Quantitative Surface-Enhanced Raman Spectroscopy Sensing of Salmonella and Listeria in a Food Matrix

Ensuring rapid, reliable, and quantitative detection of foodborne pathogenic bacteria continues to be a challenge in food safety, particularly in complex matrices where traditional culture methods are time-consuming. In this study, a surface-enhanced Raman spectroscopy (SERS) sensing platform incorporating a polymer affinity agent is developed for the sensitive and quantitative detection of bacterial foodborne pathogens. A linear poly (2-hydroxyethyl methacrylate) affinity agent (pHEMA) was employed in combination with film over nanospheres (FON) substrates to facilitate detection and discrimination of Salmonella typhimurium (Gram-negative) and Listeria monocytogenes (Gram-positive). pHEMA plays an important role in mediating interactions with both extracellular metabolites and bacterial cell wall components. Characteristic vibrational bands enabled quantitative detection with a log-linear response and an observed limit of detection of 158 CFU/mL for both Salmonella typhimurium and Listeria monocytogenes in diluted apple juice. The similar sensitivities observed for both bacteria suggest effective interactions between pHEMA and chemically distinct bacterial cell walls of Gram-negative and Gram-positive organisms. This sensing approach maintained consistent performance in complex food matrices, such as pure apple juice, across a range of temperatures. Sonication experiments provided additional practical advantages: enhanced species discrimination and a strategy for combined disinfection and detection, extending the utility of this platform for food safety applications. Overall, these results show that SERS sensing platforms incorporating polymer affinity agents offer a robust and versatile analytical approach for whole cell foodborne pathogen detection.