High-purity fluorescent carbon dots synthesized by self-polymerization driven from bottom to top and method and application thereof

Abstract

The application relates to the technical field of nanomaterials, in particular to high-purity fluorescent carbon dots synthesized from the bottom to the top by self-polymerization driving and a method and application thereof. The high-purity fluorescent carbon dots synthesized from the bottom to the top by self-polymerization driving are prepared by taking dopamine (DA) and phenolic analogs thereof as self-polymerization driving precursors, containing a polar organic solvent as a solvent system and being prepared under the regulation of iodic acid and its salt / high iodic acid and its salt. The method adopts DA and other phenolic compounds with self-polymerization properties as precursors, and effectively promotes the self-polymerization of DA and other phenolic compounds into polydopamine (PDA) or other polyphenols by regulating the iodic acid or high iodic acid induced oxidation process in a specific solvent mixture system, and then efficiently converts the PDA or other polyphenol into PDA derivative fluorescent carbon dots (PDA-CDs) or polyphenol derivative fluorescent carbon dots through a controllable solvothermal reaction.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, and in particular to a method and application of a high-purity fluorescent carbon dot synthesized efficiently from the bottom up by self-polymerization. Background Technology

[0002] As a novel type of carbon-based fluorescent nanomaterial, carbon dots have attracted widespread attention due to their excellent luminescent properties and simple synthesis process. Carbon dots are typically synthesized using either top-down or bottom-up methods, with the latter being more popular due to its versatility and practicality. In particular, solvothermal treatment of small molecule compounds, polymers, or biomass precursors has become an important bottom-up method for carbon dot preparation. However, high-temperature treatment of raw materials easily triggers complex nonlinear reaction processes (such as dehydration, condensation, crosslinking, and carbonization), leading to diverse side reaction pathways and the generation of numerous low-molecular-weight impurities, thus significantly reducing the actual conversion rate of carbon dots. These impurities are large and varied in properties, often obscuring the characteristic expression of the carbon dots themselves; for example, the typical fluorescent properties of some carbon dots actually originate from the influence of molecular fluorescent substances. Therefore, developing a new, efficient, and concise method for synthesizing carbon dots with high yield and high purity is both highly challenging and crucial.

[0003] Although researchers have paid attention to the purity of carbon dots, the field generally suffers from insufficient or even missing purification steps, leading to ongoing debates about the fundamental structure and fluorescence properties of carbon dots, which greatly hinders their practical application. Membrane dialysis, a conventional carbon dot purification technique, typically uses membranes with a molecular weight cutoff (MWCO) below 3 kDa. Unfortunately, such low MWCO membranes cannot effectively remove fluorescent macromolecular byproducts generated during synthesis, such as polymers, supramolecular molecules, or aggregates. Conversely, deep purification using high molecular weight membranes with a MWCO greater than 3 kDa promises to effectively filter out small molecule byproducts, significantly improving the purity of carbon dot products. This purity can be precisely verified using high-resolution characterization techniques such as 1H NMR spectroscopy and chromatographic separation. Therefore, in addition to optimizing reaction conversion efficiency and controllability, combining efficient high molecular weight membrane dialysis purification technology with 1H NMR purity detection is a crucial prerequisite for obtaining high-purity carbon dots.

[0004] Against this backdrop, we propose a simple and highly controllable self-polymerization-driven solvothermal method. Using DA and other phenolic compounds with inherent self-polymerization properties as precursors, a highly efficient self-polymerization reaction is triggered under solvothermal conditions guided by an iodate or periodate oxidation system, thereby achieving the efficient bottom-up preparation of high-purity carbon dots. This strategy effectively enhances the controllability of the solvothermal synthesis route and significantly improves the actual generation efficiency of carbon dots, promising the efficient preparation of controllable and pure carbon dot materials. Summary of the Invention

[0005] This invention provides a self-polymerization-driven bottom-up method for the efficient synthesis of high-purity fluorescent carbon dots. The high-purity fluorescent carbon dots are prepared using catecholamines or phenolic substances as self-polymerization-driven precursors and a polar organic solvent as the solvent system, under the oxidative induction of iodic acid and its salts / periodic acid and its salts.

[0006] In one embodiment of the present invention, the catecholamine is selected from one or more of dopamine, levodopa, gallic acid, catechol, and pyrogallol.

[0007] In one embodiment of the present invention, the dipole moment of the polar organic solvent is greater than 5 × 10⁻⁶. -30 And less than 10×10 -30 Kulen Mi.

[0008] In one embodiment of the present invention, the solvent system contains ultrapure water.

[0009] A second aspect of this invention provides a synthesis process for high-purity fluorescent carbon dots, achieved through a bottom-up, self-polymerization-driven, highly efficient synthesis. The synthesis process steps are as follows:

[0010] Iodic acid and its salt / periodic acid and its salt, along with the solvent, are added to a reaction vessel and thoroughly mixed. Then, catecholamines or phenolic substances are added to initiate the reaction. After the reaction is complete, the precipitate is removed, and the retentate obtained by dialysis using a dialysis membrane is freeze-dried and stored.

