Preparation method of flower-like silver / copper oxide composite array SERS (Surface Enhanced Raman Scattering) substrate

Abstract

The invention discloses a preparation method of a flower-like silver / copper oxide composite array SERS (Surface Enhanced Raman Scattering) substrate. According to the method, a periodic flower-shaped copper oxide array structure is conveniently prepared by taking single-layer densely-arranged polystyrene microspheres as a template and combining an oxidation reaction, and then a layer of thin silver film is modified on the flower-shaped copper oxide array structure by utilizing a vacuum thermal evaporation technology, so that the flower-shaped silver / copper oxide composite array SERS substrate with high-density nanoscale slits is obtained. The SERS substrate prepared by the invention has good self-cleaning ability, can be recycled, realizes high-stability and high-sensitivity SERS signal detection, and can significantly reduce the detection time and use cost.

Description

Technical Field

[0001] The patent of this invention belongs to the field of micro-nano structure preparation and surface enhanced Raman spectroscopy technology, and relates to a method for preparing a flower-shaped silver / copper oxide composite array SERS substrate. Background Art

[0002] Surface enhanced Raman scattering (SERS) is an ultra-sensitive non-destructive detection and analysis technology that is widely used in biochemical sensing, medical diagnosis, food safety, and environmental monitoring. Traditional SERS substrates mainly use chemical synthesis, chemical templates, electrochemical deposition, and physical processing techniques to construct precious metal nanoparticle clusters or array-type micro-nano structures with high-density nanoscale tips and gaps, and achieve high Raman detection sensitivity based on the strong local electric field formed by plasmon coupling. However, SERS substrates made of precious metal materials are not easy to remove after probe molecules are adsorbed on their surfaces. Usually, the substrate can only be used once, which increases the cost and time of SERS detection. Constructing a high-performance SERS substrate with self-cleaning function is of great significance to further expand the scope of SERS applications.

[0003] At present, a variety of metal / semiconductor composite SERS substrates have been developed, such as composite micro-nano structures modified with precious metal nanoparticles such as titanium dioxide, zinc oxide and copper oxide, which realize the recycling of SERS substrates and reduce the time and cost of substrate preparation. Among the many composite structures, the precious metal / copper oxide composite structure has attracted much attention because copper oxide has the characteristics of narrow band gap, excellent stability and good matching with the visible spectrum. This composite substrate can catalytically degrade the molecules adsorbed on its surface under white light irradiation, and at the same time achieves high SERS enhancement and recycling. However, the current preparation method of precious metal / copper oxide composite structure is to first oxidize high-purity copper sheets or copper films to prepare copper oxide sheets or wire structures, and then modify precious metal particles on their surfaces to form precious metal / copper oxide composite structures. The copper oxide prepared by these methods is randomly distributed, and the stability of the SERS signal of the prepared composite structure is poor, which limits the application range of precious metal / copper oxide composite structures. Therefore, it is an urgent problem to develop an efficient and low-cost method to prepare large-area periodic precious metal / copper oxide composite array SERS substrates to achieve sensitive, stable and recyclable SERS detection and meet the technical needs of trace substance analysis in fields such as food safety and environmental monitoring. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a large-area, periodic, and high-density nano-level gap flower-shaped silver / copper oxide composite array SERS substrate. The method is based on a single-layer close-packed polystyrene (PS) microsphere template, combined with oxidation reaction and thermal evaporation technology, to conveniently prepare a periodic flower-shaped silver / copper oxide composite array structure. The prepared substrate can be recycled and achieves high stability and high sensitivity Raman signal detection.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a flower-shaped silver / copper oxide composite array SERS substrate comprises the following steps:

[0007] S1: A single layer of closely packed polystyrene (PS) microspheres template is self-assembled on the surface of a copper sheet with the oxide layer removed to obtain a PS / Cu substrate;

[0008] S2: Sodium hypochlorite solution was drop-coated on the surface of PS / Cu substrate and then placed in a sealed container for oxidation;

[0009] S3: The substrate obtained in step S2 is fully rinsed with deionized water to obtain a flower-shaped copper oxide array structure;

[0010] S4: Using vacuum evaporation equipment to evaporate Ag thin film on the flower-shaped copper oxide array structure to obtain a flower-shaped silver / copper oxide composite array SERS substrate.

[0011] The step S1 specifically includes the following steps:

[0012] S1-1: cleaning the copper substrate and placing it in a hydrochloric acid solution to remove the surface oxide layer;

[0013] S1-2: performing hydrophilic treatment on the copper sheet substrate after removing the surface oxide layer;

[0014] S1-3: Self-assembled monolayer close-packed PS sphere film on the surface of deionized water;

[0015] S1-4: Use a hydrophilic copper substrate to slowly pick up a single layer of densely packed PS ball film, dry it naturally, and then heat it on an electric heating platform to make the PS balls adhere to the copper substrate to prepare a PS / Cu substrate.

