A magnetic field-assisted synthesis of a nitrogen-doped carbon quantum dot near-infrared II fluorescent probe, its preparation method, and its application.

Abstract

This invention discloses a near-infrared II fluorescent probe of nitrogen-doped carbon quantum dots synthesized with magnetic field assistance, its preparation method, and its application, belonging to the field of carbon-based nanomaterial preparation and biomedical technology. The method includes the following steps: using piperazine ketone as a precursor, acetone as a solvent, and hydrogen peroxide as an oxidant, a solvothermal reaction is carried out under an external magnetic field to obtain the target carbon quantum dots. The obtained carbon quantum dots exhibit good near-infrared II fluorescence response characteristics, with an emission peak above 1000 nm under 808 nm excitation conditions, and are sensitive to Cu. 2+ It exhibits a significant selective fluorescence quenching response. The obtained carbon quantum dots achieve near-infrared II emission, which is beneficial for reducing scattering from biological tissues and interference from background autofluorescence, and has potential applications in deep tissue imaging and tumor imaging. Simultaneously, these carbon quantum dots exhibit Cu... 2+ It has good selective recognition capabilities and can be used for metal ion detection, bioanalysis and related fluorescent probe construction.

Description

Technical Field

[0001] This invention relates to the fields of carbon-based nanomaterial preparation and biomedical technology, specifically to a nitrogen-doped carbon quantum dot near-infrared II fluorescent probe synthesized with magnetic field assistance, its preparation method, and its application. Background Technology

[0002] Carbon quantum dots, as a novel type of carbon-based fluorescent nanomaterial, have attracted widespread attention in recent years in fields such as bioimaging, chemical sensing, and disease diagnosis due to their advantages including small particle size, good water solubility, high biocompatibility, easy surface modification, and relatively simple preparation methods. Compared with traditional semiconductor quantum dots, carbon quantum dots typically exhibit lower toxicity and better environmental friendliness, thus possessing significant research value in biomedical applications.

[0003] In recent years, near-infrared II fluorescence imaging, with its operating wavelength typically between 1000 and 1700 nm, has shown significant advantages over visible light and near-infrared I imaging in areas such as vascular imaging, tumor identification, lymphatic tracing, and deep tissue imaging due to its lower biological tissue scattering, weaker tissue autofluorescence interference, and greater imaging penetration depth. Existing near-infrared II fluorescent probes mainly include organic small molecule dyes, rare earth-doped nanomaterials, quantum dots, and other inorganic nanomaterials. However, organic small molecule dyes often suffer from insufficient photostability and easy photobleaching; rare earth nanomaterials frequently exhibit low luminescence efficiency or complex surface modifications; and some semiconductor or inorganic nanomaterials may have complex compositions, limited biocompatibility, or potential long-term safety risks. Therefore, developing novel fluorescent nanoprobes that combine good biocompatibility, simple preparation methods, and near-infrared II emission performance is of great significance.

[0004] In comparison, carbon quantum dots combine the good biocompatibility of carbon-based materials with the optical response characteristics of fluorescent materials, making them potential candidate materials for constructing near-infrared II fluorescent probes. However, the fluorescence emission of existing carbon quantum dots is mostly concentrated in the visible light regions such as blue, green, and red, with some extending into the near-infrared I region. Carbon quantum dots that can truly achieve near-infrared II emission are still relatively few. To shift the emission wavelength of carbon quantum dots towards longer wavelengths, existing technologies typically employ heteroatom doping, designing precursors with larger conjugated structures, enhancing surface oxidation, constructing surface defect states, or using synergistic carbonization with multiple reactive components to regulate their energy level structure. For example, patent CN114921245A prepared near-infrared I carbon dots with a main emission peak at 745 nm by constructing conjugated domains formed by the fusion of conjugated molecules; patent CN110615426A obtained upconversion near-infrared carbon dots with emission peaks in the 760–790 nm range by exfoliating red-emitting carbon nanodots. Although the above methods can improve the luminescence behavior of carbon quantum dots to some extent, the following problems still exist: First, the emission peaks of the obtained carbon quantum dots are mostly located in the visible light region or near-infrared region I, and it is difficult to stably enter the near-infrared region II band; Second, some synthesis methods require the synergistic effect of multiple precursors or complex post-processing steps, resulting in a cumbersome preparation process and poor reproducibility.

