Single gold bipyramids on a silanized substrate as robust plasmonic sensors for liquid environments.

Sensitive, robust and stable sensors are required to bring biosensing techniques from the forefront of research to clinical and commercial settings. To this end, we report on the development of new robust plasmonic sensors consisting of gold nano-bipyramids (BPs) grafted to a glass substrate via silanization, associated with a novel setup based on Spatial Modulation Spectroscopy allowing the measurement of the optical response of individual nano-objects in a liquid environment. We thereby show that changes in the refractive index of the medium around individual silanized BPs can be detected by measuring their plasmonic shift with sensitivities comparable to values reported elsewhere and in good agreement with theoretical calculations.

Acoustic Mode Hybridization in a Single Dimer of Gold Nanoparticles.

The acoustic vibrations of single monomers and dimers of gold nanoparticles were investigated by measuring for the first time their ultralow-frequency micro-Raman scattering. This experiment provides access not only to the frequency of the detected vibrational modes but also to their damping rate, which is obscured by inhomogeneous effects in measurements on ensembles of nano-objects. This allows a detailed analysis of the mechanical coupling occurring between two close nanoparticles (mediated by the polymer surrounding them) in the dimer case.

Mechanisms of resonant low frequency Raman scattering from metallic nanoparticle Lamb modes.

The low frequency Raman scattering from gold nanoparticle bimodal assemblies with controlled size distributions has been studied. Special care has been paid to determining the size dependence of the Raman intensity corresponding to the quadrupolar Lamb mode. Existing models based on a microscopic description of the scattering mechanism in small particles (bond polarizability, dipole induced dipole models) predict, for any Raman-active Lamb modes, an inelastic intensity scaling as the volume of the nanoparticle.

Fano Transparency in Rounded Nanocube Dimers Induced by Gap Plasmon Coupling.

Homodimers of noble metal nanocubes form model plasmonic systems where the localized plasmon resonances sustained by each particle not only hybridize but also coexist with excitations of a different nature: surface plasmon polaritons confined within the Fabry-Perot cavity delimited by facing cube surfaces (i.e., gap plasmons).

Plasmon resonances tailored by Fano profiles in silver-based core-shell nanoparticles.

The optical absorption of bimetallic nanoparticles M-Ag involving silver as an active plasmonic compound has been the subject of very extensive experimental studies, both for a large range of sizes and a large variety of associated metals. Considering the most commonly encountered core-shell segregated configuration M@Ag involving a transition metal M, the spectral response is found to be weakly discriminating with regard to the chemical order and composition and is characterized by a large unstructured plasmon resonance in the 2 eV to 4 eV range. The plasmon band is essentially shaped by the scars made in the absorption continuum of metal M by Fano-like induced resonances and is surprisingly little sensitive to the exact nature of this metal, giving birth to a "quasi universal" optical signature for M@Ag systems.

From gold nanobipyramids to nanojavelins for a precise tuning of the plasmon resonance to the infrared wavelengths: experimental and theoretical aspects.

Anisotropic gold nanoparticles and in particular with shapes exhibiting tips are known to present an extremely strong localized electromagnetic field. This field is mostly located at the top of the tips and can be used in various optical applications. Moreover, as a consequence of their anisotropy, they present two plasmon resonance bands corresponding to the transverse and longitudinal resonance modes.

Plasmonic coupling with most of the transition metals: a new family of broad band and near infrared nanoantennas.

In this article, we show for the first time, both theoretically and empirically, that plasmonic coupling can be used to generate Localized Surface Plasmon Resonances (LSPRs) in transition metal dimeric nano-antennas (NAs) over a broad spectral range (from the visible to the near infrared) and that the spectral position of the resonance can be controlled through morphological variation of the NAs (size, shape, interparticle distance). First, accurate calculations using the generalized Mie theory on spherical dimers demonstrate that we can take advantage of the plasmonic coupling to enhance LSPRs over a broad spectral range for many transition metals (Pt, Pd, Cr, Ni etc.).

Plasmonic bipyramids for fluorescence enhancement and protection against photobleaching.

A great number of studies focus their interest on the photophysical properties of fluorescent hybrid gold nanoparticles for potential applications in biotechnologies such as imaging and/or treatment. Spherical gold nanoparticles are known to quench a chromophore fluorescent signal, when moieties are located in their close vicinity. The use of a polymer spacer on such a system allowed only partial recovery of the dye emission by controlling the surface to dye distance.

