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International audience; This study introduces a new nanocrystallization method assisted by ultrasounds that produces needles or nanocubes of CMONS, a stilbene dye, with an excellent control over the polymorphism, and with a narrow size distribution. Owing to the production of radicals from dissolved dioxygen by high-intensity ultrasounds, trans-to-cis isomerization was observed in the absence of nitrogen bubbling, with the formation of two distinct crystalline phases for the different diastereomers. The crystallinity of CMONS needles was probed by various techniques, including X-ray and electron diffractions, fluorescence spectroscopy, and dynamic nuclear polarization (DNP) enhanced solid-state nuclear magnetic resonance. The latter was used to hyperpolarize 1 H nuclei and to record 1 H-13 C and 1 H-15 N CPMAS NMR spectra at natural isotopic abundance with very high signal-to-noise ratio. With such sensitivity, one can easily discriminate between cis and trans-I forms of CMONS, detect the presence of multiple polymorphic phases (even with minor contributions) and check the absence of amorphous phase. Finally, the mechanism involved in the formation of CMONS needles was ascertained after stabilizing intermediate nanocubes against Ostwald ripening and ordered aggregation mechanisms using the CTAB surfactant.

International audience; Flexible barriers can be used to trap woody debris or debris flows. However, their small scale modelling is challenging because of their possible deformation. This article addresses how to meet the partial mechanical similitude of manufactured flexible barriers. Relevant dimensionless parameters are defined from flow velocity, barrier geometry, and component mechanical properties. These similitude criteria are validated using numerical simulations of barriers exposed to a hydrodynamic loading at various scales. The simulations also confirm the importance of accounting for the mechanical characteristics of the barrier components when designing model barriers in view of achieving realistic deformations. Next, a real barrier with complex features is scaled to conduct flume experiments. This scaled barrier is 3D-printed with material selected to achieve the mechanical similitude criterion. Another validation of this approach is performed considering hydrostatic loading and checking that simulated and measured deformations are similar. As an application case, the deformations measured during the experiments performed with woody debris are also compared to the hydrostatic loading.Introduction

Several types of Quantum Dots (QDs) (CdS, CdSe and InP, as well as core-shell QDs such as type I InP-ZnS, quasi type-II CdSe-CdS and inverse type-I CdS-CdSe) were considered for generating α-aminoalkyl free radicals. The feasibility of the oxidation of the N-aryl amines and the generation of the desired radical was evidenced experimentally by quenching of the photoluminescence of the QDs and by testing a vinylation reaction using an alkenylsulfone radical trap. The QDs were tested in a radical [3+3]-annulation reaction giving access to tropane skeletons and that requires the completion of two consecutive catalytic cycles. Several QDs such as CdS core, CdSe core and inverted type I CdS-CdSe core-shell proved to be efficient photocatalysts for this reaction. Interestingly, the addition of a second shorter chain ligand to the QDs appeared to be essential to complete the second catalytic cycle and to obtain the desired bicyclic tropane derivatives. Finally, the scope of the [3+3]-annulation reaction was explored for the best performing QDs and isolated yields that compares well with classical iridium photocatalysis were obtained.

In piezoelectric inertia motors, friction is not a synonymous of energy loss but is the source of motion. Their performances are thus prone to wear and friction coefficient variation. To address these issues, this paper first aims at improving the understanding of tribological solicitations by means of a dedicated in situ tribotesting while exploiting the 3rd body flow framework. Beyond the introduction of transparent glass pins to see inside the contact in operation, the key of this work is to consider both the mechanism effect and the friction couple. As a result, a solution has been proposed to multiply the motor lifetime by more than ten while keeping stable speed performances, and, above all, without multiplying tests with numerous friction materials.

