Cationic colloidal gold--a new probe for the detection of anionic cell surface sites by electron microscopy.

Particles of colloidal gold were coated with poly-L-lysine to prepare cationic colloidal gold. Monodispersed colloidal gold with a particle diameter of 5, 8, or 15 nm and poly-L-lysine with a molecular weight of 350,000 or 1500-8000 were used. The resulting complexes were used to label red blood cell membranes. The labeling was sensitive to neuraminidase treatment or acid hydrolysis, demonstrating that cationic colloidal gold binds preferentially to anionic cell surface constituents. Cationic colloidal gold can be used at physiological pH values and ionic strength, as well as at low pH values, making it a flexible probe for detection of anionic cellular components.