Do not fill the capsule more than about one third full with cells or they will cake during the drying procedure. Firmly fit the lid to the capsule and transfer to the critical point dryer. Critical point dry cells using a critical point drying apparatus and CO 2 . Dust the dried cells on a SEM specimen stub covered with a piece of double stick tape. Spreading is easier if cells are brushed on the tape with a fine camel hair brush while observing spreading with a dissecting microscope.
Store specimens in a dry container.
This method is simple but requires that cells or organelles stick to a coated glass coverslip. Many cells are lost during the dehydration procedure but, usually, more than enough cells will stick for SEM observation. Place a 12 mm circular coverslip on a piece of Parafilm or in a small plastic or glass petri dish. Let sit for 10-20 min. Remove the drop of polyethylenimine and rinse with one or two drops of deionized water.