Which dye is most likely used in a fluorescence-based approach to detect amyloid?

• A. Thioflavin T
• B. DAPI
• C. Eosin
• D. Crystal Violet

Answer: (A)

Amyloid detection with fluorescence relies on dyes that become highly fluorescent when bound to the cross–beta sheet structure of amyloid fibrils. Thioflavin T fits this role because it has little fluorescence in solution, but upon binding to amyloid, it lights up strongly, giving a bright signal under blue light excitation (roughly 440–450 nm) with green emission (around 480–530 nm). This property makes it a sensitive tool for visualizing amyloid deposits in tissue sections or in vitro assays.

DAPI binds DNA and emits blue fluorescence, so it’s used for nuclei rather than amyloid. Eosin is a routine brightfield dye and does not provide a specific fluorescence signal for amyloid. Crystal violet is used for Gram staining and lacks amyloid-specific fluorescence. Thus, Thioflavin T is the best choice for a fluorescence-based approach to detect amyloid.