Nile Red and Nile Blue: Applications and Syntheses of Structural Analogues

Nile red and Nile blue are highly fluorescent and photostable organic dyes from the benzo[a]phenoxazine family. They have been used as histological stains for imaging lysosomes and lipids in vitro. The dyes' high quantum yields and solvent-dependent optical properties make them ideal scaffolds for the development of pH probes and local polarity indicators. Reviews of the literature in this area are scarce with only one review ever published in 2006. It has been 10 years since and the field has evolved. This review aims to expand upon topics covered by the previous reviewers and to report on recent advances in the literature. As authors, we hope to convey a sense of scope and to spark renewed interest in this useful niche of dye chemistry.