Formation and characterization of (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine)/(1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine) supported lipid bilayers on polyelectrolyte multilayer films (original) (raw)
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The formation of lipid bilayers on surfaces
Colloids and Surfaces B-biointerfaces, 2009
The adsorption of biological molecules at solid-liquid interfaces is growing in importance due to its application to a very broad range of fields. Biomimetic systems like phospholipid mono-or bilayers are used to study such adsorption processes in great detail. Here we show how the formation of a complete lipid bilayer by vesicle adsorption and rupture depends on the type of the surface used. Fairly smooth SiO 2 surfaces and much rougher polyelectrolyte cushions are used to study this process. Depending on the chemical structure of the lipids, two different pathways are found on SiO 2 surfaces: either vesicle adsorption occurs in a first step until a critical coverage is reached followed by vesicle rupture and bilayer formation or adsorption and vesicle rupture occur almost at the same time. In the case of polyelectrolyte cushions, both neutron reflectivity and quartz crystal microbalance experiments show that the formation of homogeneous DMPC bilayers is significantly better on the negatively charged PSS surface compared to the positively charged PAH surface.
Lipid layers on polyelectrolyte multilayer supports
Soft Matter, 2008
The mechanism of formation of supported lipid layers from phosphatidylcholine and phosphatidylserine vesicles in solution on polyelectrolyte multilayers was studied by a variety of experimental techniques. The interaction of zwitterionic and acidic lipid vesicles, as well as their mixtures, with polyelectrolyte supports was followed in real time by micro-gravimetry. The fabricated lipid-polyelectrolyte composite structures on top of multilayer coated colloidal particles were characterized by flow cytometry and imaging techniques. Lipid diffusion over the macroscopic scale was quantified by fluorescence recovery after photobleaching, and the diffusion was related to layer connectivity. The phospholipid-polyelectrolyte binding mechanism was investigated by infrared spectroscopy. A strong interaction of polyelectrolyte primary amino groups with phosphate and carboxyl groups of the phospholipids, leading to dehydration, was observed. Long-range electrostatic attraction was proven to be essential for vesicle spreading and rupture. Fusion of lipid patches into a homogeneous bilayer required lateral mobility of the lipids on the polyelectrolyte support. The binding of amino groups to the phosphate group of the zwitterionic lipids was too weak to induce vesicle spreading, but sufficient for strong adsorption. Only the mixture of phosphatidylcholine and phosphatidylserine resulted in the spontaneous formation of bilayers on polyelectrolyte multilayers. The adsorption of phospholipids onto multilayers displaying quarternary ammonium polymers produced a novel 3D lipid polyelectrolyte structure on colloidal particles.
Lipid vesicle adsorption on electroactive self-assembled monolayers
Electrochemistry Communications - ELECTROCHEM COMMUN, 2004
This paper presents the results of a study of the interaction of lipid vesicles with an electroactive, ferrocene alkylthiol self-assembled monolayer (SAM) in terms of the optical changes of the adsorbed lipid layer (measured by surface plasmon resonance (SPR)) and changes in the electrochemical properties of the SAM, as measured by cyclic voltammetry. An curious change in the cyclic voltammogram following adsorption of lipid is observed. We speculate on a possible explanation for this effect.
Solid supported lipid membranes: New concepts for the biomimetic functionalization of solid surfaces
Biointerphases, 2008
Surface-layer (S-layer) supported lipid membranes on solid substrates are interfacial architectures mimicking the supramolecular principle of cell envelopes which have been optimized for billions of years of evolution in most extreme habitats. The authors implement this biological construction principle in a variety of layered supramolecular architectures consisting of a stabilizing protein monolayer and a functional phospholipid bilayer for the design and development of new types of solid-supported biomimetic membranes with a considerably extended stability and lifetimecompared to existing platforms-as required for novel types of bioanalytical sensors. First, Langmuir monolayers of lipids at the water/air interface are used as test beds for the characterization of different types of molecules which all interact with the lipid layers in various ways and, hence, are relevant for the control of the structure, stability, and function of supported membranes. As an example, the interaction of S-layer proteins from the bulk phase with a monolayer of a phospholipid synthetically conjugated with a secondary cell wall polymer (SCWP) was studied as a function of the packing density of the lipids in the monolayer. Furthermore, SCWPs were used as a new molecular construction element. The exploitation of a specific lectintype bond between the N-terminal part of selected S-layer proteins and a variety of glycans allowed for the buildup of supramolecular assemblies and thus functional membranes with a further increased stability. Next, S-layer proteins were self-assembled and characterized by the surface-sensitive techniques, surface plasmon resonance spectroscopy and quartz crystal microbalance with dissipation monitoring. The substrates were either planar gold or silicon dioxide sensor surfaces. The assembly of S-layer proteins from solution to solid substrates could nicely be followed in-situ and in real time. As a next step toward S-layer supported bilayer membranes, the authors characterized various architectures based on lipid molecules that were modified by a flexible spacer separating the amphiphiles from the anchor group that allows for a covalent coupling of the lipid to a solid support, e.g., using thiols for Au substrates. Impedance spectroscopy confirmed the excellent charge barrier properties of these constructs with a high electrical resistance. Structural details of various types of these tethered bimolecular lipid membranes were studied by using neutron reflectometry. Finally, first attempts are reported to develop a code based on a SPICE network analysis program which is suitable for the quantitative
