Université PSL



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Microchip electrophoresis profiling of AB peptides in the cerebrospinal fluid of patients with Alzheimer’s disease
Laboratoire Macromolécules et Microsystèmes en Biologie et Médecine - Mohamadi MR, Svobodova Z, Verpillot R, Esselmann H, Wiltfang J, Otto M, Taverna M, Bilkova Z, Viovy JL.
Anal. Chem. - 82(18) :7611-7 - DOI:10.1063/1.4722588 - 2010
The preferential aggregation of Aß1-42 in amyloid plaques is one of the major neuropathological events in Alzheimer's disease. This is accompanied by a relative reduction of the concentration of Aß1-42 in the cerebrospinal fluid (CSF) of patients developing the signs of Alzheimer's disease. Here, we describe a microchip gel electrophoresis method in polydimethylsiloxane (PDMS) chip that enables rapid profiling of major Aß peptides in cerebrospinal fluid. To control the electroosmotic flow (EOF) in the PDMS channel and also to reduce the adsorption of the peptides to the surface of the channel, a new double coating using poly(dimethylacrylamide-co-allyl glycidyl ether) (PDMA-AGE) and methylcellulose-Tween-20 was developed. With this method, separation of five synthetic Aß peptides (Aß1-37, Aß1-38, Aß1-39, Aß1-40, and Aß1-42) was achieved, and relative abundance of Aß1-42 to Aß1-37 could be calculated in different standard mixtures. We applied our method for profiling of Aß peptides in CSF samples from nonAlzheimer patients and patients with Alzheimer's disease. Aß peptides in the CSF samples were captured and concentrated using a microfluidic system in which magnetic beads coated with anti-Aß were self-organized into an affinity microcolumn under the a permanent magnetic field. Finally, we could detect two Aß peptides (Aß1-40 and Aß1-42) in the CSF samples.
Monodisperse Colloids Synthesized with Nanofluidic Technology
Laboratoire Microfluidique MEMS et nanostructures - F. Malloggi, N. Pannacci, R. Attia, F. Monti, P. Mary, H. Villaime, P. Tabeling, B. Cabane, P. Poncet
Langmuir - 26(4) :2369-73 - DOI:10.1021/la9028047 - 2010
Limitations in the methods employed to generate micrometric colloidal droplets hinder the emergence of key applications in the fields of material science and drug delivery. Through the use of dedicated nanofluidic devices and by taking advantage of an original physical effect called capillary focusing, we could circumvent some of these limitations. The nanofluidic (i.e., submicrometric) devices introduced herein are made of soft materials, and their fabrication relies upon rapid technologies. The objects that we have generated are simple droplets, multiple droplets, particles, and Janus particles whose sizes lie between 900 nm and 3 µm (i.e., within the colloidal range). Colloidal droplets have been assembled on-chip into clusters and crystals, yielding discrete diffraction patterns. We illustrate potential applications in the field of drug delivery by demonstrating the ability of multiple droplets to be phagocytosed by murine macrophage-type cells.
Interfacially Driven Instability in the Microchannel Flow of a Shear-Banding Fluid
Laboratoire Microfluidique MEMS et nanostructures - P. Ngher, S. Fielding, A. Ajdari, P. Tabeling
Phys. Rev. Lett. - 104(24) :248303 - DOI:10.1103/PhysRevLett.104.248303 - 2010
Using microparticle image velocimetry, we resolve the spatial structure of the shear-banding flow of a wormlike micellar surfactant solution in a straight microchannel. We reveal an instability of the interface between the shear bands, associated with velocity modulations along the vorticity direction. We compare our results with a detailed theoretical study of the diffusive Johnson-Segalman model. The quantitative agreement obtained favors an instability scenario previously predicted theoretically but hitherto unobserved experimentally, driven by a normal stress jump across the interface between the bands.
