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The article reports on the electrochemical and conductivity measurements of single-wall carbon nanotube network electrodes. Single-wall carbon nanotubes (SWNTs) are fascinating molecules composed of a graphene sheet rolled into a seamless cylinder of about 1nm in diameter. Their nanoscale size and unique electrical properties have prompted investigations into their electrochemical behavior. So, the article investigates the electrochemical behavior of SWNTs, namely, two-dimensional networks of pristine SWNTs on an insulating support. It demonstrates the significance of both metallic SWNTs and semiconducting SWNTs in determining the resulting electrochemical behavior of the SWNT network electrode.

The quantification of genotoxic impurities (GIs) such as hydrazine (HZ) is of critical importance in the pharmaceutical industry in order to uphold drug safety. HZ is a particularly intractable GI and its detection represents a significant technical challenge. Here, we present, for the first time, the use of electrochemical analysis to achieve the required detection limits by the pharmaceutical industry for the detection of HZ in the presence of a large excess of a common active pharmaceutical ingredient (API), acetaminophen (ACM) which itself is redox active, typical of many APIs. A flow injection analysis approach with electrochemical detection (FIA-EC) is utilized, in conjunction with a coplanar boron doped diamond (BDD) microband electrode, insulated in an insulating diamond platform for durability and integrated into a two piece flow cell. In order to separate the electrochemical signature for HZ such that it is not obscured by that of the ACM (present in excess), the BDD electrode is functionalized with Pt nanoparticles (NPs) to significantly shift the half wave potential for HZ oxidation to less positive potentials. Microstereolithography was used to fabricate flow cells with defined hydrodynamics which minimize dispersion of the analyte and optimize detection sensitivity. Importantly, the Pt NPs were shown to be stable under flow, and a limit of detection of 64.5 nM or 0.274 ppm for HZ with respect to the ACM, present in excess, was achieved. This represents the first electrochemical approach which surpasses the required detection limits set by the pharmaceutical industry for HZ detection in the presence of an API and paves the wave for online analysis and application to other GI and API systems. [ABSTRACT FROM AUTHOR]

The electrodeposition of Pt nanoparticles (NPs) on two-dimensional single walled carbon nanotube (SWNT) network electrodes is investigated as a means of tailoring electrode surfaces with a well-defined amount of electrocatalytic material. Both Pt NP deposition and electrocatalytic studies are undertaken using the microcapillary electrochemical method (MCEM), enabling multiple microscale measurements to be performed quickly and easily on the same SWNT sample. Using this approach, Pt catalysts with high specific surface areas relative to the geometric electrode area (defined by the meniscus contact of the MCEM probe with the Si/SiO 2 substrate bearing the SWNT network) can be controlled precisely over three orders of magnitude. This enables the influence of the specific surface area of an electrocatalyst on activity to be investigated, as demonstrated by studies of the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). [ABSTRACT FROM AUTHOR]

Scanning electrochemical cell microscopy is utilised as a read-write pipette-based probe to both electrochemically modify the local surface chemistry of boron doped diamond and ''read'' the resulting modification, at the micron scale. In this specific application, localised electrochemical oxidation results in conversion of the H-terminated surface to O, electrochemically visualised by monitoring the current change for reduction of Ru(NH3)63+. This methodology, in general, provides a platform for read-write analysis of electrodes, opening up new analytical avenues, particularly as the pipette can be viewed as a microfluidic device. [ABSTRACT FROM AUTHOR]

A novel electrochemical approach to the direct detection of hydrogen sulfide (H2S), in aqueous solutions, covering a wide pH range (acid to alkali), is described In brief, a dual band electrode device is employed, in a hydrodynamic flow cell, where the upstream electrode is used to controllably generate hydroxide ions (OH-), which flood the downstream detector electrode and provide the correct pH environment for complete conversion of H2S to the electrochemically detectable, sulfide (HS-) ion. All-diamond, coplanar conducting diamond band electrodes, insulated in diamond, were used due to their exceptional stability and robustness when applying extreme potentials, essential attributes for both local OH- generation via the reduction of water, and for in situ cleaning of the electrode, post oxidation of sulfide. Using a galvanostatic approach, it was demonstrated the pH locally could be modified by over five pH unite, depending on the initial pH of the mobile phase and the applied current. Electrochemical detection limits of 13.6 ppb sulfide were achieved using flow injection amperometry. This approach which offers local control of the pH of the detector electrode in a solution, which is far from ideal for optimized detection of the analyte of interest, enhances the capabilities of online electrochemical detection systems. [ABSTRACT FROM AUTHOR]

Abstract: A channel flow cell, fabricated using microsterolithography (MSL), has been employed to determine the rate constant for the homogenous oxidation of ascorbic acid (AA) by an electrogenerated oxidant in aqueous solution under physiological pH conditions using a dual gold microband electrode format. Specifically, the oxidation of ferrocenylmethyl trimethyl-ammonium (FcTMA+) at an upstream electrode produce FcTMA2+, which oxidises AA in solution, yielding FcTMA+ which can undergo further heterogeneous oxidation at the upstream electrode. In addition, by setting the downstream electrode potential to a value where FcTMA2+ is detected at a transport-limited rate, collection efficiency measurements are also possible in a redox titration format. The benefits of studying homogeneous kinetics, and particularly this catalytic EC′ process, in a flow through system using a dual electrode format are highlighted. Collection efficiency measurements are shown to be particularly attractive for the detection of low levels of AA and are much more sensitive than measurements at a single electrode, particularly as a range of device parameters, such as flow rate, electrode size and electrode separation can be tuned to optimise detection. Various electrode sizes operating in the generation/collection (GC) mode have been assessed, with the optimum geometry of those studied (for the highest collection efficiency in the absence of homogenous reactions) being a small upstream generator electrode (25μM long), a large downstream collector electrode (400μM long), separated by a few tens of microns, in a channel of 200μm height and 4mm width. A full model for the cell hydrodynamics and mass transport has been developed using finite element modelling and extensive experiments are reported assessing the collection efficiency for different electrode geometries and AA concentrations. The homogeneous rate constant for the reaction between FcTMA2+ and AA is 5.5 (±1.6)×105 M−1 s−1. [Copyright &y& Elsevier]

Abstract: A field ionization source based on densely spaced, vertically aligned carbon nanotubes (CNTs) has been developed and evaluated. The CNTs contained nickel particles at their tips. This source would be suitable for analytical mass spectrometry. With a positive voltage on the dense CNT arrays, the strong electric field generated around the CNT tips has effected field ionization. The ionization of inert gases, including helium, and organic compounds, including acetone and methane, and the control and the transfer of the resulting ions have been achieved. These results represent a base for application of this new ion source in mass spectrometry. [Copyright &y& Elsevier]

