A method for surface enhanced raman detection of trace explosives

Abstract

The application discloses a method for detecting trace explosives by surface enhanced Raman spectroscopy, which comprises the following steps: adding a certain amount of metal ion salt solution into silver sol solution, then adding explosive solution to be detected, shaking, standing, taking the lower precipitate and dropping on a substrate for Raman test. The metal ion plays a regulating role in the Raman spectrum of the nano-silver sol, can further enhance the Raman scattering effect, obtain good response intensity, and effectively improve the detection sensitivity of the trace explosives, and the quantitative detection limit can reach 10 ‑9 mol / L, and the qualitative detection concentration of CTNB and TNT can reach 10 ‑11 mol / L at the lowest.

Description

Technical Field

[0001] This application relates to the field of Raman spectroscopy detection technology, and more specifically, to a method for surface-enhanced Raman spectroscopy detection of trace explosives. Background Technology

[0002] Raman spectroscopy has wide applications in molecular structure research and possesses many excellent properties. However, Raman scattering effects are generally weak. Surface-enhanced Raman spectroscopy (SERS) is a spectral method that enhances Raman scattering. SERS technology has developed rapidly and is widely used in analytical science, surface science, and biological sciences, making it a very powerful analytical method. SERS technology has both quantitative and qualitative detection capabilities. In pharmaceutical analysis and pollutant monitoring, quantitative analysis of substances helps ensure product quality and environmental safety. In explosives detection, quantitative analysis helps assess the threat level of explosives, develop response measures, and conduct safety management. SERS technology is also applicable to the qualitative analysis of substances such as cells, tissues, and explosives, aiding in disease diagnosis and suitable for scenarios such as emergency scenes and border checks. In criminal investigation, it can quickly provide clues and evidence. Nano-silver sol also plays an important role in surface-enhanced Raman spectroscopy, significantly influencing the spectral enhancement effect. Raman spectroscopy enhanced by silver nanoparticles offers advantages such as rapid detection, non-destructive testing, and the ability to detect low concentrations. In the field of explosives detection, preparing silver nanoparticles and utilizing surface-enhanced Raman spectroscopy with metal ions is a commonly used method to detect trace amounts of explosives. However, although silver nanoparticles can enhance the Raman signal, their detection sensitivity for explosives is still insufficient to meet the needs of quantitative or qualitative detection of low concentrations of explosive residues or trace substances. Summary of the Invention

[0003] This invention provides a method for surface-enhanced Raman spectroscopy detection of trace explosives, the method comprising the following steps:

[0004] (1) After adding a certain amount of metal ion salt solution to the silver sol solution, add the solution of the explosive to be tested, shake well and let stand.

[0005] (2) Take the lower layer of precipitate and drop it onto the substrate for Raman testing;

[0006] The metal ions are sodium ions, potassium ions, or lithium ions; the gel particle size range in the silver sol solution is 40-60 nm, and the silver gel particle number concentration is 4 × 10⁻⁶. 11 / mL~5×10 11 / mL; the concentration of metal ions in the metal ion salt solution is 0.5mol / L to 5mol / L; the volume ratio of the silver sol solution to the metal ion salt solution is 8:1.

[0007] Specifically, the explosive is CL-20, TNT, or CTNB.

[0008] When the explosive to be detected is TNT, potassium ions are selected as the added metal ions;

[0009] When the explosive to be detected is CTNB, sodium ions are selected as the added metal ions;

[0010] When the explosive to be detected is CL-20 and its concentration is higher than 10 -6 When the concentration of CL-20 is above 10 mol / L, potassium or sodium ions should be added; when the concentration of CL-20 is below 10 mol / L... -6 At mol / L, lithium ions are selected as the added metal ions.

[0011] The metal ion salt solution is a nitrate solution of metal ions. The concentration of metal ions in the metal ion salt solution is 1 mol / L.

