Single-opening double-ring terahertz metasurface sensor, preparation method and application thereof

Abstract

The application discloses a single-opening double-ring terahertz metasurface sensor, a preparation method and application thereof. The sensor comprises a substrate, and a metasurface unit with a preset period length is arranged on the substrate. The metasurface unit comprises a rectangular metal outer ring with a first preset side length, and a rectangular metal inner ring with a second preset side length is arranged in the rectangular metal outer ring. The line width of the rectangular metal outer ring and the rectangular metal inner ring is the same. An opening gap with the same width is arranged in the middle of a side of the rectangular metal outer ring and the rectangular metal inner ring which are away from each other. The application has the advantages that micro saccharides can be effectively detected.

Description

Technical Field

[0001] This application relates to the field of biosensor technology, and in particular to a single-opening double-ring terahertz metasurface sensor, its preparation method, and its application. Background Technology

[0002] The terahertz (THz) band, with frequencies between microwaves and infrared radiation, typically refers to the range from 0.1 THz to 10 THz. Electromagnetic waves in this band are characterized by non-ionization, low scattering, low energy, and high penetration. Many biomolecules exhibit unique vibrational and rotational characteristics in the terahertz band, enabling terahertz waves to identify the "fingerprint" information of biomolecules and perform non-destructive and non-contact detection of trace substances. Terahertz metasurfaces are artificial materials with periodic structures capable of interacting with electromagnetic waves of specific frequencies (especially in the terahertz band). The basic units of metasurfaces are usually composed of micrometer- or nanometer-scale metals or dielectric materials. By precisely designing their geometry and arrangement, specific manipulation of electromagnetic waves can be achieved. Terahertz metasurfaces can significantly enhance the signal response of target molecules through local surface plasmon resonance effects. This enhancement is mainly manifested in two aspects: firstly, the ability to detect extremely low concentrations of biochemical substances; and secondly, the ability to identify weak molecular characteristic signals. Based on this principle, the sensing technology using metasurfaces can simultaneously achieve excellent detection sensitivity and significant target recognition specificity.

[0003] However, existing terahertz metasurface sensors still have several technical shortcomings, mainly due to the low sensitivity of traditional terahertz metasurface sensors, which limits their application in the detection of low-concentration biomolecules and makes it difficult to effectively detect trace amounts of sugars (such as glucose, sucrose, lactose, etc.). Summary of the Invention

[0004] The main purpose of this application is to provide a single-opening double-ring terahertz metasurface sensor, its preparation method and its application, in order to solve the technical problem that existing terahertz metasurface sensors are unable to effectively detect trace amounts of sugars.

[0005] To achieve the above objectives, this application provides a single-opening dual-ring terahertz metasurface sensor, including a substrate, on which a metasurface unit with a preset period length is disposed. The metasurface unit includes a rectangular metal outer ring with a first preset side length, and a rectangular metal inner ring with a second preset side length is disposed inside the rectangular metal outer ring. The rectangular metal outer ring and the rectangular metal inner ring have the same line width, and an opening gap of the same width is opened at the middle of the side of the rectangular metal outer ring and the rectangular metal inner ring that are far apart from each other.

[0006] Optionally, the preset period length is 104μm, the first preset side length is 50μm, the second preset side length is 24μm, the line width is 4μm, the width of the opening gap is 6μm, and the input terahertz wave frequency is 1.44THz.

[0007] Optionally, the preset period length is 120μm, the first preset side length is 58μm, the second preset side length is 26μm, the line width is 4μm, the width of the opening gap is 6μm, and the input terahertz wave frequency is 1.25THz.

[0008] Optionally, the substrate is made of quartz and has a thickness of 35 μm, and the metasurface unit is made of gold and has a thickness of 200 nm.

[0009] To achieve the above objectives, this application provides a preparation method for fabricating the aforementioned single-opening double-ring terahertz metasurface sensor, comprising the following steps: Photoresist is prepared on a pre-fabricated silicon wafer; Using ultraviolet light as a light source, a pre-set pattern is projected and developed onto photoresist through a mask to form a mask pattern; The mask pattern is gold-plated and the adhesive is removed to obtain metasurface units; The metasurface unit is transferred onto the prepared substrate.

