Thioflavin T

Thioflavin T is a cell-permeable, blue fluorescent stain that labels amyloid fibrils.

Thioflavin T (ThT), also called Basic Yellow 1 or CI 49005, is a benzothiazole salt. It is part of a family of dyes known as thioflavins, which also includes Thioflavin S. These fluorophores have found extensive use in studying protein aggregation, specifically amyloid beta in Alzheimer’s disease. 

When bound to beta sheet rich regions of proteins, such as those in amyloid oligomers, Thioflavin T undergoes a redshift in excitation and emission, producing an enhanced blue fluorescence signal. This binding does not appear to interfere with aggregation of endogenous beta-amyloid peptides into amyloid fibrils. 

Excitation and emission

Thioflavin T is a fluorescent compound which, as a free dye, has an excitation peak at 385 nm and an emission peak at 445 nm. Once bound to proteins, the excitation peak shifts to 450 nm and the emission peak shifts to 482 nm.

Mechanism and principle

Thioflavin T contains a benzylamine and a benzothiazole ring that, in solution, can freely rotate along a carbon-carbon bond. This rotation is thought to quench the fluorescence of the dye. When bound to beta-sheet rich regions of proteins, this rotation is inhibited, thereby allowing excitation and subsequence emission.