Les séminaires de l'UMET

The in situ and real-time detection of analytes in complex biological media demands robust, sensitive, and stable biosensors capable of signal amplification. Luminescent nanoparticles (LNPs) are promising candidates, offering exceptional brightness and photostability compared to traditional dyes.1 These LNPs fall into two main categories: intrinsically luminescent, such as Quantum Dots (QDs), or doped NPs, where dyes are encapsulated within a matrix. For imaging and sensing applications, LNPs aim to achieve excellent brightness, enhanced photostability, and strong colloidal stability in water, outperforming conventional organic dyes. Classical FRET nanosensors typically involve a donor LNP conjugated with bioreceptors that bind to a ligand labeled with an acceptor dye. While bioreceptors optimization has advanced detection limits and dynamic ranges, the roles of dye type and spatial configuration in these systems remained underexplored. In this talk, we will compare organic fluorophores (e.g., Cy5, Texas Red) and QDs as FRET donors or acceptors, identifying key molecular parameters that enhance sensor performance to provide guidelines for FRET-based assays and diagnostics.2-3 Additionally, Fluorescent Organic Nanoparticles (dFONs) will be introduced as metal-free alternatives to QDs, with comparable brightness per volume. Obtained via nanoprecipitation of hydrophobic dyes, dFONs remain underutilized as biosensors due to limited functionalization strategies.4 We demonstrate an innovative maleimide-thiol surface functionalization approach, enabling applications such as intracellular thiol sensing in the µM range5 and biotinylation for biomarker development. These advancements position dFONs as versatile, ultra-bright, and metal-free tools for next-generation diagnostics.

References : 

1. A. Ashoka, et al., Chem. Soc. Rev 2023, DOI : 10.1039/D2CS00464J

2. C. Grazon et al., Chemical Science 2022, DOI : 10.1039/D1SC06921G

3. C. Grazon, R. Baer et al., Nature Communications 2020, DOI : 10.1038/s41467-020-14942-5

4. J. Daniel et al., CRAS 2024, DOI : 10.5802/crchim.294

5. O. Dal Pra et al., Small Methods, DOI : 10.1002/smtd.202400716

The three peridotite massifs in the Zabargad island (northern Red Sea) document the exhumation of the mantle during continental rifting and the rift to drift transition. Deformation evolved from pervasive at the massif scale to localized in metric shear zones. To characterize the active processes and the role of melts and aqueous fluids in the deformation, we performed a petrostructural study of 40 samples representative of the different stages of deformation in the three massifs. Microstructures recording synkinematic crystallization of plagioclase, clinopyroxene, and orthopyroxene in the southern and amphibole-bearing spinel-websterite layers in the central and northern massifs indicate that pervasive deformation occurred in the presence of melts, but at lower pressure in the south. In the shear zones, deformation was accommodated by concomitant dislocation and dissolution-precipitation creep. Evolution from protomylonites to ultramylonites produced increasing volumes of a fine-grained polymineralic matrix where amphibole progressively replaces plagioclase and clinopyroxene. Fluid-assisted deformation at all stages is attested by the interstitial shapes of pyroxene neoblasts intermixed with olivine in the matrix. Local deformation at the brittle-ductile transition is accompanied by the crystallization of scapolite. Thermobarometry and thermodynamic modelling constrained by the microstructural observations document shearing under decreasing pressure and temperature from near solidus conditions at >1 GPa in the north and central massifs and ~0.7 GPa in the southern massif to < 600°C and <0.3 GPa in all three massifs. These data also imply increasing hydration, indicating fluid focusing and local aqueous fluid saturation in the shear zones, with sea water ingression to10 km depth. However, fluid supply was spatially heterogeneous and probably intermittent, withequilibrium only achieved locally in the ultramylonites. The present study documents thereforehow progressive strain localization and fluid-focusing in extensional shear zones enable thinningand exhumation of the mantle during continental rift and rift-to-drift transition.

I will discuss the implications of early processes related to planet formation like ²⁶Al heating and magma ocean outgassing on the volatile content and the atmospheric evolution of terrestrial planets Earth and Venus and exoplanets beyond our solar system.

La modélisation des déformations de marée observées pour les planètes telluriques est une approche complémentaire aux éventuelles données sismologiques pour décrypter leur organisation interne.
Elle apporte des contraintes sur les hétérogénéités internes mais également des contraintes rhéologiques et de densité sur les matériaux permettant ainsi une « tomographie » tidale.
Ces contraintes couplées à des modèles thermodynamiques permettent d’établir la structure actuelle de ces objets et contribuent à comprendre leur évolution géodynamique.
Dans ce séminaire, nous aborderons l’organisation des noyaux lunaire et martien ; le processus de retournement mantellique lors de la cristallisation de l’océan magmatique lunaire ; la persistance d’une zone potentiellement fondue dans le manteau martien et celle d’un contraste de viscosité conséquent entre le manteau supérieur de Vénus et le manteau inférieur. Nous aborderons également les contrastes de viscosité entre la lithosphère et l’asthénosphère martienne. Les enjeux sur la caractérisation des propriétés rhéologiques (rigidité, viscosité) de matériaux haute pression (selon les textures, taux de fusion) seront abordés.