Spectral Manifestations of Thioflavin T Aggregation

Abstract

Absorption, fl uorescence, and fl uorescence excitation spectra of thiofl avin T in aqueous solutions and polyvinyl alcohol fi lms were studied. The dye aggregated when its concentration was increased. This was accompanied by a hypsochromic shift of the absorption spectrum and a bathochromic shift of the fl uorescence spectrum. It was shown that fl uorescence of the probe embedded in amyloid fi brils was caused by monomers rather than dimers or other aggregates.Introduction. Thiofl avin T (ThT) has recently been the subject of numerous investigations. This is due to the fact that it is used as a fl uorescent probe to study and detect amyloid fi brils [1-4], the formation of which parallels the development of several neurodegenerative diseases (Alzheimer′s, Parkinson′s, etc.). It is thought that ThT binds specifi cally to amyloid fi brils, after which its emission intensity increases by greater than three orders of magnitude [5]. Non-aggregated proteins in the solution typically have practically no effect on the probe fl uorescence [6].The fl uorescence properties of ThT, primarily the quantum yield, are known to be determined by the solvent rigidity or viscosity, which infl uence the ability and rate of torsional relaxation of the molecular fragments [7-9]. We proposed based on experimental data and quantum-chemical calculations that ThT is a so-called molecular rotor [10,11], for which the fl uorescence characteristics were observed to depend strongly on the solvent viscosity. Therefore, it was concluded that the reason for the signifi cant amplifi cation of the fl uorescence of aqueous solutions of ThT in the presence of fi brils was incorporation into a rigid micro-environment [5,12,13].Mechanisms of the incorporation of the probe into fi brils, the stoichiometry of the ThT-fi bril complex, and the issue of the specifi city of its interaction are still being discussed. The hypothesis of Krebs et al. seems to be the most convincing [14]. They noticed that side chains of amino acids within β-sheets of amyloid fi brils formed elongated strands along the fi bril axis, between which were elongated channels. According to their model [14], probe molecules were embedded in these channels so that its long axis was situated along the fi brils. ThT embedded in the channel was in close contact with amino-acid side chains of the β-sheets. This limited the rotational motion of the molecular fragments relative to each other. This caused the fl uorescence quantum yield to increase signifi cantly after its incorporation into the amyloid fi brils.It was hypothesized in several studies that ThT was incorporated into voids in the amyloid fi brils as dimers or excimers [15][16][17] or even micelles [18,19] so that the strong ThT fl uorescence with a maximum at 480-490 nm was emission from probe aggregates. According to the researchers, ThT aggregation caused a signifi cant bathochromic shift of the absorption spectrum (from 412 to ~445 nm) and a hypsochromic shift of the fl uorescence spectrum (from ~493 to 480 nm).The present wor...

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

“…Previous studies demonstrated that ThT SERS and fluorescence signals are very sensitive to the physicochemical properties of the surrounding medium. [19,21] 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. More dye molecules on the plasmonic surface should be influenced by this signal blockage as the peptide concentration increases.…”

“…[18] The molecule also demonstrates specific Raman peaks when covalently attached to plasmonic metal nanoparticles. [19,21] 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 moleculeoriginated SERS signal. [38] Figure 3 illustrates the ThT modification on flat versus nanopillared surfaces after they have been coated with different thicknesses of Au.…”

“…[17,18] Moreover, the molecule can covalently attach to metal surfaces that allow the formation of intensified characteristic ThT SERS signals. [19][20][21] We have recently reported the nonlithographic fabrication of periodic polymer nanopillar arrays with potential applications from SERS-based sensing to antireflective coatings. [22][23][24] Nanoporous anodized alumina molds (AAMs) [25,26] were used in simple polymer processing setups like drop casting or melt infiltration to prepare large area films composed of arrays of nanostructures.…”

Self‐Assembly of Azobenzene Derivatives into Organogels and Photoresponsive Liquid Crystals

“…The 1 HNMR spectra of Azo-2 and Azo-3 at 25 and 80 8C, corresponding to the signals from gel and sol samples,r espectively,a re shown in Figure 3 and Figure S4 (in the Supporting Information). [41] To clarify the differences in molecular packing and ordering of the two gelators, wide-angle (WA)XRD analyses of the xerogel samples were performed and the results are shown in Figure S6 (in the Supporting Information). The NÀHs ignal was detected to change from 8.19 ppm at 25 8Ct o 8.00 ppm at 80 8Cf or Azo-2.As imilar change was observed for Azo-3.T his upfields hift supported the formation of intermolecular NÀH···O=Chydrogen bonding in the gel state.…”

Dissimilar Associates of Dyes in Aqueous Solutions: Experimental Study and Computer Simulation

“…The formation of dimers and more associated structures (self-associates) is recorded at concentrations of 5·10 -5 mol/L and higher [5][6][7][8][9][10][11]. DNA biochemistry [12][13][14][15][16][17][18][19][20]. For this reason, the study of regularities of cation-anionic dye association is relevant, as well as determination of the influence of several factors (first of all, the structure and charge of the ions) on the stability of associates.…”