Humidity-sensitive optode membrane based on a fluorescent dye immobilized in gelatin film Original Research Article

Humidity-sensitive optode membranes have been fabricated by immobilizing rhodamine 6G and ethylene glycol–water mixture into gelatin matrix deposited on overhead transparency films. The optode membrane shows the strong fluorescence at 568 nm when it is excited at 536 nm. The fluorescence intensity at 568 nm decreases with increasing relative humidity. It exhibits a wide linear dynamic range from 10.2% to 100% relative humidity and also shows a good linearity (correlation coefficient is 0.9952) at 20.0°C and atmospheric pressure. Both the exposure time and recovery time of the optode membrane are 1 min. The sensor has good reproducibility, photostability and long-term stability. Oxygen and carbon dioxide gases do not show any interference. Acetone, toluene vapours and NOx have slight interferences whereas ethanol, chloroform, acetic acid vapours and SO2 cause serious interferences on the optode membrane.