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.     

Some Aspects of Seedless Synthesis of Gold Nanorods

Seedless synthesis of gold nanorods with the use of sodium borohydride and hydroquinone as reductants of metal ions has been systematically studied. The effect of reaction system composition on the morphology and optical characteristics of the formed particles has been determined. It has been found that the position of the band of the longitudinal surface plasmon resonance of the nanorods varies nonmonotonically with variations in the concentration of hydroquinone or silver nitrate. The seedless synthesis has been shown to yield high-quality gold nanorods, with the tunable position of their longitudinal surface plasmon resonance in a wide spectral range (from 700 to ~1050 nm). Therewith, the conversion of metal ions is no lower than 78 wt %.     

Space‐Confined Seeded Growth of Cu Nanorods with Strong Surface Plasmon Resonance for Photothermal Actuation

Herein, we show that copper nanostructures, if made anisotropic, can exhibit strong surface plasmon resonance comparable to that of gold and silver counterparts in the near‐infrared spectrum. Further, we demonstrate that a robust confined seeded growth strategy allows the production of high‐quality samples with excellent control over their size, morphology, and plasmon resonance frequency. As an example, copper nanorods (CuNRs) are successfully grown in a limited space of preformed rod‐shaped polymer nanocapsules, thereby avoiding the complex nucleation kinetics involved in the conventional synthesis. The method is unique in that it enables the flexible control and fine‐tuning of the aspect ratio and the plasmonic resonance. We also show the high efficiency and stability of the as‐synthesized CuNRs in photothermal conversion and demonstrate their incorporation into nanocomposite polymer films that can be used as active components for constructing light‐responsive actuators and microrobots.     

Converting Ag2SCdS and Ag2SZnS into AgCdS and AgZnS Nanoheterostructures by Selective Extraction of Sulfur

A mild three‐step solution strategy is developed to prepare Ag? MS (M=Zn, Cd) nanoheterostructures composed of MS nanorods with silver tips. First, Ag₂S? MS heterostructures are synthesized by following a solution–liquid–solid mechanism with Ag₂S nanoparticles as catalysts, then the Ag₂S sections of the heterostructures are converted into silver nanoparticles by selective extraction of sulfur. Notably, for the prepared Ag? CdS heterostructures, the localized surface plasmon resonance of silver remarkably intensifies the photoluminescence of CdS by enhancing the excitation light absorption, which is beneficial for potential applications of CdS nanoparticles in the fields of biolabeling, light‐emitting diodes, and so forth. The strategy reported herein would be useful for designing and fabricating other metal–semiconductor hybrid nanostructures with desirable performances.     

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.     

A unified view of propagating and localized surface plasmon resonance biosensors

The intense colors of noble metal nanoparticles have inspired artists and fascinated scientists for hundreds of years. In this review, we describe refractive index sensing platforms based on the tunability of the localized surface plasmon resonance (LSPR) of arrays of silver nanoparticles and of single nanoparticles. Specifically, the color associated with single nanoparticles and surface-confined nanoparticle arrays will be shown to be tunable and useful as platforms for chemical and biological sensing. Finally, the LSPR nanosensor will be compared to traditional, flat surface, propagating surface plasmon resonance sensors.     

Synthesis and plasmonic properties of silver and gold nanoshells on polystyrene cores of different size and of gold–silver core–shell nanostructures

Simple methods of preparing silver and gold nanoshells on the surfaces of monodispersed polystyrene microspheres of different sizes as well as of silver nanoshells on free-standing gold nanoparticles are presented. The plasmon resonance absorption spectra of these materials are presented and compared to predictions of extended Mie scattering theory. Both silver and gold nanoshells were grown on polystyrene microspheres with diameters ranging from 188 to 543 nm. The commercially available, initially carboxylate-terminated polystyrene spheres were reacted with 2-aminoethanethiol hydrochloride (AET) to yield thiol-terminated microspheres to which gold nanoparticles were then attached. Reduction of silver nitrate or gold hydroxide onto these gold-decorated microspheres resulted in increasing coverage of silver or gold on the polystyrene core. The nanoshells were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis spectroscopy. By varying the core size of the polystyrene particles and the amount of metal (silver or gold) reduced onto them, the surface plasmon resonance of the nanoshell could be tuned across the visible and the near-infrared regions of the electromagnetic spectrum. Necklace-like chain aggregate structures of gold core–silver shell nanoparticles were formed by reducing silver nitrate onto free citrate-gold nanoparticles. The plasmon resonance absorption of these nanoparticles could also be systematically tuned across the visible spectrum.     

The effect of fructose derived carbon shells on the plasmon resonance and stability of silver nanoparticles

Carbon nanoparticles between 10 and 50 nm in diameter and carbon shells of various thickness around silver nanoparticles were synthesized by the hydrothermal reaction of fructose. The effect of the carbon shells on the plasmon resonance of the silver nanoparticles and their stability in sodium chloride solutions was investigated. The shell thickness can be adjusted to have insignificant damping of the plasmon resonance and provide stabilization of the particles in solutions with high ionic strength. Hydrazine–carbonyl cross-linking reactions were performed to link fluorescent dye molecules to carbonyl groups on the carbon shell surface.     

Photochemical and analytical applications of gold nanoparticles and nanorods utilizing surface plasmon resonance

In recent years, plasmonics has emerged as a promising tool in the fields of analytical chemistry and biochemistry. In particular, surface plasmon resonance at the surfaces of gold nanostructures has led to the development of widespread interest in gold nanoparticles. In this review, we describe some of the recent progress in the manufacture and use of gold nanoparticles, with particular emphasis on gold nanorods. Furthermore, the spectroscopic and photochemical applications of gold nanospheres and nanorods are described.     

