GoldHelix: Gold Nanoparticles Forming 3D Helical Superstructures with Controlled Morphology and Strong Chiroptical Property (original) (raw)

Plasmonic Shaping in Gold Nanoparticle Three-Dimensional Assemblies

The Journal of Physical Chemistry C, 2013

When a large number of similar gold particles are organized into complex architectures, the dipolar plasmon spectrum of the individual plasmonic entities gives rise to a broader, red-shifted feature centered around 750 nm. In this work, we show that superstructures fabricated using the convective assisted capillary force assembly method (CA-CFA) and excited at that wavelength display a subwavelength patterning of their optical field intensity that results from the self-consistent coupling between the colloidal nanoparticles. First, we demonstrate the fabrication of shape-controlled threedimensional assemblies of metallic nanocrystals using the CA-CFA method. In a second step, the absorption band resulting from the mutual coupling between the metallic building blocks is exploited to excite a coupled plasmon mode and map the twophoton luminescence (TPL) by scanning a tightly focused light beam. Highly resolved TPL images show that the morphology of the plasmonic particle assemblies has a strong impact on their optical response. A model based on a rigorous optical Gaussian beam implementation inside a generalized propagator derived from a three-dimensional Green dyadic function accurately reproduces the TPL maps revealing the influence of interparticle separation and thus coupling between the individual particles. Finally, we show that the spatial distribution of the electric field intensity can be controlled by tuning the linear polarization of the optical excitation.

Synthesis of Heterodimeric Sphere–Prism Nanostructures via Metastable Gold Supraspheres

Angewandte Chemie International Edition, 2007

Noble-metal nanoparticles of nonspherical shapes are interesting for their size-and shape-dependent optical properties and for potential applications in hyperthermia of tumors, pathogen detection, and infrared-absorbing coatings. Typically, such particles are grown in the presence of surfactants that stabilize certain crystallographic faces. For example, silver nanocubes can be prepared by stabilizing the Ag {100} faces with poly(4-vinylpyrrolidone) (PVP), while gold nanorods are grown readily in the presence of cetyltrimethylammonium bromide (CTAB), which adsorbs selectively onto Au {100} faces. Other nanostructures prepared by the latter method include gold hexagons, gold triangles, silver disks, and several other shapes. Recently, considerable effort has been devoted to the preparation of hybrid or dimer nanostructures, in which two (or more) domains of different shapes or material properties are permanently connected. Such structures are usually made by epitaxial nucleation and growth on presynthesized nanoparticle seeds or by thermal decomposition of core-shell nanoparticles. Herein, we describe a conceptually different route to a new class of nanoscopic heterodimers composed of spherical and polygonal domains. In our method, individual nanoparticles (NPs) are first assembled into metastable, supraspherical aggregates (SS, , and are then thermally decomposed into heterodimers ). These composite particles are the result of temperature-induced coalescence of individual NPs accompanied by crystal nucleation. During this process, the relative sizes and dimensions of the SS and crystalline domains change controllably and give rise to pronounced changes in the particles optical response.

Deformation, alignment and anisotropic optical properties of gold nanoparticles embedded in silica

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2007

Gold/silica composite films with single and multilayer structures were fabricated by simultaneous gold sputtering and plasma-enhanced chemical vapor deposition of SiO 2. Heating during or after deposition was performed to control particle size. Samples were irradiated, at liquid nitrogen temperature, using 15 MeV Cu 3+ ions or 27.5 MeV In 7+ ions. Microstructural analysis by transmission electron microscopy revealed that spherical or nearly spherical gold nanoparticles were transformed during the irradiation into prolate ellipsoids whose long axis is along the ion beam direction. The optical absorption band attributed to surface plasmon resonance of gold particles was located at 520 nm for single layer films and at 602 nm for multilayer structures. After ion irradiation, this band splits into two polarization-dependent bands whose positions strongly depend on the size, aspect ratio and alignment of the nanorods.

