Université PSL



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A caged retinoic acid for one- and two-photon excitation in zebrafish embryos
Laboratoire Physique des biomolécules - P. Neveu, I. Aujard, C. Benbrahim, T. Le Saux, J.-F. Allemand, S. Vriz, D. Bensimon and L. Jullien
Angew Chem Int Ed Engl. - 47(20) :3744–46 - DOI:10.1002/anie.200800037 - 2008
Specific Wetting Probed With Biomimetic Droplets
Laboratoire Pôle Microfluidique - J. Fattaccioli, J. Baudry, F. Brochard-Wyart, N. Henry and J. Bibette
Soft Matter - 4(12) :2334-40 - DOI:10.1039/B806635C - 2008
We have produced emulsion droplets of controlled size and composition coated by ligands, and studied the adhesion of these drops on a solid substrate coated by receptors and polymers. Using transmission, RICM and fluorescence microscopy we assess the size, contact angle and ligand density for each drop. We first show that non-specific interactions significantly enhance the proteins density within the adhesive patch. Then we show that binding within the patch is partially inhibited in good agreement with the hypothesis of an absence of translational diffusion. We confirm that the density of specific bonds sets the adhesive energy and therefore the final contact angle, and finally show that specific binding in our system is always associated with the existence of a positive line tension, which linearly increases with the density of receptors. These experiments describe a new scenario for specific wetting which raises the importance of the coupling between non-specific interactions and specific binding.
In situ quantitative measurement of concentration profiles in a microreactor with submicron resolution using multiplex CARS microscopy
Laboratoire Procédés - Plasmas - Microsystèmes - Dawn Schafer, Jeff A. Squier, Jan van Maarseveen, Daniel Bon, Mischa Bonn, Michiel Mu¨ller
JACS - 130(35) :11592-3 - DOI:10.1021/ja804158n - 2008
In situ quantitative imaging of concentration profiles of reactants and products inside a microfluidic reactor is achieved, with submicron spatial resolution with mM sensitivity and on ms time scales, for a given position. The label-free approach relies on quantitative vibrational spectroscopy, using Coherent Anti-Stokes Raman scattering microscopy in a spectrally resolved fashion, and is demonstrated on an elementary acid-base reaction.
A simple and universal tool to remove on-line impurities in mono- or two-dimensional liquid chromatography–mass spectrometry analysis
Laboratoire Spectrométrie de masse biologique et protéomique - Hesse A-M, Marcelo P, Rossier J and Vinh J.
J. Chrom. A - 1189(1-2) :175-82 - DOI:10.1016/j.chroma.2007.12.060 - 2008
Several recurrent problems have always hindered mono-dimensional liquid chromatography-mass spectrometry proteomic analyses. Polymer contamination is a major problem because polymers could co-elute with compounds of interest (peptides). In this case spectral suppression degrades dynamic range and sensitivity. Polyethylene glycol derivatives count among the major contaminants. They are targeted in this work. They are eluted at 35-40% acetonitrile from C18 phase in every single reversed-phase run. Moreover, they are also observed in two-dimensional liquid chromatography in every salt fraction. A simple and robust method is presented here for rapid and efficient on-line removal of these impurities using self-regenerating purification microdevices.
Determination of nanoparticle diffusion coefficients by Taylor dispersion analysis using a capillary electrophoresis instrument
Laboratoire Synthèse Electrochimie Imagerie et Systèmes Analytiques - d'Orlye F, Varenne A, Gareil P.
J. Chrom. A - 1204(2) :226-32 - DOI:10.1016/j.chroma.2008.08.008 - 2008
The collective diffusion coefficient D(C) of diluted suspensions of positively charged iron oxide maghemite particles was experimentally investigated using a capillary electrophoresis instrument on the grounds of Taylor dispersion theory. Conditions for this approach to be applicable to nanoparticles of mean solid diameter below 10nm were set in this work, enabling precisions on D(C) determination of less than 2% relative standard deviation (RSD). Significantly different D(C) values were thus measured for particle populations differing in solid number mean diameter by only 2 nm. The obtained values were compared to the z-average diffusion coefficient derived from dynamic light scattering (DLS) experiments and used for the calculation of the Stokes radius. The measured diffusion coefficients appeared to be dependent on particle volume fraction and electrolyte ionic strength. These observations were eventually discussed in terms of particle interactions.
Signal enhancement in electronic detection of DNA hybridization
Laboratoire Nanobiophysiques - C. Gentil, G. Philippin, and U. Bockelmann
Phys. Rev. E - 75(1) :011926 - DOI:10.1103/PhysRevE.75.011926 - 2007
Electronic detection of the specific recognition between complementary DNA sequences is investigated. DNA probes are immobilized at different lateral positions on a Poly(L-lysine)-coated surface of an integrated silicon transistor array. Hybridization and field effect detection are done with the solid surface immersed in electrolyte solutions. Differential measurements are performed, where DNA hybridization leads to surface potential shifts between the transistors of the array. We experimentally show that these differential signals of hybridization can be enhanced significantly by changing the salt concentration between hybridization and detection.
