CN111812059A - A kind of metamaterial terahertz biosensor and preparation method thereof - Google Patents

Abstract

The invention discloses a metamaterial terahertz biosensor and a preparation method thereof. The metamaterial terahertz biosensor includes a substrate layer and a medium layer, a metal reflective layer is arranged on the substrate layer, a metal microstructure layer is arranged on the medium layer, and the metal reflective layer and the metal microstructure layer are arranged between the A microfluidic channel for the liquid to be tested is formed, and a liquid inlet and a liquid outlet of the microfluidic channel are opened on the base layer. The metal microstructure layer is a periodic structural unit attached to the medium layer. The microstructure layer consists of a square metal ring and a double "H"-shaped cross metal structure placed in and concentric with it, wherein the double "H" shape cross metal structure consists of two identically structured "H"-shaped metal rings vertically intersected . The sensor of the present invention has a very high absorption peak, as well as high sensitivity and polarization insensitivity.

Description

A kind of metamaterial terahertz biosensor and preparation method thereof

technical field

The invention relates to a sensor, in particular to a metamaterial terahertz biosensor and a preparation method thereof.

Background technique

Terahertz (THz for short, 1THz=10 ¹² Hz) wave is an electromagnetic wave with a frequency in the range of 0.1 to 10 THz (wavelength is 30 to 3000 μm), which is in the transition from macro electronics to micro photonics. It has unique physical properties such as fingerprint spectrum, security and penetration in tissues and tissues, and has good non-destructive detection characteristics. Therefore, terahertz spectroscopy technology is especially suitable for the detection of biological molecules and cells. Because terahertz waves have a fingerprint spectrum, and most biomolecules have rotational and vibrational energy levels in the terahertz band, a specific fingerprint absorption peak will be formed in the terahertz band, and this characteristic is used to analyze the characteristic spectrum of biomolecules , can realize its qualitative and quantitative analysis. However, the absorption of most biomolecules in the terahertz band is weak, and the vibration of biomolecules is greatly affected by the external environment. Directly using terahertz spectroscopy for identification has problems such as low sensitivity and difficulty in detection.

Metamaterial is a new type of artificial electromagnetic material composed of periodically arranged subwavelength structural units. It has extraordinary electromagnetic properties that natural materials do not have, such as negative refraction, breakthrough diffraction limit imaging, stealth, etc. Metamaterials can achieve local field enhancement and high quality factor resonance through mutual coupling with terahertz waves. When the biological sample to be tested adheres to the metamaterial surface and causes the surrounding medium environment to change, the resonant frequency will shift. Therefore, metamaterial-based terahertz biosensors have attracted great attention from researchers at home and abroad.

Some scholars have proposed to design metamaterials based on split ring resonators (SRRs) as terahertz biosensors, and realize the detection of microorganisms, DNA, cancer cells, and proteins. Among them, in 2015, a terahertz biosensor composed of a single split resonator ring was proposed in the fourth volume of the Scientific Reports magazine on page 4988, which realized the rapid detection of microorganisms such as fungi and bacteria. In 2018, Optics Express magazine, volume 26, page 31589 reported a terahertz metamaterial biosensor composed of single-opening and double-opening resonant rings, which realized the identification of different types of DNA. However, SRRs are designed as transmissive sensors, and the resonance intensity formed by the single interaction between the sensor and the terahertz wave is low, which cannot generate strong local field enhancement, and the interaction between the test object and the local field is weak, resulting in the Q of SRRs Lower values and lower sensitivity.

Metamaterial perfect absorbers (Perfect Metamaterial Absorbers, PMAs) are composed of metal periodic structure layer, dielectric layer and metal reflective layer. Due to the existence of the metal reflective layer and the metal periodic structure layer, the incident terahertz wave will form multiple reflections in the dielectric layer. The terahertz wave interacts with the absorber for many times to form a Fabry-Pérot (F-P) resonant cavity, and the absorber interacts strongly with the terahertz wave to obtain a high quality factor Q and local electric field enhanced. In 2019, Optik Magazine, Vol. 194, page 163071, described a metasurface-based high-Q terahertz perfect absorber. The absorber can be used in the sensing field as a terahertz sensor with a maximum sensitivity of 190.4 GHz/RIU. When the existing PMAs-based terahertz sensor detects substances, the substance to be detected is attached to the surface of the metal periodic structure layer, which is located outside the F-P resonant cavity, and cannot spatially overlap with the local enhanced electric field. Sensitivity is not high.

