SERS substrate based on long-range surface plasmon waveguide and dielectric waveguide coupling structure

Abstract

The present invention seeks to protect a SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure, belonging to the field of micro-nano optics and spectral analysis detection technology. The SERS substrate comprises, from bottom to top, a substrate layer, a dielectric waveguide layer, a cladding layer, a long-range surface plasmon waveguide portion (including the cladding layer), and a microchannel portion. The substrate layer supports the overall structure; the dielectric waveguide layer transmits incident light; the cladding layer, in conjunction with the substrate layer, forms a complete total reflection outer cladding structure and also transmits the evanescent field generated by total reflection; the long-range surface plasmon waveguide portion amplifies the Raman signal of sample molecules; and the microchannel portion is used to load the sample solution. This invention increases the effective transmission distance, accumulates the Raman signal of sample molecules, and improves repeatability, providing a foundation for the integration of surface-enhanced Raman spectroscopy detection chips for low-concentration sample molecules.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano optics and spectral analysis and detection technology, and particularly relates to a SERS substrate based on a long-range surface plasmon waveguide and a dielectric waveguide coupling structure. Background Art

[0002] Surface-enhance Raman Spectroscopy (SERS) is an analytical method that uses the local enhanced electric field of the rough surface of nano-precious metals to amplify the Raman signal of sample molecules. At present, it is generally believed that the enhancement principles of SERS technology include physical enhancement and chemical enhancement, among which physical enhancement is dominant. Physical enhancement mainly comes from surface plasmon resonance (SPR). Surface plasmon polarization (SPP) is an electromagnetic field that exists at the interface between metal and dielectric. Its energy is concentrated at the metal-dielectric interface and can propagate along the interface. When the frequency of the incident light matches the collective oscillation frequency of free electrons on the metal-dielectric surface, resonance will be formed, namely SPR.

[0003] When the metal layer is thin, the SPPs generated at the metal-dielectric interfaces above and below the metal layer will couple, generating two surface plasmon wave modes. One is a symmetric mode, the long-range surface plasmon resonance (LRSPR) mode, in which the mode field mostly exists in the medium outside the metal, with low transmission loss and can propagate over long distances. The other is an asymmetric mode, the localized surface plasmon resonance (LSPR) mode, in which the mode field mostly resides within the metal and has a shorter propagation distance. By integrating the dielectric waveguide with the long-range surface plasmon waveguide, under certain conditions, the energy in the dielectric waveguide can be coupled with the energy of the long-range surface plasmon.

[0004] Because LRSPR can enhance the local electric field on a metal surface, the Raman signal generated by sample molecules within this local electric field is amplified. By utilizing a metal array structure, losses in the metal layer can be minimized while simultaneously coupling the incident light energy in the medium, enabling long-distance transmission and accumulation of Raman signals from sample molecules. This approach holds broad application prospects in trace molecular detection, with significant potential and advantages in improving detection sensitivity and stability.

[0005] CN101581814A, a hybrid coupling structure of long-range surface plasma waves and dielectric waveguides, comprising: a dielectric substrate layer (10); a dielectric waveguide layer (7) located on the dielectric substrate layer (10); a coupling matching layer (8) located on the dielectric waveguide layer; and a long-range surface plasma waveguide portion formed on the coupling matching layer (8) for conducting long-range surface plasma waves, wherein the long-range surface plasma waveguide portion further comprises: a dielectric buffer layer (9), a metal layer (6), and a dielectric covering layer (11). The hybrid coupling structure can be used to realize an integrable, extremely sensitive, small, and highly stable refractive index sensor, as well as a high-performance, low-power photoelectric intensity modulator. Difference: The metal layer in the patent is an uninterrupted, complete metal layer; the present patent is a discontinuous metal array. Disadvantage: The absorption loss of the metal layer in the patent is large, which is not conducive to the coupling, propagation, and detection of the metal layer energy. This patent utilizes a metal array to reduce the loss during energy propagation in the metal layer, facilitating the collection and analysis of energy signals. At the same time, by changing the incident angle of the incident light, the distance between the metal array units can be adjusted, so that the position of the metal array units can be precisely controlled at the total reflection point, thereby regulating the overall transmission distance of the long-range surface plasmon.

