The outer surfaces of three microorganisms, Giardia lamblia,
Enterococcus faecalis, and Proteus mirabilis, were
investigated by cryo-immobilization followed by sublimation of
extracellular ice and cryocoating with either Pt alone or Pt plus
carbon. Cryocoated samples were examined at −125°C in either
an in-lens field emission SEM or a below-the-lens field emission SEM.
Cryocoating with Pt alone was sufficient for low magnification
observation, but attempts to do high-resolution imaging resulted in
radiolysis and cracking of the specimen surface. Double coating with Pt
and carbon, in combination with high resolution backscatter electron
detectors, enabled high-resolution imaging of the glycocalyx of
bacteria, revealing a sponge-like network over the surface. High
resolution examination of bacterial flagella also revealed a periodic
substructure. Common artifacts included radiolysis leading to
“cracking” of the surface, and insufficient deposition of
Pt resulting in the absence of detectable surface topography.