Nanopore Electrochemistry: The Development and Applications of Nanopore Electrode Arrays as High-Performance Sensors

Pore-based structures occur widely in living organisms. Ion channels embedded in cell membranes, for example, provide pathways, where electron and proton transfer are coupled to exchange vital molecules. Electrochemical reactions at the nanoscale possess unique characteristics that are not accessible to conventional electrochemistry. Nanopore electrochemistry represents a nexus for molecular control of electron transfer reactions within confined volumes. In this thesis, these exciting advances will be highlighted by addressing three main topics.

The first topic is focuses on the the fabrication and application of nanopore electrode arrays (NEAs), which are a combination of nanopore sensing technology and nanoelectrochemistry. High areal density (10⁹ cm^-2) over large scale (3-inch wafer) NEAs with zeptoliter characteristic volumes are designed and fabricated to perform electrochemical measurements. The unique design of NEAs allows individually addressable electrodes to support high sensitivity measurement of redox reactions of analyte species. The NEAs exhibit current amplification factors, AF_RC, as large as 55-fold, indicative of capture efficiencies at the top and bottom electrodes exceeding 99%. Furthermore, any anlaytes confined in NEAs can undergo electron-transfer reactions, which shows a linear current response over five orders of magnitude and exhibits remarkably small capacitive currents, at fast scan rates (~ 100V/s).

Second topic addresses nanopore enabled enhancements to standard electrochemical measurements, such as coupling redox cycling with electrical double layer effects within NEAs. We achieve remarkably enhanced ion selectivity because of ion migration and accumulation inside the confined space. Exploiting this principle, a ~3000-fold selective determination of dopamine in the presence of electrochemical interferences, e.g. ascorbic acid, is achieved by redox cycling-enabled ion accumulation.

In the third topic, NEAs are used to achieve nanoscale electronic functions, including particle transistor action and electrochemical rectification. The movement of nanoparticles into nanopores is controlled electrically in transistor-like fashion, i.e. a voltage threshold is observed at the top electrode of the NEAs above which nanoparticles are able to access the bottom electrode of the NEAs. This work proves to be an efficient route to in situ monitoring of the nanoparticle transport and redox reactions at the single particle level. Finally, this gating behavior is further extended to a wide range of redox molecules in hierarchically organized nanostructures, such that the magnitude and direction of current flow could be controlled by the electrochemical reaction, thus achieving electrochemical diode function.