Nanoscale Chemical\nImaging of Amyloid Fibrils in Water\nUsing Total-Internal-Reflection Tip-Enhanced Raman Spectroscopy

Total-internal-reflection tip-enhanced Raman spectroscopy\n(TIR-TERS)\nimaging of amyloid-β (Aβ<sub>1–42</sub>-L34T) fibrils\nis performed with nanoscale spatial resolution in water, using TERS\ntips fabricated by bipolar electrodeposition. Ideal experimental parameters\nare corroborated by both theoretical simulations and TIR-TERS measurements.\nTIR-TERS imaging reveals the predominant parallel β-sheet secondary\nstructure of Aβ<sub>1–42</sub>-L34T fibrils as well as\nthe nanoscale spatial distribution of tyrosine, histidine, and phenylalanine\naromatic amino acids. Their proportion in TERS spectra can be qualitatively\nexplained by the combined effect of their localization in the Aβ<sub>1–42</sub>-L34T fibril structure and their molecular orientation\nwith respect to the excitation laser light polarization. Conclusions\ndrawn from the TERS experiments in water corroborate and significantly\nenrich our previous study in ambient air, thus confirming that hydration\nhas only a marginal impact on the structure of such amyloid fibrils.\nThis first TIR-TERS study in liquid opens fascinating perspectives\nfor future applications in biology.