Terahertz bielliptical all-dielectric metasurface chiral molecular sensor

Abstract

The invention discloses a terahertz bielliptical all-dielectric metasurface chiral molecular sensor, and relates to the field of optical sensors. The sensor is composed of a substrate made of a low-refractive-index medium (such as silicon dioxide or calcium fluoride) and resonator units periodically arranged above the substrate. Each resonator unit is composed of two symmetrically-arranged high-refractive-index medium (such as silicon or germanium) resonators, the two resonators are in an oval shape, and a slit area is formed between the two resonators. When circularly polarized terahertz waves are incident, the metasurface generates Mie resonance, and strong single-symbol touchable terahertz chiral light field hot spots are formed in a slit area, so that ultra-sensitive detection of chiral molecules is realized. The sensor is symmetrical and simple in structure, can realize remarkable enhancement of an electric field, a magnetic field and a chiral light field in a terahertz wave band, and has an important application prospect in terahertz ultra-sensitive chiral sensing detection.

Description

Technical Field

[0001] The present invention relates to the field of optical sensors, and in particular to a terahertz double-elliptical all-dielectric metasurface chiral molecular sensor operating in a terahertz frequency band. Background Art

[0002] Chirality is an essential property that is widely present in nature. A typical example is the human hand: the two are mirror-symmetric, but cannot be completely superimposed. At the molecular level, two non-superimposable mirror-image structures are called enantiomers. Although the left-handed and right-handed enantiomers are exactly the same in properties such as molecular weight, density, and chemical structure, their interactions with chiral cell receptors may lead to significantly different physiological or pharmacological effects. Therefore, high-sensitivity detection of chiral substances has important application value in fields such as pharmacology, toxicology, and pharmacokinetics.

[0003] Circular dichroism (CD) spectroscopy plays a key role in the detection of chiral molecules. It identifies molecular chirality by comparing the difference in the absorption spectra of left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP). However, existing optical chirality detection technologies are mainly concentrated in the ultraviolet, visible and mid-infrared bands, which limits their ability to detect the characteristic responses of certain chiral molecules (such as peptide chains, proteins, polysaccharides, alkaloids, etc.). Terahertz waves (frequency range 0.1-10 THz) have low photon energy, non-ionization, good penetration, and their frequency characteristics match the rotation and vibration modes of a variety of chiral biomolecules or molecular clusters. Therefore, they show unique advantages in the field of biosensing and have received widespread attention.

[0004] However, the chiral optical response of most chiral biomolecules in nature is extremely weak. For example, in the ultraviolet and visible light bands, the CD signal intensity of chiral molecules is about 10 -3 ~10 -6 , while in the mid-infrared and terahertz bands, the CD signal intensity is further reduced to one thousandth. This signal weakness seriously affects the signal-to-noise ratio of terahertz chiral molecule measurements. Therefore, how to effectively enhance the terahertz chiral signal of low-concentration chiral molecules to achieve high-sensitivity detection has become a key challenge in this field.

[0005] The latest development of metasurfaces provides an ideal platform for high-sensitivity chiral molecule detection. By designing specific micro-nano structures, metasurfaces can form localized superchiral hotspots, significantly enhancing the interaction between light fields and chiral molecules. According to the material properties, metasurfaces can be divided into plasmonic metasurfaces and all-dielectric metasurfaces. However, plasmonic metasurfaces usually produce non-uniform chiral fields, and the chiral enhancement effects with opposite signs will reduce the average optical chiral enhancement coefficient (C E_ave). In contrast, the all-dielectric chiral sensor effectively compensates for the defects of the plasmon structure and exhibits a higher optical chirality enhancement capability. In addition, the metasurface with chiral structure often introduces background optical chiral noise, which reduces the detection sensitivity of chiral molecules. Therefore, designing an ultra-sensitive all-dielectric metasurface sensor with a non-chiral structure has important scientific significance and broad application prospects for realizing efficient terahertz chiral molecule detection. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects in the prior art and provide a terahertz double-elliptical all-dielectric metasurface chiral molecule sensor that can realize ultra-sensitive sensing detection of chiral molecules in the terahertz band.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] A terahertz double-elliptical all-dielectric metasurface chiral molecule sensor is composed of a low-refractive index dielectric substrate and a high-refractive index dielectric resonator array. Resonator units are periodically arranged on the low-refractive index dielectric substrate to form a resonator array. Each resonator unit is composed of two high-refractive index dielectric elliptical resonators. The two high-refractive index dielectric elliptical resonators are symmetrically arranged with a slit between them for exciting Mie resonance. When a circularly polarized terahertz wave is incident, an enhanced terahertz electric field, magnetic field and a single-sign, touchable terahertz chiral light field hotspot are formed in the slit region of the resonator. The sensor can significantly enhance the circular dichroism in the terahertz band under the excitation of left-handed and right-handed circularly polarized light (LCP and RCP), thereby achieving high-sensitivity detection of chiral molecules.

[0009] The material of the low refractive index medium substrate is silicon dioxide or calcium fluoride, etc., which is used as the base of the sensor to provide stable support and optical performance; silicon dioxide is preferably used.

