Publications

2011

• Aberration-free three-dimensional multiphoton imaging of neuronal activity at kHz rates
  
  • Botcherby Edward J.
  • Smith Christopher W.
  • Kohl Michael
  • Débarre Delphine
  • Booth Martin J.
  • Juskaitis Rimas
  • Paulsen Ole
  • Wilson Tony
  Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences, 2011, 109 (8), pp.2919-2924. Multiphoton microscopy is a powerful tool in neuroscience, promising to deliver important data on the spatiotemporal activity within individual neurons as well as in networks of neurons. A major limitation of current technologies is the relatively slow scan rates along the z direction compared to the kHz rates obtainable in the x and y directions. Here,we describe a custom-built microscope system based on an architecture that allows kHz scan rates over hundreds of microns in all three dimensions without introducing aberration. We further demonstrate how this high-speed 3D multiphoton imaging system can be used to study neuronal activity at millisecond resolution at the subcellular as well as the population level. (10.1073/pnas.1111662109)
  DOI : 10.1073/pnas.1111662109
• Few femtosecond, few kiloampere electron bunch produced by a laser-plasma accelerator
  
  • Lundh Olle
  • Lim J.
  • Rechatin Clément
  • Ammoura L.
  • Ben-Ismaïl Ahmed
  • Davoine X.
  • Gallot Guilhem
  • Goddet Jean-Philippe
  • Lefebvre E.
  • Malka Victor
  • Faure Jérôme
  Nature Physics, Nature Publishing Group [2005-....], 2011, 7 (3), pp.219. Particle accelerators driven by the interaction of ultraintense and ultrashort laser pulses with a plasma(1) can generate accelerating electric fields of several hundred gigavolts per metre and deliver high-quality electron beams with low energy spread(2-5), low emittance(6) and up to 1 GeV peak energy(7,8). Moreover, it is expected they may soon be able to produce bursts of electrons shorter than those produced by conventional particle accelerators, down to femtosecond durations and less. Here we present wide-band spectral measurements of coherent transition radiation which we use for temporal characterization. Our analysis shows that the electron beam, produced using controlled optical injection(9), contains a temporal feature that can be identified as a 15 pC, 1.4-1.8 fs electron bunch (root mean square) leading to a peak current of 3-4 kA depending on the bunch shape. We anticipate that these results will have a strong impact on emerging applications such as short-pulse and short-wavelength radiation sources(10,11), and will benefit the realization of laboratory-scale free-electron lasers(12-14). (10.1038/NPHYS1872)
  DOI : 10.1038/NPHYS1872
• Combining rails and anchors with laser forcing for selective manipulation within 2D droplet arrays.
  
  • Fradet Etienne
  • Mcdougall Craig
  • Abbyad Paul
  • Dangla Rémi
  • Mcgloin David
  • Baroud Charles N.
  Lab on a Chip, Royal Society of Chemistry, 2011, 11 (24), pp.4228-4234. We demonstrate the combination of a rails and anchors microfluidic system with laser forcing to enable the creation of highly controllable 2D droplet arrays. Water droplets residing in an oil phase can be pinned to anchor holes made in the base of a microfluidic channel, enabling the creation of arrays by the appropriate patterning of such holes. The introduction of laser forcing, via laser induced thermocapillary forces to anchored droplets, enables the selective extraction of particular droplets from an array. We also demonstrate that such anchor arrays can be filled with multiple, in our case two, droplets each and that if such droplets have different chemical contents, the application of a laser at their interface triggers their merging and a chemical reaction to take place. Finally by adding guiding rails within the microfluidic structure we can selectively fill large scale arrays with monodisperse droplets with significant control over their contents. In this way we make a droplet array filled with 96 droplets containing different concentrations of fluorescent microparticles. (10.1039/C1LC20541B)
  DOI : 10.1039/C1LC20541B
• Dynamics of NO interacting with soluble guanylate cyclase from 1 ps to 0.1 s and induced structural transitions
  
  • Yoo Byung-Kuk
  • Lamarre Isabelle
  • Martin Jean-Louis
  • Rappaport Fabrice
  • Negrerie Michel
  BMC Pharmacology, BioMed Central, 2011, 11 (Suppl 1), pp.P77.
• Vibrational Motions Associated with Primary Processes in Bacteriorhodopsin Studied by Coherent Infrared Emission Spectroscopy
  
