Terahertz biosensor based on bound state effect in quasi-continuous domain and application thereof

Abstract

The invention discloses a terahertz biosensor based on a bound state effect in a quasi-continuous domain and application of the terahertz biosensor. The sensor comprises a substrate layer and a metal layer arranged on the substrate layer, the metal layer is a unit structure array formed by a first metal structure and a second metal structure which are oppositely arranged, and the unit structure array is arranged according to a square period; the bound state effect in the quasi-continuous domain is achieved by setting the distance between the first metal structure and the second metal structure, namely the offset d of the distance between the first metal structure and the second metal structure and the center of the resonator. By breaking the in-plane symmetry, a bound state in a leakage-free continuous domain can be converted into a bound state mode in a controllable quasi-continuous domain, so that low-concentration and high-sensitivity detection is realized. The method is suitable for real-time and rapid biomolecule detection, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the field of terahertz, and in particular relates to a terahertz biosensor based on a bound state effect in a quasi-continuous domain and an application thereof. Background Art

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

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

[0004] In a first aspect, an embodiment of the present invention provides a terahertz biosensor based on a bound state effect in a quasi-continuum domain, the sensor comprising:

[0005] Basal layer,

[0006] and a metal layer disposed on the base layer;

[0007] The metal layer is a unit structure array consisting of a first metal structure and a second metal structure arranged opposite to each other, and the unit structure array is arranged in a square period;

[0008] The bound state effect is enhanced by setting the distance between the first metal structure and the second metal structure, that is, the offset d from the center of the resonator.

[0009] In a second aspect, an embodiment of the present invention provides a method for preparing a terahertz biosensor based on a bound state effect in a quasi-continuum domain, the method comprising:

[0010] A titanium film with a thickness of 10 nm is deposited on the substrate as a bonding layer, and then a gold film with a thickness of 200 nm is deposited;

[0011] The gold film is then patterned according to the first metal structure and the second metal structure that are arranged opposite to each other.

[0012] In a third aspect, an embodiment of the present invention provides an application of a terahertz biosensor based on bound state effects in a quasi-continuous domain in biomolecule detection.

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

[0014] The present invention proposes a terahertz biosensor structure based on bound states in a quasi-continuous domain, aiming to achieve high-sensitivity, high-quality (Q) factor biomolecule detection. The bound state in the continuous domain breaks through the traditional wave confinement mechanism. Due to the symmetry mismatch of the structure, it is completely decoupled from the radiation mode, and can theoretically achieve an infinite quality factor. By breaking the in-plane symmetry, the bound state in the leakage-free continuous domain can be transformed into a controllable bound state mode in the quasi-continuous domain. By introducing the bound state resonance in the quasi-continuous domain in a periodic array of sub-wavelength size, the sensor generates a high-quality factor resonance peak in the terahertz frequency band, greatly enhancing the local electric field intensity, significantly improving the detection sensitivity of the target molecule, and can effectively reduce the detection limit. The local electric field enhancement on the sensor surface can achieve high-sensitivity capture of biomolecules, and is suitable for the detection of various biological samples such as proteins, DNA, and cancer cells. The sensor has real-time response capability, can quickly detect small changes in the resonant frequency, and is suitable for rapid diagnosis and biological monitoring. In addition, the biosensor designed by the present invention 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 THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0016] Figure 1 A schematic diagram of the structure of a terahertz biosensor provided in an embodiment of the present invention;

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

[0018] Figure 3 A schematic diagram of simulated transmission spectra under multiple asymmetry degrees provided by an embodiment of the present invention;

[0019] Figure 4 A schematic diagram showing the relationship between the Q factor and the asymmetry factor d of a simulated metasurface provided in an embodiment of the present invention;

[0020] Figure 5A schematic diagram of the frequency shift of the bound state in the simulated quasi-continuous domain as the thickness of the analyte is varied according to an embodiment of the present invention;

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

[0022] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of devices and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0023] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0024] It should be understood that although the terms first, second, third, etc. may be used in the present invention to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present invention, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0025] The present invention is described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the features of the following embodiments and implementations can be combined with each other.

