A single-molecule sensor based on chiral metal nanostructure arrays

Abstract

The present invention provides a single-molecule sensor based on a chiral metal nanostructure array, comprising: a transparent substrate, a chiral metal nanostructure array arranged on the transparent substrate, wherein the chiral metal nanostructure array is composed of a plurality of Z-shaped metal nanounits arranged periodically; each Z-shaped metal nanounit is a nanostructure with chiral response and three rectangular parallelepipeds arranged at intervals. The present invention uses three metal nanorectangles of the same size to form a planar Z-shaped chiral structure with a certain gap. Under the irradiation of left-handed circularly polarized light and right-handed circularly polarized light, due to the difference in the transmission of the structure to left-handed and right-handed circularly polarized light, a CD signal is generated, and a huge electric field enhancement phenomenon is generated at the edge and gap of the metal nanorectangle. When a single molecule exists in the gap of the structure, the CD signal changes to a certain extent, thereby realizing the sensing of a single molecule. The single-molecule sensor of the present invention has high sensitivity and accuracy.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano optical technology, and in particular to a single molecule sensor based on a chiral metal nanostructure array. Background Art

[0002] Localized surface plasmon refers to the phenomenon that the free electrons on the surface of a metal nanostructure resonate with the incident light field under the action of the incident light field, thereby generating a strong local oscillation phenomenon. It exhibits the characteristics of near-field enhancement at the resonant wavelength, and can produce high-intensity electric field enhancement in some special nanostructures, such as at the tip or gap. This area of ​​electric field enhancement is called a "hotspot". The phenomenon of localized surface plasmon resonance causes novel optical properties, making metal nanostructures one of the research hotspots in the fields of biosensing and detection.

[0003] Chirality refers to the fact that an object in three-dimensional space cannot be translated or rotated to coincide with its mirror image, just like our left hand and right hand cannot coincide with each other. Chirality is a hot topic in scientific research, not only because chirality is closely related to human characteristics, but also because there are a large number of substances with typical chiral characteristics in nature, such as proteins and amino acids in biology, planetary rotation and atmospheric vortex in geography, and left-handed polarized light and right-handed polarized light in optics.

[0004] The differential absorption characteristics of chiral molecules for left-handed circularly polarized light and right-handed circularly polarized light are called circular dichroism (CD), and the difference is called the circular dichroism value. The CD response of natural chiral molecules is mainly concentrated in the ultraviolet band, and the CD response intensity is relatively weak, while artificial chiral molecules can expand the response band of circular dichroism, realize the spectral response from ultraviolet to visible light-near infrared band, and have a larger CD signal than natural chiral molecules. Therefore, in order to study high-sensitivity chiral analysis technology, there are many theoretical analyses and experimental studies dedicated to chiral phenomena based on surface plasmons, especially the enhanced optical response of localized surface plasmons based on chiral metal nanostructures. Traditional single-molecule sensing detection does not have high sensitivity and accuracy due to the extremely small change signal. Based on the optical response of chiral plasmons, the CD response is used as a single-molecule sensing signal for the first time, which will greatly improve the sensitivity of the sensor. Compared with other methods such as surface enhanced Raman scattering, chiral plasmons have great analytical value and research significance in improving the sensitivity of molecular sensing. Summary of the invention

[0005] According to the above-mentioned technical problem of the difficulty of single-molecule detection, a single-molecule sensor based on a chiral metal nanostructure array is provided. The purpose of the present invention is to improve the sensitivity of single-molecule sensing detection through the CD response of chiral plasmons. The present invention mainly utilizes three metal nanocubes of the same size to form a planar Z-shaped chiral structure with a certain gap. Under the irradiation of left-handed circularly polarized light and right-handed circularly polarized light, due to the difference in the transmission of the structure to left-handed and right-handed circularly polarized light, a CD signal is generated, and a huge electric field enhancement phenomenon is generated at the edges and gaps of the metal nanocubes. When a single molecule exists in the gap of the structure, the CD signal will change to a certain extent, thereby realizing the sensing of a single molecule.

[0006] The technical means adopted by the present invention are as follows:

[0007] A single molecule sensor based on a chiral metal nanostructure array comprises: a transparent substrate, and a chiral metal nanostructure array arranged on the transparent substrate, wherein:

[0008] The chiral metal nanostructure array is composed of a plurality of periodically arranged Z-shaped metal nanounits; each Z-shaped metal nanounit is a nanostructure with chiral response composed of three rectangular blocks arranged at intervals, that is, each Z-shaped metal nanounit includes a first horizontal rectangular block, a vertical rectangular block, and a second horizontal rectangular block.

