Fluorescent probe for detecting iron ions as well as preparation method and application of fluorescent probe

Abstract

The invention relates to the field of iron ion detection, and particularly provides a fluorescent probe for detecting iron ions as well as a preparation method and application of the fluorescent probe. The fluorescent probe is a fluorescent nano material and is prepared by taking alkanet as a carbon source. The method comprises the following steps: S1, pretreating alkanet to obtain dry powder; s2, carrying out pyrolysis on the dried powder; s3, performing ultrasonic extraction and centrifugation; s4, carrying out filtration and dialysis; and S5, freeze-drying the obtained dialysate to obtain the fluorescent probe. The powdery fluorescent probe is dissolved in water and mixed with a solution to be detected, the fluorescence emission spectrum of the mixed solution is detected, and iron ions in the solution are detected through the change of fluorescence intensity. Fluorescent carbon dots are prepared based on pyrolysis of alkanet, a conjugated structure is reserved, chemical modification is not needed, the fluorescent carbon dots are green, low in toxicity and uniform in particle size, carboxyl / hydroxyl and other functional groups are contained on the surface, the fluorescent carbon dots can be coordinated with Fe < 3 + >, and high-sensitivity selective detection is achieved.

Description

Technical Field

[0001] The present application relates to the field of chiral devices, and in particular to a fluorescent probe for detecting iron ions, and a preparation method and application thereof. Background Art

[0002] Iron ions, as an essential trace element for the human body, play a vital role in life processes such as oxygen transport, DNA synthesis, and enzyme catalysis. Abnormal iron ion concentrations are closely related to a variety of major diseases, especially neurodegenerative diseases. Its abnormal accumulation can induce the occurrence and development of Alzheimer's disease, Parkinson's disease, and other diseases by promoting oxidative stress and neurotoxic reactions. Highly selective and sensitive detection of iron ions is of great significance in medical diagnosis, biomarker screening, and early disease warning. Sensitive detection of iron ions is also of great value in environmental monitoring, agricultural safety, and food quality control.

[0003] Existing iron ion detection technologies primarily include atomic absorption spectroscopy (AAS), inductively coupled plasma mass spectrometry (ICP-MS), fluorescence probes, and electrochemical sensors. While AAS and ICP-MS offer excellent sensitivity and accuracy, they are limited by expensive equipment, complex operation, long detection cycles, and high sample pretreatment requirements, limiting their application in rapid, portable detection scenarios. Fluorescent probes are a class of functional materials that specifically identify metal ions through changes in fluorescence signals. Their operating principle is based on the selective binding of metal ions to probe molecules, triggering fluorescence quenching, enhancement, or wavelength shift. Fluorescent probes have attracted attention due to their high sensitivity and excellent visualization properties. Rhodamine B derivatives are a popular choice. These derivatives typically incorporate chelating groups onto their parent molecules to enhance their metal ion recognition ability. Their synthesis involves multiple steps, including esterification, amidation, and reductive amination, requiring stringent, anhydrous, and oxygen-free conditions. Strong acids, strong bases, or toxic organic solvents are often used as reaction media, making their synthesis complex and yields limited. In addition, the molecular structure of Rhodamine B contains benzene rings and amine groups, which may cause cytotoxicity or cumulative toxicity in the body, resulting in poor biocompatibility and difficulty in direct application in in vivo detection or clinical scenarios.

[0004] In summary, existing fluorescent probes are difficult to meet the needs of green and efficient detection. Summary of the Invention

[0005] The purpose of the present invention is to provide a fluorescent probe for detecting iron ions and its preparation method and application in response to the above-mentioned deficiencies in the prior art, so as to solve the problem that existing fluorescent probes are difficult to meet the requirements of green and efficient detection.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: The present application provides a fluorescent probe for detecting iron ions. The fluorescent probe is a fluorescent nanomaterial. The particle size of the fluorescent nanomaterial is less than 10 nm. The fluorescent nanomaterial is prepared using lithospermum root as a carbon source. Carboxyl functional groups, hydroxyl functional groups, oxygen-containing functional groups, and amino functional groups are distributed on the surface of the fluorescent nanomaterial. The fluorescent nanomaterial has dual characteristic absorption peaks at 300 nm and 500 nm, corresponding to energy band gaps of 4.13 eV and 2.48 eV.

