Silver nano-cluster and preparation method and application thereof

Abstract

The invention discloses a silver nano-cluster and a preparation method and application thereof, belongs to the technical field of metal cluster materials, and aims to synthesize Ag NCs by taking PEI as a template and ascorbic acid as a reducing agent. The invention also discloses an application of the silver nanocluster in pH sensing. As the pH sensor, the Ag NCs provided by the invention can show obvious fluorescence intensity and absorbance changes along with the change of acidity, so that the Ag NCs can combine the advantages of high sensitivity of fluorescence detection and simplicity, convenience, rapidness and the like of a colorimetric method, and has more obvious advantages compared with other nanoscale pH sensors.

Description

Technical Field

[0001] This invention belongs to the field of metal cluster materials technology, and particularly relates to a silver nanocluster, its preparation method and application. Background Technology

[0002] Currently, research on the fabrication and application of sensors has made rapid progress. Among them, nanoscale optical materials with pH-sensing responses are becoming increasingly important in environmental, pharmaceutical, and biomedical fields. Tomasulo et al. (M. Tomasulo, I. Yildiz, FM Raymo. pH-sensitive quantum dots. Journal of Physical Chemistry B, 2006, 110(9):3853-3835.) reported an organic ligand that can adsorb on the surface of CdSe-ZnS quantum dots, which can change the inorganic nanoparticles' response to hydroxide anions (OH-). - The luminescence response of the quantum dots was observed. The results showed that the luminescence intensity of the coated nanoparticles decreased significantly in the presence of hydroxide ions. This mechanism can be used to detect the pH value of aqueous solutions. When the pH value increases from 7.1 to 8.5, the luminescence intensity of the quantum dots decreases by 35%. Lei et al. (J. Lei, L. Wang, J. Zhang. Ratiometric pH sensor based on mesoporous silica nanoparticles and Forster resonance energy transfer. Chemical Communications Royal Society of Chemistry, 2010, 46(44): 8445-8447.) proposed a novel ratiometric fluorescence pH sensor. This nanoparticle-based sensor combines dual fluorescence resonance energy transfer (FRET) and the mesoporous properties of silica (SiO2), and has good sensing ability for hydrogen ions under single-wavelength excitation, with a sensing range of 6.0 to 9.0. Kozlovskaya et al. (V.Kozlovskaya, E. Kharlampieva, S. Chang, et al. pH-Responsive Layered Hydrogel Microcapsules as Gold Nanoreactors. Chemistry of Materials, 2009, 21(10): 2158-2167.) obtained well-dispersed gold nanoparticles in a pH response range of 3.0 to 5.0 within a PMAA hydrogel shell.

[0003] However, existing pH sensors are mostly used in carbon quantum dots and nanoparticles, while there are few reports on the optical properties of pH response of metal nanoclusters. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a silver nanocluster, its preparation method, and its application.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing silver nanoclusters, using polyethyleneimine (PEI) as a template and ascorbic acid as a reducing agent to synthesize AgNCs.

[0007] Preferably, it includes the following steps:

[0008] After mixing PEI solution and silver nitrate solution, ascorbic acid solution is added and stirred to react, thus obtaining the solution of the silver nanoclusters.

[0009] Preferably, the concentration of the PEI solution is 0.094 g / mL; and / or,

[0010] The concentration of the silver nitrate solution is 0.001-0.01 mol / L; and / or,

[0011] The concentration of the ascorbic acid solution is 0.10 mol / L.

[0012] Preferably, the volume ratio of the PEI solution, silver nitrate solution and ascorbic acid solution is 1:2.5:(1-1.5).

[0013] Preferably, the reaction temperature is 25-180℃ and the reaction time is 1 hour.

[0014] A silver nanocluster prepared by the method described above.

[0015] An application of silver nanoclusters as described above in pH sensing.

[0016] Preferably, the spectral detection solution used in the application is obtained by mixing the silver nanocluster solution with a buffer solution at a volume ratio of 0.1:20.