The invention patent with publication number CN103499534A discloses a high-sensitivity terahertz microfluidic channel sensor. The sensor includes a substrate and a cover layer. The substrate and the cover layer are respectively provided with a metal plane mirror and a metal microstructure layer. The metal plane A microfluidic channel is formed between the mirror and the metal microstructure layer, and when there is a liquid to be tested in the microfluidic channel, the composite structure formed by the metal microstructure layer, the liquid to be tested and the metal flat mirror has a high performance in the terahertz band. Strong absorption properties due to resonance. The invention integrates the microfluidic channel between the metal flat mirror and the metal microstructure layer, and together form a composite structure with resonance absorption characteristics (the absorption at the resonance frequency can exceed 95%), due to the resonance effect, the electromagnetic field is Spatially localized in the microfluidic channel, it completely overlaps with the measured liquid, and is very sensitive to the refractive index of the measured liquid in the microfluidic channel. calculated for 5GHz). Specifically, in the fifth embodiment of the present invention, two absorption peaks can be obtained by using a sensor designed by combining two simple units. From the graph of the change of the absorption spectrum of the sensor designed in this example with the refractive index, when the refractive index of the liquid in the fluid channel changes in the range of 1 to 1.5, the maximum absorption rate of the sensor absorption peak is about 80%, and the minimum is about 40%. . In the sixth embodiment, a plurality of different metal microstructure layers and microfluidic channels are cascaded in the plane direction of the microfluidic channel, and a double absorption peak terahertz sensor is designed. It can be seen from the graph of the change of the absorption spectrum of the sensor with the refractive index in the sixth embodiment that the absorption rate of the absorption peak of the sensor fluctuates greatly in liquids with different refractive indices. The maximum absorption rate exceeds 90%, and the minimum value is lower than 40%. It can be seen from the above analysis that although the sensor of the invention obtains a higher refractive index detection limit, the absorption peak amplitude is lower and the fluctuation is larger. Due to the strong absorption characteristics of water for terahertz, adding liquid into the fluid channel will weaken the energy of the incident terahertz wave, resulting in the weakening of the resonance strength formed by the interaction between the sensor and the terahertz wave, and the absorption rate of the absorption peak will decrease. However, the sensor of the invention has a low absorption rate to form an absorption peak, and when used for liquid sensing, an absorption peak with a lower absorption rate will be obtained, which directly affects the detection effect.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a metamaterial terahertz biosensor with high absorption peak, high sensitivity and polarization insensitivity and a preparation method thereof.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions:

A metamaterial terahertz biosensor includes a base layer and a medium layer, a metal reflective layer is arranged on the base layer, and a metal microstructure layer is arranged on the medium layer, and the metal reflective layer and the metal microstructure layer are formed between the There is a microfluidic channel for the liquid to be tested, and the substrate layer is provided with a liquid inlet and a liquid outlet of the microfluidic channel, wherein the metal microstructure layer is a periodic structural unit attached to the medium layer, and the The metal microstructure layer is composed of a square metal ring and a double "H"-shaped crossed metal structure placed in and concentric with it, wherein the double "H"-shaped crossed metal structure is vertically intersected by two "H"-shaped metal rings with identical structures composition.

The metal microstructure layer in the sensor of the present invention is a quadruple rotationally symmetric structure, so that the sensor has the characteristic of being insensitive to polarization. The polarization insensitivity of the sensor is beneficial to reduce the experimental error and shorten the experimental data processing time, and realize the fast and highly sensitive detection of the object to be tested.

In the above technical solution, the metal microstructure layer is at least four periodic structural units attached to the dielectric layer. The period of the metal microstructure layer in the X-axis direction is 110-130 μm, and the period in the Y-axis direction is 110-130 μm. Under the above periodic conditions, the outer side length of the square metal ring in the metal microstructure layer structure is 100-110 μm, and the ring width is 5-10 μm; the arm length of the “H”-shaped metal ring in the double “H”-shaped cross metal structure is 25 to 30 μm, arm width of 5 to 10 μm, leaf length of 35 to 45 μm, and leaf width of 4 to 8 μm.

Preferably, the period of the metal microstructure layer in the X-axis direction is 120 μm, and the period in the Y-axis direction is 120 μm. At this time, in the metal microstructure layer structure, the outer side length of the square metal ring is 108 μm, and the ring width is 8 μm; in the double “H”-shaped cross metal structure, the arm length of the “H”-shaped metal ring is 26 μm, and the arm width is 8 μm. The leaf length is 40 μm and the leaf width is 6 μm.

In the above technical solution, the thickness of the base layer, the medium layer, the metal reflective layer and the metal microstructure layer and the height of the microfluidic channel are the same as those of the prior art. Preferably, the thickness of the base layer is 100-120 μm, and more preferably 110 μm; the thickness of the dielectric layer is 2-8 μm, more preferably 4 μm; the thickness of the metal microstructure layer is 0.1-0.5 μm, more preferably 0.2 μm; the thickness of the metal reflective layer is 0.1-0.5 μm, more preferably 0.2 μm ; The height of the microfluidic channel is 4-8 μm, more preferably 6 μm.

