to their advantages such as non-contact and non-ionization, and are expected to be applied in the field of cancer diagnosis and treatment.

[0003] Photothermal therapy (PTT) is a treatment method that uses nanomaterials with photothermal conversion capabilities to convert light energy into heat energy under the irradiation of an external light source, causing the body to heat up locally and destroy the biologically active molecules in the cells (such as protein denaturation, enzyme inactivation, etc.), thereby killing cancer cells. In vivo bioluminescence imaging can directly and quickly measure tumor growth, metastasis, and drug response in various cancer models. Its characteristic is that its extremely high sensitivity allows tiny tumor lesions (as few as a few hundred cells) to be detected. Compared with traditional methods, its sensitivity is greatly improved, making it very suitable for quantitative analysis of tumor growth in vivo.

[0004] Near infrared light (NIR) has been widely used as an advanced diagnostic and therapeutic tool in the medical field due to its non-invasive controllability, high resolution and deep tissue penetration. It has significant significance in the comprehensive diagnosis and treatment of NIR biological windows (NIR-I, 650-950 nm; NIR-II, 1000-1700nm). In particular, near infrared II light has good application prospects in the treatment of deep tumors due to its excellent penetration ability.

[0005] Traditional photosensitive materials have the disadvantages of short fluorescence emission wavelength and low photothermal conversion. In order to red-shift the fluorescence emission wavelength and improve the photothermal conversion efficiency, people have used various methods to explore new photothermal conversion materials. Carbon dots (CDs) are a new type of carbon-based fluorescent nanomaterials with a size of less than 10 nm. They have the advantages of being environmentally friendly, biocompatible, tunable photoluminescence, high quantum yield, and unique physical and chemical properties. However, most carbon dot materials have poor response in the near-infrared region II and the fluorescence emission wavelength is not as good as that in the near-infrared region, which greatly limits the application of carbon dots in the near-infrared region II and in the field of tumor diagnosis and treatment. Summary of the invention

[0006] In order to solve the problems of poor response and short fluorescence emission wavelength of current carbon dot materials in near-infrared region II, the present invention provides a nitrogen-doped carbon dot N-CDs responsive to near-infrared region II and its preparation method and application. The present invention uses citric acid as a carbon source, doping nitrogen elements to effectively improve the light conversion efficiency of carbon dots, enhance the response ability of carbon dots in near-infrared region II, and red-shift the fluorescence emission wavelength to the near-infrared region II band.

[0007] The present invention is realized by the following technical scheme: a nitrogen-doped carbon dot N-CDs responsive to the second region of near infrared, using citric acid and biuret as substrates, adding N,N-dimethylformamide DMF to carry out solvent thermal reaction, generating a red product and then dispersing it in a sodium hydroxide solution, ultrasonically treating it and centrifuging it to obtain a black precipitate, washing it with hydrochloric acid and deionized water in turn, and obtaining black nitrogen-doped carbon dot N-CDs responsive to the second region of near infrared.

[0008] The method for preparing the nitrogen-doped carbon dots N-CDs that respond in the second near-infrared region comprises the following specific steps: (1) Preparation of N-CDs: 2 g of citric acid and 4.5 g of biuret were completely dissolved in 30-40 mL of DMF to form a transparent colorless solution. The mixed solution was transferred into a reactor and the temperature was raised to 180 °C for 4 h at a heating rate of 10 °C / min. The mixture was naturally cooled to room temperature and the red product obtained by the hydrothermal reaction was dispersed in 50 mg / mL sodium hydroxide solution. The ultrasonic power was 80 W for 5 min and the mixture was centrifuged at 12,000 rpm for 10 min to obtain a black precipitate, which was N-CDs. (2) Purification of N-CDs: The obtained black precipitate was washed with 1 mol / L hydrochloric acid and deionized water in turn, and freeze-dried to obtain a black powder; the freeze-drying temperature was controlled at -40°C and the time was controlled at 24-72 h.

[0009] Further, the amount of DMF used was 40 mL.

[0010] Furthermore, the specific purification method in step (2) is as follows: the obtained black precipitate is dissolved with 1 mol / L hydrochloric acid, and the solution is centrifuged at 8000-10000 rpm for 10 min to collect the precipitate; then the precipitate is dissolved with deionized water, and the solution is centrifuged at 8000-10000 rpm for 10 min to collect the black precipitate, after the precipitate is dissolved with hydrochloric acid once, the precipitate is dissolved again with deionized water for 3 times; finally, the sample is placed in a vacuum freeze dryer and freeze-dried for 24-72 h to obtain the purified N-CDs powder.