[0011] In one embodiment of the present invention, the molecular weight cutoff of the dialysis membrane is 3-15 kDa.

[0012] In one embodiment of the present invention, the mass ratio of iodic acid and its salt to periodic acid and its salt and the precursor of catecholamine or phenolic substances is (9-11):1.

[0013] In one embodiment of the present invention, the iodic acid and its salt / periodic acid and its salt is sodium periodate or potassium iodate.

[0014] In one embodiment of the present invention, the solvent contains a dipole moment greater than 5 × 10⁻⁶. -30 And less than 10×10 -30 Coulomb-Millet polar organic solvents and buffer solvents.

[0015] In one embodiment of the present invention, the buffer solvent contains the same metal element as iodic acid and its salts / periodic acid and its salts.

[0016] The third aspect of this invention provides a high-purity fluorescent carbon dot that is efficiently synthesized from the bottom up by self-polymerization, and it is applied in the fields of sensing and chromatographic stationary phases.

[0017] By adopting the above technical solution, the present invention has the following beneficial effects:

[0018] This invention relates to a novel method for the high-efficiency and high-purity synthesis of fluorescent carbon dots (CDs) driven by self-polymerization. The method uses dopamine (DA) and other phenolic compounds with self-polymerizing properties as precursors. In a specific solvent mixture, the oxidation process induced by iodic acid or periodic acid is controlled to effectively promote the self-polymerization of DA and other phenolic compounds into polydopamine (PDA) or other polyphenols. These are then efficiently converted into PDA-derived fluorescent carbon dots (PDA-CDs) or polyphenol-derived fluorescent carbon dots through a controllable solvothermal reaction. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 Figure 1 shows a study of three typical carbon dots derived from citric acid / ethylenediamine (CA / EDA), o-phenylenediamine (OPD), and oat biomass (OM).

[0021] in Figure 1 a is an image of unpurified CA / EDA-CDs, showing the 1 kDa and 15 kDa cutoffs under sunlight;

[0022] Figure 1 b is an image of unpurified CA / EDA-CDs, with 1 kDa and 15 kDa cutoffs under a 365 nm UV lamp;

[0023] Figure 1 c represents the unpurified carbon dots of CA / EDA-CDs, and the yields and quantum yields of the 1 kDa and 15 kDa cutoffs;

[0024] Figure 1 d represents unpurified OPD-CDs, with 1 kDa and 15 kDa cutoffs photographed under sunlight;

[0025] Figure 1 e represents unpurified OPD-CDs, with 1 kDa and 15 kDa cutoffs photographed under a 365 nm UV lamp;

[0026] Figure 1f represents the unpurified, 1 kDa and 15 kDa cutoff yields and quantum yields of OPD-CD carbon dots;

[0027] Figure 1 g represents unpurified OM-CDs, 1 kDa and 15 kDa retentates under sunlight;

[0028] Figure 1 h represents unpurified OM-CDs, with 1 kDa and 15 kDa cutoffs photographed under a 365 nm UV lamp;

[0029] Figure 1 i represents the unpurified, 1 kDa and 15 kDa cutoff yields and quantum yields of OM-CDs carbon dots.

[0030] Figure 2 This is a schematic diagram illustrating the rational synthesis, rigorous purification, verification, and application of the high-purity PDA-CDs prepared in Example 1.

[0031] Figure 3 Performance testing was performed on the fluorescent carbon dots prepared in Examples 1 to 4.

[0032] in, Figure 3 a represents the crude solvothermal products from Examples 1 to 4;

[0033] Figure 3 b represents the yield and fluorescence quantum yield (QYs) of the 15 kDa cutoff products from Examples 1 to 4;

[0034] Figure 3 c shows fluorescence images of the products from Examples 1 to 4 before and after dialysis using a 15kDa membrane;

[0035] Figure 3 Yields and QYs of sodium periodate (SP) / EtOH-mediated 15 kDa cutoff prepared with different ethanol (EtOH) contents;

[0036] Figure 3 Yields and QYs of SP / EtOH-mediated 15kDa cutoff prepared with different DA contents;

[0037] Figure 3 f represents the yield and QYs of the SP / EtOH-mediated 15kDa cutoff prepared with different SP contents;

[0038] Figure 3 g is a transmission electron microscope / high resolution transmission electron microscope (TEM / HR-TEM) characterization image of SP-mediated PDA-CDs (SP-PDA-CDs);

[0039] Figure 3h represents the TEM / HR-TEM characterization of Tris-mediated PDA-CDs (Tris-PDA-CDs);

[0040] Figure 3 i is the TEM / HR-TEM characterization image of SP / EtOH mediated PDA-CDs (SE-PDA-CDs);

[0041] Figure 3 j is a TEM / HR-TEM characterization image of Tris / EtOH mediated PDA-CDs (TE-PDA-CDs).

