A terahertz biosensor based on bound state effect in quasi-continuum and application thereof

Abstract

The application discloses a terahertz biosensor based on a bound state effect in a quasi-continuous domain and application thereof. The sensor comprises a substrate layer and a metal layer arranged on the substrate layer; the metal layer is an array of unit structures composed of oppositely arranged first metal structures and second metal structures, and the array of unit structures is arranged in a square period; the bound state effect in the quasi-continuous domain is realized by setting the distance between the first metal structure and the second metal structure, i.e. the offset d of the distance from the resonator center; and the bound state in the continuous domain without leakage can be converted into a controllable bound state mode in the quasi-continuous domain by breaking the in-plane symmetry, so that low-concentration and high-sensitivity detection is realized. The application is suitable for real-time and rapid biomolecule detection and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of terahertz, and particularly relates to a terahertz biosensor based on a bound state effect in quasi-continuous domain and application thereof. BACKGROUND

[0002] With the development of terahertz technology, the terahertz biosensor has become an important tool in biological detection due to its unique response to water molecules, proteins and other biological molecules. However, the conventional terahertz biosensor still has many deficiencies in sensitivity, selectivity and response speed. In order to improve the performance of the biosensor, the sensing technology based on optical resonance phenomenon has gradually attracted attention in recent years. The bound state in the continuous domain breaks through the traditional wave bound mechanism and can achieve infinite Q value, and has extremely high sensitivity in the terahertz band, which has great potential for biological molecule detection. SUMMARY

[0003] In view of the prior art, the present application provides a terahertz biosensor based on a bound state effect in quasi-continuous domain and application thereof.

[0004] In a first aspect, the present application provides a terahertz biosensor based on a bound state effect in quasi-continuous domain, which comprises:

[0005] a substrate layer,

[0006] and a metal layer arranged on the substrate layer;

[0007] The metal layer is an unit structure array composed of oppositely arranged first metal structure and second metal structure, and the unit structure array is arranged in a square period.

[0008] The distance between the first metal structure and the second metal structure, i.e. the offset d of the distance from the resonator center, is set to enhance the bound state effect.

[0009] In a second aspect, the present application provides a preparation method of a terahertz biosensor based on a bound state effect in quasi-continuous domain, which comprises:

[0010] Depositing titanium with a thickness of 10 nm on the substrate layer as a bonding layer, and then depositing a gold thin film with a thickness of 200 nm;

[0011] Then patterning the gold thin film according to the oppositely arranged first metal structure and second metal structure.

[0012] In a third aspect, the present application provides an application of a terahertz biosensor based on a bound state effect in quasi-continuous domain in biological molecule detection.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] The present application provides a terahertz biosensor structure based on bound states in the quasi-continuous domain, aiming to realize high-sensitivity and high-quality (Q) factor detection of biomolecules. The bound states in the continuous domain break through the traditional wave constraint mechanism, and are completely decoupled from the radiation mode due to the mismatch of the symmetry of the structure, which can theoretically realize an infinite quality factor. By breaking the in-plane symmetry, the bound states in the continuous domain without leakage can be converted into controllable bound states in the quasi-continuous domain mode. By introducing the bound state resonance in the quasi-continuous domain in the subwavelength periodic array, the sensor produces a high-quality factor resonance peak in the terahertz frequency band, greatly enhances the local electric field strength, significantly improves the detection sensitivity of the target molecules, and can effectively reduce the detection lower limit. The local electric field enhancement on the surface of the sensor can realize high-sensitivity capture of biomolecules, and is suitable for detection of various biological samples such as proteins, DNA, cancer cells, etc. The sensor has real-time response capability and can quickly detect the slight change of the resonance frequency, and is suitable for rapid diagnosis and biological monitoring. In addition, the biosensor designed in the present application enhances the local electric field energy, reduces the energy loss of the sensor, greatly strengthens the interaction between light and matter, and provides a method for rapid and non-destructive trace biomedical detection. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0016] Figure 1 The structure schematic diagram of the terahertz biosensor provided by the embodiment of the present application is shown in the figure.

