Spatially-resolved Fluorescence-detected Two-dimensional Electronic Spectroscopy Probes Varying Electronic Couplings in Photosynthetic Bacteria

TL;DR

This paper introduces a fluorescence-detected 2D electronic spectroscopy technique with high spatial resolution and sensitivity, enabling mapping of electronic coupling variations in photosynthetic bacteria at sub-micron scales.

Contribution

A novel microscopy-based 2D electronic spectroscopy method that combines femtosecond resolution, sub-micron spatial resolution, and fluorescence detection sensitivity.

Findings

Detected spatial variations in electronic couplings in bacterial colonies.

Resolved electronic structure differences related to growth conditions.

Demonstrated high sensitivity and spatial resolution in complex biological samples.

Abstract

We present a variation of two-dimensional electronic spectroscopy that is capable of mapping spatially-varying differences in electronic couplings using a correlated map of excitation and detection frequencies, with sensitivity orders of magnitude better than conventional spatially-averaged electronic spectroscopies. The approach performs fluorescence-detection-based fully collinear two-dimensional electronic spectroscopy in a microscope, combining femtosecond time-resolution, sub-micron spatial resolution, and the sensitivity of fluorescence detection. We demonstrate the approach on a mixture of photosynthetic bacteria that are known to exhibit variations in electronic structure with growth conditions. Spatial variations in the constitution of mixed bacterial colonies manifests as spatially-varying peak intensities in the measured two-dimensional contour maps, which exhibit well-resolved electronic couplings between excited electronic states of the bacterial proteins.