A method for preparing an array microporous SERS substrate with a nanostructured inner wall

Abstract

The present invention belongs to the technical field of SERS substrate preparation, and specifically relates to a method for preparing an array micropore SERS substrate with a nanostructured inner wall, the steps of which include analyzing the propagation mode of light in micropores with nanostructured inner walls and the correlation between the micropore size and the light capture capability; constructing micropore units on the surface of the SERS substrate material, the bottom and side walls of the micropores forming a nanoscale rough surface with pit stacking; forming an N×N array micropore structure on the surface of the SERS substrate material through high consistency precision control; sputtering a layer of gold film on the surface of the array micropore structure; performing an absorbance test; evaluating the SERS activity through Raman spectroscopy; obtaining the minimum trace detection limit of the SERS substrate, and completing the preparation of the SERS substrate. The present invention uses the synchronous construction of array micropores and nanostructures to make the SERS substrate have a light trapping effect, thereby improving the utilization rate of the substrate surface for the excitation laser beam used for testing.

Description

Technical Field

[0001] The invention belongs to the technical field of SERS substrate preparation, and in particular relates to a method for preparing an array microporous SERS substrate with a nanostructured inner wall. Background Art

[0002] Surface enhanced Raman scattering (SERS) technology is an emerging surface spectroscopy analysis technology. SERS technology can significantly amplify weak Raman signals in the microscopic field of view, and has the advantages of high sensitivity, accurate fingerprint identification of target molecules, and real-time, on-site, rapid and non-destructive detection. Therefore, SERS technology has become one of the methods with great application potential and research value in trace detection fields such as environmental testing, food safety, and biomedicine. When applying this technology, it is key to achieve high-precision trace detection and prepare high-performance SERS substrates. However, the preparation of SERS substrates is still subject to various challenges, such as the stability of substrate performance, structural uniformity, preparation cost, and preparation efficiency. In addition, in order to prevent high-intensity excitation lasers from burning and ablating the molecules to be tested, the excitation laser power used in Raman testing is at the milliwatt level and the energy is relatively small. Therefore, from the perspective of geometric optics theory, if some SERS substrates with light trapping structures can be constructed to reduce the laser reflection on the substrate surface, the SERS substrate will obtain more energy, thereby increasing the "hot spot" intensity and improving the sensitivity of the SERS substrate.

[0003] In order to achieve accurate detection of trace amounts of molecules to be tested, the application of metal micro-nano composite structures can be considered. This structure exhibits multi-dimensional and multi-level morphological distribution characteristics at the micrometer and nanometer scales, and can construct a SERS substrate with a light-trapping structure. Compared with the current conventional SERS substrate with nanoparticle attachment structure, it has stronger stability and sensitivity. Summary of the invention

[0004] In view of the above deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing an array micropore SERS substrate with a nanostructured inner wall, by using the synchronous construction of the array micropores and the nanostructure, so that the SERS substrate has a light trapping effect, thereby improving the utilization rate of the substrate surface for the excitation laser beam used for testing.

[0005] To achieve the above objectives, the present invention provides a method for preparing an array microporous SERS substrate having a nanostructured inner wall, comprising the following steps:

[0006] S1. Based on geometric optics, analyze the propagation path of light in a micropore with a nanostructured inner wall, make a light path diagram of light reflected in the micropore, and obtain the propagation mode of light in the micropore with a nanostructured inner wall from the light path diagram;

[0007] S2, using the number of light reflections per unit wall length to compare micropores of different sizes, and thus obtain a correlation between micropore size and its light-trapping capacity;

[0008] S3, constructing micropore units on the surface of the SERS substrate material by continuous pulse plasma high-temperature processing, and forming a nano-scale rough surface with stacked pits on the bottom and sidewall of the micropores;

[0009] S4. Through high consistency precision control, array holes are processed along the X direction and the Y direction respectively. The array holes are micropore units distributed in the array, and finally an N×N array micropore structure is formed on the surface of the SERS substrate material, where N is the number of micropores in each row and column in the array.