In the above technical solution, the materials of the base layer, the dielectric layer, the metal reflective layer and the metal microstructure layer are the same as those of the prior art. Specifically, the materials of the dielectric layer and the base layer can be high-resistance silicon, polyimide, Any one of quartz crystal, cycloolefin polymer, polytetrafluoroethylene (PTFE), etc., and the material of the metal reflective layer and the metal microstructure layer can be any one of gold, silver, copper, aluminum, and the like. In this application, the material of the dielectric layer is preferably polytetrafluoroethylene, the material of the base layer is preferably high-resistance silicon, the material of the metal reflective layer is preferably silver, and the material of the metal microstructure layer is preferably silver.

The preparation method of the metamaterial terahertz biosensor provided by the present invention comprises the following steps:

1) Preparation of the top module: on the dielectric layer, through the processes of gluing, exposing, developing, coating, and peeling to form a metal microstructure layer on the dielectric layer to obtain a top module;

2) Preparation of the bottom module: etching the base layer to form a groove matching the size of the top module, then laminating a layer of metal film on the bottom surface of the groove to form a metal reflective layer, and finally opening the base layer to connect with the groove. The liquid inlet and the liquid outlet to obtain the bottom module;

3) Bonding the top module and the bottom module to form a microfluidic channel between the metal microstructure layer of the top module and the metal reflective layer of the bottom module to obtain the metamaterial terahertz biosensor.

In step 1) of the above method, when the material of the dielectric layer is polytetrafluoroethylene, plasma-enhanced chemical phase deposition can be used to obtain polytetrafluoroethylene with a corresponding thickness as the dielectric layer. The operations of gluing, exposing, developing, coating and stripping are carried out according to the existing conventional technology. The coating film is preferably formed by electron beam evaporation deposition method on the dielectric layer. The metal type of the metal film is the same as the selection of the material of the metal microstructure layer. The thickness of the metal film depends on the thickness of the metal microstructure layer.

In step 2) of the above method, the length and width of the groove are matched with the length and width of the top module respectively, and the depth of the groove is the sum of the thickness of the metal reflective layer and the height of the microfluidic channel. The groove is etched on the base layer by ICP etching technology, and a metal film is deposited on the bottom surface of the groove by electron beam evaporation deposition method. The metal type of the metal film is the same as that of the material of the metal reflection layer. depending on the thickness of the layer.

In step 3) of the above method, the top-level module and the bottom-level module are bonded with a sealant, and at this time, a microfluidic channel is formed between the metal microstructure layer of the top-level module and the metal reflective layer of the bottom-level module, and in the aforementioned step 2) The opened liquid inlet and outlet communicated with the groove become the liquid inlet and outlet of the microfluidic channel.

Compared with the prior art, the characteristics of the present invention are:

1. The metal microstructure layer is a quadruple rotationally symmetric structure, so that the sensor has the characteristics of polarization insensitivity. The polarization insensitivity of the sensor is beneficial to reduce the experimental error and shorten the experimental data processing time, and realize the fast and highly sensitive detection of the object to be tested.

2. The sensor of the present invention adopts a special metal microstructure layer structure design combined with a microfluidic channel, which greatly improves the sensing sensitivity of the sensor, and the maximum sensitivity can reach 620GHz/RIU, which effectively solves the problem of the low sensitivity of the existing metamaterial terahertz sensor. The problem.

3. The sensor of the present invention adopts a special metal microstructure layer structure design combined with a microfluidic channel, so that the obtained sensor has two high absorption rate resonance peaks in the frequency range of 0.4-1.4THz, and the absorption rate is higher than 98%, and The maximum Q value reaches 30.8.

Description of drawings

FIG. 1 is a schematic longitudinal cross-sectional view of an embodiment of the sensor according to the present invention.

FIG. 2 is a three-dimensional expanded view of the embodiment shown in FIG. 1 .

FIG. 3 is a top view of the metal microstructure layer in the embodiment shown in FIG. 1 .

FIG. 4 is a schematic structural diagram of preparing a top-level module in Example 1 of the present invention.

FIG. 5 is a schematic structural diagram of preparing a bottom layer module in Embodiment 1 of the present invention.

FIG. 6 is a schematic structural diagram of bonding a top-level module and a bottom-level module in Embodiment 1 of the present invention.

7 is a schematic structural diagram of a basic sensor structural unit for performing absorption characteristic analysis, resonance mechanism analysis, polarization insensitive characteristic analysis, and sensing performance analysis for the sensor of the present invention.

