Graphene terahertz metasurface sensor and its application in pesticide residue detection

Abstract

This invention discloses a graphene terahertz metasurface sensor and its application in pesticide residue detection, relating to the fields of sensor and detection technology. The graphene terahertz metasurface sensor comprises a substrate, a metasurface layer, a graphene film, and an aptamer layer. This invention also provides the application of the graphene terahertz metasurface sensor in pesticide residue detection. The metasurface layer of this invention is composed of an asymmetric metal wire array. When placed in the optical path of a transmission THz time-domain spectroscopy system, with the incident wave polarization direction along the x-axis, the structure itself can generate a very strong local electric field enhancement. When used to detect pesticide molecules, the interaction between the THz wave and the pesticide molecules to be measured is significantly enhanced, thereby achieving trace sensing of the target analyte. Furthermore, this invention utilizes graphene and modifies the aptamer layer metasurface to improve the sensitivity and specificity of detection.

Description

Technical Field

[0001] This invention relates to the field of sensor and detection technology, specifically to a graphene terahertz metasurface sensor and its application in pesticide residue detection. Background Technology

[0002] Pesticides are crucial for protecting crops and ensuring yields in agriculture. However, their overuse can lead to harmful residues that threaten human health and the environment. Traditional pesticide detection techniques, such as chromatography and mass spectrometry, offer high accuracy and can perform qualitative and quantitative analysis of pesticide residues. However, these methods typically rely on sophisticated instruments, are costly, have complex and time-consuming procedures, require cumbersome sample pretreatment, and must be performed by professionals in a laboratory setting. These factors collectively limit the wider adoption and application of traditional pesticide residue detection methods. Therefore, developing low-cost, rapid, and label-free detection systems for accurate pesticide detection is essential, and terahertz (THz) biosensing technology offers a promising alternative.

[0003] Terahertz waves (THz waves) have frequencies between 0.1 THz and 10 THz (1 THz = 10 THz). 12 THz waves are electromagnetic waves in the range of 100 Hz (THz), falling between microwaves and infrared waves. Due to their non-ionizing properties, low quantum energy, and fingerprint-like characteristics, THz waves are extremely powerful for biosensing. This capability allows for the identification of various biomolecules, from sugars, antibiotics, and pesticides to proteins and nucleic acids, through their unique THz absorption spectrum. THz sensors have received considerable attention for trace sample detection, primarily used to overcome the weak interaction between trace samples and THz waves. Among these, THz metasurface sensors have garnered significant attention due to their mature manufacturing processes, low cost, and miniaturization, making them ideal for achieving label-free, real-time, rapid, low-cost, and highly sensitive detection.

[0004] Early research on pesticide detection based on THz metasurface sensors mainly utilized their high sensitivity to small changes in local refractive index. For example, Liu et al. reported using a THz metasurface with TD resonance to detect chlorothalonil in concentrations ranging from 0 to 1000 mg / L, with a detection limit of 0.001 mg / L. Although the high sensitivity of metasurfaces for pesticide detection has been verified, their lack of specificity has been a limitation. To address this issue, some research teams have proposed graphene-modified metasurface sensors, utilizing the π-π stacking interaction between graphene and pesticide molecules to achieve selective detection. Recently, Wang et al. proposed a graphene-modified dual-band THz metasurface that successfully detected methyl chlorpyrifos solution at concentrations as low as 0.2 ppm. However, while existing studies have confirmed the sensitivity and specificity of graphene metasurfaces for benzene-containing pesticides, further in-depth research is needed on how to identify different pesticide molecules containing the same benzene ring. Furthermore, many metasurfaces are based on semiconductor materials (such as silicon), making in-situ detection on the surface of agricultural products difficult, which is crucial for pesticide residue detection in practical applications.

[0005] In summary, current THz metasurfaces struggle to achieve specific sensing of trace pesticide residues, especially for sampling and specific detection on fruit peels, which better meet practical detection needs. Therefore, for pesticide residue detection, achieving highly sensitive and specific sensing of trace pesticide residues while considering the in-situ detection capability, device fabrication technology, and the complexity of the detection steps requires careful consideration; currently, there is no particularly good design solution. Summary of the Invention

[0006] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a graphene terahertz metasurface sensor and its application in pesticide residue detection. Specifically, it provides a high-precision flexible THz metasurface sensor device and method that can specifically detect pesticides (such as chlorpyrifos). The flexible metasurface structure used is simple and easy to process, and can be attached to the surface of agricultural products to achieve real-time in-situ detection, so as to solve the key technical problems in existing detection technologies such as long detection cycle, high detection cost, and complex detection process.

