CN113237849B - Lithium niobate two-dimensional grating excited Bloch surface wave biosensor and method - Google Patents
Lithium niobate two-dimensional grating excited Bloch surface wave biosensor and method Download PDFInfo
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Abstract
The invention provides a lithium niobate two-dimensional grating excitation Bloch surface wave biosensor and a method thereof, comprising a defect layer, a Bragg reflector layer, a buffer layer and a lithium niobate two-dimensional grating layer which are arranged from bottom to top in sequence; the Bragg reflector layer comprises a plurality of low-porosity porous silicon layers and high-porosity porous silicon layers, wherein the low-porosity porous silicon layers and the high-porosity porous silicon layers are alternately arranged in a periodic overlapping mode; the lithium niobate two-dimensional grating layer is provided with a plurality of air holes which are arranged in a square with a lattice constant a. The invention utilizes a strict coupled wave analysis method to excite the Bloch surface wave by coupling the lithium niobate with the porous silicon for the first time, provides different detection relational expressions aiming at two different principles of macromolecular adsorption and micromolecular permeation, widens the application range of the Bloch surface wave device, and has the advantages of high detection sensitivity, simple structure, accurate detection and the like.
Description
Technical Field
The invention belongs to the technical field of biosensors, and particularly relates to a lithium niobate two-dimensional grating-excited Bloch surface wave biosensor and a method.
Background
The optical biosensor can provide high sensitivity, fast reading and low cost label-free detection of related chemical substances, and has wide application in medical diagnosis and treatment, food safety and homeland safety. When the receptor immobilized on the sensor chip is bound to the substance to be detected, it can be detected by optical sensors designed based on different physical principles to detect specific label-free bioanalytes and small molecules. In these platforms, the optical platform is usually constructed with a planar solid body, which results in a limited number of binding sites for the analyte to the receptors on the sensor chip surface, so that only a small interaction between the optical field and the analyte exists at the whole surface, resulting in a low sensitivity. In addition, the optical platform made of planar solid material cannot selectively filter and screen the target molecules to be detected, and the occurrence of porous silicon material effectively solves the above problems. Porous silicon PSi material is an attractive material due to its highly tunable optical properties, enhanced surface area and fast and economical fabrication. The sensitivity of interaction with biomolecules is improved by etching nanopores in the silicon wafer to increase the surface area. The size of the pore size is adjusted to screen and filter the object to be detected, when the biological molecules are combined with the porous silicon, the effective refractive index of the porous silicon with different structures can be changed, and the biochemical molecules are detected by observing the change of the reflection spectrum.
For example, chinese patent CN102313717B issued to a porous silicon microcavity biosensor comprising an upper Bragg mirror, a lower Bragg mirror, and a defect layer sandwiched between the upper and lower Bragg mirrors, the defect layer having a thickness 2 times the thickness of the high porosity layer. When the added detected biomolecule enters the defect layer, the resonance peak can correspondingly move, so that the concentration value of the added biomolecule can be judged according to the amount of the movement.
One key limitation faced by these PSi sensors described above is the ability to effectively detect small molecules that readily penetrate the porous matrix and large molecules that slowly diffuse into or are filtered out of the pores. In recent years, research on bio-optical sensors based on Bloch surface wave, BSW, has been drawing attention. For example, chinese patent CN109100308B issued a bloch surface wave based porous silicon biosensor that used a circular grating coupled porous silicon excited BSW for sensing detection analysis, but its detection sensitivity was only 153.3 °/RIU. In recent years, lithium niobate materials have a wide transparency range, large photoelectric and photorefractive properties, and the like as a nonlinear material, and are widely applied to sensors, resonators, modulators, and the like, and are receiving attention from researchers. In order to improve the sensitivity of the BSW device, chinese patent CN112461787A discloses a lithium niobate optical sensor based on bloch surface wave and a method thereof, which adopts lithium niobate as a defect layer material to improve the sensitivity of the prism-excited BSW device, and compared with the prism-excited BSW, the BSW structure design constructed by the grating can reduce the complexity of the large-volume optical assembly.
In summary, the optical assembly of the conventional optical biosensor has a complex structure, poor repeatability of detection of an object to be detected, low sensitivity and low detection precision, and cannot be used for respectively detecting a small molecule sample and a large molecule sample.
