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International audience; The integration of nanoparticles (NPs) into photonic devices and plasmonic sensors requires selective patterning of these NPs with fine control of their size, shape, and spatial positioning. In this article, we report on a general strategy to pattern different types of NPs. This strategy involves the functionalization of photopolymers before their patterning by two-photon laser writing to fabricate micro- and nanostructures that selectively attract colloidal NPs with suitable ligands, allowing their precise immobilization and organization even within complex 3D structures. Monolayers of NPs without aggregations are obtained and the surface density of NPs on the polymer surface can be controlled by changing either the time of immersion in the colloidal solution or the type of amine molecule chemically grafted on the polymer surface. Different types of NPs (gold, silver, polystyrene, iron oxide, colloidal quantum dots, and nanodiamonds) of different sizes are introduced showing a potential toward nanophotonic applications. To validate the great potential of our method, we successfully demonstrate the integration of quantum dots within a gold nanocube with high spatial resolution and nanometer precision. The promise of this hybrid nanosource of light (plasmonic/polymer/QDs) as optical nanoswitch is illustrated through photoluminescence measurements under polarized exciting light.

© 2014 American Chemical Society. Surface-enhanced Raman scattering (SERS) spectroscopy was employed in the present work to elucidate the adsorption of two diisocyanide molecules: 1,4-phenylenediisocyanide (PDI) and 1,4′-terphenylenediisocyanide (TPDI) on nanogaps of Ag and Au nanoparticles (NPs). The main goal of this work was the study of the adsorption of these molecules and more specifically the coordination mechanism and the orientation of these molecules on the metal surface as well as the study of the effect of the above adsorbates on the aggregation and formation of interparticle junctions. To get more insight into the above phenomena, we have investigated different experimental variables such as the numbers of phenylene rings (monophenylene vs terphenylene), the nature of the metal (Au and Ag), the excitation wavelength (532 and 785 nm), and the surface coverage provided by different adsorbate concentrations. The experiments carried out at these conditions revealed the existence concentration of critical values at 0.1 and 3 μM corresponding to changes in the coordination and a complete surface coverage of interparticle junctions. Finally, we have also deduced the great importance of charge-transfer processes occurring between the metal surface and diisocyanide molecules. This charge transfer exhibits a strong dependence on the surface coverage., This work has been supported by the Spanish Ministerio de Economia y Competitividad ́ (grant FIS2010-15405). S. SanchezCortes acknowledges Overseas Research Fellowship organized by Catalysis Research Center, Hokkaido University.

The adsorption mechanism of linear aliphatic α,ω-dithiols with chain lengths of 6, 8 and 10 carbon atoms on silver and gold nanoparticles has been studied by surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra provided the structural marker bands of these compounds and they were employed to obtain information about the adsorption and coordination mechanism, the orientation, conformational order, and packing of the aliphatic chains of dithiols on the metal nanoparticle surface. The effect of the type of metal (silver or gold) and the extent of surface coverage on all the above mentioned properties is discussed. It was found that the adsorption of dithiols on Au nanoparticles leads to a more disordered structure of the aliphatic chains of dithiols in comparison with the adsorption on Ag nanoparticles. The interaction through both thiol groups makes the adsorption of dithiols on metal surfaces substantially different from that of monothiols; in particular, the orientation of dithiols is perpendicular, while monothiols adopt a tilted orientation. Dithiols may act as linkers between metal nanoparticles and induce the formation of nanogaps with a controllable interparticle distance. The nanogaps thus formed are able to produce hot spots exhibiting a large intensification of electromagnetic field in these points which has been proved by the observation of intense SERS spectra of dithiols until a concentration of 10-8 M, corresponding to a large Raman enhancement factor of 5 × 106. © 2014 the Partner Organisations., This work has been supported by the Spanish Ministerio de Economía y Competitividad (MINECO, grant FIS2010-15405) and Comunidad de Madrid through the MICROSERES II network (grant S2009/TIC-1476), by the Agency of the Ministry of Education of Slovak Republic for the Structural Funds of the European Union, Operational program Education (Doctorand, ITMS code: 26110230013 and KVARK, ITMS code: 26110230084) and Operational program Research and Development (NanoBioSens (ITMS code: 26220220107) and CEVA II (ITMS code: 26220120040)), by the Slovak Research and Development Agency under the contract APVV-0242-11, and by the project CELIM (316310) funded by 7FP EU.

International audience; A new methodology is developed to determine the shape distribution of gold nanoparticles (NPs) from optical spectroscopic measurements. Indeed, the morphology of Au colloids is deduced by fitting their absorption spectra with an effective medium theory which takes into account the nanoparticle shape distribution. The same procedure is applied to ellipsometric measurements recorded on photoresist films which contain Au NPs. Three spaces (L2, r2, P2) are introduced to interpret the NPs shape distribution. In the P2 space, the sphericity, the prolacity and the oblacity estimators are proposed to quantify the shape of NPs. The r2 space enables the determination of the NP aspect ratio distribution. The distributions determined from optical spectroscopy were found to be in very good agreement with the shape distributions obtained by transmission electron microscopy. We found that fitting absorption or ellipsometric spectra with an adequate effective medium theory, provides a robust tool for measuring the shape and concentration of metallic NPs.

