Membrane and Arrayed Nanofluidic Devices with High Density Aligned Carbon Nanotubes
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Exceptionally high aspect ratio, smooth hydrophobic graphitic walls, and nanoscale inner diameters of carbon nanotubes (CNTs) cause the unique phenomenon of efficient transport of water and gas through these nanoscale molecular tubes. Molecular transport through the cores of CNTs is of significant interest from both fundamental and application aspects. The application of CNTs as nanofluidic channels is envisioned in many areas, ranging from desalination, carbon capture, drug delivery, DNA sequencing and translocation, protein separation, single molecule sensing, to nanofluidic transistors and diodes. A fundamental understanding of the mechanisms governing molecular transport through CNT pores is much needed and, unfortunately, still lacking, which demands further research. In this work, CNT-based smart membranes and arrayed devices are explored both as a versatile platform for fundamental studies and as exemplary devices for biosensing applications. In Chapter 3, a study of ion transport across smart, DNA-functionalized CNT membranes is reported. The diffusive transport rates of ferricyanide ions were monitored through an array of vertically aligned CNTs (VA-CNTs) functionalized with amine-modified single-stranded DNA (ssDNA) (Cy3-T15-NH2) probes. Reversible closing of CNT pores was achieved by the addition of complementary DNA (A15), gating ion transport. Our analysis suggests that pore blocking occurs due to steric hindrance at the CNT pore entrances. Chapter 4 focuses on the design and fabrication of arrayed CNT devices. Each device consists of a large number (roughly 4x105) of aligned multiwalled CNTs span a barrier separating two fluid reservoirs, enabling direct electrical chronoamperometric measurement of ion transport through the nanotubes and analyzing ion transport properties. Here we intend to demonstrate the theoretically predicted ultrahigh ion flow rate through multiplexed CNT devices that are directly electrically addressable. Compared with traditional nanopore devices, ours feature distinct advantages. The CNTs have a remarkably high aspect ratio and they can confine an entire molecule and also extend the duration of transport, which is likely to result in new translocation characteristics. Our devices have a planar design, which enable simultaneous optical and electrical probing. Results presented in this work show the potential of CNT nanofluidic devices for the fundamental studies of the nanoconfinement effects on ion transport. The developed synthesis and fabrication methods are envisioned to lead to novel biosensors based on nanofluidics, which can find a broad spectrum of significant applications such as disease diagnostics, food safety monitoring, and environmental pollution detection.