Chiral Carbon Dots for Sensitive Discrimination of Tryptophan Enantiomers via Fluorescence and Circular Dichroism Spectroscopy

Chiral amino acids are fundamental to metabolism and serve as critical indicators of physiological and pathological states. While l-amino acids constitute the essential building blocks of functional proteins, their d-enantiomers have been implicated in various disease processes and may function as diagnostic biomarkers. Herein, we report the one-step hydrothermal synthesis of chiral nitrogen and sulfur codoped carbon dots (N,S-Cdots) for the enantioselective recognition and enantiomeric excess (ee) determination of tryptophan (Trp). The resulting chiral probes function as an “on–off” fluorescent sensor, displaying markedly different quenching efficiencies toward d- and l-Trp. Notably, interaction with the enantiomers generates mirror-image circular dichroism (CD) spectra, with supramolecular aggregation amplifying the chiroptical signature without altering its spectral characteristics. Quantum mechanical calculations corroborated these observations, revealing enhanced binding affinity of the N,S-Cdots toward d-Trp relative to its l-enantiomer. This dual-modal sensing platform, integrating fluorescence and CD transduction, establishes chiral carbon dots as sensitive and selective probes for enantioselective analysis at low analyte concentrations.