How to see a billionth of a gram of protein:
Silver Enhancement

Although collodal gold and gold cluster complexes have become the electron microscopy labels of choice, a cell labeled with them will at most only become a dull red-purple, and then only when a relatively high concentration of large colloidal gold is attached.

In 1981 Gorm Danscher discovered a new reaction: in the presence of silver (I) ions and a reducing agent such as hydroquinone, colloidal gold particles will act as catalysts to reduce silver (I) ions to metallic silver; the silver was deposited onto the gold, enlarging the particles. Regions stained with colloidal gold were "developed" by this autometallographic procedure to give black staining which could be seen in the light microscope. This method, known as immunogold silver staining (IGSS) has been widely used since. In addition, it is also effective for immunoblots and gels, developing a dark spot even for a tiny quantity of protein.

IGSS, used with the Nanogold® cluster probe, is one of the most sensitive immunodetection systems available, similar to chemiluminescence and radionuclide labeling. In blots, as little as 0.1 pg of a target IgG has been detected using a Nanogold®-Fab' probe. Nanogold®-Streptavidin has proved to be highly sensitive in detecting biotinylated nucleic acid probes in in situ hybridization studies.

At Nanoprobes, our research is focused on ways to improve this process even further, such as larger clusters which are easier to visualize, and novel arrays of clusters which will be used for even more sensitive detection. We have already introduced the unique, patented FluoroNanogold probe, in which a Nanogold® particle and a fluorescein moiety are attached to a single antibody fragment: this probe may be used to followthe same process by both fluorescent microscopy in whole cells, and electron microscopy at the macromolecular level.