Scanning electrochemical microscopy (SECM) has been employed in the feedback mode to assess the electrochemical behavior of two-dimensional networks of single-walled carbon nanotubes (SWNTs). It is shown that, even though the network comprises both metallic and semi-conducting SWNTs, at high density (well above the percolation threshold for metallic SWNTs) and with approximately millimolar concentrations of redox species the network behaves as a thin metallic film, irrespective of the formal potential of the redox couple. This result is particularly striking since the fractional surface coverage of SWNTs is only ∼1% and SECM delivers high mass transport rates to the network. Finite element simulations demonstrate that under these conditions diffusional overlap between neighboring SWNTs is significant so that planar diffusion prevails in the gap between the SECM tip and the underlying SWNT substrate. The SECM feedback response diminishes at higher concentrations of the redox species. However, wet gate measurements show that at the solution potentials of interest the conductivity is sufficiently high that lateral conductivity is not expected to be limiting. This suggests that reaction kinetics may be a limiting factor, especially since the low surface coverage of the SWNT network results in large fluxes to the SWNTs, which are characterized by a low density of electronic states. For electroanalytical purposes, significantly, two-dimensional SWNT networks can be considered as metallic films for typical millimolar concentrations employed in amperometry and voltammetry. Moreover, SWNT networks can be inexpensively and easily formed over large scales, opening up the possibility of further electroanalytical applications. [ABSTRACT FROM AUTHOR]

Spatial variations in the electrical and electrochemical activity of microarray electrodes, fabricated entirely from diamond, have been investigated. The arrays contain ∼50-μm-diameter boron-doped diamond (BDD) disks spaced 250 μm apart (center to center) in insulating intrinsic diamond supports, such that the BDD regions are coplanar with the intrinsic diamond. Atomic force microscopy (AFM) imaging of the surface reveals a roughness of no more than ±10 nm over the array. Each BDD microdisk within the array contains polycrystalline BDD with a variety of different grains exposed. Using conducting-AFM, the conductivity of the different grains was found to vary within a BDD microdisk. Electrochemical imaging of the electroactivity of the microdisk electrodes using scanning electrochemical microscopy operating in substrate generation-tip collection mode revealed that, under apparently diffusion-limited steady-state conditions, there was a small variation in the response between electrodes. However, the majority of electrodes in the array appeared to show predominantly metallic behavior. For the electrodes that showed a lower activity, all grains within the microdisk supported electron transfer, albeit at different rates, as evidenced by studies on the electrodeposition of metallic silver, at potentials far negative of the flat band potential of oxygen-terminated polycrystalline diamond. The possibility of using these array electrodes for steady-state diffusion-limited measurements in electroanalytical applications is far-reaching. However, caution should be exercised in the kinetic analysis of voltammetric measurements, since wide variations in the electroactivity of individual grains are apparent when the potential is below the diffusion-limited value. [ABSTRACT FROM AUTHOR]

The use of single-walled carbon nanotube (SWNT) networks as templates for the electrodeposition of metal (Ag and Pt) nanostructures is described. Pristine SWNTs, grown on insulating SiO2 surfaces using catalyzed chemical vapor deposition, served as the working electrode. In the simplest case, electrical contact was made by depositing a gold strip on the SWNT substrate (device 1). Deposition of Ag and Pt over extensive periods (30 s) resulted in a high density of particles on the SWNTs, with almost contiguous nanowire formation from the Au/SWNT boundary moving to isolated nanoparticles at further distances from the contact. For direct electrochemical studies of Ag and Pt nucleation, the assembly was coated in a resist layer and a small window opened up to expose only the electrically connected SWNTs to solution (device 2). In this case, the electrochemical signature in voltammetric and amperometric studies of metal deposition was due solely to processes at the SWNTs. Coupled with high-resolution microscopy measurements (atomic force microscopy and field emission scanning electron microscopy), this approach provided detail on the nucleation and growth mechanisms of Ag and Pt on SWNTs under electrochemical control. In particular, Ag growth was found to be rapid and progressive with an increasing nanoparticle density with time, whereas Pt deposition was characterized by lower nucleation densities and slower growth rates with a tendency for larger particles to be produced over long times. [ABSTRACT FROM AUTHOR]

Abstract: Titania (anatase) films composed of nanoparticulate building blocks are formed in a layer-by-layer deposition procedure followed by calcination. Field emission gun scanning electron microscopy (FEGSEM) and conducting probe atomic force microscopy (C-AFM) techniques are used to assess the topography and electrical conductivity of the resulting titania films in the dry state. Two types of molecular binder, cyclohexane hexacarboxylic acid and phytic acid, are employed in the deposition process. The surface charge of the resulting titania films is dramatically affected by the presence of phosphate (from phytic acid) after pyrolysis of the molecular binder. Voltammetric responses for the redox system obtained at mesoporous titania coated electrodes immersed in aqueous KCl are strongly affected by the adsorption of in the presence of phosphate. In order to further investigate the effects of the mesoporous membrane on voltammetric features, an approximate adsorption and transport model supported by a simple numerical simulation (of explicit finite-difference type) with reversible adsorption/desorption equilibria is developed. Based on the comparison of experimental and numerical data, it is proposed that the electrical conductivity (electron diffusion) within the wet titania film in the potential range where the reduction of occurs is important in addition to ion transport. [Copyright &y& Elsevier]

A procedure for the batch microfabrication of scanning electrochemical-atomic force microscopy (SECM-AFM) probes is described. The process yields sharp AFM tips, incorporating a triangular-shaped electrode (base width 1 μm, height 0.65 μm) at the apex. Microfabrication was typically carried out on 1/4 3-in, wafers, yielding 60 probes in each run. The measured spring constant of the probes was in the range 1-1.5 N m-1. To date, processing has been carried out twice successfully, with an estimated success rate for the fabrication process in excess of 80%, based on field emission-scanning electron microscopy imaging of all probes and current-voltage measurements on a random selection of ∼30 probes. Steady-state vol tammetric measurements for the reduction of Ru(NH3)63+ in aqueous solution indicate that the electrode response is well-defined, reproducible, and quantitative, based on a comparison of the experimental diffusion-limited current with finite element simulations of the corresponding mass transport (diffusion) problem. Topographical imaging of a sputtered Au film with the SECM-AFM probes demon- strates lateral resolution comparable to that of conventional Si3N4 AFM probes. Combined electrochemical- topographical imaging studies have been carried out on two model substrates: a 10-μm-diameter disk ultrami-croelectrode (UME) and an array of 1-μm-diameter UMEs, spaced 12.5 pm apart (center to center). In both cases, an SECM-AFM probe was first employed to image the topography of the substrates. The tip was then moved back a defined distance from the surface and use to detect Ru-(NH3)62+ produced at the substrate, biased at a potential to reduce Ru(NH3)63+, present in bulk solution, at a diffusion-controlled rate (substrate generation-tip collection mode). These studies establish the success of the batch process for the mass microfabrication of SECM- AFM tips. [ABSTRACT FROM AUTHOR]

