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Revealing the Impact of Electrolyte Composition for Co-Based Water Oxidation Catalysts by the Study of Reaction Kinetics Parameters
Yan Duan, Nicolas Dubouis, Jiaqiang Huang, Daniel Alves Dalla Corte, Vanessa Pimenta, Zhichuan J. Xu, and Alexis Grimaud
ACS Publications - 7 4160–4170 - https://doi.org/10.1021/acscatal.0c00490 - 2020
Recent studies have revealed the critical role played by the electrolyte composition on the oxygen evolution reaction (OER) kinetics on the surface of highly active catalysts. While numerous works were devoted to understand the effect of the electrolyte composition on the physical properties of the catalysts’ surface, very little is known yet about its exact impact on the OER kinetics parameters. In this work, we reveal that the origin for the electrolyte-dependent OER activity for Co-based catalysts originates from two different effects. Increasing the alkaline electrolyte concentration for La1–xSrxCoO3−δ perovskites with x > 0 and for amorphous CoOOH increases the pre-exponential factor, which can be explained either by an increase of the concentration of active sites or by a change in the entropy of activation. However, changing the alkali cation results in a decrease of the apparent activation enthalpy for Fe-containing amorphous films, traducing a change in intermediates’ binding energies.
Machine Learning to Improve the Sensing of Biomolecules by Conical Track-Etched Nanopore
Nathan Meyer, Jean-Marc Janot , Mathilde Lepoitevin , Michaël Smietana ,Jean-Jacques Vasseur ,Joan Torrent and Sébastien Balme
Biosensors - 10(10) 140 - https://doi.org/10.3390/bios10100140 - 2020
Single nanopore is a powerful platform to detect, discriminate and identify biomacromolecules. Among the different devices, the conical nanopores obtained by the track-etched technique on a polymer film are stable and easy to functionalize. However, these advantages are hampered by their high aspect ratio that avoids the discrimination of similar samples. Using machine learning, we demonstrate an improved resolution so that it can identify short single- and double-stranded DNA (10- and 40-mers). We have characterized each current blockade event by the relative intensity, dwell time, surface area and both the right and left slope. We show an overlap of the relative current blockade amplitudes and dwell time distributions that prevents their identification. We define the different parameters that characterize the events as features and the type of DNA sample as the target. By applying support-vector machines to discriminate each sample, we show accuracy between 50% and 72% by using two features that distinctly classify the data points. Finally, we achieved an increased accuracy (up to 82%) when five features were implemented.
An Epigenetic Priming Mechanism Mediated by Nutrient Sensing Regulates Transcriptional Output
Natalia Stec, Katja Doerfel, Kelly Hills-Muckey, Victoria M. Ettorre, Sevinc Ercan, Wolfgang Keil, C. M. Hammell
bioRxiv - - doi.org/10.1101/2020.09.01.278127 - 2020
While precise tuning of gene expression levels is critical for most developmental pathways, the mechanisms by which the transcriptional output of dosage-sensitive molecules is established or modulated by the environment remain poorly understood. Here, we provide a mechanistic framework for how the conserved transcription factor BLMP-1/Blimp1 operates as a pioneer factor to decompact chromatin near its target loci hours before transcriptional activation and by doing so, regulates both the duration and amplitude of subsequent target gene transcription. This priming mechanism is genetically separable from the mechanisms that establish the timing of transcriptional induction and functions to canalize aspects of cell-fate specification, animal size regulation, and molting. A key feature of the BLMP-1-dependent transcriptional priming mechanism is that chromatin decompaction is initially established during embryogenesis and maintained throughout larval development by nutrient sensing. This anticipatory mechanism integrates transcriptional output with environmental conditions and is essential for resuming normal temporal patterning after animals exit nutrient-mediated developmental arrests.
Ultrafast photomechanical transduction through thermophoretic implosion
N. Kavokine, S. Zou, R. Liu, H. Zhong, A. Nigues, B. Zou and L. Bocquet
Nature Communications - 11(1) 50 - doi.org/10.1038/s41467-019-13912-w - 2020
Since the historical experiments of Crookes, the direct manipulation of matter by light has been both a challenge and a source of scientific debate. Here we show that laser illumination allows to displace a vial of nanoparticle solution over centimetre-scale distances. Cantilever-based force measurements show that the movement is due to millisecond-long force spikes, which are synchronised with a sound emission. We observe that the nanoparticles undergo negative thermophoresis, and ultrafast imaging reveals that the force spikes are followed by the explosive growth of a bubble in the solution. We propose a mechanism accounting for the propulsion based on a thermophoretic instability of the nanoparticle cloud, analogous to the Jeans’s instability that occurs in gravitational systems. Our experiments demonstrate a new type of laser propulsion and a remarkably violent actuation of soft matter, reminiscent of the strategy used by certain plants to propel their spores.
Fluids at the Nanoscale: From Continuum to Subcontinuum Transport
Nikita Kavokine, Roland R. Netz, and Lydéric Bocquet
Annual Review of Fluid Mechanics - 53 50 - https://doi.org/10.1146/annurev-fluid-071320-095958 - 2020
Nanofluidics has firmly established itself as a new field in fluid mechanics, as novel properties have been shown to emerge in fluids at the nanometric scale. Thanks to recent developments in fabrication technology, artificial nanofluidic systems are now being designed at the scale of biological nanopores. This ultimate step in scale reduction has pushed the development of new experimental techniques and new theoretical tools, bridging fluid mechanics, statistical mechanics, and condensed matter physics. This review is intended as a toolbox for fluids at the nanometer scale. After presenting the basic equations that govern fluid behavior in the continuum limit, we show how these equations break down and new properties emerge in molecular-scale confinement. A large number of analytical estimates and physical arguments are given to organize the results and different limits.
