Publications

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.

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.

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

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.

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

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.

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.

Affinity maturation is a complex dynamical process allowing the immune system to generate antibodies capable of recognizing antigens. We introduce a model for the evolution of the distribution of affinities across the antibody population in germinal centers. The model is amenable to detailed mathematical analysis and gives insight on the mechanisms through which antigen availability controls the rate of maturation and the expansion of the antibody population. It is also capable, upon maximum-likelihood inference of the parameters, to reproduce accurately the distributions of affinities of IgG-secreting cells we measure in mice immunized against Tetanus Toxoid under largely varying conditions (antigen dosage, delay between injections). Both model and experiments show that the average population affinity depends non-monotonically on the antigen dosage. We show that combining quantitative modeling and statistical inference is a concrete way to investigate biological processes underlying affinity maturation (such as selection permissiveness), hardly accessible through measurements.

Affinity maturation is a complex dynamical process allowing the immune system to generate antibodies capable of recognizing antigens. We introduce a model for the evolution of the distribution of affinities across the antibody population in germinal centers. The model is amenable to detailed mathematical analysis and gives insight on the mechanisms through which antigen availability controls the rate of maturation and the expansion of the antibody population. It is also capable, upon maximum-likelihood inference of the parameters, to reproduce accurately the distributions of affinities of IgG-secreting cells we measure in mice immunized against Tetanus Toxoid under largely varying conditions (antigen dosage, delay between injections). Both model and experiments show that the average population affinity depends non-monotonically on the antigen dosage. We show that combining quantitative modeling and statistical inference is a concrete way to investigate biological processes underlying affinity maturation (such as selection permissiveness), hardly accessible through measurements.

Freezing of alum-based vaccines drastically alters their colloidal composition and leads to irreversible cluster formation. The loss of stability is well described, but the impact of frost damage on the functionality of the induced and secreted antibody repertoire has not been studied in detail. We therefore applied our single-cell measurement platform to extract the frequencies of Immunoglobulin G-secreting cells in combination with individual secretion rates and affinities. We showed that, frost-damaged or not, the tested vaccine was able to generate similar frequencies of total and antigen-affine IgG-secreting cells. Additionally, the frost-damaged vaccine stimulated a similar T-cell cytokine secretion pattern when compared to the regularly stored vaccine. However, frost-damaged vaccines induced no efficient affinity maturation and a complete collapse of the affinity distribution was observed. This study unveiled the impact of frost-damage to alum-based vaccines on the induced secreted antibody repertoire, and illustrated the power of functional single-antibody analysis.