Peer-reviewed Publications |
Aldeek, F., Schneider, R., Fontaine-Aupart, M. - P., Mustin, C., Lecart, S., Merlin, C., & Block, J. - C. (2013). Patterned Hydrophobic Domains in the Exopolymer Matrix of Shewanella oneidensis MR-1 Biofilms. APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 79(4), 1400–1402.
Résumé: Water-dispersible amphiphilic surface-engineered quantum dots (QDs) were found to be strongly accumulated within discrete zones of the exopolymer network of Shewanella oneidensis MR-1 biofilms, but not on the cell surfaces. These microdomains showed a patterned distribution in the exopolymer matrix, which led to a restricted diffusion of the amphiphilic nanoparticles.
|
|
Bon, P., Barroca, T., Lévèque-Fort, S., & Fort, E. (2013). Label-free evanescent microscopy for membrane nano-tomography in living cells. Journal of Biophotonics, 7(11-12), 857–862.
Résumé: We show that through-the-objective evanescent microscopy (epi-EM) is a powerful technique to image membranes in living cells. Readily implementable on a standard inverted microscope, this technique enables full-field and real-time tracking of membrane processes without labeling and thus signal fading. In addition, we demonstrate that the membrane/interface distance can be retrieved with 10 nm precision using a multilayer Fresnel model. We apply this nano-axial tomography of living cell membranes to retrieve quantitative information on membrane invagination dynamics. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
|
|
Dhahri, S., Ramonda, M., & Marliere, C. (2013). In-Situ Determination of the Mechanical Properties of Gliding or Non-Motile Bacteria by Atomic Force Microscopy under Physiological Conditions without Immobilization. Plos One, 8(4), e61663.
Résumé: We present a study about AFM imaging of living, moving or self-immobilized bacteria in their genuine physiological liquid medium. No external immobilization protocol, neither chemical nor mechanical, was needed. For the first time, the native gliding movements of Gram-negative Nostoc cyanobacteria upon the surface, at speeds up to 900 μm/h, were studied by AFM. This was possible thanks to an improved combination of a gentle sample preparation process and an AFM procedure based on fast and complete force-distance curves made at every pixel, drastically reducing lateral forces. No limitation in spatial resolution or imaging rate was detected. Gram-positive and non-motile Rhodococcus wratislaviensis bacteria were studied as well. From the approach curves, Young modulus and turgor pressure were measured for both strains at different gliding speeds and are ranging from 20 +/- 3 to 105 +/- 5 MPa and 40 +/- 5 to 310 +/- 30 kPa depending on the bacterium and the gliding speed. For Nostoc, spatially limited zones with higher values of stiffness were observed. The related spatial period is much higher than the mean length of Nostoc nodules. This was explained by an inhomogeneous mechanical activation of nodules in the cyanobacterium. We also observed the presence of a soft extra cellular matrix (ECM) around the Nostoc bacterium. Both strains left a track of polymeric slime with variable thicknesses. For Rhodococcus, it is equal to few hundreds of nanometers, likely to promote its adhesion to the sample. While gliding, the Nostoc secretes a slime layer the thickness of which is in the nanometer range and increases with the gliding speed. This result reinforces the hypothesis of a propulsion mechanism based, for Nostoc cyanobacteria, on ejection of slime. These results open a large window on new studies of both dynamical phenomena of practical and fundamental interests such as the formation of biofilms and dynamic properties of bacteria in real physiological conditions.
|
|
Oh, E., Fatemi, F. K., Currie, M., Delehanty, J. B., Pons, T., Fragola, A., Lévêque-Fort, S., Goswami, R., Susumu, K., Huston, A. L., & Medintz, I. L. (2013). PEGylated Luminescent Gold Nanoclusters: Synthesis, Characterization, Bioconjugation, and Application to One- and Two-Photon Cellular Imaging. Part. Part. Syst. Charact., 30(5), 453–466.