[0042] Figure 4 The images show the X-ray photoelectron spectroscopy (XPS) characterization analysis of the products from Examples 1 to 4.

[0043] in, Figure 4 a. XPS characterization analysis of corresponding SP-PDA-CDs;

[0044] Figure 4 b corresponds to XPS characterization analysis of Tris-PDA-CDs;

[0045] Figure 4 c corresponds to XPS characterization analysis of SE-PDA-CDs;

[0046] Figure 4 XPS characterization analysis of TE-PDA-CDs corresponding to d.

[0047] Figure 5 The physicochemical properties of purified CDs obtained by dialysis of the products obtained in Examples 1 to 4 using membranes with different molecular weight cutoffs are described.

[0048] in, Figure 5 a. Comparison of the yields of SE-PDA-CDs products with QYs under different purification levels;

[0049] Figure 5 b. Fluorescence quantum yield of the dialysate fraction in the ranges of 1 kDa, 1-5 kDa, and 5-15 kDa after dialysis treatment of SE-PDA-CDs products;

[0050] Figure 5 c. Fluorescence spectra of unpurified SE-PDA-CDs products under different excitation wavelengths;

[0051] Figure 5 d. Fluorescence spectra of SE-PDA-CDs products after purification by 1kDa cutoff under different excitation wavelengths;

[0052] Figure 5e. Fluorescence spectra of the SE-PDA-CDs product after purification with a 5kDa cutoff under different excitation wavelengths;

[0053] Figure 5 f. Fluorescence spectra of the SE-PDA-CDs product after purification with a 15kDa cutoff under different excitation wavelengths.

[0054] Figure 6 Purity verification of high-purity SE-PDA-CDs.

[0055] in, Figure 6 a shows the UV-Vis spectra of the unpurified substance, the 1kDa cutoff, the 5kDa cutoff, the 15kDa cutoff, and the 15kDa dialysate;

[0056] Figure 6 b shows the Fourier transform infrared (FTIR) spectra of the unpurified substance, the 1 kDa cutoff, the 5 kDa cutoff, the 15 kDa cutoff, and the 15 kDa dialysate;

[0057] Figure 6 c. Raman spectra of the unpurified substance, 1 kDa cutoff, 5 kDa cutoff, 15 kDa cutoff, and 15 kDa dialysate;

[0058] Figure 6 d represents the unpurified substance, 1 kDa cutoff, 5 kDa cutoff, 15 kDa cutoff, and 15 kDa dialysate. 1 H NMR spectrum;

[0059] Figure 6 e represents the capillary electrophoresis (CE) spectra of the unpurified substance, 1 kDa cutoff, 5 kDa cutoff, 15 kDa cutoff, and 15 kDa dialysate.

[0060] Figure 7 Fluorescence properties of derived carbon dots prepared from different catechol precursors before and after purification.

[0061] Figure 7 a. Fluorescence spectra of L-DOPA-derived carbon dots before and after purification under different excitation wavelengths;

[0062] Figure 7 b. Fluorescence spectra of gallic acid-derived carbon dots before and after purification under different excitation wavelengths;

[0063] Figure 7 c. Fluorescence spectra of catechol-derived carbon dots before and after purification under different excitation wavelengths;

[0064] Figure 7d. Fluorescence spectra of pyrogallol-derived carbon dots before and after purification under different excitation wavelengths.

[0065] Figure 8 Example 4: Test diagram of the product's application in detecting tetracycline (TC).

[0066] in, Figure 8 (ad) shows the changes in fluorescence intensity of SE-PDA-CDs products with different degrees of purification after the addition of different analytes;

[0067] Figure 8 e) Revealed the linear relationship between the fluorescence quenching value ΔF of SE-PDA-CDs (different purity levels) and TC content (in the range of 0.5 to 40 μM);

[0068] Figure 8 f) The EOF migration rates of uncoated fused silica capillary columns, unpurified SE-PDA-CDs coated capillaries, and SE-PDA-CDs coated capillaries purified by 15 kDa dialysis membranes were compared under different buffer pH conditions. The experimental conditions were: background electrolyte 50.0 mM phosphate buffer (pH 5.0-9.0), applied voltage 25 kV.

[0069] Figure 9 Example 4: Application test diagram of the product in capillary electrochromatography - electrophoresis diagram.

[0070] in, Figure 9 a is an electrophoresis diagram showing the separation of different nucleosides (in the diagram: 1 cytosine nucleoside, 2 uridine, 3 deoxyadenosine);

[0071] Figure 9 b is an electrophoresis diagram showing the separation of different alkaloids (in the diagram: 1 theobromine, 2 theophylline, 3 xanthine).

[0072] Figure 10 Example 4: Application test diagram of the product in capillary electrochromatography - fluorescence image.