Disclosure of Invention
In view of the above technical problems, the present invention provides a lithium niobate two-dimensional grating-excited bloch surface wave biosensor and a method thereof, wherein the two-dimensional grating-excited bloch surface wave biosensor made of a lithium niobate material is used for optical biosensing. The sensor comprises a lithium niobate two-dimensional grating layer, a buffer layer, a Bragg reflector layer and a defect layer; the Bragg reflector layer is formed by alternately superposing high-porosity porous silicon and low-porosity porous silicon, and the diameter D and the hole depth h of holes in the lithium niobate layer are arranged in a square mode with a lattice constant a. The invention utilizes a strict coupled wave analysis method to excite the Bloch surface wave by coupling the lithium niobate with the porous silicon for the first time, provides different detection relational expressions aiming at two different principles of macromolecular adsorption and micromolecular permeation, widens the application range of the Bloch surface wave device, and has the advantages of high detection sensitivity, simple structure, accurate detection and the like.
The technical scheme of the invention is as follows: a lithium niobate two-dimensional grating-excited Bloch surface wave biosensor comprises a defect layer, a Bragg reflector layer, a buffer layer and a lithium niobate two-dimensional grating layer which are sequentially arranged from bottom to top;
the Bragg reflector layer comprises a plurality of low-porosity porous silicon layers and high-porosity porous silicon layers, and the low-porosity porous silicon layers and the high-porosity porous silicon layers are alternately arranged in a periodic overlapping mode;
the lithium niobate two-dimensional grating layer is provided with a plurality of air holes which are arranged in a square with a lattice constant a.
In the above scheme, the lithium niobate two-dimensional grating layer is made of lithium niobate material, and the ordinary light refractive index n o 2.28, extraordinary refractive index n e 2.2; the buffer layer is made of high-porosity porous silicon material and has a thickness d C 160 nm; the defect layer is made of a low-porosity porous silicon material, and the thickness da is 30 nm.
In the above scheme, the number of the low-porosity porous silicon layers and the number of the high-porosity porous silicon layers are both 4.
In the above embodiment, the porosity ρ of the low-porosity porous silicon layer is 42%, and the porosity ρ of the high-porosity porous silicon layer is 76%.
In the above scheme, the refractive index n of the low-porosity porous silicon layer H ＝26, thickness d of the low-porosity porous silicon layer H 70 nm; the refractive index n of the high-porosity porous silicon layer L Thickness d of high porosity porous silicon layer ═ 1.45 L ＝100nm。
In the scheme, the diameter D of the air hole is 420-490 nm, and the step length is set to be 10 nm; the hole depth h of the air holes is 60-120 nm, and the step length is set to be 10 nm; the lattice constant a is 450-520 nm, and the set step length is 10 nm.
Further, the diameter D of the air hole is 440 nm; the pore depth h of the air pore is 90 nm.
A method of exciting a bloch surface wave biosensor from the lithium niobate two-dimensional grating, comprising the steps of:
s1, constructing a lithium niobate two-dimensional grating-excited Bloch surface wave biosensor model based on a strict coupled wave analysis method, wherein the structure of the lithium niobate two-dimensional grating-excited Bloch surface wave biosensor model comprises a defect layer, a Bragg reflector layer, a buffer layer and a lithium niobate two-dimensional grating layer which are sequentially connected from bottom to top;
the Bragg reflector layer comprises a plurality of low-porosity porous silicon layers and high-porosity porous silicon layers, and the low-porosity porous silicon layers and the high-porosity porous silicon layers are alternately arranged in a periodic overlapping mode;
a plurality of air holes are arranged on the lithium niobate two-dimensional grating layer, and the air holes are arranged in a square with a lattice constant a;
s2, calculating the incident wavelength to be visible light lambda based on a strict coupled wave analysis method 0 When the diameter of the lithium niobate two-dimensional grating layer is 625nm, optimizing parameters of the lithium niobate two-dimensional grating layer to obtain optimal parameter values for exciting the bloch surface wave, wherein the optimal parameter values comprise an air hole diameter D, a lattice constant a and an air hole depth h;
s3, establishing a formula of the relation between the refractive index and the azimuth angle degree when the macromolecule is adsorbed on the surface of the device and the micromolecule permeates into the device: y is a + b x, where a is the intercept, b is the slope, y is the index of refraction, and x is the degree of the azimuth.