[0006] CN108693160B, a surface-enhanced Raman optofluidic chip based on a long-range plasma waveguide, comprising a coupling grating (1), a dielectric waveguide, a surface plasma waveguide, a microfluidic structure, and a silicon substrate (2); the dielectric waveguide is composed of a waveguide upper cladding (3), a waveguide lower cladding (4), and a waveguide core (5); the waveguide upper cladding (3) is arranged on the upper surface of the waveguide core (5), the coupling grating (1) is distributed on the upper surface of the waveguide core (5), and the coupling grating (1) does not contact the waveguide upper cladding (3); the outer surfaces of the silicon substrate (2), the waveguide lower cladding (4), and the waveguide core (5) are flush, and the outer surfaces of the waveguide upper cladding (3), the surface plasma waveguide core (9), and the microfluidic channel (8) are flush. The surface-enhanced Raman optofluidic chip based on a long-range plasma waveguide of the present invention has a simple structure and a small size, and can be fabricated into an array structure on a single chip, thereby improving detection sensitivity. Difference: The incident light in this patent is coupled into the dielectric waveguide through a metal grating; the incident light in this patent is coupled into the dielectric waveguide through the end face. Disadvantages: The core layer of the surface plasmon waveguide in this patent is a metal layer made of gold, silver, and copper, which has high metal absorption loss, and has a certain impact on the collection of Raman signals of sample molecules. This patent uses a metal array to increase the Raman signal of the sample molecules and reduce the transmission loss of the SERS signal. By changing the incident angle of the incident light and adjusting the distance between the metal array units, the position of the metal array units can be precisely controlled at the total reflection point, thereby regulating the overall transmission distance of the long-range surface plasmon, accumulating the SERS signal of the sample molecules over a long distance, and further improving the sensitivity. Summary of the Invention

[0007] The present invention aims to solve the above problems of the prior art. It proposes a SERS substrate based on a long-range surface plasmon waveguide coupled with a dielectric waveguide structure. The technical solution of the present invention is as follows:

[0008] A SERS substrate based on a long-range surface plasmon waveguide and a dielectric waveguide coupling structure, the SERS substrate comprises, from bottom to top, a substrate layer (1), a dielectric waveguide layer (2), a cladding layer (3), a long-range surface plasmon waveguide portion (including the cladding layer (3)) and a microchannel portion; wherein,

[0009] The substrate layer (1) is used to support the overall structure; the dielectric waveguide layer (2) is used to transmit the input light; the cladding layer (3) cooperates with the substrate layer (1) to form a complete total reflection outer cladding structure, and is also used to transmit the evanescent field generated by the total reflection; the long-range surface plasma waveguide part is used to increase the Raman signal of the sample molecules; and the microchannel part is used to load the sample solution.

[0010] Furthermore, the refractive index of the dielectric waveguide layer (2) is greater than the refractive index of the substrate layer (1) and the cladding layer (3).

[0011] Furthermore, the refractive index of the dielectric waveguide layer (2) is 1.5 to 2.0, and the thickness of the dielectric waveguide layer (2) is 0.25 μm to 0.75 μm;

[0012] The refractive index of the cladding (3) is 1.4 to 1.5, and the thickness of the cladding (3) is 0.3 μm to 1 μm.

[0013] Furthermore, the microchannel portion includes a first dielectric restriction layer (6) and a second dielectric restriction layer (7), and the first dielectric restriction layer (6) and the second dielectric restriction layer (7) are used to restrict the electric field distribution on the upper surface of the metal layer (4).

[0014] Furthermore, the distance between the first dielectric limiting layer (6) and the second dielectric limiting layer (7) is 50 nm to 100 nm.

[0015] Furthermore, the long-range surface plasma waveguide portion is composed of: a cladding layer (3) (the cladding layer (3) is a common portion), a metal layer (4), and a dielectric covering layer (5) from bottom to top. The metal layer (4) and the dielectric covering layer (5) are respectively (used to generate long-range surface plasma and load the sample solution to be tested)

[0016] Furthermore, the metal layer (4) is an array structure, and the spacing of the array unit structures is regulated by the incident angle of the incident light; the metal layer (4) is one of gold, silver, and copper; and the thickness of the metal layer (4) is 4nm to 30nm.

[0017] Furthermore, the dielectric covering layer (5) is a detection sample solution, and its refractive index is 1.33-1.34.

[0018] Furthermore, the incident angle of the incident light ranges from 10° to 45°.

[0019] Furthermore, the substrate layer (1) and the cladding layer (3) are both made of silicon dioxide;

[0020] The material of the dielectric waveguide layer (2) is silicon nitride; the metal layer (4) is a gold nanofilm; and the materials of the first dielectric limiting layer (6) and the second dielectric limiting layer (7) are Teflon AF2400.

