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Magnetic nanoshells with tailored surface chemistry can enhance bacterial detection and separation technologies. This work demonstrated a simple technique to detect, capture, and aggregate bacteria with the aid of end-functionalized polyclonal antibody gold-coated magnetic nanoshells (pAb-Lis-AuMNs) as surface-enhanced Raman spectroscopy (SERS) probes.  Listeria monocytogenes  were used as the pathogenic bacteria and the pAb-Lis-AuMNs, 300 nm diameter, were used as probes allowing facile magnetic separation and aggregation. An optimized covalent bioconjugation procedure between the magnetic nanoshells and the polyclonal antibody was performed at pH six  via  a carbodiimide crosslinking reaction. Spectroscopic and morphological characterization techniques confirmed the fabrication of stable pAb-Lis-AuMNs. The resulting pAb-Lis-AuMNs acted as a SERS probe for  L. monocytogenes  based on the targeted capture  via  surface binding interactions and magnetically induced aggregation. Label-free SERS measurements were recorded for the minimum detectable amount of  L. monocytogenes  based on the SERS intensity at the 1388 cm −1  Raman shift.  L. monocytogenes  concentrations exhibited detection limits in the range of 10 4 –10 7  CFU ml −1 , before and after aggregation. By fitting these concentrations, the limit of detection of this method was ∼10 3  CFU ml −1 . Using a low-intensity magnetic field of 35 G, pAb-Lis-AuMNs aggregated  L. monocytogenes  as demonstrated with microscopy techniques, including SEM and optical microscopy. Overall, this work presents a label-free SERS probe method comprised of a surface-modified polyclonal antibody sub-micron magnetic nanoshell structures with high sensitivity and magnetic induced separation that could lead to the fabrication of multiple single-step sensors.

frontiers in nanotechnology

Detection and Aggregation of Listeria Monocytogenes Using Polyclonal Antibody Gold-Coated Magnetic Nanoshells Surface-Enhanced Raman Spectroscopy Substrates