Method for determining optical properties of nanoparticles

Abstract

The invention discloses a method for determining optical properties of nanoparticles, and belongs to the technical field of nanoparticle characterization. The invention discloses a method for determining optical properties of nano-particles. The method comprises the following steps: acquiring a two-dimensional projection image of the nano-particles to be detected; performing three-dimensional reconstruction on the two-dimensional projection image to obtain a three-dimensional model of the to-be-detected nanoparticles; performing an electromagnetic simulation experiment on the three-dimensional model to obtain a simulation result; and determining optical property information of the to-be-detected nanoparticles according to a simulation result. The application realizes the determination of the real optical properties of a single nanoparticle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanoparticle characterization, in particular to a method for determining optical properties of nanoparticles. BACKGROUND

[0002] Nanoparticles, especially noble metal nanoparticles with specific morphologies (such as chiral structures), have shown great application potential in the fields of biosensing, catalysis and optical devices due to their unique optical properties. To predict the optical properties of nanoparticles, the conventional method is to analyze through theoretical simulation.

[0003] However, simulation techniques are usually based on idealized geometric models such as perfect spheres, cubes or regular helical structures. These models assume that the surface of the nanoparticle is smooth and regular, so that accurate calculations can be made through simplified mathematical models. However, actual synthesized nanoparticles often have complex features such as surface defects, irregular edges, non-ideal chiral twist, etc. These features have a significant impact on the optical properties at the nanoscale, but are difficult to accurately reflect in idealized models. Therefore, there is often a large deviation between the simulation results based on ideal models and experimental observations, limiting the application accuracy of theoretical simulation in predicting the optical properties of nanoparticles. SUMMARY

[0004] The main purpose of the present application is to provide a method for determining the optical properties of nanoparticles, which realizes the determination of the real optical properties of a single nanoparticle.

[0005] To achieve the above purpose, the embodiments of the present application provide a method for determining the optical properties of nanoparticles, comprising the following steps:

[0006] Obtaining a two-dimensional projection image of a single nanoparticle to be tested;

[0007] Three-dimensional reconstruction is performed on the two-dimensional projection image to obtain a three-dimensional model of the nanoparticle to be tested;

[0008] An electromagnetic simulation experiment is performed on the three-dimensional model to obtain a simulation result;

[0009] According to the simulation result, the optical property information of the nanoparticle to be tested is determined.

[0010] In an embodiment, the method for obtaining a two-dimensional projection image of a single nanoparticle to be tested comprises:

[0011] Providing a sample;

[0012] The sample is detected by transmission electron microscopy, and a transmission electron microscopy image of a single nanoparticle to be tested in the sample is selected as the two-dimensional projection image.

[0013] In an embodiment, the two-dimensional projection images comprise images of the to-be-tested nanoparticle at multiple tilt angles.

[0014] In an embodiment, the step of performing three-dimensional reconstruction on the two-dimensional projection images comprises:

[0015] performing three-dimensional reconstruction on the two-dimensional projection images by a three-dimensional reconstruction algorithm, wherein the three-dimensional reconstruction algorithm comprises at least one of a filtered back-projection algorithm, an algebraic reconstruction technique, a simultaneous iterative reconstruction technique, and an expectation maximization algorithm.

[0016] In an embodiment, before the step of performing three-dimensional reconstruction on the two-dimensional projection images, further comprising:

[0017] performing image alignment processing and / or normalization processing on the two-dimensional projection images.

[0018] In an embodiment, the step of performing electromagnetic simulation experiment on the three-dimensional model to obtain a simulation result comprises:

[0019] determining a set of incident directions, wherein the set of incident directions comprises a plurality of incident light directions;

[0020] performing wideband electromagnetic simulation on the three-dimensional model at each incident light direction comprised in the set of incident directions to obtain the simulation result.

[0021] In an embodiment, the step of determining a set of incident directions comprises:

[0022] determining a geometric center of the three-dimensional model as an origin to establish a spherical coordinate system;

[0023] generating a plurality of uniformly distributed discrete points in the spherical coordinate system by a Fibonacci sphere mesh algorithm and / or a uniform pseudo-random sampling algorithm;

[0024] generating the set of incident directions according to the discrete points.

[0025] In an embodiment, the simulation result comprises an extinction spectrum simulation result, and the optical property information comprises an electromagnetic hot spot distribution map, and the step of determining optical property information of the to-be-tested nanoparticle according to the simulation result comprises:

[0026] determining a resonance peak according to the extinction spectrum simulation result;

[0027] determining a potential hot spot region according to the three-dimensional model;

[0028] setting a high-resolution near-field monitor according to the potential hot spot region;

[0029] An electromagnetic simulation experiment is performed according to the wavelength of the resonance peak to obtain spatial distribution data of electric field intensity;

[0030] An electromagnetic hotspot distribution map is determined according to the spatial distribution data of electric field intensity.