[0005] Furthermore, existing research on the external field-assisted control of carbon quantum dot formation and fluorescence properties remains limited, particularly regarding the controllable preparation of near-infrared II fluorescent carbon quantum dots using an external magnetic field in a solvothermal reaction. Meanwhile, technologies that combine near-infrared II fluorescence emission performance with Cu... 2+ Selective carbon quantum dot probes are also relatively scarce. Therefore, it is necessary to develop a probe that is easy to prepare, has good luminescence properties, can achieve near-infrared II emission, and is effective against Cu. 2+ The selectively responsive carbon quantum dots and their preparation methods are of significant research importance and application value. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to solve the problem of the short emission wavelength and insufficient near-infrared II luminescence performance of existing carbon quantum dots.

[0007] The present invention solves the above-mentioned technical problems through the following technical means:

[0008] This invention proposes a method for preparing near-infrared II fluorescent carbon quantum dots using magnetic field-assisted synthesis, comprising the following steps: using piperazine ketone as a precursor, acetone as a solvent, and hydrogen peroxide as an oxidant, a solvothermal reaction is carried out under the action of an external magnetic field to obtain near-infrared II fluorescent carbon quantum dots.

[0009] Piperazinone: refers to 2-piperazinone, foreign name Piperazin-2-one, CAS number: 5625-67-2.

[0010] Preferably, the ratio of piperazine ketone, acetone, and hydrogen peroxide is 80-120 mg: 15-21 mL: 2-4 mL; more preferably, it is 80-120 mg: 15-21 mL: 3 mL; even more preferably, it is 100 mg: 18 mL: 3 mL.

[0011] Preferably, the strength of the external magnetic field is 6~9T; more preferably 7~8T; even more preferably 7.6T.

[0012] Preferably, the solvothermal reaction conditions are 160~200℃ for 6~10h; more preferably 170~190℃ for 7~9h; and even more preferably 180℃ for 8h.

[0013] Preferably, the hydrogen peroxide is a 20-40 wt% H2O2 aqueous solution; more preferably, it is 25-35 wt%; even more preferably, it is 30 wt%.

[0014] Preferably, the process further includes dialysis and freeze-drying of the product after the solvothermal reaction.

[0015] Preferably, the dialysis uses a dialysis bag with a molecular weight cutoff of 13,000 to 15,000 Da; more preferably, it is 14,000 Da.

[0016] Preferably, the dialysis time is 20-28 hours; more preferably, it is 24 hours.

[0017] Preferably, the method includes the following steps: mixing piperazine ketone, acetone, and hydrogen peroxide to obtain a reaction solution; placing the obtained reaction solution in a reaction vessel and heating it in an external magnetic field device; cooling it to room temperature after the reaction is completed, transferring the product to a dialysis bag, dialyzing it in pure water, collecting the dialyzed aqueous solution, and freeze-drying it to obtain the final product.

[0018] Preferably, the method includes the following steps: mixing piperazine, acetone, and hydrogen peroxide in a ratio of 100 mg: 15 mL: 3 mL to obtain a reaction solution; placing the obtained reaction solution in a reaction vessel and reacting it for 8 h in an external magnetic field device at a magnetic field strength of 9 T and a temperature of 180 °C; after the reaction is completed, cooling to room temperature, transferring the product to a dialysis bag with a molecular weight cutoff of 14000 Da, dialyzing it in pure water, collecting the dialysis aqueous solution, and freeze-drying it to obtain the final product.

[0019] The present invention also proposes near-infrared II fluorescent carbon quantum dots prepared by the above preparation method.

