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RECHERCHER

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Interfacial transport with mobile surface charges and consequences for ionic transport in carbon nanotubes
Laboratoire Micromégas - Timothée Mouterde, Lydéric Bocquet
Eur. Phys. - 41 148 - doi.org/10.1140/epje/i2018-11760-2 - 2018
In this paper, we explore the effect of a finite surface charge mobility on the interfacial transport: conductance, streaming currents, electro- and diffusio-osmotic flows. We first show that the surface charge mobility modifies the hydrodynamic boundary condition for the fluid, which introduces a supplementary term depending on the applied electric field. In particular, the resulting slip length is found to decrease inversely with the surface charge. We then derive expressions for the various transport mobilities, highlighting that the surface charge mobility merely moderates the amplification effect of interfacial slippage, to the noticeable exception of diffusio-osmosis and surface conductance. Our calculations, obtained within Poisson-Boltzmann framework, highlight the importance of non-linear electrostatic contributions to predict the small concentration/large charge limiting regimes for the transport mobilities. We discuss these predictions in the context of recent electrokinetic experiments with carbon nanotubes.
Transport and dispersion across wiggling nano-pores
Laboratoire Micromégas - Sophie Marbach, David S. Dean & Lydéric Bocquet
Nature Physics - 14 1108–1113 - doi.org/10.1038/s41567-018-0239-0 - 2018
The transport of fluids at the nanoscale has achieved major breakthroughs over recent years1,2,3,4; however, artificial channels still cannot match the efficiency of biological porins in terms of fluxes or selectivity. Pore shape agitation—due to thermal fluctuations or in response to external stimuli—is believed to facilitate transport in biochannels5,6,7,8,9, but its impact on transport in artificial pores remains largely unexplored. Here we introduce a general theory for transport through thermally or actively fluctuating channels, which quantifies the impact of pore fluctuations on confined diffusion in terms of the spectral statistics of the channel fluctuations. Our findings demonstrate a complex interplay between transport and surface wiggling: agitation enhances diffusion via the induced fluid flow, but spatial variations in pore geometry can induce a slowing down via entropic trapping, in full agreement with molecular dynamics simulations and existing observations from the literature. Our results elucidate the impact of pore agitation in a broad range of artificial and biological porins, but also, at larger scales, in vascular motion in fungi, intestinal contractions and microfluidic surface waves. These results open up the possibility that transport across membranes can be actively tuned by external stimuli, with potential applications to nanoscale pumping, osmosis and dynamical ultrafiltration.
MicroMegascope
Laboratoire Micromégas - Luca Canale, Axel Laborieux, Agasthya Aroul Mogane, Laetitia Jubin, Jean Comtet, Antoine Lainé, Lydéric Bocquet, Alessandro Siria, Antoine Niguès
Nature Physics - - DOI:10.1088/1361-6528/aacbad - 2018
Atomic Force Microscopy (AFM) allows to reconstruct the topography of surface with a resolution in the nanometer range. The exceptional resolution attainable with the AFM makes this instrument a key tool in nanoscience and technology. The core of the set-up relies on the detection of the mechanical properties of a micro-oscillator when approached to a sample to image. Despite the fact that AFM is nowadays a very common instrument for research and development applications, thanks to the exceptional performances and the relative simplicity to use it, the fabrication of the micrometric scale mechanical oscillator is still a very complicated and expensive task requiring a dedicated platform. Being able to perform atomic force microscopy with a macroscopic oscillator would make the instrument more versatile and accessible for an even larger spectrum of applications and audiences. We present for the first time atomic force imaging with a centimetric oscillator. We show how it is possible to perform topographical images with nanometric resolution with a grams tuning fork. The images presented here are obtained with an aluminum tuning fork of centimeter size as sensor on which an accelerometer is glued on one prong to measure the oscillation of the resonator. In addition to the stunning sensitivity, by imaging both in air and in liquid, we show the high versatility of such oscillator. The set up proposed here can be extended to numerous experiments where the probe needs to be heavy and/or very complex as well as the environment.
