Detection of Small (5-15nm) Gold-Labelled Surface Antigens Using Backscattered Electrons

The analysis of surface antigens by scanning electron microscopy represents a practicable alternative to replica techniques. It is generally observed that smaller markers provide for better labelling. In the SEM very small colloidal gold labels however are hardly discerned from contaminants or from surface structures of similar size. They are however unambiguously demonstrated by combining the surface information provided by the secondary electron signal and the material dependent signal provided by the backscattered electrons. A field emission SEM equipped with a highly sensitive single crystal backscattered electron detector allows the routine detection of 5 nm gold particles on biological surfaces. In order to obtain a clear BSE signal of the 5 nm gold particles, the use of material with a high backscattering coefficient (as staining reagent, as coating material or as specimen support) has to be avoided