A method for detecting methylmercury chloride using SERS technology

Abstract

The present invention provides a method for detecting methylmercury chloride by using SERS technology, comprising the following steps: S1. Synthesis of gold sol; S2. Synthesis of probe molecule-functionalized gold nanoparticles; S3. Detection of methylmercury chloride by SERS technology. The present invention can detect the content of methylmercury chloride in water or food and can be applied in practice; the reaction can reach equilibrium within 3 minutes, and the reaction time is short; the linear range is 10-5 g / L to 10-1 g / L (10 ppb to 100 ppm), which is lower than the minimum standard of the world's authoritative institutions.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal detection, and particularly relates to a method for detecting methylmercury chloride by using SERS technology. Background Art

[0002] In the existing methods for detecting methylmercury chloride, a colorimetric method is used to detect methylmercury. Gold nanoparticles are used as catalysts, and methylmercury reacts with formic acid. Methylmercury is rapidly reduced to elemental mercury metal, and the mercury metal combines with gold nanoparticles, causing the gold sol to aggregate. The color changes from red to purple within 1 minute. However, this method cannot perform quantitative analysis, and the detection limit is 20 ug / L.

[0003] Another method is to add polystyrene microspheres (PS) to the gold sol to prepare PS@Au, and then add 4-mercaptopyridine. 4-Mercaptopyridine is selected as an organic chemical receptor, which can strongly bind to the gold nanoparticles on the polystyrene microspheres (PS) in a highly SERS-active hybrid material, and coordinate two mercury species through its aromatic nitrogen to produce corresponding surface complexes with different SERS spectra. Through experiments, the linear relationship between the ratio of the intensities of two groups of peaks at 526 and 1096 cm -1 and at 777 and 1096 cm -1 and the content of methylmercury was obtained. However, this method is complex, requiring the prior synthesis of gold sol and polystyrene microspheres (PS) separately, and then synthesizing PS@Au through a reaction. Moreover, the reaction time is long, and it is still necessary to react for 2 hours after adding methylmercury before detection. Finally, the linear range is narrow, 1.5 ug / L - 220 ug / L. Summary of the Invention

[0004] Aiming at the above technical problems, the purpose of the present invention is to simply, rapidly and at low concentration detect methylmercury chloride by combining SERS technology with redox reaction. Specifically, in the detection process of methylmercury chloride by the present invention, only gold sol needs to be synthesized, the operation is simple, the reaction can be completed within 3 minutes, and quantitative analysis using the ratio of relative peaks in the SERS spectrum can eliminate the influence of the external environment, and the detection result is more accurate.

[0005] The technical solution is a method for detecting methylmercury chloride by using SERS technology, including the following steps:

[0006] S1. Synthesis of gold sol

[0007] Under stirring, heat the HAuCl4 solution to boiling, and add the aqueous solution of sodium citrate; stir and heat for reaction, and the color of the mixture changes from light yellow to wine red; cool the solution to room temperature under stirring to obtain gold sol, and store it in the dark at 4 °C.

[0008] The dosages of each substance in S1 are in the following ratio: 100 mL of HAuCl4 with a mass ratio of 0.01%; 4 mL of aqueous sodium citrate solution with a mass ratio of 1%.

[0009] S2. Synthesize probe molecule-functionalized gold nanoparticles

[0010] Under stirring conditions, add the aqueous solution of the probe molecule as the probe molecule to the gold sol to obtain probe molecule-functionalized gold nanoparticles;

[0011] The probe molecule is 4-mercaptopyridine. Replacing 4-mercaptopyridine with other probe molecules can achieve the same purpose.

[0012] The dosages of each substance in S2 are in the following ratio: 90 uL of 4-mercaptopyridine aqueous solution with a concentration of 10 -4 M; 2 mL of gold sol with a concentration of 1.68 × 10 -9 M.

[0013] S3. Detect methylmercury chloride by SERS technology

[0014] Incubate the probe molecule-functionalized gold nanoparticles with methylmercury chloride for 20 minutes first, and then add formic acid, and immediately perform continuous SERS measurement.

[0015] The dosages of each substance in S3 are in the following ratio: 100 uL of 4-mercaptopyridine-functionalized gold nanoparticles, 100 uL of methylmercury chloride with different concentrations, and 6 uL of formic acid.

[0016] For the continuous SERS measurement in S3, the data acquisition time is 10 s, accumulated once, and the power is 400 mW.

[0017] Beneficial effects brought by the technical solution of the present invention:

[0018] (1) It can detect the content of methylmercury chloride in water or food and can be applied in practice;

[0019] (2) The reaction can reach equilibrium within 3 minutes, and the reaction time is short;

[0020] (3) The linear range is 10 -5 g / L~10 -1g / L (10 ppb to 100 ppm). The strict limit set by international authoritative institutions for the concentration of organic mercury in food is 500 ppb to 1000 ppb, and the present invention is lower than the minimum standard of the World Health Organization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic diagram of the principle of the present invention;

[0022] Figure 2a is a graph showing the change of the intensity ratio of the embodiment over time;

[0023] Figure 2b is a graph of the linear relationship of the intensity ratio of the embodiment;

[0024] Figure 3 is the change of the SERS signal when detecting 100 ppb methylmercury chloride in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0025] The specific technical solution of the present invention will be described in conjunction with the embodiments.

