Development of a rapid response biosensor for detection of Salmonella typhimurium

An integrated optic interferometer for detecting foodborne pathogens was de veloped. The interferometer is a planar waveguide with two thin antibody-co ated channels of immunochemically selective agents that interact with antig en molecules. One channel is coated with antibody to Salmonella as a sample , and the other is coated with human immunoglobulin G as a reference channe l by using reductive amination. Salmonella was introduced onto the sensing channels through the flow cell on the channels. Phase shift (pi) generated by refractive index variation, as determined by interfering the perturbed s ample channel with an unperturbed reference channel and observing the fring e shift, was used for detection. Salmonella Typhimurium (heat-treated or bo iled) was detected by binding to antibody against Salmonella common structu ral antigen immobilized on a silane-derived sensor surface at concentration s in the range of 1 x 10(5) to 1 x 10(7) CFU/ml. Salmonella (1 x 10(7) CFU/ ml) mixed with Escherichia coli (1 x 10(7) CFU/ml) were readily detected wi thout any decrease in sensitivity by the direct assay. Application of a san dwich assay with a second antibody or a gold-conjugated antibody increased the detection limit to 1 x 10(5) CFU/ml within a 10-min reaction time. Vari ous methods for the immobilization of the capture antibody to the biosensor channels were compared. The greatest binding response was observed in a di rect reductive amination method with a long reaction period and increased t he detection limit of direct binding of Salmonella antigen to 1 x 10(4) CFU /ml. The biosensor was able to detect Salmonella Typhimurium in chicken car cass wash fluid originally inoculated at a level of 20 CFU/ml after 12 h of nonselective enrichment. The planar optic biosensor shows promise as a fas t, sensitive, reliable, and economical means of detecting food pathogens in the future.