[0007] The technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a graphene terahertz metasurface sensor, comprising:

[0009] Base;

[0010] A metasurface layer is disposed on the substrate. The metasurface layer includes a plurality of symmetrical square open rings arranged in an array along the horizontal direction of the substrate. Each symmetrical square open ring includes a first connecting arm, a second connecting arm, and a third connecting arm. The first connecting arm and the third connecting arm are mirror-symmetrically arranged on both sides of the second connecting arm with the second connecting arm as the axis of symmetry. Openings are formed between the first connecting arm and the second connecting arm, as well as between the third connecting arm and the second connecting arm.

[0011] A graphene film disposed on the metasurface layer;

[0012] An aptor layer is disposed on the graphene film.

[0013] Optionally, the first connecting arm is L-shaped, the third connecting arm is an L-shaped mirror symmetrical structure, the second connecting arm is T-shaped, two openings are formed between the two ends of the first connecting arm and the two ends of the second connecting arm, and two openings are formed between the two ends of the third connecting arm and the two ends of the second connecting arm.

[0014] Optionally, the symmetrical square open ring has the same lateral length and longitudinal length along the horizontal direction of the base, both being 65μm-75μm;

[0015] The distance between adjacent symmetrical square open rings is 9μm-11μm;

[0016] The width of the opening is 3 μm.

[0017] Optionally, the longitudinal lengths of the first connecting arm and the third connecting arm along the horizontal direction of the substrate are equal to the longitudinal length of the second connecting arm along the horizontal direction of the substrate, both being 65μm-75μm;

[0018] The first connecting arm and the third connecting arm each have a lateral length of 30μm-35μm along the horizontal direction of the substrate;

[0019] The second connecting arm has a lateral length of 55μm-60μm along the horizontal direction of the substrate.

[0020] Optionally, the substrate is a polyimide substrate, and the thickness of the polyimide substrate is 30μm-50μm;

[0021] The symmetrical square open ring is formed on a 200 nm thick gold film by laser direct writing.

[0022] Optionally, the graphene film is deposited on the metasurface layer by the following method:

[0023] Release the monolayer graphene into deionized water, keeping the monolayer graphene in a stretched and floating state, and let it stand for 1-3 hours.

[0024] The clean metasurface layer is used to retrieve the monolayer graphene floating on the water surface, ensuring that the monolayer graphene can be flatly attached to the central region of the metasurface layer.

[0025] The graphene-coated metasurface layer was placed vertically to drain the bottom moisture, and then left to stand at room temperature for 20-40 minutes before being heated and cured in an oven for 15-25 minutes at a curing temperature of 65-70°C to obtain a graphene-metasurface chip.

[0026] The cooled graphene-metasurface chip was immersed in acetone solution for 10-20 minutes.

[0027] Optionally, the aptamer layer includes a nucleic acid aptamer for the pesticide to be detected, and the aptamer layer is deposited on the graphene film by the following method:

[0028] The graphene-modified metasurface layer was immersed in TEOA buffer containing 5'-NH2-modified aptamers and incubated overnight at 3°C-5°C. The activated NHS ester reacted with the -NH2 group at the end of the aptamer to form a stable valproic acid bond, thereby fixing the aptamer onto the graphene and obtaining a metasurface layer modified with graphene and aptamers.

[0029] Remove the metasurface layer modified with graphene and aptamers and wash it with PBS containing 0.05%-0.15% Tween-20, then incubate it in 0.5%-1.5% BSA solution for 0.5-1 hour.

[0030] Secondly, the present invention provides the application of the graphene terahertz metasurface sensor in pesticide residue detection.

[0031] Thirdly, the present invention provides a method for detecting pesticide residues using the aforementioned graphene terahertz metasurface sensor, comprising the following steps:

[0032] The graphene terahertz metasurface sensor is immersed in a test solution containing the target pesticide molecule. After reacting for 10-30 minutes, it is taken out and the surface of the graphene terahertz metasurface sensor is slowly rinsed with deionized water and then placed in a drying oven to dry at a temperature of 50-60°C.

[0033] The dried graphene terahertz metasurface sensor was placed in a transmission THz time-domain spectroscopy system. The polarization direction of the incident THz wave was controlled to be along the X-axis of the graphene terahertz metasurface sensor. The transmission spectrum of the sample was obtained, and the change in transmittance was calculated. Or frequency shift change;

[0034] Change in transmittance Substitute the values ​​into the standard curve of transmittance change versus pesticide concentration, or use the frequency shift change... Substituting the values ​​into the standard curve of frequency shift versus pesticide concentration, the pesticide concentration in the test solution is calculated.

