Amyloid-β1–42 (Aβ42) forms highly stable and insoluble fibrillar structures, representingthe principal components of the amyloid plaques present in the brain of Alzheimer’s disease (AD)patients. The involvement of Aβ42 in AD-associated neurodegeneration has also been demonstrated,in particular for smaller and soluble aggregates (oligomers). Based on these findings and on geneticevidence, Aβ42 aggregates are considered key players in the pathogenesis of AD and targets for noveltherapies. Different approaches are currently used to detect the various aggregation states of Aβpeptide, including spectrophotometric methods, imaging techniques, and immunoassays, but all ofthese have specific limitations. To overcome them, we have recently exploited the peculiar propertiesof surface plasmon resonance (SPR) to develop an immunoassay capable of selectively detectingmonomers and oligomers, discriminating them also from bigger fibrils in a mixture of differentaggregated species, without any manipulation of the solution. In the present study, we extendedthese previous studies, showing that the SPR-based immunoassay makes it possible to unveil thefibril fragmentation induced mechanically, a result difficult to be conveniently and reliably assessedwith other approaches. Moreover, we show that SPR-recognized fibril fragments are more toxic thanthe larger fibrillar structures, suggesting the relevance of the proposed SPR-based immunoassay