Multifunctional scanning ion conductance microscopy

Scanning ion conductance microscopy (SICM) is a nanopipette-based technique that has historically been used for the topographical imaging of soft samples. This thesis demonstrates the development of SICM into a multifunctional tool, capable of providing a host of additional information about both biological and inert samples, whilst maintaining the structural mapping capability for which it is usually employed. Two approaches are taken to extend the functionality of SICM: (i) designing sophisticated potential, and positional, control functions that are then used with traditional single-channel nanopipettes; and (ii) incorporating an ion conductance channel into a multi-barrelled probe. In the single-channel setup, a pulsed-potential profile allows the extraction of surface charge density on extended substrates, and a ramped-potential profile permits spatially resolved mapping of redox reactions on an electrode substrate. When integrated into a more complex probe, SICM is used to study molecular uptake at cellular surfaces, and to print Cu microstructures on a Au substrate. While this thesis is primarily concerned with technique development, the studies herein have broad applications in cell biology, pharmaceuticals, materials science and beyond. In addition to developing imaging modes that allow the extraction of functional information at a surface, this thesis also contributes to the fundamental understanding of the SICM system. Finite element method simulations are performed alongside experimental studies, in order to fully understand the contributions of the pipette geometry, ion current rectification, and pipette-surface interactions on the measured ionic current. The theoretical treatment herein provides a foundation upon which future multifunctional SICM regimes could be designed, extending the scope of this increasingly powerful technique.