AVS 52nd International Symposium
    Biomaterial Interfaces Monday Sessions
       Session BI-MoP

Paper BI-MoP26
Effects of Fluorescent Dyes on the Structure of Lipid Membranes

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Biomaterial Interfaces Poster Session
Presenter: J.J. Heetderks, Penn State University
Authors: J.J. Heetderks, Penn State University
P.S. Weiss, Penn State University
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Cell membranes are complex, dynamic mixtures of lipids, proteins, and cholesterol; their precise mode of molecular organization is unknown. Transient associations of molecules form â?olipid raftsâ? in active cells that may affect membrane-associated protein activity. One model to study the lipid component of these molecular interactions is the giant unilamellar vesicle (GUV). The lipids, without contribution from membrane proteins, cytoskeletal structures, cholesterol, or outside forces, form domains in GUVs when the conditions are within an appropriate range of the multi-dimensional phase diagram of lipid composition and temperature. Fluorescently labeled phospholipids and lipid analogues are used at low concentrations to visualize the vesicles and domains, and are found to influence measured membrane properties, even at concentrations below those typically used in structural studies. Through basic membrane organization measurements, we determine the effects on the vesicle properties for which the labeling is responsible. We incorporate varying amounts of fluorescent dyes into 2-phase vesicles and find clear divisions of gel and fluid domains at room temperature. The temperature is then slowly raised while monitoring the membrane domains until the domains melt into one homogeneous phase. Preliminary results show that the incorporation of several common fluorescent labels in the membrane cause measurable changes in the demixing temperatures of the two-phase vesicles at less than one percent dye concentration.