Résumé: Biocompatible, near-infrared luminescent gold nanoclusters (AuNCs) are synthesized directly in water using poly(ethylene glycol)-dithiolane ligands terminating in either a carboxyl, amine, azide, or methoxy group. The ≈1.5 nm diameter AuNCs fluoresce at ≈820 nm with quantum yields that range from 4–8%, depending on the terminal functional group present, and display average luminescence lifetimes approaching 1.5 μs. The two-photon absorption (TPA) cross-section and two-photon excited fluorescence (TPEF) properties are also measured. Long-term testing shows the poly(ethylene glycol) stabilized AuNCs maintain colloidal stability in a variety of media ranging from saline to tissue culture growth medium along with tolerating storage of up to 2 years. DNA and dye-conjugation reactions confirm that the carboxyl, amine, and azide groups can be utilized on the AuNCs for carbodiimide, succinimidyl ester, and CuI-assisted cycloaddition chemistry, respectively. High signal-to-noise one- and two-photon cellular imaging is demonstrated. The AuNCs exhibit outstanding photophysical stability during continuous-extended imaging. Concomitant cellular viability testing shows that the AuNCs also elicit minimal cytotoxicity. Further biological applications for these luminescent nanoclustered materials are discussed.
|
|
Sarsa, A., Alcaraz-Pelegrina, J. M., Le Sech, C., & Cruz, S. A. (2013). Quantum Confinement of the Covalent Bond beyond the Born-Oppenheimer Approximation. Journal Of Physical Chemistry B, 117(24), 7270–7276.
Résumé: Dirichlet boundary conditions with different symmetries, spherical and cylindrical impenetrable surfaces, are imposed on the covalent electron pair of a molecular bond. Accurate results for different observable like energy and interparticle distances are calculated using quantum Monte Carlo methods beyond the Born-Oppenheimer approximation. The spherical confinement induces a raise in the bond energy and shortens the internuclear distances even for a relatively soft confinement. When cylindrical symmetry is considered, similar qualitative behavior is observed though only the electrons are confined. A compression followed by a relaxation process of the confined bond is shown to induce a vibrationally excited state. Finally, a brief qualitative discussion based on a simplified picture of the role of compression/relaxation cycles in enzyme catalysis is given.
|
|
Song, J., Bouchoule, S., Patriarche, G., Galopin, E., Yacomotti, A. M., Cambril, E., Kou, Q., Troadec, D., He, J. - J., & Harmand, J. - C. (2013). Improvement of the oxidation interface in an AlGaAs/AlxOy waveguide structure by using a GaAs/AlAs superlattice. Physica Status Solidi A-Applications And Materials Science, 210(6), 1171–1177.
Résumé: The wet oxidation from the mesa sidewalls of AlGaAs/GaAs epitaxial structures is investigated in details. In addition to the intended lateral oxidation of the Al-rich buried layer, we observe a parasitic vertical oxidation of the adjacent layers of lower Al content. This vertical oxidation produces a rough interface between the oxidized and non-oxidized materials and reduces the effective thickness of the adjacent layers. This detrimental phenomenon is drastically reduced when the adjacent layer is replaced by a GaAs/AlAs superlattice (SL). In this case, a sharp interface between the Al-Ga-oxide and the SL is obtained after the oxidation process. Further experiments point out the critical role of hydrogen in the oxidation process of low Al content alloys. Hydrogen atoms produced during the oxidation of the Al-rich layer are proposed to be responsible for the vertical oxidation of the adjacent layers. We devise that the SL interfaces are favorable to reduce the diffusion of the reactants in the vertical direction.
|
|
Videcoq, P., Steenkeste, K., Bonnin, E., & Garnier C. (2013). A multi-scale study of enzyme di ff usion in macromolecular solutions and physical gels of pectin polysaccharides. Soft Matter, 9, 5110–5118.
