DNA-Origami-Assembled Rhodium Nanoantennas for Deep-UV Label-Free Single-Protein Detection

Plasmonic metal nanoparticles have deeply impacted the spectroscopy field by enabling nanoscale concentration of light and powerful signal enhancement. However, their operation remains largely confined to the visible and near-infrared spectral ranges due to the poor stability and limited surface functionalization strategies of UV-active materials. Here, we establish a complete route for the fabrication of programmable UV-plasmonic nanoantennas based on rhodium nanocube dimers assembled on DNA origami scaffolds. We report on an effective surface ligand exchange protocol for functionalizing rhodium nanocubes with DNA strands enabling their assemble into dimers with a yield of 69%, and an interparticle distance of 10 nm. Thanks to the DNA origami, a single streptavidin protein is accurately positioned into the plasmonic nanogap, contrasting to other works relying only on random diffusion. In good agreement with numerical simulations, UV autofluorescence measurements on a single streptavidin indicate up to 22× brightness enhancement factor with the average value of 6.6×, shorter autofluorescence lifetimes, and over 10× increase of the total photon budget. By pioneering a robust, versatile and selective strategy for constructing UV-resonant plasmonic nanoantennas, this work broadens the applications of plasmonics into the deep UV range and opens new opportunities for label-free spectroscopy of single proteins.