Coral-like nitrogen and sulfur co-doped carbon fluorescent polymer, preparation method and application thereof

Abstract

The application discloses a coral-like nitrogen-sulfur co-doped carbon fluorescent polymer and a preparation method and application thereof, and the method is to synthesize a novel coral-like water-soluble nitrogen-sulfur co-doped carbon fluorescent polymer by a one-step hydrothermal method, with p-aminobenzenesulfonic acid, sodium hydroxide and DMSO as raw materials.The coral-like nitrogen-sulfur co-doped carbon fluorescent polymer has the advantages that: (1) when the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer is applied as a fluorescent probe for pH detection, the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer has good selectivity and high sensitivity, and has a short response time and can realize real-time detection; (2) the polymer has superior optical properties and good water solubility; when the polymer is applied as a fluorescent probe for pH detection, the polymer has good selectivity and high sensitivity, and has a short response time and a linear range of 3.0-9.0 for pH response.The fluorescent probe can be used for pH detection of commercially available phosphate buffer, and the result is consistent with the result measured by a laboratory pH meter, and the above results show that the prepared fluorescent probe has practical application potential in biochemical research.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry technology and relates to the synthesis of water-soluble fluorescent polymers and fluorescent sensors, specifically coral-like nitrogen-sulfur co-doped carbon fluorescent polymers, their preparation methods, and applications. Background Technology

[0002] Phosphate-buffered saline (PBS) is one of the most widely used balanced salt solutions in biochemical research. Its main components are Na₂HPO₄, KH₂PO₄, NaCl, and KCl. PBS is commonly used for rinsing tissue blocks, washing cells, transporting cells or tissues, preparing other reagents, and as a diluent for cell counting.

[0003] pH value, as one of the most fundamental physicochemical parameters, is of great importance in industrial, agricultural, medical, environmental, and biological fields due to its sensitivity to changes in solution pH. Therefore, accurate pH detection is crucial. Traditional glass pH sensors suffer from drawbacks such as poor interference resistance, short lifespan, and susceptibility to poisoning. Compared to traditional detection methods, fluorescence sensing analysis offers advantages such as high selectivity, fast analysis speed, high sensitivity, and visualization.

[0004] To date, organic fluorophores, fluorescent proteins, and fluorescent nanomaterials have been conveniently used to monitor the pH of water. Organic fluorophores suffer from drawbacks such as narrow and weak absorption spectra, broad photoluminescence spectra, and susceptibility to photobleaching, leading to significant errors in detection results. A potential problem with using fluorescent proteins is their relatively high cost, and the complex extraction and purification processes greatly limit their application. Currently, most reported pH fluorescent nanoprobes focus on acidic, neutral, extremely acidic, and extremely alkaline systems for pH detection, while research on fluorescent nanomaterials for a broader pH sensing range (covering acidic, neutral, and alkaline conditions) is relatively limited.

[0005] In recent years, polymer fluorescent probes have become an important platform for the development of pH probes due to their strong light-harvesting ability, good optical properties, and excellent biocompatibility. Summary of the Invention

[0006] Technical Problem Solved: To overcome the shortcomings of existing technologies, this study aims to provide a fluorescent polymer probe with good chemical and optical stability, exhibiting high selectivity and sensitivity for pH detection under acidic, neutral, and alkaline conditions. Simultaneously, from the perspective of developing novel pH fluorescent sensing probes, a novel coral-like, water-soluble nitrogen-sulfur co-doped carbon fluorescent polymer with a simple, low-cost, and highly efficient synthesis process is designed. This polymer possesses advantages such as good water solubility, resistance to photobleaching, and optical stability in high-salt environments. Its application in pH detection (covering acidic, neutral, and alkaline conditions) broadens the application range of this nitrogen-sulfur co-doped carbon fluorescent polymer, possessing significant theoretical and practical value.

[0007] Technical solution: A method for preparing a coral-like nitrogen-sulfur co-doped carbon fluorescent polymer, the method comprising the following steps:

[0008] S1. Weigh p-aminobenzenesulfonic acid, add it to 1 mol / L NaOH solution, stir and dissolve at room temperature, then add dimethyl sulfoxide, stir evenly and dispense the mixed solution into a polytetrafluoroethylene-lined high-pressure reactor.