[0007] Furthermore, the particle size of the fluorescent nanomaterial is 1.65±0.075 nm.

[0008] The present application also proposes a method for preparing a fluorescent probe for detecting iron ions, the method comprising the following steps: S1, pre-treating the lithospermum root to obtain dry powder; S2, pyrolysis of the dried powder; S3, ultrasonic extraction and centrifugation were performed; S4, followed by filtration and dialysis; S5, freeze-drying the obtained dialysate to obtain a fluorescent probe.

[0009] Furthermore, the pretreatment includes three steps: mechanical decomposition, compound enzymatic hydrolysis, and ethanol degreasing.

[0010] Furthermore, in step S2, the pyrolysis temperature is 180°C and the temperature holding time is 30 minutes.

[0011] Furthermore, in step S2, the temperature is raised to the pyrolysis temperature by a gradient heating method.

[0012] Furthermore, in step S3, anhydrous ethanol is added to the dry powder, stirred, ultrasonically dispersed, and allowed to stand, and the supernatant is collected and centrifuged.

[0013] Furthermore, in step S3, the centrifugal speed is 11000 rpm and the centrifugal time is 30 min.

[0014] Furthermore, the ratio of the mass of the dry powder to the volume of anhydrous ethanol is 1 g:20 mL.

[0015] The present application also proposes an application of the above-mentioned fluorescent probe for detecting iron ions, wherein the solid fluorescent probe is dissolved in water, mixed with the solution to be detected, the fluorescence emission spectrum of the mixed solution is detected, and the iron ions in the solution are detected by the change in fluorescence intensity.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The nano fluorescent material derived from lithospermum root proposed in this application is prepared by a one-step pyrolysis combined with ultrasonic extraction and dialysis purification process. The natural conjugated structure derived from lithospermum erythrorhizon is used as the fluorescent center to retain and stimulate its own fluorescence activity without the need to introduce additional organic synthesis modifications, avoiding the use of toxic solvents and drastic reaction conditions. The fluorescent probe of this application has a uniform particle size and is rich in functional groups such as carboxyl / hydroxyl groups on the surface. It can react with Fe 3+ The formation of a stable coordination enables a highly sensitive and selective fluorescence quenching response, enabling efficient iron ion detection. Furthermore, lithospermum root is renewable, offering the green advantages of low cost and low pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 HRTEM image of a fluorescent probe obtained by the preparation method of a fluorescent probe for detecting iron ions provided in Example 1 of the present invention; Figure 2 A particle size distribution diagram of a fluorescent probe product obtained by the preparation method of a fluorescent probe for detecting iron ions provided in Example 1 of the present invention; Figure 3 The XRD pattern of the fluorescent probe obtained by the preparation method of the fluorescent probe for detecting iron ions provided in Example 1 of the present invention; Figure 4 The fluorescence spectrum of the fluorescent probe obtained by the preparation method of a fluorescent probe for detecting iron ions provided in Example 1 of the present invention in response to different metal ions; Figure 5 The ultraviolet absorption spectrum of the fluorescent probe obtained by the preparation method of a fluorescent probe for detecting iron ions provided in Example 2 of the present invention; Figure 6 This is an infrared spectrum of a fluorescent probe obtained by the preparation method of a fluorescent probe for detecting iron ions provided in Example 3 of the present invention; Figure 7 This is a fluorescence spectrum of a fluorescent probe product obtained by the preparation method of a fluorescent probe for detecting iron ions provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0018] In order to make the implementation process of the present invention clearer, it will be described in detail below with reference to the accompanying drawings.