[0020] This invention also proposes the application of the aforementioned near-infrared II fluorescent carbon quantum dots as near-infrared II fluorescent imaging probes.

[0021] This invention also proposes the above-mentioned near-infrared II fluorescent carbon quantum dots as Cu 2+ Application of ion-specific detection probes.

[0022] The beneficial effects of this invention are as follows: (1) This invention uses the organic molecule piperazine ketone as a precursor molecule, acetone as a solvent, and hydrogen peroxide as an oxidant to obtain nitrogen-doped carbon quantum dots through a solvothermal reaction under the action of an external magnetic field. These quantum dots exhibit excellent long-wavelength fluorescence emission characteristics in the near-infrared II region and show good fluorescence emission characteristics in this band for Cu. 2+ It exhibits selective fluorescence quenching response. The fluorescence properties of the carbon quantum dots can be controllably adjusted by regulating the applied magnetic field strength. The near-infrared II fluorescent carbon quantum dots prepared in this invention can be applied to tumor imaging, biodetection, and other fields.

[0023] (2) Compared with the existing carbon quantum dot fluorescence emission mainly concentrated in the visible light region, the carbon quantum dot fluorescence emission peak prepared in this invention is located in the near-infrared II band, which can effectively reduce biological tissue scattering and autofluorescence interference, thereby improving the imaging penetration depth and signal-to-noise ratio, and is suitable for deep tissue and tumor imaging.

[0024] (3) Compared with traditional synthesis methods, this invention establishes a regulatory relationship between magnetic field strength and the fluorescence performance of carbon quantum dots by introducing an external magnetic field as a reaction control method. As the magnetic field strength increases, the fluorescence intensity of the obtained carbon quantum dots is significantly enhanced, realizing the controllable adjustment of luminescence performance.

[0025] (4) The carbon quantum dot exhibits a high degree of spectral density for Cu in the near-infrared II region. 2+ Exhibiting specific fluorescence quenching properties in Cu 2+ In its presence, the fluorescence signal is almost completely quenched, while causing minimal interference with other metal ions, making it suitable for use in Cu. 2+ Selective detection has application value in the fields of bioanalysis and early disease diagnosis.

[0026] (5) The obtained carbon quantum dots have good near-infrared II fluorescence response characteristics, with emission peaks above 1000 nm under 808 nm excitation conditions, and exhibit good fluorescence response to Cu. 2+ It exhibits a significant selective fluorescence quenching response. Compared to existing carbon quantum dots that primarily emit in the visible light region, the carbon quantum dots obtained in this invention achieve near-infrared II emission, which is beneficial for reducing biological tissue scattering and background autofluorescence interference, and has potential applications in deep tissue imaging and tumor imaging. Simultaneously, these carbon quantum dots exhibit Cu... 2+It has good selective recognition capabilities and can be used for metal ion detection, bioanalysis and related fluorescent probe construction.

