Analysis of insulin amyloid fibrils by Raman spectroscopy

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 H2O or D2O 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).