Electron transfer-driven NH₂-MIL-53(Fe,Al) for ultrasensitive colorimetric detection of E. coli O157:H7

A colorimetric assay based on the Fe/Al bimetallic organic framework NH₂-MIL-53(Fe, Al) was developed for the sensitive detection of Escherichia coli O157:H7 (E. coli O157:H7), a critical pathogen threatening food safety. The framework's high specific surface area facilitated efficient antibody immobilization, whereas the incorporation of Al³⁺ enhanced electron transfer between Fe²⁺/Fe³⁺, thereby significantly boosting peroxidase activity. The optimized NH₂-MIL-53(Fe, Al) exhibited 1.4-fold and 4.9-fold higher relative absorbance than NH₂-MIL-53(Fe) and NH₂-MIL-53(Al), respectively. And it demonstrated 40-fold and 2-fold greater affinity for TMB and H₂O₂, respectively, compared to the natural enzyme. By integrating a dual-recognition system based on antibody and aptamer, the method enabled rapid detection with a limit of detection of 10¹ CFU/mL in colorimetric mode. Its successful application in complex matrices, including lettuce, juice, pool water, and chocolate milk, had yielded satisfactory recovery and precision, confirming its promising potential for food safety monitoring.