| Carbon nanotube field-effect transistors (NT-FETs) and graphene field effect transistors (GFETs) provide a unique transduction platform for chemical and biomolecular detection. The work presented in this thesis describes the fabrication, characterization, and investigation of operational mechanisms of carbon-based biosensors. In the first set of experiments, we used carbon nanotubes as fast, all-electronic readout elements in novel vapor sensors, suitable for applications in environmental monitoring and medicine. Molecules bound to the hybrid alter the electrical properties of the NT-FET via several mechanisms, allowing direct detection as a change in the transistor conduction properties. Vapor sensors suitable for more complex system architectures characteristic of mammalian olfaction were demonstrated using NT-FETs functionalized with mouse olfactory receptor (mOR) proteins or single stranded DNA (ssDNA). Substitution of graphene as the channel material enabled production of hundreds of electronically similar devices with high yield. Etching large scale chemical vapor deposition (CVD)-grown graphene into small channels is itself a challenging problem, and we have developed novel fabrication methods to this end without sacrificing the inherent electrical quality that makes graphene such an attractive material. Large arrays of such devices have potential utility for understanding the physics of ligand-receptor interactions and contributing to the development of a new generation of devices for electronic olfaction.;Tailored and specific detection was accomplished by chemically functionalizing the NT-FET or GFET with biomolecules, such as proteins or small molecules, to create a hybrid nanostructures. Targets for detection were widely varied, indicating the utility of these techniques, such as 1) live Salmonella cells in nutrient broth, 2) a biomarker protein indicative of prostate cancer, 3) antigen protein from the bacterium that causes Lyme disease, and 4) glucose for diabetes monitoring. Further, we explored the potential of graphene as a readout element in similar transistor-based biosensors. We functionalized clean graphene devices with Histidine-tagged fluorescent proteins (FPs), producing a protein-graphene photodetector with wavelength selectivity based on the absorption spectrum of the FP. The work represents significant progress towards a general method for the tailored and specific detection of trace biological compounds using electronic readout for biomedical applications.;We also investigated the fundamental operational mechanisms behind such nanotube-based sensors with a set of pyrene compounds that alter the local electrostatic environment in a predictable manner. While this experiment makes possible tuning of nanotube transistor properties, more generally these results could inform the development of quantitative models for the response of nanotube- and graphene-based biochemical sensors. Generic protein attachment chemistry combined with biochemists' ability to express proteins with high affinity for a particular target makes this research a platform technology capable of detecting any target with excellent sensitivity. Conceptually, this opens up a very large domain of intra- and intercellular communication to electronic eaves-dropping and could serve as a powerful tool for molecular and cell biology research. |
