Thioflavine S is widely used in biological and medical research as a fluorescent dye for staining amyloid plaques in tissues. It is particularly valuable in studying neurodegenerative diseases like Alzheimer's, where it helps visualize and quantify amyloid deposits in brain samples. The dye binds selectively to beta-sheet structures in amyloid fibrils, making it a critical tool for histopathology and diagnostic applications. Additionally, Thioflavine S is employed in microbiology to study biofilms and bacterial aggregates due to its ability to stain extracellular polymeric substances. Its fluorescence properties also make it useful in various imaging techniques to monitor protein aggregation and fibril formation in vitro.