Flexible metamaterial absorber and AFB1 rapid detection method based on the absorber

Abstract

The present invention is a flexible metamaterial absorber and a rapid detection method for AFB1 based on the absorber. The main body of the absorber is a three-layer metamaterial structure arranged in close contact and stacking, which includes a pattern layer, a uniform dielectric layer and a flexible material layer from top to bottom. The pattern layer is a periodically arranged micro-nano unit, and the unit structure is a periodic structure composed of an outer ring and an inner ring nested, wherein the inner ring is a closed ring and the outer ring is an open resonant ring. The detection method is to drop AFB1 solution samples with different contents on the surface of the terahertz metamaterial absorber and obtain its spectral curve. On this basis, a standard curve of the amplitude / position and content of the metamaterial absorber at the characteristic peak of AFB1 is established. The results show that at the second reflection peak frequency, the metamaterial structure has a good correlation with the thickness of AFB1, and the correlation is as high as 0.98. The present invention is of great significance to the design of aflatoxin detection devices, the research and development of special sensors for biological metamaterials, etc.

Description

Technical Field

[0001] The present invention belongs to the field of poisonous substance detection and metamaterial sensing technology, and relates to the detection of moldy toxins in food, and in particular to a flexible metamaterial absorber and an AFB1 rapid detection method based on the absorber. Background Art

[0002] Aflatoxin B1 (AFB1), a metabolite of Aspergillus flavus, is widely distributed, highly toxic and harmful. It directly inhibits the immune system of humans or animals and increases the risk of cancer. It also has good thermal stability and is not easily decomposed by conventional cooking and heating methods. The residual toxins are very harmful to human and animal health and the environment.

[0003] Commonly used detection methods include thin layer chromatography, liquid chromatography, fluorescence spectrophotometry, etc., but these methods require professional detection equipment and a relatively clean operating environment, and are not suitable for on-site detection of toxins. With the advancement of technology, there are new methods such as enzyme-linked immunosorbent assay, colloidal gold immunochromatography and biosensors for rapid, accurate and simple detection of aflatoxin B1. These new detection methods have relatively low requirements for equipment and environment, but there is still the problem of cumbersome operating steps.

[0004] With the development of terahertz technology, terahertz time-domain spectroscopy (THz-TDS) technology has been increasingly used in non-destructive testing fields such as moisture content determination, soil detection, pest measurement, genetically modified crop detection, quality control and adulteration detection, and crop yield estimation due to its advantages of low energy, strong penetration, and fingerprint spectrum of many substances. Domestic and foreign scholars have achieved fruitful research results in the field of terahertz spectroscopy detection of mold and its metabolites, but it is not yet mature in practical technology and has great application potential. Especially in the research of THz metamaterial sensors, improving the detection sensitivity is urgently needed to carry out in-depth research. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a flexible metamaterial absorber and an AFB1 rapid detection method based on the absorber. A three-layer structure is adopted to form a terahertz metamaterial absorber. Based on the absorber, the content of aflatoxin B1 can be detected quickly and accurately.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A flexible metamaterial absorber, the main body of the absorber is a three-layer metamaterial structure arranged in close contact and stacking, the upper layer is a pattern layer, the middle layer is a uniform dielectric layer, and the lower layer is a flexible material layer, wherein the pattern layer is a periodically arranged micro-nano unit, and its unit structure is a periodic structure composed of an outer ring and an inner ring nested, wherein the inner ring is a closed ring, and the outer ring is an open resonant ring structure.

[0008] In one embodiment, the uniform dielectric layer is coated on a flexible material layer, the flexible material layer is configured to be coated on a flexible substrate, the main material of the pattern layer is silver, the dielectric material of the uniform dielectric layer is a passive non-magnetic material, and the material of the flexible material layer is polyvinyl alcohol.

[0009] In one embodiment, the inner ring and the outer ring are both micrometer-sized, and the opening and the inner material of the ring are both air.

[0010] In one embodiment, the outer ring has two openings, and the two openings are symmetrical structures with consistent sizes.

