Dominique Ausserre

Surface characterization and efficiency of a matrix-free and flat carboxylated gold sensor chip for surface plasmon resonance (SPR)

AbstractWe report the preparation and characterization of a matrix-free carboxylated surface plasmon resonance (SPR) sensor chip with high sensing efficiency by functionalizing a bare gold thin film with a self-assembled monolayer of 16-mercaptohexadecanoic acid (SAM–MHDA chip). The self assembled monolayer surface coverage of the gold layer was carefully evaluated and the SAM was characterized by infrared reflection absorption spectroscopy, X-ray photoemission spectroscopy, atomic force microscopy, X-ray reflectivity-diffraction, and SPR experiments with bovine serum albumin. We compared the SPR signal obtained on this chip made of a dense monolayer of carboxylic acid groups with commercially available carboxylated sensor chips built on the same gold substrate, a matrix-free C1 chip, and a CM5 chip with a ~100xa0nm dextran hydrogel matrix (GE Healthcare). Two well-studied interaction types were tested, the binding of a biotinylated antibody (immunoglobulin G) to streptavidin and an antigen–antibody interaction. For both interactions, the well characterized densely functionalized SAM–MHDA chip gave a high signal-to-noise ratio and showed a gain in the availability of immobilized ligands for their partners injected in buffer flow. It thus compared favourably with commercially available sensor chips.n Fig. 1The surface plasmon resonance (SPR) sensor chip efficiencies of three different carboxylated chips, from the comparison of the number of captured analyte molecules divided by the number of immobilized ligand molecules (A/L ratio).

Anti-Reflecting Absorbing Layers for Electrochemical and Biophotonic Applications

Anti-reflecting layers deposited on flat surfaces make molecular films visible in reflecting light microscopy. For centuries, single Anti-Reflecting layers have been implicitly associated with dielectric materials. We recently demonstrated that anti-reflecting layers could be achieved out of absorbing materials such as metals as well, but only when used as backside layers where illumination and detection are performed through a supporting window. Fortunately, this corresponds to the best geometry when envisaging biophotonic or electrochemical applications at the solid/liquid interface. Here we explain how single absorbing anti-reflecting layers can serve each of these applications, and both simultaneously.

Quantitative Spreading Kinetics of a Three Molecular Layer Liquid Patch

The late stage kinetics of the spreading of a smectic nanodrop on a solid surface was investigated by direct and real time imaging of a three molecular layer patch using the SEEC microscopy. Experimental data do not conform to the only available theory, which covers only weakly stratified liquids. A new model is proposed, in remarkable agreement with experiments, in which the spreading mechanism appears to be a quasi-static process ruled by solid/liquid interactions, 2D Laplace pressure, and separate edge and surface permeation coefficients.

Backside absorbing layer microscopy: Watching graphene chemistry

This new microscopy technique achieves unprecedented contrast for the study of nanomaterials and their chemical modification. The rapid rise of two-dimensional nanomaterials implies the development of new versatile, high-resolution visualization and placement techniques. For example, a single graphene layer becomes observable on Si/SiO2 substrates by reflected light under optical microscopy because of interference effects when the thickness of silicon oxide is optimized. However, differentiating monolayers from bilayers remains challenging, and advanced techniques, such as Raman mapping, atomic force microscopy (AFM), or scanning electron microscopy (SEM) are more suitable to observe graphene monolayers. The first two techniques are slow, and the third is operated in vacuum; hence, in all cases, real-time experiments including notably chemical modifications are not accessible. The development of optical microscopy techniques that combine the speed, large area, and high contrast of SEM with the topological information of AFM is therefore highly desirable. We introduce a new widefield optical microscopy technique based on the use of previously unknown antireflection and absorbing (ARA) layers that yield ultrahigh contrast reflection imaging of monolayers. The BALM (backside absorbing layer microscopy) technique can achieve the subnanometer-scale vertical resolution, large area, and real-time imaging. Moreover, the inverted optical microscope geometry allows its easy implementation and combination with other techniques. We notably demonstrate the potentiality of BALM by in operando imaging chemical modifications of graphene oxide. The technique can be applied to the deposition, observation, and modification of any nanometer-thick materials.

From Permeation to Pore Nucleation in Smectic Stacks

The last stage of the spreading of a stratified droplet in the odd wetting case is the evolution from a trilayer to a monolayer, that is, vanishing of the last bilayer in the stack. We studied it in the case of 8CB smectic liquid crystal on a hydrophilic surface. Receding of the last bilayer is accompanied by formation of pores in it, which appear in the outer part of it. From analysis of real-time experimental observations of this phenomenon, we demonstrate that the dislocation loops which border these pores are not located at the same height in the trilayer stack as the dislocation lines that border the bilayer. Also, careful analysis of our results using a recently developed theoretical approach of smectic liquid nanodrop spreading strongly suggests that pore nucleation is triggered by differences in chemical potential between adjacent layers, which contrasts with the classical scheme where it is attributed to lateral tension along the layers.

On the contribution of the chain ends to the surface tension of a polymer melt

Abstract.We propose a physical picture describing the mechanisms by which chain ends affect the surface tension of a mono-dispersed polymer melt with chain length N. The driving effect is the adsorption equilibrium of chain ends within a bulk slice adjoining the surface and acting as a confined end reservoir. The thickness of that limited space is a characteristic length of the melt. This picture conforms to a previous approach proposed years ago by de Gennes. However, the characteristic length

Backside antireflecting layer microscopy - Application to graphene imaging

aN^{1/3}

New anti-reflecting layers for high contrast imaging in biophonic experiments

aN1/3 that we consider is different from the one

Wide-field optical imaging of surface nanostructures

aN^{1/2}

New Nanocomposite Materials

aN1/2 that he considered. Our choice is carefully argued. The resulting model correctly reflects the transition between the two N regimes reported in experimental studies, with the correct exponents. Stretching contributions are also considered, and appear small compared to the above-mentioned adsorption equilibrium effects. We think that the usefulness of the newly introduced characteristic length might exceed the specific problem addressed in the present paper. The equilibrium state of a lamellar diblock copolymer is briefly discussed for illustration.Graphical abstract