A fiber optic sensor for rapid analysis of bilirubin in serum

A miniaturized fiber optic biosensor has been fabricated for rapid analysis of bilirubin. Bilirubin is detected indirectly, based on fluorescence quenching of tris(4,7-diphenyl-1,10-phenanthroline) ruthenium chloride, [Ru(dpp)3], by dissolved molecular oxygen. Oxygen is consumed in the oxidation of bilirubin to biliverdin, catalyzed by the enzyme bilirubin oxidase (BOX). Both Ru(dpp)3 and bilirubin oxidase are physically immobilized in an acrylamide polymer matrix that is attached covalently to a silanized optical fiber tip surface via controlled photopolymerization. Leaching of the ruthenium dye is minimized by the optimization of the ratio between the acrylamide monomer and the cross-linker (N,N-methylene bisacrylamide). An 8% isobutyl alcohol in a phosphate buffer at pH 6 is used for storing the fiber optic biosensor. This solution maintains the enzymatic activity and the sensor response while minimizing the leaking of bilirubin oxidase from the polymer matrix. The detection limit of the sensor is 1 × 10−7 M and its linear dynamic range is between 1 × 10−7 and 3 × 10−4 M. The response time of the sensor is about 10 s, which presents a 50-fold improvement over existing bilirubin sensing devices. A standard deviation of about 3% is observed through all measurements. The mean percent error of the prediction of unknown normal and elevated bilirubin concentrations in serum samples based on the obtained calibration curve is about 2%.