Mechanically activated ionic transport across single-digit carbon nanotubes
Alice Marcotte, Timothée Mouterde, Antoine Niguès, Alessandro Siria & Lydéric Bocquet
Nature Materials - 19 1057–1061 - https://doi.org/10.1146/annurev-fluid-071320-095958 - 2020
Fluid and ionic transport at the nanoscale has recently demonstrated a wealth of exotic behaviours1,2,3,4,5,6,7,8,9,10,11,12,13,14. However, artificial nanofluidic devices15,16,17,18 are still far from demonstrating the advanced functionalities existing in biological systems, such as electrically and mechanically activated transport19,20. Here, we focus on ionic transport through 2-nm-radius individual multiwalled carbon nanotubes under the combination of mechanical and electrical forcings. Our findings evidence mechanically activated ionic transport in the form of an ionic conductance that depends quadratically on the applied pressure. Our theoretical study relates this behaviour to the complex interplay between electrical and mechanical drivings, and shows that the superlubricity of the carbon nanotubes4,5,6,7,8,21 is a prerequisite to attaining mechanically activated transport. The pressure sensitivity shares similarities with the response of biological mechanosensitive ion channels19,20, but observed here in an artificial system. This paves the way to build new active nanofluidic functionalities inspired by complex biological machinery
Studying polymer diffusiophoresis with non-equilibrium molecular dynamics
S. Ramírez-Hinestrosa, H. Yoshida, L. Bocquet, and D. Frenkel
Chem. Phys - 152 164901 - https://doi.org/10.1063/5.0007235 - 2020
We report a numerical study of the diffusiophoresis of short polymers using non-equilibrium molecular dynamics simulations. More precisely, we consider polymer chains in a fluid containing a solute that has a concentration gradient and examine the variation of the induced diffusiophoretic velocity of the polymer chains as the interaction between the monomer and the solute is varied. We find that there is a non-monotonic relation between the diffusiophoretic mobility and the strength of the monomer–solute interaction. In addition, we find a weak dependence of the mobility on the length of the polymer chain, which shows clear difference from the diffusiophoresis of a solid particle. Interestingly, the hydrodynamic flow through the polymer is much less screened than for pressure driven flows.
Nanofluidics coming of age
Lydéric Bocquet
Nature Materials - 19 254–256 - https://doi.org/10.1038/s41563-020-0625-8 - 2020
This is a turning point for nanofluidics. Recent progress allows envisioning both fundamental discoveries for the transport of fluids at the ultimate scales, and disruptive technologies for the water–energy nexus
Local and global force balance for diffusiophoretic transport
S. Marbach , H. Yoshida and L. Bocquet
J. Fluid Mech - 892 - doi:10.1017/jfm.2020.137 - 2020
Electro- and diffusio-phoresis of particles correspond respectively to the transport of particles under electric field and solute concentration gradients. Such interfacial transport phenomena take their origin in a diffuse layer close to the particle surface, and the motion of the particle is force free. In the case of electrophoresis, it is further expected that the stress acting on the moving particle vanishes locally as a consequence of local electroneutrality. But the argument does not apply to diffusiophoresis, which takes its origin in solute concentration gradients. In this paper we investigate further the local and global force balance on a particle undergoing diffusiophoresis. We calculate the local tension applied on the particle surface and show that, counter-intuitively, the local force on the particle does not vanish for diffusiophoresis, in spite of the global force being zero, as expected. Incidentally, our description allows us to clarify the osmotic balance in diffusiophoresis, which has been a source of debate in recent years. We explore various cases, including hard and soft interactions, as well as porous particles, and provide analytic predictions for the local force balance in these various systems. The existence of local stresses may induce deformation of soft particles undergoing diffusiophoresis, hence suggesting applications in terms of particle separation based on capillary diffusiophoresis.
The Quantitative Assessment of the Secreted IgG Repertoire after Recall to Evaluate the Quality of Immunizations
Klaus Eyer, Carlos Castrillon, Guilhem Chenon, Jérôme Bibette, Pierre Bruhns, Andrew D. Griffiths and Jean Baudry
Nat Immunol. - 9 205 - doi.org/10.4049/jimmunol.2000112 - 2020
One of the major goals of vaccination is to prepare the body to rapidly secrete specific Abs during an infection. Assessment of the vaccine quality is often difficult to perform, as simple measurements like Ab titer only partly correlate with protection. Similarly, these simple measurements are not always sensitive to changes in the preceding immunization scheme. Therefore, we introduce in this paper a new, to our knowledge, method to assay the quality of immunization schemes for mice: shortly after a recall with pure Ag, we analyze the frequencies of IgG-secreting cells (IgG-SCs) in the spleen, as well as for each cells, the Ag affinity of the secreted Abs. We observed that after recall, appearance of the IgG-SCs within the spleen of immunized mice was fast (<24 h) and this early response was free of naive IgG-SCs. We further confirmed that our phenotypic analysis of IgG-SCs after recall strongly correlated with the different employed immunization schemes. Additionally, a phenotypic comparison of IgG-SCs presented in the spleen during immunization or after recall revealed similarities but also significant differences. The developed approach introduced a novel (to our knowledge), quantitative, and functional highly resolved alternative to study the quality of immunizations.

584 publications.