[0010] The resonator unit has a flexible design, and the material of each resonator can be a high refractive index material such as silicon or germanium to enhance the interaction between the terahertz wave and the resonator; preferably, silicon material is used.

[0011] The major axis, minor axis and height parameters of the two high-refractive-index dielectric elliptical resonators can be optimized according to the operating frequency; in addition to being arranged parallel to each other, the main axes of the two high-refractive-index dielectric elliptical resonators can also be set to adjust the angle between their main axes within the range of 0 to 90° to further optimize the chiral light field distribution. In addition, the shape of the elliptical resonator can be replaced with a circular or rectangular shape, and the number of resonators can also be replaced with trimer or tetramer dielectric resonators to meet different sensing needs. Under LCP and RCP excitation, terahertz Mie resonance can be achieved in the slit region between the resonators of this structure, significantly enhancing the electric and magnetic fields and generating single-sign, touchable chiral light field hotspots.

[0012] The specific size parameters of the resonator unit can be optimized according to the specific application scenario and performance requirements, specifically:

[0013] The distance a between the centers of the two resonators may be 90-110 μm.

[0014] The width b of the resonator may be 75-80 μm.

[0015] The length c of the resonator may be 225-230 μm.

[0016] The slit distance d may be 14-20 μm.

[0017] The thickness t of the substrate may be 300-310 μm.

[0018] The height h of the resonator may be 125-130 μm.

[0019] The substrate and the resonator surface are coated with a layer of chiral molecules to be detected (such as ibuprofen, glucose, lactic acid and tyrosine, etc.) with a thickness of 2 to 5 μm to achieve high-sensitivity detection of chiral molecules.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1) The present invention forms a strong Mie resonance between resonators, generating a single-sign, touchable chiral light field hotspot. When there is no chiral molecule to be measured, the maximum chiral enhancement factor (C E_max ) can reach 1800, average C E_ave When the metasurface is covered with a 3 µm layer of the chiral molecule to be tested, the Pasteur parameter of the chiral molecule is set to κ = (0.047 ± 1.5i)×10 -3 , the dielectric constant is set to ε r = 1.58 + 0.016i (where i represents the imaginary unit), C E_max Still above 1500, average C E_ave Reaching 50, it surpasses the chirality enhancement characteristics of most traditional terahertz metasurface structures and significantly improves detection sensitivity.

[0022] 2) The periodic unit structure of the present invention is flexible and diverse, and adopts different combinations and optimized designs of high-refractive-index resonator shapes (elliptical, circular or square), numbers (dimers, trimers, tetramers) and low-refractive-index substrates to further enhance the chiral light field enhancement effect.

[0023] 3) The present invention can be used to sense and detect a variety of chiral biomolecules and drugs, such as ibuprofen, glucose, lactic acid and tyrosine, filling the relative gap of all-dielectric metasurface chiral molecular sensors in the terahertz frequency band.

[0024] 4) The unit of the present invention adopts a double elliptical design, which has a simple structure and is easy to process and manufacture. In addition, due to the symmetrical structural design, no background noise is introduced, thereby further improving the accuracy and sensitivity of terahertz sensing detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of the terahertz double-elliptical all-dielectric metasurface chiral molecular sensor of the present invention;

[0026] Figure 2 This is a schematic diagram of the unit structure of the terahertz double-elliptical all-dielectric metasurface chiral molecular sensor of the present invention;

[0027] Figure 3 are the maximum chiral enhancement factor and the average chiral enhancement factor of Example 1 of the present invention;

[0028] Figure 4 are the maximum chiral enhancement factor and the average chiral enhancement factor of Example 2 of the present invention;

[0029] Figure 5 It is a schematic diagram of the terahertz double elliptical all-dielectric metasurface chiral molecular sensor of the present invention when coated with a chiral molecular layer;

[0030] Figure 6 The maximum chiral enhancement factor and the average chiral enhancement factor when the chiral molecular layer is coated in Example 1 of the present invention;

[0031] Figure 7 These are the maximum chiral enhancement factor and the average chiral enhancement factor when the chiral molecular layer is coated in Example 2 of the present invention. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0033] Example 1

[0034] This embodiment relates to a terahertz double elliptical all-dielectric metasurface chiral molecular sensor, such as Figure 1 and 2As shown, it includes a silicon dioxide substrate 1 and a plurality of periodic resonator units 2 located on the substrate and distributed in an array. The silicon dioxide substrate 1 has a dielectric constant of 3.8 and a thickness of 300 μm. The medium used in the periodic resonator unit 2 is silicon, and the dielectric constant is 11.56. The periodic resonator unit 2 includes a dimer resonator 3, and two resonators are arranged in parallel, and a slit region, i.e., a slit 4, is formed between the two. When an RCP / LCP terahertz wave is incident, the dielectric metasurface of the present invention will generate a strong Mie resonance, induce electric dipole and magnetic dipole resonance, significantly enhance the electric field and magnetic field, and generate a strong chiral light field hotspot in the central area of ​​the resonator slit, so that the detection of chiral molecules can be realized.