[0011] The present invention also provides the use of the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region or the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region obtained by the preparation method as a photosensitizer in antibacterial sterilization. The target bacteria of the antibacterial sterilization is Staphylococcus aureus; the concentration of the N-CDs aqueous solution is 0.2-1.0 mg / L, and the initial concentration of Staphylococcus aureus is 1×10 5 CFU / mL; 1060 nm and 808 nm light sources for 10 min.

[0012] The present invention also provides the use of the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region or the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region obtained by the preparation method as photosensitizers in eliminating tumors. The tumor cells are human prostate cancer cells DU145, and the concentration of the N-CDs is 1.0 mg / mL; 1.0 W / cm 2 , 808 nm or 1060 nm laser irradiation for 10 min.

[0013] The present invention also provides the use of the nitrogen-doped carbon dots N-CDs responding to the second near-infrared region or the nitrogen-doped carbon dots N-CDs responding to the second near-infrared region obtained by the preparation method as photosensitizers in fluorescence imaging. The concentration of N-CDs is 0.5 mg / kg, and the fluorescence intensity is tested after treatment for 1 hour.

[0014] The nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region prepared by the present invention are particularly suitable as photosensitizers for killing bacteria, eliminating tumors and fluorescence imaging in the field of photothermal diagnosis and treatment, and have a wide range of applications.

[0015] The present invention doped nitrogen into carbon dots CDs, successfully red-shifted the fluorescence emission wavelength of carbon dots to the near-infrared band and enhanced the light conversion ability of carbon dots in the near-infrared second region (1060 nm). The preparation process of the fluorescent photothermal material N-CDs provided by the present invention is simple, low in cost, and short in preparation time. The fluorescent photothermal material N-CDs provided by the present invention has the advantages of a wide light response range and high quantum efficiency, and can be applied to the field of photothermal diagnosis and treatment, especially in the fields of photothermal treatment, antibacterial and fluorescence imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Figure 1 is a transmission electron microscope image of nitrogen-doped fluorescent photothermal material N-CDs; Figure 1: A is a TEM image of N-CDs; B is a particle size distribution diagram of N-CDs; Figure 2The photothermal capacity curve of nitrogen-doped fluorescent photothermal material N-CDs under near-infrared light (1060 nm / 808 nm). In the figure: A is the temperature rise curve of 1.0 mg / mL N-CDs solution over time under 808 nm laser irradiation with different powers; B is 1.0 W / cm 2 Figure 1 shows the temperature rise curves of N-CDs solutions with different concentrations under 808 nm laser irradiation; C shows the temperature rise curves of 1.0 mg / mL N-CDs solutions under 1060 nm laser irradiation with different powers; D shows the temperature rise curves of 1.0 W / cm 2 The temperature rise curves of N-CDs solutions with different concentrations under 1060nm laser irradiation over time; Figure 3 Figure 2 shows the ability of nitrogen-doped fluorescent photothermal materials N-CDs to kill Staphylococcus aureus under near-infrared light (1060 nm / 808 nm). In the figure: A is the bactericidal ability of 1.0 mg / mL N-CDs solution under 808 nm or 1060 nm laser irradiation of different powers; B is 1.0 W / cm 2 The bactericidal ability of N-CDs solutions with different concentrations under 808nm or 1060nm laser irradiation; Figure 4 This is a cytotoxicity test diagram of nitrogen-doped fluorescent photothermal material N-CDs under near-infrared light (1060 nm / 808 nm); Figure 5 Live and dead cell staining of nitrogen-doped fluorescent photothermal material N-CDs under near-infrared light (1060 nm / 808 nm); Figure 6 This is the in vivo fluorescence imaging of nitrogen-doped fluorescent photothermal material N-CDs; Figure 7 This is a graph showing the in vivo anti-tumor ability of nitrogen-doped fluorescent photothermal materials N-CDs under near-infrared light (1060 nm / 808 nm). DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the disclosure and materials cited therein are hereby incorporated by reference.

[0019] Technical equivalents to the specific embodiments described that are apparent to those skilled in the art using no more than routine experimentation are intended to be encompassed by this application.

[0020] The experimental methods in the following examples are all conventional methods unless otherwise specified. The instruments and equipment used in the following examples are all conventional laboratory instruments and equipment unless otherwise specified; the experimental materials used in the following examples are all purchased from conventional biochemical reagent stores unless otherwise specified.

