An ectopic surface-enhanced Raman scattering substrate structure and its near-field detection method

Abstract

The present invention discloses a substrate structure for surface-enhanced Raman scattering at an off-site and its near-field detection method. The Raman scattering substrate structure includes a substrate and two-dimensional nanosheets assembled on the substrate by a self-assembly method. The two-dimensional nanosheets are polygon structures made of a metal material with surface plasmon characteristics and having at least a pair of parallel end faces. The thickness of the two-dimensional nanosheets is in the nanometer scale, while the side length is in the micrometer scale. When one end face of the two-dimensional nanosheet is excited by an excitation light source, a surface plasmon signal that travels along the surface of the nanosheet is formed and finally output at the other end face parallel to it. The emitted signal interacts with the analyte molecules, and Raman signals are formed at positions different from the excitation light source, thereby preventing the analyte molecules from decomposing due to the irradiation of a high-density light intensity excitation light source. At the same time, the off-site acquisition of Raman signals also avoids the interference of the excitation light source.

Description

Technical Field

[0001] The present invention relates to the field of food safety and environmental pollution detection, and specifically to an off-site surface-enhanced Raman scattering substrate structure and its near-field detection method. Background Art

[0002] As an inelastic scattering effect, Raman scattering refers to the phenomenon that when a light beam incident on a substance is scattered, the energy of the scattered photons changes. Since the characteristic peaks of the Raman spectrum reflect the vibration characteristics of the substance molecules, just like the "fingerprint information" of the substance molecules, this technology can accurately identify the composition of substances and has broad application prospects in molecular detection in chemistry, biology, food, etc. However, during the scattering process of photons, only a very small number of photons undergo Raman scattering, and its signal is only 10 -6 ~10 -10 ⁻⁶ to 10⁻¹⁴ of the incident laser intensity. At the same time, the generation of Raman scattering signals is usually accompanied by fluorescence signals. As the emission process of resonance absorption, the scattering cross-section of fluorescence is more than ten orders of magnitude larger than that of Raman scattering, making the fluorescence intensity much greater than the Raman scattering signal. Due to the above reasons, the Raman scattering signal is very weak and difficult to detect. It wasn't until 1977 that Van Duyne et al. experimentally analyzed that when such a rough silver electrode was used as a substrate, the Raman signal intensity was enhanced by 10⁶ times compared to that in solution, and they called this new Raman signal enhancement phenomenon surface-enhanced Raman scattering.

[0003] In recent years, scientists have focused on researching surface-enhanced Raman scattering substrates based on metal nanoparticles. With the help of its local field resonance enhancement effect, a great enhancement of the local electromagnetic field on the particle surface can be achieved, making it have important application value in Raman spectroscopy detection. However, due to the same position for the excitation light source and the reception position of the Raman signal, there are many technical bottlenecks in the experiment that limit the further improvement of the ultimate sensitivity of the Raman signal: (1) When exciting and receiving Raman signals at the same position, the analyte molecules will decompose due to the irradiation of the high-density light intensity excitation light source, and at the same time, there will be a relatively strong background fluorescence signal, which is not conducive to the post-processing of the Raman spectrum; (2) Metal nanoparticles all have the random scattering behavior of Raman signals at multiple angles, and the received Raman signals are interfered by scattering noise, which will cause a significant decrease in the detection sensitivity; (3) Since the Raman signal will show an exponential decay when leaving the surface of the metal nanoparticles, and conventional optical lenses can only receive the attenuated Raman signal, it limits the improvement of the ultimate sensitivity.

[0004] To solve the above problems, Xu Hongxing et al. proposed using gold nanowires as carriers. Since the surface plasmon signals transmitted by the nanowires are relatively weak, he placed a gold nanoparticle near the gold nanowires, thereby forming a coupled "hot spot" at the gap and obtaining Raman signals. However, the gap between the nanowires and the particles cannot be precisely controlled, and the repeatability of this structure is relatively poor. In addition, as an optical carrier, although the gold nanowires have achieved different positions for the excitation light source and the Raman signal reception, the surface area of the nanowires is too small, restricting the number of analyte molecules that can be adsorbed and resulting in a relatively low sensitivity of the Raman signal. Liu Jiansheng et al. proposed a Raman scattering substrate based on conductive surface plasmons and its application method (Patent No.: CN103592282A), which uses an optical waveguide structure with a polymer cladding layer and a metal core layer to achieve the separation of the incident light and the Raman signal. However, this structure is not only complex and can only be realized by the physical method of lithography technology during preparation, but also requires special equipment for the alignment of the incident light during the testing process. Moreover, the development cycle is long and the cost is high. More importantly, this structure can only be used for the testing of liquid samples, restricting its application scenarios. Summary of the Invention

[0005] In order to overcome the deficiencies in the existing surface-enhanced Raman scattering substrates, such as the easy photolysis of analyte molecules, the easy interference of Raman signals by scattering, and the exponential decay of Raman signal intensity with distance, the present invention proposes a surface-enhanced Raman scattering substrate structure with different positions and its near-field detection method.

