Terahertz microstructure filter with biosensing function and application thereof

Abstract

The application discloses a terahertz microstructure filter with a biosensing function, comprising a fiber base material, a fiber core and a cladding air hole arranged in the fiber base material, a filter sensing area arranged on the fiber base material, a graphene layer coated on the surface of the filter sensing area, and a metal electrode arranged on the outer side of the fiber base material and the graphene layer. The terahertz microstructure filter places the plasmonic material graphene and the sample to be measured on the side-polished and ground plane of the filter sensing area, avoids the complex process of coating film and filling analyte in the internal channel of the microstructure fiber, simplifies the filter unit structure, and adopts the cladding air hole as a circular hole with the same diameter, so that the terahertz microstructure filter has the advantages of simple structure, easy preparation and good mechanical stability compared with the fiber structure with a non-circular hole and simultaneously containing various holes with different diameters. The filter can also be used for sensing detection of liquid or solid biological samples, and has commercial application potential in the field of biosensing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of terahertz filtering and sensing, and relates to a terahertz microstructure filter with biological sensing function, and also relates to the application of the filter. BACKGROUND

[0002] Terahertz (THz) waves refer to electromagnetic waves with a frequency range of 0.1-10 THz, which are located between millimeter waves and infrared radiation. They are widely used in many scientific and engineering fields, including material characterization, broadband communication, environmental monitoring, medical imaging, and chemical and biological sensing. Currently, common terahertz functional devices mainly include terahertz filters, terahertz modulators, terahertz mixers, terahertz absorbers, waveguides, etc.

[0003] Terahertz filters can separate linearly polarized parts from incident electromagnetic waves, or implement band-rejection filtering on wide-band linearly polarized terahertz waves. As polarizers, they can be used in communication and sensing fields that require effective control of polarization states, and are also important devices in terahertz systems.

[0004] Graphene is used in the preparation of terahertz functional devices due to its excellent electronic, optical, and mechanical properties. Currently, terahertz microstructure filters based on graphene surface plasmon resonance (SPR) mainly use metamaterial / super surface or coupled prism structures. However, metamaterial / super surface structures require complex unit structures, and coupled prism structures are bulky and unstable. Therefore, developing high-performance terahertz filters based on optical fibers and graphene SPR is of great significance to improve the overall performance of terahertz systems. SUMMARY

[0005] The purpose of the present application is to provide a terahertz microstructure filter with biological sensing function, which overcomes the problems of complex unit structure, large volume, and unstable structure of the existing terahertz microstructure filter.

[0006] The second purpose of the present application is to provide a new use of the above-mentioned terahertz microstructure filter, which can be used as a biological sensor to detect the refractive index of liquid and solid biological samples.

[0007] The first technical solution adopted by the present application is a terahertz microstructure filter with biological sensing function, which includes an optical fiber substrate, a fiber core and a cladding air hole are arranged in the optical fiber substrate, a filter sensing region is arranged on the optical fiber substrate, a graphene layer is coated on the surface of the filter sensing region, and a metal electrode is arranged on the outer side of the optical fiber substrate and the graphene layer.

[0008] The present application is also characterized in that,

[0009] The cladding air holes are arranged around the core and are arranged in a regular triangle array.

[0010] The filtering sensing area is in a groove shape, and the graphene layer is arranged on the concave surface of the groove.

[0011] The hole spacing Lambda of the cladding air hole is 600 mu m, and the ratio of the diameter d of the cladding air hole to the hole spacing Lambda of the cladding air hole is 0.6.

[0012] The vertical distance from the concave surface of the filtering sensing area to the center of the core, i.e., the side polishing depth H, is 720-780 mu m.

[0013] The optical fiber base material is a polymer material such as a cyclic olefin polymer TOPAS, a cyclic olefin polymer Zeonex, high-density polyethylene, polymethyl methacrylate, polycarbonate, polystyrene, or high-resistance silicon.

