Defect-engineered Mn/Zn-MOF-74-L-His chiral nanozyme for “on-off-on” fluorescent chiral recognition of D/L-cysteine

Designing chiral nanozymes with high enantioselectivity and catalytic activity is crucial for amino acid recognition. L -histidine ( L -His) was used as a chiral source to synthesize a chiral bimetallic nanozyme (Mn/Zn-MOF-74- L -His) through defect engineering strategy. Defects can expose active sites and enhance peroxidase-like activity, while the chiral microenvironment enables chiral recognition. In the presence of H 2 O 2 , Mn/Zn-MOF-74- L -His can oxidize o -phenylenediamine to generate fluorescent products, which quenches its intrinsic fluorescence through fluorescence resonance energy transfer effect. D/ L -Cysteine (D/ L -Cys) inhibits the peroxidase-like activity of Mn/Zn-MOF-74- L -His, restoring its fluorescence and thereby enabling an “on-off-on” sensing strategy for chiral recognition of Cys enantiomers. Detection limits for L -Cys and D -Cys are 4.83 μM and 7.41 μM, respectively, with an enantiomeric selectivity of 2.24. Theory calculation and experiments indicate that the unique chiral microenvironment constructed through defect engineering mediated by L -His is the key to recognition. Compared with D -Cys, the chiral “pocket” has better geometric matching with L -Cys, resulting in a stronger binding affinity and electrostatic interaction. In short, this study has developed an “on-off-on” fluorescence sensing strategy based on defect-engineered chiral metal-organic frameworks, providing new ideas for designing chiral nanozymes and their application in chiral recognition of amino acids.