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A ribonucleic acid (RNA) sensor based on hybridization of its peptide nucleic acid (PNA) molecule with a target RNA oligomer of the internal ribosome entry site sequence specific to the hepatitis C virus (HCV) and the electrochemical impedance detection is described. This RNA is one of the most conservative molecules of the whole HCV RNA genome. The ammonium ion terminated PNA molecule was immobilized via its host--guest interactions with the diaza crown ring of 3-thiophene-acetamide-diaza-18-crown-6 synthesized by a simple two-step method, which forms a well-defined self-assembled monolayer (SAM) on gold. Hybridization events of the probe PNA with the target RNA were monitored by measuring charge-transfer resistances for the Fe[[(CN).sub.6].sup.3-/4-] redox probe using Fourier transform electrochemical impedance spectroscopy. The ratio of the resistances of the SAM-covered electrode measured before and after hybridization increased linearly with log[RNA] in the rat liver lysate with a detection limit of about 23 pM. 10.1021/ac1019232

The construction and characterization of platinum and gold disk electrodes with minimum radii of 7 nm (platinum) and 500 nm (gold) is reported. The electrodes were prepared with a micropipet puller using a two step procedure and have been characterized using scanning electron microscopy, scanning electrochemical microscopy, high speed chronoamperometry, and cyclic voltammetry. The formation and growth of platinum and gold oxide layers, on the electrodes at time scales from microseconds to seconds, is reported. Significantly, the apparent microscopic area as determined by forming and subsequently reducing an oxide layer in acidic electrolyte using cyclic voltammetry depends dramatically on the scan rate. While conventional roughness factors between 1.8 and 3 are observed on average for scan rates above 5 V [s.sup.-1], the apparent roughness can exceed 30 for scan rates less than 0.5 V [s.sup.-1]. Chronoamperometry, conducted on the microsecond to millisecond time scale, is used to probe the dynamics of monolayer and multilayer oxide formation as well as the reversibility of the oxide formation and removal. The latter study suggests that (at least for platinum) the growth of the oxide layer proceeds with a lower constant rate after an oxide monolayer is formed. 10.1021/ac101728a

Field-amplified sample stacking using a fused silica capillary coated with gold nanoparticles (AuNPs) embedded in poly(diallyl dimethylammonium) chloride (PDDA) has been investigated for the electrophoretic separation of indoxyl sulfate, homovanillic acid (HVA), and vanillyl-mandelic acid (VMA). AuNPs (27 nm) exhibit ionic and hydrophobic interactions, as well as hydrogen bonding with the PDDA network to form a stable layer on the internal wall of the capillary. This approach reverses electro-osmotic flow allowing for fast migration of the analytes while retarding other endogenous compounds including ascorbic acid, uric acid, catecholamines, and indoleamines. Notably, the two closely related biomarkers of clinical significance, HVA and VMA, displayed differential interaction with PDDA-AuNPs which enabled the separation of this pair. The detection limit of the three analytes obtained by using a boron doped diamond electrode was ~75 nM, which was significantly below their normal physiological levels in biological fluids. This combined separation and detection scheme was applied to the direct analysis of these analytes and other interfering chemicals including uric and ascorbic acids in urine samples without off-line sample treatment or preconcentration. 10.1021/ac101105q

This paper reports on three-dimensional synchrotron radiation/Fourier transform-infrared microspectroscopy (SR/FT-IRM) imaging studies of water inclusions at the buried interface of solid-contact-ion-selective electrodes (SC-ISEs). It is our intention to describe a nondestructive method that may be used in surface studies of the buried interfaces of materials, especially multilayers of polymers. Herein, we demonstrate the power of SR/FT-IRM for studying water inclusions at the buried interfaces of SCISEs. A poly(methyl methacrylate)--poly(decyl methacyrlate) [PMMA--PDMA] copolymer revealed the presence of micrometer sized inclusions of water at the gold/ membrane interface, while a coupling of a hydrophobic solid contact of poly(3-octylthiopheue 2,5-diyl) (POT) prevented the accumulation of water at the buried interface. A similar study with a poly (3,4-ethylenedioxythiophene)/poly (styrenesulfonate) [PEDOT/PSS] solid contact also revealed an absence of distinct micrometer-sized pools of water; however, there were signs of absorption of water accompanied by swelling of the PEDOT/PSS underlayer, and these membrane zones are enriched with respect to water. 10.1021/ac101009n