[0006] To achieve the above object, the specific solution adopted by the present invention is as follows:

[0007] A surface-enhanced Raman scattering substrate structure with different positions, comprising a substrate and two-dimensional nanosheets assembled on the substrate by a self-assembly method;

[0008] The two-dimensional nanosheets are polygon structures made of a metal material with surface plasmon characteristics and at least include a pair of parallel end faces. The thickness of the two-dimensional nanosheets is on the nanometer scale, while the side length is on the micrometer scale.

[0009] As a preferred solution, the thickness of the two-dimensional nanosheets is 70 - 150 nm, and the side length is 5 - 15 μm.

[0010] As a preferred solution, the material of the two-dimensional nanosheets is gold, silver, platinum or copper.

[0011] As a preferred solution, a surface plasmon signal is formed at one end face of the two-dimensional nanosheets under the excitation of an excitation light source, and the surface plasmon signal is transmitted along the surface of the nanosheets and output at the other end face parallel to this end face.

[0012] As a preferred solution, the shape of the two-dimensional nanosheets is quadrilateral, hexagonal or octagonal.

[0013] Preferably, the substrate is made of silicon wafer or glass.

[0014] A method for off-site surface-enhanced Raman scattering near-field detection mainly includes the following steps:

[0015] (1) Prepare an analyte molecule solution, immerse the Raman scattering substrate structure in the analyte molecule solution so that a large number of analyte molecules are adsorbed on the surface of the Raman scattering substrate structure, and then dry the Raman scattering substrate structure adsorbed with a large number of analyte molecules;

[0016] (2) Select one of the pair of parallel end faces of the two-dimensional nanosheet, and use an excitation light source to focus and irradiate this end face to form a surface plasmon signal. The surface plasmon signal propagates along the surface of the two-dimensional nanosheet and outputs from the other end face. The analyte molecules interact with the surface plasmon signal, and a Raman signal will be formed at a position different from the excitation light source;

[0017] (3) Use a near-field probe to scan and collect the Raman signal, and transmit the collected Raman signal to a Raman spectrometer for detection.

[0018] Preferably, the near-field probe collects the Raman signal in a scanning manner.

[0019] Preferably, the analyte molecules are molecules of organic dyes, environmental pollutants or substances harmful to food health.

[0020] The Raman scattering substrate structure in the present invention includes a substrate and two-dimensional nanosheets assembled on the substrate by a self-assembly method. The thickness of the two-dimensional nanosheets is on the nanometer scale, while the side length is on the micrometer scale. When one end face of the two-dimensional nanosheet is excited by an excitation light source, a surface plasmon polariton signal that propagates along the surface of the nanosheet is formed and finally outputs at the other end face parallel to it. The output signal interacts with the analyte molecules, and a Raman signal is formed at a position different from the excitation light source, thereby enabling the analyte molecules to avoid decomposition due to the irradiation of the high-density light intensity excitation light source. At the same time, the off-site acquisition of the Raman signal also avoids the interference of the excitation light source.

[0021] Advantageous effects:

[0022] 1. The Raman scattering substrate structure described in the present invention includes a substrate and two-dimensional nanosheets assembled on the substrate by a self-assembly method. The thickness of the two-dimensional nanosheets is on the nanometer scale, while the side length is on the micrometer scale. When one end face of the two-dimensional nanosheet is excited by an excitation light source, a surface plasmon polariton signal that propagates along the surface of the nanosheet is formed and finally outputs at the other end face parallel to it. The output signal interacts with the analyte molecules, and a Raman signal is formed at a position different from the excitation light source, thereby enabling the analyte molecules to avoid decomposition due to the irradiation of the high-density light intensity excitation light source. At the same time, the off-site acquisition of the Raman signal also avoids the interference of the excitation light source.

[0023] 2. The near-field detection method described in the present invention directly collects Raman signals by using a near-field probe, and these optical information can be collected before the Raman signals rapidly decay. Since the tip size of the probe is very small, smaller than the cross-sectional area of the output end, the present invention selects a scanning method to quickly collect all the Raman signals of the entire output cross-section, and finally realizes the detection of high-sensitivity Raman signals. Description of the drawings

[0024] Figure 1 It is a schematic diagram of the structure after an analyte molecule is adsorbed on a Raman scattering substrate structure.

