Silver nanoparticles (AgNPs) are widely used in the health-care sector and industrial applications because of their outstanding antibacterial activity. This bactericidal effect is mainly attributed to the release of Ag+ ions in an aqueous medium, the first step of which is the dissolution of the AgNP via the oxidation of its surface by O2. With the aim of designing more durable and less toxic antibacterial devices, it is desirable to fine-tune the rate of Ag+ release into the surrounding environment. This can be achieved by choosing an adequate coating of the AgNPs, e.g., by embedding the nanoparticles in a silica matrix. In a previous work (Pugliara, A.; et al. Sci. Total Environ.2016, 565, 863), we have shown that the toxic effect on algae photosynthesis of small AgNPs (size <20 nm) embedded in silica layers is preserved, provided that the distance between the AgNPs and the silica free surface is below ≈6–7 nm. Better control of the Ag+ release rate in these systems requires a better understanding of the elementary mechanisms at play concerning both the detachment of the Ag ions from the AgNPs and their diffusion through SiO2. A first step in this direction consists in characterizing the interface between the AgNPs surface and the silica matrix. In this context, periodic density functional theory calculations have been performed on model systems representing the interfaces between amorphous silica and the three crystalline facets of AgNPs, i.e., Ag(111), Ag(110), and Ag(100). Spontaneous breaking of the Si–O bonds and the formation of two O–Ag and one Si–Ag bonds are observed in 50% of the investigated interfaces, corresponding to 1.8 bonds/nm2 on average. The covalent nature of the bonds between Ag and O and between Ag and Si is highlighted by analysis of the electronic structure of the interfaces.

The translation apparatus has long been viewed as a mere factory until recent findings this last decade have unraveled its unexpected role in orchestrating real time gene regulation. Far from being a molecular monolith, the ribosome displays a remarkable heterogeneity along with a striking ability to orchestrate real-time control of gene expression. In the meantime, several reports connect alteration of the translation machinery with elevated cancer risk as well as in tumor initiation and progression. We aim to decipher the variety of translation mechanisms by modeling dedicated Ribo-sequencing experiments. We have designed a new set of Ribo-seq experiments with purified polysomes in order to understand the role of the ribosome density onto translation and to characterized biophysical parameters of translations (hopping rates of ribosomes, initiation rate, termination rate). Preliminary data will be modeled as a proof of concept to pave the way to a genome wide analysis with morefinely regulated genes in charge, e.g., for cell phenotype. After a presentation of the physical perspective of translation, I will discuss the usefulness of biophysical modeling approaches to estimate the codon-dependent hopping, initiation and termination rates of ribosomes from Ribo-seq data. I will discuss designed Ribo-seq experiments (purified polysomes) obtained at IGF suggesting that the ribosome dynamics depends on various conditions: modified dynamics of the first ribosome entering the newly transcripted mRNA, different paradigms for translation (cytoplasmic versus membrane translation), effect of inhomogeneous hopping rates on ribosome traffic etc. Finally, I will consider how these findings will help to understand the epithelial-mesenchymal transition: we have performed designed Ribo-seq experiments inducing a change of the ribosomes concentration level in vivo in tumor human cells and observed induced change of phenotype to mezenchymal cells.

Controlled motion and positioning of colloids and macromolecular complexes in a fluid, as well ascatalytic particles in active environments, are fundamental processes in physics, chemistry andbiology. Here we focus on an active biological system for which precise experimental results areavailable. Our work is fully inspired by studies of one of the most widespread and ancientmechanisms of liquid phase macromolecular segregation and positioning known in nature:bacterial DNA segregation systems. Efficient bacterial chromosome segregation typically requiresthe coordinated action of a three-component, fueled by adenosine triphosphate machinery calledthe partition complex. We can distinguish two steps: (i) a process of phase transition [2,3] tobuilt a membraneless region of high protein concentration (partition complex) (ii) the action ofmolecular motor action upon the complex to create a chemical force.We present a phenomenological model [1] accounting for the dynamics of this system that is alsorelevant for the physics of catalytic particles in active environments. The model is obtained bycoupling simple linear reaction-diffusion equations with a volumetric chemophoresis force fieldthat arises from protein-protein interactions and provides a physically viable mechanism forcomplex translocation. This description captures experimental observations: dynamic oscillationsof complex components, complex separation and symmetrical positioning. The predictions of ourmodel are in agreement with and provide substantial insight into recent experiments. From a non-linear physics view point, this system explores the active separation of matter at micrometricscales with a dynamical instability between static positioning and travelling wave regimestriggered by the dynamical spontaneous breaking of rotational symmetry. We also discuss thephase transition mechanism giving rise to macromolecular assembly of proteins. Our predictionsare compared to Super Resolution microscopy and microbiology experiments [1,2,3].[1] Walter J.-C., Dorignac J., Lorman V., Rech J., Bouet J.-Y., Nollmann M., Palmeri J., ParmeggianiA. and Geniet F., Phys. Rev. Lett. 119, 028101 (2017).[2] Debaugny R., Sanchez A., Rech J., Labourdette D., Dorignac J., Geniet F., Palmeri J.,Parmeggiani A., Boudsocq, Leberre V., Walter* J.-C. and Bouet* J.-Y Mol. Syst. Biol. 14, e8516 (2018).[3] David G., Walter J.-C., Broedersz C., Dorignac J., Geniet F., Parmeggiani A., Walliser N.-O. andPalmeri J., submitted to Phys. Rev. Lett. [arXiv/1811.09234] (2019).