Centrifugal Shape Sorting and Optical Response of Polyhedral Gold Nanoparticles

Advanced Materials, 2013

Metallic nanostructures are of high interest because their optical properties can be tuned throughout the visible and nearinfrared portions of the electromagnetic spectrum by adjusting nanoparticle shape, size, composition, and local dielectric environment. [ 1-4 ] In particular, the localized surface plasmon resonance (LSPR) properties of metal nanoparticles have shown promising applications in chemical and biological sensing, [ 5-7 ] waveguiding, [ 8 ] single-particle tracking, [ 9 ] and surface enhanced Raman spectroscopy (SERS). [ 10 , 11 ] Since inhomogeneous broadening resulting from nanoparticle size and shape variations causes an increase in the linewidth of bulk LSPR spectra, monodispersity of the nanoparticle population is critical for optimal performance in LSPR-based devices and sensors. [ 12 ] Towards that end, previous studies have focused on obtaining more homogeneous nanoparticle populations by means of post-synthetic separation techniques, including size exclusion chromatography, [ 13 ] gel electrophoresis, [ 14 ] and centrifugation. [ 15 ] Among these methods, density gradient centrifugation has proven to be particularly successful, resulting in narrow distributions of gold nanoparticle diameters, [ 16 ] shapes, [ 17 ] and aggregation state. [ 18 ] Recently, Akbulut et al. [ 19 ] reported the use of aqueous multiphase systems as media for rate-zonal centrifugation to separate the reaction products (i.e., nanorods, nanospheres, and large particles) of a nominal gold nanorod synthesis, ultimately increasing the nanorod purity from 48% to 99%. The shape-dependent optical properties of metal nanostructures have also motivated efforts to realize new nanoparticle shapes via novel synthetic routes [ 20-29 ] and to correlate nanoparticle structure with plasmonic behavior. [ 21 , 30-33 ] Among available nanoparticle shapes, gold bipyramids (BPs) are of interest because of their sharp tips, which lead to strong localized fi eld enhancement and high sensitivity to the surrounding dielectric www.advmat.de www.MaterialsViews.com

Controlled reshaping and plasmon tuning mechanism of gold nanostars

Journal of Materials Chemistry C, 2013

Anisotropic multi-branched gold nanoparticles exhibit intense localized electromagnetic fields at their tips/ edges and hence have attracted significant attention in surface enhanced Raman scattering (SERS), as well as in bio-sensing applications. Our quest for such complex hyper-branching in gold nanostructures has revealed that even the addition of a simple base (like NaOH) to the precursor reaction mixture enhances the fine tuning/reshaping of the 3D star/flower-like gold nanostars with controlled precision right from the nucleation stage. With increasing the basicity of the reaction mixture, the two strongly localized surface plasmon resonance (LSPR) peaks of the gold nanostars essentially merge into a broad singular peak, effectively indicating the steady transition from (non)planar structures to conventional spheroidal nanostructures, as confirmed by the transmission electron microscopy (TEM) measurements. Such pH induced size/shape transitions of gold nanostructures were monitored kinetically in detail through correlated molecular spectroscopic measurements nuclear magnetic resonance, fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy (NMR, FTIR and XPS), for the first time to the best of our knowledge, which ascertains a rational paradigm in better understanding the complex polyvinylpyrrolidone (PVP) functionality for its simultaneous reducing, as well as stabilizing action, in precisely controlling the anisotropic gold nanostructure growth mechanism and further exploiting this functionality in utilizing these as-formed extremely stable colloidal gold dispersions for various specific plasmonic applications.

Improved size-tunable synthesis of monodisperse gold nanorods through the use of aromatic additives.

We report an improved synthesis of colloidal gold nanorods (NRs) by using aromatic additives that reduce the concentration of hexadecyltrimethylammonium bromide surfactant to ~0.05 M as opposed to 0.1 M in well-established protocols. The method optimizes the synthesis for each of the 11 additives studied, allowing a rich array of monodisperse gold NRs with longitudinal surface plasmon resonance tunable from 627 to 1246 nm to be generated. The gold NRs form large-area ordered assemblies upon slow evaporation of NR solution, exhibiting liquid crystalline ordering and several distinct local packing motifs that are dependent upon the NR's aspect ratio. Tailored synthesis of gold NRs with simultaneous improvements in monodispersity and dimensional tunability through rational introduction of additives will not only help to better understand the mechanism of seed-mediated growth of gold NRs but also advance the research on plasmonic metamaterials incorporating anisotropic metal nanostructures.