[0014] The graphene layer is single-layer graphene or multi-layer graphene, and the metal electrode is Au or Pt.

[0015] The working frequency of the terahertz microstructure filter is in the sub-terahertz wave band 0.1-1 THz, which is low in water sensitivity.

[0016] The second technical solution of the present application is a terahertz microstructure filter with a biological sensing function, which can be used as a biological sensor to detect the refractive index of liquid and solid biological samples, especially for detecting liquid biological samples with a refractive index between 1.33 and 1.40.

[0017] The beneficial effects of the present application are:

[0018] (1) The terahertz microstructure filter with a biological sensing function of the present application sets a filtering sensing area, and places the plasmonic material graphene and the sample to be measured on the side polishing plane of the filtering sensing area, which avoids the complex process of coating film and filling analyte in the internal channel of the filter, simplifies the structure of the filter unit, and is conducive to improving the detection efficiency of the sensor.

[0019] (2) The terahertz microstructure filter with a biological sensing function of the present application adopts cladding air holes in the form of circular holes with the same diameter, which has the advantages of simple structure, easy preparation and good mechanical stability compared with non-circular holes and filters containing various holes with different diameters.

[0020] (3) The terahertz microstructure filter with biosensing function has the advantages that the graphene layer surface can excite a surface plasmon mode, a y-polarized base mode is resonantly coupled with the graphene surface plasmon mode near a specific frequency to cause a significant increase in loss, the loss of an x-polarized base mode is not affected, and thus the polarization filtering function is realized; when the length of the filtering area is greater than 0.5 cm, a polarization extinction ratio of more than 20 dB can be obtained; and a larger extinction ratio and a working bandwidth can be obtained by increasing the length of the filtering area.

[0021] (4) The terahertz microstructure filter with biosensing function has a dual function, and the graphene surface can be used as a polarization filter without loading any analyte, and can be used as a biosensor when the graphene surface loads a liquid or solid biological sample. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a three-dimensional structure schematic diagram of the terahertz microstructure filter with biosensing function;

[0023] Figure 2 is a cross-sectional schematic diagram of a sensing area of the terahertz microstructure filter with biosensing function;

[0024] Figure 3 is a dispersion curve and a loss spectrum diagram of an x-polarized base mode, a y-polarized base mode and an SPP mode of embodiment 1 of the present application;

[0025] Figure 4 is a mode field distribution diagram of the x-polarized base mode and the y-polarized base mode at a coupling point of embodiment 1 of the present application;

[0026] Figure 5 is a loss spectrum line diagram when the chemical potential of graphene in embodiment 1 of the present application changes;

[0027] Figure 6 is an extinction ratio diagram when the length of the filtering area in embodiment 1 of the present application is different;

[0028] Figure 7 is a diagram of the change of the radial power flow distribution in the fiber cross section with the refractive index of the liquid biological sample to be measured in embodiment 1 of the present application.

[0029] The reference signs are explained as follows, 1. fiber base material, 2. core, 3. cladding air hole, 4. side polishing plane, 5. graphene layer, 6. metal electrode, 7. analyte. DETAILED DESCRIPTION

[0030] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0031] The terahertz microstructure filter with biosensing function of the present application has the specific structure asFigure 1 As shown, a core-cladding structure is employed, primarily for use in the 0.1-1 THz Asia-Pacific Hertz band (but not limited to 0.1-1 THz). This includes fiber substrate 1, which utilizes cyclic olefin polymers TOPAS and Zeonex (material absorption losses in the Asia-Pacific Hertz band are typically below 0.2 cm⁻¹). -1 Or high-resistivity silicon (materials with absorption losses typically below 0.01 cm⁻¹ in the Asia-Pacific Hertz band). -1 The optical fiber substrate 1 is made of polymer materials such as high-density polyethylene, polymethyl methacrylate, polycarbonate, or polystyrene. A fiber core 2 and cladding air holes 3 are disposed within the fiber core 2. The cladding air holes 3 are arranged in an equilateral triangular array and are circular holes with the same diameter. The spacing Λ between the cladding air holes 3 is 600 μm, and the ratio of the diameter d of the cladding air hole 3 to the spacing Λ is 0.6.

