Improvement of piezoelectric crystal sensor for the detection of organic vapors using nanocrystalline TiO2 films

Nanocrystalline TiO2 films were used as substrate for the immobilization of beta-cyclodextrine onto the electrode surface of the piezoelectric crystal. The sensing layer consisting of beta-cyclodextrine and nanocrystalline TiO2 particles was characterized by XRD, IR spectroscopy and impedance analysis techniques. Due to the rigidity of the cast material, comparatively thick coatings could be used without a significant attenuation of the acoustic wave, and the porous morphology of the nanocrystalline TiO2 films yields a relatively fast response even for thick coatings. Piezoelectric gas sensors were successfully developed to detect organic vapors with detection limits down to 0.05 ppm. When the nanocrystalline TiO2 films were irradiated with UV lights, holes, and hydroxyl radicals were produced, which could oxidize and decompose organic materials. As fresh surface of porous TiO2 could be produced by irradiating UV light onto the beta-cyclodextrine/TiO2 composite films, piezoelectric crystal sensors fabricated on porous TiO2 substrate were found to give reproducible results. The use of such coating for fabricating piezoelectric crystal chemical and biosensors leads to significant improvements in the sensor performance and a wide scope of application. (c) 2005 Elsevier B.V. All rights reserved.