[0035] Optionally, the change in transmittance , T sample The transmittance is obtained after adding the test solution to the graphene terahertz metasurface sensor. T ref This indicates the transmittance of the graphene terahertz metasurface sensor when no solution to be tested is added.

[0036] The frequency shift change , f sample The frequency position of the resonance peak after the solution to be tested is added to the graphene terahertz metasurface sensor. This indicates the frequency position of the resonance peak when no test solution is added to the graphene terahertz metasurface sensor.

[0037] The basic working principle of this invention is as follows: The designed metasurface is composed of an asymmetric metal wire array. When placed in the optical path of a transmission THz time-domain spectroscopy system, the structure itself can generate a very strong local electric field enhancement when the incident wave polarization direction is along x. When used to detect pesticide molecules, the interaction between the THz wave and the pesticide molecules to be measured is significantly enhanced, thereby achieving the purpose of trace sensing of the target analyte. Furthermore, this invention utilizes graphene to modify the metasurface. Graphene can combine with pesticides containing benzene rings in their molecular structure through π-π stacking interactions, providing the metasurface with the ability to enrich the target analyte. After enriching the pesticide molecules, graphene can significantly modulate the interaction between the THz wave and the metasurface by changing its own Fermi level, thereby further improving the detection sensitivity. Furthermore, this invention utilizes an aptamer layer to further modify graphene, allowing for the rational construction of different aptamers based on the specific type of analyte, achieving specific detection of the target analyte. After the aptamer layer is modified, only target sample molecules can bind to the metasurface, while other non-target substances cannot or have difficulty binding to the metasurface. Therefore, the electromagnetic response between the metasurface and the target analyte is further enhanced, greatly improving sensing sensitivity and detection accuracy, thus enabling the detection of trace pesticide residues. In this invention, the concentration sensing and sample identification of the sample can be achieved through changes in the transmittance and frequency shift of the metasurface resonance peak.

[0038] This invention has at least one of the following beneficial effects:

[0039] (1) The sensor device designed in this invention adopts the combination of metasurface and graphene-aptamer, which has the advantage of high sensitivity detection of pesticide molecules, and the detection limit can reach the level of 0.1 ppm.

[0040] (2) The sensor designed in this invention is built on a flexible substrate and can be miniaturized. It can be directly attached to the surface of agricultural products for in-situ detection of pesticide residues, and has the advantages of being easy to use and having low manufacturing cost.

[0041] (3) The metasurface sensor designed in this invention, as well as the proposed metasurface modification method and detection method, are relatively simple. The device is easy to process and can be reused. The device has no special requirements for ambient temperature and can work at room temperature. The operating frequency range of the device is 0.1 THz~2 THz. It has the advantages of simple structure and high production quality. Attached Figure Description

[0042] Figure 1 This is a three-dimensional structural diagram of the graphene terahertz metasurface sensor in Embodiment 1 of the present invention.

[0043] Figure 2 This is a schematic diagram of the substrate and metasurface layer of the graphene terahertz metasurface sensor in Embodiment 1 of the present invention.

[0044] Figure 1 and Figure 2 The reference numerals in the figures are as follows: 1. Substrate; 2. Graphene film; 3. Adapter layer; 4. Symmetrical square open ring; 41. First connecting arm; 42. Second connecting arm; 43. Third connecting arm; 44. Opening.

[0045] Figure 3 Figure 2 shows the transmittance spectrum of the present invention; wherein, (a) in the figure is the transmittance spectrum of the unmodified metasurface sensor and the metasurface sensor modified only with graphene; and (b) in the figure is the THz response simulated by simulation software at different graphene Fermi levels.

[0046] Figure 4 This is the transmittance spectrum in Example 3 of the present invention; wherein, (a) in the figure is the transmittance spectrum for detecting chlorpyrifos solution with a concentration of 0.1 ppm to 1000 ppm; and (b) in the figure is the specific value of resonance transmittance and frequency shift, as well as the linear fit with the concentration of chlorpyrifos solution.

[0047] Figure 5 Transmittance spectra in Example 4 of the present invention; wherein, (a) in the figure is the detection result of different concentrations of chlorpyrifos solution by the metasurface sensor without graphene modification; and (b) in the figure is the detection result of different concentrations of chlorpyrifos solution by the metasurface sensor with only graphene modification.

