CELL-SURFACE RECEPTORS AND PROTEINS ON PLATELET MEMBRANES IMAGED BY SCANNING FORCE MICROSCOPY USING IMMUNOGOLD CONTRAST ENHANCEMENT

High resolution scanning force microscope (SFM) images of fibrinogen-e xposed platelet membranes are presented. Using ultrasharp carbon tips, we are able to obtain submolecular scale resolution of membrane surfa ce features. Corroboration of SFM results is achieved using low voltag e, high resolution scanning electron microscopy (LVHRSEM) to image the same protein molecule that is seen in the SFM. We obtain accurate hei ght dimensions by SFM complemented by accurate lateral dimensions obta ined by LVHRSEM. The use of 14- and 5-nm gold labels to identify speci fic membrane-bound biomolecules and to provide contrast enhancement wi th the SFM is explored as a useful adjunct to observation of unlabeled material. It is shown that the labels are useful for locating specifi c protein molecules on platelet membrane surfaces and for assessing th e distribution of these molecules using the SFM. Fourteen nm labels ar e shown to be visible over the membrane corrugation, whereas 5-nm labe ls appear difficult to resolve using the present SFM instrumental conf iguration. When using the 5-nm labels, collateral use of LVHRSEM allow s one to examine SFM images at submolecular resolution and associate f unction with the structures imaged after the SFM experiment is complet ed.