Vibrational density of states and thermodynamics at the nanoscale: the 3D-2D transition in gold nanostructures

International audienceSurface enhanced Raman scattering (SERS) is generally and widely used to enhance the vibrationalfingerprint of molecules located at the vicinity of noble metal nanoparticles. In this work, SERS isoriginally used to enhance the own vibrational density of states (VDOS) of nude and isolated goldnanoparticles. This offers the opportunity of analyzing finite size effects on the lattice dynamics whichremains unattainable with conventional techniques based on neutron or x-ray inelastic scattering. Byreducing the size down to few nanometers, the role of surface atoms versus volume atoms becomedominant, and the “text-book” 3D-2D transition on the dynamical behavior is experimentallyemphasized. “Anomalies” that have been predicted by a large panel of simulations at the atomic scale,are really observed, like the enhancement of the VDOS at low frequencies or the occurrence of localizedmodes at frequencies beyond the cut-off in bulk. Consequences on the thermodynamic properties atthe nanoscale, like the reduction of the Debye temperature or the excess of the specific heat, have beenevaluated. Finally the high sensitivity of reminiscent bulk-like phonons on the arrangements at theatomic scale is used to access the morphology and internal disorder of the nanoparticles

Ultra-low-energy Ion Beam Synthesis for Nanotechnology and Nanostructures

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Hyposensitivity to the amnesic effects of scopolamine or amyloid beta25-35 peptide in heterozygous acetylcholinesterase knockout (AchE+/-) mice

International audienceAcetylcholinesterase (AChE) is the main catabolic enzyme of acetylcholine, responsible for the synaptic clearance of the neurotransmitter from the synaptic cleft. Decrease in AChE expression, or activity, results in increased cholinergic tonus in the brain or periphery, with concomittant regulations of nicotinic and muscarinic receptors expression. We generated AChE knockout mice and characterized the behavioral phenotype of heterozygous animals, particularly focusing on learning and memory functions. Male and female, AChE+/- and AChE+/+ littermate controls (129sv strain), tested at 5-9 weeks of age, failed to show any difference in terms of locomotion, exploration and anxiety parameters in the open-field test. Animals were then tested for place learning in the water-maze. They were trained using a 'sustained acquisition' protocol (3 swims/day during 5 days) or a 'mild acquisition' protocol (2 swims/day during 9 days) to locate an invisible platform in fixed position (reference memory procedure). Then, during 3 days, they were trained to locate the platform in a variable position (working memory procedure). Learning profiles and probe test performances were unchanged in AChE+/- mice as compared with AChE+/+. Mice were then treated with the muscarinic M1 antagonist scopolamine (0.5, 5 mg/kg sc) 20 min before each training session (3 swims/day during 5 days). Scopolamine impaired learning at both doses in AChE+/+ mice, but only at the highest dose in AChE+/- mice. Moreover, the central injection of amyloid beta25-35 peptide (9 nmol) failed to induce learning deficits in AChE+/- mice, contrarily to AChE+/+ controls. These behavioral study shows that the increase in cholinergic tonus did not result in increased memory abilities in these heterozygous AChE+/- mice, but allowed a significant prevention of the deleterious effects of muscarinic blockade or amyloid toxicity

Hyposensitivity to the amnesic effects of scopolamine or amyloid β25–35 peptide in heterozygous acetylcholinesterase knockout (AChE+/−) mice

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Electron transport through a metallic nanoparticle assembly embedded in SiO2 and SiNx by low energy ion implantation

International audienceOriginal substrates have been developed to offer a new approach to modulate and analyse simultaneously electro‐optical and transport properties through an assembly of metallic nanoparticles (NPs). Using low energy ion implantation, silver NPs have been synthesized at the vicinity of the free surface of a SiO2 or SiNx matrix. Varying the parameters of the process allows us to modify the density of NPs and their distance to the surface. While Ag NPs surface fraction in SiO2 cannot exceed 20%, it reaches 30% in SiNx. In the latter case, NPs with mean diameter is about 2.1 nm have an interdistance compatible with tunnel effect. We then developed devices that electrically address the embedded assembly of NPs for I‐V characterization. The transport measurements on these devices show that an exploitable conduction is possible within the Ag NPs assembly in SiNx. The Arrhenius‐type temperature dependence model was successfully applied demonstrating that electron transport follows a simple thermally activated behaviour with the occurrence of a strongly localized regime