Figure 8 shows the reflection and absorption spectra of the sensor, where the dashed line represents the reflection spectrum and the solid line represents the absorption spectrum.

Figure 9 is the electric field distribution diagram of the sensor at the resonant frequency points f ₁ and f ₂ ; wherein (a) is the electric field distribution diagram of the sensor at the resonant frequency point f ₁ , (b) is the electric field distribution diagram of the sensor at the resonant frequency point f ₂ .

Fig. 10 is the surface current distribution diagram of the metal microstructure layer at the resonant frequency points f ₁ and f ₂ and the surface current distribution diagram of the metal reflective layer at the resonance frequency points f ₁ and f ₂ ; wherein (a) is the metal microstructure layer at the resonant frequency points f 1 and f 2. The surface current distribution diagram of the resonant frequency point f ₁ , (c) is the surface current distribution diagram of the metal microstructure layer at the resonant frequency point f ₂ , (b) is the surface current distribution diagram of the metal reflective layer at the resonant frequency point f ₁ , (d ₎ is the surface current distribution diagram of the metal reflective layer at the resonant frequency point f2.

为TM模式，

为TE模式。Figure 11 shows the absorption spectrum of the sensor under the action of TE and TM mode terahertz waves, where

for TM mode,

for TE mode.

Figure 12 shows the absorption spectra of the sensor under different polarization angles and incident angles, where (a) is the absorption spectrum of different polarization angles, and (b) is the absorption spectrum of different incident angles.

Figure 13 shows the absorption spectra of the sensor under different dielectric constants.

Figure 14 shows the low resonant frequency f ₁ and the high frequency resonant frequency f ₂ of the test object with different dielectric constants.

Figure 15 shows the absorption spectra of the sensor at different analyte loss tangents.

表示f₁，

表示f₂。Figure 16 shows the absorptivity of the low resonant frequency f ₁ and the high resonant frequency f ₂ at different dielectric constants of the DUT, wherein,

means f ₁ ,

represents f ₂ .

The symbols in the figure are:

1 dielectric layer, 2 metal microstructure layer, 3 microfluidic channel, 4 metal reflection layer, 5 base layer, 6 liquid outlet, 7 liquid inlet; a represents the outer length of the square metal ring, b represents the ring of the square metal ring The width is, c represents the arm length of the "H"-shaped metal ring in the double "H"-shaped cross metal structure, d represents the arm width of the "H"-shaped metal ring in the double "H"-shaped cross metal structure, and e represents the double "H" shape. The leaf length of the "H"-shaped metal ring in the ""-shaped intersecting metal structure, and f represents the leaf width of the "H"-shaped metal ring in the double "H"-shaped intersecting metal structure.

Detailed ways

The metamaterial terahertz biosensor of the present invention includes a base layer 5 and a medium layer 1, a metal reflective layer 4 is arranged on the base layer 5, and a metal microstructure layer 2 is arranged on the medium layer 1, and the metal reflective layer 2 is arranged on the medium layer 1. A microfluidic channel 3 for the liquid to be tested is formed between the layer 4 and the metal microstructure layer 2, and a liquid inlet 7 and a liquid outlet 6 of the microfluidic channel 3 are opened on the base layer 5. The metal microstructure layer 2 is a periodic structural unit attached to the dielectric layer 1. The metal microstructure layer 2 consists of a square metal ring and a double "H"-shaped cross metal structure placed in it and concentric with it, wherein the double "H" The H"-shaped cross metal structure consists of two "H"-shaped metal rings with the same structure intersecting vertically. When there is a liquid to be measured in the microfluidic channel 3, the composite structure mainly formed by the combination of the metal microstructure layer 2, the liquid to be measured and the metal reflection layer 4 has strong absorption characteristics caused by resonance in the terahertz band.

The metal microstructure layer 2 is M╳N units periodically arranged on the dielectric layer 1 , the metal microstructure layer 2 is a quadruple rotationally symmetric structure, and M and N are both integers greater than or equal to 4. The period of the metal microstructure layer 2 in the X-axis direction is 110-130 μm, and the period in the Y-axis direction is 110-130 μm. Under the above periodic conditions, the outer side length a of the square metal ring in the structure of the metal microstructure layer 2 is 100-110 μm, and the ring width b is 5-10 μm; The arm length c is 25-30 μm, the arm width d is 5-10 μm, the leaf length e is 35-45 μm, and the leaf width f is 4-8 μm.