[0010] S5, using a magnetron ion sputtering apparatus to sputter a layer of gold film on the surface of the array microporous structure;

[0011] S6. Using a spectrophotometer, the absorbance of the prepared array micro-hole light-trapping surface with nanostructured inner wall and the smooth surface is tested;

[0012] S7, soaking the SERS substrate with light trapping effect in R6G molecular solutions of different concentrations for 20 to 40 minutes, and then drying it naturally in a dust-free environment. After drying, the SERS activity was evaluated by Raman spectroscopy;

[0013] S8. Test the Raman spectrum on the SERS substrate with light trapping effect, observe several characteristic peaks of the Raman signal of the R6G molecule, obtain the minimum trace detection limit of the SERS substrate, and complete the preparation of the SERS substrate.

[0014] As a preferred embodiment of the present invention, in S1, a geometric drawing method is used to draw a light path diagram of light reflected in a microhole; the nanostructure at the bottom of the hole causes the light to be reflected in different directions. Based on this, the propagation mode of light in a microhole with a nanostructured inner wall includes four situations, namely:

[0015] In case 1, part of the light leaves after reflecting once at the bottom of the hole, and the other part of the light leaves after reflecting twice between the nanostructures;

[0016] In case 2, the light reflected from the bottom of the hole reflects again on the nanostructures on the microhole sidewalls and then leaves;

[0017] In case three, the light reflected from the bottom of the hole is reflected on the nanostructure of the microhole sidewall and reflected on the opposite sidewall or bottom surface, and then reflected again and left;

[0018] In case 4, the light reflected from the bottom of the hole is reflected twice or more on the nanostructure of the microhole sidewall and finally leaves the microhole.

[0019] As a preferred embodiment of the present invention, in S2, the correlation between the micropore size and its light capture ability is that as the pore size decreases and the depth increases, the specific surface area of ​​the micropore increases accordingly; at the same time, this size change trend leads to an increase in the average number of light reflections per unit wall length.

[0020] As a preferred embodiment of the present invention, in S3, the plasma high-temperature processing method is a method of synchronously constructing a microstructure and a nanostructure. A pulsed plasma forms a nanoscale pit on the surface of the SERS substrate material, so that the bottom and side walls of a single micropore form a nanoscale rough surface with stacked pits.

[0021] As a preferred embodiment of the present invention, in the above S4, during processing, N micropores are processed with the same spacing, and finally an N×N array micropore structure is formed on the surface of the SERS substrate material.

[0022] As a preferred embodiment of the present invention, in S5, when sputtering the gold film, the sputtering time is 20s, the current is 60mA, the sputtering vacuum is 6Pa, and the thickness of the gold film is 5-10nm.

[0023] As a preferred embodiment of the present invention, in the above S6, after absorbance testing, the light-trapping surface of the array micropores has a more obvious light absorption effect than the smooth surface.

[0024] As a preferred embodiment of the present invention, in S7, the immersion time is 30 minutes, and the concentration of the R6G molecular solution used is 10 -6 M~10 -11 M.

[0025] As a preferred embodiment of the present invention, in S8, the Raman spectrum is tested on a SERS substrate with light trapping effect, using 633nm laser excitation, power of 1mW, exposure time of 25 seconds, and observing 773cm -1 、1360cm -1 The characteristic peak of Raman signal under .

[0026] The beneficial effects of the present invention are:

[0027] The present invention fully considers the multi-dimensional and multi-level morphological distribution characteristics at the micron and nanometer scales in the micro-nano composite structure. After the excitation laser is irradiated into the micron array hole structure, the nano-concave-convex structure inside the array hole will reduce the probability of escaping from the trap pit, that is, the laser utilization rate of the overall structure is increased. At the same time, there is a coupling effect between the array micropores and the nano-rough surface, and the array micropore units.

[0028] The present invention uses the synchronous construction of array micropores and nanostructures to make the SERS substrate have a light trapping effect, thereby improving the utilization rate of the substrate surface for the test excitation laser beam. Experimental results show that the array micropore light trapping SERS substrate with nanostructured inner wall designed by the present invention has extremely high detection sensitivity.

