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Systematic evaluation of Li3PO4 coatings on LNMO for enhanced cycling stability using NMR-based interfacial probes
No full textInternational audienceHigh-voltage cathodes such as LiMn1.5Ni0.5O4 (LNMO) offer promising energy density but suffer from interfacial degradation accelerated at elevated voltages and temperatures. Here, we present a comprehensive comparative study of three Li3PO4 coating methods (precipitation, sol–gel, and dry sol–gel routes) applied to commercial LNMO powders. Coating quality and intimacy are systematically assessed using a correlative, multitechnique approach including 7Li and 31P solid-state NMR, X-ray diffraction, and electrochemical testing. A key insight from this study is the use of ssNMR relaxation behavior as a sensitive probe of coating intimacy to the active phase. The methodology is validated on commercial LNMO and reproduced in a lab-synthesized LNMO to demonstrate reproducibility across particle morphologies. Among all methods, the sol–gel route produced a uniform ∼20 nm coating with optimal surface contact, translating to improved rate capability and outstanding high-temperature cycling stability (87% retention after 100 cycles at 50 °C compared to 29% for the non-coated LNMO), while retaining rate capability. These findings establish a practical framework for designing robust interfacial coatings in high-voltage lithium-ion battery materials
Undoped and doped wurtzite GaAs probed by polarization- and time-resolved cathodoluminescence
No full textInternational audienceNanowires (NWs) offer unique possibilities to control semiconductor heterostructures and polytypes at the nanometer scale. The crystal structure of GaAs can be switched from bulk cubic zinc-blende (ZB) to hexagonal wurtzite (WZ) phase, but the properties and doping of WZ GaAs are still poorly known. Here, we grow high-quality GaAs NWs containing large segments of pure ZB and WZ phases using self-catalyzed, vapor-liquid-solid molecular beam epitaxy. Undoped, Be-doped and Si-doped WZ GaAs are investigated by high-resolution cathodoluminescence (CL) at low temperature (10K). The luminescence originating from the WZ region is unambiguously distinguished by its strong anisotropy evidenced by polarimetry.In undoped GaAs, the WZ CL peak is found ~1 meV higher than the free exciton energy in ZB. The recombination dynamics is probed by time-resolved CL and features a lifetime of 0.6 ns for the exciton recombination and 1.65 ns for the free-electron-to-acceptor transition. From Be-doped NWs, we infer an ionization energy of the Be acceptor of ~30 meV in GaAs WZ . The CL spectra broaden and redshift with increasing Be concentration due to the bandgap narrowing, following a trend similar to GaAs ZB.Si-doped WZ GaAs exhibits a low-energy CL peak (1.47 eV) attributed to the donor-acceptor pair recombination involving Si impurities.The degree of polarization of WZ luminescence decreases with higher doping level for both p-type and n-type. These results shed light on the properties and doping of WZ GaAs and show that time-resolved and polarimetry CL constitutes a powerful tool to characterize crystal phase, local defect, transport and recombination mechanism at the nanoscale
Locally activated semisynthetic fluorescent biosensors for imaging cellular biochemistry
No full textInternational audienceBiosensors based on fluorescent proteins are widely used as genetically encoded indicators due to their capacity to target various biological analytes (metal ions, reactive oxygen species, biomolecules, etc.) within cells with precise localization. However, their complex development associated with the lack of photophysical versatility constrains the scope of their application in biosensing. Alternatively, semisynthetic fluorescent biosensors that combine a small chemical indicator with a self-labeling protein tag benefit from the versatility of molecular engineering and from the selectivity of genetic encoding of the recombinant protein. The variations in photophysical properties of the chemical indicator upon analyte recognition provide high sensitivity and rapid response time, making them attractive alternatives for biosensing. Fluorogenic semisynthetic biosensors that are fluorescent only upon local activation by reaction with a genetically encoded self-labeling protein tag provide an additional level of selectivity, allowing wash-free imaging experiments. This minireview focuses on the latter class of hybrid sensors and provides an outlook on the different small molecular probe design strategies and self-labeling protein tag combinations (mostly SNAP-tag and HaloTag) for their construction. The authors expect to present new clues and ideas to researchers for further advances in this field
