Naoki Takahara

Nanoassembled thin film gas sensors. III. Sensitive detection of amine odors using TiO2/poly(acrylic acid) ultrathin film quartz crystal microbalance sensors.

Quartz crystal microbalance (QCM) gas sensors based on the alternate adsorption of TiO(2) and polyacrilic acid (PAA) were developed for the sensitive detection of amine odors. Individual TiO(2) gel layers could be regularly assembled with a thickness of approximately 0.3 nm by the gas-phase surface sol-gel process (GSSG). The thickness of the poly(acrylic acid) (PAA) layer is dependent on its molecular weight, showing different thicknesses of approximately 0.4 nm for PAA(25) (Mw 250,000) and 0.6-0.8 nm for PAA(400) (Mw 4,000,000). 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 TiO(2)/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 TiO(2)/PAA(400) film was estimated to be 0.1 ppm when exposed to ammonia. The sensor response was very fast and stable in a wide relative humidity (rH) range of 30-70%, showing almost the same frequency changes at a given concentration of ammonia. Sensitivity to n-butylamine and ammonia was higher than to pyridine, which is owing to the difference of molecular weight and basicity of the amine analytes. The alternate TiO(2)/PAA(400) films have a highly effective ability to capture amine odors, and the ambient ammonia concentration of 15 ppm could be condensed up to approximately 20,000 ppm inside the films.

Landmine detection: Improved binding of 2,4-dinitrotoluene in a γ-CD/metal oxide matrix and its sensitive detection via a cyclic surface polarization impedance (cSPI) method

Highly sensitive and selective detection of 2,4-DNT, a representative explosive, was achieved by the synergic effect of molecular imprinting and host (cyclodextrin)-guest interaction in ultrathin layers of TiO(2) and SiO(2) gel; the detection limit using cSPI measurements reached nM concentration.

Fabrication of optical gas sensors using porphyrin-based nano-assembled thin films: A comparison with bulk materials

In this study two kinds of biological origins, porphyrin and bacteriorhodopsin that were embedded into polymer matrix and into inorganic sol-gel matrix, respectively, were employed as active elements for an optical sensor. To confirm the usefulness of the consequent nano-scale matrix in the detection of volatile organic compounds (VOCs), aromatics and amine compounds, anionic tetrakis-(4-sulfophenyl)porphine (TSPP) was alternately assembled with cationic poly(diallyldimethylammonium chloride) (PDDA) on quartz plates. The performance and sensor parameters of the nano-scale thickness porphyrin-based thin film and bacteriorhodopsin thick film are compared. The sensing principle is based on monitoring the optical changes of the Q-band at 700 nm for the porphyrin film and at 570 nm for the bacteriorhodopsin film. This work was a first step in the development of a fiber-optic gas sensor which employs thin films as sensitive elements for the detection of different gases.