Steady-state electrochemical responses have been obtained at single Au nanoparticles using Pt nanoelectrodes. A Au single-nanoparticle electrode (SNPE) is constructed by chemically immobilizing a single Au nanoparticle at a SiO(2)-encapsulated Pt disk nanoelectrode, which was previously modified by an amine-terminated silane. The Au SNPE has been characterized by transmission electron microscopy, underpotential deposition of Cu, and steady-state cyclic voltammetry. It has been found that the presence of a single Au nanoparticle enhances the electron transfer from the Pt nanoelectrode to the redox molecules, and the voltammetric response at the Au SNPE depends on the size of the Au nanoparticle. The Au SNPE has been utilized to examine the oxygen-reduction reaction in a KOH solution to explore the feasibility of measuring the electrocatalytic activity at a single-nanoparticle level. It has been shown that the electrocatalytic activity of single Au nanoparticles can be directly measured using SNPEs, and the electrocatalytic activity is dependent on the size of the Au nanoparticles. This study can help to understand the structure-function relationship in nanoparticle-based electrocatalysis.

This article reviews recent work involving the development and application of nanoelectrodes in electrochemistry and related areas. We first discuss common analytical methods for characterizing the size, shape, and quality of nanoelectrodes, including electron microscopy, steady-state cyclic voltammetry, scanning electrochemical microscopy, and surface modification. We then emphasize recent developments in fabrication techniques that have led to structurally well-defined nanoelectrodes. We highlight recent advances in the application of nanoelectrodes in important analytical chemistry areas, such as single-molecule studies, single-nanoparticle electrochemistry, and measurements of neurotransmitters from single neuronal cells.

Here we report the theory and experimental study of the steady-state voltammetric behavior of a microelectrode used as a limiting pole in a closed bipolar electrochemical cell. We show that the steady-state voltammetric response of a microelectrode used in a closed bipolar cell can be quantitatively understood by considering the responses of both poles in their respective conventional two-electrode setups. In comparison to a conventional electrochemical cell the voltammetric response of the bipolar cell has a similar sigmoidal shape and limiting current, however, the response is often slower than that of the typical two-electrode setup. This leads to a broader voltammogram and a decreased wave slope which can be somewhat misleading and appear that the process being studied is irreversible when it instead can be a result of the coupling of two reversible processes. We show that a large limiting current on the excess pole would facilitate the observation of a faster voltammetric response and both redox concentration and electrode area of the excess pole affect the wave shape. Both factors should be maximized in electroanalytical experiments in order to obtain fast voltammetric responses on the main electrode of interest and to detect quick changes in analyte concentrations.

A Structures for Lossless Ion Manipulations (SLIM) module that allows ion mobility separations and the switching of ions between alternative drift paths is described. The SLIM switch component has a “Tee” configuration and allows the efficient switching of ions between a linear path and a 90-degree bend. By controlling switching times, ions can be efficiently directed to an alternative channel as a function of their mobilities. In the initial evaluation the switch is used in a static mode and shown compatible with high performance ion mobility separations at 4 Torr. In the dynamic mode, we show that mobility-selected ions can be switched into the alternative channel, and that various ion species can be independently selected based on their mobilities for time-of-flight mass spectrometer (TOF MS) IMS detection and mass analysis. This development also provides the basis of, for example, the selection of specific mobilities for storage and accumulation, and the key component of modules for the assembly of SLIM devices enabling much more complex sequences of ion manipulations.