| Description |
This dissertation presents experimental and computational investigations of nanoparticle transport and ion current rectification in conical-shaped glass nanopore membranes (GNMs). Chapter 1 provides an overview of the Coulter counter or "resistive pulse" method, ion current rectification, and finite-element simulations used in solving mass transfer problems in conical-shaped nanopores. Chapter 2 describes a fundamental study of the electrophoretic translocation of charged polystyrene nanoparticles in conical-shaped pores contained within glass membranes using the Coulter counter principle, in which the time-dependent current is recorded as the nanoparticle is driven across the membrane. Particle translocation through the conical-shaped nanopore results in a direction-dependent and asymmetric triangularshaped resistive pulse. The simulation and xperimental results indicate that nanoparticle size can be differentiated based on pulse height. Chapter 3 presents experimental, theoretical, and finite-element simulation investigations of the pressure-driven translocation of nanoparticles across a conicalshaped GNM. Analytical theory and finite-element simulation for pressure-driven flow through a conical-shaped pore were developed to compute the volumetric flow rate, the position-dependent particle velocity, and the particle translocation frequency. The translocation frequencies computed from theory and simulation were found to be in agreement with experimental observations. Chapter 4 reports the pressure-dependent ion current rectification that occurs in conical-shaped glass nanopores in low ionic strength solutions. Because the pressureinduced flow rate is proportional to the third power of the nanopore orifice radius, the pressure-driven flow can eliminate rectification in nanopores with radii of ?200 nm but has a negligible influence on rectification in a nanopore with a radius of ?30 nm. The dependence of the i-V response on pressure is due to the dependence of cation and anion distributions on convective flow within the nanopore. Chapter 5 describes pressure-reversal methods to capture and release individual nanoparticles. One (or more) particle is driven through the orifice of a conical-shaped nanopore by pressure-induced flow. A reverse of flow, following the initial translocation, drives the particle back through the nanopore orifice in the opposite direction. The sequence of particle translocations in the capture step is preserved and can be read out in the release step. The observed instantaneous transfer rate and return probability are in good agreement with finite-element simulations of particle convection and diffusion in the confined geometry of the nanopore. |