[0012] The method further includes one or more of the following (1)-(6):

[0013] (1) The preparation method of the silver sol includes: heating a certain amount of silver nitrate solution to boiling, then slowly adding a certain amount of sodium citrate solution to the boiling silver nitrate solution, continuing to heat for 1 hour, and cooling to obtain the solution;

[0014] (2) The explosive solution is an acetone solution of the explosive;

[0015] (3) The concentration of the CL-20 solution of the explosive is 1×10 -3 mol / L~1×10 -9 mol / L;

[0016] (4) The concentration of the explosive CTNB and TNT solution is 1×10⁻⁶. -3 mol / L~1×10 -11 mol / L;

[0017] (5) The Raman test is performed using a 785nm, 633nm, or 532nm laser;

[0018] (6) The substrate is a glass slide.

[0019] More specifically, in the silver nitrate solution and sodium citrate solution, the molar ratio of silver nitrate to sodium citrate is 1:1. The concentration of the silver nitrate solution and sodium citrate solution is 1×10⁻⁶. -1 mol / L~1×10 -5 mol / L.

[0020] The preparation method of the silver sol includes: taking a concentration of 1×10 -3Heat a silver nitrate solution to boiling, and add 4 × 10⁻⁶ mol / L sodium citrate solution at a volume ratio of silver nitrate solution to sodium citrate solution of 40:1. -2 The solution is prepared by heating a sodium citrate solution at mol / L for 1 hour and then cooling.

[0021] The beneficial effects of this invention include: In the Raman spectroscopy detection process enhanced by silver nanoparticle sol, potassium, sodium, or lithium metal ions are added. These metal ions play a modulating role in the Raman spectrum of the silver nanoparticle sol, further enhancing the Raman scattering effect and resulting in a good response intensity. This effectively improves the detection sensitivity for trace explosives, achieving a quantitative detection limit of up to 10. -9 The minimum concentration for qualitative detection of CTNB and TNT is 10 mol / L. -11 mol / L. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation process of surface-enhanced Raman samples according to the present invention;

[0023] Figure 2 This is a Raman spectroscopy image of silver sol and lithium metal ions against explosive CL-20 in Example 1;

[0024] Figure 3 This is a Raman spectroscopy image of silver sol and sodium ions against explosive CL-20 in Example 1;

[0025] Figure 4 This is a Raman spectroscopy image of silver sol and potassium ions against explosive CL-20 in Example 1;

[0026] Figure 5 In Example 1, silver sol and three metal ions reacted with different concentrations of explosive CL-20 at 1300 cm⁻¹. -1 1400cm -1 1500cm -1 Raman data plot;

[0027] Figure 6 This is a Raman spectroscopy image of silver sol and sodium ions reacting with explosive TNT in Example 2.

[0028] Figure 7 In Example 2, the silver sol and sodium ions reacted with the explosive TNT at 1300 cm⁻¹. -1 Raman data plot;

[0029] Figure 8 In Example 2, the concentration of the silver sol and the three metal ion pairs was 10. -6 mol / L~10 -8 mol / L of explosive TNT at 1400 cm⁻¹-1 Raman data plot;

[0030] Figure 9 This is a Raman spectroscopy image of silver sol and sodium ions against the explosive CTNB in ​​Example 3;

[0031] Figure 10 In Example 3, the silver sol and sodium ions reacted with the explosive CTNB at 1300 cm⁻¹. -1 Raman data plot;

[0032] Figure 11 In Example 3, the concentration of the silver sol and the three metal ion pairs was 10. -6 mol / L~10 -8 CTNB, an explosive of mol / L, at 1400 cm -1 Raman data plot;

[0033] Figure 12 The images shown are Raman spectroscopy results for explosives CL-20, TNT, and CTNB under conditions of adding / not adding sodium ions in Example 4, where a is the Raman spectroscopy result for explosive CL-20, b is the Raman spectroscopy result for explosive TNT, and c is the Raman spectroscopy result for explosive CTNB.

