Laterally resolved thickness maps of spin-coated membranes in dry and fully hydrated state have been measured with a nanofilm_ep3se. Bruun Nielsen et al. found that dry lipid films of POPC (1-palmitoyl-2oleoyl-sn-glycero-3-phosphocholine) have a highly ordered multilamellar structure which allows counting of the number of individual bilayers in a thick film from the progression in a concentration series.
Reference:
Bruun Nielsen, MM, Cohen Simonsen A(2013) Imaging Ellipsometry of Spin-Coated Membranes: Mapping of Multilamellar Films, Hydrated Membranes and Fluid Domains. Langmuir 29, 1525-1532.
Brewster angle microscopy is the state of the art label free imaging technique for the investigation of ultrathin organic layers like Langmuir-Blodgett films at the air-water interface. It has been applied for monitoring the phase behavior and phase transition of pure monolayers but also for imaging “real” systems like lung surfactants or tear fluids.
The new nanofilm ultrabam provides overall focused images in realtime with a lateral resolution of 2 μm based on a new optical setup.
Subnanometer-scale vertical z-resolution coupled with large lateral area imaging, label-free, noncontact, and in situ advantages make the technique of optical imaging ellipsometry highly suitable for quantitative characterization of lipid bilayers supported on oxide substrates and submerged in aqueous phases.
Reference:
Thiesen PH, Michael Howland M (2010) Characterisation of lipid bilayers by imaging ellipsometry – an overview. Bunsentagung, Bielefeld, Germany
The phase transition of individually addressable microstructured lipid bilayers was investigated by means of non-contact imaging ellipsometry. 2-D membrane compartments were created on silicon substrates by micromolding in capillaries and the thermotropic behavior of various saturated diacyl phosphatidylcholines (DPPC, diC15PC, DMPC) as well as mixed DMPC/cholesterol membranes was determined measuring area expansion and thickness of the bilayer as a function of temperature. We found an increase in the phase transition temperature of 2 – 6 °C as compared with liposomes and a reduced melting cooperativity. Individually addressable microstructured lipid bilayers are clearly advantageous over conventional bilayer preparation techniques if precise measurements are needed.
References
Faiss S., Schuy S., Weiskopf D., Steinem C., Janshoff A. (2007) Phase Transition of Individually Addressable Microstructured Membranes Visualized by Imaging Ellipsometry. Journal of Physical Chemistry 111, 13979 - 13986
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Schuy S., Faiss S., Yoder N.C., Kalsani V., Kumer K., Janshoff A., Vogel R., (2008) Structure and Thermotropic phase Behavior of Fluorinated Phospholipid Bilayers: A combined Attenuated Total Reflection FTIR Spectroscopy and Imaging Ellipsometry Study. Journal of Physical Chemistry 112, 8250-8256
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The morphology of model membranes and phospholipid bilayers is relevant to investigate membrane related proteins or glycoconjugates in a membrane environment.
The phase transition of individually addressable microstructured lipid bilayers was investigated by means of imaging ellipsometry [Geding et al., 2008, Faiss et al., 2007]. Different membrane compartments were created on silicon substrates by micromolding in capillaries. The thermotropic behavior of various saturated diacyl phosphatidyl¬cholines as well as mixed DMPC/cholesterol membranes was determined measuring area expansion and thickness of the bilayer as a function of temperature. It was shown that individually addressable micro structured lipid bilayers are clearly advantageous over conventional bilayer preparation techniques if precise measurements are needed. The input of additional components like ethanol in the buffer solution can be investigated.
Howland et al. (2007) used a UV lithographic process to form arrays of patterned lipid membranes. They formed supported lipid bilayers of the phospholipid 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC) on silicon using a standard vesicle fusion method. The lipid bilayer was then selectively exposed to deep UV light using a chrome-plated quartz photo mask. The lipid membrane was fully removed in the exposed areas, leaving behind a pattern of membrane with ‘holes’ in the fluid film, compliant with the mask. Measurements were taken of the silicon substrate before and after vesicle fusion. These measurements allow for more accurate determination of the substrate optical parameters and confirm the membrane removal. After exposure to the deep UV light, the sample was imaged using the delta mapping feature.
Szmodis et al. (2008) have studied the phase transition dynamics induced by selective gelation in a binary supported phospholipid bilayer. They used a binary mixture consisting primarily of 1 : 2 mole ratios of GalCer (galactosylceramide) and DLPC (1,2-dilauroyl-sn-glycero-3-phosphocholine) and characterises the system using imaging ellipsometry.
References
Geding M, Faiß S, Janshoff A (2008) Biointerfaces 3: 51-5
Faiss S, Schuy S, Weiskopf D, Steinem C, Janshoff A (2007) Phys. Chem. B 111, 13979-13986
Howland C, Szmodis AW, Sanii B, Parikh AN (2007) Biophys J. 92: 1306-1317
AW Szmodis, CD Blanchette, AA. Levchenko, A Navrotsky, M.L. Longo, CA Ormee, AN Parikh (2008) Soft Matter 4, 1161-1164
An example for the interaction of membrane components was part of the work of Howland et al. (2007). The cavities in the photochemical patterned phospholipid bilayer were refilled with a glycolipid (GM1 ) containing bilayer. Thickness maps were recorded from the refilled pattern and from the pattern after incubation with cholera-toxin B subunit to measure binding without the need for fluorescent labeling.
Bo Liedberg and colleagues [Klenkar et al., 2008] demonstrate a chip platform for the adressable immobilization of protein-loaded vesicles on a microarray for parallelized high-through put analysis of lipid-protein systems [5]. Imaging surface plasmon resonance in ellipsometric mode, performed with an imaging ellipsometer was used to monitor vesicle immobilization, protein tethering, protein-protein interaction and chip regeneration. The imaging ellipsometer was equipped with an SPR-cell in Kretschmann configuration. Images of the surface were taken at indicated times and difference images were calculated. The change of mass was recorded in correlation to the ellipsometric parameter Delta, in parallel at different regions of interest on the array.
References
Howland C, Szmodis AW, Sanii B, Parikh AN (2007) Biophys J. 92: 1306-1317
Klenkar G, Brian B, Ederth Th, Stengel G, Höök F, Piehler J, Liedberg B (2008) Biointerphases 3: 29-37.
Application Note Microstructured lipid bilayers