Graphene metasurface broadband terahertz molecular fingerprint identification sensor

Abstract

The invention discloses a graphene metasurface broadband terahertz molecular fingerprint recognition sensor, which comprises a periodic symmetric graphene double-opening square ring resonator deposited on a silicon dioxide substrate, and a continuous adjustable Quasi-BIC formant is generated by adjusting the Fermi level of graphene. According to the sensor, the sensitivity of 427 GHz / RIU and the quality factor of 15.2 are realized, and the absorption peak intensities of lactose and tyrosine molecules with the thickness of 0.1 mu m are respectively enhanced by 763 times and 548 times. The invention provides a new normal form for ultrasensitive trace biomolecule detection, and has important application value in the fields of biomedical diagnosis, food safety, drug detection and the like.

Description

Technical Field

[0001] This invention belongs to the field of terahertz sensing technology, specifically relating to a broadband terahertz molecular fingerprint recognition sensor based on a graphene metasurface. Background Art

[0002] The terahertz (THz) band possesses unique molecular fingerprint spectral characteristics, offering significant advantages for non-destructive and rapid biomolecular detection, making it a promising candidate for applications in numerous fields such as medical diagnostics, food safety monitoring, and environmental sensing. However, traditional terahertz metasurface biosensors face major challenges in achieving high sensitivity and accurate detection.

[0003] One key challenge stems from the inherent scale difference between terahertz wavelengths (30 μm–3 mm) and the size of nanoscale biomolecules, which severely limits the efficiency of light-matter interaction. Traditional terahertz absorption spectroscopy techniques typically require solid samples ranging from hundreds of milligrams to grams, thus necessitating advanced field-enhancing structures for the detection of trace analytes.

[0004] While metasurfaces overcome this limitation to some extent by generating localized electromagnetic field enhancement, traditional multi-pixel geometric multiplexing requires the fabrication of complex micro / nano antenna arrays, and angle-multiplexed metasurfaces rely on precise angular alignment. Both methods introduce extremely high system complexity and manufacturing costs. Furthermore, the material composition and structural parameters of traditional metallic / dielectric metasurfaces cannot be changed after fabrication, fundamentally limiting their spectral adaptability and hindering broadband resonant tunability in terahertz sensing systems. Summary of the Invention

[0005] The purpose of this invention is to provide a broadband terahertz molecular fingerprint sensor based on a graphene metasurface, in order to solve the problems of low sensitivity, insufficient detection accuracy, complex system, high cost and poor spectral adaptability of traditional terahertz biosensors mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A broadband terahertz molecular fingerprint sensor based on a graphene metasurface includes:

[0008] A periodically arranged symmetrical graphene double-opening square ring resonator, the resonator being deposited on a silicon dioxide (SiO2) substrate;

[0009] The period of the symmetrical double-opening square ring resonator is Px = Py = 4.5 μm; the length of the symmetrical open square ring is L = 3.4 μm, the width is W = 0.5 μm, and the opening gap is g = 0.2 μm;

[0010] The Fermi levels of the graphene structures on the left and right sides of the unit structure are E and E, respectively. F 1 and E F 2, where E F 1 is fixed at 1.0 eV, E F 2. It can be adjusted within the range of 0.26-0.72eV.

[0011] Preferably, the surface conductivity of the graphene is determined by the Kubo formula, and the in-band conductivity dominates in the terahertz frequency range.

[0012] Preferably, the broadband terahertz molecular fingerprint recognition method of the sensor includes the following steps:

[0013] Preparation steps: Prepare periodically arranged symmetrical graphene double-opening square ring resonators and deposit them on a silicon dioxide substrate;

[0014] Fermi level modulation step: The Fermi level of graphene is modulated by an electric gate, so that E F1 Fixed at 1.0 eV, E F2 By adjusting the voltage within the range of 0.26-0.72 eV, a continuously tunable Quasi-BIC resonance peak can be generated.

[0015] Molecular detection steps: The molecular sample to be tested is covered on the graphene metasurface, terahertz waves are incident, and transmission spectra are collected;

[0016] Signal processing and analysis steps: By comparing the acquired transmission spectrum with the reference transmittance through envelope analysis, the characteristic absorption spectrum of the molecule is obtained, thus realizing molecular fingerprint recognition.

[0017] Preferably, the analyte includes biomolecules such as lactose and tyrosine that have terahertz characteristic absorption lines.

[0018] Preferably, the Quasi-BIC resonance peak precisely overlaps with the characteristic absorption line of the analyte molecule, and the absorption peak intensity is significantly enhanced through envelope analysis.