[0019] Example 1: The present invention provides a fluorescent probe for detecting iron ions. The fluorescent probe is a fluorescent nanomaterial with a particle size of less than 10 nm. When the excitation light is irradiated on the fluorescent nanomaterial, the fluorescent center in the material is excited to transition to a high energy state, and then returns to the ground state and emits a fluorescent signal of a specific wavelength; the specific ions (ions to be detected) in the solution react with the functional groups on the surface of the nanomaterial to cause quenching or transfer of the fluorescence energy, thereby causing a significant change in the fluorescence intensity. The detection of specific ions can be achieved by detecting the fluorescence change. Preferably, the particle size of the fluorescent nanomaterial is 1.65±0.075 nm, which is small in size, large in specific surface area, and more exposed on the surface active sites, which is conducive to forming a stable coordination with specific ions, thereby improving its recognition efficiency and fluorescence response intensity for iron ions; at the same time, the nanoscale size can enhance the quantum confinement effect, making its luminescence performance more sensitive, which is helpful to achieve low concentration Fe 3+ Highly sensitive detection.

[0020] The fluorescent nanomaterials of this application are prepared using lithospermum root as a carbon source. Lithospermum root is a perennial herbaceous plant of the Boraginaceae family. It is rich in naphthoquinone compounds, such as shikonin and acetylshikonin, which have a highly conjugated structure and a natural chromophore. Acetylshikonin is a naphthoquinone skeleton structure with multiple unsaturated hydrocarbon groups, phenolic hydroxyl groups, and an acetyl substituent on the main chain. The highly conjugated structure can be effectively retained and converted into the fluorescent chromophore core of the carbon dots during the pyrolysis and carbonization process of the carbon dots, forming a stable π-π conjugated network, which helps electrons to migrate and distribute efficiently in the carbon dots, enhancing their fluorescence emission intensity and stability. During the pyrolysis process, the conjugated skeleton promotes the orderly development of the carbon nucleus, reduces structural defects, and improves quantum yield. The natural conjugated structure in lithospermum root is not only the construction basis of fluorescent carbon dots, but also directly determines its performance in metal ion detection. Lithospermum root has a hard texture, a dense structure, a horny cross-section, and a longitudinal wrinkled texture on the surface, which is conducive to the formation of a high specific surface area after crushing, which helps the efficient carbonization of the carbon dots and the formation of surface functional groups. The polar groups such as hydroxyl and carboxyl groups in Lithospermum officinale not only enhance water solubility, but also react with Fe 3+ Form a stable coordination to improve the fluorescence probe's affinity to Fe 3+ selectivity and sensitivity.

[0021] In Traditional Chinese Medicine (TCM), the dried root of Lithospermum erythrorhizon, a traditional Chinese medicinal ingredient, is cold in nature, sweet and salty in flavor, and enters the Heart and Liver meridians. Its core benefits include clearing heat and detoxifying, cooling and activating blood circulation, and clearing rashes and freckles. Due to the presence of naphthoquinone compounds such as shikonin and acetylshikonin, Lithospermum erythrorhizon has antibacterial and anti-inflammatory properties, promotes wound healing, and has anti-tumor effects. It is commonly used clinically to treat macular rashes caused by excessive blood heat and toxicity, burn-induced eczema, and gynecological inflammation.

[0022] The surface of the fluorescent nanomaterial of the present application is distributed with carboxyl functional groups, hydroxyl functional groups, oxygen-containing functional groups, amino functional groups, etc. The lone pair electrons in these groups are easily combined with Fe 3+ The vacant 3d orbitals of the Fe-O / N bond form stable coordination complexes (e.g., a five-membered ring O-Fe-O structure). This coordination effect leads to orbital hybridization of excited-state electrons in the material, creating new nonradiative transition channels and enhancing spin-orbit coupling, significantly improving the singlet-to-triplet conversion efficiency. Furthermore, vibrational relaxation of the Fe-O / N bond further accelerates thermal energy dissipation, ultimately shutting down the fluorescence signal through a static quenching mechanism.

