Materials Science & Engineering Theses and Dissertations

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Browsing Materials Science & Engineering Theses and Dissertations by Author "Barnes, Benjamin"

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    CHEMICAL SENSING WITH A TUBE-IN-A-TUBE NANOSTRUCTURE
    (2022) Barnes, Benjamin; Wang, YuHuang; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Carbon nanotube field-effect transistors (FETs) exhibit exceptional electrical properties such as ballistic conductance and record-high carrier mobility that make them attractive for potential applications in chemical sensing. Successfully translating these properties to FET chemical sensors may advance the fields of medical diagnosis and in vivo chemical detection for a revolutionary impact on public health and personalized medicine. To this end, we must address multiple challenges for electrical detection, including 1) the need for simultaneous rapid detection and sensitivity to trace amounts of target molecules, 2) the need for detection in high ionic strength conditions, which tend to dampen the field-effect. 3) New fabrication routes are needed for producing FET chemical sensors at scale without compromising their superior electrical properties, and 4) new device form factors are needed for in vivo biosensing that combine these favorable electrical characteristics with biocompatibility, mechanical flexibility, and chemical sensitivity. The commonality in these seemingly diverse challenges is a lack of structure control at multiple length scales, from 10-9 m to 1 m. Particle length and surface defects at the single-nanostructure or nanometer-level dictate the electrical properties and target-probe kinetics, and therefore provide a fundamental lower limit of signal transduction. Furthermore, controlling the surface chemical properties at this scale can be used to tune sensing characteristics in high ionic strength conditions. Controlling the interactions and positioning of multiple nanostructures within a device (on the micrometer scale) dictate sensing time, detection range, and signal transduction. At the bulk level, up to the millimeter scale, the assembly of nanostructures into organized films and coatings dictates whether sensing properties can be preserved when fabricating devices at scale. Additionally, at this scale, device form factors must be considered, which determine the biocompatibility and sensitivity in the case of implantable FET sensors. In this work, I will address the challenge of structure control at multiple length scales using Tube-in-a-tube (Tube^2) nanostructures as a test platform. Tube^2 nanostructures are double-wall carbon nanotubes (DWCNTs) with heavily functionalized outer walls and semiconducting inner walls. This combination enables the use of outer wall surface chemistry modifications to address chemical selectivity and ionic screening challenges, while preserving the electrical transport properties of the inner wall for sensitive signal transduction.