Ag doped silicon nitride nanocomposites for embedded plasmonics

International audienceThe localized surface plasmon-polariton resonance (LSPR) of noble metal nanoparticles (NPs) is widely exploited for enhanced optical spectroscopies of molecules, nonlinear optics, photothermal therapy, photovoltaics, or more recently in plasmoelectronics and photocatalysis. The LSPR frequency depends not only of the noble metal NP material, shape, and size but also of its environment, i.e., of the embedding matrix. In this paper, Ag-NPs have been fabricated by low energy ion beam synthesis in silicon nitride (SiNx) matrices. By coupling the high refractive index of SiNx to the relevant choice of dielectric thickness in a SiNx/Si bilayer for an optimum antireflective effect, a very sharp plasmonic optical interference is obtained in mid-range of the visible spectrum (2.6 eV). The diffusion barrier property of the host SiNx matrix allows for the introduction of a high amount of Ag and the formation of a high density of Ag-NPs that nucleate during the implantation process. Under specific implantation conditions, in-plane self-organization effects are obtained in this matrix that could be the result of a metastable coarsening regime

Myostatin deficiency in skeletal muscle alters the lipid composition of mitochondrial membranes

Poster également présenté lors du séminaire: "Cardiolipin as Key Lipid of Mitochondria In Health and Disease"30 September - 1 October 2015, Florence, Italie.Myostatin deficiency in skeletal muscle alters the lipid composition of mitochondrial membranes. 16. Congrès de l'Association des Chercheurs en Activités Physiques et Sportive

Myostatin deficiency in skeletal muscle alters the lipid composition of mitochondrial membranes

Poster également présenté lors du séminaire: "Cardiolipin as Key Lipid of Mitochondria In Health and Disease"30 September - 1 October 2015, Florence, Italie.Myostatin deficiency in skeletal muscle alters the lipid composition of mitochondrial membranes. 16. Congrès de l'Association des Chercheurs en Activités Physiques et Sportive

Three Dimensional design of silver nanoparticles assemblies embedded in dielectrics: application to plasmon-enhanced scattering and biocide properties

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Effects of long-term administration of saturated and n-3 fatty acid-rich diets on lipid utilisation and oxidative stress in rat liver and muscle tissues

The incidence of metabolic syndrome components including obesity, lipid deregulation, insulin resistance (IR) and non-alcoholic fatty liver disease is increasing rapidly in wealthy societies. The present study was designed to determine the effect of different nutritional lipid patterns (quantity and quality) on lipid utilisation and oxidative stress in the liver and muscle of rats in an integrated fashion. A total of forty-eight Wistar male rats were fed for 12 weeks with a mixed, lard or fish-oil diet, containing either 50 or 300 g lipid/kg. Rats developed liver steatosis associated with moderate liver injury when fed the 30% lipid diets, in spite of the absence of overt obesity or IR, except when fed the lard 30% lipid diet. The intake of the 30% lipid diets decreased hepatic lipogenesis and mitochondriogenesis and increased lipid peroxidation and protein oxidation. Surprisingly, muscle lipid content was not modified whatever the administered diet. The intake of the 30% lipid diets increased the muscle protein expression of fatty acid (FA) translocase/cluster of differentiation 36 (FAT/CD36), PPAR gamma co-activator 1 alpha (PGC-1 alpha) and muscle carnitine palmitoyltransferase 1 (m-CPT1), reflecting increased FA transport in the muscle associated with increased oxidative metabolism. The lard 30% lipid diet led to IR without modifying the muscle lipid content. The fish-oil 30% lipid diet failed to prevent the development of hepatic steatosis and made the tissues more prone to oxidation. Overall, the present study suggests that the FA composition of muscle is more important than lipid accumulation itself in the modulation of insulin sensitivity, and indicates that precaution should be taken when advising an unphysiologically high (pharmacological) supplementation with long-chain n-3 PUFA