[0016] In step S2, the concentration of the sodium hypochlorite solution is 8% to 12%, preferably 10%, and the amount of the sodium hypochlorite solution applied is 0.15 to 0.25 mL / cm 2 , preferably 0.2 mL / cm 2 The oxidation time is 6 to 10 hours, preferably 8 hours.

[0017] In step S4, the vacuum degree of the vacuum evaporation equipment is better than 4×10 -4 Pa, the thickness of the evaporated silver film is 10~60nm, preferably 35nm.

[0018] Beneficial effects of the present invention: The method for preparing a flower-shaped silver / copper oxide composite array SERS substrate designed by the present invention has the following advantages:

[0019] (1) The preparation process is simple, easy to operate and low cost;

[0020] (2) The flower-shaped silver / copper oxide composite array SERS substrate prepared by the present invention has a long-range ordered periodic structure, and the period can be easily controlled;

[0021] (3) High SERS signal detection sensitivity and excellent signal spatial distribution uniformity;

[0022] (4) It has good recycling capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a preparation flow chart of a flower-shaped silver / copper oxide composite array SERS substrate provided in Example 1 of the present invention: wherein: 1. copper sheet substrate; 2. polystyrene (PS) ball film; 3. sodium hypochlorite solution; 4. sealed container; 5. flower-shaped copper oxide array structure; 6. flower-shaped silver / copper oxide composite array SERS substrate.

[0024] Figure 2 This is a scanning electron microscope (SEM) image of the flower-shaped copper oxide array structure prepared in Example 1 of the present invention.

[0025] Figure 3 This is a SEM image of the flower-shaped silver / copper oxide composite array SERS substrate prepared in Example 1 of the present invention.

[0026] Figure 4 1 is the XRD diagram of the flower-shaped copper oxide array structure prepared in Example 1 of the present invention.

[0027] Figure 5 The SEM images of the flower-shaped silver / copper oxide composite array SERS substrates with different periods prepared in the comparative examples of the present invention are shown in Figure 1. (a) is a SEM image of the flower-shaped silver / copper oxide composite array SERS substrate prepared by a PS sphere template with a diameter of 1000 nm, and (b) is a SEM image of the flower-shaped silver / copper oxide composite array SERS substrate prepared by a PS sphere template with a diameter of 2000 nm.

[0028] Figure 6(a) is the Raman spectra of the flower-shaped silver / copper oxide composite array SERS substrate prepared by the present invention adsorbing different concentrations of R6G molecules; (b) is the Raman frequency shift of 612 cm -1 Linear plot of the logarithm of peak intensity versus the logarithm of concentration.

[0029] Figure 7 (a) is a flower-shaped silver / copper oxide composite array SERS substrate prepared by the present invention adsorbing 10 -6 Raman spectra of R6G molecules of M at 20 random positions; (b) is the Raman frequency shift of 774 cm -1 Histogram of Raman peak intensity versus measurement position.

[0030] Figure 8 (a) is the flower-shaped silver / copper oxide composite array SERS substrate prepared by the present invention for adsorption of 10 -7 The cyclic detection Raman spectrum of the R6G molecule of M, (b) is the Raman frequency shift of 612 cm -1 Peak intensity versus cycle number. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The same reference numerals in the drawings always represent the same parts. The described embodiments are only some embodiments of the present application, not all embodiments.

[0032] Example 1

[0033] like Figure 1 , which is a preparation flow chart and a schematic diagram of the structures in each step of Example 1 of the present invention. Example 1 of the present invention is a method for preparing a flower-shaped silver / copper oxide composite array SERS substrate, the steps comprising:

[0034] S1: As Figure 1 -A, a PS / Cu substrate is obtained by self-assembling a single layer of densely packed polystyrene (PS) microsphere template on the surface of a copper sheet where the oxide layer is removed;

[0035] S1-1: After cleaning the copper substrate 1, place it in a hydrochloric acid solution to remove the surface oxide layer. The copper substrate 1 is ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes in sequence to remove the surface organic matter; then the copper substrate 1 is immersed in a dilute hydrochloric acid solution to remove the surface oxide layer of the copper substrate 1. In this embodiment, the concentration of the hydrochloric acid solution is 0.2~0.3 M, preferably 0.25 M; the immersion time is 3~7 min, preferably 5 min; finally, the copper substrate 1 is ultrasonically cleaned in deionized water for 10 minutes and then blown dry with nitrogen for standby use;

[0036] S1-2: The copper substrate 1 in step S1-1 is subjected to hydrophilic treatment. The copper substrate 1 is placed in a plasma cleaning machine and cleaned at a low setting for 10 to 20 minutes to increase the hydrophilicity of the copper substrate 1, preferably 15 minutes;