[0010] To achieve the above objectives, this application provides an application of a single-opening dual-ring terahertz metasurface sensor, which is used to detect the concentration of sucrose solution or lactose solution.

[0011] Optionally, when the sensor is used to detect the concentration of the sucrose solution, the change in the sucrose solution concentration is... c and the resonant frequency offset of the sensor f satisfies a linear relationship: f=3.30 c–3.57.

[0012] Optionally, when the sensor is used to detect the concentration of the lactose solution, the change in the lactose solution concentration is... c and the resonant frequency offset of the sensor f satisfies a linear relationship: f=4.22 c-0.63.

[0013] To achieve the above objectives, this application provides an application of a single-opening dual-ring terahertz metasurface sensor, which is used to detect the concentration of a glucose solution.

[0014] Optionally, the change in glucose solution concentration c and resonant frequency offset f satisfies a linear relationship: f=2.11 c-0.63.

[0015] The beneficial effects that this application can achieve are as follows: This application includes a substrate with a preset period length, on which a metasurface unit is disposed. The metasurface unit includes a rectangular metal outer ring with a first preset side length, and a rectangular metal inner ring with a second preset side length is disposed inside the rectangular metal outer ring. The rectangular metal outer ring and the rectangular metal inner ring have the same line width, and an opening gap of the same width is opened in the middle of the side of the rectangular metal outer ring and the rectangular metal inner ring that are far apart from each other. Based on the sensor structure of this application, when terahertz electromagnetic waves are incident perpendicularly from the sensor normal (i.e., the thickness direction), an electric field polarization can be generated with the polarization direction parallel to the sensor normal. Under the action of terahertz electromagnetic waves of a specific frequency, a quasi-inductive transparent peak (i.e., quasi-EIT resonance) can be generated. By analyzing the surface electromagnetic response characteristics of the quasi-EIT peak, the left resonance valley, and the right resonance valley, it can be seen that the resonance valley is generated by the LC resonance excited by the rectangular metal inner ring. At the same time, the surface current distribution of the rectangular metal inner ring is strong and the radiation loss is low, which is a bright mode. The resonance valley is formed by the combined action of the LC resonance excited by the rectangular metal inner ring and the three pairs of dipoles excited by the rectangular metal outer ring. At this time, the surface current distribution of the structure is weak and the radiation loss is high, which is a dark mode. Therefore, the bright-dark modes formed by these two resonant points are coupled and interfere with each other, reducing radiation loss and increasing the surface current intensity to a certain extent, thus creating a transparent window. Through the resonant coupling mechanism, the sensor of this application achieves low-loss EIT-like resonance, exhibiting a high Q value (70) and sensitivity (338 GHz / RIU), making it suitable for the effective detection of trace sugars. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0017] Figure 1 This is a schematic diagram of the unit structure of a single-opening double-ring terahertz metasurface sensor in an embodiment of this application; Figure 2 This is a schematic diagram of the transmission spectrum of the initial structure of the metasurface unit in an embodiment of this application; Figure 3 The surface current and electric field distribution characteristics of the metasurface unit at three frequencies in the embodiments of this application are shown. Figure 4This is a schematic diagram of the transmission spectrum (a) of the metasurface unit under different refractive index analytes in the embodiments of this application and the fitting curve (b) of its resonance peak frequency with the refractive index of the analyte; Figure 5 This is a schematic flowchart illustrating the sensor fabrication method in an embodiment of this application; Figure 6 This is an electron microscope schematic diagram of a sensor sample with two structural parameters in an embodiment of this application; Figure 7 The figures show a comparison of simulation and experimental results for two metasurface unit structures in the embodiments of this application. Figure 8 This is a schematic diagram of the molecular structure and characteristic absorption spectrum of sucrose in the embodiments of this application; Figure 9 This is a schematic diagram of the transmission spectrum of a metasurface unit structure based on sucrose solutions of different concentrations in an embodiment of this application. Figure 10 This is a schematic diagram illustrating the fitting relationship between the sucrose solution concentration and the resonant frequency offset based on metasurface unit structure one in an embodiment of this application. Figure 11 This is a schematic diagram of the refractive index spectrum (a) of sucrose solutions of different concentrations based on metasurface unit structure one and the fitting relationship (b) between glucose solution concentration c and refractive index n in the embodiments of this application. Figure 12 This is a schematic diagram of the molecular structure and characteristic absorption spectrum of lactose in the embodiments of this application; Figure 13 This is a schematic diagram of the transmission spectrum of a metasurface unit structure based on lactose solutions of different concentrations in an embodiment of this application. Figure 14 This is a schematic diagram illustrating the fitting relationship between lactose solution concentration and resonant frequency offset based on metasurface unit structure one in an embodiment of this application. Figure 15 This is a schematic diagram of the refractive index spectrum (a) of lactose solutions of different concentrations based on metasurface unit structure one and the fitting relationship (b) between glucose solution concentration c and refractive index n in the embodiments of this application. Figure 16 This is a schematic diagram of the molecular structure and characteristic absorption spectrum of glucose in the embodiments of this application; Figure 17 This is a schematic diagram of the transmission spectrum of glucose solutions of different concentrations based on metasurface unit structure II in an embodiment of this application; Figure 18 This is a schematic diagram showing the fitting relationship between glucose solution concentration and resonant frequency offset based on metasurface unit structure II in an embodiment of this application; Figure 19This is a schematic diagram of the refractive index spectrum (a) of glucose solutions of different concentrations based on metasurface unit structure II and the fitting relationship (b) between glucose solution concentration c and refractive index n in the embodiments of this application.

