Direct Visual Chiral Discrimination of Lys and Arg Enantiomers by the Achiral MIL-101(Cr)-NH₂ Platform

Chiral discrimination of amino acid enantiomers is critical in food safety and biomedical fields due to their distinct biological activities and potential toxicity. This study presented a simple strategy using the achiral metal-organic framework MIL-101(Cr)-NH₂ as a direct fluorescent sensor for the visual enantioselective recognition and quantification of lysine and arginine. The probe operated through a "turn-on" response driven by differential host-guest interactions without requiring any chiral modification. It exhibited exceptional enantioselectivity, with a fluorescence intensity ratio (F_L/F_D) of 107 for lysine and a reverse selectivity (F_D/F_L = 1.66) for arginine, achieving nanomolar detection limits. Mechanism studies revealed that the enantiomeric preference originated from distinct hydrogen bonding and electrostatic interactions within the MOF pores. The sensor demonstrated practical utility in accurately detecting l-Lys in commercial yogurt samples with satisfactory recoveries (91.7-103.7%). Furthermore, by integrating Rhodamine B, a smartphone-based colorimetric platform was developed for the on-site visual assessment of enantiomeric excess (ee) values, showing a linear correlation (R² = 0.9943) between the RGB ratio and the ee value of Lys. This work highlights that readily available achiral MOFs can serve as cost-effective and versatile platforms for chiral discrimination, offering a promising alternative to conventional chiral sensing systems in food analysis and biomedical diagnostics.