Construction of a Chiral Fluorescent Probe for Tryptophan Enantiomers/Ascorbic Acid Identification

Chiral recognition of amino acid enantiomers is critical in enhancing drug efficacy, detecting disease markers, and understanding physiological processes. Enantioselective fluorescent identification has gained attention among researchers due to its nontoxicity, easy synthesis, and biocompatibility. In this work, chiral fluorescent carbon dots (CCDs) were produced through a hydrothermal reaction followed by chiral modification. The fluorescent probe, Fe³⁺-CCDs (F-CCDs), was constructed by complexing Fe³⁺ with CCDs to differentiate between the enantiomers of tryptophan (Trp) and determine ascorbic acid (AA) through an "on-off-on" response. It is worth noting that l-Trp can greatly enhance the fluorescence of F-CCDs with a blue shift, whereas d-Trp does not have any effect on the fluorescence of F-CCDs. F-CCDs showed a low limit of detection (LOD) for l-Trp and l-AA, with an LOD of 3.98 and 6.28 μM, respectively. The chiral recognition mechanism of tryptophan enantiomers using F-CCDs was proposed based on the interaction force between the enantiomers and F-CCDs, as confirmed by UV-vis absorption spectroscopy and density functional theory calculations. The determination of l-AA by F-CCDs was also confirmed through the binding of l-AA to Fe³⁺ to release CCDs, as seen in UV-vis absorption spectra and time-resolved fluorescence decays. In addition, AND and OR gates were constructed based on the different responses of CCDs to Fe³⁺ and Fe³⁺-CCDs to l-Trp/d-Trp, demonstrating the significance of molecular-level logic gates in drug detection and clinical diagnosis.