Scanning Electrochemical Microscopy Tip Research Articles

Use of Combined Scanning Electrochemical and Fluorescence Microscopy for Detection of Reactive Oxygen Species in Prostate Cancer Cells

Release of ROS from prostate cancer (PC3) cells was studied using scanning electrochemical microscopy (SECM) and fluorescence microscopy. One-directional lateral scan SECM was used as a rapid and reproducible tool for simultaneous mapping of cell topography and reactive oxygen species (ROS) release. Fluorescence microscopy was used in tandem to monitor the tip position, in addition to providing information on intracellular ROS content via the use of ROS-reactive fluorescent dyes. A unique tip current (iT) vs lateral distance profile was observed when the tip potential (ET) was set at -0.65 V. This profile reflects the combined effects of topographical change and ROS release at the PC3 cell surfaces. Differentiation between topographical-related and ROS-induced current change was achieved by comparing the scans collected at -0.65 and -0.85 V. The effects of other parameters such as tip to cell distance, solvent oxygen content, and scan direction on the profile of the scan were systematically evaluated. Cells treated with tert-butyl hydroperoxide, a known ROS stimulus, were also evaluated using the lateral scanning approach. Overall, the SECM results correlate well with the fluorescence results. The extracellular ROS level detected at the SECM tip was found to be similar to the intracellular ROS level monitored using fluorescence microscopy. While the concentration of each contributing ROS species has not been determined and is thus part of the future study, here we have successfully demonstrated the use of a simple two-potential lateral scan approach for analysis of ROS released by living cells under real physiological conditions.

Scanning Electrochemical Microscopy: Using the Potentiometric Mode of SECM To Study the Mixed Potential Arising from Two Independent Redox Processes

This study demonstrates how the potentiometric mode of the scanning electrochemical microscope (SECM) can be used to sensitively probe and alter the mixed potential due to two independent redox processes provided that the transport of one of the species involved is controlled by diffusion. This is illustrated with the discharge of hydrogen from nanostructured Pd hydride films deposited on the SECM tip. In deareated buffered solutions the open circuit potential of the PdH in equilibrium between its β and α phases (OCP(β→α)) does not depend on the tip-substrate distance while in aerated conditions it is found to be controlled by hindered diffusion of oxygen. Chronopotentiometric and amperometric measurements at several tip-substrate distances reveal how the flux of oxygen toward the Pd hydride film determines its potential. Linear sweep voltammetry shows that the polarization resistance increases when the tip approaches an inert substrate. The SECM methodology also demonstrates how dissolved oxygen affects the rate of hydrogen extraction from the Pd lattice. Over a wide potential window, the highly reactive nanostructure promotes the reduction of oxygen which rapidly discharges hydrogen from the PdH. The flux of oxygen toward the tip can be adjusted via hindered diffusion. Approaching the substrate decreases the flux of oxygen, lengthens the hydrogen discharge, and shifts OCP(β→α) negatively. The results are consistent with a mixed potential due to the rate of oxygen reduction balancing that of the hydride oxidation. The methodology is generic and applicable to other mixed potential processes in corrosion or catalysis.

Scanning Electrochemical Microscopy of DNA Hybridization on DNA Microarrays Enhanced by HRP-Modified SiO2 Nanoparticles

Imaging of localized hybridization of nucleic acids immobilized on a glass DNA microarray was performed by means of generation collection (GC) mode scanning electrochemical microscopy (SECM). Amine-tethered oligodeoxynucleotide probes, spotted on the glass surface, were hybridized with an unmodified target sequence and a biotinylated indicator probe via sandwich hybridization. Spots where sequence-specific hybridization had occurred were modified by streptavidin-horseradish-peroxidase-(HRP)-wrapped SiO2 nanoparticles through the biotin-streptavidin interaction. In the presence of H2O2, hydroquinone (H2Q) was oxidized to benzoquinone (BQ) at the modified spot surface through the HRP catalytic reaction, and the generated BQ corresponding to the amount of target DNA was reduced in solution by an SECM tip. With this DNA microarray, a number of genes could be detected simultaneously and selectively enough to discriminate between complementary sequences and those containing base mismatches. The DNA targets at prepared spots could be imaged in SECM GC mode over a wide concentration range (10(-7)-10(-12) M). This technique may find applications in genomic sequencing.

