Lifetime-Based Fiber-Optic Water Sensor Using a Luminescent Complex in a Lithium-Treated Nafion Membrane

A lifetime-based fiber-optic sensor that can be used to measure water content in organic solvents and relative humidity of air is described. The sensor is based on the luminescence lifetime quenching of ruthenium(II)bisphenanthrolinedipyridophenazine (Rudppz) immobilized in a Nafion™ membrane that is mechanically attached to the distal tip of an optical fiber. Treatment of the Nafion™ membrane with lithium hydroxide prior to doping with Rudppz provides a stable sensor response with intense, long-lived luminescence. The response of the sensor to relative humidity was characterized using dry air, room air, and water saturated air. The sensor is useful for measuring the water content of organic solvents below 4% (v/v) and the detection limit is determined to be 0.06, 0.07, and 0.006% (v/v) in DMSO, ethanol, and acetonitrile, respectively. It is being developed for the purpose of measuring water concentration gradients across Nafion™ membranes.