银纳米棒光学性质的离散偶极近似计算

The optical properties of metal nanoparticles are quite different from those of the bulk materials mainly due to the collective oscillations of their conduction electrons known as the surface plasmon resonance（SPR）,which is strongly dependent on the particle shape and size,and the dielectric properties of the local environment where the nanoparticles are embedded in. Based on the discrete dipole approximation（DDA）method,we studied the optical properties of silver nanorods with different aspect ratios in some special dielectric environment including air,water,acetone,methylene chloride and pyridine. The DDA simulation of the ultraviolet-visible（UV-Vis）extinction spectra of silver nanorods with varying aspect ratios shows the plasmons absorption splits into two bands corresponding to the oscillation of the free electrons along and perpendicular to the long axis of the rods. The transverse mode shows almost a fixed resonance at about 350 nm while the resonance of the longitudinal mode is red-shifted and strongly depends on the aspect ratio of the nanorods. An empirical formula was given to predict the peak position of the longitudinal palsmon band of the silver nanorods with different aspect ratios in the air. The calculation result also shows the maximum of the longitudinal plasmon band of a silver nanorod with a fixed aspect ratio depends on the medium dielectric constant in a linear way. The TEM image and corresponding UV-Vis extinction spectrum of silver nanosphere and nanorods synthesized by our lab are in good agreement with the DDA simulation results.     

Effect of the dielectric constant of the surrounding medium and the substrate on the surface plasmon resonance spectrum and sensitivity factors of highly symmetric systems: silver nanocubes

Silver nanocubes (AgNCs), 60 nm, have four extinction surface plasmon resonance (SPR) peaks. The finite difference time domain (FDTD) simulation method is used to assign the absorption and scattering peaks and also to calculate the plasmon field intensity for AgNCs. Because AgNCs have a highly symmetric cubic shape, there is a uniform distribution of the plasmon field around them, and they are thus sensitive to asymmetric dielectric perturbations. When the dielectric medium around a nanoparticle is changed anisotropically, either by placing the particle on a substrate or by coating it asymmetrically with a solvent, the plasmon field is distorted, and the plasmonic absorption and scattering spectra could shift differently. For the 60 nm AgNC, we found that the scattering resonance peak shifted more than the absorption peak. This changes the extinction bandwidth of these overlapping absorption and scattering bands, and consequently the figure of merit of the nanoparticle, as a localized SPR sensor, no longer has a constant value.     

Gold and silver nanoparticles in sensing and imaging: sensitivity of plasmon response to size, shape, and metal composition

Plasmonic metal nanoparticles have great potential for chemical and biological sensor applications, due to their sensitive spectral response to the local environment of the nanoparticle surface and ease of monitoring the light signal due to their strong scattering or absorption. In this work, we investigated the dependence of the sensitivity of the surface plasmon resonance (frequency and bandwidth) response to changes in their surrounding environment and the relative contribution of optical scattering to the total extinction, on the size and shape of nanorods and the type of metal, that is, Au vs Ag. Theoretical consideration on the surface plasmon resonance condition revealed that the spectral sensitivity, defined as the relative shift in resonance wavelength with respect to the refractive index change of surrounding materials, has two controlling factors: first the bulk plasma wavelength, a property dependent on the metal type, and second on the aspect ratio of the nanorods which is a geometrical parameter. It is found that the sensitivity is linearly proportional to both these factors. To quantitatively examine the dependence of the spectral sensitivity on the nanorod metal composition and the aspect ratio, the discrete dipole approximation method was used for the calculation of optical spectra of Ag-Au alloy metal nanorods as a function of Ag concentration. It is observed that the sensitivity does not depend on the type of the metal but depends largely on the aspect ratio of nanorods. The direct dependence of the sensitivity on the aspect ratio becomes more prominent as the size of nanorods becomes larger. However, the use of larger nanoparticles may induce an excessive broadening of the resonance spectrum due to an increase in the contribution of multipolar excitations. This restricts the sensing resolution. The insensitivity of the plasmon response to the metal composition is attributable to the fact that the bulk plasma frequency of the metal, which determines the spectral dispersion of the real dielectric function of metals and the surface plasmon resonance condition, has a similar value for the noble metals. On the other hand, nanorods with higher Ag concentration show a great enhancement in magnitude and sharpness of the plasmon resonance band, which gives better sensing resolution despite similar plasmon response. Furthermore, Ag nanorods have an additional advantage as better scatterers compared with Au nanorods of the same size.     

