This
work describes the use of fluorescence correlation spectroscopy
(FCS) and a novel amyloid-binding fluorescent probe, ARCAM <b>1</b>, to monitor the aggregation of the Alzheimer’s disease-associated
amyloid β-peptide (Aβ). ARCAM <b>1</b> exhibits
a large increase in fluorescence emission upon binding to Aβ
assemblies, making it an excellent candidate for probe enhancement
FCS (PE-FCS). ARCAM <b>1</b> binding does not change Aβ
aggregation kinetics. It also exhibits greater dynamic range as a
probe in reporting aggregate size by FCS in Aβ, when compared
to thioflavin T (ThT) or an Aβ peptide modified with a fluorophore.
Using fluorescent burst analysis (via PE-FCS) to follow aggregation
of Aβ, we detected soluble aggregates at significantly earlier
time points compared to typical bulk fluorescence measurements. Autocorrelation
analysis revealed the size of these early Aβ assemblies. These
results indicate that PE-FCS/ARCAM <b>1</b> based assays can
detect and provide size characterization of small Aβ aggregation
intermediates during the assembly process, which could enable monitoring
and study of such aggregates that transiently accumulate in biofluids
of patients with Alzheimer’s and other neurodegenerative diseases