[0037] S1-3: Self-assembled monolayer close-packed PS sphere film 2. First, prepare a 2wt% sodium dodecyl sulfate (SDS) aqueous solution. Mix a 1wt% PS sphere suspension with a diameter of 700 nm and ethanol in a ratio of 1:1 and then ultrasonically form a PS sphere dispersion for use. Then, use a micropipette to take an appropriate amount of PS sphere dispersion and slowly inject it into the surface of the deionized water along the edge of a glass container containing deionized water. After natural dispersion, inject 50-100 microliters of SDS solution on the surface of the deionized water to obtain a monolayer close-packed PS sphere film 2;

[0038] S1-4: Use the copper substrate 1 obtained in step S1-2 to slowly pick up the single-layer densely packed PS ball film 2 prepared in step S1-3, dry it naturally, and then place it on a heating table for heating for 5 minutes to make the PS balls adhere to the copper substrate 1 to obtain a PS / Cu substrate. The optimal temperature of the heating table is 100°C.

[0039] S2: Figure 1 -B, after sodium hypochlorite solution 3 is dripped on the surface of PS / Cu substrate, it is placed in a closed container 4 for oxidation. In this embodiment, the optimal concentration of sodium hypochlorite solution is 10%, and the optimal dripping amount is 0.2 mL / cm 2 , the oxidation time is preferably 8 hours;

[0040] S3: Figure 1 -C, the substrate obtained in step S2 is fully rinsed with deionized water to obtain a flower-shaped copper oxide array structure 5;

[0041] S4: Figure 1 -D, a Ag thin film is deposited on the flower-shaped copper oxide array structure 5 using a vacuum coating machine to obtain a flower-shaped silver / copper oxide composite array SERS substrate 6. In this embodiment, the vacuum degree of the vacuum coating machine is better than 4×10 -4 Pa, the Ag evaporation rate is 0.2 Å / s, and the optimal thickness of the evaporated silver film is 35 nm.

[0042] The material composition of the prepared flower-like copper oxide array structure was characterized by an X-ray diffractometer (Bruker, D8 Advance), and the morphology of the prepared array structure was characterized by a scanning electron microscope (ZEISS, Sigma 300).

[0043] Figure 2 and Figure 3Shown are SEM morphology images of flower-like copper oxide array structure and flower-like silver / copper oxide composite array SERS substrate, respectively. The prepared micro-nano structure presents a large-area, periodic flower-like array structure. Figure 4 The XRD pattern of the flower-like copper oxide array structure is shown. The peaks at 32.49° and 38.73° correspond to the (110) and (111) crystal planes of CuO, respectively, indicating that a copper oxide structure is obtained.

[0044] In this embodiment, the period of the flower-shaped silver / copper oxide composite array SERS substrate can be adjusted. In step S1, the diameter of the PS balls in the PS ball film 2 can be adjusted to obtain flower-shaped silver / copper oxide composite array SERS substrates with different periods. As a comparative example, specifically, in step S1, the diameter of the PS balls is replaced with 1000 nm and 2000 nm to obtain flower-shaped silver / copper oxide composite array SERS substrates with corresponding periods, such as Figure 5 shown.

[0045] Example 2

[0046] The SERS activity and signal stability of the flower-shaped silver / copper oxide composite array SERS substrate prepared in Example 1 were evaluated.

[0047] Using rhodamine 6G (R6G) as the probe molecule, the prepared flower-shaped silver / copper oxide composite array SERS substrate was placed in 1 mL of 10 -5 M, 10 -6 M, 10 -7 M, 10 -8 M, 10 -9 The substrate was immersed in R6G ethanol solution for 90 min, and then taken out and dried with nitrogen for Raman spectroscopy. The laser wavelength was 532 nm, the laser power was 0.2 mw, and the spectrum acquisition time was 5 s. The SERS spectrum was obtained as shown in the figure. Figure 6 As shown. Figure 6 (a) It can be seen that the flower-shaped silver / copper oxide composite array SERS substrate prepared in Example 1 has a high SERS detection activity for R6G, even at 10 -9 There is still a strong Raman response at low concentrations of M. Figure 6 (a) Raman frequency shift of different concentrations in Raman spectra is 612 cm -1 The peak intensity is plotted, and the relationship between the logarithm of the peak intensity and the logarithm of the concentration is plotted, such as Figure 6 (b). Figure 6 (b) It can be seen that there is a good linear relationship between the Raman signal intensity and the solution concentration, and the linear correlation coefficient R 2=0.988, indicating that the flower-shaped silver / copper oxide composite array SERS substrate prepared by the present invention has high SERS activity and is suitable for low-concentration molecular detection and quantitative analysis.

