Methylene Green zinc chloride double salt is widely used in biological staining and microscopy. It serves as a vital dye for visualizing cellular structures, particularly in histology and cytology studies. The compound is effective in staining nucleic acids, making it valuable for observing DNA and RNA in tissues and cells. Additionally, it is employed in redox indicator applications, where it helps monitor oxidation-reduction reactions in biochemical assays. Its use extends to photodynamic therapy research, where it acts as a photosensitizer to study light-induced cellular damage. In analytical chemistry, it is utilized as a reagent for detecting trace metals and studying electrochemical processes.