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 TiO₂ and 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/PAA₄₀₀ film 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.