Optical Anisotropy of Supported Lipid Structures Probed by Waveguide Spectroscopy and Its Application to Study of Supported Lipid Bilayer Formation Kinetics
TL;DR: Understanding of mechanistic details for an adsorption process for which conformational changes and ordering occur can be elucidated using DPI and greatly enhanced by modeling of optical birefringence.
Abstract: Supramolecular conformation and molecular orientation was monitored during supported lipid bilayer (SLB) formation using dual polarization interferometry (DPI). DPI was shown to enable real time sensitive determination of birefringence of the lipid bilayer together with thickness or refractive index (with the other a fixed value). This approach removes differences in mass loading due to anisotropy, so the mass becomes solely a function of the lipid dn/dc value. DPI measurements show highly reproducible qualitative and quantitative results for adsorption of liposomes of different lipid compositions and in buffers with or without CaCl2. The packing of solvent-free self-assembled SLBs is shown to differ from other preparation methods. Birefringence analysis accompanied by mass and thickness measurements shows characteristic features of vesicle adsorption and SLB formation kinetics previously not demonstrated by evanescent optical techniques, including indications of percolation-type rupture of clusters of li...
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TL;DR: A protocol for constructing zwitterionic SLBs supported on silicon oxide and titanium oxide, and a recently developed strategy that uses an amphipathic, α-helical (AH) peptide to form SLBs on gold and Titanium oxide substrates are presented.
Abstract: Supported lipid bilayers (SLBs) mimic biological membranes and are a versatile platform for a wide range of biophysical research fields including lipid-protein interactions, protein-protein interactions and membrane-based biosensors. the quartz crystal microbalance with dissipation monitoring (QCM-D) has had a pivotal role in understanding SLB formation on various substrates. as shown by its real-time kinetic monitoring of SLB formation, QCM-D can probe the dynamics of biomacromolecular interactions. We present a protocol for constructing zwitterionic SLBs supported on silicon oxide and titanium oxide, and discuss technical issues that need to be considered when working with charged lipid compositions. Furthermore, we explain a recently developed strategy that uses an amphipathic, a-helical (AH) peptide to form SLBs on gold and titanium oxide substrates. the protocols can be completed in less than 3 h.
479 citations
TL;DR: This review discusses the basic theory and operational arrangements of four commercially available types of optical biosensors: surface plasmon resonance, resonant mirror, resonance waveguide grating, and dual polarization interferometry.
Abstract: Biosensors have been used extensively in the scientific community for several purposes, most notably to determine association and dissociation kinetics, protein-ligand, protein-protein, or nucleic acid hybridization interactions. A number of different types of biosensors are available in the field, each with real or perceived benefits over the others. This review discusses the basic theory and operational arrangements of four commercially available types of optical biosensors: surface plasmon resonance, resonant mirror, resonance waveguide grating, and dual polarization interferometry. The different applications these techniques offer are discussed from experiments and results reported in recently published literature. Additionally, recent advancements or modifications to the current techniques are also discussed.
215 citations
Cites methods from "Optical Anisotropy of Supported Lip..."
...In addition to the same applications of SPR and RM [88,89], DPI has proven to be a powerful technique for characterizing structural dimensions of proteins [90] and has recently been shown to be an instrumental tool for characterization of membrane/liposome structure and mimetics [91-94]....
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TL;DR: This work grades every paper published in 2008 on a scale from A to F and outlines what features make a biosensor article fabulous, middling or abysmal and focuses on a few experimental, analysis and presentation mistakes that are alarmingly common.
Abstract: Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.
192 citations
TL;DR: It is found that the extracellular matrix produced by Pseudomonas aeruginosa self-assembles into a liquid crystal through entropic interactions between polymers and filamentous Pf bacteriophages, which are long, negatively charged filaments, which enhance biofilm function by increasing adhesion and tolerance to desiccation and antibiotics.
189 citations
TL;DR: The ability of α-Syn to sense lipid packing defects and to remodel membrane structure supports its proposed role in vesicle trafficking.
181 citations
Cites background from "Optical Anisotropy of Supported Lip..."
...182 ml/g, respectively, as reported previously (36, 41)....
