Increasing the sensitivity of Listeria monocytogenes assays: evaluation using ELISA and amperometric detection

An immunosensor for the detection of Listeria monocytogenes was developed. ELISA and amperometric studies were run in parallel to develop a more sensi tive and rapid assay for the bacterium. Conditions for the immunosensor wer e primarily characterised using ELISA. A direct sandwich assay was employed and the affinities of two polyclonal (goat and rabbit) and one monoclonal (mouse) anti-L. monocytogenes antibodies were compared using this format. O wing to low sensitivity being obtained with all antibodies, biotin-avidin a mplification and an indirect sandwich assay were employed. The system was t hen transferred to screen-printed electrodes (SPEs), the primary antibody b eing immobilised by cross-linking with 1-ethyl-3-(3-dimethylaminopropyl)-ca rbodiimide, and the mode of detection being amperometric. Various parameter s (limit of detection, working range, incubation time, cross-reactivity) of the systems were characterised. The effect of direct incubation in milk is also discussed. The final immunosensor had a working range of 1 x 10(6)-1 x 10(3) cells ml(-1) and a detection limit of 9 x 10(2) cells ml(-1). The a ssay took about 3.5 h to complete.