Develop Spectroscopy Techniques for Detection of Trace Bacteria and Biological Toxins in Foods

APPROACH: 1) To develop the SERS method as a rapid and routine detection technique, stability and consistency of silver SERS substrates with the storage time and fabrication batch as well as the interaction between toxin/pathogen and substrates will be examined first and 2) To develop innovative SERS nanoprobe, which could provide localized and non-destructive SERS identification from surfaces of bulk samples with large spatial selectivity.

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PROGRESS: 2006/10 TO 2007/09<BR>
Progress Report Objectives (from AD-416) 1) To develop the Surface Enhanced Raman Spectroscopic (SERS) method as a rapid and routine detection technique and, and 2) to fabricate and characterize SERS nanoprobe to provide localized and non-destructive SERS identification from surfaces of bulk samples with large spatial selectivity. Approach (from AD-416) 1) To develop the SERS method as a rapid and routine detection technique, stability and consistency of silver SERS substrates with the storage time and fabrication batch as well as the interaction between toxin/pathogen and substrates will be examined first, and 2) To develop innovative SERS nanoprobe, which could provide localized and non-destructive SERS identification from surfaces of bulk samples with large spatial selectivity. Significant Activities that Support Special Target Populations This report documents research conducted under a Specific Cooperative Agreement between ARS and the University of Maryland, College Park. Additional results of the research can be found in the report for the parent project 1265-42000-013-00D "Development of New and Improved Systems to Enhance Food Safety Inspection and Sanitation of Food Processing." Surface-Enhanced Raman Scattering (SERS) spectra of various batches of bacteria adsorbed on silver colloidal nanoparticles were collected to explore the potential of SERS technique for rapid and routine identification of E. coli and L. monocytogenes cultures. Relative standard deviation (RSD) of SERS spectra from silver colloidal suspensions and ratios of SERS peaks from small molecules (K3PO4) were used to evaluate the reproducibility, stability, and binding effectiveness of citrate-reduced silver colloids over batch and storage processes. The results suggested consistent reproducibility of silver colloids over batch processing and also stability and consistent binding effectiveness over an eight-week storage period. E. coli/L. monocytogenes cultures of varying concentrations with different colloidal batches revealed that, despite large variations in relative intensities and positions of SERS active bands, characteristic and unique bands at 712 and 390 cm-1 were consistently observed and were the strongest for the E. coli and L. monocytogenes cultures, respectively. These two specific bands were used to develop simple algorithms in the evaluation of binding effectiveness of silver colloids over storage, and further to identify E. coli and L. monocytogenes cultures with a 100 percent success. A single spectrum acquisition took 5~6 min, and a minimum of 25 uL silver colloid was directly mixed with 25 uL volume of incubated bacterial culture. The short acquisition time and small volume of incubated bacterial culture make silver colloidal nanoparticle based SERS spectroscopy ideal for potential use in the routine and rapid screening of E. coli and L. monocytogenes cultures on large scales. Monitoring activities included meetings and site visits with the Department of Food Science, University of Maryland at College Park.