Peptide-Based Biosensor Utilizing Fluorescent Gold Nanoclusters for Detection of Listeria monocytogenes

Listeria monocytogenes is a Gram-positive foodborne pathogen that is frequently the cause of listeriosis and meningitis. The high mortality rate (20–40%) from such infections designates this microbe as a high threat to humans. Rapid and specific detection methods for L. monocytogenes can help diminish some of the drawbacks associated with this pathogen. Here we report a novel peptide-based biosensor platform for selective and quick detection of L. monocytogenes species from contaminated food samples. Leucocin A, a potent antimicrobial peptide that displays specific activity against listeria, is utilized to target and bind the receptors present on L. monocytogenes surface. Leucocin A is immobilized on glass surface to obtain a self-assembled monolayer (SAM) of peptide. Peptide SAM is exposed to contaminated sample allowing target bacteria to bind to the immobilized peptide on the surface. The peptide-bound bacteria are then labeled with highly fluorescent gold nanoclusters directly on the glass surface allowing quick detection of bacteria with a limit of detection (LOD) of 2000 cfu in each 10 μL sample. The gold nanoclusters are made in situ by directly spotting aqueous tetrachloroauric acid and 3-mercaptopropionic acid (MPA) on top of bacteria on the glass slide. The MPA–gold nanoclusters thus formed label the bacteria and absorb in the UV range and emit fluorescence in the visible to near-infrared region (λex = 304 nm, λem = 612 nm). The biosensor assay is portable, simple, fast (45–50 min) and can be performed by nonexperts and has the potential to be used as a screening tool for L. monocytogenes in food and pharmaceutical products.