A Surface Enhanced Raman Spectroscopy study of aminothiophenol and aminothiophenol-C60 self-assembled monolayers: evolution of Raman modes with experimental parameters

International audienceP-aminothiophenol (PATP) is a well known molecule for the preparation of self-assembled monolayers on gold via its thiol functional group. After adsorption, it has been demonstrated that this molecule is anchored to gold through its thiol group, and standing nearly upright at the surface with the amino functional group on top. This molecule has been extensively studied by Surface Enhanced Raman Spectroscopy but its exact SERS spectrum remains unclear. Here we demonstrate that it can be strongly affected by at least two experimental parameters: laser power and layer density. Those features are discussed in terms of a dimerization of the PATP molecules. The free amino group affords the adsorption of other molecules, like C60. In this case, a complex multilayer system is formed and the question of its precise characterisation remains a key point. In this article, we demonstrate that surface enhanced Raman spectroscopy combined with X-Ray photoelectron spectroscopy can bring very important information about the organisation of such a self-assembled multilayer on gold. In our study, the strong evolution of Raman modes after C60 adsorption suggests a change in the organisation of aminothiophenol molecules during C60 adsorption. These changes, also observed when the aminothiophenol layer is annealed in toluene, do not prevent the adsorption of C60 molecules

Optical near-field mapping of plasmonic nanostructures prepared by nanosphere lithography

International audienceWe introduce a simple, fast, efficient and non-destructive method to study the optical near-field properties of plasmonic nanotriangles prepared by nanosphere lithography. Using a rectangular Fourier filter on the blurred signal together with filtering of the lower spatial frequencies to remove the far-field contribution, the pure near-field contributions of the optical images were extracted. We performed measurements using two excitation wavelengths (532.1 nm and 632.8 nm) and two different polarizations. After the processing of the optical images, the distribution of hot spots can be correlated with the topography of the structures, as indicated by the presence of brighter spots at the apexes of the nanostructures. This technique is validated by comparison of the results to numerical simulations, where agreement is obtained, thereby confirming the near-field nature of the images. Our approach does not require any advanced equipment and we suggest that it could be applied to any type of sample, while keeping the measurement times reasonably short

Fabrication and characterization of large metallic nanodots arrays for organic thin film solar cells using anodic aluminum oxide templates

International audienceWe present a soft method for the fabrication of well controlled plasmonic nanodots on large ITO substrate for organic solar cells. Masks of nanopatterned aluminum oxide are elaborated and deposited on ITO substrates before metal deposition. After removal of the mask, well organized and isolated metallic nanodots are observed. In this article, we focus on gold or silver nanostructures: they show a Surface Plasmon Resonance (SPR) in the visible region, an important feature for their integration in organic thin film solar cells and the final improvement of the optical properties of the cell. In addition, their near field enhancement capacity is also clearly demonstrated by surface enhanced Raman spectroscopy and FDTD method simulation. An additional advantage of this protocol is that it can be used on any kind of surface and with different metals, depending on the final application

Superimposed Arrays of Nanoprisms for Multispectral Molecular Plasmonics

International audienceMolecular plasmonics relies on the development of conductive nanostructures to yield large local electromagnetic enhancement enabling the detection of molecules located in their vicinity. Although various spectroscopic techniques benefit from such enhancement, performing different spectroscopic measurements on the same platform, remains a challenge. As such, the rational design of structures capable of enhancement effects over a large spectral range, particularly from the visible to the mid-infrared, is of great interest. Herein, we have developed a series of metallic patterns, consisting of superimposed arrays of gold nanoprisms, that have the potential for surface-enhanced Raman spectroscopy (SERS), surface-enhanced fluorescence (SEF), and surface-enhanced infrared absorption (SEIRA). We first demonstrate that a modified version of the nanosphere lithography method can be used to fabricate such platforms. Patterns with selected sizes can further be produced by electron-beam lithography with virtually no defects, thus yielding tunable and precise optical resonances from the visible to the mid-infrared range. The hexagonal lattices were composed of smaller prisms (0.25 mu m prism base length) incorporated for SERS and SEF applications and larger triangles (1-2 mu m base size) for SEIRA purposes. The superimposed patterns display regions that are compatible with SEF, SERS, and SEIRA, thus opening promising applications for multispectral detection of molecules

Bile acid receptor TGR5 is critically involved in preference for dietary lipids and obesity