Absorption and scattering of light by Pt, Pd, Ag, and Au nanodisks: absolute cross sections and branching ratios

Localized surface plasmons (LSPs) of metallic nanoparticles decay either radiatively or via an electron-hole pair cascade. In this work, the authors have experimentally and theoretically explored the branching ratio of the radiative and nonradiative LSP decay channels for nanodisks of Ag, Au, Pt, and Pd, with diameters D ranging from 38 to 530 nm and height h=20 nm, supported on a fused silica substrate. The branching ratio for the two plasmon decay channels was obtained by measuring the absorption and scattering cross sections as a function of photon energy. The former was obtained from measured extinction and scattering coefficients, using an integrating sphere detector combined with particle density measurements obtained from scanning electron microscopy images of the nanoparticles. Partly angle-resolved measurements of the scattered light allowed the authors to clearly identify contributions from dipolar and higher plasmonic modes to the extinction, scattering, and absorption cross sections. Based on these experiments they find that absorption dominates the total scattering cross section in all the examined cases for small metallic nanodisks (D<100 nm). For D>100 nm absorption still dominates for Pt and Pd nanodisks, while scattering dominates for Au and Ag. A theoretical approach, where the metal disks are approximated as oblate spheroids, is used to account for the trends in the measured cross sections. The field problem is solved in the electrostatic limit. The spheroid is treated as an induced dipole for which the dipolar polarizability is calculated based on spheroid geometry and the (bulk) dielectric response function of the metal the spheroid consists of and the dielectric medium surrounding it. One might expect this model to be inappropriate for disks with D>100 nm since effects due to the retardation of the incoming field across the metallic nanodisk and contributions from higher plasmonic modes are neglected. However, this model describes quite well the energy dependence of the dipolar resonance, the full width at half maximum, and the total extinction cross section for all four metallic systems, even when 100相似文献   

Optical properties of transparent copper nanorod and nanowire arrays embedded in anodic alumina oxide

Transparent copper nanorod/nanowire arrays and anodic alumina oxide composite films have been prepared by alternating current electrodeposition, and their linear optical properties have been systematically characterized by absorption spectra. In the experimental spectra, there exist transverse and longitudinal resonance peaks, which are caused by the surface-plasmon resonance along the diameter and the length of the copper nanorods, respectively. The transverse resonance peak is affected by the diameter and aspect ratio of the nanorod. The longitudinal resonance peak appears at longer wavelength when a polarized light illuminates the film with an angle of incidence of about 70 degrees , where the angle is defined with respect to the surface normal. Moreover, the longitudinal resonance mode is sensitive to the polarization direction when compared with the transverse resonance mode.     

Calculated absorption and scattering properties of gold nanoparticles of different size, shape, and composition: applications in biological imaging and biomedicine

The selection of nanoparticles for achieving efficient contrast for biological and cell imaging applications, as well as for photothermal therapeutic applications, is based on the optical properties of the nanoparticles. We use Mie theory and discrete dipole approximation method to calculate absorption and scattering efficiencies and optical resonance wavelengths for three commonly used classes of nanoparticles: gold nanospheres, silica-gold nanoshells, and gold nanorods. The calculated spectra clearly reflect the well-known dependence of nanoparticle optical properties viz. the resonance wavelength, the extinction cross-section, and the ratio of scattering to absorption, on the nanoparticle dimensions. A systematic quantitative study of the various trends is presented. By increasing the size of gold nanospheres from 20 to 80 nm, the magnitude of extinction as well as the relative contribution of scattering to the extinction rapidly increases. Gold nanospheres in the size range commonly employed ( approximately 40 nm) show an absorption cross-section 5 orders higher than conventional absorbing dyes, while the magnitude of light scattering by 80-nm gold nanospheres is 5 orders higher than the light emission from strongly fluorescing dyes. The variation in the plasmon wavelength maximum of nanospheres, i.e., from approximately 520 to 550 nm, is however too limited to be useful for in vivo applications. Gold nanoshells are found to have optical cross-sections comparable to and even higher than the nanospheres. Additionally, their optical resonances lie favorably in the near-infrared region. The resonance wavelength can be rapidly increased by either increasing the total nanoshell size or increasing the ratio of the core-to-shell radius. The total extinction of nanoshells shows a linear dependence on their total size, however, it is independent of the core/shell radius ratio. The relative scattering contribution to the extinction can be rapidly increased by increasing the nanoshell size or decreasing the ratio of the core/shell radius. Gold nanorods show optical cross-sections comparable to nanospheres and nanoshells, however, at much smaller effective size. Their optical resonance can be linearly tuned across the near-infrared region by changing either the effective size or the aspect ratio of the nanorods. The total extinction as well as the relative scattering contribution increases rapidly with the effective size, however, they are independent of the aspect ratio. To compare the effectiveness of nanoparticles of different sizes for real biomedical applications, size-normalized optical cross-sections or per micron coefficients are calculated. Gold nanorods show per micron absorption and scattering coefficients that are an order of magnitude higher than those for nanoshells and nanospheres. While nanorods with a higher aspect ratio along with a smaller effective radius are the best photoabsorbing nanoparticles, the highest scattering contrast for imaging applications is obtained from nanorods of high aspect ratio with a larger effective radius.     

