UC Irvine

Solid-state nanopores provide a versatile platform for controlling ionic transport at the nanoscale and represent promising building blocks for biomimetic iontronic devices. However, while transport through isolated nanopores is relatively well understood, the behavior of small nanopore arrays cannot necessarily be predicted by treating individual pores as independent conductors. Ion concentration polarization (ICP), characterized by the formation of ion-depleted and ion-enriched regions adjacent to ion-selective nanopores, extends beyond the physical boundaries of a pore and can therefore mediate interactions among neighboring pores and surfaces. This dissertation investigates how ICP, nanopore geometry, surface charge, interpore spacing, electrolyte concentration, and neighboring electrostatic boundary conditions collectively govern ionic transport through single nanopores and small nanopore arrays.Ionic transport was investigated experimentally using nanopores fabricated in silicon nitride membranes and computationally using three-dimensional finite-element models based on the coupled Poisson–Nernst–Planck equations. Two- and three-pore arrays were examined as functions of interpore distance and electrolyte concentration, while numerical simulations resolved the spatial distributions of ionic concentration, electrostatic potential, ion selectivity, and ionic current. Additional models examined the effects of nanopore length, patterned surface charge, and neighboring conductive surfaces under floating-potential, fixed-charge, and externally applied gate-potential boundary conditions.The results demonstrate that ICP is a central mechanism governing interactions among nanoscale ionic transport elements. Closely spaced nanopores develop overlapping depletion regions that suppress array conductance, with stronger coupling observed at lower electrolyte concentrations. ICP also produces a regime in which nanopores with substantially different physical lengths exhibit similar conductance because ion-depleted regions extending beyond the pore contribute significantly to the total transport resistance. Spatially patterned surface charge redistributes ICP and produces diode-like transport, whereas neighboring conductive surfaces modify depletion and enrichment through electrostatic coupling. Applied gate potentials provide further control over these distributions and generate spatially heterogeneous transport responses within small nanopore arrays.Collectively, these results establish that nanopore conductance is determined not solely by pore geometry and intrinsic surface properties but also by the surrounding electrochemical environment. Consequently, small nanopore arrays can exhibit collective transport behavior that cannot be described as a simple parallel combination of independent nanopores. These findings provide physical design principles for controlling coupled ionic transport and developing nanopore-based diodes, gates, selective membranes, and biomimetic iontronic circuits.