High-sensitivity SPR (Surface Plasmon Resonance) refractive index sensor with sawtooth structure and graphene-silver layer

Abstract

The invention discloses a high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer, and belongs to the technical field of sensors. A smooth prism surface is etched into a sawtooth shape, metal silver-two-dimensional nano material graphene is used as a plasma material to form silver layer-graphene, the plasma material contains silver, a silver film is covered with graphene, and the prism is etched into a sawtooth shape by optimizing the thickness of a sawtooth silver layer and the number of layers of black phosphorus. The thickness of a silver layer, the height of sawteeth and the number of layers of graphene are adjusted through the composite film plated with silver-graphene, and the prism with the sawteeth structure and the metal and two-dimensional nanometer material are provided. The average angle sensitivity of the sensor disclosed by the invention can reach 860.6 degrees / RIU in a refractive index range from 1.330 RIU to 1.335 RIU. Compared with a prism type surface plasmon resonance refractive index sensor reported in the past, the surface plasmon resonance refractive index sensor has higher angle sensitivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors and relates to a highly sensitive SPR refractive index sensor with a serrated structure and a graphene-silver layer. Background Art

[0002] Surface Plasmon Resonance (SPR) sensing is a new detection technology with broad application prospects and development potential. The SPR sensor utilizes the surface plasmon wave generated by the coupling of free electrons on the metal surface and the electromagnetic field of the incident light wave. When the incident light wave and the surface plasmon wave resonate at the metal-dielectric interface, it will cause a change in the intensity or angle of the reflected light. This change is related to the refractive index (or dielectric constant) of the adsorbate on the metal surface. Therefore, the detection of the substance to be measured can be achieved by detecting the change in the reflected light. Due to the high sensitivity of the surface plasmon resonance phenomenon to the change in the refractive index of the adsorbate on the metal surface, the SPR sensor has a high sensitivity. Compared with traditional detection methods, the SPR sensor does not need to label or process the substance to be measured and can directly perform detection. The SPR sensor can also monitor the change in the reflected light in real time, so as to achieve the dynamic monitoring of the concentration of the substance to be measured.

[0003] Currently, most practical SPR sensors are based on a prism coupling structure to generate surface plasmon resonance. The prism-type SPR sensor coupling structure has the advantages of simple structure and easy implementation, and is widely used in the fields of biomedicine, environmental monitoring, food safety, etc. For example, in the field of biomedicine, the prism-type SPR sensor can be used to detect the interaction between biomolecules, drug screening, and disease diagnosis, etc.; in the field of environmental monitoring, the prism-type SPR sensor can be used to detect the concentration of pollutants in the air and harmful substances in water bodies, etc.; in the field of food safety, the prism-type SPR sensor can be used to detect additives, pesticide residues, and harmful substances in food, etc. Currently, the angular sensitivity of the prism-type SPR refractive index sensor is about 300° - 500° / RIU. With the continuous improvement of the detection accuracy requirements of users for SPR sensors, it is particularly important to improve the performance of the prism-type SPR refractive index sensor, especially to further improve its detection sensitivity. Summary of the Invention

[0004] The present invention aims at the problems of the prior art and provides a highly sensitive SPR refractive index sensor with a serrated structure and a graphene-silver layer.

[0005] The highly sensitive SPR refractive index sensor with a serrated structure and a graphene-silver layer has a serrated structure on one plane of a triangular prism, a silver layer is plated on the serrated surface, and several graphene layers are on the surface of the silver layer.

[0006] The thickness of the silver layer is 60 - 70 nm. Preferably, the thickness of the silver layer is 64 nm.

[0007] The height of the sawtooth structure is 385 - 390 nm. Preferably, the height of the sawtooth structure is 388 nm.

[0008] The number of graphene layers is 1 - 6. Preferably, the number of graphene layers is 3.

[0009] The sawtooth period of the sawtooth structure is 800 - 1100 nm. Preferably, the sawtooth period of the sawtooth structure is 900 nm. Or the silver layer is replaced by gold, aluminum, copper or other metals, and gold, aluminum, copper or other metals are combined with graphene.

[0010] A preparation method of a high - sensitivity SPR refractive index sensor comprises the following steps: etching the surface of a triangular prism into a sawtooth shape, coating a silver layer on the sawtooth structure, and covering graphene on the silver layer to form a composite structure of the sawtooth structure and the graphene - silver layer.

[0011] A preparation method of a high - sensitivity SPR refractive index sensor further comprises the following steps: etching the smooth prism surface into a sawtooth shape, using silver - two - dimensional nanomaterial graphene as a plasmonic material to form a silver layer - graphene, the plasmonic material containing silver, covering graphene on the silver film, optimizing the thickness of the sawtooth silver layer and the number of black phosphorus layers, etching the prism into a sawtooth shape, plating a composite film of silver - graphene, and adjusting the silver layer thickness, sawtooth height and graphene layer number. There is a prism with a sawtooth structure and a metal and a two - dimensional nanomaterial, and the silver layer is replaced by gold, aluminum, copper or other metals, and gold, aluminum, copper or other metals are combined with graphene.

