An Aldehyde/Hydrazide Polymerization Technique for Biological SEM Specimen Preparation
Two water-soluble embedding techniques for transmission electron microscopy (TEM) utilizing the polymerization of glutaraldehyde were proposed in the early 1970's. Pease and Peterson introduced a glutaraldehyde-urea polymer medium and Heckman and Barrnett proposed a glutaraldehyde-carbohydrazide (GACH) medium. Both permitted the retention of lipids in tissues without the harsh extraction of cellular constituents by fixatives, organic dehydrators and embedding agents. These techniques were of limited application and yielded low contrast or negative-stained images in the TEM. This technique has not been previously considered as potentially useful for scanning electron microscopy (SEM) due to the covering and obliterating of surface morphology. Virtually all SEM techniques for biological and specimen preparation, aside from freeze-drying, replace or extract most of the native elemental compositions of cells and tissues. Freezing and freeze-drying techniques are cumbersome, time-consuming, may require elaborate equipment and can induce artifacts due to ice crystal formation. We propose a new approach of SEM sample preparation using modifications of the GACH technique employed in TEM.