Fluorescent probes used to monitor membrane interfacial polarity

The polarity of the interface between a lipid bilayer membrane and bulk water is an important physical parameter of the membrane. It is likely that several membrane-dependent biological functions are modulated by this property. However, interfacial polarity can be difficult to define because of an imprecise knowledge of the molecular nature of the interface. Nevertheless, attempts have been made to measure this quantity with the use of fluorescent probes which are sensitive to the solvent polarity. Often, however, other factors, such as the rate of solvent relaxation must be known in order to interpret the fluorescent properties in terms of the dielectric constant. In addition, the spatial orientation and location of the fluorophore are often not known precisely. Nevertheless, there have been successful efforts to gain a more accurate knowledge of this aspect of membrane physical properties and its relationship to biological phenomena is discussed.