In situ SECM study on concentration profiles of electroactive species from corrosion of stainless steel

The corrosion behaviours of type 304 stainless steel in acidic chloride solutions were investigated by cyclic voltammetric (CV) measurements at a scanning electrochemical microscope (SECM) tip combined with SECM scan imaging techniques. The results showed that the detection of electroactive species (i.e. ferrous ions) originating from the corrosion process can be accomplished as a function of position of the SECM tip above the stainless steel sample. Moreover, the variation in the tip–sample distance would allow for the tip current to be quantitatively correlated with the concentration profiles of the electroactive species or the related electrochemical activities on the sample surface. In a word, both voltammetric characteristic and three-dimensional SECM imaging related to the corrosion behaviours of 304 stainless steel will be helpful to clarify the possible pathways and reaction mechanisms involved in the corrosion processes.

Determination of Paracetamol in Presence of Ascorbic Acid in Pharmaceutical Products by Scanning Electrochemical Microscopy

AbstractThe selective amperometric determination of paracetamol in pharmaceutical formulations containing ascorbate was achieved by removing the interfering species in the diffusion layer created between a platinum substrate and a disc microelectrode in a Scanning Electrochemical Microscopy (SECM) configuration, while the target analyte was kept unconsumed. After complete depletion of ascorbate, paracetamol was detected at the SECM tip in a free‐interference solution zone. The influence of the substrate potential and the gap distance on the efficiency of ascorbate removal was systematically examined. The effectiveness of the device towards the determination of paracetamol in pharmaceutical samples was evaluated and under optimal conditions the results obtained agreed well with the labeled value.

Visualization of Oxygen Consumption of Single Living Cells by Scanning Electrochemical Microscopy: The Influence of the Faradaic Tip Reaction

The respiration activity of an individual living cell is an indicator of its metabolic vitality. Closely positioned microelectrodes have been suggested for determination of the respiration activity by monitoring the local oxygen concentration. Although first attempts for visualization of the oxygen consumption rate of single living cells by means of scanning electrochemical microscopy (SECM) were already described in 1998, evaluation of the respiratory activity of individual cells remains challenging and the complexity is often underestimated. In particular, the dimensions of the cell itself lead to limitations of conventionally used constant-height mode SECM investigations. Apart from convolution of the oxygen reduction current at the SECM tip with topographic effects, constant-height mode experiments require working distances comparable or below the height of the cell body, thus increasing the risk of tip crash. Attempts to overcome these restrictions include among others positioning of the tip to distances outside the feedback range, embedding of the cells into cavities, or efforts to subtract topographic contributions after cell death. Moreover, as living cells are irregular in dimension, the tip-to-cell distance varies with the tip position. Therefore, constant-distance mode (cd-mode) SECM techniques are inherently advantageous for this purpose. In particular, coupling SECM with scanning probe techniques, such as atomic force microscopy (AFM) and scanning ion conductance microscopy (SICM) as well as shearforce and impedance-based techniques, led to efficient strategies to control the tip-to-sample separation. Recently, we described a shearforce-based cd method (4D SF/ CD-SECM) that is able to work at various tip-to-sample separations. It can hence detect complete diffusion profiles in the surroundings of sources or sinks of redox-active species. Although SECM distance control systems are available, the detection of the respiration activity of single living cells remains challenging. Owing to the small rate of oxygen consumption by a single cell, only small current variations ontop of a high background current are measured. Even more importantly, a biological cell acts as an immiscible liquid– liquid interface in a SECM experiment. Lipophilic redox mediators are known to undergo transmembrane diffusion processes and can be utilized to investigate intracellular redox activity. However, concentration changes in the vicinity of the cellular membrane, for example by the tip reaction, may induce local concentration gradients and cause a diffusional exchange of redox species over the lipid bilayer in a socalled SECM-induced transfer (SECM-IT) mode. The high solubility of oxygen in lipids promotes this transmembrane diffusion and oxygen can easily cross the cell membrane. This diffusion process superimposes the detection of cell respiration. As a result, in most reports addressing detection of cell metabolism based on the detection of variations in the local oxygen concentration, the positioned microelectrode does not act as a passive observer but actively influences the oxygen concentration inside the gap between tip and cell, resulting in imaging artifacts that have not previously been addressed. Even though mentioned occasionally, this effect was neglected in SECM investigations of respiration activity at living cells. Herein, we address the influence of the oxygen reduction rate at the SECM tip on imaging the respiration activity at living cells. We provide strategies to avoid limitations resulting from a strong tip reaction using a potential pulse profile at the tip with a time dependent data acquisition in the shearforce-based cd-mode of SECM. Commonly, the detection of the local oxygen concentration in close proximity to the cell body is performed by means of a variation of the generator-collector mode of SECM with the tip being continuously polarized at oxygen reduction potential. The tip competes with the respiring living cell for the available oxygen inside the gap between SECM tip and cell surface. Crossing the cell body during a SECM line scan should therefore lead to a decrease of the tip current owing to a locally lowered oxygen concentration caused by cell [*] Dr. M. Nebel, S. Gr tzke, Prof. Dr. W. Schuhmann Lehrstuhl f r Analytische Chemie, Elektroanalytik & Sensorik and Center for Electrochemical Sciences, CES Ruhr-Universit t Bochum Universit tsstrasse 150, 44780 Bochum (Germany) E-mail: wolfgang.schuhmann@rub.de

