Abstract:

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 of the cell delivers laser excitation to fluorescent dye molecules and collects the fluorescent signal. In a ``sandwich'' assay, the dye molecules are bonded to Salmonella antibodies that, in turn, attach themselves to Salmonella cells that have been captured by unlabeled antibodies that have been immobilized on the surface of polystyrene microspheres. This entire structure can be manipulated acoustically. The most effective procedure is a uniform stratification of the complexes in a plane-wave field followed by a concentration along the axis of the cell by a Gaussian-profile field. The increase in the fluorescent signal, which can be an order of magnitude, indicates the presence of Salmonella. [Work supported by USDA/NRICGP and by the URI Partnership for Sensors and Surface Technology.]