The thickness of the base layer 5 is 100-120 μm, and its material can be any one of high-resistance silicon, polyimide, quartz crystal, cyclic olefin polymer, and polytetrafluoroethylene; the thickness of the dielectric layer 1 is 2 to 8 μm, and the material can be any one of high-resistance silicon, polyimide, quartz crystal, cycloolefin polymer, and polytetrafluoroethylene; the thickness of the metal microstructure layer 2 is 0.1 to 0.5 μm, and its The material can be any one of gold, silver, copper, aluminum, etc.; the thickness of the metal reflective layer 4 is 0.1-0.5 μm, and the material can be any one of gold, silver, copper, aluminum, and the like.

The preparation method of the above metamaterial terahertz biosensor includes the following steps:

1) Preparation of the top module: on the dielectric layer 1, through the processes of gluing, exposing, developing, coating, and peeling to form a metal microstructure layer 2 on the dielectric layer 1 to obtain a top module;

2) Preparation of the bottom layer module: etching the base layer 5 to form a groove matching the size of the top layer module, then laminating a layer of metal film on the bottom surface of the groove to form a metal reflective layer 4, and finally opening and concave on the base layer 5. The liquid inlet 7 and the liquid outlet 6 connected by the tank obtain the bottom module;

3) Adhering the top module and the bottom module to form a microfluidic channel 3 between the metal microstructure layer 2 of the top module and the metal reflective layer 4 of the bottom module to obtain the metamaterial terahertz biosensor.

In step 1) of the above method, when the material of the dielectric layer 1 is polytetrafluoroethylene, plasma-enhanced chemical phase deposition can be used to obtain polytetrafluoroethylene with a corresponding thickness as the dielectric layer 1 . The operations of gluing, exposing, developing, coating and stripping are carried out according to the existing conventional technology. The metal film is preferably formed on the dielectric layer 1 by electron beam evaporation deposition method. The metal type of the metal film is the same as the material of the metal microstructure layer 2.

In step 2) of the above method, the length and width of the groove are matched with the length and width of the top module respectively, and the depth of the groove is the sum of the thickness of the metal reflective layer 4 and the height of the microfluidic channel 3 . The groove is etched on the base layer 5 by ICP etching technology, and the metal film is deposited on the bottom surface of the groove by the electron beam evaporation deposition method. The metal type of the metal film is the same as that of the material of the metal reflection layer 4. It depends on the thickness of the metal reflective layer 4 .

In step 3) of the above method, the top-level module and the bottom-level module are bonded with a sealant, and at this time, a microfluidic channel 3 is formed between the metal microstructure layer 2 of the top-level module and the metal reflective layer 4 of the bottom-level module. 2) The liquid inlet 7 and the liquid outlet 6 which are communicated with the groove become the liquid inlet 7 and the liquid outlet 6 of the microfluidic channel 3 .

The present invention will be further described in detail below with reference to the preferred embodiments and accompanying drawings to better understand the content of the present invention.

Example 1

The structure and preparation of the sensor according to the present invention will be described with reference to the structure diagrams shown in FIG. 1 to FIG. 3 .

1 to 3 , the metal microstructure layer 2 is 4╳4 units periodically arranged on the dielectric layer 1 , and the period of the metal microstructure layer 2 in the X-axis direction and the period in the Y-axis direction are both 120 μm. In the structure of the metal microstructure layer 2, the outer side length a of the square metal ring is 108 μm, and the ring width b is 8 μm; the arm length c of the “H”-shaped metal ring in the double “H”-shaped cross metal structure is 26 μm, and the arm width d is 26 μm. is 8 μm, the leaf length e is 40 μm, and the leaf width f is 6 μm.

The thickness of the base layer 5 is 110 μm, and its material is high-resistance silicon; the thickness of the dielectric layer 1 is 6 μm, and its material is polytetrafluoroethylene; the thickness of the metal microstructure layer 2 is 0.2 μm, and its material is silver; The thickness of the reflective layer 4 is 0.2 μm, and its material is silver; the height of the microfluidic channel 3 is 6 μm.

The sensor designed in this application needs to be tested in a THz time-domain spectroscopy system. Since the diameter of the THz beam on the focal plane in the THz time-domain spectroscopy system is about 5mm, the effective size of the sensor should be greater than 5mm╳5mm. Specifically, this implementation In the example, it is 10mm╳10mm.

