Single Entity Behavior of CdSe Quantum Dot Aggregates During Photoelectrochemical Detection.

We demonstrate that colloidal quantum dots of CdSe and CdSe/ZnS are detected during the photooxidation of MeOH, under broad spectrum illumination (250 mW/cm). The stepwise photocurrent vs. time response corresponds to single entities adsorbing to the Pt electrode surface irreversibly.

Electrodeposition of Two-Dimensional Pt Nanostructures on Highly Oriented Pyrolytic Graphite (HOPG): The Effect of Evolved Hydrogen and Chloride Ions.

We discuss the electrodeposition of two-dimensional (2D) Pt-nanostructures on Highly Oriented Pyrolytic Graphite (HOPG) achieved under constant applied potential versus a Pt counter electrode (E = ca. -2.2 V vs.

Simultaneous Electrochemical Speciation of Oxidized and Reduced Glutathione. Redox Profiling of Oxidative Stress in Biological Fluids with a Modified Carbon Electrode.

The simultaneous electrochemical quantification of oxidized (GSSG) and reduced glutathione (GSH), biomarkers of oxidative stress, is demonstrated in biological fluids. The detection was accomplished by the development of a modified carbon electrode and was applied to the analysis of biological fluids of model organisms under oxidative stress caused by lead intoxication. Nanocomposite molecular material based on cobalt phthalocyanine (CoPc) and multiwalled carbon nanotubes functionalized with carboxyl groups (MWCNT) was developed to modify glassy carbon electrodes (GCE) for the detection of reduced and oxidized glutathione.

Stochastic electrochemistry and photoelectrochemistry of colloidal dye-sensitized anatase nanoparticles at a Pt ultramicroelectrode.

We report the stochastic interactions between dye sensitized anatase nanoparticles, suspended in a colloid, and a Pt ultramicroelectrode (UME) that result in step-wise behavior in the current vs. time response. The stochastic currents are observed in the dark and under illumination.

Electrochemical detection and sizing of colloidal ZnO nanoparticles.

We demonstrate the controlled reduction of colloidal ZnO nanoparticles (NPs) on a Hg ultramicroelectrode (UME) and its application to determine the redox potential for the deoxygenation of ZnO. The NPs are in colloidal suspension in acetonitrile (MeCN) and reach the electrode by migrational mass transport. At the electrode surface, the Zn(2+) in zinc oxide NPs is reduced to a Zn(Hg) amalgam.

Observation of individual semiconducting nanoparticle collisions by stochastic photoelectrochemical currents.

We describe a method to detect individual semiconducting nanoparticles (NPs) using the photoelectrochemical (PEC) current measured at an ultramicroelectrode (UME). We use photooxidation of MeOH by TiO2 NPs as a model system of photocatalysis in solution. NPs suspended in MeOH under constant illumination produce valence-band holes that oxidize MeOH.

Photoelectrochemical study of the band structure of Zn(2)SnO(4) prepared by the hydrothermal method.

It is fundamentally interesting to study the photoelectrochemical properties of complex oxides for applications in photovoltaics and photocatalysis. In this paper, we study the band gap (E(g)) and energetics of the conduction band (CB) and valence band (VB) for films of zinc stannate (Zn(2)SnO(4)) nanoparticles (ca. 25 nm) of the inverse-spinel structure prepared by the hydrothermal method.

Interrogation of surfaces for the quantification of adsorbed species on electrodes: oxygen on gold and platinum in neutral media.

We introduce a new in situ electrochemical technique based on the scanning electrochemical microscope (SECM) operating in a transient feedback mode for the detection and direct quantification of adsorbed species on the surface of electrodes. A SECM tip generates a titrant from a reversible redox mediator that reacts chemically with an electrogenerated or chemically adsorbed species at a substrate of about the same size as the tip, which is positioned at a short distance from it (ca.1 microm).

Screening of oxygen evolution electrocatalysts by scanning electrochemical microscopy using a shielded tip approach.

Oxygen evolution electrocatalysts in acidic media were studied by scanning electrochemical microscopy (SECM) in the substrate generation-tip collection (SG-TC) imaging mode with a 100 microm diam tip. Pure IrO2 and Sn(1-x)Ir(x)O2 combinatorial mixtures were prepared by a sol-gel route to form arrays of electrocatalyst spots. The experimental setup has been developed to optimize screening of electrocatalyst libraries under conditions where the entire array is capable of the oxygen evolution reaction (OER).

Imaging of metal ion dissolution and electrodeposition by anodic stripping voltammetry-scanning electrochemical microscopy.

We have developed a new imaging method for scanning electrochemical microscopy (SECM) employing fast-scan anodic stripping voltammetry (ASV) to provide sensitive and selective imaging of multiple chemical species at interfaces immersed in solution. A rapid cyclic voltammetry scan (100 V/s) is used along with a short preconcentration time (300-750 ms) to allow images to be acquired in a normal SECM time frame. A Hg-Pt film electrode is developed having an equivalent Hg thickness of 40 nm that has good sensitivity at short preconcentration times and also retains thin-film behavior with high-speed voltammetric stripping.

Selective insulation with poly(tetrafluoroethylene) of substrate electrodes for electrochemical background reduction in scanning electrochemical microscopy.

We describe a wet process for the fabrication of poly(tetrafluoroethylene) (PTFE)-covered electrodes in which arrays of holes ( approximately 200 microm) are formed. The PTFE coating provides electrical insulation of most of the electrode surface with selected regions exposed for electrochemical experiments. The arrays of microholes can be controllably patterned and filled with precursor solutions using a piezoelectric dispenser.

Scanning electrochemical microscopy. 59. Effect of defects and structure on electron transfer through self-assembled monolayers.

Electron transfer (ET) rate kinetics through n-alkanethiol self-assembled monolayers (SAMs) of alkanethiols of different chain lengths [Me(CH2)nSH; n=8, 10, 11, 15] on Au and Hg surfaces and ferrocene (Fc)-terminated SAMs (poly-norbornylogous and HS(CH2)12CONHCH2Fc) on Au were studied using cyclic voltammetry and scanning electrochemical microscopy (SECM). The SECM results allow determination of the ET kinetics of solution-phase Ru(NH3)63+/2+ through the alkanethiol SAMs on Au and Hg. A model using the potential dependence of the measured rate constants is proposed to compensate for the pinhole contribution.