“Dripplon: localized and super fast ripples of water confined between graphene sheets
Laboratoire Micromégas - Hiroaki Yoshida, Vojtěch Kaiser, Benjamin Rotenberg & Lydéric Bocquet
Nature Communications - 1496 - DOI:10.1088/1361-6528/aacbad - 2018
Carbon materials have unveiled outstanding properties as membranes for water transport, both in 1D carbon nanotube and between 2D graphene layers. In the ultimate confinement, water properties however strongly deviate from the continuum, showing exotic properties with numerous counterparts in fields ranging from nanotribology to biology. Here, by means of molecular dynamics, we show a self-organized inhomogeneous structure of water confined between graphene sheets, whereby the very strong localization of water defeats the energy cost for bending the graphene sheets. This leads to a two-dimensional water droplet accompanied by localized graphene ripples, which we call “dripplon.” Additional osmotic effects originating in dissolved impurities are shown to further stabilize the dripplon. Our analysis also reveals a counterintuitive superfast dynamics of the dripplons, comparable to that of individual water molecules. They move like a (nano-) ruck in a rug, with water molecules and carbon atoms exchanging rapidly across the dripplon interface.
Dramatic pressure-sensitive ion conduction in conical nanopores
Laboratoire Micromégas - Laetitia Jubin, Anthony Poggioli, Alessandro Siria, and Lydéric Bocquet
Nature Communications - 115 (16) 4063-4068 - doi.org/10.1073/pnas.1721987115 - 2018
Ion transporters in Nature exhibit a wealth of complex transport properties such as voltage gating, activation, and mechanosensitive behavior. When combined, such processes result in advanced ionic machines achieving active ion transport, high selectivity, or signal processing. On the artificial side, there has been much recent progress in the design and study of transport in ionic channels, but mimicking the advanced functionalities of ion transporters remains as yet out of reach. A prerequisite is the development of ionic responses sensitive to external stimuli. In the present work, we report a counterintuitive and highly nonlinear coupling between electric and pressure-driven transport in a conical nanopore, manifesting as a strong pressure dependence of the ionic conductance. This result is at odds with standard linear response theory and is akin to a mechanical transistor functionality. We fully rationalize this behavior on the basis of the coupled electrohydrodynamics in the conical pore by extending the Poisson–Nernst–Planck–Stokes framework. The model is shown to capture the subtle mechanical balance occurring within an extended spatially charged zone in the nanopore. The pronounced sensitivity to mechanical forcing offers leads in tuning ion transport by mechanical stimuli. The results presented here provide a promising avenue for the design of tailored membrane functionalities.
“Cross-over of the power law exponent for carbon nanotube conductivity as a function of salinity
Laboratoire Micromégas - Yuki Uematsu, Roland R. Netz, Lydéric Bocquet
J Phys Chem C - 122, 11 2992-2997 - doi.org/10.1021/acs.jpcb.8b01975 - 2018
IOn the basis of the Poisson–Boltzmann equation in cylindrical coordinates, we calculate the conductivity of a single charged nanotube filled with electrolyte. The conductivity as a function of the salt concentration follows a power-law, the exponent of which has been controversially discussed in the literature. We use the co-ion-exclusion approximation and obtain the crossover between different asymptotic power-law behaviors analytically. Numerically solving the full Poisson–Boltzmann equation, we also calculate the complete diagram of exponents as a function of the salt concentration and the pH for tubes with different radii and pKa values. We apply our theory to recent experimental results on carbon nanotubes using the pKa as a fit parameter. In good agreement with the experimental data, the theory shows power-law behavior with the exponents 1/3 at high pH and 1/2 at low pH, with a crossover depending on salt concentration, tube radius and pKa.