[0012] The advantages of the present invention are as follows: an improved prism - type SPR refractive index sensor combines a prism with a sawtooth structure and a metal and a two - dimensional nanomaterial. The smooth prism surface is etched into a sawtooth shape. On the one hand, the sawtooth - shaped prism surface increases the surface area of the prism and simultaneously increases the contact area between the silver layer - graphene layer and the analyte. On the other hand, the tips of the sawteeth can excite the tip effect. Compared with the smooth prism surface, the charge density at the tips of the sawteeth is larger and the electric field intensity near the tips is stronger. Therefore, the sawtooth - shaped prism surface can excite stronger surface plasmon waves, significantly improving the sensitivity of the SPR sensor. In addition, graphene has excellent electron mobility, a wide wavelength absorption range, a large specific surface area and a rich π - bond conjugated structure, and these characteristics all have a positive impact on the SPR curve, which is beneficial to improving the sensitivity of SPR sensing.

[0013] The graphene covering the silver film also acts as a protective layer, effectively preventing the oxidation of metallic silver. By optimizing the thickness of the serrated silver layer and the number of layers of black phosphorus, the SPR sensor exhibits ultra-high sensitivity and obtains excellent refractive index sensing performance. In the range of 1.330 RI U to 1.335 RI U, the average sensitivity of this SPR sensor can reach 860.6° / RI U. Compared with the previously reported prism-type surface plasmon resonance refractive index sensors, this sensor has significant advantages in terms of angular sensitivity and has good application value for the high-precision measurement of the refractive index of analytes in fields such as food inspection, biomedicine, and environmental monitoring.

[0014] An SPR sensor with a novel structure, in which one surface of the etched prism is serrated and coated with a composite film of silver-graphene. The angular interrogation method is used to evaluate its sensing performance. To improve the sensitivity of the sensor, the thickness of the silver layer, the serration height, the number of layers of graphene, etc. are adjusted, significantly enhancing the sensitivity and quality factor. The refractive index detection range is between 1.33 and 1.335. The sensing performance of the surface plasmon resonance sensor is studied, achieving ultra-high sensitivity and showing significant improvement compared with the previously reported prism SPR sensors, and having good application potential in the field of biomedical detection.

[0015] In the refractive index range of 1.330 RI U to 1.335 RI U, the average angular sensitivity of the sensor of the present invention can reach 860.6° / RI U. Compared with the previously reported prism-type surface plasmon resonance refractive index sensors, it has a greater angular sensitivity. It can be used in multiple fields such as food inspection, biomedicine, and environmental monitoring, and has a broad application prospect. Brief Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. As shown in the figures:

[0017] Figure 1a It is a structural diagram of the KB7 prism.

[0018] Figure 1b It is the KB7 prism with a serrated structure of the present invention.

[0019] Figure 1c It is the KB7 prism SPR sensor with a serrated structure + silver layer + graphene of the present invention.

[0020] Figure 1dThis is a partially enlarged schematic diagram of the sawtooth structure in the SPR sensor of the present invention.

[0021] Figure 2 This is a three-dimensional structure diagram of the prism.

[0022] Figure 3 This is the reflectivity curve diagram of the reflected light beam corresponding to the analyte with different refractive indices n s of the present invention.

[0023] Figure 4 This is the resonance angle θ corresponding to the reflectivity curve of the SPR sensor of the present invention at different refractive indices SPR and the refractive index n s of the substance to be measured. Detailed implementation manners

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. 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.

[0025] Embodiment 1: As shown in Figure 1a , Figure 1b , Figure 1c , Figure 1d , Figure 2 , Figure 3 and Figure 4 , a high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer is used to improve the triangular prism of KB7 material as shown in Figure 1a . As shown in Figure 1b , its ABFD surface is etched into a sawtooth shape. As shown in Figure 2 , the sawtooth on the surface of the prism is not drawn. As shown in Figure 1c and Figure 1d , a silver layer with an appropriate thickness is plated on the sawtooth surface of the KB7 prism, and several layers of graphene are covered on the silver layer to form a composite structure of a sawtooth structure and a graphene-silver layer.

[0026] The sensor detection system is composed of a light source, a prism with a sawtooth composite structure, and a photodetector. The sawtooth composite structure of the prism is in contact with the substance to be measured. The light source emits a laser beam of 633 nm, which is irradiated onto the sawtooth composite structure of the prism as shown in Figure 1c . By changing the incident angle θ of the light source, the reflection angle θ 1 of the reflected light beam can be adjusted. The photodetector receives the reflected light beam and detects the intensity of the reflected light, so that the reflectivity curve of the laser beam irradiating the sawtooth structure of the prism at different incident angles can be obtained.

