Silicon-based SERS substrate material and preparation method thereof

Abstract

The present invention discloses a silicon-based SERS substrate material and its preparation method, which mainly includes three steps: silicon surface etching, Ag chemical reduction and Au / Ag galvanic replacement reaction. The obtained silicon-based SERS substrate material has strong SERS activity (enhancement factor EF>10) under 785nm excitation light. 7 ), surface uniformity (RSD < 15%), batch consistency (RSD < 15%), chemical stability, and water stability. The method of the present invention is rapid, simple, and low-cost, and is expected to be used for the commercial production of SERS substrate materials and for potential commercial SERS applications.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of new nano functional materials, and in particular relates to a new silicon-based SERS substrate material and a preparation method thereof. Background Art

[0002] Surface-enhanced Raman spectroscopy (SERS) can significantly enhance the analytical Raman spectroscopy signal of molecules adsorbed on rough metal surfaces or nanomaterials through electromagnetic or chemical enhancement. In recent years, SERS has garnered widespread attention in the field of analytical chemistry due to its ultra-high detection sensitivity, rapidity, low cost, and ability to obtain molecular fingerprint information.

[0003] The preparation of SERS substrate materials is the basis for obtaining SERS signals and is also the key to affecting the performance of SERS analysis. A good SERS substrate material should meet the following requirements: (1) good SERS enhancement activity; (2) the substrate surface maintains uniformity, and the relative standard deviation (RSD) of the signal between different points is less than 20%; (3) repeatability, and the signal enhancement deviation of SERS substrates prepared from different batches should be less than 20%; (4) the substrate material surface is clean and has no background interference signal; (5) good chemical stability for easy storage; (6) good water stability for easy reaction in aqueous solution; (7) simple preparation and low cost, which will help the industrialization and scale-up of material preparation. Therefore, the preparation of SERS substrate materials that meet the above conditions is of great significance for promoting the development of SERS analysis technology.

[0004] Noble metal (mainly Au and Ag) nanosols are common SERS active substrate materials. They have the advantages of being easy, fast and inexpensive to prepare, but nanoparticles tend to aggregate easily in solution, making it difficult to generate reproducible SERS signals. To address the above problems, researchers have attempted to deposit highly ordered nanoparticles on the surface of solid materials (such as silicon wafers, alumina, paper, etc.) through physical (such as thermal evaporation, magnetron sputtering, etc.), chemical (such as chemical reduction, self-assembly, etc.) or advanced nanofabrication technologies (such as nanolithography, nanocopying, etc.). These methods have promoted the progress of SERS substrate material preparation methods, but there are still some shortcomings, such as high preparation costs, cumbersome steps, or the performance of the obtained SERS substrate materials still does not meet the potential commercial application requirements in terms of enhanced activity, uniformity, batch consistency, or stability. The applicant previously deposited Au-Ag nanoparticles on the surface of a silicon wafer through chemical reduction and metal replacement reaction, obtaining a silicon-based SERS substrate material with a simple preparation method, low preparation cost, high SERS activity and high substrate surface uniformity. However, if the SERS material is immersed in water for more than two hours, or if the dried substrate is placed back in the aqueous solution, the deposited nanometal film will fall off, limiting its further practical application. Therefore, how to prepare high-performance substrate materials is a key challenge that needs to be solved to promote the commercialization of SERS technology. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a method for preparing a silicon-based SERS substrate material, which has the characteristics of simple, rapid and low cost, and the obtained SERS substrate material has strong SERS activity, high material surface uniformity and batch consistency, as well as good chemical stability and water stability.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a silicon-based SERS substrate material comprises the following steps:

[0008] (1) The silicon material was ultrasonically cleaned with acetone, ethanol, and deionized water for 5 to 10 minutes each;

[0009] (2) Using a CuCl2 / H2O2 / HF mixed system to etch silicon material, a silicon wafer textured with arrays of inverted nano-pyramids (SiAINP) with Cu particles on the surface was obtained;

[0010] (3) Place the SiAINP containing Cu particles in a dilute nitric acid solution for a certain period of time to remove the Cu particles on the surface, and then wash it with purified water;

[0011] (4) After the nitric acid treatment, the SiAINP was washed with purified water and then immersed in HF solution for a period of time to remove surface oxides and form Si-H bonds;

[0012] (5) SiAINP was placed in a mixed solution of AgNO3 / HF and gently shaken at room temperature for a certain period of time to obtain Ag@SiAINP with Ag nanoparticles coated on the surface;

[0013] (6) After washing the Ag@SiAINP with purified water, soak it in HF solution again for a period of time;

[0014] (7) The Ag@SiAINP was placed in a HAuCl4 / HF mixed solution for a certain period of time, and then taken out and cleaned to obtain the product: Au-Ag@SiAINP.