[0073] in, Figure 10 a is a fluorescence image of an uncoated fused silica capillary;

[0074] Figure 10 b is a fluorescence image of an unpurified SE-PDA-CDs coated capillary;

[0075] Figure 10 c is a fluorescence image of a SE-PDA-CDs-coated capillary purified by a 15kDa dialysis membrane. Detailed Implementation

[0076] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0077] Example 1:

[0078] Synthesis of Tris-PDA-CDs: 50 mL of Tris buffer solution (50 mM, pH = 8.5) was added to a 100 mL reaction vessel, followed by the addition of 50 mg of DA. The reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed against a 15 kDa membrane for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0079] Example 2:

[0080] Synthesis of SP-PDA-CDs: 50 mL of sodium acetate buffer solution (50 mM, pH = 5) and 500 mg of SP were added to a 100 mL reaction vessel and stirred. Then, 50 mg of DA was added. The reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed with a 15 kDa membrane for 7 days, with the dialysate changed every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp and no detectable fluorescence was observed. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0081] Example 3:

[0082] Synthesis of TE-PDA-CDs: 20 mL of Tris buffer (50 mM, pH 8.5), 500 mg of SP, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of DA was added, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed against a 15 kDa membrane for 7 days, with the dialysate changed every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0083] Example 4:

[0084] Synthesis of SE-PDA-CDs: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg DA was added, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed against a 15 kDa membrane for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0085] Example 5:

[0086] Synthesis of SE-PDA-CDs under 20% EtOH volume ratio conditions: 40 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg of SP, and 10 mL of EtOH were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of DA was added, and the reaction was carried out at 220 °C for 24 h. All other operations and conditions remained unchanged to prepare SE-PDA-CDs under 20% EtOH volume ratio conditions.

[0087] Example 6:

[0088] Synthesis of SE-PDA-CDs under 40% EtOH volume ratio conditions: 30 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg of SP, and 20 mL of EtOH were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of DA was added, and the reaction was carried out at 220 °C for 24 h. All other operations and conditions remained unchanged to prepare SE-PDA-CDs under 40% EtOH volume ratio conditions.

[0089] Example 7:

[0090] Synthesis of SE-PDA-CDs with a 25 mg DA precursor: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL EtOH were added to a 100 mL reactor. After thorough mixing, 25 mg DA was added, and the reaction was carried out at 220 °C for 24 h. All other operations and conditions remained unchanged to prepare SE-PDA-CDs with a 25 mg DA precursor.

[0091] Example 8:

[0092] Synthesis of SE-PDA-CDs with 100 mg DA precursor: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL EtOH were added to a 100 mL reactor. After thorough mixing, 100 mg DA was added, and the reaction was carried out at 220 °C for 24 h. All other operations and conditions remained unchanged to prepare SE-PDA-CDs with 100 mg DA precursor.

[0093] Example 9:

[0094] Synthesis of SE-PDA-CDs with a 250 mg DA precursor: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL EtOH were added to a 100 mL reactor. After thorough mixing, 250 mg DA was added, and the reaction was carried out at 220 °C for 24 h. All other operations and conditions remained unchanged to prepare SE-PDA-CDs with a 250 mg DA precursor.

[0095] Example 10:

[0096] Synthesis of SE-PDA-CDs with 0.25 g SP oxidant: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 0.25 g SP, and 30 mL of EtOH were added to a 100 mL reactor. After thorough mixing, 50 mg DA was added, and the reaction was carried out at 220 °C for 24 h. All other operations and conditions remained unchanged to prepare SE-PDA-CDs with 0.25 g SP oxidant.

[0097] Example 11:

[0098] Synthesis of SE-PDA-CDs with 0.75 g SP oxidant: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 0.75 g SP, and 30 mL of EtOH were added to a 100 mL reactor. After thorough mixing, 50 mg DA was added, and the reaction was carried out at 220 °C for 24 h. All other operations and conditions remained unchanged to prepare SE-PDA-CDs with 0.75 g SP oxidant.

[0099] Example 12:

[0100] Synthesis of SE-PDA-CDs with 1g SP oxidant: 20mL of sodium acetate buffer solution (50mM, pH=5), 1g SP, and 30mL EtOH were added to a 100mL reactor. After thorough mixing, 50mg DA was added, and the reaction was carried out at 220℃ for 24h. All other operations and conditions remained unchanged to prepare SE-PDA-CDs with 1g SP oxidant.

[0101] Example 13:

[0102] Synthesis of high-purity carbon dots derived from levodopa: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of levodopa was added, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed against a 15 kDa membrane for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0103] Example 14:

[0104] Synthesis of high-purity carbon dots derived from gallic acid: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of gallic acid was added, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed against a 15 kDa membrane for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0105] Example 15:

[0106] Synthesis of high-purity catechol-derived carbon dots: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of catechol was added, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed against a 15 kDa membrane for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0107] Example 16:

[0108] Synthesis of high-purity carbon dots derived from pyrogallol: 20 mL of sodium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of pyrogallol was added, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed against a 15 kDa membrane for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0109] Comparative Example 1

[0110] Fluorescent carbon dots CA / EDA-CDs were prepared using citric acid / ethylenediamine (CA / EDA) as a precursor. The specific synthesis method was as follows: 10 mL of ultrapure water, 1 g of CA, and 0.335 g of EDA were added to a 25 mL reactor and thoroughly mixed. The reaction was carried out at 200 °C for 5 h. After cooling to room temperature, insoluble precipitates were removed by filtration through a 0.22 μm microporous membrane. Subsequently, the mixture was dialyzed against 1 kDa and 15 kDa membranes for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under 365 nm UV light and showed no detectable fluorescence. The resulting retentate was freeze-dried.