Qualitative and quantitative detection of DNA amplified with HRP-modified SiO2 nanoparticles using scanning electrochemical microscopy

Qualitative and quantitative detection of DNA was achieved by a “sandwich” DNA sensor through SG/TC (substrate generation and tip collection) mode of scanning electrochemical microscopy (SECM). The “sandwich” DNA structure was formed by the hybridization of thiol-tethered oligodeoxynucleotide probes (capture probe), assembled on the gold substrate surface, with target DNA and biotinylated indicator probe. HRP (horseradish peroxidase)-wrapped SiO2 nanoparticles were linked to the sandwich structure through biotin–streptavidin interaction. Hydroquinone (H2Q) was oxidized to benzoquinone (BQ) at the modified substrate surface where sequence-specific hybridization had occurred through the HRP-catalyzed reaction in the presence of H2O2. The detection was based on the reduction of BQ generated on the modified substrate by SECM tip. For SECM imaging experiment, we structured the microsensor platform through localized desorption of 1-dodecanethiol monolayer. Approach curves were employed for quantitative detection of DNA concentration. The detection limit of complementary DNA was as low as 0.8pM. This technique is promising for the application on electrochemical DNA chip.

An exchangeable-tip scanning probe instrument for the analysis of combinatorial libraries of electrocatalysts

A combined scanning differential electrochemical mass spectrometer (SDEMS)-scanning electrochemical microscope (SECM) apparatus is described. The SDEMS is used to detect and spatially resolve volatile electrochemically generated species at the surface of a substrate electrode. The SECM can electrochemically probe the reactivity of the surface and also offers a convenient means of leveling the sample. It is possible to switch between these two different scanning tips and techniques without moving the sample and while maintaining potential control of the substrate electrode. A procedure for calibration of the SDEMS tip-substrate separation, based upon the transit time of electrogenerated species from the substrate to the tip is also described. This instrument can be used in the characterization of combinatorial libraries of direct alcohol fuel cell anode catalysts. The apparatus was used to analyze the products of methanol oxidation at a Pt substrate, with the SDEMS detecting carbon dioxide and methyl formate, and a PtPb-modified Pt SECM tip used for the selective detection of formic acid. As an example system, the electrocatalytic methanol oxidation activity of a sputter-deposited binary PtRu composition spread in acidic media was analyzed using the SDEMS. These results are compared with those obtained from a pH-sensitive fluorescence assay.

When Electron Transfer Meets Electron Transport in Redox-Active Molecular Nanojunctions

A scanning electrochemical microscope (SECM) was used to arrange two microelectrodes face-to-face separated by a micrometric gap. Polyaniline (PANI) was deposited electrochemically from the SECM tip side until it bridged the two electrodes. The junctions obtained were characterized by following the current through the PANI as a function of its electrochemical potential measured versus a reference electrode acting as a gate electrode in a solid-state transistor. PANI nanojunctions showed conductances below 100 nS in the oxidized state, indicating control of the charge transport within the whole micrometric gap by a limited number of PANI wires. The SECM configuration makes it possible to observe in the same experiment and in the same current range the electron-transfer and electron-transport processes. These two phenomena are distinguished here and characterized by following the variation of the current with the bias voltage and the scan rate. The electron-transfer current changes with the scan rate, while the charge-transport current varies with the bias voltage. Finally, despite the initially micrometric gap, a junction where the conductance is controlled by a single oligoaniline strand is achieved.

