Combined Brewster Angle and Fluorescence Microscopy of DMPC/D-Cholesterol Mixed Langmuir Monolayers

Abstract

Most direct imaging studies of domains and of the mixing/demixing transition within lipid monolayers and bilayers are performed with fluorescence microscopy (FM). This technique requires the addition of a fluorescent probe, which can in principle affect the size, shape and behavior of the domains, as well as the phase diagram itself. Brewster angle microscopy allows one to image the domains in a Langmuir monolayer with and without the probe molecules to directly test their effect. The combined Brewster angle (BAM)/ fluorescence microscope allows us to image simultaneously with the two techniques exactly the same domains in the Langmuir film. In general, the images taken by the two microscopes compare well. Comparison of the techniques can then make it easier to correlate the different domain properties leading to contrast in the two techniques. Some types of domains may however be much more evident with BAM than with FM.