[0034] Figure 13 To test the explosive CL-20 at 1600 cm⁻¹ under different concentrations of sodium ions. -1 Raman data plot. Detailed Implementation

[0035] The present invention will be further described and illustrated below with reference to embodiments. However, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the present invention and the embodiments, all other inventions and embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0037] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Example 1: Raman Enhanced Detection of Explosive CL-20 (Hexanitrohexaazaisowulzane) Surface

[0038] Using CL-20 solutions of different concentrations in acetone and different types of metal ions as variables, this study discusses the effects of different CL-20 concentrations on CL-20 surface-enhanced Raman spectroscopy and the influence of different metal ions on CL-20 surface-enhanced Raman spectroscopy. The experiment used a concentration of 1×10⁻⁶ acetone. -3 mol / L~1×10 -9mol / L CL-20 acetone solution.

[0039] Flowchart as follows Figure 1 As shown, the specific steps are as follows:

[0040] (1) Preparation of aqueous solutions of silver sol and metal ion salts

[0041] a. Dissolve 36 mg of silver nitrate in 200 mL of deionized water to obtain a silver nitrate solution (concentration 1 × 10⁻⁶). -3 In a solution of mol / L, heat to boiling. Add 5 mL of the reducing agent solution dropwise to the boiling silver nitrate solution and continue heating for 1 hour. The reducing agent solution used in this example is a sodium citrate solution, which is prepared by dissolving 1 g of sodium citrate in 100 mL of deionized water, with a solution concentration of 4 × 10⁻⁶ mol / L. -2 mol / L. Cool to room temperature to obtain a silver sol solution.

[0042] b. Dissolve 13.8g of lithium nitrate in 200mL of deionized water to obtain a 1mol / L lithium nitrate solution; dissolve 17g of sodium nitrate in 200mL of deionized water to obtain a 1mol / L sodium nitrate solution; dissolve 20.2g of potassium nitrate in 200mL of deionized water to obtain a 1mol / L potassium nitrate solution.

[0043] (2) Take 1200 μL of silver sol solution and add it to a test tube. Then add 150 μL of lithium nitrate, sodium nitrate or potassium nitrate solution with a concentration of 1 mol / L, and then add 150 μL of CL-20 acetone solution of different concentrations. Let it stand. Then take the lower precipitate for Raman testing. The excitation wavelength is 532 nm and the integration time is 0.5 s.

[0044] Test results involving lithium ions are as follows Figure 2 As shown, the lower limit of the tested explosive CL-20 concentration reached 10. -9 At a concentration of mol / L, the Raman spectral intensity decreases gradually with decreasing explosive concentration. When the concentration of explosive CL-20 is 10 mol / L... -3 At mol / L, the spectral peak intensity exceeds 40,000; when the explosive concentration is 10... -9 At mol / L, the spectral peak intensity is around 3000.

[0045] The test results involving sodium ions are as follows: Figure 3 As shown, the lower limit of the tested explosive CL-20 concentration also reached 10. - 9 At a concentration of mol / L, the Raman spectral intensity also decreased gradually with decreasing explosive concentration. When the concentration of explosive CL-20 was 10 mol / L... -3 At mol / L, the spectral peak intensity reaches 60,000; when the explosive concentration is 10... -9At mol / L, the spectral peak intensity is around 2000.

[0046] The test results involving potassium ions are as follows: Figure 4 As shown, the lower limit of the tested explosive CL-20 concentration also reached 10. - 9 The Raman spectral intensity decreased gradually with decreasing explosive concentration (mol / L). When the concentration of explosive CL-20 was 10 mol / L... -3 At mol / L, the spectral peak intensity exceeds 60,000; when the concentration of the explosive CL-20 is 10... -9 At mol / L, the spectral peak intensity is around 2000.

[0047] like Figure 5 As shown, the 1300 cm⁻¹ Raman spectra of explosive CL-20 at various concentrations involving three different ions are analyzed. -1 1400cm -1 1500cm -1 A comparison of the data shows that the Raman spectra of explosive CL-20 regulated by lithium ions, sodium ions, and potassium ions decrease as the explosive concentration decreases. When the CL-20 concentration reaches 10... -7 After reaching a concentration of 10 mol / L, the change in spectral intensity decreased and tended to stabilize. This indicates that the tested concentration reached 10 mol / L. -7 The test limit was reached after mol / L.