[0111] Comparative Example 2

[0112] Fluorescent carbon dots OPD-CDs were prepared using o-phenylenediamine (OPD) as a precursor. The specific synthesis method was as follows: 10 mL of ultrapure water, 0.15 g of OPD, and 1 mL of H₂SO₄ were added to a 25 mL reactor and thoroughly mixed. The reaction was carried out at 200 °C for 6 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm microporous membrane. Subsequently, the mixture was dialyzed against 1 kDa and 15 kDa membranes for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under 365 nm UV light and showed no detectable fluorescence. The resulting retentate was freeze-dried.

[0113] Comparative Example 3

[0114] Fluorescent carbon dots OM-CDs were prepared using oat biomass (OM) as a precursor. The specific synthesis method was as follows: 10 mL of ultrapure water and 0.714 g of OM were added to a 25 mL reactor and thoroughly mixed. The reaction was carried out at 200 °C for 3 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm microporous membrane. Subsequently, the mixture was dialyzed against 1 kDa and 15 kDa membranes for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under 365 nm UV light and showed no detectable fluorescence. The resulting retentate was freeze-dried.

[0115] like Figure 1 The fluorescent carbon dots prepared in Comparative Examples 1 to 3 were studied. The derived carbon dots obtained in Comparative Examples 1 to 3 were subjected to different treatments: unpurified, purified using a 1 kDa dialysis membrane, and purified using a 15 kDa dialysis membrane. The derived carbon dots obtained from the above treatments were then irradiated under sunlight and a 365 nm UV lamp to observe the yield and QY characteristics.

[0116] in, Figure 1 a is an image of unpurified CA / EDA-CDs, showing the 1 kDa and 15 kDa cutoffs under sunlight;

[0117] Figure 1 b is an image of unpurified CA / EDA-CDs, with 1 kDa and 15 kDa cutoffs under a 365 nm UV lamp;

[0118] Figure 1 c represents the unpurified CA / EDA-CDs, yields of 1kDa and 15kDa cutoffs, and QY;

[0119] Figure 1 d represents unpurified OPD-CDs, with 1kDa and 15kDa retentates photographed under sunlight;

[0120] Figure 1e represents unpurified OPD-CDs, with 1 kDa and 15 kDa cutoffs photographed under a 365 nm UV lamp;

[0121] Figure 1 f represents the unpurified OPD-CDs, yield of 1 kDa and 15 kDa cutoffs, and QY;

[0122] Figure 1 g represents unpurified OM-CDs, 1kDa and 15kDa retentates under sunlight;

[0123] Figure 1 h represents unpurified OM-CDs, with 1kDa and 15kDa cutoffs photographed under a 365nm UV lamp;

[0124] Figure 1 i represents the unpurified carbon dots of OM-CDs, the yield of 1kDa and 15kDa cutoffs, and QY;

[0125] pass Figure 1 Characterization results revealed typical carbon dot properties prepared from three precursors: citric acid / ethylenediamine (CA / EDA), o-phenylenediamine (OPD), and oat biomass (OM). Although the unpurified sample exhibited high yields and fluorescence quantum yields (QY) under visible light and 365 nm UV irradiation, both yields and QY significantly decreased to less than 0.5% as the MWCO of the dialysis membrane increased to 15 kDa. This phenomenon reflects the difficulty of dialysis in completely removing fluorescent byproducts generated during the formation process, particularly polymers, supramolecular molecules, or aggregates.

[0126] like Figure 3 As shown, in Examples 1 to 4, fluorescent carbon dots were synthesized by PDA self-polymerization hydrothermal carbonization reaction in a Tris buffer system, and the crude product was subjected to 15 kDa membrane dialysis. The results showed that, compared to Comparative Examples 1 to 3, the product yield after dialysis increased to nearly 5%, while maintaining approximately 1% QY (see…). Figure 3 b). After the addition of 60% vol anhydrous ethanol, the post-reaction solutions of both the Tris-induced and SP-induced systems exhibited a deeper color, enhanced fluorescence, and reduced precipitate. Under these conditions, the yield and QY of the 15 kDa dialysis product were significantly improved: the Tris system achieved a yield of 12.6% and QY of 1.5%, while the SP system achieved a yield of 21.1% and QY of 3.1%. Figure 3 b) and c) indicate that the mixed solvent system effectively improves the controllability and efficiency of SP-induced DA polymerization. In Examples 2, 4, and 5-12, the yield and QY of the 15kDa retention solution gradually increased with the increase of EtOH concentration, further verifying the effect of the mixed solvent system on improving the DA polymerization efficiency. Figure 3d). Excessive increases in DA and SP concentrations lead to a significant decrease in the yield of the retention solution and QYs. Figure 3 e, f).