[0032] The specific structure of the optical fiber substrate 1 of this invention is as follows: Figure 2 As shown, a filtering sensing region 4 is disposed on the optical fiber substrate 1. The surface of the filtering sensing region 4 is coated with a single or double layer of graphene layer 5. The filtering sensing region 4 is groove-shaped, and the graphene layer 5 is disposed on the concave surface of the groove. The chemical potential of the graphene layer 5 is... μ c Between 0.2 and 1.2 eV; a metal Au or metal Pt electrode 6 is disposed on the outer side of the optical fiber substrate 1 and the graphene layer 5.

[0033] In use, analyte 7 is loaded on top of graphene layer 5. Analyte 7 can be a gas, liquid, or solid powder. The vertical distance from the concave surface of the filter sensing region 4 to the center of the fiber core 2, i.e., the side polishing depth H, is between 720-780 μm. The filter sensing region 4 in this application can be experimentally prepared using techniques such as chemical etching, laser etching, and side polishing. For polymer-based microstructured optical fibers, graphene can be prepared using common methods and then transferred to the concave surface of the filter sensing region 4. For high-resistivity silicon-based microstructured optical fibers, in addition to the above methods, a graphene layer can also be directly prepared on the concave surface of the filter sensing region 4 using chemical vapor deposition.

[0034] The components involved in the device and their interactions are explained below.

[0035] (1) The present invention sets up a filter sensing area, and places the plasma material graphene and the sample to be tested on the side polishing plane of the filter sensing area, which avoids the complicated process of coating and filling the analytes in the internal pores of the microstructure optical fiber and simplifies the filter unit structure.

[0036] (2) The present application sets the same diameter of the cladding air hole, compared with the non-circular hole and the filter containing various different diameter holes (such as the application number 202010777576.4, the name of an invention patent for a surface plasmon quasi-D type photonic crystal fiber sensor, containing two different diameter circular air holes and an elliptical hole, the ITO film and graphene layer are arranged on the polishing surface; such as the application number 202010692767.0, the name of an invention patent for a biochemical sensor based on a D type photonic crystal fiber, containing three different diameter circular air holes, the silver film layer and the graphene layer are arranged on the polishing surface), only the graphene single film layer structure is arranged on the side polishing surface, which has the characteristics of simple structure, easy preparation and high toughness. Only the three air holes on the outermost layer are polished, and one layer of air hole is reserved between the side polishing surface and the core, so that the integrity of the core is maintained, and the cross section of the optical fiber is maximally reserved. Not only the preparation difficulty is reduced, but also the coupling loss of the optical fiber is reduced;

[0037] (3) The graphene layer of the present application is used to excite surface plasmon mode, which is completely different from the role of the graphene layer in the prior art, such as the application number 202010777576.4, the name of an invention patent for a surface plasmon quasi-D type photonic crystal fiber sensor, which uses ITO film as plasmonic material, and introduces graphene layer to increase the adsorption capacity of the sensor to biological samples; such as the application number 202010692767.0, the name of an invention patent for a biochemical sensor based on a D type photonic crystal fiber, which uses silver film layer as plasmonic material, and covers graphene layer on the surface of the silver film layer to prevent oxidation of the silver film layer, enhance the corrosion resistance of the sensor, and better adsorb and fix biological molecules, increase the sensitivity of the sensor.

[0038] (4) The filter sensing area in the present application adopts a groove-shaped structure, compared with the existing D type structure optical fiber (such as the optical fiber structure disclosed in the utility model patent with the application number 201820210853.1, the name of a tunable polarization filter based on a D type photonic crystal fiber), the integrity of the core is maintained, and the cross section of the optical fiber is maximally reserved. The preparation difficulty and the coupling loss of the optical fiber are reduced.

