Silver enhancement of gold probes (5-40 nm): single and double labeling of antigenic sites on cell surfaces imaged with backscattered electrons.

Silver enhancement of immunogold-labeled cells was carried out to increase the applicability of colloidal gold probes for visualization in the backscatter electron imaging (BEI) mode of a scanning electron microscope. Optimum conditions were established for single particle discrimination and differential counting of labeling density at low magnifications. Red blood cells double-labeled with 15 + 40 nm and 5 + 20 nm gold probes were silver-enhanced for 6 min and 20 min, respectively, at which times both pairs of labels increased to about 25 + 50 nm. The gold probes still appeared spherical after enhancement and were easily discriminated. Cells were also single-labeled with the above probes and enhanced accordingly. The present method enables visualization of individual particles of any probe size, labeling one, or simultaneously two, antigenic sites on cell surfaces. The silver enhancement procedure thereby allows cells to be labeled with small probes with increased labeling efficiency.