Langmuir, 2009
We have used the quartz crystal microbalance with dissipation monitoring (QCM-D) technique to investigate how mono-and divalent cations influence the formation of supported (phospho)lipid bilayers (SPB, SLB), occurring via deposition of nanosized palmitoyloleoyl phosphatidylcholine (POPC) vesicles on a SiO 2 support. This process is known to proceed via initial adsorption of intact vesicles until a critical surface coverage is reached, where the combination of vesicle-surface and vesicle-vesicle interaction causes the vesicles to rupture. New vesicles then rupture and the lipid fragments fuse until a final continuous bilayer is formed. We have explored how this process and the critical coverage are influenced by different mono-and divalent ions and ion concentrations, keeping the anions the same throughout the experiments. The same qualitative kinetics is observed for all cations. However, different ions cause quite different quantitative kinetics. When compared with monovalent ions, even very small added concentrations of divalent cations cause a strong reduction of the critical coverage, where conversion of intact, adsorbed vesicles to bilayer occurs. This bilayer promoting effect increases in the order Sr 2+ < Ca 2+ < Mg 2+. Monovalent cations exhibit a much weaker but similar effect in the order Li + > Na + > K +. The results are of practical value for preparation of lipid bilayers and help shed light on the role of ions and on electrostatic effects at membrane surfaces/interfaces.
Most of the model lipid membrane studies on gold involve the usage of various surface-modification strategies to rupture liposomes and induce lipid bilayer formation since liposomes with polar surfaces do not interact with bare, hydrophobic gold. In this study, a thiol-modified phospholipid, 1,2-Dipalmitoyl-sn-Glycero-3-Phosphothioethanol (DPPTE) was incorporated into phosphatidylcholine (PC) based liposomes to form supported lipid bilayer (SLB) on gold surfaces without further modification. The binding kinet-ics of liposomes with different DPPTE ratio (0.01 to 100% mol/mol) and diameters were monitored by Quartz Crystal Microbalance with Dissipation (QCM-D). The dissipation change per frequency change, i.e. acoustic ratio, which is evaluated as a degree of the viscoelasticity, considerably decreased with the presence of DPPTE (from 162.3 GHz −1 for flattened PC liposomes to ca. 89.5 GHz −1 for 100% DPPTE lipo-somes) when compared to the results of two reference rigid monolayers and two viscoelastic layers. To assess the quality of SLB platform, the interpretation of QCM-D data was also complemented with Surface Plasmon Resonance. The optimum thiolated-lipid ratio (1%, lower thiol ratio and higher rigidity) was then used to determine the dry-lipid mass deposition, the water content and the thickness values of the SLB via viscoelastic modelling. Further surface characterization studies were performed by Atomic Force Microscopy with high spatial resolution. The results suggested that model membrane was almost continuous with minimum defects but showed more dissipative/soft nature compared to an ideal bilayer due to partially fused liposomes/overlapped lipid bilayers/multilayer islands. These local elevations distorted the planarity and led the increase of overall membrane thickness to ∼7.0 nm.
Decoration of lipid vesicles by polyelectrolytes: mechanism and structure
Soft Matter, 2010
This study deals with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles decorated with chitosan and hyaluronan, in dependence with respective membrane and polyelectrolyte net charges (tuned by pH). Studies are performed both on micrometric Giant Unilamellar Vesicles (GUVs) and on their nanometric Large Unilamellar Vesicle (LUV) homologues. Fluorescent microscopy observations reveal that GUVs are homogeneously decorated by both polyelectrolytes, even in the case where global charges of membrane and polyelectrolyte exhibit the same charge sign. z-Potential and light scattering experiments performed on LUVs suspensions upon chitosan addition are interpreted in terms of reversible aggregation of vesicles within the frame of a patch-like structure model. A similar aggregation-deaggregation mechanism is highlighted for GUVS in the presence of chitosan. Enthalpic variations measured by microcalorimetry and z-potential results show that the interaction between membrane and polyelectrolyte, previously demonstrated to be of electrostatic origin, is stronger when they are of opposite charge sign, as expected. For chitosan, the low saturation coverage degree is found to be nearly independent of molecular weight and interpreted in terms of polymer mainly adsorbed flat on the surface. On the contrary, maximum hyaluronan coverage degree dramatically varies with its molecular weight: hyaluronan is assumed to adsorb on the vesicle forming trains and loops. Finally, chitosan-and hyaluronan-vesicle decorations are demonstrated to be strongly resistant in a very large range of pH (