Sol-gel-based biosensor for use in stroke treatment

A fiber optic biosensor for the detection of fibrinolytic products produced during lysis of "soft" blood clots is described. The biosensor was constructed to be selective toward D dimer antigens, which form from the dissolution of cross-linked fibrin clots. The presence of D dimer antigens above a threshold level is a clinical diagnostic used to determine the presence of such occlusions following a stroke. Fluorescein-labeled D dimer antibodies are immobilized on the tip of an optical fiber by dip coating from a silica sol-gel solution. When D dimer antigens combine with the antibodies, fluorescence intensity decreases. The response of the sensor was examined in phosphate buffered saline, human plasma, and blood. Calibration plots for the sensor were obtained in the clinically significant D dimer concentration range from 0.54 microgram/ml to 6 micrograms/ml. Changes in spectroscopic properties as the sol-gel encapsulated tagged antibodies aged were examined; a decrease in fluorescence intensity with age was noted. The D dimer antibodies remain viable for at least 4 weeks while encapsulated in the sol-gel network when stored at 4 degrees C in PBS solution. This novel sensor is being developed for use with other catheter-based microtools to treat stroke resulting from occlusion in the vascular system.