[0029] The present invention fully considers the utilization rate of the detection laser beam in the process of SERS substrate detecting trace substances, and can obtain a reasonable SERS substrate composition based on the Raman test results; it can provide a solution for the preparation of SERS substrates with light trapping structures, and improve the SERS detection accuracy, especially when the concentration of the trace substance to be detected is extremely low. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process of the present invention;

[0031] Figure 2 is a schematic diagram of light reflection analysis in a microwell having a nanostructured inner wall in an embodiment of the present invention; Figure 2 (a) is a schematic diagram of reflection only at the bottom of the hole; Figure 2 (b) Schematic diagram of reflection from the bottom of the hole to the side wall; Figure 2 (c) is a schematic diagram of reflection from one side wall to the other side wall; Figure 2 (d) is a schematic diagram of reflection from the side wall to the bottom of the hole; Figure 2 (e) is a schematic diagram showing that the light is reflected to the bottom surface of the hole after being reflected twice by the side walls;

[0032] Figure 3 Schematic diagram of the preparation process of the array microporous SERS substrate with nanostructured inner wall in an embodiment of the present invention; Figure 3 (a) is a schematic diagram of processing microporous unit; Figure 3 (b) is a schematic diagram of processing array microporous structure; Figure 3 (c) is a schematic diagram of the array micropore structure of the sputtered gold film; Figure 3 (d) is a schematic diagram of the microporous unit of the sputtered gold film;

[0033] Figure 4 is a graph showing the absorbance test results of the array micro-hole light trapping structure in an embodiment of the present invention;

[0034] Figure 5 1 is a graph showing the Raman signal detection results of R6G molecular solutions of different concentrations in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The embodiments of the present invention are further described below in conjunction with the accompanying drawings:

[0036] In the process of constructing an array micropore SERS substrate with a nanostructured inner wall, the micron-scale array pore structure and the nanoscale inner wall structure can be prepared in two ways. One is to prepare the array micropores first, and then prepare the nano-rough surface of the inner wall of the micropores. Common micropore preparation methods can use micro-milling, laser processing, electron beam processing methods, etc. Common nano-rough surface preparation methods can use nano-sol particles, chemical self-assembly, etc. The other is to prepare the array micropores and the nano-rough surface of the inner wall of the micropores at the same time, that is, when preparing the array micropores, the nano-rough surface of its inner wall is also prepared. The continuous pulse plasma high-temperature processing method used in this embodiment is to prepare the micro-nano integrated light-trapping SERS substrate in this way.

[0037] like Figure 1 As shown, a method for preparing an array microporous SERS substrate with a nanostructured inner wall comprises the following steps:

[0038] S1. Based on geometric optics, analyze the propagation path of light in a micropore with a nanostructured inner wall, make a light path diagram of light reflected in the micropore, and obtain the propagation mode of light in the micropore with a nanostructured inner wall from the light path diagram;

[0039] S2. To further evaluate the light-trapping ability of micropores with nano-rough surfaces, the number of light reflections per unit wall length was used to compare micropores of different sizes, thereby obtaining the correlation between the micropore size and its light-trapping ability.

[0040] S3, constructing micropore units on the surface of the SERS substrate material by continuous pulse plasma high-temperature processing, and forming a nano-scale rough surface with stacked pits on the bottom and sidewall of the micropores;

[0041] S4. Through high consistency precision control, array holes are processed along the X direction and the Y direction respectively. The array holes are micropore units distributed in the array, and finally an N×N array micropore structure is formed on the surface of the SERS substrate material, where N is the number of micropores in each row and column in the array.

[0042] S5, using a magnetron ion sputtering apparatus to sputter a layer of gold film on the surface of the array microporous structure;

[0043] S6. Using a spectrophotometer, the absorbance of the prepared array micro-hole light-trapping surface with nanostructured inner wall and the smooth surface is tested;

[0044] S7, soaking the SERS substrate with light trapping effect in R6G molecular solutions of different concentrations for 20 to 40 minutes, and then drying it naturally in a dust-free environment. After drying, the SERS activity was evaluated by Raman spectroscopy;

[0045] S8. Test the Raman spectrum on the SERS substrate with light trapping effect, observe several characteristic peaks of the Raman signal of the R6G molecule, obtain the minimum trace detection limit of the SERS substrate, and complete the preparation of the SERS substrate.