International audience; This paper reports the complete ellipsometric characterization of gold nanoparticles (NPs) embedded in a photoresist films. The effective dielectric function of nanocomposite films as well as the shape distribution and the volume fraction of NPs are extracted from ellipsometric measurements by introducing an effective medium theory which takes into account the NP shape distribution and the intrinsic confinement effect. This theory remains valid as long as the nanoparticle interaction is negligible. We show that the magnitude of the confinement depends on the nanoparticle shape and the environment through chemical damping. This suggests that the NP shape distribution can be directly estimated by ellipsometry, while the determination of absolute radius distribution requires transmission electron microscopy measurements. The imaginary part of the effective dielectric function exhibits a strong asymmetric surface plasmon band, while a large variation of the real part occurs close to the resonance. The redshift and the broadening of the plasmon band as the gold volume fraction increases are correlated to the evolution of NP shape distribution. This evolution is attributed to a competition between the nucleation and the coalescence of NPs. This unambiguously demonstrates that ellipsometry combined with a shape-distributed effective medium theory is a powerful alternative tool to transmission electron microscopy for the NP shape analysis.

International audience; The preparation method of nanoporous poly(methyl methacrylate)( PMMA) containing silver nanoparticles self-organized in rings is highly adaptable, yielding a variety of materials of controllable pore size (ranging from 200 nm to over 5 mu m), nanoparticle size (20 to 200 nm), surface coverage and silver precursor concentration. In this article, it is optimized aiming at a best performance as enhancers for Surface Enhanced Raman Spectroscopy. The versatility of these sensors is shown by multi-wavelength excitation experiment at 457, 488, 514 and 633 nm. Finally, the efficiency of 2,2'-bipyridine, 4,4'-bipyridine and trans-bis-(4,4'-bipyridyl) ethylene as SERS probe molecules is compared using PMMA/Ag-rings. Ag+ ions are shown to play an important role in the adsorption of the target molecules on these surfaces leading to a SERS enhancement factor of 3.783 108 at 488 nm for trans-bis-(4,4'-bipyridyl) ethylene.

A comparative study of different plasmonic nanoparticles with different morphologies (nanospheres and triangular nanoprisms) and metals (Ag and Au) was done in this work and applied to the ultrasensitive detection of aminoglutethimide (AGI) drug by surface enhanced Raman spectroscopy (SERS) and plasmon resonance. AGI is an aromatase inhibitor used as an antitumoral drug with remarkable pharmacological interest and also in illegal sport doping. The application of very sensitive spectroscopic techniques based on the localization of an electromagnetic field on plasmonic nanoparticles confirms the previous study of the adsorption of drugs onto a metal surface due to the near field character of these techniques. The adsorption of AGI on the above substrates was investigated at different pH values and surface coverages, and the results were analyzed on the basis of AGI/metal affinity, considering the interaction mechanism, the existence of two binding sites in AGI, and the influence of the interface on the adsorption in terms of surface charge due to the presence of other ions linked to the surface. Finally, a comparative quantitative detection of AGI was performed on both spherical and triangular nanoprism nanoparticles, and a limit of detection lower than those reported so far was deduced on the latter nanoparticles.

International audience; Fabrication of freestanding, three-dimensional microstructures having gold nanoparticles as building blockshas been achieved using two-photon lithography. The reported constructions hold structural coherencewithout the need of a polymeric network to embed the nanoparticles. The Au nanoparticles areproduced by radical-mediated photoreduction and immediately self-arrange in micrometre-sizedcylinders, which are used as the building units of the 3D structure writing. The manufactured structurespresent plasmonic activity, as well as excellent properties as substrates for Surface-Enhanced RamanSpectroscopy, in key issues such as reproducibility in intensity or enhancement factor. Such is calculatedto be above 8 106 for the non-resonant probe molecule trans-1,2-bis-4-pyridylethylene. The optionof repeated use of the substrates is confirmed, and they are successfully applied for detection of thefungicide thiabendazole.

Linear α,ω-dithiols have been used as linkers to control the aggregation of silver nanoparticles. The characterization of the resulting nanoparticle clusters thus formed was carried out using plasmon resonance spectroscopy and transmission electron microscopy in both independent and correlated measurements. The obtained nanoparticle assemblies present morphologies that vary according to the dithiol length, displaying controllable-size interparticle gaps (plasmonic hot spots) with potential application in the detection of a large list of hydrophobic analytes. © 2013 American Chemical Society., ACKNOWLEDGMENTS This work has been supported by the Spanish Ministerio de Economía y Competitividad (grant FIS2010-15405), by the Comunidad de Madrid, through MICROSERES II network (grant S2009/TIC-1476). I.I.-L. also acknowledges CSIC and FSE 2007- 2013 for a JAE-CSIC predoctoral grant.

The controlled tuning of interparticle distance at the nanoscale level is a major challenge for nanofabrication of surface-enhanced Raman scattering (SERS) active clusters and their application to molecular sensing. In fact, the geometrical properties of the narrow gaps between nanoparticles play a key role in determining the local field enhancement (and therefore, the SERS enhancement factor) and the spatial enhancement distribution in the gap region. Besides, very short interparticle distances may block the access of the analyte to the hot zone. In this paper, we report the synthesis of silver colloid NP clusters with interparticle distances fine tuned in the ≤2 nm range, by exploiting the chemical properties of linear α,ω-aliphatic diamines as molecular linkers with varying chain length. The bifunctional diamines also form intermolecular cavities within their self-assembled monolayers, suitable to host molecular analytes for nanosensing applications, as evidenced by SERS detection of organochlorine insecticides at the trace level. In this regard, the extension of the aliphatic chain played a crucial role in determining the SAM conformation and thus the final sensitivity of the functionalized SERS substrate. © 2010 Springer Science+Business Media, LLC., Supported by the Spanish Ministerio de Ciencia e Innovación (grant no. FIS2007-63065, FIS2009-11264, and Consolider-Ingenio project EMET CSD2008-00066, Comunidad de Madrid through the MICROSERES network (grant S-0505/TIC-0191), and CSIC