[0048] Figure 6 The transmittance spectrum is shown in Example 3 of the present invention; wherein, (a) in the figure is the transmittance change for detecting different pesticides with concentrations of 0.1 ppm to 1000 ppm; and (b) in the figure is the frequency shift change for detecting different pesticides with concentrations of 0.1 ppm to 1000 ppm. Detailed Implementation

[0049] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0050] Example 1

[0051] This embodiment provides a structure and fabrication method of a graphene terahertz metasurface sensor, including the following scheme:

[0052] The structural diagram of the metasurface sensor is shown below. Figures 1-2 As shown, Figure 1 This is a schematic diagram of the three-dimensional structure of a graphene terahertz metasurface sensor. Figure 2 This is a schematic diagram of the structure of the substrate 1 and metasurface layer of the graphene terahertz metasurface sensor. The graphene terahertz metasurface sensor includes the substrate 1, the metasurface layer, the graphene film 2, and the aptamer layer 3.

[0053] In this embodiment, substrate 1 is polyimide (Pi), and the thickness of the Pi substrate is 50 μm. The metasurface layer is disposed horizontally on the upper surface of substrate 1. The horizontal direction of substrate 1 can be divided into the X-axis and Y-axis, as detailed below. Figure 1 As shown, the metasurface layer in this embodiment includes a plurality of symmetrically arranged square open rings 4. Each symmetrically arranged square open ring 4 includes a first connecting arm 41, a second connecting arm 42, and a third connecting arm 43. The first connecting arm 41 and the third connecting arm 43 are mirror-symmetrically arranged. The second connecting arm 42 is located between the first connecting arm 41 and the third connecting arm 43 and is the axis of symmetry between them. Openings 44 are formed between the first connecting arm 41 and the second connecting arm 42, and between the third connecting arm 43 and the second connecting arm 42. In this embodiment, the first connecting arm 41, the second connecting arm 42, and the third connecting arm 43 are all metal wires. Specifically, the metasurface layer in this embodiment includes a plurality of repeating unit structures. Figure 1This diagram illustrates two repeating unit structures. Each unit structure consists of multiple metal lines forming a symmetrical square open ring 4. The pattern is formed on a 200 nm thick gold film using laser direct writing technology and attached to the upper surface of the polyimide substrate 1. All metal lines (first connecting arm 41, second connecting arm 42, and third connecting arm 43) have the same longitudinal length along the Y-axis, which is 70 μm. The left and right "L"-shaped metal lines (first connecting arm 41 and third connecting arm 43) are mirror-symmetrical, with a lateral length of 32 μm along the X-axis. The middle "T"-shaped metal line (second connecting arm 42) has a lateral length of 58 μm along the X-axis. The unit structure has the same period along both the X and Y axes, which is 80 μm.

[0054] like Figure 1 As shown, a graphene film 2 is further modified on the metasurface layer, and an aptamer layer 3 is modified on the graphene film 2. The aptamer layer 3 includes a nucleic acid aptamer for the pesticide to be detected (such as chlorpyrifos). In this embodiment, the aptamer layer 3 is a nucleic acid aptamer for chlorpyrifos. The sequence of the nucleic acid aptamer for chlorpyrifos in this embodiment is: 5'-CCTGCCACGCTCCGCAAGCTTAGGGTTACGCCTGCAGCGATTCTTGATCGCGCTGCTGGTAATCCTTCTTTAAGCTGGCACCCGCATCGT-3', and the 5' of the nucleic acid aptamer for chlorpyrifos is modified with -NH2. This invention modifies the metasurface layer with a graphene film 2 to achieve the enrichment of pesticide molecules containing benzene rings; and further modifies the graphene layer 2 with a pesticide aptamer layer 3 such as chlorpyrifos to enhance the recognition ability of chlorpyrifos molecules, thereby achieving specific detection of chlorpyrifos.

[0055] A method for fabricating a graphene terahertz metasurface sensor includes the following steps:

[0056] (1) Preparation of the metasurface layer: The polyimide film was cut to a size suitable for the substrate (e.g., 1cm * 1cm) and then placed in acetone and isopropanol in sequence, and ultrasonically cleaned for 10 minutes each to remove organic contaminants. The residual solvent was thoroughly rinsed with deionized water and the surface was dried with high-purity nitrogen. Then, the treated substrate was placed in a magnetron sputtering instrument for short-term argon ion bombardment to further clean the surface. A 200 μm thick metasurface layer was formed by sputtering on a high-purity gold target using DC magnetron sputtering. A uniform and dense gold film of nm is formed. A layer of positive photoresist is spin-coated onto the surface of the gold film. A laser beam selectively scans and exposes the photoresist according to a preset pattern (i.e., a symmetrical square open ring 4). The photoresist in the laser-exposed area is dissolved, exposing the underlying gold film. The photoresist in the unexposed area is retained, forming a protective layer. The developed substrate is immersed in a gold etching solution. The etching solution etches the gold film in the areas not protected by the photoresist (i.e., the patterned area), while the areas protected by the photoresist remain intact. Finally, the etched substrate is immersed in an acetone solution and ultrasonically cleaned for 5-10 minutes to completely remove the residual photoresist mask, forming a metasurface layer on the polyimide film.

