A mid-infrared dual-mode dielectric dimer metasurface chiral molecular sensor

Abstract

A mid-infrared dual-mode dielectric dimer metasurface chiral molecular sensor comprises a calcium fluoride substrate of low refractive index medium, on which is arrayed periodic resonator units, each composed of two symmetrically arranged resonators of high refractive index medium, with a slit between the two resonators, and both resonators having hollowed-out regions in the upper and lower regions. The molecular sensor has two excitation modes: circularly polarized light and linearly polarized light, which can respectively achieve mid-infrared vibrational circular dichroism and optical rotation dispersion effect enhancement, thereby achieving ultrasensitive sensing detection of chiral molecules. The present invention has a symmetrical structure and a simple design, can achieve extremely large electric field, magnetic field, and chiral light field enhancement, and has important application prospects in mid-infrared ultrasensitive chiral sensing detection.

Description

Technical Field

[0001] The present invention relates to the field of optical sensors, and in particular to a dual-mode dielectric dimer metasurface chiral molecule sensor operating in a mid-infrared frequency band. Background Art

[0002] Chirality (C) refers to the geometric property of a substance characterized by the inability to superimpose on its mirror image through translation and rotation. The mirror image of a chiral structure is an enantiomer, which is commonly found in various macro / micro structures and constitutes the basic components of life, such as nucleic acids, enzymes and alkaloids. Although the chemical structure of enantiomers is identical, their chemical behavior is often significantly different. Changes in the chirality of chiral biomolecules may have inactivating or toxic effects on cells, leading to many diseases such as brachymelia, Parkinson's disease, Alzheimer's disease and Huntington's disease. Therefore, the sensitive detection of chiral substances has very important applications in pharmacology, toxicology and pharmacokinetics.

[0003] In recent years, a wide variety of novel complex materials have been designed with the potential for practical applications in enantiomer detection. It has been discovered that, in many cases, the electric field E and electric displacement vector D (as well as the magnetic field B and induced magnetic field H) of chiral materials are not parallel to each other. The Pasteur parameter κ can be used to describe the chiral response of a medium and can also be used to couple the electric and magnetic fields in mutually bi-anisotropic media. The electromagnetic interaction of chiral materials produces two effects: circular dichroism (CD) and optical rotation dispersion (ORD). CD displays differences in the absorption of left-handed (LCP) and right-handed (RCP) circularly polarized light. ORD can cause a rotation of the polarization direction of linearly polarized (LP) light. Consequently, these chiral reactions have become a key and versatile method for enantiomer differentiation. Over the past few decades, CD spectroscopy has developed into an effective tool for detecting molecular chirality. However, due to the small region of electromagnetic interaction, the chiral reactions of naturally occurring chiral materials are relatively weak, and ORD is even less well-studied.

[0004] Recent developments in metasurfaces have provided a high-performance platform for detecting highly sensitive chiral molecules. Studies have found that metasurfaces with strong superchiral fields can greatly enhance the weak CD signals of chiral molecules. When illuminated, metasurfaces can generate strong resonances, achieving an enhanced electromagnetic field, thereby improving sensing performance. Depending on the materials used, metasurface sensors can be divided into plasmonic chiral molecule sensors and all-dielectric chiral molecule sensors. Plasmonic chiral molecule sensors introduce a non-uniform superchiral field, and the chiral enhancement of opposite signs also reduces the average C enhancement (CE). In addition, most plasmonic chiral molecule sensors generate intrinsic background chiral optical signals, which reduces the reliability of detecting weak signals of chiral molecules. In contrast, all-dielectric chiral molecule sensors make up for the shortcomings of the plasmonic chiral molecule sensor structure and can generate strong electromagnetic resonance through Mie resonance, which makes it a research focus at this stage.

[0005] However, existing research has mostly focused on the visible and ultraviolet regions, leaving out the mid-infrared. Furthermore, the C enhancement of existing structures remains low, as they are all focused on a single illumination mode (CPL or LP). Therefore, there is an urgent need to design a mid-infrared chiral metasurface with significant CE under both CPL and LP incidence. Summary of the Invention

[0006] The main purpose of the present invention is to overcome the above-mentioned defects in the prior art and propose a mid-infrared dual-mode dielectric dimer metasurface chiral molecule sensor with two excitation modes: circularly polarized light (CPL) and linearly polarized light (LP), which can respectively achieve mid-infrared vibrational circular dichroism and optical rotation dispersion effect enhancement, thereby realizing ultra-sensitive sensing detection of chiral molecules.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A mid-infrared dual-mode dielectric dimer metasurface chiral molecular sensor comprises a calcium fluoride (CaF2) substrate of a low refractive index medium, on which periodic resonator units are arrayed. The periodic resonator units are composed of two symmetrically arranged resonators of a high refractive index medium, with a slit between the two resonators, and both resonators have hollow regions in the upper and lower regions. The molecular sensor has an extremely strong chiral light field enhancement effect, and can achieve enhanced mid-infrared vibrational circular dichroism and optical rotation dispersion effects in both circularly polarized light (CPL) and linearly polarized light (LP) excitation modes, respectively, thereby realizing ultrasensitive sensing and detection of chiral molecules.

