A 3D physical model predicting favorable bacteria adhesion.

Predicting the initial steps of bacterial biofilm formation remains a significant challenge accross various fields, such as medical and industrial ones. Here we present a straightforward 3D theoretical model based on thermodynamic rules to assess the early stages of biofilm formation on different material surfaces. This model relying also on morphological aspects of bacteria, we used Atomic Force Microscopy images of two Gram negative bacteria, Pseudomonas fluorescens and Escherichia coli to determine their dimensions and geometries as single cells or in aggregated states.

Air/Water Interface Rheology Probed by Thermal Capillary Waves.

Atomic force microscopy (AFM) was used to study the interfacial rheology of air/water interfaces by investigating the thermal capillary fluctuations of surfactant-loaded interfaces. These interfaces are formed by depositing an air bubble on a solid substrate immersed in a surfactant (Triton X-100) solution. An AFM cantilever, in contact with the north pole of the bubble, probes its thermal fluctuations (amplitude of the vibration versus the frequency).

Impact of Growth Conditions on Morphology Characterized by Atomic Force Microscopy.

This work is dedicated to the characterization by Atomic Force Microscopy (AFM) of , bacteria having high potential in biotechnology. They were first studied first in optimal conditions in terms of culture medium and temperature. AFM revealed a more-or-less elongated morphology with typical dimensions in the micrometer range, and an organization of the outer membrane characterized by the presence of long and randomly distributed ripples, which are likely related to the organization of lipopolysaccharides (LPS).

Lipid monolayer as a simple model membrane for comparative assessment of the photodynamic therapy photosensitizer efficiency via macroscopic measurements.

Cellular membrane is one of the main targets of photodynamic therapy. Its high complexity has led to the study of the efficiency of photosensitizers on artificial lipid systems mimicking membranes. However, the preliminary analysis of this efficiency remains limited due to difficulty of the model construction and/or implementation of the required measurement techniques.

Detrimental impact of silica nanoparticles on the nanomechanical properties of Escherichia coli, studied by AFM.

Despite great innovative and technological promises, nanoparticles (NPs) can ultimately exert an antibacterial activity by affecting the cell envelope integrity. This envelope, by conferring the cell its rigidity and protection, is intimately related to the mechanical behavior of the bacterial surface. Depending on their size, surface chemistry, shape, NPs can induce damages to the cell morphology and structure among others, and are therefore expected to alter the overall mechanical properties of bacteria.

Hydrocalumite Thin Films for Polyphenol Biosensor Elaboration.

Hybrid thin films based on Hydrocalumite (CaAlCl layered double hydroxide LDH) and tyrosinaseenzyme have been used for the elaboration of a high sensitive amperometric biosensor detecting polyphenols extracted from green tea. Structural properties of LDH nanomaterials were characterized by X-ray powder diffraction and Infra-Red spectroscopy, confirming its crystalline phase and chemical composition. CaAlCl-LDHs-thin films were deposited by spin-coating, and studied by atomic force microscopy to obtain information about the surface morphology of this host matrix before and after enzyme's immobilization.

Probing the threshold of membrane damage and cytotoxicity effects induced by silica nanoparticles in Escherichia coli bacteria.

The engineering of nanomaterials, because of their specific properties, is increasingly being developed for commercial purposes over the past decades, to enhance diagnosis, cosmetics properties as well as sensing efficiency. However, the understanding of their fate and thus their interactions at the cellular level with bio-organisms remains elusive. Here, we investigate the size- and charge-dependence of the damages induced by silica nanoparticles (SiO-NPs) on Gram-negative Escherichia coli bacteria.

Influence of oxidized lipids on palmitoyl-oleoyl-phosphatidylcholine organization, contribution of Langmuir monolayers and Langmuir-Blodgett films.

In this work, we studied the interaction of two oxidized lipids, PoxnoPC and PazePC, with POPC phospholipid. Mean molecular areas obtained from (π-A) isotherms of mixed PoxnoPC-POPC and PazePC-POPC monolayers revealed different behaviors of these two oxidized lipids: the presence of PoxnoPC in the monolayers induces their expansion, mean molecular areas being higher than those expected in the case of ideal mixtures. PazePC-POPC behave on the whole ideally.

Morphological and nanostructural surface changes in Escherichia coli over time, monitored by atomic force microscopy.

The present study aims at evaluating intrinsic changes in Escherichia coli (E. coli) surface over time, by Atomic Force Microscopy (AFM). For that purpose, bacteria were immobilized on mica or on mica previously functionalized by the deposition of a polyelectrolyte multilayer cushion.

Cation-Controlled Excimer Packing in Langmuir-Blodgett Films of Hemicyanine Amphiphilic Chromoionophores.

Supramolecular structure of ultrathin films of hemicyanine dye bearing a crown ether group (CrHCR) was tuned by lateral pressure and investigated by means of compression isotherms, UV-vis and fluorescence spectroscopies, and X-ray reflectivity. Two different types of aggregation were revealed, depending on the absence or the presence of metal cations in the water subphase. While CrHCR forms at high surface pressures head-to-tail stacking aggregates on pure water, changing the subphase to a metal-cation-containing one leads to the appearance of well-defined excimers with head-to-head orientation.