Microelectrochemical visualization of oxygen consumption of single living cells

The detection of cellular respiration activity is important for the assessment of the status of a biological cell. Due to its non-invasive character and high spatial resolution scanning electrochemical microscopy (SECM) is a powerful tool for single cell measurements. Common limitations of respiration studies performed by SECM are discussed and strategies provided to further adapt SECM detection schemes to the specific requirements for the investigation of single cell respiration. In particular the combination of a potential pulse technique in the redox competition mode of SECM with a shearforce-based constant-distance positioning of the SECM tip is proposed for characterising the impact of the tip reaction during SECM imaging. The adjustment of the driving force of the tip reaction and the selection of the time for data acquisition after applying the potential pulse allowed a successful visualization of cell respiration activity.

Preparation and Characterization of Carbon Powder Paste Ultramicroelectrodes as Tips for Scanning Electrochemical Microscopy Applications

We report a simple method of preparation of carbon paste ultramicroelectrodes (UMEs) for use as probe tips in scanning electrochemical microscopy (SECM). Carbon paste UMEs were prepared by packing the carbon paste into a chemically etched tip of a Pt-UME or a pulled glass capillary. Carbon-based UMEs are attractive in micrometer to nanometer gap experiments and in electrodeposition of single metal nanoparticles for electrocatalytic studies because of their high overpotential in proton and oxygen reduction. We have demonstrated the preparation of conically shaped carbon paste UMEs, appropriate for SECM measurements and micrometer to nanometer gap experiments.

Selective etching of ZnO films on an ITO substrate using a scanning electrochemical microscope

A scanning electrochemical microscope (SECM) combined with an inverse optical microscope has been used in its lithographic mode to fabricate microstructures on a ZnO coated ITO substrate. The UME electrode generated the protons which served as the etchant to dissolve the ZnO film. High resolution microstructuring was achieved with the SECM after the addition of Tris(hydroxymethyl)aminomethane (Tris) to the solution. In the etching solution, Tris was used as an efficient reactant to consume the protons, so that the etchant could not diffuse far from the tip electrode. The cyclic voltammetry technique was employed to determine the appropriate potential, about 1.2V vs. SCE, for the generation of protons at the tip electrode. The dimensions of the etched microstructures were measured using the optical microscopic images at different stages of the etching process in order to optimize the lithographic conditions. “Point by point” etching with the SECM tip was used to create the logo “FZU” of Fuzhou University on the ZnO film.

Tip generation–substrate collection–tip collection mode scanning electrochemical microscopy of oxygen reduction electrocatalysts

Concentric microring-disk tips for scanning electrochemical microscopy (SECM) were fabricated and used in a new “tip generation–substrate collection–tip collection” (TG–SC–TC) mode to determine the activity of an Au electrocatalyst for the oxygen reduction reaction (ORR), while simultaneously monitoring hydrogen peroxide produced during the reaction. ORR electrocatalysis/hydrogen peroxide detection measurements were performed by evolving O2 at the Au microring of the SECM tip while it was positioned close to an Au substrate. The O2 diffused to the Au substrate where it was reduced generating a substrate current. At the same time, hydrogen peroxide generated during the ORR was detected by oxidation at the SECM tip microdisk. The effects of the microring current, the tip-substrate distance and the substrate potential during the TG–SC–TC experiment have been determined and are described. The ability to use these SECM tips to scan electrocatalyst surfaces while generating maps containing electrocatalytic and mechanistic data is then demonstrated and the prospects for the use of these SECM tips in screening arrays of ORR electrocatalysts discussed.