[0009] Furthermore, the period of the chiral metal nanostructure array is arbitrarily selected, and the selected period is P x =P y =420~500nm.

[0010] Furthermore, the long axis of the first horizontal cuboid is perpendicular to the long axis of the vertical cuboid, the long axis of the second horizontal cuboid is perpendicular to the long axis of the vertical cuboid, and the long axis of the first horizontal cuboid is parallel to the long axis of the second horizontal cuboid.

[0011] Furthermore, the spacing between the first horizontal cuboid and the vertical cuboid is the same as the spacing between the second horizontal cuboid and the vertical cuboid, and the spacing is g=10-40 nm.

[0012] Furthermore, a center point of the first horizontal cuboid differs from a center point of the vertical cuboid by 6 to 12 nm in the x-axis direction.

[0013] Furthermore, the first horizontal cuboid, the vertical cuboid, and the second horizontal cuboid have the same size, with a length of l=120-180 nm, a width of w=50-70 nm, and a height of h=30-50 nm.

[0014] Furthermore, the first horizontal cuboid, the vertical cuboid and the second horizontal cuboid are all made of the precious metal material gold.

[0015] Furthermore, the transparent substrate is made of glass.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The single-molecule sensor based on the chiral metal nanostructure array provided by the present invention has sensitive sensing characteristics for changes in the environmental refractive index by using the extremely strong chiral electromagnetic field. By detecting the changes in the resonance peak position of the circular dichroism spectrum, chemical, biological and other molecules at the single-molecule level are detected with high sensitivity and accuracy.

[0018] 2. The single-molecule sensor based on the chiral metal nanostructure array provided by the present invention can convert the single-molecule signal into an optical signal, and detect the change of circular dichroism of the optical signal, thereby realizing the detection of the single molecule.

[0019] 3. The single-molecule sensor based on the chiral metal nanostructure array provided by the present invention, when in use, the presence or absence of a single molecule will change the change of the refractive index in space, causing the structure to change the transmittance of circularly polarized light, thereby changing the circular dichroism. By detecting the change of circular dichroism, the detection of single molecules can be achieved.

[0020] Based on the above reasons, the present invention can be widely promoted in the fields of micro-nano optics and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0022] Figure 1 It is a three-dimensional schematic diagram of a single metal nanostructure unit in the single-molecule sensor based on the chiral metal nanostructure array of the present invention.

[0023] Figure 2 Schematic diagram of the three-dimensional structure of the chiral metal nanostructure array single-molecule sensor of the present invention.

[0024] Figure 3 It is a schematic diagram of the planar structure of the chiral metal nanostructure array single-molecule sensor of the present invention.

[0025] Figure 4 This is a CD response spectrum diagram of a single-molecule sensor of a chiral metal nanostructure array provided in an embodiment of the present invention when the surrounding environment is air.

[0026] Figure 5 This is an electric field distribution diagram of the single-molecule sensor of the chiral metal nanostructure array provided by an embodiment of the present invention at a CD response spectrum peak wavelength λ=836nm in an air environment.

[0027] Figure 6 A schematic diagram of a single-molecule sensor of a chiral metal nanostructure array provided in an embodiment of the present invention being modified by a mercaptoundecanoic acid (MUA) solution and then binding to a bovine serum albumin (BSA) molecule to be detected.

[0028] Figure 7 This is a CD response spectrum diagram of a single-molecule sensor of a chiral metal nanostructure array when the number of molecules in the gap is changed according to an embodiment of the present invention.

[0029] In the figure: 1. The first horizontal cuboid; 2. The vertical cuboid; 3. The second horizontal cuboid. DETAILED DESCRIPTION

[0030] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0033] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, the numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0034] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0035] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0036] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0037] like Figure 1-2As shown, the present invention provides a single molecule sensor based on a chiral metal nanostructure array, comprising: a transparent substrate, and a chiral metal nanostructure array arranged in the transparent substrate, wherein:

[0038] The chiral metal nanostructure array is composed of a plurality of periodically arranged Z-shaped metal nanounits; each Z-shaped metal nanounit is a nanostructure with chiral response composed of three rectangular blocks arranged at intervals, that is, each Z-shaped metal nanounit includes a first horizontal rectangular block 1, a vertical rectangular block 2, and a second horizontal rectangular block 3.

[0039] When specifically implemented, as a preferred embodiment of the present invention, Figure 3 As shown, the period of the chiral metal nanostructure array is arbitrarily selected, and the selected period is P x =P y =420~500nm.

