Vapor Diffusion Method
The vapor diffusion method is a common technique used to crystallize proteins. There are two different types of techniques within this category: hanging drop and sitting drop methods. Both of them consist of having a drop with protein solution situated either on top (hanging drop) or next to (sitting drop) a reservoir containing precipitant (e.g. a concentrated salt solution). As the water from the protein solution vaporizes, it transfers to the reservoir and crystallization occurs.
File:Drop1.png Fig. 1 Hanging drop method.
File:Drop2.png Fig. 2 Sitting drop method.