Self-reference SPR sensor based on grating SPR strong coupling effect and preparation method thereof

Abstract

The embodiment of the invention discloses a self-reference SPR (Surface Plasmon Resonance) sensor based on a grating SPR strong coupling effect and a preparation method of the self-reference SPR sensor. The sensor sequentially comprises a grating layer, a substrate layer and a gold film layer, wherein the grating layer is arranged on one side of the substrate layer, comprises a plurality of parallel gratings and is made of the same material as the substrate layer; the gold film layer is deposited on the side, away from the grating layer, of the substrate layer; the SPR sensor further comprises a polystyrene sensing layer, and the polystyrene sensing layer is attached to the face, away from the substrate layer, of the gold film layer. The device does not need a prism, and has the advantages of small size, easy integration and the like; a back illumination grating form is adopted, a flat sensing interface is provided, and measurement is convenient; the polystyrene sensing layer is superposed, so that the pressure detection function can be realized on the basis of refractive index sensing; the sensor has a self-reference function, and can recalibrate the overall response of the sensor according to a reference inclination angle, thereby greatly reducing errors caused by an unstable environment.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric measurement, and in particular to a self-referenced SPR sensor based on a grating SPR strong coupling effect and a preparation method thereof. A grating is prepared on one side of the sensor, and the SPR mode is effectively excited by the grating. The other side has a flat sensing surface for better pressure or refractive index detection. Background Art

[0002] Controlling the propagation of light at the micro-nano scale is the core of modern nanophotonics research, and the goal is to design photonics on a scale comparable to electronics. Surface plasmon resonance effect is an important research part of nanophotonics. Currently, sensors based on surface plasmon resonance have become commercialized portable detectors.

[0003] Optical sensing technology mainly uses the physical and chemical properties of the medium layer of optical materials to change when external conditions change, thereby causing changes in optical parameters such as wavelength, refraction and reflection coefficient for measurement. Pressure measurement technology mainly uses the refractive index of pressure-sensitive materials to change when pressure changes, and is expected to be widely used in many fields such as ultra-thin wearable devices and robot skin. Optical RI sensing technology can be used for biological detection, mainly using the refractive index of the medium to change when the target molecule combines with the receptor on the metal surface to measure the refractive index. Bio-measurement technology can be used to detect biological molecules, such as cells, viruses, etc.

[0004] However, existing SPR sensors require a coupling prism to inject light and excite surface plasmon resonance, which limits the development of compactness and miniaturization. In recent years, the integrated development of optical fibers represents a new sensor architecture that overcomes the limitations of traditional optical sensor technology, but most of these designs are limited by the difficulty of nano-processing of the fiber sidewalls or fiber tips. Therefore, current surface plasmon sensors have low detection stability, high integration difficulty, single function, high cost, and high processing difficulty.

[0005] Therefore, how to make the existing sensors smaller, more integrated, and more multifunctional while maintaining the existing functions and sensitivity performance has become a technical problem that needs to be urgently solved in the prior art. Summary of the invention

[0006] In view of this, the embodiment of the present invention provides a self-reference SPR sensor based on the grating SPR strong coupling effect and a preparation method thereof, wherein the sensor has a flat sensing interface and an excellent self-reference function. The self-reference function can recalibrate the overall response of the sensor according to the reference tilt angle, greatly reducing the error caused by the unstable environment and improving the measurement accuracy.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] A self-reference SPR sensor based on grating SPR strong coupling effect, comprising:

[0009] The sensor comprises a grating layer, a substrate layer and a gold film layer in sequence;

[0010] The grating layer is arranged on one side of the base layer and is a plurality of parallel gratings, and is made of the same material as the base layer.

[0011] The gold film layer is deposited on a side of the base layer away from the grating layer.

[0012] Optionally, the SPR sensor further comprises a polystyrene sensing layer, and the polystyrene sensing layer is attached to a side of the gold film layer away from the base layer.

[0013] Optionally, the substrate layer is a silicon substrate, and a silicon grating is formed on the silicon substrate by etching, thereby preparing a grating layer.

