Multifunctional Carbon Nanotube Sensors for Environmental Monitoring

As a one dimensional material, a Single-walled Carbon Nanotube (SWNT) is made of a rolled up graphene sheet. With a diameter of 1∼2 nm, the SWNTs exhibit many unique properties, such as high aspect ratios, ballistic carrier transport, high mechanical strength and thermal stability. These properties enable SWNTs to have superior performances in various applications including electronics and sensors. SWNT based sensors are extremely sensitive to slight electrostatic changes in their environment and have a fast response where conductance of an SWNT is observed to change in less than 2 sec upon exposure. In addition, SWNT sensors have size advantage over traditional sensors. Hence, SWNTs have been widely explored as active sensing elements for chemical and biomolecule detection.;Despite high sensitivities observed from nanotube sensors, one drawback is their lack of selectivity. The conductance of SWNTs is susceptible to many gas molecules in air, including oxygen and moisture which are abundantly present in the ambient environment. Due to this nonspecificity, the presence of any type of gas vapors can possibly interfere with the induced signals from the target gas vapors and hence reduce S/N ratio during detection. To minimize the effects of undesirable interference signals from the environment, several functionalization methods have been developed to customize the affinities of SWNTs to specific targets, including metal nano particles, conducting polymers and biomolecules.;The objective of this thesis is to utilize SWNTs in environmental applications. The proposed research topics include: investigating the sensing characteristics of RNA oligomers on carbon nanotubes; analyzing the sensing characteristics of DNA with different sequence lengths on carbon nanotubes; integration of DNA decorated SWNTs onto CMOS chip for toxic and explosive gas monitoring; building nanosensor array based on multi-functionalized SWNTs for air quality monitoring and exploring the sensing mechanism of DNA decorated SWNTs; integration of SWNTs inside microfluidic channels for water quality monitoring. The essential procedures are composed of device fabrication (post CMOS and zincation process for CMOS chip; photolithography for silicon chip), SWNTs assembly, functionalization of SWNTs by DNA or RNA molecules, building setup for signal acquisition and processing and the measurement of sensing response to gases and liquids. These investigations will pave the way toward remote-controlled sensing arrays made of functionalized SWNTs for air and water quality monitoring. Finally a nanotube based electronic device embedded in flexible and stretchable polymer thin films is demonstrated which shows great potential to encapsulate SWNT based sensors inside flexible and stretchable substrates for structural health monitoring.