[0011] In one embodiment, by adjusting the material and thickness of the uniform dielectric layer, the dissipation degree of the interaction between the local electromagnetic waves in the pattern layer and the solution to be tested is buffered, so that the electromagnetic waves propagate back and forth between the upper layer and the lower layer and dissipate, thereby achieving perfect absorption, wherein the material refractive index of the uniform dielectric layer determines the reflection peak resonance frequency, and the material thickness determines the reflection peak intensity.

[0012] In one embodiment, the size parameters of the pattern layer directly affect the resonant frequency and mode of the flexible metamaterial absorber, wherein as the outer diameter of the outer ring increases, the reflection peak increases accordingly, and the reflection peak intensity gradually increases. At this time, the electromagnetic wave is localized on the open ring, and the current flows from one opening outside the outer ring to another opening position, and the current direction of the inner ring is opposite to that of the outer ring, and the whole presents an even symmetric mode;

[0013] As the radius of the outer ring increases, the intensity of the electric field fluctuates. The intensity of the electric field is the smallest in the middle of the inner and outer rings. When viewed toward the opening, the intensity of the electric field increases first and then decreases, and the inner side is slightly higher than the outer side.

[0014] According to the characteristic peak position of the object to be tested, the resonance position is preliminarily determined by adjusting the top pattern parameters, including the inner and outer radii of the outer ring, the opening width, the inner ring radius and the thickness of the pattern layer, and then the resonance position and intensity of the absorber are determined by adjusting the material and thickness of the uniform dielectric layer.

[0015] In one embodiment, the thickness of the pattern layer is 3.5μm, and the pattern parameters are: the outer radius of the outer open ring is 19μm, the inner radius is 16μm, the width of the open ring is 3μm, the outer radius of the inner ring is 8μm, the inner radius is 5μm, the lattice constant is 50μm, the thickness of the uniform dielectric layer is 5μm, and the thickness of the flexible material layer is 30μm.

[0016] In one embodiment, the absorber excites reflection peaks at the characteristic peaks of aflatoxin B1 at 0.3THz, 1.1THz and 2.0THz, and at the positions of the latter two characteristic peaks, there are two significantly different resonance modes; wherein, at a frequency of 1.1THz, the incident electric field is mainly localized on the inner and outer sides of the ring structure, and the remaining electromagnetic wave overflow is concentrated near the inner ring; at 2.0THz, the incident wave is completely concentrated at the opening of the outer resonant ring, and the electric field strength is slightly higher than that at 1.1THz.

[0017] The present invention also provides an AFB1 rapid detection method based on the flexible metamaterial absorber, comprising the following steps:

[0018] Step 1: Prepare AFB1 solution samples with different contents, drop them on the surface of the pattern layer, and then obtain the reflectance spectrum curve of the absorber;

[0019] Step 2: establishing a standard curve of the amplitude / position and content of the flexible metamaterial absorber at the AFB1 characteristic peak 1.1 THz according to the spectral data of different solution samples;

[0020] Step 3: Obtain the reflection spectrum curve and the amplitude and frequency position at 1.1 THz of the solution containing AFB1 to be tested according to the operation of step 1, and compare it with the standard curve to obtain the content of AFB1.

[0021] In one embodiment, before adding the test solution each time, the flexible metamaterial absorber is placed in anhydrous ethanol for ultrasonic cleaning, then placed in distilled water for ultrasonic cleaning, and then placed in a sterile environment to dry or blown dry with nitrogen before use.

[0022] In one embodiment, the AFB1 solution is dropped onto the surface of the pattern layer to ensure that the solvent evaporates before acquiring the subsequent terahertz spectrum.

