Fluorescent optosensor for humidity measurements in air

A fiber-optic sensor for relative-humidity (RH) monitoring in environmental samples is described based on the adiabatic photoreaction that produces an intramolecular charge-transfer excited state. which is the basis of the se nsor response. The sensitive membranes are obtained immobilizing a highly f luorescent dye, 4-[2-(pyrazin-2-yl)-1,3-oxazol-5-yl]benzenamine (pzoxba: fo rmerly called appzox), in hydroxypropylcellulose (HPC). The composition of the sensing films was optimized to a final ratio pzoxba/HPC of 1.8 (.) 10(- 5) mol g(-1) with a 100-mum membrane thickness. The optode response spans f rom 1.68 to 100% RH, with a detection limit of 0.56% (Table2). Typical resp onse times (t(90)) to 0-100% relative humidity are 1-2 min, the relative st andard deviation for repeated measurements being 0.77-1.8%. The optode is i nsensitive to typical organic vapor interferents of commercial capacitive s ensors (see Table 3) as well as to molecular oxygen. an important quencher of other luminescence-based optical sensors. The proposed optode was succes sfully applied and validated for continuous monitoring of the relative humi dity level in environmental samples.