[0017] Preferably, the buffer solution includes one or more of the following: disodium hydrogen phosphate-citric acid buffer solution, Tris-HCl buffer solution, sodium carbonate-sodium bicarbonate buffer solution, and BR buffer solution.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] The fluorescence intensity of Ag NCs synthesized in this invention using PEI as a template and ascorbic acid (AA) as a reducing agent is sensitive to the pH value of the medium environment. Furthermore, as a pH sensor, Ag NCs can exhibit significant absorbance changes with changes in acidity, thus combining the high sensitivity of fluorescence detection with the simplicity and speed of colorimetry. Compared with other nanoscale pH sensors, Ag NCs have more significant advantages. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 TEM images of the products obtained in Comparative Example 1(a) and Comparative Example 2(b);

[0022] Figure 2 The effect of different ratios of AgNO3 and AA on the synthesis of Ag NCs in Examples 1-4;

[0023] Figure 3 The effect of AgNO3 concentration on the synthesis of AgNCs in Examples 5-10;

[0024] Figure 4 The graph shows the fluorescence changes of Ag NCs synthesized at different temperatures in Examples 1 and 11-14.

[0025] Figure 5 The image shows a transmission electron microscope image (a), a UV-Vis spectrum, and a fluorescence spectrum (b) of the silver nanoclusters obtained in Example 1.

[0026] In this illustration, (a) is a particle size distribution diagram, and (b) is an optical photograph of silver nanoclusters diluted in aqueous solution under visible and ultraviolet light.

[0027] Figure 6 Comparison of fluorescence intensities of AgNCs in the presence of different anions;

[0028] Figure 7 Comparison of fluorescence intensities of AgNCs in the presence of different cations;

[0029] Figure 8 (a) Fluorescence spectra of the system in disodium hydrogen phosphate-citric acid buffer solutions in the pH range of 2.2 to 4.8; (b) Linearity graphs of the system in disodium hydrogen phosphate-citric acid buffer solutions at different pH values;

[0030] Figure 9(a) Fluorescence spectra of the system in Tris-HCl buffer solutions with pH range of 7.2–8.8; (b) Linearity graphs of the system in Tris-HCl buffer solutions at different pH values;

[0031] Figure 10 (a) Fluorescence spectra of the system in sodium carbonate-sodium bicarbonate buffer solutions in the pH range of 9.2 to 10.8; (b) Linearity graphs of the system in sodium carbonate-sodium bicarbonate buffer solutions at different pH values.

[0032] Figure 11 (a) Fluorescence spectrum of the system in BR buffer solutions with pH range of 2.0 to 11.0; (b) Linearity graph of the system in BR buffer solutions with different pH values; (c) Absorption spectrum of the system in BR buffer solutions with different pH values.

[0033] Figure 12 The effect of reaction time on fluorescence intensity;

[0034] Figure 13 To detect the effect of temperature on fluorescence intensity. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels;

[0038] Among them, ascorbic acid (AA), analytical grade, was purchased from Xi'an Chemical Reagent Factory;

[0039] 0.094 g / mL PEI: Accurately weigh 0.094 g of PEI, dissolve it in a 100 mL volumetric flask, and dilute to volume. Let stand for 24 h until completely dissolved, then shake well before use (protect from light and store at low temperature).

[0040] 0.1 mol / L AA solution: Accurately weigh 1.7613 g of AA, dissolve it, and dilute to 100 mL in a brown volumetric flask (store protected from light).

[0041] 1.0×10 -3mol / L AgNO3 solution: Accurately weigh 0.1698 g of AgNO3, dissolve it, and dilute it to 10 mL in a colorimetric tube. Take 1.00 mL of AgNO3 and dilute it to 100 mL (prepare fresh for use).

[0042] The water used in the experiment was ultrapure water (conductivity 18.25 MΩ / cm).

[0043] Disodium hydrogen phosphate-citric acid buffer solution (pH = 2.2-4.8): Different volumes of disodium hydrogen phosphate solution (0.1 mol / L) were added to 100 mL of citric acid solution (0.1 mol / L) to prepare buffer solutions with different pH values ​​required for the experiment.

