Ultraviolet Resonant Nanogap Antennas with Rhodium Nanocube Dimers for Enhancing Protein Intrinsic Autofluorescence

TL;DR

This paper demonstrates UV resonant nanogap antennas made from rhodium nanocubes that significantly enhance protein autofluorescence, enabling label-free detection at physiological concentrations with high stability and sensitivity.

Contribution

It introduces a new UV plasmonic nanoantenna design using rhodium nanocubes, expanding nanoantenna applications into the deep UV range for biological sensing.

Findings

Achieved up to 120-fold autofluorescence enhancement.

Enabled UV autofluorescence correlation spectroscopy at high protein concentrations.

Confirmed experimental results with numerical simulations.

Abstract

Plasmonic optical nanoantennas offer compelling solutions for enhancing light-matter interactions at the nanoscale. However, until now, their focus has been mainly limited to the visible and near-infrared regions, overlooking the immense potential of the ultraviolet (UV) range, where molecules exhibit their strongest absorption. Here, we present the realization of UV resonant nanogap antennas constructed from paired rhodium nanocubes. Rhodium emerges as a robust alternative to aluminum, offering enhanced stability in wet environments and ensuring reliable performance in the UV range. Our results showcase the nanoantenna ability to enhance the UV autofluorescence of label-free streptavidin and hemoglobin proteins. We achieve significant enhancements of the autofluorescence brightness per protein by up to 120-fold, and reach zeptoliter detection volumes enabling UV autofluorescence correlation spectroscopy (UV-FCS) at high concentrations of several tens of micromolar. We investigate the modulation of fluorescence photokinetic rates and report excellent agreement between experimental results and numerical simulations. This work expands the applicability of plasmonic nanoantennas into the deep UV range, unlocking the investigation of label-free proteins at physiological concentrations.