In the above solution, the optimal parameter values in step S2 are: the lattice constant a of the air hole is 510nm, the diameter D of the air hole is 440nm, and the hole depth h of the air hole is 90 nm.
In the above scheme, in the step S3, the relationship between the refractive index of the macromolecule and the azimuthal angle is as follows: y 2193 ± 164+ -1638 ± 123 x; the relationship between the refractive index of the small molecule and the azimuthal degree is: and y is 1486 + -108 + -568 + -41 x.
Compared with the prior art, the invention has the beneficial effects that: the invention designs a multilayer dielectric grating structure based on the BSW principle of the Bloch surface wave, a model is established by a strict coupled wave analysis method for calculation, then parameter optimization is carried out, and the optimal structural parameter is selected to obtain a reflected spectrogram of a narrower resonance peak. The invention utilizes a strict coupling wave analysis method, adopts a lithium niobate grating structure to couple a porous silicon dielectric layer for constructing the Bloch surface wave for the first time, so that the sensitivity of the BSW sensor is greatly improved, and the parameters are as follows: the Bragg reflector period number N is 4, the tetragonal lattice constant a is 510nm, the diameter D of an air hole is 440nm, the hole depth h is 90nm, the sensitivity reaches 1700 DEG/RIU when the refractive index of an analyte to be detected is 1.33-1.336, and the sensitivity reaches 80 DEG/RIU when a small-molecule analyte penetrating into a device is detected. Compared with the Chinese patent CN109100308B, the sensitivity of the porous silicon biosensor based on the Bloch surface wave and the design method thereof is improved by an order of magnitude. The BSW-based optical biosensor can realize the detection of the properties of the substance to be detected by adopting the electromagnetic waves under the conditions of TM polarization and TE polarization, and has wider application range.
Drawings
Fig. 1 is a schematic diagram of the BSW sensor structure.
Fig. 2 is a cross-sectional view of the BSW sensor.
Fig. 3 is a top view of the BSW sensor.
FIG. 4 is a graph of the effect of different air hole diameters on the reflectance spectrum in the visible wavelength band.
FIG. 5 is a graph of the effect of different air hole depths on the reflectance spectrum in the visible wavelength band.
Fig. 6 shows the effect of different lattice constants on the reflection spectrum in the visible wavelength band.
FIG. 7 shows the condition that in the visible light band, when the refractive index of the solution to be measured changes, the TE polarized electromagnetic wave excites BSW with the change of the incident azimuth angle.
Fig. 8 is a graph simulating BSW excited by the change of the incident azimuth angle due to the change of the refractive index and TE polarized electromagnetic wave at the defect layer after the BSW sensor permeates the analyte.
FIG. 9 is a graph at λ 0 The sample is a solution under 625nm, and under the condition of TE polarized electromagnetic waves, the incident angle theta in the grating is 9.8 degrees, and the optical sensor has electric field intensity corresponding to the excitation of BSW by 4 periods.
FIG. 10 is a graph of a linear regression relationship between resonance angle and analyte refractive index when external macromolecules are simulated to adsorb on the sensor surface;
FIG. 11 is a graph of a linear regression relationship between the resonance angle and the refractive index of the defect layer when external small molecules are simulated to permeate into the sensor;
wherein: the optical waveguide structure comprises a defect layer 1, a Bragg reflector layer 2, a low-porosity porous silicon layer 201, a high-porosity porous silicon layer 202, a buffer layer 3, a lithium niobate two-dimensional grating layer 4, an air hole 401 and an external dielectric layer 5.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
Fig. 1 and 2 show a preferred embodiment of the lithium niobate two-dimensional grating-excited bloch surface wave biosensor, which includes a defect layer 1, a Bragg mirror layer 2, a buffer layer 3, and a lithium niobate two-dimensional grating layer 4, which are sequentially disposed from bottom to top; the Bragg reflector layer 2 comprises a plurality of low-porosity porous silicon layers 201 and high-porosity porous silicon layers 202, wherein the low-porosity porous silicon layers 201 and the high-porosity porous silicon layers 202 are alternately arranged in a periodic overlapping mode; the lithium niobate two-dimensional grating layer 4 is provided with a plurality of air holes 401, and the air holes 401 are arranged in a square with a lattice constant a.
