Dual-metal-site MOF nanozyme with enhanced activity for highly sensitive colorimetric detection of Cr(VI) in dairy products.

A dual-metal-site metal-organic framework (DMS MOF) nanozyme was developed for highly sensitive colorimetric detection of Cr(VI) in dairy products. DMS MOF nanozyme integrates trivalent iron nodes and iron-porphyrin ligands to mimic the multi-center natural oxidoreductases, with adjacent dual-metal centers synergistically enhancing catalytic activity. Steady-state kinetic analyses and Zeta potential investigations demonstrate that the DMS MOF exhibits significantly lower Michaelis-Menten constants and enhanced substrate affinity than single-metal-site MOFs. The proposed method based on DMS MOF nanozyme enables highly sensitive colorimetric sensing of Cr(VI) within merely 5 min, achieving a broad linear range from 0.50 ppb to 5.0 ppm and a limit of detection (LOD) of 0.36 ppb. Furthermore, the developed strategy has been validated in complex dairy products including pure milk, yogurt, and milk powder, yielding recoveries of 84.0-110% with RSD ≤2.10%. Thus, engineered DMS-MOF nanozymes with enhanced activity provide a cost-effective, reliable approach for heavy-metal detection in foods.