Real-time observation of bacteriophage T4 gp41 helicase reveals an unwinding mechanism
Laboratoire Physique des biomolécules - T. Lionnet, M. M. Spiering, S. J. Benkovic, D. Bensimon and V. Croquette
Proc. Nat. Acad. Sci. USA - 104(50) :19790–95 - DOI:10.1073/pnas.0709793104 - 2007
Helicases are enzymes that couple ATP hydrolysis to the unwinding of double-stranded (ds) nucleic acids. The bacteriophage T4 helicase (gp41) is a hexameric helicase that promotes DNA replication within a highly coordinated protein complex termed the replisome. Despite recent progress, the gp41 unwinding mechanism and regulatory interactions within the replisome remain unclear. Here we use a single tethered DNA hairpin as a real-time reporter of gp41-mediated dsDNA unwinding and single-stranded (ss) DNA translocation with 3-base pair (bp) resolution. Although gp41 translocates on ssDNA as fast as the in vivo replication fork (approximate to 400 bp/s), its unwinding rate extrapolated to zero force is much slower (approximate to 30 bp/s). Together, our results have two implications: first, gp41 unwinds DNA through a passive mechanism; second, this weak helicase cannot efficiently unwind the T4 genome alone. Our results suggest that important regulations occur within the replisome to achieve rapid and processive replication.
Highly Parallel Mix-and-Match Fabrication of Nanopillar Arrays Integrated in Microfluidic Channels for Long DNA Molecule Separation
Laboratoire Pôle Microfluidique - J. Shi, A. P. Fang, L. Malaquin, A. Pepin, D. Decanini, J. L. Viovy and Y. Chen
Applied Physics Letters - 91(15) :153114 - DOI:153114 10.1063/1.2793616 - 2007
We report on a mix-and-match method based on a combination of soft UV nanoimprint lithography, contact optical lithography, and reactive-ion-etch techniques, which is applicable for high throughput manufacturing of nanostructure integrated microfluidic devices. We demonstrate the integration of high density and high aspect ratio nanopillars into microfluidic channels as electrophoresis sieving matrices. As a result, ? DNA and T4 DNA can be separated within a few minutes. By changing the pattern design, the device could be used for separation of other types of molecules.
Microcontact Printing of Living Bacteria Arrays with Cellular Resolution
Laboratoire Pôle Microfluidique - L. P. Xu, L. Robert, O. Y. Qi, F. Taddei, Y. Chen, A.B. Lindner, D. Baigl
Nano Lett. - 7(7) :2068-72 - DOI:10.1021/nl070983z - 2007
Arrays of living bacteria were printed on agarose substrate with cellular resolution using elastomeric stamps with a high aspect ratio generated by reverse in situ lithography (RISL). The printed bacteria reproduced the original stamp patterns with high fidelity and continued growing as in bulk culture. This methodology provides a simple route to any desired bacterial spatial 2D distribution and may be applied to screening as well as to studies of bacteria phenotypic variability, population dynamics, and ecosystem evolution.
Online preconcentration using monoliths in electrochromatography capillary format and microchips
Laboratoire Sciences Analytiques Bioanalytiques et Miniaturisation - V. Augustin, G. Proczek, J. Dugay, S. Descroix, M.C. Hennion
J. Sep. Sci. - 30(17) :2858-65 - PMID:17973277 - 2007
Online preconcentration and separation of analytes using an in situ photopolymerized hexyl acrylate-based monolith stationary phase was evaluated using electrochromatography in capillary format and microchip. The band broadening occurring during the preconcentration process by frontal electrochromatography and during the desorption process by elution electrochromatography was studied. The hexyl acrylate-based monolith provides high retention for neutral analytes allowing the handling of large sample volumes and its structure allows rapid mass transfer, thus reducing the band broadening. For moderately polar analytes such as mono-chlorophenols that are slightly retained in water, it was shown that enrichment factors up to 3500 can be obtained by a hydrodynamic injection of several bed volumes for 120 min under 0.8 MPa with a decrease in efficiency of 50% and a decrease of 30% for the resolution between 2- and 3-chlorophenol. An 8 min preconcentration time allows enrichment factors above 100 for polyaromatic hydrocarbons. The interest of these monoliths when synthesized in microchip is also demonstrated. A 200-fold enrichment was easily obtained for PAHs with only 1 min as preconcentration time, without decrease in efficiency.

430 publications.