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...54 nm(2) (43) and with literature mass values (36)....
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...Alternatively, where the layer on the surface of the waveguide is birefringent, as is the case for SLBs, the refractive index (or thickness) of the layer can be assumed to be constant, and the thickness (or refractive index) and birefringence can be calculated (36, 37)....
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References
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TL;DR: The uncertainty in structural results for lipid bilayers is being reduced and best current values are provided for bilayers of five lipids.
2,497 citations
TL;DR: The application of ellipsometry for the study of the adsorption behavior of proteins and synthetic macromolecules at the air-water interface has been investigated in this article.
Abstract: The application of ellipsometry of the study of the adsorption behavior of proteins and synthetic macromolecules at the air-water interface has been investigated. It is shown that for macromolecules the amount adsorbed per unit area, Γ, as determined by ellipsometry, only has a well-defined physical meaning if the refractive-index increment remains constant up to high concentrations present in the adsorbed layer. It has been found experimentally that this conditioned is fulfilled for proteins. The ellipsometric Γ values of some protein agree satisfactorily with those obtained by two independent techniques has been used to investigate the adsorption from solution of κ-casein, bovine serum albumin, and polyvinyl alcohol. For bovine serum albumin, Γ reaches a plateau value of 2.9 mg/m2 for concentrations ≥ 0.05 wt%. The thickness of the adsorbed molecules. For κ-casein, Γ steadily increases with increasing centration and multilayers are formed. The technique provides interesting information on conformational changes in adsorbed macromolecules, on the rate of the process, and on the conditions under which these occur.
1,254 citations
TL;DR: In this paper, an experimental setup has been constructed for simultaneous measurements of the frequency, the absolute Q factor, and the amplitude of oscillation of a quartz crystal microbalance (QCM).
Abstract: An experimental setup has been constructed for simultaneous measurements of the frequency, the absolute Q factor, and the amplitude of oscillation of a quartz crystal microbalance (QCM). The technical solution allows operation in vacuum, air, or liquid. The crystal is driven at its resonant frequency by an oscillator that can be intermittently disconnected causing the crystal oscillation amplitude to decay exponentially. From the recorded decay curve the absolute Q factor (calculated from the decay time constant), the frequency of the freely oscillating crystal, and the amplitude of oscillation are obtained. All measurements are fully automated. One electrode of the QCM in our setup was connected to true ground which makes possible simultaneous electrochemistry. The performance is illustrated by experiments in fluids of varying viscosity (gas and liquid) and by proteinadsorptionin situ. We found, in addition to the above results, that the amplitude of oscillation is not always directly proportional to the Q factor, as the commonly used theory states. This puts limitations on the customary use of the amplitude of oscillation as a measure of the Q factor.
1,172 citations
TL;DR: The results suggest that the molecular-level interaction between lipids and the solid support needs to be considered explicitly, to understand the rupture of vesicles and the formation of SLBs as well as to predict the properties of the resulting SLB.
Abstract: Supported lipid bilayers (SLBs) are popular models of cell membranes with potential bio-technological applications. A qualitative understanding of the process of SLB formation after exposure of small lipid vesicles to a hydrophilic support is now emerging. Recent studies have revealed a stunning variety of effects that can take place during this self-organization process. The ensemble of results in our group has revealed unprecedented insight into intermediates of the SLB-formation process and has helped to identify a number of parameters that are determinant for the lipid deposition on solid supports. The pathway of lipid deposition can be tuned by electrostatic interactions and by the presence of calcium. We emphasize the importance of the solid support in the SLB-formation process. Our results suggest that the molecular-level interaction between lipids and the solid support needs to be considered explicitly, to understand the rupture of vesicles and the formation of SLBs as well as to predict the properties of the resulting SLB. The impact of the SLB-formation process on the quality and the physical properties of the resulting SLB as well as implications for other types of surface-confined lipid bilayers are discussed.
1,071 citations
TL;DR: This work measures the kinetics of adsorption of small (12.5-nm radius) unilamellar vesicles onto SiO2, oxidized gold, and a self-assembled monolayer of methyl-terminated thiols, using a quartz crystal microbalance (QCM).
973 citations