[0031] In an embodiment, after the step of determining the optical property information of the to-be-tested nanoparticle, the method further includes:

[0032] A geometric structure parameter of the to-be-tested nanoparticle is determined according to the three-dimensional model.

[0033] A structure-property relationship of the to-be-tested nanoparticle is determined according to the geometric structure parameter and the optical property information.

[0034] In an embodiment, the geometric structure parameter includes at least one of symmetry, degree of chiral twist, surface concave-convex feature, and specific axial structure orientation.

[0035] The one or more technical solutions provided by the embodiments of the present application have at least the following technical effects: a method for determining optical properties of nanoparticles is provided, a three-dimensional model of a to-be-tested nanoparticle is established by three-dimensional reconstruction based on a two-dimensional projection image of the to-be-tested nanoparticle, an electromagnetic simulation experiment is performed based on the three-dimensional model, accurate simulation results are obtained, and optical property information of the to-be-tested nanoparticle is determined based on the simulation results. Conventional simulation methods are based on idealized geometric models and ignore complex features such as surface defects, irregular edges, and non-ideal chiral twist of nanoparticles. The three-dimensional model of the nanoparticle established based on the two-dimensional projection image can more accurately reflect the actual structure of the single nanoparticle, thereby significantly improving the accuracy of the simulation results, making them closer to experimental observation values, and obtaining accurate optical property information of the to-be-tested nanoparticle. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A flowchart of a method for determining optical properties of nanoparticles according to an embodiment of the present application is shown;

[0037] Figure 2 A two-dimensional projection image of a nanoparticle according to an embodiment of the present application is shown;

[0038] Figure 3 A three-dimensional model of a nanoparticle according to an embodiment of the present application is shown;

[0039] Figure 4 An extinction spectrum of a nanoparticle simulated according to an embodiment of the present application is shown;

[0040] Figure 5Circular dichroism spectrum obtained by simulating the nanoparticles involved in the embodiments of the present application.

[0041] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments in conjunction with the drawings. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased in the market.

[0043] Hereinafter, the embodiments of the method for determining the optical properties of nanoparticles of the present application are specifically disclosed with appropriate reference to the drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are already well known, and repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy, and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided in order for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0044] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if the ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents a shorthand notation for any real combination of integers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0046] If not particularly specified, all the technical features and optional technical features in the present application can be combined to form new technical solutions.

[0047] If not particularly specified, all the steps in the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0048] If not particularly specified, "comprise" and "include" mentioned in the present application are open-ended, and can also be closed. For example, "comprise" and "include" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0049] If not particularly specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist).

[0050] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the technical solutions of the present application will be further described below in combination with the drawings and examples. However, the present application is not limited to the listed examples, and any known changes within the scope of the claimed rights of the present application should also be included.

[0051] Here, "one embodiment" or "an embodiment" means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is separate or alternative to other embodiments.

[0052] In order to better understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with the drawings and specific embodiments.

[0053] In conventional techniques, the optical response (e.g., extinction spectrum, scattering spectrum, etc.) of a single asymmetric nanoparticle is closely related to the orientation angle of the nanoparticle in space. However, the actual experimental measurement, for example, the data obtained by a spectrometer in a solution, is an ensemble average of the signals contributed by a large number of nanoparticles randomly oriented and constantly flipping in the liquid, which is fundamentally mismatched in physical meaning from the true macroscopic experimental data of the nanoparticle, resulting in difficulty in effectively comparing and verifying the simulation results with the experimental results, and greatly limiting the accuracy and practical value of the simulation prediction. The study of nanoparticles usually not only needs to obtain the far-field spectral characteristics, but also needs to accurately understand the near-field electromagnetic field enhancement distribution (i.e., "electromagnetic hot spot") of the nanoparticle at a specific resonance wavelength. The acquisition of the far-field spectrum usually needs to perform a broadband simulation, and the accurate near-field analysis needs to perform a high-precision single-frequency simulation at the resonance wavelength. However, the conventional simulation method has a single process, and it is difficult to balance the calculation efficiency and the integrity of the information in one task. Researchers often need to perform multiple, independent and repetitive simulations, which is not only low in efficiency, but also difficult to establish a direct and efficient internal correlation between the macroscopic spectrum and the microscopic hot spot.

[0054] In the embodiments of the present application, the two-dimensional projection image of the single nanoparticle to be measured is obtained to perform three-dimensional reconstruction to establish a true three-dimensional model of the nanoparticle to be measured. Then, an electromagnetic simulation experiment is performed based on the true three-dimensional model to obtain accurate simulation results, and the optical property information of the nanoparticle to be measured is determined according to the simulation results. The conventional simulation method is based on an idealized geometric model, and ignores complex features such as surface defects, irregular edges and non-ideal chiral twist of the nanoparticle. However, the true three-dimensional model of the nanoparticle established by the two-dimensional projection image in the embodiments of the present application can more accurately reflect the actual structure of the single nanoparticle, thereby significantly improving the accuracy of the simulation results, making them closer to the experimental observation values, and obtaining accurate optical property information of the nanoparticle to be measured.

