Using differential confocal microscopy to detect the phase transition of lipid vesicle membranes

We use differential confocal microscopy, a far-field optical profilometry with 2-nm depth resolution, to monitor the thermal fluctua- tions and the deformation of the bilayer membranes of lipid vesicles. From the linear relation between the mean-square amplitudes of fluctua- tions and temperatures, we can directly determine the phase-transition temperatures of lipid bilayers. We then employ femtonewton optical force to induce submicrometer deformation of the vesicle membranes. From the deformation we obtain the bending rigidity of membranes with a simple geometric analysis. The bending modulus changes by an order of magnitude as the temperature is changed across the transition tempera- ture, such that we can detect the phase transition behaviors of the bi- layer structures. © 2001 Society of Photo-Optical Instrumentation Engineers.