New electrochemical methods for visualizing interfacial ion fluxes

This thesis is concerned with the development of new electrochemical methods for the visualization of ion fluxes at various interfaces. These techniques allow spatially resolved visualization and quantification of ion fluxes associated with various physiochemical and biological processes aiding to understand the mechanism and kinetics of such processes along with mapping the heterogeneity of such interfaces. In the first part of this thesis, a fast an inexpensive way to fabricate a nanoscale dual carbon electrode system was introduced. These electrode systems are well suited for detection and quantification of interfacial fluxes using scanning electrochemical microscopy because of their relatively small tip size enabling close positioning to an interface, while the small inter-electrode distance leads to high sensitivity. To enhance the capability of electrochemical scanning probe microscopy to simultaneous topography and potentiometric imaging of interfaces, a new pH-scanning ion conductance microscopy probe was developed and tested as a part of this thesis. Further, a quad-barrel multifunctional electrochemical and ion conductance probe for voltammetric analysis and electrochemical imaging of interfaces was developed and characterized in this study. These probes are amenable to further functionalization thus offering opportunities for functional imaging of both conducting and insulating pristine surfaces along with the capability of assembling nanoscale electrochemical cells for high sensitivity measurements. The ability of these probes for performing single molecule electrochemical detection was also explored in this thesis. Weak acids constitute an important group of molecules transported passively across the cell membrane. Most of the weak acids upon reaching specific intracellular sites produce various pharmacological responses which are widely exploited in therapeutics. It is thus extremely timely to have available experimental methods to accurately determine their permeation rates across bilayer membranes. A new method of forming lipid bilayers at the end of a glass pipet was reported in the later part of this thesis for quantitative passive permeation visualization. An attractive feature of all the techniques described herein is that they are very well-de ned and amenable to precise modelling of mass transport/reactivity. This was accomplished in this thesis using finite element modelling

Recent advances in single-cell subcellular sampling

Recent innovations in single-cell technologies have opened up exciting possibilities for profiling the omics of individual cells. Minimally invasive analysis tools that probe and remove the contents of living cells enable cells to remain in their standard microenvironment with little impact on their viability. This negates the requirement of lysing cells to access their contents, an advancement from previous single-cell manipulation methods. These novel methods have the potential to be used for dynamic studies on single cells, with many already providing high intracellular spatial resolution. In this article, we highlight key technological advances that aim to remove the contents of living cells for downstream analysis. Recent applications of these techniques are reviewed, along with their current limitations. We also propose recommendations for expanding the scope of these technologies to achieve comprehensive single-cell tracking in the future, anticipating the discovery of subcellular mechanisms and novel therapeutic targets and treatments, ultimately transforming the fields of spatial transcriptomics and personalised medicine

Fabrication and characterization of dual function nanoscale pH-scanning ion conductance microscopy (SICM) probes for high resolution pH mapping

The easy fabrication and use of nanoscale dual function pH-scanning ion conductance microscopy (SICM) probes is reported. These probes incorporate an iridium oxide coated carbon electrode for pH measurement and an SICM barrel for distance control, enabling simultaneous pH and topography mapping. These pH-SICM probes were fabricated rapidly from laser pulled theta quartz pipets, with the pH electrode prepared by in situ carbon filling of one of the barrels by the pyrolytic decomposition of butane, followed by electrodeposition of a thin layer of hydrous iridium oxide. The other barrel was filled with an electrolyte solution and Ag/AgCl electrode as part of a conductance cell for SICM. The fabricated probes, with pH and SICM sensing elements typically on the 100 nm scale, were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and various electrochemical measurements. They showed a linear super-Nernstian pH response over a range of pH (pH 2–10). The capability of the pH-SICM probe was demonstrated by detecting both pH and topographical changes during the dissolution of a calcite microcrystal in aqueous solution. This system illustrates the quantitative nature of pH-SICM imaging, because the dissolution process changes the crystal height and interfacial pH (compared to bulk), and each is sensitive to the rate. Both measurements reveal similar dissolution rates, which are in agreement with previously reported literature values measured by classical bulk methods