Shear thinning in non-Brownian suspensions
Laboratoire Micromégas - Guillaume Chatté, Jean Comtet, Antoine Niguès, Lydéric Bocquet, Alessandro Siria, Guylaine Ducouret, François Lequeux, Nicolas Lenoir, Guillaume Ovarleze and Annie Colin
Soft Matter - 14 879-893 - doi: 10.1039/c7sm01963g - 2018
We study the flow of suspensions of non-Brownian particles dispersed into a Newtonian solvent. Combining capillary rheometry and conventional rheometry, we evidence a succession of two shear thinning regimes separated by a shear thickening one. Through X-ray radiography measurements, we show that during each of those regimes, the flow remains homogeneous and does not involve particle migration. Using a quartz-tuning fork based atomic force microscope, we measure the repulsive force profile and the microscopic friction coefficient μ between two particles immersed into the solvent, as a function of normal load. Coupling measurements from those three techniques, we propose that (1) the first shear-thinning regime at low shear rates occurs for a lubricated rheology and can be interpreted as a decrease of the effective volume fraction under increasing particle pressures, due to short-ranged repulsive forces and (2) the second shear thinning regime after the shear-thickening transition occurs for a frictional rheology and can be interpreted as stemming from a decrease of the microscopic friction coefficient at large normal load.
Active sieving across driven nanopores for tunable selectivity
Laboratoire Micromégas - Sophie Marbach and Lydéric Bocqueta)
J Phys Chem C - 147 15 - doi.org/10.1063/1.4997993 - 2018
Molecular separation traditionally relies on sieving processes across passive nanoporous membranes. Here we explore theoretically the concept of non-equilibrium active sieving. We investigate a simple model for an active noisy nanopore, where gating—in terms of size or charge—is externally driven at a tunable frequency. Our analytical and numerical results unveil a rich sieving diagram in terms of the forced gating frequency. Unexpectedly, the separation ability is strongly increased as compared to its passive (zero frequency) counterpart. It also points to the possibility of tuning dynamically the osmotic pressure. Active separation outperforms passive sieving and represents a promising avenue for advanced filtration.
Connexin 43 Controls the Astrocyte Immunoregulatory Phenotype.
Laboratoire Physique des biomolécules - Boulay, Anne-Cécile; Gilbert, Alice; Oliveira Moreira, Vanessa; Blugeon, Corinne; Perrin, Sandrine; Pouch, Juliette; Le Crom, Stéphane; Ducos, Bertrand; Cohen-Salmon, Martine
Brain sciences - 8(4) - 10.3390/brainsci8040050 - 2018
Astrocytes are the most abundant glial cells of the central nervous system and have recently been recognized as crucial in the regulation of brain immunity. In most neuropathological conditions, astrocytes are prone to a radical phenotypical change called reactivity, which plays a key role in astrocyte contribution to neuroinflammation. However, how astrocytes regulate brain immunity in healthy conditions is an understudied question. One of the astroglial molecule involved in these regulations might be Connexin 43 (Cx43), a gap junction protein highly enriched in astrocyte perivascular endfeet-terminated processes forming the glia limitans. Indeed, Cx43 deletion in astrocytes (Cx43KO) promotes a continuous immune recruitment and an autoimmune response against an astrocyte protein, without inducing any brain lesion. To investigate the molecular basis of this unique immune response, we characterized the polysomal transcriptome of hippocampal astrocytes deleted for Cx43. Our results demonstrate that, in the absence of Cx43, astrocytes adopt an atypical reactive status with no change in most canonical astrogliosis markers, but with an upregulation of molecules promoting immune recruitment, complement activation as well as anti-inflammatory processes. Intriguingly, while several of these upregulated transcriptional events suggested an activation of the γ-interferon pathway, no increase in this cytokine or activation of related signaling pathways were found in Cx43KO. Finally, deletion of astroglial Cx43 was associated with the upregulation of several angiogenic factors, consistent with an increase in microvascular density in Cx43KO brains. Collectively, these results strongly suggest that Cx43 controls immunoregulatory and angiogenic properties of astrocytes.