[0009] The resonator is rectangular, circular or elliptical, and the hollow area is formed by cutting upper and lower corners of the resonator.

[0010] The resonator is arranged in a T-shape, and the upper and lower areas surrounded by the two resonators arranged relative to each other constitute the hollow area.

[0011] The resonator is a germanium dimer resonator, and may also be a trimer dielectric resonator or a tetramer dielectric resonator.

[0012] The distance a between the two resonators is 0.7-0.9 μm.

[0013] The width b of the hollow area is 0.5 to 0.6 μm.

[0014] The length c of the resonator is 3 to 3.2 μm.

[0015] The distance d of the slits is 0.2-0.3 μm.

[0016] The height h of the resonator is 0.9-1.1 μm.

[0017] The surfaces of the calcium fluoride substrate and the resonator are both provided with a chiral molecule layer to be detected with a thickness of 10 to 200 nm. The Pasteur parameter is set to κ=0+0.001i, and the dielectric constant is set to n=1.46-0.01i, wherein i represents an imaginary unit.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0019] (1) The present invention arranges an array of periodic resonator units on a calcium fluoride substrate. Each resonator unit has two upper and lower rectangular cut corners, with a hollow area formed in the middle of the cut corners, and a gap is formed between the two resonators. When left-handed (LCP) and right-handed (RCP) circularly polarized light is incident, the electric and magnetic fields are greatly enhanced through Mie resonance, and electric dipole and magnetic dipole resonances are generated, resulting in a strong chiral light field hotspot in the center area between the two resonators.

[0020] The chiral enhancement factor of the present invention is high. When there are no chiral molecules to be detected, the maximum chiral enhancement factor can reach more than 7900, and the average chiral enhancement factor in a space with a thickness of 50 nm on its upper surface can reach more than 240. When there are 50 nm chiral molecules to be detected, the maximum chiral enhancement factor still reaches more than 2000, and the average chiral enhancement factor reaches more than 160, which is much greater than that of traditional structures, greatly improving the sensitivity of chiral sensing.

[0021] (2) The structure of the present invention can also be used to distinguish chiral molecules by using optical rotation dispersion (ORD). ORD can cause the polarization direction of the linearly polarized (LP) wave to rotate. When the incident light is set to linearly polarized light with a polarization angle of 45 degrees, when there is no chiral molecule to be detected, the maximum chirality enhancement factor can reach more than 9000, and the average chirality enhancement factor in the space with a thickness of 50nm on its upper surface can reach more than 440; when there is a 50nm chiral molecule to be detected, the maximum chirality enhancement factor still reaches more than 1500, and the average chirality enhancement factor reaches more than 100.

[0022] (3) The present invention can work in two excitation modes: circularly polarized light (CPL) and linearly polarized light (LP), and has high chiral sensing sensitivity in both modes.

[0023] (4) The periodic unit structure of the present invention is flexible in design. The cut corners of the two resonators can be set to square or circular, etc., and the positions of the two resonators can also be interchanged to achieve extremely high chiral light field enhancement.

[0024] (5) The present invention can be used for mid-infrared sensing and detection of various chiral biomolecules and drugs, and can achieve the treatment of various diseases, such as phocomelia, Parkinson's disease, Alzheimer's disease and Huntington's disease, filling the gap in chiral molecular sensors in the mid-infrared frequency band.

[0025] (6) The unit structure of the present invention is simple in design and consists of only two rectangular blocks with two cut corners removed, which is convenient for processing and manufacturing. In addition, the symmetrical structure does not introduce background noise and can improve detection sensitivity.

[0026] (7) The present invention can be applied in a wide range of frequency bands. By scaling, the operating frequency of the device can be shifted, thereby being applied to ultra-sensitive chiral sensing detection in the visible light, ultraviolet light and terahertz bands. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the structure of the dielectric dimer metasurface chiral molecular sensor of the present invention;

[0028] Figure 2 Schematic diagram of the unit structure of the dielectric dimer metasurface chiral molecular sensor of the present invention;

[0029] Figure 3 is the maximum chiral enhancement factor of the dielectric dimer metasurface chiral molecular sensor of the present invention under RCP and LP incidence;

[0030] Figure 4 is the average chiral enhancement factor of the dielectric dimer metasurface chiral molecular sensor of the present invention under RCP and LP incidence;

[0031] Figure 5 Schematic diagram of the structure of the dielectric dimer metasurface chiral molecule sensor of the present invention when chiral molecules are added;

[0032] Figure 6 The maximum chirality enhancement factor of the dielectric dimer metasurface chiral molecule sensor of the present invention at RCP and LP incidence when chiral molecules are added;

[0033] Figure 7 It is the average chirality enhancement factor of the dielectric dimer metasurface chiral molecule sensor of the present invention when chiral molecules are added under RCP and LP incidence. DETAILED DESCRIPTION

[0034] 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 with reference to the accompanying drawings and embodiments.

