Single-Particle Photoluminescence Measures a Heterogeneous Distribution of Differential Circular Absorbance of Gold Nanoparticle Aggregates near Constricted Thioflavin T Molecules.

The chirality of biomacromolecules is critical for their function, but the optical signal of this chirality is small in the visible range. Plasmonic nanoparticles are antennas that can couple to this chiral signal. Here, we examine the molecular-scale mechanism behind the induced circular dichroism of gold nanorods (AuNRs) in solution with insulin fibrils and the fibril-intercalating dye thioflavin T (ThT) with polarization-resolved single-molecule fluorescence and single-particle photoluminescence (PL) imaging. We compared the PL upon excitation by left- and right-handed circularly polarized light to calculate the differential absorbance of AuNRs near insulin fibrils with and without ThT. Overall, our results indicate that AuNRs do not act as chiral absorbers near constricted ThT molecules. Instead, we hypothesize that fibrils promote AuNR aggregation, and this templating is mediated by subtle changes in the solution conditions; under the right conditions, only a few chiral aggregates with significantly higher circular dichroism signal contribute to a large net circular dichroism.