According to the invention, BSW is excited by coupling the multiple layers of Bragg porous silicon dielectrics with the lithium niobate two-dimensional grating, BSW is excited by exciting the BSW by the multiple layers of porous silicon dielectrics of the non-metal films, and the structure can be processed by electrochemically etching monocrystalline silicon in hydrofluoric acid solution.
The porosity ρ ═ 42% of the low porosity porous silicon layer 201 and the porosity ρ ═ 76% of the high porosity porous silicon layer 202, and the corresponding refractive indices can be calculated using the following equations:
where ρ is the porosity and n is pore Is the refractive index n of the air hole 401 pore ＝1，n si Is the refractive index n of Si si ＝3.864，n H Refractive index of porous silicon with low porosity; n is L Is a high porosity porous silicon refractive index.
The refractive index n of the low-porosity porous Si layer 201 H 2.6, low porosity porous silicon layer 201 thickness d H 70 nm; the high porosity porous silicon layer 202 has a refractive index n L 1.45, high porosity porous silicon layer 202 thickness d L ＝100nm。
The diameter D of the air hole is in a scanning range of 420-490 nm, and the set step length is 10 nm; the hole depth h is 60-120 nm, and the set step length is 10 nm; the scanning range of the lattice constant a is 450-520 nm, and the setting step field is 10 nm.
Preferably, the diameter D of the air hole 401 in the lithium niobate layer is 440 nm; the hole depth h is 90 nm; lattice constant a-510 nm
The lithium niobate two-dimensional grating layer 4 is made of lithium niobate material and has an ordinary light refractive index n o 2.28, extraordinary refractive index n e 2.2; the buffer layer 3 is made of a porous silicon material with high porosity and has a thickness d C 160 nm; the defect layer 1 is made of a low-porosity porous silicon material, and the thickness da is 30 nm.
The Bragg reflector layer 2, the buffer layer 3 and the defect layer 1 are formed by etching and processing a silicon wafer by an electrochemical method, and the refractive index and the thickness of the porous silicon layer are controlled by the magnitude of current and the corrosion time. The air hole 401 in the lithium niobate is processed by focused ion beam FIB, and the etching mode is hole-by-hole etching.
A method for exciting a Bloch surface wave biosensor by a lithium niobate two-dimensional grating comprises the following steps:
s1, constructing a sensor model of a lithium niobate two-dimensional grating coupled porous silicon medium layer by utilizing a Diffact mode in Rsoft optical software based on the principle of a strict coupled wave analysis method, wherein the structure of the sensor model of the lithium niobate two-dimensional grating coupled porous silicon medium layer comprises a defect layer 1, a Bragg reflector 2, a buffer layer 3 and a lithium niobate two-dimensional grating layer 4 which are sequentially connected from bottom to top, the Bragg reflector layer comprises N low-porosity porous silicon layers 201 and N high-porosity porous silicon layers 202 which are periodically and alternately circulated, a plurality of air holes 401 are arranged on the lithium niobate two-dimensional grating layer 4, and the air holes 401 are arranged in a square shape with a lattice constant a;
s2, calculating the incident wavelength to be visible light lambda based on a strict coupled wave analysis method 0 When the particle size is 625nm, optimizing parameters of the lithium niobate layer to obtain optimal parameter values of the excited bloch surface wave, wherein the optimal parameter values comprise an air pore diameter D, a lattice constant a and an air pore depth h;
and S3, an angle inquiry method based on an azimuth angle is adopted, the system analyzes a dynamic curve which causes reflection spectrum drift when the refractive index of a defect layer is changed when the object to be detected is adsorbed on the surface of the device and permeates into the defect layer in the device based on the spectral sensitivity of the optical sensor and the response characteristic of the sensor when the refractive index of the analyte is indirectly changed in the analyzed substance and the solubility of the analyzed substance is changed.