[0018] Figure label: 110 - Substrate, 120 - Metasurface unit, 121 - Rectangular outer metal ring, 212 - Rectangular inner metal ring.

[0019] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0022] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0023] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0024] Example 1 Reference Figure 1 This embodiment provides a single-opening dual-ring terahertz metasurface sensor, including a substrate 110. A metasurface unit 120 with a preset period length is disposed on the substrate 110. The metasurface unit 120 includes a rectangular metal outer ring 121 with a first preset side length and a rectangular metal inner ring 212 with a second preset side length inside the rectangular metal outer ring 121. The rectangular metal outer ring 121 and the rectangular metal inner ring 212 have the same line width. An opening gap of the same width is opened in the middle of the side of the rectangular metal outer ring 121 and the rectangular metal inner ring 212 that are far apart from each other.

[0025] In this embodiment, based on the proposed single-aperture double-ring terahertz metasurface sensor, its structural design introduces resonant coupling between the rings, exciting an EIT-like resonance with low radiation loss. For detailed explanation, the geometric parameters of the initial structure of the metasurface unit 120 are designed as follows: the substrate 110 is 35 μm thick quartz with a period length P = 100 μm (the period length determines the operating frequency range of the metasurface, thus designing and analyzing the reflection performance of the terahertz metasurface for biochemical sensing detection); the single-aperture double-ring metasurface unit 120 is 200 nm thick gold; the side length of the rectangular outer metal ring 121 is L1 = 44 μm, the side length of the inner ring is L2 = 20 μm, the structural linewidth w is 4 μm, and the width of the opening gap g is 5 μm. When the terahertz electromagnetic wave is incident perpendicularly from the sensor normal (i.e., the thickness direction), an electric field polarization is generated, and the electric field polarization direction is parallel to the sensor normal. The transmission spectrum (e.g., the transmission spectrum of the above initial structure) is obtained by simulating the above structure using electromagnetic simulation software. Figure 2As shown in the figure, the transmission spectrum reveals that the designed sensor produces a near-inductive transparency peak (i.e., a near-EIT resonance) at 1.677 THz. To explore the generation mechanism of the near-EIT peak, electromagnetic simulation analysis was conducted to study the surface electromagnetic response characteristics of the near-EIT peak (1.677 THz), the left resonance valley (1.656 THz), and the right resonance valley (1.697 THz). Figure 3 The distribution characteristics of surface currents (a, b, c) and electric fields (d, e, f) at these characteristic frequencies are shown. Figure 3 As shown in (a) and (d), the resonance valley at 1.656 THz is generated by the LC resonance excited by the rectangular inner metal ring 212. At the same time, the surface current distribution of the rectangular inner metal ring 212 is strong, and the radiation loss is low, which is a bright mode. On the other hand, the resonance valley at 1.697 THz is formed by the combined action of the LC resonance excited by the rectangular inner metal ring 212 and the three pairs of dipoles excited by the rectangular outer metal ring 121. At this time, the surface current distribution of the structure is weak, and the radiation loss is high, which is a dark mode. Therefore, the bright and dark modes formed by these two resonance points are coupled and interfered with each other, which reduces the radiation loss and improves the surface current intensity to a certain extent, creating a transparent window. Through the resonant coupling mechanism, the sensor in this embodiment achieves low-loss EIT-like resonance, exhibiting a high Q value (70) and sensitivity (338 GHz / RIU), thus making it suitable for the effective detection of trace sugars.

