Thioflavin T, when used with Congo red staining, is primarily used to assess amyloid by what modality?

• A. Fluorescence
• B. Colorimetric change
• C. Electron density
• D. Osmotic staining

Answer: (A)

Thioflavin T functions as a fluorescent dye. When it binds to amyloid fibrils, its molecular structure becomes restricted and its fluorescence increases strongly under blue-light excitation, emitting light around the blue-green range. This fluorescence provides a sensitive readout for amyloid deposits, especially when used alongside Congo red staining, which shows apple-green birefringence under polarized light. The readout here is fluorescence, not a color change, electron density, or osmotic staining, making fluorescence the primary modality for detecting amyloid with Thioflavin T.