Comparison of hexamethyldisilazane (HMDS), Peldri II, and critical-point drying methods for scanning electron microscopy of biological specimens.

Three different drying methods, critical-point drying (CPD), Peldri II, and hexamethyldisilazane (HMDS), were compared using representative animal (rat kidney, trachea, duodenum, lung, and red blood cells) and plant (leaves from ten species of monocotyledons and dicotyledons) specimens. All three drying methods produced identical results with animal specimens. Plant specimens showed signs of shrinkage regardless of which drying method was employed. The order of preservation quality from best to worst for leaves was CPD > Peldri II > HMDS, with the CPD method providing substantially better results in all but one case. Postfixation of leaves with osmium tetroxide resulted in poorer preservation in all instances. Peldri II caused complete extraction of leaf cuticular wax, while both both CPD and HMDS showed minimal extraction compared with samples air dried directly from acetone. These results indicate that HMDS provides a time-saving and inexpensive alternative to CPD for animal specimens. Plant specimens, particularly those containing cells with large central vacuoles, are adequately preserved only with the CPD method. In addition, postfixation with osmium should be avoided when processing plant specimens for scanning electron microscopy.