[0046] Step S3 is to construct a micropore unit, which reflects the simultaneous construction of the processing method and the micro-nano structure. Step S4 is to construct an array micropore structure, which reflects that the SERS substrate is realized by array micropores.

[0047] Continuous pulsed plasma high thermal processing is a technology that uses the high temperature characteristics of plasma to process materials. In this method, the plasma is usually generated by a continuous wave (CW) RF source, but by using the pulsed RF mode, the plasma parameter control window can be expanded and the flexibility of process control can be improved.

[0048] A spectrophotometer is an analytical instrument commonly used in laboratories. It is based on the law of colorimetry and quantitatively analyzes the concentration of a substance by measuring the degree of absorption or transmission of light by the substance at different wavelengths. A spectrophotometer usually consists of a light source, a grating or prism, a sample chamber, a detector, and a signal processing system. The light source can be a tungsten lamp, a deuterium lamp, a xenon lamp, etc., which is used to provide visible light or ultraviolet light. The grating or prism is used to separate light into light of different wavelengths to form a spectrum. The sample chamber holds the sample to be tested, and the detector such as a photodiode or a photomultiplier tube converts the optical signal into an electrical signal. Finally, the signal processing system processes the electrical signal and gives a numerical result of light absorption or transmission.

[0049] The minimum trace detection limit refers to the lowest concentration or amount that can be reliably detected by an analytical instrument and is often used to describe the sensitivity of an analytical method. The value of the minimum trace detection limit varies in different analytical techniques. For example, the lower limit of mass spectrometry can reach the microgram to nanogram level, while the lower limits of spectrophotometry and chemiluminescence can also reach the microgram to nanogram level. Techniques such as atomic absorption spectroscopy and inductively coupled plasma mass spectrometry are also commonly used for trace analysis, and they are able to detect very low concentrations of elements.

[0050] In S1, the geometric drawing method is used to draw the optical path diagram of light reflected in the microhole; the nanostructure at the bottom of the hole causes the light to be reflected in different directions. Based on this, the propagation mode of light in the microhole with the nanostructure inner wall includes four cases, namely:

[0051] In the first case, part of the light leaves after reflecting once at the bottom of the hole, and the other part of the light leaves after reflecting twice between the nanostructures; most of the light leaves after reflecting once at the bottom of the hole;

[0052] In case 2, the light reflected from the bottom of the hole reflects again on the nanostructures on the microhole sidewalls and then leaves;

[0053] In case three, the light reflected from the bottom of the hole is reflected on the nanostructure of the microhole sidewall and reflected on the opposite sidewall or bottom surface, and then reflected again and left;

[0054] In case 4, the light reflected from the bottom of the hole is reflected twice or more on the nanostructure of the microhole sidewall and finally leaves the microhole.

[0055] Figure 2 The reflection of light in a microwell with a nanostructured inner wall is intuitively demonstrated.

[0056] Geometric optics is a branch of optics that uses the concept of rays to describe the propagation of light in different media. This approach is usually applicable when the wavelength of light is much smaller than the size of the optical system. In geometric optics, light is viewed as particles that travel in straight lines and are subject to reflection, refraction, and scattering when they encounter different media. Geometric construction methods usually involve the following steps: determine the path of the light, draw the normal, apply the law of reflection, apply the law of refraction, and consider the absorption and scattering of the medium.

[0057] In S2, the correlation between the micropore size and its light-capturing ability is that the specific surface area of ​​the micropore increases with the decrease in pore diameter and the increase in depth; at the same time, this size change trend leads to an increase in the average number of light reflections per unit wall length.

[0058] In S3, plasma high-temperature processing is a method of synchronously constructing microstructures and nanostructures. A pulsed plasma forms a nanoscale pit on the surface of the SERS substrate material, so the bottom and side walls of a single micropore form a nanoscale rough surface with stacked pits.

