Freeze-Fracture Transmission Electron Microscopy

Abstract

Freeze-fracture transmission electron microscopy (FF-TEM) gives us useful information about the structure of molecular aggregates, colloidal dispersions, and emulsions. Rapidly frozen samples are fractured with a glass knife. Platinum (Pt) is evaporated and deposited on the fractured surface at 45° to make a thin Pt film. This “shadowing” process induces an enhancement of the contrast of the TEM image depending on the roughness of the fractured surface. Carbon (C) is then evaporated and deposited on the fractured surface at 90° to make a “replica” film. The replica film thus prepared is observed with a transmission electron microscope at high resolution. FF-TEM allows observation of almost all molecular aggregates formed by amphiphilic molecules (surfactants) and colloidal particles like emulsion dispersed in both water and organic solvents. In liposome (vesicle) systems, characteristic TEM images can be obtained depending on the conformation of hydrophobic tails of lipid molecules, that is, gel phase (L_β), ripple gel phase (P_β), and liquid crystal phase (L_α).