[0023] The fluorescent nanomaterial exhibits dual characteristic absorption peaks at 300 nm and 500 nm in the UV-visible spectrum, corresponding to band gaps of 4.13 eV (π→π transition) and 2.48 eV (n→π transition), respectively. The strong absorption at 300 nm originates from electronic excitation of the conjugated system, while the absorption at 500 nm is associated with the transition of the heteroatom lone pair electrons to π* orbitals. The coexistence of wide and narrow band gaps extends the carrier lifetime (τ>10 ns) through exciton confinement, while the 1.65 eV energy difference creates an effective Stokes shift channel, ultimately enabling fluorescence emission.

[0024] This application also proposes a method for preparing the above fluorescent probe, which comprises the following steps: S1, pre-treating the lithospermum root to obtain dry powder; The texture of lithospermum root is hard and dense, the cross section is horny, and the surface has a longitudinal wrinkled texture. In order to open the structure, remove impurities, and retain the active ingredients, the lithospermum root is pretreated. The pretreatment includes the following three steps: S11, mechanical deconstruction; In order to make full use of the longitudinal wrinkled texture of the lithospermum root epidermis and the dense keratin structure inside, the grain cutting and particle size screening were used to achieve the preliminary deconstruction and homogenization of the raw material structure. Specifically, the dried lithospermum root was cut into strips along its natural longitudinal texture direction to conform to its fiber orientation, which helps to break down its longitudinal cracks and internal pore structure; then, it was crushed into a powder of about 60 mesh using a grinder, and further sieved to select fine and uniform particles with a particle size distribution between 80-100 mesh as the raw materials for subsequent reactions. On the one hand, it increases the specific surface area of ​​the lithospermum root powder and improves the permeability and uniformity of the pyrolysis reaction liquid. On the other hand, it helps to expose the potential phenolic hydroxyl coordination groups in its internal structure, which provides the basis for the subsequent Fe 3+ The improvement of binding capacity is the foundation. While retaining the natural conjugated framework, the raw material particle size and structural dissociation state are optimized, which is conducive to the orderly development of the carbon dot carbon core formation process.

[0025] S12, destruction of the cuticle of fiber bundles (complex enzymatic hydrolysis); The structure of Lithospermum erythrorhizon is dense, the cuticle cross section is hardened, and the internal fiber bundles are obviously distributed. In order to improve its reactivity and structural openness before pyrolysis, a composite enzymatic hydrolysis and mild "soft cracking" are used. Specifically, the powder obtained by S11 is added to a phosphate buffer solution of pH 5.0, and a composite enzyme preparation (including cellulase and pectinase) is added, and the reaction is continued at 37°C for 6 hours. It effectively decomposes the lignocellulose framework and pectin cross-linking layer in Lithospermum erythrorhizon, destroys its lignified ductal structure, and makes the cuticle shell loosely peeled off, while maintaining the integrity of the internal naphthoquinone structure to avoid cracking and degradation at high temperature. After the enzymatic hydrolysis sample is fully washed with water and freeze-dried, the structure is looser and the reaction activity is higher, which is conducive to the exposure of functional groups and the improvement of carbon core uniformity during the formation of carbon dots, significantly enhancing the final carbon dots and Fe 3+ The binding efficiency and fluorescence response ability between them.

[0026] S13, degreasing treatment (ethanol degreasing).

[0027] To further enhance the structural purity of lithospermum root powder and stabilize its fluorescent precursor, the enzymatically hydrolyzed lithospermum root powder was added to 70% ethanol and 0.1% citric acid at a solid-to-liquid ratio of 1:10. The extract was then incubated at 60°C in a water bath for 2 hours, supplemented with 40 kHz ultrasonication for 20 minutes to enhance solvent penetration and component release. This step effectively removes lipids, residual pigments, and other non-polar interferences, reducing background fluorescence. It also stabilizes conjugated compounds such as shikonin under weakly acidic conditions, preventing premature degradation. The filtered solid residue was then washed with 0.01 mol / L sodium bicarbonate solution and allowed to stand for 30 minutes to expose residual phenolic hydroxyl and carboxyl groups on the surface, providing a high density of active sites for subsequent carbon dot core construction and Fe⁺ coordination recognition. The final product was repeatedly washed with water until neutral and dried at 60°C, yielding a structurally clean lithospermum root precursor with significantly enhanced chemical activity, significantly enhancing the luminescence properties of the prepared carbon dots and the sensitivity of iron ion detection.