[0015] The silicon-based SERS substrate material prepared according to the method of the present invention has strong SERS activity (enhancement factor>10 7 ), high material surface uniformity and batch consistency (Raman probe molecular signal RSD <15%), as well as good chemical stability (SERS performance remains unchanged after storage at -20°C for 6 weeks) and water stability (the surface nanometal film will not fall off when placed in water for 24 hours or the dried SERS chip is placed in water again).

[0016] The silicon material used in step (1) is a crystalline <100> of single crystal silicon wafers.

[0017] The CuCl2 concentration used in step (2) is 5-20 mM, the H2O2 concentration is 0.2-0.6 M, the HF concentration is 2.5%-10% (volume ratio), the reaction temperature is 45-65° C., and the reaction time is 15-30 min.

[0018] In step (3), the dilute nitric acid is obtained by mixing 65% concentrated nitric acid with purified water, and the soaking time is 5 to 10 minutes.

[0019] In step (4), the HF concentration is 5-10%, and the soaking time is 30-40 minutes.

[0020] In step (5), the concentration of AgNO3 is 1-5 mM, the concentration of HF is 5-10%, and the reaction time is 10-30 s.

[0021] The soaking time in step (6) is 5 to 15 minutes.

[0022] In step (7), the HAuCl4 concentration is 1.25-3 mM, the HF concentration is 5-10%, the reaction temperature is 50-60°C, and the reaction time is 10-30 min. The cleaning solutions are saturated saline, 1% HF solution, and purified water, respectively, and the cleaning time is 8-10 min.

[0023] The SERS chip prepared in step (7) has strong SERS activity (enhancement factor>10 7 ), high material surface uniformity and batch consistency (Raman probe molecular signal RSD <15%), as well as good chemical stability (SERS performance remains unchanged after storage at -20°C for 6 weeks) and water stability (the surface nanometal film will not fall off when placed in water for 24 hours or the dried SERS chip is placed in water again).

[0024] The SERS performance of the SERS chip prepared in step (7) was evaluated by Rhodamine 6G (R6G). The specific parameters of the Raman spectrometer used were: the excitation wavelength of the Raman spectrum was 785 nm, the output power was 300 mW, the exposure time was 2 s, and the spot size was 0.1 mm.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The material preparation method is simple and low-cost, without the need for expensive reagents or instruments;

[0027] (2) The preparation time is fast and can be prepared on a large scale, with all steps completed within 3 hours;

[0028] (3) The obtained substrate material has good performance in terms of SERS activity, material uniformity, batch consistency, etc., meeting the requirements of high-sensitivity analysis;

[0029] (4) The material has high chemical stability and can be stored at -20°C for 6 weeks while still maintaining SERS performance;

[0030] (5) Good water stability, successfully solving the problem of poor water stability of the silicon-based SERS substrate material prepared by the applicant in the early stage. Given the good performance of the substrate material obtained by the method of the present invention, it shows great prospects for commercial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 SEM morphology of SiAINP, where (a) is a top view and (b) is a side view;

[0032] Figure 2 SEM morphology of Au-Ag@SiAINP, where (a) is the top view and (b) is the side view;

[0033] Figure 3 Surface element analysis results of Au-Ag@SiAINP;

[0034] Figure 4 is 10 -12 M~10 -7 Raman spectrum of M's R6G adsorbed on the Au-Ag@SiAINP surface;

[0035] Figure 5 is 10 -8 Raman spectra of 30 random points collected on the surface of Au-Ag@SiAINP material by MR6G adsorption (a) and its Raman spectra at 1509 cm -1 RSD value of intensity at (b);

[0036] Figure 6 is 10 -8 Raman spectra of 45 randomly collected points on the surface of Au-Ag@SiAINP materials prepared from three different batches of MR6G adsorbed on the surface of the Au-Ag@SiAINP materials (a) and its Raman spectra at 1509 cm -1 RSD value of intensity at (b);

[0037] Figure 7 is 10 -8 Raman spectra of M R6G adsorbed on Au-Ag@SiAINP at different storage times;

[0038] Figure 8 These are pictures of different SERS substrate materials after being immersed in purified water for 24 hours, where I is Au-Ag@SiAINP and II is the silicon material with etched surface. DETAILED DESCRIPTION

[0039] The specific implementation methods of the present invention are further described in detail below with reference to specific examples.

[0040] Example 1

[0041] (1) Take the crystal form <100> The silicon material was ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes each.

