Abstract
Among the physical, chemical and biological hazards that could arise with respect to food safety, bacterial contamination has been one of the main concerns in recent years. Bacterial contamination in low moisture foods (LMFs) was an emerging threat which used to draw less attention as LMFs were considered at low risk of such a hazard. Bacteria can survive in low moisture environments and cause foodborne diseases once they enter the digestive system. Common detection methods such as ELISA and PCR are not well suited to LMFs, as most of them operate under aqueous environments. In this study, a Dual Immunological Raman-Enabled Crosschecking Test (DIRECT) was developed for LMFs using a nano-scaled surface enhanced Raman scattering (SERS) biosensor platform and multivariate discriminant analysis with a portable Raman spectrometer. It could provide a limit of detection (LOD) of 102 CFU/g of bacteria in model LMFs, with a detection time of 30–45 min. It has the potential to become a quick screening method for on-site bacteria detection for LMFs to identify food safety risks in real time.
Highlights
For many years, low moisture foods (LMFs) have been considered safe from microbial contamination because the low water content is supposed to prevent growth of microbes
LMFs are defined as foods that have less than 0.85 water activity, and most bacteria such as Salmonella and E. coli need water activity of at least 0.91 to grow [1]
Similar to the earlier report, anisotropic gold nanorods with aspect ratios of ~2–2.5, as shown in Figure S1e, were used in this study to generate specific surface enhanced Raman scattering (SERS) nanoprobes with conjugated E. coli antibodies via diazo chemistry through
Summary
Low moisture foods (LMFs) have been considered safe from microbial contamination because the low water content is supposed to prevent growth of microbes. To use them for LMFs, pathogens in the food samples typically need to be collected via washing steps, and the wash water is subject to testing These methods are not suitable for detecting pathogens directly in LMFs. Among the variety of detection methods developed, surface enhanced Raman spectro-sensing (SERS) offers an appealing potential for LMF applications as it could provide a means to detect molecular recognition events in nonaqueous environments [14,15,16]. Nonspecific binding of RMPs onto nontargets (other cells in the sample) will not create enough binding events needed for SERS enhancement, and will not create false positives This DIRECT scheme has been shown to work effectively for the detection of waterborne bacteria at extremely low levels (1–10 CFU/mL) [17,18]. As the detection mechanism was based on molecular recognition of antibody–antigen interaction, it is straightforward to modify the platform for the detection of other pathogenic bacterial species
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