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Updated: Jun 21, 2026
Polarization-Sensitive Two-Photon Microscopy for a Label-Free Amyloid Structural Characterization
Published on: September 8, 2023
Near-field scanning optical microscopy measurements of fluorescent molecular probes binding to insulin amyloid
Catherine C Kitts1, David A Vanden Bout
1Department of Chemistry and Biochemistry, Center for Nano and Molecular Science and Technology, and Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712, USA. c.kitts@bo.ismn.cnr.it
Abstract:
The binding of two amyloid fibril stain dyes, thioflavin T (ThT) and its neutral analog 2-[4'-(dimethylamino)phenyl]-benzothiazole (BTA-2), are measured using near-field scanning optical microscopy (NSOM), which is able to image individual amyloid fibrils. Polarized NSOM images reveal that both dyes bind to the fibrils with the long axis of the molecule aligned parallel to the long axis of the fibrils. This indicates that the dyes bind along the surface of the beta-sheet within the grooves of the fibril that run parallel to the fibril axis. The similarity in the binding motifs of the two dyes shows that electrostatic interaction of the charged amine group on the ThT dye plays a minimal role in the affinity of the dyes for the amyloids. The polarized NSOM images confirm that the enhanced fluorescence of the ThT and BTA-2 result from binding of the monomeric dye rather than micelles or excimer species.
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