[0048] It can be seen that for values ​​higher than 10 -6 For the detection of CL-20 at mol / L, potassium and sodium ions showed better modulating effects than lithium ions; however, when the CL-20 concentration was below 10 mol / L... -6 At a concentration of mol / L, the addition of lithium ions has a better Raman enhancement effect on explosives than that of potassium and sodium ions.

[0049] Example 2: Raman Enhanced Detection of Explosive TNT (2,4,6-Trinitrotoluene) Surface

[0050] Using TNT acetone solutions of different concentrations as variables, this study discusses the surface-enhanced Raman spectroscopy (SERS) results of TNT at different TNT concentrations. The experiment used a concentration of 1×10⁻⁶ TNT. -3 mol / L~1×10 -11 A mol / L TNT-acetone solution. The specific procedure is as follows:

[0051] (1) Preparation of silver sol and aqueous solution of metal ion salt

[0052] Same as steps a and b in Example 1.

[0053] (2) Take 1200 μL of silver sol solution and add it to a test tube. Then add 150 μL of sodium nitrate, lithium nitrate or potassium nitrate solution with a concentration of 1 mol / L, and then add 150 μL of TNT acetone solution of different concentrations. Let it stand. Take the lower precipitate for Raman testing. The Raman testing conditions are the same as in Example 1.

[0054] The test results involving sodium ions are as follows: Figure 6 As shown, the Raman spectral intensity decreases gradually with decreasing explosive concentration. When the explosive concentration is 10... -3 At mol / L, the spectral peak intensity is less than 30,000; when the explosive concentration is 10... -11 At mol / L, the spectrum is already close to the peak of the original solid sample. The Raman spectroscopy result involving sodium ions was taken at 1300 cm⁻¹. -1 Data plotting, such as Figure 7 As shown, it can be observed that when the TNT concentration of the explosive is less than 10... -8 At concentrations exceeding mol / L, the Raman intensity of the explosive tends to plateau, reaching the limit for quantitative detection of TNT; however, due to... Figure 6 It can be observed that when the TNT concentration of the explosive is 10... -9 mol / L~10 - 11 Even at a concentration of 10 mol / L, Raman spectroscopy could still clearly identify the TNT peak spectrum. This demonstrates that adding metal ions to the silver sol solution during surface-enhanced Raman spectroscopy can effectively detect TNT peaks at concentrations of 10 mol / L. -9 mol / L~10 -11 Qualitative detection of explosive TNT at mol / L.

[0055] Raman spectroscopy results of three ions were obtained at 1400 cm⁻¹. -1 The data was plotted, and the results are as follows: Figure 8 As shown, for the explosive TNT, at the same concentration, the Raman spectral peak intensity Li + <Na + <K + .

[0056] It is evident that the addition of potassium ions significantly enhances the Raman spectroscopy results for explosive TNT.

[0057] Example 3: Raman Enhanced Detection of Explosive CTNB (2,4,6-Trinitrochlorobenzene) Surface

[0058] Using CTNB acetone solutions of different concentrations as variables, the surface-enhanced Raman spectroscopy of CTNB measured at different CTNB concentrations was discussed. The experiment selected a concentration of 1×10⁻⁶. -3 mol / L~1×10 -11 A mol / L CTNB acetone solution. The specific procedure is as follows:

[0059] (1) Preparation of silver sol and aqueous solution of metal ion salt

[0060] Same as steps a and b in Example 1.

[0061] (2) Take 1200 μL of silver sol solution and add it to a test tube. Then add 150 μL of sodium nitrate, lithium nitrate or potassium nitrate solution with a concentration of 1 mol / L, and then add 150 μL of CTNB acetone solution of different concentrations. Let it stand. Take the lower precipitate for Raman testing. The Raman testing conditions are the same as in Example 1.

