Combined Fluorescence and Brewster Angle Microscopy of Dmpc/D-Cholesterol Mixed Langmuir Films

Abstract

The phase diagrams of DMPC/Cholesterol mixed Langmuir films have long been studied as an example of the critical mixing/demixing transition, with possible applications to membrane domains (rafts) in the much more complex biomembrane system. However, most of these studies have been performed with fluorescence microscopy, requiring the addition of a fluorescent probe, which can in principle affect the phase diagram. Here we combine Brewster angle and fluorescence microscopy on the same trough which allows us to verify if identical domain patterns are seen by the two techniques. Comparing Brewster angle results with and without fluorescent probe provides insight into the role of the probe on domain morphology and the surface pressure dependence of domain formation. We also compare the line tensions of the domains measured with and without the fluorescent probe and draw conclusions on the potential problems encountered when using fluorescent probes.