Identification of Multiple Colloidal Labels of Various Metallic Composition by Means of Electron Energy Loss Spectroscopy

Abstract Since it was introduced by Faulk and Taylor in 1971, colloidal gold (cAu) has become the predominant marker used for EM cell labeling. Double labeling, using cAu of two distinct sizes, was pioneered a decade later. However, as interest continues to grow of how the myriad proteins, enzymes, receptors, and other macromolecules function with respect to one another in the cellular environment, this method has proven largely inadequate for high resolution, multiple labeling because each cAu label must be of sufficiently distinct size to prevent size overlap and confusion between different labels. As the particle size increases, so does steric hindrance between different labels competing for binding sites, while the spatial resolution of the labeling and overall labeling efficiency decrease. In order to address these concerns and surmount the limitations of current labeling methodologies, we have developed colloidal particles of uniform size from various metals including Ag, Pt, Pd, Rh, Ru, Ni, and Cu, in addition to Au.