Nonexclusive Fluorescent Sensing for l/d Enantiomers Enabled by Dynamic Nanoparticle-Nanorod Assemblies

Fluorescence sensing of enantiomers is a much needed yet very challenging task due to nearly identical chemical and physical properties of the chiral isomers also known as chiral equivalence. In this study, we propose a novel strategy for fluorescence sensing of enantiomers using chiral nanoparticles and their ability to form dynamic assemblies. Fluorescence resonance energy transfer (FRET) in nanoscale assemblies consisting of either l-cysteine- or d-cysteine-modified quantum dots (QDs) and gold nanorods (GNRs) was found to be strongly dependent on traces of cysteine. This occurs due to high sensitivity of dynamic assemblies to the weak internanoparticle interactions that can exponentially increase energy transfer efficiencies from QDs to GNRs. Comprehensive analysis of the fluorescence responses in the two types of chiral nanoscale assemblies enables accurate determination of both concentration and enantiomeric composition of the analyte, i.e., cysteine. The described method can quantify the composition of a chiral sample, even the content of one enantiomer is as low as 10% in the mixture. Exceptional selectivity in respect to d/l-cysteine in comparison to analogous small molecules was observed. Versatility of nanoparticle-nanorod assemblies and tunability of intermolecular interactions in them open the road to adaptation of this sensing platform to other chiral analytes.