Sensing detection method based on continuous domain bound state metasurface with in-situ adjustable sensitivity

Abstract

The present invention discloses a sensing detection method based on a continuous domain bound state metasurface with in-situ adjustable sensitivity, belonging to the technical field of metasurface biochemical sensors. Based on a metasurface that supports symmetrically protected BIC modes, the present invention destroys the symmetry of the system by changing the incident angle, transforming the unobservable symmetrically protected BIC mode without radiation loss into a quasi-BIC mode with radiation loss. By regulating the incident angle and thus the sensing sensitivity, the quasi-BIC mode is controlled in situ, reducing the preparation difficulty and cost caused by processing metasurfaces with different structural asymmetries to obtain quasi-BIC modes with different radiation losses.

Description

Technical Field

[0001] The present invention belongs to the technical field of metasurface biochemical sensors, and specifically discloses a sensing detection method based on a continuous domain bound state metasurface with in-situ adjustable sensitivity. Background Art

[0002] Metasurfaces with periodic subwavelength nanostructures can excite a variety of resonant modes, have strong near-field enhancement and light confinement capabilities at the subwavelength scale, and are sensitive to the ambient refractive index. They are attracting increasing attention in areas such as label-free detection of biomolecules. Plasmonic metasurfaces, often through localized surface plasmon resonance, can generate strong electric fields on the surface of metal nanostructures, so they can exhibit significant spectral changes when the external refractive index changes. Compared to commercial surface plasmon polaritons, they do not require prisms. However, the accompanying dissipative losses lead to a broadening of the resonance valley, a low quality factor, and low resolution, making them inconvenient for sensing applications. In contrast, dielectric metasurfaces based on high-refractive-index dielectric materials, due to the absence of ohmic losses, exhibit smaller linewidths and higher quality factor resonances through electromagnetic polariton resonances, such as quasi-continuum bound state modes, Fano resonances, and guided-mode resonances, showing promising alternative capabilities.

[0003] Bound continuum states (BICs) are special modes in the radiative continuum where there is no energy decay. These modes are characterized by the disappearance of the resonance linewidth in real space, infinite quality factor, and cannot be directly excited by incident light, thus corresponding to points in the spectrum where the resonance disappears. Among the various types of BIC modes, symmetry-protected BIC modes have attracted widespread attention because their quality factor is more robust to periodic variations. In practical applications, BICs located at high symmetry points in the first Brillouin zone can be converted into quasi-continuum bound states (quasi-BICs) with radiative losses, usually by breaking the structural symmetry of the resonators when they are arranged in an orderly manner in an array. The radiative loss of the quasi-BIC can be further controlled by adjusting the degree of perturbation. The smaller the asymmetry, the larger the quality factor.

[0004] Typical quasi-BIC metasurfaces are constructed by adding or removing portions of the initial symmetric shape of a single metaatom. For example, structures such as asymmetric silicon nanodisk pairs and asymmetric silicon crescents have been shown to support quasi-BIC resonance peaks or valleys with high-quality factors, making them promising for sensing applications. However, these silicon-based resonator metasurfaces require further optimization to improve sensitivity, especially in the visible light band. This is because the enhanced near-field in these simple dielectric structures is primarily localized within the metaatom, limiting its overlap with the analyte, resulting in low sensing sensitivity. Currently, researchers have sought to enhance the near-field interaction with the analyte by introducing dominant toroidal dipole resonances or increasing the contact field with the analyte. However, it is worth noting that for symmetry-protected quasi-BIC metasurfaces, fabricating nanostructures with ultrasmall asymmetry parameters is extremely challenging in actual experiments, resulting in the quasi-BIC being easily submerged in noise and unobservable, especially in the visible light band. Based on these problems existing in the existing symmetry-protected quasi-BIC metasurface, it is necessary to propose new methods to regulate quasi-BIC in order to further regulate the sensing sensitivity. Summary of the Invention

[0005] The main purpose of the present invention is to address the shortcomings of the existing technology and provide a sensing detection method based on a continuous domain bound state metasurface with in-situ adjustable sensitivity. The present invention uses a metasurface with a fixed structural size to achieve in-situ regulation of the continuous domain bound state mode and at the same time achieve in-situ regulation of the sensing sensitivity, thereby expanding the sensing application scenarios based on the continuous domain bound state metasurface and being suitable for popularization and application.

