Simultaneous detection of ammonia and water vapors using surface plasmon resonance waveguide sensor

A waveguide-based SPR sensor for double analyte detections was prepared with a single waveguide, and sensing for ammonia and water vapors were carried out. A BK-7 slide glass was used as a waveguide core, and two pairs of Ag films (50 nm) / sensing polymer films with different thicknesses were prepared separately on the waveguide. White light was input from the substrate edge, and the output light spectrum was observed. SPR dips can be separately observed in the output light spectra by selecting the thickness of the polymer film, which govern the SPR condition. Poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) were used as sensing material. PAA responded to both of water and ammonia vapors, and PVA mainly responded to water vapor. Simultaneous measurement would enable precise ammonia measurement under various humidities.