[0019] Compared with the prior art, the present invention provides a broadband terahertz molecular fingerprint recognition sensor based on a graphene metasurface, which has the following advantages:

[0020] High sensitivity: This sensor achieves a sensitivity of 427 GHz / RIU and a quality factor (FOM) of 15.2, enabling it to detect trace molecules as thin as 100 nm.

[0021] Broadband tunability: By adjusting the Fermi level of graphene, a continuously tunable Quasi-BIC resonance peak was achieved in the 1.2–1.9 THz spectral range, which can cover the characteristic absorption bands of a variety of molecules.

[0022] Significant signal enhancement: Compared with traditional substrate detection methods, the absorption peak intensities for lactose and tyrosine molecules are increased by 763 times and 548 times, respectively, effectively solving the problem of weak signals that are easily drowned out by noise in traditional methods.

[0023] Simple structure and low cost: No complex micro / nano antenna arrays or precise angle alignment are required, which reduces system complexity and manufacturing costs.

[0024] High spectral adaptability: The tunable Fermi level of graphene allows it to adapt to the characteristic absorption spectra of different molecules, and it has broad application prospects. Attached Figure Description

[0025] Figure 1 Schematic diagram of a graphene symmetrical double-opening ring terahertz sensor. (a) Schematic diagram of the overall sensor layout; (b) Schematic diagram of the unit structure.

[0026] Figure 2 The effect of graphene Fermi level on resonance characteristics. (a) Fixed E F1 =1eV different E F2 (b) E F1 =1eV, E F2 Transmission spectrum at 0.8 eV. The inset shows the electric field distribution.

[0027] Figure 3 The influence of the external environment on the sensor resonance characteristics. (a) Transmission spectra under different refractive indices; (b) Transmission spectra under different analyte thicknesses; (c) Transmission spectra under different extinction coefficients (k) in different environments; (d) Relationship between resonant frequency shift and refractive index; (e) Relationship between frequency shift and thickness; (f) Amplitude variations of Dip1, Peak 2, and Dip3.

[0028] Figure 4 The influence of sensor geometry on resonance characteristics. (a) Transmittance as a function of the gap between the open rings; (b) Transmittance as a function of the width of the open rings.

[0029] Figure 5 Relationship between resonant frequency and graphene Fermi level. (a) When E F2 (a) The change in resonance when the voltage is gradually decreased from 0.72 eV to 0.26 eV in increments of 0.02 eV; (b) The relationship between the quasi-BIC resonant frequency shift and the graphene Fermi level. The geometric parameters are as follows: the period of the symmetrical open square resonator is Px = Py = 4.5 μm, the side length is L = 3.4 μm, the arm width is W = 0.5 μm, and the opening gap is g = 0.2 μm.

[0030] Figure 6Lactose molecule detection. (a) Complex refractive index of lactose molecules; (b) Changes in the transmission peak of lactose molecules coated on the metasurface when the Fermi level of graphene changes; (c) Comparison of the proposed graphene metasurface sensing method with traditional sensing methods.

[0031] Figure 7 Relationship between resonant frequency and graphene Fermi level. (a) When E F2 (a) The change in resonance when the voltage is reduced from 0.58 eV to 0.34 eV in steps of 0.02 eV; (b) The relationship between the resonant frequency and the Fermi level of the graphene. Geometric parameters are as follows: the period P of the symmetrical open-cell resonator. x =P y =10μm, side length L=8μm, arm width W=1μm, gap spacing g=0.5μm.

[0032] Figure 8 Detection of tyrosine molecules. (a) Complex refractive index of tyrosine molecules; (b) Changes in the transmission peak of tyrosine molecules coated on the metasurface when the Fermi level of graphene changes; (c) Comparison of the proposed graphene metasurface sensing method with traditional sensing methods. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] This invention provides, for example Figure 1-8 The broadband terahertz molecular fingerprint sensor based on a graphene metasurface shown includes:

[0035] A periodically arranged symmetrical graphene double-opening square ring resonator, the resonator being deposited on a silicon dioxide (SiO2) substrate;

[0036] The period of the symmetrical double-opening square ring resonator is Px = Py = 4.5 μm; the length of the symmetrical open square ring is L = 3.4 μm, the width is W = 0.5 μm, and the opening gap is g = 0.2 μm;

[0037] The Fermi levels of the graphene structures on the left and right sides of the unit structure are E and E, respectively. F1 and E F2 E F 1 is fixed at 1.0 eV, E F2 It can be adjusted within the range of 0.26-0.72 eV.