[0021] Example 1: A method for preparing near-infrared responsive nitrogen-doped carbon dots N-CDs, using citric acid and biuret as raw materials, adding DMF for solvothermal reaction, dispersing the generated red product in a sodium hydroxide solution, ultrasonically treating and centrifuging to obtain a black precipitate, washing with hydrochloric acid and deionized water in turn, to obtain black nitrogen-doped carbon dots N-CDs. The specific steps are as follows: (1) Preparation of N-CDs: Weigh 2 g of citric acid and 4.5 g of biuret and dissolve them in 40 mL of DMF. After they are fully dissolved, a clear colorless solution is formed. The solution is transferred into a 100 mL reactor and the temperature of the hydrothermal oven is increased at a rate of 10 °C / min. The reaction is carried out at 180 °C for 4 h. The reaction is cooled to room temperature and the black precipitate generated by the hydrothermal reaction is collected and dissolved in 50 mg / mL sodium hydroxide solution. Ultrasonic treatment is performed for 5 min and the reaction is centrifuged at 8000-12000 rpm for 10 min to obtain the black precipitate.

[0022] (2) The obtained black precipitate was dissolved with 1 mol / L hydrochloric acid, and the solution was centrifuged at 8000-10000 rpm for 10 min to collect the black precipitate; then, the black precipitate was dissolved with deionized water, and the solution was centrifuged at 8000-10000 rpm for 10 min to collect the black precipitate, and the process was repeated three times; the sample was placed in a vacuum freeze dryer at -40°C and freeze-dried for 24-72 h to obtain purified N-CDs powder.

[0023] The N-CDs prepared in Example 1 were tested by electron microscopy. Figure 1 As shown, it can be observed that the N-CDs sample is uniformly dispersed and has a uniform particle size distribution.

[0024] Experimental Example 1: Photothermal capacity test of N-CDs: The photothermal conversion capacity of N-CDs was evaluated under 1060 nm and 808 nm laser irradiation. The specific steps are as follows: the light sources are 1060 nm and 808 nm lasers, the laser diameter is 10 mm, and the power is determined to be 1.0 W / cm 2The N-CDs samples were prepared into aqueous solutions with concentrations of 0.2 mg / mL, 0.4 mg / mL, 0.6 mg / mL, 0.8 mg / mL, and 1.0 mg / mL, and 200 μL was taken into a 96-well plate. The temperature of the samples was recorded at 2 min, 4 min, 6 min, 8 min, and 10 min. The experimental results are shown in Figure 2. Figure 2 As shown in the figure, the results show that after irradiation at 1060 nm and 808 nm for 10 min, the sample temperature can reach a maximum of 59 ℃ and 71 ℃, respectively.

[0025] Experimental Example 2: N-CDs sterilization activity test: Staphylococcus aureus was selected as the sterilization target, and 1060 nm and 808 nm lasers were selected as light sources, respectively, with a light intensity of 1.0 W / cm 2 N-CDs solutions (0.2 mg / L, 0.4 mg / L, 0.6 mg / L, 0.8 mg / L, 1.0 mg / L) were mixed with the initial concentration of about 1×10 5 After the mixture of 1000 CFU / mL of Staphylococcus aureus was evenly mixed, it was placed in a sterile reactor and irradiated with light for 10 min. After dilution with sterile PBS solution, it was evenly spread on the agar medium and placed in an incubator at 37°C for 24 h. The number of colonies was calculated to determine the number of live bacteria. The results of the light sterilization experiment are shown in Figure 2. Figure 4 As shown in the figure, the sterilization rates of Staphylococcus aureus can reach up to 95% and 90% after irradiation at 1060 nm and 808 nm for 10 min, respectively.

[0026] Experimental Example 3: N-CDs cytotoxicity test: DU145 cells were selected as the experimental object of this experiment, and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) was used as a stain to evaluate the cytotoxicity of N-CDs. 1060 nm and 808 nm lasers were selected as light sources, respectively, with a light intensity of 1.0 W / cm 2 PBS and different concentrations of N-CDs (0.2 mg / mL, 0.4 mg / mL, 0.6 mg / mL, 0.8 mg / mL, 1.0 mg / mL) were added to DU145 cells (1×10 4 The cells were then gently rinsed with PBS to remove the unabsorbed samples and the cells were further incubated for 24 h.

[0027] In the phototoxicity experiment group, the light source was turned on for 10 min. After laser irradiation, the cells were further incubated for 24 h, and each well was stained with MTT stain. After 4 h, the supernatant of each well was aspirated, DMSO was added, and cell survival was detected at a wavelength of 492 nm.

