Preparation method of surface enhanced Raman scattering sensor for wide-range anti-interference online pH monitoring

Abstract

The invention discloses a preparation method of a surface enhanced Raman scattering (SERS) sensor for wide-range anti-interference online pH monitoring, and relates to the technical field of chemical detection.The method comprises the steps that 2-amino-5-sulfydryl-1, 3, 4-thiadiazole probe molecules are adopted, a sodium citrate reduction method is adopted for preparing gold nanoparticles (AuNPs), and a uniform SERS substrate is prepared; 2-amino-5-sulfydryl-1, 3, 4-thiadiazole probe molecules sensitive to pH change are modified on the prepared SERS substrate through sulfydryl chemical bonding, and the SERS pH sensor is constructed, so that wide-range and anti-interference online monitoring of pH of fresh water and seawater is realized, and development of pH monitoring is promoted.

Description

Technical Field

[0001] The invention relates to a method for detecting pH, in particular to a method for preparing a surface enhanced Raman scattering (SERS) sensor for wide-range anti-interference online pH monitoring, and belongs to the technical field of chemical detection. Background Art

[0002] pH refers to the acidity or alkalinity of a solution, and is an indicator of the strength of the acidity or alkalinity of a solution. Accurate measurement of pH can help us gain a deeper understanding of the chemical properties of solutions under different environmental conditions, thereby providing basic data support for environmental protection, industrial production, medical diagnosis and other fields.

[0003] The pH changes in coastal areas and human health monitoring are obvious and require long-term monitoring. Therefore, the development of online pH sensing methods is of great significance. It helps to achieve continuous monitoring of the acid-base properties of the solution and improve the timeliness and accuracy of the monitoring data. It will have broad application prospects in scenarios such as buoys, ships, stations and human health monitoring.

[0004] Conventional methods for online pH monitoring mainly include electrochemical sensors (glass pH electrode sensors) and optical (fluorescence, colorimetric) sensors. Although both can monitor pH, they both have certain problems: (1) poor resistance to temperature and salinity; (2) glass pH electrode sensors are prone to signal drift, while fluorescence sensors are prone to fluorescence quenching, which affects accuracy.

[0005] Surface enhanced Raman scattering (SERS) refers to the phenomenon that the Raman scattering signal of molecules adsorbed on the rough substrates of precious metals such as gold and silver or on the surface of nanoparticles is significantly enhanced. It has the advantages of fingerprint recognition and on-site monitoring, and can solve the problems existing in conventional methods of pH online monitoring. However, conventional SERS pH sensors mostly use SERS probes such as 4-aminothiophenol, 4-mercaptopyridine, and 4-mercaptobenzoic acid, which have problems such as narrow pH range, unclear changes, and poor probe stability. Therefore, it is urgent to develop a pH SERS sensor with a wide range, strong stability, and obvious changes to achieve online monitoring of pH. Summary of the invention

[0006] To address the deficiencies of the prior art, the present invention aims to provide a method for preparing a SERS sensor for online pH monitoring with a wide range and resistance to temperature and salinity interference, thereby achieving online monitoring of pH.

[0007] In order to achieve the above object, the present invention adopts the following technical solution: A method for preparing a SERS sensor for wide-range anti-interference online pH monitoring, characterized in that it comprises the following steps: Step 1: Synthesize AuNPs by reducing chloroauric acid with sodium citrate; Step 2: The AuNPs obtained in step 1 are placed on a silicon wafer using a solvent evaporation method to prepare a uniform SERS substrate. Step 3: Modify the SERS substrate prepared in step 2 with the probe 2-amino-5-mercapto-1,3,4-thiadiazole to prepare a SERS pH sensor.

[0008] Preferably, in step 1, the process of reducing chloroauric acid with sodium citrate to synthesize AuNPs is as follows: 200 mL 0.375 mM HAuCl 4 The solution was heated to boiling, and 4 mL of 1% sodium citrate solution was quickly added, which quickly turned into wine red. The solution was kept slightly boiling for 30 min, the reaction was stopped, and the solution was cooled in a water bath to obtain AuNPs.

[0009] Preferably, in step 2, the process of preparing a uniform SERS substrate by the solvent evaporation method is as follows: 1 mL of the AuNPs prepared in step 1 is added with a 0.1 M NaOH aqueous solution to adjust the pH to 12, centrifuged and concentrated at 6000 r / min, and then dropped onto a silicon wafer and dried at room temperature to obtain a SERS substrate.