Inverse Correlation between Endoplasmic Reticulum Stress Intensity and Antitumor Immune Response with Ruthenium(II)-Based Photosensitizers for the Photodynamic Therapy of Head and Neck Squamous Cell Carcinoma
No full textInternational audiencePhotodynamic therapy (PDT) is a promising strategy for head and neck squamous cell carcinoma (HNSCC), but the immune consequences of tumor cell death remain incompletely understood. We compared two ruthenium(II) polypyridine photosensitizers (PSs) in HNSCC models and found that both were potently phototoxic (nanomolar IC 50 s), triggered diverse cell death pathways (including autophagy and ferroptosis), and promoted hallmark danger signals of immunogenic cell death (ICD). Strikingly, only one PS induced apoptosis and strong endoplasmic reticulum (ER) stress, yet paradoxically led to immune tolerance in vivo. Conversely, the PS that did not induce apoptotic cell death with milder stress responses resulted in a better antitumor immunity in vivo. These unexpected findings challenge the prevailing view that PDT-triggered apoptosis and ER stress are essential for ICD. Our study underscores the complexity of PDT-induced cell death balance and immunogenic signals and highlights the need to redefine ICD-inducing criteria for the rational design of next-generation PSs
Assessment of indium-free transparent conductive oxide back contacts for high efficiency ultra-thin Cu(In,Ga)Se2 solar cells down to 250 nm
No full textInternational audienceThis work examines the feasibility and performance impact of replacing the usual molybdenum backcontact with indium-free transparent conductive oxides (TCOs) like fluorine-doped tin oxide (SnO2:F) and aluminum-doped zinc oxide (ZnO:Al) for ultra-thin Cu(In,Ga)Se2 (CIGS) solar cells (250-450 nm).Motivated by indium scarcity and cost reduction, these TCOs are evaluated for their figure of merit, stability under Se atmosphere, Na diffusion permeability, and band alignment with CIGS absorbers.Using simulations, prototype fabrication, and comprehensive characterizations, the compatibility of these TCOs with CIGS absorbers is assessed. Solar cells with thicknesses of 450 nm and 250 nm are fabricated. Their performance was compared under both rear and front illumination, as well as with the use of reflectors. A record efficiency of 8.6% with front illumination is achieved for a 250 nm CIGS absorber using a gold back reflector with SnO2:F, single-step CIGS deposition, and no heavy alkalines doping. The best rear-illuminated efficiencies are obtained with ZnO:Al back contacts, reaching 6% for a 250 nm CIGS, with only a 9% loss in Jsc compared to front illumination confirming a lower surface recombination rate at the ZnO:Al/CIGS interface compared to Mo/CIGS or SnO2:F/CIGS interfaces.</div
From design to formulation of peptide building blocks for nanotheranostic applications: a synergistic multidisciplinary investigation
No full textInternational audienceThis study presents the journey of a collaborative project for the development of biocompatible nanotheranostic tools, based on peptide self-assembling nanostructures. The peptide sequences were designed to combine smart drug delivery and imaging properties. For this purpose, the selected sequences present: (1) an amphiphilic character for self-assembling properties, efficient hydrophobic drugs encapsulation and efficient biodistribution; (2) a pH-sensitive self-assembly for drug delivery under pH modification in the environment of cancer cells; (3) a receptor-targeting motif within the peptide sequence, overexpressed by certain cancer cells, for specific and controlled delivery of the active ingredient to tumors; (4) accessible functions for further functionalization with a contrast agent for diagnosis. These sequences were first synthesized in a continuous flow to provide a rapid and versatile synthetic process, while lowering reactant consumption, and the synthetic route was optimized through the development of an electrokinetic method coupled to UV–visible detection (CE-UV) and mass spectrometry (CE-MS) that allowed a powerful physicochemical characterization in terms of sequence identification and purity. Few pertinent peptide sequences were then functionalized with a complex of gadolinium to generate Magnetic Resonance Imaging (MRI) properties, and this functionalization step was also optimized and controlled by CE-MS. The formulation procedure was then developed by a deep physicochemical characterization of the peptide nanostructures and the combination of analytical and physical methods to highlight the mechanisms generating the quick reversible self-assembly. Finally, MRI imaging studies on both monomers and nanostructures evidenced a good MRI contrast with properties adapted for a short half-life time