[0059] SERS substrate materials can be various well-known substrate materials such as graphene, metal organic frameworks, SERS substrates constructed of composite materials (polystyrene microspheres, flexible polymer membranes, porous anodized aluminum, etc.), enhanced material composite SERS substrates (graphene oxide and gold nanoparticle composites, boron nitride and gold nanoparticle composites, metal organic frameworks and gold nanobipyramid composites, etc.).

[0060] In S4, during processing, N micropores are processed at the same interval, and finally an N×N array micropore structure is formed on the surface of the SERS substrate material.

[0061] In S5, when sputtering the gold film, the sputtering time is 20 s, the current is 60 mA, the sputtering vacuum is 6 Pa, and the thickness of the gold film is 5~10 nm.

[0062] Figure 3 The preparation process from S3 to S5 is demonstrated, first processing the micropore unit, then processing the array micropore structure, and then sputtering the gold film.

[0063] In S6, after absorbance testing, the light-trapping surface of the array micropores has a more obvious light absorption effect than the smooth surface.

[0064] A SERS substrate with light trapping function refers to a substrate that can enhance the local field intensity of light on the substrate surface, thereby improving the detection sensitivity of Raman signals.

[0065] In S7, the immersion time was 30 minutes, and the concentration of the R6G molecular solution used was 10 -6 M~10 -11 M, M is the molar concentration.

[0066] R6G (Rhodamine 6G) is an organic compound with fluorescent properties and is widely used in biomarkers, dye lasers, fluorescence detection and other fields.

[0067] In S8, Raman spectroscopy was tested on a SERS substrate with light trapping, using 633 nm laser excitation, 1 mW power, 25 s exposure time, and observing 773 cm -1 、1360cm -1 The characteristic peak of Raman signal under .

[0068] In Raman spectroscopy, a characteristic peak is a peak at a specific wave number (in cm -1 These peaks correspond to the vibrational modes of the sample molecules. Raman spectroscopy is a non-destructive analytical technique used to study the vibrational, rotational and other low-frequency modes of molecules.

[0069] The detection results show that in the SERS substrate with light trapping effect designed in this embodiment, the Raman intensity of R6G gradually increases with the increase of concentration, and the detection sensitivity of the substrate is extremely high, which can detect 10 -11 M can effectively recognize low concentration R6G molecules.

[0070] Figure 4 The test results show the comparison of the absorbance between the array micro-hole light trapping structure surface and the smooth surface. Figure 4 The two curves in the figure represent the absorbance of the array micro-hole light trapping structure surface and the smooth surface respectively. Figure 4 It can be seen that the surface of the light-trapping structure has a more obvious light-absorbing effect than the smooth surface.

[0071] Figure 5 The representative Raman spectra of R6G molecular solutions with different concentrations measured on the array microporous substrate are shown. Figure 5 The six result curves in the figure represent the concentration of R6G molecular solution at 10 -6 M, 10 -7 M, 10 -8 M, 10- 9 M, 10 -10 M, 10 -11 The Raman intensity of M was analyzed by observing the characteristic peak at 773 cm -1 、1360 cm -1 .from Figure 5 It can be seen from the figure that the Raman intensity of R6G on the SERS substrate with light trapping function designed in this embodiment gradually increases with the increase of concentration, and the detection sensitivity of the substrate is extremely high, even at 10 -11 At low concentrations of M, the characteristic peaks of R6G can still be identified.

