A Multimodal Electronic Nose Based on High-Density Flexible Sensor Array of Carbon Nanotubes and Photoactive Macromolecules Hybrid Nanostructures

Abstract

We report a multimodal electronic nose system based on photoactive carbonaceous hybrid nanomaterials for the detection and quantification of gaseous odors. The e-nose system comprises a high-density flexible sensor array, colorimetric and electrical measurement electronics, data acquisition software, and data analysis algorithms. The e-nose system combines the unique advantages of electrical, chemical, and physical properties of single-walled carbon nanotubes (SWNTs) with optical and chemical properties of various classes of organic macrocyclic compounds, such as pyrenes, porphyrins, and phthalocyanines, for multimodal gas sensing. Photoactive macromolecules such as metalloporphyrins and metallophthalocyanines have been previously developed into colorimetric sensors to various gas analytes. Their intrinsically low electrical conductivity prevents direct application of porphyrins and phthalocyanines in chemiresistive sensors. However, when used as a secondary sensing material via functionalization onto SWNTs, which intrinsically lacks chemical selectivity, these macromolecules confer their chemical selectivity and optical properties to the intrinsically semiconducting SWNT channel. This hybrid nanostructure allows both chemiresistive sensing and colorimetric sensing modalities. Another beneficial property of this hybrid nanostructure is the optoelectronic tunability of the nanomaterial to allow for direct modulation of chemical and electrical behaviors leading to tunable gas sensing capability. Using the high-density array containing 118 individually addressable sensors, over 60 different secondary sensing materials (functionalized onto SWNTs) were investigated, which include chemical derivatives of pyrenes, porphyrins, and phthalocyanines, which have a large variety of side-groups, and metal centers. Additionally, by integrating a large variety of secondary sensing materials into each sensing element of the 118-sensor array, we take advantage of the different chemical and electrical characteristics of each macromolecules which allow for different affinities to specific VOC species to enhance overall selectivity of the e-nose system. The functionality of the multimodal e-nose system was demonstrated to distinguish and quantify various volatile organic compounds (VOCs).