[0026] like Figure 1 As shown, an embodiment of the present invention provides a terahertz biosensor based on bound state effect in a quasi-continuous domain, comprising:

[0027] Basal layer,

[0028] and a metal layer disposed on the base layer;

[0029] The metal layer is a unit structure array consisting of a first metal structure and a second metal structure arranged opposite to each other, and the unit structure array is arranged in a square period;

[0030] By setting the distance between the first metal structure and the second metal structure, that is, the offset d from the center of the resonator, the bound state effect in the quasi-continuous domain is achieved.

[0031] Furthermore, the base layer is made of polyimide (PI), and the metal layer is made of gold. Titanium metal is provided between the base layer and the metal layer as a bonding layer. The base layer has a thickness of 70 μm, the bonding layer has a thickness of 10 nm, and the metal layer has a thickness of 200 nm.

[0032] It should be noted that in this example, the material of the metal layer is gold, which has high stability and biocompatibility. The surface plasmon resonance (SPR) effect can further enhance the sensitivity of detection, thereby maximizing the bound state effect in the quasi-continuous domain. The base layer is made of polyimide (PI), which exhibits excellent flexibility, allowing it to maintain its shape under stress. By designing metamaterial structural units to flexibly manipulate their electromagnetic properties, the bound state phenomenon in the continuous domain is induced. Based on this, terahertz biosensors can achieve high quality factor resonance, thereby significantly improving the sensitivity of biomolecule detection;

[0033] Specifically, the bound state in the continuum breaks through the traditional wave binding mechanism. Its frequency exists within the continuous spectrum, but it has an infinitely high quality factor and no radiation leakage. The symmetry-protected bound state in the continuum is a type of bound state in the continuum, which is common in systems with reflection or rotational symmetry. It is a bound state located in the extended zone formed by the complete decoupling of the eigenmode and the radiation mode at a high symmetry position in the Brillouin zone due to symmetry mismatch. By breaking the in-plane symmetry of the structure, the bound state in the continuum (BIC) is converted into the bound state in the quasi-continuum (Q-BIC), and the Q value of the bound state in the quasi-continuum can be adjusted by adjusting the asymmetry parameter.

[0034] Furthermore, 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 both approximately in an "E" shape; the width of the first metal structure and the second metal structure is 6 μm;

[0035] A first gap between the first edge in the first metal structure and the first edge in the second metal structure is 11 μm; a second gap between the second edge in the first metal structure and the second edge in the second metal structure is 6 μm; a gap between the third edge in the first metal structure and the third edge in the second metal structure has the same value as the first gap;

[0036] The length difference between the first side of the first metal structure and the third side of the first metal structure is an offset d from the center of the resonator, so as to break the symmetry of the plane in the y direction.

[0037] Further, Figure 2 As shown in (a) in the figure, by changing the asymmetric parameter d of the metasurface, the change in the amplitude of the bound state transmission spectrum in the quasi-continuous domain is simulated. It can be seen that the proposed structure shows 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), the electric field distribution at the 2.15 THz resonance when d = 4. It can be seen that the local electric field is mainly concentrated in the gap of the metasurface.

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

[0039] Furthermore, in this example, the optical response of the terahertz biosensor was analyzed by using CST Studio Suite 2020 software during simulation, with unite cell conditions set in the x and y directions, and open (add space) in the z direction, and the unit cell of the metasurface was illuminated under a linear y-polarized plane wave at normal incidence.

[0040] Furthermore, the relationship between the offset from the center of the resonator and the Q factor is expressed as follows:

[0041]

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

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

[0044] On the other hand, the present invention also provides a method for preparing a terahertz biosensor based on the bound state effect in a quasi-continuous domain, the preparation method comprising:

[0045] Step S100, depositing a titanium film with a thickness of 10 nm on the base layer as a bonding layer, and then depositing a gold 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 disposed opposite to each other.