Electrospray ionization (ESI) is extensively used in the analysis of biological compounds; yet some fundamental properties of this technique are not completely understood. It is widely recognized that care should be exercised when noncovalent complexes are being studied by ESI, since weak noncovalent binding can be broken or formed during the desolvation process. In the present work, spectra from the noncovalent complex, vancomycin/diacetyl-l-lysyl-d-alanyl-d-alanine, obtained from ESI and from nanoelectrospray ionization (nanoESI), have been compared. The results indicated that the milder desolvation conditions arising as a result of the smaller sizes of droplets produced in the nanoESI source attenuated effects upon weak bonds in the desolvation process. The association constant values calculated from the relative peak intensities suggest that, when using ESI, the analyzed noncovalent complex dissociated in the condensed phase during the spraying process. The influences of experimental parameters such as tip diameter and coating for nanoESI needles were investigated. Principal component analysis, a multivariate analysis method, was applied to achieve a better evaluation of the spectra obtained using different needle diameters and coatings for the analysis of the noncovalent complex vancomycin/diacetyl-l-lysyl-d-alanyl-d-alanine. It was found that 2-microm tip diameter resulted in more reproducible spectra than the larger tip diameters tested (6-20μm). [ABSTRACT FROM AUTHOR]

Corrigendum to 'High pressure high temperature synthesis of highly boron doped diamond microparticles and porous electrodes for electrochemical applications'. On page 853 the value for the Tomes criterion of reversibility for a one electron transfer process at 298 K is incorrectly given as 59 mV; it is in fact 56.4 mV. VS acknowledges financial support from the European Union's Horizon 2020 research and innovation programme under grant agreement 792948 (NELMA). [Extracted from the article]

Single walled carbon nanotube (SWNT) network electrodes, in which a planar arrangement of SWNTs on an inert surface serve as a working electrode for voltammetry, offer considerable attributes for electroanalysis. Here, the effect of SWNT network density on the trace voltammetric analysis of a water-soluble ferrocene derivative (FcCOOH) is investigated in the presence of polyethylene glycol (PEG) or albumin, species that can foul (block) an electrode via adsorption. Fc-based analytes typically find use in redox labelling or redox shuttling, point-of-care electrochemical detection devices. Comparison is made between SWNT electrodes, grown by catalyzed chemical vapour deposition at three different surface coverages, 5, ~20 and ~30 μm SWNT μm-2, and commercial screen-printed carbon electrodes (SPCEs). In the presence of PEG (8% 2 K), for cyclic voltammetry, the lowest detectable concentration decreases as SWNT network density decreases. However, when employing differential pulse voltammetry, all three networks show a 1 nM FcCOOH limit of detection, three orders of magnitude smaller than achievable with SPCEs. This is attributed to the low capacitance of the SWNTs and absence of amorphous carbon structures which can contribute a pseudo-capacitive response. For both polyethylene glycol (PEG) and albumin (4%), repeat cycling shows the higher density SWNT network electrodes (≥20 μm SWNT μm-2) are far less susceptible to electrode fouling. Toward practical devices, a three-electrode chip, similar in design to that used in SPCEs, but using high density SWNT network electrodes, is also demonstrated to have impressive detection sensitivity for FcCOOH (nM level) in PEG solutions. The simplicity and practicality of the design widens the potential applications of these ultra-sensitive diagnostic tools based on planar network SWNTs. Comparison of single-walled carbon nanotube network and commercially available screen-printed carbon electrode for trace level electrochemical detection in biological media. Unlabelled Image [ABSTRACT FROM AUTHOR]

Square wave voltammetry (SWV) is commonly used in electroanalytical applications to enhance analyte faradaic signals and minimize nonfaradaic processes. However, little attention is given as to how best use SWV to minimize faradaic interference signals that arise from redox species present in solution that have redox potentials that convolute with that of the analyte. In conventional SWV, a series of current-time ( i - t ) transients are collected, and i is averaged over a specified window of each transient (potentiostat dependent). This average i is reported against the electrode potential, E . As the i - t response is governed by the type of electron transfer reaction under investigation, we show how by collecting all i - t data and through judicious choice of the current averaging window, it is possible to enhance the analyte response while at the same time reducing the interferent signal. We look at three different electron transfer reactions, fast electron transfer outer sphere, metal electrodeposition/stripping, and surface-confined proton-coupled electron transfer (PCET) and demonstrate different i - t behaviors in SWV, visually aided by the use of 3D i - t - E plots. In the case of PCET quinone-based voltammetric sensing of pH in the presence of a heavy metal (here Cu 2+ ), we show that the use of a much earlier current averaging window (2-10% of the i - t response) results in the pH signal being clearly distinguished from that of the overlapping heavy metal.

Electrochemical advanced oxidation (EAO) systems are of significant interest due to their ability to treat a wide range of organic contaminants in water. Boron doped diamond (BDD) electrodes have found considerable use in EAO. Despite their popularity, no laboratory scale method exists to quantify anodic corrosion of BDD electrodes under EAO conditions; all are qualitative using techniques such as scanning electron microscopy, electrochemistry, and spectroscopy. In this work, we present a new method which can be used to quantify average corrosion rates as a function of solution composition, current density, and BDD material properties over relatively short time periods. The method uses white light interferometry (WLI), in conjunction with BDD electrodes integrated into a 3D-printed flow cell, to measure three-dimensional changes in the surface structure due to corrosion over a 72 h period. It is equally applicable to both thin film and thicker, freestanding BDD. A further advantage of WLI is that it lends itself to large area measurements; data are collected herein for 1 cm diameter disk electrodes. Using WLI, corrosion rates as low as 1 nm h -1 can be measured. This enables unequivocal demonstration that organics in the EAO solution are not a prerequisite for BDD anodic corrosion. However, they do increase the corrosion rates. In particular, we quantify that addition of 1 M acetic acid to 0.5 M potassium sulfate results in the average corrosion rate increasing ∼60 times. In the same solution, microcrystalline thin film BDD is also found to corrode ∼twice as fast compared to freestanding polished BDD, attributed to the presence of increased sp 2 carbon content. This methodology also represents an important step forward in the prediction of BDD electrode lifetimes for a wide range of EAO applications., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

A finite-element model has been developed to simulate the cyclic voltammetric (CV) response of a planar electrode for a 1e outer-sphere redox process, which fully accounts for cell electrostatics, including ohmic potential drop, ion migration, and the structure of the potential-dependent electric double layer. Both reversible and quasi-reversible redox reactions are treated. The simulations compute the time-dependent electric potential and ion distributions across the entire cell during a voltammetric scan. In this way, it is possible to obtain the interdependent faradaic and non-faradaic contributions to a CV and rigorously include all effects of the electric potential distribution on the rate of electron transfer and the local concentrations of the redox species O z and R z -1 . Importantly, we demonstrate that the driving force for electron transfer can be different to the applied potential when electrostatic interactions are included. We also show that the concentrations of O z and R z -1 at the plane of electron transfer (PET) significantly depart from those predicted by the Nernst equation, even when the system is characterised by fast electron transfer/diffusion control. A mechanistic rationalisation is also presented as to why the electric double layer has a negligible effect on the CV response of such reversible systems. In contrast, for quasi-reversible electron transfer the concentrations of redox species at the PET are shown to play an important role in determining CV wave shape, an effect also dependant on the charge of the redox species and the formal electrode potential of the redox couple. Failure to consider electrostatic effects could lead to incorrect interpretation of electron-transfer kinetics from the CV response. Simulated CVs at scan rates between 0.1 and 1000 V s -1 are found to be in good agreement with experimental data for the reduction of 1.0 mM Ru(NH 3 ) 6 3+ at a 2 mm diameter gold disk electrode in 1.0 M potassium nitrate.