[0057] (2) Preparation of graphene film: release monolayer graphene into deionized water, keep it in a relaxed floating state, and let it stand for 2 h to avoid the shock of deionized water; use a clean metasurface layer to pick up the graphene floating on the water surface, and ensure that the graphene can be flatly attached to the central area of ​​the metasurface layer; place the metasurface layer after transferring graphene vertically to drain the bottom water, let it stand at room temperature for 30 min, and then heat it in an oven for 20 min to cure it at a curing temperature of 70℃ to obtain graphene-metasurface chip; immerse the cooled graphene-metasurface chip in acetone solution for 15 min to remove the polymethyl methacrylate (PMMA) on the surface of the graphene, and form a graphene film on the metasurface layer. PMMA is a commonly used support layer in the CVD graphene transfer process. Because graphene itself is too thin, it is easy to break during direct transfer, so PMMA is needed as a protection. The monolayer graphene purchased from the manufacturer in this invention has PMMA residue on its surface. Therefore, after transferring the graphene to the metasurface, it is soaked in acetone to avoid PMMA residue.

[0058] (3) Preparation of the aptamer layer: The clean metasurface layer with graphene film was immersed in TEOA buffer containing 5'-NH2 modified chlorpyrifos aptamer (approximately 1 μM-10 μM) and incubated overnight (12-16 hours) at 4°C. The activated NHS ester reacted with the -NH2 group at the end of the chlorpyrifos aptamer to form a stable valproic acid bond, thereby immobilizing the aptamer on the graphene film to obtain a graphene terahertz metasurface sensor. Then, the graphene terahertz metasurface sensor was removed and washed with PBS containing 0.1% Tween-20 to remove the physically absorbed chlorpyrifos aptamer. Finally, it was incubated in 1% BSA solution for 1 hour to block the unoccupied active ester sites on the graphene surface and reduce nonspecific absorption.

[0059] The basic working principle of this device is as follows: The graphene terahertz metasurface sensor of this invention is composed of a symmetrical metal square open ring. When the polarization direction of the incident terahertz wave is X, a strong resonance can be excited, and a clear resonance peak can be observed near 0.78 THz (when no sample is added). When a sample is added to the graphene terahertz metasurface sensor, the resonance peak changes. Moreover, the change of the resonance peak is different depending on the concentration of the sample. Therefore, the concentration of pesticide can be characterized by the change in the intensity and frequency shift of the resonance peak.

[0060] like Figure 1 As shown, compared to existing technologies, this invention further modifies the metasurface sensor with a graphene film, which can bind to pesticides such as chlorpyrifos molecules through π-π stacking interactions, providing the metasurface with the ability to accumulate chlorpyrifos. After chlorpyrifos molecules are accumulated, the graphene, through changes in its Fermi level, can significantly modulate the interaction between THz waves and the metasurface, thereby further improving the detection sensitivity. Furthermore, pesticide aptamers are modified onto the graphene film. These chlorpyrifos aptamers specifically bind to chlorpyrifos molecules, while other substances do not possess this specific binding ability and therefore cannot be detected by the metasurface sensor. Therefore, the dual modification of the graphene film and the chlorpyrifos aptamer can significantly improve the sensing sensitivity and accuracy of the metasurface sensor for chlorpyrifos.

[0061] Example 2

[0062] This embodiment provides an unmodified metasurface sensor (i.e., the graphene and aptamer in unmodified Example 1) and a metasurface sensor modified only with graphene (i.e., the aptamer in unmodified Example 1) and their transmittance spectra, and simulates the THz response at different graphene Fermi levels.

[0063] The preparation methods for the unmodified metasurface sensor and the graphene-modified metasurface sensor are the same as in Example 1, except that: the unmodified metasurface sensor is obtained by not modifying the graphene and aptamer on the metasurface layer; and the graphene-modified metasurface sensor is obtained by not modifying the aptamer on the metasurface layer.

[0064] like Figure 3 Figure (a) shows the transmittance spectra of the unmodified metasurface sensor and the graphene-modified metasurface sensor (without the sample). It can be seen that under X-polarized THz excitation, the unmodified metasurface sensor exhibits a significant resonance at 0.78 THz. When graphene is added above the metasurface, the transmittance of the graphene-modified metasurface sensor decreases significantly, and the resonance peak weakens and redshifts to 0.75 THz. This indicates that the introduction of graphene significantly weakens the resonance peak intensity of the metasurface, and also confirms that monolayer graphene can effectively modulate the interaction between terahertz waves and the metasurface.