[0062] The test results involving sodium ions are as follows: Figure 9 As shown, the Raman spectral intensity decreases gradually with decreasing explosive concentration. When the CTNB concentration is 10... -3 At mol / L, the spectral peak intensity is close to 70,000; when the concentration of the explosive CTNB is 10... -11 At mol / L, the spectrum is close to the peak of the original solid sample. The Raman spectroscopy results involving sodium ions were obtained at 1300 cm⁻¹. -1 Data plotting, such as Figure 10 As shown, it can be observed that the Raman spectral intensity decreases significantly with the concentration of the explosive, especially when the concentration of the explosive CTNB reaches 10. -10 mol / L and 10 -11 At a concentration of mol / L, the Raman intensity of the explosive tends to plateau, indicating that when the concentration of CTNB in ​​the explosive is 10 mol / L... -9 The limit for quantitative testing of explosives is reached at mol / L. However, from Figure 9 It is known that the concentration of the explosive CTNB reached 10. -11 Although the Raman spectral intensity is relatively low at mol / L, the CTNB peak spectrum can still be clearly identified. This demonstrates that adding metal ions to the silver sol solution during surface-enhanced Raman spectroscopy can achieve clear detection of peaks at a concentration of 10 mol / L. -10 mol / L~10 -11 Qualitative detection of CTNB (mol / L explosive).

[0063] Raman spectroscopy results of three ions were obtained at 1400 cm⁻¹. -1 The data was plotted, and the results are as follows: Figure 11 As shown, for the explosive CTNB, at the same concentration, the Raman spectral peak intensity Li + <K + <Na + .

[0064] It is evident that sodium ions have a higher modulatory capacity for Raman testing of CTNB explosives than lithium and potassium ions.

[0065] Example 4: Raman Enhanced Detection of Explosive Surfaces (CL-20, TNT, CTNB) with and without Metal Ion Addition

[0066] This paper discusses surface-enhanced Raman spectroscopy (SERS) measurements of explosives with only silver sol and no metal ions. The experiment used a concentration of 1×10⁻⁶. -3 A mol / L acetone solution containing explosives. The specific procedures are as follows:

[0067] (1) Preparation of silver sol and aqueous solution of metal ion salt

[0068] Same as steps a and b in Example 1.

[0069] (2) Add 1200 μL of silver sol solution to a test tube, add 150 μL of 1 mol / L sodium nitrate solution, and then add 150 μL of 1×10⁻⁶ sodium nitrate solution. -3 An acetone solution of the explosive was prepared at a concentration of mol / L and allowed to stand. As a control, 1200 μL of silver sol solution was added to a test tube, followed by 150 μL of a 1×10⁻⁶ solution. -3 An acetone solution of the explosive was prepared at a concentration of mol / L and allowed to stand. All treated samples were collected and subjected to Raman spectroscopy under the same conditions as in Example 1.

[0070] Test results are as follows Figure 12 As shown. From Figure 12 As can be seen from a, the concentration of the CL-20 acetone solution used in the Raman test preparation was 10. -3 Compared to Raman testing of explosives with added sodium ions and a concentration of mol / L, the sample without sodium ion adjustment showed a Raman peak intensity of only 10,000, but reached 60,000 after sodium ion adjustment. Figure 12 As can be seen from b, the concentration of the TNT-acetone solution used in the Raman test preparation was 10. -3 Compared to Raman testing of explosives with added sodium ions and a concentration of mol / L, the sample without sodium ion adjustment showed a Raman peak intensity of only 10,000, but reached 25,000 after sodium ion adjustment. Figure 12 As can be seen from c, the concentration of the CTNB acetone solution used in the Raman test preparation was 10. - 3 Compared to Raman testing of explosives with added sodium ions and mol / L concentration, the Raman peak intensity of the sample without added sodium ions was only around 5000, but reached 65000 after adding sodium ions.

[0071] It is evident that, at the same explosive concentration, the Raman enhancement of pure silver gel is not particularly significant. However, the Raman response increases significantly after the addition of sodium ions, indicating that the modulation using metal ions is effective.

[0072] Example 5: Raman Enhanced Detection of Explosive CL-20 Surface under Different Concentrations of Sodium Ions

[0073] This paper discusses surface-enhanced Raman spectroscopy (SERS) measurements of explosive CL-20 under different concentrations of sodium ions. The experiment used a concentration of 1 × 10⁻⁶ sodium ions. -3 mol / L and 1×10 -6 A mol / L Cl-20 acetone solution. The specific procedure is as follows:

[0074] (1) Preparation of silver sol and aqueous solution of metal ion salt

[0075] Same as steps a and b in Example 1.