[0027] Of course, implementing any product or method of the present invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0028] Figure 1 These are transmission electron microscopy (TEM) images of near-infrared II region fluorescent carbon quantum dots from Example 1 of this invention. Figure 2 This shows the particle size distribution of near-infrared II fluorescent carbon quantum dots in Example 1 of the present invention; Figure 3 The image shows the HAADF image of the near-infrared II region fluorescent carbon quantum dots in Example 1 of this invention. Figure 4 This is an atomic force microscope image of near-infrared II fluorescent carbon quantum dots in Example 1 of the present invention; Figure 5 This is an X-ray mapping image of near-infrared II fluorescent carbon quantum dots in Embodiment 1 of the present invention; Figure 6 This is a Raman characterization image of near-infrared II fluorescent carbon quantum dots in Example 1 of the present invention; Figure 7 The infrared spectrum of the near-infrared II region fluorescent carbon quantum dots in Example 1 of this invention; Figure 8 The X-ray photoelectron spectrum of the near-infrared II region fluorescent carbon quantum dots in Example 1 of this invention; Figure 9 The X-ray photoelectron spectrum (C1s) of the near-infrared II region fluorescent carbon quantum dots in Example 1 of this invention; Figure 10 The X-ray photoelectron spectrum N 1s spectrum of the near-infrared II region fluorescent carbon quantum dots in Example 1 of this invention; Figure 11 The X-ray photoelectron spectrum (O 1s) of the near-infrared II region fluorescent carbon quantum dots in Example 1 of this invention; Figure 12 This is the fine structure spectrum of the near-infrared II fluorescent carbon quantum dots in Example 1 of the present invention, showing the near-edge X-ray absorption of the K-side near-edge of the C element. Figure 13 This is the fine structure spectrum of the near-infrared II region fluorescent carbon quantum dots of the N element near the K edge in Example 1 of the present invention; Figure 14 This is the fine structure spectrum of the near-infrared II fluorescent carbon quantum dots in Example 1 of the present invention, showing the near-edge X-ray absorption of the K-side near-edge of the O element. Figure 15The electron paramagnetic resonance spectrum of the near-infrared II region fluorescent carbon quantum dots in Example 1 of this invention; Figure 16 This is the ultraviolet-visible-near-infrared absorption spectrum of the near-infrared II region fluorescent carbon quantum dots in Example 1 of the present invention; Figure 17 The fluorescence emission spectrum of the near-infrared II region fluorescent carbon quantum dots in Example 1 of this invention; Figure 18 This is a fluorescence stability diagram of the near-infrared II region fluorescent carbon quantum dots in Example 1 of the present invention; Figure 19 These are photographs of the near-infrared II fluorescent carbon quantum dot solution in Example 1 of this invention under natural light and near-infrared imaging conditions; Figure 20 The images show the fluorescence emission spectra of near-infrared II fluorescent carbon quantum dots in different solvent systems in Example 1 of this invention. Figure 21 The fluorescence response spectra of near-infrared II fluorescent carbon quantum dots to different metal ions in Example 1 of this invention are shown. Figure 22 These are near-infrared imaging images of near-infrared II fluorescent carbon quantum dots and different metal ion composite systems in Example 1 of this invention; Figure 23 This is a schematic diagram illustrating the synthesis principle of near-infrared II fluorescent carbon quantum dots in Example 1 of the present invention; Figure 24 This is a comparison of the fluorescence emission spectra of the weak near-infrared II fluorescent carbon quantum dots in Comparative Example 1 and the carbon dots in Example 1 of the present invention; Figure 25 Near-infrared imaging images of weak near-infrared II fluorescent carbon quantum dots in Comparative Example 1 and carbon dots in Example 1 of this invention; Figure 26 The fluorescence emission spectra of weak near-infrared II fluorescent carbon quantum dots in Comparative Example 2, ordinary fluorescent carbon quantum dots in Comparative Example 3, and carbon dots in Example 1 are shown. Figure 27 Near-infrared imaging images of weak near-infrared II fluorescent carbon quantum dots in Comparative Example 2, ordinary fluorescent carbon quantum dots in Comparative Example 3, and carbon dots in Example 1 of the present invention. Figure 28 This is a comparison of the fluorescence emission spectra of ordinary fluorescent carbon quantum dots in Comparative Example 4 and carbon dots in Example 1 of the present invention; Figure 29 Near-infrared imaging images of ordinary fluorescent carbon quantum dots in Comparative Example 4 and carbon dots in Example 1 of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art.

[0030] Unless otherwise specified, the test materials and reagents used in the following examples are commercially available or prepared by known methods.

[0031] Unless otherwise specified, all techniques or conditions described in the embodiments can be performed in accordance with the techniques or conditions described in the literature in this field or in the product manual. Unless otherwise specified, the quantitative experiments in the following embodiments are all repeated three times or more, and the results are averaged.