[0026] The mechanism of the EIT-like phenomenon generated by the sensor was analyzed above, and its Q value was calculated to be 70. Subsequently, its other performance index, sensitivity (S), was calculated. To study the response characteristics of the metasurface to changes in the medium environment, a 50 μm thick analytical medium layer was placed above the metasurface unit 120. By adjusting the refractive index parameter of the medium layer (gradiently varying in 0.1 steps within the range of 1.3 to 1.7), the influence mechanism of refractive index change on the optical properties of the metasurface was analyzed in depth, and the transmission spectra of the metasurface under different refractive indices were obtained, such as... Figure 4 As shown in (a), the frequency shift range of the resonance peak can be calculated based on the transmission spectrum data. The frequency shift of the resonance peak is linearly related to the change in refractive index. Figure 4 (b) The calculation yields the sensitivity of the resonance peak as S = 338 GHz / RIU.

[0027] It should be noted that the main performance indicators of terahertz sensors include: quality factor (Q), sensitivity (S), and FOM value. The quality factor (Q), through local electric field enhancement, can effectively improve the interaction between terahertz waves and matter, giving the sensor higher frequency selectivity. A higher Q value indicates a sharper resonance peak and lower energy loss. The Q value is defined as the ratio of the resonant frequency (f0) to the full width at half maximum (FWHM), calculated as: Q = f0 / FWHM. Sensitivity (S) reflects the sensor's ability to respond to small changes in the environment or the properties of the analyte. A higher S value indicates a more accurate detection of minute changes in the analyte. Refractive index sensitivity (S) is defined as the resonant frequency shift caused by a unit change in refractive index during sensing, usually expressed in GHz / RIU (frequency shift per unit change in refractive index), calculated as: S = Δf / Δn, where Δf and Δn are the refractive index change and the corresponding resonant frequency shift, respectively. To more comprehensively evaluate sensor performance, the Figure of Merit (FOM) is proposed as a comprehensive evaluation parameter. The FOM value quantifies the overall performance of the sensor by combining its sensitivity (S) and full width at half maximum (FWHM). The specific formula for calculating the FOM value is: FOM = S / FWHM.

[0028] Research has revealed that the surface plasmon resonance peak of a terahertz metasurface sensor can be designed using the functional unit structure (i.e., metasurface unit 120) to achieve the desired operating frequency, and the theoretical mechanism for enhanced coupling between the terahertz metasurface sensor resonance peak and the solute characteristic absorption peak has been established. Therefore, in this embodiment, to detect three common and important sugars—glucose, sucrose, and lactose—two different unit structure parameters were designed based on the absorption peaks of these three sugars. The structural parameters are as follows: Structure 1: The preset period length (P) is 104μm, the first preset side length (L1) is 50μm, the second preset side length (L2) is 24μm, the line width (w) is 4μm, the width of the opening gap (g) is 6μm, and the input terahertz wave frequency is 1.44THz.

[0029] Structure 2: The preset period length (P) is 120μm, the first preset side length (L1) is 58μm, the second preset side length (L2) is 26μm, the line width (w) is 4μm, the width of the opening gap (g) is 6μm, and the input terahertz wave frequency is 1.25THz.

