Reversible evanescent wave sensors for hydrazine

Abstract

We report recent progress on development of evanescent wave fiber optic sensors for hydrazine (HZ), monomethylhydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH). Chemically reversible evanescent sensors capable of detection below 10 ppb were prepared by removing cladding from commercial multimode fiber and coating the exposed core with a hydrazine-sensitive triphenylmethane dye immobilized in an inert polymer matrix, typically poly(vinylchloride). Triphenylmethane dyes bleach reversibly in the presence of hydrazines, enabling colorimetric sensing. The linear dynamic range was typically 0 - 300 ppb and overall dynamic range up to ca. 5 ppm. Sensors optimized for HZ were as much as a factor of 45 less sensitive to MMH and UDMH, suggesting that the sensor film would require optimization for each analyte. Saturation response and relaxation times were on the order of 5 - 8 min, but measurable signals for 10 ppb HZ could be obtained in under 30 s. These sensors demonstrate a novel route to reversible sensing of these highly toxic compounds.