Here we describe the electrochemical oxidation of an assembly of gold nanoparticles (Au NPs) attached to glass/indium--tin-oxide (ITO) electrodes as a function of particle size. We synthesized Au NP arrays with NP diameters ranging from 8 to 250 nm by electro-deposition of Au from HAu[Cl.sub.4] in [H.sub.2]S[O.sub.4] at potentials of -0.2 to 0.8 V versus Ag/AgCl using chronocoulometry to keep the amount of Au deposited constant. The average Au NP size increased with increasing deposition potential. The chemical reduction of HAu[Cl.sub.4] by NaB[H.sub.4] in trisodium citrate solution led to 4 nm average diameter Au NPs, which we chemisorbed to the glass/ITO electrode. Linear sweep voltammograms (LSVs) obtained on the glass/ITO/Au NP (4 to 250 nm) electrodes (with a constant coverage of Au in terms of Au atoms per [cm.sup.2]) from 0.5 to 1.1 V in 0.01 M potassium bromide plus 0.1 M HCl[O.sub.4] showed a positive shift in oxidation potential from 734 [+ or -] 1 mV to 913 [+ or -] 19 mV with increasing Au NP diameter. The shift agrees qualitatively with that predicted by a shift in the redox potential based on a difference in free energy associated with a change in surface energy as a function of particle size. On the basis of the charge during Au deposition versus the charge during oxidation, the oxidation process produces a mixture of [Au.sup.III][Br.sub.4.sup.-] (25%) and [Au.sup.I][Br.sub.2.sup.-] (75%). A glass/ITO electrode coated with a mixture of 4 and 250 nm Au NPs revealed 2 oxidation peaks, consistent with the two Au NP size populations present on the surface. 10.1021/ac101021q

Surface-enhanced infrared absorption spectroscopy (SEIRAS) in attenuated total reflection (ATR) configuration has been extended to the Fe electrode/electrolyte interface in neutral and weakly acidic solutions for the first time. The SEIRA-active Fe film electrode was obtained through a potenfiostatic electrodeposition of a virtually pinhole-free 40 nm-thick Fe overfilm onto a 60 nm-thick Au underfilm chemically predeposited on the reflecting plane of an ATR Si prism. The infrared absorption for CO adlayer at the Fe film electrode measured with ATR-SEIRAS was enhanced by a factor of larger than 34, as compared to that at a Fe bulk electrode with external infrared absorption spectroscopy in the literature. More importantly, the unipolar band shape enabled the reliable determination of the Stark tuning rates of CO adlayer at Fe electrode. In situ ATR-SEIRAS was also applied to study the electrosorption of a typical corrosion inhibitor benzotriazole (BTAH) on Fe electrode as a function of potential, providing additional spectral information at positive potentials in support of the formation of a polymer-like surface complex [Fe.sup.II.sub.m][(BTA).sub.n], as the corrosion-resistant layer. 10.1021/ac1002323

Electrochemical methods proved useful as simple and inexpensive tools for the analysis of natural as well as chemically modified nucleic acids. In particular, covalently attached metal-containing groups usually render the DNA well-pronounced electrochemical activity related to redox processes of the metal moieties, which can in some cases be coupled to catalytic hydrogen evolution at mercury or some types of amalgam electrodes. In this paper we used voltammetry at the mercury-based electrodes for the monitoring of DNA modification with cis-diamminedichloroplatinum (cisplatin), a representative of metallodrugs used in the treatment of various types of cancer or being developed for such purpose. In cyclic voltammetry at the mercury electrode, the cisplatin-modified DNA yielded catalytic currents the intensity of which reflected DNA modification extent. In square-wave voltammetry, during anodic polarization after prereduction of the cisplatinated DNA, a well-developed, symmetrical signal (peak P) was obtained. Intensity of the peak P linearly responded to the extent of DNA modification at levels relevant for biochemical studies (rb = 0.01-0.10, where rb is the number of platinum atoms bound per DNA nucleotide). We demonstrate a correlation between the peak P intensity and a loss of sequence-specific DNA binding by tumor suppressor protein p53, as well as blockage of DNA digestion by a restriction endonuclease Msp I (both caused by the DNA cisplatination). Application of the electrochemical technique in studies of DNA reactivity with various anticancer platinum compounds, as well as for an easy determination of the extent of DNA platination in studies of its biochemical effects, is discussed. 10.1021/ac902987x