[0030] Metasurface structures with the above two parameter combinations were fabricated using ultraviolet lithography, such as... Figure 6As shown, the transmission spectra of the two metasurface structures described above were measured using a THz-TDS system, and the results were compared with simulation results. For structure one, as... Figure 7 As shown in (a), the experimentally measured peak frequency of the EIT-like resonance is 1.46 THz, with a relative error of 1.4% compared to the simulation result (1.44 THz). The experimentally measured full width at half maximum (FWHM) of the EIT-like resonance valley (left side) is 0.055 THz, corresponding to a quality factor Q=26; the simulation results show an FWHM of 0.048 THz and Q=26, showing good agreement between the two. For structure two, as... Figure 7 As shown in (b), the experimentally measured peak frequency of the EIT-like resonance is 1.26 THz, with a relative error of 0.8% compared to the simulation result (1.25 THz). The experimentally measured FWHM of the EIT-like resonance valley (left side) is 0.105 THz, with Q = 12, while the simulation results show an FWHM of 0.105 THz and Q = 11, also demonstrating good consistency. The difference between the experimental and simulation results mainly stems from the influence of the fabrication process: incomplete gold layer peeling leads to the formation of rounded corners at the edges of the unit structure.

[0031] As an optional implementation, the substrate 110 is made of quartz and has a thickness of 35 μm, and the metasurface unit 120 is made of gold and has a thickness of 200 nm.

[0032] Example 2 Reference Figure 5 This embodiment provides a preparation method for preparing the above-mentioned single-opening double-ring terahertz metasurface sensor, including the following steps: Photoresist is prepared on a pre-fabricated silicon wafer; Using ultraviolet light as a light source, a pre-set pattern is projected and developed onto photoresist through a mask to form a mask pattern; The mask pattern is gold-plated and the adhesive is removed to obtain the metasurface unit 120; The metasurface unit 120 is transferred onto the prepared substrate 110.

[0033] In this embodiment, the sensor is fabricated using ultraviolet (UV) lithography. Ultraviolet light (UV) is used as the light source, and a designed pattern is projected onto photoresist through a mask. Photoresist is a UV-sensitive polymer material, and its working principle is based on photoinduced chemical changes: during UV exposure, the exposed areas of positive photoresist are removed during development due to increased photo-induced solubility, while the unexposed areas of negative photoresist are dissolved due to their continued solubility, thus achieving selective transfer of the mask pattern. Subsequently, through subsequent processes such as gold plating and photoresist removal, the pattern can be further transferred to the substrate 110 material, ultimately realizing the fabrication of the micro / nano structure sensor.

[0034] Example 3 This embodiment provides an application of a single-opening dual-ring terahertz metasurface sensor, which is used to detect the concentration of sucrose solution or lactose solution. The sensor is based on the metasurface unit 120 of structure one in embodiment 1.

[0035] When the sensor is used to detect the concentration of a sucrose solution Figure 8 A schematic diagram of the molecular structure and characteristic absorption spectrum of sucrose are shown. Based on... Figure 8 As shown in (b), sucrose exhibits a characteristic absorption peak at 1.44 THz, which shows good frequency matching with the EIT-like resonance peak (1.44 THz) of the metasurface unit 120 of the designed structure. Based on this, a sensing experiment was conducted on the sucrose solution using a sensor with structure one. Figure 9 The transmission spectral measurements of sucrose solutions at different concentrations are presented. The experimental results show that there is no frequency shift at a sucrose concentration of 2 mM compared to 0 mM. As the sucrose concentration increases from 2 mM to 14 mM, there is no frequency shift at 2 mM compared to 0 mM, but the resonant peak frequency exhibits a regular red shift, successively reaching 1.347 THz, 1.347 THz, 1.361 THz, 1.361 THz, and 1.376 THz. To quantitatively analyze the relationship between sucrose concentration and resonant frequency shift, linear regression analysis based on the experimental data is shown below. Figure 10 As shown in the figure, the fitted curve indicates the change in sucrose solution concentration. c (unit: mM) and resonant frequency offset f (unit: GHz) satisfies the following linear relationship: f=3.30 The c-3.57 (GHz) linear relationship can provide some guidance for the detection of sucrose solution concentration. The detection limit of this sensor can reach 4 mM.

