The Leica EM CPD300 Critical Point Dryer is used to preserve the sample’s morphology. Since air drying would cause severe deformation and collapse of structure due to the effects of high surface tension to air, the water in the biological specimen is replaced with a suitable inert fluid (“transitional fluid”-CO2) which has a lower surface tension to air. This would thus reduce severe structural damages during air-drying.

Because liquid CO2 is not sufficiently miscible with water, a third medium commonly Acetone or Ethanol is used as “intermediate fluid”. The specimen is first dehydrated through varying concentrations of the intermediate fluid and thus completely replacing the water in the specimen. Afterwards, the “intermediate fluid” is replaced with the “transitional fluid” (CO2) which can then convert from liquid to gas phase without surface tension effects which distort morphology and ultra-structure.