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

Abstract

The invention discloses a sensing detection method based on a continuous domain bound state metasurface with adjustable sensitivity in situ, and belongs to the technical field of metasurface biochemical sensors. On the basis of the metasurface supporting the symmetric protection type BIC mode, the symmetric protection type BIC mode which does not have radiation loss and cannot be observed is converted into the quaii-BIC mode with radiation loss by changing the incident angle and destroying the system symmetry, in-situ regulation and control of the quaii-BIC mode is achieved by regulating and controlling the incident angle and the sensing sensitivity, and in-situ measurement and control of the quaii-BIC mode are achieved. And the preparation difficulty and cost generated by processing the metasurfaces with different structural asymmetry degrees to obtain the quaii-BIC modes with different radiation losses are reduced.

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 multiple resonance modes, have strong near-field enhancement and light confinement capabilities at the subwavelength scale, and are sensitive to the ambient refractive index. They have attracted increasing attention in aspects such as label-free detection of biomolecules. Plasmonic metasurfaces can often generate strong electric fields on the surface of metal nanostructures through localized surface plasmon resonances, so they can show obvious spectral changes when the external refractive index changes. And compared with commercial surface plasmon polaritons, they do not need to rely on prisms. However, the accompanying dissipative losses lead to broadening of the resonance valley, low quality factor, and low resolution, which is not convenient for sensing applications. On the contrary, dielectric metasurfaces based on high-refractive-index dielectric materials exhibit smaller line widths and higher quality factor resonances through electromagnetic polaritons resonances due to the absence of Ohmic losses, 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 vanishing 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 vanishes. Among the various types of BIC modes, symmetry-protected BIC modes have attracted widespread attention because of their stronger robustness in quality factor variation with periodicity. 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 orderly arranged 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] A typical quasi-BIC metasurface is formed by adding or removing a part 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 very promising for sensing applications. However, these silicon-based resonator metasurfaces need to be further optimized to improve sensitivity, especially in the visible light band. This is because the near-field enhanced by the simple dielectric structure above is mainly localized inside the metaatom, limiting its overlap space with the analyte, resulting in low sensing sensitivity. Currently, researchers have increased the interaction between the near-field and the analyte by introducing a dominant toroidal dipole resonance or increasing the contact field with the analyte. However, it is worth noting that for symmetry-protected quasi-BIC metasurfaces, in actual experiments, it is very challenging to fabricate nanostructures with ultra-small asymmetric parameters, which makes it easy for quasi-BIC to be submerged in noise and not be observed, 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 deficiencies in the prior art and to 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 certain 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 solution provided by the present invention is 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 metasurface of the symmetric protected BIC mode in a solution with a refractive index n0, and use TE polarized light to incident at an incident angle θ0 to obtain a quasi-BIC mode resonant wavelength λ0 with radiation loss;

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

[0010] 3) The corresponding data points of the quasi-BIC mode resonance wavelength λ and the solution refractive index n obtained in step 2) are linearly fitted 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 certain sensitivity value S' and the corresponding incident angle θ' in step 4), and use the above metasurface to measure the refractive index of an unknown solution. Specifically, immerse the metasurface in the solution to be tested, use TE polarized light to be incident at an incident angle θ', and obtain the resonant wavelength λ1 of the quasi-BIC mode of the metasurface. 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) The sensitivity of the metasurface can be in situ controlled: The present invention is based on a metasurface that supports a symmetric-protected BIC mode. By changing the incident angle and destroying the system symmetry, the unobservable symmetric-protected BIC mode without radiation loss is transformed into a quasi-BIC mode with radiation loss. By adjusting the incident angle and the sensing sensitivity, the in situ control of the quasi-BIC mode is achieved.

[0018] 2) Low difficulty and cost in metasurface preparation: The regulation of quasi-BIC mode 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 arranged periodically in the x direction and is 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 supersurface prepared according to a specific embodiment of the present invention;

[0021] Figure 3 : is the reflection spectrum 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 : is the reflection spectrum 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 It is the measured sensitivity calculated for the metasurface of a specific embodiment of the present invention under TE polarized light (i.e., polarized light in the y direction) at different incident angles. DETAILED DESCRIPTION

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

[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 stereogram, 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 by standard MEMS process: electron beam evaporation deposition of 5nm / 100nm titanium / aluminum film; plasma enhanced chemical vapor deposition of 165nm silicon nitride; photoresist and pre-bake to prepare for exposure of the complementary pattern of the top grating; electron beam exposure, development, and fixation 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; photoresist and pre-bake to prepare for exposure of the complementary pattern of the bottom grating; overlay alignment exposure, development, and fixation 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 secondary grating structure metasurface supporting the symmetric protection 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, 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 using the metasurface supporting the symmetric protected BIC mode provided in the above specific embodiment to detect the refractive index of the solution are as follows:

[0029] (1) The prepared reflective secondary grating structure metasurface was immersed in deionized water, TE polarized light (i.e., y-direction 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, and the metasurface was blown dry;

[0030] (2) The metasurface was then 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 refractive indexes of 20wt%, 40wt%, 60wt%, and 80wt% ethylene glycol aqueous solutions are calculated to be 1.3524, 1.3719, 1.3916, and 1.4115, respectively; TE polarized light (i.e., y-direction polarized light) is incident on the metasurface at 5°, and the resonance wavelengths of the quasi-BIC mode are obtained to be 668.06nm, 674.24nm, 679.63nm, and 683.51nm, respectively; Figure 4 (1) as shown.

[0033] (3) Plotting the corresponding data points of the resonance wavelength λ and the solution refractive index n, and through linear fitting, the sensing sensitivity of the metasurface quasi-BIC mode at an incident angle of 5° is 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 in the figure, as the incident angle increases, the radiation loss of the quasi-BIC mode increases, the overlap space between its near field and the analyte increases, and the sensing sensitivity increases. The decrease in the measured sensitivity value at 20° is due to the reduction in resolution caused by the large measured loss. The above results verify that the sensitivity of the continuous domain bound state metasurface can be in-situ regulated by regulating the symmetry of the system, that is, 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 to incident 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 publishing the embodiments is to help further understand the present invention, but those skilled in the art can understand 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 subject to 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 metasurface of the symmetric protected BIC mode in a solution with a refractive index n0, and use TE polarized light to incident at an incident angle θ0 to obtain a quasi-BIC mode resonant wavelength λ0 with radiation loss; 2) repeating step 1) to place the metasurface in solutions with different known refractive indices n, and injecting the same TE polarized light as step 1) at an incident angle θ0 to obtain quasi-BIC mode resonance wavelengths λ with different radiation losses; 3) The corresponding data points of the quasi-BIC mode resonance wavelength λ and the solution refractive index n obtained in step 2) are linearly fitted 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 certain sensitivity value S' and the corresponding incident angle θ' in step 4), and use the above metasurface to measure the refractive index of an unknown solution. Specifically, immerse the metasurface in the solution to be tested, use TE polarized light to be incident at an incident angle θ', and obtain the resonant wavelength λ1 of the quasi-BIC mode of the metasurface. 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 as claimed in claim 1 is 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-axis, 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 as claimed in claim 1 is characterized in that: The metasurface supporting the symmetric protected BIC mode is applicable to the visible light band and the near-infrared band.

4. The sensing detection method based on the continuous domain bound state metasurface with in-situ adjustable sensitivity as claimed in claim 1 is characterized in that: 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 or a symmetric nanodisk pair array.

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