Critical Point Dryers
Air drying destroys soft biological specimens: as liquid evaporates, surface tension at the receding meniscus tears delicate structures apart. Critical point drying removes the liquid without ever crossing a phase boundary, preserving the specimen's three-dimensional structure for SEM.
Overview
When a wet specimen dries in air, the surface tension of the receding liquid exerts forces large enough to collapse cell walls, cilia and other fine structures — the specimen that reaches the microscope is not the one that went in. Critical point drying sidesteps this by replacing the specimen's water with a transitional fluid, usually liquid carbon dioxide, then taking that fluid above its critical temperature and pressure, where liquid and gas become indistinguishable and surface tension vanishes. The CO₂ can then be vented as a gas, leaving the specimen dry and structurally intact. It is essential preparation for SEM of tissue, insects, plant material, hydrogels and other soft or porous samples.
Manufacturer: SPI Supplies — USA
Local sales, installation, and technical support in Bangladesh by trained local engineers.
Models
SPI-Dry Critical Point Dryer, Jumbo Size
The technique, in routine use since 1970, has since expanded beyond biological specimens into aerogel and MEMS drying applications.
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