  • Groma Geza I.
  • Colonna Anne
  • Martin Jean-Louis
  • Vos Marten H.
  Biophysical Journal, Biophysical Society, 2011, 100 (6), pp.1578. The primary energetic processes driving the functional proton pump of bacteriorhodopsin take place in the form of complex molecular dynamic events after excitation of the retinal chromophore into the Franck-Condon state. These early events include a strong electronic polarization, skeletal stretching, and all-trans-to-13-cis isomerization upon formation of the J intermediate. The effectiveness of the photoreaction is ensured by a conical intersection between the electronic excited and ground states, providing highly nonadiabatic coupling to nuclear motions. Here, we study real-time vibrational coherences associated with these motions by analyzing light-induced infrared emission from oriented purple membranes in the 750-1400 cm(-1) region. The experimental technique applied is based on second-order femtosecond difference frequency generation on macroscopically ordered samples that also yield information on phase and direction of the underlying motions. Concerted use of several analysis methods resulted in the isolation and characterization of seven different vibrational modes assigned as C-C stretches, out-of-plane methyl rocks, and hydrogen out-of-plane wags, whereas no in-plane H rock was found. Based on their lifetimes and several other criteria, we deduce that the majority of the observed modes take place on the potential energy surface of the excited electronic state. In particular, the direction sensitivity provides experimental evidence for large intermediate distortions of the retinal plane during the excited-state isomerization process. (10.1016/j.bpj.2011.02.011)
  DOI : 10.1016/j.bpj.2011.02.011
• Strong Ligand-Protein Interactions Revealed by Ultrafast Infrared Spectroscopy of CO in the Heme Pocket of the Oxygen Sensor FixL
  
  • Nuernberger Patrick
  • Lee Kevin F.
  • Bonvalet Adeline
  • Bouzhir-Sima Latifa
  • Lambry Jean-Christophe
  • Liebl Ursula
  • Joffre Manuel
  • Vos Marten H.
  Journal of the American Chemical Society, American Chemical Society, 2011, 133 (43), pp.17110. In heme-based sensor proteins, ligand binding to heme in a sensor domain induces conformational changes that eventually lead to changes in enzymatic activity of an associated catalytic domain. The bacterial oxygen sensor FixL is the best-studied example of these proteins and displays marked differences in dynamic behavior with respect to model globin proteins. We report a mid-IR study of the configuration and ultrafast dynamics of CO in the distal heme pocket site of the sensor PAS domain FixLH, employing a recently developed method that provides a unique combination of high spectral resolution and range and high sensitivity. Anisotropy measurements indicate that CO rotates toward the heme plane upon dissociation, as is the case in globins. Remarkably, CO bound to the heme iron is tilted by similar to 30 degrees with respect to the heme normal, which contrasts to the situation in myoglobin and in present FixLH-CO X-ray crystal structure models. This implies protein-environment-induced strain on the ligand, which is possibly at the origin of a very rapid docking-site population in a single conformation. Our observations likely explain the unusually low affinity of FixL for CO that is at the origin of the weak ligand discrimination between CO and O(2). Moreover, we observe orders of magnitude faster vibrational relaxation of dissociated CO in FixL than in globins, implying strong interactions of the ligand with the distal heme pocket environment. Finally, in the R220H FixLH mutant protein, where CO is H-bonded to a distal histidine, we demonstrate that the H-bond is maintained during photolysis. Comparison with extensively studied globin proteins unveils a surprisingly rich variety in both structural and dynamic properties of the interaction of a diatomic ligand with the ubiquitous b-type heme-proximal histidine system in different distal pockets. (10.1021/ja204549n)
  DOI : 10.1021/ja204549n
• From Cilia Hydrodynamics to Zebrafish Embryonic Development
  
  • Supatto Willy
  • Vermot Julien
  , 2011, pp.vol. 95, 33-66. Embryonic development involves the cellular integration of chemical and physical stimuli. A key physical input is the mechanical stress generated during embryonic morphogenesis. This process necessitates tensile forces at the tissue scale such as during axis elongation and budding, as well as at the cellular scale when cells migrate and contract. Furthermore, cells can generate forces using motile cilia to produce flow. Cilia-driven flows are critical throughout embryonic development but little is known about the diversity of the forces they exert and the role of the mechanical stresses they generate. In this chapter, through an examination of zebrafish development, we highlight what is known about the role of hydrodynamics mediated by beating cilia and examine the physical features of flow fields from the modeling and experimental perspectives. We review imaging strategies to visualize and quantify beating cilia and the flow they generate in vivo. Finally, we describe the function of hydrodynamics during left-right embryonic patterning and inner ear development. Ideally, continued progress in these areas will help to address a key conceptual problem in developmental biology, which is to understand the interplay between environmental constraints and genetic control during morphogenesis (10.1016/B978-0-12-385065-2.00002-5)
  DOI : 10.1016/B978-0-12-385065-2.00002-5
• Measurement of circular dichroism dynamics in a nanosecond temperature-jump experiment
  
  • Khuc Mai-Thu
  • Mendonça Lucille
  • Sharma S.
  • Volk M.
  • Solinas Xavier
  • Hache François
  Review of Scientific Instruments, American Institute of Physics, 2011, 82 (5). The use of a fast temperature jump (T-jump) is a very powerful experiment aiming at studying protein denaturation dynamics. However, probing the secondary structure is a difficult challenge and rarely yields quantitative values. We present the technical implementation of far-UV circular dichroism in a nanosecond T-jump experiment and show that this experiment allows us to follow quantitatively the change in the helical fraction of a poly(glutamic acid) peptide during its thermal denaturation with 12 ns time resolution. Cop. 2011 American Institute of Physics. (10.1063/1.3592331)
  DOI : 10.1063/1.3592331