The chirality of biomolecules is a good indicator of their structure and function. Fluorescence-detected circular dichroism remains a primary detection scheme for chirality due to its sensitivity. However, since most biomolecules have a low dissymmetry factor in the visible range (~10<sup>3</sup>), single-molecule detection of chirality is challenging even for fluorescent molecules. To achieve single-molecule fluorescence-detected circular dichroism, we are leveraging plasmonic nanoparticle substrates, which focus incident plane waves into locally varying near fields, to enhance the dissymmetry factor. By varying the substrate design and the incident polarization of the plane wave, we are optimizing the electric field density and optical chirality to enhance the differential fluorescence intensity of proximal chiral biomolecules. In this talk, I will discuss the design of gold nanoparticle substrates and use full-field simulations to determine the electromagnetic near field produced by varying the incident polarization at the substrate. Because the electromagnetic landscape varies on the nanometer scale, the differential signal will be most enhanced within sub-diffraction-limited areas on the sample. We use single-molecule super-resolution microscopy to experimentally access these hotspots. I will present the chiroptical interactions of single pairs of cyanine dyes (aligned into J-aggregates by a double-stranded backbone to form right-handed fluorescent biomolecules) with chiral and achiral gold nanoparticles.

Measuring the chiroptical response of single molecules in the near field of plasmonic nanoparticles

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.