Wettability Patterning by UV-initiated graft polymerization of PAA in microfluidic systems of complex geometries
Laboratoire Microfluidique MEMS et nanostructures - M. Schneider, H. Willaime, Y. Tran, F. Rezgui, P. Tabeling
Anal. Chem. - 82(21) :8848-55 - DOI:10.1021/ac101345m - 2010
Many microfluidic applications require modified surface wettability of the microchannels. Patterning of wettability within enclosed microfluidic structures at high spatial resolution has been challenging in the past. In this paper, we report an improved method for altering the surface wettability in poly(dimethylsiloxane) (PDMS) microchannels by UV-induced graft polymerization of poly(acrylic acid). Our method presents significant improvements in terms of wettability contrast and spatial resolution of the patterned structures as compared to recent literature and is in particular applicable to complex microfluidic structures with a broad range of channel sizes and aspect ratios. A key part of our work is the clear description of the surface treatment process with the identification of key parameters, some of which have been overlooked, neglected, or misinterpreted in previous works. We have studied these key parameters in detail and provide recommended values for each parameter supported by experimental results. This detailed understanding of the treatment process and the effects of the critical parameters on it allowed us to significantly improve quality and reliability of the treatment process.
Thermocapillary actuation by optimized resistor pattern: bubbles and droplets displacing, switching and trapping
Laboratoire Microfluidique MEMS et nanostructures - B. Selva, V. Miralles, I. Cantat, M. C Jullien
Lab. Chip - 10(14) :1835-40 - DOI:10.1039/c001900c - 2010
We report a novel method for bubble or droplet displacement, capture and switching within a bifurcation channel for applications in digital microfluidics based on the Marangoni effect, i.e. the appearance of thermocapillary tangential interface stresses stemming from local surface tension variations. The specificity of the reported actuation is that heating is provided by an optimized resistor pattern (B. Selva, J. Marchalot and M.-C. Jullien, An optimized resistor pattern for temperature gradient control in microfluidics, J. Micromech. Microeng., 2009, 19, 065002) leading to a constant temperature gradient along a microfluidic cavity. In this context, bubbles or droplets to be actuated entail a surface force originating from the thermal Marangoni effect. This actuator has been characterized (B. Selva, I. Cantat, and M.-C. Jullien, Migration of a bubble towards a higher surface tension under the effect of thermocapillary stress, preprint, 2009) and it was found that the bubble/droplet (called further element) is driven toward a high surface tension region, i.e. toward cold region, and the element velocity increases while decreasing the cavity thickness. Taking advantage of these properties three applications are presented: (1) element displacement, (2) element switching, detailed in a given range of working, in which elements are redirected towards a specific evacuation, (3) a system able to trap, and consequently stop on demand, the elements on an alveolus structure while the continuous phase is still flowing. The strength of this method lies in its simplicity: single layer system, in situ heating leading to a high level of integration, low power consumption (P < 0.4 W), low applied voltage (about 10 V), and finally this system is able to manipulate elements within a flow velocity up to 1 cm s(-1).
Force fluctuations assist nanopore unzipping of DNA
Laboratoire Nanobiophysiques - V Viasnoff, N Chiaruttini, J Muzard, and U Bockelmann
Journal of Physics : Condensed Matter - 22(45) :454122 - DOI:10.1088/0953-8984/22/45/454122 - 2010
We experimentally study the statistical distributions and the voltage dependence of the unzipping time of 45 base-pair-long double-stranded DNA through a nanopore. We then propose a quantitative theoretical description considering the nanopore unzipping process as a random walk of the opening fork through the DNA sequence energy landscape biased by a time-fluctuating force. To achieve quantitative agreement fluctuations need to be correlated over the millisecond range and have an amplitude of order kBT/bp. Significantly slower or faster fluctuations are not appropriate, suggesting that the unzipping process is efficiently enhanced by noise in the kHz range. We further show that the unzipping time of short 15 base-pair hairpins does not always increase with the global stability of the double helix and we theoretically study the role of DNA elasticity on the conversion of the electrical bias into a mechanical unzipping force.
DNA translocation and unzipping through a nanopore : some geometrical effects
Laboratoire Nanobiophysiques - J. Muzard, M. Martinho, J. Mathe, U. Bockelmann, and V. Viasnoff
Biophys. J. - 98(10) :2170–8 - DOI:10.1016/j.bpj.2010.01.041. - 2010
This article explores the role of some geometrical factors on the electrophoretically driven translocations of macromolecules through nanopores. In the case of asymmetric pores, we show how the entry requirements and the direction of translocation can modify the information content of the blocked ionic current as well as the transduction of the electrophoretic drive into a mechanical force. To address these effects we studied the translocation of single-stranded DNA through an asymmetric alpha-hemolysin pore. Depending on the direction of the translocation, we measure the capacity of the pore to discriminate between both DNA orientations. By unzipping DNA hairpins from both sides of the pores we show that the presence of single strand or double strand in the pore can be discriminated based on ionic current levels. We also show that the transduction of the electrophoretic drive into a denaturing mechanical force depends on the local geometry of the pore entrance. Eventually we discuss the application of this work to the measurement of energy barriers for DNA unzipping as well as for protein binding and unfolding.
