Stereospecific chiral carbon dots hydrogel for dual-mode fluorescence/phosphorescence discrimination of tryptophan enantiomers

Chiral recognition is crucial for precision analysis and manufacturing in contemporary chemistry, pharmacology, and materials science, serving as a vital prerequisite for ensuring food and drug safety. This study successfully developed a chiral-selective hydrogel (CCHG) based on chiral carbon dots (CCDs), cellulose nanocrystals (CNCs), and β-cyclodextrin (β-CD) for the fluorescence/phosphorescence recognition of tryptophan (Trp) enantiomers. This hydrogel integrates the molecular recognition capability of β-CD, the photoluminescence properties of CCDs, and the signal amplification/structural support function of CNCs, establishing a stable gel-based sensing platform for L-tryptophan detection. Experimental results demonstrate a significant fluorescence enhancement effect for L-Trp in CCHG, while D-tryptophan exhibits negligible response. Furthermore, the system exhibits visible long-lived delayed emission (afterglow) lasting approximately 4 s after UV light removal, enabling visual discrimination between tryptophan enantiomers. Density functional theory (DFT) calculations were based on a simplified, β-CD-centered local recognition model. The results indicate that L-Trp exhibits a stronger binding affinity at this primary host-guest recognition site than D-Trp, providing theoretical support for the enantioselectivity observed experimentally. CCHG enables quantitative detection of L-tryptophan with a linear range of 100–800 μM and a detection limit of 1.21 μM. The method showed satisfactory spiked recoveries in Yellow River water and milk, together with good precision in 10-fold diluted serum. This study provides a new strategy for developing chiral recognition materials with high selectivity, visual readout capability, and improved mechanistic clarity.