[0036] The refractive index of sucrose solutions of different concentrations was detected using THz-TDS, and the results are as follows: Figure 11As shown in (a), refractive index data of solutions with different sucrose concentrations were extracted at the characteristic frequency of 1.347 THz and linear regression analysis was performed. The results showed that the sucrose solution concentration c and the refractive index n had a good linear relationship, which could be expressed as: n = 0.009c (e.g., ...). Figure 11 (b) Combining changes in sucrose solution concentration c and the resonant frequency shift of the metasurface f-fitting relationship: f=3.30 With c = 3.57 (GHz), the refractive index sensitivity of the metasurface to sucrose solution was calculated to be 367 GHz / RIU.

[0037] When the sensor is used to detect the concentration of lactose solution Figure 12 A schematic diagram of the molecular structure and characteristic absorption spectrum of lactose are given. Based on... Figure 12 As shown in (b), lactose exhibits a characteristic absorption peak at 1.37 THz, which is essentially matched with the EIT-like resonant mode of the designed structure at 1.44 THz (frequency deviation of approximately 4.9%). Based on this, a sensing experiment was conducted on a lactose solution using a sensor with structure one. Figure 13 The transmission spectral measurements of lactose solutions at different concentrations are presented. Experimental results show that as the lactose concentration increases from 0 mM to 10 mM, the resonant peak frequency exhibits a regular redshift, with frequencies of 1.347 THz, 1.361 THz, 1.376 THz, and 1.391 THz, respectively. To quantitatively analyze the relationship between lactose concentration and the resonant frequency shift, linear regression analysis based on the experimental data is shown below. Figure 14 As shown in the figure, the fitted curve reveals the change in lactose solution concentration. c (unit: mM) and resonant frequency offset f (unit: GHz) satisfies the following linear relationship: f=4.22 The c-0.63 (GHz) linear relationship can provide some guidance for the detection of lactose solution concentration. The detection limit of this sensor can reach 2 mM.

[0038] The refractive index of lactose solutions of different concentrations was measured using THz-TDS, and the results are as follows: Figure 15 As shown in (a), refractive index data of solutions with different lactose concentrations were extracted at the characteristic frequency of 1.347 THz and linear regression analysis was performed. The results showed that the lactose solution concentration c and the refractive index n had a good linear relationship, which could be expressed as: n = 0.017 (as shown in (a)). Figure 15 (b) Combining changes in sucrose solution concentration c and the resonant frequency shift of the metasurface f-fitting relationship: f=4.22 With c = 0.63 (GHz), the refractive index sensitivity of the metasurface to sucrose solution was calculated to be 248 GHz / RIU.

[0039] This embodiment also provides another application of a single-opening dual-ring terahertz metasurface sensor, which is used to detect the concentration of a glucose solution. This sensor is based on the metasurface unit 120 of structure two in embodiment 1.

[0040] Figure 16 The diagram shows the molecular structure and characteristic absorption spectrum of glucose. Figure 16 As shown in (b), glucose exhibits a characteristic absorption peak at 1.27 THz, which shows good frequency matching with the EIT-like resonance peak (1.26 THz) of the designed structure II. Based on this, a sensing experiment was conducted on glucose solution using a sensor with structure II. Figure 17 The transmission spectral measurements of glucose solutions at different concentrations are presented. According to the experimental data, as the glucose level in the solution increased from 4 mM to 10 mM, the resonant peak frequency exhibited a regular redshift, with frequencies of 1.200 THz, 1.193 THz, 1.186 THz, and 1.178 THz, respectively. To quantitatively analyze the relationship between glucose concentration and the resonant frequency shift, linear regression analysis based on the experimental data was performed as follows: Figure 18 As shown in the figure. The fitted curve shows the change in glucose solution concentration. c (unit: mM) and resonant frequency shift f (unit: GHz) satisfies the following linear relationship: f=2.11 The linear relationship c = 0.63 can provide some guidance for the detection of glucose solution concentration. The detection limit of this sensor can reach 4 mM.