[0032] Example 1: A method for preparing near-infrared II fluorescent carbon quantum dots with magnetic field assistance includes the following steps: Step 1: Weigh 100 mg piperazine, 15 mL acetone, and 3 mL hydrogen peroxide into a 50 mL beaker, and sonicate for 10 min to obtain a homogeneous solution. (The hydrogen peroxide is a 30 wt% aqueous solution of H2O2.) Step 2: Transfer the mixed solution obtained in Step 1 to a 25 mL Teflon-coated hydrothermal reactor and place it inside an external magnetic field device. Perform a solvothermal reaction at 180°C for 8 hours at a magnetic field strength of 9 T. Step 3: After the reaction is complete, allow the solution to cool naturally to room temperature. Transfer the reaction solution obtained in Step 2 to a dialysis bag with a molecular weight cutoff of 14000 Da. Dialyze the solution in pure water for 24 hours, changing the dialysis water every 24 hours for a total of 3 times. After dialysis, collect the solution outside the bag and freeze-dry it. The resulting brown powder is the near-infrared II fluorescent carbon quantum dot.

[0033] Transmission electron microscopy (TEM) images of near-infrared II region fluorescent carbon quantum dots in Example 1 are shown below. Figure 1 As shown.

[0034] Example 2: The difference between this embodiment and Embodiment 1 is that: Step 1 consists of 120 mg piperazine, 16 mL acetone, and 2 mL hydrogen peroxide, with the rest being the same as in Example 1.

[0035] Example 3: The difference between this embodiment and Embodiment 1 is that: Step 2 involves a solvothermal reaction at 200°C for 6 hours, with the rest of the process the same as in Example 1.

[0036] Example 4: The difference between this embodiment and Embodiment 1 is that: In step 2, the magnetic field strength is 6T, and the rest is the same as in Example 1.

[0037] Example 5: The difference between this embodiment and Embodiment 1 is that: The dosages of piperazine, acetone, and hydrogen peroxide were 80 mg, 15 mL, and 2 mL, respectively. Hydrogen peroxide is a 40wt% aqueous solution of H2O2; At a magnetic field strength of 7T; The reaction conditions were: 160℃, 10h; Dialysis bags with a molecular weight cutoff of 13,000 Da were used; The rest is the same as in Example 1.

[0038] Example 6: The difference between this embodiment and Embodiment 1 is that: The dosages of piperazine, acetone, and hydrogen peroxide were 120 mg, 21 mL, and 4 mL, respectively. Hydrogen peroxide is a 20wt% aqueous solution of H2O2; At a magnetic field strength of 7.6T; The reaction conditions were: 200℃, 6h; Dialysis bags with a molecular weight cutoff of 15,000 Da were used; The rest is the same as in Example 1.

[0039] The quantum dots prepared in Examples 2-6 have similar properties to those in Example 1.

[0040] Comparative Example 1: Preparation of weak near-infrared II fluorescent carbon quantum dots The difference between this comparative example and Example 1 is that: Step 2: No external magnetic field device is added, and the solvothermal reaction is carried out in a normal vacuum drying oven, and the rest is the same as in Example 1.

[0041] Comparative Example 2: Preparation of weak near-infrared II fluorescent carbon quantum dots The difference between this comparative example and Example 1 is that: Step 1: 1 mL of hydrogen peroxide, the rest is the same as in Example 1.

[0042] Comparative Example 3: Preparation of ordinary fluorescent carbon quantum dots The difference between this comparative example and Example 1 is that: Step 1: no hydrogen peroxide is added, and the rest is the same as in Example 1.

[0043] Comparative Example 4: Preparation of ordinary fluorescent carbon quantum dots The difference between this comparative example and Example 1 is that: Step 1: 120 mg benzophenone, the rest is the same as in Example 1.

[0044] First, the morphology of the near-infrared II fluorescent carbon quantum dots prepared in Example 1 was characterized, such as... Figure 1 As shown, the sample observed by transmission electron microscopy is uniformly nearly ellipsoidal in shape, with a diameter of about 5 nm.