[0014] Optionally, the height of the silicon substrate is 20-60nm; the width of a single silicon grating is 340-400nm, the length is 1-1.5μm, the height is 450nm-500nm, the period is 1030-1100nm, and the overall size of the silicon grating is 2μm×2μm.

[0015] Optionally, a protective layer which is substantially transparent to incident light is also provided on the surface of the grating layer.

[0016] Optionally, the overall size of the SPR sensor is 2 μm×2 μm, the thickness of the gold film layer is 30 nm-55 nm, the thickness of the protective layer is 1 μm-2 μm, and the thickness of the polystyrene sensing layer is 1 μm-2 μm.

[0017] The present invention further discloses a method for preparing the above-mentioned SPR sensor, comprising the following steps:

[0018] Grating preparation step S110:

[0019] Prepare a base layer, and etch the base layer to obtain a grating layer by FAB process;

[0020] Gold film layer preparation step S120:

[0021] A gold film layer of a certain thickness is deposited on a side of the substrate layer away from the grating layer by using magnetron sputtering technology.

[0022] Optionally, there is also a polystyrene sensing layer preparation step S130:

[0023] Polystyrene balls with a certain diameter are selected to self-assemble a large-area, tightly arranged hexagonal polystyrene nanosphere array at the air / liquid interface using a needle tip flow method, and the array is transferred to a gold film layer; after the polystyrene ball monolayer is dried, a clean glass slide is placed, and the polystyrene ball monolayer, i.e., the PS beads, is heated to 100°C to melt the nanoparticles, forming a polystyrene sensing layer and producing a smooth and flat top surface.

[0024] Optionally, there is also a protective layer preparation step S140:

[0025] Epoxy resin is coated on the surface of the grating layer to form a protective layer.

[0026] Optionally, in the grating preparation step S110,

[0027] The height of the silicon substrate is 20-60nm; the width of a single silicon grating is 340-400nm, the length is 1-1.5μm, the height is 450nm-500nm, the period is 1030-1100nm, and the overall size of the silicon grating is 2μm×2μm;

[0028] In the gold film preparation step S120,

[0029] The thickness of the gold film layer is 30nm-55nm;

[0030] In the polystyrene sensing layer preparation step S130,

[0031] The thickness of the polystyrene sensing layer is 1 μm-2 μm;

[0032] In the protective layer preparation step S140,

[0033] The thickness of the protective layer is 1 μm-2 μm.

[0034] In summary, the present invention has the following advantages:

[0035] 1. The present invention adopts grating excitation SPR. Compared with the traditional SPR sensor, it does not need to use a prism and has the advantages of small size and easy integration.

[0036] 2. The present invention adopts the form of a back-illuminated grating, and the light irradiation layer and the sensing layer are located on both sides of the sensor, so that it has a flat sensing interface, especially when used as a biosensor, it has a flat sensing surface, which is convenient for the binding of biological molecules and accurate, real-time, and label-free measurement.

[0037] 3. The present invention can also have the function of pressure detection on the basis of refractive index sensing by stacking a polystyrene sensing layer.

[0038] 4. The sensor of the present invention has a self-reference function, which can recalibrate the overall response of the sensor according to the reference tilt angle, greatly reducing the error caused by the unstable environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0040] Figure 1 is a schematic diagram of an SPR sensor according to a specific embodiment of the present invention;

[0041] Figure 2 is a schematic diagram of an SPR sensor according to another specific embodiment of the present invention;

[0042] Figure 3 is a schematic diagram of the dimensions of the grating portion of the SPR sensor according to a specific embodiment of the present invention;

[0043] Figure 4 is an electric field distribution diagram of a reference tilt angle and a measured tilt angle according to a specific embodiment of the present invention;

[0044] Figure 5 is a schematic diagram of an SPR sensor test according to a specific embodiment of the present invention;

[0045] Figure 6 is a schematic diagram of preparing a grating of an SPR sensor according to a specific embodiment of the present invention;

[0046] Figure 7 is a schematic diagram of a method for preparing an SPR sensor according to a specific embodiment of the present invention;

[0047] Figure 8 is a schematic diagram of a method for preparing an SPR sensor according to another specific embodiment of the present invention;

[0048] Fig. 9 is a sensor reflection spectrum of an SPR sensor at different refractive indices according to a specific embodiment of the present invention;

[0049] Fig.10 FIG. 4 is a sensor reflectance spectrum of an SPR sensor according to another specific embodiment of the present invention at different pressures.

