Chiral carbon quantum dots as fluorescent probe for rapid chiral recognition of isoleucine enantiomers

Chiral recognition is always a significant and challenging work in analytical chemistry. A fluorescent chiral recognition method based on chiral carbon quantum dots (CCQDs) towards isoleucine (Ile) enantiomers was developed in this work. CCQDs were synthesized by one-step hydrothermal method using l-cysteine as chiral source. The fluorescence intensity of CCQDs enhanced obviously in the presence of L-Ile, but had no observable change in the presence of D-Ile. The response speed of this chiral sensing system is fast, Ile enantiomers can be discriminated by CCQDs within 5 min, the enantioselectivity (I_L/I_D) can reach up to 2.2. Good linearity for detecting L-Ile was obtained over the concentration range from 0 to 30 mM with a LOD of 0.29 mM. The fluorescence intensity also increased linearly with the enantiomeric percentages of L-Ile in the mixture of Ile enantiomers. Thus, the developed method not only can achieve quantitative detection of L-Ile but also can determine the enantiomeric percentage in racemates. The chiral recognition mechanism can be explained by the difference in binding energy and interaction types between D-Ile and L-Ile with CCQDs by molecular modeling. The current method was applied in detecting L-Ile in real samples of functional drinks, the detection results were in consistent with the results obtained from high performance liquid chromatography, and the recoveries of standard addition were also satisfactory, which verified the reliability of the developed method.