[0006] The technical solutions provided by the present invention are as follows:

[0007] A sensing detection method based on a continuous domain bound state metasurface with in-situ adjustable sensitivity, comprising the following steps:

[0008] 1) Immerse the symmetric-protected BIC mode metasurface in a solution with a refractive index n0 and inject TE polarized light at an incident angle θ0 to obtain a quasi-BIC mode resonant wavelength λ0 with radiation loss;

[0009] 2) Repeat step 1) and place the metasurface in solutions with different known refractive indices n, inject the same TE polarized light as in step 1) at an incident angle θ0, and obtain quasi-BIC mode resonance wavelengths λ with different radiation losses;

[0010] 3) performing linear fitting on the corresponding data points of the quasi-BIC mode resonance wavelength λ obtained in step 2) and the solution refractive index n to obtain the sensing sensitivity S0 of the metasurface quasi-BIC mode at the incident angle θ0;

[0011] 4) Adjusting the incident angle θ of the TE polarized light and repeating the above steps 1)-3) to obtain the sensing sensitivity S of the metasurface quasi-BIC mode at different incident angles θ;

[0012] 5) Obtain a sensitivity value S' and the corresponding incident angle θ' in step 4), and use the above-mentioned metasurface to measure the refractive index of an unknown solution. Specifically, immerse the metasurface in the solution to be tested, use TE polarized light at an incident angle θ' to obtain the resonant wavelength λ1 of the quasi-BIC mode of the metasurface, based on The refractive index n1 of the solution to be tested is calculated, and the detection of the solution to be tested is completed.

[0013] Furthermore, the entire structure of the metasurface supporting the symmetry-protected BIC mode has periodicity in the x-axis, y-axis, or y-z-axis, or x-z-axis directions, and has C2 symmetry along the z-axis, x-axis, or y-axis.

[0014] Furthermore, the metasurface supporting the symmetric protected BIC mode is applicable to the visible light band and the near-infrared band.

[0015] Furthermore, the metasurface structure supporting the symmetric protection BIC mode is a reflective symmetric secondary grating array, a symmetric nanorod pair array, a symmetric nanocolumn pair array, a symmetric nanodisk pair array, etc.

[0016] The beneficial effects of the present invention are:

[0017] 1) In-situ controllable metasurface sensitivity: The present invention is based on a metasurface that supports a symmetric-protected BIC mode. By changing the incident angle, the system symmetry is destroyed, and the unobservable symmetric-protected BIC mode with no radiation loss is converted into a quasi-BIC mode with radiation loss. By adjusting the incident angle, the sensing sensitivity is controlled, thus achieving in-situ control of the quasi-BIC mode.

[0018] 2) Low difficulty and cost in metasurface preparation: The regulation of quasi-BIC modes and sensitivity is achieved by changing the incident conditions rather than the symmetry of the metasurface structure. Therefore, there is no need to prepare a series of metasurfaces with different structural asymmetries, which reduces the difficulty and cost of processing metasurfaces with smaller structural asymmetry to obtain quasi-BIC modes with different radiation losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the metasurface supporting the symmetric protected BIC mode of the present invention, wherein (1) is a stereoscopic diagram, wherein 1 is the top grating; 2 is the bottom grating; 3 is the metal reflector; 4 is the substrate; the structure is periodically arranged in the x direction and infinitely long in the y direction; (2) is a cross-sectional diagram of the unit structure, wherein w1 is the top grating width; t1 is the top grating thickness; w2 is the bottom grating width, t2 is the bottom grating thickness, t3 is the metal reflector thickness, and Λ is the unit structure period;

[0020] Figure 2 A scanning electron microscope image of a metasurface prepared according to a specific embodiment of the present invention;

