Thioflavin T (Basic Yellow 1, Methylene yellow, CI 49005, or ThT) is a
benzothiazole salt obtained by the methylation of
dehydrothiotoluidine with
methanol in the presence of
hydrochloric acid. The dye is widely used to visualize and quantify the presence of misfolded
protein aggregates called
amyloid, both
in vitro and
in vivo (e.g.,
plaques composed of
amyloid beta found in the brains of
Alzheimer's disease patients). Additional studies also consider
fluorescence changes as result of the interaction with double stranded DNA. This change in fluorescent behavior can be caused by many factors that affect the
excited state charge distribution of thioflavin T, including binding to a rigid, highly-ordered nanopocket, and specific chemical interactions between thioflavin T and the nanopocket. Prior to binding to an amyloid fibril, thioflavin T emits weakly around 427 nm. Quenching effects of the nearby excitation peak at 450 nm is suspected to play a role in minimizing emissions. When excited at 450 nm, thioflavin T produces a strong fluorescence signal at approximately 482 nm upon binding to amyloids. Thioflavin T molecule consists of a phenylamine and a benzothiazole ring connected through a carbon-carbon bond. These two rings can rotate freely when the molecule is in solution. The free rotation of these rings results in quenching of any excited state generated by photon excitation. However, when thioflavin T binds to amyloid fibrils, the two rotational planes of the two rings become immobilized and therefore, this molecule can maintain its excited state. undergo a spectroscopic change upon binding to precursor monomers, small oligomers, unaggregated material with a high
beta sheet content, or even
alpha helix-rich proteins. Conversely, some amyloid fibers do not affect thioflavin T fluorescence, raising the prospect of
false negative results. In adult
C. elegans, exposure to thioflavin T results "in a profoundly extended lifespan and slowed aging" at some levels, but decreased lifespan at higher levels. ==Thioflavin S==