Time-resolved fluorescence immunoassay based on glucose oxidase-encapsulated metal-organic framework for amplified detection of foodborne pathogen

Fluorescence immunoassays are commonly employed for the detection of pathogenic bacteria as a means of ensuring food safety and preserving public health. However, the challenges such as poor photostability and background interference have limited their sensitivity and accuracy. The emergence of metal-organic frameworks (MOFs) as a label probe offers a promising solution for advancing fluorescence immunoassays owing to their tunable nature. Nonetheless, the low fluorescence efficiency of MOFs and the potential risk of dye leakage pose obstacles to achieving high detection sensitivity. Therefore, there exists a pressing need to fully utilize the potential of MOF composites in fluorescence immunoassays. We explored the potential of glucose oxidase-encapsulated zeolitic imidazole framework-90 (GOx@ZIF-90) as a label probe to construct a time-resolved fluorescence immunoassay with amplified detection signal. This immunoassay involved functionalizing Fe3O4 nanoparticle with porcine antibody to specifically capture and separate the target bacteria, Staphylococcus aureus (S. aureus). The captured S. aureus was then bound by GOx@ZIF-90 modified with vancomycin, resulting in a fluorescence response in the europium tetracycline (EuTc). The encapsulation of GOx in ZIF-90 provided a confinement effect that significantly enhanced the catalytic activity and stability of GOx. This led to a highly efficient conversion of glucose to H2O2, amplifying the fluorescence signal of EuTc. The immunoassay demonstrated a high sensitivity in detecting S. aureus, with a detection limit of 2 CFU/mL. We also obtained satisfactory results in milk samples. Attractively, the time-resolved detection mode of EuTc allowed the immunoassay to eliminate background fluorescence and enhance accuracy. This study not only presented a new method for detecting foodborne pathogens but also highlighted the potential of enzyme-encapsulated MOF composites as label probes in immunoassays, providing valuable insights for the design and fabrication of MOF composites for various applications.