[0028] The results of cytotoxicity experiments were as follows Figure 5 As shown, the results showed that under dark conditions, after 10 min of illumination, DU145 cells still maintained a high cell viability of more than 80% after co-incubation with N-CDs for 24 h, indicating that the toxicity of N-CDs to cells was negligible and had good biocompatibility.

[0029] In the absence of N-CDs, there was no obvious damage to DU145 cells under illumination. In contrast, N-CDs samples of different concentrations under 1060 nm and 808 nm near-infrared light had a strong killing effect on DU145 tumor cells, which was attributed to the photothermal effect and efficient reactive oxygen production ability of N-CDs, and its temperature increase ability and reactive oxygen production ability were positively correlated with the sample concentration. This resulted in a significant increase in the degree of cell damage as the concentration of N-CDs co-incubated with DU145 cells increased. When the sample concentration increased to 1 mg / mL, the cell survival rates of DU145 cells co-incubated with it under 1060 nm and 808 nm near-infrared light irradiation decreased to about 31% and 41%, respectively. Therefore, these results show that N-CDs have a significant killing effect on tumor cells under near-infrared light irradiation, verifying its excellent photothermal conversion efficiency, indicating that N-CDs have great application potential in the photothermal therapy of tumors.

[0030] Experimental Example 4: N-CDs live and dead cell staining experiment: DU145 cells were selected as the experimental object of this experiment, and 1060 nm and 808 nm lasers were selected as light sources, respectively, with a light intensity of 1.0 W / cm 2 DU145 cells were seeded into 24-well plates (5 × 10 4 The cells were cultured in PBS (100 μg / well) for 24 h, and the old culture medium was replaced with fresh culture medium containing N-CDs solution (1 mg / mL) and incubated for 4 h to allow cell uptake. The cells were then washed with PBS and fresh culture medium was added. The light source was turned on for 10 min, and the control group was cultured in the dark for 10 min. Calcein-AM / PI staining was added for 30 min and laser confocal imaging was performed.

[0031] Live and dead cell staining results Figure 6As shown, the results show that in the control group, cells co-incubated with PBS showed strong green fluorescence signals under no light conditions, indicating good survival conditions of the cells. At the same time, cells in the PBS group also showed strong green fluorescence under near-infrared light 1060 nm and 808 nm. This shows that light alone cannot induce any actual damage to tumor cells. At the same time, bright green fluorescence was observed in DU145 cells co-incubated with N-CDs under no light conditions, indicating that the cells are in good condition under this condition and the toxicity of N-CDs to cells is negligible, once again verifying the good biocompatibility of N-CDs.

[0032] In contrast, when N-CDs were combined with near-infrared light, they effectively induced a significant degree of cell death, with the vast majority of cells in the field of view being dyed red, again demonstrating that N-CDs have great potential for application in the photothermal therapy of tumors.

[0033] Experimental Example 5: In vivo fluorescence imaging test of N-CDs: The feasibility of fluorescence imaging of N-CDs in tumor-bearing mice was studied by IVIS spectral imaging system (IVIS LuminaIII; Perki Elmer, Waltham, MA, USA). (DU145) tumor-bearing mice were selected as experimental subjects. PBS and N-CDs were injected intratumorally into tumor-bearing mice (0.5 mg / kg). In vivo fluorescence imaging was performed using IVIS Lumina III mouse imaging system 1 h, 2 h, 4 h, 8 h and 24 h after injection. After 24 h, the mice were euthanized, and the main organs and tumors were collected to record their fluorescence intensity.

[0034] In vivo fluorescence imaging results Figure 7 As shown in the figure, after the sample was injected, a strong fluorescence signal from N-CDs was observed in the tumor area. The fluorescence intensity increased with the injection time and reached the highest at 1 h after injection. This shows that the uptake of N-CDs by cells in the tumor area reached the highest level. After that, it tended to steadily decrease over time. Eight hours after the injection, the fluorescence intensity of the tumor site was significantly weakened. Until 24 h later, the fluorescence of the tumor site needed to be adjusted higher than the background intensity to be observed.