[0023] Compared with the prior art, the three-layer flexible terahertz metamaterial absorber of the present invention, especially the specific surface pattern, can provide more resonance modes and excite multiple resonance peaks. The absorber of the present invention can realize the rapid detection of low-concentration aflatoxin B1 content. Compared with the traditional detection method, the detection limit of this method is lower, and the correlation of the standard curve is as high as 0.98, with high accuracy. The absorber and detection method involved in the present invention can provide a reference for the detection of such low-concentration liquid analytes. In summary, the present invention can be used in the fields of food safety, plant protection and agricultural special sensor design. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of the three-layer flexible terahertz metamaterial absorber of the present invention.

[0025] Figure 2 It is the reflection spectrum of the absorber of the present invention in the frequency range of 0.1THz to 2.5THz.

[0026] Figure 3 This is the electric field distribution diagram of the absorber of the present invention at the resonance peak.

[0027] Figure 4 The effect of the intermediate layer thickness on the absorber performance.

[0028] Figure 5 This is a schematic diagram of the AFB1 content detection method involved in the present invention.

[0029] Figure 6 This is a standard curve of the frequency shift and the thickness of the AFB1 analyte mentioned in the present invention. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0031] As mentioned above, although terahertz time-domain spectroscopy (THz-TDS) technology has been applied in the detection of mold and its metabolites, there is still no mature application solution. The main reason is that in practical applications and national standards, the detection limit of the object to be tested is often low, so the fingerprint peak presented in the terahertz band is weak and difficult to detect accurately. Especially in practical applications, trace amounts of mold can affect food and personal safety, and the metabolites of mold are complex, which makes its detection difficult. How to steadily improve its detection sensitivity and achieve rapid detection of low-concentration molds is still a difficult problem to solve.

[0032] Based on this, the present invention provides a flexible metamaterial absorber, referring to Figure 1 The main body is a three-layer metamaterial structure stacked in close contact, which are: pattern layer 1, uniform dielectric layer 2 and flexible material layer 3 from top to bottom.

[0033] The pattern layer 1 is a periodically arranged micro-nano unit, which is arranged on a uniform dielectric layer 2, and its unit structure is a periodic structure composed of nested outer rings and inner rings, wherein the inner ring is a closed ring and the outer ring is an open resonant ring structure.

[0034] The uniform dielectric layer 2 is covered on the flexible material layer 3, and its surface is flat.

[0035] The flexible material layer 3 is used to cover other flexible substrates, which can ensure that the overall metamaterial is flexible and stretchable, and ensure that it can adapt to the shape of the detection object during detection, thereby expanding its application scenarios.

[0036] The design idea of ​​the present invention is:

[0037] By adjusting the material and thickness of the middle uniform dielectric layer 2, the dissipation degree of the interaction between the localized electromagnetic waves of the upper pattern layer 1 and the solution to be tested can be buffered, and finally the electromagnetic waves propagate back and forth between the upper and lower layers and dissipate, achieving perfect absorption, wherein the refractive index of the material determines the resonance frequency of the reflection peak, and the thickness of the material determines the reflection peak intensity. The reflection peak position and intensity of the terahertz metamaterial are regulated by selecting the material and thickness of the middle layer. The size parameters of the upper pattern structure directly affect the resonance frequency and mode of the structure. The specific influence rule is: since the inner ring is a closed ring, under the premise of unchanged height, the change of the inner ring radius only affects the size of the closed area in the ring, and the form of the electromagnetic wave incident on the ring is relatively fixed, so the inner ring radius has no effect on the reflectivity of the structure. The radius of the outer resonant ring has a great influence on the position and amplitude of the structural reflection peak. With the increase of r1, the reflection peak value increases accordingly, and the reflection peak intensity gradually increases. At this time, the electromagnetic wave is localized on the open ring, and the current flows from one end to the other end along the outer side of the open ring, and the current direction of the inner ring is opposite to that of the outer ring, and the overall even symmetric mode is present. Therefore, the change trend of the structural reflectivity within this range is more regular. As the thickness of the outer ring increases, the intensity of the electric field fluctuates. The intensity of the electric field is the smallest in the middle part of the inner and outer rings. When observed in the direction of the opening, the electric field intensity increases first and then decreases, and the inner side is slightly higher than the outer side. It can be seen that the size of the opening ring of the upper pattern structure has the most obvious effect on the optical properties of the metamaterial absorber. Therefore, based on the characteristic peak position of the object to be tested, its resonance position is preliminarily determined by adjusting the top pattern parameters. On the premise of ensuring easy processing, the resonance position and intensity of the absorber are then determined by adjusting the material and thickness of the dielectric layer, and finally the concentration / content of the solution to be tested can be accurately detected based on the metamaterial absorber.