[0009] S2. Place the high-pressure reactor of S1 in an electric heating drying oven and react at a constant temperature of 170°C for 12 hours, then allow it to cool naturally to room temperature.

[0010] S3. Centrifuge the solution after reaction S2 at 12000 rpm for 15 min to remove large particulate impurities. Take the supernatant and filter it through a 0.22 μm microporous membrane. Place the resulting solution in a dialysis bag and dialyze for 24 hours.

[0011] S4. Place the dialyzed solution in a freeze dryer to freeze dry into powder to obtain brownish coral-like water-soluble nitrogen-sulfur co-doped carbon fluorescent polymer powder. Store the powder in a refrigerator at 4°C.

[0012] Preferably, the mass-to-volume ratio of p-aminobenzenesulfonic acid to NaOH solution in S1 is g:mL = 5.2:30.

[0013] Preferably, the volume ratio of dimethyl sulfoxide to NaOH solution in S1 is 1:1.

[0014] Preferably, the molecular cutoff of the dialysis bag in S3 is MWCO = 500.

[0015] The coral-like nitrogen-sulfur co-doped carbon fluorescent polymer obtained by any of the methods described above.

[0016] The above-described coral-like nitrogen-sulfur co-doped carbon fluorescent polymer is used in the continuous detection of solution pH.

[0017] Preferably, the linear pH range of the response of the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer is 3-9.

[0018] Preferably, the detection method comprises the following steps:

[0019] (1) Prepare a 10 mmol / L phosphate buffer solution

[0020] Weigh out 0.8g NaCl, 0.02g KCl, 0.144g Na2HPO4, and 0.024g KH2PO4 respectively, dissolve them in 80mL of ultrapure water, then adjust the pH value to 3.0-9.0 with HCl solution or NaOH solution, and finally add ultrapure water to make up to 100mL.

[0021] (2) Equation for fitting the standard curve

[0022] The freeze-dried coral-like nitrogen-sulfur co-doped carbon fluorescent polymer was dissolved in ultrapure water to obtain a stock solution with a concentration of 1 mg / mL.

[0023] Accurately measure 25 μL of the stock solution, then add 1975 μL of phosphate buffer solution with pH values ​​of 3.0, 3.5, 4.0, 5.0, 6.0, 7.0, 8.0, and 9.0 respectively. After mixing, measure the fluorescence spectrum in the range of 400 nm to 750 nm at an excitation wavelength of 360 nm, and record the highest fluorescence emission peak intensity value in each fluorescence spectrum. Each group is performed in triplicate, and the standard deviation between groups is used as the error bar. Linearly fit the highest fluorescence emission peak intensity value to the pH value to obtain the standard curve equation and correlation coefficient.

[0024] (3) Detection of pH value of actual solution

[0025] Mix the storage solution obtained in step (2) with the test solution at a volume ratio of 1:80. Measure the fluorescence spectrum in the range of 400nm to 750nm at an excitation wavelength of 360nm, and record the highest fluorescence emission peak intensity value in each fluorescence spectrum. Substitute the measured fluorescence intensity value into the standard curve equation to determine the pH value of the test solution.

[0026] Beneficial effects: (1) When the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer described in this invention is used as a fluorescent probe for pH detection, it exhibits good selectivity and high sensitivity, and has a short response time, enabling real-time detection. (2) A novel coral-like water-soluble nitrogen-sulfur co-doped carbon fluorescent polymer is synthesized in one step using p-aminobenzenesulfonic acid, sodium hydroxide, and DMSO as raw materials via a hydrothermal method. (3) The polymer possesses superior optical properties and good water solubility; when used as a fluorescent probe for pH detection, it exhibits good selectivity and high sensitivity, and has a short response time with a linear pH response range of 3.0-9.0. This fluorescent probe can be used for pH detection of commercially available phosphate buffer solutions, and the results are consistent with those measured by a laboratory pH meter. These results indicate that the prepared fluorescent probe has practical application potential in biochemical research. Attached Figure Description

[0027] Figure 1 This is a transmission electron microscope (TEM) image of a nitrogen-sulfur co-doped carbon fluorescent polymer.

[0028] Figure 2 The image shows the infrared spectrum of a nitrogen-sulfur co-doped carbon fluorescent polymer.

[0029] Figure 3 The image shows the XRD pattern of the nitrogen-sulfur co-doped carbon fluorescent polymer.