The discrete circle map is the archetypical example of a driven periodic system, showing a complex resonance structure under a change of the forcing frequency known as the devil's staircase. Adler's equation can be seen as the direct continuous equivalent of the circle map, describing locking effects in periodic systems with continuous forcing. This type of locking produces a single fundamental resonance tongue without higher-order resonances, and a devil's staircase is not observed. We show that, with harmonically modulated forcing, nonlinear oscillations close to a Hopf bifurcation generically reproduce the devil's staircase even in the continuous case. Experimental results on a semiconductor laser driven by a modulated optical signal show excellent agreement with our theoretical predictions. The locking appears as a modulation of the oscillation amplitude as well as the angular oscillation frequency. Our results show that by proper implementation of an external drive, additional regions of stable frequency locking can be introduced in systems which originally show only a single Adler-type resonance tongue. The induced resonances can be precisely controlled via the modulation parameters.

International audience; Herein, we demonstrate the potential of ultrabright fluorescent silica-coated organic nanocrystals for two-photon in vivo imaging. These unique nanoparticles (NPs) containing a crystalline core of small push-pull dipolar dye are specifically designed to exhibit two-photon absorption for 2 fluorescence imaging. The NPs can be easily functionalized using click chemistry in pure water, with preservation of the organic core. A novel small-volume DLS technique was used to evaluate the effect of PEGylation on the colloidal stability of the NPs in complex media containing salts and proteins, mimicking the composition of blood serum. The potential of these bright red-emitting NPs for two-photon fluorescence imaging is demonstrated both in vitro and in vivo.

Background French Guiana, a French overseas department located in South America between Brazil and Surinam, is the only European territory geographically located in the Amazonian forest complex and is considered endemic for yellow fever (YF). In the context of the emergent threat of YF in Latin America, we conducted a large household cross-sectional survey from June to October 2017 to estimate vaccination coverage in the population and to determine associations with sociodemographic and geographical characteristics. Methodology/Principal findings In total, 1,415 households and 2,697 individuals were included from the 22 municipalities of French Guiana. YF vaccination coverage was estimated at 95.0% (95% CI: 93.4–96.2) in the entire territory but was spatially heterogeneous, with the lowest levels estimated in the western part of the territory along the Surinamese cross-border region, particularly in children under 16 years who were not enrolled in school, immigrant adults and disadvantaged populations with low socioeconomic indexes. Conclusions/Significance Despite the good vaccination coverage against YF in the general population of French Guiana resulting from the compulsory nature of YF vaccination for residents and travelers, there is an urgent need to improve vaccination coverage in vulnerable populations living in the northwestern part of the territory to limit the risk of transmission in the context of the emerging YF threat in South America. Despite the relative rarity of YF and the significant number of infectious and tropical diseases in French Guiana, clinicians should adopt a high index of suspicion for YF, particularly in vulnerable and at-risk populations., Author summary Yellow fever (YF) is the most severe arbovirus to circulate in the Americas. French Guiana, a French overseas department located in South America between Brazil and Surinam, is the only European territory geographically located in the Amazonian forest complex and is considered endemic for YF. We conducted a large general population survey from June to October 2017 to estimate vaccination coverage in the population and to identify target vulnerable populations for catch-up vaccination strategies. In total, 1,415 households and 2,697 individuals were included from the 22 municipalities of French Guiana. YF vaccination coverage was estimated at 95.0% (95% CI: 93.4–96.2) in the entire territory but was spatially heterogeneous, with the lowest levels estimated in the western part of the territory along the Surinamese cross-border region, particularly in children under 16 years who were not enrolled in school, immigrant adults and disadvantaged groups of populations with low socioeconomic indexes. Our findings showed that vaccination campaigns should be prioritized and adapted to improve vaccination coverage among vulnerable populations living in the northwestern part of the territory to limit the risk of transmission in the context of the emerging YF threat in South America. Despite the relative rarity of YF and the significant number of infectious and tropical diseases in French Guiana, clinicians should adopt a high index of suspicion for YF, particularly in vulnerable and at-risk populations.

A deeply etched pit reflector is presented in this paper. The pit is not depth sensitive and has a comparable reflection and loss to a slot. Moreover, a two-section 750 ${\mu }{\text {m}}$ laser cavity based on the pits is demonstrated. The laser achieved a side-mode suppression ratio of 40 dB, a linewidth of 280 KHz, and tuning across 40 nm.

