Nano-structuration de substrats à points chaud contrôlés (application à la diffusion Raman exaltée de surface)

L'élaboration d'assemblages de nanoparticules (NPs) couplées a suscité un grand intérêt ces dernières années, en vue d'applications en spectroscopies exaltées de surface. Dans ce cadre, la spectroscopie Raman exaltée de surface (effet SERS) s'inscrit comme étant un outil extrêmement sensible, permettant d'accéder à la détection de diverses molécules à l'état des traces (drogues, explosifs, molécules biologiques). Cela est rendu possible grâce à la présence d'agrégats de NPs couplées qui génèrent une forte amplification du champ électromagnétique au niveau de leur interstice, appelé point chaud. Cependant, une des difficultés majeures rencontrées est la non-reproductibilité de ces points chauds, générés par des agrégats généralement désorganisés. L'objectif de ce travail est d'élaborer et de caractériser par SERS des assemblages structurés de nanostructures d'or couplées. Deux voies sont explorées : (i) la fabrication de substrats où des NPs d'or couplées sont auto-assemblées de manière ordonnée. Cette stratégie a montré qu'un très petit nombre de NPs couplées est propice à la détection de traces. En revanche, le cas d'un grand nombre de NPs couplées est plutôt favorable pour des études analytiques classiques. Cette méthode est également adaptable à des NPs de forme diverses, (ii) La deuxième stratégie consiste à coupler des NPs d'or à un film d'or par l'intermédiaire d'un polymère thermosensible. Des études par électrochimie et par SERS en fonction de la température ont révélé une interaction entre le film d'or et les NPs. Cette interaction est dépendante de la distance entre ces deux entités qui est gouvernée par l'activité du polymère grâce à la température du milieu.PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Mechanical Coupling in Gold Nanoparticles Supermolecules Revealed by Plasmon-Enhanced Ultralow Frequency Raman Spectroscopy

International audienceAcoustic vibrations of assemblies of gold nanoparticles were investigated using ultralow frequency micro-Raman scattering and finite element simulations. When exciting the assemblies resonantly with the surface plasmon resonance of electromagnetically coupled nano-particles, Raman spectra present an ultralow frequency band whose frequency lies below the lowest Raman active Lamb mode of single nanoparticles that was observed. This feature was ascribed to a Raman vibration mode of gold nanoparticle " supermolecules " , that is, nanoparticles mechanically coupled by surrounding polymer molecules. Its measured frequency is inversely proportional to the nanoparticle diameter and sensitive to the elastic properties of the interstitial polymer. The latter dependence as well as finite element simulations suggest that this mode corresponds to the out-of-phase semirigid translation (l = 1 Lamb mode) of each nanoparticle of a dimer inside the matrix, activated by the mechanical coupling between the nanoparticles. These observations were permitted only thanks to the resonant excitation with the coupling plasmon excitation, leading to an enhancement up to 10^4 of the scattering by these vibrations. This enhanced ultralow frequency Raman scattering thus opens a new route to probe the local elastic properties of the surrounding medium

Nanoparticle transport in water-unsaturated porous media: effects of solution ionic strength and flow rate

International audienceThis paper presents the influence of ionic strength and flow on nanoparticle (NP) retention rate in an unsaturated calcareous medium, originating from a heterogeneous glaciofluvial deposit of the region of Lyon (France). Laboratory columns 10 cm in diameter and 30 cm in length were used. Silica nanoparticles (Au-SiO2-FluoNPs), with hydrodynamic diameter rang- ing from 50 to 60 nm and labeled with fluorescein derivatives, were used to simulate particle transport, and bromide was used to characterize flow. Three flow rates and five different ionic strengths were tested. The transfer model based on fractionation of water into mobile and immobile fractions was coupled with the attachment/detachment model to fit NPs breakthrough curves. The results show that increasing flow velocity induces a decrease in nanoparticle retention, probably as the result of several physical but also geochemical fac- tors. The results show that NPs retention increases with ionic strength. However, an inversion of retention occurs for ionic strength >5.10−2 M, which has been scarcely observed in previous studies. The measure of zeta potential and DLVO calculations show that NPs may sorb on both solid-water and air-water interfaces. NPs size distribution shows the potential for nanoparti- cle agglomeration mostly at low pH, leading to entrap- ment in the soil pores. These mechanisms are highly sensitive to both hydrodynamic and geochemical con- ditions, which explains their high sensitivity to flow rates and ionic strength

The mass load effect on the resonant acoustic frequencies of colloidal semiconductor nanoplatelets

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Acoustic Mode Hybridization in a Single Dimer of Gold Nanoparticles

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Inelastic Light Scattering by Multiple Vibrational Modes in Individual Gold Nanodimers

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Environmental effects on the natural vibrations of nanoplatelets: a high pressure study

