Mica sandwich technique for preparing macromolecules for rotary shadowing.

The sandwich technique, in which a drop of sample solution is spread into a thin layer between two pieces of freshly cleaved mica, is a simple-to-use alternative to spraying for depositing macromolecules onto mica. Test specimens of collagen molecules and actin filaments were found to suffer less shear-induced damage, they were more uniformly distributed, and only very small sample volumes were needed. Either drying from a glycerol solution (40-70% v/v) or freeze-drying can be employed. Glycerol-drying is simpler, but freeze-drying may offer better preservation of supra-molecular assemblies.