[0028] S2, pyrolysis of the dried powder; Weigh dry lithospermum root powder and spread it evenly in a ceramic crucible. Ceramic has slow heat transfer and excellent thermal insulation properties, ensuring a uniform and stable pyrolysis process. The crucible is then placed in an oven and the temperature is gradually raised to 180°C. The entire heating process takes 20 minutes (excluding the temperature hold period). This slow heating process facilitates the gradual dehydration, condensation, and carbonization of the complex natural organic compounds (such as naphthoquinones) in the lithospermum root, preserving some of the fluorescent core structure and enhancing the fluorescence performance of the carbon dots. Once the temperature reaches 180°C, the reaction is maintained for 30 minutes to complete. After the reaction is complete, the oven is closed and allowed to cool naturally to room temperature.

[0029] Lithospermum officinale powder has a dense structure, a hard cuticle, and is rich in naphthoquinone conjugated compounds. To enhance the conversion of active components and improve the quality of the carbon dots, a gradient temperature ramp was implemented. In the first stage, the temperature was slowly raised to 80°C and held for 10 minutes. This primarily serves to gently remove the residual bound water and a small amount of free water in the powder. Simultaneously, the temperature gradually softens the fiber bundle structure at low temperatures, promoting microcracks in the cuticle and releasing closed pores, providing effective diffusion pathways for subsequent pyrolysis. In the second stage, the temperature was raised to 130°C and held for 15 minutes. This temperature is close to the boiling point of various low-molecular-weight organic compounds (such as volatile resins and fatty acids), which helps selectively volatilize these impurities and prevents the production of tar-like byproducts during the high-temperature carbonization stage, which could interfere with the formation of the fluorescent carbon dots' chromogenic structure. Furthermore, this temperature control partially induces a preliminary condensation reaction of the naphthoquinone precursors, laying the foundation for carbon nucleus development. The final stage is to raise the temperature to 180℃ and maintain it for 30 minutes, which is the key step to complete the main carbonization. At this temperature, highly conjugated structures such as shikonin begin to pyrolyze, reorganize and carbonize to form a π-π conjugated carbon dot core with fluorescent activity, while retaining some functional groups such as carboxyl and hydroxyl groups, which is conducive to the subsequent reaction with Fe 3+ A stable coordination is formed, thereby achieving a highly selective fluorescence response.

[0030] Furthermore, after completing the main carbonization reaction at 180°C, the temperature is lowered and then raised again, first lowering the temperature to 150°C and maintaining it for 5 minutes, and then raising it to 200°C and maintaining it for 10 minutes for deep carbonization. Cooling down to 150°C after keeping it at 180°C can redistribute and stabilize some of the incompletely carbonized organic intermediates under milder conditions, avoiding violent decomposition at high temperatures, and helping to form a more uniform carbon dot structure. This is particularly suitable for thermosensitive naphthoquinone compounds such as shikonin and acetylshikonin contained in lithospermum root, whose conjugated systems are easier to preserve under mild conditions. After "cooling and stabilizing" at 150°C, the temperature is quickly raised to 200°C and maintained for a short time for 10 minutes, which can drive the deep dehydration condensation of residual macromolecular organic matter, making the carbon core structure more compact, the surface functional groups more stable and orderly arranged, further improving the luminescence efficiency and chemical stability of the fluorescent carbon dots, and laying a good structural foundation for the subsequent high-sensitivity detection of iron ions.