Gold and carbon electrodes have been largely used as transducers in protein and DNA sensors and arrays. Liquid mercury electrodes, with potential windows allowing detection of DNA and protein reduction processes at highly negative potentials, were considered as useless in such arrays. Here, we show that solid amalgam electrode (SAE) arrays can be prepared as a substitution of liquid mercury in the analysis of the above biomacromolecules. Vacuum metal sputtering on a glass substrate, photolithography, and galvanic mercury amalgam formation were used for fabrication of an inexpensive disposable electrode array. The resulting ultrathin (less than 1 [micro]m) amalgam microelectrodes were characterized with respect to influence of the electrode composition and size on the reproducibility and stability of electrochemical signals. Further characterization was performed using electron microscopy and the well-established ruthenium electrochemistry. Final, optimized, design was applied in protein analysis employing the recently described electrocatalytic chronopotentiometric peak H. 10.1021/ac902333s

Microbeads are used to track fluid flow over microband electrode arrays to investigate fundamentals of redox magnetohydrodynamics (redox-MHD) in a confined solution. The results may lead toward the design of micro total analysis systems with microfluidics based on the redox-MHD concept. Ion flux was generated by reduction and oxidation of electroactive potassium ferri- and ferrocyanide at selected individually addressable microelectrodes in the array. An external magnetic field was produced by a small, permanent magnet (0.38 T) placed directly below the array with its field perpendicular to the plane of the array. The cross product of ion flux and magnetic field produces a magnetic force (a portion of the Lorentz force equation) that causes the fluid to rotate around the active electrodes. Velocities up to 1.4 mm/s are demonstrated here. The effects on velocities were obtained for different concentrations of redox species, widths of electrodes, gaps between electrodes, and combinations of anodically- and cathodically polarized electrodes. The microbeads allowed mapping of flow patterns and velocities, both parallel and perpendicular to the array chip. The influence of counteracting shear forces, drag along the walls, and reinforcing flow are discussed. A significant result is the fairly fiat flow profile across 650 [micro]m, attained between electrodes that are oppositely biased. 10.1021/ac9020177

Pt-Ag nanoparticles were prepared on a glassy carbon (GC) surface by pulsed electrodeposition and tested using cyclic voitammetry and scanning electrochemical microscopy (SECM) with respect to their possible use as catalyst material for oxygen reduction in 400 mM HCl solution. For comparison, a Pt catalyst was investigated under similar conditions. The redox competition mode of scanning electrochemical microscopy (RC-SECM) was adapted to the specific conditions caused by the presence of CI ions and used to visualize the local catalytic activity of the Pt-Ag deposits. Similarly prepared Pt deposits were shown to dissolve underneath the SECM tip. Pt-Ag composites showed improved long-term stability toward oxygen reduction as compared with Pt even under multiple switching off to open-circuit potential in 400 mM HCl. 10.1021/ac902620g

Surface-enhanced Raman scattering (SERS) spectra were collected continuously during cyclic voltammetric measurements on silver electrodes in alkaline aqueous solution at room temperature. Three water librational modes as well as the bending mode peak were observed in cathodic potential range. The 2D-COS analysis of spectra collected in LiOH and KOH solutions showed that the librational bands appear prior to the bending band on the cathodic scan, while in CsOH solution the potential dependence of these bands was identical. A comparison of librational band frequencies revealed that the water molecules around [C.sup.s+] cations arranged on the electrode surface were poorly hydrogen bonded in contrast to [Li.sup.+] and [K.sup.+]. The water bending band of spectra collected in LiOH solution was found to be the convolution of two contributions, consistent with a two state model of water arranged on an electrode surface. 10.1021/ac902299u