Control of protein activity and gene expression by cyclofen-OH uncaging.
Laboratoire Physique des biomolécules - Zhang, Weiting; Hamouri, Fatima; Feng, Zhiping; Aujard, Isabelle; Ducos, Bertrand; Ye, Shixin; Weiss, Shimon; Volovitch, Michel; Vriz, Sophie; Jullien, Ludovic; Bensimon, David
Chembiochem - - 10.1002/cbic.201700630 - 2018
The use of light to control the expression of genes and the activity of proteins is a rapidly expanding field. While many of these approaches use a fusion between a light activable protein and the protein of interest to control the activity of the later, it is also possible to control the activity of a protein by uncaging a specific ligand. In that context, controlling the activation of a protein fused to the modified estrogen receptor (ERT) by uncaging its ligand cyclofen-OH has emerged as a generic and versatile method to control the activation of proteins quantitatively, quickly and locally in a live organism. We here present that approach and its uses in a variety of physiological contexts.
Rolling and aging in temperature-ramp soft adhesion.
Laboratoire Physique des biomolécules - Boniello, Giuseppe; Tribet, Christophe; Marie, Emmanuelle; Croquette, Vincent; Zanchi, Dražen
Phys. Rev. E - 97 1-1 - 10.1103/PhysRevE.97.012609 - 2018
Immediately before adsorption to a horizontal substrate, sinking polymer-coated colloids can undergo a complex sequence of landing, jumping, crawling, and rolling events. Using video tracking, we studied the soft adhesion to a horizontal flat plate of micron-size colloids coated by a controlled molar fraction f of the poly(lysine)-grafted-poly(N-isopropylacrylamide) (PLL-g-PNIPAM) which is a temperature-sensitive polymer. We ramp the temperature from below to above T_{c}=32±1^{∘}C, at which the PNIPAM polymer undergoes a transition, triggering attractive interaction between microparticles and surface. The adsorption rate, the effective in-plane (x-y) diffusion constant, and the average residence time distribution over z were extracted from the Brownian motion records during last seconds before immobilization. Experimental data are understood within a rate-equations-based model that includes aging effects and includes three populations: the untethered, the rolling, and the arrested colloids. We show that preadsorption dynamics casts a characteristic scaling function α(f) proportional to the number of available PNIPAM patches met by soft contact during Brownian rolling. In particular, the increase of in-plane diffusivity with increasing f is understood: The stickiest particles have the shortest rolling regime prior to arrest, so that their motion is dominated by the untethered phase.
DNA methylation and gene expression alterations in zebrafish early-life stages exposed to the antibacterial agent triclosan
Laboratoire Physique des biomolécules - Falisse, Elodie; Ducos, Bertrand; Stockwell, Peter A; Morison, Ian M; Chatterjee, Aniruddha; Silvestre, Frédéric
Environmental pollution - 243 1867-1877 - 10.1016/j.envpol.2018.10.004 - 2018
There is increasing evidence that toxicant exposure can alter DNA methylation profile, one of the main epigenetic mechanisms, particularly during embryogenesis when DNA methylation patterns are being established. In order to investigate the effects of the antibacterial agent Triclosan on DNA methylation and its correlation with gene expression, zebrafish embryos were exposed during 7 days post-fertilization (starting at maximum 8-cells stage) to 50 and 100 μg/l, two conditions for which increased sensitivity and acclimation have been respectively reported. Although global DNA methylation was not significantly affected, a total of 171 differentially methylated fragments were identified by Reduced Representation Bisulfite Sequencing. The majority of these fragments were found between the two exposed groups, reflecting dose-dependant specific responses. Gene ontology analysis revealed that pathways involved in TGF-β signaling were enriched in larvae exposed to 50 μg/l, while de novo pyrimidine biosynthesis functions were overrepresented in fish exposed to 100 μg/l. In addition, gene expression analysis revealed a positive correlation between mRNA levels and DNA methylation patterns in introns, together with significant alterations of the transcription of genes involved in nervous system development, transcriptional factors and histone methyltransferases. Overall this work provides evidence that Triclosan alters DNA methylation in zebrafish exposed during embryogenesis as well as related genes expression and proposes concentration specific modes of action. Further studies will investigate the possible long-term consequences of these alterations, i.e. latent defects associated with developmental exposure and transgenerational effects, and the possible implications in terms of fitness and adaptation to environmental pollutants.