Engineering nitrogen-doped porous carbon positive electrodes for high-performance sodium-ion capacitors: the critical role of porosity, structure and surface functionalities
No full textInternational audienceSodium-ion capacitors are increasingly gaining momentum thanks to their high energy and power densities. However, there is still a lack of understanding of porous carbon positive electrode properties that affect their electrochemical performance. To address this challenge, carbon materials with controlled porosity, structure and surface functionalities are strongly required. Herein, we report the synthesis of nitrogen-doped porous carbons (NDPCs) by a combined soft-salt templating approach, that allows to achieve various nitrogen doping levels (up to 8 at%) via precursor amount modification. This results in materials with ultrahigh specific surface area (up to 2412 m2 g−1) and finely tuned pore size (up to 0.92 nm) matching the desolvated PF6− anion sorption requirement of 0.8 nm, along with controlled graphitization induced by the salt type. The materials exhibit specific capacities ranging from 83 to 159 mA h g−1vs. Na/Na+, higher than that of commercial carbons. From positive linear correlations, it was identified that the improved capacity is driven by the large specific surface area, substantial microporous volume with appropriate pore size, and structural defects, which enhance ion adsorption and promote enhanced specific capacity. However, the capacity retention is improved by the mesoporous volume and graphitic domains. Moreover, the surface pseudocapacitive interactions involving Na+ and PF6− ions could be associated with specific oxygen-containing groups (phenol/ethers and anhydride) and nitrogen species (pyridinic-N/pyrrolic-N). The dual carbon full-cell configuration consisting of a hard carbon and N-doped carbon achieves a high energy density of 209 W h kg−1 and a maximum power density of 5040 W kg−1 with ∼100% coulombic efficiency
Influence of a Two-Fold Ligation Pattern on Iron-Mediated Aryl-Heteroaryl Cross-Electrophile Couplings
No full textInternational audienceAn aryl-heteroaryl Cross-Electrophile Coupling (XEC) relying on the use of a single, well-defined iron catalyst is disclosed, involving magnesium as an electron source as well as heteroaryl chlorides and aryl iodides or bromides as coupling partners. A two-fold coordination pattern featuring a π-acceptor, redox-active (N,N) ligand along with a σ-donating phosphine ensures both the two-electron reduction of the starting iron(II) precursor to enter the cycle, as well as the access to stable organoiron(II) resting states inhibiting the reductive decomposition of the catalyst
Quantifying cell traction forces at the single-fiber scale in 3D: An approach based on deformable photopolymerized fiber arrays
No full textInternational audienceThe forces exerted by cells upon the fibers of the extracellular matrix play a decisive role in cell motility in physiopathology. How the local physical properties of the matrix (density, stiffness, orientation) affect cellular forces remains, however, poorly understood. Existing approaches to measure cell three-dimensional (3D) traction forces within fibrous substrates lack control over the local properties and rely on continuum approaches, not suited for measuring forces at the scale of individual fibers. Herein, an approach is proposed to fabricate multilayer arrays of suspended deformable fibers spanning a wide range of fine-tunable geometrical and mechanical properties using two-photon polymerization. Atomic Force Microscopy is used to thoroughly investigate the properties of individual fibers, including Young’s modulus and stiffness. This approach is combined with a reference-free method for measuring traction forces in 3D, which relies on automated segmentation of the fibers coupled with finite element modeling. The force measurement pipeline is applied to study forces exerted by endothelial cells, fibroblasts, or macrophages, and reveals how these forces are influenced by fiber density and stiffness. Additionally, coupling to fast volumetric imaging with lattice light-sheet microscopy enables the measurement of the low-intensity and short-lived tractions exerted by amoeboid cells, such as dendritic cells. Our technology will be instrumental for monitoring and studying cell behavior at the single-fiber level at extracellular matrix density interfaces, which play a crucial role in both physiological and pathological contexts, such as tumor boundaries
