Université PSL



Laboratory :
Author :
Revue :
Year :
Chiral Colloidal Clusters
D. Zerrouki, J. Baudry, D. Pine, P. Chaikin, J. Bibette
Nature - 455 :380-2 - DOI:10.1038/nature07237 - 2008
Chirality is an important element of biology, chemistry and physics. Once symmetry is broken and a handedness is established, biochemical pathways are set. In DNA, the double helix arises from the existence of two competing length scales, one set by the distance between monomers in the sugar backbone, and the other set by the stacking of the base pairs1. Here we use a colloidal system to explore a simple forcing route to chiral structures. To do so we have designed magnetic colloids that, depending on both their shape and induced magnetization, self-assemble with controlled helicity. We model the two length scales with asymmetric colloidal dumbbells linked by a magnetic belt at their waist. In the presence of a magnetic field the belts assemble into a chain and the steric constraints imposed by the asymmetric spheres force the chain to coil. We show that if the size ratio between the spheres is large enough, a single helicity is adopted, right or left. The realization of chiral colloidal clusters opens up a new link between colloidal science and chemistry. These colloidal clusters may also find use as mesopolymers, as optical and light-activated structures2, and as models for enantiomeric separation.
Decompressing Emulsion Droplets Favors Coalescence
N. Brémond, A.R. Thiam, J. Bibette
Phys. Rev. Lett. - 100(2) :024501 - DOI:10.1103/PhysRevLett.100.024501 - 2008
The destabilization process of an emulsion under flow is investigated in a microfluidic device. The experimental approach enables us to generate a periodic train of droplet pairs, and thus to isolate and analyze the basic step of the destabilization, namely, the coalescence of two droplets which collide. We demonstrate a counterintuitive phenomenon: coalescence occurs during the separation phase and not during the impact. Separation induces the formation of two facing nipples in the contact area that hastens the connection of the interfaces prior to fusion. Moreover, droplet pairs initially stabilized by surfactants can be destabilized by forcing the separation. Finally, we note that the fusion mechanism is responsible for a cascade of coalescence events in a compact system of droplets where the separation is driven by surface tension.
Measuring the kinetics of biomolecular recognition with magnetic colloids
L. Cohen-Tannoudji, E. Bertrand, J. Baudry, C. Robic, C. Goubault, M. Pellissier, A. Johner, F. Thalmann, N. K. Lee, C. M. Marques, J. Bibette
Phys. Rev. Lett. - 100(10) :108301 - DOI:10.1103/PhysRevLett.100.108301 - 2008
We introduce a general methodology based on magnetic colloids to study the recognition kinetics of tethered biomolecules. Access to the full kinetics of the reaction is provided by an explicit measure of the time evolution of the reactant densities. Binding between a single ligand and its complementary receptor is here limited by the colloidal rotational diffusion. It occurs within a binding distance that can be extracted by a reaction-diffusion theory that properly accounts for the rotational Brownian dynamics. Our reaction geometry allows us to probe a large diversity of bioadhesive molecules and tethers, thus providing a quantitative guidance for designing more efficient reactive biomimetic surfaces, as required for diagnostic, therapeutic, and tissue engineering techniques.
Droplet-based microfluidic platforms for the encapsulation and screening of mammalian cells and multicellular organisms
J. Clausell-Tormos, D. Lieber, J.-C. Baret, A. El-Harrak, O.J. Miller, L. Frenz, J. Blouwolff, K.J. Humphry, S. Köster, H. Duan, C. Holtze, D.A. Weitz, A.D. Griffiths and C.A. Merten
Chem. Biol. - 15(5) :427-37 - DOI: 10.1016/j.chembiol.2008.04.004 - 2008
High-throughput, cell-based assays require small sample volumes to reduce assay costs and to allow for rapid sample manipulation. However, further miniaturization of conventional microtiter plate technology is problematic due to evaporation and capillary action. To overcome these limitations, we describe droplet-based microfluidic platforms in which cells are grown in aqueous microcompartments separated by an inert perfluorocarbon carrier oil. Synthesis of biocompatible surfactants and identification of gas-permeable storage systems allowed human cells, and even a multicellular organism (C. elegans), to survive and proliferate within the microcompartments for several days. Microcompartments containing single cells could be reinjected into a microfluidic device after incubation to measure expression of a reporter gene. This should open the way for high-throughput, cell-based screening that can use >1000-fold smaller assay volumes and has approximately 500x higher throughput than conventional microtiter plate assays.