Plasmon spectroscopy of small indium-silver clusters: monitoring the indium shell oxidation.

Owing to the very different electrovalences of indium and silver, nanoparticles made of these elements are among the simplest examples of hybrid plasmonic systems retaining a full metallic character. The optical properties of small indium-silver clusters are investigated here for the first time in relation to their structural characterization. They are produced in the gas phase by a laser vaporization source and co-deposited in a silica matrix.

Synthesis, electron tomography and single-particle optical response of twisted gold nano-bipyramids.

A great number of works focus their interest on the study of gold nanoparticle plasmonic properties. Among those, sharp nanostructures appear to exhibit the more interesting features for further developments. In this paper, a complete study on bipyramidal-like gold nanostructures is presented.

Plasmon coupling in silver nanocube dimers: resonance splitting induced by edge rounding.

Absolute extinction cross sections of individual silver nanocube dimers are measured using spatial modulation spectroscopy in correlation with their transmission electron microscopy images. For very small interparticle distances and an incident light polarized along the dimer axis, we give evidence for a clear splitting of the main dipolar surface plasmon resonance which is found to be essentially induced by cube edge rounding effects. Supported by discrete dipole approximation and finite element method calculations, this phenomenon highlights the high sensitivity of the plasmonic coupling to the exact shape of the effective capacitor formed by the facing surfaces of both particles, especially in the regime of very close proximity.

Transparent plasmonic nanocontainers protect organic fluorophores against photobleaching.

Numerous research efforts are investigating the possibility of using light interactions with metallic nanoparticles to improve the fluorescence properties of nearby molecules. Few investigations have considered the encapsulation of molecules in metallic nanocavities. In this paper, we present the optical properties of new hybrid nanoparticles consisting of gold nanoshells and fluorescent organic dyes in their liquid cores.

Absolute optical extinction measurements of single nano-objects by spatial modulation spectroscopy using a white lamp.

This article describes a high sensitivity spectrophotometer designed to detect the overall extinction of light by a single nanoparticle (NP) in the 10(-4)-10(-5) relative range, using a transmission measurement configuration. We focus here on the simple and low cost scheme where a white lamp is used as a light source, permitting easy and broadband extinction measurements (300-900 nm). Using a microscope, in a confocal geometry, an increased sensitivity is reached thanks to a modulation of the NP position under the light spot combined with lock-in detection.

Quantitative determination of the size dependence of surface plasmon resonance damping in single Ag@SiO(2) nanoparticles.

The optical extinction spectra of single silver nanoparticles coated with a silica shell were investigated in the size range 10-50 nm. Measurements were performed using the spatial modulation spectroscopy technique which permits independent determination of both the size of the metal nanoparticle under study and the width of its localized surface plasmon resonance (LSPR). These parameters can thus be directly correlated at a single particle level for the first time.

Optical properties and relaxation processes at femtosecond scale of bimetallic clusters.

The optical properties of Au-Ag and Ni-Ag clusters are measured by linear optical absorption spectroscopy and the time-resolved pump-probe femtosecond technique allowing a study of the influence of alloy or core-shell structure.

Optical response of a single spherical particle in a tightly focused light beam: application to the spatial modulation spectroscopy technique.

We develop a new and numerically efficient formalism to describe the general problem of the scattering and absorption of light by a spherical metal or dielectric particle illuminated by a tightly focused beam. The theory is based on (i) the generalized Mie theory equations, (ii) the plane-wave decomposition of the converging light beam, and (iii) the expansion of a plane wave in terms of vector spherical harmonics. The predictions of the model are illustrated in the case of silver nanoparticles.

Electron-phonon scattering in metal clusters.

Electron-lattice energy exchanges are investigated in gold and silver nanoparticles with sizes ranging from 30 to 2.2 nm embedded in different environments. Femtosecond pump-probe experiments performed in the low-perturbation regime demonstrate a strong increase of the intrinsic electron-phonon interaction for nanoparticles smaller than 10 nm due to a confinement effect.

Size-dependent electron-electron interactions in metal nanoparticles.

The internal thermalization dynamics of the conduction electrons is investigated in silver nanoparticles with radius ranging from 13 to 1.6 nm using a femtosecond IR pump-UV probe absorption saturation technique. A sharp increase of the electron energy exchange rate is demonstrated for nanoparticles smaller than 5 nm.