Dual emission chiral carbon dots as fluorescent probe for fast chiral recognition of tryptophan enantiomers

Abstract

Background

Chirality is an essential property of nature. Chiral recognition is of great significance to life sciences, pharmaceutical industry, food analysis, and so on. Chiral carbon dots (CCDs), as green nanomaterials, have great prospects in chiral sensing. However, CCDs with enantioselectivity for tryptophan (Trp) enantiomers are scarce. Moreover, most chiral sensing platforms depend on the difference of fluorescence intensity at the same emission wavelength to identify enantiomers, it is still a challenge to distinguish enantiomers by the positions of fluorescent emission peaks.

Results

Novel CCDs with specific chiral recognition ability for Trp enantiomers are synthesized using l-lysine and l-cysteine as precursors. The CCDs have two fluorescent emission peaks at 390 nm and 450 nm. Interestingly, the fluorescence intensity of CCDs at 390 nm enhances obviously on the addition of L-Trp, while it enhances slightly at 450 nm in the presence of D-Trp. This chiral sensing system not only can identify Trp enantiomers according to fluorescence intensity, but also achieves the distinguishment depending on emission wavelength. The enantioselectivity (I_L/I_D) reaches 4.5 when the concentration of Trp enantiomer is 1 mM. This chiral sensing platform not only can be used for quantitative analysis of D-Trp and L-Trp, but also can be used for determining the enantiomeric excess of racemates. The chiral recognition mechanism is investigated by molecular simulation. It is found that L-Trp has higher binding energy with CCDs.

Significance

This work presents a novel kind of CCDs with special chiral recognition performance for Trp enantiomers, and opens the door to identify chiral isomers according to wavelength difference, which has profound significance for the development of chiral sensing platforms, and may provide inspirations for the design of novel CCDs with excellent chiral recognition performance.