Analytical properties of miniaturized oxygen and glucose fiber optic sensors

A submicrometer fiber optic oxygen sensor and a micrometer sized fiber optic glucose biosensor have been fabricated. The sensors are based on the fluorescence quenching of ruthenium diimine complexes by molecular oxygen. In the oxygen sensors the ruthenium dye is immobilized in an acrylic polymer support at the end of the fiber. In the glucose sensor the enzyme glucose oxidase is immobilized in the polymeric support in addition to the oxygen indicator. The acrylamide support is attached covalently to a silanized optical fiber tip surface by photoinitiated polymerization. Leaching of the sensing reagent from the polymer host matrix has been minimized by the optimization of the ratio between the acrylamide monomer and the cross linker, N,N-methylene bisacrylamide. The sensor is fully reversible and highly reproducible. A standard deviation of around 2% within 10 consecutive fluorescence measurements has been observed for various oxygen and glucose concentrations. An absolute detection limit of sub-femtomoles is achieved. This is an improvement by a factor of 10(6) over existing fiber optic oxygen and glucose sensors. Another advantage of these miniaturized response time is their extremely short response time at the sub-second range. This is an improvement of 2-3 orders of magnitude over conventional optical sensors. An interesting feature of these miniaturized sensors is the dependence of their response on the sensor size. Unlike in larger sensors we find that under normal operating conditions the signal increases with the sensor diameter rather than its volume. This interesting dependence partially negates the signal loss due to the sensor miniaturization.