Single molecule kinetics uncover roles for E. coli RecQ DNA helicase domains and interaction with SSB
Laboratoire Physique des biomolécules - Debjani Bagchi , Maria Manosas, Weiting Zhang, Kelly A Manthei , Samar Hodeib , Bertrand Ducos , James L Keck , Vincent Croquette
Nat. Methods - 46(16) 8500-8515 - DOI: 10.1093/nar/gky647 - 2018
Most RecQ DNA helicases share a conserved domain arrangement that mediates their activities in genomic stability. This arrangement comprises a helicase motor domain, a RecQ C-terminal (RecQ-C) region including a winged-helix (WH) domain, and a 'Helicase and RNase D C-terminal' (HRDC) domain. Single-molecule real-time translocation and DNA unwinding by full-length Escherichia coli RecQ and variants lacking either the HRDC or both the WH and HRDC domains was analyzed. RecQ operated under two interconvertible kinetic modes, 'slow' and 'normal', as it unwound duplex DNA and translocated on single-stranded (ss) DNA. Consistent with a crystal structure of bacterial RecQ bound to ssDNA by base stacking, abasic sites blocked RecQ unwinding. Removal of the HRDC domain eliminates the slow mode while preserving the normal mode of activity. Unexpectedly, a RecQ variant lacking both the WH and HRDC domains retains weak helicase activity. The inclusion of E. coli ssDNA-binding protein (SSB) induces a third 'fast' unwinding mode four times faster than the normal RecQ mode and enhances the overall helicase activity (affinity, rate, and processivity). SSB stimulation was, furthermore, observed in the RecQ deletion variants, including the variant missing the WH domain. Our results support a model in which RecQ and SSB have multiple interacting modes.
UPF1-like helicase grip on nucleic acids dictates processivity
Laboratoire Physique des biomolécules -
Nat Commun - 9 1 - 10.1038/s41467-018-06313-y - 2018
Helicases are molecular engines which translocate along nucleic acids (NA) to unwind double-strands or remodel NA-protein complexes. While they have an essential role in genome structure and expression, the rules dictating their processivity remain elusive. Here, we developed single-molecule methods to investigate helicase binding lifetime on DNA. We found that UPF1, a highly processive helicase central to nonsense-mediated mRNA decay (NMD), tightly holds onto NA, allowing long lasting action. Conversely, the structurally similar IGHMBP2 helicase has a short residence time. UPF1 mutants with variable grip on DNA show that grip tightness dictates helicase residence time and processivity. In addition, we discovered via functional studies that a decrease in UPF1 grip impairs NMD efficiency in vivo. Finally, we propose a three-state model with bound, sliding and unbound molecular clips, that can accurately predict the modulation of helicase processivity.
HTLV-1 Tax plugs and freezes UPF1 helicase leading to nonsense-mediated mRNA decay inhibition.
Laboratoire Physique des biomolécules - Fiorini, Francesca; Robin, Jean-Philippe; Kanaan, Joanne; Borowiak, Malgorzata; Croquette, Vincent; Le Hir, Hervé; Jalinot, Pierre; Mocquet, Vincent
Nat Commun - 9 1 - 10.1038/s41467-017-02793-6 - 2018
Up-Frameshift Suppressor 1 Homolog (UPF1) is a key factor for nonsense-mediated mRNA decay (NMD), a cellular process that can actively degrade mRNAs. Here, we study NMD inhibition during infection by human T-cell lymphotropic virus type I (HTLV-1) and characterise the influence of the retroviral Tax factor on UPF1 activity. Tax interacts with the central helicase core domain of UPF1 and might plug the RNA channel of UPF1, reducing its affinity for nucleic acids. Furthermore, using a single-molecule approach, we show that the sequential interaction of Tax with a RNA-bound UPF1 freezes UPF1: this latter is less sensitive to the presence of ATP and shows translocation defects, highlighting the importance of this feature for NMD. These mechanistic insights reveal how HTLV-1 hijacks the central component of NMD to ensure expression of its own genome.
