ABSTRACT
Quartz crystal microbalance (QCM) gas sensors based on organic/ inorganic or organic/organic nano-assembled thin films were developed for the sensitive detection of amine odors. The gas-phase surface sol-gel (GSSG) process was employed to assemble TiO2gel and poly(acrylic acid) (PAA) layers and the QCM sensors showed a linear response to ammonia in the concentration range 0.3−15 ppm, depending on the deposition cycle of the alternate TiO2/PAA layer. The ammonia binding is based on the acid-base interaction to the free carboxylic acid groups of PAA and the limit of detection (LOD) of the 20-cycle TiO2/PAA400 (Mw 4000000) film was estimated to be 0.1 ppm when exposed to ammonia, and the
ambient ammonia concentration of 15 ppm could be condensed up to ~20000 ppm inside the TiO2/PAA400 films. Additionally, QCM electrodes modified with nano-assembled alternate layers of tet-rakis-(4-sulfophenyl) porphine (TSPP) or its manganese derivative (MnTSPP) and poly(diallyldimethylammonium chloride) (PDDA) were used for preliminary tests of real environment measurements. The sensors showed different responses to humidity changes, haz-ardous gas (ammonia) or cigarette smoke exposure and revealed a high possibility to recognize significant environmental changes.
