Colloidal Gold and Its Application in Cell Biology
This chapter discusses the scope and variety of applications of the colloidal gold method. The advantages of colloidal gold as a marker in electron microscopy (EM) immunocytochemistry include the particulate nature of colloidal gold, which allows a fine localization of marked sites, and the size range, which guarantees high flexibility in lateral resolution. Gold particles are negatively charged and can be complexed by noncovalent electrostatic adsorption with various macromolecules forming stable and bioactive gold-ligand complexes termed “gold probes,” and the characteristic X-ray signals emitted by gold could be used to image and quantify cell-bound gold markers by the application of X-ray microanalytical techniques and appropriate computer programs. The introduction of ultrasmall gold particles with increased penetration capabilities has enlarged the potential of colloidal gold reagents, particularly in the field of light microscopy. The addition of polymers is a well-established method for controlling the stability of colloidal dispersions. Nonionic macromolecules—such as polyethylene glycol and polysaccharides—as well as charged macromolecules can be adsorbed onto a metal surface. The adsorption of macromolecules onto colloidal gold depends on a number of factors, such as (1) the stability of the colloid itself, (2) the concentration, shape, configuration, and isoelectric point of macromolecules, and (3) the ionic strength, pH, and temperature of a suspending medium.