[0010] Preferably, in step 3, the process of preparing the SERS pH sensor is as follows: the SERS substrate prepared in step 2 is immersed in 100 μL 10 -4 The prepared SERS pH sensor was reacted in a 2-amino-5-mercapto-1, 3, 4-thiadiazole solution of M for 30 minutes.

[0011] The present invention is beneficial in that: (1) The present invention uses 2-amino-5-mercapto-1,3,4-thiadiazole as a SERS probe to construct a SERS pH sensor, and changes the pH to affect the conformation of 2-amino-5-mercapto-1,3,4-thiadiazole on the surface of the gold nanosphere, thereby achieving highly sensitive online monitoring of pH; (2) The SERS pH sensor prepared by the method provided by the present invention has the characteristic of being resistant to temperature interference, which provides a new idea for pH monitoring in coastal zones at different seasons and depths; (3) The SERS pH sensor prepared by the method provided by the present invention has the characteristic of being resistant to salinity interference, and has promoted the monitoring of oceans, saline-alkali lands and other fields affected by salinity; (4) The SERS pH sensor prepared by the method provided by the present invention is reversible and can be reversible multiple times, providing a basis for online monitoring; (5) The SERS pH sensor prepared by the method provided by the present invention can be stored online for up to two months under dry conditions, which provides a basis for the commercial application of the sensor; (6) The SERS pH sensor prepared by the method provided by the present invention can monitor fresh water, sea water and other systems, has wide applicability, and provides a new perspective for pH research in other actual environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a SEM image of AuNPs obtained by the method provided by the present invention; Figure 2 is a SEM image of a SERS substrate prepared by the present invention; Figure 3 The Raman spectra of the SERS pH sensor prepared by the present invention for measuring pH 1-14 and the relationship between pH and pH 790 / I 687 Relationship diagram; Figure 4 The Raman spectra of the SERS pH sensor at pH 7 and the relationship between pH and I under different salinities are shown in Figure 2. 790 / I 687 Relationship diagram; Figure 5 The Raman spectra of pH 1-14 measured by the SERS pH sensor at 500 mM and the relationship between pH and I 790 / I 687 Relationship diagram; Figure 6 When there is no NaCl and 500mM NaCl, I 790 / I 687 A comparative bar chart of Figure 7 The Raman spectra of the SERS pH sensor at pH 7 under different temperatures and I 790 / I 687 Histogram of Figure 8 The SERS pH sensor can be reversibly Raman spectra of 6 times 790 / I 687 Line chart of Fig. 9 The Raman spectra and I of the SERS pH sensor stored for 2 months 790 / I 687 Histogram of Fig.10 This is the Raman spectrum of the pH monitoring of Sanyuan Lake in Shandong and Gonghu Lake in Jiangsu by SERS pH sensor. 790 / I 687 Histogram of Fig.11 The Raman spectrum of pH monitoring of Yanda Dongmen by SERS pH sensor and I 790 / I 687 's bar chart. DETAILED DESCRIPTION

[0013] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] 1. Preparation of SERS pH Sensor By adopting the method provided by the present invention, a preparation method of a SERS sensor for wide-range anti-interference online pH monitoring is developed, which can realize online monitoring of pH. The method specifically comprises the following three steps: 1. Synthesis of AuNPs by reducing chloroauric acid with sodium citrate 200 mL 0.375 mM HAuCl 4 The solution was heated to boiling, and 4 mL of 1% sodium citrate solution was quickly added, which quickly turned into wine red. The solution was kept slightly boiling for 30 min, the reaction was stopped, and the solution was cooled in a water bath to obtain AuNPs.

[0015] The synthesized AuNPs were scanned by electron microscope, and the SEM images were shown in Figure 1 .

[0016] Depend on Figure 1 It can be seen that AuNPs with uniform size were successfully prepared, and the particle size of AuNPs was 30nm.

[0017] 2. Preparation of uniform SERS substrate by solvent evaporation method Take 1 mL of the AuNPs prepared in step 1, add a 0.1 M NaOH aqueous solution to adjust the pH to 12, and concentrate by centrifugation at 6000 r / min. Then, drop it onto a silicon wafer and dry it at room temperature to obtain a SERS substrate.

[0018] The prepared SERS substrate was scanned by electron microscope, and the SEM image obtained is shown in Figure 2 .

[0019] Depend on Figure 2 It can be seen that uniform SERS substrate AuNPs were successfully prepared.

