A new concept for biosensors is introduced based on competitive displacement of an analyte and fluorescently-labeled counter-ligand for immobilized receptor sites. A small, optical, glucose sensor has been developed. The sensing element consists of a short length of hollow dialysis fiber remotely connected to a fluorimetry instrument via a single optical fiber. This sensing element contains a carbohydrate receptor, Concanavalin A, immobilized on its inner surface and a high molecular weight fluorescein labeled dextran as a competing ligand. Glucose in the external medium diffuses through the dialysis fiber into the sensing element and competes with dextran for binding to Con A. At equilibrium, the level of free fluorescein in the hollow fiber lumen is measured via the optical fiber and is correlated to the concentration of glucose. Preliminary results for glucose measurement in phosphate buffer and in blood are presented. Response is linear from 50 to 400 mg% glucose and response time is 5–7 minutes.
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