Quartz crystal microbalance (QCM) gas sensors based on the alternate deposition of TiO2 and polymers were developed for the detection of ammonia and formaldehyde odors. For sensitive detection of both analytes, poly(acrylic acid), PAA, and poly(allyamine hydrochloride), PAH, were employed in the film along with TiO2 thin layers that were prepared by the gas-phase surface sol-gel (GSSG) process. The alternate (TiO2/PAA/TiO2/PAH) film-deposited QCM sensor showed linear responses to ammonia in the concentration range 0.5-40 ppm and to formaldehyde in the concentration range 0.3-20 ppm. The sensor response was very fast, stable, and repeatable. The ammonia or formaldehyde binding is based on the acid-base interaction to the free carboxyl or amino groups of PAA or PAH. TiO2 thin layers deposited by the GSSG process played significant roles in preventing the electrostatic interaction of polymer layers and in improving the diffusion of gaseous analytes inside the film.
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