Inhibition of the MRP1-mediated transport of the menadione-glutathione conjugate (thiodione) in HeLa cells as studied by SECM

Oxidative stress induced in live HeLa cells by menadione (2-methyl-1,4-napthaquinone) was studied in real time by scanning electrochemical microscopy (SECM). The hydrophobic molecule menadione diffuses through a living cell membrane where it is toxic to the cell. However, in the cell it is conjugated with glutathione to form thiodione. Thiodione is then recognized and transported across the cell membrane via the ATP-driven MRP1 pump. In the extracellular environment, thiodione was detected by the SECM tip at levels of 140, 70, and 35µM upon exposure of the cells to menadione concentrations of 500, 250, and 125µM, respectively. With the aid of finite element modeling, the kinetics of thiodione transport was determined to be 1.610(-7)m/s, about 10 times faster than menadione uptake. Selective inhibition of these MRP1 pumps inside live HeLa cells by MK571 produced a lower thiodione concentration of 50µM in presence of 500µM menadione and 50µM MK571. A similar reduced (50% drop) thiodione efflux was observed in the presence of monoclonal antibody QCRL-4, a selective blocking agent of the MRP1 pumps. The reduced thiodione flux confirmed that thiodione was transported by MRP1, and that glutathione is an essential substrate for MRP1-mediated transport. This finding demonstrates the usefulness of SECM in quantitative studies of MRP1 inhibitors and suggests that monoclonal antibodies can be a useful tool in inhibiting the transport of these MDR pumps, and thereby aiding in overcoming multidrug resistance.

Application of SECM in tracing of hydrogen peroxide at multicomponent non-noble electrocatalyst films for the oxygen reduction reaction

The redox competition mode of scanning electrochemical microscopy (RC-SECM) was used to study the electrocatalytic activity of three different non-noble metal O2 reduction catalysts at a pH value of 7.4, namely; multi-walled carbon nanotubes (MWCNTs), cobalt protoporphyrin (CoP) and a composite of MWCNTs/CoP. The collection efficiency of a scanning electrochemical microscopy (SECM) tip for the H2O2 generated by the reduction of O2 at the catalyst layer was almost 100%. Consequently, SECM experiments in a combined redox competition and generator/collector mode could be applied for the determination of the number of electrons exchanged during O2 reduction, leading to improved understanding of the intrinsic features of catalyst activity. This approach avoids the typical limitations encountered with rotating ring disk electrode (RRDE) voltammetry, notably, the variation of the quantity of H2O2 in the proximity of the electrode with the speed of electrode rotation or the chemical decomposition of reaction intermediates on the Pt ring, which often introduce inconsistencies and errors in the measured values of the number of exchanged electrons. It is commonly assumed that the O2 reduction reaction on most non-noble metal catalysts proceeds via formation of H2O2 as an intermediate. The follow-up reaction of H2O2, typically chemical decomposition or electrochemical reduction, influences the overall number of electrons exchanged during O2 reduction. In this study, we have confirmed by comparing the rate of electrochemical reduction of H2O2 using rotating disk electrode (RDE) measurements with its rate of chemical decomposition studied using a positioned SECM tip, that for the MWCNTs/CoP catalyst, chemical decomposition is predominantly determining the overall number of exchanged electrons per O2 molecule.

Quantification of the Surface Diffusion of Tripodal Binding Motifs on Graphene Using Scanning Electrochemical Microscopy

The surface diffusion of a cobalt bis-terpyridine, Co(tpy)(2)-containing tripodal compound (1·2PF(6)), designed to noncovalently adsorb to graphene through three pyrene moieties, has been studied by scanning electrochemical microscopy (SECM) on single-layer graphene (SLG). An initial boundary approach was designed in which picoliter droplets (radii ~15-50 μm) of the tripodal compound were deposited on an SLG electrode, yielding microspots in which a monolayer of the tripodal molecules is initially confined. The time evolution of the electrochemical activity of these spots was detected at the aqueous phosphate buffer/SLG interface by SECM, in both generation/collection (G/C) and feedback modes. The tripodal compound microspots exhibit differential reactivity with respect to the underlying graphene substrate in two different electrochemical processes. For example, during the oxygen reduction reaction, adsorbed 1·2PF(6) tripodal molecules generate more H(2)O(2) than the bare graphene surface. This product was detected with spatial and temporal resolution using the SECM tip. The tripodal compound also mediates the oxidation of a Fe(II) species, generated at the SECM tip, under conditions in which SLG shows slow interfacial charge transfer. In each case, SECM images, obtained at increasing times, show a gradual decrease in the electrochemical response due to radial diffusion of the adsorbed molecules outward from the microspots onto the unfunctionalized areas of the SLG surface. This response was fit to a simple surface diffusion model, which yielded excellent agreement between the two experiments for the effective diffusion coefficients: D(eff) = 1.6 (±0.9) × 10(-9) cm(2)/s and D(eff) = 1.5 (±0.6) × 10(-9) cm(2)/s for G/C and feedback modes, respectively. Control experiments ruled out alternative explanations for the observed behavior, such as deactivation of the Co(II/III) species or of the SLG, and verified that the molecules do not diffuse when confined to obstructed areas. The noncovalent nature of the surface functionalization, together with the surface reactivity and mobility of these molecules, provides a means to couple the superior electronic properties of graphene to compounds with enhanced electrochemical performance, a key step toward developing dynamic electrode surfaces for sensing, electrocatalysis, and electronic applications.