[0039] The following will further illustrate the terahertz microstructure filter with biological sensing function of the present application by combining with specific embodiments:

[0040] Example 1

[0041] The modeling and performance simulation analysis of the terahertz microstructure filter with biological sensing function in this embodiment are based on the optical waveguide theory and the finite element method.

[0042] The terahertz microstructure filter with biosensing function in the embodiment comprises a fiber substrate 1, the substrate adopts a cyclic olefin polymer TOPAS, the fiber substrate 1 is provided with a fiber core 2 and a cladding air hole 3, the cladding air hole 3 is arranged in two circles in a regular triangle array around the fiber core 2, a filter sensing area 4 is arranged on the fiber substrate 1, the filter sensing area 4 is in a groove shape, a graphene layer 5 is arranged on the concave surface of the groove, the side polishing depth H of the filter sensing area 4 is 720 μm, one metal electrode 6 is arranged on the outer side of the fiber substrate 1 and the graphene layer 5 respectively, the electrode arranged on the outer side of the fiber substrate 1 is a negative electrode, the electrode arranged on the graphene layer 5 is a positive electrode, the chemical potential of the graphene can be adjusted by changing the applied voltage, and the working frequency band of the device can be dynamically tuned.

[0043] Figure 3 The effective refractive index real part of the x-polarization (x-pol) and y-polarization (y-pol) fiber core modes, the effective refractive index real part of the surface plasmon polariton (SPP) mode and the loss of the x-polarization mode and the y-polarization mode with the change of frequency when the chemical potential of the graphene layer 5 is 0.6 eV and the side polishing depth is 720 μm are shown in FIG. 3. Figure 3 As shown in FIG. 3, in the frequency range of 0.4-0.8 THz, only the y-polarization mode and the SPP mode resonate and couple at 0.63 THz, which leads to a significant decrease in the fiber core power fraction and a significant increase in the loss of the y-polarization mode, and a loss peak appears in the loss spectrum, while the mode field distribution and the loss of the x-polarization mode are not affected, as shown in FIG. 4. Figure 4 Therefore, when the device works near the resonance frequency 0.63 THz of the y-polarization mode and the SPP mode, for the input non-linearly polarized terahertz wave, due to the large loss difference between the two polarization modes, the energy of the y-polarization mode will gradually be lost as the transmission distance increases, only the x-polarization mode is output, and thus the polarization filtering function is realized. In addition, the terahertz microstructure fiber can also realize band-stop filtering for broadband linearly polarized terahertz waves and switching function for single-frequency linearly polarized terahertz waves.

[0044] Figure 5 The loss spectrum when the chemical potential of the graphene changes is shown in FIG. 5. Figure 5 By adjusting the chemical potential of the graphene between 0.2-1.2 eV, the polarization filtering function can be realized at any frequency in the range of 0.3-1.0 THz, and the tuning sensitivity of the loss peak position is 637.1 GHz / eV.

[0045] An important parameter for describing the performance of the polarization filter is the polarization extinction ratio. Figure 6 The extinction ratio of the embodiment 1 of the present application at different filter area lengths L is shown in FIG. 6. μ c=0.4eV). When the filter region length is greater than 0.5cm, the extinction ratio is more than 20dB. By increasing the filter region length, a wider working bandwidth with extinction ratio more than 20dB can be obtained. When the filter region length is 5cm, the working bandwidth with extinction ratio more than 20dB is about 208.9GHz, and the maximum extinction ratio is 245dB at 0.48THz.

[0046] Figure 7 is a diagram of the change of the radial power flow distribution in the fiber cross section of embodiment 1 of the present application with the refractive index of the liquid phase biological sample to be measured, by Figure 7 It can be seen that as the refractive index of the analyte increases from 1.33 (water) to 1.40 (red blood cells), the power in the core region increases by about 2.5 times.