Claims

1. A method for preparing an array microporous SERS substrate with a nanostructured inner wall, characterized in that The following steps are involved: S1. Based on geometric optics, analyze the propagation path of light in a micropore with a nanostructured inner wall, make a light path diagram of light reflected in the micropore, and obtain the propagation mode of light in the micropore with a nanostructured inner wall from the light path diagram; S2, using the number of light reflections per unit wall length to compare micropores of different sizes, and thus obtain a correlation between micropore size and its light-trapping capacity; S3, constructing micropore units on the surface of the SERS substrate material by continuous pulse plasma high-temperature processing, and forming a nano-scale rough surface with stacked pits on the bottom and sidewall of the micropores; S4. Through high consistency precision control, array holes are processed along the X direction and the Y direction respectively. The array holes are micropore units distributed in the array, and finally an N×N array micropore structure is formed on the surface of the SERS substrate material, where N is the number of micropores in each row and column in the array. S5, using a magnetron ion sputtering apparatus to sputter a layer of gold film on the surface of the array microporous structure; S6. Using a spectrophotometer, the absorbance of the prepared array micro-hole light-trapping surface with nanostructured inner wall and the smooth surface is tested; S7, soaking the SERS substrate with light trapping effect in R6G molecular solutions of different concentrations for 20 to 40 minutes, and then drying it naturally in a dust-free environment. After drying, the SERS activity was evaluated by Raman spectroscopy; S8. Test the Raman spectrum on the SERS substrate with light trapping effect, observe several characteristic peaks of the Raman signal of the R6G molecule, obtain the minimum trace detection limit of the SERS substrate, and complete the preparation of the SERS substrate.

2. The method for preparing an array microporous SERS substrate with a nanostructured inner wall according to claim 1, characterized in that: In S1, a geometric drawing method is used to draw a light path diagram of light reflected in a microhole; the nanostructure at the bottom of the hole causes the light to be reflected in different directions. Based on this, the propagation mode of light in a microhole with a nanostructured inner wall includes four situations, namely: In case 1, part of the light leaves after reflecting once at the bottom of the hole, and the other part of the light leaves after reflecting twice between the nanostructures; In case 2, the light reflected from the bottom of the hole reflects again on the nanostructures on the microhole sidewalls and then leaves; In case three, the light reflected from the bottom of the hole is reflected on the nanostructure of the microhole sidewall and reflected on the opposite sidewall or bottom surface, and then reflected again and left; In case 4, the light reflected from the bottom of the hole is reflected twice or more on the nanostructure of the microhole sidewall and finally leaves the microhole.

3. The method for preparing an array microporous SERS substrate with a nanostructured inner wall according to claim 1, characterized in that: In S2 described above, the correlation between the micropore size and its light capture ability is that as the pore size decreases and the depth increases, the specific surface area of ​​the micropore increases accordingly; at the same time, this size change trend leads to an increase in the average number of light reflections per unit wall length.

4. The method for preparing an array microporous SERS substrate with a nanostructured inner wall according to claim 1, characterized in that: In S3, the plasma high-temperature processing method is a method of synchronously constructing microstructures and nanostructures. A pulsed plasma forms a nanoscale pit on the surface of the SERS substrate material, so that the bottom and side walls of a single micropore form a nanoscale rough surface with stacked pits.

5. The method for preparing an array microporous SERS substrate with a nanostructured inner wall according to claim 1, characterized in that: In the above S4, during processing, N micropores are processed with the same spacing, and finally an N×N array micropore structure is formed on the surface of the SERS substrate material.

6. The method for preparing an array microporous SERS substrate with a nanostructured inner wall according to claim 1, characterized in that: In the above-mentioned S5, when sputtering the gold film, the sputtering time is 20s, the current is 60mA, the sputtering vacuum is 6Pa, and the thickness of the gold film is 5-10nm.

7. The method for preparing an array microporous SERS substrate with a nanostructured inner wall according to claim 1, characterized in that: In the above-mentioned S6, after absorbance testing, the light-trapping surface of the array micropores has a more obvious light absorption effect than the smooth surface.

8. The method for preparing an array microporous SERS substrate with a nanostructured inner wall according to claim 1, characterized in that: In the above S7, the immersion time is 30 minutes, and the concentration of the R6G molecular solution used is 10 -6 M~10 -11 M.

9. The method for preparing an array microporous SERS substrate with a nanostructured inner wall according to claim 1, characterized in that: In the above S8, Raman spectroscopy was tested on a SERS substrate with light trapping effect, using 633nm laser excitation, power of 1mW, exposure time of 25 seconds, and observing 773cm -1 、1360cm -1 The characteristic peak of the Raman signal.

Images