Droplet-based microreactors for the synthesis of magnetic iron oxide nanoparticles. Angewandte
L. Frenz, A. El Harrak, M. Pauly, S. Bégin-Colin, A.D. Griffiths and J.-C. Baret
Chimie Int. Ed. - 47(36) :6817-20 - DOI: 10.1002/anie.200801360 - 2008
Microdroplets for nanoparticles: An extremely reliable method to create droplet pairs, based on hydrodynamic coupling of two spatially separated nozzles, has been developed. Droplets containing the reagents for the precipitation of iron oxide are electrocoalesced to synthesize iron oxide nanoparticles in a very fast (millisecond-scale) and reproducible reaction (see picture).
Flourescence-activated droplet sorting (FADS): efficient microfluidic cell sorting based on enzymatic activity
J.-C. Baret, O.J. Miller, V. Taly, M. Ryckelynck, A. El-Harrak, L. Frenz, C. Rick, M.L. Samuels, J. B. Hutchison, J.J. Agresti, D.R. Link, D.A. Weitz and A.D. Griffiths
Lab. Chip - 9 :1850-8 - DOI: 10.1039/B902504A - 2008
We describe a highly efficient microfluidic fluorescence-activated droplet sorter (FADS) combining many of the advantages of microtitre-plate screening and traditional fluorescence-activated cell sorting (FACS). Single cells are compartmentalized in emulsion droplets, which can be sorted using dielectrophoresis in a fluorescence-activated manner (as in FACS) at rates up to 2000 droplets s−1. To validate the system, mixtures of E. coli cells, expressing either the reporter enzyme β-galactosidase or an inactive variant, were compartmentalized with a fluorogenic substrate and sorted at rates of 300 droplets s−1. The false positive error rate of the sorter at this throughput was <1 in 104 droplets. Analysis of the sorted cells revealed that the primary limit to enrichment was the co-encapsulation of E. coli cells, not sorting errors: a theoretical model based on the Poisson distribution accurately predicted the observed enrichment values using the starting cell density (cells per droplet) and the ratio of active to inactive cells. When the cells were encapsulated at low density ( 1 cell for every 50 droplets), sorting was very efficient and all of the recovered cells were the active strain. In addition, single active droplets were sorted and cells were successfully recovered.
Microfluidic high-throughput encapsulation and hydrodynamic self-sorting of single cells
Chabert M and Viovy JL
Proc. Nat. Acad. Sci. USA - 105(9) :3191-6 - DOI:10.1073/pnas.0708321105 - 2008
We present a purely hydrodynamic method for the high-throughput encapsulation of single cells into picoliter droplets, and spontaneous self-sorting of these droplets. Encapsulation uses a cell-triggered Rayleigh-Plateau instability in a flow-focusing geometry, and self-sorting puts to work two extra hydrodynamic mechanisms: lateral drift of deformable objects in a shear flow, and sterically driven dispersion in a compressional flow. Encapsulation and sorting are achieved on-flight in continuous flow at a rate up to 160 cells per second. The whole process is robust and cost-effective, involving no optical or electrical discrimination, active sorting, flow switching, or moving parts. Successful encapsulation and sorting of 70-80% of the injected cell population into drops containing one and only one cell, with <1% contamination by empty droplets, is demonstrated. The system is also applied to the direct encapsulation and sorting of cancerous lymphocytes from a whole blood mixture, yielding individually encapsulated cancer cells with a >10,000-fold enrichment as compared with the initial mix. The method can be implemented in simple “soft lithography” chips, allowing for easy downstream coupling with microfluidic cell biology or molecular biology protocols.