[0127] in, Figure 3 a) Crude solvothermal products of Examples 1 to 4; b) Yield and QYs of 15kDa retentate of products of Examples 1 to 4; c) Fluorescence images of 15kDa products of Examples 1 to 4 before and after membrane dialysis. Figure 3 df) represents the yield and QYs of SP / EtOH-mediated 15kDa cutoff prepared in Examples 2, 4, and 5-12 with different EtOH, DA, and SP contents; Figure 3 gj) are TEM / HR-TEM characterization diagrams of SP-PDA-CDs, Tris-PDA-CDs, SE-PDA-CDs and TE-PDA-CDs, respectively.

[0128] TEM and HR-TEM characterization showed that ( Figure 3 Four types of PDA-derived fluorescent carbon dots (SP-PDA-CDs, Tris-PDA-CDs, SE-PDA-CDs, and TE-PDA-CDs) retained by 15 kDa dialysis were all spherical nanoparticles with an average diameter of approximately 1.8–2.7 nm. Among them, the SP / EtOH mediated sample had a smaller particle size and more uniform distribution, reflecting the high controllability of its DA oxidation process in a mixed solvent. HR-TEM further revealed that these particles were crystalline, with a graphite (100) interplanar spacing of 0.21 nm.

[0129] XPS analysis ( Figure 4 (ad) Confirmed that with increasing EtOH content, the O / C ratio and the proportion of C=O bonds in SE-PDA-CDs decreased, indicating that the mixed solvent inhibited the oxidative cleavage and excessive carboxylation of quinone units. The presence of EtOH also promoted an increase in the ratio of pyrrole nitrogen and C=C bonds, thus favoring the formation of cyclic structures and graphitized microstructures, which was particularly evident in SE-PDA-CDs. Considering isolated sp... 2 The graphitized microstructure plays a dominant role in the fluorescence emission of CDs, thus containing the highest proportion of sp. 2 SE-PDA-CDs in the domain have the highest quantum yield.

[0130] like Figure 5As shown, to evaluate the purity of SE-PDA-CDs after rigorous dialysis purification, we compared and analyzed the physicochemical properties of purified CDs obtained after dialysis using membranes with different molecular weight cutoffs (MWCOs). With increasing dialysis purity, the yield and quantum yield gradually decreased, and excitation-dependent emission weakened. Notably, the 15 kDa dialysis retention buffer exhibited approximately excitation-independent emission characteristics, indicating effective removal of fluorescent byproducts and achieving high purification of SE-PDA-CDs. Therefore, low MWCO dialysis cannot completely eliminate fluorescent byproducts, and strict control of dialysis conditions is crucial for obtaining high-purity PDA-CDs.

[0131] Figure 5 a) Comparison of yield and fluorescence quantum yield (QYs) of SE-PDA-CDs products at different purification levels. b) Fluorescence quantum yields of the dialysate fractions of SE-PDA-CDs products in the 1 kDa, 1-5 kDa, and 5-15 kDa ranges after dialysis. cf) Fluorescence spectra of unpurified SE-PDA-CDs products and products purified with 1 kDa, 5 kDa, and 15 kDa cutoffs under different excitation wavelengths.

[0132] Further employing UV-Vis, FTIR, Raman, 1 The purity of the carbon dots was verified by H NMR spectroscopy and electrophoresis.

[0133] Figure 6 The image shows the UV-vis spectra of the unpurified substance, as well as the 1kDa, 5kDa, and 15kDa cutoffs, including the 15kDa dialysis product, further confirming the abundance of fluorescent byproducts. The original carbon dot solution exhibits a strong absorption peak at 225nm, originating from the π-π* transition of small molecule fluorophores. After dialysis with 1kDa and 5kDa membranes, the characteristic absorption peaks remain, indicating a large retention of fluorescent byproducts. Until dialysis with 15kDa, the absorption spectrum of the cutoff exhibits a broad-range monotonic absorption without characteristic peaks, strongly demonstrating that the 15kDa dialysis process effectively removes fluorescent byproducts and improves the purity of the carbon dot sample.

[0134] Figure 6 b. FTIR analysis was used to analyze the changes in surface functional groups of each purified carbon dot sample. Compared with the unpurified sample, the CH2 oscillation vibration (1349 cm⁻¹) in the FTIR spectrum of the dialyzed CDs sample was significantly different. -1 It disappeared and at 3125cm -1 A new absorption peak appears, associated with the stretching vibrations of aromatic CH and NH groups. This is particularly evident in the 15 kDa cutoff, at 3460 cm⁻¹. -1 The -OH stretching vibration was significantly reduced, and these changes confirmed that 15 kDa membrane dialysis can efficiently remove small molecule impurities associated with DA derivatives.