Gated single-molecule transport in double-barreled nanopores

Single-molecule methods have been rapidly developing with the appealing prospect of transforming conventional ensemble-averaged analytical techniques. However, challenges remain especially in improving detection sensitivity and controlling molecular transport. In this article, we present a direct method for the fabrication of analytical sensors that combine the advantages of nanopores and field-effect transistors for simultaneous label-free single-molecule detection and manipulation. We show that these hybrid sensors have perfectly aligned nanopores and field-effect transistor components making it possible to detect molecular events with up to near 100% synchronization. Furthermore, we show that the transport across the nanopore can be voltage-gated to switch on/off translocations in real time. Finally, surface functionalization of the gate electrode can also be used to fine tune transport properties enabling more active control over the translocation velocity and capture rates

Fabrication and Characterization of Dual Function Nanoscale pH-Scanning Ion Conductance Microscopy (SICM) Probes for High Resolution pH Mapping

The easy fabrication and use of nanoscale dual function pH-scanning ion conductance microscopy (SICM) probes is reported. These probes incorporate an iridium oxide coated carbon electrode for pH measurement and an SICM barrel for distance control, enabling simultaneous pH and topography mapping. These pH-SICM probes were fabricated rapidly from laser pulled theta quartz pipets, with the pH electrode prepared by <i>in situ</i> carbon filling of one of the barrels by the pyrolytic decomposition of butane, followed by electrodeposition of a thin layer of hydrous iridium oxide. The other barrel was filled with an electrolyte solution and Ag/AgCl electrode as part of a conductance cell for SICM. The fabricated probes, with pH and SICM sensing elements typically on the 100 nm scale, were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and various electrochemical measurements. They showed a linear super-Nernstian pH response over a range of pH (pH 2–10). The capability of the pH-SICM probe was demonstrated by detecting both pH and topographical changes during the dissolution of a calcite microcrystal in aqueous solution. This system illustrates the quantitative nature of pH-SICM imaging, because the dissolution process changes the crystal height and interfacial pH (compared to bulk), and each is sensitive to the rate. Both measurements reveal similar dissolution rates, which are in agreement with previously reported literature values measured by classical bulk methods

In situ solid-state nanopore fabrication

This review summarises the development of in situ solid-state nanopore fabrication techniques. These techniques are democratising solid-state nanopore research by providing rapid and accessible methods to fabricate nanopores

An examination of the Halifax textile industry in a period of intense technological change, 1700 to 1850

SIGLEAvailable from British Library Document Supply Centre-DSC:DX196275 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Fabrication, Characterization, and Functionalization of Dual Carbon Electrodes as Probes for Scanning Electrochemical Microscopy (SECM)

Dual carbon electrodes (DCEs) are quickly, easily, and cheaply fabricated by depositing pyrolytic carbon into a quartz theta nanopipet. The size of DCEs can be controlled by adjusting the pulling parameters used to make the nanopipet. When operated in generation/collection (G/C) mode, the small separation between the electrodes leads to reasonable collection efficiencies of ca. 30%. A three-dimensional finite element method (FEM) simulation is developed to predict the current response of these electrodes as a means of estimating the probe geometry. Voltammetric measurements at individual electrodes combined with generation/collection measurements provide a reasonable guide to the electrode size. DCEs are employed in a scanning electrochemical microscopy (SECM) configuration, and their use for both approach curves and imaging is considered. G/C approach curve measurements are shown to be particularly sensitive to the nature of the substrate, with insulating surfaces leading to enhanced collection efficiencies, whereas conducting surfaces lead to a decrease of collection efficiency. As a proof-of-concept, DCEs are further used to locally generate an artificial electron acceptor and to follow the flux of this species and its reduced form during photosynthesis at isolated thylakoid membranes. In addition, 2-dimensional images of a single thylakoid membrane are reported and analyzed to demonstrate the high sensitivity of G/C measurements to localized surface processes. It is finally shown that individual nanometer-size electrodes can be functionalized through the selective deposition of platinum on one of the two electrodes in a DCE while leaving the other one unmodified. This provides an indication of the future versatility of this type of probe for nanoscale measurements and imaging