Artificial iono- and photosensitive membranes based on an amphiphilic aza-crown-substituted hemicyanine.

Artificial iono- and photosensitive membranes based on an amphiphilic aza-crown-substituted hemicyanine are assembled on liquid and solid supports and their aggregation behaviour, which is influenced by the binding of metal cations and surface density, is studied. The photoinduced charge-transfer properties of an analogous non-amphiphilic hemicyanine in solution are also demonstrated. An asymmetric sandwich dimer model is proposed and existence of such dimers in solution is evidenced by transient absorption and fluorescence anisotropy experiments.

High sensitive mesoporous TiO2-coated love wave device for heavy metal detection.

This work deals with the design of a highly sensitive whole cell-based biosensor for heavy metal detection in liquid medium. The biosensor is constituted of a Love wave sensor coated with a polyelectrolyte multilayer (PEM). Escherichia coli bacteria are used as bioreceptors as their viscoelastic properties are influenced by toxic heavy metals.

Raman study of the puroindoline-a/lysopamitoylphosphatidylcholine interaction in free standing black films.

The conformation of puroindoline-a (PIN-a), a protein extracted from wheat endosperm, in free-standing black films has been studied using confocal Raman spectroscopy. This protein is characterized by the presence in its sequence of a unique tryptophan (Trp)-rich domain and of five disulfide bridges stabilizing its three-dimensional structure. PIN-a is able to form free-standing films, which are very stable in time, because of its remarkable surface-active properties.

Characterization of hemicyanine Langmuir-Blodgett films by picosecond time-resolved fluorescence.

Hemicyanine Langmuir-Blodgett films have been elaborated and characterized using stationary and time-resolved spectroscopic techniques. Depending on the experimental conditions, especially the pH of the water subphase, the absorption spectra of the films indicate the presence of non-fluorescent H-aggregates in the monolayer. Time-resolved fluorescence measurements revealed three mono-exponential decay times: a very short one (20-23 ps) attributed to an excited intramolecular charge transfer state and two longer ones (100-120 ps and 400-590 ps) attributed to the photoisomerization of the chromophores.

Study of the interaction of beta-cyclodextrin with phospholipid monolayers by surface pressure measurements and fluorescence microscopy.

The interaction of beta-cyclodextrin (beta-CD) with different lipids has been studied, using Langmuir monolayers kept at constant surface pressure or constant spreading surface. Results show that beta-CD, injected beneath the monolayer, is able to desorb unsaturated palmitoyloleoylphosphatidylcholine (POPC) and sphingomyelin (SM) under specific experimental conditions. In this last case, SM monolayers, labeled with the fluorescent NBD-PC probe, were also observed by fluorescence microscopy, before and after beta-CD injection.

Comparison of the interaction of dihydrocholesterol and cholesterol with sphingolipid or phospholipid Langmuir monolayers.

We report here a study of the interaction of dihydrocholesterol (DChol) with palmitoyl-oleoyl-phosphatidylcholine (POPC) or sphingomyelin (SM) in Langmuir monolayers. DChol and cholesterol (Chol) have very close chemical structures, and DChol is often used in place of Chol because of its better stability. Surface pressure measurements and experiments of desorption induced by beta-cyclodextrin show that POPC-DChol monolayers behave similarly to POPC-Chol ones: condensing effects of DChol and Chol on POPC and desorption percentages are in the same range.

Study of the cholesterol-GM3 ganglioside interaction by surface pressure measurements and fluorescence microscopy.

The nature of the cholesterol/glycolipid interaction in rafts being poorly understood, the interaction of cholesterol with the GM(3) ganglioside has been studied by surface pressure measurements and fluorescence microscopy. Results have been compared to those obtained with sphingomyelin (SM)-cholesterol and palmitoyl-oleoyl-phosphatidylcholine (POPC)-cholesterol monolayers. The analysis of (pi-A) isotherms of mixed monolayers show a condensing effect of cholesterol on GM(3) molecules, in the same range than the effect observed with POPC and higher than the effect on SM.

Spectroscopic study of lysopalmitoylphosphatidylcholine Newton black films.

Lysopalmitoylphosphatidylcholine (LPC) black films have been studied by confocal Raman spectroscopy and their spectra analyzed and compared to their counterparts obtained from LPC in the solid state and aqueous solution. It appears that LPC is able to form stable and highly ordered black films, despite the presence of only one hydrophobic chain in this molecule. A complementary infrared study of LPC Gibbs monolayers suggests that the whole LPC polar head is perpendicular to the air/water interface.

Behavior of GM3 ganglioside in lipid monolayers mimicking rafts or fluid phase in membranes.

We studied the interaction of GM3 ganglioside with sphingomyelin (SM) and palmitoyl-oleoyl-phosphatidylcholine (POPC) in Langmuir monolayers mimicking, respectively, raft and fluid phase of a cellular membrane, by surface pressure measurements and fluorescence microscopy. No difference was observed in the behavior of SM-GM3 and POPC-GM3 monolayers. In both cases, a GM3 threshold concentration has been underlined between 20 and 40 mol%.