Colloidal Gold Nanostructures for Plasmonics

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Colloidal Gold Nanostructures for Plasmonics

International audienceGold nanoparticles (Au-NPs) of high crystalline quality can now be readily synthesized in large quantities thanks to significant advances in colloidal chemistry over the past decade. Assembly of such NPs leads to the appearance of new properties, still relatively poorly explored, and is therefore particularly promising for production of cost-effective devices. Our research activities concentrate on the synthesis and assembly of gold NPs and aims at providing appropriate materials for researchers working in the various fields of plasmonics (1,2,3). Over the past years, we have been developed an expertise in the synthesis of NPs with tunable sizes and shapes, such as spheres, rods, octahedra, cubes, triangles and also micro-particles. Some of them are very promising and produced only in very few laboratories worl-wide, especially in Asia. For example, thick triangles are of particular interest for ultrasensi-tive sensing and can assemble in the edge-to-edge fashion or through face to face interactions (fig.). Microplatelets (hexagonal or triangular) are very attractive due to their large atomically flat facets and can form ordered 1D-columnar aggregates. In the literature, 3D-arrays of NPs are currently related to SERS applications. Here, we report the spontaneous self-assembly of gold NPs by simply evaporating concentrated solutions on non-patterned sub-strates. The degree of reproducibility of this method, the maximum size of the perfectly organized area and the key parameters related to a controlled-deposition are presented. We are looking for collaborations to study the properties of these unusual assemblies

Gold Nanoparticles for Plasmonics and Medicine

International audienceGold-bioconjugates are studied worldwide and promising for new technologies for health. In the long term, biodegradable gold na-noparticles (NPs) are expected to have a large impact on diagnosis through the development of new contrast agents for imaging or new ultra-sensitive sensors. Gold-NPs have a high potential as contrast agents for several bioimaging modalities such as computed tomography, pho-toacoustic imaging, dark field scattering, multi-photon luminescence, high frequency ultra-sound, quantitative phase contrast. New therapies and surgeries will develop because these gold-nano are also able to generate Reactive Oxygen Species (ROS) and heat. Our research activities concentrate on the synthesis and assembly of gold nanoparticles of high quality to provide original materials for plasmonics since 2008. The irradiation of gold NPs by short laser pulses sets off a cascade of complex transient phenomena. Following this irradiation, one observe exaltation and confinement of the incident light at the surface of the NP but also singlet oxygen generation and ROS through the injection of hot electrons (or hot holes) to a nearby molecule. In short, gold na-noparticles are nanosources of light, heat and hot carriers and the morphology of the NP is a key point for these three characteristics because competitive relaxation processes depend on the size, shape and aspect ratio of NP. We use colloidal chemistry to synthesize gold nanoparticles of controlled shape and size. The figure illustrates some of the gold NPs we propose. Contrary to spherical and rod-shaped NPs that are commercially-available, other shapes such as cubes, triangles .. and plates with tunable sizes are only produced in our lab and in few laboratories worldwide. In literature, triangular-gold nanoplates are already used for ultrasensitive sensing, and the construction of original plasmon-based optical devices. The recent discovery of a third and fourth biological transparency windows centered respectively at 1.8µm and 2.2µm and the recent commercialization of new NIR-lasers make gold-nanoplates attractive for biomedicine in this still unexplored spectral domain. The synthesis of highly uniform shapes relies on trial and error procedure because it is very hard to predict the right recipe and additional purification steps are also often required. In the future, we are eager to widen the application range of these NPs to medicine through new collaborations either with biochemists for appropriate biofunctionalization, biophysicists for imaging and physicians for therapy. As a first step towards this objective, we are developing recipes to produce Au@SiO 2 core-shell NP while waiting for precise specifications. Figure 1: illustration of some of the monodis-perse gold particles (nano-and micro-) and gold hybrids (Au@SiO2) that have been synthesized , with tunable sizes and thicknesses

Large and Versatile Plasmonic Enhancement of Photoluminescence Using Colloidal Metallic Nanocubes

