Direct Detection of Domains in Phospholipid Bilayers by Grazing Incidence Diffraction of Neutrons and Atomic Force Microscopy

Abstract

The geometry of domains in phospholipid bilayers of binary (1:1) mixtures of synthetic lecithins with a difference in chain length of four methylene groups has been studied by two independent, direct and complementary methods. Grazing incidence diffraction of neutrons provided gel domain sizes of less than 10 nm in both the gel and the coexistence phase of the mixture, while no domains were detected for the fluid phase. For the coexistence region, the neutron data suggest that domains grow in number rather than in size with decreasing temperature. Atomic force microscopy was used to study gel phase size and shape of the domains. The domains imaged by atomic force microscopy exhibit a rather irregular shape with an average size of 10 nm, thus confirming the neutron results for this phase. The good agreement between atomic force microscopy and neutron results, despite the completely different nature of their observables, has potential for the future development of refined models for the interpretation of neutron data from heterogeneous membranes in terms of regularly spaced and spatially extended scatterers.

Rational Design of a Liposomal Drug Delivery System Based on Biophysical Studies of Phospholipase A 2 Activity on Model Lipid Membranes

“…Similar lipid domain patterns have been found in other lipid bilayer systems using various experimental techniques, including fluorescence spectroscopy [37], fluorescence microscopy [38], single-particle tracking techniques [39], scattering techniques [40], and atomic-force microscopy [41,42]. In particular, direct imaging techniques like atomic force microscopy applied to solid-supported bilayers and fluorescence microscopy applied to solid-supported lipid bilayers or giant unilamellar vesicles have revealed lipid domains in the range of tens of nanometers to microns, depending on the lipid membrane in question.…”

Evidence for the Formation of Symmetric and Asymmetric DLPC-DAPC Lipid Bilayer Domains

“…Using different experimental approaches DLPC (C12:0 PC) and DAPC (C20:0 PC) bilayers have been reported to have a thickness ranging from ∼3.0 to ∼4.7 nm (DLPC) and ∼6 nm (DAPC), respectively [4,7,33,34,35,36,37,38,39]. According to Fig.…”

“…Similarly, the formation of asymmetric bilayers has been demonstrated for phospholipid mixtures of DLPC-DPPC (C16:0 PC, Tm 41°C), DMPC (C14:0 PC, Tm 23°C)-DPPC and DOPC (C18:1 PC, Tm -21°C)-DPPC using neutron reflectivity and quartz crystal microbalance measurements [39]. Given the theoretical all-trans-length difference between C12:0 and C20:0 lipids of ∼1 nm [4,5,34,38,41,42,43], symmetric and asymmetric bilayers with a chain mismatch of eight methylene groups as used in this study should yield height differences of ∼2 nm for symmetric and ∼1 nm for asymmetric bilayers, respectively (Fig. 1).…”

Distribution of cooperative unit size of amphiphilic molecules in the phase coexistence region in Langmuir monolayers

“…Fischer and Sackmann observed the coexistence of fluid and solid domains with the size of the order of a few hundred lipid molecules from transmission electron microscopy and electron diffraction of monolayers transferred onto solid substrates in the two-phase coexistence region [27]. Grazing incidence diffraction of neutron study provided cluster sizes of less than 10 nm in the coexistence phase of binary phospholipid mixture [28].…”