Fluorescent optode membrane based on organogel for humidity sensing

Optode membranes for use in the quantitative detection of relative humidity were developed by entrapping a fluorescent dye, Sulforhodamin 101, in gelatine-containing microemulsion-based organogels deposited on overhead transparency films. These organogels are fabricated from solutions of Sulforhodamin 101, sodium bis(2-ethylhexyl)sulfosuccinate and gelatine in water-isooctane solvent mixtures. These optode membranes exhibit strong fluorescence emission with excitation and emission maxima at 588 and 608 nm, respectively. The fluorescence emission intensity decreases with increase in relative humidity and yields a linear response range of relative humidity from 35 to 100% with a correlation coefficient of 0.991 at room temperature. Response and recovery times are within 1 min. The optode membranes show good repeatability and photostability and a long lifetime. Oxygen and carbon dioxide gases do not cause any interference. Other organic solvent vapours have a very slight interference on the optode membranes. The optode membranes were successfully applied for the measurement of relative humidity in different laboratory airs.