[0050] 1. Grating layer; 2. Base layer; 3. Gold film layer; 4. Polystyrene sensing layer; 5. Protective layer; 6. Analysis layer. DETAILED DESCRIPTION

[0051] The present application is described below based on embodiments, but the present application is not limited to these embodiments. In the detailed description of the present application below, some specific details are described in detail. It is possible for those skilled in the art to fully understand the present application without the description of these details. In order to avoid confusing the essence of the present application, known methods, processes, flows, components and circuits are not described in detail.

[0052] In addition, persons of ordinary skill in the art will appreciate that the drawings provided herein are for illustration purposes and are not necessarily drawn to scale.

[0053] Unless the context clearly requires otherwise, the words "include", "comprising" and similar words throughout the application should be interpreted as including rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0054] In the description of this application, it should be understood that the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of this application, unless otherwise specified, the meaning of "plurality" is two or more.

[0055] Surface Plasmon Resonance (SPR) is a physical effect that occurs when light is irradiated at a specific critical angle to the interface of two media with different refractive indices, such as the air-metal interface. The free electrons in the metal are excited into a resonant state, absorbing a large amount of light energy, causing the reflected light to be significantly weakened or even completely disappear at a specific angle. This angle is called the SPR angle. The value of the SPR angle changes with the change of the surface refractive index, which is related to the object to be measured attached to the metal surface. By collecting and analyzing the reflected light information, the characteristics of the medium to be measured on the metal surface can be understood, which is the working principle of the SPR sensor.

[0056] The present invention uses a grating to excite the SPR resonance state. Specifically, a silicon (Si) grating is used to provide the momentum required to achieve the resonance condition.

[0057]

[0058] Where k0 is the free space propagation wavelength, n d is the refractive index of the incident medium, θ is the incident angle, m is the diffraction grating order, which is generally 1, Λ is the grating period, ε m is the complex dielectric constant of the metal, ε d is the real dielectric constant of the surrounding medium, and kSPP is the wave vector of the stimulated SPP mode.

[0059] The present invention aims to provide a self-referenced SPR sensor based on a back-illuminated grating. The sensor uses a back-illuminated grating combined with an Au film layer to realize a stimulated SPP mode for biomolecule detection. When a polystyrene sensing layer is superimposed on the Au layer, it can be used for pressure detection, realizing the use of two different detection modes under one basic structure. The sensor has a flat sensing interface and an excellent self-reference function. The self-reference function can recalibrate the overall response of the sensor according to the reference tilt angle, greatly reducing the error caused by the unstable environment and improving the accuracy of the measurement.

[0060] Therefore, the SPR sensor of the present invention can realize the functions of pressure detection and biological detection respectively. The SPR sensor of the present invention is described below through specific embodiments and structures.

[0061] For details, see Figure 1 , shows a schematic diagram of an SPR sensor according to a specific embodiment of the present invention.

[0062] The sensor comprises a grating layer 1, a substrate layer 2 and a gold (Au) film layer 3 in sequence;

[0063] The grating layer 1 is arranged on one side of the base layer 2 and is a plurality of parallel gratings, and has the same material as the base layer 2 .

[0064] In a specific embodiment, the grating layer is prepared on the base layer 2 by etching. For example, the base layer 2 is a silicon base, and a silicon grating is formed on the silicon base by etching, thereby preparing the grating layer 1.

[0065] The gold (Au) film layer 3 is deposited on a side of the base layer 2 away from the grating layer 1 .

[0066] At this time, the SPR sensor of the present invention can have the function of biological detection, and the gold (Au) film layer 3 directly contacts the detected organism as a detection layer, so that the biological target molecules bound by the detected object are more highly bonded to the metal film surface. In a specific embodiment, the detected object can exist in the form of an analysis layer 6.