[0040] When implementing the invention, as a preferred embodiment of the invention, see Figure 1 The long axis of the first horizontal cuboid 1 is perpendicular to the long axis of the vertical cuboid 2, the long axis of the second horizontal cuboid 3 is perpendicular to the long axis of the vertical cuboid 2, and the long axis of the first horizontal cuboid 1 is parallel to the long axis of the second horizontal cuboid 3.

[0041] When implementing the invention, as a preferred embodiment of the invention, see Figure 1 The spacing between the first horizontal cuboid 1 and the vertical cuboid 2 is the same as the spacing between the second horizontal cuboid 3 and the vertical cuboid 2, and the spacing is g=10~40nm.

[0042] When implementing the invention, as a preferred embodiment of the invention, see Figure 2 , the center point of the first horizontal cuboid 1 and the center point of the vertical cuboid 2 differ by 6 to 12 nm in the x-axis direction.

[0043] When implementing the invention, as a preferred embodiment of the invention, see Figure 1 The first horizontal cuboid 1, the vertical cuboid 2, and the second horizontal cuboid 3 have the same size, with a length of l=120~180nm, a width of w=50~70nm, and a height of h=30~50nm.

[0044] In specific implementation, as a preferred embodiment of the present invention, the first horizontal cuboid 1, the vertical cuboid 2 and the second horizontal cuboid 3 are all made of precious metal material gold. The material of the transparent substrate is glass.

[0045] Example 1

[0046] In this embodiment, the chiral metal nanostructure array has a difference in transmission of left-handed and right-handed circularly polarized light, which is manifested as the presence of a chiral resonance peak in the visible-near infrared spectral region. When a single or multiple molecules exist in a very strong electric field gap, due to a slight change in the refractive index within the nanoscale spatial range, the resonance peak in the circular dichroism spectrum is observed to be red-shifted, thereby achieving single-molecule-level sensing detection with high sensitivity and accuracy.

[0047] Based on the finite difference time domain method, the simulation experiment was carried out using FDTD Solutions simulation software. The specific parameters are as follows:

[0048] The chiral metal nanostructure array is placed on a glass substrate, and the length of the array period is P x =P y =460nm, the metal nanostructure is made of the precious metal material gold, the length of the first horizontal cuboid 1, the vertical cuboid 2, and the second horizontal cuboid 3 is l = 150nm, the width is w = 60nm, the height is h = 40nm, and the spacing between the first horizontal cuboid 1 and the vertical cuboid 2 and the spacing between the vertical cuboid 2 and the second horizontal cuboid 3 is equal to g = 16nm. Figure 2 As shown, the center point of the first horizontal cuboid 1 and the center point of the vertical cuboid 2 differ by 9 nm in the x-axis direction.

[0049] In this embodiment, the CD response is CD=|T LCP -T RCP |Calculated, where T LCP represents the transmission coefficient of the structure for left-handed circularly polarized light, T RCP represents the transmission coefficient of the structure for right-handed circularly polarized light. Figure 4 As shown in FIG. 1 , when the surrounding medium is air, the chiral zigzag structure of this embodiment has a difference in transmission when the left-handed circularly polarized light and the right-handed circularly polarized light are incident, thereby generating a CD response. It can be observed from the figure that at a wavelength of λ=836nm, the CD has a maximum value of CD max =0.0666905, showing a hybridized antibonding plasmon mode at the resonant wavelength.

[0050] like Figure 5 As shown in the figure, when the surrounding medium is air, at a wavelength of λ = 836nm, the surface electric field distribution of the chiral Z-shaped structure under the incidence of left-handed and right-handed circularly polarized light. It can be seen from the figure that there is a great electric field enhancement at the tip and gap of the cuboid, especially on the right side of the gap between the first horizontal cuboid 1 and the vertical cuboid 2, the electric field enhancement can reach up to 66 times that under the excitation of unpolarized light. Therefore, based on the strong local field enhancement effect, the chiral metal nanostructure array can be applied to single-molecule sensing to achieve high-sensitivity detection at the single-molecule level.

[0051] In this embodiment, the self-assembly of mercaptoundecanoic acid (MUA) can spontaneously form a monolayer with orderly orientation and dense structure on the surface of the gold structure in the form of polar covalent S-Au bonds. The terminal group -COOH in the self-assembled film on the gold surface can covalently couple proteins, so it can carry a variety of biologically active macromolecules.

[0052] In this embodiment, the molecule is bovine serum albumin (BSA). The chiral zigzag structure modified by MUA self-assembly is introduced into the BSA solution. Due to the great electric field enhancement at the gap between the structures, the BSA molecules will bind to the terminal group -COOH in the self-assembled membrane on the gold surface at the gap between the structures. Figure 6 shown.