Simulations show that based on this sensor, a device sensitivity of 1700 °/RIU is measured when large analytes are adsorbed on the sensor surface, and 80 °/RIU is measured when small analytes are permeated into the device. And as a result, as shown in fig. 10 and 11, a linear distribution of y ═ a + b ×, is present between the refractive index and the azimuthal degree of the analyte, which enables high-precision measurement of the sample. The specific form is the relationship between the macromolecule refractive index and the azimuth angle degree: y ═ 2193 ± 164) + (-1638 ± 123) x; the relationship between the refractive index of the small molecule and the degree of the azimuth angle is as follows: y ═ 1486 ± 108) + (-568 ± 41) x.
The invention utilizes a multilayer porous silicon dielectric structure to excite a Bloch surface wave, when light waves penetrate through a lithium niobate layer and reach a layer of porous silicon film closest to an external detection area under the combined action of the multilayer porous silicon dielectric, namely a defect layer 1, and electric field distribution with enough strength is formed at the position for sensing detection, and meanwhile, the invention also provides a method for detecting a solution to be detected by adopting the surface wave. The invention aims to provide the optical biosensor which is easy to manufacture, low in complexity of an optical component, strong in repeatability of detection of an object to be detected and high in sensitivity, so that the problem that the existing sensor is low in detection precision is solved, and the detection of a small molecule sample and a large molecule sample can be realized respectively.
Example one
As shown in fig. 1, a lithium niobate two-dimensional grating-excited bloch surface wave biosensor includes a defect layer 1, a Bragg mirror layer 2, a buffer layer 3, and a lithium niobate two-dimensional grating layer 4, which are connected in sequence from bottom to top.
As shown in fig. 2, the Bragg mirror layer 2 includes N periodic cyclically arranged low-porosity porous silicon layers 201 and high-porosity porous silicon layers 202.
As shown in fig. 3, square air holes 401 are arranged on the lithium niobate grating layer 4, and the air holes 401 are arranged in a periodic array with a lattice constant a.
A transverse electric TE or transverse magnetic TM polarized light source of the lithium niobate two-dimensional grating layer 2 is diffractively coupled into the buffer layer 3, high-order diffraction light intensity is coupled to a high-refractive-index core layer, namely the defect layer 1, in an oscillating mode through the Bragg reflector layer 2, and strong resonance characteristics are generated in far-field reflection. When a liquid, gas or molecule is introduced into the structure, the refractive index of the defect layer 1 changes, thereby producing a detectable shift in the coupling angle θ.
Comprises the following steps: establishing a porous silicon structure model of the multilayer dielectric grating based on a strict coupled wave analysis method, namely establishing a structure model of a lithium niobate coupled porous silicon biosensor based on a Bloch surface wave; designing the periodicity of the Bragg reflector layer 2 and the diameter and the depth of an air hole 401 of the lithium niobate grating layer 4, and performing preliminary calculation: and (5) carrying out optimization processing by using an RCWA algorithm to obtain an optimal result parameter.
When the porous silicon biosensor is designed, the optimal BSW excitation effect can be obtained by optimizing the lithium niobate grating layer through theoretical analysis and numerical calculation so as to realize optimal optical sensing detection. When the hole diameter is optimized as shown in fig. 4, the reflectivity is improved along with the increase of the hole diameter, when the hole diameter is 450nm, the device reflectivity is the lowest, but the total reflectivity does not have large fluctuation, and the reflectivity begins to reduce along with the increase of D, the hole diameter is increased, and the transmissivity of light entering the device is reduced. Next, the lattice constant of the pore diameter and the pore depth in the lithium niobate layer were optimized, and it was found that the peak of the reflection spectrum was the sharpest when a was 510nm and the pore depth was 90nm, as shown in fig. 5 and 6. Under the condition, the Ey field intensity distribution of the whole device is researched and analyzed, and the fact that the field intensity reaches the maximum value at the position of the defect layer and presents oscillation attenuation along the direction of the device and exponential attenuation at the position of the defect layer and the position of the solution layer to be detected, and a typical Bloch field intensity mode is presented is found from the graph 9.
