Internally referenced ammonia sensor based on an electrochemically prepared porous SiO2 photonic crystal

An oxidized porous silicon photonic crystal possessing two reflectance peaks is infused with bromothymol blue, yielding a pH-responsive ammonia vapor sensor. One reflectance peak overlaps the absorbance band of the deprotonated dye while the other appears in a clear spectral region. Simultaneous monitoring of both reflectance peaks corrects for large changes in probe light intensity.