High-Resolution SEM of Colloidal Gold Labels

Abstract

Colloidal gold, conjugated to a number of biologically active molecules, including ligand and antibody, provides a useful label for light microscopy and electron microscopy. This stems, in part, from its color, density, and regular spherical shape although the ability to make the particles in a number of defined sizes, the ease of conjugation to biological material, and the retention of activity of bound molecules are also important factors.Although nearly all sizes of colloidal gold particles, from 2.0 nm on up, can be identified in transmission or high voltage transmission electron microscopy, it has generally been the larger sized particles, 15 nm and up, that have proved useful for scanning electron microscopic studies. This is due principally to the resolution limits of conventional SEMs and the need to employ backscattered electron imaging, BEI, to unambiguously define the gold labels.