[0017] Figure 2 (a) in the figure is a schematic diagram of the transmission amplitude mapping of the bound state in the quasi-continuous domain simulated by changing the structural asymmetry provided by the embodiment of the present application, Figure 2 (b) in the figure is an electric field distribution diagram of the terahertz biosensor provided by the embodiment of the present application.

[0018] Figure 3 The schematic diagram of the simulated transmission spectrum under multiple asymmetry degrees provided by the embodiment of the present application is shown in the figure.

[0019] Figure 4 The relationship between the Q factor of the simulated super surface and the asymmetry factor d provided by the embodiment of the present application is shown in the figure.

[0020] Figure 5Fig. 2 shows a schematic diagram of the shift of the frequency of the bound state in quasi-continuous domain as a function of the thickness of the analyte according to an embodiment of the present application;

[0021] Figure 6 (a) in Fig. 1 is a simulated transmission spectrum of a terahertz biosensor with an analyte of 15 μm thickness and a refractive index n ranging from 1 to 2, Figure 6 (b) in Fig. 1 is a plot of the peak-to-peak resonance frequency shift versus the change in the refractive index of the analyte. DETAILED DESCRIPTION

[0022] The exemplary embodiments will be described in detail herein with reference to the attached drawings. The description of the exemplary embodiments is intended to apply to all alternative embodiments, as would be understood by persons skilled in the art. To the extent that they can be different, it is intended that such alternative embodiments are implicitly included in the description. The description is presented in the order of applying the disclosed embodiments to: a terahertz biosensor based on the bound state effect in quasi-continuous domain, a method for detecting an analyte using the terahertz biosensor, and a method for measuring the thickness of an analyte using the terahertz biosensor.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0024] It is to be understood that the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. It is to be understood that the term "comprising" as used herein is to be taken as meaning "including, but not limited to". It is to be understood that the term "consisting of" as used herein is to be taken as meaning "including, and limited to". It is to be understood that the term "consisting essentially of" as used herein is to be taken as meaning "including at least the recited entities and those that do not materially affect the character and composition as a whole of the closed system." It is to be understood that the phrase "consisting of" excludes any element not specified in the claim.

[0025] The present application will be described in detail below with reference to the attached drawings. The features of the embodiments and implementation described below can be combined with each other as long as there is no conflict.

[0026] As shown in Fig. 1, the present embodiment provides a terahertz biosensor based on the bound state effect in quasi-continuous domain, comprising: Figure 1 a substrate layer,

[0027] a metal layer disposed on the substrate layer; and

[0028]

[0029] ​The metal layer is a unit structure array composed of oppositely arranged first metal structures and second metal structures, and the unit structure array is arranged in a square period;

[0030] The distance between the first metal structure and the second metal structure, i.e., the offset d of the distance from the center of the resonator, is set to achieve the bound state effect in the quasi-continuous domain.

[0031] Further, the substrate layer is selected from polyimide (PI), and the material of the metal layer is selected from gold. A titanium metal is arranged between the substrate layer and the metal layer as a bonding layer. The thickness of the substrate layer is 70 μm, the thickness of the bonding layer is 10 nm, and the thickness of the metal layer is 200 nm.

[0032] It should be noted that in the present example, the material of the metal layer is selected from gold which has high stability and biocompatibility, and the sensitivity of detection can be further enhanced by surface plasmon resonance (SPR) effect, thereby maximizing the bound state effect in the quasi-continuous domain. The substrate layer is selected from polyimide (PI), which exhibits excellent flexibility and can maintain its shape under stress. By designing the super material structure unit, the electromagnetic properties thereof can be flexibly controlled to induce the bound state phenomenon in the continuous domain. Based on this, the terahertz biosensor can achieve high-quality factor resonance, thereby significantly improving the sensitivity of biological molecule detection.

