Rapid and broad-spectrum detection of salmonella in various environments by magnetic enrichment-surface enhanced Raman spectroscopy

Rapid, accurate, and broad-spectrum detection of pathogenic bacteria in food is very important and an emerging need for increasing food safety concerns. Here, we present an ultrasensitive Surface-enhanced Raman spectroscopy (SERS) based aptasensor, which consists of core-shell structure (Ag@Au) and magnetic composites (Fe 3 O 4 @Au@Ag). 4-mercaptobenzoic acid (4MBA) as Raman reporter was embedded in Ag@Au nanoparticles (Ag@4MBA@Au) based on an internal standard. The combination of Ag@4MBA@Au and Fe 3 O 4 @Au@Ag are used to form the aptasensor with strongest Raman signal. Upon exposure to salmonella, the interaction between the SERS nanotags and the magnetic substrate was disrupted, causing an inverse correlation between the Raman intensity of 4MBA and the salmonella concentration. The result shows a wide linear range from 10 to 10 8  cfu/mL with five subtypes salmonella (S. Typhimurium, S. Enteritidis, S. Kentucky, S. Indiana, S. NO) and a low limit of detection of 1.782, 1.637, 1.941, 1.632, 1.875 cfu/mL, respectively. When applied to the detection of salmonella in actual samples (lake water, milk, shrimp), no pretreatment is required, and the results show no significant difference compared to the standard.