The effect of ultrasonic irradiation on the dissociation of antigen-antibody complexes was studied. Among three frequencies tested, 28 kHz ultrasound gave a relatively high percent dissociation with the lowest decrease of immune reactivity. When dissolved antigen-antibody complexes were exposed to the ultrasonic irradiation no dissociation was observed, while antigenantibody complexes were significantly dissociated by ultrasound when the antibodies had been immobilized on CH-Sepharose 4B. The

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... mune reactivity of immobilized antibody decreased by 8% during irradiation with 28 kHz ultrasound (0.83 W/cm2) for 20 min but no further decrease was observed after another 70 min of sonication. No degradation of antibody was observed after exposure to the ultrasound for 120 min. The dissociating effect of the ultrasound was applied to a homogeneous enzyme immunoassay system with the use of EMIT digoxin assay and anti-digoxin antibody-immobilized CH-Sepharose 4B gel. It was found that the change of absorbance at 340 nm increased with the concentration of non-labeled antigen in the presence of ultrasound. The feasibility of repeated application of immobilized antibodies in conjunction with ultrasonic dissociation as an immunosensor system is discussed.