Gallocyanine is primarily used as a biological stain in histology and cytology. It is particularly effective in staining nucleic acids, such as DNA and RNA, in tissue samples, making it a valuable tool for microscopic examination. The dye binds selectively to these molecules, allowing researchers to visualize and study cellular structures and genetic material with greater clarity. Additionally, gallocyanine has been employed in the study of neurodegenerative diseases, where it helps in identifying and analyzing changes in neuronal tissues. Its application extends to the field of photodynamic therapy, where it is explored for its potential to induce cell death in targeted cancer cells when activated by light. Overall, gallocyanine plays a significant role in advancing research in biology, medicine, and related fields.