The goal of this work is the development of microfabricated electrochemical sensing systems for environmental, industrial, and security applications requiring long-term unattended operation. The specific advantages of the microfabrication approach include the capability not only to miniaturize the size of the sensor platform but also to create an intelligent design including features such as redundant sensing electrodes, on-chip reference and auxiliary electrodes, and in situ electrode regeneration/ calibration. The model system targeted here involves continuous pH monitoring in drinking water at solid-state iridium oxide electrodes. The microchips utilized consist of a flow-through silicon platform (1 cm x 1.2 cm) containing patterned gold electrodes onto which iridium oxide has been deposited eletrochemically. To simulate drinking water detection scenarios, sensors are integrated into a flow system. Microfabricated designs include as many as 11 equivalent pH electrodes whose performance was evaluated for factors such as electrode-to-electrode reproducibility, long-term drift, and response to expected interfering agents. With on-chip voltage treatment, absolute potentials measured for an electrode array are within [+ or -]4 mV, with identical ([+ or -] l mV/pH unit) calibration slopes. This performance level is sustainable over weeks of usage. 10.1021/a9020374

The effects of the architecture and surface chemistry of three-dimensionally ordered macroporous (3DOM) carbon solid contacts on the properties of ion-selective electrodes (ISEs) were examined. Infiltration of the plasticized poly(vinyl chloride) (PVC) membrane into the pores of the carbon created a large interfacial area between the sensing membrane and the solid contact, as shown by cryo-scanning electron microscopy (cryo-SEM) and elemental analysis. This large interfacial area, along with the high capacitance of the 3DOM carbon solid contacts (as determined by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) results in an excellent long-term stability of the potentiometric response, with drifts as low as 11.7/:V/ h. The comparison of 3DOM carbon solid contacts with an untemplated carbon solid contact shows that the pore structure is an essential feature for the excellent electrode performance. However, the surface chemistry of the 3DOM carbon cannot be ignored. While there is no evidence for an aqueous layer forming between the sensing membrane and unoxidized 3DOM carbon, electrodes based on oxidized 3DOM carbon exhibit potentiometric responses with the typical hysteresis indicative of a water layer. A comparison of the different techniques to characterize the solid contacts confirms that constant-current charge-discharge experiments offer an intriguing approach to assess the long-term stability of solid-contact ISEs but shows that their results need to be interpreted with care. 10.1021/ac902222n

A new, highly sensitive and selective sensor for the electrochemical assay of Hg(II) by anodic stripping voltammetry has been developed, whereby a glassy carbon electrode is modified with a novel inorganic-organic hybrid nanocomposite, namely, bimetallic Au-Pt nanoparticles/organic nanofibers (labeled as Au-PtNPs/NFs). The sensor possesses a three-dimensional (3D) porous network nanoarchitecture, in which the bimetallic Au Pt NPs serving as metal NP-based microelectrode ensembles are homogenously distributed in the matrix of interlaced organic NFs. The surface structure and composition of the sensor were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Its electrochemical performance was systematically investigated. Our results show that such a newly designed, Au PtNPs/NF nanohybrid modified electrode provides remarkably improved sensitivity and selectivity for the stripping assay of Hg(II). The detection limit is found to be as low as 0.008 ppb (S/N = 3) that is much below the guideline value from the World Health Organization (WHO). Interferences from other heavy metal ions such as Cu(II), Cr(III), Co(II), Fe(II), Zn(II), and Mn(II) ions associated with mercury analysis are effectively inhibited. Toward the goal for practical applications, the sensor was further evaluated by monitoring Hg(II) in tap and river water specimens. 10.1021/ac901846a

Formation of thin layers of the composite material by a method based on interphase polymerization induced by a transport-controlled redox reaction is described. The obtained films were of 0.2 1[micro]m thickness, consisted of polypyrrole and gold nanoparticles (up to 13.5 at %), strongly adhered to the substrate surface, and were uniform. Different carbon materials and glass wool were employed as the substrates. The first step in the synthesis was deposition of an organic layer on the substrate. This was followed by dipping the substrate in an aqueous solution containing an oxidizer and appropriate washing and drying the composite film. 10.1021/ac902426c