[0067] For further information, see Figure 2 The SPR sensor further comprises a polystyrene (PS) sensing layer 4 , and the polystyrene (PS) sensing layer 4 is attached to a side of the gold (Au) film layer 3 away from the base layer 2 .

[0068] At this time, the SPR sensor of the present invention has the function of pressure detection. The polystyrene (PS) sensing layer 4 acts as a pressure sensing layer to sense pressure. Since the refractive index of polystyrene (PS) changes linearly with pressure, it can be used as a pressure (weight) detection sensing layer, and the corresponding pressure value is obtained by SPR reflection wavelength detection.

[0069] See also Figure 3 , showing the structure and size of the grating layer according to a specific embodiment of the present invention,

[0070] The height of the silicon substrate is 20-60nm; the width of a single silicon grating is 340-400nm, the length is 1-1.5μm, the height is 450nm-500nm, the period is 1030-1100nm, and the overall size of the silicon grating is 2μm×2μm. According to the attached drawings, the overall size of the SPR sensor is also 2μm×2μm.

[0071] Furthermore, the surface of the grating layer 1 also has a protective layer 5 that is substantially transparent to the incident light. In a specific embodiment, the protective layer 5 is an epoxy resin layer, which can protect the grating layer 1 while not causing significant light attenuation to the incident light, thereby weakening the SPR resonance of the present invention.

[0072] See also Figure 5 , showing an exemplary method of using the SPR sensor of the present invention. The deuterium-halogen lamp emits white light with a wavelength range of 200-2000nm, which is approximately parallel light after passing through the double-glued achromatic lens 1. The stray light is filtered out by the aperture grating, and then the polarizer is used to deflect it into TM polarization, so that the light is incident on the grating layer of the SPR sensor of the present invention, and the grating layer is used to excite SPR. The reflected light is focused on the optical fiber probe of the spectrometer after passing through the double-glued achromatic lens 2. Finally, the spectrum collected by the spectrometer is observed by a computer, and the data is integrated. In this way, SPR detection is realized and the characteristics of the medium to be measured are obtained.

[0073] The SPR sensor of the present invention adopts a back-illuminated grating working mode, that is, light is incident on the surface of the grating layer 1 and generates reflected light, and the other side of the SPR sensor away from the back-illuminated grating is the detection layer.

[0074] In the refractive index sensing mode, the gold film layer 3 is the detection layer. The gold film layer 3 has a flat sensing interface and can directly contact the biological solution to be tested, for example, directly contact the analysis layer 6. The sample (receptor) containing the analyte interacts with the ligand, causing the refractive index of the solution on the surface of the gold film layer 3 to change. By sensing the change in the refractive index of the surface of the gold film layer 3, it is used for biological detection. The sensor has high sensitivity and high quality factor.

[0075] Specifically, when the solution containing the target passes through the metal film surface of the sensor, a specific binding reaction between the target and the biological target molecule occurs, thereby triggering a change in the refractive index of the metal film surface. At the same time, the SPR resonance angle monitored by the optical path system also changes, further achieving the purpose of quantifying the target analyte. For example, the refractive index of normal basal cells is 1.35, the refractive index of basal cancer cells is 1.38, the refractive index of cervical cancer cells (HeLa) is 1.392, and the refractive index of breast cancer cells (MDA-MID-231) is 1.399. Fig. 9 As shown, the refractive index detection result in the detection range of 1.33-1.40 of the SPR sensor of the present invention is shown in the figure.

[0076] In the pressure sensing mode, the polystyrene (PS) sensing layer 4 is the detection layer, and its refractive index changes linearly with the pressure. The corresponding pressure value can be obtained according to the position of the SPR spectrum reflection dip angle. Fig.10 In a specific embodiment, the detection range of the SPR sensor of the present invention is 0-0.5 GPa, and the pressure detection result is shown in the figure.

[0077] It can be seen that in the present invention, both the gold film layer 3 and the polystyrene (PS) sensing layer 4, when used as a detection layer, have a flat sensing interface and can be in direct contact with the detected object, thereby improving the convenience of operation.

