Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes the work of researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-forprofit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement:This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Analytical Chemistry, © American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/ac203195h A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. ABSTRACT: Scanning electrochemical cell microscopy (SECCM) is a high resolution electrochemical scanning probe technique that employs a dual-barrel theta pipet probe containing electrolyte solution and quasi-reference counter electrodes (QRCE) in each barrel. A thin layer of electrolyte protruding from the tip of the pipet ensures that a gentle meniscus contact is made with a substrate surface, which defines the active surface area of an electrochemical cell. The substrate can be an electrical conductor, semiconductor or insulator. The main focus here is on the general case where the substrate is a working electrode, and both ion-conductance measurements between the QRCEs in the two barrels and voltammetric/amperometric measurements at the substrate can be made simultaneously. In usual practice a small perpendicular oscillation of the probe with respect to the substrate is employed, so that an alternating conductance current (ac) develops, due to the change in the dimensions of the electrolyte contact (and hence resistance), as well as the direct conductance current (dc). It is shown that the dc current can be predicted for a fixed probe by solving the Nernst-Planck equation and that the ac response can also be derived from this response. Both responses are shown to agree well with experiment. It is found that the pipet geometry plays an important role in controlling the dc conductance current and that this is easily measured by microscopy. A key feature of SECCM is that mass transport to the substrate surface is by diffusion and, for charged analytes, ion migration which can be controlled and varied quantifiably via the bias between the ...

■ Abstract Scanning electrochemical cell microscopy (SECCM) is a new pipette-based imaging techniquepurposely designed to allow simultaneous electrochemical, conductance, and topographical visualization of surfaces and interfaces. SECCM uses a tiny meniscus or droplet, confined between the probe and the surface, for high-resolution functional imaging and nanoscale electrochemical measurements. Here we introduce this technique and provide an overview of its principles, instrumentation, and theory. We discuss the power of SECCM in resolving complex structure-activity problems and provide considerable new information on electrode processes by referring to key example systems, including graphene, graphite, carbon nanotubes, nanoparticles, and conducting diamond. The many longstanding questions that SECCM has been able to answer during its short existence demonstrate its potential to become a major technique in electrochemistry and interfacial science.

ABSTRACT:As a new form of carbon, graphene is attracting intense interest as an electrode material with widespread applications. In the present study, the heterogeneous electron transfer (ET) activity of graphene is investigated using scanning electrochemical cell microscopy (SECCM), which allows electrochemical currents to be mapped at high spatial resolution across a surface for correlation with the corresponding structure and properties of the graphene surface. We establish that the rate of heterogeneous ET at graphene increases systematically with the number of graphene layers, and show that the stacking in multilayers also has a subtle influence on ET kinetics.Graphene-based materials are having a huge impact in electrochemistry and electrochemical technologies, with promising applications in areas such as supercapacitors, 1 batteries, 2 electrocatalytic supports, 3 sensors for electroanalysis 4 and transparent electrodes. 5 These important technologies typically use graphene produced by chemical vapor deposition (CVD) 6 and other scalable methods, yet important fundamentals questions concerning heterogeneous electron transfer (ET) at such materials -intrinsic to many of these applications-remain to be addressed. Electrical measurements have revealed that the electron mobility 7 and the electronic band structure 8 are sensitive to the number of graphene layers and their stacking order, with implications for electrochemistry. In this communication, we thus seek to elucidate how both the number of graphene layers and arrangement of the layers influence heterogeneous ET kinetics.Graphene grown by CVD on nickel substrates 9 (see Supporting Information section 1) was optimal for the present study because it presents a heterogeneous continuous layer of microsized multilayered flakes, which can be addressed with high resolution scanning electrochemical cell microscopy (SECCM). [10][11][12][13] Thus, on one sample it is possible to make thousands of individual electrochemical (EC) measurements at different locations and relate these to the corresponding graphene structure. This provides datasets on a scale that would be unfeasible with conventional photolithographic techniques of the type employed in recent EC studies of exfoliated graphene. [14][15][16] In order to study the unambiguous electrochemical response of graphene without any interference from a conductive substrate, CVD graphene layers were transferred to a silicon substrate with a 300 nm thermal grown oxide layer. This substrate allowed optical visualization and identification of the morphological film features characteristic of graphene, 17,18 for direct correlation with the local electrochemistry. Importantly, the approach described herein makes possible the study of graphene surfaces with minimal intrusion and avoids the need for any post-processing lithographic step, which may result in unavoidable damage and possible interference of residues. 19 Ferrocene-derivatives have proven particularly suitable for the study of the ET activity of sp 2 ca...