Tribology is not only science of contacts and friction. Tribologist must also take into account the mechanism dimension of rubbing contacts: vibrations propagations, damping and friction–vibration coupling. This is especially true for piezoelectric Inertia Drive Motors. IDM use the stick-slip phenomenon to make micrometric steps along a centimetric stroke. Actuation frequency – kHz – generates parasitic vibrations coupled with the overall system. This investigation aims to understand how these vibrations are created, propagate and interact. Through three experiments on a real IDM, two ways are studied: vibration damping and actuation signal modification. Better understanding of the mechanism impact leads to an energetic balance increase of 25.5%.

International audience; We have developed a bright optical setup especially optimized for surface enhanced Raman scattering correlation spectroscopy. We show that the brightness of the experiment combined with the correlation approach permits in situ access to the size and shape of the SERS-active aggregates in solution despite a very weak SERS signal of the adsorbed molecules. As a result we demonstrate that dimers and larger SERS-active aggregates can be identified through the temporal fluctuations of the SERS signal of only a few hundred of adsorbed molecules i.e at zeptomole adsorbate concentrations. Monomers covered by a monolayer of MBA were also identified. These results open a way for single nanoparticle sensing, for single molecule SERS-active aggregate characterization or for quantitative monitoring of functionalization processes on metallic objects.

We study a system of two mutually delay-coupled semiconductor lasers for integration in a Photonic Integrated Circuit. This system is described by single mode rate equations, which are a system of delay differential equations with one fixed delay. A comprehensive frequency analysis presented, which predicts stable symmetric and symmetry-broken one-colour, periodic, quasi-periodic and undamped relaxation oscillation states for low coupling regions. These states are confirmed with the obtained bifurcation diagrams. The obtained frequencies are benchmarked against the experimental outcomes.

The photophysical and nonlinear optical properties of water-soluble chromophore-functionalised tris-dipicolinate complexes [LnL3](3-) (Ln=Yb and Nd) are thoroughly studied, revealing that only the Yb(III) luminescence can be sensitized by a two-photon excitation process. The stability of the complex in water is strongly enhanced by embedding in dispersible organosilicate nanoparticles (NPs). Finally, the spectroscopic properties of [NBu4]3 [YbL3] are studied in solution and in the solid state. The high brightness of the NPs allows imaging them as single objects using a modified two-photon microscopy setup in a NIR-to-NIR configuration.

Here we demonstrate that the encapsulation of crystal-state emitters in sol–gel matrices is an efficient way to produce bright nanotracers for bioimaging applications. We report the development of a family of fluorescent organic@silicate core–shell nanoparticles (NPs) containing an organic core surrounded by a silicate shell, with a high loading of dyes (30–40 wt%), prepared by an original spray-drying technique combining sol–gel chemistry and nanocrystallization. Four dyes were encapsulated within the silicate nanoparticles. The crystallinity of the organic core is discussed on the basis of characterization by electron microscopy and fluorescence spectroscopy. Bright, red-emitting core–shell NPs have been produced, which are promising for use in bio-imaging.

We model the situation of two lasers in a face-to-face arrangement, optically coupled through an attenuating element, where the distance between the lasers is on a scale typical in photonic integration (hundreds of micrometers to millimeters). We account for the existence of a frequency difference between the two single-mode lasers. Modified versions of the Lang-Kobayashi equations were employed to describe the interaction. By solving this delay differential equation system, we characterized different dynamical regimes including one- and two-color states and self-pulsations. We focus on the effect varying coupling strength and detuning between the lasers has on the frequencies of the lasers. Using the results of this frequency study, we identify the bifurcations causing changes between the different frequency regimes.

Silicon carbide (SiC) power devices are the only commercialized components to run at high voltage and high temperature. Normally on junction field-effect transistors (JFETs) have lower on-state resistance and lower output capacitance than other SiC switches, which reduces conduction and switching losses. However, normally on power devices induce a short-circuit in voltage-fed inverters (VFI) when the gate driver is not powered prior to the bus supply. This is a power-up limitation that has not received much attention in the literature, especially for safety systems that can be used in an integrated circuit capable of running at elevated temperature. This paper describes an original solution based on SiC JFETs to secure the inverter operation at power-up without gate driver supply for the SiC JFETs. The reliability test of the protection circuit and his impact on the ageing of the JFET of the VFI are also presented. The safety system is capable of running in elevated ambient temperatures. Experimental results have been carried out in a 540 V, 10 A inverter and at ambient temperatures from 27 to 200 °C.

