Scanning Electron Microscopy:
Scanning Electron Microscope (SEM):The Hitachi 4700 Field Emission SEM scanning electron microscope includes a Polaron cryo-stage that permits the imaging of flasht frozen materials that allows an investigator to obtain images of the surface of biological and physical materials unaltered by preparative procedures. Images on web sites of snow crystals (web link) and the detail of nearly microscopic mites (web link) shows the great power of resolution inherent in this technique. Critical point dried samples can also be observed.
Techniques developed for observing with low-temperature scanning electron microscopy are relatively easy to use and have been found to be successful in a wide range biological and samples composed primarily of water. Samples are place onto a copper metal sample plate (25 x 15 mm or 1 x 8/16 inch) and placed onto a brass bar in a bath of liquid nitrogen. Within fractions of a second these plates are rapidly cooled to -196°C which attaches these samples to the plates. Due to the low surface tension of liquid nitrogen and the extreme hardness of materials cooled to these temperatures, very fragile samples can be observed. Sample can be stored at -196°C in storage dewars for an extended period of time. Selected samples are transferred to the preparation chamber of an Polaron PolarPrep 2000 Cryotrans System for sputter coating with platinum. This renders them electrically conductive and they are placed on the precooled (-170°C) stage of a Hitachi S-4700 field emission SEM where they are imaged. High resolution 5 Meg digital images are produced which can be e-mailed or provided to the scientist via thumb drive or DVD.
Contact: Gary.Bauchan@ars.usda.gov 301-504-6649
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