VECTASHIELD Antifade Mounting Medium prevents rapid photobleaching of fluorescent proteins and dyes. It remains a semi-liquid on the slide. If desired, coverslips can be sealed around the perimeter with nail polish or a plastic sealant. Mounted slides should be stored in the dark at 4 degrees C. VECTASHIELD Mounting Medium is compatible with a wide array of fluorochromes, enzymatic substrates, and fluorescent proteins. The refractive index is 1.45. DAPI is a counterstain that binds to nuclei and causes them to fluoresce with a blue color. This is useful for Fluorescence In Situ Hybridization (FISH) assays and other techniques where a general orientation to the location of nuclei and cells is helpful.