[0031] S3, ultrasonic extraction and centrifugation were performed; Anhydrous ethanol is added to the crucible taken out by pyrolysis, and stirring is continued during the addition process to promote the full dissolution of the sample; the solution is further placed in an ultrasonic device so that the pyrolysis product is fully dispersed in the anhydrous ethanol. After the end of the ultrasound, it is allowed to stand for more than 30 minutes, and the supernatant is taken and centrifuged; the centrifugal speed is 11000rpm, and the centrifugation time is 30min, so that large particles are removed and small-sized particles are left in the solution. The ratio of the volume of the lithospermum root powder weighed in step S1 to the anhydrous ethanol added in step S3 is 1g:20mL.

[0032] In the experiment, the volume of anhydrous ethanol remained unchanged (20 mL), and 0.1g, 0.5g, 1.0g, 1.5g, and 2.0g of lithospermum root powder were weighed for preparation. By comparing the fluorescence phenomena under different lithospermum root dosages, it was found that when the lithospermum root dosage was 1.0g, the fluorescence effect of the new nanomaterial was the best. Therefore, the optimal dosage of lithospermum root under this method was determined to be 1.0g, at which point the product obtained had the highest fluorescence quantum yield; this is because too little lithospermum root powder is insufficient to generate a sufficient amount of lithospermum root-based nanofluorescent material, while too much lithospermum root powder cannot be fully pyrolyzed, resulting in a reduced fluorescence effect of the lithospermum root-based nanofluorescent material.

[0033] S4, followed by filtration and dialysis; The supernatant after centrifugation was filtered and dialyzed. The filtration membrane had a pore size of 0.22 μm, so that particles in the filtrate were smaller than 0.22 μm. Dialysis was performed using a 3000 Da dialysis bag to separate out inorganic impurities, and the dialysis time was 48 hours. This achieved the purification purpose and obtained the lithospermum root-derived nanomaterial.

[0034] S5, freeze-drying the obtained dialysate to obtain a fluorescent probe.

[0035] In order to obtain a powdered fluorescent probe, the dialysate is freeze-dried to obtain a powdered fluorescent probe. The powdered fluorescent probe is easy to control the concentration of the solution when used, and detection solutions of different concentrations can be prepared by weighing powders of different weights. The dialyzed liquid is first placed in a low-temperature refrigerator and quickly frozen at -18°C for 12-24 hours to freeze into a solid state. The frozen solid material is placed in a freeze dryer, and the freezing temperature is maintained below -80°C, and the cavity pressure is maintained below 40Pa for 24-48 hours to ensure that a dry solid powder material is finally obtained. The sample tube is sealed and packaged and placed in a dryer to avoid secondary water absorption.

[0036] Figure 1 HRTEM (high-resolution transmission electron microscopy) image of the fluorescent nanomaterial prepared by mixing the lithospermum root powder weighed in step S1 with the anhydrous ethanol added in step S3 at a volume ratio of 1 g:20 mL; Figure 2 The particle size distribution diagram of the prepared product is 1.65±0.075nm, which proves that this method can obtain nanomaterials with uniform particle size. Figure 3 The XRD pattern of the product shows a broad peak at 20°, from which it can be inferred that it is an amorphous carbon material.

[0037] The present application also proposes an application of the above-mentioned fluorescent probe. A solid fluorescent probe is dissolved in water and mixed with the solution to be detected. The fluorescence emission spectrum of the mixed solution is detected, and the iron ions in the solution are detected by changes in fluorescence intensity. First, 5 mg of the solid nanomaterial powder obtained in step S5 is dissolved in 5 mL of water, and then an equal volume of 5 mL of metal ion solution (solution to be detected) is added, and the emission spectrum is tested using a fluorescence spectrometer. Equal volume mixing is conducive to eliminating the error caused by volume mixing. During the test, the metal ion solution is 1 mmol / L. Figure 4 The fluorescence responses of the fluorescent probe prepared in this example to different metal ions show that the fluorescence intensities obtained by the metal ion probe prepared in this invention when detecting different metal ions are different. 3+ It exhibits strong fluorescence quenching, and this application indicates that it can be used for selective detection of metal ions in environmental monitoring and biomedicine.