[0055] The first aspect of the embodiments of the present application provides a method for determining the optical property of a nanoparticle, referring to Figure 1 , comprising the following steps:

[0056] Step S10, obtaining a two-dimensional projection image of a single nanoparticle to be measured;

[0057] In a feasible embodiment, in order to obtain accurate optical property information of a single nanoparticle to be measured, a two-dimensional projection image of the single nanoparticle to be measured can be obtained first.

[0058] In a feasible embodiment, the step S10 of obtaining a two-dimensional projection image of a single nanoparticle to be measured comprises:

[0059] Step S11, providing a sample;

[0060] In step S12, the sample is observed by transmission electron microscopy, and a transmission electron microscopy image of a single nanoparticle to be measured in the sample is selected as a two-dimensional projection image.

[0061] In an embodiment, a sample containing nanoparticles is prepared, the sample is observed by transmission electron microscopy, a single nanoparticle to be measured is determined from the observed nanoparticles, a transmission electron microscopy image of the single nanoparticle to be measured is obtained, and the transmission electron microscopy image is used as a two-dimensional projection image.

[0062] Optionally, an isolated and representative nanoparticle is selected as the nanoparticle to be measured.

[0063] Optionally, the transmission electron microscopy (TEM) is an imaging method that uses an electron beam to penetrate a very thin sample. When the electron beam passes through the sample, the number of electrons transmitted varies at different parts of the sample due to different scattering of electrons by different regions of the sample. The difference is recorded to form an image. Therefore, the transmission electron microscopy provides a high-resolution two-dimensional projection image that reflects the internal structure information of the sample.

[0064] Optionally, the transmission electron microscopy used in the embodiment can be a transmission electron microscope with sample tilting function, which can realize systematic tilting of the sample in a large angle range, thereby obtaining structural information at different viewing angles.

[0065] Optionally, the High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM) is used in the embodiment, which can effectively reflect the mass thickness distribution of the sample because the image contrast is approximately proportional to the square of atomic number (Z 2 ) and the local thickness of the sample. This feature not only helps to improve the accuracy of image contrast and structure recognition, but also provides a reliable data basis for subsequent high-quality three-dimensional reconstruction based on multi-angle projection images.

[0066] Optionally, the nanoparticle to be measured is systematically tilted in a preset angle range, and images at each tilting angle are obtained to construct a tilting sequence image set, which is used as a two-dimensional projection image. The preset angle range can be -70° to 70°.

[0067] In the embodiment, the images of the nanoparticle to be measured at multiple tilting angles are obtained by transmission electron microscopy, which helps to improve the accuracy of image contrast and structure recognition, and also provides a reliable data basis for subsequent high-quality three-dimensional reconstruction based on multi-angle projection images.

[0068] Step S20, three-dimensional reconstruction is performed on the two-dimensional projection images to obtain a three-dimensional model of the to-be-tested nanoparticle.

[0069] In an implementable embodiment, the two-dimensional projection images of the to-be-tested nanoparticle obtained are subjected to three-dimensional reconstruction to obtain a real three-dimensional model of the to-be-tested nanoparticle.

[0070] Optionally, to ensure the accuracy and reliability of the three-dimensional reconstruction, the two-dimensional projection images can be subjected to image alignment processing and / or normalization processing, and the two-dimensional projection images processed are subjected to three-dimensional reconstruction to obtain the three-dimensional model of the to-be-tested nanoparticle.

[0071] Optionally, since mechanical drift, rotation axis offset or local deformation of the sample can occur during tilting, the spatial positions of the images at different tilting angles are inconsistent, and thus it is necessary to accurately align the images and unify the images at different tilting angles to the same spatial coordinate system to eliminate rigid body displacement or rotation error caused by the motion of the sample stage.

[0072] Optionally, the image alignment processing can be implemented through an automatic alignment algorithm based on feature point matching and an image registration technology based on cross-correlation.

[0073] Optionally, to eliminate the image brightness difference caused by factors such as electron beam intensity fluctuation and inconsistent detector response, the images aligned can be subjected to gray value normalization processing. For example, the pixel values of each image are divided by the average gray value or the maximum gray value of the frame, so that all the images have a unified contrast range, thereby improving the consistency and stability of the projection data in the three-dimensional reconstruction process.

