Procedures and experiments described in this report were aimed at determining the feasibility of using surface-enhanced Raman spectroscopy (SERS) to detect water-borne microbial pathogens. Two laser sources were used to interrogate the biological samples with wavelength maxima of 532 nm and 632 nm, the Nd:YVO₄ and HeNe lasers, respectively. Representative Gram-negative (Escherichia coli and Salmonella enterica) and Gram-positive (Bacillus megaterium, B. globigii and B. subtilis, a surrogate for the pathogen, B. anthracis) bacteria were assayed, and a surrogate for enteric viruses was also used (the bacteriophage, PP7). Two approaches were used to develop this laser-based detection system: 1) nano-particle gold-labeled antibodies were used to distinguish the Salmonella pathogen from the other bacteria and 2) nano-particle silver was used without antibody to directly assay cell surface differences to differentiate the test microbes.

The laser assay using the antibody approach was successful in differentiating pathogen from non-pathogen, in spite of the cross-reactivity of the antibody. The silver colloid direct detection approach differentiated between Bacillus species but no interpretable signal was measurable when using either E. coli or PP7 virus. The positive results were obtained within a 5-minute period, indicating the potential for real-time detection of some water-borne pathogens.