The preparation method of the sensor includes the following steps:

1) Prepare the top-level module:

1.1) Deposition of dielectric layer 1: using plasma enhanced chemical phase deposition method to obtain polytetrafluoroethylene with a thickness of 4 μm as dielectric layer 1;

1.2) Gluing: apply AZ 5214 positive photoresist on the dielectric layer 1, and bake it in an oven at 100°C for 90s;

1.3) Exposure: mask the photoresist-coated substrate with a mask, and then expose it to ultraviolet light for 60s;

1.4) Development: place the exposed substrate in AZ300MIF developer solution for 100s to obtain the figure on the mask;

1.5) Coating: use electron beam evaporation deposition technology to form a metal silver film with a thickness of 0.2 μm on the polytetrafluoroethylene layer;

1.6) Stripping: After the coating is completed, place the sample in the acetone solution for 10 minutes, peel off the photoresist, and then clean the sample with deionized water to obtain the top module (as shown in Figure 4).

2) Prepare the underlying module:

2.1) Etch grooves on base layer 5: use ICP etching technology to etch grooves with a height of 6.2 μm on the surface of high-resistance silicon with a thickness of 100 μm;

2.2) Deposit a metal film on the bottom surface of the groove: deposit a metal silver film with a thickness of 0.2 μm on the bottom surface of the groove as a metal reflective layer 4 by using the electron beam evaporation deposition technology;

2.3) A liquid inlet 7 and a liquid outlet 6 connected to the grooves are opened on the base layer 5 to obtain a bottom module (as shown in Figure 5).

3) Bonding the top module and the bottom module (as shown in Figure 6), at this time, a microfluidic channel 3 with a height of 6 μm is formed between the metal microstructure layer 2 of the top module and the metal reflective layer 4 of the bottom module , the liquid inlet 7 and the liquid outlet 6 that are communicated with the groove in the aforementioned step 2) become the liquid inlet 7 and the liquid outlet 6 of the microfluidic channel 3, that is, the described metamaterial terahertz biosensor is obtained. .

Example 2

The absorption characteristics of the sensor are analyzed with the sensor structural unit of the structure shown in FIG. 7 .

In the sensor structural unit shown in FIG. 7 , the period (Dx) in the X-axis direction and the period (Dy) in the Y-axis direction of the metal microstructure layer 2 are both 120 μm. In the structure of the metal microstructure layer 2, the outer side length a of the square metal ring is 108 μm, and the ring width b is 8 μm; the arm length c of the “H”-shaped metal ring in the double “H”-shaped cross metal structure is 26 μm, and the arm width d is 26 μm. is 8 μm, the leaf length e is 40 μm, and the leaf width f is 6 μm. The thickness of the base layer 5 is 110 μm, and its material is high-resistance silicon; the thickness of the dielectric layer 1 is 6 μm, and its material is polytetrafluoroethylene; the thickness of the metal microstructure layer 2 is 0.2 μm, and its material is silver; The thickness of the reflective layer 4 is 0.2 μm, and its material is silver; the height of the microfluidic channel 3 is 6 μm.

In order to study the absorption characteristics of the sensor, this application uses the electromagnetic simulation software CSTMicrowave Studio based on the finite element algorithm to carry out full-wave simulation of the sensor unit structure. The solver selects the frequency domain solver and uses adaptive mesh for structural meshing. Periodic boundary conditions are set along the x- and y-axis directions, and open boundary conditions are set along the z-axis direction. The absorption rate of the sensor can be calculated by the S parameter, and the calculation formula is:

A=1-|S ₁₁ | ² -|S ₂₁ | ² (1)

Among them, A represents the absorption rate of the sensor, and S ₁₁ and S ₂₁ are the reflection coefficient and transmission coefficient of the sensor, respectively. Since the thickness of the metal reflective layer 4 is 0.2 μm, which is greater than the skin depth of metallic silver in the terahertz band, the terahertz wave does not pass through the metal reflective layer 4 , where S ₂₁ =0. Therefore, the calculation formula of the absorption rate of the above sensor can be simplified as:

A=1-|S ₁₁ | ² (2)

When there is no analyte in the microfluidic channel 3 (n=1, n represents the refractive index in a vacuum environment), the absorption and reflection spectra of the sensor are shown in Figure 8. It can be seen from the figure that the sensor forms two high absorption rate resonance peaks with absorption rate higher than 98% in the frequency band of 0.4-1.4 THz under the vertical incidence of terahertz wave in TE mode. Wherein, the resonance frequency f ₁ =0.65THz of the low-frequency absorption peak, and the absorption rate A ₁ =99.5%; the resonance frequency of the high-frequency absorption peak f ₂ =1.15THz, and the absorption rate A ₂ =98.5%.

Example 3

The resonance mechanism of the sensor is analyzed with the sensor structural unit of the structure shown in FIG. 7 .