Carbon nanotubes have attracted considerable interest for electrochemical, electrocatalytic, and sensing applications, yet there remains uncertainty concerning the intrinsic electrochemical (EC) activity. In this study, we use scanning electrochemical cell microscopy (SECCM) to determine local heterogeneous electron transfer (HET) kinetics in a random 2D network of single-walled carbon nanotubes (SWNTs) on an Si∕SiO 2 substrate. The high spatial resolution of SECCM, which employs a mobile nanoscale EC cell as a probe for imaging, enables us to sample the responses of individual portions of a wide range of SWNTs within this complex arrangement. Using two redox processes, the oxidation of ferrocenylmethyl trimethylammonium and the reduction of ruthenium (III) hexaamine, we have obtained conclusive evidence for the high intrinsic EC activity of the sidewalls of the large majority of SWNTs in networks. Moreover, we show that the ends of SWNTs and the points where two SWNTs cross do not show appreciably different HET kinetics relative to the sidewall. Using finite element method modeling, we deduce standard rate constants for the two redox couples and demonstrate that HET based solely on characteristic defects in the SWNT side wall is highly unlikely. This is further confirmed by the analysis of individual line profiles taken as the SECCM probe scans over an SWNT. More generally, the studies herein demonstrate SECCM to be a powerful and versatile method for activity mapping of complex electrode materials under conditions of high mass transport, where kinetic assignments can be made with confidence.W ithin the family of nanostructured materials, carbon nanotubes (CNTs) have attracted particular attention because they are readily synthesised at low cost, have exceptional electronic properties, exhibit chemical and mechanical stability, and are amenable to a wide range of simple chemical functionalization routes (1-3). These characteristics have led to CNTs being considered ideal substrates for electronics (4), sensing systems (5, 6), electrocatalytic supports (7), and batteries (8). Furthermore, the different configurations in which CNTs can be arranged broaden their versatility and allow custom design of devices for specific applications. Individual single-walled carbon nanotubes (SWNTs) (9), 2D networks (10-12), and 3D nanostructures (13) have all been employed successfully.Understanding heterogeneous electron transfer (HET) at CNTs is of considerable importance, due to the wide range of electroanalytical and electrocatalytic systems based on CNTs (14-17), and also because electrochemistry provides an attractive route to functionalize and tailor the properties of . Probing HET in 1D electrode materials is interesting fundamentally, given their inherent electronic structure and properties (21,22). However, as we highlight herein, despite many studies aimed at characterizing HET at CNTs, substantial questions remain unanswered, such as the location and rate of HET.A popular approach for studying electrochemistry at CNT...

A wide variety of steric and electronic features can be incorporated into transition metal coordination complexes, offering the prospect of rationally-designed therapeutic agents with novel mechanisms of action. Here we compare the chemical reactivity and anticancer activity of organometallic Os II complexes [Os(h 6 -arene)(XY)Z]PF 6 where arene ¼ p-cymene or biphenyl, XY ¼ N,N 0 -chelated phenyliminopyridine or phenylazopyridine derivatives, and Z ¼ Cl or I. The X-ray crystal structure of [Os(h 6 -p-cym)(Impy-OHLike the azopyridine complexes we reported recently (Dalton Trans., 2011, 40, 10553-10562), some iminopyridine complexes are also potently active towards cancer cells (nanomolar IC 50 values). However we show that, unlike the azopyridine complexes, the iminopyridine complexes can undergo aquation, bind to the nucleobase guanine, and oxidize coenzyme nicotine adenine dinucleotide (NADH). We report the first detection of an Os-hydride adduct in aqueous solution by 1 H NMR (À4.2 ppm). Active iminopyridine complexes induced a dramatic increase in the levels of reactive oxygen species (ROS) in A549 lung cancer cells. The anticancer activity may therefore involve interference in the redox signalling pathways in cancer cells by a novel mechanism.

(2011) Electrochemistry at nanoscale electrodes : individual single-walled carbon nanotubes (SWNTs) and SWNT-templated metal nanowires. ACS Nano, Vol. 5 (No. 12). pp. 10017-10025. ISSN 1936-0851 Permanent WRAP url: http://wrap.warwick.ac.uk/50933/ Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes the work of researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-forprofit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement:This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in ACS Nano, © American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/nn203823f A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. In the past two decades much effort has gone into the fabrication and application of nanoscale electrodes (NSEs), i.e. electrodes with at least one dimension in the sub-100 nm regime, for both the quantification of fast electron transfer (ET) kinetics 1-6 and electroanalysis. 4,7 The most popular NSEs are based on tapered or etched metal wires encapsulated by a variety means to produce disk or conical electrodes. 2,[8][9][10][11][12] While attractive in principle, the accuracy with which these NSEs can be used depends on microscopy characterization of the electrode geometry.This has often proved difficult due to the nanoscale dimensions of the electrodes, the presence of a large insulating coating and the fact that they do not reside on a planar substrate. In these instances, NSE dimensions tend to be estimated from limiting current measurements, but this may not inform on the precise electrode geometry or dimensions. In the worst cases, kinetic data obtained on illdefined NSEs may be miscalculated by an order of magnitude. 13, 14A major further drawback in the use of etching and sealing techniques for the fabrication of NSEs is the inherent variability in the electrode geometry and quality of electrode-insulator seal, for electrodes apparently produced using the same fabrication conditions. Thus, electrodes of this type are made by trial and error and many procedures may be of low yield. 21 The appro...

Here we demonstrate the use of microstereolithography (MSL), a 3D direct manufacturing technique, as a viable method to produce small-scale microfluidic components for electrochemical flow detection. The flow cell is assembled simply by resting the microfabricated component on the electrode of interest and securing with thread! This configuration allows the use of a wide range of electrode materials. Furthermore, our approach eliminates the need for additional sealing methods, such as adhesives, waxes, and screws, which have previously been deployed. In addition, it removes any issues associated with compression of the cell chamber. MSL allows a reduction of the dimensions of the channel geometry (and the resultant component) and, compared to most previously produced devices, it offers a high degree of flexibility in the design, reduced manufacture time, and high reliability. Importantly, the polymer utilized does not distort so that the cell maintains well-defined geometrical dimensions after assembly. For the studies herein the channel dimensions were 3 mm wide, 3.5 mm long, and 192 or 250 mum high. The channel flow cell dimensions were chosen to ensure that the substrate electrodes experienced laminar flow conditions, even with volume flow rates of up to 64 mL min(-1) (the limit of our pumping system). The steady-state transport-limited current response, for the oxidation of ferrocenylmethyl trimethylammonium hexaflorophosphate (FcTMA(+)), at gold and polycrystalline boron doped diamond (pBDD) band electrodes was in agreement with the Levich equation and/or finite element simulations of mass transport. We believe that this method of creating and using channel flow electrodes offers a wide range of new applications from electroanalysis to electrocatalysis.

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