BTA-1 is a probe for β-amyloid aggregates; fluorescent thioflavin-T derivative; exhibits high affinity for amyloid deposits; displays 50-fold higher affinity than thioflavin-T; selectively stains cerebral plaques and cerebrovascular amyloid deposits in the brains of PS1/APP transgenic mice, as well as Aβ fibrils in postmortem brain tissue obtained from AD patients; crosses the blood brain barrier.