SCANNING TUNNELING MICROSCOPIC STUDY OF OSMIUM-IMPREGNATED COLLAGEN

The vapor-phase osmium impregnation method was applied to increase the conductivity of the collagen specimens used in scanning tunneling mic roscopy (STM), since the application of STM to biological materials ha s been limited by the poor conductivity, irregular sample geometry, an d instability of these materials. The impregnation method was applied to collagen fibrils attached to highly oriented pyrolytic graphite, an d the STM images obtained were compared with those of routinely proces sed uncoated specimens. The osmium-impregnated collagen fibrils showed a periodicity of about 67 nm, which was also observed on the negative -stained specimens by transmission electron microscopy. In addition, t he periodicity of 3.1 nm, which corresponded to the helical cycle of t he 3 alpha-chains within collagen, was clearly demonstrated by STM. Mo reover, the comparative observations of collagen specimens without osm ium impregnation disclosed the left-handed helical structure with a pe riodicity of 3.1 nm in a single collagen filament.