[0020] 2. SERS pH sensor for wide range pH monitoring The SERS pH sensor was used to monitor pH 1-14, as follows: The prepared SERS pH sensor (prepared in step 3) was immersed in different pH solutions adjusted by HCl and NaOH for 10 min, and then the Raman signals at pH 1-14 were measured, recording the Raman signals at 790 and 687 cm -1The SERS intensity at .

[0021] Raman spectra of pH 1-14 and the relationship between pH and I 790 / I 687 See the relationship Figure 3 .

[0022] Depend on Figure 3 It can be seen that the SERS pH sensor constructed by using 2-amino-5-thiol-1,3,4-thiadiazole as the Raman probe changes significantly in the pH range of 1-14, and the Raman intensity ratios (I 790 / I 687 ) showed an obvious negative correlation, using 2-amino-5-mercapto-1,3,4-thiadiazole I 790 / I 687 The change of can realize the wide range monitoring of pH.

[0023] 3. Study on Salt Resistance of SERS pH Sensor 1.SERS pH sensor salt resistance test The salt resistance performance of the SERS pH sensor was tested using different concentrations of NaCl, as follows: Different concentrations of NaCl were added to pure water to make the final concentration of NaCl 20, 50, 100, 200, 500, 700, and 1000 mM. The SERS pH sensor was immersed in aqueous solutions containing different concentrations of NaCl for 10 min, and Raman tests were performed on it, and the SERS spectra were recorded and compared. 790 / I 687 changes.

[0024] The SERS spectra obtained and the I 790 / I 687 The change in ratio is shown in Figure 4 .

[0025] 2. SERS pH sensor wide range pH test under high salinity conditions The SERS pH sensor was used to test pH 1-14 under 500 mM NaCl conditions, as follows: NaCl was added to pH 1-14 solutions respectively, so that the final concentration of NaCl was 500mM. The SERS pH sensor was immersed in the pH solution containing 500mM NaCl for 10 minutes, and Raman test was performed on it, and the SERS signal was recorded. The result was compared with the Raman test without the introduction of NaCl to further verify the salt resistance of the sensor.

[0026] Raman spectra of pH 1-14 at 500 mM and the relationship between pH and I 790 / I 687 See the relationship Figure 5 .

[0027] When no NaCl and 500 mM NaCl were introduced, I 790 / I 687 For a comparison, see Figure 6 .

[0028] Depend on Figures 4 to 6 It can be seen that the pH SERS sensor constructed using 2-amino-5-mercapto-1,3,4-thiadiazole as the Raman probe is not significantly affected by salinity and can monitor pH under high-salt conditions. It will provide a new method for monitoring pH under high-salt conditions and lay the foundation for its highly sensitive monitoring of pH in oceans, saline-alkali lands and other places.

[0029] 4. Test of SERS pH sensor's anti-temperature interference performance The SERS pH sensor was used to conduct temperature interference resistance tests under different temperature conditions, as follows: The constructed SERS pH sensor was placed in pure water at different temperatures (0, 20, 30, 40, 50°C), Raman tests were performed, and SERS signals were recorded. 790 / I 687 of changes.

[0030] SERS signals at different temperatures and I 790 / I 687 The ratio of Figure 7 .

[0031] Depend on Figure 7 It can be seen that the pH SERS sensor constructed using 2-amino-5-mercapto-1,3,4-thiadiazole as the Raman probe is less affected by temperature and has good resistance to temperature interference, which is of great significance for monitoring the marine environment at different depths in different seasons.

[0032] 5. Reversibility test of SERS pH sensor The reversibility test was performed using the SERS pH sensor, which is as follows: The constructed SERS pH sensor was placed in a pH 4 solution for 10 min to test the Raman signal, and then placed in a pH 10 solution for 10 min to perform Raman measurement. The measurement was repeated six times. The SERS signal was recorded and the six I 790 / I 687 Make a comparison.

[0033] Reversible 6th order Raman spectroscopy I790 / I 687 See the changes in Figure 8 .

[0034] Depend on Figure 8 It can be seen that the constructed SERS pH sensor can be reversible at least 6 times between pH 4 and pH 10, with excellent reversibility, which will lay the foundation for online monitoring of SERS pH sensors.

[0035] 6. Storage and long-term stability test of SERS pH sensor The SERS pH sensor was used for long-term stability testing, which is as follows: The constructed SERS pH sensor was stored in a dry condition, and the SERS spectra of the sensors stored for 1, 7, 10, and 60 days were measured. The SERS signals were recorded and analyzed. 790 / I 687 Make a comparison.

