Dual emission probe for luminescence oxygen sensing: a critical comparison between intensity, lifetime and ratiometric measurements.

The characterization of a dual emission sensing luminescence material for water-dissolved oxygen sensing is presented in this paper. The oxygen-sensitive material is based on a dual-emitting luminescent molecule immobilized onto an adequate solid support. The metal chelate formed between the 8-hydroxy-7-iodo-5-quinolinesulphonic acid (Ferron) and aluminium (Al-Ferron) was the selected oxygen-sensitive dual-emitting luminescent complex, while the anionic exchanger Dowex 1X2-200 resin was the selected solid support. When the Al-ferron metal chelate is adsorbed onto the anionic exchanger resin it displays two largely different emission bands. The first is a fluorescence emission band, possessing a decay time in the nanosecond range, and which is insensitive to the oxygen presence (the "reference" signal). The second emission is a long-lived highly sensitive oxygen-quenchable phosphorescent emission. Under some optimised experimental conditions both emissions can be simultaneously measured when the metal chelate is excited with a 390nm light. Under these conditions, and using the same experimental set-up, oxygen concentration can be obtained by measuring the intensity of the phosphorescent emission, the triplet lifetime of the phosphorescence emission or the ratio between the intensity of the phosphorescence emission and the self-reference signal (fluorescence emission from the immobilized metal chelate). The reliability, the operational characteristics, the stability and the analytical performance characteristics for water-dissolved oxygen sensing are evaluated and critically compared for each measurement principle. Advantages and disadvantages of each measurement scheme for reliable optical sensing will be finally discussed.