Immunocytochemistry is one of the most important microscopic tools available today to localize proteins within tissues and cells with antibodies. At the light microscopic level, this technique has labeled specific cells containing a protein of interest. Using a combination of confocal microscopy and fluorescent labels, proteins have been localized to areas of cells, and sometimes to specific organelles. In the past, at the electron microscopic level, the enzyme horseradish peroxidase attached to antibodies has been used to generate a diffuse reaction product which can be poorly localized. The highest resolution is only obtained by use of small gold particles attached to antibodies and applied to cells in pre-embedding immunocytochemistry. To visualize these gold particles silver enhancement is needed. The basic mechanism is the use of a photographic developer which deposits silver around the small gold particle. The small gold particle acts much like a latent image in a silver halide crystal found in film.
These TEM images show the use of silver enhanced Nanogold to localize a synaptic vesicle protein in the brain. In the low magnification micrograph on the left, the clusters of silver enhanced particles are covering presynaptic terminals that contain synaptic vesicles. The higher magnification micrograph on the right shows a lower density of these particles labeling synaptic vesicles.