Macroscale fluorescence imaging against autofluorescence under ambient light.
Laboratoire Physique des biomolécules - Zhang, Ruikang; Chouket, Raja; Plamont, Marie-Aude; Kelemen, Zsolt; Espagne, Agathe; Tebo, Alison G; Gautier, Arnaud; Gissot, Lionel; Faure, Jean-Denis; Jullien, Ludovic; Croquette, Vincent; Le Saux, Thomas
Light - 7 97 - 10.1038/s41377-018-0098-6 - 2018
Macroscale fluorescence imaging is increasingly used to observe biological samples. However, it may suffer from spectral interferences that originate from ambient light or autofluorescence of the sample or its support. In this manuscript, we built a simple and inexpensive fluorescence macroscope, which has been used to evaluate the performance of Speed OPIOM (Out of Phase Imaging after Optical Modulation), which is a reference-free dynamic contrast protocol, to selectively image reversibly photoswitchable fluorophores as labels against detrimental autofluorescence and ambient light. By tuning the intensity and radial frequency of the modulated illumination to the Speed OPIOM resonance and adopting a phase-sensitive detection scheme that ensures noise rejection, we enhanced the sensitivity and the signal-to-noise ratio for fluorescence detection in blot assays by factors of 50 and 10, respectively, over direct fluorescence observation under constant illumination. Then, we overcame the strong autofluorescence of growth media that are currently used in microbiology and realized multiplexed fluorescence observation of colonies of spectrally similar fluorescent bacteria with a unique configuration of excitation and emission wavelengths. Finally, we easily discriminated fluorescent labels from the autofluorescent and reflective background in labeled leaves, even under the interference of incident light at intensities that are comparable to sunlight. The proposed approach is expected to find multiple applications, from biological assays to outdoor observations, in fluorescence macroimaging.
Asymmetric adhesion of rod-shaped bacteria controls microcolony morphogenesis
Laboratoire Physique des biomolécules - Duvernoy, Marie-Cécilia; Mora, Thierry; Ardré, Maxime; Croquette, Vincent; Bensimon, David; Quilliet, Catherine; Ghigo, Jean-Marc; Balland, Martial; Beloin, Christophe; Lecuyer, Sigoléne; Desprat, Nicolas
Nat Commun - 9 1120 - 10.1038/s41467-018-03446-y - 2018
Surface colonization underpins microbial ecology on terrestrial environments. Although factors that mediate bacteria-substrate adhesion have been extensively studied, their spatiotemporal dynamics during the establishment of microcolonies remains largely unexplored. Here, we use laser ablation and force microscopy to monitor single-cell adhesion during the course of microcolony formation. We find that adhesion forces of the rod-shaped bacteria Escherichia coli and Pseudomonas aeruginosa are polar. This asymmetry induces mechanical tension, and drives daughter cell rearrangements, which eventually determine the shape of the microcolonies. Informed by experimental data, we develop a quantitative model of microcolony morphogenesis that enables the prediction of bacterial adhesion strength from simple time-lapse measurements. Our results demonstrate how patterns of surface colonization derive from the spatial distribution of adhesive factors on the cell envelope.
