Black lipid membranes studied by x-ray phase contrast imaging

Beerlink, André

doi:10.17875/gup2011-108

Cited by 5 publications

(8 citation statements)

References 113 publications

(139 reference statements)

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“…BLMs as a model system for lipid bilayers are of general interest for the understanding of membranes of pro-and eukaryotic cells. The preparation as a free-standing membrane in an aqueous ambient is very similar to their native occurrence and allows investigations without any disturbing influence of a supporting substrate [6]. The local changes of the electron density in the aqueous ambient by the BLM are visible in phase contrast when illuminated with a coherent X-ray beam [7].…”

Section: First Imaging Experimentsmentioning

confidence: 99%

“…This leads to reduced sensitivity up to a short-circuit fault. For experiments that require very high resolution with a pixel size in the range of µm, a custom-built detector (PCO camera) can be integrated in the instrument [6,56,4]. It is based on thin scintillation foils that are imaged by an optical microscope with a high sensitivity CCD for visible light.…”

Section: Detectorsmentioning

confidence: 99%

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A dedicated endstation for waveguide-based x-ray imaging

Kalbfleisch¹

2013

Göttingen Series in X-Ray Physics

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Section: First Imaging Experimentsmentioning

confidence: 99%

Section: Detectorsmentioning

confidence: 99%

A dedicated endstation for waveguide-based x-ray imaging

Kalbfleisch¹

2013

Göttingen Series in X-Ray Physics

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“…Between the two detector benches a flight tube ( 14) reduces absorption and scattering in air. The size of the beam hitting the focussing optics is defined by two sets of slits (3 and 6), one of them (6) with hybrid-metal blades for the reduction of scattering [47]. A beam monitor (4) observes the intensity of the incoming beam from the source (1).…”

Section: Instrument Overviewmentioning

confidence: 99%

“…For experiments that require very high resolution with a pixel size in the range of µm, a custom-built detector (PCO camera) can be integrated in the instrument [6,56,4]. It is based on thin scintillation foils that are imaged by an optical microscope with a high sensitivity CCD for visible light.…”

Section: Detectorsmentioning

confidence: 99%

A Dedicated Endstation for Waveguide-based X-Ray Imaging

Sebastian¹

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Chapter 1 limited by the pixel size of the detector.An approach to overcome the technological limitation of Fresnel zone plate fabrication or detector resolution is coherent diffractive X-ray imaging (CDXI). CDXI relies on the coherent illumination of the sample, that can be easily realised by the selection of a coherent wavefront out of a synchrotron beam, e.g., by the use of a pinhole [49]. The sample information is encoded in the recorded diffraction signal and is reconstructed by a numerical inversion of the signal. The absence of any optical element for image formation limits the resolution of CDXI only to the highest diffraction angle at which an analysable signal is detected. The inversion suffers from the lost phase information of the wavefield, as only the intensity of the diffracted X-rays is recorded. The phase information can be retrieved by algorithms propagating the field iteratively between the detector plane (Fourier space) and the sample plane (real space) and applying a priori information of the sample, e.g., size, thickness, maximum expected phase shift, and other constraints in the Fourier space. As the undiffracted part of the beam is much more intense than the diffracted signal, it has to be blocked to avoid any saturation or overexposure of the detector. This missing information of the diffraction pattern complicates the phase retrieval and influences its uniqueness. CDXI has also been successfully combined with focussing optics [86]. The higher flux in the focus leads to an increased scattered signal of the sample, but still requires a beamstop. The resolution is not limited to the spot size, as in conventional scanning X-ray microscopy, as long as the coherence condition is fulfilled.An alternative approach to lensless X-ray imaging is offered by Xray waveguides. They act as a coherence filter and decouple the sample illumination from the coherence properties of the upstream optics and source [61]. X-ray waveguides emit a highly divergent and coherent beam from a rather small cross section. The divergence provides a geometric magnification of the sample [22]. This way, the resolution of the sample is not limited to the size of a detector pixel. Also, the intensity is distributed over a larger detector area, giving a more uniform exposure. There is no need in any beamstop leading to information loss in the diffraction pattern. The coherent illumination enables holographic imaging of the sample. As holography encodes the full wavefield information including the phase [24], the reconstruction is a deterministic single step inversion of the hologram. Holographic imaging with waveguides has been demonstrated earlier in reference beam geometry [22], but is limited to rather small samples not disturbing the reference beam. The generic inline ge-

