Time-resolved detection and analysis of single nanoparticle electrocatalytic impacts

There is considerable interest in understanding the interaction and activity of single entities, such as (electro)catalytic nanoparticles (NPs), with (electrode) surfaces. Through the use of a high bandwidth, high signal/noise measurement system, NP impacts on an electrode surface are detected and analyzed in unprecedented detail, revealing considerable new mechanistic information on the process. Taking the electrocatalytic oxidation of H2O2 at ruthenium oxide (RuOx) NPs as an example, the rise time of current–time transients for NP impacts is consistent with a hydrodynamic trapping model for the arrival of a NP with a distance-dependent NP diffusion-coefficient. NP release from the electrode appears to be aided by propulsion from the electrocatalytic reaction at the NP. High-frequency NP impacts, orders of magnitude larger than can be accounted for by a single pass diffusive flux of NPs, are observed that indicate the repetitive trapping and release of an individual NP that has not been previously recognized. The experiments and models described could readily be applied to other systems and serve as a powerful platform for detailed analysis of NP impacts

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

Dual-barrel conductance micropipet as a new approach to the study of ionic crystal dissolution kinetics

A new approach to the study of ionic crystal dissolution kinetics is described, based on the use of a dual-barrel theta conductance micropipet. The solution in the pipet is undersaturated with respect to the crystal of interest, and when the meniscus at the end of the micropipet makes contact with a selected region of the crystal surface, dissolution occurs causing the solution composition to change. This is observed, with better than 1 ms time resolution, as a change in the ion conductance current, measured across a potential bias between an electrode in each barrel of the pipet. Key attributes of this new technique are: (i) dissolution can be targeted at a single crystal surface; (ii) multiple measurements can be made quickly and easily by moving the pipet to a new location on the surface; (iii) materials with a wide range of kinetics and solubilities are open to study because the duration of dissolution is controlled by the meniscus contact time; (iv) fast kinetics are readily amenable to study because of the intrinsically high mass transport rates within tapered micropipets; (v) the experimental geometry is well-defined, permitting finite element method modeling to allow quantitative analysis of experimental data. Herein, we study the dissolution of NaCl as an example system, with dissolution induced for just a few milliseconds, and estimate a first-order heterogeneous rate constant of 7.5 (±2.5) × 10–5 cm s–1 (equivalent surface dissolution flux ca. 0.5 μmol cm–2 s–1 into a completely undersaturated solution). Ionic crystals form a huge class of materials whose dissolution properties are of considerable interest, and we thus anticipate that this new localized microscale surface approach will have considerable applicability in the future

Prostanoid receptor EP1 and Cox-2 in injured human nerves and a rat model of nerve injury: a time-course study

BACKGROUND: Recent studies show that inflammatory processes may contribute to neuropathic pain. Cyclooxygenase-2 (Cox-2) is an inducible enzyme responsible for production of prostanoids, which may sensitise sensory neurones via the EP1 receptor. We have recently reported that while macrophages infiltrate injured nerves within days of injury, they express increased Cox-2-immunoreactivity (Cox-2-IR) from 2 to 3 weeks after injury. We have now investigated the time course of EP1 and Cox-2 changes in injured human nerves and dorsal root ganglia (DRG), and the chronic constriction nerve injury (CCI) model in the rat. METHODS: Tissue sections were immunostained with specific antibodies to EP1, Cox-2, CD68 (human macrophage marker) or OX42 (rat microglial marker), and neurofilaments (NF), prior to image analysis, from the following: human brachial plexus nerves (21 to 196 days post-injury), painful neuromas (9 days to 12 years post-injury), avulsion injured DRG, control nerves and DRG, and rat CCI model tissues. EP1 and NF-immunoreactive nerve fibres were quantified by image analysis. RESULTS: EP1:NF ratio was significantly increased in human brachial plexus nerve fibres, both proximal and distal to injury, in comparison with uninjured nerves. Sensory neurones in injured human DRG showed a significant acute increase of EP1-IR intensity. While there was a rapid increase in EP1-fibres and CD-68 positive macrophages, Cox-2 increase was apparent later, but was persistent in human painful neuromas for years. A similar time-course of changes was found in the rat CCI model with the above markers, both in the injured nerves and ipsilateral dorsal spinal cord. CONCLUSION: Different stages of infiltration and activation of macrophages may be observed in the peripheral and central nervous system following peripheral nerve injury. EP1 receptor level increase in sensory neurones, and macrophage infiltration, appears to precede increased Cox-2 expression by macrophages. However, other methods for detecting Cox-2 levels and activity are required. EP1 antagonists may show therapeutic effects in acute and chronic neuropathic pain, in addition to inflammatory pain

Image-Based Remodeling: A Framework for Creating, Visualizing, and Editing Image-Based Models

