Fiber-Optic biosensor for urea based on sensing of ammonia gas

A fiber-optic biosensor for urea is described. This biosensor is based on the immobilization of urease at the sensing tip of a fluorescence-based ammonia gas-sensing fiber-optic chemical sensor. Urease is immobilized on a Teflon membrane by the well known bovine serum albumin (BSA)/glutaraldehyde cross-linking method. The indicator solution for this biosensor is composed of 0.145 M sodium chloride, 5.00 mM ammonium chloride, 9.4 μM 2′,7′-bis(carboxyethyl)-5 (and 6)-carboxyfluorescein and 0.9 μM 5 (and 6)-carboxyfluorescein. The steady-state and dynamic response properties of the sensor have been established. Results show that the urease/BSA protein layer has a significant effect on sensor response and recovery times. Also, the fluorescence-based sensor has been found to be faster than a conventional potentiometric ammonia gas-sensing electrode. In addition, the fluorescence sensor responds significantly quicker than a similar absorbance-based fiber-optic urea biosensor. The utility of the resulting urea biosensor for the determination of urea in diluted serum samples is demonstrated.