An Optochemical Humidity Sensor Based on Immobilized Nile Red in Y Zeolite

A simple and low-cost cost optical reflectance sensor has been developed based on the solvatochromic Nile Red immobilized within NaY zeolite supercages. The sensor performance has been tested with water and n -hexane vapors. The Nile Red−Y composite exhibits excellent properties as humidity sensor in terms of sensitivity (much lower than 200 ppm), response time (around 4 min), and dye stability toward migration upon high light exposures. Besides, the zeolite host provides an enhanced selectivity to moisture in mixtures where organic compounds are also present. The benefits of the dye encapsulation inside the zeolitic pores in terms of signal-to-noise ratio and baseline stability have also been demonstrated.