International audience; Les moteurs piézoélectriques pas-à-pas (SPA) utilisent le principe de stick&slip pour convertir l'énergie électrique en énergie mécanique grâce à une interface de frottement. Ces moteurs permettent une haute résolution de positionnement (10cm voire illimitées en rotation) sont proposées en conservant le même encombrement. Le développement de mécanismes à plusieurs degrés de libertés est également facilité. Ici, un banc de test expérimental et quatre prototypes - linéaire longue course, rotatif, linéaire à force d'actionnement élevée et mécanisme à trois degrés d'actionnement – sont présentés et ont permis d'apprécier rapidement les avantages de cette nouvelle structure.

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This paper presents a qualitative description of the punch-through mechanism in Silicon Carbide (SiC) JFET from Infineon/SiCED. A detailed one-dimensional analytical expression is derived for the current-voltage characteristic of the punch-through effect in the SiC JFET. The proposed model based on physical parameters is validated with experimental results for low current level.

The SiC JFET is commercially available as a normally-on device. In an inverter leg configuration, many temperature effects must be compensated. Moreover, specific safety functions have to be implemented and the JFET drivers are generally the best locations to implement latter requirements. The paper describes experimental results about a SOI CMOS core driver operated up to 250°C. Particularly, an option is presented to compensate for the decrease in the driver output current with temperature. It is also demonstrated primary results of the integration of an anti short-circuit solution previously verified as a hybrid vehicle. It is shown that the reactivity of the safety function is reduced to less than 5μs at 250°C compared to 100μs in earlier vehicle at 200°C.

This paper reports the design, fabrication and experimental performance of a 2kW, 20kHz, High Temperature, three-phase, all-SiC JFET Voltage Source Inverter (VSI). The inverter includes a specific JFET driver and a DC-link capacitor. All these elements have been validated over a wide temperature range, between 25°C and 200°C. The power device used, a 1200V, 15A, JFET from SiCED has been characterized up to 200°C. An innovative reliable protection circuit for normally-on devices is also presented and validated.

The preparation of a single phase LaNiO 2 by controlled H 2 reduction of the perovskite LaNiO 3 is reported. The different steps of the synthesis are detailed. The structural characterization is made by X-ray diffraction (XRD) and neutron powder diffraction (NPD) and discussed; the derived crystal structure is the infinite-layer CaCuO 2 . Both XRD and NPD patterns are characterized by anisotropic shape broadening originating from size effect linked to the reduction process. From NPD, the LaNiO 2 powder is composed of platelet-like crystallites having an average thickness equal to 20 nm along the [001] direction. A modulation of the neutron diffraction background is observed and discussed in connection to the reduction process.

The composition LaNi0.5Cu0.5O3−δ has been prepared by heat treating a polyacrylamide xerogel in flowing O2. A perovskite type structure starts to crystallise at 700 °C and is achieved at 1000 °C. TGA data point to the formation of a rather strongly oxidised compound (δ ≤ 0.09). As the solid state reaction of a mixture of La2O3/NiO/CuO powder oxides never yields a perovskite, the part of the sol–gel route in this synthesis proves to be crucial. On the basis of X-ray and neutron diffraction results, the existence of a cupronickelate having a rhombohedral perovskite type structure is proved. Rather unexpectedly, an electron diffraction study of the as-prepared composition at 1000 °C reveals the presence of two sets of perovskite type cupronickelate microcrystals: a copper rich one with a fixed composition 67% Cu and a nickel rich one with a small range of compositions 59 ≤ Ni% ≤ 67. The latter microcrystals feature the rhombohedral LaNiO3 perovskite whereas the former one, due to the partial presence of Cu(II), frequently shows an orthorhombic [2ap√2 × 2ap√2 × ap] supercell. Thus, the composition LaNi0.5Cu0.5O3−δ. has to be understood in terms of a nanoscale segregated pseudo solid solution formed of two lanthanum cupronickelates, enriched in copper and nickel, respectively.

