Analysis of insulin amyloid fibrils by Raman spectroscopy

Abstract The formation of amyloid fibrils from insulin is investigated using drop-coating-deposition-Raman (DCDR) difference spectroscopy and atomic force microscopy (AFM). Fibrils formed using various co-solvents and heating cycles are found to induce the appearance of Raman difference peaks in the amide I (∼ 1675 cm − 1 ), amide III (∼ 1220 cm − 1 ), and peptide backbone (∼ 1010 cm − 1 ), consistent with an increase in β-sheet content. Comparisons of results obtained from fibrils in either H 2 O or D 2 O suggest that the NH/ND stretch bands (at ∼ 3300 cm − 1 /∼ 2400 cm − 1 ) are also enhanced in intensity upon fibril formation. If there is any water trapped in the core of the fibrils its OH/OD Raman intensity is too small to be detected in the presence of the stronger NH/ND bands which appear in the same region. AFM is used to confirm the formation of fibrils of about 5 nm diameter (and various lengths).