The effects of fluorescent labels on Aβ 42 aggregation detected by fluorescence correlation spectroscopy.

Fluorescence-based methods are promising for measuring amyloid beta (A beta) oligomers, given their capacity to analyse a sample at the single-molecule level. As the attachment of fluorescent labels may influence the biochemical properties of the A beta oligomers, the effects of fluorescent labels on A beta oligomers must be evaluated. In this paper, we compared the impacts of five different fluorescent dyes on the aggregation of A beta(42) oligomers using fluorescence correlation spectroscopy (FCS). We found that fluorescent labels of BODIPY (R) FL-C5 (BP), N-hydroxysuccinimide rhodamine B ester (RB) and rhodamine B isothiocyanate (RITC) increased the propensity of labelled A beta(42) oligomers to aggregate, whereas 6-(fluorescein-5-carboxamido) hexanoic acid succinimidyl ester (5-SFX) and fluorescein 5(6)-isothiocyanate (5(6)-FITC) decreased the propensity of labelled A beta(42) oligomers to aggregate. This difference originated from the different electric charges and hydrophobicity of the fluorescent dyes. These results provide valuable information for establishing different aggregation models for A beta(42) oligomers in vitro using FCS.