[0074] In an implementable embodiment, the two-dimensional projection images can be subjected to three-dimensional reconstruction through a three-dimensional reconstruction algorithm, and the three-dimensional reconstruction algorithm can include at least one of a filtered back projection algorithm, an algebraic reconstruction technique, a simultaneous iterative reconstruction technique and an expectation maximization algorithm.

[0075] Optionally, the filtered back projection algorithm (FBP) is based on the Fourier slice theorem, and the three-dimensional volume data is synthesized by first performing filtering processing on the two-dimensional projection data at each angle and then performing reverse projection along each direction. The FBP algorithm has the advantage of high computational efficiency, but is sensitive to noise, and thus requires the input projection data to have a high signal-to-noise ratio.

[0076] Optionally, the Algebraic Reconstruction Technique (ART) is an iterative solution based on linear equations, which converts the three-dimensional reconstruction problem into a process of solving a series of sparse matrix equations. This method gradually corrects the initial estimate, so that the simulated projection data gradually approaches the actual measured value. ART can flexibly incorporate prior knowledge to improve reconstruction quality.

[0077] Optionally, the Simultaneous Iterative Reconstruction Technique (SIRT) improves the reconstruction result by updating all rays at the same time. Compared with ART, SIRT can generally provide more uniform and smooth reconstruction results, especially when dealing with data containing a large amount of noise.

[0078] Optionally, the Expectation Maximization (EM) algorithm optimizes model parameters through maximum likelihood estimation to find the probability distribution that best fits the observed data.

[0079] Optionally, through the application of the above three-dimensional reconstruction algorithm, the three-dimensional model or three-dimensional electron density distribution map of a single nanoparticle can be accurately reconstructed from the pre-processed tilt series image set.

[0080] In this embodiment, the three-dimensional model of the nanoparticle to be tested is established by the three-dimensional reconstruction algorithm, providing a reliable data basis for subsequent electromagnetic simulation experiments.

[0081] Step S30, performing electromagnetic simulation experiment on the three-dimensional model to obtain simulation results;

[0082] In a feasible implementation, the electromagnetic simulation experiment is performed on the three-dimensional model to obtain the simulation results of the single nanoparticle to be tested.

[0083] In a feasible implementation, step S30, the step of performing electromagnetic simulation experiment on the three-dimensional model to obtain simulation results includes:

[0084] Step S31, determining a set of incident directions, wherein the set of incident directions includes a plurality of incident light directions;

[0085] In a feasible embodiment, the geometric center of the three-dimensional model is determined as the origin, a spherical coordinate system is established, a plurality of (for example, N) uniformly distributed discrete points are generated in the spherical coordinate system through the Fibonacci spherical grid algorithm and / or the uniform pseudo-random sampling algorithm, so as to avoid concentration in a certain area, and a set of incident directions is generated according to the discrete points, wherein the set of incident directions includes a plurality of incident light directions.

[0086] Optionally, one discrete point corresponds to one incident light direction, i.e. each discrete point uniquely determines an incident direction vector of a plane wave light source, thereby forming an incident direction set {D1, D2,..., DN}. N}.

[0087] Optionally, the incident direction set is used for subsequent multiple times of electromagnetic simulation experiments.

[0088] Step S32, for the three-dimensional model, respectively performing broadband electromagnetic simulation on each incident light direction contained in the incident direction set to obtain simulation results.

[0089] In an available embodiment, the three-dimensional model is imported into FDTD (Finite-Difference Time-Domain) simulation software, and the broadband electromagnetic simulation is performed on each incident light direction contained in the incident direction set by the FDTD simulation software.

[0090] Optionally, the step of broadband electromagnetic simulation comprises: initializing a total extinction cross section (or other far field parameter) array σtotal(λ), and performing FDTD simulation for each direction D i (i = 1 to N) in the incident direction set. The light source of the simulation is set as a TFSF (Total Field Scattering Field) broadband light source covering the target wave band, and after the simulation is completed, the extinction spectrum σ i (λ) under the direction is calculated and recorded by a far field monitor, and is accumulated into σtotal(λ). After the simulation of all N directions is completed, each element of the accumulated total extinction cross section array σtotal(λ) is divided by N, and the ensemble average extinction spectrum σ avg (λ) is obtained.

[0091] Optionally, the extinction spectrum simulation result comprises: at least one extinction spectrum σ i (λ) under an incident light direction and an ensemble average extinction spectrum σ avg (λ).

[0092] Optionally, when performing the electromagnetic simulation experiment, corresponding simulation parameters can also be set, including at least one of: a simulation region, material properties of the to-be-tested nanoparticle, a background medium, a light source, a boundary condition and a grid.

[0093] Optionally, the real three-dimensional model of the single nanoparticle is exported into a format recognizable by electromagnetic simulation software, for example, a standard triangle language (.stl), a wavefront object file (.obj) or a grid file format specific to the software, and then the exported three-dimensional model is imported into the FDTD simulation software.

