An impedance biosensor for simultaneous detection of low concentration of Salmonella serogroups in poultry and fresh produce samples

This paper reports the design, fabrication and testing of a microfluidic based impedance biosensor for rapid and simultaneous detection of three Salmonella serogroups. The microfluidic device consists of three microchannels, each one includes a region for focusing the Salmonella cells into the centerline of the microchannel and direct them toward the sensing region to obtain highly concentrated samples using positive dielectrophoresis force. A region for bacteria sensing consists of interdigitated electrode (IDE) array with 10 pairs of fingers. Three types of Salmonella antibodies (type B, D and E) were mixed separately with the cross-linker (Sulfo-LC-SPDP) to enhance the immobalization of the antibodies to the detection electrodes. The electrode surfaces was then functionalized with the three mixtures, one for each channel. As target antigen binds to the antibody, it results in impedance change. The Salmonella samples were spiked with Salmonella type B, introduced into the biosensor via the sample inlet into the focusing region, and then toward the sensing region where they bind to the immobilized antibody, causing a change in the impedance. The performance of the devices was tested using single Salmonella serotype B and two Salmonella serotypes B, and D, with a limit of detection of 7 cells/ml. The biosensor was also able to differentiate live from dead bacteria eliminating the false positive results. Finally, the device was also able to detect Salmonella selectively when other type of pathogen was present.