[0038] In one embodiment of the present invention, the main material of the pattern layer 1 is silver, and the outer ring opening and the inner ring material are both air. The inner ring material here refers to the inner ring and between the inner and outer rings. The dielectric material of the uniform dielectric layer 2 is a passive non-magnetic material, such as Al2O3, and the material of the flexible material layer 3 is polyvinyl alcohol.

[0039] In this embodiment, silver is selected because it can produce a reflection peak at the characteristic peak position of Aspergillus flavus B1.

[0040] In one embodiment of the present invention, the inner ring (i.e., closed ring) and the outer ring (i.e., open resonant ring) are both micron-sized. Parameters in this range can concentrate the resonance of the structure in the terahertz frequency range, and the radius and opening width of the open resonant ring are adjustable.

[0041] In a specific embodiment of the present invention, the array form of the pattern layer 1 can be a rectangular array or other styles, and a specific size parameter is: thickness h1 = 3.5 μm, outer radius of the outer open ring r1 = 19 μm, inner radius r2 = 16 μm, width of the open ring d = 3 μm, outer radius of the inner ring r3 = 8 μm, inner radius r4 = 5 μm, lattice constant 50 μm. The material of the uniform dielectric layer 2 is Al2O3, and the thickness h2 = 5 μm. The material of the flexible material layer 3 is polyvinyl alcohol, and the thickness h3 = 30 μm.

[0042] like Figure 2 As shown, in this embodiment, the reflectivity of the flexible metamaterial absorber in the frequency range of 0.1THz to 2.5THz has a smaller reflection peak at 0.3THz, and two obvious reflection peaks at 1.1THz and 2.0THz, with amplitudes of 0.8 and 0.92 respectively. Among them, 0.3THz, 1.1THz and 2.0THz are the characteristic peaks of aflatoxin B1. Obviously, the flexible metamaterial absorber can excite reflection peaks at the above three positions, and there are two obviously different resonance modes at the latter two characteristic peak positions.

[0043] like Figure 3 As shown, in this embodiment, the electric field distribution of the metamaterial absorber at frequencies of 1.1THz and 2.0THz, the incident electromagnetic wave is localized at the outer ring opening of the upper structure. At a frequency of 1.1THz, the incident electric field is mainly localized on both sides of the inner and outer ring structure, and some electromagnetic waves overflow and concentrate near the inner ring; at 2.0THz, the incident wave is completely concentrated at the opening of the outer resonant ring, and the electric field intensity is slightly higher than that at 1.1THz. This shows that the terahertz metamaterial structure proposed in the present invention can produce a corresponding absorption peak near the absorption peak of Aflatoxin B1, which is expected to amplify the characteristic signal of AFB1 and improve the detection limit.

[0044] like Figure 4As shown, with the increase of the thickness of the intermediate dielectric layer, the reflection peak position of the metamaterial absorber of the present invention shifts forward, the shift amount is basically maintained at about 0.2 THz, and the peak amplitude shows a downward trend, the decrease is about 0.1, and the change trend is basically linear.

[0045] Based on the flexible metamaterial absorber, the present invention realizes the rapid detection of AFB1. The detection principle is as follows: Figure 5 As shown in the figure, the specific detection process includes:

[0046] Step 1: Prepare AFB1 solution samples with different contents, and drop them on the surface of the pattern layer 1 of the flexible metamaterial absorber to obtain its reflection spectrum curve.