[0045] like Figure 2 Further statistical Gaussian fitting distribution analysis showed that the average size of the carbon dot sample was approximately 5.4 nm.

[0046] like Figure 3 As shown, the high-resolution transmission electron microscope image shows that the sample of Example 1 has clear lattice fringes with a lattice spacing of about 0.21 nm, corresponding to the graphitic carbon (100) crystal plane.

[0047] like Figure 4 Medium atomic force microscopy images show that the carbon quantum dots in Example 1 are uniformly dispersed on the substrate surface, exhibiting a near-ellipsoidal shape. Height profile analysis indicates that the height of the carbon quantum dots is approximately 5–6 nm. Figure 4 illustration).

[0048] The X-ray diffraction pattern of the sample in Example 1 is as follows: Figure 5 As shown, the spectrum exhibits a relatively broad diffraction peak near 2θ ≈ 24°, corresponding to the (002) crystal plane of graphitic carbon, indicating that the obtained carbon dots have a certain degree of graphitization structure.

[0049] like Figure 6 As shown, Raman spectroscopy was performed on the near-infrared II fluorescent carbon quantum dots in Example 1. In the spectrum, the D peak represents the defect peak of disordered carbon, and the G peak represents the degree of graphitization. The I peak of this carbon dot... D / I G The ratio of 1.8 indicates that the sample contains many structural defects and disordered carbon structures, while still maintaining a certain degree of sp. 2 Carbon conjugated structure.

[0050] like Figure 7 The figure shows infrared measurements of near-infrared II carbon quantum dots from Example 1 using a Fourier transform infrared spectroscopy (FTIR) instrument. The positions of absorption peaks at different wavelengths represent the different functional group bond sites they possess. (Figure 3440 cm⁻¹) -1 The peak position represents the OH / NH stretching vibration, 2960 cm⁻¹ -1 The peak position represents the CH stretching vibration, 1640 cm⁻¹ -1 The peak position represents the C=O stretching vibration, 1385 cm⁻¹ -1 The peak position represents the stretching vibration of CN.

[0051] like Figure 8 As shown, the X-ray photoelectron spectroscopy full spectrum of the near-infrared II fluorescent carbon quantum dots in Example 1 shows that the sample is composed of three elements: C, O, and N, with atomic percentages of 79.1%, 12.9%, and 8.0%, respectively, verifying the successful doping of nitrogen.

[0052] like Figure 9 , 10 11 and 11 are the C1s, N1s, and O1s spectra of the near-infrared II carbon quantum dot X-ray photoelectron spectrum in Example 1, respectively, and the bond positions represented by the corresponding characteristic peaks are marked in the image.

[0053] The K-side absorption spectrum of the nonmetallic synchrotron radiation C of the carbon point in Example 1 is as follows: Figure 12 As shown, with Figure 9 The results are consistent, with characteristic absorption peaks appearing at approximately 286.5 eV and 288.0 eV, which can be attributed to electronic transitions related to C–O and C=O, respectively. Furthermore, the absorption characteristics near approximately 289.7 eV indicate the presence of certain sp2 atoms in the sample. 2 Conjugated carbon structure.

[0054] The K-side absorption spectrum of the nonmetallic synchrotron radiation N of the carbon point in Example 1 is as follows: Figure 13 As shown, with Figure 10 The results are consistent, with distinct characteristic absorption peaks appearing at approximately 400.0 eV, 402.8 eV, and 407.0 eV, which can be attributed to pyrrole-type nitrogen, graphitic nitrogen, and C–N-related nitrogen chemical environments, respectively.

[0055] The K-side absorption spectrum of the nonmetallic synchrotron radiation O of the carbon point in Example 1 is as follows: Figure 14 As shown, a distinct characteristic absorption peak appears at approximately 532.1 eV, which can be attributed to an electronic transition related to C=O, indicating the presence of carbonyl oxygen-containing functional groups in the obtained carbon dots.

