Ultraviolet optical horn antennas for label-free detection of single proteins

TL;DR

This paper introduces UV optical horn antennas that enable label-free detection of single proteins by enhancing autofluorescence, allowing real-time study of proteins without labels.

Contribution

The study presents a novel nanophotonic platform using optical horn antennas for sensitive, label-free single-protein detection in the ultraviolet spectrum.

Findings

Successful detection of UV autofluorescence from single proteins

Monitoring of protein unfolding and dissociation in real time

Enhanced fluorescence collection efficiency up to 85 degrees

Abstract

Single-molecule fluorescence techniques have revolutionized our ability to study proteins. However, the presence of a fluorescent label can alter the protein structure and/or modify its reaction with other species. To avoid the need for a fluorescent label, the intrinsic autofluorescence of proteins in the ultraviolet offers the benefits of fluorescence techniques without introducing the labelling drawbacks. Unfortunately, the low autofluorescence brightness of proteins has greatly challenged single molecule detection so far. Here we introduce optical horn antennas, a dedicated nanophotonic platform enabling the label-free detection of single proteins in the UV. This design combines fluorescence plasmonic enhancement, efficient collection up to 85{\textdegree} angle and background screening. We detect the UV autofluorescence from immobilized and diffusing single proteins, and monitor protein unfolding and dissociation upon denaturation. Optical horn antennas open up a unique and promising form of fluorescence spectroscopy to investigate single proteins in their native states in real time.