Analytical expressions for the current--potential and charge-potential curves of an electrocatalytic process taking place at redox mediator modified electrodes corresponding to the application of cyclic staircase or cyclic sweep potentials are presented. Simple equations for cyclic voltsmmetry and cyclic volteoulometry curves have been also deduced for the usual experimental case corresponding to high catalytic rate constants, showing that whereas the current reach an stationary behavior, the charge always depend on time. The value of the rate constant of the chemical step can be easily determined from the plateau of the voltammogram or from the linear anodic region of the charge potendal curves. The theoretical predictions have been tested with the electeocatalytic oxidation of ascorbate mediated by a mixed 6-(ferroeenyl)hexanethiol-butanethiol monolayer at a disk gold electrode, with an excellent agreement between theory and experiments. A catalytic rate constant 3440 [M.sup.-1] [s.sup.-1] has been obtained, which is higher than those previously reported for this system with longer alkanethiol chains.

The preparation and characterization of Pt nanoelectrodes in the range of 1 to 3 nm in radii are reported. APt microwire is sealed into a bilayer quartz capillary and pulled into an ultrasharp Pt nanowire sealed in a silica tip using a laser-assisted pulling process. The ultrasharp tip is then sealed into a piece of glass tubing, which is manually polished to expose the Pt. Transmission electron microscopy and steady-state voltammetry are utilized to characterize the nanoelectrodes. The results show that the minimum size of the Pt nanoelectrode is determined by the size of the Pt microwire and parameters used in the pulling process. The heterogeneous electron transfer rate constant for the oxidation of ferrocene, ferrocenemethanol, and potassium hexachloroiridate (III) are determined from steady-state voltammetry using the method of Mirkin and Bard and are found to be [k.sup.o] = 7.6 [+ or -] 3.4 cm/s and = 0.85 [+ or -] 0.06 for ferrocene, [k.sup.o] = 7.4 [+ or -] 6.9 cm/s and = 0.78 [+ or -] 0.16 for ferrocenemethanol, and [k.sup.o] = 6.0 [+ or -] 4.2 cm/s and [alpha] = 0.72 [+ or -] 0.15 for Ir[[Cl.sub.6.sup.3-].

A practically modified ATR configuration has been proposed for in situ electrochemical surface-enhanced IR absorption spectroscopy (SEIRAS) by sandwiching an ultrathin water interlayer between a hemicylindrical ZnSe prism and a Si wafer as an integrated window. This new ATR optics significantly enhances the throughput of an effective IR beam across the ZnSe/gap/Si/metal film, enabling high-quality spectral fingerprints down to 700 [cm.sup.-1] to be readily detected at larger incidence angles without compromising the electrochemical feasibility and stability of metallic films deposited on Si. The advantages of this modified ATR-SEIRAS have been initially applied to explore two selected systems: wide-ranged in situ ATR-SEIRA spectra provided strong evidence in support of the formate intermediate pathway for methanol electrooxidation at the Pt electrode in an acid solution; in addition, new spectral fingerprints revealed comprehensive orientational information about of the p-nitrobenzoate species at Pt electrode as a result of the dissociative adsorption of p-nitrobenzoic acid molecules from an acid solution.

The dense ([Ba.sub.x][La.sub.1-x])[sub.2][In.sub.2][O.sub.5+x] electrolytes with different compositions (x = 0.4, 0.5, 0.6) were synthesized by Pechini method. The obtained sintered ([Ba.sub.x] [La.sub.1-x])[sub.2][In.sub.2][O.sub.5+x] electrolytes showed a high relative density of ~98%, and the major phase of three electrolyte compositions was indexed as a cubic phase. The CO sensing properties of as-fabricated planar-type ([Ba.sub.x][La.sub.1-x])[sub.2] [In.sub.2][O.sub.5+x-based sensors coupled with ITO and Pt as the sensing electrode and reference electrode, respectively, were investigated. The effects of factors such as gas flow rate, chemical compositions, and density of the electrolytes on the sensing performance were investigated. The sensors showed good sensitivity to different concentrations of CO from ~100 to ~500 ppm and excellent selectivity over low concentrations of methane (