The majority of carbon based transmission electron microscopy (TEM) platforms (grids) have a significant sp 2 carbon component. Here, we report a top down fabrication technique for producing freestanding, robust, electron beam transparent and conductive sp 3 carbon substrates from boron doped diamond (BDD) using an ion milling/polishing process. X-ray photoelectron spectroscopy and electrochemical measurements reveal the sp 3 carbon character and advantageous electrochemical properties of a BDD electrode are retained during the milling process. TEM diffraction studies show a dominant (110) crystallographic orientation. Compared with conventional carbon TEM films on metal supports, the BDD-TEM electrodes offer superior thermal, mechanical and electrochemical stability properties. For the latter, no carbon loss is observed over a wide electrochemical potential range (up to 1.80 V vs RHE) under prolonged testing times (5 h) in acid (comparable with accelerated stress testing protocols). This result also highlights the use of BDD as a corrosion free electrocatalyst TEM support for fundamental studies, and in practical energy conversion applications. High magnification TEM imaging demonstrates resolution of isolated, single atoms on the BDD-TEM electrode during electrodeposition, due to the low background electron scattering of the BDD surface. Given the high thermal conductivity and stability of the BDD-TEM electrodes, in situ monitoring of thermally induced morphological changes is also possible, shown here for the thermally induced crystallization of amorphous electrodeposited manganese oxide to the electrochemically active γ-phase., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

For the detection of electrochemically produced hydroxyl radicals (HO · ) from the oxidation of water on a boron-doped diamond (BDD) electrode, electron paramagnetic resonance spectroscopy (EPR) in combination with spin trap labels is a popular technique. Here, we show that quantification of the concentration of HO · from water oxidation via spin trap electrochemical (EC)-EPR is problematic. This is primarily due to the spin trap oxidizing at potentials less positive than water, resulting in the same spin trap-OH · adduct as formed from the solution reaction of OH · with the spin trap. We illustrate this through consideration of 5,5-dimethyl-1-pyrroline N -oxide (DMPO) as a spin trap for OH · . DMPO oxidation on a BDD electrode in an acidic aqueous solution occurs at a peak current potential of +1.90 V vs SCE; the current for water oxidation starts to rise rapidly at ca. +2.3 V vs SCE. EC-EPR spectra show signatures due to the spin trap adduct (DMPO-OH · ) at potentials lower than that predicted thermodynamically (for water/HO · ) and in the region for DMPO oxidation. Increasing the potential into the water oxidation region, surprisingly, shows a lower DMPO-OH · concentration than when the potential is in the DMPO oxidation region. This behavior is attributed to further oxidation of DMPO-OH · , production of fouling products on the electrode surface, and bubble formation. Radical scavengers (ethanol) and other spin traps, here N - tert -butyl- α -phenylnitrone, α -(4-pyridyl N -oxide)- N - tert -butylnitrone, and 2-methyl-2-nitrosopropane dimer, also show electrochemical oxidation signals less positive than that of water on a BDD electrode. Such behavior also complicates their use for the intended application., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Many photoactivated processes involve a change in oxidation state during the reaction pathway and formation of highly reactive photoactivated species. Isolating these reactive species and studying their early-stage femtosecond to nanosecond (fs-ns) photodynamics can be challenging. Here we introduce a combined ultrafast transient absorption-spectroelectrochemistry (TA-SEC) approach using freestanding boron doped diamond (BDD) mesh electrodes, which also extends the time domain of conventional spectrochemical measurements. The BDD electrodes offer a wide solvent window, low background currents, and a tuneable mesh size which minimises light scattering from the electrode itself. Importantly, reactive intermediates are generated electrochemically, via oxidation/reduction of the starting stable species, enabling their dynamic interrogation using ultrafast TA-SEC, through which the early stages of the photoinduced relaxation mechanisms are elucidated. As a model system, we investigate the ultrafast spectroscopy of both anthraquinone-2-sulfonate (AQS) and its less stable counterpart, anthrahydroquinone-2-sulfonate (AH 2 QS). This is achieved by generating AH 2 QS in situ from AQS via electrochemical means, whilst simultaneously probing the associated early-stage photoinduced dynamical processes. Using this approach we unravel the relaxation mechanisms occurring in the first 2.5 ns, following absorption of ultraviolet radiation; for AQS as an extension to previous studies, and for the first time for AH 2 QS. AQS relaxation occurs via formation of triplet states, with some of these states interacting with the buffered solution to form a transient species within approximately 600 ps. In contrast, all AH 2 QS undergoes excited-state single proton transfer with the buffered solution, resulting in formation of ground state AHQS - within approximately 150 ps., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Students who undertake practical electrochemistry experiments for the first time will come face to face with the potentiostat. To many this is simply a box containing electronics which enables a potential to be applied between a working and reference electrode, and a current to flow between the working and counter electrode, both of which are outputted to the experimentalist. Given the broad generality of electrochemistry across many disciplines it is these days very common for students entering the field to have a minimal background in electronics. This article serves as an introductory tutorial to those with no formalized training in this area. The reader is introduced to the operational amplifier, which is at the heart of the different potentiostatic electronic circuits and its role in enabling a potential to be applied and a current to be measured is explained. Voltage follower op-amp circuits are also highlighted, given their importance in measuring voltages accurately. We also discuss digital to analogue and analogue to digital conversion, the processes by which the electrochemical cell receives input signals and outputs data and data filtering. By reading the article, it is intended the reader will also gain a greater confidence in problem solving issues that arise with electrochemical cells, for example electrical noise, uncompensated resistance, reaching compliance voltage, signal digitisation and data interpretation. We also include trouble shooting tables that build on the information presented and can be used when undertaking practical electrochemistry.

This work demonstrates the use of an sp 2 -bonded carbon microspot boron doped diamond (BDD) electrode for voltammetric measurement of both pH and analyte concentration in a pH-dependent speciation process. In particular, the electrode was employed for the voltammetric detection of pH and hypochlorite (OCl - ) in unbuffered, aerated solutions over the pH range 4-10. Knowledge of both pH and [OCl - ] is essential for determination of free chlorine concentration. The whole surface of the microspot BDD electrode was found active toward the voltammetric oxidation of OCl - , with OCl - showing a characteristic response at +1.5 V vs SCE. In contrast, it was only the surface integrated quinones (Q) in sp 2 -bonded carbon regions of the BDD electrode that were responsible for the voltammetric pH signal. A Nernstian response for pH (gradient = 63 ± 1 mV pH -1 ) was determined from proton coupled electron transfer at the BDD-Q electrode, over the potential range -0.4-0.5 V vs SCE. By measuring both OCl - and pH voltammetrically, over the pH range 4-10, the OCl - oxidative current was found to correlate extremely well with the predicted pH-dependent [OCl - ] speciation profile.

