The application of a biotin-anti-biotin gold technique providing a significant signal intensification in electron microscopic immunocytochemistry: a comparison with the ultrasmall immunogold silver staining procedure.

A three-step biotin-anti-biotin gold-detection system (method A) has been applied for ultraimmunocytochemistry using ultrasmall colloidal gold (0.8 nm) linked to anti-biotin antibodies which were visualized and enhanced by silver reduction. The reactivity for glucagon in human pancreatic islets and for cytochrome-c oxidase in heart mitochondria has been compared to a two-step ultrasmall immunogold technique (method B). For both antigens, method A provided significantly higher labelling indices (P<0.001): the labelling density for cytochrome-c oxidase was 223/microm2 using method A and 78/microm2 using method B. For glucagon, the labelling density was 1455/microm2 with method A and 322/microm2 with method B. The results demonstrate that the silver-intensified biotin-anti-biotin gold-detection system is a valuable immunocytochemical method for signal enhancement. The method utilizes biotinylated antibodies from different species, allowing its broad application at the electron microscopic level.