[0021] The advantages and beneficial effects of the present invention are as follows:

[0022] The present invention provides a SERS substrate based on a coupled long-range surface plasmon waveguide and dielectric waveguide structure. Microchannels are used to concentrate the energy of a metal layer at its center. Because the transmission distance of long-range surface plasmons in the metal layer is relatively short, an array structure is employed to reduce transmission losses within individual metal layers. Finally, through the coordination of the long-range surface plasmon waveguide and the dielectric confinement layer, the Raman signal of sample molecules amplified by the metal array structure is coupled with the energy in the medium, increasing the effective transmission distance, accumulating the Raman signal of sample molecules, and improving repeatability. This provides a foundation for the integration of surface-enhanced Raman spectroscopy detection chips for low-concentration sample molecules.

[0023] The innovation of the present invention lies mainly in the metal layer array structure. The use of the metal array structure can reduce the transmission loss of a single metal layer unit. By utilizing the cooperation of the long-range surface plasma waveguide part and the dielectric confinement layer part, the Raman signal of the sample molecules amplified by the metal array structure is coupled with the energy in the medium, thereby increasing the effective transmission distance, accumulating the Raman signal of the sample molecules, and further improving the sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a front view of a SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure according to a preferred embodiment of the present invention.

[0025] Figure 2 Schematic diagram showing the spacing principle of gold layer units;

[0026] Figure 3 Schematic diagram of a three-dimensional SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure. DETAILED DESCRIPTION

[0027] The following will describe the technical solutions in the embodiments of the present invention in detail with reference to the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention.

[0028] The technical solution of the present invention to solve the above technical problems is:

[0029] like Figure 1 Figure 1 shows a SERS substrate based on a long-range surface plasmon waveguide coupled with a dielectric waveguide. The substrate structure, from bottom to top, consists of a substrate layer 1, a dielectric waveguide layer 2, a cladding layer 3, a long-range surface plasmon waveguide portion (including the cladding layer 3), and a microchannel portion. The long-range surface plasmon waveguide portion comprises the cladding layer 3, a metal layer 4, and a dielectric cover layer 5; the microchannel portion includes a first dielectric confinement layer 6 and a second dielectric confinement layer 7.

[0030] The substrate layer 1 is used to support the overall structure; the dielectric waveguide layer 2 is used to transmit the input light; the cladding 3 cooperates with the substrate layer 1 to form a complete total reflection outer cladding structure, and is also used to transmit the evanescent field generated by total reflection; the long-range surface plasmon waveguide part is used to amplify the Raman signal of the sample molecules; and the microchannel part is used to load the sample solution.

[0031] Furthermore, the refractive index of the dielectric waveguide layer 2 is greater than the refractive index of the substrate layer 1 and the cladding layer 3 .

[0032] Furthermore, the refractive index of the dielectric waveguide layer 2 is 1.5 to 2.0, and the thickness of the dielectric waveguide layer 2 is 0.25 μm to 0.75 μm;

[0033] The refractive index of the cladding layer 3 is 1.4 to 1.5, and the thickness of the cladding layer 3 is 0.3 μm to 1 μm.

[0034] Furthermore, the distance between the first dielectric limiting layer 6 and the second dielectric limiting layer 7 is 50 nm to 100 nm.

[0035] Furthermore, the long-range surface plasmon waveguide portion comprises, from bottom to top: a cladding layer 3 (a common structure of the total reflection structure and the long-range surface plasmon waveguide), a metal layer 4, and a dielectric covering layer 5.

[0036] Furthermore, the metal layer 4 is an array structure, and the spacing of the array unit structures is regulated by the incident angle of the incident light; the metal layer 4 is one of gold, silver, and copper; and the thickness of the metal layer 4 is 4nm to 30nm.

[0037] Furthermore, the dielectric covering layer 5 is a detection sample solution, and its refractive index is 1.33-1.34.

[0038] Furthermore, the incident angle of the incident light ranges from 10° to 45°.

[0039] Furthermore, the substrate layer 1 and the cladding layer 3 are made of the same material as silicon dioxide;

[0040] The dielectric waveguide layer 2 is made of silicon nitride; the metal layer 4 is a gold nanofilm; and the first dielectric confinement layer 6 and the second dielectric confinement layer 7 are made of AF2400.

[0041] The medium covering layer 5 is the detection sample solution.

[0042] The detection method of the present invention involves excitation light incident at a specific angle from the end face of the dielectric waveguide layer 2, which is then transmitted over long distances within the total reflection structure consisting of the substrate layer 1, dielectric waveguide layer 2, and cladding layer 3. The evanescent field generated at the point of total reflection couples through the cladding layer 3 into the metal layer 4, generating long-range surface plasmons, which in turn excite and amplify the Raman signal of the sample molecules. This Raman signal is then collected at the other end of the dielectric waveguide layer 2.