[0044] Tris-HCl buffer solution (pH = 7.2-8.8): Different volumes of Tris solution (0.1 mol / L) were added to 100 mL of HCl solution (0.1 mol / L) to prepare buffer solutions with different pH values ​​required for the experiment.

[0045] Sodium carbonate-sodium bicarbonate buffer solution (pH = 9.2-10.8): Add different volumes of sodium carbonate solution (0.1 mol / L) to 100 mL of sodium bicarbonate solution (concentration 0.1 mol / L) to prepare buffer solutions with different pH values ​​required for the experiment.

[0046] BR buffer solutions (pH = 2.0-11.0): Different volumes of sodium hydroxide solution (0.2 mol / L concentration) are added to a mixture of 100 mL of phosphoric acid, boric acid and acetic acid (each with a concentration of 0.04 mol / L) to prepare buffer solutions with different pH values ​​required for the experiment.

[0047] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±3℃.

[0048] Example 1

[0049] A method for preparing PEI-stabilized silver nanoclusters includes the following steps:

[0050] Place a clean, dry synthesis flask on a magnetic stirrer with a magnetic stir bar inserted. Add 1.00 mL of 0.094 g / mL PEI solution and 0.50 mL of ultrapure water, and stir for 2 min. Then, while stirring, add 2.50 mL of 0.01 mol / L silver nitrate (AgNO3) solution and continue stirring for 2 min. Finally, add 1.00 mL of 0.10 mol / L ascorbic acid (AA) and continue stirring for 2 min to obtain a pale yellow solution. Transfer the resulting pale yellow solution to room temperature and stir for 1 h to obtain an Ag NCs solution.

[0051] Example 2

[0052] The difference from Example 1 is that the ratio of AgNO3 to AA is changed, specifically including the following steps:

[0053] Place a clean, dry synthesis flask on a magnetic stirrer with a magnetic stir bar inserted. Add 1.00 mL of 0.094 g / mL PEI solution and stir for 2 min. Then, while stirring, add 2.50 mL of 0.01 mol / L silver nitrate (AgNO3) solution and continue stirring for 2 min. Finally, add 1.50 mL of 0.10 mol / L ascorbic acid (AA) and continue stirring for 2 min to obtain a pale yellow solution. Incubate the resulting pale yellow solution at room temperature with stirring for 1 h to obtain an Ag NCs solution.

[0054] Example 3

[0055] The difference from Example 1 is that the ratio of AgNO3 to AA is changed, specifically including the following steps:

[0056] Place a clean, dry synthesis flask on a magnetic stirrer with a magnetic stir bar inserted. Add 1.00 mL of 0.094 g / mL PEI solution and 0.50 mL of ultrapure water, and stir for 2 min. Then, while stirring, add 2.50 mL of 0.001 mol / L silver nitrate (AgNO3) solution and continue stirring for 2 min. Finally, add 1.00 mL of 0.10 mol / L ascorbic acid (AA) and continue stirring for 2 min to obtain a pale yellow solution. Incubate the resulting pale yellow solution at room temperature with stirring for 1 h to obtain an Ag NCs solution.

[0057] Example 4

[0058] The difference from Example 1 is that the ratio of AgNO3 to AA is changed, specifically including the following steps:

[0059] Place a clean, dry synthesis flask on a magnetic stirrer with a magnetic stir bar inserted. Add 1.00 mL of 0.094 g / mL PEI solution and stir for 2 min. Then, while stirring, add 2.50 mL of 0.001 mol / L silver nitrate (AgNO3) solution and continue stirring for 2 min. Finally, add 1.50 mL of 0.10 mol / L ascorbic acid (AA) and continue stirring for 2 min to obtain a pale yellow solution. Incubate the resulting pale yellow solution at room temperature with stirring for 1 h to obtain an Ag NCs solution.