Thesis (Ph.D.)--University of Washington, 2014Image-based models are geometric models created from photographs and textured with the photographs for realistic rendering. In recent years, it has become increasingly easy to capture many photographs of an object and use computer vision techniques to model the object with image-based geometry. However, it can be difficult to display and interact with these models in a manner that reproduces the visual fidelity of the original photographs. It is even more difficult to support the interactive manipulation and editing that one might expect from other types of geometric models. The overarching goal of this thesis is to create a framework for building, visualizing, and editing image-based models. Toward this goal, I first describe the related literature and outline the associated research challenges related to geometric representation, navigation, creation, and editing of image-based geometry. One of the challenges in visualizing image-based geometry is discovering camera viewpoints and navigation paths that are both visually pleasing and enable story telling. To address this challenge, I describe a GPU-accelerated, image-based rendering algorithm that enables the creation of such visualizations in the form of camera paths and cinematic effects commonly used by cinematographers. In order to avoid objectionable rendering artifacts such as occlusion holes, the fast rendering algorithm is used to quickly sample the parameter space of camera viewpoints and define a viable region of camera parameters. This region is subsequently used to constrain an optimization for a camera path that maximizes parallax and conforms to cinematic conventions. This rendering algorithm also allows users to create more complex camera paths interactively, while experimenting with effects such as focal length, depth of field, and selective, depth-based desaturation or brightening. A greater challenge is editing image-based geometry. To move image-based models away from the limitations of view-only geometry to the broader class of editable geometry, I describe a new approach for creating and visualizing editable image-based architectural models in a photorealistic manner. Using this approach, I present an interactive system that enables modeling, and remodeling of image-based geometry in the context of home interior architecture. This system supports creation of concise, parameterized, and constrained geometry, as well as remodeling directly from within the photographs. Real-time texturing of modified geometry is made possible by precomputing view-dependent textures for all of the faces that are potentially visible to each original camera viewpoint, blending multiple viewpoints and hole-filling where necessary. The resulting textures are stored and accessed efficiently, enabling intuitive, real-time, realistic visualization, modeling, and editing of the building interior. Finally, I demonstrate how the image-based remodeling system enables lighting effects. Using a combination of the texture created in the image-based remodeling system and radiosity form-factor calculations, we estimate the irradiance at any location in the model. We can utilize this irradiance estimate to further refine light source estimates, and calculate surface reflectance properties. Given the additional estimates, edited models can be re-rendered to reflect lighting changes due to edited geometry, changing light properties, and the addition of synthetic objects

Scanning electrochemical cell microscopy (SECCM) chronopotentiometry : development and applications in electroanalysis and electrocatalysis

Scanning electrochemical cell microscopy (SECCM) has been applied for nanoscale (electro)activity mapping in a range of electrochemical systems but so far has almost exclusively been performed in controlled-potential (amperometric/voltammetric) modes. Herein, we consider the use of SECCM operated in a controlled-current (galvanostatic or chronopotentiometric) mode, to synchronously obtain spatially resolved electrode potential (i.e., electrochemical activity) and topographical “maps”. This technique is first applied, as proof of concept, to study the electrochemically reversible [Ru(NH3)6]3+/2+ electron transfer process at a glassy carbon electrode surface, where the experimental data are in good agreement with well-established chronopotentiometric theory under quasi-radial diffusion conditions. The [Ru(NH3)6]3+/2+ process has also been imaged at “aged” highly ordered pyrolytic graphite (HOPG), where apparently enhanced electrochemical activity is measured at the edge plane relative to the basal plane surface, consistent with potentiostatic measurements. Finally, chronopotentiometric SECCM has been employed to benchmark a promising electrocatalytic system, the hydrogen evolution reaction (HER) at molybdenum disulfide (MoS2), where higher electrocatalytic activity (i.e., lower overpotential at a current density of 2 mA cm–2) is observed at the edge plane compared to the basal plane surface. These results are in excellent agreement with previous controlled-potential SECCM studies, confirming the viability of the technique and thereby opening up new possibilities for the use of chronopotentiometric methods for quantitative electroanalysis at the nanoscale, with promising applications in energy storage (battery) studies, electrocatalyst benchmarking, and corrosion research

Graphical Enhancements for Voice Only Conference Calls

We present two very low bandwidth graphically enhanced interfaces for small group voice communications. One interface presents static images of the participants that highlight when one is speaking. The other interface utilizes three-dimensional avatars that can be quickly created. Eleven groups of 4 or 5 people were presented with each enhanced interface as well as conducting a live conversation and a voice only conversation. Experiments show that both graphically enhanced interfaces improve the understandability of conversations, particular with respect to impressions that others in the group could express themselves more easily, knowing who is talking, and when to speak. Little difference was found between the two graphical interfaces. Analysis of voice tracks also revealed differences between interfaces in the length and number of medium duration silences