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Robert P.,Aix - Marseille University | Nicolas A.,CNRS Laboratory for Microelectronics Technolgy | Aranda-Espinoza S.,Aix - Marseille University | Bongrand P.,Aix - Marseille University | Limozin L.,Aix - Marseille University
Biophysical Journal | Year: 2011

The binding properties of biomolecules play a crucial role in many biological phenomena, especially cell adhesion. Whereas the attachment kinetics of soluble proteins is considered well known, complex behavior arises when protein molecules are bound to the cell membrane. We probe the hidden kinetics of ligand-receptor bond formation using single-molecule flow chamber assays and Brownian dynamics simulations. We show that, consistent with our recently proposed hypothesis, association requires a minimum duration of contact between the reactive species. In our experiments, ICAM-1 anchored on a flat substrate binds to anti-ICAM-1 coated onto flowing microbeads. The interaction potential between bead and substrate is measured by microinterferometry and is used as an ingredient to simulate bead movement. Our simulation calculates the duration of ligand-receptor contacts imposed by the bead movement. We quantitatively predict the reduction of adhesion probability measured for shorter tether length of the ligand or if a repulsive hyaluronan layer is added onto the surface. To account for our results, we propose that bond formation may occur in our system by crossing of a diffusive plateau in the energy landscape, on the timescale of 5 ms and an energy barrier of 5 k BT, before reaching the first detectable bound state. Our results show how to relate cell-scale behavior to the combined information of molecular reactivity and biomolecule submicron-scale environment. © 2011 by the Biophysical Society. Source

Verreycken T.,TU Eindhoven | Sadeghi N.,CNRS Laboratory for Microelectronics Technolgy | Bruggeman P.J.,TU Eindhoven | Bruggeman P.J.,University of Minnesota
Plasma Sources Science and Technology | Year: 2014

The time-resolved OH density in a nanosecond pulsed filamentary discharge in an atmospheric pressure He-H2O(0.05%) mixture is measured using laser induced fluorescence. The lifetime of the excited OH(A) state is found to be strongly time dependent during the plasma pulse, with the shortest decay time occurring at the moment the plasma is switched off. The measured LIF intensity is corrected for this time-resolved quenching and calibrated using Rayleigh scattering. Time-resolved electron density , He (3S1) metastable density , gas temperature and optical emission are presented and used in the interpretation of the observed time dependence of the OH density. Based on these experimental data, it is shown that for the present discharge conditions, OH is mainly produced by charge transfer reactions to water followed by dissociative recombination of the water ion. In addition, two often encountered issues with the calibration of OH LIF are highlighted with an example. © 2014 IOP Publishing Ltd. Source

Tomba C.,CNRS Neel Institute | Tomba C.,CNRS Laboratory for Microelectronics Technolgy | Braini C.,CNRS Neel Institute | Wu B.,CNRS Neel Institute | And 2 more authors.
Soft Matter | Year: 2014

Neurons acquire their functional and morphological axo-dendritic polarity by extending, from competing minor processes (neurites), one long axon among numerous dendrites. We employed complementary sets of micropatterns built from 2 and 6 μm wide stripes of various lengths to constrain hippocampal neuron shapes. Using these geometries, we have (i) limited the number of neuronal extensions to obtain a minimal in vitro system of bipolar neurons and (ii) controlled the neurite width during growth by the generation of a progressive cell shape asymmetry on either side of the cellular body. From this geometrical approach, we gained a high level of control of each neurite length and of the localization of axonal specification. To analyze these results, we developed a model based on a width and polarization dependent neurite elongation rate and on the existence of a critical neurite length that sets the axonal fate. Our data on the four series of micro-patterns developed for this study are described by a single set of growth parameters, well supported by experiments. The control of neuronal shapes by adhesive micro-patterns thereby offers a novel paradigm to follow the dynamical process of neurite lengthening and competition through the process of axonal polarization. This journal is © the Partner Organisations 2014. Source

Demichel O.,CNRS Physics of Materials and Microstructures | Calvo V.,CNRS Physics of Materials and Microstructures | Besson A.,CNRS Physics of Materials and Microstructures | Noe P.,CNRS Physics of Materials and Microstructures | And 5 more authors.
Nano Letters | Year: 2010

The past decade has seen the explosion of experimental results on nanowires grown by catalyzed mechanisms. However, few are known on their electronic properties especially the influence of surfaces and catalysts. We demonstrate by an optical method how a curious electron-hole thermodynamic phase can help to characterize volume and surface recombination rates of silicon nanowires (SiNWs). By studying the electron-hole liquid dynamics as a function of the spatial confinement, we directly measured these two key parameters. We measured a surface recombination velocity of passivated SiNWs of 20 cm s-1, 100 times lower than previous values reported. Furthermore, the volume recombination rate of gold-catalyzed SiNWs is found to be similar to that of a high-quality three-dimensional silicon crystal; the influence of the catalyst is negligible. These results advance the knowledge of SiNW surface passivation and provide essential guidance to the development of efficient nanowire-based devices. © 2010 American Chemical Society. Source

Pietroy D.,CNRS Laboratory for Microelectronics Technolgy | Gereige I.,Solar and Photovoltaic Engineering Research Center | Gourgon C.,CNRS Laboratory for Microelectronics Technolgy
Microelectronic Engineering | Year: 2013

Transmission scatterometry is studied as a characterization tool for gratings nanoimprinted in a resist layer spincoated on the top of a transparent substrate. In this case, the larger part of the incident signal is transmitted which can make the reflection analysis harder. Although the backward reflections in the substrate induce an error which is difficult to correct, results are shown to be in good agreement with SEM measurements and reflection mode scatteromerty. © 2013 Elsevier B.V. All rights reserved. Source

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