Controlled proteolysis of normal and pathological prion protein in a microfluidic chip
Le Nel A, Minc N, Smadja C, Slovakova M, Bilkova Z, Peyrin JM, Viovy JL, Taverna M
Lab. Chip - 8(2) :294-301 - DOI:10.1039/b715238h - 2008
A microreactor for proteinase K (PK)-mediated protein digestion was developed as a step towards the elaboration of a fully integrated microdevice for the detection of pathological prion protein (PrP). PK-grafted magnetic beads were immobilized inside a polydimethylsiloxane (PDMS) microchannel using a longitudinal magnetic field parallel to the flow direction and a magnetic field gradient, thereby forming a matrix for enzymatic digestion. This self-organization provided uniform pore sizes, a low flow resistance and a strong reaction efficiency due to a very thin diffusion layer. The microreactor's performance was first evaluated using a model substrate, succinyl-ala-ala-ala-paranitroanilide (SAAAP). Reaction kinetics were typically accelerated a hundred-fold as compared to conventional batch reactions. Reproducibility was around 98% for on-chip experiments. This microsystem was then applied to the digestion of prion protein from brain tissues. Controlled proteolysis could be obtained by varying the on-chip flow rate, while a complete proteolysis of normal protein was achieved in only three minutes. Extracts from normal and pathological brain homogenates were finally compared and strong discrimination between normal and pathological samples was demonstrated.
Microfluidic droplet-based liquid-liquid extraction
P. Mary, V. Studer, P. Tabeling
Anal. Chem. - 80(8) :2680-7 - DOI:10.1021/ac800088s - 2008
We study microfluidic systems in which mass exchanges take place between moving water droplets, formed on-chip, and an external phase (octanol). Here, no chemical reaction takes place, and the mass exchanges are driven by a contrast in chemical potential between the dispersed and continuous phases. We analyze the case where the microfluidic droplets, occupying the entire width of the channel, extract a solutefluoresceinfrom the external phase (extraction) and the opposite case, where droplets reject a soluterhodamineinto the external phase (purification). Four flow configurations are investigated, based on straight or zigzag microchannels. Additionally to the experimental work, we performed two-dimensional numerical simulations. In the experiments, we analyze the influence of different parameters on the process (channel dimensions, fluid viscosities, flow rates, drop size, droplet spacing, ...). Several regimes are singled out. In agreement with the mass transfer theory of Young et al. (Young, W.; Pumir, A.; Pomeau, Y. Phys. Fluids A 1989, 1, 462), we find that, after a short transient, the amount of matter transferred across the droplet interface grows as the square root of time and the time it takes for the transfer process to be completed decreases as Pe-2/3, where Pe is the Peclet number based on droplet velocity and radius. The numerical simulation is found in excellent consistency with the experiment. In practice, the transfer time ranges between a fraction and a few seconds, which is much faster than conventional systems.
Nanofluidics in the Debye layer at hydrophilic and hydrophobic surfaces
C.I Bouzigues, P. Tabeling, L. Bocquet
Phys. Rev. Lett. - 101(11) :114503 - DOI:10.1103/PhysRevLett.101.114503 - 2008
By using evanescent waves, we study equilibrium and dynamical properties of liquid-solid interfaces in the Debye layer for hydrophilic and hydrophobic surfaces. We measure velocity profiles and nanotracer concentration and diffusion profiles between 20 and 300 nm from the walls in pressure-driven and electro-osmotic flows. We extract electrostatic and zeta potentials and determine hydrodynamic slip lengths with 10 nm accuracy. The spectacular amplification of the zeta potential resulting from hydrodynamic slippage allows us to clarify for the first time the dynamic origin of the zeta potential.

326 publications.