Vargas Serrano, Katherine

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    Novel surface-enhanced Raman scattering probes for water safety applications
    (2019-05-14) Vargas Serrano, Katherine; De Jesús Ruiz, Marco A.; College of Agricultural Sciences; Orellana Feliciano, Lynette E.; Ríos Velázquez, Carlos; Department of Food Science and Technology; Colón Ramírez, Silvestre
    Fresh produce safety is of great concern in the food industry, since its raw consumption and minimal processing in comparison to other food commodities, exacerbates the risks to become one of the leading sources of foodborne illnesses. As a result, there is a growing need to develop simple yet effective bacteriological identification assays, to ensure food safety and prevent outbreaks from contaminated produce. Worldwide, the utilized methods for the detection of foodborne pathogens in the food control and reference laboratories, relies mostly on methods validated by the International Organization for Standardization (ISO), applying minor adaptations among the different countries. In the specific case of United States, the standard employed by public health laboratories is the Bacteriological Analytical Manual of the United Stated Food and Drug Administration (FDA-BAM). Recently, the FDA Food Safety Modernization Act established the Produce Safety Rule named: Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption. This rule specifies the microbiological water quality parameters for pre-harvesting and post-harvesting fresh products to ensure its safety and reduce the risk of pathogen contamination. Analysis are based on conventional microbiological methods that are time consuming, costly and require specialized training and equipment. This study uses Surface-Enhanced Raman Scattering (SERS) as a rapid assay resource for early bacterial detection in aqueous media. Mix cellulose esters (MCE) membrane disc filters were tested as viable SERS substrates for the analysis of Escherichia coli. (E. coli) and Staphylococcus aureus (S. aureus) as model foodborne bacteria. MCE membranes were rendered SERS active via physical vapor deposition of silver nanoparticles. Scanning electron microscopy was used to characterize the nanocomposite substrate, while optimal silver thickness in MCE membrane, was determined using benzenethiol, as standard reference material. Results shows that a 24.3 (±0.1) nm silver coating exhibit the best performance on the MCE substrates. Use of multivariate analysis techniques such as Partial Least Squares Discriminant Analysis (PLSDA) for the interpretation of the spectroscopic data enabled the successful and rapid identification of E. coli and S. aureus at the MCE surface. Partial Least Squares (PLS) and Support Vector Machines-Regression (SVM-R) analysis enable the quantification of the target microorganism at the 101 colony forming units per milliliter (CFU/mL) level. The results demonstrate that the use of silver-MCE membranes along with multivariate analysis are a viable tool for the rapid and effective detection of foodborne pathogens in water.