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“…was used to image free standing lipid bilayers, with phase contrast arising from free space propagation of the beam traversing through the lipid bilayer 95 . A simple, yet extendable model was used to quantitate the information from the phase contrast image and a resolution down to ∼5 nm in one dimension, could be obtained 96 by using a focussed beam instead of a parallel beam. In this chapter, we extend the scope of this technique by imaging the lipid membranes formed in microfluidic channels, where the depth and planarity of the membrane are of potential importance in increasing the phase contrast, thus improving resolution.…”

Section: Introductionmentioning

confidence: 99%

Towards autonomous soft matter systems: Experiments on membranes and active emulsions

Thutupalli¹

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This thesis presents experiments on lipid bilayer membranes and non-equilibrium phenomena in active emulsion droplets. In the first part, we outline a concept of self assembled soft matter devices based on micro-fluidics, which use surfactant bilayer membranes as their main building blocks. Membranes form spontaneously when suitable waterin-oil emulsions are forced into micro-fluidic channels at high dispersed-phase volume fractions and are remarkably stable even when pumped through the micro-fluidic channel system. Their geometric arrangement is self-assembling, driven by interfacial energy and wetting forces. The ordered membrane arrays thus emerging can be used to build wet electronic circuitry, with the aqueous droplets as the 'solder points'. Furthermore, the membranes can serve as well-controlled coupling media between chemical processes taking place in adjacent droplets as is shown for the well-known Belousov-Zhabotinski reaction. We also investigate the dynamics of the fusion of vesicles with bilayer membranes. The particular process that we study is the fusion mediated by the SNARE-proteins embedded in the membranes. It is shown that the electrostatic repulsion between the membranes, due to the charged lipids that comprise them, blocks their fusion. Under such conditions, the conformational change of the membrane protein Synaptotagmin-1, under the influence of Ca 2+ binding, restores membrane fusion. Thus we show in vitro, for the first time, the massive increase in the membrane fusion due to Ca 2+ triggering, as is the case in vivo. Further, we present a propagation based x-ray phase contrast imaging to study structure and interfacial properties of ultrathin model membrane systems.A scheme of active self-propelled liquid micro-droplets which closely mimics the locomotion of some protozoal organisms, so-called squirmers, is presented. In contrast to other schemes proposed earlier, it is demonstrated that locomotion paths of the swimmers are not self-avoiding, since the effect of the squirmer on the surrounding medium is weak. Our results suggest that not only the velocity, but also the mode of operation (i.e., the spherical harmonics of the flow field) can be controlled by appropriate variation of parameters. We have studied experimentally the collective behaviour of such self-propelling liquid droplets. We find strong polar correlation of the locomotion velocities of neighboring droplets, which point to the formation of ordered rafts. This shows that pronounced textures, beyond what has been seen in simulations so far, may show up in crowds of simple model squirmers, despite the simplicity of their (purely physical) mutual interaction. As such, the self propelled droplets are not restricted by the classical equilibrium constraints such as the fluctuation dissipation theorem. We build a correlation ratchet, which relies on a broken detailed balance, to demonstrate a passive rectification scheme of a population of the swimmers. Finally, we study the collective dynamics of a population of swimmers when the...

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Black lipid membranes studied by x-ray phase contrast imaging

Cited by 5 publications

References 113 publications

A dedicated endstation for waveguide-based x-ray imaging

A dedicated endstation for waveguide-based x-ray imaging

A Dedicated Endstation for Waveguide-based X-Ray Imaging

Towards autonomous soft matter systems: Experiments on membranes and active emulsions

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