Immunosensor for detection of Salmonella typhimurium based on imaging ellipsometry

An immunosensor based on imaging ellipsometry (IE) was developed for the detection of Salmonella typhimurium (S. typhimurium). A protein G layer bound to a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) on a gold surface was adopted for immobilization of monoclonal antibody against S. typhimurium (Mab). Depositions of 11-MUA, protein G, and Mab on a gold surface was confirmed using surface plasmon resonance. To fabricate the immunosensor, protein G was spotted on a substrate modified with the SAM. After the substrate was blocked with bovine serum albumin, the Mab layer was immobilized on the protein G spot. Ellipsometric images of the protein G and the Mab spot on the substrate were acquired using the IE system based on off-null ellipsometry. Ellipsometric images of the Mab spots with binding of S. typhimurium with various concentrations were acquired. The change of mean optical intensity of the Mab spots in the ellipsometric images indicated that the lowest detection limit was 103 CFU/ml for S. typhimurium.