Gold nanorods: Synthesis and optical properties

The main results of studying the synthesis, growth mechanisms, and optical properties of gold nanorods published in the last 5–8 years are briefly reviewed. Hydrosols of gold nanorods with variable axial ratios are synthesized in the micellar solution of ionic surfactants by sead-mediated growth procedure using the stage of particle separation in the glycerol concentration gradient. Results of synthesis in systems containing one surfactant, albeit with different Ag/Au molar ratios and different amounts of gold seeding particles, agree with the published data. It is shown that, in the case of the mixture of two surfactants, the Ag/Au ratio is an efficient controlling parameter of the synthesis of nanorods with large axial ratios. The extinction and differential light scattering, spectra dynamic light scattering, and the depolarization of laser light scattering at 90° are used for the optical control of synthesis. Three fractions are observed in separated samples. One of these fractions is characterized by the only short wavelength plasmon resonance at 570 nm corresponding, in agreement with the published data, to cubic particles. Measurements of the extinction spectra of nanorods in water-glycerol mixtures reveal higher sensitivity of the longitudinal plasmon resonance to the dielectric environment relative to the transverse resonance. It is shown theoretically and experimentally that the relative shift of plasmon resonance is proportional to the relative increment of refractive index of the surrounding medium. To calculate optical properties of nanorods, we employed a model of cylinders with semispherical ends (s-cylinders) corresponding to the shape of real particles and admitting the exact solution by the T-matrix method with a computational burden that is an order of magnitude lower than that used in the discrete dipole method. The set of dependences of the longitudinal resonance wavelength on the axial ratio of different-thickness particles complies with our data and published measurements. Theoretical and experimental values of depolarization ratio I _VH/I _VV for nanorods and nanospheres with different sizes prepared with both citrate (15–46 nm) and original thiocyanate (90 nm) reduction of HAuCl₄ are compared. It is shown that the depolarization parameter of light scattered by a nanorod suspension can exceed the theoretical limit (1/3) for common dielectric particles. The measured 10%-depolarization ratio for 90-nm spheres was far beyond the set of “size-depolarization” measurements for 15–46-nm-dia particles prepared by the citrate method and is indicative of the improved spherical morphology of 90-nm particles. This assumption was confirmed by TEM data, which also revealed both the presence of a noticeable amount of nanorods with a large axial ratio and “nanowires” of about the same thickness. A new analytic calibration for determining the diameter of spherical particles (5–100 nm) by the spectral position of the sol extinction maximum is proposed.     

Recent advances in analytical and bioanalysis applications of noble metal nanorods

In the last decade the use of anisotropic nanoparticles in analytical and bioanalytical applications has increased substantially. In particular, noble metal nanorods have unique optical properties that have attracted the interest of many research groups. The localized surface plasmon resonance (LSPR) generated by interaction of light at a specific wavelength with noble metal nanoparticles was found to depend on particle size and shape and on the constituting material and the surrounding dielectric solution. Because of their anisotropic shape, nanorods are characterized by two LSPR peaks: the transverse, fixed at approximately 530 nm, and the longitudinal, which is in the visible–near infra-red region of the spectrum and varies with nanorod aspect ratio. The intense surface plasmon band enables nanorods to absorb and scatter light in the visible and near infra-red regions, and fluorescence and two-photon induced luminescence are also observed. These optical properties, with the reactivity towards binding events that induce changes in the refractive index of the surrounding solution, make nanorods a useful tool for tracking binding events in different applications, for example assembly, biosensing, in-vivo targeting and imaging, and single-molecule detection by surface-enhanced Raman spectroscopy. This review presents the promising strategies proposed for functionalizing gold nanorods and their successful use in a variety of analytical and biomedical applications.     