By changing the mole fraction of water (χwater) in the solvent acetonitrile (MeCN), we report a simple procedure to control nanostructure morphology during electrodeposition. We focus on the electrodeposition of palladium (Pd) on electron beam transparent boron-doped diamond (BDD) electrodes. Three solutions are employed, MeCN rich (90% v/v MeCN, χwater = 0.246), equal volumes (50% v/v MeCN, χwater = 0.743) and water rich (10% v/v MeCN, χwater = 0.963), with electrodeposition carried out under a constant, and high overpotential (-1.0 V), for fixed time periods (50, 150 and 300 s). Scanning transmission electron microscopy (STEM) reveals that in MeCN rich solution, Pd atoms, amorphous atom clusters and (majority) nanoparticles (NPs) result. As water content is increased, NPs are again evident but also elongated and defected nanostructures which grow in prominence with time. In the water rich environment, NPs and branched, concave and star-like Pd nanostructures are now seen, which with time translate to aggregated porous structures and ultimately dendrites. We attribute these observations to the role MeCN adsorption on Pd surfaces plays in retarding metal nucleation and growth.

Ex vivo pH profiling of the upper gastrointestinal (GI) tract (of a mouse), using an electrochemical pH probe, in both the absence and presence of pharmacological agents aimed at altering acid/bicarbonate production, is reported. Three pH electrodes were first assessed for suitability using a GI tract biological mimic buffer solution containing 0.5% mucin. These include a traditional glass pH probe, an iridium oxide (IrOx)-coated electrode (both operated potentiometrically), and a quinone (Q) surface-integrated boron-doped diamond (BDD-Q) electrode (voltammetric). In mucin, the time scale for both IrOx and glass to provide a representative pH reading was in the ∼100's of s, most likely due to mucin adsorption, in contrast to 6 s with the BDD-Q electrode. Both the glass and IrOx pH electrodes were also compromised on robustness due to fragility and delamination (IrOx) issues; contact with the GI tissue was an experimental requirement. BDD-Q was deemed the most appropriate. Ten measurements were made along the GI tract, esophagus (1), stomach (5), and duodenum (4). Under buffer only conditions, the BDD-Q probe tracked the pH from neutral in the esophagus to acidic in the stomach and rising to more alkaline in the duodenum. In the presence of omeprazole, a proton pump inhibitor, the body regions of the stomach exhibited elevated pH levels. Under melatonin treatment (a bicarbonate agonist and acid inhibitor), both the body of the stomach and the duodenum showed elevated pH levels. This study demonstrates the versatility of the BDD-Q pH electrode for real-time ex vivo biological tissue measurements.

An electrochemical sensor that contains patterned regions of sp 2 -carbon in a boron-doped diamond (BDD) matrix is presented for the quantitative detection of hypochlorite (OCl - ) at high concentrations in the alkaline, chemically oxidizing environment associated with bleach. As BDD itself is unresponsive to OCl - reduction within the solvent window, by using a laser micromachining process, it is possible to write robust electrochemically active regions of sp 2 -carbon into the electrochemically inert sp 3 -BDD electrode. In this work, four different laser patterned BDD electrodes are examined, and their response compared across a range of OCl - concentrations (0.02-1.50 M). A single macrospot (0.37 mm diameter disk) electrode and a closely spaced microspot (46 μm diameter disk) hexagonal array electrode, containing the same surface area of sp 2 -carbon, are shown to provide the most linear response toward OCl - reduction. Finite element modeling (FEM) is employed to better understand the electrochemical system, due to the complexity of the electrode geometry, as well as the need to include contributions from migration and Ohmic drop at these high concentrations. FEM data suggest that only a small percentage (∼1 × 10 -3 %) of the total laser-machined sp 2 area is active toward the OCl - reduction process and that this process is kinetically very sluggish (∼ k eff = 1 × 10 -12 cm s -1 ). The sensitivity at the array electrode (-0.127 ± 0.004 mA M -1 ; R 2 = 0.992) is higher than that at the single-spot electrode (-0.075 ± 0.002 mA M -1 ; R 2 = 0.996) due to the enhanced effect of transport to the edges of the microspots, shown via simulation. The electrodes returned a relatively stable response over a greater than 3 month period of use in the OCl - solutions, demonstrating these hybrid sp 2 -BDD electrodes show promise for long-term monitoring applications in the harsh environments associated with bleaching applications.

Boron doped diamond (BDD), given the robustness of the material, is becoming an electrode of choice for applications which require long-term electrochemical monitoring of analytes in aqueous environments. However, despite the extensive work in this area, there are no studies which directly assess the biofilm formation (biofouling) capabilities of the material, which is an essential consideration because biofouling often causes deterioration in the sensor performance. Pseudomonas aeruginosa is one of the most prevalent bacterial pathogens linked to water-related diseases, with a strong capacity for forming biofilms on surfaces that are exposed to aquatic environments. In this study, we comparatively evaluate the biofouling capabilities of oxygen-terminated (O-)BDD against materials commonly employed as either the packaging or sensing element in water quality sensors, with an aim to identify factors which control biofilm formation on BDD. We assess the monospecies biofilm formation of P. aeruginosa in two different growth media, Luria-Bertani, a high nutrient source and drinking water, a low nutrient source, at two different temperatures (20 and 37 °C). Multispecies biofilm formation is also investigated. The performance of O-BDD, when tested against all other materials, promotes the lowest extent of P. aeruginosa monospecies biofilm formation, even with corrections made for total surface area (roughness). Importantly, O-BDD shows the lowest water contact angle of all materials tested, that is, greatest hydrophilicity, strongly suggesting that for these bacterial species, the factors controlling the hydrophilicity of the surface are important in reducing bacterial adhesion. This was further proven by keeping the surface topography fixed and changing surface termination to hydrogen (H-), to produce a strongly hydrophobic surface. A noticeable increase in biofilm formation was found. Doping with boron also results in changes in hydrophobicity/hydrophilicity compared to the undoped counterpart, which in turn affects the bacterial growth. For practical electrochemical sensing applications in aquatic environments, this study highlights the extremely beneficial effects of employing smooth, O-terminated (hydrophilic) BDD electrodes.

Square wave voltammetry (SWV) is most commonly used to enhance electroanalytical current signals of a redox analyte of interest. The SWV is typically recorded in a potential region where both non-faradaic and faradaic currents are collected; however, only data in the faradaic region are analyzed. In this article, we show how by collecting the full current-time ( i- t) data, arising from the SWV potential pulse sequence, and analyzing in the region of the potential scan where non-faradaic currents arise, further analytical information can be collected, over short time periods (typically seconds). Importantly, we show how information on solution resistance, R (and solution conductivity), and double layer capacitance, C, can be extracted from this data, without the need to conduct further electrochemical experiments, such as electrochemical impedance spectroscopy or independent solution conductivity measurements. Knowledge of the latter is important for measurements in real world samples, where the electrolyte concentration is unknown. We show how SWV measurements of electrode capacitance with repeat SWV scans can also be used to determine whether a changing faradaic SWV signal is due to electrode fouling or changing analyte concentration. Finally, knowledge of both parameters ( RC) is essential for optimization of the SWV parameters, such that the faradaic SWV signal is truly free from non-faradaic contributions.