[0025] Figure 2 It is a schematic diagram of the working principle of a two-dimensional nanosheet monolithic structure.

[0026] Figure 3 It is a light transmission experiment diagram of a two-dimensional nanosheet.

[0027] Figure 4 It is a detection spectrum of the Raman signal of the R6G dye molecule in Example 1.

[0028] In the figure: 1. Excitation light source, 2. Substrate, 3. Two-dimensional nanosheet, 4. Analyte molecule, 5. Raman signal, 6. Near-field probe. Detailed implementation manners

[0029] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] A surface-enhanced Raman scattering substrate structure in situ, comprising a substrate 2 and a two-dimensional nanosheet 3 assembled on the substrate 2 by a self-assembly method; wherein, the two-dimensional nanosheet 3 is a polygonal structure prepared from a metal material with surface plasmon characteristics (such as gold, silver, platinum or copper), at least including a pair of parallel end faces, such as a quadrilateral, hexagon or octagon. The thickness of the two-dimensional nanosheet 3 is in the nanometer order, while the side length is in the micrometer order.

[0031] Specifically, the thickness of the two-dimensional nanosheet 3 is 70-150 nm, and the side length is 5-15 μm.

[0032] A surface plasmon signal will be formed at one end face of the two-dimensional nanosheet 3 under the excitation of the excitation light source 1. The surface plasmon signal is transmitted along the surface of the nanosheet and output at the other end face parallel to this end face. By changing the material, size of the two-dimensional nanosheet 3 structure and the power of the excitation light source, surface plasmon signals with different intensities can be obtained at the output end.

[0033] The material of the substrate 2 is a silicon wafer or glass. The simpler the Raman signal peak of the substrate 2, the more beneficial it is for the post-processing of the analyte Raman signal.

[0034] The two-dimensional nanosheet 3 is prepared by a chemical synthesis method, and the size of the two-dimensional nanosheet 3 can be regulated by changing parameters such as drug concentration, reaction temperature, and stirring speed.

[0035] A method for off-site surface-enhanced Raman scattering near-field detection mainly includes the following steps:

[0036] (1) Prepare an analyte molecule solution, immerse the Raman scattering substrate structure in the analyte molecule solution so that a large number of analyte molecules 4 are adsorbed on the surface of the Raman scattering substrate structure, and then dry the Raman scattering substrate structure adsorbed with a large number of analyte molecules 4;

[0037] (2) Select one of the pair of parallel end faces of the two-dimensional nanosheet 3, and use the excitation light source 1 to focus and irradiate this end face to form a surface plasmon signal. The surface plasmon signal propagates along the surface of the two-dimensional nanosheet 3 and outputs from the other end face. The analyte molecules 4 interact with the surface plasmon signal, and a Raman signal 5 will be formed at a position different from the excitation light source 1;

[0038] (3) Use the near-field probe 6 to scan and collect the Raman signal 5, and transmit the collected Raman signal 5 to a Raman spectrometer for detection.

[0039] The near-field probe 6 collects the Raman signal 5 in a scanning manner. By scanning the output end face omnidirectionally to collect the signal, more Raman signals 5 can be obtained.

[0040] Specifically, the analyte molecules 4 are molecules of organic dyes, environmental pollutants or substances harmful to food health.

[0041] In the conventional substrate, the excitation light source and the Raman signal collection are completed by the same objective lens. The analyte molecules will decompose due to the irradiation of the high-density light intensity excitation light source, and at the same time, the Raman signal will also be interfered by the excitation light source. In the present invention, since the positions of the excitation light source 1 and the collection of the Raman signal 5 are separated, the above problems can be avoided. At the same time, since the present invention also uses the near-field probe 6 to directly collect the Raman signal 5, the dissipation of the Raman signal 5 due to rapid attenuation away from the surface of the nanostructure is also avoided. Therefore, the Raman scattering substrate structure and its near-field detection method proposed by the present invention have many advantages and can meet the requirements of Raman spectral signal detection.

[0042] Example 1

[0043] An off-site surface-enhanced Raman scattering substrate structure includes a silicon wafer substrate 2 and a two-dimensional nanosheet 3 assembled on the substrate 2 by a self-assembly method; wherein, the two-dimensional nanosheet 3 is a hexagon made of gold with surface plasmon characteristics, including three pairs of parallel end faces. The thickness of the two-dimensional nanosheet 3 is 100 nm and the side length is 10 μm.

