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

Abstract

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°. The SERS 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.

Fabrication of thioflavin‐T‐modified nanopillared SERS substrates for ultrasensitive beta‐amyloid peptide detection

“…Although signal loss can be seen for several signature peaks, the 1,601‐cm −1 peak showed the clearest gradual reduction with increasing peptide content (Figure b). Previous studies demonstrated that ThT SERS and fluorescence signals are very sensitive to the physicochemical properties of the surrounding medium . The underlying reason in the current case is suspected to be the hindrance exerted by the addition of intercalating beta‐rich peptide molecules around the dye, which can reduce the probability of several vibrational modes of the ThT molecule.…”

“…To demonstrate the use of MNS substrates for SERS‐based biosensing, ThT was chosen, as it is known to specifically intercalate within the beta sheets of Aβ(1–42)‐rich amyloid plaques . The molecule also demonstrates specific Raman peaks when covalently attached to plasmonic metal nanoparticles . The potential variation of ThT SERS intensities upon Aβ(1–42) interaction forms the basis of this biosensing platform, as similar complementary/specific interactions have been utilized to detect trace amounts of target biomolecules that causes alterations in the probe molecule‐originated SERS signal .…”

“…Figure illustrates the ThT modification on flat versus nanopillared surfaces after they have been coated with different thicknesses of Au. Characteristic ThT peaks at ~539; 743; 938; 1,134; 1,392; and 1,601 cm −1 were obtained in all nanostructured films, and corresponding vibrational mode assignments are provided in Table S1.…”

“…Figure a depicts the influence of ThT concentration on the SERS signal from Au@MNS surfaces, where a gradual reduction in many of the signature peaks is seen with decreasing ThT content. In the literature, the peak at 1,601 cm −1 that originates from the C–C stretching of the dimethylaminobenzene ring of ThT (Figure S2) has been used to follow the amount of chemisorbed ThT on plasmonic surfaces . Using this peak, sub‐picomolar level ThT modification can be clearly identified on the nanostructured substrates when compared with the essentially flat baseline obtained from ThT‐free control (S/N ~ 10 for 0.1 pM ThT).…”

“…Thioflavin‐T (ThT) is a widely used fluorescent molecule to diagnose the presence of senile plaques in AD, where a significant fluorescence enhancement of the dye occurs upon incorporating into the beta sheet‐rich structures of the amyloid fibrils . Moreover, the molecule can covalently attach to metal surfaces that allow the formation of intensified characteristic ThT SERS signals …”