A hybrid sp 2 -sp 3 electrochemical sensor comprising patterned regions of nondiamond-carbon (sp 2 ) in a boron doped diamond (sp 3 ) matrix is described for the simultaneous voltammetric detection of dissolved oxygen (DO) and pH in buffered aqueous solutions. Using a laser micropatterning process it is possible to write mechanically robust regions of sp 2 carbon into a BDD electrode. These regions both promote the electrocatalytic reduction of oxygen and facilitate the proton coupled electron transfer of quinone groups, integrated into the surface of the sp 2 carbon. In this way, in one voltammetric sweep (time of measurement ∼4 s) it is possible to determine both the DO concentration and solution pH. By varying the sp 2 pattern the response can be optimized toward both analytes. Using a closely spaced sp 2 microspot array, a linear response toward DO, across the range 0.0 to 8.0 mg L -1 (0.0 to 0.25 mM; sensitivity = -8.77 × 10 -8 A L mg -1 , R 2 = 0.9991) and pH range 4-10 (sensitivity = 59.7 mV pH -1 , R 2 = 0.9983) is demonstrated. The electrode is also capable of measuring both DO concentration and pH in the more complex buffered environment of blood. Finally, we show how the peak position for ORR is independent of pH, and thus via measurement of the difference in ORR and pH peak position, internal referencing is possible. Such electrodes show great promise for use in applications ranging from biomedical sensing to water analysis.

While quinone proton coupled electron transfer (PCET) under buffered conditions is well understood, the situation is more complicated in unbuffered aqueous solutions. With a view to producing a quinone-based voltammetric pH electrode that can function universally in both buffered and unbuffered solutions by following a two-electron (2e - )/two-proton (2H + ) Nernstian pathway over a wide pH range, the voltammetric response of strongly electronically coupled surface-bound quinones, directly integrated into a boron-doped diamond (BDD) electrode, is investigated. A laser ablation process enables integration of quinones into the BDD electrode surface with a high p K a 1 (first protonation state) and with controllable, very low surface coverages (as low as 2 orders of magnitude below monolayer coverage). Under buffered conditions, one wave results for all pH values, and the 2e - /2H + pathway is followed across the entire pH range. The measured ET rate constant values, from Laviron analysis, are also high, indicative of fast ET pathways. Under unbuffered conditions, one wave is again observed for all pH values; however, deviations from the buffered 2e - /2H + behavior are seen in the neutral region (pH 6-8). While 2e - /2H + transfer is maintained at all times, we attribute the observed deviation to local pH changes caused by the consumption and generation of protons at the electrode surface during the redox electrochemistry of the quinone. The associated proton fluxes generated at such sparse surface coverages are thought to be sufficiently high enough to prevent ET from occurring exclusively via a proton-independent route. By reducing surface coverage (down to ∼4 × 10 -12 mol cm -2 ; the limit of our laser ablation process) local pH changes can be reduced but are not eradicated completely. By moving to a pulsed voltammetric technique, where for each potential step protons consumed at the electrode are immediately replaced, it is possible, provided the surface coverage is low enough, to obtain a Nernstian 2e - /2H + response across a wide pH range in unbuffered solution.

In electrodeposition the key challenge is to obtain better control over nanostructure morphology. Currently, a lack of understanding exists concerning the initial stages of nucleation and growth, which ultimately impact the physicochemical properties of the resulting entities. Using identical location scanning transmission electron microscopy (STEM), with boron-doped diamond (BDD) serving as both an electron-transparent TEM substrate and electrode, we follow this process, from the formation of an individual metal atom through to a crystalline metal nanoparticle, under potential pulsed conditions. In doing so, we reveal the importance of electrochemically driven atom transport, atom cluster formation, cluster progression to a nanoparticle, and the mechanism by which neighboring particles interact during growth. Such information will help formulate improved nucleation and growth models and promote wider uptake of electrodeposited structures in a wide range of societally important applications. This type of measurement is possible in the TEM because the BDD possesses inherent stability, has an extremely high thermal conductivity, is electron beam transparent, is free from contamination, and is robust enough for multiple deposition and imaging cycles. Moreover, the platform can be operated under conditions such that we have confidence that the dynamic atom events we image are truly due to electrochemically driven deposition and no other factors, such as electron-beam-induced movement.

Boron doped diamond (BDD) is continuing to find numerous electrochemical applications across a diverse range of fields due to its unique properties, such as having a wide solvent window, low capacitance, and reduced resistance to fouling and mechanical robustness. In this review, we showcase the latest developments in the BDD electrochemical field. These are driven by a greater understanding of the relationship between material (surface) properties, required electrochemical performance, and improvements in synthetic growth/fabrication procedures, including material postprocessing. This has resulted in the production of BDD structures with the required function and geometry for the application of interest, making BDD a truly designer material. Current research areas range from in vivo bioelectrochemistry and neuronal/retinal stimulation to improved electroanalysis, advanced oxidation processes, supercapacitors, and the development of hybrid electrochemical-spectroscopic- and temperature-based technology aimed at enhancing electrochemical performance and understanding.

Heterogeneous electron transfer (ET) processes at electrode/electrolyte interfaces are of fundamental and applied importance and are extensively studied by a range of electrochemical techniques, all of which have various attributes but also limitations. The present study focuses on the one-electron oxidation of tetrathiafulvalene (TTF) and reduction of tetracyanoquinodimethane (TCNQ) in acetonitrile solution by two powerful electrochemical techniques: Fourier-transformed large amplitude alternating current voltammetry (FTACV); and scanning electrochemical microscopy (SECM), both of which are supported by detailed theoretical models. At conventional Pt, Au and glassy carbon (GC) electrode materials, the apparent (overall) charge transfer kinetic values determined by FTACV give standard ET rate constants, k, that are fast and close to the reversible limit. They are in good agreement with highly localised k measurements determined by SECM under conditions of high mass transport rates. In contrast, the impact of both the complex heterogeneous surface of polycrystalline boron doped diamond (pBDD) and degenerate p-type doping results in a range of k values across the electrode surface compared to the overall k measured for both processes studied. Moreover, the reduced availability of charge carriers at the electrode surface, at each energy state, compared to a metal, which decreases as the potential becomes more negative, results in lower k 0 values at pBDD than Pt, Au and GC. The measurement technique also has an influence: SECM measurements are made at much higher local current density than FTACV, and for TCNQ/TCNQ˙ - , which has the more negative formal potential, limited charge carrier availability results in k > k, with unusual apparent charge transfer coefficients and voltammetric waveshapes from SECM. These data thus highlight the importance of understanding the influence of the measurement technique and further demonstrate how ET kinetics at pBDD differ from conventional electrodes, in this case for processes in an organic solvent, which has received much less attention compared to aqueous systems for studies with pBDD.