[0038] The surface conductivity of the graphene was determined by the Kubo formula, and the in-band conductivity dominated within the terahertz frequency range.

[0039] The broadband terahertz molecular fingerprint recognition method using sensors includes the following steps:

[0040] Preparation steps: Prepare periodically arranged symmetrical graphene double-opening square ring resonators and deposit them on a silicon dioxide substrate;

[0041] Fermi level modulation step: The Fermi level of graphene is modulated by an electric gate, so that E F1 Fixed at 1.0 eV, E F 2. Adjusting the voltage within the range of 0.26-0.72 eV generates a continuously tunable Quasi-BIC resonance peak;

[0042] Molecular detection steps: The molecular sample to be tested is covered on the graphene metasurface, terahertz waves are incident, and transmission spectra are collected;

[0043] Signal processing and analysis steps: By comparing the acquired transmission spectrum with the reference transmittance through envelope analysis, the characteristic absorption spectrum of the molecule is obtained, thus realizing molecular fingerprint recognition.

[0044] The molecules to be tested include biomolecules with terahertz characteristic absorption lines, such as lactose and tyrosine.

[0045] The Quasi-BIC resonance peak precisely overlaps with the characteristic absorption line of the analyte molecule, and the absorption peak intensity is significantly enhanced through envelope analysis.

[0046] The sensor is fabricated as follows:

[0047] Graphene layer preparation: Monolayer graphene is grown on a silica substrate using chemical vapor deposition (CVD). The cleaned and pretreated silica substrate is placed in a CVD reaction chamber, and reactive gases such as methane and hydrogen are introduced. Under high temperature (e.g., around 1000℃) and specific pressure conditions, carbon atoms are deposited on the substrate surface to form a continuous monolayer graphene film.

[0048] Photolithographic patterning: Electron beam lithography is used to fabricate a periodically symmetrical double-opening square ring structure on a grown graphene layer. First, an electron beam photoresist layer is spin-coated onto the graphene surface. Then, the photoresist is exposed using an electron beam exposure machine according to the designed pattern (period Px = Py = 4.5 μm, opening square ring length L = 3.4 μm, width W = 0.5 μm, opening gap g = 0.2 μm). After exposure, the photoresist undergoes development to remove unexposed areas, thus forming the desired pattern on the photoresist layer. Next, reactive ion etching (RIE) and other etching processes are used, using the photoresist pattern as a mask, to etch away unwanted graphene portions, ultimately obtaining a graphene metasurface with a periodically symmetrical double-opening square ring structure.

[0049] Electrical gate fabrication: On the prepared graphene metasurface, an electrical gate is fabricated using processes such as photolithography and metal deposition to precisely control the Fermi level of the graphene. For example, a pattern of the electrical gate is defined on both sides of the graphene structure using photolithography, and then a metal (such as gold or titanium) is deposited using methods such as electron beam evaporation or magnetron sputtering to form the electrical gate electrode. The electrode is then led out through metal wires to connect to an external power supply for Fermi level adjustment.

[0050] Detection Examples

[0051] Lactose molecular detection

[0052] Sample preparation: Lactose was dissolved in a suitable solvent and uniformly coated with a 0.1 μm thick lactose film on the prepared graphene metasurface using methods such as spin coating or drop coating. During spin coating, the spin coater speed and time were controlled to ensure uniform film thickness; during drop coating, a micropipette was used to precisely control the amount of solution added, and a uniform film was formed by the slow evaporation of the solvent.

[0053] Fermi level tuning: The prepared graphene metasurface sensor with a lactose film was connected to an external electric gate control system, and a suitable voltage was applied to adjust the Fermi level. F 1 is fixed at 1.0 eV, E F 2. Adjust to 0.8 eV. By adjusting the gate voltage, the concentration of charge carriers in graphene can be changed, thereby precisely controlling its Fermi level.

[0054] Terahertz wave incident and spectral acquisition: The sensor is placed in the terahertz spectral measurement system. A terahertz radiation source generates a y-polarized terahertz plane wave propagating along the -z axis, which is incident perpendicularly onto the sensor surface. The terahertz wave signal transmitted through the sensor is acquired by a terahertz detector and transmitted to a spectral analyzer to obtain transmission spectrum data. The spectral analyzer processes and analyzes the acquired signal to obtain transmittance information at different frequencies.