Example two
In the present example, where the sensor is used to detect large analyte species, n is the high refractive index material of Bragg mirror layer 2 H 2.6; porous silicon layer with porosity of 42%The low refractive index material is selected from n L 1.45; a porous silicon layer with a porosity of 76%, and the Bragg reflector layer 2 is formed by periodically arranging porous silicon with a porosity of 42% and porous silicon with a porosity of 76%, and the thicknesses of the porous silicon are d H 70nm and d L The thickness of the defect layer is 30nm, the thickness of the defect layer is 42% of porosity of the porous silicon dielectric layer; the buffer layer adopts a porous silicon dielectric layer with 76% porosity, and the thickness is 160 nm. The whole structure of the device is as follows: the optical waveguide structure comprises a lithium niobate two-dimensional grating layer, a buffer layer, a Bragg reflector layer and a defect layer. In this example, the detection of macromolecules adsorbed on the sensor surface was analyzed by passing the solution through the sensor surface via a microfluidic device. A wavelength interrogation method is adopted, namely a fixed incident angle of 9.8 degrees and an incident wavelength of 625nm are incident into the Bragg reflector layer 2 through the lithium niobate two-dimensional grating layer 4, and the azimuth angle scanning range is 0-20 degrees. FIG. 7 shows the defect peak shift characteristic, in which the refractive index near the sensor surface changes due to macromolecular adsorption, and the dynamic peak curve shifts. The calculated sensitivity S of the sensor macromolecule measurement azimuth angle is 1700 °/RIU, and as shown in fig. 10, compared with the sensor designed in chinese patent CN109100308B, the sensitivity is greatly improved, the sensor of the present invention shows good linearity in the azimuth angle of the refractive index interval, which indicates that the sensor has good spectral response characteristics, and can realize high-precision measurement of a sample.
EXAMPLE III
In the present example, where the sensor is used to detect small analyte species, n is chosen as the high refractive index material in Bragg mirror layer 2 H 2.6; a porous silicon layer with porosity of 42%, and a low refractive index material with refractive index n L 1.45; a porous silicon layer with a porosity of 76%, and the Bragg reflector layer 2 is formed by periodically arranging porous silicon with a porosity of 42% and porous silicon with a porosity of 76%, and the thicknesses of the porous silicon layer and the porous silicon layer are respectively d H 70nm and d L The thickness of the defect layer is 30nm, wherein the thickness of the defect layer is 100nm, the periodicity N is 4, and the porosity of the defect layer is 42%; the buffer layer adopts a porous silicon dielectric layer with 76% porosity, and the thickness is 160 nm. The whole structure of the device is as follows: lithium niobate two-dimensional grating layer-buffer layer-Bragg mirror layer — defect layer. In this case, the detection of small molecules penetrating into the sensor is analyzed by passing the solution through the sensor surface via a microfluidic device. A wavelength interrogation method is adopted, namely a fixed incident angle of 9.8 degrees and an incident wavelength of 625nm are incident into the Bragg reflector layer 2 through the lithium niobate two-dimensional grating layer 4, and the azimuth angle scanning range is 0-20 degrees. As shown in fig. 8, the defect peak shift characteristic is that the refractive index of the defect layer in the sensor changes due to the permeation of small molecules, and the dynamic peak curve shifts. The sensor small molecule measurement azimuth angle sensitivity S is calculated to be 80 °/RIU, and as shown in fig. 11, the sensor of the present invention shows good linearity in the azimuth angle of the refractive index interval, which shows that the sensor has good spectral response characteristics, and can realize high-precision measurement of a sample.
It should be understood that although the specification has been described in terms of various embodiments, not every embodiment includes every single embodiment, and such description is for clarity purposes only, and it will be appreciated by those skilled in the art that the specification as a whole can be combined as appropriate to form additional embodiments as will be apparent to those skilled in the art.
The above-listed detailed description is only a specific description of a possible embodiment of the present invention, and they are not intended to limit the scope of the present invention, and equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the scope of the present invention.
Claims (9)
1. A lithium niobate two-dimensional grating excitation Bloch surface wave biosensor is characterized by comprising a defect layer (1), a Bragg reflector layer (2), a buffer layer (3) and a lithium niobate two-dimensional grating layer (4) which are sequentially arranged from bottom to top;
the defect layer (1) is made of porous silicon material with low porosity rho 42%;
the Bragg reflector layer (2) comprises a plurality of low-porosity porous silicon layers (201) and high-porosity porous silicon layers (202), and the low-porosity porous silicon layers (201) and the high-porosity porous silicon layers (202) are alternately arranged in a periodic overlapping mode; the porosity rho of the low-porosity porous silicon layer (201) is 42%, and the porosity rho of the high-porosity porous silicon layer (202) is 76%;
the buffer layer (3) is made of porous silicon material with high porosity rho 76%;
the lithium niobate two-dimensional grating layer (4) is provided with a plurality of air holes (401), and the air holes (401) are arranged in a square with a lattice constant a.