[0041] The refractive index of glucose solutions of different concentrations was detected using THz-TDS, and the results are as follows: Figure 19 As shown in (a), refractive index data of solutions with different glucose concentrations were extracted at the characteristic frequency of 1.200 THz and linear regression analysis was performed. The results showed that the glucose solution concentration c and the refractive index n had a good linear relationship, which could be expressed as: n = 0.01c (e.g., ...). Figure 19 (b)). Combining changes in glucose solution concentration c and the resonant frequency shift of the metasurface f-fitting relationship: f=2.11 With c = 0.63 (GHz), the refractive index sensitivity of the metasurface to glucose solution was calculated to be 211 GHz / RIU.

[0042] In summary, based on the design of different structural parameters, this embodiment enables the sensor to match the characteristic absorption peaks of glucose, sucrose, and lactose, and successfully detects concentration changes in these sugar solutions. The detection limits are 4 mM, 4 mM, and 2 mM, respectively, and the refractive index sensitivities are 211 GHz / RIU, 367 GHz / RIU, and 248 GHz / RIU, respectively. This achieves highly sensitive detection of sugars and verifies the sensor's performance.

[0043] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A single-opening, double-ring terahertz metasurface sensor, characterized in that, The device includes a substrate on which a metasurface unit with a preset period length is disposed. The metasurface unit includes a rectangular metal outer ring with a first preset side length and a rectangular metal inner ring with a second preset side length. The rectangular metal outer ring and the rectangular metal inner ring have the same line width. The rectangular metal outer ring and the rectangular metal inner ring each have an opening gap of the same width at the middle of their opposite sides.

2. The single-opening dual-ring terahertz metasurface sensor as described in claim 1, characterized in that, The preset period length is 104μm, the first preset side length is 50μm, the second preset side length is 24μm, the line width is 4μm, the width of the opening gap is 6μm, and the input terahertz wave frequency is 1.44THz.

3. The single-opening dual-ring terahertz metasurface sensor as described in claim 1, characterized in that, The preset period length is 120μm, the first preset side length is 58μm, the second preset side length is 26μm, the line width is 4μm, the width of the opening gap is 6μm, and the input terahertz wave frequency is 1.25THz.

4. The single-opening double-ring terahertz metasurface sensor as described in any one of claims 1-3, characterized in that, The substrate is made of quartz and has a thickness of 35 μm. The metasurface unit is made of gold and has a thickness of 200 nm.

5. A preparation method, characterized in that, The method for fabricating a single-opening double-ring terahertz metasurface sensor as described in any one of claims 1-4 includes the following steps: Photoresist is prepared on a pre-fabricated silicon wafer; Using ultraviolet light as a light source, a pre-set pattern is projected and developed onto photoresist through a mask to form a mask pattern; The mask pattern is gold-plated and the adhesive is removed to obtain metasurface units; The metasurface unit is transferred onto the prepared substrate.

6. The application of the single-opening dual-ring terahertz metasurface sensor as described in claim 2, characterized in that, The sensor is used to detect the concentration of sucrose solution or lactose solution.

7. The application of the single-opening dual-ring terahertz metasurface sensor as described in claim 6, characterized in that, When the sensor is used to detect the concentration change of the sucrose solution, c and the resonant frequency offset of the sensor f satisfies a linear relationship: f=3.30 c–3.

57.

8. The application of the single-opening dual-ring terahertz metasurface sensor as described in claim 6, characterized in that, When the sensor is used to detect the change in lactose solution concentration, c and the resonant frequency offset of the sensor f satisfies a linear relationship: f=4.22 c-0.

63.

9. The application of the single-opening dual-ring terahertz metasurface sensor as described in claim 3, characterized in that, The sensor is used to detect the concentration of the glucose solution.

10. The application of the single-opening dual-ring terahertz metasurface sensor as described in claim 9, characterized in that, Change in glucose solution concentration c and resonant frequency offset f satisfies a linear relationship: f=2.11 c-0.63.

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