[0060] Examples 5-10

[0061] The difference from Example 1 lies in changing the concentration of the AgNO3 solution, specifically including the following steps:

[0062] A clean, dry synthesis flask was placed on a magnetic stirrer with a magnetic stir bar inserted. 1.00 mL of 0.094 g / mL PEI solution and 0.50 mL of ultrapure water were added, and the mixture was stirred for 2 min. Then, under stirring, 2.50 mL of AgNO3 solution with concentrations of 0.001 mol / L (Example 5), 0.003 mol / L (Example 6), 0.005 mol / L (Example 7), 0.007 mol / L (Example 8), 0.009 mol / L (Example 9), and 0.010 mol / L (Example 10) were added respectively. The mixture was stirred for another 2 min. Finally, 1.50 mL of 0.10 mol / L AA solution was added, and the mixture was stirred for another 2 min to obtain a pale yellow solution. The resulting pale yellow solution was stirred at room temperature for 1 h to obtain Ag NCs solutions with different amounts of silver nitrate.

[0063] Examples 11-14

[0064] The only difference from Example 1 is that the stirring reaction temperature is changed, specifically including the following steps:

[0065] A clean, dry synthesis flask was placed on a magnetic stirrer with a magnetic stir bar inserted. 1.00 mL of 0.094 g / mL PEI solution and 0.50 mL of ultrapure water were added, and the mixture was stirred for 2 min. Then, under stirring, 2.50 mL of 0.001 mol / L silver nitrate (AgNO3) solution was added, and stirring continued for 2 min. Finally, 1.50 mL of 0.10 mol / L ascorbic acid (AA) was added, and stirring continued for 2 min, yielding a pale yellow solution. This pale yellow solution was transferred to a polytetrafluoroethylene-lined reactor and reacted at 45°C (Example 11), 90°C (Example 12), 135°C (Example 13), and 180°C (Example 14) for 1 h to obtain Ag NCs solutions at different temperatures.

[0066] Comparative Example 1

[0067] The only difference from Example 1 is that AA is not added. All other process steps and parameters are the same as in Example 1.

[0068] The results are as follows Figure 1 As shown in section a, it can be seen that the solution obtained in Comparative Example 1 showed no fluorescence, indicating that silver nanoclusters cannot be synthesized without the addition of AA. This is because PEI has no reducing properties, and without the addition of AA, Ag... + It cannot be restored.

[0069] Comparative Example 2

[0070] The only difference from Example 1 is that AA is replaced with an equal volume and concentration of formaldehyde. All other process steps and parameters are the same as in Example 1.

[0071] The results are as follows Figure 1 As shown in section b, it can be seen that after replacing AA in Example 1 with formaldehyde, the synthesized solution has a certain fluorescence, indicating the successful synthesis of silver nanoclusters. However, the fluorescence intensity is weak, and the pH response sensitivity and range are worse than those of the present invention.

[0072] Application Example 1

[0073] The preparation of the spectral detection solution includes the following steps:

[0074] Take 0.5 mL of the AgNCs stock solution obtained in Example 1, dilute it with ultrapure water to a 100 mL volumetric flask, and place the diluted AgNCs solution in a cuvette. Scan the solution on a fluorescence spectrometer (λ). ex (340 nm, slit width 5 nm), and record the fluorescence intensity value.

[0075] Following the same steps as above, 10 µL of diluent was added to different volumes of BR buffer solution to prepare spectral detection solutions with different pH values. The fluorescence intensity was measured to investigate the pH response of AgNCs solutions.

