Gold interdigitated micro-immunosensor based on Mn-MOF-74 for the detection of Listeria monocytogens

Accurate and rapid detection of foodborne pathogens is a key to prevent foodborne disease outbreaks. In this study, a novel impedance immunosensor based on a metal-organic framework (Mn-MOF-74) is used to rapidly and sensitively detect Listeria monocytogenes (L. m) in milk. Divalent manganese ions are released by the MOF reduction reaction mediated by hydrogen peroxide. Consequently, the impedance signal was detected by high conductive single-crystalline gold interdigitated microelectrode to achieve quantification of L. m. First, the capture antibodies (Ab₁) are modified on the surface of the magnetic beads to generate immunomagnetic beads (MBs@Ab₁), which are used specifically to separate L. m cells in the matrices. Later, the immunosensor (Mn-MOF-74@Ab₂) is added to the matrices to form a sandwich complex (MBs@Ab₁-L. m-Mn-MOF-74@Ab₂). Henceforward, Mn²⁺ is released from the sandwich composite via the action triggered by H₂O₂. The release of Mn²⁺ significantly changes the impedance of interdigitated microelectrodes, leading to ultrasensitive detection of L. m. The recoveries for L. m cells at the concentration between 1.0 × 10⁰ and 1.0 × 10⁴ CFU/mL are 90.2%-101.7% in water and 88.5%-96.2% in milk. The detection limit of this approach for L. m cells in water and milk are 7.1 and 9.2 CFU/mL, respectively. This approach can achieve rapid quantification of L. m cells within 60 min, and can also be employed to monitor other foodborne pathogens.