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Carbon Nanostructure-Based Sensors


One-dimensional (1-D) nanostructure-based sensors provide better sensitivity as compared to conventional thin film-based sensors due to their comparable dimensions with respect to Debye length. Single-walled carbon nanotubes (SWNTs) are 1-D nanostructures having high electrical mobility, high mechanical strength and high specific surface area that facilitate building of low-power, ultrahigh density sensors within limited space. However, pristine SWNTs posses limited sensitivity and selectivity. This sensitivity issue could be resolved through surface modification of SWNTs with suitable recognition molecules. Choosing the right functional material, sensor performance, in terms of sensitivity, could be enhanced. The selectivity issue could be overcome by making an array of sensors using different functional material and combining them with suitable pattern recognition software and thus, developing an electronic nose.

The overall objective of this dissertation is the development of a high density sensor array using single-walled carbon nanotube (SWNT) hybrid structures as building blocks for the realization of highly sensitive and discriminative sensors for monitoring of pollutants in the environment. To conceive such desired sensor characteristics, SWNTs were functionalized with organic macromolecules like porphyrins and calixarene to target VOCs in the air, and with biomolecules like polyT (a ssDNA) to target mercury ions in water. Detailed analysis of SWNT hybrid formation through different routes such as solvent casting and electrochemical techniques using macromolecules was performed to investigate structure property relations and the effect of macronucleus towards sensor performance when exposed to various analytes. The SWNT-porphyrin hybrids exhibited a discriminating capability of VOCs at room temperature. However, electrochemically modified (as opposed to solvent casting) SWNT-poly(porphyrin) hybrid improved sensor sensitivity further, retaining their discriminating capabilities and providing a sub-ppm limit of detection towards VOCs. The SWNT-poly(metalloporphyrin) hybrids also showed a probable relationship between sensor response and metal present within the porphyrin depending on the metal electronegativity. ssDNA functionalized SWNT hybrid exhibited highly selective and sensitive sensing response towards mercury ions in solvent phase.

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