Electrochemical oxidation of 2'-deoxyguanosine has been performed on boron-doped diamond (BDD) electrodes, resulting in a strong adsorption of the formed oxidized products onto the BDD surface. The adsorption behavior has been investigated by studying the electrochemical behavior of a redox probe ([[Ir[Cl.sub.6]].sup.3-]) using cyclic voltammetry. The most probable situations are the formation of (A) an insulating adsorbed film resulting in a partially blocked electrode behavior, (B) a porous film, or (C) an overall conductive film. Different parameters such as the standard rate constant, the charge-transfer coefficient, the electrode/adsorbed products/solution interface resistance, and the formal potential of the redox couple were determined. Through comparison of theoretical current-potential curves obtained by analytical calculations with experimental cyclic voltammograms, we found that the oxidized products of 2'-deoxyguanosine form a continuous conductive film on BDD.

The influence of uncompensated resistance (also called the I[R.sub.u] effect, where I is current and [R.sub.u] is uncompensated resistance) and slow electrode kinetics have been assessed for the dc and first five ac harmonics derived from Fourier transformed large-amplitude ac voltammetry. Resistance and rate constant conditions emphasized correspond to those where separation of effects attributable to either parameter is essentially impossible under conditions of dc cyclic voltammetry. Results derived from simulations and experiments demonstrate that it is relatively easy to discriminate and quantify contributions from these two effects over a wide range of values using the fourth and fifth harmonic ac components derived from single large-amplitude ac voltammetry measurement. Furthermore, these ac components also are essentially devoid of background charging current. Concepts developed initially from simulations are confirmed by experimental studies on the following: (a) the oxidation of ferrocene, in moderately resistive C[H.sub.3]CN and highly resistive C[H.sub.2][Cl.sub.2] (represents examples of I[R.sub.u] effect on a reversible electron-transfer process); (b) the reduction of a low 0.2 mM concentration of [[Fe[(CN).sub.6]].sup.3-] in the highly conductive 3 M KCl electrolyte media (case of slow kinetics with negligible I[R.sub.u] effect); (c) and reduction of a high 10 mM concentration of [[Fe[(CN).sub.6]].sup.3-] in less conductive aqueous 0.5 M KCl electrolyte media (example where the simultaneous effects of both I[R.sub.u] and slow kinetics need to be resolved).

We describe a methodology to perform reliable tunneling spectroscopy in electrochemical media. Sequential in situ tunneling spectra are recorded while the electrochemical potential of the electrode is scanned. Spectroscopic data are presented as conductance maps or conductograms that show the in situ electronic structure of an electrode surface while it undergoes an electrochemical reaction. The conductance map or conductogram represents the redox fingerprint of an electrode/liquid interface in a specific medium and can serve to predict its electrochemical behavior in a quantitative energy scale. The methodology is validated studying the reversible oxidation and passivity of an iron electrode in borate buffer, and we describe the main quantitative information that can be extracted concerning the semiconducting properties of the Fe passive film. This methodology is useful to study heterogeneous catalysis, electrochemical sensing and bioelectronic systems.

High sensitivity of the microelectrode response to the difference between the substrate and the product diffusion coefficients is predicted for the charge reversal processes. This effect is anticipated from the general theoretical model developed for the diffusional--migrational transport to microelectrodes. The model predicts the voltammetric wave heights for any type of electrode processes carried out in the presence of any number and concentration of nonelectroactive ions. It involves changes in diffusion coefficients of the redox species and assumes no homogeneous complications. Handy, analytical expressions for the limiting current and limiting potential can be derived for a system of a univalent product and univalent ions of supporting electrolyte. This case covers charge reversal processes of the following type: [S.sup.z] [right arrow] [P.sup.[+ or -]] ne (n + z = sgn(n), [absolute value of n] [greater than or equal to] 2). It has been shown that under migrational conditions the change in the ratio of the product and the substrate diffusivities ([D.sub.P]/[D.sub.S]) by as little as 10% results in significant changes in the voltammetric wave height. For 2-e charge reversal processes, a 10% increase in [D.sub.P] versus [D.sub.S] leads to a drop in the voltammetric wave height of 18.3% compared to that calculated for equal diffusion coefficients. The reversed change, i.e., the 10% decrease of the [D.sub.P] value with respect to [D.sub.S], increases the voltammetric wave height by 30.5% compared to that obtained for equal diffusivities. The theoretical predictions were confronted with our recent experimental results obtained for the 2-e oxidation of sodium (6,8-diferrocenylmethylthio)octanoate, which process can be classified as the charge reversal reaction. The best fit was obtained for [D.sub.P]/ [D.sub.S] equal to 0.71.