High density gold nanoparticles immobilized on surface via plasma deposited APTES film for decomposing organic compounds in microchannels
Laboratoire Procédés - Plasmas - Microsystèmes - XiRao, CédricGuyo, StephanieOgnier, Bradley Da Silva, Chenglin Chu, MichaëlTatoulian, Ali AbouHassan
Applied Surface Science - 439 272-281 - https://doi.org/10.1016/j.apsusc.2018.01.009 - 2018
Immobilization of colloidal particles (e.g. gold nanoparticles (AuNps)) on the inner surface of micro-/nano- channels has received a great interest for catalysis. A novel catalytic ozonation setup using a gold-immobilized microchannel reactor was developed in this work. To anchor AuNps, (3-aminopropyl) triethoxysilane (APTES) with functional amine groups was deposited using plasma enhanced chemical vapor deposition (PECVD) process. The results clearly evidenced that PECVD processing exhibited relatively high efficiency for grafting amine groups and further immobilizing AuNPs. The catalytic activity of gold immobilized microchannel was evaluated by pyruvic acid ozonation. The decomposition rate calculated from High Performance Liquid Chromatography (HPLC) indicated a much better catalytic performance of gold in microchannel than that in batch. The results confirmed immobilizing gold nanoparticles on plasma deposited APTES for preparing catalytic microreactors is promising for the wastewater treatment in the future.

Isothermal crystallization of glycine in semi-continuous mode by anti-solvent addition
Laboratoire Procédés - Plasmas - Microsystèmes - Wail El Bazi, Marie-Thérèse Moufarej Abou Jaoude, Catherine Porte, Isabelle Mabille
Journal of Crystal Growth - 3 498 - DOI: 10.1016/j.jcrysgro.2018.06.013 - 2018
This article focuses on the isothermal semi-continuous crystallization of glycine aqueous solution by adding an anti-solvent, ethanol. The effect of the ethanol concentration on solubility and the impact of the ethanol flow rate on the metastable zone width and on the size distribution of the crystals were investigated. The study showed that increasing the ethanol concentration in the medium decreases solubility for the studied temperatures and that increasing the ethanol flow rate causes a widening of the metastable zone without inducing any noticeable effect on the crystals’ size distribution. In addition, nucleation kinetic models were determined for two temperatures (30 and 56 °C).
Microfluidic chips for plasma flow chemistry: application to controlled oxidative processes
Laboratoire Procédés - Plasmas - Microsystèmes - Julien Wengler, Stéphanie Ognier, Mengxue Zhang, Etienne Levernier, Cedric Guyon, Cyril Ollivier, Louis Fensterbank and Michael Tatoulian
Reaction Chemistry & Engineering - 3 930-941 - https://doi.org/10.1039/C8RE00122G - 2018
The present paper reports the integration of nonthermal plasma into a biphasic gas–liquid microfluidic chip. It evaluates the potential of plasma activation to become a synthetic tool in organic chemistry, operating under mild conditions (room temperature, atmospheric pressure) and without a catalyst. Few preceding works on plasma chemistry involved a liquid phase and none of them was able to handle the high reactivity of plasma to achieve both high conversion rates and selective reactions. We fabricated a glass-polymer microfluidic chip comprising a one metre long serpentine channel, in which a parallel gas–liquid flow was stabilized thanks to a specific step-like cross-sectional shape. Transparent ITO electrodes, deposited on both sides of the chip and linked to an AC high voltage source, produced a dielectric barrier discharge along the channel. We assessed the behaviour of the flow through optical observations and characterized the discharge through electrical measurements and real time intensified-CCD monitoring. We report the successful treatment of liquid cyclohexane with oxygen plasma inside our chip. The GC analysis of the outflowing liquid revealed only a partial oxidation of cyclohexane into a mixture of cyclohexanol and cyclohexanone (industrially known as “KA oil”), and cyclohexyl hydroperoxide, with a total selectivity above 70% and conversion up to 30%. This indicates that alkanes can be activated and functionalized by means of plasma discharges, in a controlled way. In that respect, we claim to have successfully overcome some of the barriers to industrially relevant plasma chemistry. We believe that the combined use of plasma and microfluidic technologies is essential to the development of this new field of research.

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579 publications.