[0065] To further investigate the interaction between graphene and metasurfaces, this embodiment simulates the THz response at different Fermi levels of graphene using simulation software. The graphene modeling feature of the FDTD simulation software was employed, and different transmission spectra were obtained by changing the Fermi levels of the material parameters. The simulation results are as follows: Figure 3 As shown in (b) of the figure. The results indicate that the increase in the Fermi level enhances the photoconductivity of graphene, leading to a decrease in overall transmittance, especially with more significant signal attenuation at the resonance peak position, accompanied by a blue shift of the resonance peak. Therefore, the graphene-modified metasurface can produce a more significant response to changes in pesticide molecule concentration.

[0066] Example 3

[0067] This embodiment provides the application of the graphene terahertz metasurface sensor from Embodiment 1 in the detection of chlorpyrifos, including the following steps:

[0068] (1) Preparation of chlorpyrifos acetone solution: First, prepare 100 mL of a 1000 ppm (i.e., 1000 mg / L) solution. Using an analytical balance, accurately weigh approximately 102.04 mg (98% purity of the original drug) of chlorpyrifos standard into a small beaker. Dissolve it thoroughly in a small amount of acetone and transfer the entire solution to a 100 mL volumetric flask. Rinse the beaker several times with acetone to ensure complete transfer. Dilute to the 100 mL mark with acetone, tighten the cap, and mix thoroughly by inverting. Then, use a stepwise dilution method to prepare 100 ppm, 10 ppm, 1 ppm, and 0.1 ppm chlorpyrifos acetone solutions from the 1000 ppm stock solution.

[0069] (2) The graphene terahertz metasurface sensor from Example 1 was immersed in a prepared chlorpyrifos-acetone solution and allowed to react for 20 minutes. Afterward, it was removed, its surface was slowly rinsed with deionized water, and then placed in a drying oven at 60°C for approximately 10 minutes. The dried graphene terahertz metasurface sensor was placed in a transmission THz time-domain spectroscopy system, using a frequency range of 0.1 THz to 1.5 THz, and the polarization direction of the incident THz wave was controlled to be along the X-axis of the metasurface layer (i.e.,...). Figure 1 The X-axis direction can be used for detection. By detecting the emitted wave signal, the transmission spectrum of the graphene terahertz metasurface sensor in Example 1 can be obtained when no sample is added and after the sample is added, and the change in transmittance or frequency shift can be calculated.

[0070] The change in transmittance can be defined as: (Formula 1);

[0071] in, The change in transmittance T sample This indicates the transmittance obtained after adding the sample to the graphene terahertz metasurface sensor. T ref This represents the transmittance of the graphene terahertz metasurface sensor on its own (i.e., without any sample added).

[0072] The frequency shift change can be defined as: (Formula 2);

[0073] in, This is the frequency shift change. f sample To indicate the frequency position of the resonance peak after adding the test solution to the graphene terahertz metasurface sensor. This indicates the frequency position of the resonance peak when the graphene terahertz metasurface sensor is in its original state (i.e., without any added sample).

[0074] Figure 4 This is the transmittance spectrum for detecting chlorpyrifos solutions with concentrations ranging from 0.1 ppm to 1000 ppm. Figure 4As shown in the transmittance spectrum in (a), the transmittance of the resonance peak gradually decreased from 16.7 dB to 14.5 dB as the concentration of the chlorpyrifos solution increased from 0 ppm to 1000 ppm. Overall, the transmittance spectra of samples with different concentrations were clearly distinguishable from each other, demonstrating the sensitivity of the metasurface sensor to changes in chlorpyrifos concentration. According to Equation 1 in Example 2, the transmittance of the resonance peak changed by 13% when the chlorpyrifos concentration increased to 1000 ppm. In addition to the change in transmittance, the resonance peak also underwent a significant blue shift with increasing chlorpyrifos concentration, reaching a maximum shift of 38 GHz at the highest chlorpyrifos concentration. The experimental results are very consistent with the simulation results of Example 2, which means that the accumulation of chlorpyrifos on the graphene film alters its Fermi level, thereby modulating the THz response of the metasurface sensor.