[0055] Signal Analysis and Results: The acquired transmission spectra were processed using an envelope analysis algorithm. The absorption spectra were calculated by comparing the acquired transmission spectra (T1) with the reference transmittance (T0) without the lactose film covering, using the formula A = T1 - T0. The results showed that the absorption peak intensities at the characteristic absorption frequencies of lactose (1.19 THz and 1.37 THz) were increased by 763 times compared to traditional bare substrate detection, achieving highly sensitive detection and identification of lactose molecular fingerprint characteristics.

[0056] Tyrosine molecular detection

[0057] Structural optimization and fabrication: Based on the characteristic absorption band of tyrosine molecules, the graphene metasurface structure was optimized. By adjusting the parameters of the photolithography pattern, a symmetrical open square resonator structure graphene metasurface with a period Px = Py = 10 μm, side length L = 8 μm, arm width W = 1 μm, and gap spacing g = 0.5 μm was fabricated. The fabrication process was basically the same as described above, including graphene growth, photolithographic patterning, and gate fabrication.

[0058] Sample Coverage and Fermi Level Tuning: A 0.1 μm thick tyrosine film was uniformly coated onto the optimized graphene metasurface using a method similar to that used for lactose molecule detection. Then, an electric gate control system was used to tune the E... F 1 is fixed at 1.0 eV, E F 2. The frequency is gradually adjusted within the range of 0.34-0.58 eV to achieve precise tuning of the resonant frequency, so that it covers the characteristic absorption band of tyrosine molecules.

[0059] Detection and Analysis: Similarly, in the terahertz spectroscopy measurement system, terahertz waves are perpendicularly incident on a sensor with a tyrosine thin film to acquire transmission spectra. With E... F 2. Increasing the voltage from 0.34 eV to 0.58 eV resulted in a significant change in the amplitude of the transmission resonance peak. Envelope analysis was performed on the acquired spectral data to calculate the absorption spectrum. The results showed that the absorption peak intensity at the characteristic absorption frequency of tyrosine (0.958 THz) was increased by 548 times compared to traditional detection methods, successfully achieving highly sensitive detection and recognition of tyrosine molecules.

[0060] In practical applications, the structural parameters of the graphene metasurface (such as period, side length, arm width, and gap spacing) and the Fermi level of graphene can be flexibly adjusted according to the characteristic absorption frequency range of different analyte molecules to achieve efficient and accurate detection of various biomolecules. Furthermore, this sensor can be combined with microfluidic technology to construct an integrated biomolecule detection system, enabling automated, high-throughput sample detection.

[0061] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A broadband terahertz molecular fingerprint sensor based on a graphene metasurface, characterized in that, include: A periodically arranged symmetrical graphene double-opening square ring resonator, the resonator being deposited on a silicon dioxide (SiO2) substrate; The period of the symmetrical double-opening square ring resonator is Px=Py=4.5μm; the length of the symmetrical open square ring is L=3.4μm, the width is W=0.5μm, and the opening gap is g=0.2μm. The Fermi levels of the graphene structures on the left and right sides of the unit structure are EF1 and EF2, respectively, where EF1 is fixed at 1.0 eV and EF2 can be adjusted in the range of 0.26-0.72 eV.

2. The broadband terahertz molecular fingerprint sensor based on a graphene metasurface according to claim 1, characterized in that: The surface conductivity of the graphene was determined by the Kubo formula, and the in-band conductivity dominated within the terahertz frequency range.

3. The broadband terahertz molecular fingerprint recognition method using a sensor according to claim 1 or 2, characterized in that: The following steps are involved: Preparation steps: Prepare periodically arranged symmetrical graphene double-opening square ring resonators and deposit them on a silicon dioxide substrate; Fermi level modulation steps: The Fermi level of graphene is controlled by an electric gate, so that EF1 is fixed at 1.0 eV and EF2 is adjusted in the range of 0.26-0.72 eV to generate a continuously tunable Quasi-BIC resonance peak. Molecular detection steps: The molecular sample to be tested is covered on the graphene metasurface, terahertz waves are incident, and transmission spectra are collected; Signal processing and analysis steps: By comparing the acquired transmission spectrum with the reference transmittance through envelope analysis, the characteristic absorption spectrum of the molecule is obtained, thus realizing molecular fingerprint recognition.

4. The broadband terahertz molecular fingerprinting method according to claim 3, characterized in that: The molecules to be tested include biomolecules with terahertz characteristic absorption lines, such as lactose and tyrosine.

5. The broadband terahertz molecular fingerprinting method according to claim 3, characterized in that: The Quasi-BIC resonance peak precisely overlaps with the characteristic absorption line of the analyte molecule, and the absorption peak intensity is significantly enhanced through envelope analysis.

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