Single Ion Detection in Nanotube Nanofluidics

Abstract

This dissertation demonstrated the application of organic color center (OCC)-functionalized (6,5) single-walled carbon nanotubes (SWCNTs) to detect proton diffusion in nanofluidic systems at the single-ion level. I first developed a method to encapsulate SWCNTs between two layers of Parylene-C, a polymer with exceptionally low permeability to water and oxygen. The resulting sandwiched structures were transformed into a trap-in-a-pore (TIP) platform by lithography, exposing only the 0.422 nm pore mouth of the nanotubes while preserving the integrity of the SWCNTs and OCCs. This design enables the controlled introduction of water molecules and small ions while stabilizing the photoluminescence emission of both the SWCNTs and the OCCs. I then introduced protons into the TIP using an HClO4 solution, whose bulky counterions are excluded from the pore, ensuring the selective proton entry. I observed stochastic photoluminescence blinking as excitons collide with protons at the OCC sites. Using OCCs as optical sensors, I directly tracked proton diffusion along a single-file water chain confined within the nanotube channel. The measured diffusion coefficient is five orders of magnitude lower than that in bulk water, highlighting the dramatic impact of confinement on proton transport.