[0026] S1. Synthesis of gold sol.

[0027] Under the vigorous stirring of a magnetic stirrer, 100 mL of 0.01% HAuCl4 placed in a 250 mL round-bottom flask was heated to boiling with an electric heating mantle, about 170 °C, and then immediately 4 mL of 1% aqueous sodium citrate solution was added. After heating for 15 minutes, the color of the mixture changed from light yellow to wine red. Then, the solution was cooled to room temperature with stirring and stored in the dark at 4 °C.

[0028] S2. Synthesis of 4-mercaptopyridine-functionalized gold nanoparticles.

[0029] The concentration of the above-synthesized gold colloidal solution was calculated by ultraviolet-visible absorption spectroscopy to be 1.68 × 10 -9 M, and the particle size was about 17 nm. Under stirring conditions, 90 uL of 4-mercaptopyridine (10 -4 M) aqueous solution as a probe molecule was added to 2 mL of gold sol to obtain 4-mercaptopyridine-functionalized gold nanoparticles. It was left standing for 12 h without stirring to allow 4-mercaptopyridine to fully bind to the gold nanoparticles for the modification of the gold nanoparticles. According to the literature calculation, the surface coverage of the gold nanoparticles at this time was 0.75.

[0030] S3. Detection of methylmercury chloride at different concentrations by SERS technology.

[0031] After dissolving methylmercury chloride in ethanol, it was diluted with water to prepare a stock solution of 100 mg / L methylmercury chloride. The original solution was continuously diluted with water to obtain methylmercury chloride of different concentrations. 100 μL of 4-mercaptopyridine-functionalized gold nanoparticles was incubated with 100 μL of methylmercury chloride at different concentrations (10 ppb - 100 ppm) for 20 minutes, and then 6 μL of formic acid was added, followed by immediate continuous SERS measurement. The data acquisition time was 10 s, accumulated once, and the power was 400 mW. The instrument used was a confocal micro-Raman spectrometer (TSG100-0) purchased from Shanghai Ruhai Optoelectronic Technology Co., Ltd.

[0032] The reaction principle of the present invention: As Figure 1 shown, methylmercury chloride solution was first added to the gold sol, and then formic acid was added to undergo an oxidation-reduction reaction. Formic acid was oxidized to carbon dioxide, and methylmercury chloride was reduced to metallic mercury, which combined with the gold nanoparticles to form an amalgam, resulting in a change in the SERS signal. Among them, the ratio of the peak intensities at 1004 and 1092 cm -1 changed with time and reached equilibrium within 3 minutes, indicating that the reaction was complete. As Figure 2a , as shown in Figure 2b, the concentration range was 10 -5 g / L - 10 -1 g / L (10 ppb - 100 ppm) of methylmercury had a linear relationship with the intensity ratio at 1004 and 1092 cm -1 , and the regression coefficient was (R 2 = 0.988). Taking the detection of 100 ppb methylmercury chloride as an example, the change in the SERS signal is shown as Figure 3 .

Claims

1. A method for detecting methylmercury chloride using SERS technology, characterized in that, It includes the following steps: S1. Synthesis of gold sol Under stirring, heat the HAuCl4 solution to boiling, and add the aqueous sodium citrate solution; stir and heat for reaction, and the color of the mixture changes from light yellow to wine red; cool the solution to room temperature under stirring to obtain gold sol, and store it in the dark at 4°C; S2. Synthesis of probe molecule-functionalized gold nanoparticles Under stirring conditions, add the aqueous probe molecule solution as the probe molecule to the gold sol to obtain probe molecule-functionalized gold nanoparticles; the probe molecule is 4-mercaptopyridine; S3. Detection of methylmercury chloride by SERS technology Incubate the probe molecule-functionalized gold nanoparticles with methylmercury chloride for 20 minutes first, and then add formic acid, and immediately perform continuous SERS measurements.

2. The method for detecting methylmercury chloride using SERS technology according to claim 1, characterized in that, The dosage of each substance in S1 is in the following ratio: 100 mL of HAuCl4 with a mass ratio of 0.01%; 4 mL of aqueous sodium citrate solution with a mass ratio of 1%.

3. A method for detecting methylmercury chloride using SERS technology according to claim 2, characterized in that, The amounts of each substance in S2 are in the following proportions: 90 uL of 4-mercaptopyridine aqueous solution with a concentration of 10 -4 M; 2 mL of gold sol with a concentration of 1.68 × 10 -9 M.

4. A method for detecting methylmercury chloride using SERS technology according to claim 1, characterized in that, The dosage of each substance in S3 is in the following ratio: 100 μL of 4-mercaptopyridine-functionalized gold nanoparticles, 100 μL of methylmercury chloride with different concentrations, and 6 μL of formic acid.

5. A method for detecting methylmercury chloride using SERS technology according to claim 1, characterized in that, For the continuous SERS measurement in S3, the data acquisition time is 10 s, accumulated once, and the power is 400 mW.

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