International audience; The slow flocculation of silver nanoparticle (NP) aggregates obtained through p-mercaptobenzoic acid (MBA) linker molecules was analyzed by surface-enhanced Raman scattering (SERS) correlation spectroscopy. We demonstrate that our experimental setup, together with the quantitative exploitation of the SERS intensity autocorrelation functions (ACFs) measured from the MBA molecules, enables to determine quantitatively and in situ the size of the SERS active clusters. Moreover, we show that it is possible to characterize the different states of aggregation during cluster formation simply by measuring the size of such silver aggregates. This has been accurately performed for both larger-size aggregates down to very few NPs only. We finally show that our approach is also sensitive to detect and analyze the SERS signal obtained from MBA molecules sitting on nonaggregated NPs. These experiments pave the way to the in situ characterization of functionalized metal NPs as well as the in situ monitoring of NP aggregation, in conjunction with deriving the optical properties of the as-formed clusters.

En 2011, l’Université Joseph Fourier (UJF), s'appuyant sur la force de la recherche interdisciplinaire des laboratoires grenoblois dans les Nanosciences et Nanotechnologies, a ouvert deux majeures : un M1 « Physique fondamentale et Nanosciences » et un M1 « Chimie et Nanosciences ». Dans ce cadre, des Travaux Pratiques interdisciplinaires et interplateformes ont été mis en place afin d’illustrer de manière concrète la convergence de la physique, de la chimie et de la biologie à l’échelle micro/nanométrique qui s’appuie sur les micro et nanotechnologies. Cet article décrit en détail ces TP et expose leur intérêt pédagogique pour la formation des étudiants ainsi que pour des enseignants-chercheurs.

Short synthetic sequences to carbohelicenes have been achieved under thermal conditions, without using photochemistry and high dilution. Couplings of aromatic bis(bromomethyl) moieties, in the presence of an excess of LiHMDS, are key reactions in the final ring closures to carbohelicenes. These optimized, quick and efficient reactions occur at 0°C within 10 min. and often provide [5]-helicene, [5]-helicene derivatives and [7]-helicene in ∼75% yield. Preliminary data questioned the formation of carbenoid anions and carbenes in the so called “carbenoid couplings”.

The preparation of core–shell nanoparticles constituted by organic nanocrystals embedded in amorphous organosilicate shells is based on the controlled drying of micrometer-sized droplets produced f...

10 pages; International audience; Turning off a SiC VJFET from INFINEON requires to apply a gate-to-source voltage comprised between the JFET gate threshold voltage and the punch-through voltage. Unfortunately, for applications operating over a large temperature range, these two limits vary with the temperature and reduce the useful blocking gate-to-source voltage range as the temperature rises. So, the punch-through temperature dependence is a very important feature for applications operating in a wide temperature range like aeronautic applications. This paper addresses the analysis and modeling of the punch-through phenomenon and its dependence to the temperature. The proposed model gives a good agreement with the experimental data.

International audience; SiC JFETs are experimentally tested to verify their robustness against Lightning induced strokes. The experimental set-up is fully described. A lightning surge generator is built and a SiC JFET is stressed. The full thermal response of the SiC JFET internal temperature is obtained from a specific temperature estimation technique at different time steps during the surge test. This short time thermal response is compared and validated by a conventional 1-D thermal model. This work shows that for a moderate lightning stroke, according to standards [1], the JFET temperature rise is less than 60°C, which is acceptable in most circumstances.

International audience; The aim of this paper is to investigate the ability of a vertical structure JFET to operate in an inverter leg without any internal or external diode. The JFET is characterized to show the reverse conduction capability while the gate-to-source voltage is lower than the threshold voltage. An inverter leg is tested at 540 V /5 A and 50 kHz. A specific test board is implemented to assess a safe operation over a period of time.