[0075] Figure 4 Figure (b) shows the specific values ​​of resonance transmittance and frequency shift, and their linear fit with concentration changes. The results indicate a strong linear correlation between the changes in transmittance and frequency shift and the concentration of chlorpyrifos solution, with linear relationships of y1 = (-1.34 ± 0.351) + (2.86 ± 0.105)*x1 (Equation 3) and y2 = (-5.7 ± 2.562) + (8.3 ± 0.772)*x2 (Equation 4), where y1 is the change in transmittance, y2 is the change in frequency shift, and x1 and x2 are both the concentrations of chlorpyrifos solution. R 2 The values ​​are 0.983 and 0.966 respectively. Therefore, the detection sensitivities of this sensor are: the sensitivity corresponding to the change in transmittance. S T = ΔT / Δ(log10 C) = 0.55 dB / decade, the sensitivity corresponding to the frequency shift change. S f = Δ f / Δ(log10 C) = 9.5 GHz / decade, where C is the concentration of the sample solution, and "decade" in the sensitivity unit indicates a 10-fold change in concentration (i.e., a logarithmic change in concentration of 1 unit), demonstrating that the sensor has satisfactory pesticide detection capabilities.

[0076] (3) Prepare a chlorpyrifos acetone solution by preparing a chlorpyrifos sample of unknown concentration according to the method in step (1). Then, detect the chlorpyrifos solution using the graphene terahertz metasurface sensor in Example 1 according to the method in step (2). Calculate the change in transmittance according to Formula 1 or the change in frequency shift according to Formula 2. Then, substitute the change in transmittance into Formula 3 or the change in frequency shift into Formula 4 to calculate the concentration of the chlorpyrifos sample.

[0077] (4) Specific detection: Chlorpyrifos, dichlorvos, chlorpyrifos, imidacloprid, and methomyl were prepared into acetone solutions with the same concentration gradient according to the method in step (1). Then, these solutions were detected using the graphene terahertz metasurface sensor in Example 1 according to step (2). The changes in transmittance and resonant frequency shift of different samples at different concentrations were obtained. The results are as follows: Figure 6 As shown, by Figure 6 As can be seen, the graphene terahertz metasurface sensor in Example 1 has the highest transmittance and frequency shift response for chlorpyrifos, demonstrating the sensor's specific detection capability.

[0078] Example 4

[0079] This embodiment provides the difference in detecting different concentrations of chlorpyrifos using an unmodified metasurface sensor (same as in Embodiment 2) and a graphene-modified metasurface sensor (same as in Embodiment 2), including the following steps:

[0080] (1) Prepare chlorpyrifos solution with a concentration of 0 ppm to 1000 ppm according to the method in Example 3;

[0081] (2) The chlorpyrifos solution was detected by a metasurface sensor modified only with graphene and an unmodified metasurface sensor (unmodified graphene and aptamer) according to the method of Example 3.

[0082] Figure 5 The detection results of chlorpyrifos are shown using a metasurface sensor without graphene modification and a metasurface sensor modified only with graphene. From... Figure 5 As can be observed in (a), the changes in transmittance and resonance shift are very small with variations in chlorpyrifos concentration, making it difficult to distinguish between these curves. Especially at lower concentrations (0.1 ppm and 1 ppm), the curves almost overlap, further complicating the differentiation of these samples. In contrast, Figure 5 (b) shows the detection results for the graphene-modified metasurface alone, which exhibits significantly enhanced performance compared to the unmodified metasurface. The changes in transmittance and frequency shift response clearly distinguish different concentrations of chlorpyrifos solution. Therefore, these experimental results further confirm that the π-π stacking interaction between graphene and chlorpyrifos molecules greatly enhances the metasurface's response to pesticides. Simultaneously, with... Figure 4 The comparison also proved that the metasurface sensor modified with graphene film and chlorpyrifos aptamer exhibited the best performance: its transmittance change for chlorpyrifos samples with the same concentration of 1000 ppm was more than 6 times that of the unmodified metasurface and more than 1.6 times that of the graphene-modified metasurface alone, while its frequency shift response was more than 3 times and 1.65 times that of the unmodified metasurface and the graphene-modified metasurface alone, respectively.