[0035] In practical applications, the size of the silicon dioxide substrate 1 corresponding to a periodic resonator unit 2 is selected as a side length p = 514μm, a thickness of 300-310μm, preferably 300μm. Taking the resonator 3 as an example of a silicon nanoresonator, the distance a between the centers of the two resonators 3 is 90-100μm, preferably 90μm. The width b of the resonator 3 is 75-80μm, preferably 76μm. The length c of the resonator 3 is 225-230μm, preferably 225μm. The distance d of the gap 4 is 14-20μm, preferably 14μm. The height h of the resonator 3 is 125-130μm, preferably 125μm.

[0036] When there is no chiral molecule to be measured, the chiral enhancement factor curve simulation results of the all-dielectric metasurface are as follows: Figure 3 As shown in (a), when the RCP terahertz incident at 0.497 THz, the maximum chiral enhancement factor C E_max Reach more than 1800; the average chiral enhancement factor in the 3μm air layer above the sensor can reach more than 90, such as Figure 4 As shown in (b). When the metasurface sensor is covered with a 3 μm chiral molecule layer ( Figure 5 ), whose Pasteur parameter is set to κ = (0.047 ± 1.5i)×10 -3 , the dielectric constant is set to ε r = 1.58 + 0.016i (i represents the imaginary unit), the maximum chiral enhancement factor C E_max It can still reach more than 1500, at which time the average chiral enhancement factor C E_ave It can also reach more than 50, such as Figure 6 As shown in (a) and (b) in the figure, it shows extremely high sensitivity in detecting chiral molecules.

[0037] Example 2

[0038] The structure of the terahertz double-elliptical all-dielectric metasurface chiral molecular sensor in this embodiment is basically the same as that in Embodiment 1, except that: the thickness of the silicon dioxide substrate is 500-510 μm, preferably 500 μm, the distance a between the centers of the two resonators 3 is 100-105 μm, preferably 101 μm, and the distance d of the gap 4 is 20-25 μm, preferably 23 μm.

[0039] The simulation results of the chiral enhancement factor of this embodiment are as follows Figure 4 As shown in (a) and (b) in the figure, compared with Example 1, this structure is easier to process and prepare, and can achieve a wider frequency response. When the RCP terahertz wave is incident, the maximum chiral enhancement factor C E_max Up to 270, average chiral enhancement factor C in 3μm air layer E_ave When the dielectric metasurface sensor is covered with a 3 μm chiral molecule layer, its Pasteur parameter is set to κ = (0.047 ± 1.5i)×10 -3 , the dielectric constant is set to ε r = 1.58 + 0.016i, maximum chiral enhancement factor C E_max Can reach more than 250, the average chiral enhancement factor C E_ave It can also reach 15 or more, such as Figure 7 As shown in (a) and (b), good chiral molecule detection sensitivity is shown. The sensor provided in this embodiment has the characteristics of simple structure, convenient manufacturing, excellent sensing performance, etc., and has broad application prospects in the fields of biomedicine, chemical analysis, etc.

[0040] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial changes to the present invention using this concept shall fall within the protection scope of the present invention.

Claims

1. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor, characterized in that The invention comprises a low refractive index medium substrate, on which resonator units are periodically arranged to form a resonator array, wherein each resonator unit is composed of two high refractive index medium elliptical resonators, which are symmetrically arranged with a slit between them for exciting Mie resonance; when a circularly polarized terahertz wave is incident, an enhanced terahertz electric field, a magnetic field and a single-sign, touchable terahertz chiral light field hotspot are formed in the slit region of the resonator, thereby realizing high-sensitivity detection of chiral molecules.

2. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The material of the low refractive index medium substrate is silicon dioxide or calcium fluoride, which is used as the base of the sensor to provide stable support and optical properties, and silicon dioxide is preferred.

3. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The resonator unit has a flexible design. The material of each high refractive index dielectric elliptical resonator is silicon or germanium to enhance the interaction between the terahertz wave and the resonator, preferably silicon.

4. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The major axis, minor axis and height parameters of the high refractive index dielectric elliptical resonator are optimized according to the operating frequency; the angle between the main axes of the two high refractive index dielectric elliptical resonators is adjusted within a range of 0 to 90° to optimize the chiral light field distribution.

5. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The shape of the elliptical resonator is replaced with a circular or rectangular shape, and the number of resonators is replaced with a trimer or tetramer dielectric resonator to meet different sensing requirements.

6. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The width of the resonator is 75-80 μm, the length of the resonator is 225-230 μm, and the height of the resonator is 125-130 μm.

7. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The distance between the centers of the two resonators is 90-110 μm.

8. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The distance between the slits is 14-20 μm.

9. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The thickness of the low refractive index medium substrate is 300-310 μm.

10. A terahertz double elliptical all-dielectric metasurface chiral molecular sensor as claimed in claim 1, characterized in that The low refractive index medium substrate and the resonator array surface are coated with a chiral molecule layer to be detected, with a thickness of 2 to 5 μm.

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