Shape and size effects in the optical properties of metallic nanorods

The influence of size and geometrical shape on the optical properties of randomly oriented metallic nanorods is investigated using the discrete dipole approximation (DDA). Our calculations provide a benchmark for an accurate characterisation of nanorod suspensions by frequently used optical spectroscopic techniques. Our DDA results confirm the longitudinal plasmon resonance to be primarily affected by the nanorod aspect ratio, and also verify that the quasi-static (dipole) approximation for ellipsoidal particles is only valid for very small sizes. For prolate ellipsoidal and cylindrical nanorods with an identical aspect ratio, the latter exhibit a longitudinal resonance at significantly longer wavelengths. The importance of phase retardation and multipole contributions for larger nanorod dimensions is discussed. Also, we investigate the influence on the optical spectra of electron surface scattering, which arises from the limited size of the nanorods in comparison to the electron mean free path.     

Plasmon coupling in nanorod assemblies: optical absorption, discrete dipole approximation simulation, and exciton-coupling model

The shape anisotropy of nanorods gives rise to two distinct orientational modes by which nanorods can be assembled, i.e., end-to-end and side-by-side, analogous to the well-known H and J aggregation in organic chromophores. Optical absorption spectra of gold nanorods have earlier been observed to show a red-shift of the longitudinal plasmon band for the end-to-end linkage of nanorods, resulting from the plasmon coupling between neighboring nanoparticles, similar to the assembly of gold nanospheres. We observe, however, that side-by-side linkage of nanorods in solution shows a blue-shift of the longitudinal plasmon band and a red-shift of the transverse plasmon band. Optical spectra calculated using the discrete dipole approximation method were used to simulate plasmon coupling in assembled nanorod dimers. The longitudinal plasmon band is found to shift to lower energies for end-to-end assembly, but a shift to higher energies is found for the side-by-side orientation, in agreement with the optical absorption experiments. The strength of plasmon coupling was seen to increase with decreasing internanorod distance and an increase in the number of interacting nanorods. For both side-by-side and end-to-end assemblies, the strength of the longitudinal plasmon coupling increases with increasing nanorod aspect ratio as a result of the increasing dipole moment of the longitudinal plasmon. For both the side-by-side and end-to-end orientation, the simulation of a dimer of nanorods having dissimilar aspect ratios showed a longitudinal plasmon resonance with both a blue-shifted and a red-shifted component, as a result of symmetry breaking. A similar result is observed for a pair of similar aspect ratio nanorods assembled in a nonparallel orientation. The internanorod plasmon coupling scheme concluded from the experimental results and simulations is found to be qualitatively consistent with the molecular exciton coupling theory, which has been used to describe the optical spectra of H and J aggregates of organic molecules. The coupled nanorod plasmons are also suggested to be electromagnetic analogues of molecular orbitals. Investigation of the plasmon coupling in assembled nanorods is important for the characterization of optical excitations and plasmon propagation in these nanostructures. The surface plasmon resonance shift resulting from nanorod assembly also offers a promising alternative for analyte-sensing assays.     

Optical properties of gold nanorods: DDA simulations supported by experiments

Simulations of the absorption efficiency using the discrete dipole approximation (DDA) method and taking into account the real shape of gold nanorods are reported. A dominant surface plasma band corresponding to the longitudinal resonance is observed. Its maximum position lambda(max) shifts to the red as the aspect ratio increases. The transversal dipolar and multipolar mode wavelength positions are also discussed. These data are in good agreement with previous theoretical work based on classical electrostatic predictions and assuming that gold nanorods behave as ellipsoidal particles. From the experimental point of view, good agreement with the published data for gold nanorods is obtained.     