[0135] Figure 6 c. Raman spectroscopy was used to investigate the structural differences in carbon dot samples with different dialysis levels. All samples were analyzed at 1340 and 1570 cm⁻¹. -1 The surrounding area shows characteristic peaks of D and G bands, reflecting sp 3 and sp 2 Hybrid carbon coexists in high-purity SE-PDA-CDs. Compared to unpurified samples, the half-maximum width of the 15 kDa cutoff is significantly reduced and baseline noise is eliminated, indicating that its composition is purer.

[0136] Figure 6 d. Carbon dot samples with different purification levels were separated and identified by capillary electrophoresis (CE). Peak 1, representing low molecular weight byproducts, was observed at 225 nm, while the target carbon dot product showed a broad monochromatic absorption curve (peak 2). As the MWCO of the dialysis bag increased, peak 1 gradually weakened, while only peak 2 was observed in the 15 kDa cutoff. This further demonstrates that strictly using a 15 kDa membrane for dialysis can effectively remove small molecule fluorescent byproducts.

[0137] Figure 6 e uses nuclear magnetic resonance hydrogen spectrum ( 1 The purity of carbon dots was verified by ¹H NMR (hydrogen spectroscopy) for unpurified samples. 1 The 1H NMR spectra showed strong, sharp signals in the fatty (1-4 ppm) and aromatic (7-8.5 ppm) regions, revealing the presence of residual molecular species. In the smaller MWCO (1 kDa and 5 kDa) dialysis products, although the signal intensity decreased, the sharp signal persisted. Only the 15 kDa cutoff showed a strong signal. 1 In the 1H NMR spectrum, the sharp signal was almost completely eliminated, showing only broadband unresolved peaks associated with carbon dots. In contrast, the 15kDa dialysate reproduced a similar sharp signal in the unpurified sample. The combined results of NMR and other characterization methods consistently confirm the importance and effectiveness of the 15kDa membrane dialysis method for obtaining high-purity PDA-CDs.

[0138] like Figure 7 All the catechols shown in the ad include L-DOPA, gallic acid, catechol, and pyrogallol. The derived high-purity CDs prepared using similar synthetic methods all exhibit good non-excitation-dependent characteristics, similar to high-purity SE-PDA-CDs. This indicates that the self-polymerization-driven bottom-up synthesis strategy is suitable for synthesizing high-purity CDs from various phenolic precursors. Furthermore, the synthesized high-purity fluorescent CDs possess different fluorescence properties and high yields.

[0139] The optimal excitation wavelength, optimal emission wavelength, quantum yield, and yield of the 15 kDa retentates in Examples 13-16 are shown in Table 1. All phenolic compounds were effectively converted into high-purity fluorescent CDs with different QYs, and the yields of the 15 kDa retentates after rigorous purification were all no less than 15%.

[0140] In summary, UV-Vis absorption spectroscopy, infrared spectroscopy, Raman spectroscopy, electrophoresis, and nuclear magnetic resonance collectively verified that rigorous dialysis treatment can effectively improve the purity of the prepared high-purity polydopamine-derived carbon dots. Furthermore, by changing different polyphenolic substances, high-purity CDs with varying fluorescence properties, QY, and yields can be prepared.

[0141] application:

[0142] 1. Application of tetracycline detection in sensing technology

[0143] Having verified the high purity and excellent stability of high-purity PDA-CDs, they can be applied to the field of highly selective sensing. The specific operation is as follows:

[0144] (1) Add 100 μL of high-purity PDA-CDs solution (1 mg / mL), 3.5 mL of ultrapure water, and 400 μL of TC solution of different concentrations to centrifuge tubes in sequence.

[0145] (2) Stir the mixture evenly and record the fluorescence spectrum at 360 nm for analysis.

[0146] (3) The selectivity of high-purity polydopamine-derived carbon dots for common metal cations, anions and antibiotics was studied using the same detection method, except that the detection solution was changed.

[0147] (4) All experiments were conducted at room temperature, and each measurement was repeated three times.

[0148] like Figure 8 As shown, the interference of other analytes on the TC response behavior of the retained product gradually weakens as the dialysis bag size increases from 1 kDa to 15 kDa. When the dialysis bag size is 15 kDa, only tetracycline shows a significant fluorescence quenching effect on its retained product. Figure 8 d), while the coexisting analytes have the least impact on fluorescence intensity.

[0149] 2. Applications in capillary electrochromatography

[0150] Due to the abundance of functional groups on the carbon dot surface, small particle size, and moderate adsorption performance, the prepared high-purity PDA-CDs can be used in the development of novel electrochromatographic stationary phase materials. The specific operation is as follows:

[0151] (1) Dissolve an appropriate amount of disodium hydrogen phosphate (Na2HPO4) in ultrapure water to prepare a 50 mM phosphate buffer, and adjust the pH values ​​of different gradients (5, 6, 7, 8 and 9) using 1.0 M phosphate solution or 0.1 M NaOH.

[0152] (2) The running buffer used in the CEC experiment is a mixture of phosphate buffer and acetonitrile in an appropriate ratio.