[0094] Optionally, in the FDTD simulation environment, a proper simulation region is set around the imported single nanoparticle model, and the size of the region should be large enough to accommodate the nanoparticle and allow the field distribution around it to fully develop.

[0095] Optionally, according to the composition elements of the nanoparticle to be measured, the complex permittivity of the nanoparticle in the target wavelength range is determined to set the material properties of the nanoparticle to be measured.

[0096] Optionally, according to the medium properties of the environment in which the nanoparticle to be measured is located, the background medium is set. For example, water (refractive index n ≈ 1.33), vacuum, air, etc. can be set according to the actual application scenario.

[0097] Optionally, according to the specific target of the simulation, a suitable light source type is selected. For example, for the simulation of extinction spectrum, a total field scattered field (TFSF) light source and / or a plane wave light source can be selected, which can effectively cover the required wavelength range (e.g. 200-1200 nm). For the simulation of circular dichroism (CD) spectrum, left circularly polarized (LCP) light and right circularly polarized (RCP) light are respectively set as incident light sources, which can be realized by superimposing two orthogonal linearly polarized plane waves with a phase difference of ±π / 2.

[0098] Optionally, in order to simulate the open boundary condition, a perfect matched layer (PML) can be set at the boundary of the simulation region to absorb the outgoing electromagnetic wave, thereby reducing the influence of non-physical reflection on the result.

[0099] Optionally, fine grid division is the basis for ensuring calculation accuracy, for example, the minimum grid size is set to be between 0.5-5 nm, and the specific value needs to be adjusted according to the size and structural details of the nanoparticle.

[0100] Optionally, it is also necessary to arrange monitors in the simulation region, such as power monitors and field monitors, which can be used to measure the scattering cross section, absorption cross section and electromagnetic field distribution.

[0101] Optionally, for CD spectrum analysis, the extinction cross sections σLCP and σRCP under LCP and RCP illumination can be calculated respectively, and the CD signal can be represented as Δσ = σLCP-σRCP, thereby revealing the chiral characteristics of the nanoparticle to be measured.

[0102] Optionally, after setting the simulation parameters, the FDTD simulation software is run, for example, multiple calculations are performed according to different polarization states and wavelength conditions to obtain the simulation results.

[0103] Optionally, the simulation results include extinction spectrum simulation results and / or circular dichroism spectrum simulation results, so that relevant data can be extracted from the simulation results to draw the extinction spectrum, CD spectrum and other optical property information of the nanoparticle to be measured.

[0104] Optionally, the electromagnetic field distribution around the surface of the nanoparticle at a specific wavelength, especially the "hot spot" region with high electric field intensity, can be further analyzed in depth using the data of the field distribution monitor, which is of great significance for understanding the local enhancement effect of the nanoparticle.

[0105] In the embodiment, the high-precision spatial distribution calculation of the electromagnetic field on the nanoscale can be realized by the spatial discretization and time-domain solution characteristics of the FDTD method, so as to obtain accurate optical property information of a single nanoparticle to be measured.

[0106] In an implementable embodiment, the simulation result includes an extinction spectrum simulation result, the optical property information includes an electromagnetic hot spot distribution map, and the step S40 of determining the optical property information of the nanoparticle to be measured includes:

[0107] The step S41 is to determine a resonance peak according to the extinction spectrum simulation result.

[0108] In an implementable embodiment, automatic peak searching calculation is performed on the ensemble average extinction spectrum σ avg (λ) in the extinction spectrum simulation result, at least one plasmonic resonance peak with the strongest optical response is determined, and the wavelength corresponding to the resonance peak is determined as {λ1, λ2,..., λ N}.

[0109] The step S42 is to determine a potential hot spot region according to the three-dimensional model.

[0110] In an implementable embodiment, the curvature calculation is performed on the surface grid of the three-dimensional model by using a geometric analysis algorithm, and all regions with a curvature value greater than a preset threshold value are automatically identified and marked as potential hot spot regions.

[0111] Optionally, the region with the curvature value greater than the preset threshold value in the surface grid of the three-dimensional model usually corresponds to a tip, an edge, a narrow gap or the like of the model.

[0112] The step S43 is to set a high-resolution near-field monitor according to the potential hot spot region.

[0113] In an implementable embodiment, the setting position of the high-resolution near-field monitor is determined according to the potential hot spot region, and the high-resolution near-field monitor is set at the position.

[0114] Optionally, the high-resolution near-field monitor is set in the vicinity of the potential hot spot region.

[0115] The step S44 is to set a simulation light source according to the wavelength of the resonance peak, and perform electromagnetic simulation experiment to obtain spatial distribution data of the electric field intensity.