In order to explore the resonance mechanism of the sensor, CST Microwave Studio was used to simulate the electric field distribution and surface current distribution of the sensor at the resonance frequency point. The simulation obtains the electric field distribution of the structural unit at the resonant frequency points f ₁ and f ₂ under the action of the TE mode terahertz wave, as shown in Figure 9. It can be seen from Fig. 9(a) that at the resonant frequency point f ₁ , a significant local enhanced electric field is formed on the upper and lower sides of the square metal ring, and at the resonant frequency point f ₂ , the longitudinal "H" type metal structure forms an obvious local enhanced electric field. . It can be seen that the absorption peak at _f1 is due to the mutual coupling between the square metal ring and the terahertz wave, while the absorption peak at f2 is obtained by the _double “H” type cross metal structure. Further, the resonance type of the sensor can be determined by analyzing the surface current distribution excited by the sensor. Fig. 10(a) and (c) show the surface current distribution of the metal microstructure at the resonant frequency points f ₁ and f ₂ under the action of TE mode terahertz wave, respectively, (b) and (d) give The surface current distribution of the metal reflective layer 4 at the resonant frequency points f ₁ and f ₂ is shown. It can be seen from Fig. 10 that at the resonant frequency, the surface currents excited by the metal microstructure and the metal reflective layer 4 are in opposite directions, and a current loop is formed between the two layers, resulting in magnetic dipole resonance. wave absorption.

Example 4

The polarization insensitivity characteristics of the sensor are analyzed with the sensor structural unit of the structure shown in FIG. 7 .

Due to the linear polarization of the terahertz measurement system, the polarization angle and incident angle of the terahertz wave generated by the system fluctuate. If the designed sensor is a polarization-sensitive structure, there will be errors in the measurement data, resulting in the inability of the sensor to achieve fast and highly sensitive detection. In practical applications, a high-performance terahertz sensor not only needs high absorption peak, high quality factor and high sensitivity, but also has the characteristics of polarization insensitivity. Therefore, the sensor structural unit designed by the present invention is a quadruple rotationally symmetric structure (the structures are still overlapped after rotating 90°, 180°, 270°, and 360° at the center point of the structure), and the sensor has good polarization insensitivity characteristics. The present invention verifies the polarization insensitivity characteristic of the proposed sensor. First, to verify the polarization characteristics of the sensor under the action of TE and TM mode terahertz waves, as shown in Figure 11, under the action of TE and TM mode terahertz waves, the absorption spectra of the sensor almost completely overlap; second, to verify that in different Polarization characteristics of the sensor under the action of TE mode terahertz waves with polarization angles and incident angles (0°, 10°, 20°, 30°, 40°, and 50°). As shown in Figure 12, under the action of terahertz waves with different polarization angles and incident angles, the resonant frequency points f ₁ and f ₂ did not shift significantly, and the absorption amplitude did not change. The above results show that the sensor proposed by the present invention has good polarization insensitivity characteristics.

Example 5

The sensing performance of the sensor is analyzed with the sensor structural unit of the structure shown in FIG. 7 .

When the traditional metamaterial perfect absorber detects the object to be tested, the object to be tested is attached to the surface of the metal periodic structure layer, so that the object to be tested cannot fully overlap with the local field enhancement space, and the interaction between the two is weak, resulting in a relatively low detection sensitivity of the sensor. Low. In the present invention, by integrating the microfluidic channel 3, the analyte will fully overlap with the local enhanced electric field space in the F-P resonant cavity, which greatly enhances the interaction between the analyte and the local enhancement, and can effectively improve the sensitivity of the sensor.

Sensitivity and quality factor are important indicators to measure the sensing performance of a sensor. The sensitivity S represents the degree of frequency shift under the unit refractive index change of the object to be tested, and its calculation formula is:

Among them, Δf is the resonant frequency offset, and Δn is the change in the refractive index of the measured object. Then according to the relationship between the dielectric constant and the refractive index:

In the formula, n represents the refractive index of the object to be tested; ε represents the dielectric constant of the object to be tested; μ ₀ is the magnetic permeability, and the value is 1. The sensing sensitivity of the sensor when adding different dielectric constants to be tested can be calculated.

The quality factor Q represents the loss degree of the coupling effect between the terahertz wave and the sensor. The larger the Q value, the smaller the resonance loss and the sharper the resonance peak. The formula for calculating the quality factor Q is:

where f ₀ is the resonant frequency and FWHM is the full width at half maximum.

