Acoustic standing-wave enhancement of a fiber-optic Salmonella biosensor

An enhanced fluorescent fiber-optic biosensor system using ultrasonic concentration of particles and cells has been developed and applied in the detection of Salmonella typhimurium. A biosensor test chamber also serves as an ultrasonic standing-wave cell that allows microspheres or cells to be concentrated in parallel layers or in a column along the axis of the cell. A fiber probe along the axis delivers laser excitation to fluorescent-labeled antibodies of Salmonella and collects the fluorescent signal. The labeled-antibodies themselves do not respond to the ultrasound, but, when attached to Salmonella cells, the Salmonella-antibody complexes can be moved acoustically to the axis of the cell, increasing the fluorescent signal. In a second, more robust, type of immunoassay, the Salmonella-labeled-antibody complexes attach to unlabeled antibodies that have been immobilized on the surface of polystyrene microspheres. This entire structure can be manipulated acoustically and the increase in the fluorescent signal, which can be an order of magnitude, indicates the presence of Salmonella.