[0035] In the present invention, the terms "first", "second", "third", etc. are only used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. In the description, the directions or positional relationships indicated by "upper", "lower", "left", "right", "front", and "back" are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and are not intended to indicate or imply that the device referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention. For those skilled in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0036] Example 1

[0037] See also Figure 1 、 Figure 2 A mid-infrared dual-mode dielectric dimer metasurface chiral molecule sensor includes a calcium fluoride substrate 1 and a plurality of periodic resonator units 4 arranged in an array on the substrate. The calcium fluoride substrate 1 has a dielectric constant of 1.39 and a thickness of 2.35 μm. The periodic resonator unit 4 uses germanium as the dielectric medium with a dielectric constant of 4.01. The periodic resonator unit 4 includes a dimer resonator 3, which forms two hollow regions 2 at the upper and lower parts of the periodic resonator unit, and a slit 5 is formed between the two resonators 3. When RCP / LCP is incident, Mie resonance occurs in the slit region, triggering electric and magnetic dipole resonances and generating significant electric and magnetic field enhancements. This generates a strong chiral hotspot in the central slit region, enabling the detection of chiral molecules.

[0038] In practical applications, the size of the calcium fluoride substrate 1 corresponding to a periodic resonator unit 4 is selected as a side length p = 4.581 μm. Taking the resonator 3 as an example, a germanium nanoresonator is used as the example, the distance a between the two resonators 3 is 0.7 to 0.9 μm, preferably 0.79 μm. The width b of the hollow area 2 is 0.5 to 0.6 μm, preferably 0.59 μm. The length c of the resonator 3 is 3 to 3.2 μm, preferably 3.1 μm. The distance d of the gap 5 is 0.2 to 0.3 μm, preferably 0.23 μm. The height h of the resonator 3 is 0.9 to 1.1 μm, preferably 1.08 μm.

[0039] The chiral enhancement factor curve obtained by simulation analysis is as follows Figure 3 As shown in Figure 2, at 5.294 μm, the maximum chiral enhancement factor reaches over 7900 when the RCP incident light is incident, and the maximum chiral enhancement factor also reaches over 9000 when the LP incident light is incident. Figure 4 As shown in Figure 3, the average chiral enhancement factors in the 50 nm air layer above the sensor can reach over 240 and 440, respectively.

[0040] Example 2

[0041] A mid-infrared dual-mode dielectric dimer metasurface chiral molecular sensor, whose main structure is the same as that of Example 1, except that: Figure 5 As shown, it is Figure 2 On the basis of the structure shown, the surface of the calcium fluoride substrate 1 and the surface of the resonator 3 are both provided with a chiral molecule layer 6 to be detected, with a thickness of 50 nm, a Pasteur parameter κ=0+0.001i, and a dielectric constant n=1.46-0.01i.

[0042] Using the structure of this embodiment, the chiral enhancement factor curve obtained by simulation analysis is as follows: Figure 6 As shown in , the maximum chiral enhancement factors can reach over 2000 and 1500 at RCP and LP incidence, respectively. Figure 7 As shown in Figure 5, the average chiral enhancement factor in the 50 nm chiral molecular layer above the sensor can also reach above 150 and 100.

[0043] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A mid-infrared dual-mode dielectric dimer metasurface chiral molecular sensor, characterized by: The invention comprises a calcium fluoride substrate of a low refractive index medium, on which a periodic resonator unit is arrayed. The periodic resonator unit is composed of two symmetrically arranged resonators of a high refractive index medium, with a slit between the two resonators, and both resonators have hollow regions in the upper and lower regions. The molecular sensor has two excitation modes, circularly polarized light and linearly polarized light, which can respectively achieve mid-infrared vibrational circular dichroism and optical rotation dispersion effect enhancement, thereby realizing ultrasensitive sensing and detection of chiral molecules. The resonator is arranged in a T-shape, and the upper and lower areas surrounded by the two resonators arranged relative to each other constitute the hollow area; the distance a between the two resonators is 0.7-0.9 μm; the width b of the hollow area is 0.5-0.6 μm; the length c of the resonator is 3-3.2 μm; the distance d of the slit is 0.2-0.3 μm; the height h of the resonator is 0.9-1.1 μm; the calcium fluoride substrate and the resonator surface are both provided with a chiral molecule layer to be detected, with a thickness of 10-200 nm, and the Pasteur parameter is set to κ =0 + 0.001 i， The dielectric constant is set to n = 1.46 - 0.01 i ,in i Represents an imaginary unit.

2. The mid-infrared dual-mode dielectric dimer metasurface chiral molecular sensor according to claim 1, characterized in that: The resonator is rectangular, circular or elliptical, and the hollow area is formed by cutting upper and lower corners of the resonator.

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