Diffusion de particules dans des gels de protéines et aux interfaces

The objective of the thesis was to investigate the mobility of tracer particles in complex media byConfocal Laser Scanning Microscopy (CLSM) combined with multiple particle tracking (MPT)and fluorescence recovery after photobleaching (FRAP).First, we investigated the diffusion of tracer particles in gels formed by globular proteins. Gelswith a variety of structures were prepared by varying the protein and salt concentrations. Thestructure was characterized by analysis of the CLSM images in terms of the pair correlationfunction. The mobility of particles with a broad range of sizes (2nm - 1μm) was investigatedboth in homogeneous and heterogeneous gels and related to the gel structure.Second, we studied water-in-water-emulsions prepared by mixing aqueous solutions of PEO anddextran. It is shown that when colloidal particles are added they become trapped at the waterwaterinterface because they reduce the interfacial tension. The structure and the displacement ofthe particles at the interface were determined using CLSM combined with MPT.L'objectif de la thèse était d'étudier la mobilité de traceurs particulaires dans des milieuxcomplexes par microscopie confocale à balayage laser (CLSM) combinée avec le suivi demultiple particules (MPT) et le recouvrement de fluorescence après photoblanchiment (FRAP).Tout d'abord, nous avons étudié la diffusion de particules dans les gels formés par des protéinesglobulaires. Dans ce but, des gels avec structures variés ont été préparés en faisant varier lesconcentrations en protéine et en sel. La structure a été caractérisée par l'analyse des imagesobtenues par CLSM en termes de fonction de corrélation de paires. La mobilité de particulesavec une large gamme de tailles (2nm - 1 micron) a été étudiée à la fois dans des gels homogèneset hétérogènes et reliée à la structure du gel.Deuxièmement, nous avons étudié des émulsions eau dans eau préparées en mélangeant dessolutions aqueuses de PEO et de dextran. Il a été montré que lorsque des particules colloïdalessont ajoutées, elles sont emprisonnées à l'interface eau-eau, car elles réduisent la tensioninterfaciale. La structure et le déplacement des particules à l'interface ont été déterminés parCLSM combinée avec MPT

Diffusion de particules dans des gels de protéines et aux interfaces

L'objectif de la thèse était d'étudier la mobilité de traceurs particulaires dans des milieuxcomplexes par microscopie confocale à balayage laser (CLSM) combinée avec le suivi demultiple particules (MPT) et le recouvrement de fluorescence après photoblanchiment (FRAP).Tout d'abord, nous avons étudié la diffusion de particules dans les gels formés par des protéinesglobulaires. Dans ce but, des gels avec structures variés ont été préparés en faisant varier lesconcentrations en protéine et en sel. La structure a été caractérisée par l'analyse des imagesobtenues par CLSM en termes de fonction de corrélation de paires. La mobilité de particulesavec une large gamme de tailles (2nm - 1 micron) a été étudiée à la fois dans des gels homogèneset hétérogènes et reliée à la structure du gel.Deuxièmement, nous avons étudié des émulsions eau dans eau préparées en mélangeant dessolutions aqueuses de PEO et de dextran. Il a été montré que lorsque des particules colloïdalessont ajoutées, elles sont emprisonnées à l'interface eau-eau, car elles réduisent la tensioninterfaciale. La structure et le déplacement des particules à l'interface ont été déterminés parCLSM combinée avec MPT.The objective of the thesis was to investigate the mobility of tracer particles in complex media byConfocal Laser Scanning Microscopy (CLSM) combined with multiple particle tracking (MPT)and fluorescence recovery after photobleaching (FRAP).First, we investigated the diffusion of tracer particles in gels formed by globular proteins. Gelswith a variety of structures were prepared by varying the protein and salt concentrations. Thestructure was characterized by analysis of the CLSM images in terms of the pair correlationfunction. The mobility of particles with a broad range of sizes (2nm - 1 m) was investigatedboth in homogeneous and heterogeneous gels and related to the gel structure.Second, we studied water-in-water-emulsions prepared by mixing aqueous solutions of PEO anddextran. It is shown that when colloidal particles are added they become trapped at the waterwaterinterface because they reduce the interfacial tension. The structure and the displacement ofthe particles at the interface were determined using CLSM combined with MPT.LE MANS-BU Sciences (721812109) / SudocSudocFranceF

