Critical point drying (CPD) is the final drying step for delicate samples prior to viewing/imaging with scanning electron microscopy. It preserves surface structures that might otherwise be damaged due to surface tension when changing from the liquid to gaseous state. Critical Point Drying can produce better preserved samples than lyophilization. Chemical drying with hexamethyldisilizane (HMDS) is also available, but works best on animal, bacterial or cultured cells. It is suggested that users without established protocols try all available drying options to determine which method is best for their samples.
The FreeZone freeze dryer may be used for lyophilizing SEM samples. It has an LCD display, collectors that reach -40° C and collector capacity of 2.5 liters, suitable for lyophilizing aqueous SEM samples.