International audienceResonant acoustic modes from ultrathin CdS colloidal nanoplatelets (NPLs) are probed under high pressure using low frequency Raman spectroscopy. In particular we focus on the characterization of the recently evidenced mass load effect that is responsible for a significant downshift of the NPL breathing frequency due to the inert mass of organic ligands. We show that a key parameter in the observation of the mass effect is whether the surrounding medium is able to support THz acoustic wave propagation, at a frequency close to that of the inorganic vibrating core. At low pressures, surface organic molecules show a single particle-like behavior and a strong mass effect is observed. Upon pressure loading the ligands are compacted together with the surrounding medium and slowly turned into a solid medium that supports THz acoustic phonons. We observe a continuous transition towards a fully embedded NPL with a frequency close to that of a freely vibrating slab and a progressive loss of the mass effect. The quality factor of the detected vibration significantly decreases as a result of the appearance of a "phonon-like" behavior of the environment at the origin of damping and energy dissipation. Resonant acoustic modes arise from a structure when the phonon wavelength becomes comparable to the confinement dimension. These modes have been investigated in the past few years for various geometries of nanomaterials such as spherical metallic, 1,2 semiconducting 3,4 and dielectric NPs. 5 Low frequency Raman experiments have essentially focused on nano-objects embedded in solid environments such as glassy matrices, which aroused theoretical studies to understand the coupling with the matrix. 6,7 This coupling essentially results in a damping of the modes i.e., a broadening of the Raman peaks without significant shifting of the resonance frequency as compared to a free vibration. The damping mainly originates from energy dissipation in the matrix due to the emission of THz acoustic waves. Inorganic materials can accommodate acoustic phonons with relatively high frequencies. For instance in inorganic glass, 8 metallic, 9 CdS and CdSe systems, the maximum of acoustic phonon frequency reaches several THz at the maximum of the dispersion relations. For this reason, experimental Raman spectra of embedded NPs (position and width of the resonances) have been so far well explained by core-shell 10 or core-matrix 11 models. However, the recent finding of a mass load effect from CdS and CdSe NPLs loaded with oleic acids at their surfaces suggests that the sound propagation within the organic molecules should be neglected. This is the basis of the mass loaded model where only the inertial mass of the ligands is taken into account to explain the lowering of the NPL breathing frequencies. 12 The discovery of this effect with two-dimensional nano-objects was recently extended to QDs explaining the temperature dependence of acoustic vibrations of CdSe and CdSe-CdS core-shell nanocrystals 13 and the modulation of QD acoustic vibration frequencies through the choice of surface ligands. 14 It can also provide insights into more complex geometries such as nanorod heterostructures. 15 Resonant acoustic modes in finite size structures arise when the phonon wavelength matches the confinement dimension. In the case of nanomaterials with a 3D confinement , such as nanoparticles, breathing acoustic modes with an angular momentum ℓ = 0 have been extensively studied in particular because they are Raman active. The breathing motion of a free sphere involves a radial displacement of the surface with a frequency given by ν 3D ' 0:9=D ffiffiffiffiffiffiffiffiffiffiffiffi C 11 =ρ p where D, C 11 and ρ are the sphere diameter, elastic constant and density, respectively. 1D confinement geometries such a

Influence of the Number of Nanoparticles on the Enhancement Properties of Surface-Enhanced Raman Scattering Active Area: Sensitivity versus Repeatability

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Gadolinium-Based Nanoparticles and Radiation Therapy for Multiple Brain Melanoma Metastases: Proof of Concept before Phase I Trial

Nanoparticles containing high-Z elements are known to boost the efficacy of radiation therapy. Gadolinium (Gd) is particularly attractive because this element is also a positive contrast agent for MRI, which allows for the simultaneous use of imaging to guide the irradiation and to delineate the tumor. In this study, we used the Gd-based nanoparticles, AGuIX®. After intravenous injection into animals bearing B16F10 tumors, some nanoparticles remained inside the tumor cells for more than 24 hours, indicating that a single administration of nanoparticles might be sufficient for several irradiations. Combining AGuIX® with radiation therapy increases tumor cell death, and improves the life spans of animals bearing multiple brain melanoma metastases. These results provide preclinical proof-of-concept for a phase I clinical trial

Feasibility of intratumoral 165Holmium siloxane delivery to induced U87 glioblastoma in a large animal model, the Yucatan minipig

International audienceGlioblastoma is the most aggressive primary brain tumor leading to death in most of patients. It comprises almost 50-55% of all gliomas with an incidence rate of 2-3 per 100,000. Despite its rarity, overall mortality of glioblastoma is comparable to the most frequent tumors. The current standard treatment combines surgical resection, radiotherapy and chemotherapy with temozolomide. In spite of this aggressive multimodality protocol, prognosis of glioblastoma is poor and the median survival remains about 12-14.5 months. In this regard, new therapeutic approaches should be developed to improve the life quality and survival time of the patient after the initial diagnosis. Before switching to clinical trials in humans, all innovative therapeutic methods must be studied first on a relevant animal model in preclinical settings. In this regard, we validated the feasibility of intratumoral delivery of a holmium (Ho) microparticle suspension to an induced U87 glioblastoma model. Among the different radioactive beta emitters, 166Ho emits high-energy β(-) radiation and low-energy γ radiation. β(-) radiation is an effective means for tumor destruction and γ rays are well suited for imaging (SPECT) and consequent dosimetry. In addition, the paramagnetic Ho nucleus is a good asset to perform MRI imaging. In this study, five minipigs, implanted with our glioblastoma model were used to test the injectability of 165Ho (stable) using a bespoke injector and needle. The suspension was produced in the form of Ho microparticles and injected inside the tumor by a technique known as microbrachytherapy using a stereotactic system. At the end of this trial, it was found that the 165Ho suspension can be injected successfully inside the tumor with absence or minimal traces of Ho reflux after the injections. This injection technique and the use of the 165Ho suspension needs to be further assessed with radioactive 166Ho in future studies