[0076] Technical effects:

[0077] 1. Effect of the ratio of AgNO3 to AA on the fluorescence intensity and stability of AgNCs

[0078] When the amount and concentration of PEI and AgNO3 are constant, different ratios of ultrapure water and AA will result in different synthesized products, and the fluorescence intensity and color will change with the storage time. Figure 2These are optical photographs of the AgNCs (denoted as 1-4) obtained in Examples 1-4 on the second day (left) and the seventh day (right). As can be seen from the figures, the color change of synthesis bottle 1 was: pale green → yellow; the color change of synthesis bottle 2 was: colorless → yellow; the color change of synthesis bottle 3 was: pale yellow → orange; and the color change of synthesis bottle 4 was: pale yellow → light brown. Fluorescence testing results showed that, among synthesis bottles 1 and 2, the fluorescence intensity of synthesis bottle 2 was more stable and greater than that of synthesis bottle 1. Among synthesis bottles 3 and 4, the fluorescence intensity of synthesis bottle 4 was more stable and greater than that of synthesis bottle 3. Therefore, it can be concluded that, with a constant concentration and amount of PEI and AgNO3, the fluorescence intensity and stability of the synthesized AgNCs increase with increasing AA dosage.

[0079] 2. Effect of different concentrations of AgNO3 solution on the synthesis of AgNCs

[0080] Figure 3 The images show optical photographs of the AgNCs obtained in Examples 5-10, from left to right. It can be seen that no silver mirror reaction occurred in synthesis flask 1. In synthesis flasks 2-5, the silver mirror phenomenon became more severe with increasing AgNO3 concentration, having a greater impact on the synthesis of pure AgNCs. Therefore, it can be concluded that when the concentrations of PEI and ascorbic acid are constant, varying degrees of silver mirroring will occur in the synthesis solution as the AgNO3 concentration increases.

[0081] 3. Synthesis temperature

[0082] Figure 4 The fluorescence changes of AgNCs obtained in Examples 1 and 11-14 are shown in the graphs. It can be seen that the overall fluorescence intensity of the synthesized AgNCs decreases with increasing synthesis temperature, indicating that synthesis temperature has a significant impact on the fluorescence intensity of AgNCs. Lower temperatures are more favorable for synthesizing AgNCs with higher fluorescence intensity. Comparing the stability of AgNCs synthesized at a certain temperature reveals that the fluorescence intensity of the AgNCs obtained in the first four days after synthesis continuously increases, then decreases slightly, and stabilizes after one week. Therefore, the synthesized AgNCs should be used after one week of stabilization.

[0083] 4. Performance Characterization

[0084] The silver nanoclusters obtained in Example 1 were characterized using transmission electron microscopy (TEM), fluorescence spectroscopy, and UV-Vis spectroscopy. The results are as follows: Figure 5 As shown.

[0085] Figure 5 The particle size was analyzed in part (a), and the results showed that the particle size was about 2.0 nm, and the particles were uniformly dispersed without clumping. Figure 5Part (b) shows the UV-Vis and fluorescence spectra of the silver nanoclusters after dilution in aqueous solution. It can be seen that the UV-Vis absorption spectrum shows absorption at 340 nm (curve 1), and the maximum excitation wavelength (curve 2) and maximum emission wavelength (curve 3) are 340 nm and 443 nm, respectively. Figure 5 In the illustration of section (b), the silver nanoclusters, after being diluted in water, appear very pale yellow under visible light and emit blue fluorescence under ultraviolet light. Quinine sulfate was used as a reference (quinine sulfate and Ag NCs were diluted and their absorbance was measured under the same conditions to ensure that the absorbance values ​​were all less than 0.05, and then their fluorescence emission spectra were scanned and the peak areas were obtained by integration). The peak areas were calculated according to the formula... , (where: Φ S Φ represents the quantum yield of quinine sulfate. S =0.55. A S F S (A and F are the absorbance and fluorescence integral area of ​​the reference material, respectively; A and F are the absorbance and fluorescence integral area of ​​AgNCS, respectively) to calculate the quantum yield of AgNCs. The fluorescence quantum yield of silver nanoclusters was found to be approximately 4.1%.

