Nile Blue A is used to differentiate melanins and lipofuscins. It is also useful for staining fats and preparation of an amperometric glucose sensor. In Vitro: Nile blue A is a basic oxazine dye which is soluble in water and ethyl alcohol. Nile blue A is a satisfactory stain for PHB granules in bacteria and is in fact superior to Sudan black B for this purpose. Poly-p3-hydroxybutyrate granules exhibits a strong orange fluorescence when stained with Nile blue A. Nile blue A appears to stain many more PHB granules than Sudan black B does and is not as easily ished from the cell by decolorization procedures^[1]. Nile blue A is used as a stain for polyhydroxyalkanoic acid-accumulating microorganisms or to detect polyhydroxyalkanoic acids in microorganisms. Escherichia coli cells that do not accumulate detectable polyhydroxyalkanoic acids can be stained with Nile blue A and that this staining is sufficient for identifying these cells in fluorescence-activated cell sorting (FACS) experiments. Nile blue A staining does not affect either surface display of peptides or specific labeling of these peptides by a second fluorescence. Staining E. coli for flow cytometry using Nile blue A is an easy-to-handle and low-cost alternative to other fluorescent dyes or the intracellular expression of, for example, green fluorescent protein^[2]. Nile blue A is one of the most studied benzophenoxazine dyes, as a potent photosensitizer for photodynamic therapy. The dye when administered intravenously disperses throughout the body by circulating through blood and is taken up by most cells that emphasize its interaction with various biomolecule^[3].