[0030] Figure 4 X-ray photoelectron spectroscopy characterization of nitrogen-sulfur co-doped carbon fluorescent polymer.

[0031] Figure 5 The UV-Vis absorption spectrum (a), fluorescence excitation spectrum (b), and emission spectrum (c) of the nitrogen-sulfur co-doped carbon fluorescent polymer are shown in the inset (the inset shows the solution under fluorescent lamp (left) and 365nm UV lamp (right) illumination).

[0032] Figure 6 The effect of different concentrations of NaCl solution on the stability of nitrogen-sulfur co-doped carbon fluorescent polymer.

[0033] Figure 7 The photostability of nitrogen-sulfur co-doped carbon fluorescent polymers.

[0034] Figure 8 This study investigates the selectivity of interfering agents on nitrogen-sulfur co-doped carbon fluorescent polymers.

[0035] Figure 9 The fluorescence spectra of nitrogen-sulfur co-doped carbon fluorescent polymers in phosphate buffer solutions (pH range 3.0–9.0) at different pH values ​​are shown.

[0036] Figure 10 The graph shows the linear relationship between the fluorescence intensity and pH of the nitrogen-sulfur co-doped carbon fluorescent polymer.

[0037] Figure 11 The fluorescence intensity was cycled between pH 3 and 9. Detailed Implementation

[0038] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are all within the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0039] Example 1

[0040] The preparation method of the nitrogen-sulfur co-doped carbon fluorescent polymer in this embodiment includes the following steps:

[0041] First, weigh 5.2 g of p-aminobenzenesulfonic acid and add it to 30 mL of 1 mol / L NaOH solution. Stir at room temperature until dissolved. Then add 30 mL of dimethyl sulfoxide (DMSO) and stir until homogeneous. Dispense the mixture into a polytetrafluoroethylene-lined high-pressure reactor and place it in an electrically heated drying oven at 170°C for 12 hours. After natural cooling to room temperature, centrifuge the resulting solution at 12,000 rpm for 15 minutes using a benchtop high-speed centrifuge to remove large particulate impurities. Filter the supernatant through a 0.22 μm microporous membrane and dialyze the resulting solution in a dialysis bag (molecular weight cutoff MWCO = 500) for 24 hours. Finally, freeze-dry the dialyzed solution into a powder to obtain a brownish-red, coral-like, water-soluble nitrogen-sulfur co-doped carbon fluorescent polymer with a yield of approximately 60%.

[0042] Example 2

[0043] The sulfur-co-doped carbon fluorescent polymer of Example 1 was characterized as follows:

[0044] The morphology and particle size of nitrogen-sulfur co-doped carbon fluorescent polymers were observed using transmission electron microscopy (TEM). Figure 1 It can be determined that the nitrogen-sulfur co-doped carbon fluorescent polymer synthesized in this patent has a coral-like network structure. For example... Figure 2 This is the infrared spectrum of a nitrogen-sulfur co-doped carbon fluorescent polymer, at 3440 and 3379 cm⁻¹. -1 The broad peak at 2916 cm⁻¹ can be attributed to the stretching vibrations of -OH and -NH. -1 The stretching vibration belonging to CH, 1635cm -1 Bending vibrations belonging to NH, 1496 cm -1 Stretching vibrations attributed to CN, 1188 and 1034 cm -1 The absorption peak at 833 cm⁻¹ is attributed to the stretching vibrations of S=O and SO.-1 The absorption peak at 694 cm⁻¹ is attributed to the bending vibration of the SOC. -1 The absorption peak at the point is attributed to the out-of-plane bending vibration of S=O, proving that the nitrogen-sulfur co-doped carbon fluorescent polymer synthesized in this application has -NH2, -SO3H, etc., and therefore has good water solubility. Figure 3 The X-ray powder diffraction pattern of the nitrogen-sulfur co-doped carbon fluorescent polymer is shown below. Figure 3 It can be seen that the nitrogen-sulfur co-doped carbon fluorescent polymer has a characteristic peak at 2θ = 21°, which is consistent with the amorphous peak of carbon. Therefore, it can be determined that the nitrogen-sulfur co-doped carbon fluorescent polymer is amorphous carbon.