[0027] At a specific incident angle, the laser beam can excite a strong surface plasmon resonance phenomenon in the plasma material (silver layer and graphene). At this time, most of the energy in the laser beam will be transferred to the surface wave formed by the surface plasmon resonance, resulting in a significant reduction in the reflectivity of the laser beam detected by the detector. Therefore, there will be an obvious depression in the reflectivity curve at a specific angle, and the angle corresponding to this depression is called the resonance angle. When the refractive index of the substance to be measured changes, the corresponding resonance angle will also change accordingly. Therefore, using this property can precisely measure the refractive index of the sample.

[0028] The specific parameters of the composite structure composed of the sawtooth structure and the graphene-silver layer need to refer to Figure 1d .

[0029] The thickness t of the silver layer coated on the KB7 material Ag is 60 - 70 nm, preferably 64 nm.

[0030] The height H of the sawtooth structure on the surface of the KB7 prism S is 385 - 390 nm, preferably 388 nm.

[0031] The number of graphene layers Ng is 1 - 6, preferably 3.

[0032] The sawtooth period Period of the sawtooth structure is 800 - 1100 nm, preferably 900 nm.

[0033] A preparation method of a high-sensitivity SPR refractive index sensor includes the following steps: etching the surface ABFD of a triangular prism made of KB7 material into a sawtooth shape ( Figure 1b ), coating a silver layer on the sawtooth structure of the KB7 material, and covering graphene on the silver layer to form a composite structure of the sawtooth structure and the graphene-silver layer, where silver and graphene are used as plasma materials to achieve surface plasmon resonance. By changing the period and height of the sawtooth structure on the KB7 prism, the thickness of the silver layer, and the number of black phosphorus layers, the sensitivity of this sensor can be optimized.

[0034] Example 2: As Figure 1a , Figure 1b , Figure 1c , Figure 1d , Figure 2 , Figure 3 and Figure 4 shown, a high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer etches the smooth prism surface into a sawtooth shape, uses metal silver - two-dimensional nanomaterial graphene as the plasma material to enhance the interaction between the analyte and the sensing surface, and significantly enhances the performance of the SPR sensor.

[0035] In the refractive index range of 1.330 RIU to 1.335 RIU, the average angular sensitivity of the sensor can reach 860.6° / RIU. Using a BK7 prism as the structural substrate, the smooth prism surface is etched into a serrated shape. Silver layer and multi-layer graphene are used as plasmonic materials. Silver is first deposited on the serrated surface of the modified BK7 prism through electron beam evaporation process, and then a serrated microstructure is formed on the surface of the silver layer by using techniques such as nanoimprinting. The enlarged schematic diagram of the serrated silver layer details the serrated microstructure.

[0036] Several layers of graphene are covered on the silver layer. Graphene is a two-dimensional material with strong adhesion. It adheres to the surface of the silver layer, enhancing the interaction between the analyte and the sensitive surface, thereby improving the performance of the sensor. Graphene also acts as a protective layer, effectively preventing the oxidation of metallic silver.

[0037] The main parameter characterizing the performance of the prism-type SPR refractive index sensor is the sensitivity S. When the prism SPR sensor operates in the angular interrogation mode, the sensitivity is defined as the ratio of the shift of the resonance angle θ of the reflection spectrum to the change in the refractive index of the analyte:

[0038]

[0039] Here, the shift of the resonance angle is Δθ SPR , and the change in the refractive index is Δn.

[0040] The finite element analysis method is one of the most widely used numerical analysis methods in the field of micro-nano photonics structure research. Its principle is to approximately solve by solving the boundary value problem of partial differential equations, and it has high analytical accuracy.

[0041] The finite element analysis method is used to simulate and evaluate the performance of the designed SPR sensor in the range of serration period Period of 900 nm and refractive index from 1.330 RIU to 1.335 RIU.

[0042] A laser with a wavelength of 633 nm is selected as the incident light, and the refractive indices of all materials correspond to this wavelength. When the metal surface is irradiated with TM polarized light, the optimal parameters of the sensor with the best sensitivity are obtained by optimizing three geometric parameters: the thickness of the silver layer, the amplitude of the serrations in the serrated structure, and the number of graphene layers.

[0043] Table 1 summarizes the structural parameters of the optimized prism SPR refractive index sensor.

[0044] Table 1 Refractive index and structural parameters of the designed improved prism-type SPR sensor

[0045]

[0046] Optimal thickness t of the silver layer Ag is 64 nm.

