The Tousimis Critical Point Drying System is used to complete the dehydration of biological specimens and other materials from their native hydrated states prior to observation in the SEM. Water is removed from the samples by passing them through a series of increasingly concentrated ethanol solutions, and the pure ethanol-saturated samples are then transferred to the system's high-pressure chamber where the ethanol is replaced by liquid carbon dioxide. The chamber temperature is then raised to bring the carbon dioxide saturated samples to the CO2 critical point; that being the combination of temperature and pressure where the phase boundary between the liquid and gas phases disappears and the two phases coexist. The chamber pressure is then vented very slowly, allowing the CO2 to leave the sample in the gas phase, but without surface tension effects that would otherwise cause damage to sample ultrastructure. This semi-automated system is reliable and easy to operate.
- Biological specimens (bulk tissues, cell cultures, single cells)