One-step immobilization of antibodies on ZIF-8/Fe₃O₄ hybrid nanoparticles for the immunoassay of Staphylococcus aureus

Zeolitic imidazolate framework-8 (ZIF-8)-coated Fe₃O₄ magnetic nanoparticle clusters (MNCs) were synthesized and used to detect pathogenic bacteria in milk. Hydrothermally synthesized MNCs were encapsulated with ZIF-8 via sonochemical reactions. Half fragments of monoclonal Staphylococcus antibodies were conjugated to the low-coordinated Zn sites located on the outer layer of ZIF-8 via Zn-S bonding, which allows one-step immobilization of antibodies with favorable orientations on ZIF-8. Furthermore, ZIF-8 encapsulation improved the stability of MNCs in water by suppressing the Fe₃O₄ oxidation. After the capture and magnetic separation of Staphylococcus in milk using hybrid nanoparticles, bacteria concentration was determined with a portable ATP luminometer and the detection limit was found to be 300 cfu mL^-1.