Improving phosphor photoluminescence efficiency is a key parameter to boost the performances of many optical devices. In this work, colloidal silver nanocubes, homogeneously spread on a luminescent surface, have proved to help both injecting and extracting light in and out of the photoluminescent layer and hence contributed significantly to the enhancement of the fluorescence. This approach has been applied to two materials: the well-known Y$_3$Al$_5$O$_{12}$:Ce yellow phosphor and an optical quartz. The emission efficiency, for sol-gel derived YAG:Ce layers, has increased of 80\% in the presence of an optimal nanoparticle density -- whereas for quartz, a weakly fluorescent material, the photoluminescence signal can be enhanced by a 200-fold factor. A physical analysis based on simulations shows that the disorder is an important factor and that the surface density of Ag nanoparticles is a crucial parameter

Nouveaux substrats bimétalliques ultra-sensibles pour la diffusion Raman exaltée de surface

Driven by the interest in finding ultrasensitive sensors devices, reliable surface enhanced Raman scattering (SERS) based substrates are fabricated. Silver and gold nanoparticles are two of the best candidates for SERS substrates where Ag nanoparticles exhibit large enhancing ability in Raman intensity while Au nanostructures are stable in biological systems. Hence, combining the two metals in bimetallic nanostructures appeared to be a promising approach in order to sum the merits of Au surface properties and Ag enhancing ability. Thermal annealing of thin metallic films is used as a simple and relatively inexpensive technique to elaborate homogenous and reproducible Ag/Au bimetallic nanoparticles SERS substrates with high enhancing ability. The fabricated nanoparticles proved their enhancing stability even after one year of fabrication. Manipulating the composition of Ag/Au bimetallic NPs resulted in tuning the Localized Surface Plasmon Resonance (LSPR) over the whole visible spectrum, where the substrates are characterized with higher SERS enhancement when they exhibit LSPR closer to the Raman excitation wavelength. Additionally, bimetallic nanoparticles patterns with different size, composition and lattice constants have been conducted by electron beam lithography. The systematic study of their interesting plasmonic and SERS enhancing properties revealed maintenance in the LSPR-SERS relation by changing the nanoparticle sizeAfin de développer des capteurs ultrasensibles des substrats fiables pour la diffusion Raman exaltée de surface (SERS) ont été fabriqués. Les deux meilleurs candidats de matériaux constituant les nanoparticules pour des substrats SERS sont l’argent et l’or. L’argent présente un meilleur facteur d’exaltation de l'intensité Raman et l’or est stable dans les milieux biologiques. C’est pourquoi la combinaison de ces deux métaux dans des nanostructures bimétalliques semble être une approche prometteuse qui combine les propriétés de surface de l’or et d’exaltation de l’argent. Le recuit thermique des couches métalliques minces est utilisé comme une technique simple et peu coûteuse. Cette dernière permet d’élaborer des substrats homogènes et reproductibles de nanoparticules bimétalliques or-argent ayant un facteur d’exaltation importante. Ces nanoparticules gardent leurs propriétés d’exaltation même après une année de fabrication. En jouant sur la composition de nanoparticules bimétalliques il est possible d’avoir une résonance de plasmons de surface localisés (LSPR) sur tout le spectre visible. Ces substrats sont caractérisés par une exaltation SERS supérieure lorsque la résonance plasmon est plus proche de la longueur d'onde d'excitation Raman. En outre, les nanoparticules bimétalliques de différentes tailles, compositions ont été réalisés par lithographie électronique. L’étude systématique de leurs propriétés plasmoniques et de leur exaltation SERS a révélé une conservation du lien entre résonance plasmon et signal SER

Colloidal Gold Nanostructures for Plasmonics

International audienc

Colloidal Gold Nanostructures for Plasmonics

International audienc

Colloidal Gold Nanostructures for Plasmonics

International audienc

Colloidal Gold Nanostructures for Plasmonics

International audienc

Colloidal Gold Nanostructures for Plasmonics

International audienc