Deguo Du

The process of amyloid-β (Aβ) amyloid formation is pathologically linked to Alzheimer’s disease
(AD). The identification of Aβ amyloids and intermediates that are crucial players in the
pathology of AD is critical for exploring the underlying mechanism of Aβ aggregation and the
diagnosis of the disease. Herein, we performed a gold nanoparticle (AuNP)-based study to detect
the formation of Aβ amyloid fibrils and oligomers. Our results demonstrate that the intensity of
the surface plasmon resonance (SPR) absorption band of the AuNPs is sensitive to the quantity of
Aβ40 amyloids. This allows the SPR assay to be used for detection and semi-quantification of
Aβ40 amyloids, and characterization of the kinetics of Aβ amyloid formation. Furthermore, our
study demonstrates that the SPR band intensity of the AuNPs is sensitive to the presence of
oligomers of both Aβ40 and an Aβ40 mutant, which forms more stable oligomers. The kinetics of
the stable oligomer formation of the Aβ40 mutant can also be monitored following the SPR band
intensity change of AuNPs. Our results indicate that this nanoparticle based method can be used
for mechanistic studies of early protein self-assembly and fibrillogenesis.

The process of amyloid-β (Aβ) fibril formation is genetically and pathologically linked to
Alzheimer's disease (AD). Thus, a selective and sensitive method for the quantification of Aβ
amyloid fibrils in complex biological samples enables a variety of hypotheses to be tested. Herein
we report the basis for a quantitative in vitro kinetic aggregation assay that detects seeding competent
Aβ aggregates in mammalian cell culture media, in Caenorhabditis elegans lysate and
in mouse brain homogenate. Sonicated, proteinase K treated Aβ-fibril-containing tissue
homogenates or cell culture media were added to an initially monomeric Aβ1–40 reporter peptide
to seed an in vitro nucleated aggregation reaction. The reduction in the half time (t50) of the
amyloid growth phase is proportional to the quantity of seeding-competent Aβ aggregates present
in the biological sample. An ion exchange resin amyloid isolation strategy from complex
biological samples is demonstrated as an alternative to improve the sensitivity and linearity of the
kinetic aggregation assay.