[0047] It needs to be further explained that the filter in the present application can also be used as a biosensor. The terahertz microstructure filter with biosensing function of the present application works in (but not limited to) the sub-terahertz wave band of 0.1-1THz. Compared with the frequency band above 1THz, the water sensitivity of the sub-terahertz wave is lower, which is suitable for liquid phase detection of biological samples. Since the photon energy of the terahertz wave is low, it will not cause ionization risk to most biological tissues, and can excite the collective oscillation mode of biological molecules, thereby improving the sensing sensitivity of biological molecules. In addition, it can also be used for dynamic research on micrometer-level particles such as biological molecules; the present application uses graphene as the terahertz plasmonic material, and adjusts the chemical potential of graphene by external bias to make the filter have a dynamically tunable working frequency band after being prepared and shaped. When used as a biosensor, the hexagonal ring structure of graphene is more easily combined with organic molecules to form π-π bond stacking, showing higher molecular adsorption capacity, which is conducive to improving the biosensing sensitivity.

[0048] When liquid or solid biological samples are added above the graphene layer 5 of the terahertz microstructure filter in embodiment 1, the function of a biosensor can be realized, especially for detecting liquid biological samples with refractive index between 1.33 and 1.40, such as the refractive index of plasma, white blood cells, hemoglobin and red blood cells in blood components is 1.35, 1.36, 1.38 and 1.40 respectively. The terahertz microstructure filter as a biosensor can be used to determine the type of biological sample. On the one hand, when a broadband THz signal is input, due to the different refractive indices of different analytes, the generated SPR frequency is also different, resulting in the red shift of the position of the output spectrum loss peak with the increase of the refractive index of the analyte, so the type of biological sample can be determined according to the position of the loss peak, realizing frequency modulation type sensing. On the other hand, at a certain fixed frequency, the intensity of the output THz wave will change with the change of the refractive index of the analyte. For example, 0.56 THz corresponds to the resonance frequency of the analyte being water (na=1.33), and resonance coupling causes the power in the core to be coupled to the evanescent wave and SPP mode in the cladding. At a frequency of 0.56 THz, the power in the core region has a minimum value when the analyte is water compared to other liquid biological analytes, and the power in the core region gradually increases with the increase of the refractive index of the analyte. Therefore, according to the change of the intensity of the output THz wave, the type of biological sample can be determined, realizing intensity modulation type sensing.

Claims

1. A terahertz microstructure filter having a biosensing function, characterized by, The application relates to a terahertz microstructure filter, which comprises a fiber base material (1) provided with a core (2) and a cladding air hole (3), and a filter sensing area (4) is arranged on the fiber base material (1), the surface of the filter sensing area (4) is coated with a graphene layer (5), and a metal electrode (6) is arranged on the outer side of the fiber base material (1) and the graphene layer (5) respectively. The cladding air hole (3) is arranged around the core (2) and is arranged in a regular triangle array. The filter sensing area (4) is in a groove shape, and the graphene layer (5) is arranged on the concave surface of the groove; the vertical distance from the concave surface of the filter sensing area (4) to the center of the core (2) is a side polishing depth H of 720-780 mu m. The hole diameters of the cladding air holes (3) are the same, the hole spacing Lambda of the cladding air holes (3) is 600 mu m, and the ratio of the diameter d of the cladding air holes (3) to the hole spacing Lambda of the cladding air holes (3) is 0.

6.

2. The terahertz microstructure filter with biosensing function according to claim 1, characterized in that, The fiber base material (1) is a cyclic olefin polymer TOPAS, a cyclic olefin polymer Zeonex, high-density polyethylene, polymethyl methacrylate, polycarbonate, polystyrene or high-resistance silicon.

3. The THz microstructure filter with biosensing function according to claim 1, wherein, The graphene layer (5) is single-layer graphene or multi-layer graphene, and the metal electrode (6) is Au or Pt.

4. The terahertz microstructure filter with biosensing function according to any one of claims 1-3, characterized in that, The working frequency of the above-mentioned terahertz microstructure filter is 0.1-1 THz, which is a sub-terahertz wave band with low water sensitivity.

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