2. The lithium niobate two-dimensional grating-excited bloch surface wave biosensor according to claim 1, wherein the lithium niobate two-dimensional grating layer (4) is made of lithium niobate material, and the refractive index n of ordinary light is o 2.28 extraordinary refractive index n e 2.2; the thickness of the buffer layer (3) is d C 160 nm; the thickness da of the defect layer (1) is 30 nm.
3. The lithium niobate two-dimensional grating-excited bloch surface wave biosensor according to claim 1, wherein the number of the low-porosity porous silicon layers (201) and the high-porosity porous silicon layers (202) is 4.
4. The lithium niobate two-dimensional grating-excited bloch surface wave biosensor of claim 1, wherein the low porosity porous silicon layer (201) has a refractive index n H 2.6, thickness d of low porosity porous silicon layer (201) H 70 nm; the high porosity porous silicon layer (202) has a refractive index n L 1.45, high porosity porous silicon layer (202) thickness d L ＝100nm。
5. The lithium niobate two-dimensional grating-excited bloch surface wave biosensor according to claim 1, wherein the diameter D of the air hole (401) is 420-490 nm, and the step size is set to 10 nm; the hole depth h of the air hole (401) is 60-120 nm, and the step length is set to be 10 nm; the lattice constant a is 450-520 nm, and the set step length is 10 nm.
6. The lithium niobate two-dimensional grating-excited bloch surface wave biosensor according to claim 5, wherein the diameter D of the air hole (401) is 440 nm; the hole depth h of the air hole (401) is 90 nm; the lattice constant a is 510 nm.
7. A method for exciting a bloch surface wave biosensor with a lithium niobate two-dimensional grating according to any one of claims 1 to 6, comprising the steps of:
the method comprises the following steps that S1, a lithium niobate two-dimensional grating excited Bloch surface wave biosensor model is constructed based on a strict coupled wave analysis method, and the structure of the lithium niobate two-dimensional grating excited Bloch surface wave biosensor model comprises a defect layer (1), a Bragg reflector layer (2), a buffer layer (3) and a lithium niobate two-dimensional grating layer (4) which are sequentially connected from bottom to top; the Bragg reflector layer (2) comprises a plurality of low-porosity porous silicon layers (201) and high-porosity porous silicon layers (202), and the low-porosity porous silicon layers (201) and the high-porosity porous silicon layers (202) are alternately arranged in a periodic overlapping mode; a plurality of air holes (401) are formed in the lithium niobate two-dimensional grating layer (4), and the air holes (401) are arranged in a square with a lattice constant a;
s2, calculating the incident wavelength to be visible light lambda based on a strict coupled wave analysis method 0 When the particle size is 625nm, parameters of the lithium niobate two-dimensional grating layer (4) are optimized, and the optimal parameter values for exciting the Bloch surface wave are obtained and comprise an air hole diameter D, a lattice constant a and an air hole depth h;
s3, establishing a formula of the relation between the refractive index and the azimuth angle degree when the macromolecule is adsorbed on the surface of the device and the micromolecule permeates into the device: y is a + b x, where a is the intercept, b is the slope, y is the index of refraction, and x is the degree of the azimuth.
8. The method for exciting a bloch surface wave biosensor using a lithium niobate two-dimensional grating as claimed in claim 7, wherein the optimum parameter values in the step S2 are: the lattice constant a of the air hole (401) is 510nm, the diameter D of the air hole (401) is 440nm, and the hole depth h of the air hole (401) is 90 nm.
9. The method for exciting a bloch surface wave biosensor using a lithium niobate two-dimensional grating as set forth in claim 8, wherein in the step S3, the relationship between the refractive index of the macromolecule and the degree of the azimuth angle is: y ═ 2193 ± 164) + (-1638 ± 123) x; the relationship between the refractive index of the small molecule and the azimuthal degree is: y ═ 1486 ± 108) + (-568 ± 41) x.
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