[0021] Figure 3 : The reflection spectra of the metasurface of a specific embodiment of the present invention under TE polarized light (i.e., y-direction polarized light) at different incident angles;

[0022] Figure 4 : The reflection spectra of the metasurface of a specific embodiment of the present invention under TE polarized light (i.e., y-direction polarized light) at different incident angles;

[0023] Figure 5 This is the measured sensitivity of the metasurface of a specific embodiment of the present invention calculated under TE polarized light (i.e., y-direction polarized light) at different incident angles. DETAILED DESCRIPTION

[0024] In order to better understand the present invention, the following examples further illustrate the in-situ control method of the sensing sensitivity based on the quasi-continuous domain bound state metasurface involved in the present invention, but the content of the present invention is not limited to the following examples.

[0025] The present invention is based on a metasurface supporting a symmetric protected BIC mode and adopts a reflective secondary grating structure. The schematic diagram of the structure is shown in FIG. Figure 1 As shown, 1-(1) is a stereoscopic diagram and 1-(2) is a cross-sectional diagram of the unit structure. The unit period of the structure is Λ = 440nm, the top grating width w1 = 220nm, the thickness t1 = 75nm, the bottom grating width w2 = 330nm, the thickness t2 = 90nm, and the metal reflector thickness t3 = 100nm.

[0026] The metasurface was prepared using a standard micro-electromechanical system process: electron beam evaporation deposition of 5nm / 100nm titanium / aluminum film; plasma enhanced chemical vapor deposition of 165nm silicon nitride; coating and pre-baking to prepare for exposure of the complementary pattern of the top grating; electron beam exposure, development, and fixing to obtain the complementary line pattern of the top grating; reactive ion etching and dry stripping to obtain a top grating with a period of Λ=440nm, a width of w1=220nm, and a thickness of t1=75nm; coating and pre-baking to prepare for exposure of the complementary pattern of the bottom grating; overlay alignment exposure, development, and fixing to obtain the complementary line pattern of the bottom grating; reactive ion etching and dry stripping to obtain a bottom grating with a width of w2=330nm and a thickness of t2=90nm, thus obtaining a reflective two-level grating structure metasurface supporting a symmetrically protected BIC mode, as shown in the scanning electron microscope image. Figure 2 shown.

[0027] The present invention is based on the generation of a resonance valley in the reflection spectrum of the metasurface supporting the symmetric protected BIC mode, and the radiation loss increases with the increase of the incident angle, which is reflected in the gradual increase of the line width of the resonance valley and the gradual decrease of the quality factor, such as Figure 3 As shown in Figure 3, by changing the incident angle, the system symmetry is destroyed, and the unobservable symmetry-protected BIC mode without radiation loss is transformed into a quasi-BIC mode with radiation loss.

[0028] The specific steps of the present invention for detecting the refractive index of a solution using the metasurface supporting the symmetrically protected BIC mode provided in the above specific embodiment are as follows:

[0029] (1) The prepared reflective secondary grating structure metasurface was immersed in deionized water, and TE polarized light (i.e., y-polarized light) was incident on the metasurface at an incident angle of 5°. The reflectance spectrum of the metasurface was measured, and the resonance wavelength of the quasi-BIC mode was obtained to be 664.96 nm. The metasurface was then blown dry.

[0030] (2) The metasurface was placed in 20wt%, 40wt%, 60wt%, and 80wt% ethylene glycol aqueous solutions, respectively. According to the Litchtennecher model, the ethylene glycol mass fraction w and the refractive index n EG The relationship is

[0031] lnn=lnn EG w+(1-w)lnn DI

[0032] where n EG =1.4318, the refractive index of deionized water n DI=1.3333, the calculated refractive indices of 20wt%, 40wt%, 60wt% and 80wt% ethylene glycol aqueous solutions are 1.3524, 1.3719, 1.3916 and 1.4115 respectively; using TE polarized light (i.e., y-polarized light) incident on the metasurface at 5°, the resonant wavelengths of the quasi-BIC mode are 668.06nm, 674.24nm, 679.63nm and 683.51nm respectively; Figure 4 (1) shown.

