K114, a fluorescent Congo Red analogue, binds tightly to amyloid fibrils with an EC50 of 20-30 nM[1]. K114 is an efficient detector of semen-derived enhancer of virus infection (SEVI)[2].
K114's unusually low buffer fluorescence is due to self-quenching in sedimentable aggregates or micelles which upon interacting with amyloid fibrils undergo an enhancement in fluorescence intensity and shifts in the excitation and emission spectra[1].
References:
[1]. LeVine H 3rd, et al. Mechanism of A beta(1-40) fibril-induced fluorescence of (trans,trans)-1-bromo-2,5-bis(4-hydroxystyryl)benzene (K114). Biochemistry. 2005 Dec 6;44(48):15937-43.
[2]. Selmani V, et al. K114 (trans, trans)-bromo-2,5-bis(4-hydroxystyryl)benzene is an efficient detector of cationic amyloid fibrils. Protein Sci. 2015 Mar;24(3):420-5.