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 with photoexcitation capability, colorimetric and electrical measurement hardware, 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, both chemiresistive sensing and colorimetric sensing modalities are possible. Another beneficial property of this hybrid nanostructure is the optoelectronic tunability of the material to allow for direct modulation of chemical and electrical behaviors leading to tunable gas sensing capability.
Each flexible sensor array contains 118 individually addressable sensing elements. For each sensor element, source-drain electrodes were connected by a semiconducting sensing layer comprising single-walled carbon nanotubes (SWNTs) functionalized with various photoactive macromolecules as secondary sensing materials. Secondary sensing materials used include chemical derivatives of pyrenes, porphyrins, and phthalocyanines, which have a large variety of side-groups, and metal centers. Therefore, each sensor array can be fabricated to have up to 118 unique sensing elements by functionalization with different macromolecules. 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. We demonstrated the functionality of the multimodal e-nose system to distinguish and quantify various volatile organic compounds (VOCs).