[0048] 10 -6 M R6G molecules, randomly select 20 different positions on the substrate and measure their corresponding Raman spectra, such as Figure 7 As shown, the Raman spectra corresponding to the 20 different positions are basically the same. Specifically, the extracted Figure 6 (a) The Raman frequency shift in the Raman spectrum is 774 cm -1 The peak intensity of Figure 6 As shown in (b), the relative standard deviation (RSD) of the peak intensity is 10%, indicating that the flower-shaped silver / copper oxide composite array SERS substrate prepared in Example 1 of the present invention has good uniformity in spatial distribution of SERS signals.

[0049] Example 3

[0050] The copper oxide band gap is narrow. Under the irradiation of white light, electron transfer occurs between copper oxide and Ag, generating positively charged holes and negatively charged electrons. The holes and electrons react with OH in water. - Combined with oxygen to form highly oxidative hydroxyl radicals (•OH) and superoxide anion radicals (•O 2 - ), these free radicals can effectively degrade the molecules adsorbed on the flower-shaped silver / copper oxide composite array SERS substrate prepared in Example 1, and realize the recycling function of the SERS substrate. In order to test the recycling ability of the flower-shaped silver / copper oxide composite array SERS substrate prepared in Example 1. The flower-shaped silver / copper oxide composite array SERS substrate was placed in 10 -7 The R6G probe molecule was adsorbed into the R6G solution of M and the corresponding Raman spectrum was measured. The Raman characteristic peak of the R6G molecule was clearly visible. After the measurement was completed, the flower-shaped silver / copper oxide composite array SERS substrate adsorbed with the R6G probe molecule was placed in deionized water. After irradiation with a xenon lamp for 60 minutes, the Raman spectrum corresponding to the SERS substrate was measured again. The characteristic peak of the R6G molecule disappeared. Repeat the above steps and the Raman spectrum obtained is as follows Figure 8 As shown, the flower-shaped silver / copper oxide composite array SERS substrates all exhibit good enhancement and degradation capabilities, indicating that the flower-shaped silver / copper oxide composite array SERS substrate prepared in Example 1 of the present invention has good recycling capabilities and can effectively reduce the substrate preparation time and cost.

[0051] The above-described embodiment provides a detailed description of the preparation method of a flower-shaped silver / copper oxide composite array SERS substrate, which is illustrative rather than restrictive. Many equivalent substitutions and improvements can be made without departing from the principles of the present invention, and these should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a flower-shaped silver / copper oxide composite array SERS substrate, characterized in that: The preparation method comprises the following steps: S1: A single layer of closely packed polystyrene (PS) microspheres template is self-assembled on the surface of a copper sheet with the oxide layer removed to obtain a PS / Cu substrate; S2: Sodium hypochlorite solution was drop-coated on the surface of PS / Cu substrate and then placed in a sealed container for oxidation; S3: The substrate obtained in step S2 is fully rinsed with deionized water to obtain a flower-shaped copper oxide array structure; S4: Using vacuum evaporation equipment to evaporate Ag thin film on the flower-shaped copper oxide array structure to obtain a flower-shaped silver / copper oxide composite array SERS substrate.

2. The method for preparing a flower-shaped silver / copper oxide composite array SERS substrate according to claim 1, characterized in that: Step S1: self-assembling a single layer of densely packed polystyrene (PS) microsphere template on the surface of a copper sheet where the oxide layer has been removed to obtain a PS / Cu substrate, comprising the following steps: S1-1: cleaning the copper substrate and placing it in a hydrochloric acid solution to remove the surface oxide layer; S1-2: performing hydrophilic treatment on the copper sheet substrate after removing the surface oxide layer; S1-3: Self-assembled monolayer close-packed PS sphere film on the surface of deionized water; S1-4: Use a hydrophilic copper substrate to slowly pick up a single layer of densely packed PS ball film, dry it naturally, and then heat it on an electric heating platform to make the PS balls adhere to the copper substrate to prepare a PS / Cu substrate.

3. According to the method for preparing a flower-shaped silver / copper oxide composite array SERS substrate according to claim 2, the concentration of the hydrochloric acid solution in step S1-1 is 0.2~0.3M, and the immersion time is 3~7 min.

4. The method for preparing a flower-shaped silver / copper oxide composite array SERS substrate according to claim 1, characterized in that: In step S2, the concentration of sodium hypochlorite solution is 8% to 12%, and the amount of sodium hypochlorite solution applied is 0.15 to 0.25 mL / cm 2 , the oxidation time is 6~10 hours.

5. The method for preparing a flower-shaped silver / copper oxide composite array SERS substrate according to claim 1, characterized in that: The thickness of the Ag film deposited in step S4 is 10-60 nm.

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