Polymer brushes and AFM cantilevers for nanosensing and nanocatalysis

The Atomic Force Microscope is a powerful tool for probing the surface of a sample at the nanoscopic scale. Indeed it can give information about the sample topography and map various physical or chemical surface properties. But in parallel to these "classical" applications, there exist other very interesting techniques. They include sensing applications in which the adsorption of molecules on the cantilever is quantitatively monitored and surface engineering applications in which the tip is used as a pen to write chemical features on a substrate. The aim of this thesis was to develop innovative ways to go further in these two series of applications and to improve their performances. The main strategy was to increase the number of reactive sites on the cantilevers in order to interact faster and with more sensitivity. To reach this objective, AFM cantilevers were functionalized with polymer brushes which provide stable surfaces that can contain a large amount of reactive side groups per unit area. First, the study of the kinetics of (physico)chemical reactions at the submicrometric scale was undertaken with cantilevers bearing reactive brushes. Two different methods were investigated: the frequency shift method and the deflection method. The first method was based on the fact that the resonance frequency of a lever is inversely proportional to its mass which was increased upon adsorption of analytes by the reactive brushes while the second one was based on the variation of the surface stress of the cantilever upon adsorption of molecules by the reactive brushes. Second, a surface-confined "click" reaction was catalyzed at the nanoscopic scale with functionalized polymer brushes bearing ligands for metals that were grafted from an AFM tip. The scan speed was a determining parameter and in every case, the patterns were thicker than a monolayer of the grafted molecules. The proposed mechanism of the lithography involves two steps: the formation of crystal seeds by the catalysis of the reaction and the subsequent pi stacking of aggregates that were absorbed in the brush.(FSA 3) -- UCL, 201

Bidimensional Response Maps of Adaptive Thermo- and pH-Responsive Polymer Brushes

We depict the collapse transition of adaptive thermo- and pH-responsive copolymer brushes based on poly(di(ethylene glycol) methyl ether methacrylate-co-methacrylic acid) random copolymer chains (P(MEO(2)MA-co-MAA)) by drawing bidimensional (2D) maps of the swelling ratio versus temperature and pH for different brush compositions. The collapse transition is probed by quartz crystal microbalance measurements with dissipation monitoring (QCM-D). While P(MEO(2)MA) brushes exhibit a thermo-collapse transition around 22 degrees C and P(MAA) brushes display a pH-induced collapse transition at pH = 5.5, P(MEO(2)MA-co-MAA) brushes undergo a collapse transition modulated by either temperature or pH from a swollen state at low temperature and high pH to a collapsed state at high temperature and low pH. By varying the composition of the copolymer in MAA units from 4 to 14 mol %, the brushes switch from a pH-modulated thermo-responsive behavior to a temperature-modulated pH-responsive behavior in water. The 2D maps of swelling ratio also illustrate the complex interplay between pH and temperature, and provide a unique view of the response of adaptive brushes

Surface and Bulk Collapse Transitions of Thermoresponsive Polymer Brushes.

We elucidate the sequence of events occurring during the collapse transition of thermoresponsive copolymer brushes based on poly(di(ethyleneglycol) methyl ether methacrylate) chains (PMEO2MA) grown by atom-transfer radical polymerization (ATRP). The collapse of the bulk of the brush is followed by quartz crystal microbalance measurements with dissipation monitoring (QCM-D), and the collapse of its outer surface is assessed by measuring equilibrium water contact angles in the captive bubble configuration. The bulk of the brush collapses over a broad temperature interval (approximately 25 degrees C), and the end of this process is signaled by a sharp first-order transition of the surface of the brush. These observations support theoretical predictions regarding the occurrence of a vertical phase separation during collapse, with surface properties of thermoresponsive brushes exhibiting a sharp variation at a temperature of T(br)(surf). In contrast, the bulk properties of the brush vary smoothly, with a bulk transition T(br)(bulk) occurring on average approximately 8 degrees C below T(br)(surf) and approximately 5 degrees C below the lower critical solution temperature (LCST) of free chains in solution. These observations should also be valid for planar brushes of other neutral, water-soluble thermoresponsive polymers such as poly(N-isopropylacrylamide) (PNIPAM). We also propose a way to analyze more quantitatively the temperature dependence of the QCM-D response of thermoresponsive brushes and deliver a simple thermodynamic interpretation of equilibrium contact angles, which can be of use for other complex temperature-responsive solvophilic systems

Pathogenesis of dermatophytosis

Despite the superficial localization of most dermatophytosis, host-fungus relationship in these infections is complex and still poorly elucidated. Though many efforts have been accomplished to characterize secreted dermatophytic proteases at the molecular level, only punctual insights have been afforded into other aspects of the pathogenesis of dermatophytosis, such as fungal adhesion, regulation of gene expression during the infection process, and immunomodulation by fungal factors. However, new genetic tools were recently developed, allowing a more rapid and high-throughput functional investigation of dermatophyte genes and the identification of new putative virulence factors. In addition, sophisticated in vitro infection models are now used and will open the way to a more comprehensive view of the interactions between these fungi and host epidermal cells, especially keratinocytes

Immunization and Dermatophytes

PURPOSE OF REVIEW: Despite the availability of effective vaccines for certain animal species, vaccination against dermatophytosis requires improvement and further development in both animals and humans. This review provides an update on the current situation and focuses on recent advances in host-dermatophyte relationships that could have implications for future vaccination against the most prevalent of the fungal diseases. RECENT FINDINGS: Numerous dermatophytic virulence factors have recently been isolated and characterized at the molecular level, notably secreted proteases involved in the invasion of the keratin network. Their precise roles in the different steps of the infectious process and in immunopathogenesis are being studied, while all aspects of the host immune response against dermatophytes, including the innate response, are becoming increasingly documented. In addition, new molecular tools are now available for studying dermatophytes, which will accelerate research on this topic. SUMMARY: The growth of knowledge concerning all aspects of the host-dermatophyte relationship should contribute towards sound strategies for the development of effective and safe vaccines against dermatophytosis