Quantitative studies of electron transfer processes at electrode/electrolyte interfaces, originally developed for homogeneous liquid mercury or metallic electrodes, are difficult to adapt to the spatially heterogeneous nanostructured electrode materials that are now commonly used in modern electrochemistry. In this study, the impact of surface heterogeneity on Fourier-transformed alternating current voltammetry (FTACV) has been investigated theoretically under the simplest possible conditions where no overlap of diffusion layers occurs and where numerical simulations based on a 1D diffusion model are sufficient to describe the mass transport problem. Experimental data that meet these requirements can be obtained with the aqueous [Ru(NH 3 ) 6 ] 3+/2+ redox process at a dual-electrode system comprised of electrically coupled but well-separated glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Simulated and experimental FTACV data obtained with this electrode configuration, and where distinctly different heterogeneous charge transfer rate constants (k 0 values) apply at the individual GC and BDD electrode surfaces, are in excellent agreement. Principally, because of the far greater dependence of the AC current magnitude on k 0 , it is straightforward with the FTACV method to resolve electrochemical heterogeneities that are ∼1-2 orders of magnitude apart, as applies in the [Ru(NH 3 ) 6 ] 3+/2+ dual-electrode configuration experiments, without prior knowledge of the individual kinetic parameters (k 0 1 and k 0 2 ) or the electrode size ratio (θ 1 :θ 2 ). In direct current voltammetry, a difference in k 0 of >3 orders of magnitude is required to make this distinction.

Scanning electrochemical microscopy (SECM) is a powerful tool that enables quantitative measurements of fast electron transfer (ET) kinetics when coupled with modeling predictions from finite-element simulations. However, the advent of nanoscale and nanogap electrode geometries that have an intrinsically high surface area-to-solution volume ratio realizes the need for more rigorous data analysis procedures, as surface effects such as adsorption may play an important role. The oxidation of ferrocenylmethyl trimethylammonium (FcTMA(+)) at highly oriented pyrolytic graphite (HOPG) is used as a model system to demonstrate the effects of reversible reactant adsorption on the SECM response. Furthermore, the adsorption of FcTMA(2+) species onto glass, which is often used to encapsulate ultramicroelectrodes employed in SECM, is also found to be important and affects the voltammetric tip response in a nanogap geometry. If a researcher is unaware of such effects (which may not be readily apparent in slow to moderate scan voltammetry) and analyzes SECM data assuming simple ET kinetics at the substrate and an inert insulator support around the tip, the result is the incorrect assignment of tip-substrate heights, kinetics, and thermodynamic parameters. Thus, SECM kinetic measurements, particularly in a nanogap configuration where the ET kinetics are often very fast (only just distinguishable from reversible), require that such effects are fully characterized. This is possible by expanding the number of experimental variables, including the voltammetric scan rate and concentration of redox species, among others.

Boron doped diamond (BDD) electrodes have shown considerable promise as an electrode material where many of their reported properties such as extended solvent window, low background currents, corrosion resistance, etc., arise from the catalytically inert nature of the surface. However, if during the growth process, non-diamond-carbon (NDC) becomes incorporated into the electrode matrix, the electrochemical properties will change as the surface becomes more catalytically active. As such it is important that the electrochemist is aware of the quality and resulting key electrochemical properties of the BDD electrode prior to use. This paper describes a series of characterization steps, including Raman microscopy, capacitance, solvent window and redox electrochemistry, to ascertain whether the BDD electrode contains negligible NDC i.e. negligible sp(2) carbon. One application is highlighted which takes advantage of the catalytically inert and corrosion resistant nature of an NDC-free surface i.e. stable and quantifiable local proton and hydroxide production due to water electrolysis at a BDD electrode. An approach to measuring the local pH change induced by water electrolysis using iridium oxide coated BDD electrodes is also described in detail.

The development of a voltammetric boron doped diamond (BDD) pH sensor is described. To obtain pH sensitivity, laser micromachining (ablation) is utilized to introduce controlled regions of sp(2) carbon into a high quality polycrystalline BDD electrode. The resulting sp(2) carbon is activated to produce electrochemically reducible quinone groups using a high temperature acid treatment, followed by anodic polarization. Once activated, no further treatment is required. The quinone groups show a linear (R(2) = 0.999) and Nernstian (59 mV/(pH unit)) pH-dependent reductive current-voltage response over a large analyzable pH range, from pH 2 to pH 12. Using the laser approach, it is possible to optimize sp(2) coverage on the BDD surface, such that a measurable pH response is recorded, while minimizing background currents arising from oxygen reduction reactions on sp(2) carbon in the potential region of interest. This enables the sensor to be used in aerated solutions, boding well for in situ analysis. The voltammetric response of the electrode is not compromised by the presence of excess metal ions such as Pb(2+), Cd(2+), Cu(2+), and Zn(2+). Furthermore, the pH sensor is stable over a 3 month period (the current time period of testing), can be stored in air between measurements, requires no reactivation of the surface between measurements, and can be reproducibly fabricated using the proposed approach. The efficacy of this pH sensor in a real-world sample is demonstrated with pH measurements in U.K. seawater.

Voltammetric studies of dopamine (DA) oxidation on pristine and acid-treated single-walled carbon nanotube (SWNT) network electrodes were undertaken in order to investigate both the effect of network density and acid treatment times on the voltammetric characteristics for DA oxidation and the susceptibility of the electrodes to fouling. Through careful control of catalysed chemical vapour deposition growth parameters, multiply interconnected and randomly oriented SWNT networks of two significantly different densities were grown (high density, HD, coverage ≫10 μm length of SWNT per μm(-2) and low density, LD, coverage = 5 (±1) μmSWNTμm(-2)). Acid treatment was performed to provide materials with different electrochemical properties and SWNT coverage, as determined by field emission-scanning electron microscopy, atomic force microscopy and micro-Raman spectroscopy. A high concentration of DA (100 μM) was deliberately employed to accelerate the fouling phenomenon associated with DA oxidation in order to evaluate the lifetime of the electrodes. HD pristine SWNT networks were found to promote more facile electron transfer (ET) and were less susceptible to blocking, compared to LD pristine SWNT networks. Acid treatment resulted in both a further enhancement of the ET rate and a reduction in susceptibility towards electrode fouling. However, lengthy acid treatment detrimentally affected ET, due to a decrease in network density and significant damage to the SWNT network structure. These studies highlight the subtle interplay between SWNT coverage and degree of acid functionalisation when seeking to achieve the optimal SWNT electrode for the voltammetric detection of DA.