[0033] Specifically, the bound state in the continuous domain breaks through the traditional wave bound mechanism, and its frequency exists in the continuous spectrum, but has an infinite high quality factor and no radiation leakage. The symmetry-protected bound state in the continuous domain is a type of bound state in the continuous domain, which is commonly found in systems with reflection or rotational symmetry, and is an intrinsic mode and radiation mode located at a high-symmetry point in the Brillouin zone which is completely decoupled due to the mismatch of symmetry, thereby forming a bound state in the extended region. By breaking the in-plane symmetry of the structure, the bound state in the continuous domain (BIC) will be converted into the bound state in the quasi-continuous domain (Q-BIC), and the Q value of the bound state in the quasi-continuous domain can be adjusted by adjusting the asymmetric parameter.

[0034] Further, the cross section of each unit in the metal layer is a square with a side length of 40 μm. The first metal structure and the second metal structure are approximately in the shape of an "E" character; the width of the first metal structure and the second metal structure is 6 μm;

[0035] The first gap between the first edge of the first metal structure and the first edge of the second metal structure is 11 μm; the second gap between the second edge of the first metal structure and the second edge of the second metal structure is 6 μm; the gap between the third edge of the first metal structure and the third edge of the second metal structure has the same value as the first gap.

[0036] The length difference of the first edge in the first metal structure and the third edge in the first metal structure is the offset distance d from the resonator center to break the symmetry in the y direction in the plane.

[0037] Further, Figure 2 As shown in (a) of FIG. 6, by changing the asymmetric parameter d of the metasurface, the change of the amplitude of the bound state transmission spectrum in the quasi-continuous domain is simulated. It can be seen that the proposed structure exhibits geometric dependence. When d = 0, the resonance peak disappears, indicating that it is a bound state in the continuous domain without leakage. Figure 2 As shown in (b) of FIG. 6, the electric field distribution at the 2.15 THz resonance when d = 4 in the metasurface. It can be seen that the local electric field is mainly concentrated in the gap of the metasurface.

[0038] Specifically, by changing the asymmetric factor d, the transition from the bound state in the continuous domain to the bound state in the quasi-continuous domain is realized. Figure 3 The transmission spectrum calculated under different asymmetric parameters d is given. It can be seen that the proposed structure exhibits geometric dependence, that is, the resonance amplitude can be adjusted by adjusting the asymmetric parameter d. By moving the asymmetric factor d, the ideal bound state in the continuous domain is converted into the bound state in the quasi-continuous domain, which can be directly excited under free space illumination. The asymmetric parameter d of each sample is different from 0, 1, 2, 3, to 4 μm. When d = 0 μm, there is no resonance peak in the simulated transmission spectrum. When the offset d increases from 0 to 4 μm, a typical sharp resonance feature appears, and the line width gradually increases. By adjusting the asymmetric factor d to control the asymmetry of the structure, the resonance line width and Q factor can be designed and adjusted as needed.

[0039] Further, in the simulation process of the present example, CST Studio Suite 2020 software is used for simulation, and the optical response of the terahertz biosensor is analyzed. The unit cell is set in the x and y directions, and open (add space) is set in the z direction. The unit cell of the metasurface is illuminated under linear y polarization plane wave at normal incidence.

[0040] Further, the relationship expression between the offset distance d from the resonator center and the Q factor is as follows:

[0041]

[0042] In the formula, a1, a2 and b are real constant factors, ω0 and γ are the resonance frequency and damping rate respectively, and Q = ω0 / 2γ. And R 2 > 0.99. Figure 4The relationship between the Q factor and the asymmetry parameter d is shown, and the Q factor can reach 123 at most.

[0043] Further, the resonance peak frequency point of the transmission spectrum generated by the terahertz super surface biosensor is at 2.15 THz, and the sensitivity is 480 GHz / RIU.

[0044] In another aspect, the application also provides a preparation method of a terahertz biosensor based on the bound state effect in the quasi-continuous domain, the preparation method comprising:

[0045] Step S100, depositing titanium with a thickness of 10 nm as a bonding layer on a substrate layer, and then depositing a gold thin film with a thickness of 200 nm;

[0046] Step S200, patterning the gold thin film according to the first metal structure and the second metal structure arranged oppositely.

