Evidence is accumulating that in cell membranes microdomains exist, also referred to as rafts or detergent resistant membranes. In this study, atomic force microscopy is used to study supported lipid bilayers, consisting of a fluid phosphatidylcholine, sphingomyelin and cholesterol. Domains were visualized of which the morphology and size depended on the cholesterol concentration. The presence of cholesterol was found to induce bilayer coupling. At 30 mol% cholesterol, a change in percolation phase was observed, and at 50 mol%, when both fluid lipids and solid lipids are saturated with cholesterol, phase separation was still observed. In addition, we were able to directly visualize the resistance of domains against non-ionic detergent.
