Cryo-transmission Electron Microscopy

Abstract

Cryogenic transmission electron microscopy (cryo-TEM) is a valuable technique for viewing and studying the structure of various molecular aggregates such as spherical micelles, rodlike micelles, vesicles, and emulsions. In cryo-TEM, the sample under observation is usually frozen. A small amount of sample solution is placed on a grid. Excess sample is blotted away with a filter paper to form a very thin liquid film (<200 nm). This thin liquid film is rapidly plunged into a cold medium (usually liquid ethane) at temperatures lower than 170 C. This rapid freezing induces the formation of vitrified ice, and the water molecules do not arrange into a crystalline lattice, which preserves the structure of molecular aggregates. The freezing rate is one of the most sensitive parameters for determining the quality of the structure preservation. The frozen sample is transferred to a cryospecimen holder using a cryo-transfer system under a liquid nitrogen atmosphere and is observed directly by TEM while the sample is kept in the frozen state.