Metal-phthalocyanine modified doped polyaniline for VOC sensing applications

The identification and measurement of volatile organic compounds (VOCs) is needed in a variety of applications including air quality monitoring, air pollution measurement, food quality monitoring, and breath analysis-based disease diagnosis etc. The monitoring of the VOCs related to different applications areas can ensure quality health and safety. Arrays of chemical sensors have the features to provide the required identification and measurement of the VOCs. Chemical sensors made from nanostructures of polyaniline (PANI) as the base sensing material have several advantages including tunable properties, room temperature sensing and the potential of being amenable to the printing processes. Metal (M) phthalocyanines (Pc), on account of different cavity structures, have the ability to selectively interact with different gases. In the reported studies most of the MPcs have been non-covalently deposited on the sensing platforms, or attached with the base polymer via pi-pi conjugation. The covalent bonding of MPcs with the sensing polymer may have several possible advantages including stability (no leaching or evaporation of the compounds), well-defined available interfaces for interaction and a longer operational lifetime. In this work, the camphor sulphonic acid (CSA) doped PANI nanostructures were covalently bonded with six metal embedded phthalocyanines (Cu-Pc, Mn-Pc, Zn-Pc, Fe-Pc, Ni-Pc and Co-Pc) and investigated as the sensor materials for the sensing of four VOCs: acetone, isopropanol, ethanol and formaldehyde, in a 150-500 ppb concentration range. The resultant chemical sensor array response in terms of relative change in resistance of the sensing materials upon VOC exposure was analysed using principal component analysis, which resulted in clear discrimination among the subjected VOCs, thus making it useful for selective VOC sensing applications.