[0045] X-ray photoelectron spectroscopy (XPS) was used to analyze the elemental composition of nitrogen-sulfur co-doped carbon fluorescent polymers. The four binding energy peaks at 166.38, 286.62, 400.80, and 532.51 eV are attributed to S, respectively. 2p C 1s N 1s and O 1s ( Figure 4 The nitrogen-sulfur co-doped carbon fluorescent polymer is mainly composed of 72.71% C, 14.47% O, 8.03% N and 4.79% S.

[0046] The optical properties of nitrogen-sulfur co-doped carbon fluorescent polymers were further investigated using ultraviolet-visible absorption spectroscopy and fluorescence spectroscopy. An aqueous solution (1 mg / mL) of the nitrogen-sulfur co-doped carbon fluorescent polymer was diluted with pure water, and the ultraviolet-visible absorption and fluorescence spectra were measured. Figure 5 As shown, the UV-Vis absorption spectrum (curve a) shows absorption peaks at 262 nm and 376 nm. The maximum excitation wavelength (curve b) and maximum emission wavelength (curve c) of the nitrogen-sulfur co-doped carbon fluorescent polymer are at 360 nm and 479 nm, respectively. As can be seen from the inset, the aqueous solution of the nitrogen-sulfur co-doped carbon fluorescent polymer is transparent light yellow under natural light, while it exhibits sky blue fluorescence under ultraviolet light (365 nm).

[0047] Example 3

[0048] The fluorescence stability of nitrogen-sulfur co-doped carbon fluorescent polymers was investigated in NaCl solutions of different concentrations. Figure 6 As can be seen, the fluorescence intensity of the nitrogen-sulfur co-doped carbon fluorescent polymer did not decrease significantly with increasing NaCl solution concentration. This indicates that the prepared nitrogen-sulfur co-doped carbon fluorescent polymer has strong salt resistance.

[0049] Example 4

[0050] The photostability of a nitrogen-sulfur co-doped carbon fluorescent polymer solution was evaluated by irradiating it with a UV lamp (365 nm) for different durations. Figure 7 It can be seen that after the solution of nitrogen-sulfur co-doped carbon fluorescent polymer was continuously irradiated under a UV lamp for 60 min, the fluorescence intensity did not decrease significantly, indicating that the obtained nitrogen-sulfur co-doped carbon fluorescent polymer has good photostability.

[0051] Example 5

[0052] To verify the specific fluorescence response of this nitrogen-sulfur co-doped carbon fluorescent polymer to pH, the selectivity of the assay method was investigated by adding various ions or small organic molecules to the detection system. The K... + Ca 2+ Mg 2+ Na + Mn 2+ Al 3 + Zn 2+ S2O5 2- The effects of substances such as citric acid, sodium citrate, sucrose, glucose, and glacial acetic acid (10 μmol / L each) on pH measurement. Figure 8 As shown, the nitrogen-sulfur co-doped carbon fluorescent polymer has almost no specific fluorescence response to most anions, cations, and small biological molecules. The experimental results show that the nitrogen-sulfur co-doped carbon fluorescent polymer only has a high fluorescence response to the acidity or alkalinity of the solution.

[0053] Example 6

[0054] like Figure 9 As shown, the fluorescence intensity of the nitrogen-sulfur co-doped carbon fluorescent polymer gradually changes with the increase of the acidity or alkalinity of the phosphate buffer solution, indicating that the nitrogen-sulfur co-doped carbon fluorescent polymer has a significant pH-dependent behavior. When the pH changes from acidic to alkaline, the intensity of the emission peak at approximately 479 nm also gradually increases. When the pH varies within the range of 3.0–9.0, the pH and the fluorescence intensity (F) of the nitrogen-sulfur co-doped carbon fluorescent polymer at 479 nm show a good linear relationship, with the linear equation being: F = 129.2497pH + 33.9773, and the correlation coefficient (R²) being [missing value]. 2 The value is 0.9911. Figure 10 Furthermore, the detection process is rapid, with pH detection completed within 1 minute. Therefore, this fluorescent probe has great potential in pH sensing.

[0055] Example 7

[0056] Experiments were conducted to investigate the acid-base reversibility of the nitrogen-sulfur co-doped carbon fluorescent polymer. After adjusting the pH value between 3 and 9 with NaOH and HCl solutions five times, it still exhibited significant pH-cyclic luminescence characteristics. Figure 11 This indicates that N,S-CQDs possess excellent reversible pH properties. Overall, nitrogen-sulfur co-doped carbon fluorescent polymers exhibit high photoluminescence stability and are promising fluorescent nanosensing materials.