[0038] Example 2: On the basis of Example 1, 1.0g of lithospermum root powder was weighed, and the reaction temperature of the oven was set to 120°C, 140°C, 160°C, 180°C, and 200°C, and the reaction time was 30 minutes; 20mL of anhydrous ethanol was added to the crucible; other experimental parameters and steps were the same as in Example 1. As the oven reaction temperature increased, the fluorescence intensity of the prepared novel fluorescent nanomaterial showed a trend of first increasing and then decreasing. At 180°C, the fluorescence effect was best, because when the temperature was low, the lithospermum root part maintained the properties of the original natural biomass itself and did not have a fluorescent phenomenon; as the temperature increased, the lithospermum root, as a natural organic matter, was directly produced CO or CO2 gas was discharged after being carbonized, and the amount of product obtained was less, which affected the expression of its performance. Therefore, the temperature of the pyrolysis main reaction was 180°C.

[0039] Figure 5 The results show that the prepared fluorescent nanomaterial has three obvious absorption bands in the ultraviolet region, at 210nm, 300nm, and 500nm, respectively. This shows that the fluorescent material contains multiple absorption energy levels, mainly because it has rich functional groups. The 210nm is the solvent absorption peak; the absorption at 300nm corresponds to the high-energy ultraviolet region, which means that the material has a band gap E g =1240 / 300≈4.13eV, which is easy to produce π→π* transition; the absorption at 500nm corresponds to the visible light region, which means that the material has an energy band gap E g =1240 / 500≈2.48eV, which easily produces n→π* transition. The above-mentioned rich band gap is a prerequisite for the generation of fluorescence phenomenon.

[0040] Example 3: On the basis of Example 1, 1.0g Radix Lithospermi powder was weighed, and the reaction temperature of the baking oven was set to 180 DEG C, and the pyrolysis reaction of 10min, 20min, 30min and 40min was carried out respectively. After the reaction was completed, 20mL of anhydrous ethanol was added, and other experimental parameters and steps were the same as in Example 1. As the reaction time increased, the fluorescence intensity of the novel fluorescent nanomaterial prepared showed a trend of first increasing and then decreasing. At 30min, the fluorescence effect was best. When the reaction time was insufficient, the Radix Lithospermi partially maintained the properties of the original natural biomass itself and did not have a fluorescent phenomenon. As the reaction time lengthened, the Radix Lithospermi, as a natural organic matter, was directly produced CO or CO after carbonization. The gas was discharged, and the amount of product obtained was less, which affected the expression of its performance. Therefore, the optimal main reaction time was preferably 30min.

[0041] Figure 6 The infrared spectrum of the nanomaterial obtained in Example 3 with an oven reaction time of 30 min shows that the product has a rich surface functional group structure, which makes it possible to have many applications. 3+ It is easy to form a stable coordination complex, causing the excited state electrons to dissipate energy through non-radiative transitions and achieve static quenching.

[0042] Example 4: On the basis of Example 1, 1.0g of Radix Lithospermi powder was weighed, and the reaction temperature of the baking oven was set to 180°C, and the reaction time was maintained for 30min. After the reaction was completed, 5mL, 15mL, 20mL, 25mL, and 30mL of anhydrous ethanol were progressively added thereto while continuously stirring to promote its full dissolution. Other experimental parameters and steps were the same as in Example 1. Along with the increase of anhydrous ethanol content, the fluorescence intensity of the novel fluorescent nanomaterial prepared showed a trend of first increasing and then decreasing. When the volume of anhydrous ethanol reached 20mL, it reached a peak value and then began to gradually decline. Therefore, the volume of anhydrous ethanol was preferably 20mL, thereby also determining the ratio of Radix Lithospermi mass and anhydrous ethanol volume.

