Scanning Electron Microscopy critical point drying

Fig. 2.2. Mycelium of Hebeloma crustuliniforme after colonization of a potassium feldspar surface for seven months. The sample was prepared by fixation and critical point drying followed by gold coating and analysis by scanning electron microscopy. Hyphae (H) and bacteria (B) are visible. Scale bar = 10 pm. The hyphal surface contact is mediated by a fdm of extracellular mucilage (arrow) and bacteria are seen in the mucilage.

Fig. 8.5. Human RBC after radiolabeling, examined by scanning electron microscopy. No sign of morphological alteration is visible. Perfusion fixation, critical point drying, xl500...

Scanning electron microscopy -- Leaf samples for scanning electron microscopy (SEM) were fixed in acrolein and dehydrated in ethanol. Samples were critical-point dried (Evans, Gmur, and Da Costa, 1977) and a layer of carbon or silver was applied to each sample in a vacuum evaporator with a rotating and processing stage. The scanning electron microscope (Model 700, Materials Analysis Co., Palo Alto, CA 94303) was operated at 5 kV or 10 kV. 

Use of the microanalysis attachment in conjimc-tion with electron microscopy can provide a visual representation of concentrations. When finked to nondestructive preparation techniques, such as critical point drying, this offers the potential of assessing specific soil processes. Adamo et al. used scanning electron microscopy in back-scattered electron mode to examine the soil-root interface of plants grown at a range of soil pH and soil phosphorus concentrations. Excellent spatial resolution is, however, covm-terbalanced by relatively poor detection limits due to poor spectral resolution resulting in severe peak overlap. 

Figure 4.49. Scanning electron microscopy images show a comparison between fracturing of a wet membrane after immersion in liquid nitrogen (A) and after critical point drying (B). Fracturing after freezing results in a deformed ductile failure, whereas the fracture after critical point drying shows no deleterious effects of surface tension and the result is a brittle fracture with excellent detail of the internal morphology.

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