Sum frequency generation spectroscopy of amyloid fibrils and oligomers at air/water interface

Structure of beta-amyloid oligomers and fibrils at air/water interface was studied by sum frequency generation (SFG) spectroscopy. It was found that both small (1-3 nm) and large (4-10 nm) oligomers as well as fibrils adsorb in ordered fashion at air/water interface. Intense resonances from methyl group stretching vibrations at 2875 and 2937 cm -1 and "ice-like" structured water bands were characteristic for adsorbed fibrils. Similar spectral pattern was observed for large oligomers. However, small oligomers exhibited intense SFG resonance near 2912 cm -1 due to methylene or methine C-H stretching vibration. No "ice-like" water band was observed in this case. The possibility of discrimination between the small (toxic) oligomers, large (non-toxic) oligomers and fibrils was demonstrated.