Etude et contrôle de la charge de surface dans les dispositifs micro/nanofluidiques (nouveaux outils pour les sciences séparatives)

Ce travail de thèse a consisté à développer les outils technologiques et les modèles corrélant expériences et théorie, permettant de mieux appréhender le rôle et l évolution de la charge de surface ainsi que des phénomènes électrocinétiques dans les systèmes micro et nanofluidiques. Afin d étudier les propriétés de charge surfacique dans les dispositifs micrométriques, un système de mesure dédié à la mesure du flux électroosmotique (FEO) a été réalisé : le Pont de Wheatstone Fluidique (PWF). Cette plateforme fondée sur l analogie électrique-microfluidique a permis de mettre en évidence l instabilité de l interface eau-verre. Le contrôle de la charge de surface a été mené au travers de deux stratégies : (i) chimiquement, avec l utilisation de divers prétraitements acides ou basiques et au travers de l étalement de multicouches de polymères chargés ; (ii) physiquement, au travers d interfaces conductrices polarisables en contact direct avec le liquide (transistors fluidiques). Cette dernière stratégie permet notamment de contrôler la charge de surface et le FEO dynamiquement pour une large gamme de tampons biologiques. A l échelle nanométrique, l étude des phénomènes électrocinétiques s est focalisée sur une étude expérimentale et théorique (calculs par éléments finis) du phénomène d électropréconcentration. Ces travaux ont débouché sur une vision phénoménologique globale de ce phénomène mettant en avant le rôle majeur de la charge de surface sur l efficacité et la sélectivité de ce processus. Au-delà de l approche fondamentale, ce travail de thèse a aussi permis de proposer de nouveaux outils pour la séparation électrophorétique d objets biologiques.This work is based on the development of technological, experimental and theoretical tools dedicated to the study of the surface charge developing at the liquid-solid interface of micro and nanofluidic devices. The control of electrokinetic phenomena involved in most of electrophoretic separation processes was also investigated from a chemical and physical point of view in order to provide new routes for the design of smart electrophoretic separation devices. A plateform dedicated to the measurement of electro-osmotic flows (EOFs) was achieved on the basis of an analogy between microfluidics and electronics: the microFluidic Wheatstone Bridge ( FWB). This indirect method enabled us to study the stability issues of the Glass-water interface. In order to control the surface charge, two strategies were confronted: (i) chemically, the influence of acido-basic pretreatments on the hysteresis of glass surface was investigated and multilayer of poly-electrolytes were deposited as surface charge stabilizer; (ii) Physically, conducting polarisable interfaces were used to directly fix the surface potential at the liquid interface (Flow-FETs). This original structure enables to control the surface charge and the EOF dynamically for a wide range of biological buffers. At the nanoscale, our study focused on the electro-preconcentration phenomena through experimental and numerical works. The role of surface charge on preconcentration rate efficiency was highlighted through 1D finite element calculations; this study also enabled us to provide a global understanding of the various preconcentration regimes observed in the literature. Beyond this fundamental study, novel tools were proposed to improve electrophoretic analysis of biological species.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Ionic transport phenomena in nanofluidics: Experimental and theoretical study of the exclusion-enrichment effect on a chip

In nanometer-sized apertures with charged surfaces, the extension of the electrical double layer results in the electrostatic exclusion of co-ions and enrichment in counterions, which affects the permselectivity of such structures. A modeling of this phenomenon is proposed and is compared with quantitative measurements of the ionic permeability change of a Pyrex nanoslit at low ionic strength. The comparison of experimental results with theoretical predictions justifies that electrostatic forces are the governing forces in nanofluidics

Polarised potential: Novel nanotech

International audienceScientists at the Laboratory for Photonics and Nanostructures have been developing a microfluidic device forthe control and measurement of electrokinetic phenomena that aims to blows previous models out of the water

Polarised potential: Novel nanotech

International audienceScientists at the Laboratory for Photonics and Nanostructures have been developing a microfluidic device forthe control and measurement of electrokinetic phenomena that aims to blows previous models out of the water

Glass-based nanofluidic device for biomolecule preconcentration study

The fabrication of a hybrid micro/nano-fluidic device to study electropreconcentration of biomolecules is presented. A nanoslit surrounded by glass is formed between two access microchannels and an “H” configuration bio-analysis system is developed. The optimized know-how for this biochip fabrication is transferred and the key steps are discussed. Fluorescence spatiotemporal profile in the preconcentration area is recorded and quantitatively analyzed. The reliability of the applied technology for studies of charged biomolecule transport phenomena across nanochannels is proven giving two examples for different preconcentration geometries