We describe an electrochemical cell containing a single faradic electrode (a Pt ultramicroelectrode) and a blocked (polarized) electrode (Si with an insulating Si[O.sub.2] film) that served as a capacitive counter electrode. When a bias was applied between the two electrodes, a current was observed from a faradic process at Pt and a capacitive current at the blocking electrode. A steady charging current was obtained when the solution was moved along the insulator to continuously contact fresh surface (emersing a layer of charged ions and electronic countercharge into the gas phase). Electrogenerated chemiluminescence was clearly observed from a system containing Ru[(bpy).sub.3.sup.2+] in this kind of cell under pulsed excitiation, demonstrating that faradaic reactions can be carried out in an electrochemical cell without generation of any products at a counter electrode. The use of such a system for coulometric addition of desired species in nanosystems and in synthesis is suggested.

Irreversible adsorbed bismuth can be used to determine the fraction of (111) domains on a given platinum sample. On Pt(111) electrodes, the surface redox process of adsorbed bismuth takes place at 0.63 V in a well-defined peak. The behavior of this redox process on the Pt(111) vicinal surfaces indicates that the bismuth atoms involved in the redox process are only those deposited on the (111) terrace sites and that the charge under the peak at 0.63 V is directly proportional to the number of sites on (111) ordered domains (terraces). The good linear relationship obtained between the charge for the bismuth redox process and the number of (111) terrace sites on the vicinal surfaces allows construction of a calibration curve. This calibration curve has been used to directly estimate the amount of (111) ordered domain terrace sites on polycrystalline platinum samples with different surface ordered domains. The results agree with what we would expect from our knowledge of these surfaces.

Nanocomposite electrodes made of sol-gel-derived ceramic--carbon nanotube are fabricated by doping mutli-walled carbon nanotubes (MWNTs) into a silicate gel matrix. The electrochemical behavior and potential electrochemical applications of the ceramic--carbon nanotube nanocomposite electrodes (CCNNEs) are also studied. The as-prepared CCNNEs exhibit a tunable dimension ranging from conventional electrode to nanoelectrode ensemble (NEE), depending on the amount of the MWNT dispersed in the silica sol and finally doped within the gel matrix. A high content of the MWNT (i.e., higher than 1.5 mg/mL in the sol) leads to the formation of the CCNNE characteristic of an electrode of conventional dimension, while a low content (typically lower than 0.10 mg/mL) essentially yields the CCNNE like a nanoelectrode ensemble. The NEE is demonstrated to possess good electrocatalytic activity toward the oxidation of ascorbic acid (AA), and the CCNNE of conventional dimension is found to possess remarkable electrocatalytic activity toward the oxidation of glutathione (both reduced and oxidized forms, GSH and GSSG). These properties of the CCNNEs essentially offer a new electrochemical approach for the detection of AA, GSH, and GSSG. The possible essence of the tailor-made dimensions of the CCNNEs is also presented and discussed.

The fabrication and electrochemical characterization of truncated cone-shaped nanopore electrodes are reported. A nanopore electrode is a Pt disk electrode embedded at the bottom of a conical pore, the circular orifice of the pore having nanometer dimensions. The electrochemical properties of nanopore electrodes with orifice radii of 39 and 74 nm are presented. Both the steady-state and transient voltametric behavior of the nanopore electrode are reported and compared to predictions obtained using finite-element simulations. The truncated cone-shaped pore electrode possesses a unique transport property--the steady-state flux of molecules into a deep pore is limited by the restriction near the pore orifice, and thus, the steady-state current is independent of the pore depth. This characteristic is potentially useful in studying transport through nanometer-scale orifices.