[0078] The SPR sensor of the present invention also has an excellent self-reference function, see Figure 4 , shows the electric field distribution diagram of the reference tilt angle and the measurement tilt angle of the SPR sensor according to the present invention, the SPR sensor has two SPR reflection tilt angles, in the pressure sensing mode and the refractive index sensing mode, the self-reference tilt angle of the SPR sensor does not change with the change of the refractive index, and the measurement tilt angle is used to detect the change of the external pressure and the refractive index. The light at the reference tilt angle is concentrated in the dielectric layer, and an electric field constraint is generated at the interface between the grating and the resin. Therefore, the resonant wavelength does not change with the change of the refractive index. Therefore, it can be used as a reference tilt angle. However, the field enhancement of the measurement tilt angle is concentrated at the detection layer (gold film layer / polystyrene (PS) sensing layer 4)-analyte interface, and extends into the analyte. Therefore, it can be used as a measurement tilt angle to detect the analyte.

[0079] In order to further achieve the goal of miniaturization, the sensor size of the present invention is as follows: the overall size of the SPR sensor is 2μm×2μm, the thickness of the gold (Au) film layer 3 is 30nm-55nm, the thickness of the protective layer 5 is 1μm-2μm, the thickness of the polystyrene (PS) sensing layer 4 is 1μm-2μm, and the thickness of the analysis layer 6 is not limited.

[0080] The present invention further discloses a flow chart for preparing the above-mentioned SPR sensor, comprising the following steps:

[0081] Grating preparation step S110:

[0082] A base layer 2 is prepared, and a grating layer 1 is obtained by etching the base layer through a FAB process;

[0083] In a specific embodiment, the base layer 2 is a silicon base, and a silicon grating is formed on the silicon base by etching through a FAB process, thereby preparing the grating layer 1.

[0084] Those skilled in the art know that FAB process overview FAB is a key process in integrated circuit manufacturing and is also an existing process involving thin film deposition, photolithography and etching. Figure 6 , showing a schematic diagram of grating preparation of the SPR sensor of the present invention.

[0085] In a specific embodiment, the height of the silicon substrate is 20-60 nm; the width of a single silicon grating is 340-400 nm, the length is 1-1.5 μm, the height is 450 nm-500 nm, the period is 1030-1100 nm, and the overall size of the silicon grating is 2 μm×2 μm.

[0086] Gold (Au) film preparation step S120:

[0087] A gold (Au) film layer 3 with a certain thickness is deposited on a side of the substrate layer 2 away from the grating layer 1 by using magnetron sputtering technology.

[0088] The thickness of the gold (Au) film layer is 30 nm-55 nm, and in a specific embodiment, can be 40 nm.

[0089] Therefore, see Figure 7 Through steps S110 and S120, an SPR sensor with a refractive index sensing mode can be prepared.

[0090] The present invention also has a polystyrene (PS) sensing layer 4 preparation step S130:

[0091] Polystyrene (PS) spheres with a certain diameter, for example, about 690 nm, are selected and self-assembled into a large-area, closely arranged hexagonal polystyrene (PS) nanosphere array at the air / liquid interface by a needle tip flow method, and the array is transferred to a gold (Au) film layer; after the polystyrene (PS) sphere monolayer is dried, a clean glass slide is placed, and the polystyrene monolayer, i.e., the PS spheres, is heated to 100° C. to melt the nanoparticles, thereby forming a polystyrene (PS) sensing layer 4 and producing a smooth and flat top surface.

[0092] Since polystyrene material is extremely sensitive to pressure changes, changes in pressure will cause changes in the refractive index of polystyrene, so that the polystyrene sensing layer can be used for pressure sensing.

[0093] In a specific embodiment, the thickness of the polystyrene (PS) sensing layer 4 is 1 μm-2 μm.

[0094] Therefore, see Figure 8 Through steps S110-S130, an SPR sensor with a pressure sensing mode can be prepared.

[0095] The present invention further comprises a protective layer preparation step S140:

[0096] Epoxy resin is coated on the surface of the grating layer 1 to form a protective layer 5 .

[0097] In a specific embodiment, the protective layer 5 has a thickness of 1 μm-2 μm.

[0098] Therefore, through the above method, SPR sensors with refractive index sensing and pressure sensing functions can be prepared respectively.