[0057] Example 8

[0058] The relevant fluorescence tests were performed on real samples of commercially available phosphate buffer solution. The results are shown in Table 1. The relative standard deviation was less than 3.0%, and the results were basically consistent with the pH meter measurement data. This proves that the pH fluorescence probe detection method in this study is accurate and reliable, and can be used for pH detection of commercially available phosphate buffer solution.

[0059] Table 1. pH determination of commercially available phosphate buffer samples.

[0060]

Claims

1. A method for preparing a coral-like nitrogen-sulfur co-doped carbon fluorescent polymer, characterized in that, The method includes the following steps: S1. Weigh p-aminobenzenesulfonic acid, add it to 1 mol / L NaOH solution, stir and dissolve at room temperature, then add dimethyl sulfoxide, stir evenly and dispense the mixed solution into a polytetrafluoroethylene-lined high-pressure reactor. S2. Place the high-pressure reactor of S1 in an electric heating drying oven and react at a constant temperature of 170°C for 12 hours, then allow it to cool naturally to room temperature. S3. Centrifuge the solution after reaction S2 at 12000 rpm for 15 min to remove large particulate impurities. Take the supernatant and filter it through a 0.22 μm microporous membrane. Place the resulting solution in a dialysis bag and dialyze for 24 hours. S4. Place the dialyzed solution in a freeze dryer to freeze dry into powder to obtain brownish-red, coral-like, water-soluble nitrogen-sulfur co-doped carbon fluorescent polymer powder. Store the powder in a refrigerator at 4°C.

2. The method for preparing the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer according to claim 1, characterized in that, The mass-to-volume ratio of p-aminobenzenesulfonic acid to NaOH solution in S1 is g:mL = 5.2:

30.

3. The method for preparing the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer according to claim 1, characterized in that, The volume ratio of dimethyl sulfoxide to NaOH solution in S1 is 1:

1.

4. The method for preparing the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer according to claim 1, characterized in that, The molecular cutoff of the dialysis bag in S3 is MWCO = 500.

5. The coral-like nitrogen-sulfur co-doped carbon fluorescent polymer prepared by any one of the methods described in claims 1-4.

6. The application of the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer of claim 5 in the continuous detection of phosphate buffer pH.

7. The application according to claim 6, characterized in that, The linear pH range of the response of the coral-like nitrogen-sulfur co-doped carbon fluorescent polymer is 3-9.

8. The application according to claim 6, characterized in that, The steps of the detection method are as follows: (1) Prepare a 10 mmol / L phosphate buffer solution Weigh out 0.8g NaCl, 0.02g KCl, 0.144g Na2HPO4, and 0.024g KH2PO4 respectively, dissolve them in 80mL of ultrapure water, then adjust the pH value to 3.0-9.0 with HCl solution or NaOH solution, and finally add ultrapure water to make up to 100mL. (2) Equation for fitting the standard curve The freeze-dried coral-like nitrogen-sulfur co-doped carbon fluorescent polymer was dissolved in ultrapure water to obtain a stock solution with a concentration of 1 mg / mL. Accurately measure 25 μL of the stock solution, then add 1975 μL of phosphate buffer solution with pH values ​​of 3.0, 3.5, 4.0, 5.0, 6.0, 7.0, 8.0, and 9.0 respectively. After mixing, measure the fluorescence spectrum in the range of 400 nm to 750 nm at an excitation wavelength of 360 nm, and record the highest fluorescence emission peak intensity value in each fluorescence spectrum. Each group is performed in triplicate, and the standard deviation between groups is used as the error bar. Linearly fit the highest fluorescence emission peak intensity value to the pH value to obtain the standard curve equation and correlation coefficient. (3) Detection of pH value of actual solution Mix the storage solution obtained in step (2) with the test solution at a volume ratio of 1:

80. Measure the fluorescence spectrum in the range of 400nm to 750nm at an excitation wavelength of 360nm, and record the highest fluorescence emission peak intensity value in each fluorescence spectrum. Substitute the measured fluorescence intensity value into the standard curve equation to determine the pH value of the test solution.

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