[0035] Experimental Example 6: Application of N-CDs photothermal diagnosis and treatment: DU145 (human prostate cancer cell) tumor-bearing mice were divided into 6 groups (three mice in each group) for in vivo anti-tumor experiments. They were (1) PBS, (2) N-CDs, (3) 1060 nm light irradiation, (4) 808 nm light irradiation, (5) N-CDs+1060 nm, and (6) N-CDs+808 nm. After intratumoral injection of PBS or N-CDs (1.0 mg / mL, 200 μL), 808 nm or 1060 nm (1.0 W / cm 2 ) laser irradiation for 10 min, and the temperature of the tumor site was monitored by photothermal imaging. The weight of mice was recorded every two days, and the tumor volume of each group of mice was measured and calculated as follows: V = (width 2 × length) / 2. After 14 days of treatment, the mice were killed and the tumors and major organs (heart, liver, spleen, lung, and kidney) were removed for H&E staining. Figure 7 As shown, the results showed that the tumor could be completely ablated under 808 nm light irradiation, and the tumor volume was greatly reduced under 1060 nm irradiation.

[0036] Example 2: A method for preparing near-infrared responsive nitrogen-doped carbon dots N-CDs, wherein the amount of DMF used is 30 mL, and the rest of the method is the same as that described in Example 1.

[0037] Example 3: A method for preparing near-infrared responsive nitrogen-doped carbon dots N-CDs, wherein the amount of DMF used is 35 mL, and the rest of the method is the same as that described in Example 1.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nitrogen-doped carbon dot N-CDs with near-infrared second-region response, characterized in that: Citric acid and biuret were used as substrates, and N,N-dimethylformamide (DMF) was added for solvothermal reaction. The red product was dispersed in sodium hydroxide solution, and then ultrasonically treated and centrifuged to obtain a black precipitate. The black precipitate was washed with hydrochloric acid and deionized water in turn to obtain black nitrogen-doped carbon dots N-CDs that responded in the second near-infrared region.

2. A method for preparing the nitrogen-doped carbon dots N-CDs with near-infrared second-region response according to claim 1, characterized in that: The specific steps are as follows: (1) Preparation of N-CDs: 2 g of citric acid and 4.5 g of biuret were completely dissolved in 30-40 mL of DMF to form a transparent colorless solution. The mixed solution was transferred into a reactor and heated to 180 °C for 4 h at a heating rate of 10 °C / min. The mixture was naturally cooled to room temperature and the red product obtained by the hydrothermal reaction was dispersed in 50 mg / mL sodium hydroxide solution. The product was ultrasonically treated at 80 W for 5 min and centrifuged at 8000-12000 rpm for 10 min to obtain a black precipitate, which was N-CDs. (2) Purification of N-CDs: The obtained black precipitate was washed with 1 mol / L hydrochloric acid and deionized water in turn, and freeze-dried to obtain a black powder; the freeze-drying temperature was controlled at -40°C and the time was controlled at 24-72 h.

3. The preparation method according to claim 2, characterized in that: The amount of DMF used was 40 mL.

4. The preparation method according to claim 2, characterized in that: The specific purification method in step (2) is as follows: the obtained black precipitate is dissolved with 1 mol / L hydrochloric acid, and the solution is centrifuged at 8000-10000 rpm for 10 min to collect the precipitate; then the precipitate is dissolved with deionized water, and the solution is centrifuged at 8000-10000 rpm for 10 min to collect the black precipitate, after the precipitate is dissolved with hydrochloric acid once, the precipitate is dissolved again with deionized water for 3 times; finally, the sample is placed in a vacuum freeze dryer and freeze-dried for 24-72 h to obtain the purified N-CDs powder.

5. Use of the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region as described in claim 1 or the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region obtained by the preparation method described in any one of claims 2 to 4 as photosensitizers in antibacterial and sterilization.

6. The use according to claim 5, characterized in that: The target bacteria of the antibacterial sterilization is Staphylococcus aureus; the concentration of the N-CDs aqueous solution is 0.2-1.0 mg / L, and the initial concentration of Staphylococcus aureus is 1×10 5 CFU / mL; 1060 nm and 808 nm light sources for 10 min.

7. Use of the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region as described in claim 1 or the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region obtained by the preparation method described in any one of claims 2 to 4 as photosensitizers in eliminating tumor cells.

8. The use according to claim 7, characterized in that: The tumor cells are human prostate cancer cells DU145, the concentration of N-CDs is 1.0 mg / mL; 1.0 W / cm 2 , 808 nm or 1060 nm laser irradiation for 10 min.

9. Use of the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region according to claim 1 or the nitrogen-doped carbon dots N-CDs responsive to the second near-infrared region obtained by the preparation method according to any one of claims 2 to 4 as a photosensitizer in fluorescence imaging; characterized in that: The concentration of N-CDs was 0.5 mg / kg, and the fluorescence intensity was tested after 1 hour of treatment.

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