Characterisation of Colloidal Particles in Seawater by Light Scattering Techniques

Static (SLS) and dynamic (DLS) light scattering techniques are assessed for their capacity to detect colloidal particles with diameters between d = 0.1 and 0.8 &amp;micro;m at very low concentrations in seawater. The detection limit of the apparatus was determined using model monodisperse spherical polystyrene latex particles with diameters 0.2 &amp;micro;m and 0.5 &amp;micro;m. It is shown that the concentration and size of colloids can be determined down to about 10-6 g/L. Seawater obtained from different locations in western Europe was characterized using light scattering. It was found that seawater filtered through 0.45 &amp;micro;m pore size membrane filters was within the experimental error the same as that of ultrapure Milli-Q water containing the same amount of sea salt and no colloids could be detected with DLS. When the seawater was filtered through 0.8 &amp;micro;m pore size filters, colloidal particles were detected. The measurements show that the concentration of colloids in the seawater samples is not higher than 10-6 g/L and that they have an average diameter of about 0.6 &amp;micro;m. We stress that these particles are not necessarily nanoplastics. </jats:p

Quantification of Very Low Concentrations of Colloids with Light Scattering Applied to Micro(Nano)Plastics in Seawater

The detection and quantification of micro(nano)plastics in the marine environment are essential requirements to understand the full impacts of plastic pollution on the ecosystem and human health. Here, static light scattering (SLS) and dynamic (DLS) light scattering techniques are assessed for their capacity to detect colloidal particles with diameters between d = 0.1 and 0.8 &micro;m at very low concentrations in seawater. The detection limit of the apparatus was determined using model monodisperse spherical polystyrene latex particles with diameters of 0.2 &micro;m and 0.5 &micro;m. It is shown that the concentration and size of colloids can be determined down to about 10&minus;6 g/L. Light scattering measurements on seawater obtained from different locations in Western Europe show that colloidal particles were detected with DLS in seawater filtered through 0.8 &micro;m pore size filters. The concentration of these particles was not higher than 1 &micro;g/L, with an average diameter of about 0.6 &micro;m. We stress that these particles are not necessarily plastic. No particles were detected after filtration through 0.45 &micro;m pore size filters

Heat-induced gelation of aqueous micellar casein suspensions as affected by globular protein addition

International audienceThe aim of this work was to investigate how the heat-induced gelation of micellar casein (MC) suspensions (6% w/w MC) is affected by the addition of three globular proteins (GP) (whey proteins (WP), pea proteins (PP) and soy proteins (SP); from 0 to 6% w/w) at pH ≤ 6.0. Storage moduli (G′) were measured as a function of temperature from 20 °C to 90 °C. Heat-induced gelation was characterised by a sharp increase in G′ at a critical temperature (Tc). The suspensions were then held at 90 °C for 1h to determine the stiffness of the gels. Regardless of the pH, Tc of MC suspensions increased with the addition of GP. Interestingly, this increase depended on the type of GP and was stronger in the order SP > PP > WP. This effect was mainly explained by differences in calcium binding efficiency between the different GP (SP > PP >> WP) and/or the mineral composition of the ingredients. Native GP influence gelation of MC by binding calcium, thus reducing the amount available for MC to bridge, leading to an increase in Tc. Tc of the suspensions decreased with decreasing pH due to both decrease in the net charge density of MC and release of Ca2+ that in turn favoured heat-induced gelation of MC. Gel stiffness was not influenced much by PP or SP addition. However, it increased significantly in the presence of WP, due to co-aggregation of denatured WP with MC above 70 °C, which reinforced the MC network

Towards more realistic reference microplastics and nanoplastics: preparation of polyethylene micro/nanoparticles with a biosurfactant

International audienc

Particle diffusion in colloid gels

International audienc