Total Internal Reflection‐Based Extinction Spectroscopy of Single Nanoparticles

Herein we report a reflection‐mode total internal reflection microscopy (TIRM) to measure the extinction spectrum of individual dielectric, plasmonic, or light‐absorbing nanoparticles, and to differentiate absorption and scattering components from the total optical output. These capabilities were enabled via illuminating the sample with evanescent wave of which the lightpath length was comparable with the size of single nanoparticles, leading to a dramatically improved reflectance change (ΔI/I₀) up to tens of percent. It was further found that scattering and absorption of light contributed to bright and dark centroids, respectively, in the optical patterns of single nanoparticles, allowing to distinguish scattering and absorption components from the extinction spectrum by the use of an appropriate image processing method. In addition, wide‐field feature of TIRM enabled the studies on tens of nanoparticles simultaneously with gentle illumination.     

Silver nanodisks: optical properties study using the discrete dipole approximation method

The simulated optical properties of silver nanodisks are presented. The extinction, absorption, and scattering efficiencies are calculated using the discrete dipole approximation. The influence of the nanodisk size, truncature (snip), aspect ratio, and environment on the plasmon resonance bands is investigated. In particular, the dipolar and multipolar resonance peak positions have been related to the specific features of the nanodisk geometry. An interpretation of the origins of each multipolar mode is proposed for the first time taking into account this geometry.     

Atomistic structure dependence of the collective excitation in metal nanoparticles

From a simple time-dependent tight-binding model, we calculate the absorption spectra of a series of metallic nanoparticles of varying size and shape. Spheres and spheroids of varying aspect ratios as well as a number of polyhedral particle shapes are studied. The frequency of the maximum absorption is found to scale linearly with the surface to volume ratio of the particle with a slope and intercept, which depends on particle shape, in particular, on the deviation from sphericity. In the case of spheroids, the shifts of the two different plasmon peaks that are observed are characterized as a function of the aspect ratio. The influence of shape is seen to be a determining factor for the frequency of the plasmon resonance. The influence of adatoms is studied. Linear relations between surface adatom concentration and the width of the spectral feature as well as the peak energy are observed.     

CdS nanocrystallites sensitized ZnO nanorods with plasmon enhanced photoelectrochemical performance

A novel architecture of CdS/ZnO nanorods with plasmonic silver (Ag) nanoparticles deposited at the interface of ZnO nanorods and CdS nanocrystallites, was designed as a photoanode for solar hydrogen generation, with photocurrent density achieving 4.7 mA/cm² at 1.6 V (vs. RHE), which is 8 and 1.7 times as high as those of pure ZnO and CdS/ZnO nanorod films, respectively. Additionally, with optical absorption onset extended to ～660 nm, CdS/Ag/ZnO nanorod film exhibits significantly increased incident photo-to-current efficiency (IPCE) in the whole optical absorption region, reaching 23.1% and 9.8% at 400 nm and 500 nm, respectively. The PEC enhancement can be attributed to the one-dimensional ZnO nanorod structure maintained for superior charge transfer, and the extended visible-light absorption of CdS nanocrystallites. Moreover, the incorporated plasmonic Ag nanoparticles could further promote the interfacial charge carrier transfer process and enhance the optical absorption ability, due to its excellent plasmon resonance effect.     

CdS nanocrystallites sensitized ZnO nanorods with plasmon enhanced photoelectrochemical performance

A sandwiched structure of CdS/Ag/ZnO nanorod photoanode exhibits greatly enhanced photoelectrochemical activity for solar hydrogen generation, due to synergistic effect of CdS nanocrystallites and plasmonic Ag nanoparticles for the enhanced optical absorption and the promoted charge carrier separation.     

Grating-induced plasmon mode in gold nanoparticle arrays

We study the dipolar coupling of gold nanoparticles arranged in regular two-dimensional arrays by extinction micro-spectroscopy. When the interparticle spacing approaches the plasmon resonance wavelength of the individual particles, an additional band of very narrow width emerges in the extinction spectrum. By systematically changing the particles dielectric environment, the particles shape, the grating constant and angle of incidence, we show how this band associated to a grating induced-resonance can be influenced in strength and spectral position. The spectral position can be qualitatively understood by considering the conditions for grazing grating orders whereas the strength can be related to the strength of dipolar scattering from the individual particles.     

