Structure of Anionic Phospholipid Coatings on Silica by Dissipative Quartz Crystal Microbalance

Abstract

The adsorption of anionic phospholipids on silica was investigated by the dissipative quartz crystal microbalance (QCM) technique. Liposomes composed of 1 mM 80:20 mol % of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphatidylcholine (POPC)/phosphatidic acid, POPC/phosphatidylglycerol, or POPC/phosphatidylserine in N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) buffer at pH 7.4 (with or without 3 mM of CaCl2) were examined. We have previously demonstrated that similar phospholipid coatings can be used in capillary electrochromatography as a stationary phase for the separation of analytes. In this work, we focus on the formation of the coatings and on the type of lipid structure formed on silica. The QCM investigation comprised qualitative results based on changes in frequency and resistance, and quantitative modeling of the obtained results. The latter was performed using the dissipative QCM, which measures the quartz crystal impedance, combined with equivalent circuit analysis. A previously developed coating and cleaning procedure for phospholipid-coated fused silica capillaries was adopted in this study, and the same silica-coated crystal was used throughout the QCM study. We will demonstrate in this work that the type of lipid structure formed on silica, that is, a rather rigid supported lipid bilayer or a viscoelastic supported vesicle layer (SVL), is highly dependent on the lipid and solvent composition. We also show for the first time that the modeling of the dissipative QCM data can be used to extract a more quantitative picture of an adsorbed SVL, because, so far, published studies have merely used the QCM data in a qualitative sense.

Influence of the molecular architecture on the adsorption onto solid surfaces: comb-like polymers

“…Fast shifts in Df/n were observed during the injection and rinsing, however, they were not taken into account for the analysis of the adsorption process. 24 The shift in the signal after the rinsing can be attributed to swelling/deswelling processes of the layers. The latter agree with the scenario of irreversible adsorption of grafted polymers reported previously by other authors.…”

Characterization of phosphatidylcholine/polyethylene glycol‐lipid aggregates and their use as coatings and carriers in capillary electrophoresis

“…In such cases, measuring the electrical properties of the quartz crystal and the adsorbed layers at multiple overtones is a useful way to determine the mechanical properties of the layer. By using equivalent circuit modeling, one can then estimate the mechanical properties of the added layers on the quartz crystal, such as mass, density, thickness, and viscoelastic properties [24,25]. The modeling in this study was performed using proprietary QCM Impedance Analysis software (KSV Instruments, software version 2.30).…”

“…The modeling in this study was performed using proprietary QCM Impedance Analysis software (KSV Instruments, software version 2.30). Data was simultaneously acquired at the fundamental frequency of 5 MHz (N = 1) and at several overtone frequencies (15,25,35,45, and 55 MHz). If not stated otherwise, the changes in the measured data of the third overtone (N = 3; f = 15 MHz) are reported.…”

“…QCM and AFM measurements were carried out to test this hypothesis. Recently we studied negatively charged liposomes of sizes around 100 nm by QCM and found that, depending on the lipid and the composition of the buffer solution, two distinct types of structures appeared: a rather rigid supported lipid bilayer (SLB) or a viscoelastic supported vesicle layer (SVL) [25].…”

Formation of an intact liposome layer adsorbed on oxidized gold confirmed by three complementary techniques: QCM‐D, AFM and confocal fluorescence microscopy

“…However, the tension in the membrane of the spherical cap of the adsorbing vesicles caused by these attractive forces does not exceed the threshold for disruption of the membrane. [18] To investigate the intact nature of the immobilized liposomes, several techniques have been used, namely, quartz crystal microbalance with dissipation (QCM-D) [8,[20][21][22][23] atomic force microscopy (AFM), [8,15,16,24] laser scanning confocal fluorescence microscopy (LSCFM) [25,26] and surface plasmon resonance. [27] The objective of the present work is to demonstrate to the researchers interested in the process of immobilizing vesicles that adsorption on oxidized gold is a simple method to form stable monolayers of intact liposomes.…”