[0076] (2) Take 1200 μL of silver sol solution and add it to a test tube. Then add 150 μL of sodium nitrate solution with concentrations of 0.5 mol / L, 1 mol / L, and 2 mol / L, respectively. Finally, add 150 μL of sodium nitrate solution with a concentration of 1×10⁻⁶. -3 Add 1200 μL of CL-20 acetone solution and let stand. Similarly, add 150 μL of 0.5 mol / L, 1 mol / L, and 2 mol / L sodium nitrate solution respectively to a test tube, followed by 150 μL of 1×10⁻⁶ mol / L sodium nitrate solution. -6 A solution of 1 mol / L CL-20 in acetone was prepared and allowed to stand. All treated precipitates were collected for Raman spectroscopy analysis under the same conditions as in Example 1.

[0077] Test results are as follows Figure 13 As shown. From Figure 13 It can be seen from this that when the concentration of CL-20 is 1×10 -3 mol / L and 1×10 -6 At a sodium ion concentration of 1 mol / L, the surface Raman enhancement intensity of CL-20 obtained was greater than that obtained at sodium ion concentrations of 0.5 mol / L and 2 mol / L. Therefore, the preferred experimental condition for detecting explosives is a sodium ion concentration of 1 mol / L.

Claims

1. A method of surface enhanced Raman detection of trace amounts of explosives, characterized in that, The method comprises the following steps: (1) adding a certain amount of metal ion salt solution into the silver sol solution, then adding the explosive solution to be detected, shaking and standing; (2) taking the lower sediment and dropping it on the substrate for Raman test; The silver sol solution contains gel particles with a particle size range of 40-60 nm and a silver gel particle number concentration of 4 × 10⁻⁶. 11 / mL-5×10 11 / mL; the metal ion salt solution is a sodium nitrate, potassium nitrate, or lithium nitrate solution, and the metal ion concentration in the metal ion salt solution is 0.5 mol / L-5 mol / L; the volume ratio of the silver sol solution to the metal ion salt solution is 8:1; the explosive is CL-20, TNT, or CTNB; When the explosive to be detected is TNT, the added metal ion is potassium ion; When the explosive to be detected is CTNB, the added metal ion is sodium ion; When the explosive to be detected is CL-20 and its concentration is higher than 10 - 6 mol / L, the added metal ion is selected from potassium ion or sodium ion; when the concentration of CL-20 is lower than 10 - 6 mol / L, the added metal ion is selected from lithium ion.

2. The method of claim 1, wherein, The concentration of the metal ion in the metal ion salt solution is 1 mol / L.

3. The method of claim 2, wherein, One or more of the following (1)-(6) are included: (1) the preparation method of the silver sol comprises: heating a certain amount of silver nitrate solution to boiling, then slowly dropping a certain amount of sodium citrate solution into the boiling silver nitrate solution, continuing to heat for 1 h, and cooling to obtain the silver sol; (2) the explosive solution is an explosive acetone solution; (3) the explosive CL-20 solution concentration is 1 x 10 -3 mol / L - 1 x 10 -9 mol / L; (4) The explosive CTNB and TNT solution concentration is 1 x 10 -3 mol / L-1 x 10 -11 mol / L; (5) the Raman test selects 785 nm, 633 nm or 532 nm laser; (6) the substrate is a glass slide.

4. The method of claim 3, wherein, In the silver nitrate solution and the sodium citrate solution, the molar ratio of silver nitrate to sodium citrate is 1:

1.

5. The method of claim 4, wherein, The concentration of the silver nitrate solution and the sodium citrate solution is 1 x 10 -1 mol / L - 1 x 10 -5 mol / L.

6. The method of claim 5, wherein, The preparation method of the silver sol comprises the following steps: taking silver nitrate solution with a concentration of 1×10 -3 mol / L and heating to boiling; adding sodium citrate solution with a concentration of 4×10 -2 mol / L according to a volume ratio of 40:1 of the silver nitrate solution to the sodium citrate solution; continuously heating for 1 h; and cooling to obtain the silver sol.

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