[0083] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A graphene terahertz metasurface sensor, characterized in that, Comprise: a substrate (1); a metasurface layer disposed on the substrate (1), the metasurface layer comprising a plurality of symmetric square open rings (4) arranged in an array along the horizontal direction of the substrate (1), the symmetric square open ring (4) comprising a first connecting arm (41), a second connecting arm (42) and a third connecting arm (43), wherein the first connecting arm (41) and the third connecting arm (43) are mirror symmetrically arranged on both sides of the second connecting arm (42) with the second connecting arm (42) as the axis of symmetry, and an opening (44) is formed between the first connecting arm (41) and the second connecting arm (42) and between the third connecting arm (43) and the second connecting arm (42); a graphene film (2) disposed on the metasurface layer; an aptamer layer (3) disposed on the graphene film (2); the first connecting arm (41) is L-shaped, the third connecting arm (43) is mirror symmetrically structured with the L-shaped first connecting arm (41), the second connecting arm (42) is T-shaped, and two openings (44) are formed between the two ends of the first connecting arm (41) and the two ends of the second connecting arm (42), and two openings (44) are formed between the two ends of the third connecting arm (43) and the two ends of the second connecting arm (42); the transverse length of the symmetric square open ring (4) along the horizontal direction of the substrate (1) is equal to the longitudinal length, both of which are 65μm-75μm; the distance between adjacent symmetric square open rings (4) is 9μm-11μm; the width of the opening (44) is 3μm; the longitudinal length of the first connecting arm (41) and the third connecting arm (43) along the horizontal direction of the substrate (1) is equal to the longitudinal length of the second connecting arm (42) along the horizontal direction of the substrate (1), both of which are 65μm-75μm; the transverse length of the first connecting arm (41) and the third connecting arm (43) along the horizontal direction of the substrate (1) is 30μm-35μm; the transverse length of the second connecting arm (42) along the horizontal direction of the substrate (1) is 55μm-60μm.

2. The graphene terahertz metasurface sensor according to claim 1, wherein: the substrate (1) is a polyimide substrate with a thickness of 30μm-50μm; the symmetric square open ring (4) is prepared by laser direct writing on a gold film with a thickness of 200 nm.

3. The graphene terahertz metasurface sensor of claim 1, wherein, The graphene film (2) is disposed on the metasurface layer by the following method: Release single-layer graphene into deionized water, keep the single-layer graphene in a relaxed and floating state, and stand for 1h-3h; Use a clean metasurface layer to catch the single-layer graphene floating on the water surface, and ensure that the single-layer graphene can be flatly attached to the central area of the metasurface layer; vertically place the metasurface layer with graphene attached to drain the bottom moisture, stand at room temperature for 20min-40min, then heat and solidify in an oven for 15min-25min, the solidification temperature is 65℃-70℃, and a graphene-metasurface chip is obtained; The cooled graphene-super surface chip is immersed in acetone solution for 10-20 min.

4. The graphene terahertz metasurface sensor of claim 1, wherein, The aptamer layer (3) comprises nucleic acid aptamer of the pesticide to be detected, and the aptamer layer (3) is arranged on the graphene film (2) by the following method: The graphene-modified super surface layer is immersed in a TEOA buffer solution containing 5'-NH2 modified aptamer, incubated at 3-5°C overnight, the activated NHS ester reacts with the -NH2 group at the end of the aptamer to form a stable valproic acid bond, so as to fix the aptamer on the graphene, and a graphene and aptamer modified super surface layer is obtained. The graphene and aptamer modified super surface layer is taken out and washed with PBS containing 0.05%-0.15% Tween-20, and then incubated in a 0.5%-1.5% BSA solution for 0.5-1 hours.

5. The graphene terahertz super surface sensor according to any one of claims 1-4 is applied to pesticide residue detection.

6. The method for detecting pesticide residues using the graphene terahertz metasurface sensor according to any one of claims 1-4, characterized in that, The method comprises the following steps: The graphene terahertz super surface sensor is immersed in a to-be-tested solution containing target pesticide molecules, taken out after sufficient reaction for 10-30 min, slowly washed with deionized water, and then placed in a drying box and dried at a temperature of 50-60°C. The dried graphene terahertz metasurface sensor was placed in a transmission THz time-domain spectroscopy system. The polarization direction of the incident THz wave was controlled to be along the X-axis of the graphene terahertz metasurface sensor. The transmission spectrum of the sample was obtained, and the change in transmittance was calculated. Or frequency shift change; The change in transmittance The change in transmittance and the concentration of the pesticide are substituted into a standard curve, or the change in frequency shift The change in frequency shift and the concentration of the pesticide are substituted into a standard curve, and the concentration of the pesticide in the solution to be measured is calculated.

7. The method of claim 6, wherein, The transmittance change amount , T sample The transmittance obtained after adding the to-be-tested solution on the graphene terahertz metasurface sensor, T ref Indicates the transmittance when no to-be-tested solution is added on the graphene terahertz metasurface sensor. The frequency shift change amount , f sample The frequency position of the resonance peak after adding the to-be-measured solution on the graphene terahertz metasurface sensor, The frequency position of the resonance peak when no to-be-measured solution is added on the graphene terahertz metasurface sensor.

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