Surface-enhanced Raman spectroscopy for detection of toxic amyloid β oligomers adsorbed on self-assembled monolayers

Surface-enhanced Raman spectroscopy (SERS) was used to detect different spectral features of small (1–2 nm) and large (5–10 nm) synthetic amyloid Aβ-42 oligomers, exhibiting high and no detectable neurotoxicities, respectively. Adsorption of peptides at self-assembled monolayers (SAM) terminated by methyl and pyridinium groups was employed to differentiate toxic and non-toxic oligomers. Three SAMs were analyzed: hydrophobic heptanethiol (HT) and octadecanethiol (ODT) as well as positively charged N-(6-mercapto)hexylpyridinium (MHP) chloride. SERS study revealed twofold adsorption effect, changes in the monolayer structure and appearance of new bands associated with the adsorbed peptides. A band at 1387 cm−1, observed as a result of the SAM and Aβ-42 interaction, is tentatively assigned to the peptide symmetric stretching vibration of carboxylate groups, and appears to be the most prominent spectral feature distinguishing toxic oligomers from the non-toxic Aβ-42 forms. This band was identified in the spectra of Aβ-42 adsorption on heptanethiol and MHP monolayers, while no clear perturbations were observed in the case of ODT monolayer.

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► Detection of toxic β amyloid oligomers by SERS.
► Adsorption of oligomers on SAMs was used to discriminate the toxic and non-toxic species.
► 1387-cm−1 band in the difference SERS spectrum is characteristic of toxic oligomers.