Development of core@shell magnetic framework composite for immunoselective detection and capture of Salmonella typhimurium

Abstract

Metal–organic frameworks (MOFs) are emerging as novel probes in the biosensing research field. In this work, for the first time, we report the separation and optical detection of Salmonella typhimurium using a magnetically recoverable binary core@shell composite, Fe₃O₄/Si@MIL-125 (Ti). The magnetic framework composite was prepared by in situ encapsulating silica-coated magnetic nanospheres of Fe₃O₄ with an NH₂-MIL-125 (Ti) MOF. This luminescent material was bio-interfaced with a monoclonal anti-Salmonella antibody (Ab) via carbodiimide cross-linking chemistry. The formation of the bioprobe was verified by several spectroscopic and microscopic characterization methods such as FTIR, UV-vis and fluorescence spectroscopy, powder X-ray diffraction analysis, HR-TEM and FE-SEM analysis. The magnetic bioprobe could attach the bacterial cells under the influence of a strong neodymium magnet. Further, the Ab/Fe₃O₄/Si@MIL-125 (Ti) biosensor exhibited detection of S. typhimurium over a wide range of concentrations (1.6 × 10¹–1.6 × 10⁶ CFU mL⁻¹) with a detection limit of 4 CFU mL⁻¹. After the optimization of sensing parameters and inter-/intra-precision assays, the probe has been found to yield reproducible, specific and stable results even in the propinquity of other interfering bacteria. The robustness of the method was supported by the specific and sensitive detection of Salmonella sp. in real samples. This work may help in mitigating the occurrence of food-borne illnesses caused by S. typhimurium.