This product is a revolutionary new immunocytochemical reagent. This unique antibody probe contains a molecular label which contains both the 1.4nm ultra-small gold particle and fluorescein, enabling both fluorescence and electron microscope observation of a sample stained in a single labelling procedure. This probe is smaller than a whole IgG molecule, does not aggregate, and fluorescence quenching due to the goold particle is negligible. Normal methologies may be used successfully with this product. Due to some quenching of fluorescence by the gold particle, slightly higher concentrations of antibody are recommended for incubations. A blocking agent of 5% non-fat dried milk has been found to reduce background in some cases: this should be used before incubation with probe (in standard wash/blocking steps), and additionally, the Fluorescein-ultra-small gold probe should be diluted in a solution also containing 5% non-fat dried milk before it is applied.