Conducting, boron doped diamond (BDD), in addition to its superior material properties, offers several notable attributes to the electrochemist making it an intriguing material for electrochemical research. These include the widest solvent window of all electrode materials; low background and capacitive currents; reduced fouling compared to other electrodes and; the ability to withstand extreme potentials, corrosive and high temperature/pressure environments. However, BDD is not your typical electrode material, it is a semi-conductor doped degenerately with boron to present semi-metallic characteristics. Input from materials scientists, chemists and physicists has been required to aid understanding of how to work with this material from an electrochemical viewpoint and improve electrode quality. Importantly, depending on how the BDD has been grown and then subsequently treated, prior to electrochemical measurement, the resulting material properties can vary quite significantly from one electrode to the next. This likely explains the variability seen by different researchers working on the same experimental systems. The aim of this "protocols" article is not to provide a state-of-the-art review of diamond electrochemistry, suitable references are provided to the interested reader, but instead serves as a reference point for any researcher wishing to commence work with diamond electrodes and interpret electrochemical data. It provides information on how best to characterise the material properties of the electrode before use and outlines the interplay between boron dopant density, non-diamond-carbon content, grain morphology, surface chemistry and redox couple identity. All should ideally be considered when interpretating electrochemical data arising from the diamond electrode. This will aid the reader in making meaningful comparisons between data obtained by different researchers using different diamond electrodes. The guide also aims to help educate the researcher in choosing which form of BDD is best suited to their research application.

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been used to study the interaction of the tris(2,2'-bipyridine)ruthenium(II) complex, [Ru(bpy)(3)](2+), at both native silica surfaces and surfaces modified with polyelectrolyte films. Both poly-l-lysine (PLL) and PLL/poly-l-glutamic acid (PGA) bilayer functionalized interfaces have been studied. Concentration isotherms exhibit Langmuir-type adsorption behavior on both silica and PGA-terminated surfaces from which equilibrium constants have been derived. The pH-dependence of the [Ru(bpy)(3)](2+) adsorption to silica and the PLL/PGA film has also been investigated. For the latter substrate, the effective surface pK(a) of the acid groups was found to be 5.5. The effect of supporting electrolyte was also investigated and was shown to have a significant effect on the extent of [Ru(bpy)(3)](2+) adsorption. A thin-layer electrochemical cell arrangement, in which a working electrode was positioned just above the substrate, was used to change the solution pH in a controlled way via the potential-pulsed chronoamperometric oxidation of water. By measuring the optical absorption using EW-CRDS during such experiments, the desorption of [Ru(bpy)(3)](2+) from the surface has been monitored in real time. Experiments were carried out at different cell thicknesses and at various pulse durations. By combining data from the EW-CRDS experiments with fluorescence confocal laser scanning microscopy (CLSM) to determine the pH at the substrate surface, the pK(a) of the PLL/PGA film could be ascertained and was found to agree with the static pH isotherm measurements. These studies provide a platform for the further use of electrochemistry combined with EW-CRDS to investigate dynamic processes at interfaces.

The electrodeposition of metal (Pd and Pt) nanoparticles on networks of pristine single walled carbon nanotubes (SWNTs) has been investigated using a microelectrochemical cell. A microcapillary containing electrolyte solution and a reference electrode is contacted with a silicon oxide substrate bearing a SWNT network, connected as the working electrode. Electrodeposition is promoted by applying a potential between the SWNT network and the reference electrode. By combination of analysis of the resulting current-time curves with atomic force microscopy and field emission scanning electron microscopy imaging of the network surfaces after electrodeposition, the nature of metal nanoparticle formation on SWNTs has been elucidated. In particular, the parameters controlling nanoparticle number density, distribution, and size have been identified, with short deposition times and high driving forces favoring the formation of ultrasmall particles at high density. Capacitance and network resistance effects are minimized in the microcapillary configuration, making it possible to accurately analyze short time-scale deposition processes (millisecond time scale). Furthermore, it is also possible to make many measurements on a pristine sample, simply by moving the position of the microcapillary to a new location on the substrate.

A combination of high-resolution electrical and electrochemical imaging techniques, in conjunction with cathodoluminescence (CL), is used to investigate the electrochemical behavior of oxygen-terminated highly doped polycrystalline boron doped diamond (BDD). The BDD has a dopant density approximately 5 x 10(20) atoms cm(-3), grain size ca. 5-40 microm, and thickness 500 microm. CL imaging demonstrates that boron uptake is nonuniform across the surface of BDD, and conducting atomic force microscopy (C-AFM) highlights how this impacts on the local conductivity. While C-AFM shows no evidence for enhanced grain boundary conductivity, two characteristic conductivity domains are found with resistances of ca. 100 kOmega and ca. 50 MOmega. With the use of scanning electrochemical microscopy (SECM), local heterogeneities are also observed in the electroactivity of the BDD surface, consistent with the two different types of conducting regions. Local currents of the magnitude expected for metal-like behavior are observed in some regions, suggesting degenerative doping of the grains (supported by CL studies). In other regions, slower electron transfer is apparent. However, even for the reduction of Ru(NH(3))(6)(3+), which occurs at potentials far negative of the flat-band potential for oxygen-terminated BDD, all areas of the surface show some electroactivity. This study highlights that the spatially heterogeneous conductivity and corresponding electroactivity of BDD are readily resolved using a combination of C-AFM, SECM, and CL.

This paper reports the first comparison of the structure and electrical conductivity properties of spin cast (SC) and Langmuir-Schaeffer (LS) films of regioregular poly(3-hexylthiophene) (P3HT). In addition, the effect of incorporating highly monodisperse Au nanoparticles (NPs), with a core diameter of approximately 5 nm, into SC and LS P3HT films is described. A detailed picture of molecular organization in the films has been obtained using ultraviolet-visible absorption spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. Film morphology was correlated with pseudo-two-dimensional conductivity measured using scanning electrochemical microscopy, with P3HT in the semiconducting regime. It was found that SC films, which were slightly thicker than those formed with the LS technique, exhibited greater organization. This resulted in an order of magnitude higher lateral conductivity for the SC films. Inclusion of Au NPs (50 wt %) into both SC and LS films resulted in the formation of uniform and relatively flat (rms roughness approximately 1 nm) composite films. Surprisingly, the addition of NPs did not disrupt the characteristic crystal structure found for the native P3HT films. The effect of Au NPs on film lateral conductivity was found to be determined by the distribution of Au NPs within the polymer, which varied significantly between SC and LS films. Whereas Au NPs aggregated into hexagonally packed clusters in SC films, NPs in LS films were predominantly uniformly distributed between the lamella bilayer. It was found that, while the inclusion of Au NPs caused the lateral conductivity to decrease in SC films, in LS films, the lateral conductivity increased by a factor of 2.

We describe a method for the production of nanoelectrodes at the apex of atomic force microscopy (AFM) probes. The nanoelectrodes are formed from single-walled carbon nanotube AFM tips which act as the template for the formation of nanowire tips through sputter coating with metal. Subsequent deposition of a conformal insulating coating, and cutting of the probe end, yields a disk-shaped nanoelectrode at the AFM tip apex whose diameter is defined by the amount of metal deposited. We demonstrate that these probes are capable of high-resolution combined electrochemical and topographical imaging. The flexibility of this approach will allow the fabrication of nanoelectrodes of controllable size and composition, enabling the study of electrochemical activity at the nanoscale.