[0043] How it works

[0044] The excitation light is transmitted over long distances with low loss in a total reflection structure consisting of substrate layer 1, dielectric waveguide layer 2, and cladding layer 3. The generated evanescent field is coupled into metal layer 4 through wave vector matching in cladding layer 3. A metal unit is placed above the evanescent field generated at each total reflection point. Each metal unit generates long-range surface plasmons, which in turn excite and amplify the Raman signal of the sample molecules. The Raman signal energy is then coupled into dielectric waveguide layer 2 for long-distance alternating transmission.

[0045] The metal layer array unit spacing L is controlled by the incident angle θ of the incident light. The principle is as follows:

[0046] Assuming the core layer has a refractive index of n2, a height of h, and a cladding layer with a refractive index of n1, n2>n1, when the incident light is incident at an angle θ at the center of the core layer, then

[0047]

[0048] Innovation of the present invention

[0049] 1. Use the incident angle of the incident light to adjust the metal array unit spacing and reduce the overall metal layer transmission loss.

[0050] 2. The problem of short transmission distance of Raman signal of sample molecules in plasma waveguide is solved by alternately transmitting energy in dielectric waveguide and plasma waveguide.

[0051] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0052] The above embodiments should be understood as merely illustrating the present invention and not as limiting the scope of protection of the present invention. After reading the contents of the present invention, technicians may make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure, characterized in that: The SERS substrate comprises, from bottom to top, a substrate layer (1), a dielectric waveguide layer (2), a cladding layer (3), a long-range surface plasma waveguide portion, and a microchannel portion; wherein, The substrate layer (1) is used to support the overall structure; the dielectric waveguide layer (2) is used to transmit the input light; the cladding layer (3) cooperates with the substrate layer (1) to form a complete total reflection outer cladding structure, and is also used to transmit the evanescent field generated by the total reflection; the long-range surface plasmon waveguide portion is used to amplify the Raman signal of the sample molecules; the long-range surface plasmon waveguide portion includes the cladding layer (3), and the microchannel portion is used to load the sample solution; The long-range surface plasma waveguide portion comprises, from bottom to top, a cladding (3), which is a common portion. The lower portion can serve as a total reflection structure cladding, and the upper portion can form a dielectric-metal-dielectric (IMI) structure supporting long-range surface plasma together with the metal layer and the dielectric covering layer; the metal layer (4) and the dielectric covering layer (5) are respectively used to amplify the Raman signal of the sample molecules and load the sample solution to be tested; The microchannel portion comprises a first dielectric restriction layer (6) and a second dielectric restriction layer (7), wherein the first dielectric restriction layer (6) and the second dielectric restriction layer (7) are used to restrict the electric field distribution on the upper surface of the metal layer (4); The metal layer (4) is an array structure, and the interval between the array unit structures is regulated by the incident angle of the incident light; the metal layer (4) is one of gold, silver, and copper; the thickness of the metal layer (4) is 4nm to 30nm; The metal layer array unit spacing L is controlled by the incident angle θ of the incident light. The principle is as follows: Assuming the core layer has a refractive index of n2, a height of h, and a cladding layer with a refractive index of n1, n2>n1, when the incident light is incident at an angle θ at the center of the core layer, then 2. The SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure according to claim 1, characterized in that: The refractive index of the dielectric waveguide layer (2) is greater than the refractive index of the substrate layer (1) and the cladding layer (3).

3. The SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure according to claim 2, characterized in that: The refractive index of the dielectric waveguide layer (2) is 1.5 to 2.0, and the thickness of the dielectric waveguide layer (2) is 0.25 μm to 0.75 μm; The refractive index of the cladding (3) is 1.4 to 1.5, and the thickness of the cladding (3) is 0.3 μm to 1 μm.

4. The SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure according to claim 1, characterized in that: The distance between the first dielectric limiting layer (6) and the second dielectric limiting layer (7) is 50 nm to 100 nm.

5. The SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure according to claim 1, characterized in that: The medium covering layer (5) is a detection sample solution, and its refractive index is 1.33-1.

34.

6. The SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure according to claim 1, characterized in that: The incident light angle ranges from 10° to 45°.

7. The SERS substrate based on a long-range surface plasmon waveguide and dielectric waveguide coupling structure according to claim 1, characterized in that: The substrate layer (1) and the cladding layer (3) are both made of silicon dioxide; the dielectric waveguide layer (2) is made of silicon nitride; the metal layer (4) is a gold nanofilm; and the first dielectric limiting layer (6) and the first dielectric limiting layer (7) are made of Teflon AF2400.

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