For many years critical point drying (CPD) has been the method of choice for preparing cells for scanning electron microscopy (SEM). Described herein is a simple, efficient, inexpensive, reproducible, and safe procedure using Peldri II, a proprietary fluorocarbon compound that is solid at room temperature and a liquid above 25 degrees C, as a sublimation dehydrant for processing specimens for SEM. The utility of Peldri II was demonstrated in studies using leukocytes from the blood of healthy donors and patients with leukemia as well as from long-term lymphoblastoid cell lines. The application of the proposed Peldri II procedure was further documented in SEM studies in which the expression and distribution of the interleukin-2 receptor (IL-2R) on leukocyte surface membranes was imaged using colloidal gold-labeled antibodies (i.e., immunogold). When compared with current SEM preparation procedures using CPD, Peldri II is a useful alternative that is thought to offer several important advantages.

The scanning electron microscope (SEM) has been used for many years to visualize the distribution of various antigens expressed on cell surfaces. Several markers were used for that purpose, as reviewed by Molday; they were recognized on cell surfaces on the basis of their size and/or shape. However, it is only after colloidal gold particles were demonstrated to be markers of almost universal applicability that the significance of inmuno-SEM in cell biology became evident. The unique properties of the colloidal gold marker can be summarized as follows: it can be prepared in a range of sizes (5 to 40 nm) which accommodates well the resolution of both TEM and SEM; under the light microscope it can be seen as a red stain, or under polarized light epi-illumination; almost all proteins can easily be electrostatically conjugated to it, without noticeable alteration of their biological properties;

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