Certain kinds of cellulose, such as a hydroxyethylcellulose, swell in a humid atmosphere and show a decrease in refractive index. Using this effect, a simple optical humidity sensor with fast response and high sensitivity, which is based on the plastic optical fibre structure change from leaky to guided, was easily fabricated and could be used for real-time humidity monitoring.

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The plastic fiber humidity sensor, the mechanism of which is based on an ionization reaction between water vapor and the fluorescent dye-doped polymer cladding, was studied. The conditions under which to obtain the maximum sensitivity were derived from the theory and experimental data. Under these conditions, the fluorescent plastic fiber could be used as an excellent optical humidity sensor head with good linearity over the wide humidity range. Due to its reproducibility and fast response property, its application to a breathing-condition monitor became possible.

A large-scale, high-efficiency and low-cost platform for structural genomics studies". Acta Crystallogr D Biol Crystallogr. (2006) 62 (8):843-51