Samples need to be electrically conductive and dry for imaging in an SEM. Generally, biologically samples do not possess these characteristics and more extensive preparation is required. Dehydration is usually accomplished using various solvents, though prior consideration has to be given to preservation of structure. Often, initial treatment in a buffered fixative such as glutaraldehyde or osmium tetroxide is necessary to retain structures and features of interest. Dehydration methods such as air drying can contribute to loss of surface integrity even if the sample has been appropriately fixed, meaning alternative methods such as critical point drying or HMDS may be necessary. Conductivity can be achieved by coating the processed sample with gold prior to imaging. Preparation techniques for biological specimens are variable and often sample-specific. It is best to seek advice as to what is required before collecting samples to ensure the best possible outcome.
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