On-chip microlaser sources in the blue constitute an important building block for complex integrated photonic circuits on silicon. We have developed photonic circuits operating in the blue spectral range based on microdisks and bus waveguides in III-nitride on silicon. We report on the interplay between microdisk-waveguide coupling and its optical properties. We observe critical coupling and phase matching, i.e. the most efficient energy transfer scheme, for very short gap sizes and thin waveguides (g = 45 nm and w = 170 nm) in the spontaneous emission regime. Whispering gallery mode lasing is demonstrated for a wide range of parameters with a strong dependence of the threshold on the loaded quality factor. We show the dependence and high sensitivity of the output signal on the coupling. Lastly, we observe the impact of processing on the tuning of mode resonances due to the very short coupling distances. Such small footprint on-chip integrated microlasers providing maximum energy transfer into a photonic circuit have important potential applications for visible-light communication and lab-on-chip bio-sensors.

Polymeric materials are largely employed for the manufacturing of implants for variousreasons, but they are typically invisible by conventional imaging methods. To improve surgicalprocedure and postoperative implant follow-up though, biomaterials are needed which allow anaccurate and efficient imaging. Here, we present a direct and versatile strategy that allows tocovalently immobilize T1 magnetic resonance imaging (MRI) contrast agents at the surface ofvarious clinically relevant polymeric biomaterials. An aryl-azide bearing complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and gadolinium (Gd) has beensynthesized for easy photografting onto polymer surfaces. Polycaprolactone (PCL), polylactide(PLA), polyurethane (PU), polyetheretherketone (PEEK) and polypropylene (PP) have beenselected as clinically relevant substrates and successfully functionalized with the photosensitiveMRI probe DOTA/Gd. Following in vitro assessment of their biocompatibility and MRIvisibility, commercial MRI-visible PP hernia repair meshes (MRI-meshes) have been prepared.MRI-meshes have been implanted in rats for in vivo evaluation of their imaging capacities over1 month. Histological evaluation and Gd biodistribution studies have been carried outconfirming the potential of this straightforward approach to simply yield imageable medicaldevices.

Low-dimensional materials have been examined as electrocatalysts for the hydrogen evolution reaction (HER). Among them, two-dimensional transition metal dichalcogenides (2D-TMDs) such as MoS2 have been identified as potential candidates. However, the performance of TMDs toward HER in both acidic and basic media remains inferior to that of noble metals such as Pt and its alloys. This calls for investigating the influence of controlled defect engineering of 2D TMDs on their performance toward hydrogen production. Here, we explored the HER activity from defective multilayered MoS2 over a large range of surface S vacancy concentrations up to 90%. Amorphous MoS2 and 2H MoS2 with ultrarich S vacancies demonstrated the highest HER performance in acid and basic electrolytes, respectively. We also report that the HER performance from multilayered MoS2 can be divided into two domains corresponding to "point defects" at low concentrations of surface S vacancies (Stage 1) and large regions of undercoordinated Mo atoms for high concentrations of surface S vacancies (Stage 2). The highest performance is obtained for Stage 2 in the presence of undercoordinated Mo atoms with a TOF of similar to 2 s(-1) at an overpotential of 160 mV in 0.1 M KOH which compares favorably to the best results in the literature. Overall, our work provides deeper insight on the HER mechanism from defected MoS2 and provides guidance for the development of defect-engineered TMD-based electrocatalysts.