[0053] like Figure 7 As shown in the figure, under circularly polarized light, the CD response spectrum of the chiral Z-shaped structure modified by MUA in the surrounding solution is whether there are BSA molecules. It can be clearly seen from the figure that the maximum CD peak wavelength λ1=966nm when there are no molecules in the surrounding solution, and the CD max =0.0667517; when a single BSA molecule exists in the gap where the electric field is greatly enhanced in the chiral zigzag structure (on the right side of the gap between the first horizontal cuboid 1 and the vertical cuboid 2), the CD maximum peak wavelength λ2 = 966nm, CD max =0.0666848; when two BSA molecules exist in the gap where the electric field is greatly enhanced in the chiral "Z"-shaped structure (on the right side of the gap between the first horizontal cuboid 1 and the vertical cuboid 2), the CD maximum peak wavelength λ3 = 966nm, CD max =0.0666437; when three BSA molecules exist in the gap where the electric field is greatly enhanced in the chiral "Z"-shaped structure (on the right side of the gap between the first horizontal cuboid 1 and the vertical cuboid 2), the CD maximum peak wavelength λ4 = 967nm, CD max =0.0665737.

[0054] In this embodiment, since the slight change of the refractive index in space causes the CD response spectrum to change, the CD signal is used as the sensing signal, so the sensing sensitivity S is calculated using S = △CD / △n. In order to calculate the refractive index change caused by the BSA molecule in the nanogap when the biological binding reaction occurs, the refractive index space range calculated in this embodiment is the range of a single array unit, that is, 460nm×460nm×1000nm, where 460nm is the period in the x and y directions, and 1000nm is the distance between the chiral metal nanostructure and the boundary condition of the perfect absorption layer in the +z direction. Therefore, a single molecule causes a spatial refractive index change of △n = 6.033×10 -7, sensing sensitivity S1 = △CD / △n = 110.89; two molecules cause a spatial refractive index change △n = 1.206×10 -6 , sensor sensitivity S2 = △CD / △n = 89.51; three molecules cause a spatial refractive index change △n = 1.809×10 -6 , sensor sensitivity S3 = △CD / △n = 98.35.

[0055] Example 2

[0056] On the basis of Example 1, this embodiment can also realize the detection of other single molecules. The surface of the gold nanostructure is an organic molecule that can form a self-assembled film for a molecular probe, which can also be mercapto undecanoic acid or other organic molecules. In this embodiment, the single molecule can also be other molecules.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single-molecule sensor based on a chiral metal nanostructure array, characterized in that: include: A transparent substrate, and a chiral metal nanostructure array disposed on the transparent substrate, wherein: The chiral metal nanostructure array is composed of a plurality of Z-shaped metal nanounits arranged periodically; each Z-shaped metal nanounit is a nanostructure with chiral response composed of three rectangular parallelepipeds arranged at intervals, that is, each Z-shaped metal nanounit comprises a first horizontal rectangular parallelepiped (1), a vertical rectangular parallelepiped (2), and a second horizontal rectangular parallelepiped (3); The spacing between the first horizontal cuboid (1) and the vertical cuboid (2) is the same as the spacing between the second horizontal cuboid (3) and the vertical cuboid (2), which is g =10~40 nm.

2. The single-molecule sensor based on chiral metal nanostructure array according to claim 1, characterized in that: The selection period of the chiral metal nanostructure array is P x = P y =420~500 nm.

3. The single-molecule sensor based on chiral metal nanostructure array according to claim 1, characterized in that: The long axis of the first horizontal cuboid (1) is perpendicular to the long axis of the vertical cuboid (2), the long axis of the second horizontal cuboid (3) is perpendicular to the long axis of the vertical cuboid (2), and the long axis of the first horizontal cuboid (1) is parallel to the long axis of the second horizontal cuboid (3).

4. The single-molecule sensor based on chiral metal nanostructure array according to claim 1, characterized in that: The center point of the first horizontal cuboid (1) and the center point of the vertical cuboid (2) are x The axial direction differs by 6~12 nm.

5. The single-molecule sensor based on chiral metal nanostructure array according to claim 1, characterized in that: The first horizontal rectangular parallelepiped (1), the vertical rectangular parallelepiped (2), and the second horizontal rectangular parallelepiped (3) have the same size and length. l =120~180 nm, width is w =50~70 nm, height is h =30~50 nm.

6. The single-molecule sensor based on chiral metal nanostructure array according to claim 1, characterized in that: The first horizontal rectangular parallelepiped (1), the vertical rectangular parallelepiped (2) and the second horizontal rectangular parallelepiped (3) are all made of the precious metal material gold.

7. The single-molecule sensor based on chiral metal nanostructure array according to claim 1, characterized in that: The transparent substrate is made of glass.

Images