International audienceWe investigated the implication of Takeda G protein-coupled receptor 5 (TGR5) in fat preference and fat sensing in taste bud cells (TBC) in C57BL/6 wild-type (WT) and TGR5 knock out (TGR5-/-) male mice maintained for 20 weeks on a high-fat diet (HFD). We also assessed the implication of TGR5 single nucleotide polymorphism (SNP) in young obese humans. The high-fat diet (HFD)-fed TGR5-/- mice were more obese, marked with higher liver weight, lipidemia and steatosis than WT obese mice. The TGR5-/- obese mice exhibited high daily food/energy intake, fat mass and inflammatory status. WT obese mice lost the preference for dietary fat, but the TGR5-/- obese mice exhibited no loss towards the attraction for lipids. In lingual TBC, the fatty acid-triggered Ca2+ signaling was decreased in WT obese mice; however, it was increased in TBC from TGR5-/- obese mice. Fatty acid-induced in vitro release of GLP-1 was higher, but PYY concentrations were lower, in TBC from TGR5-/- obese mice than those in WT obese mice. We noticed an association between obesity and variations in TGR5 rs11554825 SNP. Finally, we can state that TGR5 modulates fat eating behavior and obesity

Bile acid-receptor TGR5 deficiency worsens liver injury in alcohol-fed mice by inducing intestinal microbiota dysbiosis

International audienceBackground & aims: Bile-acid metabolism and the intestinal microbiota are impaired in alcohol-related liver disease. Activation of the bile-acid receptor TGR5 (or GPBAR1) controls both biliary homeostasis and inflammatory processes. We examined the role of TGR5 in alcohol-induced liver injury in mice.Methods: We used TGR5-deficient (TGR5-KO) and wild-type (WT) female mice, fed alcohol or not, to study the involvement of liver macrophages, the intestinal microbiota (16S sequencing), and bile-acid profiles (high-performance liquid chromatography coupled to tandem mass spectrometry). Hepatic triglyceride accumulation and inflammatory processes were assessed in parallel.Results: TGR5 deficiency worsened liver injury, as shown by greater steatosis and inflammation than in WT mice. Isolation of liver macrophages from WT and TGR5-KO alcohol-fed mice showed that TGR5 deficiency did not increase the pro-inflammatory phenotype of liver macrophages but increased their recruitment to the liver. TGR5 deficiency induced dysbiosis, independently of alcohol intake, and transplantation of the TGR5-KO intestinal microbiota to WT mice was sufficient to worsen alcohol-induced liver inflammation. Secondary bile-acid levels were markedly lower in alcohol-fed TGR5-KO than normally fed WT and TGR5-KO mice. Consistent with these results, predictive analysis showed the abundance of bacterial genes involved in bile-acid transformation to be lower in alcohol-fed TGR5-KO than WT mice. This altered bile-acid profile may explain, in particular, why bile-acid synthesis was not repressed and inflammatory processes were exacerbated.Conclusions: A lack of TGR5 was associated with worsening of alcohol-induced liver injury, a phenotype mainly related to intestinal microbiota dysbiosis and an altered bile-acid profile, following the consumption of alcohol

Post-mortem analysis of tungsten plasma facing components in tokamaks: Raman microscopy measurements on compact, porous oxide and nitride films and nanoparticles

International audienceRaman microscopy is one of the methods that could be used for future post-mortem analyses of samples extracted from ITER plasma facing. This study shows that this technique is useful for studying tungsten-based materials containing impurities including oxides and nitrides. Here, we apply pulsed laser deposition and DC argon glow discharges to produce tungsten-containing synthetic films (compact, porous) and nanoparticles and investigate the influence of their morphology on the measured Raman spectra. The amounts of oxygen and/or nitrogen in the films are also investigated. Comparative data are obtained by X-ray Photoelectrons Spectroscopy, Atomic Force Microscopy, Electron Microscopies (Scanning and Transmission), Energy Dispersive X-ray spectroscopy, Time-of-Flight Elastic Recoil Detection Analysis. The power density of the laser beam used to perform Raman microscopy is varied by up to 4 orders of magnitude (0.01-20 mW/μm 2) to investigate thermal stability of films and nanoparticles. As a first result, we give evidence that Raman microscopy is sensitive enough to detect surface native oxides. Secondly, more tungsten oxides are detected in porous materials and nanoparticles than in compact films, and the intensities of the Raman band correlate to their oxygen content. Thirdly, thermal stability of these films (i.e. structural and chemical modification under laser heating) is poor when compact films contain a sufficiently large amount of nitrogen. This finding suggests that nitrogen can be substituted by oxygen during Raman laser induced heating occurring in ambient air. Finally, our methodology can be used to rapidly characterize morphology and chemistry of the samples analyzed, and also to create oxides at the micrometer scale. keywords: PLD, Raman spectroscopy, tungsten oxide, tungsten nitride, plasma wall interaction, laser heating, post-mortem analysis