FIG. 13 is the absorption spectrum of the sensor under different dielectric constants of the test object, and FIG. 14 is the change of the resonant frequency with the dielectric constant of the test object. It can be seen from Figure 13 and Figure 14 that as the dielectric constant of the object to be measured increases, the resonant frequency of the sensor undergoes a red shift. After linear fitting, the sensitivity of the low resonance frequency f ₁ is S ₁ =330GHz/RIU, and the quality factor Q ₁ =28; the sensitivity of the high resonance frequency f ₂ is S ₂ =620GHz/RIU, and the quality factor Q ₂ =30.8. In addition, the integrated microfluidic channel 3 can realize solution analyte detection, and the loss angle of the solution analyte is also a factor affecting the performance of the sensor. Figure 15 shows the absorption spectra of the sensor at different analyte loss tangents when the dielectric constant of the analyte is fixed at 1. It can be seen from Figure 15 that when the loss tangent value of the analyte increases from 0.02 to 0.1, the resonant frequency of the sensor remains unchanged, and the absorption rate of the absorption peak decreases significantly due to impedance matching failure and electromagnetic loss, as shown in Figure 16 , but when the loss tangent value reaches 0.1, the absorption peak of the sensor can still maintain a high absorption rate, and the absorption rate is greater than 60%. In addition, the sensor can also distinguish the loss of the DUT at different loss angles according to the change of the absorption rate at the resonant frequency point.

Claims (10)

1. A metamaterial terahertz biosensor comprises a substrate layer (5) and a dielectric layer (1), a metal reflecting layer (4) is arranged on the substrate layer (5), a metal microstructure layer (2) is arranged on the dielectric layer (1), a micro-flow channel (3) for the circulation of the liquid to be detected is formed between the metal reflecting layer (4) and the metal micro-structure layer (2), a liquid inlet (7) and a liquid outlet (6) of the micro-flow channel (3) are arranged on the basal layer (5), it is characterized in that the metal microstructure layer (2) is a periodic structure unit attached on the dielectric layer (1), the metal microstructure layer (2) consists of a square metal ring and a double H-shaped crossed metal structure which is arranged in the metal ring and is concentric with the metal ring, wherein the double H-shaped crossed metal structure is composed of two H-shaped metal rings with the same structure which are vertically crossed.

2. The metamaterial terahertz biosensor as claimed in claim 1, wherein the period of the metal microstructure layer (2) in the X-axis direction is 110-130 μm, and the period in the Y-axis direction is 110-130 μm.

3. The metamaterial terahertz biosensor as claimed in claim 2, wherein in the structure of the metal microstructure layer (2), the outer side length (a) of the square metal ring is 100-110 μm, and the ring width (b) is 5-10 μm; in the double H-shaped crossed metal structure, the arm length (c) of the H-shaped metal ring is 25-30 μm, the arm width (d) is 5-10 μm, the leaf length (e) is 35-45 μm, and the leaf width (f) is 4-8 μm.

4. The metamaterial terahertz biosensor as claimed in any one of claims 1 to 3, wherein the period of the metal microstructure layer (2) in the X-axis direction is 120 μm, and the period in the Y-axis direction is 120 μm.

5. The metamaterial terahertz biosensor as claimed in claim 4, wherein in the structure of the metal microstructure layer (2), the outer side length (a) of a square metal ring is 108 μm, and the ring width (b) is 8 μm; in the double H-shaped crossed metal structure, the arm length (c) of the H-shaped metal ring is 26 μm, the arm width (d) is 8 μm, the leaf length (e) is 40 μm, and the leaf width (f) is 6 μm.

6. The metamaterial terahertz biosensor as claimed in any one of claims 1 to 3, wherein the thickness of the base layer (5) is 100 to 120 μm, and the thickness of the dielectric layer (1) is 2 to 8 μm.

7. The metamaterial terahertz biosensor as claimed in any one of claims 1 to 3, wherein the thickness of the metal microstructure layer (2) is 0.1 to 0.5 μm.

8. The metamaterial terahertz biosensor as claimed in any one of claims 1 to 3, wherein the thickness of the metal reflective layer (4) is 0.1 to 0.5 μm.

9. The metamaterial terahertz biosensor as claimed in any one of claims 1 to 3, wherein the height of the microfluidic channel (3) is 4 to 8 μm.

10. The preparation method of the metamaterial terahertz biosensor as claimed in claim 1, comprising the following steps:

1) preparing a top module: forming a metal microstructure layer (2) on the dielectric layer (1) through the processes of gluing, exposing, developing, coating and stripping on the dielectric layer (1) to obtain a top layer module;

2) preparing a bottom layer module: etching a substrate layer (5) to form a groove with the size matched with that of the top module, then laminating a metal film on the bottom surface of the groove to form a metal reflecting layer (4), and finally forming a liquid inlet (7) and a liquid outlet (6) which are communicated with the groove on the substrate layer (5) to obtain a bottom module;

3) and (3) bonding the top layer module and the bottom layer module, and forming a microfluidic channel (3) between the metal microstructure layer (2) of the top layer module and the metal reflecting layer (4) of the bottom layer module to obtain the metamaterial terahertz biosensor.

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