[0086] 5. Effects of anions on Ag NCs

[0087] Under an experimental environment where all other factors remained constant and the temperature was 25°C, the Ag NCs solution obtained in Example 1 was divided into several equal portions (2.00 mL each), and then an equal volume (20 μL of 1.0 × 10⁻⁶) of [unspecified ingredient] was added to each portion. -3 Different anions (mol / L) were allowed to react for 10 min. Anions included: NO3-. - NO2 - SO4 2- SO3 2- CO3 2- SiO 3- S 2- F - Cl - ,Br - I - The results of the comparison of fluorescence intensity changes before and after reaction with AgNCs under different anions are as follows: Figure 6 As shown, the overall fluorescence intensity of AgNCs in the system does not change much. Therefore, the addition of common anions to the system has little overall impact on the fluorescence intensity of AgNCs.

[0088] 6. Effects of cations on Ag NCs

[0089] In an experimental environment where other factors remain constant and the temperature is 25°C, equal volumes (20 μL each of 1.0 × 10⁻⁶) of 1.0 × 10⁻⁶ ppm were added to the Ag NCs solution obtained in Example 1. -3 (mol / L) cations were allowed to stand for 10 min to react. The cations included: Al 3+ Fe 3+ Pb 2+ Hg 2+ Ca 2+ Cu 2+ Mg 2+ Zn 2+ K + The results of the fluorescence intensity changes before and after reaction with AgNCs in the presence of different cations are as follows: Figure 7 As shown, the fluorescence intensity of Ag NCs increased slightly after the addition of cations to the system compared to the blank sample, but the change was so small as to be negligible. Therefore, the effect of these common metal cations on the fluorescence intensity of Ag NCs is essentially negligible.

[0090] 7. Response of Ag NCs to pH of different buffer types

[0091] 7.1 Disodium hydrogen phosphate-citric acid

[0092] Different pH values ​​(2.2, 2.8, 3.2, 3.8, 4.2, 4.8) of disodium hydrogen phosphate-citric acid buffer solutions were added to the Ag NCs solution obtained in Example 1. The ratio of Ag NCs solution to buffer solution added was 1:20. The results are as follows. Figure 8 As shown, the fluorescence intensity of Ag NCs changes systematically with the pH of the disodium hydrogen phosphate-citric acid buffer solution added to the system, and is influenced by various factors. Figure 6 As shown in section b, pH value and the fluorescence intensity of Ag NCs exhibit a certain linear relationship. The linear regression equation is F = -618.92 pH + 7709.4, and the correlation coefficient is R. 2 = 0.995.

[0093] 7.2 Tris-HCl

[0094] Tris-HCl buffer solutions with different pH values ​​(7.2, 7.6, 8.0, 8.4, 8.8) were added to the Ag NCs solution obtained in Example 1, with the ratio of Ag NCs solution to buffer solution being 1:20. The fluorescence intensity of the Ag NCs was then investigated. The results are as follows: Figure 9As shown, the fluorescence intensity of Ag NCs changes systematically with the pH of the Tris-HCl buffer solution added to the system. Meanwhile, from... Figure 9 As shown in section b, the pH value of the system exhibits a certain linear relationship with the fluorescence intensity of Ag NCs. The linear regression equation is F = -254.25 pH + 3376.8, and the correlation coefficient is R. 2 = 0.992.

[0095] 7.3 Sodium carbonate - Sodium bicarbonate

[0096] Sodium carbonate-sodium bicarbonate buffer solutions with different pH values ​​(9.2, 9.6, 10.0, 10.4, 10.8) were added to the Ag NCs solution obtained in Example 1, with the ratio of Ag NCs solution to buffer solution being 1:20. The fluorescence intensity of Ag NCs was investigated. The results are as follows: Figure 10 As shown, the fluorescence intensity of Ag NCs changes systematically with the pH of the sodium carbonate-sodium bicarbonate buffer solution added to the system. Meanwhile, due to... Figure 10 As shown in section b, the pH value of the system exhibits a certain linear relationship with the fluorescence intensity of Ag NCs, with the linear regression equation being F = -121.5 pH + 2254.2 and R... 2 = 0.995.