[0043] Figure 7 When the volume of anhydrous ethanol in Example 4 reached 20 mL, the fluorescence spectrum of the product showed bright blue emission near 400 nm at an excitation wavelength of 290 nm. 3+ There are multiple absorption peaks in the range of 200-350nm, corresponding to Fe 3+ The dd electron transition and ligand-metal charge transfer usually have a typical absorption peak located near 290nm, which just overlaps with the excitation spectrum of the material prepared by the present invention, indicating that there is competitive absorption of the excitation light energy, resulting in fluorescence quenching of the material.

[0044] In summary, the present invention provides a method for preparing a novel fluorescent nanomaterial using lithospermum root as raw material. The process is simple, the operating conditions are mild, and the raw materials used are derived from renewable lithospermum root biomass, which has significant advantages such as green environmental protection, low cost, and easy resource availability. The prepared lithospermum root-derived fluorescent nanomaterial has a stable particle size and good biocompatibility. It is a typical nanoscale material with rich functional groups on its surface, which can react with Fe 3+ The material binds specifically, exhibiting excellent fluorescence response and highly selective recognition, creating an on-off fluorescent probe with excellent anti-interference properties and detection sensitivity. This material has broad application potential in iron ion detection and is suitable for a variety of fields, including biomedical analysis, environmental monitoring, and chemical materials. It provides an innovative path for the high-value utilization of natural medicinal resources and the development of functional nanomaterials.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A fluorescent probe for detecting iron ions, wherein the fluorescent probe is a fluorescent nanomaterial with a particle size of less than 10 nm, characterized in that: The fluorescent nanomaterial is prepared using lithospermum root as a carbon source; carboxyl functional groups, hydroxyl functional groups, oxygen-containing functional groups, and amino functional groups are distributed on the surface of the fluorescent nanomaterial, and the fluorescent nanomaterial has dual characteristic absorption peaks at 300nm and 500nm, corresponding to energy band gaps of 4.13eV and 2.48eV.

2. The fluorescent probe for detecting iron ions according to claim 1, wherein The particle size of the fluorescent nanomaterial is 1.65±0.075 nm.

3. A method for preparing a fluorescent probe for detecting iron ions, characterized in that: The method comprises the following steps: S1, pre-treating the lithospermum root to obtain dry powder; S2, pyrolyzing the dried powder; S3, ultrasonic extraction and centrifugation were performed; S4, followed by filtration and dialysis; S5, freeze-drying the obtained dialysate to obtain the fluorescent probe.

4. The method for preparing a fluorescent probe for detecting iron ions according to claim 3, wherein The pretreatment includes three steps: mechanical decomposition, compound enzymatic hydrolysis and ethanol degreasing.

5. The method for preparing a fluorescent probe for detecting iron ions according to claim 4, wherein In step S2, the pyrolysis temperature is 180° C., and the temperature is maintained for 30 minutes.

6. The method for preparing a fluorescent probe for detecting iron ions according to claim 5, wherein In step S2, the temperature is raised to the pyrolysis temperature by a gradient heating method.

7. The method for preparing a fluorescent probe for detecting iron ions according to claim 6, wherein: In the step S3, anhydrous ethanol is added to the dry powder, stirred, ultrasonically dispersed, and allowed to stand, and the supernatant is collected and centrifuged.

8. The method for preparing a fluorescent probe for detecting iron ions according to claim 7, wherein: In step S3, the centrifugal speed is 11000 rpm and the centrifugal time is 30 min.

9. The method for preparing a fluorescent probe for detecting iron ions according to claim 8, wherein The ratio of the mass of the dry powder to the volume of the anhydrous ethanol is 1 g:20 mL.

10. Use of the fluorescent probe for detecting iron ions according to claim 1 or 2, characterized in that: The solid fluorescent probe is dissolved in water and mixed with the solution to be detected. The fluorescence emission spectrum of the mixed solution is detected, and the iron ions in the solution are detected by the change of the fluorescence intensity.

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