[0036] Raman spectra of the SERS pH sensor stored for 2 months and I 790 / I 687 See the changes in Fig. 9 .

[0037] Depend on Fig. 9 It can be seen that as the SERS pH sensor is stored for 2 months, its A 790 / A 687 The ratio did not change significantly, indicating that the probe had good stability. The SERS pH sensor constructed with this probe had good stability and could be transported and stored, laying the foundation for the commercial application of the sensor.

[0038] 7. Physical Application of SERS pH Sensor 1. pH monitoring of freshwater system using SERS pH sensor

[0039] 2. pH monitoring of freshwater system using SERS pH sensor The pH of water samples from Sanyuan Lake in Shandong and Gonghu Lake in Jiangsu were monitored using the SERS pH sensor, as follows: The pH of water samples from Sanyuan Lake in Shandong and Gonghu Lake in Jiangsu was adjusted to 1, 4, 7, 10, 12, and 14 by adding HCl and NaOH, and then the pH SERS sensor was immersed in the above pH solution for 10 minutes, and then Raman test was performed. SERS signal and pH and I 790 / I 687 relationship.

[0040] Raman spectroscopy of pH monitoring of water samples from Sanyuan Lake in Shandong and Gonghu Lake in Jiangsu 790 / I 687See the changes in Fig.10 .

[0041] 2. pH monitoring of seawater system using SERS pH sensor The pH of seawater samples from the East Gate of Yanda was monitored using the SERS pH sensor, as follows: The pH of the water sample of Yanda Dongmen Seawater was adjusted to 1, 4, 7, 10, 12, and 14 by adding HCl and NaOH, and then the pHSERS sensor was immersed in the above pH solution for 10 minutes, and then the Raman test was performed. The SERS signal and pH and I 790 / I 687 relationship.

[0042] Raman spectroscopy of pH monitoring of water samples from Yandadongmen and I 790 / I 687 See the changes in Fig.11 .

[0043] Depend on Fig.10 and 11 It can be seen that the SERS pH sensor invented by this method can be used not only for monitoring freshwater systems, but also for monitoring seawater systems, which shows that this method has a wide range of applications and good application prospects.

[0044] In summary, the SERS pH sensor prepared by the method provided by the present invention is resistant to temperature and salinity interference, reversible, can realize online monitoring of a wide pH range, and can be stored for a long time under dry conditions. It is widely used in pH monitoring of fresh water, seawater and other systems, has broad application prospects, and will promote the development of online pH monitoring.

[0045] It should be noted that the above examples of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the embodiments here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a surface enhanced Raman scattering (SERS) sensor for wide range anti-interference online pH monitoring, characterized in that: The SERS sensor preparation method includes pH-sensitive SERS probe molecule solution, SERS substrate preparation, and SERS probe molecule modification; The SERS probe molecule is a 2-amino-5-thiol-1,3,4-thiadiazole solution with a concentration of 10 -6 -10 -2 M. The SERS substrate is a noble metal nanomaterial; The SERS probe molecules are modified by mixing a probe molecule solution with a SERS substrate, and are modified onto the surface of the SERS substrate by thiol chemical bonding.

2. The method for preparing a SERS sensor for wide-range anti-interference online pH monitoring according to claim 1, characterized in that: The process of reducing gold chloroaurate nanoparticles (AuNPs) with the noble metal material, i.e. sodium citrate, is specifically as follows: Heat 200 mL of 0.375 mM HAuCl4 solution to boiling, quickly add 4 mL of 1% sodium citrate solution, and it quickly turns to wine red. Continue to keep it slightly boiling for 10-40 minutes, stop the reaction, cool it in a water bath, and obtain AuNPs.

3. The method for preparing a SERS sensor for online pH monitoring with wide range anti-interference according to claim 1, characterized in that: The process of constructing the SERS substrate of the noble metal material is as follows: The prepared AuNPs were added to a NaOH aqueous solution to adjust the weak alkalinity, concentrated by centrifugation at 4000-6000 r / min, and then dropped onto a silicon wafer and dried at room temperature to obtain a SERS substrate.

4. The method for preparing a SERS sensor for online pH monitoring with wide range anti-interference according to claim 1, characterized in that: The process of preparing the SERS pH sensor is as follows: The prepared SERS substrate was immersed in a 2-amino-5-mercapto-1,3,4-thiadiazole solution (with a concentration of 10 -6 -10 -2 M) for 10-50 min, and the probe molecules that are not modified on the SERS substrate are removed by washing to obtain the prepared SERS pH sensor.

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