Résumé: Pectin accounts for one of the major polysaccharides of the plant cell wall. Pectin methylesterases (PMEs)are enzymes that are able to alter the pectin structure and affect its gelling properties by de-esterifying galacturonic acid. In this work, the diffusion of two PMEs with different origins and modes of action
was characterised with a multi-scale approach in different media consisting of pectin macromolecular solutions and physical gels. Fluorescence Recovery After Photobleaching (FRAP) and Fluorescent Correlation Spectroscopy (FCS) investigations showed similar diffusion behaviour for both enzymes at a microscopic scale. In contrast, their behaviours tended to differ when increasing the observation scale up to mm. Indeed, fungal PMEs diffused faster and in a larger range than plant PMEs. These results are discussed with regard to the respective modes of action, processivity and in vivo roles of the two enzymes.
|
|
Actes de Conférences |
Barroca, T., Bon, P., Leveque-Fort, S., & Fort, E. (2013). Supercritical self-interference fluorescence microscopy for full-field membrane imaging. In Three-Dimensional And Multidimensional Microscopy: Image Acquisition And Processing Xx (Vol. 8589).
Résumé: We present a new technique based on the self-interference of Supercritical Angle Fluorescence (SAF) emission in order to perform full-field cell membrane imaging. We show that our Point Spread Function (PSF) engineering technique allows us to obtain a 100 nm axial sectioning while conserving the original lateral resolution of the microscope. The images are acquired using an optical module that can be connected to any fluorescent microscope to simultaneously monitor in real time both the cell membrane and in-depth phenomena.
|
|
Bon, P., Barroca, T., Leveque-Fort, S., & Fort, E. (2013). Supercritical scattering microscopy for quantitative phase in the vicinity of a lamella. In Three-Dimensional And Multidimensional Microscopy: Image Acquisition And Processing Xx (Vol. 8589).
Résumé: In this paper, we discuss the possibility of making a super-axially-resolved image of a biological sample using supercritical angle diffusion. This labeling-free approach is suitable to any microscope equipped with a N A(obj) > 1.33 microscope objective and can be used either for conventional intensity imaging or for quantitative phase imaging. We expose some results on beads an cells showing the potential of this method.
|
|
Dupuis, G., Benabdallah, N., Chopinaud, A., Mayet, C., & Leveque-Fort, S. (2013). Time-resolved wide-field optically sectioned fluorescence microscopy. In Three-Dimensional And Multidimensional Microscopy: Image Acquisition And Processing Xx (Vol. 8589).
Résumé: We present the implementation of a fast wide-field optical sectioning technique called HiLo microscopy on a fluorescence lifetime imaging microscope. HiLo microscopy is based on the fusion of two images, one with structured illumination and another with uniform illumination. Optically sectioned images are then digitally generated thanks to a fusion algorithm. HiLo images are comparable in quality with confocal images but they can be acquired faster over larger fields of view. We obtain 4-D imaging by combining HiLo optical sectioning, time-gated detection, and z-displacement. We characterize the performances of this set-up in terms of 3-D spatial resolution and time-resolved capabilities in both fixed- and live-cell imaging modes.
|
|
|
Quoilin, C. C., Mouithys-Mickalad, A., Lecart, S., Gallez, B., Fontaine-Aupart, M. - P., & Hoebeke, M. (2013). Disruption in energy metabolism and mitochondrial function in a cellular model of inflammation-induced acute kidney injury. In Free Radical Biology And Medicine (Vol. 65, pp. S44–S45).
|
|
Sivankutty, S., Barroca, T., Dupuis, G., Lefumeux, C., Mayet, C., Dubois, A., Marquer, C., Lecart, S., Potier, M. C., Fort, E., & Leveque-Fort, S. (2013). Towards STED microscopy with nanometric optical sectioning. In Single Molecule Spectroscopy And Superresolution Imaging Vi (Vol. 8590).
Résumé: Circumventing the limit imposed by diffraction is a major issue in the instrumental development to realize finer resolutions in biological samples. With STED microscopy, we exploit the molecular transitions of the fluorescent marker to image well below the Rayleigh criterion. Also in combination with STED, we propose to use an alternative technique for optically sectioning fluorescent emitters close to the water-glass interface by selectively filtering the supercritical emission at the pupil plane. We discuss the instrumental development of such a system and its combination with other imaging techniques.
|
|