[0047] When the period of the sawtooth is fixed, the sensitivity of the SPR sensor can be improved by changing the height of the sawtooth. When the height H of the sawtooth S is 388 nm, the sensitivity of the sensor reaches the maximum value. Therefore, the optimal value of the sawtooth height is 388 nm.

[0048] When the number of graphene layers Ng is 3, the sensitivity of the sensor reaches the maximum value. Therefore, attaching 3 layers of graphene on the silver layer is the best choice.

[0049] Analyze the sensing performance of the improved prism-type SPR sensor after optimization, and conduct reflection spectrum analysis in the range of the refractive index of the substance to be measured from 1.330 RIU to 1.335 RIU.

[0050] Figure 3 Shows the reflectivity curves of the reflected light beams corresponding to the substances to be measured with different refractive indices n s when detected by the designed SPR sensor. According to Figure 3 the resonance angle corresponding to the depression position of each reflectivity curve in, the circular data points in Figure 4 can be obtained.

[0051] The sensing performance of the SPR sensor in the range of 1.330 RIU to 1.335 RIU is linearly fitted based on the circular data points in Figure 4 . The dashed line in the figure is the linear equation after fitting: Incident = -860.6x + 1233.0, R 2 is the degree of closeness between the original data and the fitting equation. The closer it is to 1, the better the fitting effect. According to the fitted equation, R 2 = 0.99439 can be obtained at this time, and the fitting effect is almost perfect.

[0052] Therefore, the absolute value of the slope |k| of the fitting equation can be used as the average sensitivity of the designed SPR sensor, which is 860.6° / RIU.

[0053] Compared with the currently reported prism-type SPR refractive index sensors (angle sensitivity is about 300° - 500° / RIU), the SPR sensor of the present invention has obvious advantages in sensing performance.

[0054] Example 3: As Figure 1a , Figure 1b , Figure 1c , Figure 1d , Figure 2 , Figure 3 and Figure 4As shown, like the above embodiment, a high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer uses silver as the metal layer combined with graphene. It is not limited to silver material, and other metals such as gold, aluminum, and copper can also be used in combination with graphene to achieve SPR sensing to meet different detection requirements.

[0055] That is: sawtooth structure + silver layer + graphene → high-sensitivity SPR sensing.

[0056] Sawtooth structure + gold layer (aluminum layer / copper layer) + graphene → high-sensitivity SPR sensing (the corresponding reflection curves and resonance angles will be different for different selected metals).

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A highly sensitive SPR refractive index sensor with a sawtooth structure and a graphene-silver layer, characterized in that: The invention discloses a high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer. One plane of the triangular prism has a sawtooth structure, a silver layer is plated on the sawtooth surface, and a plurality of graphene layers are arranged on the surface of the silver layer.

2. The high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer according to claim 1, characterized in that: The thickness of the silver layer is 60-70 nm.

3. The high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer according to claim 1, characterized in that: The thickness of the silver layer was 64 nm.

4. The high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer according to claim 1, characterized in that: The height of the sawtooth structure is 385-390 nm.

5. The high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer according to claim 1, characterized in that: The height of the sawtooth structure is 388 nm.

6. The high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer according to claim 1, characterized in that: The number of graphene layers is 3.

7. The high-sensitivity SPR refractive index sensor with a sawtooth structure and a graphene-silver layer according to claim 1, characterized in that: The sawtooth period of the sawtooth structure is 800 to 1100 nm.

8. The high-sensitivity SPR refractive index sensor having a sawtooth structure and a graphene-silver layer according to any one of claims 1 to 7, characterized in that: The silver layer is replaced with gold, aluminum, copper or other metals, and the gold, aluminum, copper or other metals are combined with graphene.

9. A method for preparing a high-sensitivity SPR refractive index sensor, characterized in that: The method comprises the following steps: etching the surface of the triangular prism into a sawtooth shape, coating a silver layer on the sawtooth structure, and covering the silver layer with graphene to form a composite structure of the sawtooth structure and the graphene-silver layer.

10. The high-sensitivity SPR refractive index sensor having a sawtooth structure and a graphene-silver layer according to claim 9, characterized in that: The method also includes the following steps: etching a smooth prism surface into a sawtooth shape, using metal silver-two-dimensional nanomaterial graphene as a plasma material to form a silver layer-graphene, wherein the plasma material contains silver, and graphene is covered on the silver film. By optimizing the thickness of the sawtooth silver layer and the number of black phosphorus layers, the prism is etched into a sawtooth shape, and a silver-graphene composite film is plated to adjust the thickness of the silver layer, the sawtooth height and the number of graphene layers. The prism has a sawtooth structure, and the metal and two-dimensional nanomaterial, or the silver layer is replaced by gold, aluminum, copper or other metals, and gold, aluminum, copper or other metals are combined with graphene.

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