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

Abstract

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.

Chirality‐Based Biosensors

“…Due to sophisticated optically active NPs construction methodology, various NPs chiral assemblies have been developed in recent years. Individual optically active NPs modified with a chiral ligand are one type of building block for assemblies that can be used for the detection of l ‐ or d ‐enantiomers . Other individual nanomaterials that can be used for chiral enantiomer detection were reported for Au NRs.…”

“…Intrinsic chiral Au NRs or chiral ligand‐modified NPs have been reported for the discrimination of chiral amino acids . This important feature was based on the chirality of either chiral ligand‐modified NPs (Au NPs or QDs) or intrinsic chiral nanomaterials that could be used for chiral recognition . The chiral ligand‐modified NPs used for chiral recognition were adapted to introduce enantiomeric bio‐interaction systems for modulating the morphology of cell growth …”

“…To distinguish nanomolar levels of enantiomers from the nearly identical chemical and physical properties of isomers is very challenging . The ability to recognize and sensitively quantify enantiomers in biological systems constitutes the basis of many critical issues in drug development and metabolite probing .…”

Chiral Ag and Au Nanomaterials Based Optical Approaches for Analytical Applications

“…Because the aptamer has a higher affinity toward the l ‐form than the d ‐form of arginine, the assay allows recognition of the enantiomers, with linear relationships of the fluorescence intensity against the d ‐ and l ‐arginine over the concentrations ranges of 0–300 and 0–400 n m , respectively. Using Au nanorods and Cys enantiomer modified CdTe@CdS quantum dots, a fluorescence sensing approach was employed for the detection of d ‐Cys and l ‐Cys . In the presence of l ‐Cys, the interaction of the l ‐Cys modified CdTe@CdS quantum dots with the Au nanorods increases through the zwitterionic interactions, leading to decreases in the fluorescence of the quantum dots as a result of fluorescence resonance energy transfer.…”

“…Using Au nanorods and Cys enantiomer modified CdTe@CdS quantum dots, a fluorescence sensing approach was employed for the detection of d-Cys and l-Cys. [68] In the presence of l-Cys, the interaction of the l-Cys modified CdTe@CdS quantum dots with the Au nanorods increases through the zwitterionic interactions, leading to decreases in the fluorescence of the quantum dots as a result of fluorescence resonance energy transfer. The assay provides an LOD of 0.8 nm for l-Cys.…”