Dual-analyte fiber-optic sensor for the simultaneous and continuous measurement of glucose and oxygen

A fiber-optic sensor for the continuous and simultaneous determination of glucose and oxygen is described. The sensor is comprised of dual-analyte sensing sites in defined positions on the distal end of an imaging fiber (350 microns o.d.). Each sensing site is an individual polymer cone covalently attached to the activated fiber surface using localized photopolymerization. The oxygen sensor consists of a double-layer polymer cone. The inner polymer cone is a hydrophobic gas-permeable copolymer containing an oxygen-sensitive ruthenium dye, and the outer layer is a poly(hydroxyethyl methacrylate) (HEMA) polymer. The glucose sensor is an oxygen sensor with a poly-HEMA outer layer containing immobilized glucose oxidase. The fluorescence images of both sensing sites are captured with a CCD camera, and the measured fluorescence intensities are related to analyte concentrations. Oxygen quenching data for both sensing sites fit a two-site Stern-Volmer quenching model. The sensor has been used to simultaneously monitor independent changes in glucose and oxygen concentrations. Glucose calibration curves were obtained under varying oxygen tensions, and the detection limit is 0.6 mM glucose. The effect of fluctuations in oxygen partial pressure on the glucose response can be used to calibrate the sensor. The sensor response time varies from 9 to 28 s, depending on the different thicknesses of the enzyme layer. The sensor maintains the same sensitivity for 2 days. Multiple glucose sensing sites with different enzymatic activities can be immobilized on the distal end of the fiber, affording control of the linear range.