International audience; We present the first non-resonant and non-enhanced Raman correlation spectroscopy experiments. They are conducted on a confocal microscope combined with a Raman spectrometer. The thermal fluctuations of the Raman intensities scattered by dispersions of polystyrene particles of sub-micrometric diameters are measured and analysed by deriving the autocorrelation functions (ACFs) of the intensities. We show that for particles of diameter down to 200 nm, RCS measurements are successfully obtained in spite of the absence of any source of amplification of the Raman signal. For particles of diameter ranging from 200 to 750 nm, the ACFs present a time-decay behaviour in accordance with the model of free Brownian particles. For particles of 1000 nm in diameter, the AFCs present a different behaviour with a much smaller characteristic time. This results from the dynamics of a single-Brownian particle trapped in the confocal volume by the optical forces of the focus spot.

International audience; Normally-On Silicon Carbide (SiC) JFETs are good candidates for power switches in high temperature applications, in Three-Phase Voltage-Fed Inverters used to drive Electro-Mechanical Actuators (EMA) for the more electrical aircraft where the ambient varies from -55 °C to 200 °C. The power of the EMA is in the 1 to 5 kW range, the DC bus voltage is 540 V. It is also necessary to implement passive subsystems such as Electro-Magnetic-Interference (EMI) flters, power inductors, transformers, packaging and interconnection solution that withstand the wide temperature range. The gate driver for normally-On devices must include a safe solution against short-circuit in the event of a power supply failure. The experimental converter is built using engineering samples such as SiC JFETs, SOI drivers and laboratory made components such as inductive wire wound, nano-crystalline core components, SOI integrated driver, assembled with a high temperature package and technology. Finally, the Smart EMA test bench is presented.

International audience; We have developed a versatile, one-step process to synthesize in large amounts hybrid core-shell nanoparticles (NPs) made up of an organic crystallized core embedded in amorphous organosilicate shells. These NPs exhibit a hydrophilic surface and a high fluorescence intensity arising from the organic crystal core. Their preparation is based on a controlled drying process of micrometre-sized droplets (spray) from sol-gel solutions leading simultaneously to the confined nucleation and growth of dye nanocrystals and to the formation of silica-based shells. In this paper, we present several experimental optimizations of the spray-drying process to reduce the average NP size and size distribution. This was achieved by combining several physical parameters of spray-drying and the chemistry of the initial sols. Original precursors were developed for the formation of optimized silicate shells. TEM analysis in diffraction mode showed that organic cores are single crystals. On the other hand, the negatively charged silicate shells led to colloidally stable NPs which is promising for the development of bright fluorescent tracers excited by two-photon absorption for in vivo imaging.

International audience; The SiC JFET is commercially available as a normally-on device. In an inverter leg configuration, many temperature effects must be compensated. Moreover, specific safety functions have to be implemented and the JFET drivers are generally the best locations to implement latter requirements. The paper describes experimental results about a SOI CMOS core driver operated up to 250°C. Particularly, an option is presented to compensate for the decrease in the driver output current with temperature. It is also demonstrated primary results of the integration of an anti short-circuit solution previously verified as a hybrid vehicle. It is shown that the reactivity of the safety function is reduced to less than 5μs at 250°C compared to 100μs in earlier vehicle at 200°C.

International audience; A multi-physics model of the VJFET with a lateral channel is presented. The model has been implemented and tested in SABER using the MAST language. The model includes an asymmetric representation of the lateral channel which is the main contribution of the paper. The blocking condition is not so obvious and it is presented in details. Each junction of the structure is represented as a Shockley pn-junction model in parallel with the associated junction capacitance. The comparison between simulations and experiments yields to satisfying results, both in static and dynamic conditions. The analysis of the remaining difficulties to be solved is given.

International audience; Normally-on Silicon Carbide (SiC) JFETs are powerful power switches that allow improvement of the efficiency and high temperature operation of Voltage Fed Inverter (VFI). Moreover, the need for heavy and costly cooling system can be radically decreased due to the high thermal conductivity that exhibits the SiC material compared to Si counterpart. However some safety considerations have to be taken against short-circuit and voltage breakdown. In this paper, it is proposed an overview of the failure mechanisms of the SiC JFET. Fast and reliable solutions to protect SiC JFETs are also presented. Experimental validation of such protections and investigation of gate destruction mode are proposed.