[0056] like Figure 15 As shown, the electron paramagnetic resonance spectrum of the carbon quantum dots in Example 1 exhibits a significant resonance signal near g = 2.003. This g value is close to the typical characteristic value of defect-related unpaired electrons in carbon materials, indicating that there are paramagnetic centers in the obtained carbon dots caused by edge defects, dangling bonds, or surface states.

[0057] like Figure 16 This is the UV-Vis-NIR absorption spectrum of the sample from Example 1. The absorption signals of this carbon quantum dot at 203 nm and 290 nm can be attributed to sp[…]. 2The sample exhibits π–π transitions in the conjugated carbon structure and n–π transitions related to surface functional groups. Furthermore, an absorption signal is observed near 960 nm, suggesting the possible presence of low-energy electronic transitions related to luminescence or related surface and defect state energy levels in the near-infrared region.

[0058] like Figure 17 The figure shows the fluorescence emission spectrum of the sample from Example 1 under 808 nm laser excitation. As shown, the main emission peak of this carbon quantum dot is located at 1018 nm, which is in the near-infrared II region, and the emission spectrum has a wide coverage.

[0059] like Figure 18 This indicates that the near-infrared II fluorescence of the carbon dot did not show significant attenuation within a 60-minute test period, demonstrating good fluorescence stability.

[0060] like Figure 19 The results visually demonstrate that the sample in Example 1 exhibits a bright fluorescence signal under 808nm laser irradiation, further showcasing its excellent near-infrared II fluorescence imaging capability.

[0061] like Figure 20 As shown, the carbon quantum dots in Example 1 exhibit near-infrared II fluorescence emission in different solvents, but their emission intensity and spectral profile show significant differences, indicating that the samples have significant solvent-dependent fluorescence response characteristics.

[0062] like Figure 21 This demonstrates the fluorescence response behavior of the carbon dots in Example 1 to different metal ions. The sample responds to Cu... 2+ It exhibits a significant fluorescence quenching response, while other metal ions have little effect on its fluorescence, indicating that this carbon quantum dot exhibits a strong fluorescence quenching response to Cu. 2+ It has good selective detection capabilities.

[0063] like Figure 22 The near-infrared fluorescence imaging results of the carbon quantum dots obtained in Example 1 in the presence of different metal ions are presented visually. Correspondingly, Cu was added... 2+ The near-infrared fluorescence imaging signal of the sample was significantly weakened afterward, while strong fluorescence could still be observed under other metal ion conditions, further verifying the effect of the carbon quantum dots on Cu. 2+ The specific quenching phenomenon.

[0064] Figure 21-22 The specific experimental methods are as follows: Metal ion fluorescence response detection: Prepare 10mM Na solutions respectively. + K + Mn 2+ Ce 3+ Cu 2+ Fe 3+ Co2+ and Ni 2+ Metal ion solutions. Take 900 μL of a 1 mg / mL near-infrared II fluorescent carbon quantum dot aqueous solution into a centrifuge tube, add 100 μL of the above-mentioned different metal ion solutions, mix well, and incubate at room temperature for 10 min. After incubation, record the near-infrared II fluorescence emission spectra of each system under 808 nm excitation conditions to obtain... Figure 21 Simultaneously, each test system was placed under a near-infrared imaging system for fluorescence imaging, yielding... Figure 22 By comparing the changes in fluorescence spectra and imaging signal intensity of carbon quantum dots in the presence of different metal ions, their fluorescence response behavior to different metal ions and their effect on Cu were evaluated. 2+ Its selective recognition capability.

[0065] The near-infrared II fluorescent carbon quantum dots obtained in this invention are prepared by reacting piperazine ketone, acetone, and hydrogen peroxide under an external magnetic field of 9 T. They exhibit near-infrared II fluorescence emission characteristics and are effective against Cu. 2+ Its specific recognition capability, and its working principle diagram are shown below. Figure 23 As shown.