Mathematical description of bacterial traveling pulses
Laboratoire Physico-biologie aux méso-échelles - Saragosti J., Calvez V., Bournaveas N., Buguin A., Silberzan P., Perthame B.
PLoS Comp. Biol. - 6 :e1000890 - DOI:10.1371/journal.pcbi.1000890 - 2010
The Keller-Segel system has been widely proposed as a model for bacterial waves driven by chemotactic processes. Current experiments on Escherichia coli have shown the precise structure of traveling pulses. We present here an alternative mathematical description of traveling pulses at the macroscopic scale. This modeling task is complemented with numerical simulations in accordance with the experimental observations. Our model is derived from an accurate kinetic description of the mesoscopic run-and-tumble process performed by bacteria. This can account for recent experimental observations with E. coli. Qualitative agreements include the asymmetry of the pulse and transition in the collective behaviour (clustered motion versus dispersion). In addition, we can capture quantitatively the traveling speed of the pulse as well as its characteristic length. This work opens several experimental and theoretical perspectives since coefficients at the macroscopic level are derived from considerations at the cellular scale. For instance, the particular response of a single cell to chemical cues turns out to have a strong effect on collective motion. Furthermore, the bottom-up scaling allows us to perform preliminary mathematical analysis and write efficient numerical schemes. This model is intended as a predictive tool for the investigation of bacterial collective motion.
Velocity fields in a collectively migrating epithelium
Laboratoire Physico-biologie aux méso-échelles - Petitjean L., Reffay M., Grasland-Mongrain E., Poujade M., Ladoux B., Buguin A., Silberzan P.
Biophys. J. - 98(9) :1790-800 - DOI:10.1016/j.bpj.2010.01.030 - 2010
We report quantitative measurements of the velocity field of collectively migrating cells in a motile epithelium. The migration is triggered by presenting free surface to an initially confluent monolayer by using a microstencil technique that does not damage the cells. To avoid the technical difficulties inherent in the tracking of single cells, the field is mapped using the technique of particle image velocimetry. The main relevant parameters, such as the velocity module, the order parameter, and the velocity correlation function, are then extracted from this cartography. These quantities are dynamically measured on two types of cells (collectively migrating Madin-Darby canine kidney (MDCK) cells and fibroblastlike normal rat kidney (NRK) cells), first as they approach confluence, and then when the geometrical constraints are released. In particular, for MDCK cells filling up the patterns, we observe a sharp decrease in the average velocity after the point of confluence, whereas the densification of the monolayer is much more regular. After the peeling off of the stencil, a velocity correlation length of 200 microns is measured for MDCK cells versus only 40 microns for the more independent NRK cells. Our conclusions are supported by parallel single-cell tracking experiments. By using the biorthogonal decomposition of the velocity field, we conclude that the velocity field of MDCK cells is very coherent in contrast with the NRK cells. The displacements in the fingers arising from the border of MDCK epithelia are very oriented along their main direction. They influence the velocity field in the epithelium over a distance of 200 microns.
Physical model of the dynamic instability in an expanding cell culture
Laboratoire Physico-biologie aux méso-échelles - Mark S., Shlomovitz R., Gov N. S., Poujade M., Grasland-Mongrain E., Silberzan P.
Biophys. J. - 98(3) :361-70 - DOI:10.1016/j.bpj.2009.10.022 - 2010
Collective cell migration is of great significance in many biological processes. The goal of this work is to give a physical model for the dynamics of cell migration during the wound healing response. Experiments demonstrate that an initially uniform cell-culture monolayer expands in a nonuniform manner, developing fingerlike shapes. These fingerlike shapes of the cell culture front are composed of columns of cells that move collectively. We propose a physical model to explain this phenomenon, based on the notion of dynamic instability. In this model, we treat the first layers of cells at the front of the moving cell culture as a continuous one-dimensional membrane (contour), with the usual elasticity of a membrane: curvature and surface-tension. This membrane is active, due to the forces of cellular motility of the cells, and we propose that this motility is related to the local curvature of the culture interface; larger convex curvature correlates with a stronger cellular motility force. This shape-force relation gives rise to a dynamic instability, which we then compare to the patterns observed in the wound healing experiments.

414 publications.