[0047] In another aspect, the application also provides an application of a terahertz biosensor based on the bound state effect in the quasi-continuous domain in biomolecular detection, the application comprising the following steps:

[0048] Step S1, selecting different thickness gradient analytes, obtaining the relationship between the resonance peak frequency shift and the thickness, and thus obtaining the optimal thickness value m n . x As shown in (a) of FIG. Figure 5 .

[0049] Step S2, selecting analytes with different refractive indexes {n1, n2, …, n n} and the same thickness m x , obtaining the terahertz transmission spectrum thereof, and calculating the resonance peak frequency point values {f1, f2, …, f n} of different analytes; as shown in (a) of FIG. Figure 6 .

[0050] Step S3, fitting the resonance peak frequency point values of the analytes with the same thickness and different refractive indexes, and calculating the sensitivity of the terahertz biosensor; as shown in (b) of FIG. Figure 6 .

[0051] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the application be limited only by the scope of the claims, including any amendments thereof, and that the specification and drawings be interpreted broadly.

[0052] It is to be understood that the application is not limited to the precise construction already described above and shown in the drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope thereof.

Claims

1. A terahertz biosensor based on bound state effects in quasi-continuous domains, characterized in that, The sensor comprises: a substrate layer, and a metal layer arranged on the substrate layer; the metal layer is an array of unit structures composed of oppositely arranged first metal structures and second metal structures, and the array of unit structures is arranged in a square period; the bound state effect in quasi-continuous domain is realized by setting the distance between the first metal structure and the second metal structure, i.e. the offset d of the distance from the resonator center; the first metal structure and the second metal structure are approximately in the shape of an "E" character; the width of the first metal structure and the second metal structure is 6 μm; the first gap between the first edge of the first metal structure and the first edge of the second metal structure is 11 μm; the second gap between the second edge of the first metal structure and the second edge of the second metal structure is 6 μm; the gap between the third edge of the first metal structure and the third edge of the second metal structure has the same value as the first gap; the offset of the distance from the resonator center is the length difference between the first edge of the first metal structure and the third edge of the first metal structure; when the offset d of the distance from the resonator center is 0, the terahertz metasurface biosensor does not produce a resonance peak in the transmission spectrum; when the offset d of the distance from the resonator center is 4, the resonance peak in the transmission spectrum produced by the terahertz metasurface biosensor is at 2.15 THz, and the sensitivity is 480 GHz / RIU.

2. The terahertz biosensor based on the bound state effect in quasi-continuous domain according to claim 1, characterized in that, The substrate layer is made of polyimide, and the material of the metal layer is gold.

3. The terahertz biosensor based on the bound state effect in quasi-continuous domain according to claim 1 or 2, characterized in that, Titanium is arranged between the substrate layer and the metal layer as a bonding layer.

4. The terahertz biosensor based on the bound state effect in quasi-continuous domain according to claim 3, characterized in that, The thickness of the substrate layer is 70 μm, the thickness of the bonding layer is 10 nm, and the thickness of the metal layer is 200 nm.

5. The terahertz biosensor based on the bound state effect in quasi-continuous domain according to claim 1, wherein, The cross section of each unit in the metal layer is a square with a side length of 40 μm.

6. The terahertz biosensor based on the bound state effect in quasi-continuous domain according to claim 1, wherein, The relationship expression between the offset d of the distance from the resonator center and the Q factor is as follows: ； wherein , and are real constant factors, and are the resonance frequency and damping rate, respectively, .

7. A method of producing a terahertz biosensor based on the effect of bound states in quasi-continuous domains according to any one of claims 1 to 6, characterized in that, The preparation method comprises: depositing titanium with a thickness of 10 nm on the substrate layer as a bonding layer, and then depositing a gold thin film with a thickness of 200 nm; then patterning the gold thin film according to the oppositely arranged first metal structure and the second metal structure.

8. Application of the terahertz biosensor based on the bound state effect in quasi-continuous domain according to any one of claims 1-6 in biomolecule detection.

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