[0047] Specifically, in this step, a micropipette can be used to draw 1 mL of a 50% glycerol-water solution, which is slowly injected into the conical flask along the inner wall of the conical flask, and the spores on the surface of the culture medium are washed down, and the conical flask is gently shaken to mix the spores with the glycerol-water solution. Repeat the above process until a sufficient suspension of Aspergillus flavus spores is obtained. Use a micropipette to transfer the suspension to a test tube for standby use. Then, AFB1 solution samples with different gradient contents in the range of 0 to 100 ppb are configured, dropped on the surface of the terahertz metamaterial absorber, and placed in a THz-TDS system (CCT-1800) for spectral measurement. The detection process uses a spectral line mode and a transmission module; each sample is detected at four different positions, and its reflection spectrum data is obtained after averaging. In the process, after the AFB1 solution is dropped onto the surface of the pattern layer 1 of the flexible metamaterial absorber, it is necessary to ensure that the solvent evaporates before the subsequent terahertz spectrum is acquired.

[0048] Step 2: A standard curve of the amplitude / position and content of the flexible metamaterial absorber at the AFB1 characteristic peak 1.1 THz is established based on the spectral data of different solution samples.

[0049] Analysis of the spectral data of different AFB1 solution samples revealed that the frequency shift at the reflection peak was more obvious, and was different from the influence of changes in the parameters of the structure itself on the electromagnetic transmission characteristics. When AFB1 analyte began to appear on the absorber surface, the THz metamaterial had three reflection peaks at 0.6THz, 1.37THz and 2THz. As the AFB1 concentration increased, the first reflection peak red-shifted, and the amplitude gradually decreased until it disappeared. As the AFB1 analyte concentration continued to increase, the position of the second reflection peak regularly red-shifted from 1.37THz to 0.83THz, and the offset completely covered an absorption peak of AFB1 (1.1THz). In particular, at 1.08THz, since a large amount of the incident electromagnetic wave is localized at the open rings at both ends, a small amount of electric field is concentrated on both sides of the inner ring due to the boundary effect. A standard curve of the amplitude / position and content of the metamaterial absorber at this point was established. The standard curve is as follows: Figure 6 As shown, the formula is expressed as follows:

[0050] y=0.007963x 2 -0.1312x+1.247

[0051] The correlation coefficient of the fitting curve is R=0.9816, and the root mean square error RMSE is 0.022.

[0052] Step 3: Obtain the reflection spectrum curve and the amplitude and frequency position at 1.1 THz of the solution containing AFB1 to be tested according to the operation of step 1, and compare it with the standard curve to obtain the content of AFB1.

[0053] After each test, the terahertz metamaterial needs to be processed later, that is, the metamaterial absorber is ultrasonically cleaned in anhydrous ethanol, then ultrasonically cleaned in distilled water, and then placed in a sterile environment to dry or blown dry with nitrogen for later use to ensure that no other impurities affect the subsequent test process.

[0054] In summary, the metamaterial absorber of the present invention can obtain two obvious resonance peaks and modes in the frequency range of 0.1 to 2.5 THz. Based on the absorber combined with a terahertz time-domain spectrometer, rapid detection of AFB1 content can be achieved, with a detection limit of 1.7 ppb, which is much smaller than the national standard of 5 ppb.

Claims

1. A flexible metamaterial absorber, characterized in that: The main body of the absorber is a three-layer metamaterial structure arranged in close contact and stacking, wherein the upper layer is a pattern layer (1), the middle layer is a uniform dielectric layer (2), and the lower layer is a flexible material layer (3), wherein the pattern layer (1) is a periodically arranged micro-nano unit, and its unit structure is a periodic structure composed of an outer ring and an inner ring nested, wherein the inner ring is a closed ring and the outer ring is an open resonant ring structure; the outer ring has two openings, and the two openings are symmetrical structures with the same size; The main material of the pattern layer (1) is silver, the dielectric material of the uniform dielectric layer (2) is Al2O3, the thickness of the pattern layer (1) is 3.5 μm, and the pattern parameters are: the outer radius of the outer open ring is 19 μm, the inner radius is 16 μm, the width of the open ring is 3 μm, the outer radius of the inner ring is 8 μm, the inner radius is 5 μm, the lattice constant is 50 μm, and the thickness of the uniform dielectric layer (2) is 5 μm.