[0153] (3) Before use, all solutions are filtered through a 0.45μm membrane filter and degassed by ultrasonication for 3 minutes.

[0154] (4) For the electrophoresis procedure, the fused silica capillary (50 μm, effective length 40 cm) is continuously rinsed with ultrapure water and buffer solution for 5 minutes.

[0155] (5) Between consecutive sample injections, the column was rinsed sequentially with ultrapure water and the buffer was run for 1.5 min. The sample was injected into the pump at a pressure of 50 mbar for 5 s, and the separation process was carried out under optimized voltage conditions.

[0156] (6) CEC separation was performed at a controlled temperature of approximately 25°C and the detection wavelength was 200 nm.

[0157] like Figure 9 As shown, unpurified PDA-CDs and high-purity PDA-CDs after dialysis at 15 kDa were used as novel stationary phases for open-tube capillary electrochromatography (OT-CEC). After optimizing the CEC conditions, both nucleosides and alkaloids could be expressed on high-purity PDA-CDs coated columns with a relatively high theoretical plate number (1.0 × 10⁻⁶). 5 Baseline separation was achieved. In contrast, under the same electrophoresis conditions, the separation efficiency of uncoated columns and unpurified carbon dot-modified columns for complex samples of nucleosides and alkaloids was significantly lower than that of high-purity carbon dot-modified columns, indicating that improving the purity of carbon dots is crucial to improving their electrochromatographic separation performance.

[0158] Example 17

[0159] Preparation of PDA-CDs in an ultrapure water system. The synthesis method is as follows: 50 mL of ultrapure water and 50 mg of DA were added to a 100 mL reaction vessel, mixed thoroughly, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed through a 15 kDa membrane for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp and no detectable fluorescence was observed. The resulting retentate was freeze-dried.

[0160] Example 18

[0161] Preparation of PDA-CDs in an anhydrous ethanol system. Synthetic method: 50 mL of anhydrous ethanol and 50 mg of DA were added to a 100 mL reaction vessel, mixed thoroughly, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 μm filter membrane. Subsequently, the mixture was dialyzed against a 15 kDa membrane for 7 days, with the dialysate replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The resulting retentate was freeze-dried.

[0162] Example 19

[0163] Preparation of PDA-CDs in an ammonium acetate buffer system. Synthetic method: 20 mL of ammonium acetate buffer solution (50 mM, pH = 5), 500 mg SP, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg DA was added, and the reaction was carried out at 220 °C for 24 h. After cooling to room temperature, insoluble precipitates were removed by filtration through a 0.22 μm filter membrane. Subsequently, dialyzing was performed using a 15 kDa membrane for 7 days, with the dialysate changed every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp with no detectable fluorescence. The obtained retentate was freeze-dried. Finally, the obtained powder was dissolved in ultrapure water and stored at 4 °C for further characterization and analysis.

[0164] The yields and quantum yields of the unpurified samples, 1 kDa cutoff, and 15 kDa cutoff in Examples 17-19 are shown in Table 2. Among them, the high-purity PDA-CDs prepared in Example 4 (i.e., the 15 kDa cutoff of SE-PDA-CDs) showed the best yield and quantum yield, significantly outperforming the traditional hydrothermal or solvothermal carbon dot synthesis systems without self-polymerization driving capabilities represented by Examples 15-17.

[0165] Table 1

[0166]

[0167] Table 2

[0168]

[0169] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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 or all of the technical features; and these modifications or substitutions 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. The application of a high-purity fluorescent carbon dot synthesized efficiently from the bottom up by self-polymerization in the detection of tetracycline, characterized in that, The preparation steps of the high-purity fluorescent carbon dots are as follows: 20 mL of 50 mM sodium acetate buffer solution, pH = 5, 500 mg of sodium periodate, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of dopamine was added, and the mixture was reacted at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 µm filter membrane. Subsequently, the mixture was dialyzed with a 15 kDa membrane for 7 days, with the dialysate being replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp and showed no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored in a refrigerator at 4 °C.

2. The application of a high-purity fluorescent carbon dot synthesized efficiently from the bottom up by self-polymerization as a stationary phase in open-tube capillary electrochromatography, characterized in that... The preparation steps of the high-purity fluorescent carbon dots are as follows: 20 mL of 50 mM sodium acetate buffer solution, pH = 5, 500 mg of sodium periodate, and 30 mL of anhydrous ethanol were added to a 100 mL reaction vessel. After thorough mixing, 50 mg of dopamine was added, and the mixture was reacted at 220 °C for 24 h. After cooling to room temperature, the insoluble precipitate was removed by filtration through a 0.22 µm filter membrane. Subsequently, the mixture was dialyzed with a 15 kDa membrane for 7 days, with the dialysate being replaced every 4 hours, until the dialysate was visually transparent under a 365 nm UV lamp and showed no detectable fluorescence. The resulting retentate was freeze-dried. Finally, the powder was dissolved in ultrapure water and stored in a refrigerator at 4 °C.

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