[0116] In an embodiment, for each determined resonance peak wavelength λ, a new FDTD simulation setting is performed, i.e., the simulation light source is set as a single-frequency plane wave light source with wavelength λ and electromagnetic simulation experiment is performed, and then the spatial distribution data of the electric field intensity (or the square of its modulus) is extracted from the high-resolution near-field monitor.

[0117] In step S45, the electromagnetic hotspot distribution map is determined according to the spatial distribution data of the electric field intensity.

[0118] In an embodiment, the electromagnetic hotspot distribution map is determined according to the spatial distribution data of the electric field intensity at the resonance peak wavelength.

[0119] Optionally, the electromagnetic hotspot distribution map can reflect the electromagnetic field distribution of the nanoparticle under the resonance condition, and can also reveal the core mechanism of the optical function of the nanoparticle.

[0120] In the embodiment, the physical correlation problem between the single-particle simulation result and the macroscopic ensemble experimental measurement result is solved by the multi-angle incidence averaging strategy, so that the simulation prediction can be compared with the real experimental data with high precision, and the accuracy and reliability of the simulation are greatly improved. Through the two-step collaborative simulation strategy of "wideband average spectrum" and "single-frequency hotspot imaging", the macroscopic optical response and the microscopic field distribution are efficiently associated, the repetitive and blind simulation settings are avoided, the calculation efficiency and the integrity of information acquisition are significantly improved, and the deep transition from "phenomenon observation" to "physical mechanism analysis" can be realized.

[0121] In an embodiment, after the step S40 of determining the optical property information of the nanoparticle to be measured, the method further includes:

[0122] In step S50, the geometric structure parameters of the nanoparticle to be measured are determined according to the three-dimensional model.

[0123] In step S60, the structure-activity relationship of the nanoparticle to be measured is determined according to the geometric structure parameters and the optical property information.

[0124] In an embodiment, in order to further analyze the topographic features of the nanoparticle to be measured and obtain quantitative geometric information, the three-dimensional model can be visualized and image segmented to extract the surface profile of the nanoparticle to be measured from the complex three-dimensional data, and finally the real three-dimensional geometric structure parameters thereof are obtained; and then the geometric structure parameters and the optical property information are directly compared and correlated to determine the structure-activity relationship of the nanoparticle to be measured.

[0125] Optionally, the structure-activity relationship refers to the relationship between the structure of a material and its performance (or property).

[0126] Optionally, the voxel data can be rendered into surface models or isosurface maps by three-dimensional image processing software, so as to intuitively observe the overall morphology, internal density distribution, interface relationship and possible defects or non-uniform regions of the nanoparticles.

[0127] Optionally, in order to accurately extract the boundary and geometric features of the nanoparticles to be measured, a segmentation operation can be performed on the three-dimensional data. For example, the target structure is separated from the background or other adjacent structures according to the gray value, density difference or morphological features. Further, a surface reconstruction algorithm can be used to extract the surface profile of the nanoparticles to generate a high-precision triangular mesh model. The model not only retains the true shape of the particles, but also can be used to measure the geometric parameters thereof, such as volume, surface area, aspect ratio, curvature distribution, principal axis direction, etc.

[0128] Optionally, the optical property information extracted from the simulation results includes extinction spectrum and / or CD spectrum. Further, spectral features such as peak position, peak intensity, g-factor, etc. can be obtained.

[0129] Optionally, the peak position corresponds to the energy position of the localized surface plasmon resonance (LSPR) or other optical transition process.

[0130] Optionally, the peak intensity reflects the scattering or absorption intensity, which is closely related to the degree of local field enhancement.

[0131] Optionally, the g-factor is defined as g = Δσ / (0.5*(σLCP+σRCP), where Δσ = σLCP-σRCP represents the extinction difference under left-handed and right-handed circularly polarized light excitation, and is used to quantify the chiral response intensity. This parameter is widely used in chiral optical research and can effectively measure the chiral intensity and selective response ability of the nanostructure to circularly polarized light.

[0132] Optionally, the spectral features not only reflect the overall optical response behavior of the nanoparticles, but also contain information about the internal electromagnetic field distribution and symmetry.

[0133] Optionally, based on the three-dimensional model of the nanoparticles to be measured, a series of structural parameters can be further extracted to describe the geometric morphology and symmetry thereof, such as at least one of symmetry, chiral twist degree, surface concave-convex features and specific axial structural orientation.

[0134] Optionally, the symmetry refers to whether the nanoparticles have rotational symmetry, mirror symmetry, etc., and the symmetry directly affects the light scattering and resonance mode.

[0135] Optionally, the chiral twist degree is quantified by calculating the deviation angle between the principal axis directions or the helicity index to quantify the chiral degree of the structure.

[0136] Optionally, the surface relief features can be quantitatively analyzed using surface curvature, local height fluctuations, or fractal dimension, etc. to evaluate their influence on the local field enhancement.