2. The flexible metamaterial absorber according to claim 1, characterized in that: The uniform dielectric layer (2) is coated on a flexible material layer (3); the flexible material layer (3) is configured to be coated on a flexible substrate; the material of the flexible material layer (3) is polyvinyl alcohol.

3. The flexible metamaterial absorber according to claim 1, characterized in that: The inner ring and the outer ring are both micrometer-sized, and the opening and the inner ring material are both air.

4. The flexible metamaterial absorber according to claim 1, characterized in that: By adjusting the material and thickness of the uniform dielectric layer (2), the dissipation degree of the interaction between the local electromagnetic wave of the pattern layer (1) and the solution to be tested is buffered, so that the electromagnetic wave propagates back and forth between the upper layer and the lower layer and dissipates, thereby achieving perfect absorption, wherein the refractive index of the material of the uniform dielectric layer (2) determines the reflection peak resonance frequency, and the material thickness determines the reflection peak intensity.

5. The flexible metamaterial absorber according to claim 1, characterized in that: The size parameters of the pattern layer (1) directly affect the resonant frequency and mode of the flexible metamaterial absorber, wherein as the outer diameter of the outer ring increases, the reflection peak increases accordingly, and the reflection peak intensity gradually increases. At this time, the electromagnetic wave is localized on the open ring, and the current flows from one opening outside the outer ring to another opening position, and the current direction of the inner ring is opposite to that of the outer ring, and the whole presents an even symmetric mode; As the radius of the outer ring increases, the intensity of the electric field fluctuates. The intensity of the electric field is the smallest in the middle of the inner and outer rings. When viewed toward the opening, the intensity of the electric field increases first and then decreases, and the inner side is slightly higher than the outer side. With respect to the characteristic peak position of the object to be tested, the resonance position is preliminarily determined by adjusting the top pattern parameters, including the inner and outer radii of the outer ring, the opening width, the inner ring radius and the thickness of the pattern layer (1), and then the resonance position and intensity of the absorber are determined by adjusting the material and thickness of the uniform dielectric layer (2).

6. The flexible metamaterial absorber according to claim 1, characterized in that: The thickness of the flexible material layer (3) is 30 μm.

7. The flexible metamaterial absorber according to claim 6, characterized in that: The absorber excites reflection peaks at the characteristic peaks of aflatoxin B1 at 0.3THz, 1.1THz and 2.0THz, and there are two significantly different resonance modes at the latter two characteristic peaks; among them, at a frequency of 1.1THz, the incident electric field is mainly localized on the inner and outer sides of the ring structure, and the remaining electromagnetic wave overflow is concentrated near the inner ring; at 2.0THz, the incident wave is completely concentrated at the opening of the outer resonant ring, and the electric field intensity is slightly higher than that at 1.1THz.

8. The AFB1 rapid detection method based on the flexible metamaterial absorber according to claim 1 is characterized in that: The steps include: Step 1: preparing AFB1 solution samples with different contents, and dropping them on the surface of the pattern layer (1), and then obtaining the reflectance spectrum curve of the absorber; Step 2: establishing a standard curve of the amplitude / position and content of the flexible metamaterial absorber at the AFB1 characteristic peak 1.1 THz according to the spectral data of different solution samples; Step 3: Obtain the reflection spectrum curve and the amplitude and frequency position near 1.1 THz of the solution containing AFB1 to be tested according to the operation of step 1, and compare it with the standard curve to obtain the content of AFB1.

9. The AFB1 rapid detection method according to claim 8, characterized in that: Before adding the test solution each time, the flexible metamaterial absorber is placed in anhydrous ethanol for ultrasonic cleaning, and then placed in distilled water for ultrasonic cleaning, and then placed in a sterile environment to dry or blown dry with nitrogen before use.

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