Ultraviolet Nanophotonics Enables Autofluorescence Correlation Spectroscopy on Label-Free Proteins With a Single Tryptophan

TL;DR

This paper demonstrates a significant sensitivity enhancement in ultraviolet fluorescence correlation spectroscopy, enabling detection of single-tryptophan proteins using nanophotonics and background reduction techniques.

Contribution

The study introduces a novel combination of nanophotonic antennas and background suppression to achieve single-tryptophan UV-FCS detection, expanding its applicability.

Findings

Signal-to-background ratio improved by over tenfold

Enabled UV-FCS on proteins with a single tryptophan

Broadens the range of label-free proteins for analysis

Abstract

Using the ultraviolet autofluorescence of tryptophan aminoacids offers fascinating perspectives to study single proteins without the drawbacks of fluorescence labelling. However, the low autofluorescence signals have so far limited the UV detection to large proteins containing several tens of tryptophan residues. This limit is not compatible with the vast majority of proteins which contain only a few tryptophans. Here we push the sensitivity of label-free ultraviolet fluorescence correlation spectroscopy (UV-FCS) down to the single tryptophan level. Our results show how the combination of nanophotonic plasmonic antennas, antioxidants and background reduction techniques can improve the signal-to-background ratio by over an order of magnitude and enable UV-FCS on thermonuclease proteins with a single tryptophan residue. This sensitivity breakthrough unlocks the applicability of UV-FCS technique to a broad library of label-free proteins.