Phase Transition of Individually Addressable Microstructured Membranes Visualized by Imaging Ellipsometry

Abstract

The phase transition of individually addressable microstructured lipid bilayers was investigated by means of imaging ellipsometry. Microstructured bilayers were created on silicon substrates by micromolding in capillaries, and the thermotropic behavior of various saturated diacyl phosphatidylcholine (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dipentadecoyl-sn-glycero-3-phosphocholine, and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)) bilayers as well as DMPC/cholesterol membranes was determined by measuring the area expansion and thickness of the bilayer as a function of temperature. We found an increase in the main phase transition temperature T(M) of 2-6 degrees C and a substantially reduced cooperativity compared to multilamellar vesicles. Measurements of lateral diffusion constants D employing fluorescence recovery after photobleaching revealed, however, only a marginal decrease in D compared to those found for vesicles and multibilayers. The known dependencies of T(M) both on the chain length of diacyl PC membranes and on the cholesterol content were reproduced on a solid support. Microstructured bilayers offer the unique advantage of integrating an internal standard of known thermotropic properties, which turned out to be important for reducing the measurement error and for ruling out the slightly changing impact of the surface on the phase transition behavior due to the surface pretreatment.

An Assemblable, Multi-Angle Fluorescence and Ellipsometric Microscope

“…While the spatial resolution is limited by diffraction optics, the thickness-resolution is typically sub-nm. The technique has applications in semiconductor industries [23] and biology, particularly supported lipid bilayers [24, 25]. Imaging ellipsometry is a variant of the technique which spatially resolves thin films on the surface [26].…”

Lipopeptides derived from HIV and SIV mimicking the prehairpin intermediate of gp41 on solid supported lipid bilayers

“…Experiments were performed with an Imaging Ellipsometer (EP 3 -SW, Nanofilm Technology, Göttingen, Germany) as described previously (Faiss et al, 2007;Gedig et al, 2008).…”

“…Hydrophilic silica substrates were prepared according to Faiss et al (2007). After the silicon substrate was placed in the ellipsometric measuring cell the substrate was rinsed with PBS 5.9.…”

“…After 20 min, the bilayer formation was complete and the ellipsometric angle D remained constant at around 175°. After excess vesicles were removed by rinsing with PBS 6.8 the layer thickness was determined to be d = (3.7 ± 0.2) nm by 4 zone nulling procedure, assuming a refrac- tive index of DOPC * of n DOPC = 1.53 (Faiss et al, 2007). The low thickness could be due to defects in the membrane.…”

Thermally induced phase separation in supported bilayers of glycosphingolipid and phospholipid mixtures

“…These parameters relate to polarization dependent optical reflectivities through a simple relation: tan ⌿e i⌬ = R p / R s , where R p and R s represent Fresnel reflectivities for p-and s-polarization, respectively. 42 Described in detail previously, 41,43 IE offers an attractive alternative to widely used fluorescence and atomic force microscopy ͑AFM͒, because of its many unique features. First, in imaging mode, ellipsometry takes advantage of the spatial differences in the optical properties of coexisting surface phases 44 making it a label-free method of investigation.…”