[0099] In summary, the present invention has the following advantages:

[0100] 1. The present invention adopts grating excitation SPR. Compared with the traditional SPR sensor, it does not need to use a prism and has the advantages of small size and easy integration.

[0101] 2. The present invention adopts the form of a back-illuminated grating, and the light irradiation layer and the sensing layer are located on both sides of the sensor, so that it has a flat sensing interface, especially when used as a biosensor, it has a flat sensing surface, which is convenient for the binding of biological molecules and accurate, real-time, and label-free measurement.

[0102] 3. The present invention can also have the function of pressure detection on the basis of refractive index sensing by stacking a polystyrene sensing layer.

[0103] 4. The sensor of the present invention has a self-reference function, which can recalibrate the overall response of the sensor according to the reference tilt angle, greatly reducing the error caused by the unstable environment.

[0104] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A self-referenced SPR sensor based on grating SPR strong coupling effect, characterized in that: include: The sensor comprises a grating layer, a substrate layer and a gold film layer in sequence; The grating layer is arranged on one side of the base layer and is a plurality of parallel gratings, and is made of the same material as the base layer; The gold film layer is deposited on a side of the base layer away from the grating layer.

2. The self-referenced SPR sensor according to claim 1, characterized in that include: The SPR sensor further comprises a polystyrene (PS) sensing layer, and the polystyrene (PS) sensing layer is attached to a side of the gold film layer away from the base layer.

3. The self-reference SPR sensor according to claim 1 or 2, characterized in that include: The base layer is a silicon base, and a silicon grating is formed on the silicon base by etching, thereby preparing a grating layer.

4. The self-referenced SPR sensor according to claim 3, characterized in that include: The height of the silicon substrate is 20-60nm; the width of a single silicon grating is 340-400nm, the length is 1-1.5μm, the height is 450nm-500nm, the period is 1030-1100nm, and the overall size of the silicon grating is 2μm×2μm.

5. The self-referenced SPR sensor according to claim 3, characterized in that include: A protective layer which is substantially transparent to incident light is also provided on the surface of the grating layer.

6. The self-referenced SPR sensor according to claim 3, characterized in that include: The overall size of the SPR sensor is 2μm×2μm, the thickness of the gold film layer is 30nm-55nm, the thickness of the protective layer is 1μm-2μm, and the thickness of the polystyrene sensing layer is 1μm-2μm.

7. A method for preparing the SPR sensor according to any one of claims 1 to 6, characterized in that: The steps include: Grating preparation step S110: Prepare a base layer, and etch the base layer to obtain a grating layer by FAB process; Gold film layer preparation step S120: A gold film layer of a certain thickness is deposited on a side of the substrate layer away from the grating layer by using magnetron sputtering technology.

8. The method for preparing the SPR sensor according to claim 7, characterized in that: include: The method also includes a polystyrene sensing layer preparation step S130: Polystyrene balls with a certain diameter are selected to self-assemble a large-area, tightly arranged hexagonal polystyrene nanosphere array at the air / liquid interface using a needle tip flow method, and the array is transferred to a gold film layer; after the polystyrene ball monolayer is dried, a clean glass slide is placed, and the polystyrene ball monolayer, i.e., the PS beads, is heated to 100°C to melt the nanoparticles, forming a polystyrene sensing layer and producing a smooth and flat top surface.

9. The method for preparing the SPR sensor according to claim 7 or 8, characterized in that: include: There is also a protective layer preparation step S140: Epoxy resin is coated on the surface of the grating layer to form a protective layer.

10. The method for preparing the SPR sensor according to claim 9, characterized in that: include: In the grating preparation step S110, The height of the silicon substrate is 20-60nm; the width of a single silicon grating is 340-400nm, the length is 1-1.5μm, the height is 450nm-500nm, the period is 1030-1100nm, and the overall size of the silicon grating is 2μm×2μm; In the gold film preparation step S120, The thickness of the gold film layer is 30nm-55nm; In the polystyrene sensing layer preparation step S130, The thickness of the polystyrene sensing layer is 1 μm-2 μm; In the protective layer preparation step S140, The thickness of the protective layer is 1 μm-2 μm.

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