Lateral surface potential distribution of a phospholipid monolayer

A new experimental set-up is described to measure surface potentials at a lateral resolution of 40 μm with an accuracy better than 5 mV. It is used to investigate the heterogeneity of a phospholipid monolayer on a solid support. By comparing the lateral potential distribution with corresponding fluorescence micrographs different surface potentials can be assigned to different monolayer phases. From this one derives that the surface potential of the fluid phase of the phospholipid dimyristoyl-phosphatidylethanolamine is lower than that of the solid phase by 90±10 mV. If account is also taken of changes in molecular densities the result leads to an estimate of the decrease in tilt angle of the hydrocarbon chains with respect to the surface normal in going from the fluid to a liquid crystalline phase. We discuss the role of water during transfer and assess various support cleaning procedures and possible transfer artifacts.