局域表面等离子体共振辅助的金纳米棒/聚合物纳米复合材料的双光子聚合

本文研究了金纳米棒的局域表面等离子体共振效应在双光子聚合过程中的作用,即当激发光与金纳米棒表面等离子体共振波长相匹配时,会在金纳米棒表面产生很强的局域电磁场,从而引发双光子聚合。通过采用与金纳米棒表面等离子体共振波长相同的飞秒激光,在低于光刻胶聚合阈值的功率下照射含有金纳米棒的光刻胶,制备聚合物包覆金纳米棒的纳米复合材料。透射电子显微镜结果表明,当飞秒激光功率为0.6 W、光斑直径为1.6 cm、照射时间为0.3 s时,金纳米棒表面成功聚合上厚度为5 nm左右的聚合物。本研究在制备聚合物/金属纳米粒子方面提供了一种简单可行的方法,有望在纳米光子学、纳米传感器等新兴领域得到应用。     

An indium tin oxide electrode modified with gold nanorods for use in potential-controlled surface plasmon resonance studies

The modification of electrodes with gold nanoparticles results in an increased electrode surface area, enhanced mass transport, and improved catalytic properties. We have extended this approach to indium tin oxide (ITO) electrodes to obtain optically transparent gold nanorod-modified electrodes which display enhanced electrochemical capabilities and have the additional advantage of showing a tunable surface plasmon resonance. The procedures for attaining high surface coverage (15 gold nanorods per square µm) of such electrodes were optimized, and the potential-dependent surface plasmon resonance was studied under controlled electrical potential. In an exemplary sensor application, we demonstrate the detection of mercury via potential-dependent formation of an Au-Hg amalgam.

Single-step synthesis of gold-silver alloy nanoparticles in ionic liquids by a sputter deposition technique

The simultaneous sputter deposition of gold and silver onto ionic liquids formed bimetallic alloy nanoparticles, which exhibited composition-sensitive surface plasmon resonance, the peak wavelength being red-shifted with an increase in the surface area of the gold foil targets sputtered.     

Novel silver nanostructures from silver mirror reaction on reactive substrates

Novel silver clusters have been prepared by simply carrying out the silver mirror reaction on certain reactive substrates. Leaflike fractal silver microstructures and perpendicularly aligned silver nanosheets were produced on a commercially available copper foil and sandpaper-rubbed copper foil, respectively. The surface features of copper foils and the chemical state of Cu atoms play important roles in regulating the morphological structures of the resulting silver clusters. Silver nanoclusters with various morphologies ranging from the leaflike to flowerlike hierarchical structures can be produced from the silver mirror reaction on commercially available copper foils after being treated with a dilute aqueous HCl solution under different conditions. The aqueous solution of silver nanosheets shows an optical absorption spectrum with a broad light-scattering peak at about 350 nm, compared to a corresponding surface plasmon absorption band around 430 nm for silver nanoparticles from the conventional silver mirror reaction on glass.     

金纳米棒的光学性质研究进展

金纳米棒在紫外-可见-近红外(UV-Vis-NIR)波段具有独特的可调节表面等离子体共振(SPR)光学特性,其良好的稳定性、低生物毒性、亮丽的色彩和在催化、信息存储、生物医学等领域广阔的应用前景受到相关研究领域的广泛关注.结合已有的研究基础,本文主要综述了金纳米棒光学性质的研究进展,包括表面等离子体共振、局域场增强效应、共振耦合效应及荧光特性,并对金纳米棒的应用做了展望.     

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.     

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.     

Interaction of DNA bases with silver nanoparticles: assembly quantified through SPRS and SERS

Colloidal silver nanoparticles were prepared by reducing silver nitrate with sodium borohydride. The synthesized silver particles show an intense surface plasmon band in the visible region. The work reported here describes the interaction between nanoscale silver particles and various DNA bases (adenine, guanine, cytosine, and thymine), which are used as molecular linkers because of their biological significance. In colloidal solutions, the color of silver nanoparticles may range from red to purple to orange to blue, depending on the degree of aggregation as well as the orientation of the individual particles within the aggregates. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and absorption spectroscopy were used to characterize the assemblies. DNA base-induced differential silver nanoparticle aggregation was quantified from the peak separation (relates to color) of surface plasmon resonance spectroscopy (SPRS) and the signal intensity of surface-enhanced Raman scattering (SERS), which rationalize the extent of silver-nucleobase interactions.     

纳米银碗阵列结构的高效制备及荧光增强性能

报道了一种以自组装单层聚苯乙烯纳米微球阵列为模板, 通过真空热蒸镀银纳米粒子高效制备大面积银碗阵列结构的方法. 测试结果表明, 制得的银碗阵列结构为微纳米复合分级结构, 银碗由平均粒径为10 nm的银纳米粒子组成. 紫外-可见吸收光谱测试结果表明, 银碗阵列结构表面具有银纳米粒子的局域表面等离子体共振吸收峰. 将荧光分子N,N'-二正丁基喹吖啶酮(DBQA)分别蒸镀到普通银膜和银碗阵列结构表面并测试了荧光光谱. 结果表明, 在银碗阵列结构表面的荧光分子强度得到了显著增强, 说明制备的银碗阵列结构是优良的荧光增强基底.     

One-step synthesis of silver nanoparticles, nanorods, and nanowires on the surface of DNA network

Here, we describe a one-step synthesis of silver nanoparticles, nanorods, and nanowires on DNA network surface in the absence of surfactant. Silver ions were first adsorbed onto the DNA network and then reduced in sodium borohydride solution. Silver nanoparticles, nanorods, and nanowires were formed by controlling the size of pores of the DNA network. The diameter of the silver nanoparticles and the aspect ratio of the silver nanorods and nanowires can be controlled by adjusting the DNA concentration and reduction time.