[0137] Optionally, the specific axial structural orientation can be determined by principal component analysis to determine the main extension direction, and combined with parameters such as aspect ratio to evaluate the degree of anisotropy.

[0138] Optionally, the geometric structure parameters and optical property information of the nanoparticles to be tested can be cross-compared to construct the mapping relationship between them, and the structure-activity relationship of the nanoparticles to be tested is obtained.

[0139] Optionally, the structure-activity relationship includes: the relationship between the symmetry of the nanoparticles to be tested and the resonance peak position; asymmetric structure often leads to multi-mode or multi-peak response, while highly symmetric structure tends to have a single dominant resonance peak.

[0140] Optionally, the structure-activity relationship includes: the correlation between the degree of chiral twist and the g factor; the stronger the structure of chirality, the higher the g factor value, and the more significant the CD signal.

[0141] Optionally, the structure-activity relationship includes: the relationship between the surface roughness and the local field enhancement effect; the surface relief structure can induce local electric field concentration to form "hot spots", thereby significantly enhancing the scattering or absorption efficiency.

[0142] Optionally, the structure-activity relationship includes: the matching of the main axis orientation and the polarization-dependent response; the structural extension in a specific direction will enhance the light coupling efficiency along that direction, resulting in a polarization-selective response.

[0143] Exemplarily, the structure-activity relationship of a single particle of chiral gold nanocornerrcuboid (L-NC-II) is determined, i.e. the correlation between the geometric structure and the optical property.

[0144] Step S101, synthesis of chiral gold nanoparticles.

[0145] The gold nanocornerrcuboid (AuNCs, average side length about 44.6 nm) is used as a seed, reduced by chloroauric acid (HAuCl4) in a cetyltrimethylammonium bromide (CTAB) solution, and chiral growth is carried out at 30°C for 2 hours under the condition of L-glutathione (L-GSH, concentration 1 μM) as a chiral inducer. After centrifugal purification, the product is dispersed in a 1 mM CTAB solution to obtain an L-NC-II sample, which has a main morphology of chiral characteristic rhombic dodecahedron.

[0146] Step S102, three-dimensional reconstruction of single particles.

[0147] The L-NC-II sample is drop-casted on a transmission electron microscopy (TEM) copper grid, dried, and a single L-NC-II particle is selected as the target nanoparticle using a Thermo Fisher Talos F200X field emission transmission electron microscope in the high-angle annular dark-field scanning transmission electron microscopy mode. A tilt series of images is collected in the range of -70° to +70° with a step of 2°, and two-dimensional projection images are obtained (see Figure 2 ). The camera length is set to 98 mm, the beam current is 0.069 nA, and the acceleration voltage is 200 kV. The sequence images are aligned, and a three-dimensional reconstruction algorithm (e.g., the SIRT algorithm or the EM algorithm) is used for three-dimensional reconstruction with 20 to 40 iterations to obtain a three-dimensional model of the single L-NC-II particle. The three-dimensional model shows that the nanoparticle has a distorted rhombic dodecahedron structure with three-fold and four-fold chiral rotational symmetry axes. The model is exported in the.stl format.

[0148] Step S103, FDTD simulation.

[0149] The above-mentioned three-dimensional model in the.stl format is imported into the FDTD software, and the simulation parameters are set, in which the background medium is water (n = 1.33), the simulation region is set with a PML boundary condition, and the grid is set to 0.5 nm near the particle surface and gradually transitions to a coarser grid outside. For extinction spectrum simulation, a total field scattered field (TFSF) light source is used with a wavelength range of 400-1000 nm, and the monitor records the total scattering and absorption cross sections to obtain the extinction spectrum. For CD spectrum simulation, LCP and RCP plane wave light sources (wavelength 400-1000 nm) are used respectively, and the monitor records the extinction cross sections σLCP and σRCP under LCP and RCP light, and the CD signal is calculated as Δσ = σLCP - σRCP.

[0150] Step S104, structure-activity relationship analysis.

[0151] Referring to Figure 3 , the single L-NC-II particle reconstructed in three dimensions has a chiral distorted rhombic dodecahedron morphology, and the surfaces at the three-fold and four-fold rotational symmetry axes exhibit specific concave-convex and distortion. Referring to Figure 4 , the simulated extinction spectrum has a plasmon resonance peak near about 620 nm. Referring to Figure 5The simulated CD spectrum (circular dichroism spectrum) has a significant negative signal peak at about 620 nm. By analyzing the electric field distribution map at the peak wavelength (620 nm) of the CD spectrum corresponding to the three-dimensional structure of the particle, it is found that the electromagnetic field "hot spots" are mainly distributed on the edges and vertex regions of the triple and quadruple chiral rotation symmetry axes of the particle. The specific chiral twist structure of these regions interacts strongly with the circularly polarized light, resulting in a significant CD signal. It can be seen that the simulated single-particle spectrum is basically consistent with the spectrum measured in the ensemble experiment in terms of trend, but there are certain differences in peak position and peak width. Single-particle simulation reveals a sharper peak and possibly stronger CD signal, while ensemble averaging and structural heterogeneity lead to broadening of the experimental spectrum and possible weakening of the signal. This proves the advantage of the embodiments of the present application in accurately revealing the optical properties of single particles.