Ultrafast studies of gold, nickel, and palladium nanorods

Steady state and ultrafast transient absorption studies have been carried out for gold, nickel, and palladium high aspect ratio nanorods. For each metal, nanorods were fabricated by electrochemical deposition into approximately 6 microm thick polycarbonate templates. Two nominal pore diameters(10 and 30 nm, resulting in nanorod diameters of about 40 and 60 nm, respectively) were used, yielding nanorods with high aspect ratios (>25). Static spectra of nanorods of all three metals reveal both a longitudinal surface plasmon resonance (SPR(L)) band in the mid-infrared as well as a transverse band in the visible for the gold and larger diameter nickel and palladium nanorods. The appearance of SPR(L) bands in the infrared for high aspect ratio metal nanorods and the trends in their maxima for the different aspect ratios and metals are consistent with calculations based on the Gans theory. For the gold and nickel samples, time resolved studies were performed with a subpicosecond resolution using 400 nm excitation and a wide range of probe wavelengths from the visible to the mid-IR as well as for infrared excitation (near 2000 cm(-1)) probed at 800 nm. The dynamics observed for nanorods of both metals and both diameters include transients due to electron-phonon coupling and impulsively excited coherent acoustic breathing mode oscillations, which are similar to those previously reported for spherical and smaller rod-shaped gold nanoparticles. The dynamics we observe are the same within the experimental uncertainty for 400 nm and infrared (5 microm) excitation probed at 800 nm. The transient absorption using 400 nm excitation and 800 nm probe pulses of the palladium nanorods also reveal coherent acoustic oscillations. The results demonstrate that the dynamics for high aspect ratio metal nanorods are similar to those for smaller nanoparticles.     

Influence of particle aspect ratio on the midinfrared extinction spectra of wavelength-sized ice crystals

We have used the T-matrix method and the discrete dipole approximation to compute the midinfrared extinction cross-sections (4500-800 cm(-1)) of randomly oriented circular ice cylinders for aspect ratios extending up to 10 for oblate and down to 1/6 for prolate particle shapes. Equal-volume sphere diameters ranged from 0.1 to 10 microm for both particle classes. A high degree of particle asphericity provokes a strong distortion of the spectral habitus compared to the extinction spectrum of compactly shaped ice crystals with an aspect ratio around 1. The magnitude and the sign (increase or diminution) of the shape-related changes in both the absorption and the scattering cross-sections crucially depend on the particle size and the values for the real and imaginary part of the complex refractive index. When increasing the particle asphericity for a given equal-volume sphere diameter, the values for the overall extinction cross-sections may change in opposite directions for different parts of the spectrum. We have applied our calculations to the analysis of recent expansion cooling experiments on the formation of cirrus clouds, performed in the large coolable aerosol and cloud chamber AIDA of Forschungszentrum Karlsruhe at a temperature of 210 K. Depending on the nature of the seed particles and the temperature and relative humidity characteristics during the expansion, ice crystals of various shapes and aspect ratios could be produced. For a particular expansion experiment, using Illite mineral dust particles coated with a layer of secondary organic matter as seed aerosol, we have clearly detected the spectral signatures characteristic of strongly aspherical ice crystal habits in the recorded infrared extinction spectra. We demonstrate that the number size distributions and total number concentrations of the ice particles that were generated in this expansion run can only be accurately derived from the recorded infrared spectra when employing aspect ratios as high as 10 in the retrieval approach. Remarkably, the measured spectra could also be accurately fitted when employing an aspect ratio of 1 in the retrieval. The so-deduced ice particle number concentrations, however, exceeded the true values, determined with an optical particle counter, by more than 1 order of magnitude. Thus, the shape-induced spectral changes between the extinction spectra of platelike ice crystals of aspect ratio 10 and compactly shaped particles of aspect ratio 1 can be efficiently balanced by deforming the true number size distribution of the ice cloud. As a result of this severe size/shape ambiguity in the spectral analysis, we consider it indispensable to cross-check the infrared retrieval results of wavelength-sized ice particles with independent reference measurements of either the number size distribution or the particle morphology.     

Reversible plasmonic circular dichroism of Au nanorod and DNA assemblies

Reversible plasmonic circular dichroism (CD) responses are realized for the first time based on temperature-dependent assembly and disassembly of Au nanorod (Au NR) and DNA hybrids. Compared with the conventional UV-vis absorption spectra, the changes in both intensity and line shape of plasmonic CD signals are much more pronounced, leading to a preliminary detection limit of DNA as low as 75 nM. The mechanism and influence factors of reversible plasmonic CD responses are explored.