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Measurement of thickness and phase transitions in supported lipid bilayers using quantitative differential interference contrast microscopy

Regan, David 2019. Measurement of thickness and phase transitions in supported lipid bilayers using quantitative differential interference contrast microscopy. PhD Thesis, Cardiff University.
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Abstract

Supported lipid bilayers are one of the most commonly used model membrane systems, studied with a wide variety of different techniques. One family of microscopy techniques is quantitative phase imaging, which measures the phase shift of light passing through a sample. This phase shift is determined by a sample’s thickness and refractive index, and so the phase information provides meaningful structural information about the sample. Here, we seek to investigate how a relatively new form of quantitative phase imaging, quantitative differential interference contrast (qDIC), can be used to further the study of supported lipid bilayers. Of particular interest is the thickness of the supported bilayer, since this is an important parameter which can affect protein-membrane interactions. Given a known refractive index of the bilayer, the thickness can be extracted from the phase information. Using literature values for the refractive index of lipids we obtain thickness values which are in good agreement with those in the literature obtained using other techniques. We show that qDIC can detect differences in the thicknesses of supported bilayers of less than one nanometre, revealing that the hydrophilicity of the glass support causes significant reductions in the thickness of the supported bilayer in closest contact with it, and that this effect is modulated by the choice of fluorophore and the degree of coverage at the surface. Another application of qDIC is in the study of the supported bilayer phase behaviour. We use qDIC to study the main phase transition during cooling from the solid-ordered to liquid-disordered phase, and measure thickness changes which take place during the transition. We also show that qDIC can be used to image liquid-liquid phase coexistence, with the liquid-ordered phase distinguished from the liquid-disordered by its greater optical thickness, and we measure the difference in thickness between these phases.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: -Supported lipid bilayer; -Label-free; -Liquid-liquid phase coexistence; -Bilayer phase transition; -Quantitative phase imaging; -Differential interference contrast; -Interferometry
Date of First Compliant Deposit: 11 December 2019
Last Modified: 19 Dec 2019 11:49
URI: http://orca.cf.ac.uk/id/eprint/127460

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