[0152] In the present embodiment, the three-dimensional reconstruction is performed on the two-dimensional projection images of the single to-be-measured nanoparticles obtained to establish a real three-dimensional model of the to-be-measured nanoparticles; then the electromagnetic simulation experiment is performed based on the real three-dimensional model to obtain accurate simulation results, and the optical property information of the to-be-measured nanoparticles is determined according to the simulation results. The conventional simulation method is based on an idealized geometric model, ignoring complex features such as surface defects, irregular edges, and non-ideal chiral twist of nanoparticles, while the real three-dimensional model of nanoparticles established by the two-dimensional projection images in the embodiments of the present application can more accurately reflect the actual structure of a single nanoparticle, thereby significantly improving the accuracy of the simulation results, making them closer to the experimental observation values, and thus obtaining accurate optical property information of the to-be-measured nanoparticles.

[0153] The above is only a preferred embodiment of the present application, and does not limit the patent scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the patent protection scope of the present application.

Claims

1. A method of determining the optical properties of nanoparticles, characterized in that, The method comprises: acquiring a two-dimensional projection image of a single to-be-tested nanoparticle; performing three-dimensional reconstruction on the two-dimensional projection image to obtain a three-dimensional model of the to-be-tested nanoparticle; performing electromagnetic simulation experiment on the three-dimensional model to obtain a simulation result; determining optical property information of the to-be-tested nanoparticle according to the simulation result.

2. The method of claim 1, wherein, The method for acquiring the two-dimensional projection image of the single to-be-tested nanoparticle comprises: providing a sample; performing transmission electron microscope detection on the sample, and selecting a transmission electron microscope image of a single to-be-tested nanoparticle in the sample as the two-dimensional projection image.

3. The method of claim 1 or 2, wherein, The two-dimensional projection image comprises images of the to-be-tested nanoparticle at multiple tilt angles.

4. The method of claim 1, wherein, The step of performing three-dimensional reconstruction on the two-dimensional projection image comprises: performing three-dimensional reconstruction on the two-dimensional projection image by using a three-dimensional reconstruction algorithm, wherein the three-dimensional reconstruction algorithm comprises at least one of a filtered back-projection algorithm, an algebraic reconstruction technique, a simultaneous iterative reconstruction technique, and an expectation maximization algorithm.

5. The method of claim 4, wherein, Before the step of performing three-dimensional reconstruction on the two-dimensional projection image, the method further comprises: performing image alignment processing and / or normalization processing on the two-dimensional projection image.

6. The method of claim 1, wherein, The step of performing electromagnetic simulation experiment on the three-dimensional model to obtain a simulation result comprises: determining a set of incident directions, wherein the set of incident directions comprises multiple incident light directions; performing wideband electromagnetic simulation on the three-dimensional model at each incident light direction included in the set of incident directions to obtain the simulation result.

7. The method of claim 6, wherein, The step of determining the set of incident directions comprises: determining a geometric center of the three-dimensional model as an origin to establish a spherical coordinate system; generating multiple uniformly distributed discrete points in the spherical coordinate system by using a Fibonacci spherical grid algorithm and / or a uniform pseudo-random sampling algorithm; generating the set of incident directions according to the discrete points.

8. The method of claim 1, wherein, The simulation result comprises extinction spectrum simulation result, and the optical property information comprises electromagnetic hot spot distribution map, and the step of determining the optical property information of the to-be-tested nanoparticle according to the simulation result comprises: determining a resonance peak according to the extinction spectrum simulation result; determining a potential hot spot region according to the three-dimensional model; setting a high-resolution near-field monitor according to the potential hot spot region; setting a simulation light source according to a wavelength of the resonance peak, and performing electromagnetic simulation experiment to obtain spatial distribution data of electric field intensity; determining an electromagnetic hot spot distribution map according to the spatial distribution data of electric field intensity.

9. The method of claim 1, wherein, After the step of determining the optical property information of the to-be-tested nanoparticle, the method further comprises: determining a geometric structure parameter of the to-be-tested nanoparticle according to the three-dimensional model; determining a structure-activity relationship of the to-be-tested nanoparticle according to the geometric structure parameter and the optical property information.

10. The method of claim 9, wherein, The geometric structure parameter comprises at least one of symmetry, chirality twist degree, surface concave-convex feature, and specific axial structure orientation.

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