[0097] 7.4 BR Buffer Solution

[0098] BR buffer solutions with different pH values ​​(2.0~11.0, with intervals of 0.2 pH units) were added to the Ag NCs solution obtained in Example 1, with the ratio of Ag NCs solution to buffer solution being 1:20. An experiment was conducted to investigate the fluorescence intensity of the Ag NCs. The results are as follows: Figure 11 As shown, the fluorescence intensity of these Ag NCs changes systematically with the pH of the added BR buffer solution. Figure 11 As shown in section b, the pH value of the system in the range of 2.4 to 9.4 exhibits a linear relationship with the fluorescence intensity of Ag NCs. The linear regression equation is F = -532.81 pH + 6048.1, and the correlation coefficient is R. 2 = 0.991. To further verify the regular changes in pH on Ag NCs, a spectral scan was performed, and the results are as follows: Figure 11 As shown in section c, it can be seen that the absorbance of the solution at 340 nm gradually decreases as the pH of the system increases.

[0099] 8. Exploring the Influence of Stability and Temperature on Sensing

[0100] Three BR buffer solutions with different pH values ​​were selected, and their fluorescence was measured at regular time intervals (1, 3, 5, 10, 20, 30, 60, 120, and 240 min). The results are as follows. Figure 12 As shown in the figure, the fluorescence intensity decreased rapidly within 30 minutes and then remained basically unchanged. Therefore, the measurement was performed 30 minutes after adding BR buffer.

[0101] The reaction time at different temperatures was investigated, and the results are as follows: Figure 13 As shown, the fluorescence intensity of the system decreases slightly with increasing temperature, but the decrease is not significant, so pH measurement can be performed at room temperature.

[0102] 9. Testing of actual samples

[0103] The pH of Fanta, Sprite, Red Bull, and green tea was measured using the Ag NCs solution obtained in Example 1. The specific steps included: taking an appropriate amount of the beverage to be tested in a clean small beaker and degassing it using sonication. Adding 0.10 mL of AgNCs probe to 2.00 mL of the degassed beverage, allowing it to react for 30 min, and then measuring the fluorescence intensity before calculating the pH value using a linear equation; another degassed beverage was used to measure its pH value using a pH meter for comparison.

[0104] The test results are shown in Table 1:

[0105] Table 1. pH measurement results of AgNCs on different beverages (n=3)

[0106]

[0107] It can be seen that there is no significant difference between the measured value and the pH meter value, indicating that this method has certain application value in the actual sample pH detection.

[0108] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing silver nanoclusters, characterized in that, Ag NCs were synthesized using polyethyleneimine as a template and ascorbic acid as a reducing agent.

2. The method for preparing silver nanoclusters according to claim 1, characterized in that, Includes the following steps: After mixing polyethyleneimine solution and silver nitrate solution, ascorbic acid solution is added and stirred to react, thus obtaining the solution of the silver nanoclusters.

3. The method for preparing silver nanoclusters according to claim 2, characterized in that, The concentration of the polyethyleneimine solution is 0.094 g / mL; and / or, The concentration of the silver nitrate solution is 0.001-0.01 mol / L; and / or, The concentration of the ascorbic acid solution is 0.10 mol / L.

4. The method for preparing silver nanoclusters according to claim 3, characterized in that, The volume ratio of the polyetherimide solution, silver nitrate solution, and ascorbic acid solution is 1:2.5:(1-1.5).

5. The method for preparing silver nanoclusters according to claim 2, characterized in that, The reaction was carried out at a temperature of 25-180℃ for 1 hour.

6. A silver nanocluster prepared by the preparation method according to any one of claims 1-5.

7. An application of the silver nanoclusters as described in claim 6 in a pH sensor.

8. The application according to claim 7, characterized in that, The spectral detection solution used in the application is obtained by mixing the solution of the silver nanoclusters with a buffer solution at a volume ratio of 0.1:

20.

9. The application according to claim 8, characterized in that, The buffer solution includes one or more of the following: disodium hydrogen phosphate-citric acid buffer solution, Tris-HCl buffer solution, sodium carbonate-sodium bicarbonate buffer solution, and BR buffer solution.

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