[0047] On the other hand, the present invention also provides an application of a terahertz biosensor based on bound state effects in a quasi-continuous domain in biomolecule detection, the application comprising the following steps:

[0048] Step S1, the refractive index of the given analyte changes from n1 to n n , select analytes with different thickness gradients, obtain the relationship between the resonance peak frequency shift and thickness, and thus obtain the optimal thickness value m x .like Figure 5 shown.

[0049] Step S2, select different refractive indices {n1, n2, ..., n n Same thickness m x analytes, obtain their terahertz transmission spectra, and calculate the peak values ​​of the resonance peak frequencies {f1, f2, …, f n};like Figure 6 As shown in (a) in .

[0050] Step S3, fitting the resonance peak frequency value pairs of the analytes with the same thickness but different refractive indices to calculate the sensitivity of the terahertz biosensor; Figure 6 As shown in (b) in .

[0051] Those skilled in the art will readily appreciate other embodiments of the present application after considering the description and practicing the contents disclosed herein. The present application is intended to cover any variations, uses or adaptations of the present application, which follow the general principles of the present application and include common knowledge or customary technical means in the art that are not disclosed in the present application. The description and examples are intended to be exemplary only.

[0052] It should be understood that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. A terahertz biosensor based on bound state effect in quasi-continuous domain, characterized in that: The sensor comprises: Basal layer, and a metal layer disposed on the base layer; The metal layer is a unit structure array consisting of a first metal structure and a second metal structure arranged opposite to each other, and the unit structure array is arranged in a square period; By setting the distance between the first metal structure and the second metal structure, that is, the offset d from the center of the resonator, the bound state effect in the quasi-continuous domain is achieved.

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

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

4. A terahertz biosensor based on bound state effect in quasi-continuous domain according to claim 3, characterized in that: The thickness of the base 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 bound state effect in quasi-continuous domain according to claim 1, characterized in that: 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 bound state effect in quasi-continuous domain according to claim 1, characterized in that: The first metal structure and the second metal structure are both approximately in an "E" shape; the width of the first metal structure and the second metal structure is 6 μm; A first gap between the first edge in the first metal structure and the first edge in the second metal structure is 11 μm; a second gap between the second edge in the first metal structure and the second edge in the second metal structure is 6 μm; a gap between the third edge in the first metal structure and the third edge in the second metal structure has the same value as the first gap; The difference between the length of the first side of the first metal structure and the length of the third side of the first metal structure is an offset from the center of the resonator.

7. A terahertz biosensor based on bound state effect in quasi-continuous domain according to claim 1 or 6, characterized in that: When the offset distance from the center of the resonator is d = 0, there is no resonance peak in the transmission spectrum produced by the terahertz metasurface biosensor; When the offset distance from the center of the resonator is d=4, the resonance peak frequency in the transmission spectrum generated by the terahertz metasurface biosensor is at 2.15THz, and the sensitivity is 480GHz / RIU.

8. A terahertz biosensor based on bound state effect in quasi-continuous domain according to claim 1 or 6, characterized in that: The relationship between the offset from the center of the resonator and the Q factor is expressed as follows: Where a1, a2 and b are real constant factors, ω0 and γ are the resonant frequency and damping rate respectively, and Q = ω0 / 2γ.

9. A method for preparing a terahertz biosensor based on bound state effect in a quasi-continuous domain, characterized in that: The preparation method comprises: A titanium film with a thickness of 10 nm is deposited on the substrate as a bonding layer, and then a gold film with a thickness of 200 nm is deposited; The gold film is then patterned according to the first metal structure and the second metal structure that are arranged opposite to each other.

10. Application of a terahertz biosensor based on bound state effect in quasi-continuum domain in biomolecule detection.

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