A New Concept for Development of Quartz Crystal Microbalance Fire Prevention Sensors Modified with Nano-Assembled Thin Films

Abstract

In this report, we describe a new concept for the development of quartz crystal microbalance (QCM) fire prevention sensors modified with nano-assembled thin films. The first example is the fabrication of QCM gas sensors based on alternate adsorption of TiO2and poly(acrylic acid) (PAA) for the sensitive detection of amine odors. The QCM sensors showed a linear response to ammonia at concentrations of 0.3--15 ppm, depending on the deposition cycle of the alternate TiO2/PAA layers. Ammonia binding is based on acid--base interaction with the free carboxylic acid groups of PAA, and the limit of detection of the 20-cycle TiO2/PAA400film under exposure to ammonia was estimated to be 0.1 ppm. The second example, monitoring of relative humidity, used porphyrin-based nano-assembled thin films prepared by a layer-by-layer approach on QCM resonators. These films were also used to detect significant environmental changes (due to smoke, humidity, or hazardous material release), and the results revealed that QCM-based real-environment monitoring devices can be implemented.