[0066] Comparative Example 1 synthesized carbon quantum dots with weak near-infrared II fluorescence under the same raw material amounts, reaction temperatures and reaction times, without the application of an external magnetic field during a solvothermal reaction. Figure 24-25 To evaluate the near-infrared II fluorescence performance of Comparative Example 1, at the same concentration, the near-infrared II fluorescence emission peak intensity and imaging signal of the Comparative Example 1 sample were significantly weaker than those of Example 1. These data indicate that the introduction of an external magnetic field plays a crucial role in improving the near-infrared II fluorescence emission performance of carbon quantum dots.

[0067] Comparative Examples 2 and 3 synthesized weak near-infrared II fluorescent carbon quantum dots and ordinary fluorescent carbon quantum dots, respectively, under the same reaction temperature, time, and external magnetic field conditions, by reducing the amount of hydrogen peroxide oxidant and by carrying out a solvothermal reaction without adding an oxidant. Figure 26-27 To evaluate the near-infrared II fluorescence performance of Comparative Examples 2 and 3, at the same concentration, the near-infrared II fluorescence emission peak intensity of Comparative Example 2 was significantly lower than that of Example 1, while Comparative Example 3 showed almost no near-infrared II fluorescence emission. Correspondingly, the imaging signal of Comparative Example 2 was significantly weakened, while the near-infrared II fluorescence imaging signal of Comparative Example 3 was almost completely eliminated. These data indicate that the participation of the oxidant plays a crucial role in the formation of near-infrared II fluorescent carbon quantum dots, and changes in its dosage significantly affect the fluorescence emission performance of the resulting carbon dots.

[0068] Comparative Example 4 synthesized ordinary fluorescent carbon quantum dots by changing the precursor to other ketones without nitrogen element and carrying out a solvothermal reaction under the same reaction temperature, time and external magnetic field conditions. Figures 28-29 To evaluate the near-infrared II fluorescence performance of Comparative Example 4, at the same concentration, the sample of Comparative Example 4 showed almost no near-infrared II fluorescence emission characteristics; neither a significant fluorescence emission peak was detected, nor was a significant imaging signal observed. These data demonstrate the necessity of nitrogen doping in the precursor for obtaining near-infrared II fluorescent carbon quantum dots.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing near-infrared II fluorescent carbon quantum dots synthesized with magnetic field assistance, characterized in that: The product is obtained by a solvothermal reaction under an external magnetic field using piperazine as a precursor, acetone as a solvent, and hydrogen peroxide as an oxidant; the ratio of piperazine, acetone, and hydrogen peroxide is 80~120mg:15~21mL:2~4mL; the hydrogen peroxide is a 20~40wt% H2O2 aqueous solution.

2. The preparation method according to claim 1, characterized in that: The ratio of piperazine ketone, acetone, and hydrogen peroxide used is 80-120 mg: 15-21 mL: 3 mL.

3. The preparation method according to claim 1, characterized in that: The strength of the external magnetic field is 6~9T.

4. The preparation method according to claim 1, characterized in that: The conditions for the solvothermal reaction are 160~200℃ for 6~10h.

5. The preparation method according to claim 1, characterized in that: The hydrogen peroxide is a 25-35 wt% H2O2 aqueous solution.

6. The preparation method according to claim 1, characterized in that: It also includes dialysis and freeze-drying of the products after solvothermal reaction.

7. The preparation method according to claim 6, characterized in that: The dialysis specifically uses a dialysis bag with a molecular weight cutoff of 13,000 to 15,000 Da; the dialysis time is 20 to 28 hours.

8. Near-infrared II fluorescent carbon quantum dots prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the near-infrared II fluorescent carbon quantum dots as described in claim 8 as a near-infrared II fluorescent imaging probe.

10. The near-infrared II fluorescent carbon quantum dots of claim 8 as Cu 2+ Application of ion-specific detection probes.

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