A fluorescent affinity probe for amyloid-β with ex./em. spectra of 498/578 nm, respectively; binds to Aβ40 monomers and aggregates, as well as Aβ42 monomers, dimers, and oligomers (Kds = 68.8, 52.4, 159.7, 162.9, and 85.7 nM, respectively); fluorescence decreases when bound; labels amyloid plaques and cerebral amyloid angiopathy both in APP/PS1 mouse brain sections and in live mice following i.v. administration; inhibits copper-induced and naturally occurring Aβ crosslinking ,