[0042] (2) The cleaned silicon material is placed in a mixed solution containing 20mM CuCl2, 0.55M H2O2 and 2.5% HF, and reacted at 45°C for 15 minutes. This step of reaction can obtain SiAINP with Cu particles on the surface and an inverted pyramid array etched on the silicon surface structure. Its SEM morphology is shown in Figure 1 After soaking in purified water for 24 hours, the following picture is obtained: Figure 8 As shown in II;

[0043] (3) The SiAINP containing Cu particles was placed in a dilute nitric acid solution (obtained by mixing 65% concentrated nitric acid with purified water in a ratio of 1:1) and reacted for 5 minutes to remove the Cu particles on the surface.

[0044] (4) After nitric acid treatment, the SiAINP was washed with purified water and then immersed in a 5% HF solution for 30 min to remove surface oxides and form Si-H bonds;

[0045] (5) The HF-treated SiAINP was placed in a mixed solution containing 3 mM AgNO3 and 5% HF and gently shaken at room temperature for 20 s to obtain Ag@SiAINP with Ag nanoparticles coated on the surface;

[0046] (6) After washing the Ag@SiAINP with purified water, immerse it in 5% HF solution for 10 min.

[0047] (7) The Ag@SiAINP was placed in a mixed solution containing 2.5 mM HAuCl4 and 5% HF and reacted at 60°C for 15 min to obtain a material with Au-Ag nanoparticles deposited on the surface;

[0048] (8) The material in step (7) was soaked in saturated salt water, 1% HF solution and purified water for 10 min in sequence, and then taken out and dried to obtain the final SERS substrate material Au-Ag@SiAINP. The SEM morphology is shown in FIG. Figure 2 , the surface element analysis results are shown in Figure 3 After soaking in purified water for 24 hours, the following picture is obtained: Figure 8 As shown in I.

[0049] The SERS performance of the obtained SERS substrate was evaluated after adsorption of R6G. The specific parameters of the Raman spectrometer used were: the excitation wavelength of the Raman spectrum was 785nm, the output power was 300mW, the exposure time was 2s, and the spot size was 0.1mm. The results are shown in Figures 4 to 7 .

Claims

1. A method for preparing a silicon-based SERS substrate material, characterized in that: The steps include: (1) The silicon material was ultrasonically cleaned with acetone, ethanol, and deionized water for 5 to 10 minutes each; (2) using a CuCl2 / H2O2 / HF mixed system to etch the silicon material, obtaining a silicon surface structure SiAINP containing Cu particles and etched with an inverted pyramid array; (3) Placing the SiAINP containing Cu particles in a dilute nitric acid solution to remove the Cu particles on the surface; (4) After the nitric acid treatment, the SiAINP was washed with purified water and then immersed in an HF solution to remove surface oxides and form Si-H bonds; (5) SiAINP was placed in a mixed solution of AgNO3 / HF and gently shaken at room temperature to obtain Ag@SiAINP with Ag nanoparticles coated on the surface; (6) After washing the Ag@SiAINP with purified water, immerse it in HF solution again; (7) placing Ag@SiAINP in a HAuCl4 / HF mixed solution for reaction, taking it out and washing it to obtain the product; In step (2), the CuCl2 concentration is 5-20 mM, the H2O2 concentration is 0.2-0.6 M, and the HF volume concentration is 2.5%-10%; In step (5), the AgNO3 concentration is 1-5 mM, the HF volume concentration is 5-10%, and the reaction time is 10-30 s; In step (7), the HAuCl4 concentration is 1.25-3 mM, the HF volume concentration is 5-10%, the reaction temperature is 50-60°C, and the reaction time is 10-30 min; The cleaning solutions in step (7) are saturated saline, 0.5-1% HF solution and purified water, respectively, and the cleaning time is 8-10 minutes.

2. The method for preparing a SERS substrate material according to claim 1, wherein: The silicon material used in step (1) is a crystalline <100> of single crystal silicon wafers.

3. The method for preparing a SERS substrate material according to claim 1, wherein: In step (2), the reaction temperature is 45-65° C., and the reaction time is 15-30 min.

4. The method for preparing a SERS substrate material according to claim 1, wherein: In step (3), the dilute nitric acid is obtained by mixing 65% concentrated nitric acid with purified water, and the soaking time is 5 to 10 minutes.

5. The method for preparing a SERS substrate material according to claim 1, wherein: In step (4), the HF volume concentration is 5-10%, and the soaking time is 30-40 minutes.

6. The method for preparing a SERS substrate material according to claim 1, wherein: The soaking time in step (6) is 5 to 15 minutes.

7. A silicon-based SERS substrate material, characterized in that: It is prepared according to the preparation method according to any one of claims 1 to 6.

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