Sensing polymer inhomogeneity in coated metals during the early stages of coating degradation

Negative-feedback scanning electrochemical microscopy (SECM) is successfully applied to visualize spatially resolved differences in the topography of coated metal samples upon exposure to aqueous electrolyte solutions of different composition. This method allows the investigation of the uptake of reactants from the electrolyte phase through the polymeric matrix to the metal/polymer interface to be performed even at early exposures. Yet, the method must be carefully checked to discard transport processes from the organic matrix into the solution phase, such as those related to lixiviation. In this later case, the topography of the polymer layer may evolve with time accordingly, not longer exclusively responding to the uptake by the polymer matrix of components from the electrolyte phase. Furthermore, lixiviated species may also react with the SECM tip, eventually leading to the continuous modification of the active surface area of the electrode during the measurements. In this work, the effect of lixiviation from a nickel foil coated with plasticized PVC (PVC Plastisol) on its topographic characterization by SECM was investigated.

On the use of mercury-coated tips in scanning electrochemical microscopy to investigate galvanic corrosion processes involving zinc and iron

The corrosion processes related to zinc dissolution that take place in an iron–zinc galvanic pair exposed to a chloride solution were investigated by scanning electrochemical microscopy (SECM) using a mercury-coated platinum microelectrode as SECM tip. Both the release of zinc ions and the consumption of dissolved oxygen that occur in separate sites at the iron–zinc galvanic pair were monitored. Zinc ion quantification could be performed by stripping the zinc metal collected at the Hg-coated tip using linear sweep voltammetry.

Achieving Nanometer Scale Tip-to-Substrate Gaps with Micrometer-Size Ultramicroelectrodes in Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) tips with rounded glass insulation around the metal wire (radius a = 5 μm) were fabricated (apparent RG < 1.1, where RG is the ratio of the radius of the insulation sheath divided by the electrode radius), and their SECM feedback approach curves were studied in solutions of tris(2,2'-bipyridine)ruthenium(2+) (Rubpy) in acetonitrile and ferrocenemethanol in water with a platinum disk as the substrate electrode (radius a(s) = 1 mm). Considerable enhancement of the normalized feedback current, I(T)(L) = i(T)/i(T,∞), where L = d/a and d is the distance traveled by the SECM tip, was observed in both systems (e.g., I(T)(L) = 15 in organic solutions and I(T)(L) = 30 in aqueous solutions) with good electrode alignment. This shows that tip-to-substrate gaps of ca. d = 110 nm can be achieved. To account for any deviations from the usual disk UME behavior and currents caused by possible changes in the tip electrode geometry, simulations of the feedback response were performed for a 2D axisymmetric environment. All simulated results match in a point-to-point comparison with experimental values (average relative standard deviation (RSD) = 0.01 ± 0.005).

Scanning electrochemical microscopy for the investigation of corrosion processes: Measurement of Zn 2+ spatial distribution with ion selective microelectrodes

Ion-selective microelectrodes can be employed as tips in scanning electrochemical microscopy (SECM) for chemical imaging of corrosion processes. They present higher chemical selectivity than conventional amperometric microdisks, and may be the only effective option to visualize the dissolution of metals with negative redox potentials in aqueous environments when the use of Pt microelectrodes is limited by the onset of oxygen reduction and hydrogen evolution reactions. A robust micro-sized ion selective electrode has been developed which allows the spatial distribution of Zn 2+ during galvanic corrosion of a model Fe/Zn couple to be investigated using SECM. Owing to the low internal contact potential achieved with the novel design, the resistance of the micropipette electrodes is only fractions of the resistance of conventional micropipette electrodes of the same size. As a result, no special shielding of the microelectrodes is required and higher scanning rate can be used for scanning in the potentiometric modes using these micropipette tips. Concentration profiles over corroding surfaces measured with this technique will be presented.