Membrane and Arrayed Nanofluidic Devices with High Density Aligned Carbon Nanotubes

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.1 yea

Reversible gating of ion transport through DNA-functionalized carbon nanotube membranes

Carbon nanotubes (CNTs) can be used to create unique fluidic systems for studying ion transport in nanochannels due to their well-defined geometry, atomically smooth and chemically inert surface, and similarity to transmembrane protein pores. Here, we report the reversible molecular gating of ion transport across DNA-functionalized CNT membranes. The diffusive transport rates of ferricyanide ions through membranes, each with an array of aligned transmembrane CNT channels, were monitored. Single-stranded DNA (T15) gate molecules were covalently linked to CNT channel entrances, and reversible opening and closing of CNT channels were achieved by the addition and removal of complementary DNAs (A15) with a remarkable open/close flux ratio of > 1000, which is substantially higher than the protein-gated CNT systems reported previously. Furthermore, at least two-orders of magnitude difference in ion fluxes was observed when single base-pair mismatched DNAs were used in place of the complementary DNAs. Comprehensive theoretical analysis is also presented. The experimental results can be explained by steric hindrance, ion partitioning, and electrostatic repulsion at the CNT entrances, as well as the thermodynamics of DNA binding.This research is financially supported by a Discovery grant from the Natural Sciences and Engineering Research Council of Canada (NSERC)

Fabrication of Three-Dimensional Carbon Nanotube and Metal Oxide Hybrid Mesoporous Architectures

Three-dimensional (3D) vertically aligned carbon nanotube (CNT) patterns were utilized as templates for fabricating mesoporous hybrid architectures composed of CNTs and various crystalline metal oxide (MO; M = Co, Zn, Mn) nanoparticles by a microwave-assisted chemical approach. Post-synthesis thermal treatment of the CNT/MO patterns culminated in structural reorganization, depending on the treatment conditions. In air, CNTs were removed by oxidation. The remaining MO architectures preserved the shape and alignment of the original 3D CNT patterns, but with different porosity characteristics and improved MO crystallinity. Elastocapillary condensation and bending were demonstrated to be useful tools for further architecture alternation. The mesoporous nature of the CNT/MO hybrids and the MO materials were confirmed by N₂-BET measurements. CNT/Co₃O₄ aligned strips were used as an example to demonstrate the potential application of the CNT/MO architectures as electrode materials for supercapacitive storage. Galvanostatic measurements showed that the CNT/Co₃O₄ strips were stable up to 1000 charge–discharge cycles at a current density of 377 μA/cm² with a specific capacitance as high as 123.94 F/g