Adsorption and Detection of Amyloid Marker Thioflavin T on Ag Nanoparticles by Surface-Enhanced Raman Scattering

The vibrational characterization of the dye most commonly used for detection of amyloid aggregates Thioflavin T (ThT) was carried out by means of Raman and surface-enhanced Raman scattering (SERS) at different excitation wavelengths. The vibrational spectra obtained experimentally were subsequently analyzed using DFT calculations at the B3LYP/6-31+G** level. The Raman spectrum of ThT in aqueous solution correlates very well with the calculated spectrum of ThT with the torsional angle between the benzothiazole (BT) and dimethylaminobenzene (DMB) moieties of 37 degrees. The SEAS technique was very useful for the detection of two structures of ThT molecules in the vicinity of the metal nanoparticles: (i) directly adsorbed onto the metal surface and (ii) molecules forming multilayers. The structure of ThT molecules in multilayers is similar to the structure of free ThT in aqueous solution. The molecules directly adsorbed on the metal surface actually correspond to the molecules with 90 torsional angle between the BT and DMB rings.