[0033] (3) The corresponding data points of the resonance wavelength λ and the solution refractive index n were plotted. After linear fitting, the sensing sensitivity of the metasurface quasi-BIC mode at an incident angle of 5° was obtained to be 255.98 nm / RIU;

[0034] (4) Adjust the incident angle to 10°, 15°, and 20°, and repeat steps (1) to (3) to obtain the reflection spectra of the quasi-BIC mode at 10°, 15°, and 20°, respectively. Figure 4 (2), (3), (4). The corresponding resonance wavelength λ and the solution refractive index n were linearly fitted to obtain the sensing sensitivities of the metasurface quasi-BIC mode at 10°, 15°, and 20° to be 370.25nm / RIU, 431.42nm / RIU, and 420.65nm / RIU, respectively. Figure 5 As shown, increasing the incident angle increases the radiative loss of the quasi-BIC mode, increasing the overlap between its near-field and the analyte, and thus increasing the sensing sensitivity. The decrease in the measured sensitivity at 20° is due to the reduced resolution caused by the large measured loss. These results demonstrate that in situ control of the sensitivity of continuum-based bound-state metasurfaces can be achieved by regulating the system's symmetry, namely the incident angle.

[0035] (5) Use the metasurface to measure the refractive index of an unknown solution. Select S' = 431.42nm / RIU and confirm that the corresponding incident angle θ' = 15°. Immerse the metasurface in the solution to be tested and use y-direction polarized light at an incident angle of 15° to obtain the resonant wavelength λ1 = 665.39nm. The refractive index of the solution to be tested is calculated to be n1=1.3343, and the detection of the solution to be tested is completed.

[0036] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments, and the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A sensing detection method based on a continuous domain bound state metasurface with in-situ adjustable sensitivity, comprising the following steps: 1) Immerse the symmetric-protected BIC mode metasurface in a solution with a refractive index n0 and inject TE polarized light at an incident angle θ0 to obtain a quasi-BIC mode resonant wavelength λ0 with radiation loss; 2) Repeat step 1) and place the metasurface in solutions with different known refractive indices n, inject the same TE polarized light as in step 1) at an incident angle θ0, and obtain quasi-BIC mode resonance wavelengths λ with different radiation losses; 3) performing linear fitting on the corresponding data points of the quasi-BIC mode resonance wavelength λ obtained in step 2) and the solution refractive index n to obtain the sensing sensitivity S0 of the metasurface quasi-BIC mode at the incident angle θ0; 4) Adjusting the incident angle θ of the TE polarized light and repeating the above steps 1)-3) to obtain the sensing sensitivity S of the metasurface quasi-BIC mode at different incident angles θ; 5) Obtain a sensitivity value S' and the corresponding incident angle θ' in step 4), and use the above-mentioned metasurface to measure the refractive index of an unknown solution. Specifically, immerse the metasurface in the solution to be tested, use TE polarized light at an incident angle θ' to obtain the resonant wavelength λ1 of the quasi-BIC mode of the metasurface, based on The refractive index n1 of the solution to be tested is calculated, and the detection of the solution to be tested is completed.

2. The sensing detection method based on the continuous domain bound state metasurface with in-situ adjustable sensitivity according to claim 1, characterized in that: The entire structure of the metasurface supporting the symmetry-protected BIC mode is periodic in the x-axis, y-axis, or y-z-axis, or x-z-axis directions, and has C2 symmetry along the z-axis, x-axis, or y-axis.

3. The sensing detection method based on the continuous domain bound state metasurface with in-situ adjustable sensitivity according to claim 1, characterized in that: Metasurfaces supporting symmetric protected BIC modes are applicable to the visible and near-infrared bands.

4. The sensing detection method based on the continuous domain bound state metasurface with in-situ adjustable sensitivity according to claim 1, characterized in that: The metasurface structure supporting the symmetric protected BIC mode is a reflective symmetric secondary grating array, a symmetric nanorod pair array, a symmetric nanopillar pair array or a symmetric nanodisk pair array.

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