Rapid Detection of Listeria by Bacteriophage Amplification and SERS-Lateral Flow Immunochromatography

A rapid Listeria detection method was developed utilizing A511 bacteriophage amplification combined with surface- enhanced Raman spectroscopy ( SERS) and lateral flow immunochromatography ( LFI). Anti- A511 antibodies were covalently linked to SERS nanoparticles and printed onto nitrocellulose membranes. Antibody- conjugated SERS nanoparticles were used as quantifiable reporters. In the presence of A511, phage- SERS nanoparticle complexes were arrested and concentrated as a visible test line, which was interrogated quantitatively by Raman spectroscopy. An increase in SERS intensity correlated to an increase in captured phage- reporter complexes. SERS limit of detection was 6 X 106 pfu mL (-1), offering detection below that obtainable by the naked eye ( LOD 6 X 107 pfu mL(-1)). Phage amplification experiments were carried out at a multiplicity of infection ( MOI) of 0.1 with 4 different starting phage concentrations monitored over time using SERS- LFI and validated by spot titer assay. Detection of L. monocytogenes concentrations of 1 X 107 colony forming units ( cfu) mL -1, 5 X 10(6) cfu X mL -1, 5 X105 cfu - mL -1 and 5X 10(4) cfu mL-1 was achieved in 2, 2, 6, and 8 h, respectively. Similar experiments were conducted at a constant starting phage concentration ( 5 X 105 pfu mL-1) with MOIs of 1, 2.5, and 5 and were detected in 2, 4, and 5 h, respectively.