[0044] The two-dimensional nanosheet 3 structure in the present invention is prepared by a chemical synthesis method and then assembled on the substrate 2 by a self-assembly method.

[0045] A method for near-field detection of surface-enhanced Raman scattering in different positions mainly includes the following steps:

[0046] (1) Prepare a methanol solution of dye R6G molecules with a concentration of 10 -7 mol / L. Immerse the substrate 2 in the solution for 2 hours, then a large number of R6G molecules will be adsorbed on the surface of the substrate 2. Subsequently, dry it on a heating table at 40°C for 0.5 h (as Figure 1 shown);

[0047] (2) Next, use a near-field Raman spectrometer to test the two-dimensional nanosheet 3. First, find the two-dimensional nanosheet 3 under the eyepiece and adjust the focal length to make the image of the nanosheet clearly visible. Then, irradiate one end face of the two-dimensional nanosheet 3 with an excitation light source 1 with a wavelength of 532 nm. By finely adjusting the position of the excitation light source 1, a surface plasmon polariton signal will be formed and transmitted along the surface of the two-dimensional nanosheet 3 (as Figures 2 - 3 shown), and the surface plasmon polariton signal will be output at the other end face parallel to it. Due to the existence of the inherent loss of the material, the intensity of the optical signal seen at the output end is significantly weaker than that at the excitation position. Finally, the output surface plasmon polariton signal interacts with the R6G molecules, and a Raman signal 5 will be formed at a position different from the excitation light source. To avoid the rapid attenuation of the Raman signal 5 when it leaves the surface of the two-dimensional nanosheet 3, a near-field probe 6 is used to scan and collect the Raman signal 5, and the obtained signal is transmitted to the Raman spectrometer through an optical fiber, thereby obtaining the Raman spectrum curve of the R6G molecules, as Figure 4 shown, as can be seen from Figure 4 .

[0048] The above is only a preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Any equivalent transformation or modification made according to the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A substrate structure for surface-enhanced Raman scattering at a heterotopic position, characterized in that It includes a substrate and two-dimensional nanosheets assembled on the substrate by a self-assembly method; The two-dimensional nanosheets are polygon structures made of a metal material with surface plasmon characteristics and having at least a pair of parallel end faces. The thickness of the two-dimensional nanosheets is on the nanometer scale, while the side length is on the micrometer scale; A surface plasmon signal will be formed on one end face of the two-dimensional nanosheet under the excitation of an excitation light source. The surface plasmon signal travels along the surface of the nanosheet and is output from the other end face parallel to this end face.

2. The surface enhanced Raman scattering substrate structure with ectopic position according to claim 1, characterized in that The thickness of the two-dimensional nanosheets is 70 - 150 nm, and the side length is 5 - 15 μm.

3. The surface-enhanced Raman scattering substrate structure at an ectopic position according to claim 1, wherein The material of the two-dimensional nanosheets is gold, silver, platinum or copper.

4. The surface-enhanced Raman scattering substrate structure at an ectopic position according to claim 1, characterized in that, The shape of the two-dimensional nanosheets is quadrilateral, hexagonal or octagonal.

5. The surface enhanced Raman scattering substrate structure at an ectopic position according to claim 1, characterized in that The material of the substrate is a silicon wafer or glass.

6. A method for near-field detection of surface-enhanced Raman scattering in an ectopic position, characterized in that, It mainly includes the following steps: (1) Prepare an analyte molecule solution, immerse the Raman scattering substrate structure in the analyte molecule solution so that a large number of analyte molecules are adsorbed on the surface of the Raman scattering substrate structure, and then dry the Raman scattering substrate structure adsorbed with a large number of analyte molecules; (2) Select one of the parallel end faces of the two-dimensional nanosheets, and use an excitation light source to focus on and irradiate this end face to form a surface plasmon signal. The surface plasmon signal travels along the surface of the two-dimensional nanosheet and is output from the other end face. The analyte molecules interact with the surface plasmon signal, and a Raman signal will be formed at a position different from the excitation light source; (3) Use a near-field probe to scan and collect the Raman signal, and transmit the collected Raman signal to a Raman spectrometer for detection.

7. The surface enhanced Raman scattering near-field detection method for ectopic sites according to claim 6, wherein The acquisition method of the near-field probe for the Raman signal is a scanning type.

8. The surface enhanced Raman scattering near-field detection method at an ectopic position according to claim 6, wherein, The analyte molecules are organic dyes, environmental pollutants or molecules of substances harmful to food health.

Images