A polymerizable amphiphile polymer containing PEG was synthesized and used to encapsulate quantum dots in micelles. The quantum dot micelles were then polymerized using a “clean” electron beam process that did not require any post-irradiation purification. Fluorescence spectroscopy revealed that the polymerized micelles provided an organic coating that preserved the quantum dot fluorescence better than nonpolymerized micelles, even under harsh conditions.

We review our work on several strategies to elaborate multifunctional nanoparticules for two-photon imaging or/and photodynamic therapy. Our first strategy is based on the incorporation of two-photon hydrophobic fluorophors in bio-compatible pluronic micelles using the mini-emulsion technique. Our second strategy is based on fluorescent organic nanocrystal grown in silicate spheres. These core-shell hybrid nanoparticles are obtained by a spray-drying process from sol-gel solutions. Our third strategy consists in the encapsulation of hydrophilic molecules in the water core of gold nanospheres. They are obtained by a stabilized emulsion in biphasic liquid-liquid medium without surfactant. Keywords: Copolymer micelles, Core-shell hybrid nanoparticles, silicate nanoshells, Gold nanoshells, Two-photon imaging, Photodynamic phototherapy 1. INTRODUCTION Cerebral imaging has become an important diagnostic tool in medicine. In many cases, it is necessary to visualize capillaries as deep as possible in the cortex to image the 3D tumor microvascularization (angiography). The two-photon fluorescence scanning microscopy uses fluorescent dyes injected in the blood vessels. The relative difficulties are to synthesize non diffusible and brilliant labels combining several properties: high intensity of two-photon excited fluorescence, biocompatibility and large size (a few tens of nm) to avoid diffusion across the blood vessel walls, which show often an increased permeability in tumors

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Short syntheses of [5]-helicene have been accomplished under thermal conditions, without using photochemistry and high dilution. Key reactions comprised a McMurry coupling of a dialdehyde or a carbenoid-type coupling of aromatic bis(bromomethyl) moieties. The last coupling provided a 7290 yield of [5]-helicene on a gram-scale (15 min., 0°C).

International audience; The sol-gel chemistry combined to a spray-drying process allowed us to control the formation of original hybrid core-shell nanoparticles constituted by molecular nanocrystals of rubrene embedded in biocompatible silicate spheres. With a good management of all the physical (gas flows, temperatures) and chemical (dye, solvent and alkoxide natures, concentrations, and hydrolysis and condensation conditions) parameters, we optimized a one-step and self-assembly process allowing to obtain nanoparticles exhibiting promising optical properties such as highly fluorescent labels (two-photon excitation) for medical imaging. Moreover, the presence of Si-OH functions on the silicate shell surface make easy to functionalize these fluorescent nanoparticles by grafting biomolecules for targeting properties. The confined nucleation and growth of rubrene nanocrystals in sol-gel silicate spheres during their drying in the air laminar flows, prevents any phase segregation or particle coalescence and stabilizes mechanically and chemically the organic cores. The first particle sizes obtained in these first experiments are ranging between 80 and 600 nm, but lower diameters will be easily prepared by increasing the solvent amount. Transmission electron microscopy was used to characterize the rubrene organic cores. The electron diffraction patterns performed at 100 K, under low-dose illumination to avoid amorphization of the samples during electron irradiation, have shown the good crystallinity of the NP rubrene cores that seem to be constituted by single rubrene nanocrystals. Finally, optical confocal microscopy, used in reflection and fluorescence modes, showed that all the core-shell particles are strongly fluorescent. This high fluorescence intensity arises from the high molecule numbers of rubrene nanocrystals, which enhance the absorption and emission cross sections.

International audience

Water soluble fluorescent nanocrystals were obtained by encapsulation of hydrophobic quantum dots (QDs) with amphiphilic phospholipids derived from the ring opening metathesis of norbornene-based monomers. The robustness of the newly coated quantum dots was assessed by comparative studies under various ionic conditions which indicated an overall enhancement of their fluorescence stability.